Friction Stir Welding of Ceramic Particle Reinforced Aluminium Based Metal Matrix Composites

The mechanical and microstructural properties of 6061+20% Al₂O_3p and 7005+10% Al₂O_3p aluminium based metal matrix composites joined by friction stir welding were analyzed in the present study. The two materials were welded into the form of sheets of 7 mm thickness after T6 treatment and were tested in tension at room temperature. The microstructure of the joints was observed by optical microscopy and the fracture surfaces were analyzed by employing a scanning electron microscope equipped with field emission gun in order to study the micromechanisms involved during the deformation.     

Mechanical Behavior Enhancement of AM60/Al2O3p Magnesium Metal–Matrix Nanocomposites by ECAE

The effect of equal channel angular extrusion (ECAE) on the mechanical behavior of AM60/Al₂O_3p magnesium metal–matrix nanocomposites was investigated. ECAE is a useful technique to produce bulk nanostructured materials through severe plastic deformation. The present magnesium metal–matrix composites (Mg MMCs) with 1 wt% nanosized Al₂O₃ particles for ECAE were fabricated using stir-casting method. The significantly enhanced mechanical behavior of AM60/Al₂O_3p magnesium metal–matrix nanocomposites at room temperature, for instance, yield strength (YS), ultimate tensile strength (UTS), and ductility, can be obtained after ECAE process. The AM60/Al₂O_3p MMC after 4 passes of ECAE exhibited greater YS, UTS, and ductility (+135%, +107%, and +245% increase, respectively) than those of as-cast AM60. Experimental results show that the AM60/1wt %Al₂O_3p MMC after 4 passes of ECAE exhibits the superior mechanical behavior.     

Effect of Y3+ codoping on luminescence decays of the 4I13/2 level in Er3+-doped Al2O3 powders prepared by a sol-gel method

The luminescence lifetime of the 0.01 mol.%-0.1 mol.% Er³⁺- and 0–20 mol.% Y³⁺-codoped Al₂O₃ powders prepared at a sintering temperature of 900°C in a non-aqueous sol-gel method has been investigated to explore the enhanced mechanism of photoluminescence properties of the Er³⁺-doped Al₂O₃ by Y³⁺ codoping. For the 0.1 mol.% Er³⁺-Y³⁺-codoped Al₂O₃ powders, the measured lifetime of Er³⁺ gradually increases with increasing Y³⁺ concentration. Consequently, codoping with 20 mol.% Y³⁺ leads to an increase in the measured lifetime from 3.5 to 5.8 ms. By comparing the measured lifetime for different Er³⁺ concentrations in the Al₂O₃ powders, the radiative lifetime of both the Er³⁺-doped and the Er³⁺-Y³⁺-codoped Al₂O₃ powders is estimated to be about 7.5 ms. Infrared absorption spectra indicate that Y³⁺ codoping does not change the-OH content in the Er³⁺-Y³⁺-codoped Al₂O₃ powders. The prolonged luminescence lifetime of the ⁴I_13/2 level of Er³⁺ in Er³⁺-doped Al₂O₃ powders by Y³⁺ codoping is ascribed to the decrease in the energy transfer rate between the Er³⁺ ions and the Er³⁺ and -OH, respectively, due to the suppressed interaction between Er³⁺ ions.     

The interface in Al2O3 particulate-reinforced aluminium alloy composite and its role on the tensile properties

The interface characterization of the aluminium alloy reinforced with Al₂O₃ particulates ((Al₂O₃)_p/AI composite) was performed using X-ray diffractometry and energy dispersive X-ray spectroscopy. A layer of MgAl₂O₄ single crystals was observed at the (Al₂O₃)_p/Al interface in the as-received extruded composites. Such MgAl₂O₄ crystals formed at the surface of (Al₂O₃)_p are believed to grow by consuming a certain amount of (Al₂O₃)_p. Upon loading, interfacial debonding was observed to occur at the boundary between MgAl₂O₄ and the aluminium alloy, or along the MgAl₂O₄ layer itself. These experimental observations are correlated with the tensile properties of such composites.     

