Parent Glass Composition Research Articles

Control of the preferentially orientated growth of Sr2TiSi2O8 crystals in a SrO – TiO2 – SiO2 – Al2O3 – K2O parent glass

A polar glass-ceramic containing Sr-fresnoite Sr2TiSi2O8 (STS) as single crystalline phase was developed through the controlled crystallization of a parent glass composition containing SrO, TiO2, SiO2, K2O, and Al2O3. The objective of this work is to obtain a piezoelectric substrate exhibiting a well-defined orientation of the polar direction of the STS crystals over a depth suitable for the design of surface acoustic waves (SAW) devices. For that purpose, the crystallization mechanism of the parent glass was first studied by Differential Scanning Calorimetry (DSC). Based on this study, heat treatments were applied to transform the glass into glass-ceramics. Two aspects were investigated: i). The influence of the surface state of parent glass and of its environment on the nucleation of preferentially orientated STS crystals at the surface of the parent glass; ii). The growth of a preferentially orientated crystallized layer from the surface into the bulk. The microstructures of resulting glass ceramics were characterized by X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy (TEM). We demonstrate that growth of the surface crystallized layer is governed by diffusion mechanisms through a transition glass composition separating the crystalized layer and the subjacent parent glass. The control of the growth rate of the crystalline layer plays the key role to keep a high and constant orientation of the (002) STS plans parallel to the surface of the substrate.

Optimized growth of LiZnBO3 monoclinic phase in lithium zinc borate glass ceramics for electrode material

Glass-ceramics (GCs) of glass composition 20ZnO.30Li2O.50B2O3 were prepared via controlled heat treatment at hold times of 2h, 4h, 6h and 8h at crystallization peak temperature (846K). The effect of the hold time of heat treatment on the physical, structural, optical, and electrochemical properties was studied. XRD study revealed the formation of a pure LiZnBO3 crystalline phase. FTIR study revealed the transformation of BO4 units to BO3 units with an increase in the time of heat treatment. Optical band gap energy has been estimated from Diffuse Reflectance spectroscopy and, its values range from 3.26eV–3.36eV. Electrochemical properties were studied using Cyclic Voltammetry and compared with parent glass composition. The GC 20ZnO.30Li2O.50B2O3 heat treated for 8h exhibits the highest value of specific capacitance (∼48 mAh/gV) and energy density (∼18 J/g) indicating that it can be used as an electrode material in Li-ion batteries.

Influence of Sr2+ ions on structural, optical and bioactive behaviour of phosphoborate glass system

Glass system having composition xSrO−3P2O5−21NaO−26CaO−(50-x)B2O3 (x = 0, 1, 2, 3 & 4 mol%) are synthesized via conventional melt quench method. Density and molar volume measurements are performed to examine the physical properties. Bioactivity of prepared samples is checked using phosphate buffer solution (PBSol) under static conditions at 37 °C. XRD, Infrared Spectroscopy and FESEM are used to analyze the assessment of hydroxyapatite (HAp) conversion. Analysis of XRD data indicates HAp formation. Optical absorption spectra are used to analyze optical band gap, refractive index and Urbach energy of the prepared composition. pH and weight loss measurements are also carried out to check the solubility of glasses. FESEM micrographs reveal visible change in morphology of glass after immersion in PBSol. Interpretations of observations as a function of composition and duration of soaking in PBSol have been done. pH values of PBSol, in which the samples were soaked for twelve days, showed enhancement in alkalinity, indicating the dissolution of the phospho-borate units in PBSol supporting the formation of HAp. Samples with higher SrO content show higher values of weight loss during the degradation in PBSol, suggesting their enhanced degradability in PBSol as compared to parent glass composition. Structural and morphological studies investigated by FESEM also predict the formation of HAp layer over glass surface. The developed compositions can be potential candidates for bone-bonding materials.

