Al2O3 Composite Powders Research Articles

Structural, optical, morphological and thermal properties of TiO2–Al and TiO2–Al2O3 composite powders by ball milling

The microstructure and morphology of 70% TiO2–30% Al, 70% TiO2–30% Al2O3, 55% TiO2–045% Al and 55% TiO2–45% Al2O3 composite powders were prepared by Smart Mini Ball Miller. They are characterized by XRD, SEM, EDAX, FTIR and TG/DSC. The XRD results showed that composite powders were mainly in the amorphous anatase phase with high crystallinity. The SEM study of composite powders reveals the average particle size is 100±20 nm. In FTIR, peaks observed at around 460 cm−1–560 cm−1 represent bending vibrations of Ti–O–Ti groups in the composite powders. In TG/DSC analysis, there is weight gain in TiO2–Al composite powders where as weight loss in TiO2–Al2O3 composite powders. Finally, microstructure and characterizations of the composite powders during ball milling were investigated to propose an optimal route for obtaining composite powders suitable for thermal spray process.

Suppressing Al2O3 nanoparticle coarsening and Cu nanograin growth of milled nanostructured Cu-5vol.%Al2O3 composite powder particles by doping with Ti

Both the coarsening of Al2O3 nanoparticles and the growth of Cu nanograins of mechanically milled nanostructured Cu-5vol.%Al2O3 composites with, and without, trace amounts of Ti during annealing at 973K for 1h were investigated. It was found that doping with a small amount of Ti (e.g. 0.2wt%) in a nanostructured Cu-5vol.%Al2O3 composite effectively suppressed the coarsening of Al2O3 nanoparticles during exposure at this temperature. Further, the Ti addition also prevented the concomitant abnormal growth of the copper grains normally caused by the coarsening of the Al2O3 nanoparticles. Energy dispersive X-ray spectroscopy analysis of the Al2O3 nanoparticles in the annealed Cu-5vol.%Al2O3-0.2wt%Ti sample suggested that the Ti atoms either diffused into the Al2O3 nanoparticles or segregated to the Cu/Al2O3 interfaces to form Ti-doped Al2O3 nanoparticles, which was more stable than Ti-free Al2O3 nanoparticles during annealing at high homologous temperatures.

The influence of milling parameters on the characteristics of milled and spray-dried NiCoCrAlY–Al2O3 composite powders

ABSTRACTSpray-drying process was selected to agglomerate ball milled NiCoCrAlY–Al2O3 composite powders. The effect of the starting alloy powder size on the morphology of composite powder was studied. The parameters of milling were optimised by orthogonal experiment to improve the powder’s flowability and apparent density. Then the optimised powder was sprayed by air plasma spray to prepare NiCoCrAlY–Al2O3 composite coating. The results showed that the size distribution of starting particles decided the deformation of alloy particles and the characteristics of agglomerated powders eventually. With the decreasing size range of the starting alloy particles, the sphericity of agglomerated powders increased. The optimised milling parameters were as follows: solid content, 60 wt-%; BPR, 4:1; the rotating speed, 350 rev min−1; and milling time, 5 h. And the contribution of solid content was the largest. The Al2O3 splats showed good adhesion with alloy matrix when the composite powder melted in good condition.

Aluminum matrix functional coatings with high microhardness on the basis of Al–Sn + Al2O3 composite powders fabricated by cold gas dynamic spraying

The ultimate operational capabilities of antifriction composite coatings on the basis of Al–Sn + Al2O3 composite powders fabricated by cold gas dynamic spraying are studied for the case study of friction pair with 20Kh13 steel in extreme modes.

Microstructure and mechanical properties of Mo2Ni3Si–Al2O3 nanocomposite synthesized by mechanical alloying

Abstract

A solid-state precursor route to MB2-Al2O3 composite powders

MB2-Al2O3 in situ composite powders were synthesized at 1500°C via a novel solid-state precursor route using Group IV–V metal (M, M=Ti, Zr, Hf, Nb, Ta) oxide, Al, and BN as raw materials. As a moderate cost boron source, BN has a well-defined stoichiometry and low impurity. In these precursor powder systems, the TiO2-Al-BN is an exception, which gives rise to the final TiB2-Al2O3-AlN product, whereas the rest produce the diboride-Al2O3 composite powders. As to HfB2–Al2O3 and TaB2–Al2O3 composite powders, the diboride phases have a smaller particle size (submicrometer) while the Al2O3 phase possesses a larger size (several micrometers). Besides, these diboride-alumina products produced by the solid-state precursor route form an interwoven network and are intimately mixed on a microscopic scale.

