THERMAL EXPANSION COEFFICIENTS OF GRAPHITE CRYSTALS. Page: 6 of 21
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where a and c are the crystal lattice a- and c- spacings at temperature, T,
a0 and co are the lattice spacings at T = 0*K,
Ua = 3 RT F(ea), Uc = 3 RT F(0c), and
F(T) are the Debye functions, which have been numerically evaluated and
tabulated by Beattie.(3)
The Debye Temperatures for Graphite
Riley used the Debye Temperatures derived by Magnus(4) from specific
heat measurements made over the temperature range 44 to 1100*K.
A considerable amount of specific heat data has been accumulated since
that time and various analyses have been made to derive Debye temperatures from
the data; however, the primary emphasis has been on explaining the characteristic
' features of the specific heat curve at low temperatures(5,6). Because of this
difference in emphasis and the lack of agreement on Debye temperatures, it was
deemed preferable to derive the Debye temperatures using'the best available
specific heat data over the temperature range of interest in this study.
McDonald() has recently made precision measurements of heat content
and derived the specific heats of graphite over the temperature range 300 to 1800*K;
these data match well with the data of DeSorbo and Tyler(8) taken below 300*K.
Moreover, except for differences of 2-3% near room temperature, these two sets
of data are in excellent agreement with NBS evaluations of previous specific
The combined data of DeSorbo and Tyler(8) and McDonald (7 were reduced to
specific heat at constant volume using the approximation:
Cv = C' (1 - 6 C' T), (9)
C' = C - y T, and
6 = v V , evaluated at room temperature.
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Morgan, W.C. THERMAL EXPANSION COEFFICIENTS OF GRAPHITE CRYSTALS., report, October 31, 1971; Richland, Washington. (https://digital.library.unt.edu/ark:/67531/metadc1033287/m1/6/: accessed May 27, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.