McCullough, J.P., Scott, D.W., Finke, H.L., Gross, M.E., Williamson, K.D., Pennington, R.E., Waddington, G., H u h , H.M., I b i d . 74,2801 (1952). McCullough, J.P., Scott, D.W., Finke, H.L., Hubbard, W.N., Gross, M.E., Katz, C., Pennington,R.E., Messerly, J.F., Waddington, G., I b i d . 75, 1818 (1953). Mechanical Engineering 57,710 (1935). Osbome, N.S., Stimson, H.F., Ginnings, D.C., J . Res. Natl. Bur. Std. 23, 261 (1939). Pennington, R.E., Scott, D.W., Finke, H.L., McCullough, J.P., Messerly, J.F., Hossenlopp, I.A., Waddington, G., J . Am. Chem. SOC.78,3266 (1956). Rossini, F.D., Mair, B.J., Streiff, A.J., “Hydrocarbons in Petroleum,” p. 198, Reinhold, New York, 1953. Rossini, F.D., Pitzer, K.S., Amett, R.L., Braun, R.M., Pimentel, G.C., “Selected Values of Physical and Thermodynamic Properties of Hydrocarbons and Related Compounds,” Carnegie Pres4, Pittsburgh, Pa., Table 5k, 1953. Scott, D.W., Douslin, D.R., Finke, H.L., Hubbard, W.N., Mewrly, J.F., Hossenlopp, I.A., McCullough, J.P., J . Phys. Chem. 66, 1334 (1962). Scott, D.W., Finke, H.L., Gross, M.E., Guthrie, G.B., Huff72, 2424 (1950). man, H.M., J . Am. Chem. SOC. Scott, D.W., Finke, H.L., Hubbard, W.N., McCullough, J.P., Katz C., Gross, M.E., Messerly, J.F., Pennington, R.E., Waddington G., I b i d . 75, 2795 (1953). Scott, D.W., Finke, H.L., Hubbard, W.N., McCullough. J.P., Oliver, G.D., Gross, M.E., Katz, C., Williamson, K.D., Waddington, G., Huffman, H.M., I b i d . , 74,4656 (1952). Scott, D.W., Finke, H.L., McCullough, J.P., Gross, M.E., Pennington, R.E., Waddington, G., I b i d . , 74, 2478 (19523.
Scott, D.W., Finke, H.L., McCullough, J.P., Gross, M.E., Williamson K.D., Waddington, G., Huffman, H.M., I b i d . 73, 261 (1951). Scott, D.W., Finke, H.L., McCullough, J.P., Messerly, J.F., Pemington, R.E., Hossenlopp, I.A., Waddington, G.. I b i d . 79, 1062 (1957). Scott, D.W., Good, W.D., Todd, S.S., Messerly, J.F., Berg, W.T., Hossenlopp, I.A., Lacina, J.L., Osbom, A,, McCullough, J.P., J . Chem. Phys. 36, 406 (1962). Scott, D.W., McCullough, J.P., Hubbard, W.X., Messerly, J.F., Hossenlopp, I.A., Frow, F.R., Waddington, G., J . Am. Chem.Soc. 78, 5463 (1956). Scott, D.W., McCullough, J.P., Messerly, J.F., Pennington, R.E., Hownlopp, I.A., Finke, H.L., Waddington, G., I b i d . 80, 55 (1958). Stimson, H.F., J . Res. Natl. Bur. Std. 65A,139 (1961). Swietoslawski, W., “Ebulliometric Measurements,” p. 11, Reinhold, New York, 1945. Waddington, G., Knowlton, J.W., Scott, D.W., Oliver, G.D., Todd, S.S.,Hubbard, W.N., Smith, J.C., Huffman, H.M.. J . Am. Chem. SOC.71,797 (1949). White, P.T., Bamard-Smith, D.G., Fidler, F.A., Ind. Eng Chem. 44, 1430 (1952). Willingham, C.B., Taylor, W.J., Pignocco, J.M., Rossini, F.D., J . Res. Natl. Bur. Std.35, 219 (1945).
RECEIVED for review May 2, 1966. Accepted July 3, 1966. American Petroleum Institute Research Project 48A on the “Production, Isolation, and Purification of Sulfur Compounds and Measurement of Their Properties,” which the Bureau of Mines conducts at Bartlesville, Okla. and Laramie, Wyo.
