Segui questo link per vedere altri tipi di pubblicazioni sul tema: Zn diffusion.
Tesi sul tema "Zn diffusion"
Cita una fonte nei formati APA, MLA, Chicago, Harvard e in molti altri stili
Vedi i top-38 saggi (tesi di laurea o di dottorato) per l'attività di ricerca sul tema "Zn diffusion".
Accanto a ogni fonte nell'elenco di riferimenti c'è un pulsante "Aggiungi alla bibliografia". Premilo e genereremo automaticamente la citazione bibliografica dell'opera scelta nello stile citazionale di cui hai bisogno: APA, MLA, Harvard, Chicago, Vancouver ecc.
Puoi anche scaricare il testo completo della pubblicazione scientifica nel formato .pdf e leggere online l'abstract (il sommario) dell'opera se è presente nei metadati.
Vedi le tesi di molte aree scientifiche e compila una bibliografia corretta.
1
Peksa, Mikulás̆, Sareeya Bureekaew, Rochus Schmid, Jan Lang e Frank Stallmach. "On the nature of adsorption sites for CO 2 in MOF Zn 2 (bdc) 2 dabco". Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-183198.
Testo completo
2
Wehring, Markus, Saeed Amirjalayer, Rochus Schmid e Frank Stallmach. "Anisotropic self-diffusion of guest molecules in Zn 2 (bdc) 2 dabco". Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-185473.
Testo completo
3
Wehring, Markus, Saeed Amirjalayer, Rochus Schmid e Frank Stallmach. "Anisotropic self-diffusion of guest molecules in Zn 2 (bdc) 2 dabco". Diffusion fundamentals 16 (2011) 60, S. 1-2, 2011. https://ul.qucosa.de/id/qucosa%3A13803.
Testo completo
4
Seehamart, Kompichit, Tanin Nanok, Jörg Kärger, Christian Chmelik, Rajamani Krishna e Siegfried Fritzsche. "Examining the reason of the observed influence of the lattice flexibility on the diffusion of ethane in Zn(tbip)". Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-189728.
Testo completo
5
Peksa, Mikulás̆, Sareeya Bureekaew, Rochus Schmid, Jan Lang e Frank Stallmach. "On the nature of adsorption sites for CO 2 in MOF Zn 2 (bdc) 2 dabco". Diffusion fundamentals 20 (2013) 55, S. 1, 2013. https://ul.qucosa.de/id/qucosa%3A13631.
Testo completo
6
Seehamart, Kompichit. "Investigation of the diffusion mechanisms of several hydrocarbons in the Metal-Organic-Framework Zn(tbip)". Doctoral thesis, Universitätsbibliothek Leipzig, 2011. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-68125.
Testo completoAbstract (sommario):
Most of the computer simulations of molecules in Metal-Organic Frameworks (MOFs) to be found in the literature are done with rigid framework. But, Molecular Dynamics (MD) simulations of the self-diffusivity, Ds, of ethane within the one-dimensional 4.5 Å channels of the MOF type Zn(tbip)(H2 tbip = 5-tert-butyl isophthalic acid) presented in this work have shown not only quantitative, but also qualitative, differences in the Ds values for fixed and flexible lattices. Particularly, the dependence of Ds upon the concentration of molecules, c, is strongly influenced by the lattice flexibility. The reasons for this influence are investigated with the aid of probability density plots, free energy landscapes and barriers, along with a determination of the structural changes accompanying increasing c. It is found that for flexible lattices, the tighter, more constrained parts of the channels become wider at higher c; this allows more molecules to diffuse in the central region of the channels.
The investigations for Zn(tbip) have been extended to three equimolar mixtures of ethane/ethane, CO2/ethane and CO2/methanol. The simulations take into account the lattice flexibility. The diffusional characteristics are discussed in relation to molecule properties and lattice geometry. The results show that Zn(tbip) may be a useful material for separating methane/ethane and CO2/ethane mixtures at low concentrations, and CO2/methanol mixtures at high concentrations.
The temperature and concentration dependence of the self-diffusivity of propane diffusion in Zn(tbip) have been investigated as well by performing normal MD and hyper-MD with bias potential simulations. The obtained temperature dependence of the self-diffusivities is analyzed using an Arrhenius relationship, yielding the activation energy to be 9.53 kJ/mol and the pre-exponential factor to be 4.48×10-9 m2s-1. Using this hyper-MD method, interesting mechanisms of the propane molecules able to pass each other and exchange their sites in the channels can be observed. Because of mutual hindrance of propane molecules, the propane self-diffusivities decrease with increasing concentration.
7
Seehamart, Kompichit, Tanin Nanok, Jörg Kärger, Christian Chmelik, Rajamani Krishna e Siegfried Fritzsche. "Examining the reason of the observed influence of the lattice flexibility on the diffusion of ethane in Zn(tbip)". Diffusion fundamentals 11 (2009) 38, S. 1-2, 2009. https://ul.qucosa.de/id/qucosa%3A13988.
Testo completo
8
Gumbmann, Eva Maria. "The effect of minor alloying elements (Mg, Ag, Zn) on the nucleation and precipitation behaviour in AlCuLi alloys". Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GREAI092.
Testo completoAbstract (sommario):
Les alliages Al-Cu-Li sont particulièrement attractifs pour les applications aéronautiques du fait de leur faible densité, haute limite d'élasticité et bonne ténacité. Ils reçoivent une attention particulièrement importante actuellement, depuis le développement de la troisième génération qui contient des concentrations relativement élevées pour le cuivre et relativement basses pour le Li. Ces nouveaux alliages sont caractérisés par une dureté élevée, une bonne résistance à la fatigue et une bonne stabilité thermique. La phase principale de durcissement est la phase T1 – Al2CuLi qui se présente sous la forme de plaquettes d'environ 1 nm d'épaisseur et 50 nm de diamètre, situées sur les plans {111} de la matrice avec une structure hexagonale. La germination efficace de cette phase durcissante entre en compétition avec d'autres précipités des sous-systèmes constituant ces alliages (comme Al-Cu et Al-Li), et nécessite des conditions particulières, en particulier la présence de dislocations (introduites par pré-déformation) et d'éléments d'alliage mineurs (Mg, Ag, Zn). Bien qu'il soit connu depuis longtemps que l'addition de ces éléments favorise la cinétique de précipitation dans ces alliages et le durcissement associé, leurs mécanismes d'action sont encore très mal compris.Dans ce contexte, l'objectif de la thèse est d'évaluer systématiquement l'effet des additions mineures de Mg, Ag et Zn sur la germination, la cinétique de précipitation et le durcissement correspondant. La caractérisation détaillée de la microstructure est utilisée pour comprendre les mécanismes de modification de la microstructure par les éléments mineurs. Les mesures de la diffusion des rayons X à petits angles et la DSC fournissent respectivement la cinétique de précipitation et la séquence de formation des phases. La microscopie électronique en transmission, utilisée en mode conventionnel, en résolution atomique et en mode de cartographie chimique met en évidence la structure et la distribution spatiale des phases. La dureté donne accès au durcissement. Des matériaux à gradient de concentration ont été élaborés et caractérisés pour évaluer l'effet de la concentration des alliages sur la précipitation et le durcissement.Les résultats mettent en évidence que le Mg est l'élément le plus efficace pour accélérer la cinétique de précipitation et de durcissement. L'addition d'Ag et de Zn augmente également la cinétique de précipitation mais dans une moindre mesure. L'addition de Mg change la séquence de précipitation tout au long de la séquence de vieillissement. La différence principale liée à la présence de Mg pour les premiers stades de traitement thermique est observée par rapport à la précipitation sur les dislocations. Dans les alliages qui contiennent du Mg, les dislocations sont décorées par des phases précurseur contenant de Cu et Mg. Par contre dans les alliages sans Mg celles-ci sont associés à des zones GP qui évoluent ensuite en précipités θ'. Cette différence est attribuée à la germination favorable de T1 sur les phases précurseur de Cu/Mg dans les alliages contenant du Mg, et par la saturation des sites de germination hétérogène par θ' dans les alliages sans Mg.L'augmentation de dureté associée à l'addition d'Ag et Zn est attribuée à une fraction volumique plus élevé de la phase T1. Ag est ségrège à l'interface entre T1 et la matrice et Zn est incorporé dans la structure de T1. Ces résultats suggèrent que les additions de Zn et Ag stimulent la formation de T1.L'influence de la concentration en éléments d'addition mineurs a été caractérisée par une approche résolue en temps et en espace, sur les matériaux contenant un gradient en composition. Cela révèle que l'effet de l'addition de Mg sur la précipitation se produit à une valeur seuil de ~0.1% en poids, suggérant que cela est la concentration