Dissertations / Theses on the topic 'Low temperature sintering'

Low temperature sintering has become a very important research area in ceramics processing and sintering as a promising process to obtain grain size below 100nm. For electronic ceramics, low temperature sintering is particularly difficult, because not only the required microstructure but also the desired electronic properties should be obtained. In this dissertation, the effect of liquid sintering aids and particle size (micrometer and nanometer) on sintering temperature and Positive Temperature Coefficient Resistivity (PTCR) property are investigated for Ba1-xSrxTiO3 (BST) doped with 0.2-0.3mol% Sb3+ (x = 0.1,0.2,0.3,0.4 and 0.5). Different sintering aids with low melting point are used as sintering aids to decrease the sintering temperature for micrometer size BST particles. Micrometer size and nanometer size Ba1-xSrxTiO3 (BST) particles are used to demonstrate the particle size effect on the sintering temperature for semiconducting BST. To reduce the sintering temperature, three processes are developed, i.e. 1 using sol-gel nanometer size Sb3+ doped powders with a sintering aid; 2 using micrometer size powders plus a sintering aid; and 3 using nanometer size Sb3+ doped powders with sintering aids. Grain size effect on PTCR characteristics is investigated through comparison between micrometer size powder sintered pellets and nanometer size powder sintered pellets. The former has lower resistivity at temperatures below the Curie temperature (Tc) and high resistivity at temperatures above the Curie temperature (Tc) along with higher ñmax/ñmin ratio (ñmax is the highest resistivity at temperatures above Tc, ñmin is the lowest resistivity at temperatures below Tc), whereas the latter has both higher ñmax and ñmin. Also, ñmax/ñmin is smaller than that of pellets with larger grain size. The reason is that the solid with small grain size has more grain boundaries than the solid with large grain size. The contribution z at room temperature and high temperature and a lower ñmax/ñmin ratio value.

Thesis (Ph. D.)--Ohio State University, 2004.
Title from first page of PDF file. Document formatted into pages; contains xxvi, 249 p.; also includes graphics (some col.). Includes bibliographical references (p. 241-249).

The automobile industry has set the demand regarding Powder Metallurgy (PM) parts for decades, since this near-net shape technology is a cost-effective manufacturing process allying good mechanical properties with dimensional and geometrical precision. Aiming at the future of the electric automobiles high production and demand, many changes are on the way to guarantee the competitiveness of PM against other manufacturing process. The high costs of alloying elements such as Ni and Cu, the changes in health and safety regulations as well as light weighting of components are the topics of major importance in the field of PM and focus of main R&D around the globe. The use of high temperature sintering and different alloying elements are possible solutions to overcome properties obtained by using Ni as an alloying element sintered at conventional temperatures. Materials with Cr, Mo and Si were investigated using high temperature sintering (1180°C and 1250°) in comparison to traditionally high Ni materials sintered at conventional temperature (1120°C). The dimensional stability, geometrical precision, density, and microstructure of ring-shaped specimens were studied by using a coordinate measuring machine (CMM) and the effect of HTS on the mechanical properties were estimated through the fraction of the load bearing section. The effect of HTS on the dimensional precision and geometrical stability was later investigated in real parts manufactured by industrial partners through an EPMA Club Project. The 4%Ni material sintered at 1120°C was also compared to Ni-less/Ni-free materials sintered at 1250°C using tensile testing, impact testing, and hardness. The use of HTS to improve the mechanical properties without impairing the dimensional and geometrical stability was confirmed in parts with both low and high complexity designs. This project sets the blueprint for future material developments using HTS as manufacturing process.

This research has developed a lead-free semiconductor device interconnect technology by studying the processing-microstructure-property relationships of low-temperature sintering of nanoscale silver pastes. The nanoscale silver pastes have been formulated by adding organic components (dispersant, binder and thinner) into nano-silver particles. The selected organic components have the nano-particle polymeric stabilization, paste processing quality adjustment, and non-densifying diffusion retarding functions and thus help the pastes sinter to ~80% bulk density at temperatures no more than 300°C. It has been found that the low-temperature sintered silver has better electrical, thermal and overall thermomechanical properties compared with the existing semiconductor device interconnecting materials such as solder alloys and conductive epoxies. After solving the organic burnout problems associated with the covered sintering, a lead-free semiconductor device interconnect technology has been designed to be compatible with the existing surface-mounting techniques with potentially low-cost. It has been found that the low-temperature sintered silver joints have high electrical, thermal, and mechanical performance. The reliability of the silver joints has also been studied by the 50-250°C thermal cycling experiment. Finally, the bonging strength drop of the silver joints has been suggested to be ductile fracture in the silver joints as micro-voids nucleated at microscale grain boundaries during the temperature cycling. The low-temperature silver sintering technology has enabled some benchmark packaging concepts and substantial advantages in future applications.
Ph. D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2006.
Includes bibliographical references (p. 181-189).
Conventional methods used to fabricate co-fired tungsten/alumina composites usually rely on high temperature processing (>1500C). As it would be beneficial or even necessary for some applications to produce such composites at relatively low firing temperatures, low-temperature processing techniques and the attendant knowledge of processing-property relationships need to be developed. In this thesis, a set of experiments and simulations are performed to obtain a better understanding of sintering and joining of the tungsten/alumina system processed at temperatures near or below 12000C. The technique of activated sintering for tungsten is investigated, whereby a minimal content of additives enables low firing temperatures through a change in the sintering mechanism for tungsten. Tungsten compacts produced by this method are found to sinter only to the "initial stage" and are characterized by high residual porosity level. Hardness and fracture toughness of such partially-sintered materials are examined experimentally and analytically, and dependence of mechanical properties on the relative particle neck size is observed. Various studies are carried out to examine both fundamental and practical aspects of joining co-fired tungsten/alumina.
(cont.) First, contributions to adhesion of co-sintered bilayers are studied where the properties of the tungsten layer are controlled using the process of activated sintering. Using a bending delamination test, improvements in sintered density of tungsten are found to increase the adhesive strength of the system only up to a point, beyond which shrinkage mismatch compromises the intrinsic toughness of the interface. A study of low-temperature co-fired tungsten/alumina is then focused on composite shells for an investment casting application. The influences of various processing parameters in a slurry-based route on the sintering and adhesion properties of tungsten/alumina are investigated. Binder content, stucco sand application, and powder characteristics are among the parameters found to critically control the quality of tungsten/alumina shells produced. Finally, the feasibility of several joining strategies, which involve the use of chemical additives, is examined on co-fired tungsten/alumina compacts processed at low temperatures. Some bonding techniques are verified to help improve the bonding of the co-sintered composites.
by Yuttanant Boonyongmaneerat.
Ph.D.

Abstract In the first part of the thesis, novel glass-ceramic compositions based on Al2O3 and BaTiO3 and bismuth-zinc borosilicate (BBSZ) glass, sintered at ultra-low temperatures, were researched. With adequate glass concentration, dense microstructures and useful dielectric properties were achieved. The composite of BaTiO3 with 70 wt % BBSZ sintered at 450 °C exhibited the highest relative permittivity, εr, of 132 and 207 at 100 kHz and 100 MHz, respectively. Thus, the dielectric properties of the composites were dominated by the characteristics of glass, BaTiO3, and Bi24Si2O40 phase, especially the contribution of Bi24Si2O40 for the samples with 70-90 wt % glass. Actually, the existence of the secondary phase Bi24Si2O40 may not hinder but enhance the dielectric properties. The Al2O3-BBSZ composition samples showed a similar situation, not only for densification but also for their microstructures and phases (Al2O3, BBSZ, Bi24Si2O40), explaining the achieved dielectric properties. The second part of the thesis mainly discusses the composite of BaTiO3 with 50 wt % BBSZ with different thermal treatments. After sintering at 720 °C, dense microstructures and the existence of Bi4BaTi4O15, BaTiO3, Bi24Si2O40 phases were observed. The results also showed that the size of glass powder particles did not influence the dielectric properties (εr = 263-267, tan δ = 0.013 at 100 kHz) of sintered samples, but the addition of LiF degraded the dielectric properties due to the features and amount of Bi4BaTi4O15. These results demonstrate the feasibility of the BBSZ based composites for higher sintering temperature technologies as well. At the end, a novel binder system, which enables low sintering temperatures close to 300 °C, was developed. A dielectric multilayer module containing BaTiO3-BBSZ and Al2O3-BBSZ composites with silver electrodes was co-fired at 450 °C without observable cracks and diffusions. These results indicate that these glass-ceramic composites provide a new horizon to fabricate environmentally friendly ULTCC materials, as well as multilayers for multimaterial 3D electronics packages and high frequency devices
Tiivistelmä Väitöstyön ensimmäisessä osassa tutkittiin ja kehitettiin uudentyyppisiä, ultramatalissa sintrauslämpötiloissa (ULTCC) valmistettuja lasi-keraami komposiitteja käyttäen vismuttisinkkiborosilikaatti -pohjaista lasia (BBSZ). Täyteaineina olivat alumiinioksidi (Al2O3) ja bariumtitanaatti (BaTiO3). Materiaaleille saatiin riittävän suuren lasipitoisuuden avulla tiheät mikrorakenteet ja sovelluskelpoiset dielektriset ominaisuudet. BaTiO3:n komposiitti, joka sisälsi 70 p-% BBSZ lasia, saavutti 450 °C lämpötilassa sintrattuna korkeimman suhteellisen permittiivisyyden: εr=132 (@100 kHz) ja εr=207 (@100 MHz). Komposiittien dielektrisiä ominaisuuksia määrittivät tällöin lasi-, BaTiO3- ja Bi24Si2O40- faasien ominaisuudet ja erityisesti Bi24Si2O40 -faasi näytteissä, joissa on 70-90 p-% lasia. Sekundäärinen faasi Bi24Si2O40 ei välttämättä heikentänyt, vaan jopa paransi dielektrisiä ominaisuuksia. Vastaavilla Al2O3-BBSZ –komposiiteilla saavutettiin samanlaisia tuloksia tihentymisen, mikrorakenteiden ja faasien (Al2O3, BBSZ, Bi24Si2O40) suhteen. Lisäksi tässä tapauksessa saavutetut dielektriset ominaisuudet voidaan selittää näiden kolmen faasin yhdistelmän olemassaololla. Väitöstyön toinen osa käsitteli pääasiassa eritavoin lämpökäsiteltyjä BaTiO3:n komposiitteja, joissa on 50 p-% BBSZ-lasia. Näillä saavutettiin tiheä mikrorakenne sintrattaessa 720 °C lämpötilassa ja havaitiin Bi4BaTi4O15-, Bi24Si2O40-faasien muodostuminen BaTiO3 lähtöfaasin rinnalle. Tulokset osoittivat myös, että lasijauheen partikkelikoko ei vaikuttanut sintrattujen näytteiden dielektrisiin ominaisuuksiin (εr = 263-267, tan δ = 0.013 (@100 kHz)). LiF -lisäys sen sijaan heikensi dielektrisiä ominaisuuksia ja vähensi Bi4BaTi4O15 faasin muodostumista. Tämä aiheutui Bi4BaTi4O15-faasin ominaisuuksista ja oli riippuvainen kyseisen faasin määrästä. Nämä tulokset osoittivat BBSZ -pohjaisten komposiittien käytettävyyden myös korkeampien sintrauslämpötilojen teknologioihin. Viimeisenä kehitettiin uudentyyppinen sideainesysteemi, joka mahdollistaa ultramatalien keraamien yhteissintraamisen jopa noin 300 °C lämpötilassa. Hyödyntäen kehitettyä sideainesysteemiä monikerrosrakenne, jossa käytettiin dielektrisiä BaTiO3-BBSZ- ja Al2O3-BBSZ-komposiitteja ja hopeaelektrodeja, yhteissintrattiin 450 °C lämpötilassa. Valmistetuissa rakenteissa ei havaittu murtumia eikä diffuusioita. Tulokset osoittavat, että kehitetyt lasi-keraami komposiitit mahdollistavat ympäristöystävällisten ULTCC -materiaalien valmistuksen. Lisäksi osoitettiin kehitettyjen materiaalien soveltuvuus monikerroksisten rakenteiden käyttöön monimateriaali-3D-elektroniikan pakkauksissa ja suurtaajuuskomponteissa

