Development of Aerogel Additives for the Foundry Industry

Abstract

The foundry industry produces castings by solidification of molten metal in sand or permanent moulds. Special sand cores are used to get specific cavities within the casting material. These cores have the negative shape of the required hole. Many cast defects are known to appear on account of the thermal, mechanical and/or chemical transformation of the sand cores. The thermal decomposition of the most often used organic binder system, leads to a strong gas evolution and the occurrence of special cast defects. To avoid this expensive and time consuming ceramic coatings are used. Alternatively the cast quality can be improved by refining the cores themselves using aerogels. Aerogels as nanostructured additives restrain many typical cast defects. Their large inner surface, high gas absorption capacity and lower thermal conductivity are able to minimize common defects in castings. Resulting exhaust gases can be bound physically or chemically on the inner surface. Within the last years granulated aerogels as additives lead to benefits in aluminum and brass alloy castings. Recently they enabled positive results even in grey cast iron. Due to the high casting temperatures, the different solidification behavior of bronze and the mechanical treatment at the bronze foundry industry aerogels as additives are exposed to different thermal and mechanical circumstances. They need to withstand temperatures above 1200-1300°C for a period of time and be stable under oxidizing conditions. Si-O-C aerogels could be synthesized by pyrolysis of the appropriate organic-inorganic hybrid system. They are stable under high temperatures and may be used as additives in bronze casting. The poster describes the synthesis of the Si-O-C aerogels, their thermal and mechanical properties as well as their ability of gas adsorption by measuring the inner surface.