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Fused quartz is essentially impermeable to most gases, but helium, hydrogen, deuterium and neon may diffuse through the glass. The rate of diffusion increases at higher temperatures and differential pressures.
The selective diffusion of helium through fused quartz is the basis for a method of purifying helium by essentially "screening out" contaminants by passing the gas through thin-walled quartz tubes.
The diffusion of helium, hydrogen, deuterium and neon through fused quartz is accelerated with increasing temperature. According to General Electric Research Laboratory, the permeability constants for these gases through fused silica at 700°C are estimated to be:
Helium 2.1 x 10-8 cc/sec/cm2/mm/cm Hg
Hydrogen 2.1 x 10-9
Deuterium 1.7 x 10-9
Neon 9.5 x 10-10
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Diffusion Through Quartz
For semiconductor applications, the diffusion of various ions through the quartz is of critical importance. The attached table shows the time for various ions to diffuse through different thicknesses of quartz. These calculated values are based on the diffusion coefficient and a temperature of 1000°C.
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Momentive Performance Materials
