Добірка наукової літератури з теми "Sintered glass discs"

The aim of the study was to investigate the influence of ZrO2 on the crystallization and properties of leucite phase from K2O -Al2O3- SiO2 glass-forming melts. A starting glass composition of weight %; 60.7-63.2% SiO2, 16.6% Al2O3, 11.6% K2O, 5.10% Na2O, 2.5-5.0% ZrO2, 0.5% TiO2 and 0.5% LiO2 was melted in an electric furnace, followed by quenched in cool water to produce glass frit. Malaysian silica sand from Terengganu was used as the SiO2 source. The glass powders were ball milled and compressed to form 13mm diameter discs using cool isostatic pressing. The discs were sintered at 650°C, 700°C, 750°C, 800°C and 850°C for 1 hour and characterised using X-ray diffraction (XRD) and field emission scanning electron microscope (FESEM). The results indicate that the amount of ZrO2 additive is one of the key factors controlling of leucite crystallization. The properties of sintered disc specimens were studied using three point bending, diametral and Vickers microhardness test. The results showed that the mechanical properties of leucite glass-ceramics increased as the amount of ZrO2 was increased.

In this study, the following compositions were produced: Al2O3-YAG laser with 2, 4, 6 and 15% by weight of niobophosphate glass (30mol%P2O5-30mol%Nb2O5-20mol%CaO-20mol%CaF2). Sintered discs were characterized by scanning electron microscopy (SEM), X-Ray diffraction (XRD) with the refinement by the Rietveld method and density. The YAG-Al2O3 composite sintered at 1450 °C showed densification of 90%, which indicates the effectiveness of the sintering additive.

The two principal mechanisms thought to be responsible for the mellowing (or weakening) of moulded soils during rapid wetting are air entrapment and differential swelling. These were investigated in order to obtain a quantitative estimate of the effect each mechanism has on the tensile strength of soils. Rapid wetting experiments were conducted on dry soil discs which had been prepared from moulded moist soil. The discs were wetted on sintered-glass funnels using two different wetting fluids at three different ambient air pressures. Discs were dried again and crushed between flat parallel plates to determine their tensile strengths. For the two soils used in this study, it was found that air entrapment on its own did not generate sufficient stress to induce mellowing, and furthermore that differential swelling on its own also had a limited effect. When the two processes acted simultaneously, however, a marked reduction in the tensile strength of between 35% and 47% resulted.

AbstractTo test the rate at which a lifeless but habitable environment (uninhabited habitat) can be colonized, artificial endolithic habitats were constructed in the laboratory and exposed to the natural environment. They were composed of sterile stacked sintered glass discs (stacks) containing CHNOPS elements, liquid water, energy and a carbon source, making them habitable for aerobic respiring organisms and phototrophs. One set of stacks was exposed fully to atmospheric conditions and one set was covered from direct overhead atmospheric input and precipitation. The process of colonization was heterogeneous across the stacks. After 3 months, all uninhabited habitats were colonized at all depths in both fully exposed and covered stacks. However, uninhabited habitable conditions persisted in covered stacks after 1 month, demonstrating the importance of the hydrological cycle in the connection between inhabited habitats and uninhabited habitats. Low porosity rocks were found to retard the extent of colonization compared with higher porosity rocks. Examination of genomic DNA demonstrated that the habitats were colonized by a community dominated byProteobacteria. Covered stacks had a higher abundance of fungal sequences among eukaryotic colonizers. These data demonstrate the tight coupling between the appearance of habitable conditions and life and the reasons for the rarity of uninhabited habitats on the present-day Earth. On other planetary bodies, such as Mars, with more inclement atmospheres and less vigorous hydrological cycles or a lack of life, uninhabited habitats could persist for longer with consequences for the interpretation of data sent back by planetary science missions.

Disks of seven soils were prepared by moulding the soils at water contents in excess of their plastic limits and by drying. The disks were placed on edge on sintered glass funnels, were wetted from an arbitrary point on their circumference and were then dried isotropically. Disks that had been wetted were weaker than control disks that had not been wetted. For some soils there is a water potential, termed the critical mellowing potential, in excess of which little or no mellowing occurs. For three of the soils studied the mellowing occurred to different extents in different directions. Anisotropic mellowing was investigated as a function of the potential of the source of water causing wetting. Results from multiple wettings of disks indicate that anisotropic mellowing may lead to equilibrium states for a number of soil physical properties including structure and strength.

