492 INDUSTRIAL AND ENGINEERING CHEMISTRY VOL. 29, NO. 5

By means of Equation 9 it is possible to calculate the aver- age void diameter of certain compacted powders over a wide range of void contents after having determined experimen- tally the relation a t some convenient void content. As pointed out previously (2) , Equation 9, with a value for slope m of 0.019, will hold for a large number of mineral powders. How- ever, for powders with unusual particle shapes or nonuni- formity of particle shape, it is necessary to determine experi- mentally the average void diameter a t different void contents. Further, it is admitted that the relation given by Equation 9 does not hold for very low void contents since the plot of log d vs. per cent voids must curve in the region of very low per cent voids in order to pass through the origin. But, in the work discussed here, we are not interested in mixtures where the volume per cent of liquid is very low because such systems are non-Newtonian or plastic.

The value for C of Equation 8 for seventeen of twenty-three mineral powders (thirty-two of forty-four liquid-solid com- binations) studied showed an average deviation of less than 6 per cent when the average void diameters of the powders as present in the mixtures were calculated by means of Equation 9; twenty combinations showed less than 2 per cent deviation. An average deviation of 6 per cent is considered satisfactory because of the experimental error encountered in measuring the void content and permeability (void diameter) of the compacted powder and the viscosities of the asphalt and mixtures.

Of the six mineral powders (used in twelve combinations) that gave an average deviation for G greater than 6 per cent, all had unusual particle shapes or showed irregularity of particle shape (3) as measured by the ratio of the three axial

lengths. Since Equation 9 did not hold for these powders, experimental data a t various degrees of compaction had to be obtained and values for the average void diameter of the powder? as present in the mixtures, interpolated from the curve for per cent voids us. void diameter. When these inter- polated values for d were used in Equation 8, the deviation of C for a particular liquid with a given solid for all combinations was less than 6 per cent.

The data obtained from a study of forty-four combinations of different liquids and mineral powders indicate that the absolute viscosity of any system is inversely proportional to the average void diameter of the pulverulent solid as present in the mixture.

The average void diameter is a secondary property of a pulverulent solid and is influenced by such primary properties as particle size, particle size distribution, particle shape, and regularity of particle shape. Consequently, these primary properties of the powder will indirectly influence the vis- cosity of liquid-solid mixtures through their effect on the average void diameter.

Literature Cited (1) Traxler, R. N., IND. ENQ. CHIOM., Anal. Ed., 8, 185 (1936). (2) Traxler, R. N., and Baum, L. A. H.,PhysiCs, 7,9 (1936). (3) Traxler, R. N., Baum, L. A. H., and Pittman, C. U., IND. ENG.

(4) Traxler, R. N., and Schweyer, H. E., Proc. Am. Soc. Testing CHEM., Anal. Ed., 5, 165 (1933).

Materials, 36, 11, 518 (1936).

RECEIVED Ootober 29,1936. Presented before the Division of Colloid Chem- istry &t the 92nd Meeting of the American Chemical Society, Pittsburgh, Pa., September 7 t o 11, 1936.

Thermochemical Examination of Nitrocellulose

P. R. MILUS E. I. du Pont de Nemours & Company, Inc., Wilmington, Del.

INCE discrepancies exist in the published values for the heats of formation of nitrocelluloses of various nitrogen contents, thermochemical constants calculated from

these data are not very reliable where accuracy is essential. Numerous calorimetric determinations,, gas analyses, and

calculations of the equation of decompositlon and tempera- ture of explosion were made on nitrocelluloses of 12.62 to 13.45 per cent nitrogen content. The heat of explosion and gas analysis data, together with the most recent data on the heats of formation of the gases formed by the explosive decomposition, were used to calculate the heats of formation of these nitrocelluloses. The heat of formation can be ex- pressed by the following formula:

where F, = heat of formation, C,

S

F, = K," - El, K," = sum of heats of formation of products of explosion,

E, = heat of explosion, C, C*

Materials and Apparatus The nitrocelluloses, of 12.62 to 13.45 per cent nitrogen content,

used in these experiments were of regular plant manufacture. The nitrogen content was determined by the du Pont nitrometer

method and is reproducible by 10.02 per cent nitrogen. Each sample was dried 24 hours at 40" to 50' C. and 2 hours at 100" C. to ensure complete dryness.

