Synthesis of ceramics by sol-gel method in molybdenum, silicon and carbon containing systems. Thermogravimetric studies

The results of investigations on synthesis of ceramics in nanometric systems containing molybdenum compounds, silicon compounds and active carbon have been presented. As precursors ammonium molybdatetetrahydrate ((NH4)(6)Mo7O24 4H(2)O) and tetraethyl orthosilicate (Si(OC2H5)(4)) were used. The samples for analysis were obtained by sol-gel method. The course of the process was investigated by thermogravimetric method. The gaseous products were analysed by mass spectrometry. X'ray diffraction (XRD) method was used for identification of solid phases, and morphology of the samples was studied by scanning electron microscopy (SEM). The process proceeded in the following way. At temperature t <= 673 K (NH4)(6)Mo7O24 4H(2)O decomposes into MoO3. Then at temperature range of 1046 <= t <= 1065 K MoO3 is reduced into MoO2 (or also into Mo). Synthesis of MO2C proceeds at temperature in the order of 1273 K. Before the carbothermal reduction of SiO2 and synthesis of compounds containing molybdenum and silicon we have the MO2C-SiO2-active carbon mixtures. In one stage, at temperature of 1523 K in argon, the synthesis of SiC and the synthesis of compounds containing molybdenum and silicon takes place. In the wide range of initial compositions of the mixtures Mo4.8Si3C0.6 was obtained as the main phase. (C) 2014 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.