Increasing Al2O3 Content Research Articles

Analysis of corrosion of corundum refractory castables in relation to increased MgO content in dendromass ashes

Biomass ash has a significantly lower proportion of Al2O3 and higher proportions of K2O, CaO and SiO2 than coal ash. Biomass combustion in power plants increases demands on refractory linings and metal fittings in boilers. Grates and linings of combustion chambers in furnaces and boilers are more susceptible to clogging and are degraded by bio-ash slag. The results of this study suggest that the addition of approximately 2% of powder magnesite waste to the wood-chip fuel can significantly mitigate ash slagging and also corrosion of the corundum refractory material. With regard to the resulting increased MgO content in the dendromass ash, the corrosion of corundum refractory material was studied. The MgO content in the ash was increased by adding powder magnesite waste to ash samples. The results of corrosion tests (1450 °C/7 h) showed that ash slag with MgCO3 addition corroded the corundum material less. Analyses of the post-mortem slag and corrosion interface confirmed: (i) higher K2O concentration in the ash caused increased corundum material corrosion by both vapours (g-s) and melt (l-s); (ii) K2O reacted with Al2O3 at the corrosion interface and also penetrated intensively into the fine-grain matrix by surface diffusion; (iii) MgO remained in the slag; (iv) increased Al2O3 content in the molten slag initiated a liquation of MA-spinel. These results (especially MA spinel liquation from the slag and K2O diffusion through the matrix followed by micro-grain dissolution) indicate that replacing the mullite binder phase in the matrix with MgO and/or spinel could lead to improved resistance of the refractory material to biomass ash slag.

Exploration of the amphoteric transition of Al2O3 on melt structure and viscosity of silicate slag

The amphoteric oxide Al2O3 has different behaviors in different chemical environments. In an acidic environment, Al3+ breaks the network structure while in an alkaline environment, Al3+ forms a three-dimensional network like Si4+. In this paper, the amphoteric effect of Al2O3 on the structure and viscosity of a five-oxide silicate system (SiO2–Al2O3–FeO–CaO–MgO) is studied. The viscosities with different Al2O3 contents were experimented on an inclined plane and compared by the flow length of liquid slags. The study shows that the melt viscosity increases and then decreases with increasing Al2O3 content. As Al2O3 increases, the coordination number of the basic cations increases, changing from a network destruction ion to a charge balance ion. And the coordination number of Al3+ has a higher shift from four to five. The detailed reaction pathways of the structural units are revealed through the variation of oxygen types. The addition of Al2O3 leads to the replacement of [SiO4]4- by [AlO4]5-, with a decrease in the contents of Si–O–Si and Si–O-M while an increase of Si–O–Al, Al–O–Al and TO. Therefore, the network strength increases first and then decreases which is consistent with the tendency of viscosity.

Study of Dendromass Ashes Fusibility with the Addition of Magnesite, Limestone and Alumina

The fusibility of ash from woodchip combustion is characterised in the present work. The impact of the increase in MgO, CaO, and Al2O3 content in the bio-ash on the classification of ash into categories according to slagging and fouling indices was evaluated. The ash was characterized based on the chemical composition using slagging and fouling indices. However, these ash composition changes did not assign the ash into categories of the indices FU, SR, RS, and B/A (fouling, slagging, slag viscosity, basicity), with less ash inclination to slagging and fouling. The indices were primarily derived for ashes from coal combustion. The indices values characterizing the ash were compared with measured results of ash melting according to STN ISO 540. The measured ash fusibility values showed that the addition of magnesite, limestone, and alumina to dendro-ashes increases the DT (temperature of deformation), HT (temperature of hemisphere), and the AFI (ash fusibility index). There is no conformity between the values of the indices and the measurement of ash fusibility temperatures. In terms of temperatures in the combustion chamber, the measured sintering (Tsin) and DT are suitable for evaluating the tendency of ash to slagging and fouling as well as an accretion of ash particles sticking to the lining.

