Structure and properties of high Li2O-containing aluminophosphate glasses

The present study reports on the characterisation of the structure and properties of 50Li₂O·xAl₂O₃·(50 ? x)P₂O₅ glasses. The objective of the work has been to study the influence of the alumina content on the properties of lithium phosphate glasses, and the room temperature ionic conductivity in particular, with potential application as solid electrolytes in lithium secondary batteries. The glass formation domain has been also determined, proving that Al₂O₃ can be introduced only up to 5 mol%. The addition of alumina results in the increase of the glass transition temperature and decrease of the molar volume of the glasses. Furthermore, both chemical durability and room temperature conductivity increase as a function of the alumina content. The structure of the glasses has been followed by means of Fourier-transformed infrared spectroscopy (FTIR) and NMR spectroscopy, which has been used to establish the structure–properties relationship.     

Structural dependence of chemical durability in modified aluminoborate glasses

Alkali and alkaline earth aluminoborate glasses feature high resistance to cracking under sharp contact loading compared to other oxide glasses. However, due to the high content of hygroscopic B₂O₃, it is expected that applications of these glasses could be hindered by poor chemical durability in aqueous solutions. Indeed, the compositional and structural dependence of their dissolution kinetics remains unexplored. In this work, we correlate the dissolution rates of aluminoborate glasses in acidic, neutral, and basic solutions with the structural changes induced by varying the aluminum-to-boron ratio. In detail, we investigate a total of seventeen magnesium, lithium, and sodium aluminoborate glasses with fixed modifier content of 25 mol%. We show that the structural changes induced by alumina depend on the network modifier. We also demonstrate a correlation between the chemical durability at various pH values and the structural changes in Mg-, Li- and Na-aluminoborate glasses. The substitution of alumina by boron oxide leads to a general decrease in chemical corrosion in neutral and acidic solutions. The lowest dissolution rate value is observed in Mg-aluminoborate glasses, as a consequence of the intermediate character of magnesium which can increase the network cross-linking. For basic solutions, the chemical durability is almost constant for the different amount of alumina in the three series, likely because B₂O₃ is susceptible to nucleophilic attack, which is favored in high-OH⁻ solutions.     

Bioactive glasses and direct effect of increased K2O additive for nuclear shielding performance: A comparative investigation

This study aimed to provide a large-scale investigation on direct effect of K₂O additive nuclear radiation shielding properties of calcium phosphate based bioactive quaternary P₂O₅–CaO–Na₂O–K₂O glasses. A gamma ray attenuation setup has been modeled in MCNPX (v-2.6–0) simulation code using Monte Carlo simulation technique. Next, all the bioactive glasses have been defined considering their chemical properties and material densities, respectively. The mass attenuation coefficients (MAC) have been calculated by using MCNPX code and obtained results have been used for determination of another vital gamma-ray shielding parameters. Moreover, a detailed calculation has been done for determination of exposure buildup factor (EBF) and energy absorption buildup factor (EABF) of investigated bioactive glasses which should be considered as important parameters for interaction properties of ionizing radiation with material environment. In addition, effective removal cross sections for fast neutrons have been calculated. To compare our results, obtained HVL values of the present investigation have been compared with copper oxide and cobalt oxide substituted bioactive glasses. Among the investigated bioactive glasses, the maximum MAC values were reported for PCNK60 sample with higher K₂O additive. It can be concluded that chemical structure of additive materials in the bioactive glasses is strongly related with the radiation attenuation properties of bioactive glasses.     

Surface Analysis of Cr2O3‐, CoO‐, and Al2O3‐Doped Iron–Phosphate Glasses at High Temperature

Surface structures of iron–phosphate glasses were examined using X‐ray photoelectron spectroscopy (XPS). Cr₂O₃, CoO, and Al₂O₃ were introduced to the glass by the replacement of a part of Fe₂O₃, and the simulated fission products are also added. The obtained glasses showed high chemical durabilities by MCC‐1 test. In situ high‐temperature and room‐temperature XPS measurements were conducted on the polished sample surfaces and also those after 1‐week chemical durability test. Unique trends were observed in XPS spectra on heating and after the chemical durability test, respectively. Nature of the glass surface of iron–phosphate glasses was explained from the point of view of surface energy, and the origin of high chemical durability and the effect of chromium ions were discussed based on the changes on surface composition and valence states of transition‐metal ions.     

