INDUSTRIAL AND ENGINEERING CHEMISTRY
February 1954
ACKNOWLEDGMEYT
This research program on dextran has been carried out with the cooperation of several groups of workers a t the Xorthern Regional Research Laboratory. The authors wish particularly t o thank R. J. Dimler, H. M. Tsuchiya, J. Corman, V. Sohns, P. Rogovin, and H. Conway for their assistance in supplying the native dextran used as starting material; C. 5. Wise for carrying out analyses for fructose; J. C. Rankin for periodate analyses; R. L. Lohmar for performing the experiments on fractionation of dextran hydrolyzates at different polysaccharide concentrations; Allene Jeanes for supplying the isomaltose and isomaltotriose samples used as standards in reducing power determinations; and members of the Analytical, Physical-Chemical, and Physics Division for assistance in the physical and chemical characterizations and for discussions concerning fractionation procedurea. LITERATURE CITED (1) Bixler, G. H., Hines, G. E., McGhee, R. M., and Shurter, R. A., IND.ENO.CHEM.,45, 692-705 (1953). (2) Colin, H., and Belval, H., Compt. rend., 210, 517-20 (1940). (3) Cragg, L. H., J . Colloid Sci., 1 , 261-9 (1946). (4) Cragg, L. H., and Hammerschlag, H., Chem. Revs., 39, 79-135 (1946). (5) Daniels, F., “Outlines of Physical Chemistry,” pp. 88, 365, Xew York, John Wiley & Sons, 1948. ( G ) Erbring, H., and Wenstop, K., Kolloid-Z., 85, 342-50 (1938). (7) Gray, D. J. S., Analyst, 75, 314-17 (1950). (8) Gronwall, A. T. J., and Ingelnian, B. G. A. ( t o Aktiebolaget Pharmacia), U. S. Patent 2,437,518 (March 9, 1948), 2,644,815 (July 7, 1953). (9) Ingelman, Bjorn, Acta Chem. Scand., 2, 803-12 (1948). (10) Jeanes, A,, Haynes, N‘. C., Wilham, C. A , Rankin, J. C.. and Rist, C. E., Division of Agricultural and Food Chemistry Symposium on Microbial Polysaccharides, 122nd Meeting, AMERICAN CHEMICAL SOCIETY, Atlantic City, N. J., 1952. (11) .Jeanes, A., and Wilham, C.A., .J. Am. Chcm. Soc., 72, 2655-7 (1950).
377
(12) Jeanes, A,, Wilham, C. A., and Miers, J. C., J. Riol. C h m . , 176, 603-15 (1948). (13) Landis, Q., and Redfern, S., CereaE Chem., 24, 157-66 (1947). (14) Lockwood, A. R., James, A. E., and Pautard, F. G., Research (London), 4, 46-8 (1951). (15) Lockwood, A. R., and Swift, G. (to Tell and Usher, Ltd.). U. S. Patent 2,565,507 (Aug. 28, 1951). (16) M f g . Chemist, 23 (2), 49-54 (1952). (17) Lfehltretter, C. L., in “Report of Working Conference OII Dextran,” National Research Council, Subcommittee on
Shock, and Northern Regional Research Laboratory, Peoria. Ill., October 29, 1951, p. 30. (18) Moelwyn-Hughes, E. A., Trans. Faraday Soc., 25, 503 20 (1929). (19)
(20) (21) (22) (23) (24)
Seifter, S., Dayton, S., Novio, B., and Muntwyler, E., Arch. Biochem., 25, 191-200 (1950). Senti, F. R., and Hellman, N. N., Abstracts of Papers, 121st Meeting, AM. CHEM.SOC.,Milwaukee, Wis., March 30 t o April 3, 1952, p. 8. Somogyi, M., J. Biol. Chem., 160, 61-8 (1945). Stacey, M., Abstracts of Papers, XIIth International (’oriqrrss of Pure and Applied Chemistry, New York, N. Y . , Sept. 10 to 13, 1951, p. 623. Starey, M., Research (London), 4, 48 (1951). Stacey, hf., and Pautard, F, G., Chemistry and frd,u&tri/, 1952,
1058-9. (25) Tsuchiya, H. M., Koepsell, H. J., Corman, J., Biysnt. G . , Rogard, M. Feger, V. H., and Jackson, R. J . Hncteriol., 64, 521-6 (1952). (26) U. S . Government, military medical purchase description for dextran injection, stock number 1-161-890, May 24, 1951. (27) Wales, hi., Marshall, P. A,, and Weissberg, S. G., J . Pollirn~r Sci., 10, 229-40 (1953). (28) Wilham, C. A,, and Jeanes, A., Northern Regional Laboratorv,
o.,
w.,
unpublished results.
