MgO Al2O3 SiO2 Glass-ceramics Research Articles

Effect of TiO2 on crystallization and mechanical properties of MgO–Al2O3–SiO2 glasses containing P2O5

MgO–Al2O3–SiO2 glass-ceramics have been widely used in military, industrial, and construction applications. The nucleating agent is one of the most important factors in the production of glass-ceramics as it can control the crystallization temperature or the grain size. In this study, we investigated the effect of replacing P2O5 with different amounts of TiO2 on the crystallization, structure, and mechanical properties of an MgO–Al2O3–SiO2 system. The crystallization and microstructure were investigated by differential scanning calorimetry, Raman spectroscopy, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The mechanical properties were investigated by measuring the Vickers hardness, Young's modulus, and fracture toughness. The results showed that adding TiO2 favored the precipitation of fine grains and significantly increased the Vickers hardness, Young's modulus, and fracture toughness of the glasses. Introducing an appropriate amount of TiO2 can make a glass structure more compact, promote crystallization, and improve the mechanical properties of MgO–Al2O3–SiO2 glass-ceramics.

Ultrahigh hardness Li2O–MgO–Al2O3–SiO2 glass–ceramics containing multiphase nanocrystals

AbstractLi2O–Al2O3–SiO2‐based glass–ceramics containing nanocrystals have attracted much attention due to their low expansion coefficient, good mechanical properties, for different applications, such as fire‐safe glass, dental materials, and electronic devices protectors. In current research, ultrahigh hardness Li2O–MgO–Al2O3–SiO2 glass–ceramics were prepared by conventional melt‐quenching and subsequent heat‐treatment method. MgO was introduced via Li2O substitution to change glass crystallization and mechanical properties. The differential scanning calorimetry analysis indicated the glass transition and crystallization temperatures increased with MgO/Li2O ratio increase, for better glass network connectivity from Raman spectra analysis. In addition, the main crystal phase changed from Li2SiO5 and LiAlSi4O10, to the combination of LiAlSi2O6 and MgAl2Si4O12, and finally to MgAl2Si4O12. The Vickers hardness of glass–ceramics was highly dependent on MgO/Li2O ratios in glass components and heat‐treatment temperatures, corresponding with the crystal phases in glass–ceramics. The highest hardness could reach 9.34 GPa, which was much higher than traditional silicate glass–ceramics. The scanning electron microscope images confirmed the crystal diameters that varied from 30 to 100 nm and were determined by MgO content. Transmission electron microscope images and energy‐dispersive spectroscopy mapping also confirmed the precipitation of multiphase nanocrystals in glass matrix. The changes of glass structure, and corresponding crystal combinations in glass–ceramics resulting from MgO introduction, were responsible for the ultrahigh hardness glass.

Influence of Y2O3 on microstructure, crystallization, and properties of MgO-Al2O3-SiO2 glass-ceramics

The effect of Y2O3 on the microstructure, crystallization, and properties of MgO-Al2O3-SiO2 (MAS) glass-ceramics was investigated. Y2O3 addition increased the crystallinity and promote the formation of Indialite, and thereby adjusted the coefficient of thermal expansion. Sintering kinetics and crystallization kinetics indicated that doping Y2O3 reduced the sintering activation energy and the crystallization activation energy. A proper amount of Y2O3 improved the densification of sintering process and the precipitation of crystal phase, and thus significantly enhanced mechanical properties. MAS glass-ceramics with 1 wt% Y2O3 achieved the best performances: a high Young's modulus of 89 GPa, a high flexural strength of 211 MPa, an appropriate CTE of 4.68 × 10−6 /°C, a low dielectric loss of 1.99 × 10−3, and a low dielectric constant of 5.99.

Effects of BaO on crystallization, structure and dielectric properties of MgO–Al2O3–SiO2 glass–ceramics for LTCC applications

