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

IX.1 Sulfur compounds and complexes 221
from dissociation pressure measurements; Mills [1974MIL] evaluated these results.
Sharma and Chang [1986SHA/CHA] regard this compound as a metastable phase and
not part of the equilibrium S-Sn phase diagram. This conclusion was corroborated by
the careful preparative and analytical work of [2003CRU/MOR] and is adopted here.
“Sn 3 S 4 ” has probably been confused with a mixture of SnS + Sn 2 S 3 .
IX.1.1.2.6 Sn 4 S 5 (cr)
This compound was postulated [1937GER/KRU] as an intermediate product in the
decomposition of SnS 2 . It is not considered part of the equilibrium S-Sn phase diagram
([1961ALB/SCH], [1962MOH], [1969MOH]). This conclusion was corroborated by
[2003CRU/MOR] and is adopted here. “Sn 4 S 5 ” has probably been confused with a
mixture of 2 SnS + Sn 2 S 3 .
IX.1.1.2.7
Cu 8 SnS 6 (cr)
Ternary tin sulfides
The heat capacity was measured [1989ALI/DZH] at 55 to 100 K by adiabatic
calorimetry (uncertainty ± 1%) and at 77 to 420 K by light pulse heating (uncertainty
ο
± 8%). The data were not tabulated, and appear only in a graph. The C p,m vs. T curve
shows a smooth rise from 55 to 300 K, after which there is a local narrow peak (from
365 to 1250 J·K –1·mol –1 ). The peak is clearly defined at 328 K, after which the heat
capacity returns to its previous value. This thermal event was called a first-order
transition [1989ALI/DZH], i.e., a solid-solid transformation. The enthalpy change in the
phase transition was reported as (5.1 ± 0.3) kJ·mol –1 .
Cu 4 SnS 4 (cr)
There is no report of the enthalpy of formation of this compound.
The selected heat capacity at 298.15 K is (365 ± 29) J·K –1·mol –1 .
The heat capacity was measured at 80 to 400 K by adiabatic calorimetry and DSC
[1983ALI/ARA]. The data were not tabulated and appear only in a graph. The heat
capacity varied approximately linearly over the experimental temperature range, from
180 to 257 J·K –1·mol –1 ο
. Its value at 298 K was read from the C p,m vs. T plot. There is a
local maximum [1974KHA/RIV], [1983ALI/ARA] at 232 K which may be attributed to
a solid-solid transition. The enthalpy of this phase transition is ≈ 2.5 kJ·mol –1
[1983ALI/ARA]. The compound decomposes at 1083 K before melting
[1974KHA/RIV].
Cell potential measurements were performed at 300 to 420 K
ο
ο
[1987MUS/ABB]. Both S m (Cu 4 SnS 4 , cr, T ) and Δ fHm(Cu 4 SnS 4 , cr, T ) were derived
therefrom.
CHEMICAL THERMODYNAMICS OF TIN, ISBN 978-92-64-99206-1, © OECD 2012