Mixed oxide ceramic powders, synthesis

The first six reactions form mixed oxide ceramic powders. The last three reactions are carbothermal reductions to produce different metal carbides. The most famous is the Atcheson process for synthesis of SiC from Si02 and carbon, where the carbon in the mixture of reactant powders is used as a resistive electrical conductor to heat the mixture to the reaction temperature. This reaction is performed industrially in a 10-20 m long bunker fixed with two end caps that contain the source and sink for the cLc current. The reactant mixture is piled to a height of 2 m in the bunker and a current is applied. The temperature rises to the reaction temperatures, and some of the excess C reacts to CO, providing further heat. The 10-20 m bunker is covered with a blue flame for most of the reaction period. The resulting SiC is loaded into grinding mills to produce the ceramic powders and abrasives of desired size distributions. 

Herrig, H., Hempelmann, R. Microemulsion mediated synthesis of ternary and quaternary nanoscale mixed oxide ceramic powders. Nanostruct. Mater. 9,241-244 (1997)... 

Vapor—sohd reactions (13—17) are also commonly used ia the synthesis of specialty ceramic powders. Carbothermic reduction of oxides, ia which carbon (qv) black mixed with the appropriate reactant oxide is heated ia nitrogen or an iaert atmosphere, is a popular means of produciag commercial SiC, Si N, aluminum nitride [24304-00-3], AIN, and sialon, ie, siUcon aluminum oxynitride, powders. 

Vittayakorn N. (2006) Synthesis and a crystal structural study of microwave dielectric zirconium titanate (ZrTiO ) powders via a mixed oxide synthesis route. J Ceram Proc Res 7 288-91. 

The many and varied chemical preparation routes for the production of electronic ceramic powders are too numerous to discuss in detail here. Typical precursors include chlorides organometallics such as oxalates and alcohol-based complexes The processes involved include hydrothermal synthesis coprecipitation precipitation of one component followed by coatings of successive dopants, sol-gel preparation polyiner1sation etc. It will be some time before the benefits of the processes can be assessed. Questions concerning their flexibility for producing different compositions, the quality of results and the problems of cost and scaling up still need to be resolved. What is not in doubt is that chemical methods offer potentially much improved powders compared to those prepared by traditional mixed oxide routes. 

Most of the kinetic studies of Sn02-based ceramic are developed to oxide mixed synthesis compressed into pellets, where significant amounts of mass are used. However, the appearance of thick and thin films makes possible the integration of smaller electric devices, and thus new techniques for the s)mthesis and deposition of powders on conductive and insulating rigid substrates have been studied. 

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