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INDUSTRIAL AND ENGINEERING CHEMISTRY
BETWEEN PREDICTED DENSITIES TABLE IV. DISCREPANCIES AND VALUES FROM Tnn LITERATURE
from Literature Present authors 0.74070 0.7250d 0.7139 0.7281 0.7246C 0,7390s 0.’7229 0.7225 0.734e 0.734c 0.7691 0.7691C 0.7750 0.77409 Dl0
Compound 4-Ethylhe tane 2,3-D/metEylheptane 2,5-Dimethylheptane
DSo Ca1cd.a 0.730b 0.727 0.716 0.7258 0.728 0.7377 0.721 0.7385 0.7564 0,773851
Egloff (4) 0.7407 0.7235 0.7147 0.72805 0.724fY
nlHexadeca6e a From Tables I1 and 111. b See text. c Only one literature value ava/lable. d Difference in selected values is due t o the new value available to present authors. 8 Caloulated t o 20’ by present authors. f Selected value (see text): equation gives 0.7737. a Value selected without reference to values for other n-alkanes.
dimethyl, and the 2,2’-dimethyl derivatives-appear t o be as definitely aligned as the 3-methyl series, and a similar accuracy of 0.0008 in the calculated densities is indicated. (The primed numbers refer to the positions from the opposite end of the chain: thus, the 2,2’-dimethyl series is 2,3-dimethylbutane, 2,4-dimethylpentane, 2,5-dimethylhexane, etc.). The other series (2,3-, 2,4-, and 2,3‘-dimethyl, 2,2,2’-trimethyl, and 3-ethyl derivatives) are also as well aligned as it is
Vol. 33, No. 1
reasonable to expect from the data available, and their calculated densities are probably accurate to 0.0010-0.0015. The interrelations between the different series also suggest other approximate alignments which may be useful in estimating densities for compounds outside of these series. For example, the estimated AA values for 3-ethylpentane and 5ethylnonane are each about -3.00, so that a similar value can be predicted for 4-ethylheptane, giving it a calculated density of 0.730. In general, substitution of a given single group in any position more than two removed from the ends of the chain has approximately the same effect on the molecular volume. To illustrate the utility of the alignment equations in detecting erroneous or suspicious literature data, Table IV compares (for a number of hydrocarbons) the densities predicted by the alignment method with those taken by Egloff (4) or by ourselves as the best selection from the literature.
Literature Cited (1) Calingaert and Hladky, J. Am. Chem. Soc., 58, 153 (1936). (2) Dornte and Smyth, Ibid., 52,3540 (1930). (3) Edgar and Calingaert, Ibid., 51, 1540 (1929). (4) Egloff, “Physical Constants of Hydrocarbons”, Vol. 1, New York, Reinhold Pub. Corp., 1939. (5) Grosse and Egloff, Universal Oil Products Co., Booklet 219 (1938). (6) Smyth and Stoops, J . Am. Chem. Sac., 50, 1883 (1928). (7) Vet, van der, Proc. dnd Wortd Petroleum Congr., Paris, 2, Sect. 2 , 515-21 (1937).
Heat Conductivitv of Zinc Oxide J
Produced by Flash Calcination of Zinc Sulfite H. F. JOHNSTONE, H. G. JACOBSON, AND G . W. PRECKSHOT University of Illinois, Urbana, 111.
HE flash calcination of hydrated zinc sulfite produces an oxide of extremely low bulk density as shown in Table I (1). This suggests that the powder should have a low heat conductivity and perhaps be useful as an insulating material.
T
OF CALCIWED ZINC OXIDE TABLE I. DENSITY
Compression Load K g . / s q . om. Lb./sq. in.
Density Grank/cc.
Lb./cu. p.
