Acid-base interaction of the components in sodium-borosilicate glasses

Abstract

The effect of the coordination groups of boron, aluminum, and silicon on the acid-base properties of the glass mass and the change in the redox state of copper in boron-containing melts are studied. Indicators are proposed for evaluating the redox potential of the glass mass. The acid-base properties of commercial alkalialumoborosilicate glasses are compared using these indicators.Redox processes, occurring in melts, between elements with variable valence (EVV) play an important role in glass production technology. They are introduced into colorless or colored glasses according to the initial material (for example, iron and sulfur) or a colorant (chromium, copper, iron, and so on). In the glass mass they are always present in several valence states which are associated with redox equilibria of the type [1]Uncontrollable shifts of the equilibrium (1) between the valence of EVV have a large and often negative effect on the technological (diathermancy, surface tension of melts) and spectral (coefficient of directed transmission of light) characteristics of glasses and change their operating properties and the technical and economic performance of industrial machines [2]. For this reason, to optimize technological processes or color a glass mass it is important to have quantitative expressions for evaluating the redox state of the glass mass. They must give information on the composition, structural features, and properties of glasses. Since glass is a complicated chemical compound, the fractional participation (additivity) of the components comprising the glassy matrix must be taken into account in the quantitative expressions.The substantial difference, existing in any commercial glass, between the concentration of the basic components (glass formers, modifiers) and impurity components (impurities from the initial materials and the decomposition of refractories, stains, fining agents, decolorants, gases) makes it possible draw an analogy, within the framework of inorganic chemistry, between a glass mass and a maximally diluted liquid solution [3,4]. A silicate melt must be viewed as a solvent and the EVV impurities as the dissolved substance. Since the acidity (basicity) of a solvent, evaluated quantitatively by the pH (pOH), determines the valence-coordination state of a dissolved substance, the salient behavior of EVV in a glass mass can be viewed from the standpoint of the concept of acid-base relations [4].The modern picture of the nature of acid-base interaction of the components in solutions is based on the theory of Lewis acids and bases [3]. According to this theory, a base is any compound (atoms, ions, radicals, molecules) that can contribute an electron pair for forming a covalent bond (for example, the ion OH -in water solutions) and an acid is any compound that accepts this pair.The activity of the ions of free oxygen O 2-, which do not enter into silicon -oxygen groups, can serve as a measure of the basicity determining the acid-base properties of multicomponent silicate melts. These ions are distingui...