热压烧结碳化硼陶瓷的化学计量比控制研究

Phase composition control of hot pressed boron carbide ceramics

摘要:

碳化硼陶瓷具有极高的硬度和良好的热传导性能,但这些性能极大地依赖于其化合硼碳比。当化合硼碳比偏离4(B₄C)时,其性能会有大幅下降。然而,相关标准和应用中多关注其总硼碳比,对陶瓷中富硼碳化硼及杂相的控制研究较少。本文以几种商业碳化硼粉体为研究对象,通过对其X射线衍射谱图的细致分析,从重叠峰中分离出富硼碳化硼的衍射峰并进行标定。在此基础上,研究了不同烧结工艺下碳化硼陶瓷的物相组成及富硼相的转变过程。研究结果表明,商业碳化硼粉体通常为B₄C与B_6.5C等富硼相及其他杂相的混合相。XRD及拉曼光谱结果显示,在热压烧结过程中,粉体中的富硼相会与游离碳反应生成B₄C,采用商业碳化硼粉在2100 ℃、40 MPa条件下热压60 min制备得到了纯相的B₄C陶瓷。

Abstract:

Boron carbide ceramic has been known to possess ultrahigh hardness and good thermal conductivity. However, these properties greatly depend on the phase composition of boron carbide, that is, the B/C ratio. As the combined B/C ratio in boron carbide deviates from the stoichiometry of B₄C, all these properties decrease dramatically. In some standards and industrial applications, the ratio of total boron and total carbon which may be easy to control has been concerned, rather than the combined B/C ratio. Few investigations have been conducted on the control of the boron-rich phases and other impurities in B₄C ceramics. In this paper, the phase compositions of several commercial boron cabide powders were confirmed through the detailed analysis of their X-ray diffraction patterns, from which the diffraction peaks of the boron-rich phases were separated and calibrated from the overlapping peaks. The final phase compositions of hot pressed boron carbide ceramics and the transformation of boron-rich phases to B₄C under different sintering temperatures were then investigated. The results show that the commercial boron carbide powder is usually a mixture of B₄C and boron-rich phases such as B_6.5C as well as other impurities. The results of X-ray diffraction and Raman spectroscopy show that the boron-rich phases react with free carbon to form B₄C as the sintering temperature increases. A boron carbide ceramic with pure B₄C phase was prepared using a commercial boron carbide powder by hot pressing at 2100^_oC and 40MPa for 60min.