Advanced Materials Research Vols. 105-106

Abstract: Performance of slag glass ceramic largely depends on the phase separation structure formed in heat treatment. In the paper, the crystallization properties and its relation with phase separation structure of blast furnace slag (BFS) are researched. Three water-quenched samples and an air-quenched sample were respectively prepared. After conducting temper experiments and analyzing XRD and DTA results, the following conclusions have been acquired. Two crystallization regions exist in BFS system. In parent glass with phase separation structure, Ca3Mg(SiO4)2 and Ca2MgSi2O7 would form at lower temperature but Ca2Al2Si2O7 would appear at higher temperature than that in parent glass with homogenous structure. The former contributes to the existence of lower polymerized [SiO4] units and more Ca2+ or Mg2+ in Ca-rich phase of phase separation glass, while the later is due to the diffusing hindrance of [AlO4] in diffusing path and interface resistance in phase separation structure.

Abstract: γ-aluminum oxynitride (γ-ALON) powder was prepared by carbothermal reduction method using γ-Al2O3 and activated carbon as raw materials. Effects of activated carbon content, synthesizing temperature, holding time and carbon impurity on ALON powder were studied. It was found a ‘two-step’ procedure, first sintering at about 1550°C-1650°C then at about 1750°C-1850°C, was effective to prepare high-purity ALON powder. The removal of carbon impurity was crucial for the preparation of ALON powder, which effectively improved the purity of ALON powder. The prepared powder was characterized by XRD and SEM, which indicated that pure ALON powder prepared by a ‘two-step’ procedure had well-developed crystalline and homogenous granularity. Transparent ALON ceramics were prepared by hot-press sintering at 1850~1900°C for up to 2~4h using ALON powder and some sintering additive, the transmission of sample with thickness of 1mm was 81% at infrared wave.

Abstract: Barium strontium titanate/magnesium oxide composite ceramic plates were prepared by non-aqueous gel-casting using barium strontium titanate and MgO as the raw materials. The rheological properties of the non-aqueous slurries, the dosages of the catalyst and initiator, micro structures and phase structures of the sintering ceramic plates were investigated and analyzed. The results showed that the slurry with solid content of 50wt% in non-aqueous gel-casting had excellent rheological properties and operating characteristics. Ba0.6Sr0.4TiO3/MgO plates with a smooth surface and dense structure were fabricated through desiccation and sintering at 1300°C, and the relative density is up to 4.14g/cm3. The polished surface of the ceramic substrate was composed of 35% MgO and 65% Ba0.6Sr0.4TiO3, and the content of Ba0.6Sr0.4TiO3 was obviously higher compared to the content in the raw materials which was explained by the phenomena of surface phase enrichment.

Abstract: The success of ceramic companies is highly dependent on research and development (R&D). Thus, a pivotal aim of management is to allocate resources to the best scientific and financial R&D projects. But the valuation of ceramic R&D is a difficult task for managers. The conventional discounted cash flow (DCF) methods fail to consider the value of managerial flexibility provided by R&D projects. Real options Analysis (ROA) offers a superior way of capturing the value of flexibility. It enables decision-maker to value projects more accurately by incorporating managerial flexibilities into the valuation model. However, ROA can’t effectively deal with the volatility of parameters in itself under high uncertain circumstance. In view of the limitation of ROA, this paper uses Monte Carlo simulation to solve the parameters volatility problems. In the end, the case study proves that Monte Carlo simulation can improve R&D investment decisions, especially for highly unpredictable ceramic R&D projects.

Abstract: Cordierite is an excellent material with good thermal shock resistance and used at high temperature for its low thermal expansion coefficient. Cordierite ceramics were prepared by using talc, alumina and kaolin clay as starting materials. The thermal expansion coefficient, phase composition and microstructure were studied and the results showed that: in order to get samples with low thermal expansion coefficient, the optimum chemical composition was a little rich in Al2O3 compared with the theoretical composition, the optimum sintering temperature was 1350°C, and adding 10% starch as pore-forming agent could effectively decreased the thermal expansion coefficient of the samples even to 0.8×10-6/°C. The samples contained majority of cordierite phase, with trace mullite and glass, the acicular cordierite crystals in samples developed very well and there were 10% starch powder used as pore-forming agent in formula. All these were the reasons to decrease the thermal expansion coefficient of cordierite material.

