THERMAL EXPANSION COEFFICIENTS OF GRAPHITE CRYSTALS. Page: 4 of 21
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In 1924, Gruneisen and Goens(2) derived a theory on the relationships
between thermal expansion, elastic moduli and heat capacities of hexagonal
crystals at low temperatures; in 1945, Riley extended this theory to higher
temperatures and with specific application to graphite. A significant amount
of additional data, especially in regard to thermal expansion at higher tempera-
tures, has become available since publication of Riley's results; this paper
presents the results of an analysis of currently available data, undertaken
to obtain improved estimates of the lattice thermal expansion coefficients
Riley has shown(1) that the heat capacity at constant volume, Cv, for a
graphite crystal can be considered as composed of two components:
CV = a + C
The components, C and C refer to vibrations parallel and perpendicular to
the basal planes, respectively, and are expressible by the Debye functions
C, = 3 RD( a); C = 3 RD(c). (2)
where ea and ec are the characteristic Lemperatures associated with the lattice
vibrations, T is the absolutetemperature of measurement and R is the ideal gas
The heat capacity at constant pressure, Cp, can be written in terms of
the well-known relationship
C= C+ ay2VT (3)
where av is the volumetric coefficient of thermal expansion, V is the molar
volume, and K is the volumetric compressibility. Since the temperature variations
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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/m1/4/: accessed April 19, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.