Low-melting glasses based on phosphate ore processing products

The possibility of producing low-melting glasses using phosphate ore processing products as batch components is investigated. Glasses of various shades of green, yellow, and brown with satisfactory properties are synthesized. The resulting glasses have a unique decorative effect imitating the gem texture. Translated from Steklo i Keramika, No. 5, pp. 3–5, May, 2000.     

Influence of the micro-addition of Mo on glass forming ability and corrosion resistance of Cu-based bulk metallic glasses

(Cu₄₇Zr₁₁Ti₃₄Ni₈)_100−xMo_x bulk metallic glasses (BMGs) with x = 0, 1 and 2 at.% and a bulk metallic glass matrix composite with x = 5 at.% were successfully prepared by water-cooled copper mold casting. The effect of the addition of a small amount of Mo on the glass forming ability (GFA), thermal properties of the base alloy (i.e. x = 0) were investigated by X-ray diffraction (XRD), differential scanning calorimetry (DSC) and differential thermal analyzer (DTA). It is found that the addition of appropriate amount of Mo can enhance the GFA of the Cu-based BMG, as indicated by the increase in the reduced glass transition temperature T_rg (=T_g/T_l) and the parameter γ (=T_x/(T_g + T_l)) with the increase of Mo. On the other hand, the corrosion resistance of the Cu-based BMGs with different Mo contents was examined by electrochemical polarization and weight loss measurement in 1 mol/L H₂SO₄ and 1 mol/L NaOH solutions, respectively. It is found that the corrosion resistance of Cu-based BMGs increased with increasing Mo content with the lowest corrosion rate of (0.9 ± 0.2) × 10⁻³ mm/year in 1 mol/L H₂SO₄ solution and (0.3 ± 0.1) × 10⁻³ mm/year in 1 mol/L NaOH solution, respectively, for the BMG containing 2 at.% Mo. X-ray photoelectron spectroscopy (XPS) results revealed that the improvement of corrosion resistance of Cu-based BMG containing appropriate amount of Mo originated from the enrichment of ZrO₂ and TiO₂, but depletion in Cu- or Ni-oxides in the passive films formed during electrochemical polarization. Finally, the galvanostatic-step measurement was performed to investigate the kinetics of the formation of passive films on the BMG surfaces. It is demonstrated that the addition of an appropriate amount of Mo can effectively improve the stability and uniformity of the passive film. The role of Mo addition on the glass forming ability and corrosion behavior is discussed.     

Bone bonding ability behavior of some ternary borate glasses by immersion in sodium phosphate solution

Some ternary borate glasses of varying compositions were prepared and corrosion behaviors of such ternary borate glasses after immersion in aqueous dilute phosphate solution were studied using different immersion times. Fourier transform infrared (FTIR) absorption spectral measurements were done before and after immersion in the mentioned solution for extended times up to 3 days to justify the appearance of the characteristic FT infrared bands due to calcium phosphate (hydroxyapatite (HA)) which is considered as the potential indication of bone bonding ability.Experimental IR data confirm the beginning of the appearance of FTIR bands at about 580 and 650 cm⁻¹ after 1 day and the complete resolution with its characteristic split form after 3 days and more.The corrosion behavior of the studied borate glasses is explained in relation to a suggested hydrolysis and direct dissolution mechanism. The ease of dissolution of all the borate glasses constituents explains the rapid conversion and formation of hydroxyapatite within the borate glass matrix as indicated and confirmed by X-ray diffraction.     

Vitreous phosphate coatings on silicate glasses

Translated from Steklo i Keramika, No. 4, pp. 14–15, April, 1991.     