Cordierite-based glass–ceramics for LTCC applications were prepared by traditional sintering method. And the effects of BaO addition on the crystallization, structure and dielectric properties were investigated by differential scanning calorimetry (DSC), scanning electron microscopy (SEM), X-ray diffractometer (XRD), dilatometer and impedance instrument. The DSC curves displayed that the glass transition temperature (Tg) slowly decreased with the BaO content increasing from 0 to 4 mol%. However, the onset of crystallization temperature (Tx) and crystallization peak temperature (Tc) showed the opposite trend. XRD analysis revealed that μ-cordierite was the major crystal phase for all the glass–ceramic samples, while α-cordierite precipitated as the minor crystal phase with BaO addition. As more BaO was added, the bulk density gradually increased, while the porosity decreased, indicating that BaO improved the sinterability of the glass samples. The dielectric constant showed minimum value with the addition of 2 mol% BaO, and the dielectric loss reached the minimum value when the content of BaO was 3 mol%. Wherein, after heated at 950 °C, glass–ceramics doped with 2 mol% BaO showed a dense structure, a relatively low dielectric constant (4.53), a low dielectric loss (2 × 10−3) at 1 MHz, and a proper CTE value (3.74 × 10–6/°C), which can be used to prepare LTCC materials.

Crystallization behavior and structure of CaO–MgO–Al2O3–SiO2 glass ceramics prepared from Cr-bearing slag

Glass ceramics were successfully prepared from Cr-bearing slag and the effect of the slag content (40–70 wt%) on the crystallization behavior and morphology of the glass ceramics was investigated. The values of the crystallization activation energy and crystallization index for crystal growth calculated using various methods were consistent. The crystallization activation energies of the samples exhibited in the range of 165–252 kJ/mol, and it tended to decrease with increasing Cr-bearing slag content. The crystallization index results indicated that the crystallization mechanism of the samples is bulk crystallization. Additionally, the principal phase composition of the glass ceramics with Cr-bearing slag contents of 40, 50, and 60 wt% was diopside; however, anorthite precipitated as a second phase when the slag content was 65% or 70%. Furthermore, the results suggesting that the CMAS glass ceramics could also be synthesized from Cr-bearing slag without using an additional nucleating agent.

Optimization of heat treatment of glass-ceramics made from blast furnace slag

AbstractCaO–MgO–Al2O3–SiO2 glass-ceramics with diopside as the main crystalline phase were prepared by melting blast furnace slag obtained from Baotou Iron and Steel Company. The effect of heat treatment on the crystallization behavior of glass-ceramics, containing a large proportion of melted blast furnace slag, was studied by means of differential thermal analysis and scanning electron microscopy. The optimum heat-treatment regime was obtained by orthogonal experimental results for glass-ceramics in which blast furnace slag comprised 70% of the composition and 1% Cr2O3 and 4% TiO2 were used as nucleating agents. The nucleation temperature was 750°C for 2.5 h and the crystallization temperature was 930°C for 1 h. Under this regime, the performance of the glass-ceramic was better than that of other groups in the orthogonal experiment.

Effects of Li2O replacing Na2O on glass forming, structure and properties of Na2O–MgO–Al2O3–SiO2 glass and glass-ceramics

Glasses and glass-ceramics in the xLi2O-(5-x)Na2O–20MgO–20Al2O3–54SiO2 system have been prepared by using a conventional melt quenching technology and subsequently a two-step heat-treating method. The effects of Li2O replacing Na2O on crystallization, structural and electrochemical properties of Na2O–MgO–Al2O3–SiO2 glasses and glass-ceramics are studied. The results reveal that the glass forming ability, the bending strength, micro-hardness and ionic conductivity of parent glasses firstly decrease and then increase as Li2O gradually replacing Na2O from 0 mol.% to 5 mol.% due to the disconnection of Si–O–Si network, the suppression of the mobile species and the electrodynamic interaction between the Na–O- and Li–O- oscillating electric dipoles. The main crystalline phase of glass-ceramics is cordierite and the ionic conductivity is three orders of magnitude higher than that glasses. The ionic conductivity of MgO–Al2O3–SiO2 glass-ceramics with 5.0 mol.% Li2O replacing Na2O reaches the highest ionic conductivity (3.4 × 10−6 S/cm), which provides a potential application for glass-ceramics as solid electrolytes in the future.

