【作者】 谢宏；

【导师】 凌宏江；

【作者基本信息】 华中科技大学 ， 材料加工工程， 2006， 硕士

【摘要】 自蔓延高温合成(SHS)技术以其自身独特的优点,在制备高熔点陶瓷、金属间化合物及其复合材料方面显示出巨大的潜力。但是,由于SHS反应的热力学和动力学限制,许多体系的SHS反应难以发生,这在一定程度上阻碍了SHS技术的发展。本文以受SHS反应热力学限制的Mo-C-Si体系为研究对象,利用电场的诱发作用实现该体系的自蔓延燃烧,旨在合成所需的MoSi2-SiC复合材料。着重采用计算机模拟的方法,系统研究电场作用下Mo-C-Si系的SHS过程,并分析电场的作用机制和对SHS过程的影响规律。本文首先基于二维傅立叶(Fourier)热平衡方程,将SHS反应的热效应、外加电场的焦耳(Joule)热效应及试样的传热过程耦合起来,建立了电场作用下Mo-C-Si系SHS过程的数理模型,并提出了该模型中各耦合项的计算方法及其求解的边界条件。在此基础上,采用有限差分法对电场作用下Mo-C-Si系的SHS过程进行了数值模拟,系统研究了外加电场强度对体系SHS过程的影响。结果表明:随着外加电场强度的增加,体系发生SHS反应的点火时间缩短,而燃烧温度、燃烧波蔓延速度和产物的转化率均增加;在SHS过程中,电流密度主要集中在燃烧区域,并使该区域的电流密度和燃烧温度均处于最+大值,从而导致燃烧波的自动持续蔓延。更多还原

【Abstract】 Self-propagating high-temperature synthesis (SHS) demonstrates enormous potentiality in preparing high melting-point pottery, chemical compound among the metal and composites because of its advantages. However, due to its limits in thermodynamics and kinetics, the SHS processes of many systems are difficult to take place, restricting the development of SHS to a certain extent.In the study, the system of Mo-C-Si, which is restricted by the limit of SHS thermodynamics, is chosen as the research object, and by the electric-field-inducing, the SHS process of the reactive system was self-sustained, aiming at synthesizing the compound of MoSi2-SiC. Mainly by computer simulation, the SHS process of the reactive system under an electrical field is investigated, and the effect of the electric field on SHS reaction and its activating mechanism are analyzed.Firstly, the paper is based on a two-dimensional Fourier heat balance equation, a mathematic model of self-propagating high-temperature synthesis (SHS) process under an external electric field was presented, by coupling the heat effect of SHS reaction, the Joule heating effect of an external electric field and the heat transfer of a reactant perform. In addition, the calculating methods of the coupling items in the model and the boundary condition for the model solution were also given. This work provides a foundation for the numerical simulation of the field-activated SHS process. On the above basis, by a finite difference scheme, the electric field-activated SHS process of Mo-C-Si reactive system was numerically simulated to investigate the effect of an electric field on self-propagating high-temperature synthesis (SHS) reaction and its activating mechanism. Simulating results show that, with an increase of the field strength, the ignition time becomes short, whereas the combustion temperature, the combustion wave-propagating velocity and the degree of conversion to the product are all improved. Moreover, during the SHS process, the current is primarily restricted to the combustion zone where the current density and the combustion temperature are the highest. As a result, the field-activated reaction can become self-sustaining.更多还原