Al2O3 SiO2 Research Articles

Preparation of monolithic Al2O3–SiO2 aerogels with high-temperature resistance using boehmite nanorods

In this study, monolithic Al2O3–SiO2 aerogels with excellent thermal stability were synthesized by ambient pressure drying (APD) or supercritical drying (SCD) using tetraethyl orthosilicate and boehmite nanorods (L = 20–30 nm, D = 3–5 nm) as precursors. The high specific surface area of aerogels prepared by APD or SCD was maintained after calcination at 800 °C (585 m2/g or 664 m2/g), 1000 °C (415 m2/g or 487 m2/g), and 1100 °C (175 m2/g or 231 m2/g). The anti-sintering mechanism of the aerogels prepared with boehmite nanorods as the aluminum source was discussed in detail. Successful preparation by APD offers the possibility of low-cost and large-scale application of monolithic Al2O3–SiO2 aerogels. Al2O3–SiO2 aerogels with excellent thermal stability have the potential to be used as high-temperature thermal insulating materials in aerospace applications.

Characteristics of Ce-doped phosphate inorganic glass scintillators for gamma- and X-ray detection

We report on the structural, photoluminescence (PL), and scintillation properties of Ce-doped P2O5–Al2O3–Cs2O–BaO glass scintillators having different Ce concentrations (1.96, 3.85, 7.41, 10.7, and 13.8 mol%) for gamma- and X-ray detection. The highest density (3.57 g/cm3) was achieved with Ce concentration of 13.8 mol%. The PL emission and X-ray-induced radioluminescence spectra showed emission peaks corresponding to the allowed transition from the Ce3+ 5d excited state to the 4f ground states. The highest scintillation light yields (approximately 2200 photons/MeV) were achieved with Ce concentrations of 7.41, 10.7, and 13.8 mol%. These light yields are higher than those previously reported for glasses containing heavy elements, such as Eu-doped SiO2–Al2O3–HfO2 (630 photons/MeV), Ce-doped P2O5–Li2O–GdI3–Al2O3–CaCO3 (1600 photons/MeV), and Ce-doped SiO2–Al2O3–BaF2–Gd2O3 (2050 photons/MeV). For all glasses, short scintillation decay times (28.5–34.0 ns) corresponding to the transition from the Ce3+ 5d excited state to the 4f ground states were observed. These results indicate that the fabricated glass with an optimal Ce concentration of 13.8 mol% is suitable for gamma- and X-ray detection.

Methane dry reforming: influence of the SiO2 and Al2O3 supports on the catalytic properties of Ni catalysts

The effect of the support nature (SiO2, Al2O3, SiO2–Al2O3) on the catalytic performance of Ni-based catalysts prepared by the incipient wetness method was explored in the dry reforming of methane reaction, and the catalysts were characterized by TG-DTA, SEM-EDX, XRD and UV-VIS methods. The results demonstrate that NiO supported on SiO2-modified Al2O3 exhibits superior catalytic performance in methane dry reforming in the temperature range of 650–700 °C.

Preparation and characterization of SiO2–Al2O3–MgO–CaO–based ceramic foams mainly from Ca–Mg–rich molybdenum tailings

Molybdenum tailings (MTs) and kaolinite were used as the main materials in the fabrication ceramic foams (CFs) via the high-temperature sintering method, with the addition of SiC as a foaming agent. The effects of MT content on the basic physical properties, pore structure, and chemical characterization were investigated. Results showed that MT enhanced the foaming capability. When the MT content was 60% and the sintering temperature was 1170 °C, the optimum CFs obtained demonstrated bulk density, porosity, water absorption, and compressive strength of 0.55 g/cm3, 77.3%, 6.94%, and 6.74 MPa, respectively, and the pore structure was relatively homogeneous with an average pore diameter of 0.67 mm. The results revealed that SiO2–-Al2O3–-MgO–-CaO system CFs can be prepared from Ca–Mg-rich MT, which provided a feasible strategy for value-added utilization of Ca–Mg-rich MT.

