Presence Of Al2O3 Research Articles

Mixed convection flow caused by an oscillating cylinder in a square cavity filled with Cu–Al2O3/water hybrid nanofluid

The aim of this paper is to examine the effects of Cu–Al2O3/water hybrid nanofluid and Al2O3/water nanofluid on the mixed convection inside a square cavity caused by a hot oscillating cylinder. The governing equations are first transformed into dimensionless form and then discretized over a non-uniform unstructured moving grid with triangular elements. The effects of several parameters, such as the nanoparticle volume fraction, the Rayleigh number, the amplitude of the oscillation, and the period of the oscillation of the cylinder are investigated numerically. The results indicate that the motion of the oscillating cylinder toward the top and bottom walls increases the average Nusselt number when the Rayleigh number is low. Furthermore, the presence of Al2O3 and Cu–Al2O3 nanoparticles leads to an increase in the values of the average Nusselt number Nuavg for cases of low values of the Rayleigh number. It is found that the natural convection heat transfer rate of a simple Al2O3/water nanofluid is better than that of Cu–Al2O3/water hybrid nanofluid.

Structure of Al2Au Intermetallic Compound Obtained by Mechanochemical Synthesis

The structure of Al2Au intermetallic compound mechanically synthesized from a nanoscale gold powder and aluminum particles of about 0.5 mm in size has been studied by X-ray diffraction and transmission and scanning electron microscopy. It has been established that the intermetallic compound is formed as a powder with a particle size of 0.3–3 μm. In addition to intermetallic compound, some aluminum has been found in the powder, along with traces of gold and aluminum oxide Al2O3, and the appearance of an amorphous phase has been registered. The microstructure of compacts formed from the obtained powder has been studied, and heat treatments have been carried out. It has been found that compacting and subsequent annealing contribute to the agglomeration of intermetallic particles. Increasing the treatment temperature to 600°C results in the refinement of the structural elements as a result of their cracking in the surface layer. Compacts that are dark purple in their original state acquire a color ranging from pink to dark red as a result of annealing. After heat treatment, the presence of Al2O3, as well as of intermetallic phases enriched in gold (AlAu and AlAu4), has been detected in compacts in addition to the intermetallic compound Al2Au.

Effect of Ni content and Al2O3 particle size on the thermal and mechanical properties of Al2O3/Ni composites prepared by spark plasma sintering

Alumina-nickel composites were prepared by carrying out spark plasma sintering (SPS) of nano-sized and micro-sized Al2O3 particles with 15–45 wt% Ni powders. The powder materials were sintered at a temperature of 1400 °C under a constant uniaxial pressure of 50 MPa. FESEM micrographs of the products showed uniformly dispersed nickel inclusions in both matrices at intergranular positions. Presence of Al2O3 as the major phase along with Ni as the minor phase was confirmed using XRD analysis. Thermal and mechanical properties of the nano- and micro-sized Al2O3/Ni composites were investigated. The thermal conductivity of nano-sized alumina composites was seen to increase with the increase in nickel content, however, an opposite trend was observed for micro-sized alumina-based composites. Moreover, thermal conductivities of all the composites decreased with increase in temperature. The composites also showed high hardness and fracture toughness values of up to 19.6 GPa and 4.71 MPa ∗ m1/2, respectively, and relative density values, between 79 and 99%, that decreased with increasing Ni content. Furthermore, the nano-sized Al2O3/Ni composites showed thermal and mechanical properties superior to those of the micro-sized Al2O3/Ni composites.

Microstructure and Mechanical Properties of Zn-Ni-Al₂O₃ Composite Coatings.