nécessaire pour germer des phases précurseur sur les dislocations dans les premiers stades de la précipitationAl-Cu-Li alloys are very attractive for aerospace applications alloys due to their low density, high modulus and high strength. They are experiencing a strong interest since the so-called 3rd generation alloys, with relatively high Cu and low Li content, have been developed with high toughness, fatigue resistance and thermal stability. The main precipitating phase in these alloys is the T1-phase which precipitates on {111}Al-planes with a hexagonal structure. It is known that obtaining a fine dispersion of T1, and hence a high strength requires the presence of dislocations as nucleation sites. In addition, commercial Al-Cu-Li alloys contain several minor alloying elements such as Mg, Ag and Zn, which help reaching the desired properties. Although the effect of these minor additions on precipitation of T1 has been characterized, it has not been understood yet.In this context the aim of this thesis is to systematically investigate the effect of minor additions of Mg, Ag and Zn on precipitation nucleation, precipitation kinetics and related strengthening, and to use a detailed characterization of the microstructure to understand the mechanisms by which the modifications induced by these minor additions take place. In-situ Small-Angle X-ray Scattering and Differential Scanning Calorimetry provide the precipitation kinetics and sequence, respectively. Transmission Electron Microscopy, both in conventional mode, atomically-resolved and in chemical mapping mode, reveals the structure and distribution of phases. Hardness gives access to the strengthening. Compositionally gradient materials are fabricated and characterized to evaluate the effect of alloy composition on precipitation and strengthening.The results reveal that Mg is most effective in order to enhance precipitation kinetics and hardening. Additional Ag and Zn further enhance precipitation kinetics but to a lower extent. The addition of Mg changes the precipitation sequence at all times of ageing. The main differences in early aging conditions are observed with respect to precipitation on dislocations. In Mg-containing alloys, dislocations are decorated by Cu-Mg precursor phases, whereas dislocations in Mg-free alloys are mainly associated to GP-zones which evolve subsequently into θ'-phase. In fully precipitated conditions the microstructure of Mg-containing alloys is dominated by the T1 phase, whereas that of Mg-free alloys is dominated by the θ'-phase. This difference is attributed to the favourable nucleation of T1 on Mg-Cu precursor phases in the Mg-containing alloys, and to the consumption of T1-heterogeneous nucleation sites by the θ'-phase in the Mg-free alloys.The increase of hardness associated to the addition of Ag and Zn is associated to a higher volume fraction of the T1-phase. Ag was found to segregate at the T1/matrix interface and Zn was incorporated into the T1-phase, so that it is assumed that their additions stimulate the formation of T1.The influence of the concentration of the minor solute additions has been characterised by combined space and time-resolved experiments on compositionally gradient materials. It reveals that the effect of an Mg addition on precipitation occurs at a threshold level of ~0.1wt%, suggesting that this concentration is that necessary to form the precursor phase at the dislocations during early ageing
9
Degaga, Gemechis D. "Physicochemical, Spectroscopic Properties, and Diffusion Mechanisms of Small Hydrocarbon Molecules in MOF-74-Mg/Zn| A Quantum Chemical Investigation". Thesis, Michigan Technological University, 2018. http://pqdtopen.proquest.com/#viewpdf?dispub=10791501.
Testo completoAbstract (sommario):
In petroleum refining industries, the fracturing process allows for the cracking of long-chain hydrocarbons into a mixture of small olefin and paraffin molecules that are then separated via the energetically and monetarily demanding cryogenic distillation process. In an attempt to mitigate both energetic and capital consumptions, selective sorption of light hydrocarbons by tunable sorbents, such as metal-organic frameworks (MOFs), appears to be the most promising alternative for a more efficient gas separation process. MOFs are novel porous materials assembled from inorganic bricks connected by organic linkers. From a crystal engineering stand point, MOFs are advantageous in creating a range of microporous (0.2–2.0 nm) to mesoporous (>50 nm) void cavities, presenting unique opportunities for the functionalization of both the organic linkers and the void. Of significant importance is the MOF-74-M family (M = metal), characterized by a high density of open metal sites, that is not fully coordinated metal centers. This family of MOF is also known as CPO-27-M. MOF-74 have demonstrated more separation potential than other known MOFs and zeolites. Density functional theory (DFT), as implemented within a linear combination of atomic orbital (LCAO) approach, has been used to investigate the selective sorption of C1-C4 hydrocarbons in MOF-74-Mg/Zn. The study was first implemented by adopting a molecular cluster approach, and later by applying periodic boundary conditions (PBC). While both modellistic approaches agree in showing significant differences in binding energies between olefins and paraffins adsorbed at the MOFs’ open metal sites, results reported at the molecular cluster level show underestimation when compared to those obtained at the PBC level. The use of PBC models allow for the correcting of binding energies for basis set superposition error (BSSE), molecular lateral interaction (LI), zero-point energy (ZPE), and thermal energy (TE) contributions. As such, results obtained at the PBC level are directly comparable to experimental calorimetric values (i.e., heat of adsorptions). This work discusses, for the first time, the origin of the fictitious agreement between binding energies obtained with molecular clusters and experimental heats of adsorption, identifying its origin as due to compensation of errors. Spectroscopy studies based on the intensities and frequency shifts with respect to the molecules in the gas phase are presented as a further investigation of the interaction of the small hydrocarbons (C1-C 2) with the open metal sites in MOF-74-Mg. In an attempt to provide a more comprehensive description of the behavior of the hydrocarbon molecules, results from diffusion mechanism studies are also presented. The investigations of the diffusion mechanisms are based on the use of climbing-image nudge elastic band (CI-NEB) simulations, coupled with van der Waals functional (vdW-DF) and ultra-soft pseudopotentials as implemented within the plane-wave (PW) DFT approach. The CI-NEB studies showed that paraffin molecules are more energetically favored to diffuse within and along the cavity of MOF-74-Mg with respect to their olefin counterparts.
10
Landaverde, Alvarado Carlos Jose. "Sorption, Transport and Gas Separation Properties of Zn-Based Metal Organic Frameworks (MOFs) and their Application in CO₂ Capture". Diss., Virginia Tech, 2016. http://hdl.handle.net/10919/73214.
Testo completoAbstract (sommario):
Adsorption, separation and conversion of CO₂ from industrial processes are among the priorities of the scientific community aimed at mitigating the effects of greenhouse gases on the environment. One of the main focuses is the capture of CO₂ at stationary point sources from fossil fuel emissions using porous crystalline materials. Porous crystalline materials can reduce the energy costs associated with CO₂ capture by offering high adsorption rates, low material regeneration energy penalties and favorable kinetic pathways for CO₂ separation. MOFs consist of polymeric inorganic networks with adjustable chemical functionality and well-defined pores that make them ideal for these applications. The objective of this research was to test the potential for CO₂ capture on Zn-based MOFs by studying their sorption, transport and gas separation properties as adsorbents and continuous membranes.
Three Zn-based MOFs with open Zn-metal sites were initially studied. Zn4(pdc)4(DMF)2•3DMF (1) exhibited the best properties for CO₂ capture and was investigated further under realistic CO₂ capture conditions. The MOF exhibited preferential CO₂ adsorption based on a high enthalpy of adsorption and selectivity of CO₂ over N₂ and CH₄. Sorption dynamics of CO₂ indicated fast adsorption and a low activation energy for sorption. Diffusion inside the pores is the rate-limiting step for diffusion, and changes in the process temperature can enhance CO₂ separation. Desorption kinetics indicated that CO₂ has longer residence times and lower activation energies for desorption than N₂ and CH₄. This suggests that the selective adsorption of CO₂ is favored.