In this work, the sol-gel synthesis of AP40 bioactive glass system was reported. The obtained powder was fully characterised in terms of microstructure, composition and thermal behaviour by X-ray diffraction (XRD) measurements, Fourier transform infrared (FT-IR) spectroscopy, thermogravimetry and differential thermal analysis (TG-DTA).In vitrodissolution tests were performed in order to assess the degradation behaviour of sol-gel derived AP40 samples thermally treated at different temperatures. Finally, preliminary results on cytocompatibility are reported, based on bioresorption activity of human peripheral blood monocytes differentiated into osteoclasts on sintered disks.

Fusion energy is considered a promising source of energy for the near future. The most efficient reaction for that purpose is the fusion of deuterium and tritium, two hydrogen isotopes, to release helium, neutrons and energy. To assure the correct operation of this technology, new online devices able to monitor hydrogen isotopes will be required. Electrochemical sensors based on solid-state proton conductor ceramics can be used for that purpose. These materials have attracted significant interest because of their chemical and physical durability, especially at elevated temperatures. These electrolytes are perovskite-type materials with electrical carriers, positive holes, excess electrons and oxide ion vacancies. In previous work [1], amperometric hydrogen sensors based on BaCe0.6Zr0.3Y0.1O3-α (BCZY) electrolyte have been developed and tested in hydrogen atmospheres obtaining good results. These prototypes were constructed using 13 mm BCZY disks obtained by uniaxial pressure. In the present work, hydrogen sensors based on BCZY were constructed and evaluated in amperometric mode. The BCZY powder was disk-shaped using uniaxial pressure and 3D printing. Sensors were constructed as follows: first, sintered disks were platinized using platinum ink. Then, disks were sealed with a glass binder to alumina tubes. This way, the external face of the disk acted as a working electrode (WE) and the inner part of the sensor as a counter electrode (CE). 3D printed disks were fabricated using a Delta WASP 2040 ceramic 3D printer. For that, the ceramic powder was mixed with PEG400 and water until a viscous paste was obtained. Once green bodies were dried, they were heated for debinding and sintering using an optimized thermal program to reduce porosity. XRD (for crystallographic phases) and SEM (for microstructural defects and sintering) were used for the 3D printed and uniaxial pressed sintered disks characterization. The amperometric response of sensors constructed with both electrolytes (the uniaxially pressed and the 3D printed disks) was compared. [1] A. Hinojo, I. Soriano, J. Abellà, S. Colominas, Evaluation of High-Temperature Hydrogen Sensors Based on BaCe0.6Zr0.3Y0.1O3-α and Sr(Ce0.9Zr0.1)0.95Yb0.05O3-α Perovskites for Industrial Applications, Sensors. 20 (2020) 7258. https://doi.org/10.3390/s20247258.

The consumer market requests infrared (IR) optical components, made of relatively abundant and environmentally friendly materials, are intended to be integrated or attached to smartphones. For this purpose, three new chalcogenides samples, namely Ge23.3Zn30.0Se46.7 (d_GZSe-1), Ge26.7Zn20.0Se53.3 (d_GZSe-2), and Ba4.0Ge12.0Zn17.0Se59.0I8.0 (d_GZSe-3), were obtained by mechanical alloying and processed by spark plasma sintering into dense bulk disks. Obtaining a completely amorphous and homogeneous material proved to be difficult. d_GZSe-2 and d_GZSe-3 are glass-ceramics with the amount of the amorphous phase being 19.7 and 51.4 wt. %, while d_GZSe-1 is fully polycrystalline. Doping with barium and iodine preserves the amorphous phase formed by milling and lowers the sintering temperature from 350 °C to 200 °C. The main crystalline phase in all of the prepared samples is cubic ZnSe or cubic Zn0.5Ge0.25Se, while the amorphous phase is formed GeSe4 clusters in d_GZSe-3. The color of the first two sintered samples is black (the band gap values are 0.42 and 0.79 eV), while d_GZSe-3 is red (Eg is 1.37 eV) and is transparent in IR domain. These results are promising for future research in IR materials and thin films.