Electrical conductivity and structure of glasses in the Na<Subscript>2</Subscript>O-Na<Subscript>2</Subscript>S-P<Subscript>2</Subscript>O<Subscript>5</Subscript> and Na<Subscript>2</Subscript>S-P<Subscript>2</Subscript>S<Subscript>5</Subscript> systems

The glasses, in which oxygen was partially replaced with sulfur, have been synthesized in the Na₂O-P₂O₅-Na₂S system. The chemical and chromatographic analyses of the glasses synthesized have been performed. The temperature-concentration dependences of electrical conductivity of the glasses have been studied over a wide temperature range; the glass transition temperatures and the nature of charge carriers have been determined. The IR spectra and Raman spectra have been recorded at room temperature; the density and microhardness of the glasses and ultrasound velocity have been measured. A comparison of the electrical conductivities of the investigated glasses with those of the earlier studied glasses in the Na₂O-P₂O₅ system has shown their fair coincidence. The introduction of sodium sulfide into the Na₂O-P₂O₅ system is accompanied by an approximately threefold increase in electrical conductivity, although the concentrations of charge carriers (sodium ions) in the glasses amount to ∼17 and ∼26 mmol/cm³, respectively. The rise in electrical conductivity has been assumed to be caused by the increase in the degree of dissociation of polar structural chemical units including sulfide ions and by the higher mobility of sodium ions in the oxygen-free matrix.     

Electret Properties of Radiation-Charged Phosphate Glasses

The process of formation of a surface charge in phosphate glasses depending on polarization conditions is investigated. A relationship is established between the chemical composition of glass and its capacity for forming internal electric fields under radiation for glasses of type 0.50P₂O₅ – 0.45RO – 0.05R₂O₃.     

Reduction of crystallization ability of sodium zinc phosphate glass under X-ray radiation

The effect of X-ray radiation on the crystallization ability of maximally homogenized sodium zinc phosphate glass with a minimal light scattering value of V _v = 4 × 10^?6 cm^?1 has been investigated. The crystallization kinetics of the sodium zinc phosphate glass of the 33.9P₂O₅ · 56.6ZnO · 9.5Na₂O (mol % from analysis) composition under the conditions of homogeneous nucleation and X-ray radiation have been studied. It has been demonstrated that the crystallization properties of phosphate glasses are more sensitive to the synthesis method than those of silicate glasses. It has been established that sodium zinc phosphate glass crystals represent the main crystalline phase precipitated in the glass of the above composition. The main parameters of nucleation have been determined in glass without preliminary radiation, including stationary nucleation rate I _st, nonstationary nucleation time ??, and nucleation activation energy E _??. It have been found that the effect of the CuK _?? X-ray radiation leads to the slowing down or even cessation of the nucleation of crystals in glass (the result depends on the change in the radiation intensity along the sample depth) in the case when radiation takes place immediately during the nucleation thermal treatment of the sample in a high-temperature chamber of the X-ray device. The kinetics of sodium zinc phosphate crystallization in the samples upon their pretreatment by CuK _?? X-ray irradiation has been investigated. It has been shown that the rate of crystal nucleation in glasses exposed to X-ray radiation is lower than that in glasses without preliminary irradiation.     

