Molybdenum carbides and oxides with Co addition: evaluation of doping route effect and of kinetic parameters for the gas-solid reaction synthesis.
molybdenum carbide, cobalt, doping, wet route, solid state, kinetics.
The development of new materials with improved properties is interesting for several industrial segments from the catalysis of chemical reactions for environmental legislation compliance, to the development of new electronic devices. Carbides and Mo oxides with cobalt addition may exhibit a diversity of intrinsic properties of great interest. In this work two methodologies for the addition of Co in these compounds with Mo (CoMoO4 and Mo2C-Co) were studied: solid and wet, having commercial molybdenum molybdate [(NH4) 6 [Mo7O24]4H2O] and cobalt nitrate [Co(NO3)2.6H2O] as the starting material. The doped precursors were characterized and the products of the thermal treatment (oxides) and the carbo-reduction reaction (carbides) were evaluated according to morphological (SEM), compositional (FRX) and crystallographic (XRD) aspects. It was verified that the dopant’s addition via solid state methodology presented itself, in both cases, as a more robust route; producing materials with smaller crystal sizes (~ 30nm to the carbide) and with higher dopant retention (δ ~ 10%) than the wet method (dp ~ 50nm and δ ~ 40%). A study of the conditions for obtaining Mo2C with and without addition of dopant was performed using interval reactions. In the kinetic evaluation, Avrami’s nucleation and growth models were tested, as well as those proposed by Levenspiel of Shrinking Core. It was verified that the reaction proceeds according to MoO2àMoà Mo2C and that the model that best represents the actual behavior of the gas-solid reaction is that of Avrami with grain growth rate of M = 85.4 and dimensional parameter N = 0.34.