MOF/Polymer membranes were synthesized via a solvothermal method with structural defects sealed by a polymer coating. This method facilitates the permeation measurements of materials that cannot form uniform-defect-free layers. The membrane permeation of CO₂, CH₄, N₂ and H₂ exhibited a linear relation to the inverse square root of the molecular weight of the permanent gases, indicating that diffusion occurs in the Knudsen regime. Permselectivity was well-predicted by the Knudsen model with no temperature dependence, and transport occurs inside the pores of the membrane. MOF (1) exhibits ideal properties for future applications in CO₂ capture as an adsorbent.Ph. D.
11
Kammerer, Catherine. "Interdiffusion and Impurity Diffusion in Magnesium Solid Solutions". Master's thesis, University of Central Florida, 2013. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5652.
Testo completoAbstract (sommario):
Magnesium, being lightweight, offers potential to be developed into extensive structural applications. The transportation segment has particular interest in Mg and Mg alloy for applications where reduced vehicle weight is proportional to increased fuel efficiency. Aluminum and zinc are two of the most common alloying elements in commercial Mg alloys. They improve the physical properties of Mg through solid solution strengthening and precipitation hardening. Diffusion plays a key role in the kinetics of and microstructural development during solidification and heat treatment. However, there is limited diffusion data available for Mg and Mg alloys. In particular, because Al is mono-isotopic, tracer diffusion data is not available. Interdiffusion of Mg solid solution with Zn also does not exist in literature. The diffusional interaction of Al and Zn in Mg solid solution at temperatures ranging from 623 – 723K was examined using solid-to-solid diffusion couple method. The objective of this thesis is two-fold: first, is the examination of interdiffusion in the Mg solid solution phase of the binary Mg-Al and Mg-Zn systems; second, is to explore non-conventional analytical methods to determine impurity diffusion coefficients. The quality of diffusion bonding was examined by optical microscopy and scanning electron microscopy with X-ray energy dispersive spectroscopy, and concentration profiles were determined using electron probe microanalysis with pure standards and ZAF matrix correction. Analytical methods of concentration profiles based on Boltzmann-Matano analysis for binary alloys are presented along with compositional dependent interdiffusion coefficients. As the concentration of Al or Zn approaches the dilute ends, an analytical approach based on the Hall method was employed to estimate the impurity diffusion coefficients. Zinc was observed to diffuse faster than Al, and in fact, the impurity diffusion coefficient of Al was smaller than the self-diffusion coefficient of Mg. In the Mg solid solution with Al, interdiffusion coefficients increased by an order of magnitude with an increase in Al concentration. Activation energy and pre-exponential factor for the average effective interdiffusion coefficient in Mg solid solution with Al was determined to be 186.8 KJ/mole and 7.69 x 10-1 m^2/sec. On the other hand, in the Mg solid solution with Zn, interdiffusion coefficients did not vary significantly as a function of Zn concentration. Activation energy and pre-exponential factor for the average effective interdiffusion coefficient in Mg solid solution with Zn was determined to be 129.5 KJ/mole and 2.67 x 10-4 m^2/sec. Impurity diffusion coefficients of Al in Mg was determined to have activation energy and pre-exponential factor of 144.1 KJ/mole and 1.61 x 10-4 m^2/sec. Impurity diffusion coefficients of Zn in Mg was determined to have activation energy and pre-exponential factor of 109.8 KJ/mole and 1.03 x 10-5 m^2/sec. Temperature and composition-dependence of interdiffusion coefficients and impurity diffusion coefficients are examined with respect to reported values in literature, thermodynamic factor, ?, diffusion mechanisms in hexagonal close packed structure, and experimental uncertainty.M.S.M.S.E.
Masters
Materials Science Engineering
Engineering and Computer Science
Materials Science and Engineering
12
Belgrand, Thierry. "Etude par diffusion Raman du diagramme de phases (P,T) d'un composé présentant des phases incommensurables : le tétraméthylammonium tétrachlorozincate (TMATC-Zn)". Lille 1, 1987. http://www.theses.fr/1987LIL10127.
Testo completoAbstract (sommario):
Etude sur un dispositif permettant de suivre les variations en fonction de la température (-40* °C à +40° C et de la pression (1 à 4000 bar) ; analyse des évolutions des fréquences, des largeurs et des intensités des bandes correspondant aux modes de réseau, en fonction de la pression pour les isothermes 32°, 29°, 14° et 5° C et établissement d'un diagramme de phases présentant un bon accord avec le diagramme obtenu à partir des mesures de la constante diélectrique. Les résultats obtenus suggèrent l'existence de nouvelles transitions de phase et la possibilité d'un mécanisme ordre-désordre
13
Belgrand, Thierry. "Etude par diffusion raman du diagramme de phases (P,T) d'un composé présentant des phases incommensurables le tétraméthylammonium tétrachlorozincate (TMACT-Zn) /". Grenoble 2 : ANRT, 1987. http://catalogue.bnf.fr/ark:/12148/cb37602751p.
Testo completo
14
Frontier, Jean-Pierre. "Contribution à la détermination de profils de concentration par émission X induite par bombardement de protons : application à l'étude de la diffusion du zinc dans l'alliage Ag-Zn". Paris 11, 1987. http://www.theses.fr/1987PA112006.
Testo completoAbstract (sommario):
Ce travail est une contribution à l'étude des possibilités d'utiliser l'émission de rayonnements X induits par bombardement de protons (P. I. X. E. ) pour relever la répartition des éléments présents sous la surface des corps solides, dans une gamme de profondeurs comprise entre 1 et 10 micromètres et plus. On exprime sous forme d'une intégrale de convolution l'intensité des rayonnements X caractéristiques de l’élément étudié, et l'on montre que l'on peut, en principe, relever la concentration de cet élément en fonction de sa distance à la surface, en déconvoluant les intensités mesurées lors d'une série d'expériences dans laquelle on a fait varier systématiquement l'énergie des protons incidents (donc leur pénétration). La procédure directe de déconvolution, qui conduit inverser une matrice mal conditionnée, ne convient pas. Aussi nous avons généralisé une procédure itérative qui avait déjà été utilisée par Yegh pour résoudre un problème similaire. Alternativement, nous avons montré que l'on obtenait des résultats sensiblement meilleurs en utilisant une procédure d'ajustement paramétrique. Avec l'un et l'autre de ces deux algorithmes, et pour des protons de 0,45 à 2 MeV, cette technique, non destructive, nous a permis de relever, sur une profondeur maximum de 6 micromètres, des profils d'appauvrissement du zinc sous la surface d'alliages Ag-Zn-3 atomes % de zinc, recuits sous vide. Pour les profondeurs plus grandes, nous avons développé avec succès une technique destructive, par analyse des tranches successives prélevées parallèlement à la surface. Nous avons comparé tous nos résultats expérimentaux à ceux obtenus à la microsonde électronique et à ceux prévus par la théorie de la diffusion. Nous discutons enfin les possibilités d'améliorer la résolution en profondeur en développant des techniques, soit d'abrasion contrôlée de la surface, soit d'analyse de coupes biaises.
15
Ben, Ali Neji. "Caractérisation et modélisation micromécanique de la propagation de fissures fragiles par effet de l'hydrogène dans les alliages AA 7xxx". Phd thesis, Ecole Nationale Supérieure des Mines de Saint-Etienne, 2011. http://tel.archives-ouvertes.fr/tel-00648428.
Testo completoAbstract (sommario):
Nous étudions la fragilisation par l'hydrogène de l'alliage d'aluminium 7108. Une technique expérimentale spécifique a été développée : Un pré-chargement en hydrogène des échantillons, à travers un dépôt de nickel de quelques dizaines de microns, qui empêche la dissolution du substrat d'aluminium, est utilisé. Il permet la comparaison de la résistance à la fragilisation de différentes microstructures modèles. Nous étudions l'effet du traitement thermique et de la précipitation sur la sensibilité à l'hydrogène pour des vitesses de déformation macroscopiques imposées variables. Différents modes de rupture sont observés ainsi que des transitions entre eux. Au moyen de simulations numériques à l'échelle mésoscopique, l'effet de taille des précipités intergranulaires pré-fragilisés sur la ténacité des joints de grains est estimé, en utilisant un modèle de zone cohésive. Nous analysons la compétition entre la diffusion de l'hydrogène vers la pointe de la fissure et la vitesse de fissuration par un couplage mécanique - diffusion basé sur la diffusion de l'hydrogène assistée par la contrainte hydrostatique. Une vitesse critique au-delà de laquelle l'hydrogène ne peut plus suivre la fissure, est mise en évidence. L'influence de la microstructure du joint de grains sur cette vitesse est analysée. La valeur est comparée à une estimation des vitesses de propagation expérimentales obtenues pour différentes vitesses de déformation macroscopiques. Nous analysons l'effet du piégeage de l'hydrogène par les précipités intergranulaires et la désorption sur la répartition de l'hydrogène le long du joint de grains en imposant un flux au niveau de l'interface précipités - matrice.