Dental ceramics is a highly esthetic material and its surface properties can impact its roughness, bonding properties, as well as strength and wear. The aim of the study is to analyze the surface characteristics by the determination of the roughness parameters of three dental ceramics used in computer-aided design/computer-aided manufacturing (CAD/CAM) technique: lithium disilicate (LS2), zirconium oxide-reinforced lithium silicate (ZLS), and zirconium oxide (ZrO2), prepared using two different processing techniques, polishing (self-glaze) and glazing with three different glazes. Both glass ceramics, pre-crystallized LS2 and crystallized ZLS, were cut into disks, and the surface was ground and polished. Crystallization was performed for LS2 samples, while ZrO2 samples were fabricated using CAD/CAM and sintered. Then, the glaze was applied and the samples were reheated as per the manufacturer’s instructions. The contact surface topographies of the tested ceramics were measured by atomic force microscopy (AFM) and the roughness parameters: average surface roughness (Ra), root-mean-square roughness (Rq), and surface area difference (SAD) were evaluated. Changes in the morphological characteristics of the tested ceramics were examined by scanning electron microscopy (SEM), and the surface chemical composition was determined by attenuated total reflection Fourier-transform infrared spectroscopy (FT—IR). In the spectroscopic analysis, a characteristic signal for ZrO2 was obtained for ZLS samples. A significant decrease in surface roughness was observed after glazing in all tested ceramics (p < 0.05). The abstract should be an objective representation of the article and it must not contain results that are not presented and substantiated in the main text and should not exaggerate the main conclusions.

Fusion energy is a promising solution for the expected energy problems in the mid-term future. This technology is expected to use deuterium and tritium, two hydrogen isotopes, as fuel. Deuterium can be obtained from natural sources, but tritium, which is a non-stable hydrogen isotope, must be in situ generated. To assure the correct monitoring of both isotopes, it will be required the design and qualification of high-temperature sensors. The construction of H2 sensors based on solid-state electrolytes can be the first step towards the development of new analytical tools able to monitor hydrogen isotopes in that aggressive environment. In previous work [1], amperometric sensors based on BaCe0.6Zr0.3Y0.1O3-α (BCZY) solid-state electrolyte have shown good analytical parameters for hydrogen monitoring. However, these materials need high temperatures during sintering to obtain full density due to their refractory nature. This lack of densification can affect their electrochemical response due to their low ionic conductivity. The use of sintering aids, like ZnO, can improve the densification of these ceramics at lower temperatures. In the present work, hydrogen sensors based on BCZY were constructed and evaluated in potentiometric mode. Different sintering conditions for this electrolyte were tested and their potentiometric response was compared. The following disk-shaped electrolytes were prepared for that purpose: 1400 ºC – 30 h, 1650 ºC – 6h. Simultaneously, BCZY was sintered at 1400 ºC -12 h with 5 mol% of ZnO as a sintering aid. Samples were characterized using XRD (to determine the crystallographic phases) and SEM (for microstructural defects and sintering). Then, disks were platinized and sealed with a glass binder to alumina tubes for sensor construction. Measurements were performed at 400 and 500 ºC. The hydrogen concentration in the RE was 1000 ppm H2 in Ar. The response obtained with the three sensors was compared with the theoretical Nernst potential. [1] A. Hinojo, I. Soriano, J. Abellà, S. Colominas, Evaluation of High-Temperature Hydrogen Sensors Based on BaCe0.6Zr0.3Y0.1O3-α and Sr(Ce0.9Zr0.1)0.95Yb0.05O3-α Perovskites for Industrial Applications, Sensors. 20 (2020) 7258. https://doi.org/10.3390/s20247258.