A structure-oriented elucidation for viscous flow of SiO2-MnO-Al2O3 fused submerged arc welding fluxes

Understanding the physiochemical properties of flux is critical to addressing the challenges towards developing high heat input welding flux. In this study, the viscous behavior and structure of ternary SiO2-MnO-Al2O3 submerged arc welding fluxes were investigated using the rotating cylinder method for viscosity measurement, Raman spectroscopy and X-ray photoelectron spectroscopy for structure analysis. The results showed that the viscosity increased with the substitution of MnO with Al2O3, which is correlated to the enhancement in the degree of polymerization of the flux as the activation energy increased from 71.36 to 119.71 kJ/mol with increasing Al2O3 content from 0 to 20 wt.pct. The enhanced (Q2+Q3+Al-O0)/(Q0+Q1+Al-O+AlO6) ratio indicated the continuous polymerization of the flux structure, which was further confirmed by the distribution characteristics of various oxygen species and thermodynamic analysis.

Effect of CaO/Al2O3 Ratio on Physical Properties of Lime-Alumina-Based Mould Powders

High-aluminium steels contain a significant amount of aluminium. The reaction between Al in the liquid steel and SiO2 in lime-silica-based mould powders during the continuous casting process of high Al steel causes chemical compositional changes in the mould powders, subsequently affecting the surface quality of slabs. In order to solve the aforementioned problem, lime-alumina-based mould powders have been developed, which can lead to an increase in the surface quality of cast slabs by inhibiting steel/slag interaction. However, the mould slag tends to crystallise easily, which leads to a deterioration of the mould lubrication. In view of this aspect, it is important to develop and optimize lime-alumina-based mould powders to meet the requirements of continuous casting of high-aluminium steels. In this study, the changes in crystallinity, viscosity and melting temperature of lime-alumina-based mould powders with the effects of increasing the CaO/Al2O3 ratio have been observed through STA (Simultaneous Thermal Analysis), HSM (Hot Stage Microscopy), XRD (X-ray Diffraction), IPT (Inclined Plate Test) and rotational viscometer. The crystallisation behaviour of these mould powders was evaluated by generating CCT (continuous cooling transformation) diagrams. Additionally, the changes in steel chemistry have also been analysed using XRF (X-ray fluorescence) and ICP (Inductively Coupled Plasma Mass Spectrometer). The results of these analyses demonstrated that crystallinity of lime-alumina-based mould powder is increased while the initial crystallisation temperature and viscosity are decreased by CaO/Al2O3 additions. However, the degree of steel/slag interaction decreases with an increase in Al2O3 content.

Study on the effect of Al2O3 on the crystallization behaviour of MnO–SiO2–MgO inclusions in tire cord steel

ABSTRACT Aiming at avoiding the formation of high melting point inclusions containing Al2O3 and reducing the wire breakage rate of the tire cord steel. MnO–SiO2–10wt.%MgO–(5wt.%, 10wt.%, 15wt.%, 20wt.%) Al2O3 system were designed to investigate the crystallization behaviour by XRD, SEM-EDS, FactSage 8.0. The results indicate that the Mn/Mg element ratio of the Mg-Mn olivine phase precipitated from the system varies. Mg–Mn olivine phase is formed by the interaction of the components in the melt or by the occurrence of homogeneity and the liquidus temperature of the system decreases with the increase of Al2O3 content. Al2O3 lowers the melting point of the whole system by forming the low melting point phase Mn3Al2Si3O12. To obtain low melting point plasticized inclusions, the Al2O3 content of the system needs to be controlled in the range of 15–20 wt.%.

Influence of TiO2, Al2O3, and Basicity on Viscosity and Structure of High Titanium-Bearing Blast Furnace Slag

The viscosity of high-titanium blast furnace slag with different TiO2 content, Al2O3 content, and basicity was measured at 1653-1773 K using the rotational cylinder method. The phase composition of the slag is measured by XRD. Phase diagram of the slags is calculated by FactSage software. Ionic network structure of the slags is analyzed by FT-IR. Results show that TiO2 depolymerizes the silicate network structure, reducing viscosity at high temperature, while increasing Al2O3 content generates a more complicated silicate, increasing viscosity. Basicity affects viscosity, with higher basicity resulting in lower viscosity above 1733 K. Perovskite significantly affects the viscosity of slag. This study provides an in-depth understanding of the relationship between the composition and viscosity of high-titanium blast furnace slag, which is very important for improving production efficiency.