Abstract: This paper puts forward a new method for the preparation of 99.999% high-purity alumina used for the LED underlay sapphire, which has above 99.999% high-purity aluminum atomized the active aluminum powder by the supersonic multistage cooling way, then makes the powder form the hydrate of the alumina through the hydrolyzing reaction, and finally gets 99.999% high-purity alumina by means of the calcinations and the follow-up granularity treatment. By the processing way, the reactant is only aluminum and water, and there is no other additive, which profitably keeps the product pure and completely satisfies the requirements of synthetic crystals while tested.

Abstract: Good dispersing stability is required for nano-SiO2 which, however, tends easily to conglomerate, to be widely applied as an important functional material of high toughness, high resistance to corrosion and good high-temperature performance. Through ultrasonic treatment, the suspension of SiO2 nano-powder in water was prepared utilizing sodium dodecylbenzenesulfonate (SDBS) as the dispersant. The effect of SDBS content and ultrasonic treatment time on the suspension stability was investigated by way of testing the particle size of SiO2 nano-powder, the Zeta potential and transmittance of the suspension. The results show that with increasing SDBS content, the particle size of SiO2 nano- powder decreases and then increases, which is similar to the case of increasing the ultrasonic treatment time. With optimum SDBS content, the suspension of SiO2 nano-powder possesses a good dispersing stability due to the existence of electrostatic and steric effects resulting from the particular structure of SDBS. The optimum dispersing condition is SDBS of 1.6 wt% with the ultrasonic time of 18 min.

Abstract: We investigated the formation behavior of ternary rare earth sulfide LnxGd2-xS3 (Ln: La, Tb). Ternary rare earth sulfide LnxGd2-xS3 (Ln: La, Tb) was synthesized via the sulfurization of their commercial oxide powders using CS2 gas for short sulfurization time. It was found that ternary rare earth sulfide LnxGd2-xS3 (Ln: La, Tb) could be synthesized for a short sulfurization time of 3 h at 1100°C. For LaxGd2-xS3, it crystallizes in α phase (Orthorhombic phase), the crystal structure is different from rare earth sulfide La10S14-xOx which crystallizes in β phase (Tetragonal phase) but is same with rare earth sulfide α-Gd2S3. TbxGd2-xS3 also crystallizes in α phase, the crystal structure is same with rare earth sulfide α-Tb2S3.

Abstract: Metatitanic acid was adopted as the raw material to prepare Fe-doped TiO2 nanocrystalline composite particles using suspension polymerization and sol-gel method, which were then characterized with XRD, TEM, TG-DTA and IR, etc.. The results showed the samples were nanocrystal accumulated porous particles, with average particle size of 29nm. Through doping of Fe3+ ion, the photo catalytic activities of particles under Xe lamp were investigated by photodegrading the methyl orange. It was found that, the TiO2 nanocrystal doped with 0.5% Fe3+ ion (accounted as mass fraction) had the highest catalytic activity. The Fe-doped TiO2 nanocrystalline composite particles prepared in this study has high activity, is easy for separation, recovery and reuse.

Abstract: Superfine nanometer SrTiO3 with size of near 50-60nm was prepared by citrate process and sol-gel method. XRD and TEM characterizations indicate that sol-gel method is appropriate to prepare high-purity powders at far lower temperature than other methods. The Ni-based catalysts were prepared by using SrTiO3 powder as support through impregnation and sol-gel method. These catalysts were applied to the reaction of CO2 reforming CH4 to synas and showed high activity. The catalytic activity of Ni-based catalyst is investigated by reaction temperature, the method of support preparation, and the method of catalyst preparation; It shows that the catalyst possesses higher catalytic activity with the increasing of temperature; and the catalytic rate is near 90% at 973 K; and the catalyst show higher catalytic activity when support is prepared by sol-gel method than by citrate process; and the catalyst shows better catalytic activity when catalyst is prepared by sol-gel method than by impregnation method.