Ceramics microwave drying

Microwave Drying of Granuiar Ceramics, Soi-Gei Precursors, and Cement... 

Ananthakumar, S. Hareesh, U.S. Microwave drying of sol-gel alumina-30 vol.%SiC precursor for particulate ceramic matrix composites. Brit. Ceram. Trans. 1998, 97 (5), 236-239. 

There are numerous systems in the lumber, furniture, textile, paper, food, tire, and ceramic industries, to name but a few. A brief description of these follows. In only a few cases, such as the postdrying of crackers, cookies, and biscuits or the drying of fonndry sand cores, are there many systems utilizing the same basic equipment. In most cases, the systems are customized or one of a kind so the number of actual applications is mnch larger. The same holds true for microwave drying. 

Evans, W.A., Rapid casting trials in a microwave drying oven. TSJ Brit Ceram Soc, 72 365-369, (1973). 

There have been a variety of uses of microwave ovens in the laboratory these include the processing of ceramics, development of various plastics, catalysis, and acid dissolution of various materials.3 One developing use of microwave ovens is the drying of samples for weighing.3-6... 

The silicon carbide-based ceramic layer is obtained by CVD activated by a microwave plasma (2.45 GHz) on the tantalum previously cleaned by an argon plasma (56 min, 133 Pa, 250 W) at a temperature identical to the deposition temperature (T = 570°C), lower than the substrate annealing temperature. After readjustment of the total pressure and microwave power by introduction of a precursor (TMS) in the argon flow, the SiC coating is produced under selected conditions (66 Pa, TMS/Ar = 0.2/5.5 l.h-, T = 570°C, 350 W) derived from a previous parametric study. Coatings obtained then presented low dry friction coefficients. The mechanical properties, which are essential in order to be able to appreciate the mechanical stability, were acquired by several methods ... 

Mixer-granulators Continuous high-shear (e.g., Shugi mixer) Batch high-shear (e.g., vertical mixer) 0.1-0.5 0.1-2 Low Moderate to high Up to 50 tons/h Up to 500-kg batch Handles cohesive materials, both batch and continuous, as well as viscous binders and nonwettable powders Fluid-bed, tray, or vacuum/ microwave on-pot drying Chemicals, detergents, clays, carbon black Pharmaceuticals, ceramics, clays... 

Another ceramic processing technique that involves drying as a key step is that of the sol-gel production of ceramic powders. Sol-gel precursors consist of small particles weakly bound together, permeated with networks of fine, interconnected pores. These pores typically are filled with either an alcohol-based or a water-based liquid. Microwave heating has been successfully applied to dry sol-gel precursors. ... 

Sizgek, E. Sizgek, G.D. Drying characteristic of porous ceramic microspheres in microwave heated fluidized bed. Chem. Eng. Technol. 2002, 25 (3), 287-292. 

The ceramic industry has, for many years, examined the use of microwaves for drying purposes. Today, several uses are operating successfully. One such system, MCB Ceramics in Toronto, Canada, uses microwaves at two stages to replace a slow, hand-operated batch system with a continuous process. A 27 kW microwave oven is used to speed up the initial drying in the mold to 20 min from its previous 1 h, during which the microwaves are applied for only 2 min. The final drying used to take 24 h but now is done with microwaves in only 8 min, after which the piece is glazed and fired. The process is used to produce small bathroom accessories such as towel bar holders and soap dishes [23]. 

In another process, ceramic filters that are used to clean the slag in foundries before pouring the liquid metals are uniquely produced with microwaves. These filters that may be as large as 12 in. and 2 in. thick are made by coating, both internally and externally, an expanded polyurethane or rubber foam with a ceramic slurry. This is then dried in about 25 min for even heating, and then the filter is placed into a kiln that bums away the foam leaving the porous ceramic structure (Krieger, 1994, private communication). 

Itaya, Y., S. Uchiyama, and S. Mori (2001). Internal heating effect on ceramic drying by microwaves. Proceedings of Asia-Australia Drying Conference Malaysia, Institution of Chemical Engineers Publication, Bali. 

Anon, (1992). Microwave/vacuum drying of cast ceramic ware. Energy Efficiency Office Best Practice Programme, New Practice Final Profile 40, September. 

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