Optimal Alkalinity Model of Ladle Furnace Slag for Bearing Steel Production Based on Ion–Molecule Coexistence Theory

The fatigue life of bearing steel is closely related to the total oxygen content (T(O)) of the liquid steel. In order to stably and effectively control the T(O) during the ladle furnace (LF) refining process, we established a calculation model of optimal alkalinity for the refining slag CaO–SiO2–Al2O3–MgO–FeO–CaF2 at 1853 K based on ion–molecule coexistence theory (IMCT). Here, the influencing factors are discussed. The results show that the maximum value of NFeO occurred when the optimal alkalinity was around five at varied FeO contents, and that the optimal alkalinity basically remained the same with changes in FeO content. With the increase of MgO content, the optimal alkalinity decreased. However, the change in the value of NFeO against the higher alkalinity was not obvious at a given MgO content. The effect of Al2O3 content on the optimal alkalinity was opposite to that of MgO. With the increasing Al2O3 content, the optimal alkalinity obviously increased, while the maximum value of NFeO occurred when the Al2O3 content varied from 35 wt% to 45 wt% at higher alkalinity. The higher w(CaO)/w(Al2O3) mass ratio had a distinct effect on the value of NFeO against alkalinity, while the effect of alkalinity on the value of NFeO was not obvious at a fixed CaF2 level. This optimal alkalinity model based on IMCT can provide a certain guiding role in the process of refining slag composition optimization and is conducive to effectively controlling total oxygen content in the refining process.

New linear high-temperature thermistors based on the xAl2O3-(1-x)CaMnO3 ceramics

It is very important for a thermistor to have linear electrical properties, which can effectively reduce the complexity of circuit design. Phase structure modulation through introducing a second phase is crucial to achieve high performance electronic ceramics. Herein, new linear high-temperature thermistors based on the xAl2O3-(1-x)CaMnO3 ceramics were synthesized by the solid phase reaction method. With increasing Al2O3 content, CaMn2O4 and CaAl2O4 phase were observed, which formed internal conducting network and induced linear electrical properties. The ceramics exhibited negative temperature coefficient (NTC) thermistor characteristics in the temperature range of 523 K–1173 K. Their resistance-temperature (R-T) relationship displayed a good linear characteristic, especially for x = 0.3, which showed the highest linearity (R2: 0.9984) in the temperature range of 523 K–1173 K, covering medium to high temperature region. The mechanism of linear electrical properties was explained by a parallel conductive model in combination with complex impedance analysis. This approach could be generalized for designing linear high-temperature thermistors with a wide temperature range.

Effect of high temperature tempering on the phase composition and structure of steelmaking slag

Abstract Blast furnace slag and steelmaking slag, as the main accessory products of iron and steel smelting, are piled up in large quantities due to their huge output, high treatment difficulty and low comprehensive utilization rate, which has a serious impact on the land and environment. In order to improve the comprehensive utilization of steelmaking slag, low basicity blast furnace slag was added to the existing steel slag for quenching and tempering. The influence of basicity on the chemical composition and phase precipitation of mixed slag was analyzed. In the research process, the phase composition and morphology of blast furnace slag and steel slag of Baotou Steel were analyzed using FactSage7.1 thermodynamic calculation software, ZEISS high-resolution scanning electron microscope (SEM), modern fast high-resolution Bruker energy dispersive spectrometer and AMICS-Mining automatic mineral analysis software. The results show that the mineral phase composition of blast furnace slag is mainly calcium aluminum yellow feldspar and that of steelmaking slag is mainly dicalcium silicate(C2S), magnesium-iron phase solid solution, rose pyroxene and calcium iron aluminate. When the basicity of the mixed slag is 2.0, it can effectively inhibit the formation of non-cementitious mineral anorthite and promote the formation of better cementitious mineral C2S. At the same time, it is found that the melting temperature of mixed slag decreases with the increase in Al2O3 content.

