Effect of P2O5 on evolution of microstructure of MgO–Al2O3–SiO2 glass ceramics

Abstract

MgO–Al₂O₃–SiO₂ (MAS) cordierite based glass ceramics were prepared by volume crystallisation. X-ray diffraction, Scanning electron microscopy and Energy diffraction scanning were used to investigate crystallisation behaviour and the influence of P₂O₅ on microstructure MAS based glass ceramics. The results showed that P⁵⁺ could promote the phase separation of MAS glass and that the glass was divided into two areas, such as Mg₄Al₂Ti₉O₂₅ and the containing P⁵⁺ area at <900°C. Mg₄Al₂Ti₉O₂₅ and Mg₃(PO₄)₂ in the area were both advantageous to the precipitation of μ cordierite, which further transformed to α cordierite due to P⁵⁺ in the residual glassy phase. However, P⁵⁺ inhibited the presence of cordierite when the heat treatment temperature was >900°C.     

Effect of CaO doping on the properties and crystallization behavior of Y2O3–Al2O3–SiO2 glass

Nowadays, Y₂O₃–Al₂O₃–SiO₂ (YAS) glass joining is considered to be a promising scheme for nuclear-grade continuous silicon carbide (SiC) fiber reinforced SiC matrix composites (SiC/SiC). CaO has great potential for nuclear applications since it has low reactivity and low decay rate under nuclear irradiation. In this paper, the effect of CaO doping on the structure, thermophysical properties, and crystallization behavior of YAS glass was systematically studied. As the CaO doping content increased, the number of bridge oxygens and the viscosity at high temperatures reduced gradually. After heat treatment at 1400 °C, the main phases in YAS glass were β-Y₂Si₂O₇, mullite, and SiO₂ (coexistence of crystalline and glass phases), while that with 3.0% CaO doping turned into a single glassy phase under the same treatment conditions. Moreover, a structural model and the modification mechanism were proposed, which provided a theoretical basis for the subsequent component design and optimization.     

Surface and bulk crystallization in Nd2O3–Al2O3–SiO2–TiO2 glasses

Neodymium aluminosilicate (Nd₂O₃–Al₂O₃–SiO₂; NdAS) glasses have been investigated for the effect of concentration of TiO₂ on the crystallization mechanism and for the effect of surface condition on crystal growth. NdAS glasses with 0–10 wt.% TiO₂ were heat-treated for nucleation and crystal growth and were examined for phase separation and morphology of surface crystals as well as for crystal growth rate. All the glasses exhibit surface crystallization, however, the glass having 8 wt.% TiO₂ also exhibits internal crystallization after a two-stage heat treatment. Surface crystallization was dependent on the condition of the glass surface and the amount of TiO₂. The crystal growth on the cut surface was faster than on the fractured surface and the growth rate in surface increased with increasing TiO₂. The phase separation found in NdAS glasses containing above 8 wt.% TiO₂, was confirmed to be an important factor controlling the internal crystallization process in Nd₂O₃–Al₂O₃–SiO₂–TiO₂ glasses.     

Dual effect of ZrO2 on phase separation and crystallization in Li2O–Al2O3–SiO2–P2O5 glasses

ZrO₂ is an effective nucleation agent for low-expansion lithium–aluminum silicate (LAS) glass–ceramic (GC) with high Al₂O₃ content. However, the effect of ZrO₂ is still not fully understood in LAS glasses with low contents of Al₂O₃ and P₂O₅. In this work, the effect of ZrO₂ on the phase separation and crystallization of Li₂O–Al₂O₃–SiO₂–P₂O₅ glasses were investigated. The results revealed that ZrO₂ significantly increased T_g and the crystallization temperature of Li₂SiO₃ and Li₂Si₂O₅ crystals. Li₃PO₄ crystals precipitated preferentially in the glass containing 3.6-mol% ZrO₂, wherein Zr was stable in the network and no precipitation of ZrO₂ nanocrystals was observed. Moreover, the separation of phosphate-rich phases in the as-quenched glasses increased with the addition of ZrO₂. The findings of the study revealed a dual role of ZrO₂. First, ZrO₂ acted as a glass network former rather than a nucleation agent, increasing glass viscosity and the nucleation barrier of Li₂SiO₃ through its strong network connectivity. Second, as Zr preferentially combined with non-bridging oxygen to form Si–O–Zr linkages, a sufficient amount of charge-balancing Li⁺ ions existed in the network, which promoted the separation of phosphate-rich phases. It indicated that the incorporation of ZrO₂ contributes to the activation of the nucleation role of P₂O₅, thus contributing to the formation of nanocrystals and fine microstructure of GCs.     