Effect of Al2O3 addition on the thermal expansion of sodium alkaline-earth silicate glasses: A molecular dynamics study

Coefficient of thermal expansion (CTE) is an important property to consider when utilizing oxide glasses in thermal treatment processes to avoid thermal damage at the interfaces of the glasses with heterogeneous materials. It is thus important to know the effect of additives on CTE for designing glasses. The use of alumina efficiently improves chemical and mechanical durability of oxide glasses while maintaining the functionality and productivity; however, alumina-doping often induces nonlinear variation of CTE. In this work, we therefore tried to investigate the relationship between CTE and the microstructure of sodium alkaline-earth aluminosilicate glasses using classical molecular dynamics (MD) simulations. To accurately model the glasses, we extended a force-matching potential by optimizing the parameter sets for Ca–O, Mg–O, and Na–O pair interactions using Bayesian optimization. The MD simulations reproduced the nonlinear variation of CTE as a function of alumina content, and detailed structural analyses identified inhomogeneous expansion in the glasses. It was found that the nonuniform CTE change at the nanoscale was related to the formation of an alumina-rich region, in which more fivefold-coordinated aluminum exist, when alumina content exceeded Na₂O content. Accordingly, the microstructural change by alumina-doping was identified as the origin of the nonlinear variation in the CTE of the glasses.     

Thermal properties of ecological phosphate and silicate glasses

The present work deals with ecological phosphate and silicate glasses that belong to the oxide systems: Li₂O-MgO-P₂O₅, Li₂O-CaO-P₂O₅, Li₂O-MgO-P₂O₅-Fe₂O₃; Li₂O-CaO-P₂O₅-Fe₂O₃ and SiO₂-R₂O-R′O (R = Na, K; R′ = Mg, Ca), the last system contains certain amounts of ZrO₂, ZnO, TiO₂. These ecological glasses do not contain toxic substances as BaO, PbO, As₂O₃, As₂O₅, fluorine, CdS, CdSe and they have applications as regards the retention and counteracting action of the harmful compounds resulted from the nuclear plants. The replacement of MgO by CaO leads to an insignificant increasing of the thermal expansion index and a slight decreasing of the characteristic temperatures, except the softening point where the effect is opposite. Adding of iron oxide in the phosphate glass composition causes the increasing of characteristic temperatures and the decreasing of thermal expansion index, both in MgO and CaO-containing phosphate glasses. The ecological silicate glasses are used as opal glasses free of fluorine as well as for lead-free crystal glass (CFP) where BaO and PbO are replaced by non-toxic oxides as K₂O, MgO, ZrO₂, and TiO₂. The paper presents different glass compositions and the technological parameters to prepare the ecological glass samples. Both ecological phosphate and silicate glasses have been characterized as regards the characteristic temperatures (vitreous transition point, low and high annealing points, softening point) and the thermal expansion coefficient. This study presents the changes of the thermal parameters when CaO replaces MgO in phosphate glass samples and the role of iron oxide in the vitreous network. In the case of silicate glasses, the viscosity and wetting angle dependency of temperature are presented. The elemental analysis of the ecological glasses was made by XPS (X-ray photoelectron spectroscopy) which also put in evidence the iron species from the vitreous network.     

Thermal analysis of plasma sprayed oxide coatings sealed with aluminium phosphate

Thermal analysis by thermogravimetry and differential scanning calorimetry was carried out for plasma-sprayed alumina and chromia coatings to study their stability after plasma spraying and for aluminum phosphate sealant to study phosphate reactions during the sealing heat treatment. Thermogravimetric analysis for alumina coating did not show any change in the coating due to the heat treatment, though the phase structure had changed from metastable γ-Al₂O₃ to stable α-Al₂O₃. In the chromia coating thermogravimetric analysis showed 1.7 wt.% weight increase due to the oxidation of the sprayed coating. During plasma-spray process the chromia coating had gained some under-stoichiometry or some of the chromia had decomposed into metallic chromium or other oxides. Thermal analysis for aluminum phosphate sealant showed weight loss of about 27 wt.%. This corresponds well to the formation of metaphosphates via dehydration of aluminum phosphate solution during the sealing heat treatment. Thermal analysis for the mixture of sealant and alumina coating showed slightly different behaviour than plain sealant. The sealant reacted with the alumina coating forming a crystalline phase, berlinite-type orthophosphate AlPO₄. Thermal analysis for the mixture of sealant and chromia coating showed nearly similar behaviour than plain sealant and no indications of the chemical reactions were detected.     