Fabrication of Al and large radii mismatch As codoped p-ZnO thin film and homojunction

We report Al³⁺ and large radii mismatched As⁵⁺ codoped p-ZnO thin films by As back diffusion from GaAs substrate and sputtering Al₂O₃ (1, 2 and 4 at%) mixed ZnO target. Hall effect measurements showed that the hole concentration increased upon codoping (As⁵⁺ and Al³⁺) compared to the monodoped (As⁵⁺) film. Also, it showed that 1 at% Al doped ZnO:As has low resistivity with high hole concentration due to best codoping. The crystallinity of the films has been studied by X-ray diffraction. The p-type formation mechanism has been investigated by X-ray photoelectron spectroscopy and low temperature photoluminescence analysis. It implies that As⁵⁺ substitutes on Zn²⁺ instead on O^2 − site that leads to the formation of (As_Zn-2V_Zn) complex which gives rise to p-conductivity. Further, the fabricated p-n homojunction using best codoped p-ZnO film shows typical rectifying characteristics of a diode.     

Hydrogen substitutes for the in situ generation of H2O2: an application in the Fenton reaction

This study investigates the ability of formic acid, hydrazine and hydroxylamine to act as H₂ substitutes in conducting phenol degradation by Fenton reaction using in situ generated hydrogen peroxide. The processes were performed with semi-heterogeneous (Pd/Al₂O₃ + soluble Fe²⁺) and fully heterogeneous (FePd/Al₂O₃) catalytic systems under ambient conditions. In contrast to bulk H₂O₂ production conditions, hydrazine is able to produce H₂O₂in situ followed by phenol degradation using Pd/Al₂O₃ + Fe²⁺ at pH 3 without the need for halide ions. However, a degree of mineralization exceeding 37% could not be achieved. The significant production of in situ H₂O₂ at the inherent acidic pH of hydroxylammonium sulfate in the presence of Pd/Al₂O₃ + Fe²⁺ was also found to differ from the bulk production of H₂O₂, in which no H₂O₂ was detected. A remarkable degree of mineralization (ca. 65%) as well as fast phenol degradation during the reaction started at pH 7 over FePd/Al₂O₃ may be an advantage of using hydroxylamine. On the other hand, using formic acid, H₂O₂ was produced at a moderate rate, thereby achieving higher efficiency in the mineralization of phenol. Most importantly, the catalysts were more stable in the presence of formic acid than hydrazine or hydroxylamine.     

Enhancing tensile/compressive response of magnesium alloy AZ31 by integrating with Al2O3 nanoparticles

AZ31 nanocomposite containing Al₂O₃ nanoparticle reinforcement was fabricated using solidification processing followed by hot extrusion. The Al₂O₃ nanoparticle reinforcement was isolated prior to melting by wrapping in Al foil of minimal weight (<0.50 wt% with respect to AZ31 matrix weight). The AZ31 nanocomposite exhibited slightly smaller grain and intermetallic particle sizes than monolithic AZ31, reasonable Al₂O₃ nanoparticle distribution, non-dominant (0 0 0 2) texture in the longitudinal direction unlike monolithic AZ31, and 30% higher hardness than monolithic AZ31. Compared to monolithic AZ31, the AZ31 nanocomposite exhibited higher 0.2%TYS, UTS, failure strain and work of fracture (WOF) (+19%, +21%, +113% and +162%, respectively). Also, compared to monolithic AZ31, the AZ31 nanocomposite exhibited higher 0.2%CYS and UCS, similar failure strain, and higher WOF (+5%, +5%, −4% and +11%, respectively). Inclusive of crystallographic texture changes, the effect of Al₂O₃ nanoparticle integration on the enhancement of tensile and compressive properties of AZ31 is investigated in this paper.     

