Conditions for Transformation and Equilibrium of Iron Oxides in Glass Melting

Guloyan, Yu. A.

doi:10.1023/b:glac.0000026759.69686.89

Glass and Ceramics

2004

DOI: 10.1023/b:glac.0000026759.69686.89

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Conditions for Transformation and Equilibrium of Iron Oxides in Glass Melting

Yu. A. Guloyan

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Cited by 7 publications

(6 citation statements)

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“…The determination of the diffusion coefficient yields results that are close to the data obtained in studying the transformation of iron oxides [1].…”

supporting

confidence: 77%

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Kinetics of Chromium Oxide Transformations in Glass Melting

Guloyan

2005

Glass Ceram

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The kinetics of chromium oxide transformations in glass batch under heating and in glass melt has been studied. The different degrees of transformation of CrO 3 and Cr 2 O 3 is demonstrated. The conditions of equilibrium between chromium oxides in the case of their simultaneous presence in glass melt is determined. The conditions of the interaction between chromium and iron oxides in the glass melt are investigated, including the surface layer in which an equilibrium between the colorant oxides can be achieved in accordance with the reaction conditions and the composition of the gaseous atmosphere. The low reaction velocities in the glass melt are due to its high viscosity and low values of diffusion coefficients.The nature of the transformation of colorant compounds in glass melting is important for the technology of producing tinted glass, especially for automated glass container production. The processes of transformation of pigments occurring in the initial period of melting and later in the glass melt are insufficiently studied.The study in [1] considered the conditions for the transformation and equilibrium of iron oxides. It is demonstrated that during melting of glasses containing iron oxides the transformations of the latter mainly occur in the solid phase and the ratio of two forms of iron oxides in glass melt is determined by the melt temperature. The valence state of iron oxides in industrial glass-melting furnaces does not satisfy the condition of equilibrium with the ambient medium due to a high melt viscosity and low values of the diffusion coefficients.Chromium oxides are common colorants for container glasses; therefore, the present study is focused on the physicochemical parameters of transformations of chromium pigments.We investigated the conditions of transformations of chromium oxides in melting industrial container glass. Chromium oxides were introduced in the amount of 0.10 -0.25% (above 100%) of the main glass composition in the form of chromium anhydride CrO 3 , potassium bichromate K 2 Cr 2 O 7 , and chromium oxide Cr 2 O 3 . The content of chromium oxide in batches and glasses was found through chemical analysis using the diphenylcarbacide method. Laboratory electric furnaces adapted for the development and control of a corresponding atmosphere were used for experimental melting. The gaseous medium was characterized through partial oxygen pressure P O 2 . This parameter is universal and can be used to estimate both oxidizing and reducing conditions. Compounds of hexavalent chromium introduced in the batch decompose under heating and produce Cr 2 O 3 . The nature of this transformation is determined by the thermal resistance of oxides which, in turn, is related to dissociation pressure. Figure 1a shows the transformation kinetics of the initial compounds in air (log P O 2 = -1.68) upon introducing CrO 3 and K 2 Cr 2 O 7 into the batch. The parameter accepted as the main characteristic is the degree of transformation a, i.e., share of the decomposed colorant. It can be seen that the rate...

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“…The determination of the diffusion coefficient yields results that are close to the data obtained in studying the transformation of iron oxides [1].…”

supporting

confidence: 77%

“…The study in [1] considered the conditions for the transformation and equilibrium of iron oxides. It is demonstrated that during melting of glasses containing iron oxides the transformations of the latter mainly occur in the solid phase and the ratio of two forms of iron oxides in glass melt is determined by the melt temperature.…”

mentioning

confidence: 99%

Kinetics of Chromium Oxide Transformations in Glass Melting

Guloyan

2005

Glass Ceram

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“…The difference of the diffusion coefficients for different gases at low temperatures is greater than at high temperatures. Investigations of the diffusion of oxygen and reducing gases are presented in [20,21].…”

mentioning

confidence: 99%

Transport phenomena in glass technology (Review)

Guloyan

2007

Glass Ceram

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The role of transport phenomena and technological processes in glass production is noted. The salient features of a change in transport phenomena accompanying changes of the temperature and chemical composition of glasses for fused and solidified states of glass are examined. The interrelationship of transport phenomenon is also examined. Glass forming melts possess a high viscosity. The latter has a large effect on transport phenomena associated with particle motion; this effect is also expressed by definite relations. The results of experimental and theoretical investigations, presented in the scientific and technical literature, are discussed from structural and technological standpoints.Transport phenomena are encountered in every technological process. They include processes where mass or energy transfer occurs from certain particles of a nonuniform material system to other particles in the system. It is usually assumed that the system consists of one phase but its properties are nonuniform.If a material or energy gradient is present in a system or body, then transport of the corresponding kinetic units (atoms, ions, phonons, and so forth) occurs:where F is the flux of the kinetic units determining some property, K is the coefficient of proportionality, and dF/dx is the gradient of the determining characteristics: flow velocity, temperature, concentration, electric potential.The most important types of transport are transport of impulse or momentum, heat, mass, and electric charge.During heat conduction, thermal energy is transferred from particles with higher energy to particles with lower energy.When regions with different chemical potentials are present (this difference arises, as a rule, because of a concentration difference), mass transfer occurs as a result of diffusion. A special limiting case of diffusion is self-diffusion, which is associated with disordered displacement as a result of the thermal motion of molecules, atoms, or ions within a phase with uniform properties.During electric conduction, electric charge is transferred as a result of a difference in the electric potentials.Transport phenomena play an important role in the technological processes involved in the production of glass articles, starting with the process of founding glass and ending with processes involved in working articles and in the interaction with the environment when glass articles are used.In what follows, the characteristic features of transport phenomena, predominately in the high-temperature processes of glass technology, are examined. Predominantly domestic review literature containing many references to the original works, including those of foreign authors, is used.It should be noted that the authors of [1] analyzed, using the SciGlass system, the investigation of the properties of glass over the period 1976 -2001. It was found that over this time the number of investigations concerning transport phenomena (including dielectric properties) comprised 18.3% of the total number of investigations concerning the proper...

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“…At the same time, it is known [2,3] that the oxidation-reduction potential of the batch determines the ratio of iron oxides with different valence of the iron in the glass and, correspondingly, the color of the glass.…”

mentioning

confidence: 99%

Salient features of melting white glass enamels containing titanium

Rodtsevich

Minkevich

2007

Glass Ceram

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Conditions for Transformation and Equilibrium of Iron Oxides in Glass Melting

Cited by 7 publications

References 2 publications

Kinetics of Chromium Oxide Transformations in Glass Melting

Kinetics of Chromium Oxide Transformations in Glass Melting

Transport phenomena in glass technology (Review)

Salient features of melting white glass enamels containing titanium

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