Influence Of Al2O3 Content Research Articles

Influence of Al2O3 content on microstructure and oxidation resistance of glass-ceramic coatings for 06Ni9DR alloy steel

Glass-ceramic coatings with different Al2O3 content were prepared for oxidation protection of 06Ni9DR alloy steel. The microstructure and oxidation protection rate of coatings with different content of Al2O3 at 1200 °C were investigated. The results showed that the average internal pore size decreased with Al2O3 content and the protection of the coating increased after oxidation test for 3 h. The oxidation protection rate of coating with 20 wt% Al2O3 was the worst due to many large-size pores in the coating and bad thermal stability, and the melting of FeO into the liquid phase accelerated the formation of cracks inside the steel and further deteriorate the oxidation protection. As the alumina content increased, the liquid phase in the coating significantly decreased, and correspondingly the thermal stability increased; At the same time, a large number of 0.5–3 μm pores were formed in the coating, which effectively prolonged the oxygen diffusion path, further enhanced the oxidation resistance of the coating. The glass-ceramic coating with 80 wt% Al2O3 exhibited good oxidation protection, reaching 73.6 ± 1.6 % at 1200 °C for 3 h.

ZSM-5@ceramic foam composite catalyst derived from spent bleaching clay for continuous pyrolysis of waste oil to produce monocyclic aromatic hydrocarbons

Spent bleaching clay, a solid waste generated during the refining process of vegetable oils, lacks an efficient treatment solution. In this study, spent bleaching clay was innovatively employed to fabricate ceramic foams. The thermal stability analysis, microstructure, and crystal phase composition of the ceramic foams were characterized by TG-DSC, SEM, and XRD. An investigation into the influence of Al2O3 content on the ceramic foams was conducted. Results showed that, as the Al2O3 content increased from 15 wt% to 30 wt%, there was a noticeable decrease in bulk density and linear shrinkage, accompanied by an increase in compressive strength. Additionally, the ceramic foams were used as catalyst supports, to synthesize ZSM-5@ceramic foam composite catalysts for pyrolysis of waste oil. The open pores of the ZSCF catalyst not only reduced diffusion path length but also facilitated the exposure of more acid sites, thereby increasing the utilization efficiency of ZSM-5 zeolite. This, in turn, engendered a significant enhancement in monocyclic aromatic hydrocarbons content from 39.15 % (ZSM-5 powder catalyst) to 78.96 %. Besides, a larger support pore size and a thicker ZSM-5 zeolite coating layer led to an increase in monocyclic aromatic hydrocarbons content. As the time on stream was extended to 56 min, the monocyclic aromatic hydrocarbon content obtained with the composite catalyst remained 12.41 % higher than that of the ZSM-5 powder catalyst. These findings validate the potential of the composite catalyst. In essence, this study advances the utilization of spent bleaching clay and introduces a novel concept for ceramic foam fabrication. Furthermore, it contributes to the scaling up of catalytic pyrolysis technology.

Influence of Al2O3 content on microstructure, electrical conductivity and adhesion strength of cold sprayed Al-Al2O3 coatings on PEEK substrate

Due to its low process temperature, cold spray (CS) is considered an excellent metallization method to deposit thick coatings on temperature-sensitive polymeric materials. However, in previous studies, the properties (such as electrical conductivity and adhesion strength) of the cold sprayed metallic coating on the polymeric substrate are relatively low. To address this issue, large-sized spherical Al2O3 particles were added into Al powder in different proportions (i.e. 0, 10, 20, 30, 40 wt%) to prepare dense Al-Al2O3 coatings on PEEK by CS. The effect of Al2O3 content on microstructure, deposition efficiency (DE), microhardness, electrical conductivity, and adhesion strength of Al-Al2O3 coatings was systematically studied. Results show that adding an appropriate amount of Al2O3 to the feedstock can effectively improve the Al-Al splat bonding, electrical conductivity, and adhesion strength of the prepared coating on PEEK substrate, which is attributed to the ‘in-situ tamping effect’ of spherical Al2O3 particles. Moreover, the molecular structure of the substrate was not damaged or affected after the impact of Al and Al2O3 particles during the CS process. The prepared Al-Al2O3 coating exhibits better performance and provides a novel approach for polymer metallization.