Effect of MgO/Al2O3 ratio on the crystallization behaviour of Li2O–MgO–Al2O3–SiO2 glass-ceramic and its wettability on Si3N4 ceramic

The composition governs the crystallization ability, the type and content of crystal phases of glass-ceramics. Glass-ceramic joining materials have generated more research interest in recent years. Here, we prepared a novel Li₂O–MgO–Al₂O₃–SiO₂ glass-ceramic for the application of joining Si₃N₄ ceramics. We investigated the influence of the MgO/Al₂O₃ composition ratio on microstructure and crystallization behaviour. The crystallization kinetics demonstrated that the glasses had excellent crystallization ability and high crystallinity. β-LiAlSi₂O₆ and Mg₂SiO₄ were precipitated from the glass-ceramics, and the increase of MgO concentration was conducive to the precipitation of Mg₂SiO₄. Among the glass-ceramic samples, the thermal expansion coefficient of LMAS2 glass-ceramic was 3.1 × 10^?6/°C, which was very close to that of Si₃N₄ ceramics. The wetting test showed that the final contact angle of the glass droplet on the Si₃N₄ ceramic surface was 32° and the interface was well bonded.     

Effect of Al2O3 particles on mechanical and tribological properties of Al–Mg dual-matrix nanocomposites

This article aims to manufacture homogenous dual-matrix Al–Mg/Al₂O₃ nanocomposite from their raw materials and give insight into the correlation between powder morphology, crystallite structure and their mechanical and tribological properties. Al–Mg dual-matrix reinforced with micro/nano Al₂O₃ particles was manufactured by a novel double high-energy ball milling process followed by a cold consolidation and sintering. Microstructure and phase composition of the prepared samples were characterized using FE-SEM, EDS and XRD inspections. Mechanical and wear properties were characterized using compression and sliding wear tests. The results showed that a milling of Mg with Al₂O₃ particles in an initial step before mixing with Al has the beneficial of well dispersion of Al₂O₃ nanoparticles in Al–Mg dual matrix. The Al–Mg dual matrix reinforced with nano-size Al₂O₃ showed 3.29-times smaller crystallite size than pure Al. Moreover, the hardness and compressive strength are enhanced by adding nano-size Al₂O₃ with Al–Mg dual matrix composite while the ductility is maintained relatively high. Additionally, the wear rate of this composite was reduced by a factor of 2.7 compared to pure Al. The reduced crystallite size, the dispersion of Al₂O₃ nanoparticles and the formation of (Al–Mg)_ss were the main improvement factors for mechanical and wear properties.     

Effect of Ta2O5 addition on the structure,crystallization mechanism,and properties of CaO–B2O3–SiO2 glasses for LTCC applications

CaO–B₂O₃–SiO₂–Ta₂O₅ (CBST) glass-ceramics, with different Ta₂O₅ content, (up to 6 mol%), have been prepared by using glass melt quenching followed by heat treatment between 800 and 880 °C. The Fourier Transform Infrared (FTIR) results showed that the stronger the attraction of Ta⁵⁺ to the oxygens in the BO₃^3? and SiO₃^2? structures, the more easily the B–O and Si–O bonds will be destroyed. The underlying reason is most probably the high field strength of Ta⁵⁺, which results in a weakening of the vibration intensities of the [BO₃] and [SiO₄] units. Moreover, the Differential Scanning Calorimetry (DSC) results showed that the softening point (T_g), crystallization starting temperature (T_c1), and exothermic crystallization peak temperature (T_p1), of the CaSiO₃ phase, shifted to higher values with the addition of Ta₂O₅. Also, the crystallization activation energy (E_a) and the glass stability factor (ΔT) of the CaSiO₃ phase increased, which indicated that the CaSiO₃ phase of the glass became inhibited by the addition of Ta₂O_5. It was, thus, obvious that there was a need of glass characterization. The results of the crystallization kinetics showed that the critical cooling rate decreased with the addition of Ta₂O₅, which indicated that the viscosity of the system had increased. The CBST glass-ceramics, containing 1 mol% Ta₂O_5, that were sintered at 875 °C for 15 min showed excellent dielectric properties: ε_r = 6.22 and tanδ = 1.19 × 10^?3 (1 MHz). To sum up, CaO–B₂O₃–SiO₂–Ta₂O₅ glass-ceramics are potential low temperature co-fired ceramic substrate materials.     

