Kinetics and Mechanisms of Rapid Heterogeneous Reactions During Combustion Synthesis

这项工作的目的是对燃烧合成的基本理解，特别是在体积燃烧合成（VCS）模式。了解VCS的反应机理和化学动力学，包括相变和微观结构演变，是控制产品结构和性能所必需的。为此，采用了一套新的实验方法。用计算机辅助电热法（CAE）研究了加热速率高达106 oK/秒的高温（高达3000k）非均相反应的动力学。为了克服从反应速率的时间依赖性来确定规律的困难，采用了时间分辨x射线衍射（TRXRD）；这提供了在反应条件下相形成动力学的连续测量。通过一组热电偶和高速红外成像系统监测VCS各阶段样品的温度分布。直接观察微观结构的变化是通过一个改进的数字高速显微视频录像机，其速率高达12000帧/秒。研究的第一阶段将研究氮化物和镍、铝、钛和铌的二元金属间化合物的形成。在第二阶段，将研究更复杂的系统，包括直接形成陶瓷-金属复合材料。

Abstract - VarmaThis work aims at a fundamental understanding of combustion synthesis especially in the volume combustion synthesis (VCS) mode. A knowledge of reaction mechanisms and chemical kinetics of VCS that incorporates phase changes and microstructure evolution is necessary to control product structure and properties. To achieve this, a set of new experimental methods is used. The kinetics of high-temperature (up to 3000o K) heterogeneous reactions at heating rates up to 106 oK/sec is studied by computer-assisted electrothermo- graphy (CAE). To overcome difficulties in determining laws from the time dependence of the reaction rate, time-resolved X-ray diffraction (TRXRD) is used; this provides continuous measurement of the kinetics of phase formation under reaction conditions. Temperature distribution across the sample during all stages of VCS is monitored by a set of thermocouples and by a high-speed infrared imaging system. Direct observation of microstructural transformation is done with a modified digital high-speed microscopic video recorder with rates up to 12,000 frames/sec. The first stage of the research will look at formation of nitrides and binary intermetallics of nickel, aluminum, titanium, and niobium. In the second stage, more complex systems will be examined including direct formation of ceramic-metal composites.