Effect of SiO2/Al2O3 ratio on the structure and electrical properties of MgO–Al2O3–SiO2 glass-ceramics doped with TiO2

Glass-ceramics of the MgO–Al2O3–SiO2 (MAS) ternary system were successfully prepared through a melting method with borax, quartz sand, and chemical reagents as the main raw materials. The effects of SiO2/Al2O3 ratios on the structure and properties of glass-ceramics were systematically investigated by differential thermal analysis (DSC), X-ray diffraction (XRD), scanning electron microscope (SEM), dielectric properties and electrical resistivity measurements. The results show that the average coefficient of thermal expansion (CTE) (30–800 °C) of all the samples increased with increasing of the SiO2/Al2O3 ratio, but the density of the glass-ceramics and the grain refinement decreased at the same time. The crystalline phase of all the samples was a prepared sapphirine phase when the SiO2/Al2O3 ratio was equal or greater than 1.78 and a second phase of enstatite precipitation. The electrical performance was the best when the SiO2/Al2O3 ratio was equal to 1.27, and its dielectric constant, dielectric loss, and electrical resistivity (room temperature) were 8.78 (1 MHz), 3.55 × 10−3 (1 MHz), and 10.57 × 10 11 Ω m, respectively.

Effect of CuO on crystallisation and properties of red R2O–CaO–MgO–Al2O3–SiO2 glass-ceramics from granite wastes

Granite waste occupies valuable land, pollutes the environment, and may cause health hazards; however, it contains the building blocks of glass-ceramics. Further, copper red glass-ceramics are valuable as high-grade decorative architectural materials. Therefore, we developed a method for creating copper red glass ceramics from granite waste. This study focused on the effect of 3, 5, 7, 9 and 15 wt% CuO on the crystallisation and properties of the R2O–CaO–MgO–Al2O3–SiO2 glass-ceramics prepared from granite wastes. Differential scanning calorimetry results determined that the 5 wt% CuO dopant level produced the most stable glass-ceramic. X-ray diffraction and scanning electron microscopy with energy dispersive X-ray spectrometry showed the presence of rod-like richterite(Na, F)syn (Na(Na, Ca)Mg5Si8O22F2) and granular cuprite (Cu2O) phases. X-ray photoelectron spectroscopy indicated that the Cu+ atomic percentages (ACu+) in the 5 wt% CuO glass-ceramic was 86.4%, higher than any other sample. The colour of the 5 wt% CuO sample was copper red, and further increasing the CuO content did not significantly change the colour. The mechanical properties of the 5 wt% CuO glass-ceramic were suitable for structural applications, with a bending strength 167.80 MPa and a Vickers hardness of 7.62 GPa. Therefore, we showed that 5 wt% CuO doped granite waste can be processed into copper red glass-ceramics that are suitable for high-grade architectural decorative materials.

Crystallization, sinterability, and dielectric properties of MgO–Al2O3–SiO2 glass-ceramics doped with TiO2

The effects of TiO2 on crystallization, microstructure, thermal, and dielectric properties of MgO–Al2O3–SiO2 (MAS) glass-ceramics were investigated. The results showed that with the TiO2 content increasing, the glass transition temperature (Tg) increased gradually, while the onset of crystallization temperature (Tx) and crystallization peak temperature (Tp) increased firstly and then decreased. The main crystalline phase for all the samples was μ-cordierite. β-Quartz and α-cordierite precipitated as the minor crystalline phases with TiO2 content ≥ 2 mol%. A small amount of TiO2 could promote the sintering process and improve the dielectric properties of MAS glass-ceramics. However, an excess of TiO2 addition could worsen the sintering and dielectric properties. The addition of TiO2 was beneficial to decrease the coefficient of thermal expansion (CTE). The MAS glass-ceramics doped with 2 mol% TiO2 heated at 925 °C showed excellent properties: high density (2.64 g/cm3), low CTE value (3.34 × 10–6/°C), low dielectric constant (5.44), and dielectric loss (2.17 × 10–3) at 1 MHz, which was a promising material for LTCC applications.

Influence of Cr2O3 on the viscosity and crystallization behavior of glass ceramics based on blast furnace slag

CaO–MgO–Al2O3–SiO2 glass-ceramics with various Cr2O3 contents are successfully prepared from blast furnace slag as the main raw material using a conventional melting method. The influence of Cr2O3 addition on the viscosity, crystallization kinetics, structure, and properties of the obtained materials are systematically determined by viscometry, differential scanning calorimetry, Fourier-transform infrared spectroscopy, X-ray powder diffraction, thermal-field-emission environmental scanning electron microscopy, and corrosion-resistance property tests. The results showed that the obtained glass-ceramics is composed of dendritic diopside (main crystalline phase) and bulk spinel (second crystalline phase). With increasing amount of Cr2O3, the viscosity of the slag glass melt increases. In addition, the samples exhibit crystallization activation energies in the range 378–454 kJ/mol, with slight fluctuations. Moreover, the crystallization index increases from 0.84 to 2.80. The obtained glass-ceramics exhibit a maximum density, bending strength, and acid and alkali resistances of 2.97 g/cm3, 196.69 MPa, 97.61%, and 98.04% respectively, demonstrating their wide application potential for various industrial applications.

