Role Of Al2O3 Research Articles

Research on viscosities and structural characteristics of coal slags with various Al2O3 contents

AbstractThe corrosion of the alumina‐based refractory in coal slags would increase the Al2O3 contents of the coal slag and the influences of that on coal slag performances need to be further considered. The effects of Al2O3 on viscosities and structures of SiO2‐MgO‐CaO‐Fe2O3‐(10–22 wt%)Al2O3 coal slags were investigated in this work. The viscosity of the coal slag increased first with increasing the content of Al2O3 from 10 wt% to 14 wt% and further declined with the addition of Al2O3 content to 22 wt%. The role of Al2O3 in the present coal slag was identified. Al2O3 mainly behaved as an acidic oxide in coal slags when the Al2O3 content was less than 14 wt%, which polymerized the slag structure and increased the viscosities, and with further addition of Al2O3 to 22 wt%, a part of Al2O3 behaved as network modifiers due to the deficiency of enough metal cations for charge compensation, which could simplify the slag networks and reduce the viscosity. The variations of slag viscosities were consistent with the change tendencies of structures analyzed by spectra techniques.

B4C-SiC composites with tuneable mechanical properties: Role of Al2O3 - Y2O3 sintering additives

While outstanding properties of boron carbide (B4C)-silicon carbide (SiC) composites make them potential candidates for ballistic and wear resistance applications, the applicability is rather limited due to processing challenges to obtain high density and superior mechanical properties. In the present work, B4C-10 wt% SiC composites are spark plasma sintered without additives and with 6 wt% (Al2O3 -Y2O3) additives at 1600 °C, 1700 °C and 1800 °C. When sintered at 1600 °C, the relative density increased from 94% for the composites without additives to ∼99% with Al2O3-Y2O3 additives. The formation of liquid phase comprising Al-Y-Si-O improved density and mechanical properties of the composites. TEM analysis of the composite sintered with (2 wt% Al2O3 - 4 wt% Y2O3) additives at 1800 °C confirmed clean grain boundaries between B4C, SiC and liquid phase precipitates. When sintered at 1700° C, the indentation fracture toughness increased from 4.3 MPa.m0.5 for the composite without additive to 6.0 MPa.m0.5 for the composite with 6 wt% Al2O3 additive due to increased instances of crack splitting, bridging and deflection.

Influence of alumina on the formation process and morphology of silicon nitride whisker

β-Si3N4 whiskers were synthesized by heat treatment of α-Si3N4 and Y2O3 mixed powder, and different content of Al2O3 powder was introduced to adjust the synthesis condition and L/D. Introducing Al2O3 significantly accelerated the phase transformation from α-Si3N4 to β-Si3N4. The phase transformation can be completed at 1650 °C by introducing only 0.3 wt% Al2O3, and the phase transformation temperature was reduced by about 100 °C after 1.8 wt% Al2O3 was introduced. Y2O3 orients β-Si3N4 grain growth, while the role of Al2O3 is to reduce liquid viscosity, promote mass transfer, and accelerate grain growth. Introducing a small amount of Al2O3 and appropriately extending the holding time at a lower treatment temperature has been proven to be an effective method to obtain β-Si3N4 whiskers with higher length and diameter ratio (L/D) under mild conditions. High purity β-Si3N4 whiskers (99 wt%) were proved to be synthesized at low temperature (1650 °C) without pickling.

Role of Al2O3, WO3, Nb2O5, and PbO on the physical, elasto-mechanical and radiation attenuation performance of borotellurite glasses

Role of Al2O3, WO3, Nb2O5, and PbO on the physical, elasto-mechanical and radiation attenuation performance of borotellurite glasses

Role of Al2O3 in Al2O3–Bi2O3–P2O5 glasses

Role of Al2O3 in Al2O3–Bi2O3–P2O5 glasses

The role of Al2O3, MgO and CeO2 addition on steam iron process stability to produce pure and renewable hydrogen

