V. G. Konakov

On the possibility of forming complexes with the participation of O2- ions in melts and glasses of the Na2O-SiO2-CU2O system

The structural role of copper ions in melts (glasses) of the Na2O–SiO2–Cu2O–CuO system is analyzed in the framework of the acid–base concept with due regard for the geometric (the radius ratio for Cu2(1)+ and O2– ions) and energy (the mean enthalpies of the Cu2(1)+–O bonds) factors. It is demonstrated that copper ions in the structure fulfill the function of modifier cations. In these melts, the Cu1+–Cu2+ redox equilibrium can be described without regard for the formation of [Cu2(1)+O4/2 ]2(3)– ionic complexes (which could be incorporated into the structure of silicon–oxygen anions) and [Cu2+Ob/k ]2 – b/k polyhedra providing the interaction between Cu2+ ions and anions. The influence of the formation of these polyhedra on the redox equilibrium is considered within the formalism of chemical thermodynamics. The composition dependence of the oxygen ion exponent pO is measured by an electromotive force (emf) technique. The ratio between the numbers of copper atoms with different valences is determined by chemical analysis. The experimental data obtained are in agreement with the theoretical inferences.

Specific Features of the Synthesis of Porous Materials Based on a Magnesium–Aluminum Spinel

Ultrafine powders are synthesized through cocrystallization of magnesium, aluminum, and silicon compounds. Spinel–cordierite two-phase composites are prepared based on these powders. The leaching of a chemically unstable phase in hydrofluoric acid solutions is studied. The optimum conditions are determined for treatment of two-phase materials with the aim of preparing ceramics based on the magnesium–aluminum spinel with an accessible porosity of higher than 50%.

A Study of the Acid–Base Properties of Melts in the Na2O–B2O3–SiO2System: I. Composition Joins with a Na2O Content of Less Than 20 mol %

Three composition joins in the Na2O–B2O3–SiO2system at constant Na2O contents of 5, 10, and 15 mol % are studied by the high-temperature method of determining oxygen ion exponents pO for oxide melts. It is found that the basicity of melts increases in going from the binary sodium borate system to the sodium silicate system. The acid–base properties of ternary melts are simulated under the assumption that their basicity is determined by the interaction in pseudobinary systems. It is shown that the basicity of the studied melts is governed, to a large extent, by the formation of the Na2O · B2O3· 2SiO2ternary compound.

Synthesis of Nanopowders in the ZrO2–HfO2–Y2O3 System

Powders with a crystallite size of 3–5 nm are prepared using back coprecipitation. The effect of the precipitation temperature on the size of crystallites and agglomerates is investigated. It is established that, for the chosen compositions, only the cubic phase is formed at a temperature above 550°C.

A study of the acid-base properties of melts in the Na2O-B2O3-SiO2 system: III. Composition joins with a constant sodium oxide content from 40 to 50 mol %

Three joins in the Na2O–B2O3–SiO2 system at constant Na2O contents of 40, 45, and 50 mol % are studied by the high-temperature method of determining oxygen ion exponents pO for oxide melts. It is found that, unlike the melts with a lower sodium oxide content, the basicity of the studied melts increases when changing over from the pseudobinary silicate system to the sodium borate system. The acid–base properties of ternary melts are simulated under the assumption that their basicity is determined by the interaction in pseudobinary systems. It is shown that the basicity of the melts under investigation is governed, to a large extent, by the dissociation of structural–chemical groupings of the sodium metasilicate–sodium metaborate composition.

A Study of the Acid–Base Properties of Melts in the Na2O–B2O3–SiO2 System: II. Composition Joins with Sodium Oxide Contents of 25, 30, and 35 mol %

AbstractThe exponent of oxygen ion activity pO =

A Study of the Acid-Base Properties of Melts in the Na 2 O-B 2 O 3 -SiO 2 System: III. Composition Joins with a Constant Sodium Oxide Content from 40 to 50 mol %

- \log a_o ^{2 - }

A study of the relative bacisity of melts in the K2O-GeO2 system

for melts in the Na2O–B2O3–SiO2 system along the composition joins with constant sodium oxide contents of 25, 30, and 35 mol % is studied by an electromotive force (emf) technique at 950°C. Measurements are performed using two variants of the technique of determining pO, namely, in high-temperature salt solutions of oxide systems in KF and with a salt bridge between two oxide melts. It is shown that the basicity of melts increases with an increase in the Na2O content at a constant concentration ratio of glass-forming oxides. The acid–base properties of sodium borosilicate melts are simulated under the assumption of acid–base interaction between the components. It is found that the basicity of the studied melts along the composition joins with constant sodium oxide contents of 30 and 35 mol % is governed primarily by the acid–base interaction in Na2O–B2O3 and Na2O–SiO2 binary systems and, to a lesser extent as compared to low-alkali composition joins (below 20 mol % Na2O), by the formation of Na2O · B2O3 · 2SiO2 and Na2O · B2O3 · 6SiO2 ternary compounds.