Effect of B2O3 on the crystallization, structure and properties of MgO–Al2O3–SiO2 glass-ceramics

The formation of α-cordierite glass-ceramics in the MgO–Al2O3–SiO2 system without and with addition of B2O3 was investigated. Moreover, the effects of different contents of B2O3 on the crystallization behavior, structure variation, thermal and physical properties of glass-ceramics were studied, and the action mechanism of B2O3 was systematically discussed by XRD, FT-IR and XPS. The results show that a proper amount of B2O3 shortens the crystallization route and reduces formation temperature of α-cordierite, which further promotes the direct precipitation of α-cordierite in MAS system. The glass-ceramics undergo the phase transitions from intermediate phases of MgO·Al2O3·SiO2 and Mg0·6Al1·2Si1·8O6 to pure α-cordierite without the addition of B2O3. However, the pure α-cordierite directly precipitates in the glass-ceramics adding 4 mol% B2O3 without intermediate phases. Low B2O3 content (4 mol%) promotes the crystallization of α-cordierite, while high B2O3 content (8–12 mol%) inhibits it, which is accompanied by the increase of thermal expansion coefficient from 1.70 × 10−6 °C−1 to 3.72 × 10−6 °C−1 and the decrease of Vickers hardness from 9.4 GPa to 6.9 GPa. B2O3 is confirmed to be very important in controlling the crystallization process of α-cordierite in this glass-ceramics system, and this study is helpful for providing the reference value for others to choose B2O3 and its content.

Evolution of crystal growth in MgO–Al2O3–SiO2 glass ceramics

A new explanation for crystal growth limitation in MgO–Al2O3–SiO2 glass ceramics is proposed using TEM and molecular dynamics simulation.

Effect of replacement of Na2O by Fe2O3 on the crystallization behavior and acid resistance of MgO[sbnd]Al2O3[sbnd]SiO2 glass-ceramics

MgOAl2O3SiO2 glass-ceramics were prepared by melting method. The effects of replacement of Na2O by Fe2O3 on crystallization behavior and acid resistance of glass-ceramics were studied. The results showed that with Fe2O3 addition, the crystallization peak around 860 °C increased firstly and then decreased, while the peak around 1120 °C showed opposite changes. The crystallization peak around 1000 °C shiftted to low temperatures. With heat treatment temperature increasing from 880 to 1200 °C, μ-cordierite, spinel, sapphirine and α-cordierite precipitated successively in the glass samples. Fe2O3 had little effect on the type of crystal phases, but had a great influence on their crystallinity and precipitation temperature. After heat treatment at 1200 °C, the main crystalline phase changed from μ-cordierite to α-cordierite for the glass sample without Fe2O3. The addition of Fe2O3 promoted the crystallization of α-cordierite at low temperatures, especially for 1 mol% Fe2O3 doped sample, α-cordierite obviously precipitated at 1100 °C. All the base glass samples had poor acid resistance, which was greatly improved by heat treatment. When honeycomb structure α-cordierite appeared as the main crystalline phase, acid resistance deteriorated rapidly. A small amount of Fe2O3 addition reduced the acid resistance. With Fe2O3 content increasing, the acid resistance gradually improved.

Effect of Zn/Zr ratio on mechanical, dielectric, and thermal properties of MgO-Al2O3-SiO2 glass-ceramics

The influence of Zn/Zr ratio on the crystallization, microstructure, and properties of MgO-Al2O3-SiO2 (MAS) glass-ceramics was investigated. The sintering and crystallizing kinetics suggested that Zn/Zr ratio of 5/3 was beneficial to the sintering process and the crystallization. XRD indicated that the increase of Zn/Zr ratio changed the crystal phases and promoted the crystallinity. It was found that the coefficient of thermal expansion (CTE) was strongly dependent on the crystal phases. The mechanical properties were markedly improved by the increase of bulk density, crystallinity, and microstress. MAS glass-ceramics with Zn/Zr ratio of 5/3 sintered at low temperature of 900 °C shows good properties: εr = 5.7, tanδ = 0.32 × 10−3, σ = 279 MPa, φ = 96 GPa, α = 3.46 × 10−6/°C, which is compatible with silicon chips.