Structural Features and Water Resistance of Glass–Matrix Composites in a System of RNO3-KHSO4-P2O5 Containing Different Additives

Low-temperature (350 °C) vitrification in a KNO3-NaNO3-KHSO4-NH4H2PO4 system, containing various additives to improve the chemical durability of the obtained material, was investigated. It was shown that a glass-forming system with 4.2–8.4 wt.% Al nitrate admixtures could form stable and transparent glasses, whereas the addition of H3BO3 produced a glass–matrix composite containing BPO4 crystalline inclusions. Mg nitrate admixtures inhibited the vitrification process and only allowed obtaining glass–matrix composites with combinations with Al nitrate and boric acid. Using ICP and low-energy EDS point analyses, it was recognized that all the obtained materials contained nitrate ions in their structure. Various combinations of the abovementioned additives favored liquid phase immiscibility and crystallization of BPO4, KMgH(PO3)3, with some unidentified crystalline phases in the melt. The mechanism of the vitrification processes taking place in the investigated systems, as well as the water resistance of the obtained materials, was analyzed. It was shown that the glass–matrix composites based on the (K,Na)NO3-KHSO4-P2O5 glass-forming system, containing Al and Mg nitrates and B2O3 additives, had increased water resistance, in comparison with the parent glass composition, and could be used as controlled-release fertilizers containing the main useful nutrients (K, P, N, Na, S, B, and Mg).

Effect of SrO and ZnO on Densification and in Vitro Behaviors of P<sub>2</sub>O<sub>5</sub>-CaO-Na<sub>2</sub>O-SiO<sub>2</sub>-TiO<sub>2</sub> Bioactive Glass-Ceramics

Phosphate based-glass ceramics in the system of P2O5-CaO-Na2O-SiO2-TiO2 were obtained by the sintering method. For evaluating the effect of strontium and zinc, different amounts of these elements were doped in the parent glass instead of calcium oxide. Sintering behavior of the glasses was evaluated through the measurement of bulk density, liquid absorption, and open porosity percentages. Based on the results, 600 °C was determined as the optimum sintering temperature. Based on the X-Ray diffractometry, calcium pyrophosphate was precipitated during the sintering process as the main crystallized phase. It is worth noting that changing the parent glass composition led to its phase transformation. Variation in the pH and ion concentration in the simulated body fluid as well as weight loss percentages of the samples were considered to evaluate the dissolution behavior of the samples. The in vitro tests showed that increasing the amount of strontium and zinc intensified the dissolution rate. According to scanning electron micrographs, hydroxyapatite nuclei precipitated on the surfaces of the samples after three days of simulated body fluid (SBF) soaking; but, they were dissolved in the solution after 28 days due to the dissolution of the substrate. Some residues of the grown apatite-like layer were observed on the surface of the composition when 25 and 2.5 molar percent of calcium were substituted for strontium and zinc, respectively.

Improvements on sintering and thermal expansion of lithium aluminum silicate glass-ceramics

Glass-ceramics (GCs) are inorganic, non-metallic materials prepared by controlled crystallization of glasses, which contain at least one functional crystalline phase and a residual glass. In this work, to find the best compromise between coefficient of thermal expansion (CTE) and high sinterability on the LAS GCs, we accomplish changes in the minority oxides (MgO, ZnO, B2O3, P2O5, K2O, and SnO2) of a LAS glass composition (Li2O–Al2O3–SiO2). All LAS GCs were sintered non-isothermally. We propose the use of glass stability parameters (KA, KH, and KM) to point out the most promising glass composition concerning sintering. Indeed, the glass compositions which presented a low tendency to crystallization during the heating, resulted in GCs with the lowest porosities. The porosity analysis was performed through image analysis of optical micrographs. The compositional changes in the most sinterable glasses consisted of MgO reduction (from 1.64 to 0.85 mol%), increases in B2O3 (from 1.4 to 1.9 mol%), and keeping the sum of ZnO and K2O between 1.7 to 1.8 mol%. The changes in minority oxides of the parent glass composition significantly modified the CTE values of the LAS GCs, mainly due to changes in GC crystallinity. The changes in the glass composition allowed to obtain a highly dense sintered GC (0.4 ± 0.1% in porosity), having an appropriated CTE (0.34 × 10−6 K-1) to applications as induction cooktop plates.

