Re: Temperature & Diffusion coefficient  

Posted by on June 29, 2005 at 09:29:15:

In Reply to: Temperature & Diffusion coefficient posted by Ray O'Halloran on June 28, 2005 at 16:48:33:

Dear Ray,

If you would like to use a weighing method for the measuring of the solubility and diffusivity of vapours and gases then the thickness of the sample is indeed of importance.

Although the enthalpy of mixing during the adsorption of molecules in the polymer is positive, the enthalpy of condensation is negative. Depending on the temperature, the resulting enthalpy may be negative, heating up the sample. This will disturb the solubility and diffusivity at the required temperature and pressure.

Based on the type of permeant(s) and polymer a minimum thickness for the sample to reduce the temperature effect to +/- 1 degrees Celsius can be given by us.

If you want to use another experimental set-up than gravimetric methods, please do not hesitate to inform us.

: I am working on polyurethane insulation on oil, chemicals & gas offshore pipelines and need to produce useable experimental data related to firstly obtaining a diffusion coefficient and secondly to measure the effects of temperaure change on 'D'.

: I am told that there is some debate as to the thickness of sample to be used as too thin a sample can give inaccurate results, any advice on this would be greatly appreciated.

: Thanks,

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