The calorific value or heat of explosion, &, was determined in a calibrated calorimetric apparatus. The bomb (Fi ure 1) of 35- cc. capacity was charged with 3.4 grams of nitrocelfulose. Igni- tion was obtained from a &volt storage battery usin 0 10 ram of nitrocellulose as a primer charge. This corresponfs tb a foad- ing density of 0.1. The temperature rise, 3.5' to 5.0' C., was measured by means of a Beckman type thermometer.

The permanent gas volume was measured by allowing it to exDand into an evacuated calibrated system. The increase in prkssure was noted and the gas calculated to cubic centimeters per gram at standard temperature and pressure.

roduced was expelled from the bomb by heating i t to 5040" 8, and the vapors were absorbed by calcium chlo- ride contained in a U-tube and calculated to cubic centimeters

The water

per gram (gaseous) S. T. P. Analysis of the permanent gases, which consisted of carbon

dioxide, carbon monoxide, methane, hydrogen, and nitrogen, was made by means of a gas analysis apparatus according to standard procedure for gasesof this type.

The results thus obtained--&, permanent gas volume, gaseous water, and gas composition-were used to calculate the equation of decomposition and the Centigrade temperature of explosion for nitrocelluloses of 12.62 to 13.45 per cent nitro- gen content (Table I). -

MAY, 1937 INDUSTRIAL AND ENGINEERING CHEMISTRY 493

TABLE I. THERMOCHEMICAL CONSTANTS OF NITROC~LLULOSE~ 7 Nitrocellulose:

. -Blends of Pyro and high-grade- Pyro High-grade

lot 94 No. 1080 No; 1248 No. 1192 lot 819 (12.6270 (13.00% (13.15% (13.2070 (13.45%

N) N) N) N) N)

Q cal /gram (HzO liquid) 973 1025 1046 1055 1096 Apparent thermochemical constants:

688 711 705 698 169 169 170 169

Pkrminent gas vol., cc./gram S. T. P. 730 857

170 868

Ha0 gas vol.. cc./gram 9. T. P. Total pas vol. 900 880 874 Gas analysis: coz co .

HP CHc Na

21.2 23.8 24.3 24.5 27.0 45.9 43.9 43.7 43.5 41.0 18.7 17.3 16.7 16.5 16.1 0.4 0.4 0.4 0.4 0.3 13.8 14.6 14.9 ' 15.1 15.6

Calorifia corrections: CHI formation 8 7 7 7 Ht0 condensation 74 73 73 73 Hz0 gas reaction 26 20 20 20 True Q. cal./mam (Ha0 eas) 865 925 946 955

6 74 21 995 _. . _

Vol. correction for CH4 formation 6 6 6 6 4 Vol. at To C. of explosion 906 886 880 874 ' 861 Gas Empn. at To C. of explosion, vol.

10.5 13.9 14.3 14.4 16.0 43.8 40.8 40.5 40.2 38.6 9.5 9.6 9.2 9.0 7.9

12.5 11.1 11.7 11.9 12.1 25.1 24.0 24.1 24.3 25.0 7.12 7.35 7.44 7.47 7.62 0.3045 0,3055 0,3057 0.3047 0.3086

C 6 : co HE N2 HzO

HnO gas equilibrium, K Sp. heat of products of explosion Ta C. of explosion 2840 3025 3095 3130 3245

a Loading density = 0.10.

TABLE 11. THERMODYNAMIC DATA HzO Gas

To C. Equilibrium, -----Mean Mol. Heat CV, 0-4000° C.- X 100 K coz co Hz N HzO

17 18 19 '

20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40

4.47 4.80 5.14 5.42 5.73 5.95 6.18 6.36 6.54 6.72 6.88 7.04 7.20 7.32 7.44 7.56 7.68 7.79 7.89 8.03 8.18 8.31 8.41 8.52

10.79 10.88 10.97 11.05 11.12 11.20 11.29 11.36 11.44 11.48 11.53 11.58 11.64 11.69 11.74 11.79 11.85 11.91 11.96 12.01 12.06 12.12 12.17 12.22

