Abstract: Many experiments show the amount of products formed by tradition heating is different from that of microwave heating even though the reaction is heated with the two methods from the same initial temperature up to the same ending temperature. In this paper, we proved this possibility from the chemical kinetics theory. Furthermore, we verified this in calcium sulfate crystallization under microwave irradiation. Through specially designed device, the same temperature rising was achieved in microwave heating and traditional water bath. The phase
and figure of calcium sulphate crystals were investigated. The results show the ingredients by microwave heating are appreciably different to that of tradition heating, but the crystal shape looks quite different. There may be some “special effects” in the calcium sulfate crystallization under the irradiation of microwave.

Key words: microwave, calcium sulfate crystal, temperature rising, special effects