Chemical Thermodynamics of Tin - Volume 12 - OECD Nuclear ...

Chapter V
Elemental tin
V.1 Tin crystal
V.1.1
General considerations
Solid tin exists in two forms. The low-temperature cubic modification (also called α-Sn
or “grey” tin) transforms to a tetragonal solid (also called β-Sn or “white” tin). Both the
temperature and enthalpy of transformation are somewhat uncertain because the
transition is sluggish. β-Sn can be supercooled to very low temperatures.
Cohen and coworkers carried out early measurements of the α → β transition
temperature [1899COH/EIJ], [1908COH], [1927COH/DEK], [1935COH/LIE] using
electrical and dilatometric methods. They reported temperatures between 285 and
293 K, the most reliable being T trs = (286.35 ± 0.10) K [1935COH/LIE]. The careful
and systematic experiments of Raynor et al. [1958RAY/SMI] by dilatometry showed
that the transition temperature was significantly influenced by the state of the white tin
in the sample. They reported a transition temperature for strain-free Sn of
(283.55 ± 0.45) K and (286.5 ± 0.3) K for strained Sn. In compilations/evaluations,
Hultgren et al. [1963HUL/ORR] and [1973HUL/DES] recommend (286.2 ± 3.0) and
(286.2 ± 0.5) K, respectively, while Gurvich et al. [1991GUR/VEY] states 287 K
without further discussion or qualification. The selected value for the present evaluation
has been obtained from the value for strain-free tin [1958RAY/SMI] and the one of
[1935COH/LIE] by the method described in example C.2 (see Appendix C):
T trs = (285 ± 2) K.
There is thought to be evidence of a transition in white tin between 420 and
470 K. Bartenev [1947BAR] found an anomaly in the heat capacity-temperature curve
at about 440 K. This was corroborated by Klemm and Niermann [1963KLE/NIE], who
observed a slight, abrupt discontinuity in the enthalpy curve (≈ 200 J·mol –1 ) at about
448 K. Klemm and Niermann [1963KLE/NIE] also presented data showing a
discontinuity in the temperature dependence of the a-axis lattice parameter of tetragonal
tin (the c-axis showed no such discontinuity). The temperature dependence of the
electrical conductivity showed (less convincing) anomalies at about the same
temperature. These observations were later discussed by Grønvold [1974GRO], whose
ο
very careful adiabatic calorimetric measurements showed no discontinuity. This
C p,m
CHEMICAL THERMODYNAMICS OF TIN, ISBN 978-92-64-99206-1, © OECD 2012