Internal reserves for enhancing the efficiency of glass-melting furnaces

Zaitseva

2005

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The effect of some additives on the equilibrium of valence forms of iron is investigated. It is demonstrated that tin and carbon more significantly than fluorine reduce iron. The redox potential of the glass matrix affects the equilibrium between difference valence forms of iron much less than additives correcting spectral characteristics of glass. Glass can be clear or tinted, depending on its purpose and application area. Signaling used by railroad, automobile, or air transport is impossible without color filters with strictly specified color characteristics. About 100 varieties of tinted glass find applications in the production of precise instruments.Coloring is imparted by d-elements which can exist each in several valence-coordination states and, depending on this particular state, selectively absorb light radiation in a strictly fixed spectral range. The ratio between different valence-coordination forms depends on numerous factors: glass composition, its thermal history, type of initial material, presence of extraneous inclusions, etc.[1].When two variable-valence elements are present together, they mutually influence each other according to the following redox series [2]:Each higher-valence oxide in the upper series by losing part of oxygen can oxidize any oxide to the right in the lower-valence second series.Iron is used to impart heat-shielding properties and obtain color filters selectively absorbing IR radiation or suppressing the violet part of the spectrum. This element is present in glass in two valence states: Fe(II) with an absorption band around 1000 -1100 nm and Fe(III) with a maximum in the short-wave range near 380 -400 nm. To obtain required spectral characteristics, it is necessary to strictly maintain the Fe(II) : Fe(III) ratio.The purpose of the present study is to investigate the equilibrium of iron in silicate glasses.The concentrations of bivalent and trivalent iron in tinted optical glasses were calculated based on the Russian glass catalog [3]. In these calculations the authors were guided by the spectrophotometric method for identifying colorant ions in glasses developed at the S. I. Vavilov State Optical Institute (OST 3-4728-79). The development and implementation of this method was carried out under the direction of L. I. Demkina. The method is based on the Buger -LambertBaire law stating that when several colorants are simultaneously present in a particular glass, the absorption coefficient a l of this glass for any wavelength l is equal to the sum of the products of the specific absorption coefficient of the individual ion c l by it weight content w i in the glass:where m l and r l are the attenuation and scattering coefficients, respectively, of the glass at the wavelength l. Table 1 correlates the results of calculating the content of Fe(II) and Fe(III) with the total content of iron in glasses determined by synthesis. It can be seen that calculated data differ from experimental ones by 3 -6%, consequently, the results can be regarded as reliable.The following reaction can t...

Section: At the Same Timementioning

confidence: 95%

Section: At the Same Timementioning

confidence: 96%

Redox Equilibrium of Iron in Silicate Glasses

Zaitseva

2005

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“…Since a reliable and simple method of determining the acid-base properties of a glass mass for application under production conditions has not been developed, and considering the interrelationship of acid-base and redox processes, impurity EVV are widely used as indicators to make an indirect evaluation of the basicity of melts [2,6]. A shift of the equilibrium in the direction of higher valence indicates an increase of basicity (decrease of acidity) of the glass mass and vice versa.…”

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confidence: 99%

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

Kiyan

2007

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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...

“…The maximum flame and furnace roof radiation corresponds to approximately 1100 nm [1]; therefore, the reduced form Fe 2 decreases the diathermancy of the melt, impairs the transfer of thermal radiation into the glass melt depth, impedes melting, clarification, and homogenization, and impairs the homogeneity of glass [3]. Trivalent iron has an opposite effect.…”

mentioning

confidence: 99%

“…According to the known principle of the theory of acids and bases in silicate melts [1,4] regarding the correlation between the acid-base processes (reactions between the basic glass components: SiO 2 , Al 2 O 3 , MeO, Me 2 O) and the redox processes (reactions between the variable-valence impurity oxides), we used the glass basicity indicator [3], i.e., the fraction of bivalent iron, for the quantitative estimate of changes in the oxidation state of the melt (glass melt ROP). The increase in this fraction indicates a decreased oxidizing (increased reducing) potential of the glass melt, and vice versa:…”

mentioning

confidence: 99%

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

Kiyan

2006

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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...