Abstract The recent trend in low temperature co-fired ceramic (LTCC) technology is to integrate more elements into multilayer modules. This thesis describes work specifically aimed at developing ferroelectric barium strontium titanate (BST) for integration into such modules. In particular, an objective was the development of a novel, electric field controlled, tunable component to be used at microwave frequencies (2–26 GHz). For the application envisaged, relative permittivity is required to be low (100–1000) and adjustable by a suitable applied electric field, the dissipation factor at room temperature must be low (~0.001) at 2–26 GHz, and most importantly, the sintering temperature must be suited to the LTCC technology (~900 °C) Initial work was focused on sol-gel derived Ba0.7Sr0.3TiO3 powders with boron oxide addition, which were sintered at 900 °C, the dissipation factor was 0.006. The dissipation factor was not low enough for the desired microwave application, and attention turned to powders prepared by the mixed-oxide route. The Ba0.7Sr0.3TiO3 powders, fluxed with the optimum amounts of boron oxide and lithium carbonate, could be sintered at 890 °C to the same density as is achieved with un-fluxed Ba0.7Sr0.3TiO3 sintered at 1360 °C. The dissipation factor for this fluxed powder was acceptably low, although permittivity was too high for the particular objective. Subsequently, research was on BST modified by magnesia, 0.4Ba0.55Sr0.45TiO3-0.6MgO (BSTM). With the optimum fluxing additives, the sintering temperature necessary to achieve a dense BSTM-based ceramic was reduced to 950 °C. The developed microstructure was good, and the relative permittivity and dissipation factor values (221, 0.0012 at 1 kHz) at room temperature indicated good microwave properties. Studies were also undertaken with organic-based tape-casting slurries, laminating procedures and burn-out and sintering schedules. Several kinds of tapes were fabricated and characterized. A test structure for the measurement of dielectric properties at 26 GHz of the optimized BSTM-based ceramic was constructed. The specimen was 50 μm thick layer of BST on an alumina substrate. The relative permittivity and tunability were 130 and >15 % at 4 V μm-1 at room temperature. A tunable phase-shifter was fabricated from the same BSTM-based tape using a novel gravure printing technique, and measurements at 26 GHz showed phase shift from 10 to 35° when the electric field was increased from 1 V μm-1 to 2.5 V μm-1. Some exploratory experiments are described to assess the compatibility of the developed BST-based LTCC with commercial LTCC and some electroceramics.

Die attachment is one of the most important processes in the packaging of power semiconductor devices. The current die-attach materials/techniques, including conductive adhesives and reflowed solders, can not meet the advance of power conversation application. Silver paste sintering has been widely used in microelectronics and been demonstrated the superior properties. The high processing temperature, however, prevents its application of interconnecting power semiconductor devices. This research focuses processing and characterization of micron-scale and nanoscale silver paste for power semiconductor devices attachment. Lowering the processing temperature is the essential to implement sintering silver paste for power semiconductor devices attachment. Two low-temperature sintering techniques - pressure-assisted sintering micro-scale silver paste and sintering nanoscale silver paste without external pressure - were developed. With the large external pressure, the sintering temperature of micro-scale silver paste can be significantly lowered. The experimental results show that by using external pressure (>40MPa), the commercial micro-scale silver paste can be sintered to have eighty percent relative density at 240oC, which is compatible with the temperature of solder reflowing. The measured properties including electrical conductivity, thermal conductivity, interfacial thermal resistance, and the shear strength of sintered silver joints, are significantly better than those of the reflowed solder layer. Given only twenty percent of small pores in the submicron range, the reliability of the silver joints is also better than that of the solder joints under the thermal cycled environment. The large external pressure, however, makes this technique difficult to automatically implement and also has a potential to damage the brittle power semiconductor devices. Reducing silver particles in the paste from micro-size to nanoscale can increases the sintering driving force and thus lowers the sintering temperature. Several approaches were developed to address sintering challenges of nanoscale silver particles, such as particles aggregation and/or agglomeration, and non-densification diffusion at low temperature. These approaches are : nanoscale silver slurry, instead of dry silver powder, is used to keep silver particles stable and prevent their aggregation. Ultrasonic vibration, instead of conventional ball milling, is applied to disperse nanoscale silver particles in the paste from to avoid from agglomerating. Selected organics in the paste are applied to delay the onset of mass-diffusion and prevent non-densification diffusion at low temperature. The measured results show that with heat-treatment at 300oC within one hour, the sintered nanoscale silver has significantly improved electrical and thermal properties than reflowed solders. The shear strength of sintered silver interconnection is compatible with that of solder. The low-temperature sinterable nanoscale silver paste was applied to attach the bare Silicon carbide (SiC) schottky barrier diode (SBD) for high temperature application. Limited burn-out path for organics in the silver layer challenges the sintering die-attach. This difficulty was lessened by reducing organics ratio in the silver paste. The effects of die-size and heating rate on sintering die-attach were also investigated. The single chip packaging of SiC SBD was fabricated by sintering die-attach and wire-bonding. The tested results demonstrate that the sintering nanoscale silver paste can be applied as a viable die-attach solution for high-temperature application.
Ph. D.

As the first level interconnection in electronic packages, chip attachment plays a key role in the total packaging process. Sintered nanosilver paste may be used as a lead-free alternative to solder for die-attachment at sintering temperature below 300 °C without applying any pressure. Typically, the substrate, such as direct bond copper (DBC) substrates, has surface metallization such as silver or gold to protect the copper surface from oxidation during the sintering process. This study focused on developing techniques for die-attachment on pure copper surface by low-temperature sintering of nanosilver paste. One of the difficulties lies in the need for oxygen to burn off the organics in the paste during sintering. However, the copper surface would oxidize, preventing the formation of a strong bond between sintered silver and copper substrate. Two approaches were investigated to develop a feasible technique for attachment. The first approach was to reduce air pressure as a means of varying the oxygen partial pressure and the second approach was to introduce inert gas to control the sintering atmosphere. For the first method, die-shear tests showed that increasing the oxygen partial pressure (PO2) from 0.04 atm to 0.14 atm caused the bonding strength to increase but eventually decline at higher partial pressure. Scanning electron microscopy (SEM) imaging and energy dispersive spectroscopy (EDS) analysis showed that there was insufficient oxygen for complete organics burnout at low PO2 condition, while the copper surface was heavily oxidized at high PO2 levels, thus preventing strong bonding. A maximum bonding strength of about average 8 MPa was attained at about PO2 = 0.08 atm. With the second method, the die-shear strength showed a significant increase to about 24 MPa by adjusting the oxygen exposure temperature and time during sintering. The processing conditions necessary for bonding large-area chips (6 mm à 6 mm) directly on pure copper surface by sintering nanosilver paste was also investigated. A double-print process with an applied sintering pressure of less than 5 MPa was developed. Die-shear test of the attached chips showed an average bonding strength of over 40 MPa at applied pressure of 3 MPa and over 77 MPa under 12 MPa sintering pressure. SEM imaging of the failure surface showed a much denser microstructure of sintered silver layer when pressure was applied. X-ray imaging showed a bond layer almost free of voids. Because the samples were sintered in air, the DBC surface showed some oxidation. Wirebondability test of the oxidized surface was performed with 250 μm-diameter aluminum wires wedge-bonded at different locations on the oxidized surface. Pull test results of the bonded wires showed a minimum pull-strength of 400 gram-force, exceeding the minimum of 100-gf required by the IPC-TM-650 test standard.
Master of Science

This study focused on the development and evaluation of die-attach material and substrate technology for high-temperature applications. For the die-attach material, a low-temperature sintering technique enabled by a nanoscale silver paste was developed for attaching large-area (>100 mm2) semiconductor chips. The nanoscale silver paste can be sintered at a much lower temperature (<300 oC) than in the conventional sintering process (>800 oC), and at the same time reached about 80 vol% bulk density. Analyses of the sintered joints by scanning acoustic imaging and electron microscopy showed that the attachment layer had a uniform microstructure with micron-sized porosity with the potential for high reliability under high temperature applications. We also investigated the effects of a large temperature cycling range on the reliability of direct bonded aluminum (DBA) substrate. DBA substrates with different metallization were thermally cycled between -55 oC and 250 oC. Unlike with the DBC substrate, no delamination of aluminum from the aluminum nitride ceramic base-plate was observed for the DBA substrates. However, aluminum surface became roughened during the thermal cycling test. It was believed that in the high-temperature regime, the significant amount of thermomechanical stress and grain-scale deformation would cause recrystallization and grain-boundary sliding in the aluminum layer, which would further lead to the observed increase in surface roughness. The influence of metallization over the aluminum surface on the extent of surface roughness was also characterized. In addition to evaluating the reliability of nanoscale silver paste and DBA substrate individually, this work also conducted experiments that characterize the compatibility of nanoscale silver paste on DBA substrate in terms of reliability in a high-temperature environment. In the large-area attachment, the sintered silver was found to be very compliant with the deformed aluminum. The device-to-silver and silver-to-substrate interfaces remain intact after up to 800 cycles. No large scale delamination and horizontal cracks were observed. However, some vertical crack lines began to show after certain number of cycles. It was believed that these vertical cracks were caused by the thermomechanical stresses in the sintered silver layer. In addition, with regard to the thermal performance, since most of the heat was generated from the semiconductor devices and were transferred vertically through the die-attach material to substrate, these vertical cracks were also considered more advantageous than horizontal cracks.
Ph. D.