Effect of Li2O on melt crystallization of CaO–SiO2–CaF2 based glasses

This paper presents the effects of Li₂O on the kinetics and structural aspects of the Cuspidine (Ca₄Si₂F₂O₇) crystallization behavior of CaO–SiO₂–CaF₂ glass (basicity 1.7). In order to elucidate the crystallization characteristics during differential scanning calorimetry (DSC) measurements, the kinetic parameters have been determined using the Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation. The crystallization rate constant and negative activation energy thus calculated indicated that the limiting step of crystallization was nucleation. Also, Raman spectroscopy and Solid-state MAS NMR spectroscopy analyses indicated that lithium could interact with fluorine, thereby disturbing the interaction between calcium and fluorine. This retards Cuspidine nucleation at the initial stage of melt crystallization. These findings on CaO–SiO₂–CaF₂-based glass lubricants can be used to optimize essential properties such as viscosity and crystallization temperature during continuous casting of steels.     

Effect of adding Y2O3 on structural and mechanical properties of Al2O3–ZrO2 ceramics

The effects of adding 1–8 wt% Y₂O₃ on phase formation and fracture toughness of Al₂O₃–xZrO₂–Y₂O₃(AZY) ceramics were studied. Phase formations of the samples were characterized by the X-ray diffraction (XRD) technique. It was found that the major phase was rhombohedral-Al₂O₃, while the minor phase consisted of the monoclinic-ZrO₂, tetragonal-ZrO₂ and monoclinic-Y₂O₃. It was found that Y₂O₃ contents did not clearly influence grain shape of AZY ceramics. The results obtained from the microhardness test could be used to evaluate the fracture toughness. It was found that the smaller grains had high fracture toughness. The maximum fracture toughness of 4.827 MPa m^1/2 was obtained from 4 wt% Y₂O₃. Refinement of lattice parameters using Rietveld analysis revealed the quantitative phases of AZY ceramics. This shows that under adding Y₂O₃ conditions the proportion of tetragonal-ZrO₂ phase plays an important role for the mechanical properties of AZY ceramics.     

Effect of ZrO2 addition on in-vitro bioactivity and mechanical properties of SiO2–Na2O–CaO–P2O5 bioactive glass-ceramic

Herein, a multicomponent bioactive glass (0Z, 46SiO₂–30CaO–18Na₂O–6P₂O₅, wt.%) is prepared via melting. ZrO₂ is introduced into the bioglass using two different methods, and then three types of glass-ceramic bulks are manufactured using low-cost pressureless sintering. The effect of ZrO₂ addition on the bioactivity and mechanical properties of the bioactive glass-ceramic is assessed. The results indicate that the main crystalline precipitate from the bioactive glass-ceramic is Na₂Ca(Si₂O₆). The crystallisation ability of the 5Z glass-ceramic, bioactive glass-ceramic with ZrO₂ added during melting at high temperature, is reduced because ZrO₂ participated in the reconstruction of the glass network. Further, the ZrO₂ addition led to a low rate of cation release when soaked in simulated body fluid, indicating a decreased bioactivity. At the same time, the 5Y bioactive glass-ceramic, prepared by mixing YSZ particles with 0Z using ball-milling, possesses not only the highest mechanical strength (about twice the strength of 0Z) but also a high bioactivity. This study presents a promising method for the production of excellent bioactive glass-ceramic and a candidate (5Y) for the clinical applications where load bearing is required.     

Effect of surface properties of MgO on its dissolution and spinel growth in CaO–SiO2–Al2O3 slag

The dissolution behavior of MgO in CaO–SiO₂–Al₂O₃ ternary slag at the interface of single-crystal, dense poly-crystal, and porous poly-crystal MgO was investigated to evaluate the effect of the surface properties of the MgO. The experimental results revealed that a detached spinel layer formed at the MgO interface due to the change in thermodynamic condition of the slag, which was independent of the surface properties. On the other hand, it was also confirmed that the growth rate and morphology of the detached spinel layer strongly depended on the surface properties, such as porosity and curvature of MgO. During the formation of the spinel layer at the interface during MgO dissolution, a kinetic approach adopting parabolic relation theory was employed to determine the correlation between the surface properties and the spinel growth mechanism.     