Influence of excitation wavelengths on luminescent properties of Sr3Al2O6:Eu, Dy phosphors prepared by sol-gel-combustion processing

Eu²⁺ and Dy³⁺ ion co-doped Sr₃Al₂O₆ red-emitting long afterglow phosphor was synthesized by sol-gel-combustion methods using Sr(NO₃)₂, Al(NO₃)₃·9H₂O, Eu₂O₃, Dy₂O₃, H₃BO₃ and C₆H₈O₇·H₂O as raw materials. The crystalline structure of the phosphors were characterized by X-ray diffraction, luminescent properties of phosphors were analyzed by fluorescence spectrophotometer. The effect of excitation wavelengths on the luminescent properties of Sr₃Al₂O₆:Eu²⁺, Dy³⁺ phosphors was discussed. The emission peak of Sr₃Al₂O₆:Eu²⁺, Dy³⁺ phosphor lays at 516 nm under the excitation of 360 nm, and at 612 nm under the excitation of 468 nm. The results reveal that the Sr₃Al₂O₆:Eu²⁺, Dy³⁺ phosphor will emit a yellow-green light upon UV illumination, and a bright red light upon visible light illumination. The emission mechanism was discussed according to the effect of nephelauxetic and crystal field on the 4f⁶5d¹ → 4f⁷ transition of the Eu²⁺ ions in Sr₃Al₂O₆. The afterglow time of (Sr_0.94Eu_0.03Dy_0.03)₃ Al₂O₆ phosphors lasts for over 600s after the excited source was cut off.     

Preparation and photoluminescence of Er-doped Al2O3 films by sol-gel method

The 0-1.5 mol% Er³⁺-doped Al₂O₃ films have been prepared on the thermally oxidized SiO₂/Si(100) substrate in the dip-coating process by the sol-gel method, using the aluminium isopropoxide [Al(OC₃H₇)₃]-derived γ-AlOOH sols with the addition of erbium nitrate [Er(NO₃)₃·5H₂O]. The continuous Er³⁺-doped Al₂O₃ films with the thickness of about 1.2 μm were obtained for nine coating cycles at a sintering temperature of 900 °C. The aggregate size for the Er³⁺-doped Al₂O₃ films increased with increasing the Er³⁺ doping concentration from 0 to 1.5 mol%. The root-mean-square roughness of the films was independent on the Er³⁺ doping, which was about 1.8 nm for the 0-1.5 mol% Er³⁺-doped Al₂O₃ films. The γ-Al₂O₃ phase with a (110) preferred orientation was produced for the Al₂O₃ film. The photoluminescence (PL) spectra of 0.1-1.5 mol% Er³⁺-doped Al₂O₃ films were observed at the measurement temperature of 10 K. There was no significant change for the PL peak intensity with the increase of Er³⁺ doping concentration from 0.1 to 1.5 mol%, and similar full width at half maximum of about 40 nm was detected for the 0.1-1.5 mol% Er³⁺-doped Al₂O₃ thin films. The Er³⁺-doped Al₂O₃ films possess the available PL properties for use in planar optical waveguides.     

RF magnetron sputtered aluminium oxide coatings on iridium

The effects of process parameters on the microstructural morphology of aluminium oxide (Al₂O₃) coatings on Ir have been studied. Al₂O₃ coatings were deposited on Ir-coated isotropic graphite (IG) substrates at substrate temperatures of room temperature (RT)-1073 K, RF power of 200–600 W in an Ar, or Ar+1–10% O₂, sputtering gas atmosphere by RF magnetron sputtering. Al₂O₃ coatings which were deposited at high substrate temperatures and high RF powers in an Ar, or an Ar+O₂, sputtering gas atmosphere were found to contain a dense, fine columnar structure with a -Al₂O₃ phase, low Ar content and a relatively high hardness value of ca. 1050 H _v. Furthermore, high resolution transmission electron microscopy (HRTEM) results revealed the epitaxial growth of Al₂O₃ coatings on Ir-coated IG substrate. It was found that the interface between Al₂O₃ and Ir coatings was sharp and Al₂O₃ coatings remained intact with the Ir-coated IG substrate.     