Structure and electrical conductivity of glasses in the Na<Subscript>2</Subscript>O-Na<Subscript>2</Subscript>SO<Subscript>4</Subscript>-P<Subscript>2</Subscript>O<Subscript>5</Subscript> system

The temperature-concentration dependence of the electrical conductivity of glasses in the Na₂SO₄-NaPO₃ and Na₂O-P₂O₅ systems has been investigated. Based on the obtained experimental data (IR spectra, density, microhardness, sound velocity, and paper chromatography), it has been demonstrated that SO₄²⁻ ions form terminal groups through the incorporation into polyphosphate fragments of the structure of glasses in the Na₂SO₄-NaPO₃ system. An increase in the electrical conductivity of glasses in this system by a factor of ∼1000 (as compared to NaPO₃) at 25°C and a decrease in the activation energy for electrical conduction from 1.40 to 1.10 eV have been interpreted from the viewpoint of the decrease in the dissociation energy E _d of polar sulfate phosphate structural chemical fragments formed in the glass bulk upon introduction into sodium metaphosphate Na₂SO₄. This leads to an increase in the number of dissociated sodium ions, which are charge carriers, and to a decrease in the energy (E _a) of their activation shift in the sublattice formed by sulfate phosphate fragments of the structure.     

Mechanical properties of phosphate glasses as a function of the total bonding energy per unit volume of glass

The dependences of the structural strength and the elastic modulus on the chemical composition of phosphate glasses are analyzed. The structural strength and the elastic modulus of phosphate glasses are determined for different types of both the modifier ion and the second glass-former (B₂O₃ or SiO₂) introduced into the glass. The total bonding energy per unit volume of the glass is calculated from the data on the dissociation energy for the oxides entering into the glass composition and the data on the atomic packing density. For four systems of phosphate glasses, it is demonstrated that the Young’s modulus depends linearly on the total bonding energy per unit volume of the glass. The dependence of the structural strength on the chemical composition exhibits a more complex behavior and is governed by other additional factors, such as the formation of new structural groups or the change in the structure of the anionic network of the glass. Original Russian Text ? L.G. Baikova, V.P. Pukh, Yu.K. Fedorov, A.B. Sinani, L.V. Tikhonova, M.F. Kireenko, 2008, published in Fizika i Khimiya Stekla.     

Glass formation and electrical conductivity of glasses in the Na<Subscript>2</Subscript>Se-P<Subscript>2</Subscript>Se<Subscript>5</Subscript> system in a wide temperature range

The glass formation region in the Na₂Se-P₂Se₅ system and the temperature-concentration dependences of the electrical conductivity of glasses have been investigated over a wide range of temperatures. The densities and glass transition temperatures T _g of glasses have been determined. A comparison of the electrical conductivity of glasses in the Na₂Se-P₂Se₅ and Na₂O-P₂O₅ systems has demonstrated that the conductivity of selenium-containing glasses (at 25°C) is approximately three orders of magnitude higher than the electrical conductivity of oxide glasses. The assumption has been made that an increase in the electrical conductivity of glasses with selenium is caused by the increase in the degree of dissociation of Na⁺[Se⁻PSe_3/2] polar structural chemical units and the higher mobility of sodium ions in the oxygen-free matrix.     

On the fluctuation structure of single-phase glasses in the SrO-B<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript> system

The structure of single-phase glasses in the SrO-B₂O₃-SiO₂ system has been studied by the small-and large-angle X-ray scattering technique. The glasses containing 35, 40, and 45 mol % SrO upon equimolar replacement of B₂O₃ by SiO₂ have been investigated. It has been demonstrated that the glasses do not contain chemical inhomogeneity regions. The inhomogeneity of the glasses is determined only by thermal density fluctuations. The isothermal compressibility varies insignificantly upon replacement of B₂O₃ by SiO₂ and decreases with an increase in the SrO content. The glass structure is consistent with the model of ideal associated solutions.     