Zn-Ni-Al2O3 composite coatings with different Ni contents were fabricated by low-pressure cold spray (LPCS) technology. The effects of the Ni content on the microstructural and mechanical properties of the coatings were investigated. According to X-ray diffraction patterns, the composite coatings were primarily composed of metallic-phase Zn and Ni and ceramic-phase Al2O3. The energy-dispersive spectroscopy results show that the Al2O3 content of the composite coatings gradually decreased with increasing of Ni content. The cross-sectional morphology revealed thick, dense coatings with a wave-like stacking structure. The process of depositing Zn and Ni particles and Al2O3 particles by the LPCS method was examined, and the deposition mechanism was demonstrated to be mechanical interlocking. The bond strength, micro hardness and friction coefficient of the coatings did not obviously change when the Ni content varied. The presence of Al2O3 and Ni increased the wear resistance of the composite coatings, which was higher than that of pure Zn coatings, and the wear mechanism was abrasive and adhesive wear.

Fabrication of as-cast Al matrix composite reinforced by Al2O3/Al3Ni hybrid particles via in-situ reaction and evaluation of its mechanical properties

In this work, an attempt was made to synthesize Al2O3/Al3Ni hybrid reinforcement particles in Al-matrix to fabricate an AMC using stir casting technique. The molten metal was stirred while NiO powder was injected into the melt using blowing inert argon. During the production process, aluminothermy reaction took place explosively. The reaction products were alumina as the first reinforcements and pure nickel metal. This reaction was followed by the formation of eutectic structure of (Al3Ni)eut at 1113 K. Adiabatic temperature of aluminothermy reaction was obtained 1923 K. A reaction occurs between aluminum and nickel at the melting point of aluminum during the solidification and Al3Ni intermetallic compound is formed which acts as the second reinforcement. The presence of Al2O3 and Al3Ni in the matrix was verified by EDS/XRD analysis. Significant increase happened in UTS, hardness, and microhardness values. It is due to the presence of created reinforcement particles uniformly dispersed in Al matrix.

Application of La-Doped SrTiO3 in Advanced Metal-Supported Solid Oxide Fuel Cells

Composite materials frequently allow the drawbacks of single components to be overcome thanks to a synergistic combination of material- and structure-specific features, leading to enhanced and also new properties. This is the case of a metallic-ceramic composite, a nickel-chromium-aluminum (NiCrAl) foam impregnated with La-doped Strontium Titanate (LST). This particular cermet has very interesting properties that can be used in different fields of application, namely: mechanical robustness provided by the metal foam; and chemical stability in harsh conditions of temperature and atmosphere by promotion of a thin protective layer of alumina (Al2O3); high electronic conductivity given by a percolating ceramic conducting phase, i.e., La-doped Strontium Titanate. In this paper, its application as a current collector in a metal-supported Solid Oxide Fuel Cells (SOFC) was studied. Firstly, the electronic properties of different compositions, stoichiometric and under stoichiometric, of LST were analyzed to choose the best one in terms of conductivity and phase purity. Then, LST chemical stability was studied in the presence of Al2O3 at different temperatures, gas compositions and aging times. Finally, stability and conductivity of LST-impregnated NiCrAl foam composite materials were measured, and LST was found to be fully compatible with the NiCrAl foam, as no reactions were detected in oxidizing and reducing atmosphere after up to 300 h operation at 750 °C and 900 °C between the Al2O3 layer and LST. Results showed that the composite is suitable as a current collector in innovative designs of metal-supported SOFC, like the Evolve cell, in which the metallic part is supposed not only to provide the structural stability to the cell, but also to play the role of current collector due to the impregnation of ceramic material.

Study on Microstructure and Properties of Nanocomposite Coating Prepared on the Surface of Exhaust Pipe for Ship

In order to improve the high temperature oxidation resistance of exhaust pipes, the nanocomposite coatings are carried out on the surface of exhaust pipe by electrodeposition technology, and the microstructure and oxidation behavior of the nanocomposite coatings are investigated experimentally. This paper mainly focuses on the experimental work to determine the structural characteristics and oxidation resistance of nanocomposite coatings in presence of Al2O3 and cerium oxide CeO2. The results show that the amount of the Al2O3-CeO2 has significant influence on the structural properties of nanocomposite coatings. The surface of coating becomes more compact and smooth with the increase of the amount of the Al2O3 and CeO2. Furthermore, the anti-oxidation performance of the nanocomposite coatings formed with Al2O3 and CeO2 were both better than those of the composite coatings formed without Al2O3 and CeO2.