Effect of crystallinity and microstructure on mechanical properties of CaO-Al2O3-SiO2 glass toughened by precipitation of hexagonal CaAl2Si2O8 crystals

In order to identify the most effective level of crystallinity and microstructure to increase the toughness of CaO–Al2O3–SiO2 glass with precipitated hexagonal-CaAl2Si2O8 crystals, we measured the fracture toughness and investigated the microcracking behavior of samples containing different amounts of the crystalline phase. The glass-ceramics were prepared in the range of 10–48 wt% crystallinity by changing the parent glass composition. Five glass compositions, xCaO–yAl2O3–zSiO2 wt% (x= = 25.6–22.7, y= = 18.0–28.1, z= = 56.4–49.2), were examined by Single Edge V-Notched Beam (SEVNB) method for fracture toughness measurement, and Vickers indentation tests for hardness measurement. Although the fracture toughness increased for a crystal content of up to 21 wt%, it remained constant at 21–40 wt%, and then started to decrease at 48 wt%. The Vickers hardness showed a minimum in the range of 21–35 wt% crystallinity. Microcrack formation around indentations was clearly observed in the same range of crystallinity. Also, non-elastic behavior was found at the same levels of crystallinity during bending tests for measurement of fracture toughness, with more fractured surface area. The microstructure of these glass-ceramics was characterized as a “house-of-cards” structure, suggesting that this microstructure was most effective at decreasing the brittleness of the glass by microcrack toughening.

Infrared Glass–Ceramics with Multidispersion and Gradient Refractive Index Attributes

AbstractInfrared (IR) glass–ceramics (GCs) hold the potential to dramatically expand the range of optical material solutions available for use in bulk and planar optical systems in the IR. Current material solutions are limited to single‐ or polycrystalline materials and traditional IR‐transparent optical glasses. GCs that can be processed with spatial control and extent of induced crystallization present the opportunity to realize an effective refractive index variation, enabling arbitrary gradient refractive index elements with tailored optical function. This work discusses the role of the parent glass composition and morphology on nanocrystal phase formation in a multicomponent chalcogenide glass. Through a two‐step heat treatment protocol, a Ge–As–Pb–Se glass is converted to an optical nanocomposite where the type, volume fraction, and refractive index of the precipitated crystalline phase(s) define the resulting nanocomposite's optical properties. This modification results in a giant variation in infrared Abbe number, the magnitude of which can be tuned with control of crystal phase formation. The impact of these attributes on the GCs' refractive index, transmission, dispersion, and thermo‐optic coefficient is discussed. A systematic protocol for engineering homogeneous or gradient changes in optical function is presented and validated through experimental demonstration employing this understanding.

Crack-healing during two-stage crystallization of biomedical lithium (di)silicate glass-ceramics

ObjectiveThe study is aimed to evaluate the two single commercially available two-step lithium-(di)silicate systems by analyzing their parent glass composition and studying the quantitative crystalline and glass phase evolution during the second stage heat-treatment. The mechanical repercussions of the crystallization firing were evaluated using strength and fracture toughness tests. MethodsXRF and ICP-OES were used to determine the oxide composition of the parent glasses in Suprinity PC (Vita Zahnfabrik) and IPS e.max CAD (Ivoclar-Vivadent). The crystalline phase of both materials was determined by quantitative XRD and the G-factor method in the partially and post-crystallization states. The oxide composition of the residual glass phase was derived by subtracting the chemistry of the crystalline phase fractions from the parent glass composition. Mechanical testing of biaxial flexural strength and fracture toughness were used to demonstrate how crack-like defects behave during crystallization. ResultsThe two tested lithium (di)silicate systems showed strong differences in oxide composition of the parent glass. This showed to influence the transformation of lithium metasilicate in lithium disilicate, with the former remaining in high vol.% fraction in the post-crystallization Suprinity PC. In IPS e.max CAD cristobalite precipitated at the surface during the second-heat treatment. Strength and fracture toughness tests revealed that crack in both materials, whether introduced by grinding or indentation, heal during the crystallization firing. Cristobalite seemed to have contributed to a surface strengthening effect in IPS e.max CAD. SignificanceAccurate crystalline phase quantification aids in the determination of the residual glass composition in dental glass-ceramics. For both systems crystallization firing induced healing of cracks generated by CAM grinding.

