Partial Reduction of Reactive NiAl2O4 Spinel Prepared from a Sulfate Solid Solution
Keiji DAIMON*, Toshihiro ISOBE, Yasuo HIKICHI and Toshitaka OTA
Department of Materials Science and Engineering, Nagoya Institute of Technology; Gokiso-cho, Showa-ku, Nagoya-shi 466-8555 Japan
Partial reduction of highly reactive NiAl2O4 spinel was investigated concerning with the raw spinel powder prepared by thermal decomposition of Al2(SO4)3-NiSO4 solid solutions. Solid solution of Al2(SO4)3 with NiSO4 was prepared from mixed aqueous solutions by a rapid dry using micro wave heating. The Ni2+ ion is soluble in the anhydrous aluminum sulfate crystal lattice over a wide range up to 65 mol% of (NiSO4)/(NiSO4+Al2(SO4)3). The anhydrous sulfate thermally decomposed to form the crystalline phases of spinel, η-Al2O3 and NiO at 900 °C. The lattice parameter of the spinel changed linearly with the Ni content ranging from about 20 mol% to 50 mol% of (NiO)/(NiO+Al2O3) without any other crystalline phases coexisted. The compacted NiAl2O4 spinel powder buried in a carbon powder was heated to partially reduce. On heating up to 700 °C the NiO segregated from the spinel leading to its enrichment in Al2O3. Metal Ni appeared above 800 °C, coexisting with the NiO and the spinel. The lattice parameter of the spinel decreased with decreasing the content of Ni in the spinel. The α-Al2O3/Ni composite was formed after heating at 1300 °C, while three phases of the NiO, the metal Ni and the spinel were coexisted until heating at 1200 °C.