Rapid development in the field of deep-sea exploration in the middle of the 20th century was one of the main reasons for development of hollow glass microsphere (HGM) technology. Development engineers of deep submergence vehicles required new structural materials with densities less than those of water but of high compression strength and water resistance. Syntactic composites based on HGMs were able to meet these requirements. Structural elements made using these materials are capable of withstanding water pressure down to 6000 m.
Hollow glass microspheres form a white coloured powder consisting of tiny bubbles with diameters ranging between 20-150 μm with walls thicknesses less than 1 μm. The glass composition and the near perfect spherical shape of the microspheres provide high compressive strength. The main distinction between high and low grade HGMs is their shape and structure. Lower quality HGMs fail under less load, less predictably, compared to high grade HGMs. Other key properties include low water absorption, low heat conductivity, high chemical resistance and radio transparency.
Good adhesion of HGMs towards polymer binders makes them ideal for composites giving a unique combination of properties. All the above-mentioned factors define a wide variety of applications for HGMs.
The technology for HGM manufacture is a combination of complex hydrodynamic and chemical processes that take place in the course of forming of hollow bubbles blown from microparticles of glass melt. An exact dosage of gas into the melted powder blows microspheres with the required diameter and wall thickness. With such a complex technological process it is impossible to make microspheres with a strictly identical predetermined diameter. Therefore calibration of microspheres is performed according to their dimensions. The strength of the microspheres is established by testing the hydrostatic pressure at which not more than 10% of the HGMs fail. It is natural that microspheres with a greater density – and thus with thicker walls – are stronger.
This article comes from materialstoday edit released