Stability and electronic properties of two-dimensional Ga2O3 and (MxGa1-x)2O3 (M = Al, Ga) alloys

The alloying of Ga2O3 monolayer with oxides of the same main group element (Al and In) is simulated by the special quasirandom structures method. The stability and electronic properties of the Ga2O3 monolayer and (MxGa1-x)2O3 monolayer alloys are systematically investigated by first-principles calculations. The (AlxGa1-x)2O3 monolayer alloy becomes more stable with the increase of Al2O3 content, but the stability of (InxGa1-x)2O3 monolayer alloy worsens with the increase of In2O3 content. The (AlxGa1-x)2O3 monolayer alloy has relatively better thermodynamic stability, which would be easily synthesized at room temperature. The orbital-projected band structure and charge density reflect that the effect of alloying Ga2O3 with Al2O3 and In2O3 on the electronic properties of materials is mainly on the conduction band. Interestingly, we find that the charge density of the VBM and CBM states for Ga2O3 monolayer and its monolayer alloys exhibit the characteristic of complete separation in real space, i.e., an abnormal carrier separation. Through the calculation of the band-gap bowings parameter, it is predicted that the band gap of the monolayer alloy can continuously be tuned in the range of 3.38 ∼ 7.02 eV. These results would shed some light on the application of the Ga2O3 monolayer and its monolayer alloys in optoelectronic devices.

High temperature compression of Mo(Si,Al)[formula omitted]-Al[formula omitted]O[formula omitted] composites

The aim of this study was to investigate the effect on high temperature of mechanical properties of adding Al2O3 particles to polycrystalline Mo(Si,Al)2. Mo(Si,Al)2-Al2O3 composites, containing 0–25 wt% Al2O3 particles have been compression tested at 1300 °C, and the microstructure after deformation was studied using electron backscatter diffraction. It was shown that even small amounts (5 wt%) of Al2O3 particles resulted in a grain-refined material through inhibition of grain growth during sintering, which lead to lower flow stresses compared to the coarse-grained Al2O3-free material. The inverse grain size effect and post-test microstructure investigations suggest that creep-like deformation mechanisms dominate in fine grained Mo(Si,Al)2-Al2O3 composites at 1300 °C. In the materials containing 5–15 wt% Al2O3, the maximum stress decreased with increasing Al2O3 content. In materials with higher Al2O3 additions, the maximum stress increased with the Al2O3 addition, but did not reach the strength levels in the Al2O3-free reference material. It is suggested that the deformation behaviour is affected by electroplasticity effects as resistive heating was used. Electroplasticity contributes to the decrease in maximum stress observed in the lower Al2O3 containing materials, while this is outweighed by particle strengthening at higher Al2O3 contents.

Effect of Al2O3 on migration and distribution of chromium and chromium fixation effect in stainless-steel slag glass-ceramics

Stainless-steel slag was used to prepare glass-ceramics, which could solidify chromium (Cr) in the slag. The migration and distribution state of chromium in the slag during the preparation of the glass-ceramics have a great influence on the chromium fixation ability of the glass-ceramics. In this paper, the effects of Al2O3 content in the glass-ceramics on the migration and distribution of chromium during the nucleation and crystallization steps, and on the chromium fixation effect of the glass-ceramics were systematically studied. The results show that in the nucleation stage, with the increase of Al2O3 content, the number of chromium spinel (Cr-spinel) nanocrystals formed in the glass first increases and then decreases, and Cr in the glass phase gradually migrates to Cr-spinel nanocrystals. TEM and XPS analyses show that during crystallization, part of Cr in Cr-spinel diffuses into diopside lattice, and the other part of Cr still exists in Cr-spinel wrapped by diopside. Cr in the glass phase also diffuses and migrates into the diopside lattice with the formation of diopside crystals. The optimal Al2O3 content is 11.8wt.%, which results in 97.94wt.% of the total Cr being fixed in the diopside crystalline phase. The ability of chromium fixation is very high giving a very low Cr leaching concentration of 0.004mg/l. The research results provide theoretical and technical support for increased chromium fixation and realizing harmless and high-value utilization of stainless-steel slag.