Formation of Na-A and -X zeolites from waste solutions in conversion of coal fly ash to zeolites

Na-A and -X zeolites were synthesized from waste solutions in conversion of coal fly ash (Fa) to zeolite. The amorphous SiO₂ and Al₂O₃ of Fa were completely dissolved to form Po, Pt, and Pc type zeolites in NaOH solutions at 85°C. Only 24% of Si⁴⁺ eluted from Fa were converted to the zeolites and the remaining waste solutions contained high Si⁴⁺ concentrations. When molar ratio SiO₂/Al₂O₃ of the waste solutions was modified at 1.0≤SiO₂/Al₂O₃≤2.0 by addition of NaOH-NaAlO₂ solutions and the solutions were agied at 85°C, a single phase of Na-A zeolite was formed. The Na-X zeolite was formed at SiO₂/Al₂O₃≥2.5 and its crystallinity was increased with increasing the SiO₂/Al₂O₃ ratio, whereas the crystallinity of Na-A zeolite was decreased. At SiO₂/Al₂O₃=7.3, a single phase of Na-X zeolite was produced.     

Morphology and luminescent properties of Al<Superscript>3+</Superscript>/Mg<Superscript>2+</Superscript>-doped Y<Subscript>2</Subscript>O<Subscript>3</Subscript>:Eu<Superscript>3+</Superscript> phosphor

Al³⁺/Mg²⁺ doped Y₂O₃:Eu phosphor was synthesized by the glycine-nitrate solution combustion method. In contrast to Y₂O₃:Eu which showed an irregular shape of agglomerated particles (the mean particle size >10 μm), the morphology of Al³⁺/Mg²⁺ doped Y₂O₃:Eu crystals was quite regular. Al³⁺/Mg²⁺ substituting Y³⁺ in Y₂O₃:Eu resulted in an obvious decrease of the particle size. Meanwhile, higher the Al³⁺/Mg²⁺ concentration, smaller the particle size. In particular, the introduction of Al³⁺ ion into Y₂O₃ lattice induced a remarkable increase of PL and CL intensity. While, for Mg²⁺ doped Y₂O₃:Eu samples, their PL and CL intensities decreased. The reason that causes the variation of PL and CL properties for Al³⁺ and Mg²⁺ doped Y₂O₃:Eu crystals was concluded to be related to sites of Al³⁺ and Mg²⁺ ions inclined to take and the difference of ion charge.     

Characterization of Al2O3 composites with Mo particulates,II. Densification and mechanical properties

Three processes were employed to mix MoO₃ or Mo powder with submicrometric Al₂O₃ powder in the preparation of the Mo/Al₂O₃ precursors. The first two processes employed a dissolution route which dissolved MoO₃ powder in ammonia solution, followed by spray-drying or hot-plate-drying to obtain ammonium molybdate/Al₂O₃ granules. Then, the granulated powders were reduced in H₂ atmosphere and hot-pressed to obtain Mo/Al₂O₃ composites. The third process involved mechanically mixing metallic Mo particles with Al₂O₃. The composites normally can achieve 99% relative density after hot-pressing. Microstructural results of hot-pressed composites reveal that intergranular Mo grains of micrometer size dispersed at the grain boundaries of dense Al₂O₃ matrix, and some fine grain Mo grains of nanometric size were entrapped within the Al₂O₃ grains in the composite. The four-point bending strength and the toughness of the dense composites increases 26% and 32% respectively, with the addition of Mo content, but are controlled by the uniformity of the microstructure of the composites. The hardness of the composites basically obeys the prediction of the rule of mixture. The strengthening and toughening mechanisms of the composites with respect to the microstructure are analyzed.     

