Binary Potassium Silicate Glasses Research Articles

Potassium-silicate glass foil irradiated with electrons – Asymmetry in migration and space distribution given by the elastic scattering of electrons on potassium atoms

Binary potassium silicate glass 15K2O·85SiO2 was prepared in the form of a thin foil and was irradiated with electrons in the transmission mode. A defocused beam of 10, 20, 30, and 50 keV energy was used to prevent a significant temperature increase. Both, the front and back surfaces were depleted of potassium by the irradiation, but not to the same extent; the front surface was quickly fully depleted of potassium, but the backside only partially. The potassium depth distribution was not consistent with the assumed shape of the electric field established in the solid, but was significantly shifted from the middle of the foil. The found asymmetry is due to the momentum transfer from the elastic scattering of the incident electron to the potassium ion, which acts as an additional effective force.

Potassium-silicate glass exposed to low energy H+ beam

Pristine surface of binary potassium silicate glass 85SiO2·15K2O was prepared in vacuum and irradiated with a 5keV proton beam within the range of 0.6–103C/m2. The response of glass surface was monitored by XPS and the evolution of atomic concentrations divided it into two stages. During the first one, amounts of both potassium and non-bridging oxygen (NBO) increase in the surface layer and are governed by surface relaxation. The second stage is characterised by a continuous decrease of NBO and K. Comparison of K and NBO concentrations yielded a constant surplus of K proving the existence of potassium elemental state on the glass surface. Ratio of bridging oxygen (BO) and silicon is conserved during proton bombardment. The extrapolation of the glass response to the enhanced irradiation predicts a formation of substoichiometric SiOx with some elemental K on the topmost surface.

Reduced Young modulus and hardness of electron irradiated binary potassium-silicate glass

Binary potassium silicate glass of composition 15mol%K2O+85mol%SiO2 was irradiated with 50keV electrons. Dependence of mechanical properties of the irradiated glass on electron doses were measured by means of nanoindentation. The reduced Young modulus and hardness decrease for higher doses. The changes in mechanical properties are dominantly determined by the density variation and silica network depolymerisation during the electron bombardment.

Ion Transport Mechanism in Glasses: Non-Arrhenius Conductivity and Nonuniversal Features

In this article, we report non-Arrhenius behavior in the temperature-dependent dc conductivity of alkali ion conducting silicate glasses well below their glass transition temperature. In contrast to the several fast ion-conducting and binary potassium silicate glasses, these glasses show a positive deviation in the Arrhenius plot. The observed non-Arrhenius behavior is completely reproducible in nature even after prolonged annealing close to the glass transition temperature of the respective glass sample. These results are the manifestation of local structural changes of the silicate network with temperature and give rise to different local environments into which the alkali ions hop, revealed by in situ high-temperature Raman spectroscopy. Furthermore, the present study provides new insights into the strong link between the dynamics of the alkali ions and different sites associated with it in the glasses.

Binary potassium-silicate glass irradiated with electrons

Binary potassium-silicate glass of composition 15 mol% K 2O + 85 mol% SiO 2 was irradiated with 2.5 MeV. The thickness of glass was chosen so as electrons stopped near the back surface. After the high-energy irradiation both, back and top surfaces, were depleted from potassium; the back surface was depleted more than the top one. The decay curves were recorded on pristine glass, and on top and back surfaces of the glass pre-irradiated with high-energy electrons. The incubation times of the top surface increased while the incubation time of the back one decreased in comparison with the pristine glass. Observation of the volume changes induced by the following impaction of 50 keV revealed the top surface is closer to the pristine glass than the back one.

Test of the Anderson–Stuart model and correlation between free volume and the ‘universal’ conductivity in potassium silicate glasses

Following recent finding it is shown that using conductivity and molar volume in binary potassium silicate glasses (considering the same batches) there is a common cubic scaling relation between them due to increase in alkali content. Emphasis is placed on the application of Anderson–Stuart model to describe the variation of activation enthalpy for conduction E A with potassium concentration. In this analysis were considered experimental parameters, like shear modulus G and relative dielectric permittivity ɛ, in wide composition range (between 1.7 and 40 K 2O mol%). The effects of G, ɛ and free volume are taken into account. The drastic drop in conductivity up to 17 orders of magnitude for so many ion-conducting binary alkali silicate glasses is then mainly caused by the structure and the ion content. In particular, it is suggested that the glass network expansion, which is related to the available free volume, is a parameter that could explain the increase in ionic conductivity for this binary system.