The influence of Sb on glass‐forming ability of Ga‐containing As2Se3 glasses

Effect of As to Sb substitution on glass‐forming ability of As₂Se₃ glass under Ga additions was comprehensively studied using optical spectroscopy in visible and IR regions, differential scanning calorimetry, X‐ray diffraction as well as Raman scattering techniques. The crystallization processes enhanced by Ga additions to As₂Se₃ glass were significantly suppressed under such As to Sb substitution. Following conventional synthesis, it was possible to substitute up to 50% of As by Sb within Ga_y(As_0.40?xSb_xSe_0.60)_100?y cut‐section without essential impact on glassy state, thus improving optical properties in the IR region by lowering the phonon energy. In the case of Ga_y(As_0.28Sb_0.12Se_0.60)_100?y cut‐section, up to 8 at.% of Ga can be introduced without crystallization, whereas in case of Ga_y(As_0.40Se_0.60)_100?y system, glass‐forming ability is limited just up to 3 at.% of Ga. The prepared Ga₅(As_0.28Sb_0.12Se_0.60)₉₅ glass composition was shown to be the richest in Ga keeping its vitreous state, good optical and thermodynamic properties allowing further rare‐earth doping and fiber drawing.     

Transport of potassium ions in niobium phosphate glasses

The influence of Nb₂O₅ on the structure and ionic conductivity of potassium phosphate glasses was investigated in glasses with composition xNb₂O₅–(100-x)[0.45K₂O–0.55P₂O₅], x = 10–47 mol%. The Raman spectra of glasses reveal a transition from predominantly orthophosphate to predominantly niobate glass network with increasing Nb₂O₅ content. In the glass structure, niobium forms NbO₆ octahedra which are interlinked with phosphate units for the glass containing 10 mol% Nb₂O₅, but for higher Nb₂O₅ content they become mutually interconnected via Nb-O-Nb bonds. The transport of potassium ions was found to be strongly dependent on the structural characteristics of the glass network. While the mixed niobate-phosphate glass network hinders the diffusion of potassium ions by providing traps that immobilize them and/or by blocking the conduction pathways, predominantly niobate glass network exhibits a rather facilitating effect which is evidenced in the trend of DC conductivity as well as in the features of the frequency-dependent conductivity and typical hopping lengths of potassium ions.     

The influence of MgO on the crystallization behaviour and properties of SrO-rich phosphosilicate glasses

A series of glass was produced to investigate the effect of MgO/SrO replacement on the crystallization characteristics and properties of phosphosilicate glasses containing high SrO content. The glass samples were synthesized by conventional melting technique based on 5CaO-(40-X)SrO-X MgO– 43SiO₂–7P₂O₅–5CaF₂ (where; X = 10, 20, 30 and 40 mol%). The influence of MgO/SrO replacement on phase assemblages, microcrystalline structures, thermal expansion, and mechanical properties was examined as a function of basic chemical compositions and crystallization parameters. Predominant strontium meta-silicates together with strontium fluoroapatite phases are crystallized from the base glass free of magnesium. The substitution of strontium by magnesium up to 50% led to formation strontium akermanite phase Sr₂MgSi₂O₇ at the expense of SrSiO₃ phase. Whereas the increase of the MgO/SrO of more than 50%, which led to the crystallization of the clino-enstatite MgSiO₃ as a predominant phase. The results show that the α-values of the glass-ceramics are ranged in 94–125 × 10⁻⁶ K⁻¹ over the temperature range (25–500 °C). On the other hand, MgO/SrO replacements led to enhancing the microhardness of the resultant crystalline materials from 4713 Mpa to 6744 Mpa. As a result of the designed glass compositions, promising crystalline phases were obtained as well as good thermal and mechanical properties for the resultant glass-ceramics. Therefore, the designed glass-ceramics can be strongly used as biomaterials especially for bone reconstruction applications.     

Improving the quality of the charges of colored phosphate glasses

Translated from Steklo i Keramika, No. 10, pp. 21–22, October, 1992.     