Efficient preparation of ultrathin ceramic wafer membranes for the high-effective treatment of the oilfield produced water

Efficient preparation of ceramic membranes helps to reduce costs and makes them more competitive in the field of wastewater treatment. In this work, an ultrathin Al2O3 ceramic wafer membrane with a thickness of 250 µm and the mean pore size of approximately 200 nm was prepared from the Al2O3/polysulfone slurries via a casting-phase inversion/sintering approach. This ultrathin and hydrophilic ceramic wafer has a fully sponge-like and slightly asymmetric structure and desirable porosity, endowing it with an exceptionally high pure water permeability of ∼ 45,000 L m-2h−1 bar−1, an ultrahigh and stable emulsion flux of 2500 ∼ 3500 L m-2h−1 bar−1, as well as a high oil rejection of 99 % against real oilfield produced water (OPW). In addition, the increased Al2O3 content enhanced the thermodynamic instability of the ceramic slurry, leading to the enhanced interfacial instability, which contributes to the uniform distribution of Al2O3 particles on the precursor membrane surface to some extent during the phase inversion process, thus to reduce the surface defects of ceramic membranes after sintering. The membrane fouling analysis revealed that the dominant fouling mechanism was cake filtration, indicating the formation of a relatively dense and smooth skin layer of the ceramic wafer, which endow it with a high flux recovery ratio of 97.8 % by a simple chemical cleaning after OPW filtration.

Analysis of scale and frame interface effects on the solidification properties of solar salt in mesopores

The intermittency and instability of solar irradiation can be effectively overcome by using medium- and high-temperature composite phase change materials (PCMs) for latent heat storage. Studies using metals and organics as phase change materials show that the phase change behavior of mesoporous composite phase change materials is affected by the constraint effect, and its thermophysical parameters (such as phase change point and phase change latent heat) are significantly different from those of macro volume. However, at present, research on molten salt phase change materials, which are widely used in the field of medium- and high-temperature research, is insufficient. Molecular dynamics simulations combined with experimental methods were used to analyze the changes in the freezing point, supercooling degree and enthalpy of solidification of solar salt in mesoporous composite phase change materials, which were based on the self-diffusion coefficient and the potential energy-temperature curve. The results show that a larger mesoporous size leads to a higher freezing point of the solar salt. At the same scale, with the increase in Al2O3 content in the framework, the freezing point of the solar salt first decreases and then increases. The supercooling degree of solar salt decreases with increasing scale. When the mass content of Al2O3 in the framework is in the range of 25 wt%-40 wt%, the supercooling degree of solar salt increases gradually; in contrast, it decreases in the range of 40 wt%-50 wt%, and finally, it increases again in the range of 50 wt%-75 wt%. The latent heat of phase transition increases with increasing scale. With the increase in Al2O3 content in the framework, the latent heat of phase transformation first decreases, then increases, and finally stabilizes. Al2O3 and SiO2 in the interface of the frame can promote heterogeneous nucleation and provide a substrate for the nucleation of molten solar salt. They also reduce the degree of supercooling. It is found that the effect of Al2O3 on nucleation is more significant.

Phase evolution and pulverization mechanism of self‐pulverizing carbonatable clinkers

AbstractThis paper investigates the phase evolution and pulverization mechanism of a self‐pulverizing carbonatable clinker (SPCC) with a variety of raw material compositions. The particle size, mineral phases, and microstructure of SPCC, produced by sintering at 1400°C for 3 h, were systematically studied by laser particle size testing, XRD/QXRD and SEM/EDS. Results show that clinkers sintered by raw materials with low‐Ca/low‐Al (Ca/Si < 1.6; Al2O3 < 10 wt.%) or high‐Ca/medium‐Al (Ca/Si > 2.6; Al2O3 ≈ 10 wt.%) are non‐pulverized after cooling. The mineral phases of C2AS, CA, and C12A7 are considered to facilitate clinker pulverization at low γ‐C2S contents. With the increase of Al2O3 content in raw materials, SPCC is refined in particle size, accompanied by the significant decrease in the content of calcium silicates. Based on the results, guidelines for producing SPCC are proposed.

Thermophysical properties of liquid CaO-SiO2-Al2O3-MgO-TiO2-V2O3 slags

The present work investigated the effect of V2O3 in the range of 0 to 10.5 wt% on the thermophysical properties (viscosity, density, and surface tension) of CaO-SiO2-Al2O3-MgO-TiO2 slags with the CaO/SiO2=1.3 and varied content of Al2O3 and TiO2. The obtained experimental results were then supported by thermodynamic calculation with FactSage 7.2. The results shown that, with the increase of the V2O3 content, the viscosity of all studied slags decreased. Moreover, the addition of TiO2 up to 10 wt% to the matrix slag led to a decrease in viscosity and the addition of Al2O3 up to 20 wt% increased the viscosity without the presence of V2O3. Thereby the behavior of critical temperature on all viscosity curves corresponded with the behavior of crystallization temperature of melilite. The increase in the content of V2O3 to 10.5 wt% in all slags with and without additional TiO2 or Al2O3 resulted in an increase in density at temperatures of 1450–1650°C. The surface tension increased with increasing Al2O3 content and decreased with increasing TiO2 and V2O3.

