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

Abstract 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 ((NH 4 ) 6 Mo 7 O 24 4H 2 O) and tetraethyl orthosilicate (Si(OC 2 H 5 ) 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 (NH 4 ) 6 Mo 7 O 24 4H 2 O decomposes into MoO 3 . Then at temperature range of 1046 ⩽  t  ⩽ 1065 K MoO 3 is reduced into MoO 2 (or also into Mo). Synthesis of Mo 2 C proceeds at temperature in the order of 1273 K. Before the carbothermal reduction of SiO 2 and synthesis of compounds containing molybdenum and silicon we have the Mo 2 C–SiO 2 -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 Mo 4.8 Si 3 C 0.6 was obtained as the main phase.