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To satisfy the requirements of alumina castables in specific environment and enhance their properties, alumina castables were prepared using tabular alumina, various alumina powders (07RAL, 15RA, 22RABL, 40CA, 99-20um, and 99-325mesh), and calcium aluminate cement as main raw materials, and heat treating at 110, 1 000, 1 600 °C, respectively. Their flowability and physical properties were tested, and the morphology was researched. The results show that compared with calcined alumina and tabular alumina powders, reactive alumina has higher specific surface area and better filling performance leading to lower water demand and higher viscosity, and the castables prepared with reactive alumina have higher CCS and CMOR after heat treating at 110, 1 000 and 1 600 °C as well as lower PLC than those with calcined alumina and tabular alumina powders. [ABSTRACT FROM AUTHOR]

Effective utilization of industrial solid wastes is of great benefit for environmental and economic needs. In order to clarify the theoretical issues and pave the way to synthesize high quality Ca-α-SiAlON powder from coal gasification slag by carbothermal reduction nitridation (CRN), in this study, the theoretical issues including the network structure of the slag as well as the phase and morphological transformation stages of raw slag during CRN process were comprehensively studied at different temperatures (1350, 1400, 1450 and 1500 °C). It was found that the CRN process was dominated by nitridation of the Ca-Si-Al-O glass component in slag. With the increase of processing temperature, spherical Ca-Si-Al-O particles were firstly nitrided into porous Ca-Si-Al-O-N spheres, plate-like O-SiAlON grains, and then nitrogen-rich SiAlONs (β-SiAlON, 15R polytypoid and α-SiAlON). At the end of CRN, Ca-α-SiAlON was found to be the only SiAlON phase presenting elongated prismatic morphology. In addition, high concentration Ca-α-SiAlON powder was obtained through a two-step purification process with a conversion rate as high as 45 wt%. The obtained results shed light on the preparation of Ca-α-SiAlON products from coal gasification slag and related wastes. [ABSTRACT FROM AUTHOR]