(29) Wolff, I. A., Watson, P. R., Sloan, J. W., and Rist, C. E., ENQ.CHEX., 45, 755-9 (1953).
[VI).
RECEIVIOD for review June 20, 19% ACCJOPTED October 29, 1053. Presented before the Division of Carbohydrate Chemistry at the 124th Meeting of t h e A 4 x E R I C A N CHIMICAL SOCIETY, Chicago, Ill.
Enthalpy-Concentration Diagram for System Ferrous Sulf ate-Water J
KENNETH A. KOBE AND EARL J. COUCH, JR., Unicersity of Texas, Austin, Tex.
T
HE usefulnees of the enthalpy-concentration diagram in
making refrigeration, crystallization, and evaporation calculations for salt solutions has been pointed out by Bosnjakovic (6) and hlcCabe (26‘). I n view of the importance of the system ferrous sulfate-water in connection with processes for the recovery of waste pickle liquor, it is desirsble to have such a diagram for this system. PREVIOUS THERMAL DATA
.4 survey of the thermal data available in the literature is presented in Table I. Values selected for enthalpy calculations include the accurate heat capacity data for anhydrous ferrous sulfate determined by Moore and Kelley ( 2 8 ) ,for ferrous sulfate heptahydrate by Lyon and Giauque (26), and for ice b y Giauque and Stout (11); the extensive and accurate heat of solution data presented by Perreau (29) for ferrous sulfate heptahydrate; and the heat of formation data tabulated by Bichowsky and Rossini
(4) AFPARATUS AND PROCEDURE
The literature values for the heat capacity of ferrous sulfate solutions are considered to be inadequate as a basis for the calculation of enthalpies of ferrous sulfate solutions.
I n order t o measure the heat capaeitie.: of ferrous sulfate solutions, a calorimeter similar to that described by Kobe and Anderson (22) and Kobe and Sheehy (95’)was constructed as shown in Figure 1. Two 6-volt storage batteries served as a power source to the calorimeter heating element, which was constructed in a manner similar to that described by Randall and Taylor ( S I ) . The power input to the heating element was measured by the ammetervoltmeter method and the length of the heating period was nieasured by an electric stop clock to the nearest 0.1 second. The calorimeter temperature was measured by means of a calibrated thermometer graduated a t 0.1O C. intervals. Distilled water was used as the calorimeter fluid in determining the heat capacity of the calorimeter over the temperature range 5” to 95” C. A determination consisted of making time-temperature readings before and after a heating period during which the known weight of water was heated through a temperature rise of approximately 10’ C. ( 3 2 ) . The ferrous sulfate solutions used in this work were prepared from C.P. Baker’s analyzed ferrous sulfate heptahydrate. In order to minimize oxidation of the solutions, boiled distilled water, through which nitrogen was bubbled during cooling and storage, was used. A few drops of sulfuric acid were added to each solution as an oxidation inhibitor ( 7 ) . All containers for solutions were flushed with nitrogen and the solutions kept in a nitrogen atmosphere. A fresh solution was prepared immediately before each calorimetric dctcrmination.
Vol. 46,No. 2
INDUSTRIAL A N D ENGINEERING CHEMISTRY
378
Ref.
and Holtmann ( I ) , reapecLively, This agreement is well within the experimental error.
( 8 , 20)
EW'HALPY CALCULATIONS
TABLE 1. PREVIOUST H E R X A L DATA I t e m of D a t a H e a t capacities FeSOa(s) FeSOc4H?O(s) FeSOp7HaO(s)
HaOM
H e a t of formation H e a t of solution
293-393' IC. 53-295' K . 282' K. 291-319' IC. 83-295' IC. 1-300' K. 10-270' Ii.