Measurements of the heat conductivity were made in a guarded-disk type calorimeter in which the temperature drop across the powder, the thickness of the powder, and the power input to the heater disk were measured. The apparatus was the same as that used by Kistler and Caldmell (g) in their study of the heat conductivity of aerogels. A detailed description may be found in the earlier paper. Since standardization had previously been made, the accuracy of the method was not rechecked. The heat conductivity of several samples of commercial Celotex were measured for comparison. The
results agreed closely with the values given in the literature for this material. The zinc oxide was a sample collected dry from the calciner constructed in the pilot plant for recovery of sulfur dioxide from waste gases ( 1 ) . The oalciner consisted of a 10-foot section of 4-inch 0. d. 11-gage stainless steel tubing. This was surrounded by cylindrical firebrick tile, 6 inches 0. d. and 1 inch thick, for protection against the direct action of the gas flames used for firing. The outer wall of the furnace was constructed of 4.5-inch firebrick with nine burner ports arranged for tangential flames. The temperatme of the wall of the calciner was recorded by a six-point recording pyrometer operating on thermocouples peened into the metal. Calcination of the zinc sulfite used for these tests was made at a wall temperature of 750” C. (1382” F.) and a t a feed rate of 1.12 grams per minute per sq. cm. (2.3 pounds per minute per square foot). The original zinc sulfite was prepared by adding sulfur dioxide t o a suspension of pure zinc oxide until the zinc sulfite first formed was entirely dissolved. The solution was then evaporated in a vacuum oven, and the crystals of reprecipitated zinc sulfite were collected and dried. The analysis of this product corresponded to the partially dehydrated hemipentahydrate: ZnO 45.7 per cent, SO2 33.7, total sulfur as SO2 35.2; calculated for ZnSOa.21/2Hz0: ZnO 42.8, SO, 33.6. Before calcination the crystals were
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INDUSTRIAL A N D ENGINEERING CHEMISTRY
107
insulating materials are listed in Table I11 for comparison with the observed values. It is evident that the conductivity of the zinc (Area of cylinder under test, 78.5 sq. om.) oxide approaches that of the best type of comGas Thickness Energy Temp. Av. Thermal Compression Pressure of Sample Input Drop Temp. Conductivity merCia1 insulating mrtterial. Because Of its exCal./(aec.) (84. cm.) tremely low bulk density when loosely packed, Kg./SQ. cm. Mm. Cm. Watt C. C. (” C./cm.)( X f O 6 ) its insulating value per unit weight of material Calcined Oxide, as Received is superior to that of most of the common in0.015 750 2.10 0.308 27.9 38 7.0 sulators. When the material is packed under 0.015 750 0.67 0.288 7.7 28 7.5 0.015 750 4.80 0.313 71.9 60 6.4 compression, however, its thermal conductivity increases rapidly. This is shown graphically in Calcined Oxide, Dried in Vacuum Oven at 200’ C. 2.60 0.269 31.6 39 6.7 Figure 1. Extrapolation t o zero compression 0.015 0.044 750 2.27 0.269 17.9 33 10.4 load to eliminate the effect of the weight of the 750 2.25 0.266 10.2 29 17.9 0.071 0.093 750 2.25 0.266 6.9 27 26.7 disk gives a value of 5.8 X 10-6 calorie per second 0.015 25 1.99 0.272 40.2 44 4.1 per sq. cm. per O C./cm. for the thermal con0.015 7 0.79 0.269 16.6 32 3.9 ductivity of the loose material. This agrees with Celotex, as Received 750 3.81 0.307 29.5 39 12.1 the value for still air a t 34’ C., the average tem0.015 perature of the measurements, and indicates that Celotex, Dried in Vacuum at 100’ C. the principal cause of the high thermal resistance 0.0151 750 1.27 0.301 14.6 31 8.0 is the low conductivity of the air entrapped in the porous mass. When the particles are compressed, the conductivity from solid to solid is increased. passed through a small hammer mill, but the feed was not At low gas pressures the conductivity of the loose material is decreased as a result of the decreased conductivity of the screened to uniform size. For this reason the product was still air. These measurements indicate that the calcined not so completely decomposed as was usually the case. The oxide is in an extremely fine state of subdivision. composition was as follows: ZnO 89.2 per cent, SO2 4.42, total sulfur as SOn 9.5. Oxide prepared in this way exists as soft fluffy balls, 30 per cent of which are retained on a 9-mesh screen. It can be crushed to an impalpable powder between the fingers and easily dispersed in water. When compressed, , ~ ~ ~ R ~ its bulk volume is decreased. It has some resiliency, however, Thermal and even after considerable handling the percentage of fines Material Density Conductivity Reference Caal./(sec.)( 8 4 . cm.) is not greatly increased. Gram/cc. ( “ C . / c m )( X f 05) TABLE 11. THERMAL CONDUCTIVITIES O F CALCINED ZINC OXIDE AND OB CELOTEX
O
Tt”,”,”,”,,
Bilic?, aerogel, 4-10 mesh Calcined ZnO, loose Kapok Corkboard Hair felt Rock wool Sil-0-Cel Celotex Celotex
28 X
324
s
0.10 0.029 0.016-0.03 0.09 -0.23 0.18 -0.21 0.10 -0.30 0.17 0.21 -0.24
...
5.1 5.8 8.3- 8.6 8.6-10.7 8.8 8.8-10.0 10.7 11.7 12.1
(8)
Obsvd. (8)
(3) (3) (5)
Obsvd.
$20
si
3
16
With the calorimeter used, it was not possible to make measurements a t high temperatures. The data on the crude oxide, however, while less exact, do not indicate any tendency toward higher values as the average temperature is increased over a short range.
5
d I2 E. p a au 4
Literature Cited COMPRESSlON LOAD,
KC./%.
CM.
CONDUCTIVITY OF CALCINED ZINC FIGURE 1. THERMAL OXIDE
Measurements were made both on the crude oxide and on the same material after being heated in a vacuum oven at 200” C. to remove the last traces of moisture and sulfur dioxide. This treatment gave a material of slightly lower conductivity. All of the measurements were made a t an average temperature of the oxide layer slightly above room tcmperature. Measurements were made a t atmospheric pressure with the oxide under the compressive load of the disk alone and under additional weights added to the disk. Two measurements were also made with the calorimeter evacuated to 7 and 25 mm. of mercury, respectively. The results are shown in Table I1 along with those obtained on Celotex slabs. The thermal conductivities of various
(1) Johnstone, H.F.,and Singh, A. D., IND.ENG.CHIUM., 32, 1037 (1940). (2) Kistler, 5. S., and Caldwell, A. G., Ibid.,26, 658 (1934). (3) U.8.Bur. Standards, Letter Circ. 227 (April 19, 1927).
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