INDUSTRIAL AND ENGINEERING CHEMISTRY
866
Vol. 36, No. 9
The results of entropy calculations follow: Gal./' K./Mole Ti Tic 0.401 0.08 6.844 5.71 7 24 * 0 . 0 7 6 . 8 =k 0 1. ~
-
0 60.12" K.,extrapolated 50.12' 298.16' K.,graphical
-
Slo8.18
Ii:xtra allowance of error has been made in the entropy of titanium carbide t o account for possible uncertainty in the correction for impurities. The entropy of titanium previously in use is 6.6 (4, 6). 'rliis figure is based upon a single mean specific heat measurement made thirty years ago and deserves no weight in compariml with the present result. No previous low-temperature specific heat or entropy ditta are available for titanium carbide, but an e3tirnate of Szss.,~= 5.5 had been made (3) by analogy with silicon carbide. The present result, of cotirpe, rests upon firmer ground. LITERATURE CITED I 0
100
FIGUEE1.
I
I
I
I
I
380
200
T OK.
SPECIFIC HEATOF TITANIUM (A) TITANIUM CARBIDE (B)
AND
ing an the temperature, and from 0.23 to 12.97% for the titanium carbide. The corrected specific heat values are given in Table I and graphically in Figure 1. No irregularities were found in the specific heats of either substance. The specific heat per mole of titanium carbide is lower than that per gram atom of titanium metal at temperatures below 189' K. This decrease in the specific heat of a carbide below that of the corresponding metal is noted also in the data for silicon carbide (2) and tantalum carbide ( I ) . Entropies at 298.16' K. The entropies were rornputed kq gaphically integrating under Cypvs. log T curves between the limits of 50.12' and 298.16"K., and adding the portions obtained by extrapolating the measured specific heats below 50.12" KIi.. In the case of titanium the Debye function, D(358/T), was found to fit the measured results t b 120' K. and was employed in thp extrapolation. For the titanium carbide the specific heat a t the lowest temperature studied is so low that no significant error c a n be introduced by employing the T3 law for extrapolation
TOLE
I. SPECIFICHEATSOF TITANIUM AND
T, K. 53.6 57.1 61.4 65.9 70.5 75.1 80.1 83.8 92.7 102.9 55.1 58.6 62.3 65.9 69.8 14.2 81.2 86.5 95.7 105.3 5
CP
T, K.
T ,'? IC
CP
Titai?ium" (Atomio 'u'eight = 47.9 Grama) 1.278 112.7 3.765 214.6 128.2 4.081 224.9 1.464 133.3 4.306 236.0 1.679 143.4 4.516 244.9 1.915 154.0 4.707 255,5 2.142 163.9 4.878 265.7 2.357 2.682 174.3 5,015 276.1 184.2 5.142 285,8 2.737 5,259 295.1 3.101 194.4 3.460 204.7 5.355 Titanium Carbideb (Molecular Weight 115.6 2.389 0.312 2.789 0.384 125.7 3.190 0.473 135.6 3.606 146.0 0.571 4.010 0.686 156.2 166.5 4,402 0.821 176.2 4.750 1,055 186.3 5.113 1.242 5.474' 1,587 196.8 1.960 206,5 5.778
C p expressed as calories per gram atom. expressed as calories per gram molecule.
b Cp
OF
CARBIDE
=
( I ) Kelley, I