Mechanochemical behavior of Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>–Al–Fe powder mixtures to produce Fe<Subscript>3</Subscript>Al–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanocomposite powder

Mechanical treatment of Fe₂O₃, Al and Fe powder mixtures was carried out in a high energy ball mill to synthesize Fe₃Al–Al₂O₃ intermetallic matrix nanocomposite. Different compositions including 3Fe + Al, Fe₂O₃ + 2Al, 3Fe₂O₃ + 8Al and Fe₂O₃ + 3Al+Fe were chosen in this study. Phase development and structural changes occurring during ball milling were investigated by X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The results showed that during MA, Fe₂O₃, Al, and Fe react to give a nanocrystalline Fe₃Al intermetallic compound matrix. The presence of pure Fe in initial powder mixture changed the modality of mechanochemical process from sudden to gradual reaction. The Fe₃Al–Al₂O₃ compound had a finer microstructure and particles size compared to the Fe₃Al compound.     

Preparation and characterization of Sr4Al2O7:Eu, Eu phosphors

A new composition of red strontium aluminate phosphor (Sr₄Al₂O₇:Eu³⁺, Eu²⁺) is synthesized using a solid state reaction method in air and in a reducing atmosphere. The investigation of firing temperature indicates that a single phase of Sr₄Al₂O₇ is formed when the firing temperature is higher than 1300 °C and that a Sr₃Al₂O₆ phase is formed as the main peak below 1300 °C. The effects of firing temperature and doping concentration on luminescent properties are investigated. Sr₄Al₂O₇ phosphors exhibit the typical red luminescent properties of Eu³⁺ and Eu²⁺. A comparison photoluminescence study with Sr₃Al₂O₆ phosphor shows that Sr₄Al₂O₇ has higher emission intensity than Sr₃Al₂O₆ as a result of the higher optimum doping concentration of Sr₄Al₂O₇ phosphor.     

Optical and scintillation properties of Nd-doped complex garnet

Nd 1% doped complex garnet scintillators were prepared by Furukawa and their optical and scintillation properties were investigated on a comparison with previously reported Nd-doped YAG. Chemical compositions of newly developed complex garnets were Lu₂Y₁Al₅O₁₂, Lu₂Y₁Ga₃Al₂O₁₂, Lu₂Gd₁Al₅O₁₂, Lu₂Gd₁Ga₃Al₂O₁₂, Gd₁Y₂Al₅O₁₂, Gd₁Y₂Ga₃Al₂O₁₂, and Gd₃Ga₃Al₂O₁₂. They all showed 50–80% transmittance from ultraviolet to near infrared wavelengths with several absorption bands due to Gd³⁺ or Nd³⁺ 4f–4f transition. In X-ray induced radioluminescence spectra, all samples exhibited intense lines at 310 nm due to Gd³⁺ or 400 nm due to Nd³⁺ depending on their chemical composition. Among them, the highest scintillation light yield was achieved by Lu₂Y₁Al₅O₁₂. Typical scintillation decay times of them resulted 1.5–3 μs. Thermally stimulated glow curve after 1 Gy exposure and X-ray induced afterglow were also investigated.     

Luminescent properties of Al2O3:Ce single crystalline films under synchrotron radiation excitation

The paper is dedicated to study the luminescent and scintillation properties of the Al₂O₃:Ce single crystalline films (SCF) grown by LPE method onto saphire substrates from PbO based flux. The structural quality of SCF samples was investigated by XRD method. For characterization of luminescent properties of Al₂O₃:Ce SCFs the cathodoluminescence spectra, scintillation light yield (LY) and decay kinetics under excitation by α-particles of Pu²³⁹ source were used. We have found that the scintillation LY of Al₂O₃:Ce SCF samples is relatively large and can reach up to 50% of the value realized in the reference YAG:Ce SCF. Using the synchrotron radiation excitation in the 3.7–25 eV range at 10 K we have also determined the basic parameters of the Ce³⁺ luminescence in Al₂O₃ host.     

