1266
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 26, No. 12
contents a t this acidity factor are taken as cz. From these are found corresponding values of c1 at some other acidity factor, fi, and a functional relationship is obtained which may be plotted. The results are shown in Figure 3. These curves, sensibly linear, relating the titanium oxide contents of corresponding solutions of titanium sulfate, reveal an analogy to Duhring’s rule relating the temperatures of two liquids for which the vapor pressures are the same (4). It will be of interest to compare the curves obtained in this way with those derived mathematically from the simple hypotheses that have been made. If in Equation 2 , f 2 = 1.02, then: ~2 = (2.44 f i ) ~ i / 3 . 4 6 Kci (3) where K = a constant depending only upon acidity factor fi If fi 0.10, K = 0.734
+
= 0.19, K 0.760 ji = 0.52, K = 0.855 fi = 1.02, K = 1.000 fi
FIGURE4. EXPERIMENTAL CURVESRELATING TITANIUM OXIDE CONTENT WITH EQUIVALENT TITANIUM OXIDECONTENT AT ACIDITY FACTOR1.02
Solutions which are “equivalent” should therefore show similar curves of titanium oxide yield us. time for solutions hydrolyzed a t the boiling point. Hixson and Plechner (1) have obtained such curves for a number of pure titanium sulfate solutions a t acidity factors of 0.10, 0.19, 0.52, and 1.02. The corresponding types for these acidity factors have been selected from similarities in the shapes of the curves of titanium oxide yield us. time. While admittedly somewhat inexact, these selections are not too difficult, as may be verified from an examination of the data from which they are derived. The highest acidity factor is chosen as a standard of comparison. Thus f2 equals 1.02 and the various titanium oxide
In Figure 4 the several curves have been plotted from these equations, and they bear a close resemblance to the curves of Figure 3. With due correction for change in concentration of sulfuric acid which has been neglected in this derivation, the curves approach still more closely those experimentally determined. In the industry the situation is further complicated by the presence in the solutions of ferrous sulfate, titanous sulfate, and other salts, and the deliberate addition of seeding material, all of which seriously modify both the rate of precipitation and the character of the product.
LITERATURE CITED (1) Hixson, A. W., and Plechner, W. W., IND.ENQ.CHEM.,25, 262 (1933). (2) Lewis, G . N., and Randall, M., “Thermodynamics and the Free Energy of Chemical Substances,” p. 38, McGraw-Hill Book Co., New York, 1933. (3) Perry, J. H., Chemical Engineers’ Handbook, p. 241, McGrawHill Book Co., Xew York, 1934. (4) Perry, J. H., and Smith, E. R., IND.ENQ.CHEM.,25, 195 (1933). (5) Stutz, G. F. A , , Jr., and Pfund, A. H., Zbid., 19, 51 (1927).
* * * * *
Effect of Precipitation, Calcination, and Subsequent Treatment LINCOLNT. WORKAND SIDKEY B. TUWINER Calcination tests reveal marked diferences in the character of the precipitate. The recognized effect of seeding is of dominant importance. Pigments produced f r o m unseeded solutions tend to be coarse in size when distribution curues are shown. The effect of calcining temperature has been studied and shown lo be of limited importance over a normal range but to vary appreciably
I
N T H I S section a number of variables, besides the composition of the solution, which affect the ultimate quality of the pigment are considered. PIGMENTS FROM COhlMERCIAL PRECIPITATES
It has been shown that the pure solution did not yield sufficient nuclei as treated to give a pigment of high hiding power. It is recognized that these nuclei play an important part in the ultimate quality of this type of pigment. I n order to make a comparison on commercial precipitates, two samples, X and Y, were supplied by the Titanium Pigment Com-
at temperatures above 850” C. The character of the pigment appears to be agglomerate rather than crystalline, and milling produces signgcant effects in oil absorption and hiding power. Microscopic examination of milled particles shows the structure of indioidual particles and clusters. The counting of doublets, triplets, etc., is used as a criterion of this effect. pany as representative precipitates from commercial manufacturers. They were calcined in a similar manner to that used for the precipitates from pure solutions. Turbidimetric measurements were made on both the pigment as obtained from calcination and on the same material ground for one hour in an agate mortar. Oil absorption and tinting strength mere measured on milled materials alone. Tinting strength was run in accordance with the procedure of the National Lead Company, and the oil absorption by the method of Gardner ( 2 ) . However, smaller samples were used, and the results are
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