Potassium Silicate Glasses Research Articles

The structural groups of alkali silicate glasses determined from 29Si MAS-NMR

Lithium, sodium and potassium silicate glasses containing 20–56 mol% alkali oxide were investigated by 29Si nuclear magnetic resonance (MAS-NMR) spectroscopy. In the spectrum of each sample, at least two to four distinct peaks were identified. The distributions of SiO 4 structural units, Q n , where n is the number of bridging oxygen atoms bound to other Si atoms, were determined as a function of composition. The equilibrium constants of the reactions, 2Q n ⇌ Q n−1 + Q n+1 ( n = 3, 2, 1), were determined. The reaction proceeds to the right direction as cationic power of alkali ion ( Z/ r) increases (Li +>Na +>K +) at the same alkali oxide concentration. The apparent equilibrium constants of the above reactions are discussed along with a proposed thermodynamic model. The 29Si chemical shifts assigned to each structural unit increase linearly with alkali oxide contents. The slope of these lines decreases as the numbers of attached bridging oxygen (BO) atoms decrease. The average chemical shifts also increase linearly with an increase of alkali content. A close relationship between the average chemical shifts and the theoretical optical basicity was observed.

The interaction of lithium with sodium and potassium silicate glasses

AbstractThe interaction of lithium with sodium and potassium glass surfaces in UHV has been characterized with XPS. Earlier studies of the Li/SiO2 system have shown the formation of a partially passivating layer upon initial Li deposition. Following breakdown of this layer, substantial reduction of the glass matrix occurs. In the present study, several compositions of sodium silicate and potassium silicate glasses were found to be more resistant than SiO2 to lithium attack owing to the presence of non‐bridging oxygens in the matrix. The proposed corrosion mechanism involves charge transfer from Li to the modifying cations at the glass surface followed by desorption of neutral Na or K and interdiffusion of Li+ into the glass. For thick (metallic) Li films on sodium silicates, the formation of a dilute Li—Na intermetallic and sodium metal are identified from distinct plasmon structure in the Na(1s) line. Matrix reduction of glasses with low alkali content has been observed subsequent to the atom exchange.

Optical Absorption Spectra of the Pulse Irradiated Oxide Glasses (Part 5)

Pulse radiolysis was applied to the lithium-, sodium- and potassium-silicate glasses. The obtained spectra in micro and milli second ranges were the same as those observed by steady state X-ray irradiation at cryogenic temperature. The peak energies increased with a decrease in the radius of alkali ion. The lifetimes of these transient components were relatively long. In one second after irradiation the spectra of lithium and sodium silicate glasses resemble those by X-ray irradiation at room temperature, while the additional absorption due to trapped electrons located on the potassium ion remained in the same time range. The absorption due to the transient components in the sodium silicate glasses decreased with increasing temperature as well as by doping an electron scavenger such as Cd(II) ion. The emission due to recombination of the electron centers with some hole centers was reduced by the presence of Cd(II) ion.

ChemInform Abstract:29Si-MAS-NMR Studies of Binary Potassium Silicate Glasses. A Contribution to the Controversy of Interpretation.

Chemischer InformationsdienstVolume 17, Issue 47 Physical Inorganic Chemistry ChemInform Abstract: 29Si-MAS-NMR Studies of Binary Potassium Silicate Glasses. A Contribution to the Controversy of Interpretation. A.-R. GRIMMER, A.-R. GRIMMERSearch for more papers by this authorW. + MUELLER, W. + MUELLERSearch for more papers by this author A.-R. GRIMMER, A.-R. GRIMMERSearch for more papers by this authorW. + MUELLER, W. + MUELLERSearch for more papers by this author First published: November 25, 1986 https://doi.org/10.1002/chin.198647006Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume17, Issue47November 25, 1986 RelatedInformation

S-character of Cd+ centre in ?-irradiated alkali silicate glasses

The s-character of Cd+ centres and its fluctuation in γ-irradiated alkali silicate glasses were investigated using ESR spectroscopy. With increasing alkali content, the s-characters of Cd+ centres in sodium and potassium silicate glasses decrease monotonically whereas the s-character in lithium silicate glasses shows a maximum and then decreases. The temperature effect on compositional dependence of the s-character of a Cd+ centre is rarely observed in lithium silicate glasses. On the other hand, the temperature effect is clearly observed in sodium and it is suggested that local structures around Cd+ centres in sodium and potassium silicate glasses is relaxed by annealing at room temperature.