Effect of addition of TiO2 on reaction sintered MgO–Al2O3 spinels

Three different spinel compositions with MgO:Al₂O₃ molar ratios 2:1, 1:1 and 1:2 were studied using TiO₂ as an additive up to 2 wt.%. Solid state reaction sintering technique was employed for all the compositions in the temperature range of 1550–1650°C. Attrition milling was done for the reduction of particle size. Sintered products were characterised in terms of densification and shrinkage studies, phase analysis, strength evaluation both at ambient temperature and at elevated temperature, strength retention after different number of thermal cycles at 1000°C, quantitative elemental analysis and microstructural studies.     

Effect of varying Al2O3 contents of CaO–Al2O3–SiO2 slags on lumped MgO dissolution

This study utilized the single hot thermocouple technique to examine the dissolution behavior of lumped magnesium oxide (MgO) in CaO–Al₂O₃–SiO₂ ternary slags. The aluminum oxide (Al₂O₃) content in the slag (C/S = 1) varied from 10% to 30%; the MgO sphere with a diameter of 1 mm was placed in molten slags at 1,550 °C. Results showed that the dissolution rate decreased as the Al₂O₃ content increased up to 20%. Over 20% Al₂O₃, MgAl₂O₄ was formed at the interface of MgO and it did not fully melt at 30% Al₂O₃. The dissolution behavior and the formation of MgAl₂O₄ were analyzed by a phase diagram provided by Factsage 7.0 software. In the case of less than 20% Al₂O₃ content, apparent sphere radii were measured; the shrinking core model was then applied to understand the dissolution mechanism. The dissolution rate of both slags was controlled by boundary layer diffusion. The dissolution rate at 20% Al₂O₃ slag appeared to fit the behavior to the boundary layer diffusion, although it deviated during the middle stage of the dissolution because of MgAl₂O₄ formation. The 10% Al₂O₃ slag fitted well to the boundary layer diffusion curve; the obtained diffusion coefficient was 0.94 × 10⁻⁹ m²/s.     

Effect of Al2O3 and K2O content on structure,properties and devitrification of glasses in the Li2O–SiO2 system

The effect of Al₂O₃ and K₂O content on structure, sintering and devitrification behaviour of glasses in the Li₂O–SiO₂ system along with the properties of the resultant glass–ceramics (GCs) was investigated. Glasses containing Al₂O₃ and K₂O and featuring SiO₂/Li₂O molar ratios (3.13–4.88) far beyond that of lithium disilicate (Li₂Si₂O₅) stoichiometry were produced by conventional melt-quenching technique along with a bicomponent glass with a composition 23Li₂O–77SiO₂ (mol.%) (L₂₃S₇₇). The GCs were produced through two different methods: (a) nucleation and crystallization of monolithic bulk glass, (b) sintering and crystallization of glass powder compacts.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 phase separation in all investigated compositions. The extent of segregation, as judged from the mean droplet diameter and the packing density of droplet phase, decreased with increasing Al₂O₃ and K₂O content in the glasses. The crystallization of glasses richer in Al₂O₃ and K₂O was dominated by surface nucleation leading to crystallization of lithium metasilicate (Li₂SiO₃) within the temperature range of 550–900 °C. On the other hand, the glass with lowest amount of Al₂O₃ and K₂O and glass L₂₃S₇₇ were prone to volume nucleation and crystallization, resulting in formation of Li₂Si₂O₅ within the temperature interval of 650–800 °C.Sintering and crystallization behaviour of glass powders was followed by hot stage microscopy (HSM) and differential thermal analysis (DTA), respectively. GCs from composition L₂₃S₇₇ demonstrated high fragility along with low flexural strength and density. The addition of Al₂O₃ and K₂O to Li₂O–SiO₂ system resulted in improved densification and mechanical strength.     

SiO2–Al2O3–CaO glass-ceramics: Effects of CaF2 on crystallization,microstructure and properties

The effects of fluorine content on the nucleation and crystallization behavior of SiO₂–Al₂O₃–CaO glass ceramics system have been investigated. The crystalline phases were determined by X-ray diffraction (XRD). The crystallization kinetics was determined by differential thermal analysis (DTA). The microstructures were examined by using scanning electron microscope (SEM). Fourier transformed infrared spectra (FTIR) analysis was used to study the glass structure. The results showed that by increasing the fluorine content, both the crystallization peak temperature (T_p) and activation energy (E) decreased. Wollastonite, anorthite and gehlenite are the main crystalline phases that exist in the glass ceramics system. The study shows that fluorine promoted initial crystallization of glass and can be used as an effective nucleating agent in the SiO₂–Al₂O₃–CaO system.     