16
Seehamart, Kompichit [Verfasser], Jörg [Akademischer Betreuer] Kärger e Berend [Akademischer Betreuer] Smit. "Investigation of the diffusion mechanisms of several hydrocarbons in the Metal-Organic-Framework Zn(tbip) / Kompichit Seehamart. Gutachter: Jörg Kärger ; Berend Smit. Betreuer: Jörg Kärger". Leipzig : Universitätsbibliothek Leipzig, 2011. http://d-nb.info/1020088958/34.
Testo completo
17
Elsayed, Mohamed [Verfasser], R. [Akademischer Betreuer] Krause-Rehberg, Nicolaas A. [Akademischer Betreuer] Stolwijk e H. S. [Akademischer Betreuer] Leipner. "The appearance of vacancies during Cu and Zn diffusion in III-V compound semiconductors / Mohamed Elsayed. Betreuer: R. Krause-Rehberg ; Nicolaas A. Stolwijk ; H. S. Leipner". Halle, Saale : Universitäts- und Landesbibliothek Sachsen-Anhalt, 2011. http://d-nb.info/1025135849/34.
Testo completo
18
Desplat, Joël. "Mesures et simulation par Monte-Carlo d'ordre local et de déplacements élastiques dans l'alliage Al-Zn". Grenoble INPG, 1994. http://www.theses.fr/1994INPG0040.
Testo completoAbstract (sommario):
La présence d'une énergie élastique, modifie les caractères des transitions ordre/désordre ou démixtion dans les alliages. Cette influence a généralement été étudiée d'un point de vue thermodynamique par des approches macroscopiques. D'autre part, la diffusion diffuse de neutrons permet d'accéder simultanément à l'ordre à courte distance et aux déplacements atomiques dans les cristaux. Ce travail vise à discuter l'influence des effets de taille sur les diagrammes de phases (dissymétrie et fluctuations). Nous avons utilisé un modèle microscopique, basé sur l'Hamiltonien d'Ising ferromagnétique limité aux premiers voisins, qui permet de prendre en compte les effets élastiques. A partir d'une approximation de champ moyen, (théorie de Landau), nous avons relié par un calcul analytique ces effets au déplacement d'une lacune de démixtion. En utilisant un algorithme de Métropolis, nous avons ensuite construit des programmes de simulation de Monte-Carlo. Ceux-ci ont permis de calculer à la fois le diagramme de phases et fa diffusion diffuse de systèmes à démixtion cfc, et de confirmer les tendances mises en évidence par le champ moyen. Cette technique a été appliquée au cas du système Al-Zn. Des mesures de diffusion diffuse nous ont permis de vérifier la présence d'effets de taille, et d'obtenir des potentiels d'interaction de paires à partir de l'ordre local. Par simulation de notre modèle, ces derniers nous ont permis de reproduire qualitativement le diagramme de phases et la section efficace de diffusion diffuse expérimentaux. Le comportement critique, expérimental et simulé, de ce système est voisin de celui de l'Hamiltonien d'Ising non perturbé. Ces résultats sont en accord avec ceux d'études plus anciennesThere is strong evidence of size effect influence during order/disorder or demixing phase transitions. From a thermodynamic point of view, these phenomena have usually been studied using macroscopic models. Moreover, neutron diffuse scattering experiments have yielded informations about both local order and static displacements. We have studied the interaction between elastic effects and phase diagrams (dissymetry and fluctuations). Starting from a ferromagnetic Ising Hamìltonian limited to nearest neighbour interaction, we have used a microscopic model accounting for elastic_displacements. A mean field type method and Landau theory have enabled us to obtain an analytical relation between elastic effects and the position of a miscibility gap. Monte-Carlo simulation following Metropolis algorithm have yielded simultaneously phase diagrams and diffuse scattering cross sections of a cfc demixing system. The former was in agreement with the results of our mean field approximation. We have used this method to study the case of an Al-Zn alloy. Neutron diffuse scattering experiments have enabled us to verify the existence of size effects in this system and to obtain effective pair interactions. We were able to reproduce with Monte-Carlo both phase diagrams and elastic diffuse scattering cross-sections, at least qualitatively. In the critical region, both simulated and experimental scattering were very similar to that of an unperturbed Ising Hamiltonian. These results present a satisfying agreement with those of previous studies
19
Frontier, Jean-Pierre. "Contribution à la détermination de profils de concentration par émission X induite par bombardement de protons application à l'étude de la diffusion du zinc dans l'alliage Ag-Zn /". Grenoble 2 : ANRT, 1987. http://catalogue.bnf.fr/ark:/12148/cb376052186.
Testo completo
20
Calzavara, Yoann. "Liens entre évolution structurale et propriétés physiques de fluides autour de leur point critique par absorption X et diffusion X aux petits angles". Université Joseph Fourier (Grenoble ; 1971-2015), 2001. http://www.theses.fr/2001GRE10086.
Testo completoAbstract (sommario):
Cette these a pour but l'etude de l'evolution electronique et structurale a l'echelle microscopique de fluides au voisinage de leur point critique par absorption x ou diffusion x aux petits angles. Les experiences ont ete effectuees grace a un appareillage specifique hautes temperatures / pressions installees sur les lignes bm32 et bm2 de l'esrf de grenoble, synchrotron de 3 e m e generation. Nous nous sommes tout d'abord interesses a un systeme fondamental, le selenium, qui est un liquide covalent presentant une transition electronique semiconducteur-metal-isolant au voisinage du point critique. Le travail effectue a permis de mettre en evidence les changements electronique et structural intervenant dans le domaine supercritique, expliquant ainsi l'apparition du caractere metallique du selenium au voisinage du point critique. Nous avons en outre mis en exergue l'existence d'une phase dont la structure locale est de type metallique alors qu'elle est macroscopiquement isolante. Nous avons egalement porte notre interet sur une etude des proprietes de solvatation / precipitation d'un sel, le znbr 2, en solution aqueuse. Nous avons pu suivre in situ les changements structuraux de l'anion et du cation en solution a haute t & p. Nous avons considere les influences respectives de differents parametres, comme la pression, la temperature ou la concentration. Une precipitation a ete observee pour ce compose uniquement dans le cas d'une forte concentration. L'analyse des spectres exafs couplee a des simulations ab initio du xanes de ces spectres a permis de proposer un modele precis des complexes formes en conditions supercritiques en accord avec des resultats de raman. Nous avons clairement montre la difference de comportement du cation et de l'anion. Finalement, les modifications de la structure ont pu etre reliees aux proprietes du solvant.
21
Kirmse, Holm. "Transmissionselektronenmikroskopische Untersuchungen von II-VI-Verbindungshalbleitern unterschiedlicher Dimensionierung". Doctoral thesis, [S.l. : s.n.], 2000. http://deposit.ddb.de/cgi-bin/dokserv?idn=962717835.
Testo completo
22
Tardot, Alain. "Diffraction de rayons X et interdiffusion dans les superréseaux CdTe/CdZnTe et CdTe/HgTe". Grenoble 1, 1993. http://www.theses.fr/1993GRE10090.
Testo completoAbstract (sommario):
Ce travail concerne la caracterisation structurale et l'etude de l'interdiffusion dans les superreseaux contraints cdte/cdznte et cdte/hgte, elabores par epitaxie par jets moleculaires, au moyen de la double diffraction de rayons x. Les parametres structuraux (composition, epaisseur, etat de deformation) sont obtenus de facon precise en utilisant conjointement l'experience et la simulation en theorie cinematique. Les coefficients d'interdiffusion des couples cd/zn (400c) et cd/hg (200c) sont mesures par diffraction x. Ils permettent de calculer les profils de concentration des superreseaux en fonction de la temperature et du temps de recuit. Par extrapolation, nous precisons les conditions de croissance pour obtenir des interfaces raides, qui sont necessaires pour des dispositifs optoelectroniques performants
23
Milani, Narges. "Zinc oxide nanoparticles in the soil environment : dissolution, speciation, retention and bioavailability". Thesis, 2012. http://hdl.handle.net/2440/82374.