Isotropically conductive adhesives (ICAs) are promising as a lead-free interconnect material; However, ICAs have a higher resistivity compared to tin/lead solder. The higher resistivity of ICAs results from the large contact resistance between conductive fillers. Several novel approaches to engineer the interface between electrically conductive fillers were studied to develop highly conductive ICAs. Shown in this dissertation are three methodologies to reduce contact resistance: low temperature sintering, fast sintering and in-situ reduction. Furthermore, two approaches, surface modification and in-situ protection, were developed to prevent oxidation and corrosion of silver-coated copper flakes to produce low cost ICAs. The findings and insights in this dissertation significantly contribute to (1) understanding of filler-filler, filler-polymer and structure-property relationships of ICAs; (2) the structural design and formulation of high performance ICAs; and (3) the wider use of ICAs in emerging applications such as printed electronics and solar cells.

Abstract This thesis describes a detailed investigation of new glass 10Li₂O−10Na₂O−20K₂O−60MoO₃ (LNKM), ceramic (α-MoO₃) and ceramic-commercial glass (PZ29-GO17, rutile TiO₂-GO17) composites to satisfy the future requirements for ultra-low fabrication temperature materials and their associated processes. The initial part of the thesis is devoted to the development of the LNKM glass by a glass-melting and quenching process, followed by an investigation into its structural, microstructural and microwave dielectric properties. The prepared glass had ultra-low glass transition and melting temperatures of 198 and 350 °C, respectively. The glass pellet heat-treated at 300 °C had a relative permittivity (εr) of 4.85 and a dielectric loss (tan δ) of 0.0009 at 9.9 GHz. The temperature dependence of the relative permittivity was (τε) 291 ppm/°C. Another part of the work concerns α-MoO₃ ceramic, its preparation by uniaxial pressing and sintering at 650 °C followed by an investigation of its structural, microstructural, thermal and microwave dielectric properties. It had an εr of 6.6, tan δ of 0.00013 (at 9.9 GHz) and τε of 140 ppm/°C. In addition to this, a functional ultra-low temperature co-fired composite was developed based on commercial PZ29 and 50 wt.% of GO17 glass followed by tape casting and co-firing with Ag at 450 °C. The average values of the piezoelectric (d₃₃) and voltage (g₃₃) coefficients were 17 pC/N and 30 mV/N, respectively. The sintered sample had an average CTE value of 6.9 ppm/°C measured in the temperature range of 100–300 °C. The εr and tan δ of the sintered substrates were 57.8 and 0.05 at 2.4 GHz, respectively. Additionally, a new ceramic-glass composite was developed using rutile TiO₂-GO17, and co-fired with Ag at 400 °C. It had an average CTE value of 8.3 ppm/°C measured in the temperature range of 100–300 °C. This composite substrate showed εr of 15.5 and tan δ 0.003, at 9.9 GHz. Moreover, it also had τε of -400 ppm/°C at 9.9 GHz measured in the temperature range of −40 to 80 °C. The findings of the thesis reveal the feasibility of the ultra-low temperature co-fired ceramic (ULTCC) technology for high-frequency telecommunication devices as well as for electronics packages. Additionally, a first step to develop functional ULTCC has been taken
Tiivistelmä Tässä väitöskirjassa kuvataan uuden lasin 10Li₂O−10Na₂O−20K₂O−60MoO₃ (LNKM), keraamin (α-MoO₃) sekä keraami-lasi (PZ29-GO17, rutiili TiO₂-GO17) komposiittien tutkimustulokset, jotka mahdollistavat tulevaisuuden sähkökeraamisten materiaalien ja komponenttien valmistuksen ultra-matalissa valmistuslämpötiloissa. Väitöskirjan alkuosa keskittyy LNKM lasin kehitykseen lasin sulatus- ja karkaisuprosessilla, sekä tämän materiaalin mikrorakenteen sekä mikroaaltoalueen dielektristen ominaisuuksien tarkasteluun. Valmistetulla lasilla oli ultra-matala lasittumislämpötila 198 °C sekä sulamislämpötila 350 °C. Lasipelletin, joka lämpökäsiteltiin 300 °C:ssa, suhteellinen permittiivisyys (εr) oli 4,85 ja dielektriset häviöt (tan δ) 0,0009 9,9 GHz taajuudella. Suhteellisen permittiivisyyden lämpötilariippuvuus (τε) oli 291 ppm/°C. Toinen osa työtä käsittelee α-MoO₃ keraamia, josta valmistettiin näytteet mikrorakenne ja mikroaaltoalueen dielektristen ominaisuuksien tutkimuksiin aksiaalisella puristuksella ja sintraamalla 650 °C:ssa. Valmistetun materiaalin suhteellinen permittiivisyys oli 6,6, häviöt 0,00013 (9,9 GHz:ssa) ja permittiivisyyden lämpötilariippuvuus 140 ppm/°C. Näiden lisäksi kehitettiin toiminnallinen ultra-matalan lämpötilan yhteissintrattu komposiitti perustuen kaupalliseen pietsosähköiseen keraamiin (PZ29) ja lasiin (GO17). Komposiitista valmistetiin monikerrosrakenne nauhavalulla ja yhteissintraamalla hopeaelektrodien kanssa 450 °C:ssa. Keskimääräiset arvot pietsosähköiselle varausvakiolle (d₃₃) sekä jännitevakiolle (g₃₃) olivat 17 pC/N ja 30 mV/N. Sintratun näytteen keskimääräinen lämpölaajenemiskerroin oli 8,3 ppm/°C lämpötila-alueella 100–300 °C. Tämän komposiittisubstraatin suhteellinen permittiivisyys oli 15,5 ja häviötangentti 0,003 9,9 GHz:n taajuudella. Lisäksi suhteellisen permittiivisyyden lämpötilariippuvuus oli -400 ppm/°C samalla 9,9 GHz:n taajuudella, kun lämpötilan mittausalue oli −40–80 °C. Tämän väitöstyön tulokset osoittavat ultra-matalan lämpötilan yhteissintrattavan keraamiteknologian (ULTCC) soveltuvuuden korkean taajuuden tietoliikennesovelluksiin ja elektroniikan pakkausteknologiaan. Lisäksi työssä on otettu ensimmäiset askeleet funktionaalisten ULTCC materiaalien kehittämiseksi

The present thesis focuses on the preparation of tetragonal zirconia doped with yttria oxide, ceric dioxide, and magnesium oxide. In its theoretical part the thesis covers the characteristics of doped ceramics, the possible methods of powders preparation and of their further processing. The experimental part describes the precipitation synthesis of zirconia in base environment and further processing for ceramics. Also studied were the influences of dopant and of the processing technique used on the phase composition and microstructure of the resulting ceramics. To describe the powder structure, the thermal, dilatometric, surface area, and x-ray analyses were performed; as well as both the scanning and transmission electron microscopy employed. Dry processed ceramics showed the average grain size of 87–94 nm and the relative density in the range of 84,0–99,3 %. In comparison, the ceramics produced of hydrothermally synthesised powders proved the average grain size of 75–85 nm and the relative density between 92,7-99,9 %. As the next step, samples were subjected to low-temperature degradation for the time of 5 and 15 hours. Samples consisting of pure tetragonal ZrO2 were resistant to 5 and 15 hours of low-temperature degradation at 180 °C.

