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Ca-α-SiAlON powder was prepared by carbothermal reduction nitridation process at nitrogen atmosphere without using high pressure and long holding time. The precursor was prepared by a novel colloidal sol-gel process consisting of silica, alumina, calcium oxide and carbon. The obtained powders were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The XRD and SEM analysis results revealed that by heating at 1200 °C for 2 h, spherical particles consisting of amorphous calcium aluminosilicate liquid phase were formed. With increasing temperature to 1360 °C and held for 2 h, the spherical particles with the dominant phase of O–SiAlON were observed. Finally, as the temperature climbed to 1500 °C and held for 2 h, spherical particles disappeared and Ca-α-SiAlON was formed. The XRD analysis of the products showed that with increasing temperature from 1360 °C to 1500 °C, O–SiAlON, β-SiAlON and Ca-α-SiAlON were formed, respectively, and colloidal sol-gel method, due to the high homogeneity of the reactants, had a significant role in increasing the purity of Ca-α-SiAlON. [ABSTRACT FROM AUTHOR]

Porous SiC-Si-C ceramics were produced by reaction sintering (RS) of silicon carbide, silicon, and carbon powder compacts in the temperature range of 1400-1600°C. The effects of chemical composition of the starting powder, initial SiC particle size, and reaction sintering temperature and duration on the densification and microstructure of ceramic materials were studied. The results showed that increasing the amount of Si and/or C powders in the starting powder mixture had a detrimental influence on the densification of ceramic material as a result of higher amount of remained silicon and carbon phases in the ceramic specimen. Increasing the RS temperature also degraded densification due to the melting of Si and coming out of it from compact during heating. Nevertheless, densification was improved by increasing the RS duration. Using nanometric SiC particles in the starting powder mixture improved the densification compared to that of micrometric ones especially at longer RS processing duration. [ABSTRACT FROM AUTHOR]

TiB2/Al2O3 powder composite was synthesized via simultaneous aluminum reduction of TiO2 and B2O3 according to self-spreading high temperature (SHS) reaction in an oxidizing atmosphere. Using controlled atmosphere and high temperature is not necessary in this method. Based on the Taguchi experimental technique, various experiments were carried out and some characteristic parameters were determined. Due to the formation of intermolecular phases between Al2O3 end CaO which are soluble in HCl, CaO powder was added to the starting materials to make pure TiB2. The most appropriate powder was obtained from the materials of stoichiometric composition, purified with an optimum amount of HCl. Characteristics of the produced samples were studied with X-ray diffraction, atomic absorption spectroscopy and particle size analysis. [ABSTRACT FROM AUTHOR]