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Handbook of Solvents - George Wypych - ChemTech - Ventech!

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1488 Victor Cherginets<br />

The important fact found was the relatively high PtO solubility, therefore, platinum<br />

gas oxygen electrode, sometimes considered as metal-oxide one, cannot be used for measurement<br />

<strong>of</strong> pO in strongly acidic media because <strong>of</strong> complete dissolution <strong>of</strong> the oxide film<br />

over its surface. Pt|PtO electrode was attempted for pO index measurements in buffer solutions<br />

Ni 2+ /NiO. 18<br />

Shapoval et al. 19-21 studied saturated solutions <strong>of</strong> different oxides by polarographic<br />

technique. A degree <strong>of</strong> interaction between oxide dissolved and the melt has been estimated<br />

taking into account potential and polarogram shifts and their deviations from theoretical<br />

ones. Rate <strong>of</strong> cation reduction has been found to be limited by the acid-base dissociation<br />

stage. Stability constants <strong>of</strong> some oxides have been found to be (in mol%): CoO -<br />

(9.9±1.9)×10, NiO - (6.8±0.8)×10 3 , PbO - (3.4±1.3)×10 3 ,Bi2O3- (8.7±3.5)×10 3 . Cadmium,<br />

copper (I) and silver oxides have been shown to completely dissociate under the experimental<br />

conditions (400-600 o C) this was in a good agreement with Delarue’s results. 14,15<br />

Stabilities <strong>of</strong> iron (II) and (III) oxides in the chloride melt at 470 o C have been investigated.<br />

22,23 2- 2-<br />

Oxide precipitation by carbonate CO3 ≡ O has been shown by potentiometric<br />

and diffractometric data to result in formation <strong>of</strong> FeO from Fe II solutions. Fe III precipitation<br />

led to formation <strong>of</strong> solid solutions LiFeO2-LiyFe1-yO. Solubility products in molarity scale<br />

have been determined as FeO-10 -5.4 ,Fe3O4-10 -36.3 ,Fe2O3-10 -29.16 . Cations Fe 3+ have been<br />

found to oxidize chloride melt with chlorine evolution, that is in good agreement with the<br />

results <strong>of</strong> other studies. 14,15 Carbonate ion as oxide donor had its dissociation to O 2- essentially<br />

incomplete and, therefore, obtained solubility products gave systematic error. 20,21<br />

Cherginets and Rebrova 24,25 studied oxide solubilities in this melt at 700 o C. Solubility<br />

products <strong>of</strong> CoO (pP=4.43±0.11) NiO (pP=5.34±0.2) and MgO (pP=5.87±0.05) were<br />

higher than those in molten eutectic KCl-NaCl. The shift <strong>of</strong> the solubilities in molar fraction<br />

scale was ~3.36 log units and allowed to estimate solubilities <strong>of</strong> other MeO oxides on the<br />

base <strong>of</strong> the known values in KCl-NaCl. It has been shown that acidic properties <strong>of</strong> Pb 2+ and<br />

Cd 2+ cations were suppressed by those <strong>of</strong> Li + , therefore, these cations and Ba 2+ and Sr 2+ did<br />

not change oxoacidic properties <strong>of</strong> the molten KCl-LiCl.<br />

21.3.3.2 Molten KCl-NaCl (0.50:0.50)<br />

One <strong>of</strong> the first works devoted to oxide solubilities determination in this melt has been performed<br />

by Naumann and Reinhardt. 8 CaO, SrO and BaO solubilities have been determined<br />

by isothermal saturation technique with isotopic control <strong>of</strong> the saturation in temperature<br />

range from melting point to 900 o C. KCl-NaCl and individual molten chlorides, KCl and<br />

NaCl, have been used as solvents. Oxide solubilities have been stated to increase in the sequence<br />

CaO

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