Various ways of overcoming poor temperature profiles in some products have been explored. One of the more successful is the use of both radiant and microwave heating methods, especially on those materials that need to be processed at temperatures above 1,472°F (800°C).
C-Tech Innovation Ltd., in Capenhurst near Chester, England, is one company working to develop microwave-assisted heating technology (MAT), in which microwaves provide an additional heating mechanism in support of conventional gas or electric radiant heating. With MAT technology, while the microwaves provide a thermal equalizing effect, the radiant heating retains the controllability essential for many advanced materials.
According to the company, this approach is being used successfully for batch and continuous processes and at laboratory and production scales. For C-Tech, the combined approach offers advantages over both radiant-only and microwave-only systems. The company reports that more consistent product properties, greater strength, improved yield, reduced formation of undesirable phases, and lower quantities of emissions can be achieved through the use of MAT.
The specific process developed by C-Tech was patented by the company, and Carbolite now has a technology transfer and license agreement with the company to manufacture and sell equipment with MAT heating technology in Europe. The first models with the combined microwave and radiant equipment were laboratory-scale chamber furnaces with maximum temperatures between 649 and 871°F (1,200 and 1,600°C). Molybdenum disilicide elements are used in these furnaces in order to avoid the microwave uptake that would occur with the more common silicone carbide elements.
Carbolite has identified a number of applications in which MAT heating could speed up processing times or produce more consistent results. Development work also has revealed that MAT heating has a beneficial effect on the properties and performance of some materials, according to the companies. For instance, sintering high-performance ceramics such as zirconia in a MAT furnace has been found to produce more consistent grain size, which is particularly important for semi-conductor applications and nano-materials.