玻璃分相结构形态与MgO/CaO摩尔比的相互关系

本文研究MgO/CaO比值不同的两种玻璃的分相结构。结果发现高MgO/CaO比的玻璃在热处理的过程中分相液滴由连通结构逐渐长大而转变为孤立的液滴结构。而低MgO/CaO比的玻璃在热处理的过程中分相液滴则由小尺度的连通结构长大为大尺度的连通结构。     

Bone-like forming ability of apatite-wollastonite glass ceramic

This research describes the preparation, characterisation and in vitro behavior of a bioactive glass ceramic containing 44.8 wt% apatite, 28.0 wt% wollastonite-2 M and 27.2 wt% of amorphous phase. The biomaterial was obtained by a specific thermal cycle process that caused the devitrification of the Ca₃(PO₄)₂-CaSiO₃ binary system's stoichiometric eutectic composition. Overall, the material combines the properties of a resorbable Si-Ca-rich glass, in addition to bioactive properties of wollastonite and apatite phases. The bioactivity of this material was studied by soaking the samples in a simulated body fluid (SFB) for 3, 7, 14 and 21 days at 36.5 °C. During the soaking, the amorphous phase and also wollastonite-2 M phase underwent steady dissolution by releasing Si and Ca ions into the SBF medium. After 7 days, a porous hydroxy-carbonate apatite (HCA) layer was formed at the SBF-glass ceramic interface. The micro-nanostructured apatite-wollastonite-2 M glass ceramics with improved mechanical properties, in comparison with the parent glass, could serve as a promising platform for hard tissue regeneration.     

Optical properties of ternary zinc magnesium phosphate glasses

Ternary phosphate glasses of the system (ZnO)₃₀(MgO)_x(P₂O₅)_70−x with x ranging from 5 to 20 mol% were prepared by melt quenching technique. The optical absorption spectra of these glasses were measured at room temperature in the wavelength range between 190 and 1100 nm while the refractive index at wavelength 632.8 nm. The optical absorption indicates that the electronic transition is indirect and associated with phonon-assisted transition. From the absorption spectra, the optical energy band gap (E_opt) and Urbach energy (E_U) values for all the glass samples were calculated from their ultraviolet edges. The values of E_opt is found to increase from 3.36 to 3.44 eV and values of E_U decrease from 0.47 to 0.29 eV with the increase of MgO content. Variation in these optical parameters, density and molar volume is discussed and correlated with the structural changes within the glassy matrix.     

Optical and mechanical properties of calcium phosphate glasses

Binary calcium phosphate glasses in the system, xCaO-(100 ? x) P₂O₅ with x = 30, 35, 40, 45, and 50 mol % were prepared by conventional melt quenching technique. The density, molar volume and refractive index of the glasses were found to increase with the increase in CaO content. Structural investigation by FTIR spectroscopy revealed that the substitution of P₂O₅ by CaO depolymerizes the phosphate glass network by systematic conversion of Q³ structural units to Q² structural units by breaking the P-O-P links. From the optical absorption studies, the optical band gap values were found to decrease with increasing CaO content which can be due to increase in the concentration of non-bridging oxygens in the glass network. Vickers hardness increased with the calcium oxide content due to densification. The fracture toughness decreases with the increase in CaO content due to the increase in the bond density between the modifying cations and the non-bridging oxygens in the glass network. It was observed that brittleness increases with the addition of CaO content which can be mainly attributed to the decrease in the molar volume.     

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.     

Structure and properties of cerium phosphate and silicophosphate glasses

We report on the fabrication, properties, and structure of cerium pyrophosphate glasses and partially substituted cerium silicophosphates. In those glasses, cerium occurs predominantly as Ce(III). A combination of dynamic nuclear magnetic resonance and electrical impedance spectroscopy is used to overcome the problem of assessing cerium speciation. While optical spectroscopy is unable to quantify the ratio of Ce(III)/Ce(IV) due to spectral overlap, proxy observations of the effect of silica-for-cerium substitution on optical extinction and the shape and width of the UV band gap corroborate vibrational spectroscopic data of the structural roles of cerium and silica. While silica bonding to phosphate units appears to stabilize Ce(IV), it also impedes the polaron transport, leading to higher polaron activation energy and lower electronic conductivity. On the other hand, Ce(III) is stabilized by coordinating to P = O.