Membrane filtration has revolutionised water treatment, enabling safer provision of drinking water due to its high efficiency to block human infectious pathogens commonly present in raw water sources. Accumulation of substances on membrane surfaces and pores during operation, referred to as fouling, is considered one of the biggest barriers to wider adoption of membrane technology in water treatment. Maintaining continuous low-pressure filtration requires significant amounts of chemicals to clean off the accumulated fouling substances. Chemical use comes with economic and environmental costs associated with acquisition, transportation, storage, usage and disposal of chemicals, especially in disadvantaged and remote communities. By conservative estimates, supply of household water to a remote community of 100 people using a membrane system would require continuous supply of at least 10 L of polyaluminium chloride coagulant and 4 L of sodium hypochlorite (in concentrated form) every month. The main aim of this thesis is to demonstrate a sustainable, innovative, low cost membrane solution harnessing conveniently available solar energy to offset these chemical demands. Coating membrane substrates with semiconductor photocatalysts such as titanium dioxide (TiO2) is an effective method for mitigating fouling in membranes through induced superhydrophilicity, enabling cleaning from the available water without chemicals. TiO2 also enables water contaminant degradation and pathogen inactivation through reactive oxygen species (ROS) facilitated advanced oxidation. Despite these well- known effects, a major challenge limiting practical adoption comes from light absorption and scattering by the turbid contaminants in the feed stream before reaching the TiO2. This thesis proposed a novel solution to this challenge by transmitting light to the TiO2 through cheap porous borosilicate glass substrates with between 10% and 80 % transmission in the 340-400 nm wavelength range relevant to activating commercial Degussa P25 TiO2 photocatalyst. The concept novel membrane was produced using commercial glass substrates modified by simply dip- coating and heat sintering Degussa P25. The formed asymmetric membrane’s mean pore size was measured at 0.5 μm, which classifies the membrane as a microfiltration (MF) membrane, which are utilised in the industry as a barrier to water-borne pathogens such as protozoa and bacteria, and partially to viruses. To demonstrate the membrane’s photocatalytic ability, photocatalytic reactions stimulated by a UV lamp (365 nm peak) facing the glass substrate side in an ex-situ setup led to a 52% degradation of methyl orange in aqueous solution, being only slightly lower than the 58% degradation when the TiO2 active layer faced the UV light source. The membrane was then operated in-situ using a custom module with a quartz window and UV LED installed on the permeate side, enabling simultaneous microfiltration of model fouling solutions. Results showed significant reductions in trans-membrane pressure (TMP) rise rates directly linked to UV light application. Specifically, UV light was responsible for up to 3.0-fold reduction in total filtration resistance and up to 4.2-fold reduction in irreversible fouling indices. Testing continued on simulated indirect solar light with a real non-potable water. The membrane itself showed up to 94% turbidity removal and up to 80% total organic carbon (TOC) rejection. The sunlight was directly responsible for an 8-fold reduction in the irreversible fouling index. The significant practical findings were followed by an investigation to confirm the fundamental basis for improvement. Analysis by scanning electron microscopy (SEM) coupled with fouling modelling showed the beneficial photocatalytic fouling reduction effects during microfiltration stemmed from reduced intrusion of organic fouling material inside the TiO2 membrane pores, as well as reduced cake layer resistance. Analysis of results and photocatalysis mechanisms from literature led to the conclusion this was due to both superhydrophilicity minimising organic attractions to the surface and photocatalytic oxidation of organics approaching the surface. The potential for advanced oxidation to participate in reacting with organic matter surfaces attracted to the membrane was confirmed from a measurable increase in the presence of hydroxyl radicals using para-chlorobenzoic acid (pCBA) probe experiments. The practical benefits for industry towards chemical consumption and energy reduction were also measured. For example, a 4.5-fold extension to the time needed for a clean-in-place (CIP) was realised when the membrane was operated in photocatalytic mode. A 50% reduction in filtration pump electricity demand was also calculated, which translates to a reduction in height of the feed water for a flux of 300 L/m2/h from 8.6 m to 3.7 m over a 5 hour run. Future work suggested includes using recycled glass to improve affordability and minimise glass manufacture environmental impact, as well as experimentally establishing the relationship hydroxyl radical concentration and TOC reduction. Optimisation of the glass material for enhancing light transmission efficiency and development of porous glass monoliths like current commercial ceramic membranes for full-scale use, as well as optimisation to increase contaminant degradation are also suggested.