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等离子体CVD 法合成Si_3N_4/SiC复合陶瓷超细粉末的研究
Thesis Advisor郑国梁
Degree Grantor中国科学院研究生院
Abstract本文从热力学及实验上,研究探讨了超细氮化硅/碳化硅陶瓷粉末的等离子CVD法合成。在热力学的分析中,采用计算机软件对Si-C-N-Cl-H五元系进行了化学热力学平衡计算。主要考察了温度,CH_3SiCl_3/SiCl_4摩尔比率,氢气流量和氨气流量等参数对体系热力平衡的影响。系统中的硅,碳来源于三氯甲基硅烷和四氯化硅;氮来源于作氮化剂的氨气。计算结果表明,在一定的条件下,用CH_3SiCl_3-SiCl_4-NH_3-H_2体系可以合成Si_3N_4/SiC粉末,在不同的氨气及氢气流量下,以摩尔比率CH_3SiCl_3/SiCl_4对温度作图得到了凝聚相的平衡图;以凝聚相各物质的摩尔数量对温度作图的到了凝聚相组成图。结果表明,对上述体系,热力学上凝聚相可以存在Si_3N_4 + C, Si_3N_4 + SiC + C, Si_3N_4 + SiC, SiC, 或者是SiC + C的多相区或单相区。对于Si_3N_4 + SiC相,当氢气或氨气的流量较大时,它可以在较大的区域内存在。这是由于氢气降低了固相中的洲离碳,增加了碳化硅,氨气则增加氮化硅的缘故。Si_3N_4 + SiC相的存在温度平均在1600 K以上;随着CH_3SiCl_3/SiCl_4 的增加,该相区的消失温度下降很快。平衡气相组成在1000 K~3000 K温度区间内,主要是由HCl, H_2, N_2, SiCl_4, SiCl_3, SiCl_2, SiCl, C_2H_2, CH_4, Cl, HCN, Si和H组成的。温度对气相平衡的影响比CH_3SiCl_3/SiCl_4和NH_3都更显著。在实验中我们采用CH_3SiCl_3 + SiCl_4 = NH_3 + N_2 + Ar体系,用等离子CVD法合成了Si_3N_4/SiC超细陶瓷粉末。为了探索最佳实验条件,实验采用正交设计。实验中发现,氨气流量是影响粉末组成的主要因素。当氨气的流量较小时,粉末中的碳化硅比例明显升高;当氨气的流量较大时,氮化硅的比例升高。借助于X射线衍射(XRD),红外光谱(IR),透射电子显微镜(TEM)和X射线光电子能谱(XPS),我们对粉末的特性进行了研究。仪器的测试和分析表时,粉末中的氮化硅是无形体(amorphous),碳化硅是β形晶体。粉末颗粒呈现球形,并具有很大的比表面积(>70 m~2/g),粒度在15~60纳米。粉末的重量组成为Si_3N_4 68.20~88.08%, SiC 4.67~41.30%。优化实验表明,氨气和氢气分别有利于氮化硅和碳化硅的生成。
Other AbstractPlasma CVD synthesis of ultrafine Si_3N_4/SiC ceramic powders was studied in this paper. In the thermodynamic analysis, a computer code was employed to calculate the chemical thermodynamic equilibrium of the five-element system of Si-C-N-Cl-H. Several parameters such as termperature, CH_3SiCl_3/SiCl_4 mole ratio, hydrogen flow rate and ammonia flow rate, which affect the thermodynamic equilibrium of the system, were studied. In this system, silicon and carbon come from trichloromethylsilane and silicon tetrachloride; and nitrogen comes from ammonia which was served as nitriding agent. As the calculation results show, at certain conditions, the Si_3N_4/SiC powders could be synthesized with CH_3SSiCl_3 + SiCl_4 + NH_3 + H_2 system. While at different flow rate of hydrogen and ammonia, respectively, the condensed phase equilibrium diagrams were plotted as a function of temperature and CH_3SiCl_3/SiCl_4 mole ratio; and so were the composition diagrams as a function of temperature and mole quantity of the condensed matters. The results show that, as to the above system, there exsist such phase areas as Si_3N_4 + C, Si_3N_4 + SiC + C, Si_3N_4 + SiC, SiC or SiC + C. As far as being concerned about Si_3N_4 + SiC phase, it appears that it could exsist in wide areas, where at high hydrogen flow rate or high ammonia flow rate, because the hydrogen can lower the free carbon content and can raise the SiC content in the condensed phase. Meanwhile nitrogen raised Si_3N_4 content. Si_3N_4 + SiC phase exsists at average temperatures above 1600 K, and with the increasing of CH_3SiCl_3/SiCl_4 ratio, the disappearing temperature was lowered rapidly. At temperatures from 1000 K to 3000 K, the gaseous phase were mainly composed of HCl, H_2, N_2, SiCl_4, SiCl_3, SiCl_2, SiCl, C_2H_2, CH_4, Cl, HCN, Si and H. The gaseous equilibrium was influenced more easily by temperature than by CH_3SiCl_3/SiCl_4 ratio and ammonia. In the experiments, plasma CVD technique was employed to synthesize ultrafine Si_3N_4/SiC ceramic powders. The experiment was designed with orthogonal method, in order to investigate the optimal conditions. The experiment results show that ammonia is a main factor in influencing the powder compositions. And high ammonia flow rate resulted in high Si_3N_4 percentage and lowered SiC percentage in the condensed phase. The powder characterization was studied by X-Ray diffraction (XRD), Infrared spectrum(IR), TEM and XPS. Instrument analysis showed that Si_3N_4 is amorphous and SiC is β -type crystalline in the powders obtained. The particles are spherical with very large specific surface area (>70 m~2/g), and have mean size between 15~60 nm. The chemical compositions of the powders are Si_3N_4 68.20~88.08 wt%, and SiC 4.67~14.30 wt%. Optimal experiments show that the ammonia and hydrogen can increase Si_3N_4 content and SiC content respectively.
Document Type学位论文
Recommended Citation
GB/T 7714
邢阳川. 等离子体CVD 法合成Si_3N_4/SiC复合陶瓷超细粉末的研究[D]. 中国科学院研究生院,1991.
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