Aerogels for Directional Solidification

An alloy melt should nominally solidify with exactly the pulling speed. The temperature gradient at the melting front is determined in principle by the temperature profile and the slope of it at the melting temperature T. The information about the temperature field during solidification is usually determined by thermocouples or thermistors, which are placed either in the sample or in the cartridge. 

The information that can be obtained by this method is only pointwise and because of the varying conditions during the solidification process often not satisfying. The velocity of the solid-liquid interface may then be determined as a function of position. The temperature field in the sample is calculated from the thermocouple readings. 

At the moment the technology is developed further to include different sources for electromagnetic stirring like traveling magnetic fields or to built facilities for use in strong magnetic fields. 

Polymeric aerogels based on RF were developed in the last years for application in foundry practice as a new nanostructured binder for foundry sands. Their properties allow, for instance, to replace conventional polymeric binders, since they solve certain problems of core removal, penetration, surface reactions, blow holes, and other casting defects especially in light metal casting. RF aerogels as polymeric binders are at the verge of being used by industry. 

Campbell J (2000) Castings. ButterwOTth-Heinemaim, Oxford,Paperback Edition Beeley PR (2001) Foundry Technology. Butterworth-Heinemann,Oxford, 2nd Edition Briick S, Ratke L (2002) RF Aerogels A new binding material for foundry application. J Sol-Gel Sci Tech 26 663 66 

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