Steam iron process represents a technology for H2 production based on iron redox cycles. FexOy are reduced by syngas/carbon to iron, which is subsequently oxidized by steam to produce pure H2. However, the system shows low stability.In this work, the effect of promoters (Al2O3, MgO and CeO2) on FexOy stability is investigated (10 consecutive redox cycles). Bioethanol is used as a reducing agent. The particles are synthesized by coprecipitation method, analysed by BET, XRD, SEM and tested in a fixed bed reactor (675 °C, 1 bar). Pure H2 is obtained controlling the FexOy reduction degree feeding different amounts of ethanol (4.56–1.14 mmol) until no CO is detected in oxidation. The results show that the promoters not only improve the thermal stability of FexOy but also affect its redox activity and react with iron forming spinel structures. MgO led to the highest activity and cyclability (H2 = 0.15 NL; E = 35%).

Effect of K2O:Al2O3 Ratio on Crystallization Phenomena and Microstructure of Lithium Silicate Glass-Ceramics

K2O plays an important role as glass modifier in glass systems. In the present study,the effect of K2O:Al2O3 ratio on crystallization and microstructural evolution in Li2O-SiO2- K2O-MgO-Al2O3-ZnO-ZrO2-P2O5 glass system has been reported. K2O mol% has been varied from 1 to 3 mol% while keeping Al2O3 at 2 mol%. The glass structure was analyzed by MAS-NMR spectroscopy. Heat treated glass systems were studied by using XRD, SEM and DTA to analyse the sintering and crystallization behavior. Increased amount of K2O modified the role of Al2O3, which acted as glass network former and formed [AlO4/2] tetrahedron unit, which eventually polymerized the glass structure. Consequently, lithium disilicate (LS2) crystallization was suppressed and crystallization of lithium metasilicate (LS) was promoted. As a result, while in the sample with 1 mol% K2O LS2 appeared as the main crystalline phase and LS as minor phase, 3 mol% K2O samples did not show any lithium disilicate throughout the sintering temperature range. The K2O:Al2O3 ratio did not have a significant impact on densification of these glass-ceramics.

The insight into the role of Al2O3 in promoting the SO2 tolerance of MnOx for low-temperature selective catalytic reduction of NOx with NH3

This research aims to enhance the SO2 tolerance of manganese oxide (MnOx) catalysts for low-temperature selective catalytic reduction (SCR) de-NOx. Based on the deactivation mechanism of MnOx, we target at the promotion of the byproduct (NH4HSO4) decomposition and the inhibition of the byproduct (MnSO4) formation. To achieve this target, thermogravimetric (TG) and temperature programmed desorption of SO2 (SO2-TPD) are performed upon as many as 21 kinds of single metal oxides to explore the potentially effective chemical composition as the additive of MnOx catalysts. The TG result indicates that Al2O3 can remarkably decrease the thermal stability of NH4HSO4. In addition, the SO2-TPD analysis reveals that the formed species after SO2 adsorption are weakly adsorbed on Al2O3. Thus, Al2O3 is selected to mix with MnOx to optimize its SO2 tolerance. Further experimental results demonstrate that the proper introduction of Al2O3 can effectively enhance the low-temperature SCR de-NOx activity and the SO2 tolerance of MnOx. It is revealed that the introduction of Al2O3 into MnOx can not only facilitate the decomposition of NH4HSO4 but also lead to reduced thermal stability of the adsorbed SO2 species to some extent. As compared to the pristine MnOx, the slight introduction of Al2O3 as the additive is beneficial to the low-temperature SCR de-NOx activity and SO2 tolerance of MnOx.

Fabrication of ZnZrO2@Al2O3@SAPO-34 tandem catalyst for CO2 conversion to hydrocarbons

