Sintered Silicon Carbide: A New Ceramic Vessel Material for Microwave Chemistry in Single-Mode Reactors
Sintered Silicon Carbide: A New Ceramic Vessel Material for Microwave Chemistry in Single-Mode Reactors
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DOI：
10.1002/chem.201001703
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发表时间：
2010-01-01
影响因子：
4.3
通讯作者：
Kappe, C. Oliver
中科院分区：
文献类型：
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作者：
Gutmann, Bernhard;Obermayer, David;Kappe, C. Oliver
碳化硅（SIC）是一种强烈的微波，吸收了化学惰性陶瓷材料，由于其高熔点和非常低的热膨胀系数，可以在极高的温度下使用。微波辐照在半导体陶瓷中诱导电子流，该电子通过耐药加热机制非常有效地加热材料。使用SIC碳化物反应容器与单模微波反应器结合使用，几乎完全屏蔽了电磁场内部的内容物。因此，这样的实验不涉及对化学的电磁场影响，因为半导体陶瓷小瓶有效防止微波辐射穿透反应混合物。通过比较在同一反应温度的SIC小瓶中进行的实验，评估了电磁场效应（特定/非热微波效应）对21个选定化学转化的参与。对于21个反应中的大多数，使用两种不同的小瓶类型的转化/纯度/产品产生的结果实际上是相同的，这表明电磁场对反应途径没有直接影响。由于SIC的耐化学耐药性高，可以在不降解血管材料的情况下进行涉及腐蚀性试剂的反应。例子包括使用三乙胺三氟化物的高温氟 - 氯交换反应，以及用氢氧化钾水解硝酸盐的水解。另一方面，高微波吸收性，导热率和积液的独特组合以及良好的温度，压力和耐腐蚀性，使得这种材料非常适合在微波反应堆中制造反应容器。
Silicon carbide (SiC) is a strongly microwave absorbing chemically inert ceramic material that can be utilized at extremely high temperatures due to its high melting point and very low thermal expansion coefficient. Microwave irradiation induces a flow of electrons in the semiconducting ceramic that heats the material very efficiently through resistance heating mechanisms. The use of SiC carbide reaction vessels in combination with a single-mode microwave reactor provides an almost complete shielding of the contents inside from the electromagnetic field. Therefore, such experiments do not involve electromagnetic field effects on the chemistry, since the semiconducting ceramic vial effectively prevents microwave irradiation from penetrating the reaction mixture. The involvement of electromagnetic field effects (specific/nonthermal microwave effects) on 21 selected chemical transformations was evaluated by comparing the results obtained in microwave-transparent Pyrex vials with experiments performed in SiC vials at the same reaction temperature. For most of the 21 reactions, the outcome in terms of conversion/purity/product yields using the two different vial types was virtually identical, indicating that the electromagnetic field had no direct influence on the reaction pathway. Due to the high chemical resistance of SiC, reactions involving corrosive reagents can be performed without degradation of the vessel material. Examples include high-temperature fluorine-chlorine exchange reactions using triethylamine trihydrofluoride, and the hydrolysis of nitriles with aqueous potassium hydroxide. The unique combination of high microwave absorptivity, thermal conductivity, and effusivity on the one hand, and excellent temperature, pressure and corrosion resistance on the other hand, makes this material ideal for the fabrication of reaction vessels for use in microwave reactors.