Synthesis and formation mechanism of ZrB2–Al2O3 composite powder starting from ZrO2, Al, and BN

ZrB2–Al2O3 in situ composite powders were synthesized at 1550°C via a novel solid-state precursor route using ZrO2, Al, and BN as raw materials. The final ZrB2–Al2O3 composite powders, consisting of large crystal Al2O3 particles (several micrometers) and fine ZrB2 particles (100–400nm), form an interwoven network and are intimately mixed on a microscopic scale. The formation mechanism for ZrB2–Al2O3 composite powders comprises two steps: aluminothermic reduction of ZrO2, which generates Zr–Al alloy compounds and the coproducts Al2O3, then followed by a series of solid reactions between Zr and BN to give the ZrB, ZrN, and ZrB2 products. The aluminothermic reduction is a fast reaction, while the reaction between Zr and BN to obtain the final ZrB2 product is the limiting step in the conversion process of the precursor powders.

Effect of Organic Fuel on High-Frequency Magnetic Properties of Fe–Al2O3 Composite Powders Synthesized by a Combustion Method

Nanocrystalline Fe–Al2O3 soft-magnetic composite powders were synthesized by a conventional combustion method followed by a H2 reduction process. In this paper, we analyzed the effect of the types and compositions of organic fuel on the dispersive magnetic properties of the composite powders for improving the soft-magnetic properties. To understand the properties, the microstructural and thermal characterization of as-synthesized oxide powders and their reduced powders were analyzed by an X-ray diffractor, a scanning electron microscope, and a thermogravimetric and differential thermal analyzer. In addition, the high-frequency dispersive magnetic simulation using the Landau–Lifshitz–Gilbert (LLG) equation and extended Maxwell–Garnet effective medium theory mixing rule was carried out. As a result, the microstructural and thermal analyses showed that the high-frequency dispersive magnetic behaviors of nanocrystalline Fe–Al2O3 composite powders were dependent on the types and the compositions of fuel by controlling the released heat amount during the combustion redox reaction. In particular, a relative real permeability ( $\text{u}^{\prime }_{r}$ ) of 3.6 at 1 GHz was obtained in Fe–Al2O3 (Fe: ${\rm{ Al}}=95$ :5, wt%) composite powders combusted by a mixed fuel composed of a 50 mol% glycine and a 50 mol% urea.

Dynamic strain ageing in fine grained Cu-1 wt%Al2O3 composite processed by two step ball milling and spark plasma sintering

Cu-1 wt%Al2O3 composite powder, prepared by mechanical milling and consolidated by spark plasma sintering to have about 98–99% of theoretical density, were characterized by scanning electron microscope, focused ion beam microscope, X-ray diffraction, nanoindentation and transmission electron microscope. The mechanically milled powders, upon consolidation, exhibited a finer grain size of 2 μm. Tensile deformation behavior of this composite, at ambient temperature but over the strain rates of 10−4 s−1 to 5 × 10−2 s−1, exhibited typical manifestations of dynamic strain ageing in the form of serrations and negative strain rate dependence of flow stress. The yield and ultimate tensile strengths, and so also the elongation decrease gradually with increase in strain rate. Such variation was also shown by nanoindentation hardness as a function of loading rate over 1–100 mN/s. The observed results are explained by the dislocation structure evolved from its interaction with Al2O3 dispersoids and impurity atoms like Fe, C and O coming from the powder processing.

Sub-micron Co–Al2O3 composite powders prepared by room-temperature ultrasonic-assisted electroless plating

Sub-micron Co–Al2O3 composite powders were synthesized by ultrasonic-assisted electroless plating process at room temperature with a one-step activating method pretreatment. The effect of process parameters on plating rate, Co content, and the uniformity of cobalt layer was analyzed by transmission electron microscopy (TEM). The results show that as the initial pH values of plating bath increase, the plating rate increases. The plating rate declines as the load increases when the load of powders is less than 12 g·L−1, but increases when the load is greater than 12 g·L−1. The relative Co content of the Co–Al2O3 powder declines with the powder load increasing.

Mechanism and microstructural evolution of combustion synthesis of ZrB2–Al2O3 composite powders

Mechanism of combustion synthesis (CS) of ZrB2–Al2O3 composite powders was systematically analyzed by a combustion front quenching method (CFQM). The microstructural evolution during the CS process was investigated by field-emission scanning electron microscopy (FESEM) equipped with energy dispersive X-ray spectrometer (EDS). The combustion temperature and wave velocity were measured by the data acquisition system. Moreover, the phase constituents of the final product were examined by X-ray diffraction (XRD). The thermal behaviors of the stoichiometic powders under the thermal exposure were characterized using differential scanning calorimetry (DSC) and thermogravimetric (TG). The results showed that the combustion reaction started from the melting of the B2O3 and Al particles, which was followed by the formation of ZrO2–B2O3–Al solution. The ignition temperature of this system was determined to be around 800°C. B and Al2O3 were then precipitated from the solution. As the CS reaction proceeded, Zr and Al2O3 were produced by the reaction between ZrO2 particles and Al and precipitated from the solution. ZrB2 could then be formed by the direct reaction between Zr and B. Finally, the ZrB2–Al2O3 composite powders were obtained. Furthermore, a model corresponding to the dissolution–precipitation mechanism was proposed.

