Comportements Chimique et Électrochimique dans les Hydroxydes Alcalins Fondus. I. Si(IV) ET Ge(IV)

Abstract

The study of the dissolution reaction of the silicium and germanium dioxides was carried out in the NaOH-KOH (49 mole91 eutectic mixture at 2 l O O C and in pure NaOH at 350'C.The initial acidobasicity of these solvents as well as the Cg2-and CH20 modifications after addition of the Si(1V) and Ge(1V) solutes were measured by M original method using linear sweep voltammetry at a platinum electrode. This procedure was nevertheless ineffective in acidic NaOH medium because of the diotortion of the water reduction peak by the cathodic front. In this case, the water liberated by the reaction was eliminated by a flow of dry nitrogen and collected in a cell containing anhydrous MgClO .

Chemical and Electrochemical Behavior in Molten Alkali Hydroxides: III . Chemistry of Tin (II) and (IV) in the Eutectic Mixture and in Pure

“…Acido-basic properties of the melts.--The melt preparation was described in earlier papers (5,6). All the determinations were carried out at 483 K in the case of the eutectic mixture and at 623 K in the case of pure sodium hydroxide.…”

“…a light stream of dry nitrogen, the water concentration remained constant during the experiments. The water and oxide ion concentrations were adjusted by adding known amounts respectively of hydrated potassium hydroxide (5) or sodium oxide.…”

“…Equation [1] relates the water concentration (CH2o) to its partial pressure (PH2o) in the gas phase PH20 = kH20" CH20 [1] The Henry coefficient kn2o used in this work was determined by Hoyt (10) and yields 195 mm Hg.M -1 at 623 K. This value is in excellent agreement with controls carried out in our laboratory. Details on the experimental device and on the electrochemical measurements were provided in previous papers (5,6).…”

“…Determination of the nature of the dissolved oxyanionic complexes.--The stoichiometries of the dissolved species were characterized by accurately measuring the amounts of water produced in acidic media or the amounts of oxide ions consumed in basic solutions by the dissolution of given quantities of chemicals containing the elements at their investigated oxidation state (5). up in the nitrogen atmosphere and allowed to cool down until solidification occurred.…”

“…In this paper, the chemical properties of tin (II) and (IV) in the eutectic mixture NaOH-KOH (49M%) at 483 K and in sodium hydroxide at 623 K are described. Silicium and germanium, two other Group IV elements were considered in detail in a previous paper (5).…”