Thermoreversible Gel Casting of Ceramics (joint with Prof. Katherine T. Faber)

The thermoreversible gels that we have developed are ideally suited for a unique ceramics processing method that we refer to as 'thermoreversible gel-casting'. A mold of an object (a United States quarter in our example) is made by curing a silicone elastomer around the object. A concentrated suspension of ceramic particles (aluminum oxide in our case) can then be poured into the mold at a temperature above the gel point of about 60 °C. This solution is then cooled to room temperature, where the suspension forms a strong gel (T<Tgel). The material retains its shape after it is removed from the mold, but can be remelted by heating, if desired (T>Tgel). After evaporation of the solvent, the material can be fired at a high temperature to form a dense, ceramic object (Top left). Very complex ceramic parts can easily be formed in this manner. The thermoreversible gelcasting technique was introduced in reference 56, and was applied to the formation of ceramic laminates with graded porosity in reference 59.

The technique has several advantages in comparison to conventional gel-casting systems that are based on chemically cured gels. First, because gelation is thermally induced and completely reversible, the time available to process the material in the liquid state is unlimited. Also, the acrylic polymers used to make the gels are environmentally benign, as are the processing solvents (ethanol or higher alohols). The acrylic block copolymers are responsible for stabilizing the ceramic particles in suspension at temperatures above the gel point, and for providing the elastic character of the gel at temperatures below the gel point.