Diffusion Coefficients of Helium in Fused Quartz

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Abstract
The diffusion of helium through the walls of high-purity fused quartz hollow cylinders was studied using a mass spectrometer as a detecting device. By surrounding the outside of the hollow cylinder with helium and observing it diffuse through into the mass spectrometer, permeation rates and diffusion coefficients were measured in the temperature range of 24° to 1034°C. The diffusion process appeared to be relatively simple with only small deviations from Fick's laws occurring. The activation energy was found to be different in the temperature range of 24° to 300°C than in the range of 300° to 1034°C. In the low-temperature range the diffusion coefficients are expressed by D=3.04×10−4exp(−5580±56 cal/g atomRT)cm2/sec,and in the high-temperature range they are expressed by D=7.40×10−4 exp(−6613±40 cal/g atomRT)cm2/sec.The solubility was also determined by dividing the permeability by the diffusion coefficients. This was expressed by S=1.99×1017 exp(−−680±60 cal/g atomRT)atoms/cm3in the temperature range of 24° to 300°C and by S=1.28×1017 exp(−−1174±120 cal/g atomRT)atoms/cm3in the range 300° to 1034°C.

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