Testo completoAbstract (sommario):
Zinc oxide nanoparticles (ZnO NPs) have unique physical and chemical characteristics which deviate from larger particles of the same material, due to their extremely small size, higher specific surface area and surface reactivity. The peculiar properties of ZnO NPs could potentially improve zinc (Zn) fertilizers for sustainable agriculture. This is based on the assumption that ZnO NPs provide a more soluble and bioavailable source of Zn in soil compared to micron- or millimetre- sized (bulk) ZnO particles currently used for Zn fertilizers in Zn deficient soils. However, a thorough understanding of the fate and reactions in soils and interactions of nanoparticles with plants of ZnO NPs is required prior to the recommendation for use of these novel materials. Therefore, there is a need to investigate dissolution, diffusion, transformation, partitioning and availability of manufactured ZnO NPs in soil to ensure safer and more sustainable application of ZnO NPs as a new source of Zn fertilisers for plants, and better management of their potential risks. Given inclusion of Zn in macronutrient fertilizers is the common procedure for their field application, ZnO NPs and bulk ZnO were coated onto macronutrient fertilizers (monoammonium phosphate (MAP) and urea) and dissolution kinetics, diffusion and solid phase speciation of Zn from coated fertilizers were evaluated. Coating of ZnO on macronutrient fertilizers significantly affected solubility and dissolution kinetics of the ZnO sources, but nano-sized ZnO did not show any enhanced solubility over bulk ZnO. The low pH value of ZnO-coated MAP granules resulted in greater and faster dissolution of ZnO compared to ZnO-coated urea granules. However, interactions of ZnO particles with phosphate in MAP granules likely resulted in precipitation of Zn-phosphate species. The high pH and ionic strength of the dissolving solution resultant from hydrolysis of urea likely promoted aggregation of any ZnO NPs released from coated urea granules and also hindered dissolution of ZnO. To evaluate changes in Zn speciation with coating of the ZnO sources and after incorporation of the coated-fertilizers into an alkaline calcareous soil, synchrotron-based micro X-ray absorption fine structure (μ-XAFS) method was used. The findings confirmed precipitation of Zn-phosphate species at the surface of MAP fertilizer granules irrespective of the size of ZnO particles used for coating. For coated urea, the Zn remained as ZnO species for both nano-sized and bulk ZnO coatings. Solid phase speciation in the fertilized soil varied with distance from the point of fertilizer application. Significant amounts of Zn(OH)₂ and ZnCO₃ species were identified in the soil some distance from coated urea and MAP, respectively, indicating dissolution/precipitation processes were active. Moreover, limited and comparable diffusion of Zn from coated fertilizers with nanoparticulate or bulk ZnO into soil was observed using micro x-ray fluorescence mapping (μ-XRF). Transformation of Zn at the surface of MAP granules, mass flow of water towards the hygroscopic fertilizer granules or strong aggregation of ZnO nanoparticles released from urea granules could have been the mechanisms which restricted Zn diffusion. Given that coating of ZnO on macronutrient fertilizers markedly reduced Zn solubility, reactions of ZnO NPs and bulk ZnO in soil were studied when applied as the pure oxides. Availability of Zn for durum wheat (Triticum durum) plants from nanoparticulate and bulk sources of ZnO was evaluated in an acidic and an alkaline soil using an isotopic dilution procedure (L value). Significant dissolution and plant acquisition of Zn from ZnO was observed (ca. 50 – 100 % of added), even with limited pre-incubation of soils with the Zn sources. However, no significant effect of particle size was observed on plant acquisition of Zn from the ZnO. Retention and dissolution of ZnO NPs and dissolved Zn species from ZnO NPs was further investigated in five soils with diverse physical and chemical properties. Strong retention of ZnO NPs and/or dissolved Zn species from ZnO NPs was found in all soils especially in alkaline and calcareous soils. The adsorption affinity of ZnO NPs was generally greater than that of soluble Zn, which suggested ZnO NPs were retained more strongly than soluble Zn in soils. Soil pH and clay content of soil were the most important soil properties affecting retention, although the number of soils used was too small to draw firm conclusions as soil parameters co-varied. Generally, nanoparticulate forms of ZnO appear to offer little advantage over bulk-sized ZnO as a source of fertilizer Zn to crops. Rapid dissolution of ZnO NPs and partitioning of dissolved Zn species derived from ZnO NPs and/or high retention of ZnO NPs in soils suggested that soil application of manufactured ZnO NPs would not appear to offer any benefits over bulk ZnO, whether applied in pure form or along with macronutrient fertilisers. However, from an ecotoxicological point of view, ZnO NPs would not be persistent in soil systems and hence their mobility in soil would be limited. Therefore the risks associated with application of ZnO NPs in soil would be similar to that of soluble Zn.Thesis (Ph.D.) -- University of Adelaide, School of Agriculture, Food and Wine, 2012
24
Bo-JyunCiou e 邱柏鈞. "The dipole evolution caused by the outward diffusion of Zn atoms during the oxidization process of Zn dots". Thesis, 2019. http://ndltd.ncl.edu.tw/handle/rk3k3f.
Testo completo
25
Hu, Ding Da, e 胡頂達. "Fabrication of vertical cavity surface emitting laser by selective Zn-diffusion". Thesis, 1995. http://ndltd.ncl.edu.tw/handle/26607173243910418317.
Testo completo
26
Sun, Ju-Ying, e 孫如瑩. "A Combined Superplastic Forming/Diffusion Bonding Processing of an Al-Zn-Mg Alloy and a SiCp/Al-Zn-Mg Alloy Composite". Thesis, 1997. http://ndltd.ncl.edu.tw/handle/75609922489236525144.
Testo completoAbstract (sommario):
碩士大同工學院
材料工程學系
85
ABSTRACT In this study the SPF, the DB and the combined SPF/DB of a superplastic 7475 Al alloy were studied. The solid state diffusion bonding and the transient liquid Zn interlayer bonding techniques to join similar materialsincluding superplastic 7475 Al alloy, non-superplastic 7075 Al alloy and SiCP/7075 Al alloy composite sheets were examined. A variety of bonding techniques have been investigated on Al alloys including solid state diffusion bonding (SSDB) with or without a thin 7475 Al alloy interlayer and trientliquid phase bonding (TLPB) using a thin foil Zn interlayer. Diffusion bonding of Al alloys specimens were carried out under a variety of bonding parameters including compressive stress of 2, 4 and 6 MPa, bonding times from 2 to 4 hours and bonding temperatures of 515 and 530℃ in 10-4 torr vacuum. The integrity of the bonds were examined using optical and scanning electronmicroscopies. The bond strengths were evaluated using a single overlap shear test. The results showed that, with proper bonding conditions and surfacepre- treatment, successful bonds with lap shear stress (T6 condition) greater than 90 % of that of the parent alloy can be achieved. The process variables of the combined SPF/DB practices of superplastic 7475 Al alloy specimens were diffusion bonding at 515 or 530℃ for 2~4 hours under 2, 4 and 6 MPa compressive stress in 10-4 torr vacuum and superplastic bulge forming at the same temperature under 0.3 MPa gas pressure for 30 minutes. Theresults showed that the bonding strengths in the combined SPF/DB processed specimens were similar to those in DB processed specimens under similar bondingconditions, and that the properties in the joisection of the SPF/DB specimens were not influenced by the latter SPF processing. In addition to these, an attempt of the combined SPF/DB process on a SiCP/7075 Al alloy composite was conducted and the results was briefly discussed. From the attainable dome height data and the uniformity in thickness distribution of bulged domes, it was found that the SPF behavior in the two-sheet SPF/DB superplastic 7475 Al alloy specimens was better than in the two-sheet SPF/DB SiCp/7075 Al alloy composite specimens.
