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INDUSTRIAL AND ENGINEERING CHEMISTRY
June 1955
m = - 1000 .-Table 111. Partial Molal-Volume, Fz,of HsPO4 in Phosphoric Acid Solutions, Cc./Mole HaPo4 Wt. yo HsP04 LO
20
30 40 50 60 70 80 90 100
1 5 O C.
25OC. 47.12 47.92 48.68 49.43 50.16 50.84 51.43 51.90 52.18 52.29
46.64 47.47 48.28 49.08 49.85 50.57 51.19 51.66 51.96 52.06
40°C. 47.77 48.52 49,23 49.91 50.59 51.24 51.81 52.25 52.54 52.64
6OoC.
48.26 49.09 49,80 50,48 51.14 51.75 52.30 52.74 53.03 53.13
80°C. 49.16 49.63 50.20 50.83 51.52 52.18 52.78 53.26 53.57 53.68
dm =
wt. % HsPOa 10
L
20 30 40 50 00
70 80 90 100
15OC.
25OC.
4OOC.
60’C.
0.0164 0,0434 0.0932 0.1730 0.2893 0.4517 0,6639 0,9247 1.2427 1.5825
o.oo90 0.0360 0.0827 0.15711 0.2675 0,4209 0,6233
0.0104 0.0347 o.0780 0.1462 n.2489 0.3948 0,5896 0.8347 1.1377 1.4900
0.0115 0.0380 o.0820 0.1495 0.2491 0.3875 0.5761 0.8190 1.1161 1.4880
0.8814
1.1827 1.5112
o.oo811 0.0586
0.1222 0.2264 0,3756 0.5815 0.8477 1.1719 1.5014
t o concentration, and t h e corresponding density-temperature coefficients are shown in Table 11. T h e present measurements a t 25” C. are included in Table 11 for comparison with the more accurat,e values in Table 111 of Christensen and Reed (p. 1277). For simplicity in calculation, the equations ( 2 ) relating partial molal quantit.ies t o molality
- 20)
1000 M P [(loo loo - w)’] d w
&fz
+[o
-
9v =
(100 PO W
a@t v* = + w(100 - w )aw @v
-
(VI
8OOC.
0.0235
(100
T h e constancy of T,P , . a n d n1 permitted a substitution of the partial derivatives for t h e total derivatives t o yield, after simplification of terms
Table IV. Relative Partial Molal Volume, -(TI - T:), of HzO in Phosphoric Acid Solutions, Cc./iMole HzO c
W
M z
-
-
V:) =
M I
wz
a@ =
- M-n 100 aw
wz
-0.183839 -
a@
100 a w
where p is the density of t h e acid solution, po is the density of water at the same temperature, and t h e other terins have their usual significance. T h e density and & were calculated a t 2.5y0intervals for each temperature. T h e slope, a&,/aw, was determined b y means of seven-point first-derivative coefficients (6). Calculated values of and of (71 a t concentration intervals of 10% are given in Tables I11 and IV, respectively. Values of for concentrations below 5% H3P04 a t 25’ C., as calculated from the density measurements reported in the preceding article approach = with a rapidly increasing slope that vitiates an extrapolation to Although this relation of t o w is not evident from t h e present measurements, it is assumed to hold at the other temperatures and is the reason for putting values of v z instead of ( v z - 72)in Table 111.
vy)
vz
v2
vz
LITERATURE CITED
V2 =
@u
(1) Farr, T. D., “Phosphorus-Properties
of the Element and Some of Its Compounds,” TVA Chem. Eng. Rept. No. 8, 1950. ( 2 ) Glasstone, S., “Thermodynamics for Chemists,” Chap. 18, Van
a@ + m dm 2
Nostrand, New York,
( V I - v:) = - ~.m2
55.51
were converted t o a basis of weight the relations
b& bm
yo,w,by substituting therein
1947.
(3) International Critical Tables, Vol. 3, p. 61, McGraw-Hill Rook Co., New York, 1928. (4) Ibid., p. 24. ( 5 ) Salzer, H. E., Natl. Bur. Standards, Washington 25, D. C., Applied Mathematics Ser. 2, 1948. RECEIVED for review April 2, 1954.
ACCEPTED November 29, 1951.
Combination of Rubber and Carbon Black on Cold Milling W. F. WATSON British Rubber Producers’ Research Association, 48 Tewin Road, Welwyn Garden City, Herts, England
T
HE mechanism for the degradation of elastomers by cold milling (3) can be represented by:
+
Scission by shear forces Radical recombination Z. Radical acceptor reaction Termination to noncross-linked products R - R ++ Termination to cross-linked products
R - R + R. R. R. R. + R - R R. + X + RX. or RY RX. or Z.
+
-+
R., R X . , or Z.
+
where the term “radical acceptor” denotes a substance competing significantly with recombination. Although t h e structure of carbon black is imperfectly known, x-ray analysis has shown it t o consist of layers of condensed rings of carbon atoms. Unsaturation and discontinuities in t h e layers a r e likely t o provide sites for attack of free radicals, and thus
make carbon black a radical acceptor of a special polyfunctional type. hssuming combination of rubber radicals and carbon black, a particle could terminate more than one sheared rubber chain. Furthermore, rubber chains attached to a carbon black particle could also undergo scission by shear and be terminated by combination with other particles. T h e result anticipated on this picture is a network of rubber and carbon black held together by chemical bonds. I n rubber solvents such a network would be insoluble and merely become swollen gel. Insolubiliaation of rubber on milling with carbon black has been reported on occasion, but t h e evidence is not sufficiently extensive t o draw reliable conclusions as t o its cause. This paper reports a systematic investigation of t h e occurrence of rubber-carbon black gel on cold milling. This gel has been shown t o form, and t h e conditions for its formation and its prop-
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INDUSTRIAL AND ENGINEERING CHEMISTRY
erties have been interpreted as strong evidence for t h e above hypothesis of chemical-bond attachment of rubber and carbon black. EXPERIMENTAL MATERIALS AND METHODS
Materials. Deproteinized crepe of oxygen content
