Increasing Aluminum Content Research Articles

The Effect of Annealing Temperature on Microstructure and Mechanical Properties of Lightweight Steel with Increased Aluminium Content

A demand for enlightening of constructions in an automotive industry resulted in an intensive development of high strength steels and in attempts to decrease the weight of the steel by intensive alloying by lighter elements. This work used chemical concept of AHSS (advanced high strength steel) TRIP (transformation induced plasticity) steel with 0.2%C and micro-alloyed by 0.06%Nb and increased manganese content to 4% and aluminium to 6.5% to produce lightweight steel, which was cast and re-forged and subsequently annealed at various temperatures in the range of 300°C - 800°C. The resulting microstructures were analysed by light microscopy, laser scanning confocal microscopy, scanning electron microscopy and X-ray diffraction phase analysis and mechanical properties were measured by a tensile test. Tensile strengths in the region of 600 MPa - 757 MPa and total elongations around 20% were obtained for annealed samples.

Hydrophilicity-controlled MFI-type zeolite-coated mesh for oil/water separation

Abstract MFI-type zeolite was prepared on porous stainless steel mesh by in situ and secondary growth method, respectively. The zeolite mesh consisting of well-grown polyhedral crystals showed great hydrophilicity, which absorbed water passing through the mesh driven by gravity and rejected oil simultaneously. In order to obtain better oil/water separation performance, Al3+ ions were introduced into the zeolite structure to control the hydrophilicity of the zeolite-coated mesh. With increasing aluminum content in the coated zeolite, the contact angle measurement demonstrated that the hydrophilicity of the membrane increased with the oil contact angle changing from 136.8° to 163.5°. When the Al/Si ratio was 0.04, the zeolite-coated mesh showed super-hydrophilicity and underwater super-oleophobicity. The oil rejection rate of the membrane reached >99% with the water flux of >80,000 L m−2 h−1 at this ratio. The zeolite-coated mesh showed high chemical stability in an oil rejection rate, when the filtrations were repeated 15 times successively with the same membrane. The zeolite-coated meshes were successfully reproduced by a simple re-calcination step due to their thermal stability. When the re-calcination step had been carried out for three times on the same membrane, the oil rejection performance was slightly reduced only less than 1%. The MFI-type zeolite-coated mesh were also used to separate various oils such as n-hexane, cyclohexane, mineral oil and vegetable oil. The oil rejection rates were above 96% for all these oils.

Phase variation and thermophysical properties of La2Hf2O7 with alumina addition

La2O3-Al2O3-HfO2 ceramics were prepared by solid reaction of La2Hf2O7 ceramic powders which were synthesized by solution combustion and commercial alumina powders at 1600°C in air for 10h. Phase variation and thermophysical properties of La2O3-Al2O3-HfO2 ceramics were investigated. With the increase of alumina content, LaAlO3, HfO2 and LaAl11O18 phase structures appeared. The thermal expansion coefficients gradually increased with the increase of alumina content from 1000°C to 1300°C. The thermal conductivities of La2O3-Al2O3-HfO2 ceramics had nonlinear variation with the increase of alumina content and reached the lowest value around 1.1W·m−1·K−1 when the ratio of La2Hf2O7 to Al2O3 was 1:0.25. Therefore, the La2O3-Al2O3-HfO2 ceramics with a proper content of alumina can be considered as a new thermal barrier materials. Meanwhile, as potential application as interface layer in TBC, La2O3-Al2O3-HfO2 ceramics are beneficial to improve the effectiveness of the thermal barrier coating.

Characteristic of Cu–Al2O3 composites prepared by internal oxidation–remelting solidification

Copper (Cu)–aluminum oxide (Al2O3) composite sheets were prepared by internal oxidation of copper–aluminum (Al) alloy sheets with different aluminum contents. For the same internal oxidation temperature and time, the microstructures and properties of the copper–aluminum oxide composite sheets were compared. In order to prepare a densified copper–aluminum oxide bulk composite, the remelting solidification method of copper–aluminum oxide composite sheets was tried. The results show that with increasing aluminum content, the internal grains become coarser and the depth of the internal oxidation layer becomes narrower for the same internal oxidation time. The hardness of internal oxidation layer gradually decreases from the surface to the inner layers. For the same internal oxidation time, the higher the aluminum content, the higher the hardness of the internal oxidation layer at the same depth. Aluminum oxide particles inside the molten composite sheets are more likely aggregate and rise during the remelting–solidification process. The preparation of copper–aluminum oxide bulk composites by the internal oxidation–remelting solidification method is infeasible.

