Hysycvd/dn processing of nitride porous composites

Because of the relevance of its chemical, mechanical, thermal, electrical and optical properties, silicon nitride and oxynitride are considered highly technological materials. In this paper, authors present a study on the synthesis of Si₃N₄ and Si₂N₂O during the processing of silicon porous particulate substrates via hybrid precursor system chemical vapor deposition/direct nitridation (HYSYCVD/DN). The effect of different processing parameters (nitrogen precursor atmosphere, time, gas flow rate and amount of Na₂SiF₆) on the amount and morphology of the Si/Si₃N₄/Si₂N₂O composites was investigated using a Taguchi design experiment. Subsequently, the optimization of the process parameters on the formation of nitrides by analysis of variance (ANOVA) was performed. The specimens were analyzed by XRD, SEM and EDS. In order to elucidate the formation pathway of nitride phases in the processed samples, the study was complemented by thermodynamic predictions of the possible reactions within the reacting system using a software and database. Finally, mechanical properties were evaluated in four-point bending tests and using an ultrasonic method. Experimental results show that the microstructure and properties were influenced by the processing conditions.