Ceramic foam is a lightweight, highly porous material used in engineering and other applications. It is created by impregnating a foam structure with ceramic slurry and firing it at high temperatures. Ceramic foam is known for its low thermal conductivity, ability to withstand thermal shocks, and high porosity. It has been used in space shuttle thermal protection systems and filtration applications, and is being studied for potential medical uses.
Ceramic foam is a lightweight structure consisting of a small percentage of highly porous ceramic and a high percentage of gas-filled pores. Typical ceramic foams are 75 to 90% porous, although some are even more porous. Such foams have valuable material properties that make them suitable for a variety of engineering and other applications.
Most manufacturing techniques for such a foam generally involve impregnating another foam structure with a ceramic slurry. This structure is then fired at a high temperature in a kiln. The ceramic hardens as the heat from the kiln destroys the basic structure upon which it was built.
Thus, a light and highly porous ceramic structure is created as the final product of this manufacturing process. The created material can have individually sealed pores. This type of structure is known as closed cell foam. When the pores of the foam are interconnected throughout the structure, it is called open cell foam.
The specific characteristics of the particular foam being created depend on a variety of factors, but this class of material is known for a few common properties. The low thermal conductivity makes ceramic foam particularly useful as a heat insulating material. Its ability to withstand relatively large thermal shocks also makes it suitable for harsh environments such as industrial and aviation applications. The high porosity characteristic of these foams means that they are relatively lightweight materials useful in applications where excessive weight needs to be avoided.
The tiles used in US space shuttle thermal protection systems were classic examples of the use of ceramic foam for these properties. Spacecraft traveling between the earth and space, during launch or re-entry, encounter extreme temperature changes as they pass through the atmosphere at high speed. Isolation from these extreme changes was necessary to protect the ships from this extremely hostile environment. However, it is very expensive and energy-intensive to move mass through space, so weight had to be kept to a minimum. The lightweight nature of ceramic foam combined with its thermal properties have made it attractive for use in some of the tiles installed on the shuttle fleet.
In addition to its use as an insulating material, ceramic foam is also commonly employed in filtration applications. When used in the refining of other materials, ceramic foam filters generally provide three modes of filtration. Upon contact with the filter inlet, particles larger than the pore size are deposited on the filter surface because they are too large to pass through. This support material forms a layer, known as a cake layer, on the filter surface which in turn captures the smallest particles. Finer particles may pass through the cake layer but are then trapped within the pores of the filter.
Potential new uses for ceramic foam are also under development. For example, in the medical industry it is being studied for possible use to stimulate bone growth where bone has been removed, such as in cancer patients. Very small segments of ceramic foam are also being considered for use in delivering drugs to the body over time through a controlled release process.
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