Low-temperature behavior of potassium and sodium silicate glasses.

In a study of the low-temperature anomalies which appear in disordered solids we have measured the specific heat, thermal conductivity, thermal expansion, and dielectric dispersion for a carefully prepared series of (${\mathrm{SiO}}_{2}$${)}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$(${\mathrm{K}}_{2}$O${)}_{\mathrm{x}}$ and (${\mathrm{SiO}}_{2}$${)}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$(${\mathrm{Na}}_{2}$O${)}_{\mathrm{x}}$ glasses. Each sample had a known glass transition temperature ${T}_{g}$, mass density, phonon velocities, covalency, and density and concentration fluctuations. The only significant correlation occurred between the phonon mean free path and the glass-transition temperature. No explicit support was found for any model developed to explain the specific heat and/or thermal conductivity of glasses.

On the structure of defect centers in γ-irradiated alkali silicate glasses

An EPR study after room temperature γ-irradiation on potassium silicate glasses of two chemical compositions and different 17O and 29Si isotopic enrichments has been carried out. Isochronal anneal experiments on 17O-enriched samples have confirmed the model for the trapped-hole center HC 1 as comprising a trapped hole on a pure 2p π orbital of a single nonbridging oxygen. Besides the well known HC 1 and HC 2 EPR spectra, new resonances have been isolated and identified as due to three types of oxygen-related defects (interstitial O 2 − ions; O 2 − bonded to the glass network; and interstitial ozonide ions O 3 −). Using 29Si-enriched samp simulations a 370 G doublet has been demonstrated to arise from an E'-like defect for which a tentative model is given. The formation of all these defects by irradiation depends on chemical composition of the glass.

Property/Morphology Relations in Alkali Silicate Glasses

The effects of glass composition and thermal history on the glass‐transformation range behavior, as indicated by thermal expansion curves, and on chemical durability, as indicated by the acid etch rate, were measured for binary lithium, sodium, and potassium silicate glasses and for the lithinm/sodium and lithiumlpotassium mixed‐alkali silicate glasses. The results were used to determine the phase‐separation boundaries and the limits of interconnectivity of each phase for all five systems. The results demonstrate the utility of such studies for the characterization of the morphology of glass‐forming systems.

Mechanism of Glass Darkening by a Low Pressure Mercury Discharge

A study was made of the darkening of sodium and potassium silicate glasses by a low pressure mercury discharge, using electron spectroscopy, Rutherford backscattering, and transmission electron microscopy. Initial changes in glass exposed to a mercury discharge are twofold: (i) mercury from the discharge penetrates very rapidly into the glass to depths of the order of 1 nm. (ii) Alkali ions migrate more slowly away from the surface in a photoelectric field that is caused mainly by trapping of photoelectrons. However, mercury entering the glass does not replace alkali ions. Rather, the mercury penetrates into voids in the glass network that are sufficiently close to the surface. From this “surface reservoir” mercury migrates slowly deeper into the glass. This migration is slower in mixed than in single alkali glasses. We assume that mercury migrates as ions in a photoelectric field, assisted by photoelectrons. Ultimately the mercury ions are reduced by photoelectrons to atoms that agglomerate into droplets of metallic mercury reponsible for glass darkening. A mercury discharge provides not only (i) mercury ions and (excited) atoms entering the glass and (ii) photons, creating a photoelectric field in the glass. The discharge also provides (iii) low energy electrons flooding the glass. The latter greatly enhance the strength of the photoelectric field in the glass by recombination with photoholes in the glass near the surface. As regards the effect on the darkening of the glass composition, not only the overall composition is considered (e.g., conductivity, molar volume, shear modulus), but also superficial changes in the composition.

ChemInform Abstract: RAMAN STUDY OF ARSENIC‐CONTAINING POTASSIUM SILICATE GLASSES

Raman spectra are given of potassium silicate glasses with batch composition xK2CO3-(100—x)SiO2-0.5As2O3 in which x varies from 10 to 50. To isolate the contribution of the As2O3 additions to the spectra from that of the silicate network, difference spectra were prepared from spectra of glasses with and without As2O3 added to the batch. To obtain a precision sufficient for this purpose, the spectral data were collected in multiple scans under full computer control using photon counting and a correction for laser-source fluctuations. It is concluded from the polarized and depolarized difference spectra that arsenic in potassium silicate glasses with x>35 is mainly present in the pentavalent state as AsO43- ions. For glasses with x<35 it is concluded that As5+ is present in As2O74- or As3O105- ions and As3+ as AsmO2m+1-m-2 chains of AsO3 pyramids. In these chains, m increases with decreasing x. From the intensity ratio of Raman peaks, caused by arsenite (As3+) and arsenate (As5+) ions in the glasses, it is concluded that there is a significant increase of the As3+/As5+ ratio with x increasing from 50 to 10. The effect of melting temperature on the As3+/As5+ ratio in 30K2O-70SiO2-0.5As2O3 glasses at 1300° to 1600°C was also studied. No clear temperature effect could be concluded from the Raman spectra.