5.96 5.99 6.03 6.06 6.10 6.13 6.17 6.20 6.23 6.25 6.27 6.30 6.33 6.35 6.36 6.37 6.39 6.40 6.42 6.44 6.46 6.47 6.49 6.50

5.43 5.47 5.61 5.55 5.60 5.64 5.68 5.72 5.76 5.79 5.83 5.86 5.89 5.93 5.96 5.99 6.02 6.06 6.09 6.13 6.16 6.19 6.23 6.26

5.69 5.81 5.93 5.99 6.03 6.06 6.09 6.12 6.15 6.17 6.20 6.22 6.25 6.27 6.29 6.31 6.34 6.36 6.37 6.39 6.40 6.42 6.43 6.45

8.15 8.24 8.33 8.42 8.52 8.61 8.71 8.80 8.89 8.96 9.04 9.10 9.16 9.23 9.31 9.38 9.46 9.52 9.58 9.64 9.71 9.77 9.83 9.90

Equation of Decomposition and Temperature of Explosion

Since the heat of explosion, the products of decomposition, and their mean molecular heats are known, the temperature of explosion can be calculated by the relation:

T. = H/C, where T. i= temp. of ex losion, O C.

H = true heat o?explosion, cal./gram C, = mean sp. heat of products of explosion at constant

The true heat of explosion is obtained by correcting for

vol.

the secondary reaction, methane formation:

CO + 3H2 % CHa + HzO + 58.7 Cal. at 25' C.

liquid water, and the heat of vaporization of the water, A correction is also made for the shift in the water gas reaction equilibrium. This can be obtained by using the proper thermodynamic data which satisfy the estimated temperature of explosion. The equation of decomposition, a t a low loading density and constant volume, is simplified in explosive reac-

tions of this type, which are completely gasified, by the fact that only the water gas reaction is considered:

CO + HzO = COz + Hz + 9.8 Cal.

The values for the equilibrium con- stant,

and the mean molecular heats of the gases are based on the data of Lewis and von Elbe (2) and are shown in Table 11.

Heats of Formation of Nitrocellulose

The calorimetric data obtained were used to calculate the heats of formation of the nitrocelluloses by subtracting the heat of explosion (liquid water) from the sum of the heats of formation of the products of explosion (permanent gases and liquid water).

FIGURE 1. CROSS SECTION OF BOMB MADE

TYPE MACHINE STEEL FROM 0.35-0.45 CARBON, SPECIAL MANGANESE

1. Insulated firing terminal 2. Firing head looking nut 3. Circulating ports 4. Neoprene gasket 5. Bridgman type firing head 6. Fiber washers 7. Neoprene washers 8. Insulated firing terminal locking nut 9. Grounded ignition wire binding post 10. Mica washer 11. Gas release valve

494 INDUSTRIAL AND ENGINEERING CHEMISTRY VOL. 29, NO. 5

TABLE 111. THERMOCHEMICAL CONSTANTS OF NITROCELLULOSE Thermochemioal Values (Corrected for CHI Formation)

Heat Heat Heat of forma- of of

Freezing tion of explo- forma- 7 Composition . Gas HgO Total point, -- Cas analysis---- produoba, sion, tion.

c c . / g . co./g. Cc./g. Per cent by uohme Cal./g. Cal. /g. Cn l . /g . Nitrocellulose C H 0 N vol. gas gas vol. K COz CO HZ Nz Kcv Ew Fm

Gram atom per gram Pyro lot 94 (12.62% N):

Calod. 0.02201 0.02787 0.03636 0.00901 738.6 166.1 904.7 2.51 21.1 45.7 19.5 13.7 1559 594 Exptl. 0.02197 0,02786 0,03632 0.00898 738.7 167.1 905.8 2.51 21.0 45.7 19.7 13.6 1557 965 592

Blend of Pyro and high- grade nitrocellulose 1080 (13.00% N):

Blend of Pyro and high- grade nitrocellulose 1248 (13.15% N):

Blend of Pyro and high- grade nitrocellulose 1192 (13.20y0 N):

High-grade lot 819 (13.45%

Calcd. 0.02156 0.02664 0.03653 0.00929 716.0 167.3 883.3 2.35 23.3 44.3 18.0 14.4 1582 564 Exptl. 0.02159 0.02854 0.03655 0.00926 719.3 166.2 885.5 2.35 23.5 43.8 18.3 14.4 1588 1018 570