27
Zhang, Yinan. "Experimental investigation of the Ca-Mg-Zn system via Diffusion Couples and Key Experiments". Thesis, 2011. http://spectrum.library.concordia.ca/7575/1/Zhang_MASc_S2011.pdf.
Testo completoAbstract (sommario):
Nine diffusion couples and 32 key samples have been used to study the phase diagram of the Ca-Mg-Zn system at 335ºC and crystal structures of ternary intermetallics. Four ternary compounds have been found in this system: Ca3MgxZn15-x (4.6≤x≤12 at 335ºC) (IM1); Ca14.5Mg15.8Zn69.7 (IM2); CaxMgyZnz (x = 8.2-9.1; y = 27.1-31.0; z = 60.8-64.7 at 335ºC) (IM3) and Ca1.5Mg55.3Zn43.2 (IM4). Phase relations and solubility limits have been determined for binary and ternary compounds using Scanning Electron Microscopy, Electron Probe Microanalysis and X-ray Diffraction techniques. Crystal structures of the IM1 and IM3 ternary compounds have been studied by means of XRD, Transmission Electron Microscopy and Electron Back Scattered Diffraction. The refinement of the XRD patterns for IM1 ternary compound has been carried out by Rietveld analysis. XRD data has shown that this solid solution crystallizes in hexagonal structure having P63/mmc (194) space group and Sc3Ni11Si4 prototype. The lattice parameters decrease linearly with decreasing Mg content obeying Vegard’s law. The fractional atomic occupancy of 6h, 4f, 2b and 12k sites of this compound are function of Mg concentration. Focused Ion Beam has been used to lift Transmission Electron Microscopy specimen of the ternary compound and the hexagonal structure has been confirmed by means of Selected Area Electron Diffraction data. Based on the atomic occupancy results and the crystallographic details, a three sublattice (Ca)(Zn)(Mg,Zn)4 model is proposed for this compound.
Three binary compounds are found to have extended solid solubility into the ternary system. CaZn11, CaZn13 and Mg2Ca are forming substitutional solid solutions where Mg substitutes Zn atoms in the first two compounds, and Zn substitutes both Ca and Mg atoms in Mg2Ca. Based on the current experimental results, the isothermal section of Ca-Mg-Zn phase diagram at 335ºC has been constructed. The morphologies of diffusion couples have been studied in the Ca-Mg-Zn system at 335ºC. Depending on the terminal compositions of the diffusion couples, the morphology of the two-phase regions in the diffusion zone has: ‘tooth-like’ morphology or matrix phase with isolated and/or dendritic shape precipitates morphology.
28
Chang, Ting-wei, e 張庭瑋. "Study of Structure and Corrosion ofSolid-Diffusion Zn Coating on Low Carbon Steel SAE1010". Thesis, 2009. http://ndltd.ncl.edu.tw/handle/70648469320853303417.
Testo completoAbstract (sommario):
碩士國立成功大學
材料科學及工程學系碩博士班
97
Zn coating is better and cheaper than other metal coatings in resisting the Cl- ion corrosion, so it is widely used for protecting the steel tools which are working under seawater environment. Lately the coating methods like hot-dip galvanizing, electroplating and CVD/PVD by using vacuum furnace or fluidized bed are extensively applied in fabricating of Zn coating. But, it still exists some problems with cost, environment pollution, and workpiece measurement in continuous process by using these coating methods. Solid-diffusion coating method can form a continuous Fe-Zn outer layer in uniform thickness by controlling the process conditions. In this study, Zn coating is formed using solid-diffusion coating method by heating the substrate to 400℃ for 2 hours. The multi-layer films not only enhance the corrosion resistance and surface hardness, but also improve the recyclability and reusability of Zn powder by some specific repeated cycles. Although the addition of Al powder in Zn coating reduces the coating thickness, it improves the anti-corrosion property under alkaline environment. After electrochemical analysis, the Zn coatings made by solid-diffusion method reveal the best corrosion resistance and the highest corrosion potential under alkaline environment. So we can expect the Zn coating with lower corrosion probability to provide better sacrificed protection.
29
傅安教. "Study of Zn diffusion and its application for compositional mixing in quantum well heterostructures". Thesis, 2013. http://ndltd.ncl.edu.tw/handle/81328668546642556175.
Testo completoAbstract (sommario):
碩士國立清華大學
電子工程研究所
101
In this study, we used the sealed-quartz-ampoules to produce ZnAs2 as our diffusion source to perform Zn diffusion, and optimized the deposition process by varying parameters to deposit silicon nitride films and adjust the refractive indices to be in the range of 2.0 to 2.05, utilizing its characteristics of having a denser and less permeable structure than SiO2 to inhibit the Zn diffusion and IILD. We used sealed quartz ampoules to do all diffusion experiments. At first, we did the Zn diffusion into n+GaAs (Si doped~1018cm-3) substrates with ZnAs2 as the diffusion source at different diffusion temperatures for various times. Among three temperatures, we chose 600℃ to perform our Zn diffusion studies for different Al contents of AlxGa1-xAl (~2um) layer on GaAs substrate and Al1-xGaxAs / GaAs structures. We have demonstrated layer disordering in two Al1-xGaxAs/GaAs structures, Sample A and B. The disordering was induced by Zn diffusion with ZnAs2 as the diffusion source. The PL data show that we can effectively control the extent of disordering by varying the diffusion time at 600℃. Moreover, we can use a SiNx as diffusion mask to effectively inhibit Zn diffusion to preserve the crystal "quality" and keep the active layer during Zn diffusion as sharp as the as-grown one.
30
Seehamart, Kompichit. "Investigation of the diffusion mechanisms of several hydrocarbons in the Metal-Organic-Framework Zn(tbip)". Doctoral thesis, 2010. https://ul.qucosa.de/id/qucosa%3A11169.
Testo completoAbstract (sommario):
Most of the computer simulations of molecules in Metal-Organic Frameworks (MOFs) to be found in the literature are done with rigid framework. But, Molecular Dynamics (MD) simulations of the self-diffusivity, Ds, of ethane within the one-dimensional 4.5 Å channels of the MOF type Zn(tbip)(H2 tbip = 5-tert-butyl isophthalic acid) presented in this work have shown not only quantitative, but also qualitative, differences in the Ds values for fixed and flexible lattices. Particularly, the dependence of Ds upon the concentration of molecules, c, is strongly influenced by the lattice flexibility. The reasons for this influence are investigated with the aid of probability density plots, free energy landscapes and barriers, along with a determination of the structural changes accompanying increasing c. It is found that for flexible lattices, the tighter, more constrained parts of the channels become wider at higher c; this allows more molecules to diffuse in the central region of the channels.
The investigations for Zn(tbip) have been extended to three equimolar mixtures of ethane/ethane, CO2/ethane and CO2/methanol. The simulations take into account the lattice flexibility. The diffusional characteristics are discussed in relation to molecule properties and lattice geometry. The results show that Zn(tbip) may be a useful material for separating methane/ethane and CO2/ethane mixtures at low concentrations, and CO2/methanol mixtures at high concentrations.
The temperature and concentration dependence of the self-diffusivity of propane diffusion in Zn(tbip) have been investigated as well by performing normal MD and hyper-MD with bias potential simulations. The obtained temperature dependence of the self-diffusivities is analyzed using an Arrhenius relationship, yielding the activation energy to be 9.53 kJ/mol and the pre-exponential factor to be 4.48×10-9 m2s-1. Using this hyper-MD method, interesting mechanisms of the propane molecules able to pass each other and exchange their sites in the channels can be observed. Because of mutual hindrance of propane molecules, the propane self-diffusivities decrease with increasing concentration.
31
Hsin, Chien-Chih, e 辛健智. "Wide-Angle Optical Power Splitter Using Zn-Ni Co-diffusion Waveguide with Simplified Coherently-Coupled Segments". Thesis, 2004. http://ndltd.ncl.edu.tw/handle/33635513694243379279.
Testo completo
32
Tsai, Pei-Jung, e 蔡佩蓉. "The Effect of Sintering Parameters on Silver Diffusion of (Zn,Mg)TiO3-based Mulitlayer Ceramic Capacitor". Thesis, 2009. http://ndltd.ncl.edu.tw/handle/26728307842647892482.