18' C. 180 c. 18" C .
13.6' C .
19-200 C . Diesociation preMsures Heptahydrate 10-46' C.
Workers
Bnnotation
Range
Too hinli: obsolete S e l e c t d Galues Doubtful accuracy Single mean value reported Mean values reported Extensive and accurate: selected Jralues Selected values Mean values reported for 19-21' C.
Avogadro Moore and Kelley Rolla and Accame
(28)
( 1 4. 331
R E F E R E N CSET A T E : .All e n t h a l p y calculations were limed upon the assumption of ( 11 ) zero enthalpy for liquid water Perreau :29) a n d c r y s t a1 1i n e anhydrous ferrous sulfate a t 0" C. This Thomsen (36) Single value reported reference state is the same as i i g d e and I-Ioltmann (1) Mean values reported for 2;-45' C . that used in the steam tables (191 and in the enthalpyI.C.T. (18) Obsolete Bichonsky and Rossini (4) Selected values concentration diagram for sul(3.5) Single value reported for S 7 W a in 400 Thomsen furic acid-water (12). moles water Single values reported for 8 , SF,S 4 W , DeForcrand (9) The effect of pressure on S.7W in 110 moles water the enthalpies of solid and ($0) D a t a reported for S4'W over entire Perreau concentration range: selected ralues liquid phases was neglected. (8) Used t o calculate heat of decomposition Bonnell and Burridge Enthalpy data for the vapor for S.7W &6W Cohen and Visser (8) phase were taken from steam Prccht and K i a u t (SO) Shumb ($4) tables ( 1 9 ) and thus required Wiedemann (37) no correction for the effect of (16) Used t o calculate heat of drying for I.C.T. S.W s pressure, E K T H A L P I EOSF S O L I D S . Enthalpies of ice were taken from the steam tables of K r e n a n and Keyes ( 1 9 ) . Enthalpies of anhydrous frirous sulfate and the mono-, tetra-, MOTOR and heptahydrates of feirouq d i a t e were calculated from the relationchip .Jac'k'son Lyon and Giauque Giauque and Stout
1%
--t
Monohydrate
S
20-60' C.
anhydrous FeSO?. W = water of hydration. =
THERMOMETEh o TO i o o 4 c IN 010-
-
COVER LAMINATED BAKELITE
r
-
FOUR-LITER STAINLESS STEEL BEAKER
Heat capacitv data used
PINT DEWAR
Lvon and Giauque ( 2 6 ) io1 ferrous sulfate heptahydrate Heat capacities for the mono- and tetrahydrates were calcu1:tted by assuming additive molar heat capacities. For each of the hydrates, the quantitv Ha is equal to the heat of miction at 0' C for the reaction FeSO,( s)
HEATING COIL GLASS INSULATED N O 30 CONSTANTAN
SCALE
I~quationI included those repoited
1 ~ 5Mooie and Kelley ( 2 8 ) foi anhj dious ferious sulfate and by
FLASK
GLASS WOOL INSULATION-
in
ELECTRICAL LEADS
-
-- /zH,O(I
+
FebOa nHzO( s)
and n as evaluated by mean* of the ielationship
The heat of reaction a t 18 C. vias calculated in the usual manner by use of the heat of formation datn of Bichowsky and Rossini
(4).
ONE INCH
Figure 1. Calorimeter RESULTS
The experimentally determined heat capacities are eholi-n in Figure 2. Linear equations were fitted to each set of data for constant ferrous sulfate percentage by the method of least squares. Values calculated from the resulting equations vere smoothed by a cross plot of heat capacity against percentage of ferrous sulfate with temperature as parameter. The cmetants for the smoothed set of empirical equations of the form C, = a bt are presented in Table 11. Heat capacities calculated from these equations show an average deviation of 0.7% and a maximum deviation of 1.7% from the experimental values shown in Figure 2. Based on the precision of the individual quantities measured, the accuracy of the heat capacities of Table I1 was estimated to be approximately 2%. The heat capacities here reported show an average deviation of 0.9 and 1.2% from those reported by Perreau (29) and Agde
+
The resulting enthalpies ,for the various solid phases are presented in Table 111. ESTHILPIEBOF SOI,UTIO~-S. Erithalpy data for liquid water at various temperatures were taken from Meenan and Keyeu (19). I n calculat,ing the 20' C. base isotherm for the solution region, the integral heat of solution data reported hy Perreau (29) for ferrous sulfate heptahydrate iyere used.
