CHEMICAL SYNTHESES BY MEANS OF MICROWAVE DIGESTION AS A FOCUSED OPEN-VESSEL SYSTEM - STRUCTURAL-PROPERTIES OF OXIDES AND HYDROXIDES AS POWDERS

By means of a focused microwave (monomode system) apparatus, it is pos sible to carry out some chemical syntheses in very short times. Variou s kinds of oxides and hydroxides have been irradiated by this method. Different transition phases and different reduction and oxidation reac tions have been observed in the course of the heating treatments. The most important results are provided by black powder, which absorbs the microwave energy and quickly becomes incandescent red at low temperat ure. However, the absorptance is a function of the dielectric constant and dielectric loss values, which vary from one oxide to another. Com pared with some previous results obtained using multimode closed-vesse l domestic ovens, the focused system allows us to homogenize the heati ng inside the powder and to reach higher temperatures in the cases of a few absorbent materials (particularly white powders).