Testo completoAbstract (sommario):
碩士國立屏東科技大學
材料工程所
97
Multi-layered ceramiccapacitors (MLCC) have been developed for many years. Ag, Ag/Pd,and Ni are often used as the internal electrode, and its thickness is usually about 1~2μm. Previous studies indicatedthat the electrode migration could reduce the insulationresistance (IR) and eventually destroy the capacitors afterprolonged service. In this study, different proportions of silver-palladium alloy used as an inner electrode are adopted to fabricate (Zn,Mg)TiO3-based (ZMT) multilayer ceramic capacitors (MLCC). The influence of heating rate, two-stages sintering, sintering method and different proportions of the Pd-Ag inner electrode on the dielectric properties of the specimens are investigated. When the pure silver is applied in ZMT MLCC as inner electrode, the two-stages sintering and microwave sintering are important roles in decreasing the concentration of Ag diffusion into dielectric layer. However, it was found that insulation resistance of sample with pure silver as inner electrodes was degraded apparently by convention sintering to compare with the silver/palladium inner electrodes or compare to microwave sintering under R.H. 85% and 85℃ measuring. For Ag electrodes by conventional sintering, it could be explained that the pure silver is easily to migrate into the dielectrics layer along grain boundary during co-firing. On the other hand, the microwave sintering also can suppress Ag diffusion into dielectric layer due to different heating mechanism. The results of ZMT-based MLCCs indicate that higher silver diffusion into dielectric layer changes dielectric properties and decreases insulation resistance.
33
Wang, Tian. "Experimental investigation of the Al-Mn-Zn system through diffusion couples and key samples coupled with thermodynamic modeling". Thesis, 2013. http://spectrum.library.concordia.ca/976921/1/Tian%2DWang_MASc_S2013.pdf.
Testo completoAbstract (sommario):
Al-Mn-Zn ternary system is experimentally investigated at 400℃ via diffusion couples and key samples experiments. Three new ternary compounds have been found in the current study. Phase relations and homogeneity ranges are determined for binary and ternary phases through EPMA, SEM/EDS and XRD. Compositions of the ternary intermetallic compounds τ1, τ2 and τ3 have been found as Al62Mn16Zn22,Al76Mn13Zn11 and AlxMnyZnz (x=9.5-12.7 at%; y=11-15 at%; z=74.6-77.2 at%). Al4Mn is found to form quasicrystal or stable equilibrium phase in the presence of Zn and depending on the solidification conditions. Binary compounds Al4Mn, Al11Mn4, Al8Mn5 and β-Mn exhibit limited ternary solid solubility. Experimental data on this system from the literature is spare, isothermal section of the Al-Mn-Zn phase diagram at 400℃ is constructed based on the current phase analysis results and experimental data.
DSC analysis approach is also used to investigate this ternary system. Partial vertical sections at 13, 14 and 15 at% Mn have been experimentally investigated and compared with preliminary thermodynamic calculations. Discrepancy is observed due to the absence of the ternary phases in the thermodynamic database. Thus, this ternary system has to be remodeled in the future.
34
LIN, CHE-YANG, e 林哲揚. "A study on interfacial reactions in lead-free solder joints-using co-deposited Co(P) and Co(Zn) as diffusion barrier". Thesis, 2017. http://ndltd.ncl.edu.tw/handle/58371526988694472883.
Testo completoAbstract (sommario):
碩士國立中正大學
化學工程研究所
105
Co system is the most promising diffusion barrier on the electronic package, but the interfacial reaction between Co and Sn was extremely fast, which led to the massive Sn-Co IMC growth, so that the reliability of the solder joint is reduced. In our past studies, we prepared Co-0.7wt.%P diffusion barrier by electroless plating, that showed great inhibition of Sn-Co IMC growth. Besides, Sn solder with minor Zn addition also had very good inhibition between Sn/Co interfacial reactions. But electroless plating method had higher processing temperature (90oC) and slow deposition rate, that make it difficult to be applied to electronic packaging process. However, the electroplating process had lower processing temperature(55oC) and the deposition rate was relatively fast, that make it suitable for electronic packaging. In this study, we used a simple and convenient electroplating method to deposit Co(P) or Co(Zn) diffusion barrier, by adding NaH2PO2∙H2O or ZnSO4∙7H2O into commercial Co plating bath. The P or Zn element was then co-deposited with the Co on the substrate during plating process. This study investigate whether the P or Zn element had great inhibition on the Sn-Co interfacial reaction, and compared the results with Sn/Co/Cu system. The Co(P) and Co(Zn) exhibited columnar structures was observed in FIB cross-sections. In Co(P) system, the prefer orientation of Co showed Co(0 0 2) in XRD, and Co(1 0 0) in GIXRD. In Co(Zn) system, with the increase of Zn from 0.56wt.% to 8.78wt.%, the prefer orientation in XRD changed from Co(1 1 0) to Co(0 0 2). However, in GIXRD, the prefer orientation were Co(0 0 2), indicating that with the addition of P and Zn would affect the crystal growth of Co. In the results of Co(Zn) heat treatment, several fine grains were observed in FIB cross-sections, and a broad peak appeared in XRD analysis showed the existence of 1-CoZn7 phase. The formed IMC in Sn/Co(P)/Cu system and Sn/Co(Zn)/Cu system were analyzed by EPMA and XRD. Both CoSn3 and CoSn4 were identified, and ternary Co-Sn-P phase were formed in Sn/Co-2.5wt.%P/Cu and Sn/Co-3.0wt.%P/Cu system. The growth of the IMCs showed great inhibition from Co-0.5wt.%P to Co-2.0wt.%P, it retarded about 88%、93.7% and 94% of IMC growth. For Co-2.55wt.%Zn and Co-6.77wt.%Zn system, it retarded about 88% and 98% of IMC growth. To discuss the inhibition behavior of the IMC growth, in the results of EPMA analysis, the existence of P and Zn in Sn-Co IMC in Sn/Co(P)/Cu and Sn/Co(Zn)/Cu system were identified. It is inferred that the P element doped into the lattice of the Sn-Co IMC, so it was hard for Sn atoms to diffuse, cause the inhibition of IMC growth. In the Co (Zn) system, the 1-CoZn7 phase precipitated in Co(Zn) during reaction, and a sufficient amount of Zn element can doped into the lattice of Sn-Co IMC, so that the growth of IMC were inhibited.
35
Huang, Bo-Rung, e 黃柏融. "InAs Photodiode on Semi-Insulating GaAs Substrate with Zn-Diffusion Guard-Ring for Room Temperature High-Speed and Low Dark Current Performance". Thesis, 2010. http://ndltd.ncl.edu.tw/handle/59168531305349898960.
Testo completoAbstract (sommario):
碩士國立中央大學
電機工程研究所
98
InAs is an attractive material system for fabricating high-speed photodiodes in far-infrared wavelengths due to its extremely high electron mobility and a cut-off frequency as long as around 3.4μm. However, the reported InAs PD is usually grown on the conductive InAs substrate, which should result in a significant parasitic capacitance and further limit the speed performance of PD. In addition, the serious surface state and huge leakage current of InAs based PDs at RT operation is usually observed. In this paper, we demonstrated a novel high-speed InAs photodiode (PD), which was grown on semi-insulating (S.I.) GaAs substrate with the Zn-diffusion guard ring to suppress the leakage current. Such novel PD exhibits a 3-dB optical-to-electrical (O-E) bandwidth as wide as 20GHz, a reasonable dark current density (11A/cm2), under a small reverse bias voltage (-0.2V) and RT operation.
36
Chi, Kai-Lun, e 紀凱倫. "High-Speed (>50 Gbps) Vertical-Cavity Surface-Emitting Lasers with Zn-Diffusion and Oxide-Relief Structures for 200 Gbps Shortwave Wavelength Division Multiplexing (SWDM) Applications". Thesis, 2018. http://ndltd.ncl.edu.tw/handle/p72747.
