Effects of Pressure on the Chemical Properties of Solid Surface. VI. The Surface Acidity of the Compressed Zinc Sulfate

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In order to clarify the mechanism of the acidity change due to compression, zinc sulfate was compressed under various pressures, ranging from 0 to 7000 kg/cm2, and the surface acidity was measured and compared with the data of the structural change in the sample. According to the experimental results, the surface acidity varied on compression. At lower compacting pressures (P∼2500 kg/cm2), the content of weak acid (H0=1.5–3.3) was high and that of the strong acid was poor. These facts were explained by the higher content of anion-water, or heptahydrate, in the sample. In the pressure region of P=2500<5500 kg/cm2, the acidity-pressure curve showed a maximum at 4500 kg/cm2. Further, in this pressure range, the acidity-pressure curve paralleled well the respective curves of the X-ray peak width of hexahydrate pressure, the relative intensity of the IR v1(SO42−)-pressure, and the half width of the IR v3(SO42−)-pressure. It was considered that the acidity change in this pressure range is caused by the change in the content of the distorted structural unit of hexahydrate in the sample. In the highest pressure range, the content of weak acid was found to increase, whereas the content of strong acid was found to decrease. These results were discussed by considering the increased inclusion of tetrahydrate in the sample.
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