Antibacterial efficiency of alkali-free bio-glasses incorporating ZnO and/or SrO as therapeutic agents

A series of seven alkali-free silica-based bioactive glasses (SBG) with ZnO and/or SrO additives (in concentrations of 0–12 mol%) were synthesized by melt-quenching, aiming to delineate a candidate formulation possessing (i) a coefficient of thermal expansion (CTE) similar to the one of titanium (Ti) and its medical grade super-alloys (crucial for the future development of mechanically adherent implant-type SBG coatings) and (ii) antibacterial efficiency, while (iii) conserving a good cytocompatibility. The SBGs powders were multi-parametrically evaluated by X-ray diffraction, Fourier transform infrared and micro-Raman spectroscopy, dilatometry, inductively coupled plasma mass spectrometry, antibacterial (against Staphylococcus aureus and Escherichia coli strains) suspension inhibition and agar diffusion tests, and human mesenchymal stem cells cytocompatibility assays. The results showed that the coupled incorporation of zinc and strontium ions into the parent glass composition has a combinatorial and additive benefit. In particular, the “Z6S4” formulation (mol%: SiO2—38.49, CaO—32.07, P2O5—5.61, MgO—13.24, CaF2—0.59, ZnO—6.0, SrO—4.0) conferred strong antimicrobial activity against both types of strains, minimal cytotoxicity combined with good stem cells viability and proliferation, and a CTE (~ 8.7 × 10−6 × °C−1) matching well those of the Ti-based implant materials.

Relationship between electrical conductivities and structure of hybrid materials derived from mixtures of zinc phosphate glasses with different phosphate-chain lengths and benzimidazole

Here, we report unique anhydrous proton-conducting hybrid materials derived from mixtures of benzimidazole and zinc metaphosphate glass. Benzimidazole, which melts at 170 °C, caused breaking of the phosphate chains in the glasses, resulting in the formation of hybrid materials. In the present work, various hybrid materials were prepared to clarify the effects of parent glass composition on their electrical conductivities. In the case of 53P2O5 · 47ZnO glass, which contains Qp1 and Qp2 and Qp3 groups, the phosphate chains were broken easily to form benzimidazole and Qp0 groups. Qpn, where n is the number of bridging oxygens to neighboring tetrahedral, describes the bonding of PO4 tetrahedron. Hybrids prepared using benzimidazole and 42P2O5 · 58ZnO glass (which contains many Qp1 groups) formed the smallest amounts of the Qp0 group-containing products. The hybrid material prepared with 53P2O5 · 47ZnO glass showed the highest conductivity (e.g., ∼1 mS/cm at 190 °C). The electrical conductivities of the hybrid materials may be related to the amounts of Qp0 group-containing products and benzimidazole.

Structure, properties and crystallization of non-stoichiometric lithium disilicate glasses containing CaF2

The role of CaF2 on the structure, crystallization behaviour and properties of a relatively simple non-stoichiometric lithium disilicate (Li2Si2O5) based glass composition was studied. Different x amounts (x=0, 1, 3 and 5mol%) of CaF2 were added to (100−x) of a parent glass (22.96Li2O–2.63K2O–2.63Al2O3–71.78SiO2) composition. The glasses were produced by conventional melt-quenching technique, whilst glass–ceramics were produced via crystallization of monolithic bulk glasses.A scanning electron microscopy (SEM) examination of as cast non-annealed monolithic glasses revealed precipitation of nanosize droplet phase in glassy matrices suggesting the occurrence of liquid phase separation in all investigated compositions. The extent of phase segregation, as judged from the mean droplet diameter and the packing density of droplets, decreased with increasing CaF2 content in the glasses. A slight depolymerisation of the glass network was observed according to magic angle spinning nuclear magnetic resonance (MAS-NMR) and Fourier transform infrared (FTIR) spectroscopic studies, suggesting a network modifier role for CaF2. The presence of CaF2 enhanced the crystallization at lower temperatures in comparison to CaF2-free glass.

