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The dehydroxylation reaction of kaolinite in a vacuum at 425 degrees C is halted by introducing a water vapor pressure of 47 mm-Hg, and is resumed when the vacuum is reestablished. The sample gains weight corresponding to an approximately monomotecular layer of water on the kaolinite surface. At the temperatures and vapor pressures involved, the sorption is considered to be a chemisorption process.

Single-crystal electron-diffraction data reveal features of metakaolin. The basal plane parameters increase 2.2 percent in formation of metakaolin produced by heating kaolinite in air at 700 degrees C for 12 hours. This increase results from removal of the distortion of sheet structure (relaxation).