碳热还原/氮化合成Si3N4在1 300～1 600 ℃下N2或N2-H2混合气中进行。反应物由非晶SiO2与C粉以1∶4.5摩尔比混合、压片。产生的CO由红外传感器监测，样品中氧、氮、碳含量由LECO元素分析仪测得，混合物各相由X射线衍射(XRD)检测。SiO2还原反应在1 300 ℃以下开始，速率随温度升高增大；温度高于1 570 ℃时，速率因反应物表面被生成物覆盖降低。由于还原产物CO平衡分压差别小，选择生成Si3N4或SiC的临界温度不明显。碳热还原/氮化法合成氮化硅的原理需进一步探讨。

Carbothermal reduction and nitridation synthesis of silicon nitride was conducted at 1 300～1 600 ℃ in nitrogen or nitrogen-hydrogen mixture. Fumed silica was mixed with graphite using molar ratio of SiO2∶C=1∶4.5. Powder samples were pressed into pellet before reaction. CO evolution in the process was monitored by an infrared sensor. The oxygen， nitrogen， carbon content of reacted sample was analysed by LECO element determinators. XRD was used to identify phases formed in the reacted sample. Reduction of SiO2 commenced below 1 300 ℃. The reduction rate increased with increasing temperature， but slowed down when temperature was higher than 1 570 ℃， since the residual reactant was covered by product. Due to the small difference of the equilibrium CO partial pressure between Si3N4 and SiC formation， the boundary temperature was not obvious. The mechanism of carbothermal reduction/nitridation synthesis of silicon nitride needs further investigation.