Glass ceramic materials of the SiO2-CaO-MgO-Al2O3 system: Structural characterization and fluorine effect

ABSTRACTGlass-Ceramic monoliths of the SiO2-CaO-MgO-Al2O3 system are obtained in this research. Due to its potential dual role as a flux and as a nucleating agent, two CaF2 levels (X = 3 and X = 6 mol.%) are investigated in the parent glass composition. Due to its good mechanical properties, we intend to obtain Diopside-type pyroxene [(Ca)(Mg,Al)(Al,Si)2O6] as the main crystalline phase in the synthesized glass-ceramics. Vickers microhardness (HV), density and type of crystallization are determined in the latter materials. The morphology and size of the Diopside crystals, as well as the crystallized fraction, are determined with the help of Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD). Both materials exhibit surface crystallization with Diopside-type pyroxene phase with acicular morphology homogeneously distributed in the glassy matrix. The specimen with the least amount of added fluorine shows the highest microhardness value, as well as the largest and thickest acicular crystals of Diopside-type pyroxene, the lowest apparent density and the largest crystallized fraction. Our results indicate that CaF2 added in the amounts used by us does not act as nucleating agent, but it does affect the growth of the acicular crystals of the Diopside-type pyroxene phase. This is attributed mainly to the effect of fluorine on the glass structure and properties. The materials developed in this study may be considered as viable alternatives for applications in abrasive and corrosive environments, as well as for substrates for metallic coatings, and for abrasion-resistant floor tiles and other structural applications.

Stable glass-ceramic sealants for solid oxide fuel cells: Influence of Bi2O3 doping

Abstract Diopside (CaMgSi2O6) based glass-ceramics in the system SrO–CaO–MgO–Al2O3–B2O3–La2O3–Bi2O3–SiO2 have been synthesized for sealing applications in solid oxide fuel cells (SOFC). The parent glass composition in the primary crystallization field of diopside has been doped with different amounts of Bi2O3 (1, 3, 5 wt.%). The sintering behavior by hot-stage microscopy (HSM) reveals that all the investigated glass compositions exhibit a two-stage shrinkage behavior. The crystallization kinetics of the glasses has been studied by differential thermal analysis (DTA) while X-ray diffraction adjoined with Rietveld-R.I.R. analysis have been employed to quantify the amount of crystalline and amorphous phases in the glass-ceramics. Diopside and augite crystallized as the primary crystalline phases in all the glass-ceramics. The coefficient of thermal expansion (CTE) of the investigated glass-ceramics varied between (9.06–10.14) × 10−6 K−1 after heat treatment at SOFC operating temperature for a duration varying between 1 h and 200 h. Further, low electrical conductivity, good joining behavior and negligible reactivity with metallic interconnects (Crofer22 APU and Sanergy HT) in air indicate that the investigated glass-ceramics are suitable candidates for further experimentation as sealants in SOFC.

Optimization of La 2O 3-containing diopside based glass-ceramic sealants for fuel cell applications

We report on the optimization of La 2O 3-containing diopside based glass-ceramics (GCs) for sealant applications in solid oxide fuel cells (SOFC). Seven glass compositions were prepared by modifying the parent glass composition, Ca 0.8Ba 0.1MgAl 0.1La 0.1Si 1.9O 6. First five glasses were prepared by the addition of different amounts of B 2O 3 in a systematic manner (i.e. 2, 5, 10, 15, 20 wt.%) to the parent glass composition while the remaining two glasses were derived by substituting SrO for BaO in the glasses containing 2 wt.% and 5 wt.% B 2O 3. Structural and thermal behavior of the glasses was investigated by infrared spectroscopy (FTIR), density measurements, dilatometry and differential thermal analysis (DTA). Liquid–liquid amorphous phase separation was observed in B 2O 3-containing glasses. Sintering and crystallization behavior, microstructure, and properties of the GCs were investigated under different heat treatment conditions (800 and 850 °C; 1–300 h). The GCs with ≥5 wt.% B 2O 3 showed an abnormal thermal expansion behavior above 600 °C. The chemical interaction behavior of the glasses with SOFC electrolyte and metallic interconnects, has been investigated in air atmosphere at SOFC operating temperature. Thermal shock resistance and gas-tightness of GC sealants in contact with 8YSZ was evaluated in air and water. The total electrical resistance of a model cell comprising Crofer 22 APU and 8YSZ plates joined by a GC sealant has been examined by the impedance spectroscopy. Good matching of thermal expansion coefficients (CTE) and strong, but not reactive, adhesion to electrolyte and interconnect, in conjunction with a low level of electrical conductivity, indicate that the investigated GCs are suitable candidates for further experimentation as SOFC sealants.