Effect of the ZrO2 concentration on the crystallization behavior and the mechanical properties of high-strength MgO–Al2O3–SiO2 glass–ceramics

High-strength, colorless glass–ceramics in the MgO/Al2O3/SiO2 system with high concentrations of ZrO2 and a great potential for technical application, e.g., as high-performance hard disc substrates, are investigated. ZrO2 concentrations from 6 to 9 mol% are added to a stoichiometric cordierite glass to investigate the influence of the concentration of the nucleating agent on the crystallization behavior and the mechanical properties. The phase formation and the microstructure of the glass–ceramics are studied using X-ray diffraction and scanning electron microscopy including electron backscatter diffraction. It is shown that the volume crystallization of ZrO2, a low-/high-quartz solid solution (low-/high-QSS), and spinel is accompanied by the surface crystallization of indialite. This phase offers a much smaller coefficient of thermal expansion than the other crystal phases, which may induce high compressive stresses in the surface layer of the glass–ceramics after cooling and seems to result in excellent mechanical properties of the material. Biaxial flexural strengths of up to 1 GPa were measured. Higher ZrO2 concentrations reduce the surface crystallization of indialite and decrease the mean size of the crystals resulting in a higher translucency. The volume-crystallizing phases and the mechanical properties of the glass–ceramics do not seem to be significantly affected by the analyzed ZrO2 concentrations.

CaO–MgO–Al2O3–SiO2 glass-ceramics from lithium porcelain clay tailings for new building materials

Lithium porcelain clay tailings (containing 1.2wt.% Li2O) blended with other chemical raw materials were used to develop a new glass-ceramic of CaO–MgO–Al2O3–SiO2 system for rolling process. The effects of TiO2 and ZnO oxides on melting and crystallization behaviors of glasses were investigated by DTA, XRD, EPMA and viscosity test. The results showed that melting temperature, forming temperature and glass transition temperature (Tg) of glasses were decreased with the increase of ZnO addition. Nevertheless, the crystallization temperature was shifted from 864 to 901°C when the addition of TiO2 decreased from 2wt.% to 0.5wt.%. Diopside as a major crystalline phase and spinel as a minor phase are precipitated in M3 specimen with 2.5wt.% ZnO and 0.5wt.% TiO2. The columnar and granular crystalline phases were distributed in M3 specimen nucleated at 750°C for 2h and followed by crystallization at 1110°C for 2h, which resulted in proper appearance suitable for decorative materials.

Crystallization and microstructure of CaO–MgO–Al2O3–SiO2 glass–ceramics containing complex nucleation agents

The CaO–MgO–Al2O3–SiO2 (CMAS) glass–ceramics containing binary complex nucleation agents were prepared by body crystallization process, and the effects of complex nucleation agents on the crystallization and microstructure of CMAS glass–ceramics were investigated by differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The complex nucleation agents consist of constant fluorine (8.0wt.% CaF2) and different oxides (3.0wt.% TiO2, ZrO2, or P2O5). Compared with the CMAS glass with only CaF2, the respective addition of oxides promotes the crystallization of CMAS glass, especially TiO2 or P2O5. The addition of TiO2 or ZrO2 has no obvious effect on the compositions of main crystalline phases, while P2O5 results in the precipitation of pyroxene phase instead of diopside phase, with the existence of more small crystals. The CMAS glass–ceramic containing CaF2+TiO2 or CaF2+P2O5 achieves full body crystallization with high crystallization ratio, and has high hardness, good chemical resistance and water absorption.

Molecular dynamics simulation for the rapid solidification process of MgO–Al2O3–SiO2 glass–ceramics

A molecular dynamics simulation method was used to study the effects of the microstructure on the solidification process of different cooling rates in the MgO–Al2O3–SiO2 glass–ceramics with cordierite as the main crystalline phase. The reasons for changes in the microstructure during the solidification process were analysed by the radial distribution function curve, the bond angular distribution, the coordination number and the volume changes. The results showed that the cooling rate greatly affected the crystallisation process and the glass transition process. When the cooling rate was too fast, the atoms could not undergo a massive displacement before they were “frozen”, and the ability of atoms to achieve an equilibrium position was limited. Some amorphous phases were formed as a result of the disorder of the atomic arrangement, then some crystalline phase precipitated from the vitreous, and a glass–ceramic material was eventually formed.

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

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.