Auto-ignition synthesis of CoFe2O4 with Al3+ substitution for high frequency applications

Abstract A series of CoAl x Fe 2−x O 4 (0 ≤ x ≤ 1.0) was synthesized by sol-gel auto combustion method using nitrates of respective elements and by keeping 1:3 ratio of metal nitrate to citrate. The resultant powders were investigated by various techniques. Fourier transform infrared spectroscopy (FT-IR) is employed to determine the local symmetry in crystalline solids and to shed light on the ordering phenomenon. The XRD revealed that the powders obtained are single phase with inverse spinel structure. Evaluation of TEM confirms fine particle nature of the particles. SEM analysis and EDAX indicate that the samples were homogeneous and had the expected Fe-Co-Al ratios. As aluminium content increases, the measured magnetic hysteresis curves become broader and the saturation magnetization decreased. Coercivity increased from 975 to 4191 Oe with Al 3+ substitution. An increase in electrical resistivity, coercivity and dielectric characterization made present samples suitable for use in high frequency device applications.

The effect of Al substitution on the structural and magnetic properties of epitaxial thin films of epsilon ferrite

Epitaxial growth of aluminum substituted epsilon ferrite by pulsed laser deposition on strontium titanate and yttrium-stabilized zirconium substrates is demonstrated for a wide range of aluminum substitution. Linear decrease of the out-of-plane lattice parameter with aluminum substitution correlates with the decrease of the coercive magnetic field, while the magnetization first increases and then decreases with increasing aluminum concentration. A characteristic inflexion in the hysteresis loops has been attributed to the presence of a small quantity of magnetite. Epitaxial growth on yttrium-stabilized zirconium is technologically significant due to its use as buffer layer for the growth of complex oxides on silicon.

Enhancement of the physical properties of novel (1−x) NiFe2O4 + (x) Al2O3 nanocomposite

NiFe2O4, Al2O3 and their nanocomposites; (1−x) NiFe2O4 + (x) Al2O3, 0.0 ≤ x ≤ 1; were synthesized using the citrate–nitrate technique. The crystal structure was examined by X-ray diffraction, the microstructure was observed by transmission electron microscopy. The Curie temperature T C grows until reaching more than 1100 K with increasing alumina content (x), while the saturation magnetization (M s) decreased. The large improvement of room temperature resistivity which achieved two orders of magnitude from x = 0 to x = 70% was interpreted from the fact that the NiFe2O4 grains become electrically isolated and the conduction path is broken by the insulating Al2O3 nanoparticulates in the composite. The electrical properties of the nanocomposite could thus be tuned easily by adjusting the Al2O3 ratio to realize the targeted value of losses and resistivity at any temperature and frequency.

Protective properties of Al2O3 + TiO2 coating produced by the electrostatic spray deposition method

Abstract Mechanical resistance of Al 2 O 3 + TiO 2 nanocomposite ceramic coating deposited by electrostatic spray deposition method onto X10CrAlSi18 steel to thermal and slurry tests was investigated. The coating was produced from colloidal suspension of TiO 2 nanoparticles dispersed in 3 wt% solution of Al 2 (NO 3 ) 3 , as Al 2 O 3 precursor, in ethanol. TiO 2 nanoparticles of two sizes, 15 nm and 32 nm, were used in the experiments. After deposition, coatings were annealed at various temperatures, 300, 1000 and 1200 °C, and next exposed to cyclic thermal and slurry tests. Regardless of annealing temperature and the size of TiO 2 nanoparticles, the outer layer of all coatings was porous. The first five thermal cycles caused a rapid increase of aluminum content of the surface layer to 30–37 wt%, but further increase in the number of thermal cycles did not affect the aluminum content. The oxidation rate of coating-substrate system was lower during the thermal tests than during annealing. The oxidation rate was also lower for smaller TiO 2 particles (15 nm) forming the coating than for the larger ones (32 nm). The protective properties of Al 2 O 3 + TiO 2 coating against intense oxidation of substrate were lost at 1200 °C. Slurry tests showed that coatings annealed at 1000 °C had the best slurry resistance, but thermal tests had weakened this slurry resistance, mainly due to decreasing adhesion of the coating.