Effect of Al2O3 in Refining Slag on the Cleanliness and Fatigue Property of Ultra-low-carbon Automotive Steel

The influence of Al2O3 content in refining slag on the cleanliness and fatigue property of ultra-low-carbon (ULC) automotive steel were investigated based on the industrial experiments. The inclusion-adsorption capacity of the refining slag was calculated and the total [O] (T.O) content of ULC automotive steel was measured. The number density, size distribution and morphology of inclusions were analyzed and their effects on the cleanliness and fatigue property of ultra-low-carbon (ULC) automotive steel were investigated. The results showed that as the Al2O3 content in refining slag increased from 19.92% to 39.73%, the inclusion-adsorption capacity of ULC automotive steel decreased from 210.30 down to 57.12, and the fatigue life from 1.4x104 down to 0.9x104 cycles, while the T.O content of steel increased from 12 up to18 ppm and the inclusion number density from 4 up to 9 per mm2.

Influence of Al2O3 content on mechanical properties of silica-based ceramic cores prepared by stereolithography

Silica ceramic cores have played an important part in the manufacture of hollow blades due to their excellent chemical stability and moderate high-temperature mechanical properties. In this study, silica-based ceramics were prepared with Al2O3 addition by stereolithography, and the influence of Al2O3 content on mechanical properties of the silica-based ceramics was investigated. The Al2O3 in silica-based ceramics can improve the mechanical properties by playing a role as a seed for the crystallization of fused silica into cristobalite. As a result, with the increase of Al2O3 content, the linear shrinkage of the silica-based ceramics first decreased and then increased, while the room-temperature flexural strength and the high-temperature flexural strength first increased and then decreased. As the Al2O3 content increased to 1.0 vol%, the linear shrinkage was reduced to 1.64% because of the blocked viscous flow caused by Al2O3. Meanwhile, the room-temperature flexural strength and the high-temperature flexural strength were improved to 20.38 and 21.43 MPa with 1.0 vol% Al2O3, respectively, due to the increased α-cristobalite and β-cristobalite content. Therefore, using the optimal content of Al2O3 in silica-based ceramics can provide excellent mechanical properties, which are suitable for the application of ceramic cores in the manufacturing of hollow blades.

Structure and Efficiency of Gas-Dynamic Deposition of Hybrid Coatings Based on a Nanocrystalline Aluminum Matrix

Gas-dynamic deposition of mechanically synthesized hybrid powders based on a nanocrystalline matrix AMg2 strengthened by nanocrystalline graphite and micro-sized Al2O3 particles is performed. The effect of Al2O3 content in a charge, varied in the range of 10–90 wt.%, on the grain size composition of the synthesized hybrid powder is studied. The structure-phase composition of synthesized hybrid powders and formed coatings was studied by X-ray diffraction analysis. Quantitative estimates are obtained of the Al2O3 content in the hybrid coatings formed. The influence of Al2O3 content in the powder on the efficiency of the gas-dynamic spraying of a hybrid coating is determined. The rational content of Al2O3 in powder is determined ensuring efficient hybrid coating deposition.

The Influence of Al2O3 Content on ZrO2-Al2O3 Nanocomposite Formation – The Comparison between Sol-Gel and Microwave Hydrothermal Methods

Compositions of ZrO2-Al2O3 nanocomposites in the range 10 to 90% wt. of Al were obtained using microwave hydrothermal (MW) synthesis, and sol-gel (SG) method. The use of nanomaterial components as starting ingredients yielded a new nanocomposite material were t-ZrO2 is stabilized by Al2O3 presence after annealing up to 1450°C. Characterization of nanopowders was conducted using X-Ray diffraction (XRD), differential scanning calorimetry and termogravimetry (DSC-TG) methods, specific surface area measurement by BET, density, Raman spectroscopy, and by scanning electron microscopy (SEM). The MW synthesis produces more consistent samples then SG method which yield in amorphous product. All powders after heating up to 1450°C showed fully crystalline phases where the amount of t-ZrO2 increased with increasing percentage quantity of Al (isolation effect).

Influence of Al2O3 content on microstructure and properties of different binary basicity slag glass ceramics

Glass–ceramic samples were prepared from a mixture that was composed of blast furnace slag, tailing and coal fly ash. FactSage software was used to calculate the batch viscosity and plot of the CaO–Al2O3–SiO2–6 wt-%MgO system phase diagram. The main mechanical properties, crystal morphology and crystalline phase transition of glass–ceramics were investigated as functions of batch viscosity, binary basicity (CaO/SiO2) and Al2O3 content by differential thermal analysis, X-ray diffraction, SEM-EDX and Fourier transform infrared spectroscopy techniques. Research results indicate that Al3+ cations play different roles in samples with various binary basicity values and Al2O3 contents for the formation of [AlO4] tetrahedral or [AlO6] octahedral structure, which is different from the role of Ca2+ ones. With the increase in binary basicity, the formula of high performance has a trend toward higher Al2O3 content region.