Raman Study of Arsenic‐Containing Potassium Silicate Glasses

Raman spectra are given of potassium silicate glasses with batch composition xK2CO3‐(100—x)SiO2‐0.5As2O3 in which x varies from 10 to 50. To isolate the contribution of the As2O3 additions to the spectra from that of the silicate network, difference spectra were prepared from spectra of glasses with and without As2O3 added to the batch. To obtain a precision sufficient for this purpose, the spectral data were collected in multiple scans under full computer control using photon counting and a correction for laser‐source fluctuations. It is concluded from the polarized and depolarized difference spectra that arsenic in potassium silicate glasses with x&gt;35 is mainly present in the pentavalent state as AsO43‐ ions. For glasses with x&lt;35 it is concluded that As5+ is present in As2O74‐ or As3O105‐ ions and As3+ as AsmO2m+1‐m‐2 chains of AsO3 pyramids. In these chains, m increases with decreasing x. From the intensity ratio of Raman peaks, caused by arsenite (As3+) and arsenate (As5+) ions in the glasses, it is concluded that there is a significant increase of the As3+/As5+ ratio with x increasing from 50 to 10. The effect of melting temperature on the As3+/As5+ ratio in 30K2O‐70SiO2‐0.5As2O3 glasses at 1300° to 1600°C was also studied. No clear temperature effect could be concluded from the Raman spectra.

Raman study of arsenic in potassium silicate glasses

A Raman study of arsenic in potassium silicate glasses: xK 2O. (1−x)SiO 2, with x = 0.2, 0.3, 0.4 and 0.5 is given. Difference spectra were prepared for glasses with and without an addition of 0.005 As 2O 3 in order to isolate the contribution of aresenic to the spectra from that of the silicate network. It is concluded that for the glass with x = 0.5 only pentavalent arsenic is present, as AsO 4 3−. At lower alkali concentrations part of the arsenic is in the trivalent state as (AsO 2 −) ∞ while As 5+ forms short chains of AsO 4 tetrahedra, probably As 2O 7 4−.

A molecular dynamic calculation of the structure of sodium silicate glasses

Molecular dynamic calculations of the structure of a series of sodium silicate glasses, a common soda–lime glass, a sodium borosilicate glass and a sodium–potassium silicate glass were made. Calculated radial distribution functions are in good agreement with existing x-ray diffraction data and a previous MD calculation on silica glass. During the dynamical runs alkali and alkaline earth cations cluster around nonbridging oxygen atoms. In the borosilicate glass studied, the boron atoms enter the silica network and are tetrahedrally coordinated by oxygen. Other features of the simulated glasses include the coordination number of cations, the degree of inhomogeneity, the distribution of bridging and nonbridging oxygen atoms, the Si–O–Si bond angles, the ring structure, etc. Some preliminary diffusion studies will be presented.

Raman Study of the Reactions in a Glass‐Forming Mixture with Molar Composition:30K2CO3‐70SiO2‐1As2O3

The results of a study of the reactions in a glass‐forming batch with molar composition 30K2CO3‐70SiO2‐lAs2O3 are given. Laser Raman spectroscopy was used for nondestructive identification of silicate, carbonate, arsenite (As3+), and arsenate (As5+) ions in the vitreous or crystalline state, occurring in quenched reaction mixtures. It is shown that in the first stage of melting a potassium‐rich liquid phase is formed, containing metasilicate chains (SiO2−3)x and carbonate ions, in which all arsenic is present in the pentavalent state as AsO13‐ ions. When this liquid phase reaches the final product glass composition the AsO13‐ ions condense to As2O4−7 (As5+) ions and AsO−2 (As3+) groups, during which process O2 is formed. The preliminary results of studies on crystalline and vitreous potassium arsenates and arsenites and of arsenic‐containing potassium silicate glasses are given for identifying arsenate and arsenite groups. It is argued that the reaction mechanism found describes the effectiveness of As2O3 as a fining agent. Contrary to the current view in the literature for the fining action of As2O3, which states that an O2 evolution which is triggered by a temperature increase causes fining, an important effect is found in the O2 evolution triggered by alkali oxide concentration variations during melting.

