Algorithm for calculating nonisothermal diffusion-limited outgassing rates

Timothy J. Girard; Richard M. Payton

doi:10.1117/12.140749

18 December 1992 Algorithm for calculating nonisothermal diffusion-limited outgassing rates

Timothy J. Girard, Richard M. Payton

Author Affiliations +

Proceedings Volume 1754, Optical System Contamination: Effects, Measurement, Control III; (1992) https://doi.org/10.1117/12.140749
Event: San Diego '92, 1992, San Diego, CA, United States

Abstract

Formulas exist for prediction of diffusion limited outgassing rates under isothermal conditions. An algorithm has now been developed that predicts outgassing rates for material species that outgas via diffusion mechanisms for non-isothermal conditions. The algorithm uses initial species mass, diffusion coefficient, activation energy and a temperature history to determine outgassing rates at prescribed times. The algorithm accounts for bulk material temperature variations through time but does not account for thermal gradients through the material thickness. The non-isothermal mass loss equation is derived from a basic isothermal mass loss equation with the term that indicates species molecular propagation for the non-isothermal conditions. For isothermal conditions, the product of D(T) (where temperature T, is constant) and time is a measure of the species molecular propagation. This term in the isothermal mass loss equation is replaced with the term for nonisothermal molecular propagation, which is the integral over time of D(T) (where temperature, T, is time dependent). Temperature dependent outgassing rates are calculated by numerically differentiating the time and temperature dependent mass loss predictions. Mass loss rates for the non-isothermal conditions are compared to isothermal mass loss rates.

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Timothy J. Girard and Richard M. Payton "Algorithm for calculating nonisothermal diffusion-limited outgassing rates", Proc. SPIE 1754, Optical System Contamination: Effects, Measurement, Control III, (18 December 1992); https://doi.org/10.1117/12.140749

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