TABLE
11. EMPIRICAL EQUATIOSS FOR HEAT CAPACITIES AQCEOCSFERROCS SLLFATE SOLUTIONS
+
OF
(Cp = a bt, calories per gram per degree C. where t is in degrees C.) Ferrous Sulfate, Temp. Range, 70 a b X 104 c. 2 . 4 -0.65 t o 100.1 0.927 5 - 1 . 3 to 100.2 3,7 10 0.873 4 . 5 t o 100.4 0.825 4.4 15 1 7 . 4 t o 100.7 4.4 0.783 20 30.4 t o 96.5 0.745 4.5 25 4 3 . 3 to 81.3 4.3 30 0.711 55.8 to 66.1 4.4 0.677 35
379
INDUSTRIAL AND ENGINEERING CHEMISTRY
February 1954
TABLE111. ENTHALPIES O F SOLID PHASES FOR SYSTEMFERROUS SULFATE-WATER [Reference state. HzO(1) and FeSOi(s) a t 0' C. a n d own vapor Enthalpy, Calories per Gram or P.C.U./Lb. HeDtaTetraMonohvdrate Ice Temp., , (6'7.83% (0% FeBOa) c. FeSOd) -76.7 -49.6 - 40 -98.33 -66.8 -76.3 -48.8 -35 -96.15 -65.6 -73.9 -47.9 -64.4 -30 -93.92 -72.5 -47.0 -63.2 - 25 -91.65 -71.0 -46.0 -61.9 - 20 -89.33 -45.1 -69.5 -86.98 - 15 -60.6 -44.2 -68.0 - 10 -59.4 -84.57 -43.2 -58.0 -66.4 -82.13 -5 ... -65.4 -80.55 -1.82 ,.. -1.5 ... ... -80.38 ... -80.14 -1.0 , . . -0.6 -79.89 -42:28 -64:86 -56:72 -79.64 0 -63.3 -55.4 -41.3 5 , . . -61.7 -54.0 -40.3 10 ,.. -60.0 -52.6 -39.3 ... 15 -38 3 -58.4 -51.2 , . 20 -49.8 25 .. -56,7 -37.3 -48.4 -36.3 ... -55.0 30 -46.9 -35.3 -53.2 , . . 35 -45.4 -34.2 -51 5 , . . 40 -43.9 45 -33.2 -49.7 ... -42.4 50 -32.1 -47.9 ... -31.1 -46.1 -40.9 55 , . . -45.*5 -40.4 56.7 , . . . -39.4 ,.. -30.0 60 -38.1 -29.1 64.1 , . . -29.0 ... ,.. 65 -27.9 , . . ... 70 -26.8 , . . ... ,.. 75 -25.6 ... ... .. 80 -24.5 85 ... -23.4 90 ... ... -22.2 95 -21.1 100 ... -20.9 100.9 , . ... -20.0 105 110 . . , 18.8 .
I
I . .
.
TABLE
THE
IV.
ENTHALPIES O F AQUEOUS FERROUS SULFATE SOLUTIONS
pressure] Temp., a
An-
c.
0 6 10 15 20 25 30 35 40 45 50 55 60 66 70 75 80 85 90 95 100
-5.8 -5.1 -4.4 -3.7 -3.0 -2.2 -1.5 -0.8
...
...
.... ..