High Glass Transition Temperature Barium Silicophosphate Glasses Designed with Topological Constraint Theory

Alkali‐free glasses have attracted tremendous attentions for their high glass transition temperature (T_g). Such a feature broadens their potential applications, especially in the area of high‐density and high‐power laser glasses. BaO–P₂O₅ glasses, as one of the major matrix materials due to its high‐T_g, can be applied in high‐power laser glasses. Introducing SiO₂ is an effective method to improve the thermal, refractive index, and mechanical properties of phosphate glasses. Herein, we studied the barium silicophosphate glasses with MAS NMR and the T_g was successfully calculated by the topological constraint theory. The designed glass (20BaO–26.7SiO₂–53.3P₂O₅, mol%) with a high T_g (789K) was prepared and it also exhibited high refractive index and high Vickers hardness, suggesting the barium silicophosphate glasses have widespread applications in high‐power laser glasses and optical fibers.     

Development and mechanical characterization of Al2O3 platelet-reinforced glass matrix composites obtained from glasses coming from dismantled cathode ray tubes

A cold-pressing and pressure-less viscous flow sintering treatment for the manufacturing of dense alumina platelet-reinforced glass matrix composites was proposed for the recycling of glasses coming from dismantled cathode ray tubes (CRTs). Mixtures of three different glasses from CRTs and Al₂O₃ platelets were investigated regarding the introduction in glass of rigid, non-sintering, inclusions and the nature of the matrix glasses. An innovative short-time sintering procedure was found to be advantageous, leading to significant increases in bending strength, microhardness and fracture toughness, despite the relatively low Al₂O₃ platelet addition. Both the morphology of the residual porosity, due to the sintering process and particular chemical and physical interactions within the matrix, and the crack deflection effect, due to the specific matrix-reinforcement combination, were found to be the determinant of the observed mechanical properties. The obtained bending strength, Vickers’ microhardness and fracture energy are comparable to the values reported for glass-ceramics for technical applications in the building industry.     

Enhancement of the radiation resistance of cerium-containing fluorophosphate glasses through codoping with Sb2O3 and Bi2O3

The growing demand for radiation-resistant optical glasses for space and nuclear radiation applications has attracted significant research interest. However, radiation-resistant fluorophosphate glasses have been poorly studied. In this work, we report on the tailoring and performance of radiation-resistant fluorophosphate glasses that contained cerium through codoping with Sb₂O₃ and Bi₂O₃. The physical properties, optical properties, microstructure, and defects of fluorophosphate glasses were investigated using transmittance measurements, absorption measurements, as well as Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and electron paramagnetic resonance (EPR) spectroscopy. The results showed that the radiation resistance of all codoped fluorophosphate glasses was better than the undoped cerium-containing fluorophosphate glasses after 10–250 krad(Si) irradiation. Especially in glasses doped with Bi₂O₃, the optical density increment at 385 nm was only 0.1482 after 250 krad(Si) irradiation. The CeO₂ prevented the development of phosphate-related oxygen hole center (POHC) defects, whereas further codoping with Bi₂O₃ suppressed the formation of oxygen hole center (OHC) and POEC defects, reducing the breaking of phosphate chains caused by CeO₂. Bi³⁺ is more likely than Sb³⁺ to change the valence, affecting the transition equilibrium of intrinsic defects and reducing the concentration of defects produced by irradiation. When codoping with Sb₂O₃ and Bi₂O₃, Bi₂O₃ does not enhance radiation resistance owing to the scission effect of Sb₂O₃ on the phosphate chain, which is not conducive to the radiation resistance of glasses. This indicates that the cerium-containing fluorophosphate glasses doped with Bi₂O₃ can effectively suppress the defects caused by irradiation and improve the radiation resistance of the glasses.     

Dissolution,bioactivity behavior,and cytotoxicity of rare earth-containing bioactive glasses (RE = Gd,Yb)

