Determination of Rate of Water Uptake into Protective Paint Films by the Electric Capacitance Method
スポンサーリンク
概要
- 論文の詳細を見る
The electric capacitance method, which was originally proposed by Brasher and Kingsbury to determine the amount of absorbed water in a paint film, involves a few problems in its basic assumption. As an example, the water distribution in the paint film was assumed to be always uniform even when the stage of water absorption was transient. Therefore, the authors investigated the accuracy of the B-K method by the simulation with the digital computer and also by the immersion test.<BR>Firstly, the distribution of water through the paint film was calculated on the basis of the onedimentional diffusion theory, and then the overall amount of water uptake W<SUB>1</SUB> was estimated by the integration as a function of time duration. Furthermore, the overall electric capacitance of the painted specimen was estimated by integrating the local electric capacitance which varied in accordance with the amount of absorbed water. The amount of absorbed water W<SUB>2</SUB> was again estimated from this ovarall electric capacitance by the ordinal B-K method. The comparison of the values of W<SUB>1</SUB> with that of W<SUB>2</SUB> revealed the fact that the error of the B-K method must be in practical quite small except the initial period of water absorption.<BR>In the immersion tests of the painted specimens in the sodium chloride solution, however, a rather great discrepancy was found between the directly obtained water uptake by the weight method and the estimated by the electric capacitance method. Several reasons were speculated for explaining the observed discrepancy. In the most case, the plots of the weight and the electric capacitance against the time nearly followed the analytical equations derived in this investigation as a rough approxi-mation.<BR>A method of estimation of the diffusion constant of water in the paint film was devised by using these analytical equations. By this method, the values ranging from 10<SUP>-9</SUP> to 10<SUP>-11</SUP> cm<SUP>-2</SUP>/sec was obtained as diffusion constants through various protective paint films from the observed electric capacitancetime relations. Faculty
- Japan Society of Colour Materialの論文