Papers by Keyword: Glas Ceramics

Abstract: In this paper, application of multilayered circuit substrates has been studied, the glass ceramic (50%Al₂O₃-50%glass) with low temperature co-fired and good performance as the raw material was used, by means of calculating the apparent activation energy of densification in the experiment and observing the SEM images of glass ceramic substrate section, the densification mechanism of glass ceramic substrate sintering is analyzed.

Abstract: Bioglass Ceramics having molar composition 40SiO2-(44-X)CaO-10MgO-6P2O5-XCaF2 (where X = 0 to 8%) were prepared by conventional melting process in an electric globar furnace at 1400±10°C. Controlled crystallizations were carried out to convert the bioglasses to their corresponding ceramics. Nucleation and crystallization regimes were carried out by differential thermal analysis. The crystalline phases termed hydroxy fluoroapatite, akermanite and wollastonite were identified by using x-ray diffraction analysis. The investigation of bioactivity for the prepared glass and glass ceramics was done by infrared absorption and infrared reflection spectra after immersion in simulated body fluid (SBF) for different periods at 37.8°C. Scanning electron microscope (SEM) analysis was carried out to investigate the surface texture. Micrographs show the formation of HCA layer on the surface of the bioglass ceramics samples after 7 days of SBF treatment. The surfaces of the samples were completely covered with irregular and needle-like aggregates of Ca–P layer. The released ions were estimated by atomic absorption spectroscopy. The chemical durability of these materials was determined by pH measurement methods and it was found that pH of the solution increases up from 1 to 7 days. Further, pH decreases with increasing time period, from 15 to 30 days in SBF solution.

Abstract: A new glass-ceramic coating material on nickel based super alloy substrate had been found, the glass¬-ceramic coating material was developed from a glass based on MgO–Al2O3–TiO2 system. The coating material was characterized through X-ray diffractometry (XRD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), hardness, thermal expansion coefficient testing. XRD analysis of the coating materials and the resultant coatings showed presence of a number of microcrystalline phases. SEM micrographs indicated microstructure of the material. Optical micrographs showed smooth glossy impervious free surface with defects. Hardness analysis showed the glass-ceramic coating material had higher microhardness. The thermal expansion coefficient of the nimonic alloy was much higher compared to the coating material at specific temperature.

Abstract: The nucleation and crystallization of Li₂O-Al₂O₃-SiO₂(LAS) glass ceramic with one(P₂O₅, TiO₂, ZnF₂) and two nucleating agents(P₂O₅+TiO₂, P₂O₅+ZnF₂) are investigated by the differential thermal analysis(DTA)，X-ray diffraction(XRD) and the scanning electron microscopy(SEM). Research results show that the LAS glass ceramic with nucleating agent of P₂O₅ can obtain ideal micro spherical crystal grains and the crystallization behavior can be better controlled.

Abstract: Strontium barium niobate-based glass-ceramics are prepared by melt-casting followed by controlled crystallization. Results show that Ba_0.25Sr_0.75Nb₂O₆ with tungsten bronze structure forms as the dielectric phases from the glass matrix at 800°C. However, a secondary phase NaSr_1.2Ba_0.8Nb₅O₁₅ occurrs when crystallization temperature exceeds 850°C. The glass-ceramics formed through controlled crystallization exhibit the excellent stability of the temperature and frequency dependence of dielectric properties. The breakdown strength increases with the crystallization temperature. The glass-ceramic material heated at 800°C/3h+950°C/3h shows a breakdown strength of 1400 kV/cm and its energy storage density can reach up to 4.0 J/cm3, which may be strong candidate for high energy density storage capacitors for portable or pulsed power applications.

Abstract: The planar solid oxide fuel cell (p-SOFC) is a promising configuration of a high-T fuel cell. Barium alumosilicate glass ceramics are suggested to use as sealants by many authors since these materials seem to meet the requirements to establish a hermetic and electrically insulating seal between the steel components of the SOFC. However, in long-term application, the formation of BaCrO₄ may degrade the interfacial strength between glass-ceramics and metallic interconnect and disrupt the cell components. In this work, a series of barium-free glass-ceramics in the system of CaO-MgO-B₂O₃-Al₂O₃-SiO₂ were prepared. The selected compositions were located within the constitutional range of åkermanite – forsterite –anorthite. The thermal properties including glass transition temperature (T_g) and crystallization temperature (T_c) of the produced glasses were measured. The effect of boron oxide additions was studied in order to optimize the softening and flow behavior. For the experiments, a hot – stage microscope was used. Some glass compositions were mixed with high – CTE akermanite powder in order to increase their CTE after sintering. The CTE of the investigated materials after sintering at 900 °C, 2 h, ranged from 10.5 to 11.8 10⁻⁶ K⁻¹.

Abstract: Needle-like apatite-leucite glass-ceramics were synthesized in the SiO2-Al2O3-Na2O-K2O-P2O5 CaO-CaF2 system. Four glass batches were prepared by varying SiO2/P2O5 ratio, then melted and quenched. Crystallization was studied in compacted powder samples at different temperatures. Glasses were characterized for chemical bonding by FT-IR, phases and crystal structure by XRD, microstructure by SEM and hardness and fracture toughness by Vickers microhardness.

Abstract: Lithium zinc silicate (LZS) glasses containing Li₂O–ZnO–SiO₂–Na₂O–B₂O₃–BaO–P₂O₅ with different BaO/(BaO+ZnO) ratios were prepared by conventional melt and quench technique and subsequently converted into glass-ceramics. The effect of BaO/(BaO+ZnO) ratio on various thermo-physical properties was investigated by changing the ratio from 0 to 0.226. The crystalline phases were characterized by X-ray diffraction technique on the composite glass-ceramics, including Li₃Zn_0.5SiO₄, Li₂OZnSiO₄ and cristobalite phase. The thermal expansion coefficient (TEC) in the temperature range 70–400 oC increased from 107 × 10^-7 to 141 ×10^-7 / oC. The increase in expansion coefficient was associated with the formation of different phases which in turn influenced the rigidity/bonding in the glass-ceramics. The microstructure was analyzed by scanning electron microscopy (SEM), and the grain size became bigger after the addition of BaO.

Abstract: Using fly ash from the power plant and SiO₂ as the main raw materials, glass-ceramic was prepared by melting method. By means of DSC, XRD and SEM, the crystallizations of CaO-Al₂O₃-SiO₂ system glass-ceramic were studied. The results show that it is more and more difficult to crystallize as the content of SiO₂ increases. When the content of SiO₂ reaches to 41.5%, the crystal nucleus form in the form of shuttle shape, the crystals develop in the same direction for a certain zone. But the crystals develop into hexagon shape finally when they are heated for 1 h at 1100°Cafter nucleation at 780°C.The developed crystals are anorthite. The sizes of crystals are between 1- 1.5μm, their microhardness can reach HV804.

Abstract: In order to utilization the molybdenum tailings which be deposited in large quantities. Test used it to prepare glass-ceramics as main raw material, TiO₂ as nucleation agents and CaO-Al₂O₃-SiO₂ system and wollastonite as the principal crystalline phase. Heat treatment system of glass-ceramics was based on the differential thermal analysis. The crystalline phase, microstructure and characteristics of glass-ceramics were analysis by XRD, SEM and physical, chemical properties test. The result shows that the performance of glass-ceramics was superior to the other types of building decoration stone.