[EN] Zirconia has become a widely utilized structural ceramic material with important applications in dentistry due to its superb mechanical properties, biocompatibility, aesthetic characteristics and durability. Zirconia needs to be stabilized in the t-phase to obtain improved mechanical properties such as hardness and fracture toughness. Fully dense yttria-stabilized tetragonal zirconia polycrystalline (Y-TZP) materials are normally consolidated through the energy-intensive processing of powders at very high temperatures (>1000 °C). Innovative non-conventional approaches are being developed to reduce time and energy consumption and, consequently, environmental impact in ceramic powder processing. Microwave sintering is one such approach aimed at fully-densifying ceramics by using a different heating mechanism based on the material's inherent dielectric properties. The main purpose of this work is to obtain highly dense Y-TZP dental materials from commercial and lab-prepared sources via microwave sintering with mechanical and microstructural qualities that are similar or even improved with respect to their conventionally sintered counterparts. Therefore, its effect on important aspects related to dental applications has been studied. First, Y-TZP ceramics have been characterized upon sintering to determine whether the resulting properties meet the minimum mechanical requirements for structural dental applications. Second, the influence of microwave sintering on hydrothermal degradation, a spontaneous ageing phenomenon that affects zirconia materials in wet conditions, has been investigated. And third, the behavior under fretting wear conditions of microwave and conventionally sintered materials has been assessed to evaluate their durability and performance. The main conclusions indicate that microwave sintering allows proper consolidation of dental Y-TZP materials resulting in a finer microstructure due to shorter processing time and mechanical properties comparable, and in some cases enhanced, to those obtained in conventional sintered materials at lower dwell temperatures. Additionally, a higher resistance to hydrothermal degradation has been determined for microwave sintered materials due to a finer grain size and lower sintering temperatures that reduce the presence of cubic phase, which is responsible for destabilizing neighboring tetragonal phase grains. Finally, a similar wear rate has been obtained between microwave and conventional sintering of zirconia materials under fretting wear conditions. In addition, humidity can reduce the wear volume loss due to the lubricative effect of water and wear of degraded materials might increase the resistance due to the formation of a protective debris layer. In general, microwave sintering can be an interesting alternative for obtaining fully-densified Y-TZP dental materials providing certain advantages over conventional methods. Nonetheless, more studies are still necessary to have a better understanding of the advantages and disadvantages of microwave sintering of zirconia ceramics.
[ES] La circona es un material ampliamente utilizado como cerámica estructural con aplicaciones en el ámbito dental debido a sus propiedades mecánicas, biocompatibilidad, características estéticas y durabilidad. Para poder aprovechar las altas propiedades mecánicas de la circona, es necesario estabilizarla en su fase tetragonal. Los materiales de circona policristalina estabilizada con itria (Y-TZP) se consolidan normalmente a través de polvos mediante procesos energéticamente intensivos a altas temperaturas (>1000 °C). Actualmente, se están desarrollando técnicas basadas en métodos no convencionales para reducir el tiempo y el consumo energético en el procesado de polvos cerámicos. La sinterización por microondas tiene por objetivo la densificación completa mediante la utilización de mecanismos de calentamiento basados en las propiedades dieléctricas del material. El objetivo principal es la obtención de materiales dentales de Y-TZP altamente densos mediante la sinterización por microondas con propiedades mecánicas y microestructurales similares, o incluso por encima de las obtenidas por el método convencional. Para ello, se estudian aspectos relevantes al ámbito dental. En primer lugar, los materiales son caracterizados con el fin de determinar si las propiedades finales cumplen con los requisitos mecánicos para aplicaciones dentales. Además, se ha investigado la influencia de la sinterización por microondas en la degradación hidrotérmica, un fenómeno espontáneo de envejecimiento que afecta a los materiales de circona en condiciones de humedad. Finalmente, se ha evaluado el comportamiento en condiciones de desgaste fretting de los materiales sinterizados para determinar su durabilidad. Las conclusiones principales indican que la sinterización por microondas permite la consolidación adecuada de estos materiales, resultando en una microestructura más fina debido a los tiempos más cortos de procesado y en propiedades mecánicas comparables a las de materiales obtenidos mediante el método convencional, incluso a temperaturas más bajas. Una mayor resistencia a la degradación hidrotérmica se ha determinado en materiales sinterizados por microondas. Al emplear temperaturas más bajas se reduce la presencia de fase cúbica, la cual es responsable por la desestabilización de granos adyacentes de fase tetragonal. Tasas de desgaste similares han sido observadas entre materiales sinterizados por microondas y convencionalmente bajo condiciones de desgaste fretting. Adicionalmente, la humedad puede reducir sustancialmente la pérdida de volumen de desgaste debido al efecto lubricante del agua y los materiales degradados pueden aumentar la resistencia a este tipo de desgaste como consecuencia de la formación de una capa protectora de material que se desprende más fácil. En general, la sinterización por microondas es una alternativa interesante para obtener materiales dentales de Y-TZP altamente densos con ciertas ventajas sobre los métodos convencionales pero deben considerarse también las desventajas de esta técnica.
[CAT] La circona és un material àmpliament utilitzat com a ceràmica estructural amb aplicacions en l'àmbit dental a causa de les seues propietats mecàniques, biocompatibilidad, característiques estètiques i durabilitat. Per a poder aprofitar les altes propietats mecàniques de la circona, és necessari estabilitzar-la en la seua fase tetragonal. Els materials de circona policristalina estabilitzada amb itria (Y-TZP) es consoliden normalment mitjançant processos energèticament intensius a altes temperatures (>1000 °C). Actualment, s'estan desenvolupant tècniques basades en mètodes no convencionals per a reduir el temps i el consum energètic en el processament de la pols ceràmicas. La sinterització per microones té per objectiu la densificació completa mitjançant la utilització de mecanismes d'escalfament basats en les propietats dielèctriques del material. L'objectiu principal d'aquesta tesi és l'obtenció de materials dentals de Y-TZP altament densos mitjançant la sinterització per microones amb propietats mecàniques i microestructurals superiors a les obtingudes per mètodes convencionals. En primer lloc, els materials seràn caracteritzats per a determinar si les propietats finals compleixen amb els requisits mecànics per a aplicacions dentals. En segon lloc, s'investigarà la influència de la sinterització per microones en la degradació hidrotèrmica, un fenomen espontani d'envelliment que afecta als materials de circona en condicions d'humitat. I en tercer lloc, s'avaluarà el comportament en condicions de desgast fretting dels materials sinteritzats per a determinar la seua durabilitat. Les conclusions principals indiquen que la sinterització per microones permet la consolidació adequada i millorada de materials de Y-TZP, amb una microestructura més fina a causa dels temps més curts de processament i propietats mecàniques comparables a les de materials obtinguts mitjançant el mètode convencional, fins i tot a temperatures més baixes. Un factor positiu ha sigut la major resistència a la degradació hidrotèrmica en materials sinteritzats per microones. A més, al emprar temperatures més baixes es redueix la presència de fase cúbica, la qual és la responsable de la desestabilització de grans adjacents de fase tetragonal. Finalment, sota condicions de desgast fretting, s'han observat taxes de desgast similars entre materials sinteritzats per microones i via convencional. Addicionalment, en condicions de 100% d'humitat es pot reduir substancialment la pèrdua de volum de desgast a causa de l'efecte lubrificant de l'aigua i materials degradats, els quals poden augmentar la resistència a aquest tipus de desgast com a conseqüència de la formació d'una capa protectora de material que es desprèn amb més facilitat. En general, la sinterització per microones és una alternativa molt interessant per a obtindre materials dentals Y-TZP òptims i amb certes avantatges sobre els mètodes convencionals, però han de considerar-se també algunes desavantatges d'aquesta tècnica.
Presenda Barrera, Á. (2016). ADVANCED CERAMIC MATERIALS FOR DENTAL APPLICATIONS SINTERED BY MICROWAVE HEATING [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/68510
TESIS

Des poudres de phosphates de calcium carbonatés amorphes ou cristallisés en apatite ont été synthétisées par voie aqueuse. La carbonatation est effectuée de deux manières différentes : pendant la synthèse où la quantité de carbonates introduits dépend du rapport molaire carbone/phosphore des réactifs et de la température de synthèse, ou par post carbonatation de poudres phosphocalciques grâce à des échanges ioniques de surface en solution. Les phosphates de calcium amorphes sont composés de cluster de Posner de formule chimique générale : Ca9-x-y(PO4)6-2x-2y(HPO4)2x(CO3)2y,nH2O. Les poudres d’apatite sont decristallinité variable en fonction des paramètres de synthèse. Composées à coeur de nanocristaux d’apatite de formule chimique générale Ca10-x-y(PO4)6-x-y(HPO4)x(CO3)y(OH)2-x-y-2z(CO3)z, elles peuvent comporter en surface une couche hydratée phosphocalcique et non-apatitique plus ou moins importante. Ces poudres sont consolidées par frittage flash ou Spark Plasma Sintering (SPS) à basse température. Ce frittage, réalisé à 150°C, ne conduit qu'à peu ou pas de consolidation lorsque des poudres cristallisées et sans couche hydratée superficielle sont utilisées. A l’inverse, des poudres amorphes ou nanocristallines avec une importante couche hydratée densifient. La consolidation mène à la formation de joints de grains et à la croissance des cristaux des apatites nanocristallines dans le coeur des particules amorphes. La composition chimique des grains cristallisés est Ca10xy(PO4)6xy(HPO4)x(CO3)y(OH)2-x-y-2z(CO3)z. La consolidation est activée par l’application conjointe d’une charge et d’un courant éléctrique pulsé sans lesquels elle n’est pas possible à aussi basse température. Les céramiques résultantes sontmicroporeuses et très cohésives avec de bonnes propriétés mécaniques (résistance à la flexion = 18 MPa). Ces céramiques miment la composion chimique de la phase minérale de l’os et sont suceptibles de présenter des propriétés biologiques supérieures aux matériaux courament utlisés en tant que substituts osseux
Carbonated calcium phosphates amorphous or crystallized to apatite powders have been synthesized by aqueous route. Carbonation is carried out in two different ways: during the synthesis in which the amount of carbonates introduced depends on the carbone/phosphor molar ratio of reactant and on the synthesis temperature, or by post carbonation of phosphocalcic powders thanks to surface ion exchange in aqueous solution. Amorphous calcium phosphates carbonated are composed of Posner's cluster of general chemical formula: Ca9-x-y(PO4)6-2x-2y(HPO4)2x(CO3)2y,nH2O. Apatite powders are of varying crystallinity depending on the synthesis parameters. It is composed of nanocrystals consisting of an apatitic core of general chemical formula Ca10-x-y(PO4)6-x-y(HPO4)x(CO3)y(OH)2-x-y-2z(CO3)z and may comprise on the surface a hydrated layer phosphocalcic and non-apatitic more or less important. These powders are consolidated by flash sintering or Spark Plasma Sintering (SPS) at low temperature (150°C). This sintering only led to little or no consolidation when crystallized powders without superficial hydrated layer were used, while amorphous powders densified. Consolidation phenomena, leads to the formaton of grain boundaries and crystal growth in the amorphous particles or crystal growth of apatitic nanocrystals. The chemical composition of the crystallized grains is Ca10-x-y(PO4)6-xy(HPO4)x(CO3)y(OH)2-x-y-2z(CO3)z. Consolidation is activated by the combined application of a load anda pulsed electric current, without which it is not possible at such a low temperature. The resulting ceramics are crystallized into calcium-deficient carbonated apatite, microporous and highly cohesive with good mechanical properties (flexural strength = 18 Pa).These ceramics mimic the chemical composition of the mineral phase of the bone and are susceptible to exhibiting superior biological properties to materials commonly used as bone substitutes

