Syntactic foam
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Syntactic foams are composite materials synthesized by filling a metal, polymer or ceramic matrix with hollow particles called microballoons. The presence of hollow particles results in lower density, higher strength, a lower thermal expansion coefficient, and, in some cases, radar or sonar transparency.
Tailorability is one of the biggest advantages of these materials. The matrix material can be selected from almost any metal, polymer or ceramic. A wide variety of microballoons are available, including cenospheres, glass microspheres, carbon and polymer microballoons. The most widely used and studied foams are glass microballoon-epoxy, glass microballoon—aluminum and cenosphere-aluminum.
The compressive properties of syntactic foams primarily depend on the properties of microballoons, whereas the tensile properties depend on the matrix material used in their structure. There are two ways of modulating properties of these materials. The first method is to change the volume fraction of microballoon in the syntactic foam structure. The second method is to use microballoons of difference walls.
Syntactic foams can also be modified by the addition of larger diameter fiberglass or carbon fiber-reinforced macrospheres. The resulting "composite" foams are less dense and often less expensive than so-called "solid" foams. In general, the compressive strength of the material is proportional to its density.
These materials were developed in early 1960s as buoyancy aid materials for marine applications; the other characteristics led these materials to aerospace and ground transportation vehicle applications. Among the present applications, some of the common examples are buoyancy modules for marine drilling risers, boat hulls, and parts of helicopters and airplanes. New applications are coming up in sports industry; snow skis and Adidas soccer balls are some of the examples.