Meat Capacities of the liquid Phase in the System CaO-P205-H20 EDWARD P. EGAN, Jr., and BASIL B. LUFF Division of Chemical Development, Tennessee Valley Authority, Muscle Shoals, Ala.
Measurements were made of the heat capacities at 25’, 5 0 ° , and 80’ C. of solutions in the system CaO-P205-H?0, and the measured specific heats were converted to partial I . H20, Ca( HiPo?)2 , molal heat capacities of the calcium phosphates Ca( HIPO~) CaHP01.2H20, and CaHP04.
THERMAL data on the solid and liquid phases in the system CaO-P?OS-H20 are useful in interpretation of the
MATERIALS AND APPARATUS
reactions involved in fertilizer manufacturing processes and in the behavior of fertilizers in the soil. Measurements were made of the specific heats of liquid phases in the system a t 2 5 ” , 50”. and 8OoC.,and the partial molal quantities were derived from the results. The specific heats, with the heats of solution a t the same composition ( 2 ) , may be used to determine the temperature dependence of other physical properties of the solutions, such as vapor pressure and electrochemical potentials. The specific heats of the solution are of direct value in engineering calculations involving calcium phosphate solutions. The measured specific heats of the solutions were converted t o partial molal heat capacities of the calcium phosphates Ca(H2P04)2. H20, Ca(H?P0J2, CaHP04, and C a H P 0 4 .2H20. For these conversions, the solution compositions were recalculated to represent each of the four ternary systems comprising a single calcium phosphate, phosphoric acid, and water.
Phosphoric Acid. Phosphoric acid hemihydrate, 2 H 7 P 0 4 . H 2 0 ,was twice recrystallized from reagent phosphoric acid ( 3 ) . The drained, unwashed crystals were melted to form a stock solution (90% H 3 P 0 4 ) ,the exact composition of which was established by its density ( 1 ) . Dicalcium Phosphate. A solution (5) containing 5% CaO, 21% PZO;, and 74% H20 was prepared from reagent dicalcium phosphate and the stock phosphoric acid. The solution was filtered, then heated to crystallize anhydrous dicalcium phosphate. Preparation of Solutions. The compositions of the solutions used in the measurements were intersections of “water rays” (9) of constant ratios P205:Ca0 with tielines between Ca(H?P04)2and 0.5, 1, 1.5, 2, 3, 4, 6, 8, and 10 molal phosphoric acid solutions. The weight ratios P205:Ca0 selected for the water rays were 39.180, 19.081, 12.706, 9.514, 7.596, 6.314, 5.396, 4.705, and 4.161. The most concentrated solution on each water ray was prepared by
VOL. 1 1, No. 4, OCTOBER 1966
5 09
Table I. Test Solutions Expressed in Terms of System C ~ ( H Z P O ~ ) ~ . H ~ ~ - H ~ P O ~ - H ~ ~ H2Od Molality, m2
10 8 6 4 3 2
ICa(H2PO1)2 H20 Molality, P206 CaO ml Wt. ratio P205:Ca0= 39.18 36.83 0.94 0.3477 33.74 0.86 0.2918 28.60 0.73 0.2178 21.08 0.54 0.1369 17.74 0.45 0.1069 12.87 0.33 0.0718 Wt. 5%"
Wt. ratio PzOs:CaO = 19.081 10 37.66 1.97 0.7647 8 33.78 1.77 0.6118 6 28.82 1.51 0.4588 4 22.28 1.17 0.3058 3 18.16 0.95 0.2294 2 13.26 0.69 0.1529 1.5 10.44 0.55 0.1147 1.0 7.32 0.38 0.0765 0.5 3.86 0.20 0.0383 8 6 4 3 2
6 4 3
Wt. ratio PzOs:CaO= 12.706 34.85 2.74 0.9951 29.94 2.36 0.7463 23.36 1.84 0.4975 19.16 1.51 0.3732 14.09 1.11 0.2488 Wt. ratio PZO5:CaO= 9.514 31.16 3.28 1.0874 24.56 2.58 0.7250 20.27 2.13 0.5437
H3POd Ca(H2POA. Wt. %" Molality, HzO Molality, m? PZOS CaO m3 Wt. ratio P20s:CaO = 7.596 4 25.90 3.41 0.9995 3 21.53 2.83 0.7497 2 16.10 2.12 0.4998 4.93 0.65 0.1249 0.5
4 3 2 1.5 1.0
Wt. ratio PzO5:CaO= 6.314 27.40 4.34 1.3382 22.97 3.64 1.0037 17.36 2.75 0.6691 13.95 2.21 0.5018 10.02 1.59 0.3346
3 2 1.5 0.5 0.1
Wt. ratio P2Os:CaO = 5.396 24.63 4.57 1.3253 .. ~. . ~ 18.85 3.49 0.8836 0.6626 15.26 2.83 6.05 1.12 0.2209 1.31 0.24 0.0442
2 1.5 1.0
Wt. ratio P2O5:CaO= 4.705 1.1644 20.63 4.38 0.8733 16.86 3.58 2.62 0.5822 12.34
2.0 1.5 1.0 0.5 0.1
Wt. ratio P20S:Ca0= 4.164 22.81 5.48 1.5502 1.1626 18.85 4.53 0.7751 13.99 3.36 0.3875 7.89 1.90 0.0775 1.76 0.42
~~
~
~
.