Le frittage et le traitement par laser sont des techniques remarquables, couramment utilisées dans de nombreux domaines d’applications du fait des qualités qu’ils confèrent aux surfaces traitées. Ces technologies permettent de substantielles économies d’énergie comparée aux traitements de surfaces conventionnels. Le chauffage est par ailleurs, strictement localisé à la zone choisie. Notre recherche a pour objectif de développer une fine couche de verre de silice à la surface de céramiques poreusescomposites : le diborure de zirconium-carbure de silicium (ZrB2-SiC) et le diborure de titane-carbure de silicium (TiB2-SiC) frittées avec une porosité contrôlée d’environ 30%. La principale application de ces matériaux concerne les piles à combustibles protoniques fonctionnant à basse température (de type LTPCFCs). Les poudres ZrB2-SiC et TiB2-SiC sont soigneusement mélangées et pressées à froid dans un moule à la pression de 40 MPa. Le frittage naturel est conduit dans un four à 1900 et 2100 °C durant 2,5 heures, sous atmosphère contrôlée d’argon. Après polissage, le traitement de surface est effectué par laser verre-ytterbium. Les paramètres du traitement ont été optimisés (puissance et trajet du faisceau laser, temps de traitement, atmosphère) et ont permit d’obtenir une couche superficielle d’un verre à forte conduction protonique, sans affecter la structure et la composition des couches situées au-dessous de la surface. Les échantillons ont été caractérisés en utilisant les méthodes classiques : EDS, XRD, MEB, microscopie optique. Les meilleurs résultats ont été obtenus avec des échantillons de composition 61 mol. % ZrB2-SiC et 61 mol. % TiB2-SiC traités thermiquement a 1900 °C. La porosité obtenue, de l’ordre de 30%, assure une bonne circulation des gaz. La couche de verre produite sur le composite ZrB2-SiC, d’une épaisseur moyenne de 8 μm, est continue et exempte demacro fissuration. Une microfissuration est cependant détectée par MEB aux plus forts grossissements. Les essais ont été conduits à plus haute température de frittage (2100 °C) et avec des compositions différentes dans le but d’améliorer les propriétés du substrat. ZrB2-SiC. A la composition de 80 mol. % ZrB2-SiC les analyses révèlent la présence de cristaux de forme cuboïdale, attribuée à la formation de carbure de bore B4C dont la formation est admise par l’analyse thermodynamique. Les essais sur le composite ZrB2-SiC conduisent à l’apparition de bulles et de défauts dans la couche de verre. Une optimisation des conditions de traitement sera nécessaire pour contrôler ce phénomène. Cette étude démontre qu’il est possible de développer des couches poreuses de matériaux céramiques de type ZrB2-SiC, et de former à leur surface une couche de verre dense et exempte de fissuration par traitement laser. Les propriétés générales de cette couche permettent d’envisager une utilisation comme électrolyte solide dans les piles à combustibles de type LTPCFCs
Sintering and laser are a remarkable technology with a broad range of applications especially material processing. It offers a wide variety of desired surface properties depending on the type of usage. Sintering allows high reliability and repeatability to the large mass production. Laser benefits in the aspect of energy saving compared to conventional surface heat treatment due to the heating is restricted and localized only to the required area. Therefore, this research aims to develop a silica-glass-layer onto a porous non-oxide, Zirconium Diboride-Silicon Carbide (ZrB2-SiC) and Titanium Diboride-Silicon Carbide (TiB2-SiC) ceramic composites by sintering and laser surface treatment for potential application in the Low-Temperature Protonic Fuel Cells (LTPCFCs). ZrB2-SiC and TiB2-SiC mixed powders at different composition were cold-pressed around 40 MPa under ambient environment. Next, the composites were pressureless sintered at 1900 °C and 2100 °C for 2.5 h dwell time under argon atmosphere, respectively. The pressureless sintering was conducted by Nabertherm furnace and followed by surface treatment via an ytterbium fibre laser (Yb). Anew round spiral laser pattern was inspired, designed and scanned onto the surface of pellets to obtain a smooth glass surface layer that acted as proton-conducting (electrolyte) while preserving the beneath structures of laser-treated pellets that served as an electrode. Characterization techniques such as Scanning Electron Microscope (SEM) equipped with Energy Dispersive X-Ray Spectroscopy (EDS) and X-ray Diffraction (XRD) were performed accordingly onto the samples. Pressureless sintering of 61 mol.% ZrB2-SiC and 61 mol.% TiB2-SiC pellets at 1900 °C exhibited ca. 29% porosity. The resulting porosity was in the best range of effectiveness for gas diffusion. SEM micrographs revealed the formation of semiglassy layer on the surface of sintered 61 mol.% ZrB2-SiC pellets. The bulk structures remained unaffected and unoxidized. SEM micrographs and EDS patterns displayed thatsilica (SiO2) at a thickness of 8 μm, presence on the surface of ZrB2-SiC structures. It demonstrated that the surface treatment by Yb-fibre laser on sintered ZrB2-SiC ceramic composites at 1900 °C had accomplished. The laser surface treatment was ineffective for TiB2-SiC pellets due to several bubbles formation and crack deflection. Nevertheless, at higher magnification of the SEM for laser-treated ZrB2-SiC ceramic composites, cracks were observed. Therefore, the pressureless sintering at high temperature was conducted to improve the ZrB2-SiC structural properties. Sintering at 2100 °C had demonstrated increment of density and at 80 mol.% ZrB2-SiC sintered pellet unpredictably exhibited the presence of boron carbide (B4C) compounds. SEM micrographs revealed the dark cuboidal shapes and XRD patterns identified as B4C peaks. The reactions of B4C formation were proposed andsupported by thermodynamic analysis. In conclusion, the present research had developed a glassy layer on the surface of ZrB2-SiC ceramic composites which has potential in the application of LTPCFCs. It proved that B4C was possible to be developed by pressureless sintering at 2100 °C and it might assist in developing better morphology for ZrB2-SiC ceramic composites

Les nanoparticules métalliques ont la particularité de fritter à des températures bien inférieures que les microparticules. Les pâtes de frittage à base de nanoparticules d'argent (Ag) sont commercialisées pour assembler des puces d'électronique de puissance à leur substrat. L’assemblage se fait classiquement entre 200 et 300°C, sous contrainte. Le joint métallique final obtenu possède d’excellentes propriétés de conductivités électrique et thermique. La température de fusion théorique du joint, une fois densifié, est égale à la température de fusion de l’Ag massif (962°C). Cette propriété fait de ce nanomatériau une excellente alternative dans l’électronique de puissance « haute température ». Le coût de l’argent, qui est un métal précieux, reste un frein à l’utilisation de ces pâtes de frittage. Une alternative pour baisser les coûts est de remplacer les nanoparticules d’argent par des nanoparticules de cuivre. Le cuivre possède des propriétés de conductivités très proches de celles de l’argent. Un obstacle majeur à l’intégration de nanoparticules de cuivre dans des pâtes de frittage est la propension du cuivre à s’oxyder. L’oxydation des nanoparticules empêche le frittage et diminue fortement les propriétés mécaniques ainsi que la conductivité du joint métallique final. En plus de cela, le cuivre, même non oxydé, est moins réactif lors du frittage et nécessite des températures plus élevées pour une bonne densification que l’argent. La stratégie choisie pour protéger les nanoparticules de cuivre de l’oxydation a été de les encapsuler dans un polymère ou avec une fine couche d’argent. L’obtention de systèmes cœur-coquille Cu@Ag, en plus d’augmenter la résistance face à l’oxydation, permet d’améliorer le frittage des joints. Une fois densifiés, les joints à base de nanoparticules Cu@Ag sont capables de résister à des contraintes mécaniques élevées
Metallic nanoparticles have the particularity to sinter at lower temperatures compared to microparticles. Silver (Ag) nanoparticles based sintering pastes are commercially available for assembling power electronics chips to their substrates. The assembly is performed between 200 and 300°C, generally under pressure (Hot Pressing) and the resulting metallic joint has excellent thermal and electrical conductivity properties. The theoretical melting temperature of the resulting densified joint corresponds to the melting temperature of bulk silver (962°C), making the silver nanoparticles an alternative for "high temperature" power electronics compared to traditional solder. Nevertheless, the cost of Ag, which is a precious metal, remains a barrier to the use of these sintering pastes. The cost can be reduced by replacing the silver nanoparticles with copper (Cu) nanoparticles. Copper has conductive properties very close to silver. The major hurdle to the integration of copper nanoparticles in sintering pastes is the proneness of copper to oxidation. The oxidation of Cu nanoparticles prevents sintering and greatly reduces the mechanical properties and conductivity of the final metallic joint. Moreover, copper is less reactive during sintering and requires higher temperatures to densify. We chose to protect copper nanoparticles by encapsulation. In a first step copper nanoparticles were synthetized at laboratory scale and semi-industrial scale. In a second step the copper nanoparticles were encapsulated either with a polymer or very thin layer of Ag. The oxidation properties of the core-shell nanoparticles were studied. In a third step the Cu@Ag nanoparticles were formulated in a paste in order to obtain metallic joints. The sintering and density properties of the metallic joints were evaluated and positively compared to the joints obtained with a commercial Ag based paste. The Cu@Ag core-shell system prevents oxidation but also improves the sintering process

La voie de synthèse classiquement utilisée pour la fabrication des combustibles carbures consiste à carboréduire à haute température (1600°C) et sous vide primaire un mélange des poudres d'AnO2 et de graphite. Ces conditions sont pénalisantes pour la synthèse des carbures mixtes (U,Pu)C, à cause de la volatilisation du plutonium. C'est pourquoi l'un des buts principaux des travaux réalisés a été de diminuer la température de carboréduction. Nos travaux se sont portés principalement sur l'abaissement de la température de carboréduction de l'oxyde d'uranium. Ce résultat a pu être obtenu en augmentant la surface réactionnelle entre le carbone et l'oxyde d'uranium. Pour ce faire des suspensions colloïdales de nanoparticules d'oxyde d'uranium ont été préparées et stabilisées par des éthers cellulosiques. Les éthers cellulosiques servent à la fois de stabilisant pour les nanoparticules d'oxyde d'uranium mais aussi comme source de carbone pour la carboréduction. Ces précurseurs ont démontré être plus performant vis-à-vis de la carboréduction par rapport aux précurseurs de référence : une réduction de 300 °C de la température de carboréduction a été obtenue sous vide primaire. L'impact de ce type de précurseurs sur la carboréduction et les proriétés physico-chimiques ainsi que les caractérisations structurales et microstructurales des carbures obtenus ont été réalisées
The synthetic route conventionally used to manufacture carbides fuels involves carboreduction of a mixture of AnO2 powders and graphite at high temperature (1600 °C) and under a low vacuum. These conditions are disadvantageous for the synthesis of mixed carbides (U,Pu)C due to volatilization of plutonium. This is why one of the main goals of this work was to reduce the temperature of carboreduction. Our work was mainly carried on the lowering of the temperature of carboreduction of uranium oxide. This result was achieved by increasing the reaction surface between the carbon and uranium oxide. To do this colloidal suspensions of uranium oxide nanoparticles were prepared and stabilized with cellulose ethers. Cellulose ethers serve both as a stabilizer for the uranium oxide nanoparticles, but also as a carbon source for the carboreduction. These precursors have shown to be more efficient for the carboreduction compared to the standard precursors: a reduction of 300 °C on the carboreduction temperature was obtained under low vacuum. The impact of this type of precursors on the carboreduction and physicochemical properties and the structural and microstructural characterization of obtained carbide were performed

Quenching and partitioning (Q&P) steels show a good balance between strength and ductility due to a special heat treatment that allows to adjust a microstructure of martensite with a fraction of stabilized retained austenite. The final heat treatment step is performed at low temperatures. Therefore, joining of Q&P steels is a big challenge. On the one hand, a low joining temperature is necessary in order not to influence the adjusted microstructure; on the other hand, high joint strengths are required. In this study, joining of Q&P steels with Ag nanoparticles is investigated. Due to the nano-effect, high-strength and temperature-resistant joints can be produced at low temperatures with nanoparticles, which meets the contradictory requirements for joining of Q&P steels. In addition to the Ag nanoparticles, activating materials (SnAg and Sn) are used at the interface to achieve an improved bonding to the steel substrate. The results show that the activating materials play an important role in the successful formation of joints. Only with the activating materials, can joints be produced. Due to the low joining temperature (max. 237 °C), the microstructure of the Q&P steel is hardly influenced.