An exploration into the influence of interfacial characteristics between ZnZrO2 and SAPO-34 on CO2 hydrogenation to lower olefins was conducted. This was achieved by fabricating ZnZrO2@Al2O3@SAPO-34 tandem catalyst based on a chemical coating strategy. Physically blended ZnZrO2/SAPO-34 and hydrothermally coated ZnZrO2@SAPO-34 were employed as references for exploring the correlation between interfacial characteristic and catalytic performance. The results showed that ZnZrO2@SAPO-34 fabricated via hydrothermal coating method exhibited inferior catalytic performance resulting from the inactivation of ZnZrO2 active components after hydrothermal treatment. However, post pre-coating modification by Al2O3 of ZnZrO2 prevented the deactivation of ZnZrO2 active components, as well as facilitating the formation of chemically interfacial phase between ZnZrO2 and SAPO-34 with encapsulated structure based on micro-mesoporous system and rich acid-base active centers. The collective contributions aroused by the role of Al2O3 are the crucial to enhanced catalytic performance of ZnZrO2@Al2O3@SAPO-34 tandem catalyst. Under 3 MPa, 3500 ml g−1·h−1 and 380 °C reaction conditions, CO2 hydrogenation on ZnZrO2@Al2O3@SAPO-34 tandem catalyst exhibited a high C2–C4 (75% C2=- C4=, 20% C20–C40) selectivity of 95% with the CH4 selectivity of 3% among hydrocarbon products at the CO2 conversion of 21% and 45% selectivity of CO by-product. Compared with ZnZrO2@SAPO-34, the selectivity of C2–C4 over ZnZrO2@Al2O3@SAPO-34 tandem catalyst increased by 55%. In addition, this work also opens a new window for designing the excellent bifunctional tandem catalysts for the other applications.

Insight into the Relationship Between Viscosity and Structure of CaO-SiO2-MgO-Al2O3 Molten Slags

This article elucidates the quantitative relationship between viscosity and structure in a basic slag system of CaO-SiO2-MgO-Al2O3 and focuses on the role of Al2O3. Slag viscosity was measured by the rotating cylinder method, and structural information was obtained using Fourier transformation infrared, Raman and magic angular spinning nuclear magnetic resonance (MAS-NMR) techniques. The results show that, as the Al2O3 content increased, slag viscosity increased initially and decreased afterwards, directly indicating that Al2O3 had an amphoteric effect on slag viscosity. The Raman spectra verified that with increasing Al2O3 content, the concentrations of Q0(Si) and Q2(Si) decreased first and then increased, while that of Q1(Si) kept increasing and that of Q3(Si) increased first and then decreased. The 27Al MAS-NMR spectra proved that the mole ratios of AlO5 and AlO6 to AlO4 kept increasing with the increase of Al2O3 content, and, overall, Al2O3 changed from a network former to a network modifier. The relationship between the viscosity and structure of the molten slags was further analyzed quantitatively based on the modified (NBO/T), denoted as (NBO/T)′, and we found a fine linear correlation between the logarithm of viscosity and (NBO/T)′. Moreover, the variations of thermodynamic properties of this system also indirectly supported the present experimental results.

Physical and Structural Properties Conformed the Role of Al2O3 in Barium Alumino Borate Glasses Doped with Cr3+ ions

Physical and Structural Properties Conformed the Role of Al2O3 in Barium Alumino Borate Glasses Doped with Cr3+ ions

Understanding the Role of Nano‐Aluminum Oxide in All‐Solid‐State Lithium‐Sulfur Batteries

AbstractAluminum oxide (Al2O3) is a well‐known electrolyte filler for stabilizing the Li‐metal (Li0) anode in all‐solid‐state Li0‐based batteries. However, its strong interactions with lithium polysulfides (PS) hinder the direct application of Al2O3‐added electrolytes in all‐solid‐state lithium‐sulfur batteries (ASSLSBs). Herein, the role of Al2O3 in ASSLSBs both as electrolyte filler and cathode additive is studied. The combination of Al2O3‐added electrolyte and Al2O3‐added S8 cathode with optimum cell configuration could deliver an unprecedented discharge capacity of 0.85 mAh cm−2 (C/10, 30 cycles) for polymer‐based ASSLSBs. These results suggest that the rational incorporation of Al2O3 can lead simultaneously to PS anchoring and Li0 anode stabilizing benefits from the ceramic filler, thus improving the electrochemical performance of ASSLSBs.