Thermal Atomic Layer Etching of Titanium Nitride Using Sequential, Self-Limiting Reactions: Oxidation to TiO2 and Fluorination to Volatile TiF4

The thermal atomic layer etching (ALE) of TiN was demonstrated using a new etching mechanism based on sequential, self-limiting oxidation and fluorination reactions. The oxidation reactant was either O3 or H2O2, and the fluorination reactant was hydrogen fluoride (HF) derived from HF-pyridine. In the proposed reaction mechanism, the O3 reaction oxidizes the surface of the TiN substrate to a TiO2 layer and gaseous NO. HF exposure to the TiO2 layer then produces TiF4 and H2O as volatile reaction products. The overall reaction can be written as TiN + 3O3 + 4HF → TiF4 + 3O2 + NO + 2H2O. Quartz crystal microbalance studies showed that HF can spontaneously etch TiO2 films. Spectroscopic ellipsometry and X-ray reflectivity analysis showed that TiN films were etched linearly versus the number of ALE cycles using O3 and HF as the reactants. The TiN etching also occurred selectively in the presence of Al2O3, HfO2, ZrO2, SiO2, and Si3N4. The etch rate for TiN ALE was determined at temperatures from 150 to 350 °C. Th...

Area-Selective Atomic Layer Deposition of SiO2 Using Acetylacetone as a Chemoselective Inhibitor in an ABC-Type Cycle.

Area-selective atomic layer deposition (ALD) is rapidly gaining interest because of its potential application in self-aligned fabrication schemes for next-generation nanoelectronics. Here, we introduce an approach for area-selective ALD that relies on the use of chemoselective inhibitor molecules in a three-step (ABC-type) ALD cycle. A process for area-selective ALD of SiO2 was developed comprising acetylacetone inhibitor (step A), bis(diethylamino)silane precursor (step B), and O2 plasma reactant (step C) pulses. Our results show that this process allows for selective deposition of SiO2 on GeO2, SiNx, SiO2, and WO3, in the presence of Al2O3, TiO2, and HfO2 surfaces. In situ Fourier transform infrared spectroscopy experiments and density functional theory calculations underline that the selectivity of the approach stems from the chemoselective adsorption of the inhibitor. The selectivity between different oxide starting surfaces and the compatibility with plasma-assisted or ozone-based ALD are distinct features of this approach. Furthermore, the approach offers the opportunity of tuning the substrate-selectivity by proper selection of inhibitor molecules.

Phosphonium salts derived from α-ferrocenylvinyl cation in situ generated in sc-CO2 from ethynylferrocene by Nafion film

A protonation of ethynylferrocene by nafion in sc-CO2 in the presence of triphenylphosphine (PPh3) or 1,2-bis(diphenylphosphino)ethane (DPPE) leads to a formation of novel (1-ferrocenylvinyl)phosphonium or ferrocenyl substituted bisphosphonium salt isolated as tetrafluoroborates 3 and 4, respectively. Ferrocenyl substituted bisphosphonium tetrafluoroborate 4 undergoes the hydrolytic cleavage of the P+-C(Fc) bond in the presence of Al2O3 at 25°C to form ferrocenyl substituted phosphinyl phosphonium tetrafluoroborate 5. Complexes 3–5 were completely characterized by NMR spectra and their molecular structures elucidated by X-ray studies.