Le développement de nouveaux matériaux à hautes performances dépend fortement des procédés de frittage mis en oeuvre. La réduction de l’énergie libre de surface, force motrice de la densification, peut être activée en appliquant une pression extérieure et/ou en améliorant les processus de diffusion en phase solide ou liquide à l’aide de chauffages ultra rapides, les procédés associés requérant de hautes températures. Ainsi, le challenge est de permettre une densification à basse température afin de surmonter les verrous technologiques actuels (procédé peu coûteux et économe en énergie ; frittage de matériaux métastables, à basse température de décomposition et/ou nanométriques ; cofrittage de multimatériaux). Dans ce contexte, un procédé innovant de frittage hydrothermal inspiré des processus géologiques de densification a été développé : une contrainte uniaxiale est appliquée à une poudre en présence d’eau en conditions hydrothermales sur des durées relativement courtes. La force motrice principale réside dans les gradients de contrainte intragranulaires générant des phénomènes de dissolution-précipitation aux interfaces liquide/solide. Outre une optimisation du procédé, l’objectif principal a été la compréhension des mécanismes complexes spécifiques au frittage hydrothermal d’un matériau modèle, la silice nanométrique. Il a été montré que les effets mécano-chimiques à l’origine du fluage par dissolution sous contrainte sont assistés avec synergie par des effets chimiques de type polycondensation. L’influence de chaque paramètre de frittage (température, pression, durée de palier, rampe de montée en température, quantité de solvant, utilisation d’un co-solvant ou d’un agent minéralisateur) a été identifiée et a permis d’optimiser la densification de la silice (86-88% de compacité). De plus, du quartz-α massif polycristallin et nanométrique a pu être obtenu avec une densité relative de 98%. Enfin, le frittage hydrothermal a été mis en oeuvre pour la densification de multimatériaux complexes. Des nanocomposites de type 0-3 où des nanoparticules de pérovskite de manganèse sont dispersées dans une matrice de silice ont ainsi été obtenus. L’apport de cette nanostructuration sur les propriétés de magnétotransport a été évalué
The development of new high performance advanced materials is strongly dependent on the mastering of sintering processes. The driving force for densification is the decrease of surface free energy, which can be promoted either by applying a pressure and/or by enhancing diffusional mechanisms in a solid or liquid phase with ultra-fast heating routes. High temperatures are then usually required in the as-involved processes. The challenge is to perform densification at low temperature in order to overcome current technological barriers (energy- and cost-efficiency of the process; sintering of metastable, low temperature decomposition and/or nanometric materials; cosintering of multimaterials). In this context, we have developed an innovative hydrothermal sintering process which is geologically-inspired: a powder mixed with water is externally and mechanically compressed under hydrothermal conditions over short time periods. The main driving force is the stress gradient within grains induced by external uniaxial compression which allows the activation of the dissolution/precipitation phenomenon at solid/liquid interfaces. Besides the technological development of the apparatus, our goal was to understand all the complex mechanisms involved in the hydrothermal sintering of a model material, nanometric silica. We have shown that the mechanical-chemical effects (pressure solution creep) were synergistically assisted by chemical ones (polycondensation). The influence of each parameter (temperature, pressure, time, heating rate, solvent amount, use of a co-solvent or of a mineralizer) were investigated. Consequently, the densification of silica was optimized, reaching 86-88% of relative density. In addition, bulk polycrystalline nanometric α -quartz with 98% of relative density was obtained. Finally, the hydrothermal sintering process has been implemented to densify complex multimaterials. In this way, 0-3 type nanocomposites where nanometric manganese perovskite are embedded in a silica matrix have been obtained. The advantage of nanostructuration on magnetotransport properties was evaluated

The present masters's thesis informs about the development and application of low-temperature sintering pastes in the manufacture and assembly of PCB components of the enclosing lead-free using nanoparticles of metals and their compounds. Lead-free brazing technology which s using in the present time, which has its drawbacks, however, and thus gaining other appropriate alternatives that seek to replace or further refined lead brazing. The introduction of the theoretical part inform about retrieval method of the type, composition and properties of low-temperature sintering pastes consisting of metal nanoparticles and their compounds. This section describes and explains the reaction mechanisms taking place during the sintering process. The end of the first chapter is dedicated to nanotechnology and production of nanoparticles and their compounds for the needs of the low-temperature sintering and possible related problems. Folowing section is devoted to examples of practitioners of the application and use of low-temperature sintering pastes and tests with which to assess the characteristics and quality of the related sintering conection. At the end of the thesis is a summary perspective and the use of low-temperature sintering technology nanoparticle past into the future. The experimental part is devoted to the application of conductive ink on the base of graphite for the production of 1V, 2V and 4V structures and their electroplated by the copper. There were created technological processes of 2V and 4V structures and test proposed methodologies resistance conductive theme to environmental influences. Filling pasta was tested in implementing 4V structure. There were made microsections various technological applications and their results were processed and evaluated.

On propose de preparer un materiau a haute constante dielectrique a couches d'arret aux joints de grains par un frittage a basse temperature (1100**(o)c) de srtio::(3) dope et reduit en presence d'un sel de lithium. La formation de la seconde phase isolante constituee de bi::(2)o::(3) est envisagee au cours de ce meme cycle thermique. La poudre de srtio::(3) est prealablement dopee par des composes de structure perovskite afin de faciliter l'incorporation du dopant, et reduite a 1350**(o)c sous atmosphere reductrice. La physico-chimie de frittage a 1100**(o)c en presence d'un sel de lithium et les proprietes dielectriques et microstructurales de srtio::(3) dope par srli::(1/4)nb::(3/4)o::(3) d'une part, la::(2/3)tio::(3-epsilon ) d'autre part, sont etudiees puis comparees a celles de srtio::(3) dope par la la::(2)o::(3) et srtio::(3) non dope

In der vorliegenden Arbeit werden nanopartikelhaltige Suspensionen auf Ag- und Ni-Basis sowie Ag-Precursoren, die während des Erwärmungsprozesses Nanopartikel bilden, bezüglich ihrer Eignung zum Fügen bei niedrigen Temperaturen untersucht. Dabei wird die, im Vergleich zum entsprechenden Massivmaterial, verringerte Schmelz- und Sintertemperatur von Nanopartikeln ausgenutzt. Da nach dem Schmelz- und Sinterprozess der Partikel die thermischen Eigenschaften des Massivmaterials vorliegen, ergibt sich ein großes Potential für die Herstellung hochfester und temperaturbeständiger Verbindungen bei gleichzeitig niedrigen Fügetemperaturen, was für eine Vielzahl von Fügeaufgaben von großem Interesse ist. In der Arbeit wird zunächst eine kommerzielle Ag-Nanopaste insbesondere bezüglich ihres thermischen Verhaltens charakterisiert. In der Folge werden Fügeverbindungen mit Cu-Substraten hergestellt, die in Abhängigkeit verschiedener Prozessparameter bzgl. der Festigkeiten, der Mikrostruktur sowie der Bruchflächen detailliert charakterisiert werden. Dabei zeigt sich, dass insbesondere der Fügedruck einen signifikanten Einfluss auf die erreichbaren Festigkeiten ausübt. Mit hohen Fügedrücken können bei einer Fügetemperatur von 300 °C höhere Verbindungsfestigkeiten als mit einem konventionellen Hartlot auf AgCu-Basis (Löttemperatur: 780 °C) erreicht werden. Weiterhin werden erste Ergebnisse zum Fügen von Stählen mit einer Ni-Nanopaste vorgestellt, mit der hohe Verbindungsfestigkeiten erzielt werden können. Schließlich wird mit Ag-Precursoren eine weitere Klasse möglicher Fügewerkstoffe vorgestellt, die erst während des Erwärmungs- bzw. Fügeprozesses Nanopartikel bilden, was in einer deutlich vereinfachten Handhabbarkeit resultiert. Die Arbeit liefert zudem Ansätze für weitere Forschungstätigkeiten
In this thesis, Ag- and Ni-based nanoparticle-containing suspensions and Ag precursors, which form nanoparticles during heating, are examined with regard to their suitability for joining at low temperatures. Nanoparticles exhibit a decrease in sintering and melting temperature in comparison to the corresponding bulk material. After melting and sintering of the nanoparticles, the material behaves like the bulk material. Therefore, high-strength and temperature-resistant joints can be produced at low temperatures, which is of great interest for various joining tasks. First, a commercially available Ag nanopaste is characterized in particular regarding to its thermal behavior. Subsequently, joints (substrate: Cu) are prepared with the Ag nanopaste. The influence of different process parameters on the strength behavior of the joints, the microstructure and the fracture surfaces is investigated. It is shown, that in particular the joining pressure exerts an essential influence on the achievable strengths. With high joining pressures, the strengths of conventionally brazed joints (AgCu brazing filler metal, brazing temperature: 780 °C) can be exceeded at a joining temperature of only 300 °C. Furthermore, first results for the joining of steels with a Ni nanopaste are presented, whereby high strengths can be achieved. Finally, with Ag precursors, an additional class of possible joining materials is presented, which form nanoparticles only during heating. This results in a significantly simplified handling. The work also provides approaches for further research activities

碩士
大同大學
材料工程研究所
90
ZnO based varistors exhibit highly nonlinear current-voltage characteristics and have been used extensively as electrical circuit protectors against power and voltage surges. We prepare the low melting point compounds with B2O3 and Bi2O3, and add them into basic materials (without Bi) to reduce the sintering temperature (below 961℃) and to eliminate the problems when using Ag-Pd internal-electrode. Finally, we expect to enhance the nonlinear property of ZnO varistor when sintering at low temperature. In this research, the addition of B-Bi compounds can enhance the densification to 99% relative density, when the sintering temperatures are below 1100℃. Adding glass powders can reduce the leakage current and increase the nonlinear coefficient. Increasing the sintering temperature can decrease the breakdown voltage by growing up the grain size, but the leakage current will be enhanced. When ZCMCS, which is calcined at 1250℃, sintered at 900℃ with 3B-Bi glass, the nonlinear coefficient is more than 34. The nonlinear coefficient reaches to maximum 40 with 5wt% 3B-Bi glass, and the leakage current is 3.28μA. When tempered in air at 600℃ for 2 hours, the sample sintered at 1000℃ possesses the best properties. The nonlinear coefficient can reach more than 60.

