X-ray diffraction patterns were obtained on twenty-five heavy metal soaps at room temperature after air drying, oven drying, and cooling slowly from elevated temperatures.These data have potential value in elucidating the behavior of greases, surface coatings, and other products made from these soaps by their solution or mechanical incorporation in oils. It is also possible, to a certain extent, to identify which of several metal soaps is present from the appearance of the x-ray diffraction pattern. In all of the soaps examined, the metal ions are arranged in parallel planes separated by a distance somewhat less than twice that of the fatty acid radical. Soaps of zinc, magnesium, lithium, and aluminum give patterns different from one another and from the remaining soaps.Calcium, strontium, and barium soaps give patterns similar to one another, more so for strontium and INDUSTRIAL AND ENGINEERING CHEMISTRY Vol. 41,No. 10 as such through the courtesy of the Metasap Chemical Company. They were made from single-pressed technical stearic acid and, consequently, must contain considerable amounts of unsaturated fatty acids and homologous saturated fatty acids. Constants of this stearic acid are also given in the preceding table.
faintly resolvable shoulders may reflect the fact that partial recrystallization has occurred, but the crystallites must be verysmall or imperfect.Iron, cobalt, and nickel soaps appear to have been in a pseudoglassy state initially. Thermal treatment does not effect any further changes except in the case of nickel soaps where the patterns were slightly more sharply defined initially, so that broadening of the lines and reduction of intensity in the long spacings after heating are noticeable.To summarize, after the thermal treatment, aluminum soaps and iron, cobalt, and nickel soaps, which were essentially noncrystalline at first, are unchanged. Zinc palmitato and lithium stearate have recrystallized completely and give patterns as sharp as or sharper than the original and showing no important changes in line position or intensity. All the others apparently are in varying stages intermediate between their original state and an undercooled form usually characterized by a slightly shortened long spacing, which is nevertheless sharply defined, and a side spacing consisting of a single halo at about 4.1 to 4.2 A. which would correspond to the mean distance between parallel hydrocarbon chains if they were hexagonally close-packed. Mercury, lead, and barium soaps are closer to the original crystal than are some of the others, notably magnesium soaps. Likewise, the palmitates seem, on the whole, to recrystallize somewhat more readily than the stearates. This difference, however, may reflect a different degree of purity of the stearic and palmitic acids used rather than any fundamental difference between palmitates and stearates as such.
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