Preparation of nitrides from 1:1 type clay minerals by carbothermal reduction

In order to investigate the possibility of the use of 1:1 type clay minerals as raw materials for nitride production, kaolinite and antigorite were converted into nitrides by carbothermal reduction. Kaolinite or antigorite was mixed with carbon in two separate experiments. The resulting mixture was heated in N₂. Kaolinite was converted into β'-sialon and AIN. Kaolinite was initially transformed into cristobalite and mullite, which were then reduced. In addition to the nitrides, SiC and α-Al₂O₃ also formed as the reactions proceeded. Essentially, both the SiO₂ and Al₂O₃ components were converted into nitrides and oxynitrides by carbothermal reduction. From the antigorite-carbon mixture, α- and β-Si₃N₄ were obtained. Forsterite initially crystallized and was reduced. Additionally, MgSiN₂ and MgO formed during the conversion. α-Fe and Fe_xSi were also detected. MgSiN₂ seemed to act as an intermediate for Si₃N₄ formation. Therefore, all the Mg-containing phases can not be present as nitrides finally; magnesium was lost as the reactions proceeded.