THE PREPARATION AND SINTERING OF FINELY DIVIDED SODIUM CHLORIDE. II

Abstract

The sintering of unpacked samples of sodium chloride of high specific surface has been investigated. The sintering occurred in the presence of known pressures of water vapor and at temperatures below 70 °C. The progress of the change of specific surface was followed by measuring the physical adsorption of carbon dioxide at approximately −80 °C. It has been shown that an unchanging value of the surface area of a given sample exists at each relative pressure of water vapor. The area attained is independent of the number of exposures to water vapor at pressures below the final pressure. The fractional change of area of all samples in the range 35 to 80 m•2/g. depends only upon the relative pressure of water vapor. Preliminary observations of the behavior of loaded samples showed that packing the samples does not affect the character of the sintering.A qualitative theory to account for these findings is given. It is postulated that certain ion pairs become mobile when the binding energy to the crystal is reduced by the adsorbed water. On increasing the amount of adsorbed water additional ion pairs become free to migrate and the process resulting in loss of specific surface continues to a further extent.