分子吸附对聚乙烯醇在氧化铝粉末压缩体中扩散系数的影响

EFFECT OF ADSORPTION ON DIFFUSION COEFFICIENT OF POLYVINYL ALCOHOL IN ALUMINA POWDER COMPACT

利用氧化铝粉末压缩球状体和Ｆｉｃｋ第二扩散定律，系统地研究了聚乙烯醇在多孔介质和实验系统ｐＨ值为８．４０±０．２条件下的扩散行为，以及聚乙烯醇在球体外表面吸附对扩散系数的影响．实验结果和相应计算得到的扩散系数表明：发生在氧化铝表面的分子吸附，不仅导致扩散平衡状态时的Ｍｔ（聚乙烯醇在时间ｔ的扩散量）高于理论计算值Ｍ∞，而且使实验初始阶段计算的扩散系数远大于其它过程扩散系数．由分子吸附产生的实验误差和扩散系数计算误差，可通过修正浓度分配系数Ｋ，或者直接从Ｍｔ中去除可能存在的吸附量得到解决．

Diffusion of polyvinyl alcohol (PVA) in alumina powder compact was carefully examined in the case pH=8.40±0.2, and the diffusion coefficient D was calculated by the Fick′s diffusion law. The experimental and calculation results show that adsorption of polyvinyl alcohol on the outer surface of the alumina compact causes M t in the diffusion equilibrium larger than the theoretical M ∞ ( M t/M ∞>1) and D in the initial process larger than those in the subsequent processes. However, the influence of PVA adsorption on D could be minimized by modifying the concentration parameter K or eliminating the possible adsorbance directly from the measured M t .