Terahertz acoustic phonon detection from a compact surface layer of spherical nanoparticles powder mixture of aluminum, alumina and multi-walled carbon nanotube

We present terahertz spectroscopy study on spherical nanoparticles powder mixture of aluminum, alumina, and MWCNTs induced by surface mechanical attrition treatment (SMAT) of aluminum substrates. Surface alloying of AL, Al2O3 0.95% and MWCNTs 0.05% powder mixture was produced during SMAT process, where a compact surface layer of about 200 μm due to ball bombardment was produced from the mixture. Al2O3 alumina powder played a significant role in MWCNTs distribution on surface, those were held in deformation surface cites of micro-cavities due to SMAT process of Al. The benefits are the effects on resulted optical properties of the surface studied at the terahertz frequency range due to electrical isolation confinement effects and electronic resonance disturbances exerted on Al electronic resonance at the same range of frequencies. THz acoustic phonon around 0.53–0.6THz (17–20cm−1) were observed at ambient conditions for the spherical nanoparticles powder mixture of Al, Al2O3 and MWCNTs. These results suggested that the presence of Al2O3 and MWCNTs during SMAT process leads to the optically detection of such acoustic phonon in the THz frequency range.

Absorption of nitrogen hemioxide in aqueous solutions of gas treatment systems upon dissolution of UN in nitric acid

The absorption of N2O from an air flow in various aqueous solutions at 293–298 K was studied. The maximal N2O absorption under the experimental conditions is reached for water (~22–24%) and saturated solution of K2Cr2O7 in concentrated H2SO4 in the presence of Al2O3 and without it (~34 and ~30%, respectively). In concentrated HNO3 and NH4OH solutions and in 1.0 M NaOH and N2H4·nH2O solutions, the degree of the N2O absorption varied from ~7.5 to ~11.5%. Similar degree of absorption was obtained with 0.5 M (NH2)2CO (~11%). In the other solutions tested, the degree of the N2O absorption did not exceed ~4.0%.

Gold Nanoparticles Supported on Fe₂O₃–MO(x) (M = Al, Zr, Zn) Composite Oxides for Partial Oxidation of Methanol.

Selective production of hydrogen by partial oxidation of methanol (POM), using gold supported on composite metal oxides, Fe2O3–MO x (M: Al, Zr, Zn) was investigated. The catalysts were characterized by TGA, XRD, TEM and XPS analyses. TGA and DTGA analysis indicates that minimum decomposition temperature required to obtain α-Fe2O3 in Fe2O3–ZrO2 composite support is 570 K. The catalytic activity and stability of Au/Fe2O3 catalyst is improved by using Al2O3 as an additional support, but there is no improved activity was observed with ZrO2. The uncalcined catalysts shows high activity for selective formation of hydrogen. The presence of Al2O3 in Au/Fe2O3–Al2O3 stabilize the gold particles against sintering during calcination as evidenced from TEM analysis. XPS analysis revealed that in the uncalcined catalysts gold is present as Au2O3 and Auº. The amount of metallic gold (Auº) in the catalyst increases with increase in calcination temperature. The catalytic behavior is related to the presence of highly dispersed Au of partially oxidized state in the catalyst. Under the optimized condition, the most active catalyst Au/Fe2O3–Al2O3 shows 100% conversion and 48% H2 selectivity at 523 K. The catalytic activity of Au/Fe2O3–Al2O3 catalysts in the temperature range 423–548 K showed that methanol conversion increased with rise in temperature and attains 100% at 448 K; Hydrogen selectivity increased with rise in temperature up to 523 K and then decreased at high temperatures. The overall reactions involved are methanol combustion, partial oxidation, steam reforming and decomposition. CO produced by methanol decomposition and/or by reverse water gas shift is subsequently transformed into CO2 and H2 by the water gas shift and/or CO oxidation thereby reduce the CO selectivity. The low hydrogen selectivity at high temperature is due to reverse water gas shift and/or hydrogen combustion.