Rare earth-containing bioactive glasses (RE-BGs) have been poorly explored in the biomaterials field, although RE has optical, nuclear, and magnetic properties that could be used in different biomedical applications. In order to verify whether these glasses can be promising as biomaterials, we studied the dissolution, bioactivity, and cytotoxicity of RE-BGs based on the SiO₂–Na₂O–CaO–P₂O₅–RE₂O₃ (RE = Gd, Yb) system. The glasses were obtained by melting-quenching and their particle size was determined by laser diffraction. Their dissolution behavior was studied in Tris-HCl, while bioactivity was performed in simulated body fluid solution under physiological conditions during several periods. The cytotoxicity test was performed using glass-derived conditioned medium and mesenchymal stem cell derived from deciduous teeth. The dissolution results showed that the glasses dissolved under two different kinetics, which are lower for rare earth-containing glasses, due to the more covalent character of Si–O–RE bonds. The bioactivity results evidenced that all glasses showed bioactivity after 24 hours. However, gadolinium and ytterbium promoted a more calcium phosphate deposition, which contrasts with the slower dissolution kinetics of rare earth-containing glasses. All the glasses were considered biocompatible, showing cell viability higher than 80%. The overall results showed that RE-BGs are promising materials for applications that require bioactivity and/or biocompatibility.     

Gel-derived SiO2–CaO–P2O5 bioactive glasses and glass-ceramics modified by SrO addition

The effect of SrO substitution for CaO in two sol–gel glasses with different chemical compositions (mol%) A2Sr: (54−x)CaO–xSrO–6P₂O₅–40SiO₂ and S2Sr: (16−x)CaO–xSrO–4P₂O₅–80SiO₂ (x=0, 1, 3 and 5) stabilized at 700 °C on their structure (XRD, FTIR) and bioactive properties (SBF test) was investigated. Preliminary in vitro tests using human articular chondrocytes of selected A2Sr glass were also conducted. Moreover, the subject of this study was to detect the changes on material properties after heat treatment at 1300 °C. The results show that the effect of strontium substitution on structure, bioactivity and crystallization after treatment at both the above temperatures strongly depends on CaO/SiO₂ molar ratio. The presence of 3–5 mol% of strontium ions creates more expanded glass structure but does not markedly affect crystallization ability after low temperature treatment. Sintering at 1300 °C of A2 type glasses results in crystallization of pseudowollastonite, hydroxyapatite and also Sr-substituted hydroxyapatite for 3–5 mol% of SrO substitution. The increase of strontium concentration in silica-rich materials after sintering leads to appearance of calcium strontium phosphate instead of calcium phosphate. Bioactivity evaluation indicates that substitution of Sr for Ca delays calcium phosphate formation on the materials surface only in the case of silica-rich glasses treated at 700 °C. Calcium-rich glasses, after both temperature treatments, reveals high bioactivity, while crystal size of hydroxyapatite decreases with increasing Sr content. High temperature treatment of high-silica glasses inhibits their bioactivity. Preliminary in vitro tests shows Sr addition to have a positive effects on human articular chondrocytes proliferation and to inhibit cell matrix biomineralization.     

Comparative studies on the bioactivity of some borate glasses and glass–ceramics from the two systems: Na2O–CaO–B2O3 and NaF–CaF2–B2O3

Combined FTIR spectroscopy and X-ray diffraction analysis have been employed to investigate the bone-bonding ability or bioactivity of some prepared borate glasses and their glass–ceramic derivatives from the two systems (Na₂O–CaO–B₂O₃) and (NaF–CaF₂–B₂O₃). The present study includes the mentioned FTIR spectral and X-ray analytical techniques before and after immersion of the glasses and glass–ceramics for 2 weeks in 0.025 M sodium phosphate (Na₂HPO₄) solution. Also, the work extends to evaluate the corrosion behavior for specified grains of the studied samples (0.3–0.6 mm) after immersion in phosphate solution for 2 weeks at 37 °C. The FTIR spectra of the two glass systems after immersion show some changes in the vibrational bands than before immersion. The generation of the characteristic peaks at about 580 and 680 cm⁻¹ after immersion confirms the bone bonding ability by the formation of hydroxyapatite phase. The X-ray diffraction studies show the separation of (CaF₂) which is known to be an efficient nucleator. Weight loss data show a difference in solubility in the sodium phosphate solution between fluoride and oxide glass systems due to the strong action of the leaching solution and ease of solubility of fluoride glasses than corresponding oxide glasses in this solution. SEM data indicate the formation of small rounded or nodular shape crystals which are characteristics for the formation of hydroxyapatite layer and complete agreement with X-ray data.