Silicon nitride has been obtained by carbothermal nitridation of silica using Constant Rate Thermal Analysis (CRTA) method. This method permits to maintain the CO concentration generated in the reaction in a constant value previously selected by the user. The results obtained have shown that the synthesis of alpha -Si3N4 is improved by increasing the partial pressure of CO in the vicinity of the sample. The previous grinding of the mixture of carbon/silica to be used as raw material in the synthesis of silicon nitride leads to an important reduction of the temperature, at which the carbothermal reduction occurs at the time that an important modification of the particle morphology takes place.