Reduction of Solid Al2O3 with Electrolysis of CaCl2-Based Melt

Cyclic and square-wave voltammetry methods are used to investigate the mechanism of the cathode process on molybdenum in a CaCl2-CaF2 melt at 750°C. It is shown that calcium reduces on an inert cathode in the form of its solution in catholyte at potentials more positive than are required for metallic calcium formation. The presence of Al2O3 in the catholyte increases currents of calcium reduction on the forward cathodic wave at potentials more positive than are required for metallic calcium formation. A decrease in the ohmic resistance between the anode and cathode is observed to have been caused by the appearance of electronic conduction during the calcium cathodic reduction in the studied melt. A mechanism for the reduction of Al2O3 in the catholyte during electrolysis of the CaCl2-CaF2 melt, including Ca+ subions and calcium cathode formation and the secondary reduction of Al2O3, is proposed. In order to demonstrate the supposed mechanism for the Al2O3 reduction, the electrolysis tests were performed in two laboratory-scale electrolyzers with different separation type of anolyte and catholyte. The necessity of separating the anolyte and catholyte for providing stable continual electrolysis in the CaCl2-based melt is demonstrated.

Phosphorous Diffusion in N2+-Implanted Germanium during Flash Lamp Annealing: Influence of Nitrogen on Ge Substrate Damage and Capping Layer Engineering

In this work we present a systematic study on post-implantation phosphorous diffusion control in Ge by co-implanted nitrogen in combination with various surface capping layers (Al2O3, SiO2 and Si3N4). Phosphorous has been implanted at low energy (11 keV) and high dose (1015 cm−2) in p-Ge (100) already implanted or not with low energy (10 keV−5 × 1014 cm−2) N2+. Flash Lamp Annealing (FLA) at 800–850°C for 20 ms in inert ambient has been used as post-implantation annealing scheme. In the absence of nitrogen, significant substrate damage and capping layer deterioration prevents a reliable comparison among the three capping materials. The presence of nitrogen in the Ge substrate, effectively suppresses the damage observed after the FLA. In this case, P diffusion is additionally retarded in the presence of Al2O3 as compared to SiO2 and Si3N4. The experimental results constitute a direct evidence of the action of the three capping layers as sinks for Ge vacancies with different interface recombination velocities. On the contrary, the nitrogen diffusion data suggest that interface recombination velocities of Ge interstitials are almost independent of the capping layer choice.

Thermal–Hydraulic Characteristics of Novel Configurations of Wavy Channel: Nanofluid as Working Fluid

ABSTRACTIn the present study, thermal-hydraulic specifications of the wavy channel with variable wave lengths are investigated numerically in the presence of Al2O3–water nanofluid. The nanofluid concentration and Reynolds number range are 0–9% vol. and 200–1400, respectively. Four nonuniform arrangements of the wave length, including low to high, high to low, low to high to low, and high to low to high, are evaluated in comparison with the uniform one. Furthermore, the effects of the channel height and wave amplitude on the performance of the wavy channels are examined. The results show that the wave length variations have significant effects on the performance of the wavy channel. At the studied ranges, the wavy channel with the low to high wave length variations depicts the best performance, and the channel with the high to low to high comes in the second. Also, the nanofluids with the higher concentration propose the greater values of Nusselt number and friction factor. Finally, correlations are developed for both the uniform and the nonuniform wavy channels as function of Reynolds number, Prandtl number, nanofluid concentration, and geometrical parameters.

Calorimetry and other methods in the studies of reactive magnesia–hydratable alumina–microsilica hydrating mixtures