Nanoindentation Hardness and Modulus of Al2O3–SiO2–CaO and MnO–SiO2–FeO Inclusions in Iron

AbstractOxide inclusions appear in steel as a subproduct of steelmaking. These are generally detrimental to alloy properties; however, variations exist in the extent to which different inclusions are harmful because their properties vary as a function of their chemical composition. We use nanoindentation to measure the local elastic modulus and hardness of individual oxide particles, produced by precipitation within liquid iron, that belong to the systems Al2O3–SiO2–CaO and MnO–SiO2–FeO. Measured inclusion hardness values are typically in the range of 8 to 13 GPa and can reach 26 GPa for alumina-rich inclusions. Calcium aluminates rich in alumina are significantly stiffer than iron, with elastic moduli that can reach 350 GPa. On the contrary, calcium aluminates that are expected as a result of successful calcium treatment (i.e., with less than about 80 wt pct Al2O3 content) have elastic moduli below that of iron. This is also the case for the wide range of calcium aluminosilicates and of manganese silicates studied here. In addition, silicates containing about 70 to 80 wt pct MnO are observed to have a fine multiphase structure and an elastic modulus of ≈ 180 GPa. Those inclusions thus emerge as possible candidates if one aims to minimise, in loaded steel, stress concentrations associated with matrix-inclusion elastic mismatch.

Reusable, high specific surface areas, and excellent thermal stability Al2O3–SiO2 aerogel composites as high-temperature thermal insulators for radome applications

In this study, monolithic Al2O3–SiO2 aerogels with excellent thermal stability and high specific surface area were synthesized using boehmite nanorods (L=20–30 nm, D=3–5 nm). The high specific surface area of aerogels was maintained after calcination at 800 °C (663.54 m2/g), 1000 °C (486.91 m2/g), and 1100 °C (230.76 m2/g). The anti-sintering mechanism of the Al2O3-SiO2 aerogels was discussed. Thanks to the composite of Al2O3-SiO2 aerogel and mullite fibers, the disadvantages of brittleness and low strength of aerogel are overcome. The thermal conductivity of the composite is extremely low at 0.034 W/(m·K)-0.089 W/(m·K) (25 °C-1000 °C). Five muffle cycle back-temperature tests at 1000 °C and a butane blowtorch back-temperature test at 1350 °C also proved that the composites have excellent thermal insulation properties. Composites with excellent thermal insulation properties combined with lightweight, thinness, machinability, and good dielectric properties meet the need for high-temperature thermal insulating-wave transmitting integrated materials for hypersonic missile radomes.

Crystallization and rheology of Na2O–CaO–Al2O3–SiO2 melt in the vitrification of technological waste

AbstractVitrification of solid technological waste is currently under investigation. For this type of waste made up of metals, minerals, and organic matters, formulation studies were carried out in the NCAS (Na2O–CaO–Al2O3–SiO2) system in order to define a vitrifying additive to treat the entire waste deposit, while maximizing the waste loading. Main challenge related to this type of waste comes from the presence of alumina in very large quantities in the glass/glass–ceramics melt, enhancing the risk of melt solidification due to a fast and massive crystallization. Melt lock‐up can potentially occur at the operating temperature envisaged for the process (1400°C) and is prohibitive because it would lead to a premature stoppage of the process. The results obtained from casting tests, rheological experiments, and thermodynamic modeling enabled to provide an accurate estimation of the risk of melt lock‐up for NCAS compositions. It was highlighted that the composition had a major influence on the temperature at which massive crystallization might occur. From all the results obtained, the maximum Al2O3 content that could be incorporated in the final material was determined to be close to 50 wt%. The composition of a vitrifying additive was also statistically designed to treat the technological waste of interest.