Changes in surface morphology of silicate glass induced by fast electron irradiation

Binary potassium-silicate glass was irradiated with a defocused electron beam. During the irradiation the alkali ions migrate from the surface into the depth and alkali ions depleted layer is created near the surface. Such changes in the chemical composition are also accompanied with changes of the glass structure and finally result in the volume changes of the irradiated glass. This was directly studied using atomic force microscope (AFM). A series of exposures with energy of electrons of 7–50 keV and with different doses were performed. For low doses the irradiated glass is continuously depressed with the increasing dose, indicating this way the structural changes leading to the volume compaction. It is suggested the compaction is caused by the relaxation processes of the silica subnetwork. A further increase of the electron dose causes a formation of the small bump inside the center of the depression. The bump arises with the dose and finally exceeds the surrounding surface. It is suggested that the expansion is connected with the migration of alkali ions and the formation of Si–O–O–Si bonds which result in the formation of new rings with new space requirements.

Partial volumes and volume fluctuations in potassium-silicate glass: Molecular dynamic simulations

Partial volumes and partial volume fluctuations were studied by means of Voronoi polyhedra (VP) in binary potassium-silicate glass simulated by molecular dynamics. The volume fluctuation of VP turned to be a sensitive indicator of the structural changes induced by conditions, under which glass was prepared. Volume fluctuations distinguish between the static (given by the frozen structural disorder) and dynamic (given by kinetics) contributions to the overall fluctuations. The glass transition was identified with the point where the dynamic volume fluctuation achieve the space-related fluctuation frozen in glass.

NMR study of Q-speciation and connectivity in K 2O–SiO 2 glasses with high silica content

The structure of binary potassium silicate glasses with SiO 2 content ranging between 76.0 and 97.6 mol% has been studied with 29Si and 17O NMR spectroscopy. Besides the Q 3 species, two broadly different types of Q 4 species have been identified in the 29Si MAS NMR spectra of glasses with >83.5 mol% SiO 2. These species correspond to Q 4 connected to one or more Q 3 nearest neighbors and Q 4 with only Q 4 nearest neighbors, and are denoted as Q 4–3 and Q 4–4, respectively. The compositional variation of the concentration of Q 4–3 species implies a statistically random distribution of Q 3 and Q 4 species in these glasses. Such a silicate network with random connectivity between Q 3 and Q 4 species is shown to be consistent with the strongly non-linear compositional variation of the transport properties of binary alkali silicate glasses with high silica content.

Voronoi polyhedra analysis of MD simulated silicate glasses

The relationship between the volume and the surface of Voronoi polyhedra (VP) appeared to be an effective tool for the characterization of the structure of MD simulated silicate glasses. This feature was demonstrated on the series of binary potassium-silicate glasses with the alkali content ranging from 5 to 20 mol%. Moreover, the temperature dependence of the slope of the above dependence, when expressed for various types of central atoms (Si, O and K in our case) was studied. Each type of central atom is characterised by its own iron line linearly relating the volume of VP to its properly powered surface, so that new geometrical constrains to the VP was found.

Molecular dynamic modelling of potassium transport in a potassium-silicate glass irradiated by fast electrons

The binary potassium-silicate glass has been prepared from an ionic liquid by molecular dynamics (MD) using 900 ions interacting via Born–Mayer type pair potentials. The standard MD procedure was adapted so that an electric field and/or momentum transfer, corresponding to the elastic scattering of primary electrons, could be applied to a particular set of ions. Results have shown that the electric field itself should cause dielectric breakdown to drive the ions out of their sites. If the electric field is accompanied by momentum transfer from the primary electron, then potassium ions can be released from their sites and can be further driven by the macroscopic electric field, created by trapped electrons in the glass. The depth and width of the potassium potential well has been estimated by studying the motion of ions in a high electric field.

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