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Untitled - Sciencemadness Dot Org

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PETN<br />

4.4 Refractive Indices.s<br />

Omega<br />

Epsilon<br />

Birefringence<br />

Double refraction<br />

5. THERMAL PROPERTIES<br />

134<br />

5.1 Phase Changes.7*e*10<br />

Type<br />

.bETN Polymorph’<br />

Form I<br />

1.556<br />

1.551<br />

0.005<br />

negative<br />

Form II<br />

1.556<br />

1.551<br />

0.02<br />

--_<br />

“Form I is also called Alpha, and Form II is also called<br />

Beta.<br />

Temperature<br />

(“C)<br />

W/g)<br />

Latent Heat<br />

(kcal/mole)<br />

PETN I-to-PETN II 130.0 --- ___<br />

Solid-to-liquid 142.9 37.4” 11.82<br />

Solid-to-gas _-- 91;9b 29.1<br />

---------<br />

“Reference 9 indicates that the heat of fusion varies with the method of crystallization.<br />

Imperfect or very disordered crystals had heats of fusion as low as 31 kcal/g.<br />

The latent heat of sublimation was computed from the vapor pressure data given in Ref. 10.<br />

5.2 Vapor Pressure.lo*ll<br />

loglo P(mm Hg) = 14.44 - 6352/T(K) for 323 < T < 371 K.<br />

log,, P(mm Hg) = 17.73 - 7750/T(K) for 383 < T < 412 K.

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