Silicic Acid Gels

Abstract

Workers in various sciences have occasion to prepare special silicic acid gels but specific directions are lacking. Requirements for such gels made from the desired acid, setting in a convenient time, and of a definite silica content, should be met. This paper offers information for such needs as well as new work on the effect of high concentrations of the acid mixed with the sodium silicate and the comparative effect of weak and strong acids on silicic acid. A study of the influence of higher temperatures on silicic acid gels is also included.Flemming,1 under the direction of W. Ostwald, has made the most important contribution to this phase of the subject although Kohlrausch2 studied the effect of age on water glass solutions as measured by change in conductivity and van Bemmelen3 did invaluable work in connection with the dehydration and hydration of silicic acid gels. Maschke4 added some work on the time of formation of these gels. Methods of WorkA water glass solution sold for general purposes by a prominent chemical company was used for most of the experiments. Since carbon dioxide has a marked influence on the time of set of silicic acid gels it was necessary to have a water glass free from this substance. We diluted this sodium silicate, acidified and boiled. No carbon dioxide could be detected in the issuing gases. Some samples of commercial water glass contain iron salts in appreciable quantities but only a trace of iron was to be found in the product we selected. It was practically colorless. Analysis showed the composi-

Studies on Silicic Acid Gels. IV. The Effect of the Hydrogen-ion Concentration upon the Time of Set.

“…We may admit the assumptions first proposed by Hurd and Letteron, namely, (1) that in dealing with the mechanism involved in the setting of a silicic acid gel we are dealing with a process which follows the laws of an ordinary chemical reaction, so far as its velocity is concerned, and (2) that for a given silica content, the time of set measures the time when a certain fixed proportion of the silica, in whatever form, in solution has reacted.…”

“…This research was supported by a Grant-in-Aid of the National Research Council 2. A report was made on the first half of these results before the Colloid Division of the American Chemical Society at the meeting held in Washington, March, 1933 8.…”

Studies on Silicic Acid Gels. X. The Time of Set of Gel Mixtures Containing High Concentrations of Mineral Acids.

“…It has been shown (4) that silicic acid gel mixtures show minimum time of set with pH slightly above 7. Mixtures containing a high concentration of strong acids also set rapidly (3). The optimum limits for setting have been published (11), and also the curve for time of set against acid concentration (8).…”

The Effect of Additives on the Physical–Chemical Properties of Soap Gels in Organic Solvents

“…Further, the per cent acceleration of the setting process decreases in the order: An attempt was made to see whether the per cent increase or decrease in setting time is related to the atomic weight of the cations in the added soaps. The various curves in figures 3 and 4 show that straight lines are obtained for both the palmitates and the stearates, and further that these are almost parallel to each other. Also, the points for calcium, strontium, and barium soaps lie on one straight line, whereas those for magnesium, zinc, cadmium, and mercurysoaps lie on another.…”