Raman Scattering of Carbonate Ions Dissolved in Potassium Silicate Glasses

Raman spectra of glasses, prepared from a mixture of K2CO3 and SiO2, give evidence for the presence of almost isolated planar CO32‐ ions, dissolved in the glass. It appears that measurement of the Raman spectra is a useful nondestructive method for the determination of the CO32‐ concentration in glasses.

Continuous dissolution of sodium and potassium silicate glass in a tower dissolver

AbstractSodium and potassium silicate glass was continuously dissolved in a tower dissolver operated at atmospheric pressure. In pilot experiments the rate, controlled by the dissolution process occurring at the glass/liquor interface, was dependent on surface area, temperature, type, and chemical composition of the glass, but was independent of concentration and flowrate. Activation energies for the dissolution process lay in the range 22‐48 kJ/mol, while typical rates of dissolution were 26 and 21 kg m−3 h−1 for 2.0 and 3.2 SiO2/Na2O weight ratio sodium silicate glass at 99°C. The corresponding rate for potassium silicate glass of SiO2/K2O weight ratio 2.0was 195 kgm−3h−1 at 80°C. Loss of potassium silicate due to the formation of insoluble compounds was prevented by operating below 93°C. Tower dissolvers warrant further consideration as an alternative to conventional digestors, having the advantages of continuous operation and uniform product density.

Continuous dissolution of sodium and potassium silicate glass in a tower dissolver

Sodium and potassium silicate glass was continuously dissolved in a tower dissolver operated at atmospheric pressure. In pilot experiments the rate, controlled by the dissolution process occurring at the glass/liquor interface, was dependent on surface area, temperature, type, and chemical composition of the glass, but was independent of concentration and flowrate. Activation energies for the dissolution process lay in the range 22-48 kJ/mol, while typical rates of dissolution were 26 and 21 kg m−3 h−1 for 2.0 and 3.2 SiO2/Na2O weight ratio sodium silicate glass at 99°C. The corresponding rate for potassium silicate glass of SiO2/K2O weight ratio 2.0was 195 kgm−3h−1 at 80°C. Loss of potassium silicate due to the formation of insoluble compounds was prevented by operating below 93°C. Tower dissolvers warrant further consideration as an alternative to conventional digestors, having the advantages of continuous operation and uniform product density.

Compound‐Glass Waveguides Fabricated by a Metal Evaporation Technique

Glass fiber optical waveguides consisting of a potassium silicate glass core and SiO2 cladding were produced by a potassium metal evaporation technique. An evacuated fused‐silica tube containing an evaporated deposit of K was heated to temperatures sufficient to form a uniform potassium silicide layer on its inner surface. This layer was oxidized and reacted with the SiO2tubing at high temperatures to form a potassium silicate glass. The tube was then collapsed to give a solid rod preform with a potassium silicate core. Fibers drawn from such preforms exhibit moderately low optical loss. The fabrication technique is described, and a representative loss spectrum is presented.

Infrared absorption spectra of lithium and potassium silicate glasses at high pressure

Infrared absorption spectra of five lithium silicate and six potassium silicate glasses of varying composition (20–35 mole% Li2O and 15–40 mole% K2O, respectively) are examined in the range 1500–100 cm−1. The frequencies of the main absorption bands decrease with an increase of alkali-metal oxide (M2O) content, with the exception of the −960 cm−1 shoulder for the lithium silicate glasses. The pressure dependences to [inverted lazy s]40 kbar, of all the main infrared absorption frequencies, which are pressure sensitive, are found to be positive. The values of d νi/d P are higher for potassium silicate glasses than for sodium and lithium silicate glasses. The effects of pressure are found to be opposite to the compositional effects. The Grüneisen mode γ's, γi, evaluated from the pressure dependence of the infrared absorption frequencies, are apparently related to the polarizing power of the alkali-metal ion. The results discussed in light of previous high-pressure infrared absorption studies of fused silica and sodium silicate glasses clearly indicate that γi, γth, and γHT generally increase with M2O content in alkali silicate glasses.

On two types of luminescence centers in sodium silicate and potassium silicate glasses activated by trivalent dysprosium

On two types of luminescence centers in sodium silicate and potassium silicate glasses activated by trivalent dysprosium