Effect of MgO additions on the phase stability and degradation ability in ZrO2–Al2O3 composite systems

The present study investigates the effect of MgO additions in the ZrO2–Al2O3 composite system. An in situ citrate–nitrate sol–gel process was used to carry out four different concentrations of MgO additions in the ZrO2–Al2O3 composite system and the results were compared with the pure ZrO2–Al2O3 composite system synthesized by the similar process. The characterization results confirmed the formation of pure tetragonal zirconia (t-ZrO2) phase for all the investigated compositions at 900°C. Pure ZrO2–Al2O3 composite powders resulted in the degradation to yield monoclinic zirconia (m-ZrO2) at 1100°C whereas the MgO containing ZrO2–Al2O3 composite powders restricted the formation of m-ZrO2 till 1200°C. The reaction between MgO and Al2O3 to form magnesium aluminate (MgAlO4) started to occur from 1000°C and its quantitative yield was dependent on the two important factors namely the MgO content and heat treatment temperatures. The complete formation of MgAlO4 at 1200°C resulted in the onset of ZrO2 degradation to yield m-ZrO2 at 1200°C.

Microstructure, mechanical properties and oxidation resistance of Mo5Si3–Al2O3 composite

Mo5Si3–Al2O3 composite powders were successfully synthesized by ball milling MoO3, Mo, Si and Al powders. A dense nanostructure Mo5Si3–Al2O3 composite was consolidated by hot pressing sintering. Microstructure, mechanical properties and oxidation resistance of Mo5Si3–Al2O3 composite were investigated. Results showed that Mo5Si3–Al2O3 composite has good mechanical properties and oxidation resistance compared with Mo5Si3 alloy. Mo5Si3–Al2O3 composite with a relative density of 96.1% and the average grain size was approximately 1–3μm. The hardness, flexure strength and fracture toughness of Mo5Si3–Al2O3 composite are 15.2GPa, 630MPa and 6.53MPam1/2, respectively. Meanwhile, the composite has higher strength (~276MPa) at 1400°C. The oxidation test at 600°C showed that the addition of Al2O3 effectively restrained the pest oxidation of Mo5Si3. The oxide scale consists of SiO2–Al2O3 was formed on the surface of Mo5Si3–Al2O3 composite at 1200°C, and the SiO2–Al2O3 film presents good oxidation resistance compared to the pure SiO2 film.

Development of Al356–Al2O3 Nanocomposite Coatings by High Velocity Oxy-fuel Technique

In this research, development of Al356–Al2O3 nanocomposite coatings has been investigated. Al356–Al2O3 composite powders were prepared by mechanical milling of Al356 powder and 5 vol.% micro and nanoscaled alumina particles. The milled powders were used as feedstock to deposit composite coatings on A356–T6 aluminum alloy substrate using high velocity oxy-fuel (HVOF) process. X-ray diffractometry, optical and scanning electron microscopy, microhardness and wear tests were used to characterize the composite powders and coatings. The hardness of composite coatings containing micro and nanosized Al2O3 were 114.1 ± 5.9 HV and 138.4 ± 6.9 HV, respectively which were higher than those for substrate (79.2 ± 1.1 HV). Nano and microcomposite coatings revealed low friction coefficients and wear rates, which were significantly lower than those obtained for Al356–T6 substrate. Addition of 5 vol.% micro and nanoscaled alumina particles improved the wear resistance by an average of 85% and 91%, respectively. This is mainly caused by the presence of Al2O3 in matrix and nanocrystalline structure of matrix. Scanning electron microscopy tests revealed different wear mechanisms on the surface of the wear test specimens.

Preparation of Graphene Nanosheet/Alumina Composites

Graphene nanosheet (GNS)/ Al2O3 composite powder with homogeneously distributed GNSs has been fabricated from wet ball milled expanded graphite and Al2O3, and then followed by the rotary evaporator at relatively low temperature to dry the mixture and the residual solvent was removed in atmosphere-vacuum pipe-type furnace accessing mixed gases of Argon and Hydrogen at 600 for 6h. During the process, homogeneously dispersed and mixed GNS/ Al2O3 composite powders with quite few damage of GNSs structure and properties have been obtained. The microstructures and grain sizes of GNS/ Al2O3 composite powders have been investigated. The results showed that the addition of GNSs had diminished the size of Al2O3 particles and also the as-prepared GNSs/ Al2O3 composite powders can be dispersed and mixed more homogeneously remarkably with the presence of GNSs.