5% H20= 100 - (% P20s+ CaO). weight from the stock phosphoric acid solution, recrystallized dicalcium phosphate, and water, and its composition was checked by chemical analysis. Solutions along each water ray were prepared by weight dilution of the concentrated solution. The compositions of solutions so prepared are listed in Table I. The authors discovered after the measurements were completed that the dilutions along the 39.180 water ray had been miscalculated, so that the compositions of the solutions along this ray in Table I were displaced slightly from the desired intersections. These departures from the desired compositions, however, did not affect the validity of the subsequent calculations. The compositions of saturated solutions in the system CaO-P205-H20 a t 250C. are listed in Table 11. These compositions are from both published results (5, 6) and recent unpublished measurements of solutions near the Ca(H2P04)2.H20-CaHP04 invariant point. Calorimeter. Only minor modifications were made to the solution calorimeter ( 4 ) . The hollow stirrer shaft was closed with a neoprene plug. At 80°C. there was some difficulty from condensation of water on the calorimeter cover and upper walls during the time that the solution, heated to about 75" C., was placed in the calorimeter, and the assembled calorimeter began to approach temperature equilibrium with the bath. To prevent this condensation, the calorimeter cover was preheated to 90" C. on a formed Calrod unit and, while the weighed charge was being preheated to 75"C., a small copper-jacketed oil bath, heated to 95" C., was inserted into the neck of the calorimeter. As in previous measurements ( 4 ) , a weighed charge of constant volume (850 ml.) was used. The vapor space in the calorimeter was about 160 ml., and a vaporization correction was made for the water required for saturation of this space, based on vapor pressures a t 25" C. (9). Vapor pressures at 50" and 80" C. were not available, but the isobars at 510
Table 11. Compositions of Solutions on Saturation Isotherms at 25" C. CaHPO, Isotherm % P 2 0 s % CaO 1.55 0.55 4.90 1.55 8.25 2.44 11.51 3.22 14.61 3.90 17.52 4.49 20.22 5.01 22.69 5.46 24.53 5.80"
Ca(HIP0d)2.H20 Isotherm % P905 %CaO . . 24.53 5.80' 27.19 5.20 29.72 4.62 32.00 4.09 34.06 3.62 . ._ 36.81 3.00 39.94 2.32 42.58 1.80
Invariant point.
25"C. were almost straight lines with small slopes, and the vapor pressure of each solution was assumed to increase with rising temperature a t the same rate as phosphoric acid solutions (6). The largest vaporization correction was 0.25% of the energy input, and the correction probably was in error by no more than 10%. In each specific-heat measurement ( 4 ) , the energy input was adjusted to yield a temperature rise of 0.5"C. The energy measurements were based on the. defined calorie of 4.1840 absolute joules. The temperature base was 0°C. (273.15" K.). All temperatures were measured to O.OO0loC.; the last two places are significant only in determining small temperature differences, and three decimal places were used for consistency in calculating the variation of the specific heat with temperature. SPECIFIC HEATS The measured specific heats a t the midpoint of each temperature interval a t 25", 50°, and 80" C. are listed in Tables 111, IV, and V. Pairs of measurements at the same temJOURNAL OF CHEMICAL AND ENGINEERING DATA
Table IV. Observed Specific Heats at 50" C.
Table I l l . Observed Specific Heats at 25" C . H ,PO, Molality, rn
t.,
c.
Cal. / G . Soln.
H iP0, Molality, m
t.oC.
Cal.iG. Soln.
