Synthesis of SiAlON-type compounds by carbothermal reduction and nitridation of nanoparticulate geopolymers

Various types of SiAlON compounds were synthesized by heating of carbon-mixed, geopolymer compositions of M2O & BULL;Al2O3 & BULL;4.5SiO(2)& BULL;12H(2)O + 9C. A fixed molar ratio of carbon to silica of 2 and charge-balancing cations Na+, K+, or Cs+ were used to prepare the geopolymer-carbon precursor resins. After curing, the precursors were ground to powders and then fired at 1400 to 1600 & DEG;C for 2 h under flowing nitrogen. In contrast to previous studies, powdered forms of the precursors and moderate carbon ratios were used in these syntheses. X-ray diffraction results indicated that phase-pure & beta;- or O-SiAlON powders were synthesized, in the case of potassium at 1400 or 1500 & DEG;C (for & beta;-SiAlON) and sodium cations at 1400 & DEG;C (for O-SiAlON), respectively. In the cases of cesium, high purity & beta;-SiAlON with some corundum and pollucite were synthesized. Furthermore, depending on the cation type and temperatures, tailored compositions of SiAlON or other compounds (mainly Al2O3) were formed by other reactions between precursors in this systematic study.