The reactivities of the binary and ternary mixtures of reactive magnesia (MgO≡M), hydratable alumina (Al2O3≡A) and microsilica (SiO2≡S) micropowders were investigated by calorimetric method and other analytical techniques (X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), differential thermal/thermogravimetric (DTA-TG) analysis and scanning electron microscope (SEM) observations). Effect of water/solid mass ratio and temperature on the hydration behavior of the M–A, M–A–S, M–S, A–M–S and A–S hydratable binders were established. The methodological considerations on both in situ and ex situ mixing techniques have also been taken. The initial mixing peak was due to wetting of the binder particles and initial dissolution reactions. A second, extensive heat peak was associated with the formation of crystalline and noncrystalline hydration products, i.e., brucite Mg(OH)2, magnesium aluminate hydrate (MAH; H≡H2O)-like phase, magnesium silicate hydrate (MSH)-like phase and magnesium aluminum silicate hydrate gels (MASH). Negligible heat was evolved during the hydration reaction of A–S mixture, and the second reaction peak was not observed. Nevertheless, the presence of Al2O3 and SiO2 in other combinations contributes to the consumption of Mg(OH)2 which was formed during the initial stages of hydration and leads to the formation of cementitious products, like M–A–H, M–S–H and M–A–S–H.

Interfacial behaviors of magnesia partially stabilized zirconia with nickel-based superalloy

Interfacial behaviors of magnesia partially stabilized zirconia (MgO-PSZ) ceramic by nickel-based superalloy were investigated. And the effect of zirconia reduction on interfacial behaviors was considered. The contact angle became stable at 1390°C and was larger than 90° during the continuous temperature rise, and the equilibrium contact angle was 92°. The interfacial reaction between MgO-PSZ ceramic and nickel-based superalloy occurred at high temperature. The ZrO2 was reduced to suboxide (ZrO2−x), and the loss of oxygen led to the formation of Al2O3. The interfacial reaction was influenced by the reduction of ZrO2. The destabilization of MgO-PSZ ceramic was caused by the presence of Al2O3.

Influence of CuO and Al2O3 addition on the optical properties of sodium zinc phosphate glass absorption filters

The phosphate glasses having chemical composition of 45P2O5-(35-y)ZnO-(20-x)Na2O-xCuO-yAl2O3 (0≤x≤5, 0≤y≤4) have been prepared using the melt quenching technique. XRD analysis has been carried out on the investigated samples in order for confirming the amorphous nature. The density has been measured using Archimedes method and then the molar volume has been calculated. It is found that the density, unlike molar volume, increases with increasing CuO content. This is due to the difference in atomic weight between Cu and Na. Addition of Al2O3 causes a slight decrease in density and a large increase in molar volume. The ionic concentration, inter ionic distance and oxygen packing density have been calculated for all investigated glasses. Using optical absorption, the optical bandgap has been calculated and found to decrease with increasing CuO concentration. This decrease becomes slower in the presence of Al2O3 which makes an increase in the bandgap at the the absence of CuO. The transmission spectrum of the investigated glasses shows that the samples containing CuO behave as bandpass filters. the characterized parameters of these filters, i.e. area, center, width, height and full wave half maximum (FWHM) of bandpass, have been estimated. These parameters have been found to be more affected by CuO and Al2O3 addition. The refractive index, extinction coefficient, real and imaginary part of the dielectric constant have also been calculated at the bandpass.

Effect of Al2O3 Ceramic Particles on Corrosion Behaviour and Tribological Properties of Nickel Composite Coatings

The paper presents a study on corrosion behaviour and tribological properties of nickel composite coatings deposited by electrochemical method on aluminium alloy from 2xxx series (AlCu4MgSi). The nickel composite coatings were produced in a Watts bath of the following chemical composition: NiSO4·7H2O 150 g/l, NiCl2·6H2O 30 g/l, H3BO3 30 g/l with the addition of saccharin in an amount of 2 g/l. As hard ceramic dispersed particles embedded in the coating, alumina (Al2O3) was used in an amount of 12,5; 25; 50 and 75 g/l. Coatings were produced using cathodic current density of 6 A/dm2, bath temperature of 60°C, pH 4, and the time 60 minutes. The electroplating bath was stirred with a mechanical stirrer (350 rpm). The results obtained were compared with a nickel coating deposited without the ceramic particles. It was found that the presence of Al2O3 increases the wear resistance of composite coatings, but does not significantly improve the corrosion properties.