Effect of CuO addition on crystallization and thermal expansion properties of Li2O–ZnO–SiO2 glass-ceramics

A Li₂O-ZnO-SiO₂ (LZS) glass system was modified with CuO, and its phase development, microstructure evolution, crystallization kinetics and thermal expansion properties were investigated as a function of heat treatment temperature. As a result of the X-ray diffraction study and microstructure observation, lithium zinc silicate formed as the first crystalline phase with increasing heat treatment temperature. Silica polymorph developed as minor crystalline phase at higher temperatures. From the X-ray diffraction patterns, CuO addition led to a decrease in both the crystallization temperature of lithium zinc silicate phase and the volume fraction of quartz phase. According to the crystallization kinetics, the crystallization activation energy for lithium zinc silicates is almost equal to the diffusion activation energy of Zn²⁺ in glass, it suggests that the diffusion of network modifier Zn²⁺ dominates the crystallization of lithium zinc silicates. Additionally, CuO addition caused the transition of Zn²⁺ from network modifiers to network formers. From the thermal expansion coefficient measurements, two abrupt changes in slope of the thermal expansion curves were observed and attributed to the phase transitions of cristobalite and lithium zinc silicate, respectively. Comparison of the thermal expansion coefficient of two types of glass-ceramics revealed that CuO addition in the LZS system can partly inhibit the formation of cristobalite at high temperatures.     

Effect of substitution of ZrO2 by SnO2 on crystallization and properties of environment-friendly Li2O–Al2O3–SiO2 system (LAS) glass-ceramics

In this study, a transparent and environmentally friendly Li₂O–Al₂O₃–SiO₂ (LAS) glass-ceramic was prepared by melt-quenching and two-step heat treatment. The influence of the substitution amount of ZrO₂ by SnO₂ on the crystallization, microstructure, transparency, and mechanical properties of LAS glass and glass-ceramics was investigated by means of differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Ultraviolet–visible Spectrophotometer, three-point bending strength test, and microhardness test. The results indicate that the main crystalline phase of LAS glass ceramics was a β-quartz solid solution when heat treated at 780 °C for 2 h and 870 °C for 1.5 h. When the substitution amount of ZrO₂–SnO₂ increased from 0.4 mol% to 2.5 mol%, the grain size and thermal expansion coefficient of LAS glass-ceramics first decreased and then increased, and the crystallinity first increased and then decreased. When the substitution amount of ZrO₂–SnO₂ was 0.8 mol%, the transparency of the LAS glass-ceramics was maximum, the bending strength was 96 MPa, and the Vickers hardness was 10.9 GPa.     

Effect of bimodal microstructure on high-temperature properties of nano-reinforced Al2O3–MgO–C refractories

The beneficial effects of adding nanostructured expandable graphite (EG) hybridized yttrium aluminium garnet (EG\YAG) powder as a composite reinforcement in improving the oxidation resistance, hot-strength, and microstructure development in Al₂O₃–MgO–C refractories were studied. The refractory components reinforced with EG\YAG exhibited more than 60% of oxidation resistance enhancement and as high as 200% increase in hot-strength performance over the standard refractories, formulated without EG\YAG. Correlating the damage parameter (D_E) calculations based on ultrasonic measurements with residual strength data (R_c, R_b) showed that there was a progressive increase in R_c and R_b values with consistent reduction in the oxidative damage of EG\YAG reinforced refractories. Analysis indicated that these beneficial features were majorly ascribed to the in-situ development of bimodal microstructure with EG\YAG sintered framework throughout the refractory interior in these new class of reinforced systems. Additionally, the mechanism of toughening and implications of these results to materials design are discussed.     

Effects of Sr and Mg dopants on biological and mechanical properties of SiO2–CaO–P2O5 bioactive glass

In the present study, the effects of Sr and Mg were investigated on mechanical and biological properties of 58S bioactive glass (BG). SiO₂-P₂O₅-CaO BG with different contents of Sr and Mg were synthesized via the sol-gel method and immersed in simulated body fluid (SBF) for several days to explore their biocompatibility. Precise analyses of the BG using X-ray powder diffraction, scanning electron microscopy, and transmission electron microscopy showed that the Mg-doped BG containing 8 wt % MgO possessed better biocompatibility. It was also found that mechanical properties of the BG could be improved by increasing the amounts of MgO and SrO. Both 5Sr-BG and 8Mg-BG samples did not exhibit any cytotoxicity while showing high alkaline phosphatase activity in comparison with control specimens. However, the Sr-doped BG sample including 5 wt % SrO demonstrated enhanced bioactivity and biocompatibility.