Polar phonons in polycrystalline SrTiO3 thin films: The role of the substrate

Recently we have demonstrated that out-of-plane dielectric properties of polycrystalline SrTiO3 (ST) films depend on the strain/stress induced by the substrates due to thermal expansion misfit. Here, we present a complementary infra-red (IR) spectroscopy investigation of the role of Al2O3 and MgO substrates on the lattice dynamics and in-plane dielectric properties of ST thin films also prepared by sol-gel. We verify that ST films deposited on Al2O3 substrates, being under a tensile stress, present the soft mode behaviour similar to that of ST single crystals, deviating just below 150 K. In contrast, ST films deposited on MgO substrates, being under compressive stress, have higher soft mode frequency from 10 to 300 K. It is thus proved that for polycrystalline ST films the intrinsic in-plane relative permittivity may be tuned through an induced stress state.

Effect of Al2O3 on the densification and oxidation behavior of SiC coating for carbon/carbon composites

A silicon carbide (SiC) coating was prepared on carbon/carbon (C/C) composites by pack cementation using Si, C and Al2O3 powers as raw materials. The role of Al2O3 on the densification of the SiC coating was investigated. The results show that the densification and thickness of the SiC coating obviously increase with the increase of Al2O3 content, which is attributed to the enhanced material transport through liquid Al2O3 at high temperature. Moreover, to study the effect of Al2O3 on the oxidation behavior of SiC coating itself at 1773 K in air, the synthetic SiC powders by pack cementation were sintered. The results present that after oxidation for 40 h, only a few holes are observed in the generated glass layer of the SiC ceramic without Al2O3, while more holes appear in the surface of the oxidized Al2O3 doped SiC ceramic, owning to the doped Al atom destroying the SiO2 network and causing the permeability of oxygen to increase.

Detection of triethylamine with fast response by Al2O3/α-Fe2O3 composite nanofibers

Pure α-Fe2O3 nanotubes and a series of Al2O3/α-Fe2O3 composite nanofibers were synthesized via facile electrospinning and subsequent calcination at 500 °C in air for 2 h. The morphologies and nanostructures of these samples were characterized through various experimental techniques. It was found that the composite samples were composed of crystal α-Fe2O3 and amorphous Al2O3. The composite Al2O3/α-Fe2O3 nanofibers have smaller grain size than that of pure α-Fe2O3 nanotubes prepared by the same process. Furthermore, comparative gas sensing investigation between Al2O3/α-Fe2O3 composite nanofibers and pure α-Fe2O3 nanotubes was performed to show the superior sensing properties of the composite samples. When the mass ratio of Al source and Fe source was 1:4, the sensor exhibited the highest response to 100 ppm triethylamine at 250 °C. It is worth noting that the response times were no more than 2 s at operating temperatures ranged from 175 °C to 300 °C. Finally, the related mechanism of gas sensing and the role of Al2O3 in the composite nanofibers were discussed in this paper.

Wüstite-based catalyst for ammonia synthesis: Structure, property and performance

Fused iron catalyst is an active and classical catalyst both for ammonia synthesis and Fischer-Tropsch synthesis which are two typical industrial processes. As it is of significance to catalysis science as well as its importance to industry, fused iron catalyst is an ideal model system for heterogeneous catalysis research. However, the precursors of fused iron catalysts were confined to Fe3O4 in the most studies. The discovery of wüstite (Fe1-xO) based catalyst is a key innovation for fused iron catalyst which necessitates the further research to obtain deeper insight into this novel catalyst.This paper summarized three major scientific issues involved in the development of wüstite based catalyst, namely, the physicochemical properties, characteristics of wüstite, as well as the mechanism leading to the high activity. Based on this novel catalyst, new concepts and opinions were proposed, and the insights and principles obtained are as follow. Hump like activity trend of reduced catalyst was first obtained with varying of Fe2+/Fe3+ in the catalyst precursor. Molecular ratio of iron oxides, single phase theory and structure of active sites were suggested to elucidate the high activity of wüstite based catalyst. In addition, new concepts and opinions such as the disproportionation of metastable wüstite and its inhibition, matching of promoters with the structural characteristics of wüstite, synergy between acidic site and basic site on the surface of catalyst, role of Al2O3 in the re-structuring of catalyst surface, mechanism of competitive reduction, strong H2 adsorption, active sites, micro-structure of α-Fe and the essence of high activity were proposed to bring light to the structure-activity relationship forming the theory system with single phase theory as the kernel of wüstite catalyst. These regularities and the theory system significantly promoted and enriched the scientific knowledge of fused iron catalyst. It is unexpected that a knowledge based improvement of a catalyst would have a strong effect on other fields of catalysis research.