Effect of Sheet Nanocarbon on Properties of Low Carbon Al<sub>2</sub>O<sub>3</sub>-C Refractories

Sheet nanocarbon-Al2O3 composite powders were produced by vibratory milling using expanded graphite and Al2O3 powders as raw materials. The effect of different vibratory milling time on phase compositions and microstructure of the composite powders were investigated by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM). Then sheet nanocarbon-Al2O3 composite powders were used as additives to produce low carbon Al2O3-C refractories which had a carbon content of 6%. The results showed that about 50nm thickness sheet nanocarbon and Al2O3 composite powders were produced via 15h milling with expanded graphite to Al2O3 powders weight ratio of 1:2. With the increasing of milling time, the (002) diffraction peaks of graphite wear off gradually and nanosheet was desquamated from expanded graphite; It is beneficial to improve the bulk density, cold modulus of rupture (CMOR) and thermal shock resistance of Al2O3-C refractories when adding certain sheet nanocarbon-Al2O3 composite powders. The sample containing 0.5% sheet nanocarbon had a CMOR of 18.51MPa after 1000 °C heat processing in N2 atmosphere, while sample without adding any sheet nanocarbon was only 12.35MPa; The residual cold modulus of rupture (CMORTS) of sample containing 1% sheet nanocarbon was 4.22MPa after thermal shock test, while that of sample without nanocarbon was only 2.18MPa.

The Preparation of Core-Shell Al2O3/Cu Composite Powders by Electroless Plating in the Alkaline Solution

In this study, Cu-coated Al2O3 composite powders were synthesized by using electroless plating method. The influence of the plating bath composition and ceramic powder concentration on the Cu plating was characterized by scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction techniques. The results showed that the electroless bath composition plays an important role for the structure of nano core-shell Al2O3/Cu composite powders. The content of copper in the composite powders could be effectively controlled by adjusting the content of copper sulfate and formaldehyde in the plating solution. Furthermore, the pretreatment of the Al2O3 powders is also a key factor to form a uniform shell copper layer coating on Al2O3 particles. DOT: 10.12693/APhysPolA.123.238

The preparation of core–shell Al2O3/Ni composite powders by electroless plating

Core–shell nanostructured Ni-coated Al2O3 composite powders were synthesised by using the electroless plating method. The influence of the chemical components and powder concentration in the Ni coating was investigated by scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction techniques. The results show that the concentration of the plating components plays an important role in the formation of core–shell Al2O3/Ni composite powders. The nickel content in the composite powders could be effectively controlled by adjusting the nickel chloride content and the concentration of NaH2PO2·H2O in the plating solution. The nanostructure of the crystalline Ni coatings was observed to be very attractive for achieving good bonding between ceramic particles and matrices for composite production.

Catalytic characteristics of a copper–alumina nanocomposite formed by the mechanochemical route

Mechanochemical synthesis has been successfully employed to prepare Cu0–Al2O3 composite powders. The formation of the designed compound is due to the self-propagating reaction of CuO and Al0 powders by high-energy ball milling using a planetary ball mill (Pulverissette 6, Fritsch GmbH). The products were characterized by means of nitrogen adsorption (BET surface area), X-ray diffraction, scanning electron microscopy and temperature-programmed reduction of hydrogen. The catalytic properties of the prepared materials were tested in the methanol steam reforming (SRM) process. The results show that the Cu0–Al2O3 system is active towards hydrogen in SRM. Hydrogen yields are satisfactory; however, methanol conversion to CO as a by-product is observed.

Effects of amount of methanol on characteristics of mechanically alloyed Al–Al2O3 composite powders

In this study, an Al–10 wt-%Al2O3 composite powder prepared by mechanical alloying was investigated at different milling times. To evaluate the effects of the amount of methanol as a process control agent on the characteristics of mechanical alloyed Al–Al2O3 composite powder and the properties of the composite materials, the composite powders and the composite materials have been successfully produced with different amounts of methanol, namely, 1, 2 and 3 wt-%. The composite powders were characterised using scanning electron microscope (SEM), laser particle size analyser, X-ray diffraction analysis and Vickers microhardness test. The milled powders were pressed and sintered under argon gas control. The microstructure of the produced composite was investigated by SEM. The results show that varying amounts of methanol produce considerable effects on the morphology, particle size and structural behaviour of the as milled composite powders. Moreover, different microhardness values were obtained for different amounts of methanol at the same milling time.