I N D U S T R I A L AND E N G I N E E R I N G CHEMISTRY
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Vol. 31, No. 7 Temp. Incpase of Acid, C.
QUALITATIVE TESTS. To determine the relative value of some
of the materials, a qualitative spot test was run in which the effect of nitrating acid (15% nitric in concentrated sulfuric) was observed. Compositions containing polyisobutylene with no rubber are almost inert and undergo little change when test strips are immersed in the acid, If cured rubber is added in equal proportions to polyisobutylene, the mix is attacked vigorously by nitrating acid. This action is reduced if sulfur content is increased, but the specimen is still far less resistant to attack than are polyisobutylene compositions when no rubber is present. Rubber alone is attacked vigorously by nitrating acid. Table 111 summarizes the data obtained. Blends of crepe rubber and polyisobutylene with no other compounding ingredients behave similarly in nitrating acid as do the finished liners. As the polyisobutylene content is increased, the resistance to attack is increased, I n the following tests one-gram samples were placed in 20 ml. of mixed acid (85% concentrated sulfuric, 15% concentrated nitric), and the increase in solution temperature was measured:
49.4 47.2
0
20 40
38.9 16.1 0
60
100
ACKNOWLEDGMENT
The advice, encouragement, and assistance of M. D. Mann, Jr., L. B. Turner, H. G. Schneider, and H. C. Evans are greatly appreciated. LITERATURE CITED
Drakeley, 1'. J., Ann. Rept. Prograss Rubber Technol., 3, 46 (1939).
Evans, H. C., and Young, D. W., IND. ENQ. CHEIM., 34, 461 (1942).
Flory, P.J., J . Am. Chem. Soc., 65, 372 (1943). Krannich, Walter, Chm. Fabrik, 13, 233-52 (1940). Thomas, R. M., Sparks, W. J., Frolioh, P. K., Otto M., and Mueller-Cunradi, M., J. Am. C h m . Soo., 62,276 (1940). Vandsrbilt News, 11, No.2 , 19 (March-April, 1941).
Hydrolysis of Titanvl Sulfate Solutions ARTHUR W. HIXSON AND RALPH E. C. FREDRICKSON' Columbia University, New York 27, N. Y . Results are presented of a fundamental study of the precipitation characteristics of titanyl sulfate solutions. The data suggest that the first step in the precipitation reaction was a rapid splitting off of half the sulfuric acid of the salt to give a basic colloidal complex in which the molar ratio of titanium oxide to sulfur trioxide was about 2 to 1. This complex then hydrolyzed more slowly to give increasingly basic complexes which finally precipitated. The oxide formed by this mechanism appeared to be easily peptized at the boiling point in weakly acid solutions. Light transmission measurements indicate that the above mechanism prevailed in solutionswhich were less than 1.25 to 1.5 molar in free sulfuric acid, regardless of the titanium concentration. The abnormal precipitation curves previously reported by Hixson and Plechner were found to be characteristic of solutions containing less than the above acid concentration. Their normal curves proved to be characteristic of solutions in which the acid concentration was higher than 1.5 molar.
B
ASICALLY the manufacture of titanium oxide pigments consists of the following steps: (a) solution of the tita-
nium ore in acid, (a) precipitation of the titanium oxide by heating the above solution under conditions favorable to the hydrolysis of the dissolved titanium, and (c) calcination of the precipitated oxide whereby pigment qualities are developed. This paper is concerned with the results of a fundamental study of the second step, the hydrolysis of titanium sulfate solutions. One of the early fundamental studies of this important reaction was reported by Hixson and Plechner (6). They boiled various solutions of titanyl sulfate and sulfuric acid to precipitate titanium oxide. From time to time samples were with:Present address, A. E. Staley Monufaoturinp Company, becstur. Ill.
drawn from the boiling flask and analyzed for the amount of precipitated titanium oxide. The amounts precipitated were then plotted against time of boiling to give the curves illustrated in Figure 1. These three typical curves were taken from series 400 of the in which the acid factor was 1.0: earlier paper (6), acid factor =
% total acid
- % acid equiv. to Ti(S04)t %Ti02
Similar families of curves were obtained with other acid factors. Curve 400 (Figure 1) was obtained from a solution that was 2.45 molar in sulfuric acid and 1.34 molar in titanyl sulfate. Solution 404 was derived from 400 by simple dilution with water until the acid molarity was 1.83 and the titanyl sulfate molarity was 1.0. Solution 407 was obtained by diluting 400 to an acid molarity of 0.9 and a titanyl sulfate molarity of 0.5. Thus in all of these solutions the molar ratio of acid to titanyl sulfate was 1.83 and the acid factor waa unity. FrGm these curves it was evident that the precipitation characteristics of titanyl sulfate solutions were a function of dilution. Further, the differences were probably not merely differences in degree. Hixson and Plechner made a number of attempts to explain these peculiar curves. Analyses of the hydrolytic products could not be correlated with the observed phenomena. Plots of density against titanium oxide concentration for solutions with a given acid factor gave no indication of any complex formation. Parravano and Cagliotti (8) also observed the anomalies previously cited. They plotted refractive index against titanium oxide concentration for a series of solutions in which the molar ratio of sulfuric acid to titanyl sulfate was about 1.67. They obtained two straight lines with slightly different slopes intersecting a t a titanium concentration of 1.2 molar. The corresponding acid concentration was 2.0 molar. No successful correlation of this observation with precipitation characteristics was reported.