Calod. 0.02138 0.02624 0.03660 0.00939 710.4 168.6 879.0 2.39 24.3 43.2 17.7 14.8 1599 560 Exptl. 0.02151 0.02606 0.03656 0 00936 713.3 166.2 879.5 2.39 24.0 43.6 17.7 14.7 1592 I039 553

Calcd. 0.02132 0.02610 0.03862 0.00943 706.7 169.5 876.2 2.42 24.5 43.2 17.4 14.9 1604 566 Exptl. 0.02133 0.02594 0.03642 0.00940 706.4 167.2 573.6 2.42 24.2 43.4 17.5 14.9 1591 1048 543

N I * C&i. 0.02103 0.02543 0.03673 0.00961 696.6 167.7 864.3 2.18 26.8 40.9 16.9 15.4 1631 54 1 Exptl 0.02101 0,02532 0.03678 0.00958 694.4 166.9 861.3 2.18 26.8 40.9 16.9 15.4 1627 l%O 537

The heats of formation in kilocalories (Cal.) a t 25' C. and constant volume for the several gases are:

coz 94.2 Clayton and Giauque (1) co 26.9 Roasini (4 HIO ( as) 57.5 Rossini $1 HzO &quid) 67.3 Rossjnj IS) CHI 18.4 Rossini (4)

A comparison of the experimental and theoretical gas, composition at the freezing point, as well as the heats of ex- plosion, the sums of the heat of formation of the products of explosion, and the heats of formation, is shown in Table 111.

The freezing point of the water-gas reaction is the tempera- ture below which the reaction

CO + Hz0 * COz + H2

proceeds so slowly that no sensible change in the gas com- position occurs. It is derived by calculation from the analysis of the products of explosion, fixed gases, and liquid water.

The experimental value for K a t the freezing point was used in the derivation of the calculated values in Table 111.

The theoretical equations of decomposition were derived by using the water-gas reaction:

CO + H2O CO2 + HZ

If x is the nitrogen content of the nitrocellulose in per cent by weight, then each 100 grams will have the following values in gram atoms:

C = 3.7019 - 0.1189 x H = 6.1698 - 0.2696 x 0 = 3.0849 + 0.0437 x N = 0.7142 x

when using the following formulas for pyroxylin and gun- cotton types of nitrocellulose:

C,HalOasNs = pyroxylin = 11.96% N, C24H2s042N11 = guncotton = 13.48% Pr

As an example, for guncotton ( C Z ~ H S O ~ ~ N I ~ ) the decom- position is:

then zCO + y COz + zH2 + uHzO + 5 . 5 N z

2 + y = C = 24

0 ~ + 2 y + u = - ' = 4 2 2

z + u = Hz = 14.5

~ = 2 4 - ~ ~ ~ x - 6 z = 20.5 - x - (CO)(HzO) =

(COz)(Hz) Kt x (24 - 2)

(24 - ~ ) ( 2 0 . 5 - X)

Kt corresponds to the temperature which satisfies the thermo- dynamic equilibrium of the reaction.

The heats of explosion and heats of formation can be ex- pressed algebraically by the following formulas, obtained from a graphical presentation of the experimental values,

Heat of explosion, E, = 145.8 x - 874 Heat of formation, F, = 1428.2 - 66.26 x

at constant volume, 25" C., where x is the per cent nitrogen by weight for nitrocelluloses of 12.62 to 13.45 per cent ni- trogen content.

The accuracy of these values is controlled by the calibra- tion of the calorimetric apparatus and the gas measuring equipment. Duplicate determinations are reproducible within 0.5 per cent on Q and total gas volume. This would indi- cate an error of *l per cent in the constants.

Acknowledgment The author wishes to express appreciation for the coopera-

tion and assistance of members of the staff of Burnside Laboratory, Explosives Department, E. I. du Pont de Yemours & Company, Inc.

Literature Cited (1) Clayton and Giauque, J . Am. Chem. SOC., 54,2610 (1932) (2) Lewis and von Elbe, Ibid., 57, 612 (1936). (3) Rossini, Bur. Standards J . Research, 6 , l (1931). (4) Ibid. , 6, 37 (1931).

RECEIVED October 28, 1936.