Electromagnetic simulations of microwave heating experiments using reaction vessels made out of silicon carbideElectronic supplementary information (ESI) available: dielectric constant and loss data and details of simulation technique. See DOI: 10.1039/c0cp00080a

There is a growing body of literature which reports the use of silicon carbide vessels to shield reaction mixtures during microwave heating. In this paper we use electromagnetic simulations and microwave experiments to show that silicon carbide vessels do not exclude the electric field, and that dielectric heating of reaction mixtures will take place in addition to heat transfer from the silicon carbide. The contribution of dielectric heating and heat transfer depends on the dielectric properties of the mixture, and the temperature at which the reaction is carried out. Solvents which remain microwave absorbent at high temperatures, such as ionic liquids, will heat under the direct influence of the electric field from 30-250 °C. Solvents which are less microwave absorbent at higher temperatures will be heated by heat-transfer only at temperatures in excess of 150 °C. The results presented in this paper suggest that the influence of the electric field cannot be neglected when interpreting microwave assisted synthesis experiments in silicon carbide vessels. A reaction mixture cannot be shielded from the electric field during microwave heating when silicon carbide vessels are used.