INDUSTRIAL AND ENGINEERING CHEMISTRY
March 1955
be the use of the Karl Fischer reagent. Gilman (9) used the method t o determine hydroxyl content of RsSiOH structures. The hydroxyl content alone was of little value but the hydroxyl content per square meter of surface proved t o be related t o the tensile strength a t break: as HYdroxyl, G/
Silica Du Pont G S 1998 German Aerosil Santocel C
S. Tensile a t Break Lb./Sq. Inch droxyl/ 24 hours Area As at 106 molded 2 5 O O C .
H ~ -
Area,
100 G.
Size, MM
0.52 0.75 0.8G
12.0 21.4 23.5
T.indn
1.Ro
17.4
n u Pont Hyperfine Hydrolyzed Sic1
0 45 3 28
88.2 44.5
274 133 121 161’
1.90 5.64 7.11 8.39
8890 4560 2390 3060
567 3290 1092 1680
34
13.20. 43.80
1585
785 240
75
270
The hydroxyl content as determined by Karl Fischer reagent on a sample desiccated 3 days at 25” C. is a relative number. Other methods of drying were tried, but, after heating t o 150” C., the absolute level of hydroxyl is too low t o be determined accurately by this method. Accordingly, the desiccation at 25” C. leaves water but presumably only in proportion t o its =SiOH content. Effectively, in drying t o a constant vapor pressure of water, silanol groups are being “tagged” b y adsorbed water.
0 PARTICLE
SIZE
HYDROXYL
49 1
sensitivity t o some variables. Particle size of the filler is of greater importance in silicone rubber than in hydrocarhori elastomers. Structure of the filler seems t o prevent dispersion into ultimate particles and so limits filler benefits. Polymer size influences tensile properties t o a greater extent with silicone elastomers. Polymer-filler bindings of energies similar to that of hydrogen bonding are found, but these seem to contribute only to a minor extent t o ultimate tensile strength. The chemical nature of the filler surface is of considerable importance, and the more inert fillers seem most beneficial. The principal function of a filler must be something other than a means of providing temnorary bindings between polymer molecules. ACKNOWLEDGMENT
The x-ray pictures of silicone rubber films were taken by L. E Alexander of the staff of the Department of Chemical Physics, Mellon Institute, Pittsburgh, Pa. LITERATURE CITED
(1) Blanchard, 8.F., and Parkinson, D., IND.ENG.CHEX, 44,799 (1952). (2) Blanchard, A. F., and Parkinson, D., Rubber Chem. and Technol., 23, 615 (1950). (3) Bondi, A., J . Phys. & Colloid Chem., 55, 1355-63 (1951). (4) Boyer, R. F., Dow Chemical Co., unpublished. (5) Catton, N. L., and Thompson, D. S., IND.ENGCHEM.,40, 1523 (1948). (6) Flory, P. J., Chem. Rev., 35, 51 (1944); IND.ENG.CHEM.,38, 417 (1946). (7) Flory, P. J.,‘and Rehner, J., Jr., J . Chem. Phys., 11, 521 (1943). (8) Gee, G., J . Polymer. Sci., 2,451 (1947). (9) Gilman, H., and Miller, L. S.,J . A m . Chem. Soc., 73, 2367 (1951). (10) Hunter, &I. J., Hyde, J. F., and coworkers, Ibid., 68, 667 (1946). (11) Mullins, L., J. Rubber Research, 16, 275 (1947). (12) Park, Chullchai, and Yoshida, Usabura, Rubber Chem. and Technol., 23, 581 (1950). (13) Rose, H. E., J. A p p l . Chem., 2, 511 (1952). (14) Schweitzer, C . W., and Lyon, F., IND.ENG.CHEM.,44, 125 (1952). (15) Villars, D. S., Rubber Chem. and Technol., 24, 1944 (1951). (16) Zapp, R. L., and Guth,,.:!I IND.ENG.CHEM.,43, 430 (1951). RECEIVEDfor review September 2, 1964. ACCEPTED October 28, I%:+. Contribution from the multiple fellowship sustained a t Mellon Institute, Pittsburgh, P a . , b y the Corning Glass Works and Dow Corning Corp.
P A R T I C L E SIZE
3
HYDROXYL
‘g8
Figure 12. Effect of particle size and hydroxyl concentration o n tensile at break for siloxane rubber as molded The relative hydroxyl content does not correlate with S,the tensile a t break, either as molded ( A M ) or after 24 hours’ aging at 250’ C. However, the grams of hydroxyl per square meter of silica surface do correlate with tensile a t break; the highest tensiles are obtained from the driest silicas. The conclusion is presented clearly in Figure 12 where the tensile at break is plotted against particle size (with open circles) and against hydroxyl content per square meter (filled circles). The curve drawn fits the hydroxyl content quite well, but the particle-size data are still quite erratic. The driest silicas, which show the best tensile properties as molded, are the materials that have organic coatings t o block silanol structures on the surface, such as D u Pont’s GS 199s. This observation would suggest that an ideal filler would be completely inert. SUMMARY
The filler phenomena in silicone rubber parallel effects in hydrocarbon elastomers but exhibit a few deviations and a greater
Radiant Heat Transfer from Flames in a Turbojet Combustor-Correction I n the article on “Radiant Heat Transfer from Flames in a Turbojet Combustion” [Topper, Leonard, IND. ENG.CHEW,46, 2551 (1954)] scales were omitted from some of the figures. The following should be added. Abscissa Scale
Figure
Ordinate Scale 3 Wave length, microns 4 Absorption strength, K L 5 Red-brightnzss temperature, R. 6 Wave length, microns
8
___
. .. . . . .
11 Flame temperature,
12
Emissivity
Tq,
70
Radiation transmitted,
%
Reference ( 2 ) in title Tr%nsmittanoe,
7 Wave length, microns
10
Remarks
Relative luminous in, tensity, J ~ / e ? pB.t.u. /(hr.)(sq. ft.)(cnl.1 Emissivity a t wai’e length of 2.0 microns
......
R.
Combustor inlet-air pressure, inches H g abs.
Combustor inlet-air pressure, inches Hg ahs.
From left t o right, A , B, C From left to right, A, B From left to right A, B