廃棄物溶融－徐冷スラグの結晶化挙動に及ぼす主成分組成の影響

Effect of the composition of major components on the crystallization behavior of the melt-solidified slag by slow cooling process (2 K·min−1) was studied. In case of the synthetic melt-solidified slag with minor components, crystallization of the slag is progressed by slow cooling process when the basicity (= (%CaO)/(%SiO2)) is higher than 0.8. The precipitated crystalline phase is only Gehlenite (2CaO·Al2O3·SiO2). Crystallization of the slag initiates from the interface of the slag and the crucible, and from the surface of the slag. The basicity higher than 0.9 is required in order to precipitate the crystal phases over the entire slag. The influence of Al2O3 content on the crystallization is very little compared with that of the basicity. On the other hand, in case of SiO2-CaO-Al2O3 slag without minor components, the crystallization is promoted at higher Al2O3 content and lower basicity. Only few amounts of minor components in the slag can influence on the crystallization behavior, and even change the crystallized phase.

Effects of Nano-Al<sub>2</sub>O<sub>3</sub> Additions on Microstructures and Properties of WC-8Co Hard Metals

To investigate the role of nano-Al2O3, WC–Al2O3–8wt%Co hard metals was mixed with 0-1.2 wt% nano-Al2O3 and prepared by conventional sintering (CS) for 2 h at 1440°C to see whether the addition of Al2O3 could improve densification behaviour, the microstructure and mechanical properties of the samples. The results showed that the use of Al2O3 nanoparticles as dispersions could reduce the porosity of WC-Co alloy and decrease the relative density; it could also inhibit the growth of the grains of WC-Co hardmetal to enhance the hardness and transverse rupture strength of the alloy in a proper range. The influence of Al2O3 content on the magnetic properties including coercive force and saturated magnetic intensity of the WC–Al2O3–8wt%Co hardmetals manifested the additive of nano-Al2O3 have effect on the WC grain growth inhibition and the formation of decarbonization phase in the alloy.

Alumina Doped Ni/YSZ Anode Materials for Solid Oxide Fuel Cells

AbstractThe Al2O3–Ni–YSZ (Y2O3 stabilised ZrO2) anode materials with 0–6 wt% Al2O3 were prepared by tape casting method after being ball‐milled for 48 h. The influence of Al2O3 content on flexural strength, electrical conductivity, open porosity, relative density and thermal expansion coefficient (TEC) of Al2O3–Ni–YSZ anode was investigated. The introduction of Al2O3 significantly enhances the flexural strength of Al2O3–Ni–YSZ anode. The flexural strengths of 430 and 299 MPa are achieved for the specimen containing 0.25 wt% Al2O3 before and after reduction, respectively, while the flexural strengths are 201 and 237 MPa for the Ni–YSZ samples. The density decreases with increasing Al2O3 content and the open porosity increases correspondingly, after being sintered at 1350 °C for 4 h. The electrical conductivity at ambient temperature does not fall off when Al2O3 content is less than 1 wt%, but decreases rapidly when the content is above 3 wt% due to the formation of NiAl2O4. A maximum electrical conductivity of 1418 S cm–1 is obtained in the sample containing 0.5 wt% Al2O3. The TEC of the samples decreases with the introduction of Al2O3 in the temperature range of 20–850 °C.

Properties of a ceria-based (C6S2G2) solid oxide electrolyte sintered with Al2O3 additive

Ceria-based Al2O3 composite electrolytes were prepared using (CeO2)0.6(SmO1.5)0.2(GdO1.5)0.2 (C6S2G2) and Al2O3 powders, employing sol-gel and low temperature combustion synthesis methods (SGLCS). The influence of Al2O3 content on the sintering behavior and electrical properties was studied. The results showed that electrical properties could be improved by adding 10wt% Al2O3. The sintered density was up to 5.61g/cm3. Most measurements of open circuit voltage (OCV) ranged between 0.8 and 1.2V; an OCV value of 1.15V was obtained at 370oC. The performance of intermediate- temperature solid oxide fuel cells (ITSOFCs) with a properly Al2O3 doped electrolyte was better than when a pure ceria-based one was used. The highest power density was 200mWcm-2.