Wt. ratio P,O.:CaO = 39.18 kvt. ratio P?O;:CaO = 9.514 cont. 2 24.750 0.8278 10 24.742 0.6255 25.276 0.8296 25.288 0.6264 1.5 24.750 0.8611 10 24.742 0.6256 25.277 0.8618 25.289 0.6261 1 24.749 0.9001 8 24.613 0.6543 25,275 0.9002 25.152 0.6547 0.1 24.750 0.9887 6 24.667 0.7043 25.275 0.9589 25.202 0.7035 4 24.749 0.7781 Wt. ratio P > O :CaO = 7.596 25.278 0.7788 4 24.747 0.7098 3 24.727 0.8110 25.271 0 7101 25.254 0.8111 0 75,54 3 24.752 2 24.729 0.8605 25.282 0 7,557 25.281 0.8607 2 24.750 0 8132 Wt. ratio P O.:CaO = 19.081 25.282 0.8137 0.5 24.750 0.9:W 10 25.130 0.6106 25.278 0.9:19:! 25.674 0.6123 10 24.795 0.6146 Wt. ratio P?O;:CaO = 6.314 25.373 0.6176 10 24.733 0.6124 4 24.752 0.6925 25.276 0.6130 25.287 0.6896 8 24.679 0.6469 4 24.751 0.688,5 25.215 0.6474 25.285 0.6889 6 24.768 0.7082 3 24.749 0.7347 25.315 0.7111 25.280 0.7352 6 24.753 0.6979 2 24.755 0.7979 25.287 0.6986 25.288 0.7979 1.5 24 744 0.8337 6 24.747 0.6956 25.280 0.6966 25.273 0.8338 1.0 24.746 0.8771 4 24.727 0.7606 25.278 0.8780 25.260 0.7607 3 24.749 0.8041 Wt. ratio PD,:CaO = 5.396 25.285 0.8064 3 24.729 0.8026 3 24.750 0.7146 25.262 0.8023 25.280 0.7145 2 24.727 0.8517 2 24.736 0.7756 25.258 0.8500 25.270 0.7759 2 24.734 0.8522 1.5 24.746 0.8155 25.265 0.8519 25.277 0.8151 1.5 24.723 0.8918 0.5 24.746 0.9238 25.253 0.8932 25.277 0.9230 1 24.746 0.9166 0.1 24.753 0.9818 25.272 0.9171 25.279 0.9812 0.5 24.750 0.9536 Wt. ratio P205:Ca0 = 4.705 25.277 0.9542 2 24.753 0.7532 Wt. ratio P 2 0 i : C a 0= 12.706 25.284 0.7532 1.5 24.738 0.7987 8 24.752 0.6306 25.292 0.6305 25.270 0.8020 1.5 24.723 0.7937 6 24.750 0.6780 25.281 0.6786 25.246 0.7947 4 24.769 0.7468 1 24.737 0.8505 25.314 0.7515 25.269 0.8465 4 24.741 0.7454 1 24.737 0.8461 25.273 0.7456 25.267 0.8455 3 24.734 0.7891 Wt. ratio P,05: CaO = 4.164 25.263 0.7884 2 24.751 0.8419 2 24.742 0.7243 25.273 0.8423 25.287 0.7246 1.5 24.718 0.7685 Wt. ratio P20;:Ca0 = 9.514 25.244 0.7692 6 24.752 0.6619 1 24.720 0.8242 25.248 0.8240 25.286 0.6620 0.6 24.736 0.8956 4 24.751 0.7282 25.263 0.8958 25.286 0.7289 3 24.756 0.7729 0.1 24.727 0.9745 25.289 0.7736 25.249 0.9751
H ,PO, Molality, rn
L,~C.
Cal. (;. Soln.
Wt. ratio P20;:Ca0= 39.18 Wt. ratio P1O-:CaO= 9.514 cont. 1 49.727 0.9080 10 49.742 0.6408 50.252 0.9081 50.269 0.6429 0.1 39.767 0.9905 10 49.742 0.6416 !50.290 0,9907 50.269 0.6424 8 49.749 0.6697 Wt. ratio P.0 :CaO = 7 . 3 6 50.282 0.6704 6 49.750 0.7214 4 49.770 0.7246 50.272 0.7178 50.321 0.7240 6 49.740 0.711x 4 49.739 0,7671 50.267 0.7108 0.7700 6 49.753 0.7191 3 49.742 0.7671 50.290 0.7213