Testo completoAbstract (sommario):
博士國立中央大學
電機工程學系
106
In today's optical communications (OI) market, vertical-cavity surface-emitting lasers (VCSELs) with central wavelengths at 850 nm have mainly been used as the primary signal emitters for short distances (<300 m). This is because VCSELs have a low-cost of fabrication, small device area, low power consumption, and most importantly have the capability of high-speed direct modulation. Data centers require an enormous number of links, which makes cost and energy efficiency critical issues. Therefore, many research teams are trying to solve this problem, some by using shortwave wavelength division multiplexing (SWDM) technology which utilizes multiple VCSELs at different wavelengths coupled into one multimode fiber (MMF). Consequently, the number of MMFs can be reduced. In addition to the cost of fiber, the data rate of each channel is also a very important issue. The targeted the on-off keying (OOK) modulation speed of a VCSEL is 56 Gbit/s to meet the requirements of the next generation of OI channels. Up till now, almost all high-speed VCSELs utilize the wet oxidation process for current confinement, but this thin oxide layer causes significant parasitic capacitance, which is one of the factors limiting bandwidth. In order to overcome this problem, we demonstrate an oxide-relief technique which uses selective wet chemical etching to remove AlOx and replace it with air, whose dielectric constant is lower than that of AlOx. As the parasitic capacitance is reduced, the speed will increase. In addition, the lattice constant of AlOx does not match that of the surrounding AlGaAs layers, which may cause some defects during high-current operation. The oxide-relief technique can solve this problem and increase the reliability of the devices. Therefore, the oxide-relief technique not only can enhance the bandwidth but also can increase the reliability. In addition to the problem of speed, transmission distance is also very important. With the rapid development of the Internet of Things and the Cloud, the amount of data that needs to be handled has increased enormously and data centers are becoming bigger and bigger, making long-distance transmission an issue. Under long-distance transmission, problems of mode and chromatic dispersion arise, which distorts the data to be transmitted. Therefore, we utilize the Zn-diffusion technique, which disorders the top Distributed-Bragg-Reflector (DBR) mirrors and reduces the reflectivity in the diffused area, to suppress the higher-order modes. Since the number of modes becomes less, the influence of modal dispersion will thus decrease, which will help to achieve long-distance transmission without distortion. In this dissertation, we incorporate the Zn-diffusion and oxide-relief technique to fabricate a VCSEL. First, we demonstrated single-mode 850 nm VCSELs with a side-mode suppression ratio (SMSR) of more than 30 dB, and obtained a maximum data rate up to 26 Gbit/s. Under OOK modulation formats we successfully demonstrated a high bit rate-distance product (14 Gbit/s × 2.0 km) for OM4 MMF transmission. In addition, we have demonstrated a single-mode 850 nm VCSEL array structure with excellent lasing performance. A stable (invariable) near circular far-field pattern with a narrow full-width half maximum (FWHM) divergence angle (~4°) under the full range of bias current and a high maximum single-lobe output power (187.4 mW) under continuous wave (CW) operation can be achieved. This has enabled the development of high-speed VCSELs, one of which is a 850 nm VCSEL whose electrical-to-optical (E-O) bandwidth achieves 29 GHz. In addition by using forward error correction (FEC) and decision feedback equalization (DFE) processing, at room-temperature (RT) we were able to obtain error free data transmission for 54 Gbit/s back-to-back (BTB) through a 1 km OM4 fiber. With another 940 nm VCSEL, an E-O bandwidth of 31 GHz was achieved with and 50 Gbit/s BTB data transmission under RT. Error-free transmission over a 50 meter OM5 fiber can be successfully achieved without using pre-emphasis or equalization techniques. These high-speed VCSELs have been applied to SWDM systems. A Zn-diffusion/oxide-relief VCSEL structure with a novel active layer design, which can achieve invariant high-speed performance from RT to high temperature (85 °C), has been studied. When the ambient temperature increases to 150 °C, it can achieve 25 Gbit/s error-free data transmission.
37
Tsai, Cheng-Yang, e 蔡承洋. "Preparation bcc Mg-12Li-XAl-Zn Alloy(X=3, 9) by Electrolytic Diffusing Method and Performance of them as Anode Materials for Magnesium Battery". Thesis, 2007. http://ndltd.ncl.edu.tw/handle/83577257470011631302.
Testo completoAbstract (sommario):
碩士中興大學
材料工程學系所
95
A body-centered cubic (bcc) Magnesium-Lithium-Aluminum-Zinc alloys of different aluminum content (3wt% and 9wt%) were fabricated by electrolytic diffusing method and via annealing and rolling process, 0.2 mm thick foils were obtained, which are further adopted as anode materials for magnesium battery. The experimental results show that, in electrochemical behaviors (corrosion resistance, open-circuit potential, discharge voltage, capacity of cell, anode efficiency), LAZ1231 and LAZ1291 alloy have better performance than AZ31 alloy, and LAZ1291 has better performance than LAZ1231. Therefore the aluminum content will affect the potential and corrosion resistance of Mg-Li-Al-Zn alloys. In surface analysis after immersion test, Mg(OH)2 passive layer of uniform thickness were observed on the surfaces of both LAZ1231 and LAZ1291 alloys, however the extent of densification of Mg(OH)2 passive layer of LAZ1291 was higher then that of LAZ1231, and it had more elemental Al particles spread over. Elemental Al particles helps densification and stabilization of Mg(OH)2 layer, therefore LAZ1291 has better corrosion resistance than LAZ1231. Moreover, AlLi phase is unstable in aqueous solution and tends to transform into elemental Al and releases Li atoms, which were easily oxidized in aqueous solution and discharge electrons while producing hydrogen gas, therefore AlLi phase has high oxidation potential. The performance of open-circuit potential and discharge voltage of LAZ1291 alloy is better than that of LAZ1231 alloy due to high content of AlLi phase. LAZ1291 alloy has high potential, good corrosion resistance, demonstrates stable working voltage and outstanding anode efficiency when assembled into a magnesium battery, therefore it is a potential anode material for magnesium battery.
38
Lin, Meng-Chang, e 林孟昌. "The Investigation of the Phase Formation of Body Centered Cubic Mg-Li Alloy and the Composition Control of Li, Na, K Element- A Non-Traditional Preparation Process of Mg-Li-Al-Zn Alloy by Electrolytic Diffusing method". Thesis, 2005. http://ndltd.ncl.edu.tw/handle/82326293227322147535.
Testo completoAbstract (sommario):
碩士國立中興大學
材料工程學研究所
93
Electrolytic diffusing method was conducted at 500C to prepare Mg-Li-Al-Zn master alloy in air. A mixture of 45 wt% lithium chloride (LiCl) and 55 wt% potassium chloride (KCl) was employed as the electrolyte. Mg- 9wt% Al- 1wt% Zn (AZ91) alloy was used as cathode material while graphite selected as anode. Experimental results showed that the electrolysis current linearly depended on the applied working voltage. Deposition of lithium occurred on the cathode surface. At working voltage of 4.2 V and one hour electrolysis, the hexagonal-closed-pack AZ91D sheet (1.5-mm thickness) was fully converted to body-centered-cubic Mg-Li-Al-Zn alloy. After the electrolysis experiments, Mg- 12wt% Li- 9wt% Al- 1wt% Zn alloy sheet can be obtained. The formation of Mg-Li phase during electrolysis was studied by inductively coupled plasma-atomic emission spectrometer (ICP), X-ray diffraction, and optical microscopy. It is diffusion rather than deposition rate (electrolysis current) that controlled the depth of Mg-Li phase formed in the cathode sample. Solubility of different element and the formation of β-Mg phase was reduced the content of sodium and potassium in Mg-Li-Al-Zn cathode material. It was also explored for the melting and casting of Mg-Li alloy in air, as the Mg-Li-Al-Zn master alloy used as raw material. The Mg-Li-Al-Zn alloy used as master alloys could be melted and casted in air without ignition. However, the content of lithium in the as-cast block was reduced to 3.77 mass %, properly due to evaporation of lithium metal during melting. After electrolysis experiments, the Mg-13Li-9Al-1Zn alloy plate can be obtained, the hexagonal-closed-pack AZ91 plate (3mm in thickness) was fully converted to the mixture of α-Mg and BCC Mg phase (4.6mm in thickness). The Mg-13Li-9Al-1Zn alloy plate (thickness changed to 4.6mm) could be cold rolled into 1.5mm strip, After heat treatment, the Mg-13Li-9Al-1Zn alloy strip exhibits elongation ~ 22%, which is 7 times more than the AZ91D alloy.