Properties of a ceria-based (C6S2G2) solid oxide electrolyte sintered with Al2O3 additive

Ceria-based Al2O3 composite electrolytes were prepared using (CeO2)0.6(SmO1.5)0.2(GdO1.5)0.2 (C6S2G2) and Al2O3 powders, employing sol-gel and low temperature combustion synthesis methods (SGLCS). The influence of Al2O3 content on the sintering behavior and electrical properties was studied. The results showed that electrical properties could be improved by adding 10wt% Al2O3. The sintered density was up to 5.61g/cm3. Most measurements of open circuit voltage (OCV) ranged between 0.8 and 1.2V; an OCV value of 1.15V was obtained at 370oC. The performance of intermediate- temperature solid oxide fuel cells (ITSOFCs) with a properly Al2O3 doped electrolyte was better than when a pure ceria-based one was used. The highest power density was 200mWcm-2.

On the Mechanical Properties of Cooper–Al<sub>2</sub>O<sub>3</sub> Cermets of a Low Reinforcing Level, Processed by Powder Metallurgy

There is investigated the influence of Al2O3 content on the density and mechanical properties of Cu-Al2O3 (2.0 ÷ 10.0 [vol.%] Al2O3) cermets processed by classical routes of powder metallurgy. The obtained results show that the cermets relative density remains quite constant, at a value of over 95 [%], up to a content of ~4 [vol.%] Al2O3. Together with reinforcing effect of the hard Al2O3 particles, proved by the apparition of an elastic zone on the Stress-Strain curve of tensile test, determine a notable increasing of ultimate tensile strength (UTS) and hardness with a small variation of elongation. Over about 4÷5 [vol.%] Al2O3, a decrease in UTS and also in toughness, proved by the Fracture energy decreasing, occurs. Consequently, from the considered points of view, is not recommended to adopt higher reinforcing levels. For electrical applications, the relative density of the processed cermets can be further increased with 3 ÷ 4 [%] by die cold repressing.

The Elaboration of Composite Materials from the Cu-Al<sub>2</sub>O<sub>3</sub> System Using CuO and Al<sub>2</sub>O<sub>3</sub> Powders

The main objective of this study is to find out a simple method to ensure a good dispersion of Al2O3 in the Cu matrix. The method should avoid the segregation effect due to the high difference of the densities of Cu (8.93 g/cm3) and Al2O3 (3.96 g/cm3). In the process of obtaining of the Cu-Al2O3 composite we have considered starting with a material whose density is closer to the density of Al2O3. We have chosen CuO whose density is about 6 g/cm3 so the composite material was obtained starting with copper oxide and alumina powder. We have studied the influence of Al2O3 content and of the compacting pressure upon material’s compactness and hardness. The dispersion finer is highlighted by the microstructure of the surfaces.

Preparation of β-SiAION from silica-alumina gel

Amorphous aluminosilicate gel powders have been subjected to carbothermal reduction and nitridation reaction at high temperature (1673 K). The influence of Al2O3 content in the gel powder on the nature and structure of the product phases has been examined. Between 5% and 9% Al2O3 in the gel powder, it is found that only β-SiAION is formed as the product of CTR/N reaction.

Influence of Al2O3 on the reoxidation of aluminum in molten cryolite

The influence of Al2O3 content on the reoxidation reaction at 1293 K between CO2 and Al dissolved in molten cryolite was examined. The rate and extent of the reaction were evaluated as the concentration of Al2O3 was varied from 0 to 12 wt pct at 4 pct intervals. The cryolite, under an argon atmosphere, was saturated with Al before CO2 was introduced. High initial reaction rates were observed with a quasisteady state condition established 30 to 60 min after beginning an experiment. Increasing the Al2O3 content of the melt significantly reduced the initial rate, but it was not found to alter the steady rate for a given flow system. This phenomenon was observed for systems where CO2 was passed over or bubbled through the molten cryolite. Bubbling the CO2 through the molten cryolite led to increases in both the initial and steady state rates.

Complex susceptibility of high-resistivity ferrites

A new method of presentation of the variation with frequency of the complex susceptibility of ferrites brings out clearly its behaviour at high frequencies. This method is applied to results of measurements made at very close frequency intervals on Mg–Al and Ni–Zn ferrites. The susceptibility of some of these ferrites presents several anomalies which appear on the curves as sinuosities or loops. The possible causes of these anomalies are discussed with the help of a comparison of results obtained on the same samples with and without superimposed d.c. magnetic fields. The influence of Al2O3 content on permeability and losses of Mg–Al ferrites is also examined.