碩士
義守大學
電子工程學系碩士班
96
Ba2Ti9O20, with high dielectric constant, low loss and temperature stable is suitable for dielectric resonators and is adopted as a material in the fabrication of high permittivity ceramic substrates. In this study, the barium titanate with different ratio of Ba/Ti were synthesized by using solid-state reaction technique. The calcinations was carried out at 1200℃ for 2 h. The effect of Bi2O3、V2O5 and B2O3 additions on low-temperature sintering have been investigated. The samples were sintered in the temperature range of 950–1050°C for 2 h. For Ba2Ti9O20 doped with 10 wt% Bi2O3 + 0.5 wt% V2O5 + 3 wt% B2O3 sintered at 1000 °C , the relative density was 91% ,single Ba2Ti9O20 phase was obtained dielectric. Dielectric constant is 36 , low-temperature coefficient of resonant frequencyτf is 13.5 ppm/℃ and Q×f =17098. Microstrip filters are with the advantage of low insertion loss and compact size. In order to reduce the dimension of filters, higher dielectric constant materials were adopted in this study. A bandpass filter with center frequency at 2.39GHz and 3dB bandwidth 150MHz was implemented on Ba2Ti9O20 ceramic substrates. The insertion loss and return loss of the bandpass filter was -2.96 and -32.47dB,respectively.

碩士
大同大學
材料工程學系(所)
102
Ba2MgWO6 (BMW) is a double perovskite-structured dielectric ceramic with high quality factor (Q). However, its sintering temperature reaches as high as 1575 ℃, which could not meet the requirements of ceramic multilayer technology. In addition, this ceramic forms BaWO4 phase when the temperature is over 1400 ?aC. The BaWO4 phase will degrade the dielectric properties and lower Q values of BMW. In order to alleviate these problems, we doped Sr to partly substitute Ba on one hand and added B2O3, 2Bi2O3‧B2O3, Bi2O3‧CuO, 3ZnO‧B2O3 and Li2O as sintering aids to lower sintering temperature on the other. Results of Ba2-xSrxMgWO6 (x = 0.0, 0.5, 1.0, 1.5) showed that when x=0.5 (i.e., Ba1.5Sr0.5MgWO6 ) Qxf value reached maximum. Further increase of Sr doping decreased Qxf value. The Sr doping had no significant changes in the dielectric constant εr while temperature coefficient of frequency drift τf increased from -27.7 ppm / ?aC to 24 ppm /?aC. For Ba1.5Sr0.5MgWO6 Qxf value was 152,603 GHz, dielectric constant εr was 20.6 and temperature coefficient of resonance frequency drift τf was 24 ppm/ ?aC. The addition of B2O3 had significant effect on the sintering of BMW. The sintering temperature decreased from 1575 ℃ to 1150 ?aC with 0-5 wt% of B2O3 addition. But when B2O3 addition was more than 2 wt%, the samples would exhibit substantial decrease in the Qxf value. Although 2Bi2O3‧B2O3, Bi2O3‧CuO, 3ZnO‧B2O3 and Li2O addition to BMW effectively reduce the sintering temperature, Qxf value is greatly reduced. The best conditions was to add 2wt% B2O3. The sintering temperature of BMW-2 wt% B2O3 dropped to 1350 ?aC. Its Qxf value could reach 138,595 GHz. The dielectric constant was 16.6 and the temperature coefficient of resonance frequency drift was -11 ppm /?aC. When Ba1.5Sr0.5MgWO6 was added with 2wt% B2O3 the sintering temperature was further lower from 1400℃ to 1200?aC, but the Qxf becomes low.

碩士
國立臺北科技大學
資源工程研究所
96
For the widespread commercialization of satellite communications today and in view of its future advancement, cell phone must become miniaturized and light weight, so the development of low temperature co-fired ceramic of high dielectric constant has become more important. Barium titanate, BaTiO3 has many kinds of crystal structures; few researchers to date have focused on a high-temperature hexagonal polymorph (h-BaTiO3).In this study, traditional solid-state reaction method was used to incorporate Mn dopant (x=0.15) to stabilize hexagonal BaTiO3 and then mix different aids to reduce the sintering temperature and still retain the best microwave dielectric properties. So, the microstructures and properties of the Ba(Ti1-xMnx)O3 samples are analyzed by measuring dielectric parameters, XRD and SEM . The results show that Bi2O3, B2O3, Li2CO3 and (5ZnO•2B2O3) can effectively reduce the sintering temperature and keep the main phase as hexagonal. Good microwave dielectric properties of εr = 54.4, Q • f =3448 GHz and τf =254.5 ppm/℃can be obtained for 10wt% B2O3 doped Ba(Ti0.85Mn0.15)O3 ceramics sintered at 1100℃ for 2h.

碩士
國立臺北科技大學
材料及資源工程系碩士班
91
Sintered BaO-(La1-xNdx)2O3-4TiO2 at 1450℃ show microwave dielectric properties : εr=99, Q×f=5120GHz.However, excellent microwave dielectric properties cannot fit the requirements The objective of present work is to evaluate the glass compositions to decrease sintering temperature without influence dielectric properties. The results exhibited that Li2CO3-B2O3-SiO2 and B2O3-SiO2-ZnO were suitable additives for BaO-(La1-xNdx)2O3-4TiO2.Moreover the dielectric conatant is enhanced by the increasing relative density, and decreased by increasing the amount of glasses ,so as the Q×f values. Based on dense bulks with 10 wt% Li2CO3-B2O3-SiO2 glasses addition, the densification temperature is 1150℃ under the good microwave dielectric properties： εr＞84, Q×f＞3000.Furthermore 10wt% B2O3-SiO2-ZnO(+1wt%Na2O、K2O) added BaO-(La1-xNdx)2O3-4TiO2 can be sintered to achieve theoretical densities of 90% at 1050℃, and giveεr ＞70, Q×f＞3500. As the consequence, the sintering temperature of the BaO-(La1-xNdx)2O3-4TiO2 can be effectively lowered with glasses addition and keep the good dielectric properties for LTCC materials applied to multilayer microwave devices.

碩士
國立交通大學
材料科學與工程研究所
86
Multi-layers and miniaturization of High frequency dielectiric devices can improve volume effects. Lower sintering temeperature can be co-fired with conductors. like Au, Ag and so on having low dielectric loss. Due to the rapid growth of communications industry using microwave frequencies, cellular phones with small volume and light weight become necessary trend. 　　In this study, first, we fabricate high-temp. sintering bulks of BaO-Re2O3-TiO2 (Re=La, Nd, Sm) ternary systems, after analyzing calcined powders (T=900-1300℃) microstructures and phase transitions. These bulks' microwave properties have been measured. BaO-Nd2O3-4TiO2 system owning needed mecrowave properites., which εr=67, Q=1138 (3 Ghz), τf=+24ppm/℃ (1300℃ sinter 1hr) is the favorite ceramic system for low-temp.sintering fabrications. Microwave properties of ceramic bulks containing different components (5-20vol%) commercial glasses GP032 (ZnO-B2O3-SiO2) sintering at low temperature (900-1000℃) have also been studied. Based on dense bulks with 15vol% GP032 addition, which εr=42, Q=648 (3 GHz) (1000℃ sinter 4hr) and adding proper binder (HEC) and plasticizer (Glycerin) the apueous slurry was formed to be slips using doctor tape casting method. The sinitered substrates, whose green tape contains 4 pressed layer, have density, 4.99g/cm3 lower than high-temp.sintered bulks (5.22g/cm3).

碩士
國立臺北科技大學
資源工程研究所
100
The recent rapid progress in communications in microwave frequencies, such as portable phones and car telephones, has increased demand for the miniaturization of components such as band pass filters and local oscillators. In the fabrication of multilayer microwave devices, low-firing microwave dielectric materials with high dielectric constant εr , low dielectric loss and near-zero temperature coefficient of resonant frequency τf are needed. In this thesis, pure BiSbO4 ceramics with monoclinic structure were synthesized via solid-state reaction method, furthermore, discus the microwave dielectric properties of (1-x)BiSbO4 + xCaTiO3 (x = 0-7 wt%). According to the result, x=0 wt%, as BiSbO4, has good microwave dielectric properties with dielectric constant εr～21.0, Qf～53,336 GHz, but the value of τf～-47.2 ppm/℃ which limits the application. When x=1 wt%, εr improve to 21.9, Qf improve to 61,150 GHz, τf improve to -40.0 ppm/℃. Due to the shift of the frequency of interest from 900 MHz to 2.4, 5.2, or even 5.8 GHz, their dielectric constants need not be as high as required in the past. A high-quality factor becomes important because Qf is almost constant in the microwave region. Although Mg(Zr0.05Ti0.95)O3 has good dielectric properties, the sintering condition increase the production cost. Addition of low melting point oxides is an often used method to lower the sintering temperature of microwave dielectric ceramics. Effects of 3 wt% 3ZnO-B2O3 mixture addition on the sintering behavior, phase composition and microwave dielectric properties of Mg(Zr0.05Ti0.95)O3 ceramics have been investigated. Dense Mg(Zr0.05Ti0.95)O3 ceramics sintered at 1290℃ with 3 wt% 3ZnO-B2O3 mixtures addition , which exhibited good microwave dielectric properties with dielectric constant εr ~ 17.8, Qf values ~ 584.343 GHz.

