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

418
A Discussion of selected references
present, cassiterite had not yet had time to form. The universal appearance of romarchite
on corroding tin suggests that it is a required step in the oxidation of pure tin to the final
most stable phase of cassiterite.
The authors state that no data are available in the literature on the
(thermodynamic) stability of abhurite and hydroromarchite. This is not true for abhurite
whose thermodynamic stability has been determined by Edwards et al.
[1992EDW/GIL]. Moreover the composition of abhurite has been determined to be
Sn 21 Cl 16 (OH) 14 O 6 by its single-crystal structure [1981SCH/NES].
[2004GUR/GAV2]
This paper has been translated from Geokhimiya, No. 10, (2004) pp. 1096-1105,
[2004GUR/GAV]. Gurevich et al. [2004GUR/GAV2] measured the heat capacity of
cassiterite in the temperature range of 13.4 to 336 K using adiabatic calorimetry and
they calculated values of heat capacity, entropy and enthalpy increment which are
presented in Tables A-71 and A-72.
The experimental data were approximated by a Debye-Einstein-Kieffer
equation
o
Cp, m( T) = naD [
1
( θ1/ T) + aD
2
( θ2/ T) + aD
3
( θ3/ T) + aE
4
( θE/ T) + aK
5
( θL/ T, θU/ T)
(A.88)
where n is the number of atoms in the formula (n = 3, for SnO 2 ), D, E, and K are Debye
function, Einstein function and K-function of Kieffer [1979KIE]: θ 1 , θ 2 , θ 3 , θ E , θ L , and
θ U are their characteristic temperatures; a 1 , a 2 , a 3 , a 4 , and a 5 are linear coefficients. Thus
eleven adjustable parameters have to be selected. D, E, and K functions can be
expressed as follows
θ / T
−3 4
exp( ξ )
D( θ / T) ≡ 3 R( θ / T) ∫ ξ dξ
(A.89)
2
(exp( ξ )-1)
0
2
( θE
/ T) exp( θE
/ T)
E 2
(exp( θE
/ T )-1)
E( θ / T) ≡ 3R
(A.90)
θU
/ T 2
3R
ξ exp( ξ)
K( θL
/ T, θU
/ T) ≡
dξ
θ θ ξ
2
U
/ T −
L
/ T
∫ (A.91)
θ /
(exp( )-1)
L T
CHEMICAL THERMODYNAMICS OF TIN, ISBN 978-92-64-99206-1, © OECD 2012