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

258
A Discussion of selected references
[1899COH/EIJ]
Summary of results
1. The disintegration of the white tin into gray tin, first described in 1851, is a
reversible phase transformation.
2. The transition temperature, T trs = 293 K, has been determined by dilatometry
and using the electrochemical cell Sn(white) | Sn-salt | Sn(grey).
3. A transition temperature of 20 °C means that, apart from warm days, our whole
“tin world” is metastable.
4. The rate of phase transformation Sn(white) → Sn(grey) has been determined
and has a maximum at 225 K.
5. Contact of white tin with an aqueous (NH 4 ) 2 SnCl 6 solution or with grey tin or
simultaneous contact with (NH 4 ) 2 SnCl 6 solution and grey tin accelerates the
phase transformation. In this way it is easy to prepare any quantity of grey tin.
[1902RUB]
Tin(II) hydroxide was precipitated from freshly prepared tin(II) chloride solutions by
adding sodium hydroxide. The precipitate was washed and surplus water was squeezed
out. Then the precipitate was equilibrated with carbon dioxide free sodium hydroxide
solutions in the concentration range 0.5 < c NaOH /mol·dm −3 < 4.7. During this procedure
black-blue crystals of tin(II) oxide were formed. Saturated solutions were obtained after
reaction periods of 5h. The tin content of the saturated solutions was transformed to
SnO 2 (s) and determined gravimetrically. Equilibration was certainly carried out under
ambient conditions, but no precise value of temperature was reported. No attempt was
made to characterise “Sn(OH) 2 (s)” stoichiometrically and/or structurally. In Table A-1
Rubenbauer’s original data are listed in columns 1 and 2 and converted into
concentrations in columns 3, 4 and 5.
Table A-1: Solubility of “Sn(OH) 2 (s)” in NaOH solutions.
ρ Na /g·cm −3 ρ Sn /g·cm −3 [NaOH] tot /mol·dm −3 [OH − ] free /mol·dm −3 [Sn(II)] tot /mol·dm −3
0.012400 0.009520 0.53937 0.45917 0.08020
0.018400 0.013070 0.80036 0.69026 0.11010
0.031970 0.021520 1.39062 1.20934 0.18128
0.041630 0.027800 1.81081 1.57662 0.23418
0.048305 0.039245 2.10115 1.77056 0.33060
0.106170 0.094670 4.61814 3.82065 0.79749
CHEMICAL THERMODYNAMICS OF TIN, ISBN 978-92-64-99206-1, © OECD 2012