0.00
0.8 1.6 2.3 3.1 3.9 4.7 5.5 6.3 7.1 7.9 8.7
0 0.00 5.03 10.04 15.03 20.02 25.01 30,OO 34.99 39.98 44.97 49,96 54,94 59,93 64.94 69.94 74.94 79.95 84.96 89.98 95.01 1!00.04
Enthalpy, Calories per Grain or P.C.U./Lb. 5 10 15 20 25 30 Per cent ferrous sulfate -4.2 0.4 5.0 9.7 14.4 19.0 23.7 28.4 33.0 37.7 42.4 47.1 51.8 56.5 61.2 66.0 70.7 75.4 80.2 84.9 89.7
-8.8 -4.5 -0.1 4.3 8.7 13.1 17.5 22.0 26.4 30.8 35.3 39.7 44.2 48.7 53.2 57.7 62.2 66.7 71.2 75.8 80.3
..
-9.4 -5.2 -1.1 3.1 7.2 11.4 15.6 19.8 24.0 28.3 32.5 36.8 41.0 45.3 49.6 53.9 58.2 62.5 66.8 71.2
..
-2.6 1.4 5.4 9.4 13.4 17.4 21.4 25.4 29.5 33.5 37.6 41.7 45.8 49.8 54.0 58,l 62.2
..
, .
,.
. ,
, .
, .
.. .. .. 3:2 7.0 10.8 14.7 18.5 22.4 26.2 30.1 34.0 37.9 41.8 45.7 49.7
35
,. . ,
:: 4:3 8.0 11.7 15.3 19.0 22.7 26.4 30.2
..
.. ,.
..
..
structed from the freezing point data of Kahlenberg ( 1 8 ) ; solubility data of Meyer ( 2 7 ) , International Critical Tables ( I S ) , and ... 9.5 Belopolskil and Shpunt ( 3 ) ; and the normal boiling points re... ported bv Gwlach (10) and Kahlenberg (18), and is shown in 10.3 11.2 Figure 3. 12.0 12.8 Enthalpy-concentration data for the freezing point and solu13.7 bility curves were determined by extrapolation of the solution 14.5 15.4 isotherms of Table IV to the composition indicated by the phase 16.2 ... diagram These data are presented in Table V. 17.0 The enthalpies of solutions a t the normal boiling point, estab17.8 lished by similar eutrapolations, are presented in Table VI. The enthalpy-concentration diagram for the system ferrous sulfate-water shown in Figure 4 as constructed from the data of Tables 111, IV, I 1 11, and VI. Enthalpy data are given in calories per gram, which is numerically equal t o pound centigrade units per pound, so that calculations can be carried out on a pound basis. This diagram should be useful in making heat and material balance calculations in connection vith various processes employed for the utilization of waste pickle liquor. It is difficult to estimate the accuracy of the enthalpy data presented in Figure 4. However, it is believed that values taken from this diagram represent the true thermal state of the system to within a maxic 30 40 50 60 70 80 90 10c mum error of 5% and are therefore of sufficient T E ' A P E R A T L R E "C accuracy t o serve as a basis for process calculaHeat Capacities of Ferrous Sulfate Solutions tions. . . I
j-71
Figure 2.
NOMENCLATURE
Consideration of the heat effects involved in the formation of one gram of solution at 20" C. by the addition of m grams of heptahydrate to (1 - m ) grams of liquid water, both a t 20' C., leads to the following equation
a = empirical constant in heat capacity equation 6 = empirical constant in heat capacity e uation C, = heat capacity at constant pressure, cJ./(gram)( C.) ,C, = mean heat capacity, cal./(gram)( C.) O
It
Enthalpies for solutions of 5 to 35% ferrous sulfate were calculated for the 20' C. isotherm by means of Equation 3. Enthalpies in the solution region a t other temperatures were calculated from the relationship
Ht
Ho
+ at + ( 6 / 2 ) t 2
(4)
where a and b are functions of composition as tabulated in Table 11. The quantity NOwas evaluated from the 20" C. isotherm a t various concentrations. The resulting isotherms calculated from Equation 4 are presented in Table IV. A pha8e diagram for the system ferrous sulfatewater was con-
= enthalpy, calories per gram AH8 = inte ral heat of solution, calories per gram of ferrous s3fate heptahydrate AHl* = heat of reaction at 18" C. m = grams of heptahydrate per gram of solution n = number of moles of water of crystallization S = anhydrous ferrous sulfate t = temperature, O C. W = water of hydration
Subscripts 0 = value a t 0" C. 7 = ferrous sulfate heptahydrate 20 = value at 20" C. a = anhydrous ferrous sulfate h = hydrate t = value a t t, O C. w = water
380
INDUSTRIAL AND ENGINEERING CHEMISTRY
Figure 3.
