Nanophase materials by a novel microwave-hydrothermal process

While there are many techniques for the production of nanophase materials, we have been using a hydrothermal process because it is a low-temperature method that can lead to energy savings. A recent innovation is the introduction of microwaves in the hydrothermal system, and we named this process the microwave-hydrothermal (M-H) process. M-H synthesis is a novel processing technology for the production of a variety of nanophase ceramic oxide and metal powders under closed-system conditions. This closed-system technology not only prevents pollution at its source, but also saves energy and, thus, could substantially reduce the cost of producing nanophase powders of all kinds. With several examples, the value of this technique is reviewed here. The M-H technique leads to (a) rapid heating to temperature of treatment, which can save energy and time; (b) increased reaction kinetics by one to two orders of magnitude, which also saves time and energy; (c) formation of novel phases; and (d) selective crystallization.