Application of SCMs and seawater to cement-bonded calcareous sand: Macro performance, micro mechanism, and strength prediction

Cement-bonded calcareous sand (C-BCS) demonstrates promising potential for marine island construction due to its exceptional mechanical properties. However, challenges such as freshwater scarcity and the erosive effects of seawater hinder the extensive utilization of C-BCS. To address this, this study comprehensively examines the feasibility of incorporating supplementary cementitious materials (SCMs) and seawater in C-BCS, focusing on macroscopic properties, microscopic mechanisms, and strength prediction. Macroscopic tests reveal that blast furnace slag and silica fume effectively enhance the hydration process and mechanical properties of C-BCS. Moreover, the cemented specimens developed in this study partially meet the strength standards for road pavement sub-base and airport runway upper-base applications. Microscopic analyses indicate that calcareous sand serves as a plentiful source of calcium, facilitating the formation of calcium aluminate silicate hydrate (C-A-S-H) and tobermorite when combined with Al2O3 and reactive SiO2 from slag and silica fume. This enhances the mechanical properties of the samples and their resistance against seawater erosion. Additionally, a back propagation (BP) neural network model accurately predicts the unconfined compressive strength of the cemented specimens. The findings of this study support the broader implementation of SCMs and seawater in practical island engineering projects involving C-BCS.

Preparation of Li2O–Al2O3–SiO2–B2O3（LASB）glass-ceramic with low thermal expansion coefficient from spent hydrogenation catalysts and crystallization kinetics

The recovery of spent hydrogenation catalysts occupies advantages in both alleviating environmental burden and resource shortage. Whereas, the development of conventional hydrometallurgical recovery of molybdenum (Mo) and nickel (Ni) from spent MoNi/Al2O3 catalysts has been limited by the numerous processes and the accompanying generation of waste liquids and residues. Herein, A new recycling route for the preparation of spent hydrogenation catalysts with low thermal expansion coefficients (CTE) was proposed, which has the advantages of short process, green environment and high value utilization. The Li2O–Al2O3–SiO2–B2O3 (LASB) parent glass containing Mo and Ni were obtained by melting with different contents of the spent catalysts. The thermal expansion coefficient of the glass was minimized to 6.08 × 10−6/°C at an addition of 25 wt% of the spent catalysts. Moreover, according to the crystallization peak in DTA curve, glass-ceramics were prepared by one-step crystallization heat treatment at different crystallization temperatures. The main crystalline phase of the glass-ceramic precipitated by heating at 685 °C is β-quartz (Li2Al2Si3O10), which gives the glass-ceramics the lowest coefficient of thermal expansion (0.96 × 10−6/°C) of glass-ceramic as well as the maximum density (2.45 g/cm3) and Vickers hardness (705.8 Hv). Furthermore, the activation energy (354.65 ± 17.42) kJ/mol) and Avrami index (5.39) associated with crystallization were extracted from the fitting of different theoretical model, indicating the three-dimensional crystallization of the LASB glass-ceramics. This technology provides a waste-to-material strategy for hazardous waste and a clean production route for the preparation of the functional glass-ceramics.

Effect of Zn/Si ratio on conversion luminescent properties of Er3+/Yb3+ co-doped oxyfluoride glasses used for solar cells

Er3+/Yb3+ co-doped Na2O–CaF2–ZnO–Al2O3–SiO2 glasses with different Zn/Si ratios were prepared using the melt-quenching technique. The thermal stability was investigated by differential scanning calorimetry. Additionally, the absorption spectra were also analyzed to gather more information about their properties. The down-conversion luminescence corresponding to the strongest fluorescence at a wavelength of 547 nm was obtained under the 378 nm excitation, and a 4S3/2 level fluorescence lifetime was studied. By utilizing a laser pump with a wavelength of 980 nm, the process of both up-conversion and down-conversion luminescence was accomplished. In particular, the glasses substantially enhance fluorescence properties when the Zn/Si ratio is about 0.16. The changes in the Zn/Si ratio lead to modifications in the glass network structure, changing the coordination field environment around the fluorescence center and ultimately impacting the luminescence properties of the rare-earth ions. These effects are evidenced through the findings obtained from Fourier transform infrared spectroscopy and fluorescence spectroscopy analysis of the glass material.