Vol. 46, No. 2
Phase Diagram of Sjstem Ferrous S u l f a t e Water
1. VaporFeSOdIzO 2. Vapor-solution 3. Solution 4. Solution-ice 5. Ice-FeSOa.7HzO 6. Solution-FeSOc711i0
FeSOa.7HzO-FeSOc4H20 8. Solution-FeSOa.4H~O 9. Solution-FeSOcHIO LO. F ~ S O A . ~ H ~ O - F ~ S O ~ I , O 11. FeSOa.IIzO-FeSO1
3
70
IO
70
41
50
7C
GO
BO
9C
O?
7.
A
Figure 4.
-I
r - -FUT
FPCC4
Enthalp) -Concentration Diagram Ferrous SulfateWater System
for
l,IT~lt.4'ILI~K ClTEU
Agde, G , , and Holtniann, H., %. nnorg. a l l g ~ m Chori., . 158, 8 l ( i 20 (1928). FeSOa,
Typ., C. 0 -0 -1 -1 -I 0
%
5 0
5 82
5 10 15 20 25 30 35
i?nthal]~y, Cal./Gram 0.0 -3.9 -7.8 -11.3 -13.1 -12 I -9.0 -7 3
Solid Phase?
14, 7 1 6 3 3 (1941). iiiohowsky, F. R., aiid Iloasini, F.I)., "Thermochemistry of the Chemical Substances," 12. 90, New York, Reinhold I'ublishing Corp., 1936. I3onnel1, D. G. It.. mid F3ui.ridgr. L. IT'., Trans. Farodo?/ S u r . , 31, 473-8 (1935).
Bosnjakovic, F., 2. ges. Kijlte-Lnd., 9, 165-8, 182-5 ( l W 2 ) .
-.5 4 -3 7 -S.lines. fiu21. 371, 68 (1934).
Ibid., 476, 209 (1949). Kobe, K. A , , and Ariderson,
('.
ti.,J . P h y s . Chem., 40, 429-33
(1938).
Kobe, K. A , , and Sheehy, T. >I., IXD. ESG. CHEM.,40, 99- 103 (1948). Kopp, IT., Truns. 1Zuy. Soc. ( L o n d o n ) , A155, 71-202 (1865). Lyon, D. N.,and Giauque. IT. F., J . Am. Chem. Soc., 71, 1647-55 (1949). IIcCabe, W ,L., 7'ruri.s.. A m . I n s t . Citem. Engrs., 31, 120-62 (1 935).
February 1954
INDUSTRIAL A N D ENGINEERING CHEMISTRY
(27) SIeyer, R. J . , t l nl., “Gmelins Handbuch der .inorganischcn Chemie,” Yol. 59B, pp. 400-1, Berlin, Verlng Chemie G.m.b.H., 1932. (28) Moore, G. E., and Kelley, K. K., J . Am. Chem. Soc., 64, 2949-51 (1942). (29) Perreau, J., Compt. rend., 213, 286-9 (1941). (30) Precht, H., and Kraut, K., Ann., 178, 129-49 (1875). (31) Randall, AI., and Taylor, AI. D., J . Phys. Chant., 45, 959-67 (1941). (32) Hire, R. J3., A S T M Btd., 157, 72-4 (1949).
381
(33) Rolla, L., and Accame, L., Atti. accud. nazl. Lincei, 22, 11, 109 (1913). (34) Schumb, W. C., J . Am. Chem. SOC.,45, 342-55 (1923). (35) Thomsen, J., “Thermochemische Untersuchungen,” Vol. 111, p. 202, Leipzig, Verlag von Johann Anibrosius Barth, 1883. (36) Thomsen, J., “Thermochemistry,” p. 184, London, Longmans, Green and Co., 1920. (37) Wiedemnnn, G., J . p r a k t . Chem., 11, 9, 338-56 (1874).
RECEIVED for review July 30, 1953.
ArcEPrED
September 26. 195:3.