Improvement of performances HfO2-based RRAM from elementary cell to 16 kb demonstrator by introduction of thin layer of Al2O3

In this article, the reliability of HfO2-based RRAM devices integrated in an advanced 28nm CMOS 16kbit demonstrator is presented. In order to improve the memory performance, a thin Al2O3 layer is inserted in the HfO2-based memory stack (TiN/Ti/HfO2/Al2O3/TiN). Thanks to extensive electrical characterizations on both single layer HfO2 and bilayer HfO2/Al2O3 memory stacks at device and array levels, the potential of the bilayer is put forward. From the experimental results, the thin Al2O3 layer has allowed to improve the endurance (memory window of about one decade after 1M cycles) and data retention (both the low and the high resistance states are stable after 6h at 200°C). Finally, thanks to our 3D model based on calculation of the Conductive Filament resistance using trap assisted tunneling (TAT) the role of Al2O3 as series resistance is highlighted.

Gas sensing characteristics of composite NiO/Al2O3 for 2-chloroethanol at low temperature

Composite NiO/Al2O3 was prepared by calcination of Ni/Al hydrotalcite for gas sensing materials. Methods of XRD, SEM, TEM, EDS and BET were used to analyze the structure, composition and morphology of the composite oxide. It was found that the sample was composed of crystal NiO and amorphous Al2O3. Furthermore, the composite NiO/Al2O3 has smaller grain size and larger surface area than that of pure NiO obtained by the same process. In the gas sensing experiments, the sensor based on NiO/Al2O3 showed superior gas sensing response and selectivity to 2-chloroethanol at low temperature. The response (Rg/Ra) of NiO/Al2O3 was 6.8–20ppm 2-chloroethanol at 160°C. The role of Al2O3 in the composite was also discussed.

Effect of magnesium additive on structure and properties of Al2O3–B2O3–SiO2 glass system

Printed wiring board is an important component of electronic devices. Low dielectric constant materials are expected to reduce the time delay of signal propaganda and dielectric loss. E-glass fibre as reinforcing material of printed wiring board does not meet the requirements. To reduce the operating temperature of glass, bivalent metal oxides must be introduced, often at the expense of dielectric properties. Aluminoborosilicate glass is a typical glass system with low dielectric constant. Al2O3–B2O3–SiO2 glasses that replaced Al2O3 by MgO were melted, and their microstructure, some physical properties and chemical durability were investigated. In addition, the role of Al2O3 in borosilicate glasses was investigated. The glass system was characterised with lower dielectric constant (4·8–5·7) and loss tangent (10−3) at 1 MHz. By replacing Al2O3 with MgO, the density and viscosity–temperature characteristic points of the studied glasses showed a decreasing tendency. The average dissolution rate of the studied glasses was <4·51×10−8 g cm−2 min−1. When the molar ratio of RO/Al2O3 is >2·5 (R = Ca2+, Mg2+), the trivalent, tetrahedral [BO4] and [AlO4] network units increased at the same time as indicated by infrared spectra. The paper has designed a group of glasses that has both satisfactory processing properties and dielectric properties. The present glass system could substitute E-glass and be a possible candidate for many applications.

Effect of thermal treatment on microstructure and phase of partially-stabilized zirconia

ZrO2-MgO-Y2O3-CaO-Al2O3 composites with a multiphase microstructure were fabricated by die pressing process and sintered at various thermal programs. The microstructure of this polycrystalline was examined to clarify the role of Al2O3 on grain growth. Environmental scanning electron microscopy (ESEM) micrographs revealed that spinel was beneficial to refine grain. The effect of thermal treatment on the formation of monoclinic phase was discussed. It can be found that, the grain size and the fraction of the monoclinic phase in this partially stabilized zirconia(PSZ) increases after heat treatment at 1 150 °C. The temperature of heat-treatment, not the time for holding, is the governing factor of the fraction of monoclinic phase.