Optical properties and luminescence behavior of Tb3+-Doped SiO2–Al2O3–BaO–BaF2 oxyfluoride glasses and glass ceramics

In this study, oxyfluoride glasses with chemical composition of 45SiO2–15Al2O3–10BaO–30BaF2-xTbF3 (x = 0.2, 0.4 and 0.6 (mole ratios)) were prepared through the conventional melt-quenching method. Raman and FTIR spectra as well as molar volume calculations proved the creation of more non-bridging oxygens (NBOs) in presence of more TbF3 content. Accordingly, absorption edge in UV–Vis spectra showed a slight red-shift to longer wavelengths. The glass with 0.4 mol ratios of TbF3, exhibited the highest photoluminescence emission and its green-to-blue intensity ratio was 0.66. Therefore, this sample was chosen and heat treated at 630, 650 and 675 °C to prepare glass ceramic samples. For the sample heat treated at 650 °C, photoluminescence intensity increased and green-to-blue intensity ratio reached 0.69. Also, lifetimes of green and blue emissions increased from 3.35 ms to 3.67 ms and from 2.95 ms to 3.10 ms, respectively, when the base glass heat treated at 650 °C. Formation of BaF2 nanocrystals in glass ceramics moved the UV–Vis absorption edge to longer wavelengths significantly. Increment of the weak and dangling bonds in crystallized samples reduced Fermi energy, indirect and direct optical band gap energies from 3.792 eV to 3.301 eV, from 3.522 eV to 3.093 eV and from 4.095 eV to 3.582 eV respectively, which led to higher semiconducting behaviors.

Radio-photoluminescence Properties of Sm-doped HfO2–Al2O3–SiO2 Glass Ceramics

Radio-photoluminescence Properties of Sm-doped HfO2–Al2O3–SiO2 Glass Ceramics

Study on the Causes and Control Measures of Mg–Al Spinel Inclusions in U75V Heavy Rail Steel

U75V heavy rail steel production uses an aluminum-free deoxidation process; however, large particles of MgO–Al2O3 inclusions form in the steel, which has a great impact on product quality. In this paper, we try to explain how spinel inclusions, which affect the metallurgical quality of heavy rail steel, are produced by thermodynamic and experimental methods, and then determined measures for avoiding such inclusions. The formation mechanism of spinel inclusions in U75V heavy rail steel was determined through the analysis of nozzle clogging in the pouring process and typical inclusions in steel. The results show that there are two types of spinel inclusions in heavy rail steel: one is pure Mg–Al spinel inclusions and the other is Mg–Al spinel inclusions coated with calcium aluminate. The small, pure Mg–Al spinel inclusions were precipitated during the solidification of the molten steel, and the precipitation temperature was related to the composition of the molten steel. The large spinel inclusions were derived from clogging of the submersed nozzle. Mg–Al spinel inclusions coated with calcium aluminate were transformed from CaO–SiO2–Al2O3–MgO complex inclusions in the steel during cooling, and the formation temperature was related to the content of Al2O3 and MgO in the inclusions. The content of Al2O3 and MgO in the inclusions was the key to the formation of the Mg–Al spinel inclusions. Therefore, in order to control the production of spinel inclusions in steel, it is necessary to strictly control the content of impurity elements such as magnesium and aluminum in the alloy auxiliary materials, to reduce the secondary oxidation of liquid steel and to reduce the erosion of refractory materials.