Sintering and crystallization of akermanite-based glass–ceramics

Akermanite-based glass–ceramics were successfully produced from the SiO2–Al2O3–B2O3–MgO–CaO–Na2O–F system via sintering and crystallization of glass-powder compacts at low temperatures between 750 and 800 °C. The experimental results indicated that the amount of Al2O3 in the parent glass composition is seemingly a key factor with regard to the potential of this system to crystallize into a mono-mineral akermanite glass–ceramic. The aesthetics and the mechanical, the chemical and the thermal properties of the produced glass–ceramics in conjunction with the evaluation of the economic processing route proposed qualify these glass–ceramics for further investigation as potential materials suitable for applications in restorative dentistry.

Crystallization study of (TiO2, ZrO2)-rich SiO2-Al2O3-CaO glasses Part I Preparation and characterization of zirconolite-based glass-ceramics

Nuclear power reactors generate long-lived radionuclides such as minor actinides (Np, Am, Cm) which are mainly responsible for the long term radiotoxicity of high level nuclear wastes obtained after reprocessing of nuclear spent fuel. Specific highly durable matrices such as glass-ceramics appear as good candidates for the immobilization of minor actinides. This work concerns the synthesis and the characterization of zirconolite (CaZrTi2O7) based glass-ceramics prepared by controlled devitrification of (TiO2, ZrO2)-rich SiO2-Al2O3-CaO parent glasses for which neodymium was selected to simulate the radioactive trivalent minor actinides. The present study reports the effect of increasing TiO2, ZrO2 and CaO amounts in glass composition on the structure and the composition of the zirconolite crystals (formed as the only crystalline phase in the bulk of the glass), on their nucleation rate I(Z) and on the volume proportion of crystalline phase V of the glass-ceramics. It appears that I(Z) and V strongly increase when the parent glass composition changes. Neodymium electron spin resonance (ESR) shows that the total amount of Nd3+ ions incorporated in the zirconolite phase increases with TiO2, ZrO2 and CaO amounts in parent glass composition.

Zirconolite-based glass-ceramics for actinides immobilization: Effects of glass composition and of actinides simulant nature

ABSTRACTZirconolite (CaZrTi2O7) based glass-ceramics, in which the crystalline phase (aimed at preferentially incorporating minor actinides or Pu) is embedded in a durable calcium aluminosilicate glassy matrix, can be envisaged as good waste form candidates. In this study, the effect of parent glass composition – and particularly of TiO2, ZrO2, CaO and Al2O3 amounts -on the microstructure and the structure of the glass-ceramics obtained after controlled devitrification (nucleation + crystal growth) is reported. It clearly appears that the volume percentage of zirconolite crystals and their nucleation rate in the bulk of the glass strongly depends both on (CaO + ZrO2 + TiO2) and Al2O3 amounts in parent glass. Neodymium is mainly used to simulate trivalent minor actinides whereas several samples were also prepared with other lanthanides (Ce, Eu, Gd, Yb) in order to investigate the effect of simulant field strength in glass on the nature and the composition of the crystals formed. The effect of partial or total molar substitution of ZrO2 by HfO2 in parent glass composition was also studied in order to prepare Ca(Zr1-xHfx)Ti2O7 (0 < × ≤ 1) based glass-ceramics which could be interesting in order to minimize criticality problems.

Effect of K2O addition on crystallization and microstructural behaviour of the strontium titanate-borosilicate glass-ceramic system

The crystallization and microstructural behaviour of glass ceramics in the system (SrO · TiO 2 )-(SiO 2 · B 2 O 3 ) with varying wt% of K 2 O have been investigated. The glass samples were crystallized based on DTA studies. Crystalline phases were identified by X-ray diffraction. The addition of K 2 O in the parent glass composition plays an important role in the precipitation of different crystalline phases in glassy matrix and controls the microstructure of the resulting glass ceramic. In our studies it has been observed that careful selection of the K 2 O content and heat-treatment conditions results in crystallization of strontium titanate as the major phase.