The permeability factor (P, g∙mm/m2∙d) and the solubility coefficient (S, weight %) of water and hydrochloric acid solutions at 70°C enclosed in plastic tubes have been measured using gravimetric techniques. The materials in the tubes were commercial grades of the fluoropolymers PTFE, MFA and PFA. The experimental data of the mass decrease of the tubes as a function of time were treated using a numerical curve-fitting procedure to estimate the separate water and hydrochloric acid permeability of the materials. The numerically-calculated curves and the experimental data points for the HCl solutions showed good agreement. For the 5% and 15% HCl solutions, the mass decrease of the tubes was due to permeation of water. In the 25% HCl solution the mass decrease of water was about four times higher than that of HCl. The concentration of the 35% HCl solution decreased to 28-30%, which indicated dominant permeation of the HCl component. The permeability factors of the materials (P) showed a minimum for the 25% HCl solution. This minimum in P is not an optimum condition for the use of the polymer as lining, because any permeation of HCl is detrimental with respect to the corrosion of the underlying substrate.

Subject
Water, Materials, Diffusion, Permeability, Tubes, Penetrants, Sorption, Solubility, Permeation, Liquids, Polymers, Experimental data, Hydrochloric acid
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2000
Association for Materials Protection and Performance (AMPP)
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