SODIUM METHYLSILICONATE Nature and Applications WILLIAM S. KATHER AND ARNOLD TORKELSON Silicone Products Oept., General Electric Co., Waterford, N. Y .
NUMBIX of different silicones have come to be widely accepted as water repellents for treating a host of different materials. I n general, their utility is based on their inertness and their maintenance of a high degree of water repellency. This durability may be attributed to the tenacious retciition of the silicone film through secondary valence or van der Waals forces (11).
Dimethylsilovane Hulds are one of the common types of silicones used to obtain water repellency. They are prepared by the hydrolysis of dichloro dimethyl silane with small amounts of c-hlorotrimethylsilano to yield products having the general formula,
n
Thcse fluids ai(’ usrti in most commercial ituto polishes, where one of their functions is t o impart water repcllency (6, ?). Maximum durability of water repellency can only be attained when the fluid film is polymerized by heating at elevated temperatures. T h r fluids are applied to pharmaccutical bottles to provide drainage of aqueous suspensions, and curing of the sili(’one is obtained by heating for 1 hour at 300” C. (10). ,4s another example, thr fluids (in combination with other materials) are applied with heat to glass fibers (%!j), where the water repellency imparted rnaltes the fibers useful in life jacketfi. The use of silicone fluids as water repellents is greatly rcstrictcd in many fields, either because high temperature application cannot be readily accomphhed or because the material to be treated is not heat stahle. Retention of a silicone Huid film can be improved by using a thickening agent such as silica (2). Silicone greases of this type are useful in improving the electrical propel ties of aircraft or automobile ignition systems, but the use of grease 1s impractical for many water-repellent applications. One of the early solutions to the problem of providing silicone films which could be laid down and cured in place without the application of heat was found in the chlorosilanes-trichloromethylsilane or mixtures of trichloromethylsilane and dichlorodimethylsilane ( 1 , 5, 12, 19, $0, 21, $4). These reactive chemicals hydrolyze rapidly with adsorbed water on the surfacc of the material being treated to form a resin film and liberate hydrogen chloride. They havr been used in the treatment of electrical ceramic insulators and asbvstos fibers (3). However, there are severe problems, such as flammability, toxicity, and the cor-
rosion of equipment by hydrogen chloride, attending the use of chlorosilanes. Another easily polymerizable silicone type is methylsiloxane which is prepared by the hydrolysis of dichloromethylsilane (8, 18, 22, $6) and small amounts of chlorotrimethylsilane to yield
r
1
When such fluids are heated for 5 minutes a t 150’ C., hydrogen is evolved and a highly cross-linked resin is formed. Methylsiloxane enjoys considerable usage in the textile field where it R i applied from dilute padding solutions obtained by dilution of the silicone with solvent or by emulsification. The disadvantages of this material are the problems of handling solvent in textilc mills or the problems of emulsion instability. The methylsiloxane generally evolves hydrogen on prolonged storage, which creates an explosion hazard. Another common water repellent is a silicone resin which is usually prepared by hydrolyzing a mixture of dichlorodimethylsilane and trichloromethylsilane in the presence of solvent. The material is sold already polymerized by the manufacturer, and it imparts watcr repellency to treated surfaces ( 4 ) as soon as the solvent has evaporated. It is currently used in the treatment of masonry and asbestos shingleu. Its primary limitation is the Haminability and toxicity of the carrying solvent. These are the principal types of silicone water repellents which have hecn introduced commercially during the last half a dozen years. Each type has been used for particular applications for which it is well adapted. However, each has limitations which have prevented or reduced its use in certain fields. Recently, a water-soluble silicone water repellent, sodium methylsiliconate, has become available. It possesses advantages over each of the silicone types available previously. I n contrast to the dimethylsiloxane fluids it cures on air drying without the application of heat. It differs from silicone greases in that the nonviscous water solution of siliconate may be easily applied to a material by spraying, brushing, or dipping. Sodium methylsiliconate does not present the corrosion and other problems associated with the chlorosilanes. It obviates the emulsion stability problems incurred with methylsiloxanes. It avoids the solvent dangers of the silicone resin. Thus, sodium methylsiliconate is a useful addition to the available types of silicone water repellents.