Effect of Alumina Content on Structure and Properties of High Refractive Index Glass

In this paper, BaO-ZnO-TiO2-SiO2 is used as the research system of high refractive index glass, and IR, XRD and DTA are used to study the structure, thermal behavior, crystallization and chemical stability of different glasses when Al2O3 gradually replaces CaO. The results show that when Al2O3 replaces CaO, the glass still has an amorphous structure. With the increase of Al2O3 content, the glass structure first becomes tight, and then due to the formation of [AlO6], the glass network becomes loose, and the glass density peaks with the increase of Al2O3 content. DTA analysis showed that with the increase of Al2O3 content, the devitrification trend of the glass increased during the cooling process, the crystallization peak moved to the low temperature direction, and the exothermic effect weakened, indicating that the surface crystallization trend of the glass increased and the overall crystallization became weaker. The results show that the density, refractive index and water resistance of glass microspheres containing only CaO are the best, but the crystallization of glass is obvious during heat treatment.

Microstructure and wear behaviors of Cr2O3-Al2O3 composite coatings deposited by atmospheric plasma spraying

The Cr2O3 and Cr2O3-Al2O3 composite coatings were deposited by atmospheric plasma spraying on 304 stainless steel. The cross-sectional morphology and porosity of the coatings have been compared, indicating that the structure defects reach the minimum when Al2O3 content is 20 wt%. The phase composition of coatings was measured, while the shift of the Cr2O3 phase peak increased with the increase of Al2O3 content. The wear tests were carried out to reveal the role of Al2O3 hard particles in the Cr2O3-Al2O3 composite coating in terms of tribological properties. The results indicated that the addition of Al2O3 hard particles would contribute to improving the wear-resistance performance. Compared with the Cr2O3 coating, the Cr2O3-Al2O3 composite coatings exhibited less brittle fracture and generated more refined particles, which was favorable for the formation of tribo-film. In addition, a model diagram of protection from re-destruction of peeling pits with the assistance of refinement particles was proposed.

Design of Refining Slag Based on Structural Modifications Associated with the Boron Removal for SoG-Si.

Solar grade silicon (SoG-Si) is the core material of solar cells. The removal of boron (B) has always been a challenge in the preparation of high purity Si. Slag refining has always been considered as one of the effective methods to remove B, but the design of refined slag has been limited by the cognition of the relationship between slag structure and impurity removal, and can only rely on the apparent basicity and oxygen potential adjustment of slag based on a large number of conditional experiments. In order to clarify the B removal mechanism of slag refining from Si, nuclear magnetic resonance (NMR) and Raman vibrational spectroscopy were used to investigate in detail the behavior and state of B and aluminum (Al) in the SiO2–CaO–Al2O3–B2O3 slag. The role of the degree of B–Si cross linking on the B activity in slag was highlighted by comparing the partition ratio (LB) between slag and Si. Q2 structural unit of slag is an important site for capturing B. BO4 (1B, 3Si) species is the main form of connection between B and silicate networks, which determines the activity of B in the slag. The addition of Al2O3 into SiO2–CaO slag can change the relative fraction of Q2 and BO4 (1B, 3Si). Increasing Al2O3 content from 0 to about 20 wt% can lead to the overall increase of Q2 population, and a tendency to decrease first and then increase of BO4 (1B, 3Si) fraction under both basicity conditions (0.6 and 1.1). When Al2O3 content is less than 10 ± 1 wt%, the decrease of BO4 (1B, 3Si) population plays a major role in deteriorating the connectivity between B and aluminosilicate network, which leads to a higher activity of B. When the Al2O3 content is greater than 10 ± 1 wt%, B is incorporated into the silicate network more easily due to the formation of more Q2 and BO4 (1B, 3Si), which contributes to a rapid decline in activity of B in slag.