由碳化钙高压高温合成钙-碳骨架化合物的实验研究

Metal carbide is a big family that are focused for their excellent mechanical, electrical and catalytic properties. With the developing of carbon materials in recent years, metal fullerides, graphenide and many other metal carbon-skeletal materials join in this family. Theoretical approaches indicate that applying pressure on unsaturated carbon groups such as acetylides will drive them to get polymerized to form conjugated-π skeleton, which is highly conductive and has wide applications. In our previous work, we discovered that the polymerization of cyanide groups under high pressure will enhance the electrical conductivity for 1000 times, and applying high pressure on calcium acetylide will enhance the conductivity for seven orders of magnitude, which is highly promising for applications. In this program we plan to probe the high temperature-high pressure phase diagram of calcium carbide with multiple HT-HP apparatus, and perform in-situ Raman, IR, XRD, neutron diffraction, impedance spectrum analysis, and spectral, chemical analysis on the recovered samples. The aims of this research include: 1. improve the crystallinity of the high pressure phase by carefully controlling the temperature-pressure conditions, and identify the existence of calcium polyacetylide, calcium polyacene, and calcium graphenide as predicted by the theorists or other unknown calcium carbon-skeletal materials. 2. Understand the mechanism of the polymerization of acetylide anion by determining the crystal and local structures before, in and after the polymerization. 3. Combining with electrical measurement, understand the relationship between the structural transformation and the variation of conductivity.

金属碳化物是一类具有良好的机械、电学、化学催化性能的化合物。随着碳材料的发展，金属碳化物也从简单的离子化合物、合金发展到金属掺杂的碳骨架材料。理论计算表明外加高压（几十万大气压）可以驱动乙炔根等不饱和碳基离子聚合生成导电骨架，得到新颖的导电金属碳材料。申请人及团队在前期工作中发现了高压下氰基三键聚合引起电导显著增加，乙炔钙（电石）在常温加压更是可以引起电导七个数量级的增加。因此本项目计划以多种高压高温装置和原位的拉曼、红外、X射线衍射、中子衍射、阻抗谱以及离位的谱学、化学手段来研究乙炔钙在高温-高压条件下的物相、晶体结构与电学性质的变化。本研究希望通过控制温度压力条件促进高压产物晶化，寻找文献预测的聚乙炔钙、聚并苯钙、石墨烯钙与未知的新型金属碳骨架化合物。通过表征反应前后的结构理解高压下乙炔根离子的聚合机理；结合电学测量揭示其导电性的变化与结构变化的关系。

本项目基于已有文献中对钙-碳体系高压下新结构的预测，致力于运用高温高压实验手段探索乙炔钙的聚合反应与相变过程，希望合成具有钙-碳骨架的化合物。本项目主要研究了以下两个方面的内容。1、常温高压条件下乙炔钙聚合的反应。2、高温高压下乙炔钙的相变与聚合过程。本项目将气相色谱-质谱联用方法创造性地运用到高压产物的表征之中，半定量地确认乙炔钙的聚合产物。本项目运用金刚石对顶砧压机激光加热结合原位同步辐射X射线衍射的方法，以及六面顶压机电阻加热结合原位中子衍射的方法，研究了乙炔钙高压下的相关系，确认了个别已知相，发现了多个不能被已有研究指认的未知相。本项目的研究报道了乙炔钙聚合的中间产物，揭示了乙炔钙在高压下的聚合过程。本项目的研究同时表明，乙炔钙的高温高压相图十分复杂，其中蕴含多个没有被认识的结构，需要进一步深入探索。