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
July, 1945
679
Hixson and Stetkewicz (6)atAT ROOM TEMPERATURE FROM pH TABLE I. AMOUNTOF TiOSOI.2HpO HYDROLYZED tacked the problem by measuring MEMUREMENTS refractive index, dispersion, den-TiOSOa. 0.12-M -TiOB04,0.6 -M -TiOSOi, 1.2 dfMolar- %&xx Molar- % hyMolar- % hysity, and viscosityof a large numity of drcity of drober of titanium sulfate solutions Time pH %&? 4! lysed Time pH H:804 lyaed Time pH H t S 0 4 lyerd n 6.0 6.0 .. 13in min. 0.18 0 6.0 .. in which the molar ratio of sulfur .. 0:31 62 0:85 o:ois 16 7 i min. 0 . 6 64 6 min. 1.57 trioxide to titanium oxide varied 0.18 24 62 0.029 0.6 0.81 0.65 64 166 86 10 1.88 64 0.16 0.061 0.32 0.66 211 116 60 0.48 68 21 1.15 from 1.001 to 3.004, and the 64 0.16 0.32 0.69 56 hr. 119 0.070 0.48 68 68 26 1.1 0.19 54 0.07 0.32 0 . 4 8 63 0.64 92 184 58 31 1.1 per cent titanium oxide from 0.5 0.19 0.64 146' .. 64 hr. 0.072 0.69 63 60 36 1.09 0:31 62 0.070 to 26%. The data were then 68 90 0.60 44 1.10 144" 53 0.088 66 0.49 0.32 2.6hr. 1.08 plotted against titanium oxide 0.088 1.02 71.6 71.6 0.088 112 21 1.02 concentration in the hope that ir92 0.112 4 no. 0.92 regularities in the curvemight be Blight preoipitate. correlated with the Deculiaritiw in the precipitation curves. No such correlation waa found. We therefore undertook a fundamental study of the hydrolysis of meter used for the titanium solutions. The percentage hydrolysimple aqueous dispersions of pure titanyl sulfate in both the pressis of the titanium salt was then calculated from the derived acid ence and absence of sulfuric acid. It wss hoped that information concentration. so developed might be useful in explaining the data reported by It was evident from these data that the dispersion of titanyl Hixson and Plechner. sulfate in water was accompanied by an initial rapid drop in pH Titanium tetrachloride was triple-distilled over zinc amalgam during the first 20-30 minutes. Then the pH decreased slowly and solid sodium hydroxide. The fraction boiling at 134-136' C. but did not reach a constant value. For all three solutions the was collected and hydrolyzed. Sulfuric acid was then added, amount of hydrolysis corresponding to the period in which the followed by concentration to 5540% acid by evaporation at 30 pH changed only slightly was about 50%. When the above meast o 60 mm. The titanyi sulfate was precipitated by boiling under urements were being made, it was observed that the period of slow reflux for 24 hours. The precipitate was wsshed with alcohol to pH change set in at about the time the solutions became clear. remove the excess acid and then washed several times with ether. The early section of the pH curve was, therefore, principally a The product wm air-dried for several hours and then oven-dried measure of the rate of dispersion of the solid titanyl sulfate. The at 105-110' C. This procedure yielded a product whose analysis percentage hydrolysis calculated for the 5 and 10 minute points corresponded precisely to the formula TiOS0,.2H,O. The salt was therefore fictitious since these figures were based on the total wm chloride-free and contained less than 0.003% iron as deterweight of titanyl sulfate taken rather than on the amounts dismined with ammonium thiocyanate. solved at those times. As a whole, however, the data indicated that the dispersion of titanyl sulfate in water a t room temperHYDROLYSIS IN ABSENCE OF SULFURIC ACID atures was accompanied by rapid hydrolysis of half its sulfuric acid. The remainder of the hydrolysis seemed to occur at a The first experiments consisted of following the dispersion of much slower rate, requiring more than 4 months in a 0.12 molar titanyl sulfate dihydrate in water by pH measurements. The apsolution. propriate quantity of titanyl sulfate, prepared by the above proTo check the results of the pH measurements, the dispersion of cedure, was weighed into a voltimetric flask. Water was added to a 0.12 molar titanyl sulfate solution w&s followed conductometthe mark and a uniform sample of the slurry immediately placed rically. Immediately after the addition of water to the salt, a in the measuring cell of a Beckman pH meter equipped with a uniform slurry was placed in a conductivity cell at 25' C., and glass electrode. The pH was then measured a t various time interits conductivity determined at one-minute intervals. The data vals (Table I). Figure 2 is a plot of the data for the 0.12 molar are presented in Figure 3. The curve marked "second difference" titanyl sulfate solution. The time data were measured from the is the second derivative of the conductivity curve. time of water addition. The sulfuric acid concentrations were deThe conductivity data indicated the same general result as the rived from the pH measurements by referring them t
