Dynamics of the redox state of the melt in the continuous production of clear glass

Abstract

The effect of a set of external factors on the redox equilibrium of iron and sulfur, changes in melt properties, and light transmission of clear sheet glass is investigated for continuous production of glass. A quantitative estimate of trends in the variations of the redox potential of glass melt is proposed. Practical measures improving the efficiency of a tank furnace by correcting the oxidation state of the melt are considered.A prompt response to problems of stabilizing the glassmelting process in continuous production is an essential factor in producing high-quality products. This is especially important in the case of significant changes occurring in the process, such as a modification of the batch : cullet ratio or the glass compositions, using different grades of materials, etc. These modifications result in the process parameters going beyond the technological standards. As a consequence, glass quality is often impaired and the production volume decreases.The experience shows that in carrying out the above specified works it is important to adequately estimate the current situation and to use various techniques to stabilize the prescribed redox potential (ROP) of the glass melt. Note that such technological situations cannot be to a full extent simulated in the laboratory conditions in view of their complexity; therefore, laboratory results, as a rule, differ perceptibly from data obtained in continuous industrial furnaces. Therefore, it is necessary to study in detail the regularities of the variations of the redox state and technological properties of glass melt in continuous production.The factors influencing the glass melt in continuous production can be arbitrarily divided into two groups:-staff-controlled systems (hereafter "controlled" systems); they include the batch ROP, the chemical composition (basicity) of the glass, the furnace temperature conditions, and the gas : air ratio;-uncontrollable factors, such as variations in the granulometric composition of materials, fluctuations in composition of gas-air mixtures fed to the furnace for combustion, and uncontrolled impurities brought by materials, i.e., iron from refractories and sulfurous compounds from the fuel.As a rule, uncontrolled factors in practical glass melting are neglected due to their diversity and narrow variation limits; the lack of statistical data due to irregular or lacking monitoring of these factors aggravates the problem. We should especially stress the impurities of the variable-valence elements (VVE), namely iron (d element) and sulfur ( p element) coexisting in the melt in the state of the redox equilibrium [1]:Laboratory studies of silicate glasses of a simple composition have demonstrated that the ratio between the oxidized and the reduced forms of these variable-valence elements may vary within wide limits and is closely related to the controlled factors of the first group. A decrease in the batch ROP, and increase in melting temperature, a decrease in glass basicity, or transition from the oxidizing atmosphere to the...

Effect of the oxidation – reduction potential on the proneness of glass to form bubbles

“…For this reason it can be supposed that the equilibrium Fe 2+ « Fe 3+ in white glass is shifter farther to the left as compared with green glass, and therefore in accordance with [4] its reduction potential is somewhat higher.…”

“…The sol prepared thickened during aging or careful heating, converting into a gel which was further dried, heat-treated to a powder state, and used for glassmaking. The ORP was evaluated using an indication index of the basicity level -the fraction of Fe 2+ [4], which in a sol-gel is much higher than in glass made from the conventional mix: 12.5 and 4.3%, respectively. We shall examine the reasons for this phenomenon.…”

“…1 (taken from [9], p. 177): the SO4 2-concentration is directly proportional and S 2-inversely proportional to the oxygen pressure p Î 2 . The fraction of bivalent iron in the glass was used as the p Î 2 indicator.…”

The transparent discolored glass for industrial and high-speed transport

“…It has been established that the change in the light transmission of colorless glass and the disruption of the stability of the technological process is due to the total iron content [4][5][6], the equilibrium state of Fe (II) ⟷ Fe (III). The course of the reaction in the glass mass is affected by the oxidation-reduction conditions (ORC) of the glass melting process.…”