The impact of Si/Al ratio on properties of aluminosilicate aerogels

The Si/Al ratio is a key parameter of acid-base, structural, textural and, consequently, catalytic properties of amorphous crystalline (micro- and mesoporous) aluminosilicates. The changes of structural and textural characteristics of Al-Si aerogels with gradual increase of aluminum content are investigated. Aerogels were prepared via sol-gel method using prehydrolysed tetraethoxysilane and aluminium isopropoxide stabilized by acetylacetone. The gelation of the obtained sols took place in the presence of ammonia with the following drying in supercritical isopropanol. It was shown all aluminum reacts with prehydrolyzed tetraethoxysilane forming spherical particles in case the content of Al in the samples is less than 20 mol %. Aluminum drives the increase of interparticle coupling leading to the particle agglomeration, which is associated with the increase of the particle size and decrease of specific surface area and pore volume. For the samples with the aluminum content of >50 mol % the formation of pseudoboehmite plate-like particles is observed. The pseudoboehmite particles prevent the sintering of SiO2 particles that leads to the increase of the aerogel specific surface area and pore volume. In case the high aluminum content (>80 mol %) the silica particles serve as a connector between boehmite plates. The ratio between Brønsted and Lewis acid sites decreases gradually with the increase of aluminum content of the aluminosilicate aerogels.

Propagation of isobaric spherical flames in hybrid aluminum-methane fuel mixtures

The propagation of constant-pressure flames through hybrid aluminum-methane-oxidizer mixtures in transparent latex balloons is investigated using high-speed cameras that record both the dust dispersal and the subsequent spherical flame propagation processes. For mixtures without excess oxygen in the post-methane flame zone, the aluminum acts only as an inert diluent at low concentrations, resulting in a decline of the flame speed with aluminum concentration. Past a critical concentration around 100 g/m3, the flame speed stops decreasing and remains constant with increasing aluminum concentration, a behavior which is attributed to the formation of a high-temperature aluminum flame front that thermally couples to the methane flame. When there is excess oxygen to react with the aluminum, the flame speed monotonically increases with aluminum concentration before reaching a plateau at aluminum concentrations above 150 g/m3. The difference in behavior at low concentrations in mixtures with and without excess oxygen is explained by the ability of aluminum particles reacting with free oxygen to ignite and burn in the diffusion-limited combustion mode. The igniting particles are able to form high-temperature micro-diffusion flames which attain high combustion rates even at the relatively low bulk gas temperatures typical for methane flames.

A study of microstructure and optical absorption properties of Cu(In,Ga,Al)Se2 powders

CuInxGayAl1‐x‐ySe2 powders were prepared using a solvothermal reaction technique in ethylenediamine at 290°C for 20 hours. The microstructure and optical absorption properties of the powders were investigated by XRD, SEM, TEM, XPS and UV‐Vis‐NIR spectra. The results indicated that the Al atom was successfully incorporated into the CuInxGa1‐xSe2 lattices, and Al doping had a significant effect on the microstructure, especially at the (112) crystal orientation. It was found that the peak of (112) shifted obviously to higher 2θ values with the increasing aluminum content. Transmission electron microscope observation revealed that the size of the CuInxGayAl1‐x‐ySe2 nanoparticles could be adjusted by varying the stoichiometric ratio of the In, Ga and Al, and the proper Al incorporation could reduce the density of the stacking faults and nanotwins in the CuInxGayAl1‐x‐ySe2 materials. XRD analysis indicated that the Al incorporation could effectively substitute In and Ga atoms. Finally, the band gap was obtained by UV‐Vis‐NIR spectra, and the results implied that the optical absorption value decreased and optical band gap increased significantly with the incorporation of Al, and it is close to the optimal band gap (1.37 eV) of solar cells when the stoichiometric ratio of the Al was between 0.2 and 0.3.

Short-range structure and thermal properties of alumino-tellurite glasses

Alumino-tellurite glasses with wide range of Al2O3 concentration (1 to 20-mol%) are prepared and their short-range structural and thermal properties are studied by Raman spectroscopy, 27Al Magic Angle Spinning Nuclear Magnetic Resonance (MAS-NMR) and Differential Scanning Calorimetry (DSC). Glass sample with 1-mol% of Al2O3 has TeO co-ordination of 3.66, which is close to the value of 3.68 reported in pure TeO2 glass. TeO co-ordination decreases steadily to 3.33 on increasing alumina content to 20-mol%. 27Al MAS-NMR studies found that Al ions exist in hexa, penta and tetrahedral co-ordination in the alumino-tellurite network. On increasing alumina content from 3 to 20-mol%, the concentration of hexa-co-ordinated AlO units decreases from 54% to 35% with a simultaneous increase in the concentration of penta and tetra co-ordinated AlO units. Glass transition temperature increases with increase in Al2O3 concentration and correlates directly with the average single bond enthalpy of the glass network.

