Processing of glass-ceramics in the SiO2–Al2O3–B2O3–MgO–CaO–Na2O–(P2O5)–F system via sintering and crystallization of glass powder compacts (original) (raw)
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Synthesis of glass–ceramics in the CaO–MgO–SiO2 system with B2O3, P2O5, Na2O and CaF2 additives
Journal of the European Ceramic Society, 2006
Glass-ceramics based on the CaO-MgO-SiO 2 system with limited amount of additives (B 2 O 3 , P 2 O 5 , Na 2 O and CaF 2 ) were prepared. All the investigated compositions were melted at 1400 • C for 1 h and quenched in air or water to obtain transparent bulk or frit glass, respectively. Raman spectroscopy revealed that the main constituents of the glass network are the silicates Q 1 and Q 2 units. Scanning electron microscopy (SEM) analysis confirmed liquid-liquid phase separation and that the glasses are prone to surface crystallization. Glass-ceramics were produced via sintering and crystallization of glass-powder compacts made of milled glass-frit (mean particle size 11-15 m). Densification started at 620-625 • C and was almost complete at 700 • C. Crystallization occurred at temperatures >700 • C. Highly dense and crystalline materials, predominantly composed of diopisde and wollastonite together with small amounts of akermanite and residual glassy phase, were obtained after heat treatment at 750 • C and 800 • C. The glass-ceramics prepared at 800 • C exhibited bending strength of 116-141 MPa, Vickers microhardness of 4.53-4.65 GPa and thermal expansion coefficient (100-500 • C) of 9.
Journal of Thermal Analysis and Calorimetry, 2016
Glass-ceramic materials due to the various physical and chemical parameters have a more and more wide application in various areas of engineering. This paper presents a glass-ceramic material originating from the Al 2 O 2-SiO 2-Na 2 O-K 2 O-CaO/MgO modified by the addition of barium oxide. For the oxide composition which the molar ratio of SiO 2 /Al 2 O 3 is constant and equal to 6.42, and containing 0.375 mol% of Na 2 O ? K 2 O and 0.625 mol% of MgO was introduced barium oxide in quantities: 4, 9 and 14 mass%. For research of the sintering process, the following thermal analysis techniques were used: differential scanning calorimetry, dilatometry measurement and hot-stage microscopy. Analysis of the observed thermal transitions, marked on the respective charts, allows for appropriate design of the sintering curves in order to obtain a material with a high degree of crystallisation. The results of thermal analysis were compared with the phase compositions determined by X-ray diffraction and images from electron scanning microscopy of polished samples of glass-crystalline materials. Phenomena related to the influence of addition of barium oxide and heating treatment are analytically discussed.
Journal of the American Ceramic Society, 2008
In this work several complementary techniques have been employed to carefully characterize the sintering and crystallization behavior of CaO-Al 2 O 3 -ZrO 2 -SiO 2 glass powder compacts after different heat treatments. The research started from a new base glass 33.69 CaO-1.00 Al 2 O 3 -7.68 ZrO 2 -55.43SiO 2 (mol%) to which 5 and 10 mol% Al 2 O 3 were added. The glasses with higher amounts of alumina sintered at higher temperatures (9531C [lower amount] vs. 9871C [higher amount]). A combination of the linear shrinkage and viscosity data allowed to easily find the viscosity values corresponding to the beginning and the end of the sintering process. Anorthite and wollastonite crystals formed in the sintered samples, especially at lower temperatures. At higher temperatures, a new crystalline phase containing ZrO 2 (2CaO . 4SiO 2 . ZrO 2 ) appeared in all studied specimens.
Ceramics International, 2010
The effect of increasing MgO/Na 2 O replacements (on mole basis) on the crystallization characteristics of glasses based on the CaO-Na 2 O(MgO)-P 2 O 5 -CaF 2 -SiO 2 system were studied by using DTA, XRD, and SEM. The crystallization characteristics of the glasses, the type of crystalline phases formed and the resulting microstructure were investigated. The main crystalline phases formed after controlled heat-treatment of the base glass were diopside, wollastonite solid solution, fluoroapatite and sodium calcium silicate phases. The increase of MgO at the expense of Na 2 O led to decrease the amount of sodium calcium silicate phase. The Vicker's microhardness values (5837-3362 MPa) of the resulting glassceramics were markedly improved by increasing the MgO-content in the glasses. The obtained data were correlated to the nature and concentration of the crystalline phases formed and the resulting microstructure. Crown
Fabrication of magnesium aluminum silicate glass ceramics by sintering route
Magnesium aluminum silicate (MAS) glass ceramic material was prepared by the sintering route. A three-stage heat treatment, consisting of calcination, nucleation and crystallization, was developed with MgF 2 as a nucleating agent. The effect of the percentage chemical composition and the sintering temperature on the density of the compacted material was also studied. The thermal stability of MAS was measured by thermogravimetry (TG), differential thermal analysis (DTA). TG/DTA studies revealed that the powder exists as MgO–Al 2 O 3 –SiO 2 –H 2 O in solid state, and then transforms to MgO–Al 2 O 3 –SiO 2 via some metastable intermediates above 300 °C. The microstructure and phases were analyzed by X-ray diffractometry (XRD). XRD analysis revealed the formation of various phases such as magnesium sili-cate, fluorophlogopite, nobergite, siliminite etc. at various processing temperatures.