Relationship between viscosity, foaming, and structure of CaO–SiO2–Al2O3–MgO–FeO slag with the addition of SiO2 and Al2O3

Optimizing the foaming characteristics of slag in electric arc furnaces (EAF) presents a challenging task, affecting electrode heating efficiency and increasing smelting cost. This study explores the impact of adding silicon dioxide (15–35 wt%) and a small quantity of alumina (5–10 wt%) on the viscosity and foaming properties of CaO–SiO2–Al2O3–MgO–FeO slag. Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) were employed to investigate structural changes in the slag melt. The findings reveal that higher levels of silica or a slight increase in alumina content enhance slag polymerization and foaming efficiency. Specifically, a 10 wt% alumina content, in contrast to 5 wt%, leads to high silica content, leading to faster polymerization but relatively lower viscosity. Structural analysis confirms that increasing alumina content, particularly when silica content is high, results in a less stable Al–O–Si structure, causing a shift from Q0 and Q1 units to Q2 and Q3 units, which ultimately reduces viscosity. When the alumina content remains at 5 wt% and silica content increases from 15 wt% to 35 wt%, foaming efficiency improves from 13.06 cm min to 94.97 cm min, a remarkable 627% rise. Moreover, when silica content is 30 wt% and alumina is slightly increased by 5 wt%, there is a notable enhancement in foaming efficiency, rising from 47.11 cm min to 89.16 cm min, while the effect on viscosity is not prominent.

Evolution of MnO–SiO2–Al2O3–MgO inclusions during heat treatment at 1100 °C

Evolution of MnO–SiO2–Al2O3–MgO inclusions during heat treatment at 1100 °C

Preparation of innovative glass-ceramic materials based on mica schist within the CaO–MgO–Al2O3–SiO2 system

The preparation of affordable glass-ceramic materials by induced crystallization of glass-based mica schists and other natural raw materials (dolomite & limestone), as well as magnesite as a mine waste, was investigated for the first time. Five glass batches were designed based on the eutectic composition of the diopside-anorthite ratio with increasing the enstatite content from 0–40 wt.% within the quaternary CaO–MgO–Al2O3–SiO2 system. After melting at 1400 to 1500 °C, casting into discs & rod shapes, and annealing process, the prepared glasses were subjected to careful heat treatment schedules. Several techniques were used to characterize the applied raw materials, glass, and glass-ceramic materials such as X-ray Fluorescence (XRF), Differential Thermal Analysis (DTA), X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Polarizing-light Microscopy. The produced glass-ceramic from the glass batch with 30 wt% enstatite that was nucleated at 750 °C /2h followed by crystallization at 950 °C /h, displayed the well-developed product on the level of volume crystallization and pore formation.

Viscosity modelling of ternary CaO–Al2O3–SiO2 melts assisted by in situ high temperature Raman spectroscopy

In this study, the evolution of microstructure and its correlation with the viscosity of CaO–SiO2-based melts, incorporating various Al2O3 additives, have been investigated by employing in situ high temperature Raman spectroscopy and viscosity model. Raman spectra of the melts were procured at 1823 K by using in situ high temperature Raman spectroscopy. After considering the intricate influences of temperature and Raman scattering cross section (RSCS), the original Raman spectra of aluminosilicate melts underwent calibration. Subsequently, the distribution of microstructure species Qi (i = 0–4) was quantitatively performed through meticulous deconvolution of calibrated Raman spectra. The evolution of Qi species with the increasing Al2O3 content reveals a decrease in Q1 and Q2 species, while the fully polymerized Q4 experiences a continuous and significant growth. Concurrently, Q3 initially exhibits an upward trend followed by a subsequent decline. The Qi evolution culminates in an overall enhancement of the degree of polymerization. Viscosity was determined by utilizing a rigorously selected viscosity model, elucidating a consistent upward trajectory as Al2O3 content is incrementally added. Furthermore, a quantitative analysis of the relationship between viscosity and structure was conducted based on the average number of non-bridging oxygen per network-forming tetrahedron (NBO/T). The findings demonstrate a robust linear relationship between the logarithm of viscosity and NBO/T, thereby offering valuable insights for examining and predicting viscosity behavior of aluminosilicate systems.