Effect of a small amount of liquid-forming additives on the microstructure of Al2O3 ceramics

Sintering behaviour and microstructure of Al₂O₃ ceramics without additives and with 0.02–0.25 mol% CaO + SiO₂ (CaO/SiO₂ = 1) were investigated. When Al₂O₃ bodies were sintered at 1400 °C, the sinterability and the grain size decreased as the content of CaO + Si₂ increased. When Al₂O₃ ceramics with 0.05 – 0.25 mol% CaO + SiO₂ were sintered at higher sintering temperature, both CaO and SiO₂ reacted with Al₂O₃ to produce the liquid phase along grain boundaries, and exaggerated platelet Al₂O₃ grains, with an aspect ratio of about 4.5, were formed. Because the size of platelet grains decreased as the content of CaO + SiO₂ increased, the distribution of either SiO₂ particles or this intergranular phase of CaO – Al₂O₃ – SiO₂ might control the microstructure.     

Influence of Mg<Superscript>2+</Superscript>/Ga<Superscript>3+</Superscript> doping on luminescence of Y<Subscript>3</Subscript>Al<Subscript>5</Subscript>O<Subscript>12</Subscript>:Ce<Superscript>3+</Superscript> phosphors

Mg²⁺/Ga³⁺ doped Y₃Al₅O₁₂:Ce³⁺ phosphors were synthesized through a solid state reaction. The phase and luminescent of the synthesized phosphors were investigated. For Ga³⁺ codoped Y_2.96Ce_0.04Al_(5?x)Ga_xO₁₂ phosphors, the emission intensity increases with the increase of Ga³⁺ concentration up to Y_2.96Ce_0.04Al_4.80Ga_0.20O₁₂ and then decreases with a further increase of Ga³⁺ concentration, but the emission peak shifts to shorter wavelength continuously in the Ga³⁺ doping concentration range of 0.05–0.25. For Mg²⁺/Ga³⁺ codoped Y_2.96Ce_0.04Al_(4.8?y)Ga_0.20Mg_yO₁₂ phosphors, the emission intensity decreases and the emission peak shifts to longer wavelength continuously in the Mg²⁺ doping concentration range of 0.02–0.12. The emission spectra of Y_2.96Ce_0.04Al_(4.8?y)Ga_0.20Mg_yO₁₂ phosphors demonstrate that the codoped Mg²⁺/Ga³⁺ ions not only induce the enhancement of Y_2.96Ce_0.04Al₅O₁₂ emission intensity but also lead to the red shift of Y_2.96Ce_0.04Al₅O₁₂ emission peak. The decay lifetimes decrease in Mg²⁺/Ga³⁺ codoped Y_2.96Ce_0.04Al₅O₁₂ phosphors due to defects formed by substitutions of Y³⁺ by Mg²⁺/Ga³⁺.     

Hot corrosion of atomized iron aluminides doped with boron and reinforced with alumina

The hot corrosion resistance of sprayed and atomized Fe–40 at.% Al, Fe40Al+0.1B and Fe40Al+0.1B+10Al₂O₃ intermetallic materials have been evaluated in NaVO₃ at 625 and 700°C using polarization curves and linear polarization resistance measurements. Also, the results were supported by X-ray diffractometry and electron microscopy studies. The tests lasted 10 days. At 625°C, the Fe40Al+0.1B+10Al₂O₃ material exhibited the lowest corrosion rate, whereas the Fe40Al had the highest corrosion rate. At 700°C the three materials exhibited erratic behavior during the first 100 h, and after this all the intermetallics had the same corrosion rate. However, the corrosion rate was higher at 625 than at 700°C. The results are discussed in terms of an electrochemical mechanism, the establishment of an Al₂O₃ layer, which is more protective in the Al₂O₃-containing aluminide and seems to increase its protectiveness as the temperature increases from 625 to 700°C.