Fabrication and Characterization of AlxCoFeNiCu1−x High Entropy Alloys by Laser Metal Deposition

High entropy alloys are multicomponent alloys that have at least five different principal elements as alloying elements. Each of these elements has an atomic percentage between 5% and 35%. Typically, they form body-centered cubic (bcc) or face-centered cubic (fcc) structure and are known to possess excellent mechanical properties, corrosion resistance, excellent electric and magnetic properties. Owing to their excellent corrosion and wear resistance, researchers are focusing on employing these materials as coatings. In this research, Laser Metal Deposition (LMD) was used to fabricate AlxCoFeNiCu1−x (x = 0.25, 0.5, 0.75) high entropy alloys from elemental powder based feedstocks. Thin wall claddings fabricated via LMD were characterized by a variety of techniques. Data from X-ray Diffraction (XRD) and Electron Back Scatter Diffraction (EBSD) suggested that with increase in Al content and decrease in Cu content, a change in crystal structure from a predominantly fcc to a combined fcc and bcc structure can be observed. The microstructure of the material was observed to be columnar dendritic. Data from standard less EDS analysis showed that the dendritic phase was Fe and Co enriched while the matrix was Cu and Al enriched in all the considered high entropy alloy fabrications. The Vickers hardness data was used to estimate the mechanical properties of these deposits. Results also showed that with the increase in aluminum content, AlxCoFeNiCu1−x displayed higher hardness. The high hardness values imply potential applications in wear resistant coatings.

A mechanistic basis for the effect of aluminum content on ethene selectivity in methanol-to-hydrocarbons conversion on HZSM-5

Increasing crystallize size or aluminum content in MFI-type zeolites independently enhances the propagation of the aromatics-based methylation/dealkylation cycle relative to that of the olefins-based methylation/cracking cycle in methanol-to-hydrocarbons (MTH) conversion and consequentially results in higher ethene selectivity. Ethene selectivity increases monotonically with increasing aluminum content for HZSM-5 samples with nearly identical crystallite size consequent to an increase in the intracrystalline contact time analogous to our recent report detailing the effects of crystallite size (Khare et al., 2015) on MTH selectivity. The confected effects of crystallite size and site density on MTH selectivity can therefore, be correlated using a descriptor that represents the average number of acid sites that an olefin-precursor will interact with before elution.

Magnetostructural phase transitions and magnetocaloric effects in as-cast Mn1-xAlxCoGe compounds

Abstract The structural and magnetic properties of as-cast Mn 1-x Al x CoGe (0 ≤ x ≤ 0.05) have been studied by X-ray diffraction, differential scanning calorimetry, and magnetization measurements. The partial substitution of Al for Mn in Mn 1-x Al x CoGe results in a decrease in the martensitic transition temperature T M . For the concentration range 0 ≤ x ≤ 0.01, T M was found to coincide with ferromagnetic transition temperature (T C ) resulting in a first-order magnetostructural transition (MST). A further increase in aluminum concentration resulted in a splitting of the phase transition temperatures, which included a drastic decrease in the martensitic temperature. The compounds with x > 0.02 showed a single transition at T C . The maximum values of the magnetic entropy changes (-ΔS M ) were ∼18 J/kgK, 12 J/kgK, and 7 J/kgK for ΔH = 5T at 313 K (x = 0.00), 286 K (x = 0.01), and 220 K (x = 0.02), respectively. The maximum value of the relative cooling power (RCP) was found to be 303 J/kg for x = 0.01 at T = 286 K for ΔH = 5T. It has been established that as-cast samples of this system show large value of MCE near room temperature making this system a promising material for magnetic cooling technologies.

Spin structure, magnetism, and cation distributions of NiFe2−xAlxO4 solid solutions

