Glass microspheres are microscopic spheres of glass manufactured for wide a variety of uses in research, medicine, consumer goods and various industries. Glass microspheres are usually between 1 to 1000 micrometers in diameter. The term is also used for glass spheres between 100 nanometers to 5 millimeters in diameter. 1 Hollow glass microspheres, sometimes termed microballoons, have diameters ranging from 10 to 300 micrometers. 2
Hollow spheres are also used as a lightweight filler in composite materials such as syntactic foam and light weight concrete3. Microballoons give syntactic foam its light weight, low thermal conductivity, and a resistance to compressive stress that far exceeds that of other foams.4 These properties are exploited in the hulls of submersibles and deep-sea oil drilling equipment, where other types of foam would implode. Hollow spheres of other materials create syntactic foams with different properties, for example ceramic balloons can make a light syntactic aluminium foam.5
Glass microspheres can be made by heating tiny droplets of dissolved water glass in a process known as ultrasonic spray pyrolysis, and properties can be improved somewhat by using an acid treatment to remove some of the sodium.6
Microspheres are also used in composites to fill polymer resins for specific characteristics such as weight, sandability and sealing surfaces. When making surfboards for example, shapers seal the EPS foam blanks with epoxy and microballoons to create an impermeable and easily sanded surface upon which fiberglass laminates are applied.