Sintering and crystallization of a glass powder in the MgO-Al2O3-SiO2-ZrO2 system
Journal of Materials Science, 1993
The sintering and crystallization behaviour was studied of a glass powder in the MgO-AI203-SiO2-ZrO= system in which the main crystal phases to form are clino-enstatite (MgSi03) and cubic zirconia (c-Zr02). During isothermal, atmospheric sintering of the glass powder, a fine dispersion of c-Zr02 particles, 50-1 O0 nm diameter, was observed to form, but this did not appear to inhibit the sintering process. Nucleation of the main crystal phase, clino-enstatite, occurred both within the original glass powder particles and at the former particle surfaces, but the rate of crystallization was greater at the former particle surfaces. The c-Zr02 precipitates are thought to act as nucleation sites for the crystallization of the clino-enstatite. Relative densities of up to 98% were attainable during sintering, and were reached at a stage where a significant degree of crystal phase development had already taken place, proving that completion of sintering prior to the commencement of crystallization is not always a prerequisite for the attainment of high final densities. In the material studied, the large volume contraction (~ 11%) on crystallization and the possible release of dissolved gases led to a decrease in relative density as crystallization proceeded. The relative density after complete crystallization was found to be 94% _+ 1%, irrespective of the temperature and duration of the initial sintering stage of heat-treatment and it appeared that most of the residual porosity was a result of the volume contraction on crystallization rather than poor densification during sintering.
Ceramics International, 2011
The alumina addition effects on the crystallization, sintering behaviors and dielectric properties of BaO-ZnO-SrO-CaO-Nd 2 O 3-TiO 2-B 2 O 3-SiO 2 (Ba-Zn-Sr-Ca-Nd-Ti-B-Si) glass powder were investigated using the differential thermal analyzer (DTA), thermo-mechanical analyzer (TMA), X-ray diffractometer (XRD). The results showed that the addition of alumina powder into Ba-Zn-Sr-Ca-Nd-Ti-B-Si glass changed the crystallization sequence from Nd 2 Ti 4 O 11-Nd 0.66 TiO 3 to Nd 2 Ti 3 O 8.7-Nd 2 Ti 2 O 7-Nd 2 Ti 4 O 11 and increased the densification activation energy due to the dissolution of Al 3+ ions into the glass structure. Fully densified 30 vol.% alumina-added Ba-Zn-Sr-Ca-Nd-Ti-B-Si glass can be obtained via glass viscous flow before the second and third crystalline phases, Nd 2 Ti 2 O 7 and Nd 2 Ti 4 O 11 crystallization. The 30 vol.% alumina-added Ba-Zn-Sr-Ca-Nd-Ti-B-Si glass-ceramics sintered at 900 8C exhibited a high dielectric constant of 17 and a quality factor of about 820, which provided a promising candidate for LTCC applications.
Sintering and crystallization of SrO-CaO-B2O3-SiO2 glass-ceramics with different TiO2 contents
Journal of Non-crystalline Solids, 2017
Glass and glass-ceramics (GCs) of the CaO-SrO-B 2 O 3 -TiO 2 -SiO 2 system are promising candidates as sealants for solid oxide fuel cells (SOFCs), mainly because of the possibility of the formation of Sr 2 SiO 4 and Sr(TiO 3 ) as crystalline phases, which minimizes the interfacial reaction between the interconnection elements and the sealant. Four glass compositions of this system, with different TiO 2 content, were obtained. The crystalline phases formed after crystallization were identified by X-ray diffraction (XRD). Combining Differential Scanning Calorimetry (DSC) and Optical Microscopy (OM), it was found that the overall activation energy for crystallization did not change with TiO 2 content. The predominant crystallization mechanism is controlled by the surface, and the growth of the crystalline layer is governed by diffusion. The sintering behavior was investigated by DSC and Hot Stage Microscopy (HSM). All glass compositions exhibited a single-stage shrinkage behavior, but...
A new model formulation of the SiO2–Al2O3–B2O3–MgO–CaO–Na2O–F glass-ceramics
Biomaterials, 2005
Mono-phase glass-ceramics of akermanite were successfully produced from a Ca-mica and wollastonite via low-temperature sintering and crystallization. Doping with P 2 O 5 considerably improves sintering behaviour since P 2 O 5 increases the stability of glass against crystallization at the temperature of sintering onset. The resulting glass-ceramics feature good in vitro acceptance from osteoblasts, and moderate bioactivity due to the enrichment of the glassy phase with Ca and Si. The good quality of the white colour at the surface and throughout the bulk, the matching of microhardness with tooth enamel, and the possibility to coat other biomaterials such as ZrO 2 , Ti or hydroxyapatite make these materials promising for medical applications.