Redox Equilibrium of Iron in Silicate Glasses

Abstract

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...

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.…”

Salient features of melting white glass enamels containing titanium

“…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.…”