Enhanced performance of low-pressure sintered CaO–MgO–Al2O3–SiO2–CaCl2 glass-ceramic by using Cr2O3 as the nucleating agent

The sintered glass-ceramic always has an uneven microstructure due to the surface crystallization, which limits the enhancement of its mechanical properties. In the present work, Cr2O3 was added into CaO–MgO–Al2O3–SiO2–CaCl2 glass as the nucleating agent, and the low-pressure (14 kPa) sintering technology was utilized to promote the densification process of the glass frits (0.42–2 mm). It was found that by adding 1 wt% of Cr2O3, the bulk crystallization can be achieved inside the glass particle and the microstructure of the glass-ceramic became more homogeneous. Correspondingly, the bending strength was improved from 127 to 147 MPa, and the Vickers hardness was enhanced from 6.5 to 6.7 GPa, comparing with the Cr2O3-free glass-ceramic. The current study confirmed the positive impact of nucleating agent in the performance of sintered glass-ceramic, which also provided a route for the utilizations of CaCl2-and Cr2O3-bearing wastes.

Radiation Shielding Properties of Aluminosilicate Glass Systems using Phy-X Software

In this work, we studied the radiation shielding properties of aluminosilicate glasses with constant SiO2 content. By applying Phy-X software, we calculated different radiation attenuation factors for the chosen glasses. The linear attenuation coefficient (LAC) for the chosen CaO–Al2O3–SiO2 glass systems showed an exponential decrease as the energy changes from 0.015 to 15 MeV. For the glass with composition of 35CaO-5Al2O3-60SiO2, the LAC decreases from 29.80 to 1.279 cm-1 between 0.015 and 0.05 MeV. The LAC decreases with the increase in the Al2O3 content. The minimum LAC is found for the glass with the composition of 20CaO-20Al2O3-60SiO2. The effective atomic number (Zeff) was reported, and we found that the highest Zeff is occurred at 0.015 MeV and varied between 14.55 and 16.09. The Zeff decreases when we replaced the CaO by Al2O3. The half value layer was reported and we discussed the impact of the density of the glasses on the HVL values. In the low energy range, the HVL values are small and the different compositions have close HVL. For E>0.08 MeV, the HVL is higher than 1 cm for all glasses, while for E> 0.2 MeV, the HVL becomes higher than 2 cm for all glasses. The glass with composition of 35CaO-5Al2O3-60SiO2 has better attenuation performance than the other glasses in this study.

Effect of heating rate on crystallisation and properties of R2O–CaO–MgO–CuO–Al2O3–SiO2 glass-ceramics

R2O–CaO–MgO–CuO–Al2O3–SiO2 (RNa, K) glass-ceramics were fabricated using the melt-quenching method and the effect of heating rate on the microstructure and properties of the glass-ceramics was investigated. The results demonstrated that the main crystal phase of the samples was clinoenstatite, and the secondary crystal phases were forsterite and diopside. With an increase in heating rate, the diffraction peak intensity of clinoenstatite gradually increased, and the morphology of the particles changed from short columns to long needles. When the heating rate was 1 °C/min, the sample exhibited flexural strength and Vickers hardness of 7.38 GPa and 84.33 MPa, respectively. When the heating rate was 10 °C/min, the Cu+ content in the sample reached the maximum of 2.1 wt%, which is 1.4 times of Cu+ in the brown sample obtained by heat-treatment at 1 °C/min. The colour of the sample intensified as the heating rate was increased from 1 °C/min to 20 °C/min, and the sample heated at 10 °C/min was brownish-red. The heating rate has a significant effect on the colour of glass-ceramics with the same CuO content, providing a new approach for regulating the colour of glass-ceramics. Further, this study has significant prospects in enriching the colour of glass-ceramics for architectural decoration and reducing production costs.