Low temperature Mössbauer spectroscopy together with isothermal magnetization and zero-field-cooled and field-cooled measurements have been used to perform a systematic investigation of the cation distributions and magnetic properties of solid solutions of NiFe2−xAlxO4 with x=0.0, 0.4, 0.8, 1.2, 1.6, and 2.0. Mössbauer spectroscopy for the starting member of the series, NiFe2O4, shows that nickel atoms occupy the octahedral sites and are in 2+ oxidation state, while iron atoms, all in 3+ oxidation state, occupy equally the tetrahedral and the octahedral sites. When low concentration of aluminum, x=0.4, is incorporated into the system, they substitute preferentially iron atoms in the octahedral sites. As the concentration of aluminum is increased, there are distributions of them in both the tetrahedral and octahedral sites leading to complex cation distributions. The magnetic characters of iron and nickel atoms and the diamagnetic nature of aluminum atoms and the complex cation distributions result in interesting magnetic properties for this class of materials. As the concentration of aluminum increases, the saturation magnetization decreases drastically and then gradually increases. In the end member of the series, NiAl2O4, the absent of any super-exchange interaction between the A-sites and the B-sites due to presence of Ni ions as the only magnetic atoms in the B-sites results in a paramagnetic structure and a magnetization close to zero although the nickel atoms have a spin moment of 2μB. This paramagnetic feature makes this compound to be considered as a magnetic resonant imaging agent. Another very interesting feature is the back and forth switching of the dominance of the magnetic moments in the tetrahedral sites and the octahedral sites as aluminum concentration increases.

Behavior of triplex steel containing different aluminum content

Abstract Medium-carbon alloy steels containing different aluminum contents were hot forged by 95% reduction at 1200°C followed by air cooling. Optical and scanning electron microscopes were used to investigate the morphologies of the different phases present. An austentizing process followed by water quenching (after hot forging) was carried out to obtain different hardness values. The intensity of the different planes was investigated using X-ray diffraction. The mechanical properties were characterized using tensile and hardness tests. Optical and scanning electron micrographs revealed a great effect of aluminum content on the steel properties. A matrix of bainite and pearlite and traces of ferrite was revealed for hot forged steel type 1 containing 1% Al. Steel type 2 containing 2% Al showed a matrix of pearlite and ferrite with the absence of bainite. The hardness increased with increasing the temperature to a maximum value then decreased for steel containing 1 and 2% aluminum. After austentizing at 925°C, the maximum hardness of 649Hv was recorded for hot forged steel type 2 of 2% aluminum, while steel type 1 of 1% aluminum showed a maximum hardness of 531Hv after austentizing at 1000°C. Thus, the maximum hardness of hot forged steels decreased with increasing aluminum content. In addition, the maximum tensile and yield strength were decreased by increasing the aluminum content in the steel. The changes in microstructure and mechanical properties of these steels could be explained by the effect of aluminum as a ferrite forming element.

Improved Oxidation Resistance of a New Aluminum-Containing Austenitic Stainless Steel at 800 °C in Air

The oxidation resistance of austenitic stainless steels modified with various aluminum contents was investigated. The weight gain per unit area is in parabolic relation to oxidation time, and the oxidation rate significantly decreases with increased aluminum content. Outer layer oxides of austenitic stainless steel transform from Cr2O3 to a composite oxide layer comprising Cr and Al, and more dense Al-containing oxides formed with increasing the added Al contents. Since the diffusion of element Al is enhanced and the diffusion of element Cr is inhibited, the oxides enriched in Al dramatically contribute to the improved oxidation resistance of austenitic stainless steels at high temperature. The possible oxidation mechanisms are also proposed based on microstructural observations.

The Influence of Al Content and Thickness on the Microstructure and Tensile Properties in High-Pressure Die Cast Magnesium Alloys

The influence of Al content and section thickness on the microstructural features and tensile properties of high-pressure die cast AM series magnesium alloys is quantified in order to better understand the relationship between microstructure and tensile properties. It is found that with increasing aluminum content, the yield strength increases and the ductility decreases. Increasing the plate thickness results in a decrease in both the yield strength and ductility. The grain size, β-Mg17Al12 phase volume fraction, and solute content are all quantified through the thickness of the plates. It is found that the plates have a skin with increased hardness, due to a fine grain structure. The primary factors affecting strengthening in these alloys, including microstructural variations through the thickness, are accounted for using a linear superposition model. We conclude that yield strength is dominated by grain boundary strengthening and solid solution strengthening effects. The through-thickness grain size and solute concentration were quantified and these variations were found to play an important role in controlling the yield strength of these alloys.

Mechanical properties of lightweight aerated concrete with different aluminium powder content

Aerated concrete is produced by introducing gas into a concrete, the amount dependent upon the requirements for strength. One method to achieve this is by using powdered aluminium which reacts with the calcium hydroxide produced upon hydration of the cement. The aim of the current study was to investigate the influence of the powder content on the mechanical properties of aerated concrete namely; compressive and flexural strengths, modulus of elasticity, density and porosity. The results indicated that an increase in aluminium content caused a decrease in the compressive and tensile strengths. It also produced a decrease in the modulus of elasticity. When the aluminium content increased, the density decreased and the porosity increased.