The controllable α/β ratio of Si3N4 powder was synthesized using tetraethyl orthosilicate (TEOS), glucose, MgCl2 and YCl3·6H2O by sol-gel assisted carbothermal reduction and nitridation (CRN). This study aimed to investigate the impact of various parameters, including a H2O/TEOS mol ratio of the sol, a C/Si mol ratio, sintering aids, and the temperature of CRN on the phase transformation of α-Si3N4. The results demonstrated that the H2O/TEOS ratio significantly influenced the relative content of α and β phase in Si3N4 by changing the morphological characteristics of SiO2. When the H2O/TEOS ratio was 100, β-Si3N4 powder with an approximate β content over 88 wt% was synthesized at 1500 °C. This remarkable phase transformation was likely facilitated by the eutectic liquid phase consisting of MgSiO3/Mg2SiO4. The SEM image revealed rod-like whiskers with a length around 1.4 μm for the β-Si3N4 grains. Due to the presence of liquid phase, the synthesis of spherical-like α-Si3N4 nano-powder with an α-phase content of 91 wt% was achieved at a lower temperature of 1450 °C, with an H2O/TEOS ratio of 15 and a C/Si ratio of 4. The size of the particles was about 70 nm due to the reduced reaction temperature. Furthermore, without the addition of any sintering aids or Si3N4 seeds, high purity α-Si3N4 with an α phase content approaching 96 wt% could be synthesized at 1500 °C, using an H2O/TEOS ratio of 15 and a C/Si ratio of 4. The resulting α-Si3N4 powder exhibited an extremely regular hexagonal prism shape with a length of approximately 2 μm.

中文翻译：

---

溶胶-凝胶辅助碳热还原氮化合成α/β比例可控的Si3N4粉末


以原硅酸四乙酯(TEOS)、葡萄糖、MgCl2和YCl3·6H2O为原料，通过溶胶-凝胶辅助碳热还原氮化(CRN)合成了α/β比可控的Si3N4粉末。本研究旨在研究各种参数（包括溶胶的 H2O/TEOS 摩尔比、C/Si 摩尔比、烧结助剂和 CRN 温度）对 α-Si3N4 相变的影响。结果表明，H2O/TEOS比例通过改变SiO2的形貌特征，显着影响Si3N4中α相和β相的相对含量。当H2O/TEOS比为100时，在1500℃下合成了β含量大约超过88wt%的β-Si3N4粉末。这种显着的相变可能是由 MgSiO3/Mg2SiO4 组成的共晶液相促进的。 SEM 图像显示 β-Si3N4 晶粒呈棒状晶须，长度约为 1.4 μm。由于液相的存在，在1450℃的较低温度、H2O/TEOS比为15和C/Si比为4。由于反应温度降低，颗粒尺寸约为70 nm。此外，在不添加任何烧结助剂或Si3N4晶种的情况下，使用H2O/TEOS比为15、C/Si比为15时，可以在1500℃下合成α相含量接近96wt%的高纯度α-Si3N4。 4.所得α-Si3N4粉末呈极其规则的六棱柱形状，长度约为2μm。