碩士
國立臺北科技大學
材料科學與工程研究所
102
This study had prepared Mg(Ti0.95Zr0.05)O3&;#8210;high quality factor (Q×f), distinct waveform , and high sintering temperature&;#8210;by solid state reaction. But the high sintering temperature is disfavored for application. To reduce sintering temperature and to remain excellent performance of electrical properties, six kinds of glasses or low melting point ceramic were introduced into Mg(Ti0.95Zr0.05)O3. From the result of SEM, proper adding of sintering aid could promote growth of grain, therefore could improve block density and quality factor. If the aid added more than its critical amount then caused ceramic precipitated a large number of second phase, suppressed growth of grain, and reduced quality factor. From the result, adding 7 wt% of 3ZnO-B2O3 could reduce the sintering temperature of Mg(Ti0.95Zr0.05)O3 from 1420oC to 1290oC, increase the density, and excellent quality of Q×f (reached to 676,918 GHz). Adding 1 wt% of Bi2CuO4 could reduce the sintering temperature from 1420oC to 1200oC, density, and Q×f reached to 134,357 GHz. For adding 1 wt% of 2Bi2O-B2O3, the grain grew significantly while sintering at 1175oC; by electrical analysis, the Q×f could reach 139,918 GHz. While the sintering temperature increased to 1225oC the second phase (CaTiO3) increased; as the result, the temperature coefficient approximately equaled to zero. Sintering at 1225oC, the addition of Li2CO3 promoted the growth of grain, increased the density of blocks, and while addition reached 1.5 wt% the best Q×f was 181,132 GHz. During liquid phase sintering experiment, while Mg(Ti0.95Zr0.05)O3 added with silicate aid (5ZnO-2SiO2 and CaSiO3) ,the result from SEM showed that growth of grain was suppressed and Q×f was low. The result from XRD showed that both aid would induce the block to precipitate second phase (Ca2Ti5O12) &;#8210;increased the temperature coefficient.

碩士
國立清華大學
奈米工程與微系統研究所
103
This research proposed a sequential copper nanoparticle sintering process, which includes low pressure drying, near infrared sintering, and intensive pulsed light reduction. This process was designed for copper nanoparticle inks with lower solid contents and larger particle sizes, making the reduced copper thin film by inkjet printing or coating having the sane order resistivity as the bulk one. The result proved that the low pressure drying accumulated copper nanoparticles during solvent evaporation, resulting flat surfaces for continuous sintering. The near infrared sintering was efficient because of similar near infrared and copper absorption spectra, improving the copper delamination resulted from intensive pulsed light-only sintering. The low intensive pulsed light dose was used for copper-oxide reduction and avoided uniformity issue of stitching multiple areas. The final copper thin film resistivity reached 7.1×10-8 Ω-m, which equals to 24 % of the bulk conductivity.

碩士
國立臺北科技大學
材料及資源工程系所
93
The dielectric properties of BaO-R2O3-TiO2 ceramic system possesses a high dielectric constant (70 – 100), which are miniaturization of the dimensions of devices. In this study, the BaO-R2O3-TiO2 ceramics were prepared by a solid reaction method with replacement of lanthanide series by barium. The effects of composition and processing on the densification behavior, microstructural evolution and microwave dielectric properties of BaO-R2O3-TiO2 ceramics were investigated. The results exhibited that the Ba4.5(Sm1-xNdx)9Ti18O54 solid solutions with x = 0 had excellent dielectric properties (εr = 76.5, Q×f= 3500GHz, τf = 3.8 ppm/℃). In addition, Ba5.1(Sm1-xNdx)8.6Ti18O54 solid solutions with x = 0.25 also showed excellent dielectric properties (εr = 85.2, Q×f= 2200GHz, τf = -0.8 ppm/℃ ). Furthermore, Ba3.9(Sm1-xNdx)9.4Ti18O54 solid solutions with x = 0.5 also showed excellent dielectric properties (εr = 81.8, Q×f= 11050GHz, τf = 19.8 ppm/℃ ).The Ba4.5(Sm1-xNdx)8.6Ti18O54 solid solutions（x = 0.7）with addition of 10wt%glass sintered at the sintering temperature of 1115℃ possesses excellent dielectric properties ofεr = 63.6, Q×f= 5192GHz, τf = 9.6 ppm/℃. Further additions of MnCO3 and Bi2O3 in glass could enhance the densification of ceramics, increase the permittivity and obtain a near zero of temperature coefficient of the resonant frequency. Besides, reducing the particle size could promote the densification of ceramics at lower temperature, increase the dielectric constant and narow down the range of Q×f value.

博士
國立成功大學
電機工程研究所
81
Two indirect routes used to prepare the densely sintered cordierite ceramics are examined. The routes involve sintering of cordierite glass or ceramic cordierite together with lead borosilicate glass, respectively. With the addition of lead borosilicate glass, cordierite glass/ceramic can be densified at lower firing temperature which is attributed to the fluxing effect of lead borosilicate glass. Viscous flow of the flux coalescences the cordierite glass/ceramic particles and densifies the green body. An Avrami-type equation can well describe the sintering of cordierite glass during the initial sintering prior to the crystallization of the glass. Phase transformation from cordierite glass to high temperature stable cordierite form is the major crystallization of the glass. For excess lead borosilicate glass added composites, chemical reaction between lead borosilicate glass and cordierite glass takes place accompanied with the crystallization of cordierite glass. The reaction between lead borosilicate glass and cordierite glass results in crystalline phase lead aluminum silicate. Dielectric constant of the sintered composites is determined by both the existing crystalline structure and the completeness of densification. The relationship between the volume fraction of lead borosilicate glass and dielectric constant can be approximated by a linear equation. During the sintering of ceramic cordierite with lead borosilicate glass, only densification of ceramic cordierite takes place. Besides sintering temperature, physical properties of the composites can be controlled, by changing the amount of lead borosilicate glass to be added, to meet the requirement of ceramic substrates.

碩士
國立成功大學
材料科學(工程)研究所
83
Along with the rapid development of LSI and VLSI, mult ilayer substrates are the only answers to the high density of electric circuits, high calculation rate, and small size of the electronic products. To enable the application of metallic materials of low electric resistivity, namely, Pd-Ag, Cu and Ag, as the conductor in multi-layer subst rates, reducing sintering temperature to below 1000 ℃ is the major issue to be tackled for the substrates.Thus the oxidation of metallic wirings substrate can be excluded during the sintering process.In this study, the compo sition of substrates were based on ZrSiO4/MgSiBO (molar ratio MgO:SiO2:B2 O3=1:1:1) and BaAlxSiyOz.The properties of the studied specimens shows:dielectic constant: 5.34(1KHz);tanδ:0.0475(1 kHz) ;electric resistivity:1E12ohm-cm(500volt);thermal expension coeff icient 3.906 E-6/℃;bending strength:1000 kg/ cm2.

碩士
國立成功大學
材料科學(工程)研究所
83
In this study, powder of the composition BaAlxSiyOz(30wt%) -SiZrO4(10wt%)-MgSiBO(60wt%) is used as the fundation material to be deposited with a metallic aluminum layer on each particle by the vacuum vapor deposition technique. The as- coated powders are then press formed into disk shape before experiencing the sintering process at 700 ℃ for 2 hours in a nitrogen atmosphered tubing furnace. Then sintering at 850 ℃ and 875 ℃ in air. The effects of the amount of aluminum coating, sintering temperature and holding time to the linear shrinkage rate, dielectric constant,lost fact or and microstructure of the as sintred specimensare carefully inves - tigated.For the specimen that is with 2.8 wt% aluminum coating, and sin-tered at 875 ℃ for 7 hours, the electric resistivity( ρ ) is 8.44x1011 ohm-cm, dielectric constant is 4.93(1kHz),loss fac- tor(tan δ ) is 0.073 (1kHz).

博士
國立中央大學
化學工程與材料工程學系
107
Increasing demands for artificial intelligence, automatic systems, and intelligent robots have driven the development of power module packaging. Due to the issues of low re-melting temperature for Sn-based solder ball, warpage induced by CTE mismatch, low packaging lifetime of Sn-based solder, low electromigration resistance for Ag nanoparticle sintering and high cost of Ag, the Cu direct bonding is a potential method for assembling power electronics. Therefore, the development of Cu direct bonding is a main trend for 3D IC packaging in high-power device. Researchers are seeking new materials and novel approaches for low temperature bonding. Traditional bonding requires a temperature for bonding at around 250 oC or above. Usually low temperature bonding requires additional pressure. This study reports a method that can greatly reduce the warpage of the chip. Bonding without pressure also saves the chip from damage due to stress. In this study, we develop a Cu paste of oxidized micron-size Cu particles and water-based fluid of ascorbic acid and gelatin. The Cu paste is successfully applied to Cu foils, Cu pillars and Cu wires direct bonding at 50 oC for 30 min without bonding pressure. The interfacial reaction is investigated by scanning electron microscopy, focus ion beam, transmission electronic microscopy, grazing incidence X-ray diffraction and electron backscatter diffraction. In the sintering processes, we find that the Cu nanoparticle sintering is controlled by oriented attachment. The DLVO theory and kinetic calculation are employed to verify the oriented attachment mechanism in Cu sintering process. This study suggests a very effective method to achieve sintering of Cu at low temperature without pressure, which would greatly reduce the cost of the processing.

碩士
國立臺灣科技大學
材料科學與工程系
102
Phenol formaldehyde resin foams are known for its low density, fire-resistance, low thermal conductivity, good soundproofing, and thermal insulation which have a wide variety of applications. In this research, we aim to make a material that has low density, high heat resistance, and good oil resistance properties by sintering phenolic foam with low temperature. Through the oxidation process with various temperatures and heating rates, a series of resin oxides comprised of different compositions were made. The free foam expansion ratios were found between 2.5 and 5.5 with different formulas of phenolic foams. The densities and bending stresses of oxidized resins decreased while the volume shrinkages increased with the raising sintering temperatures. Thermal gravimetric analysis(TGA) was used to investigate the thermal stabilities of phenolic foams, and the results showed that the stabilities improved with the higher oxidation temperature. Furthermore, the densities and bending stresses declined while the thermal resistances and volume shrinkages increased with larger foam expansion ratio. The phenolic resin foams are found with high Limiting Oxygen Index(LOI) , and met the V-0 level of UL 94, no matter the resins were sintered or not.