New first principles of microwave-material interaction. discovering the role of the h field, and anisothermal reactions

摘要

While microwave processing of ceramics was extensively researched in the 1980's, no striking results with respect to interesting materials or enhanced kinetics, or understanding of the microwave mater interaction, was achieved. In the last several years, however, we have established a new and comprehensive equipment assemblage including special insulated cavities, continuous processing and laser-microwave combinations. This has led to basic scientific advances in the application of 2.450 and 0.915 GHz radiation to increase the kinetics of reaction of many inorganic material families: insulators, semi-conductors, and recently, most surprisingly, metals. Reaction-kinetics in the synthesis of many significant inorganic phases such as phosphors, pigments, and electroceramics (e.g. BaCO_3 + TiO_2) are increased by more than two orders of magnitude and shown to occur by different reaction paths because of the unique "anisothermal reaction" condition one can create in a microwave field. Benchmark achievements include: sintering at 1 atm pressure to transparent, fully dense ceramics, hydroxyapatite in 5 minutes and some key ceramics such as Al_2O_3, mullite, spinel, AlN, AlON in 20-30 minutes, and sintering of commercial WCCo cutting tool green blanks of all shapes and sizes to full density in <30 minutes. In all these cases the properties of the microwave sintered parts are markedly superior. Electroceramics of major families including multilayer capacitors with base metal (Ni, Cu) have been sintered in commercial lots giving superior properties. The most surprising and valuable result is the ability to sinter powder metal compacts, including some commercial samples supplied by several different companies, in less than 30 minutes to yield standard powder metal parts in net shape with superior properties.