Aluminum Powder Mixtures Research Articles

Detection Mechanisms of Phosphate Sensitive Electrodes

Phosphate sensors are composed of inorganic solid/ solid solutions and have a three dimensional network structure with interstitial ions. They have been fabricated by constructing a crystal disk consisting of mixtures of aluminum powder (Al), aluminum phosphate (AlPO4), and powdered copper (Cu). The membrane sensor exhibits linear potential response in the concentration range of 10−1 to 10−6 mol L−1. The electrode/solution interfaces presumably aid phosphate selective crystallizations or phosphate ion chemisorptions thereby leading to a membrane potential charge. The charge separation process caused by phosphate ion adsorption and the potentiometric response of the electrode contribute to the response mechanism.

Effect of Different Types of Pore-Forming Agent on the Macro Pore Size of Ceramic

The aim of this study is to determine the effect of different types of pore-forming agent and sintering temperature on the pore size of ceramics. The porous ceramic material was developed by mixing of alumina, zeolite and calcium oxide (CaO) as the main materials and ethylene glycol as the binder. Meanwhile, two types of pore-forming agent were used, i.e., yeast and a mixture of aluminium powder and expandable polymeric spheres (EPS). The content of pore-forming agent was at 10 wt% of the mixture and the samples were shaped by using plaster of paris mould. After being dried, the samples were sintered at temperature range of 1000 up to 1500 °C for two hours. Microstructural analysis and pores size measurement were performed to determine the effect of pore-forming agent and sintering temperature on the ceramic. The result showed that yeast yielded larger pore sizes in the porous ceramic upon being sintered at 1400 °C for two hours, which were up to 402 μm. Therefore, yeast has the potential to be utilized as pore-forming agent in development of filter and wall insulation material.

Effects of Al Content and Addition of Third Element on Fabrication of Ti-Al Intermetallic Coatings by Heat Treatment of Warm-Sprayed Precursors

Four powder mixtures of titanium and aluminum with 50:50, 40:60, 30:70, and 20:80 atomic ratios were used as feedstock for Warm Spray process to produce composite coatings. A two-stage heat treatment at 600 and 1000 °C was applied to the deposits in order to obtain titanium aluminide intermetallic phases. The microstructure, chemical, and phase composition of the as-deposited and heat-treated coatings were investigated using SEM, EDS, and XRD. It was found that the Al content affects on the thickness expansion of the heat-treated Ti-Al coatings significantly and also has a major influence on the porosity development, which is caused by the Kirkendall effect. The effects of adding a third element Si and heat treatment with pressure to produce denser Ti-Al intermetallic coating were also examined. The investigated hot-pressed coatings with addition of Si exhibited much denser microstructure and contained Ti-Al intermetallic phases with titanium silicide precipitates.

Synthesis of mullite-based coatings from alumina and zircon powder mixtures by plasma spraying and laser remelting

A mechanical mixture of alumina and pulverized zircon sand in 3:2 M ratio has been plasma sprayed to obtain mullite coating. Thereafter, the top layer of the coating has been remelted using laser. The presence of a mullite phase in the as-sprayed and laser remelted coatings has been confirmed qualitatively using X-ray diffraction. Both as-sprayed and laser remelted coatings have been characterized for their microstructure, hardness and porosity. The ultrafine grain structure of the coating produced by rapid quenching has been analyzed using transmission electron microscope. Presence of a mullite phase in the coatings has also been confirmed using small angle electron diffraction. Laser remelting has resulted in an appreciable reduction in porosity and increase in hardness in the coatings.

Impact of the Surface Morphology on the Combustion of Simulated Solid Rocket Motor

An advanced and intensive computational solution development is integrated with an asymptotic technique, to examine the impact of the combustion surface morphology on the generated rotational flow field in a solid rocket chamber with wide ranges of forcing frequencies. The simulated rectangular chamber is closed at one end and is open at the aft end. The upper and lower walls are permeable to allow steady and unsteady injected air to generate internal flow mimicking the flow field of the combustion gases in real rocket chamber. The frequencies of the unsteady injected flow are chosen to be very close or away from the resonance frequencies of the adapted chamber. The current study accounts for a wide range of wave numbers that reflect the complexity of real burning processes. Detailed derivation for Navier-Stokes equations at the four boundaries of the chamber is introduced in the current study. Qualitative comparison is performed with recent experimental work carried out on a two-inch hybrid rocket motor using a mixture of polyethylene and aluminum powder. The higher the percentage of aluminum powder in the mixture, the more the corrugations of the combustion surface. This trend is almost similar to the computational and analytical results of a simulated solid rocket chamber.

マルチパス摩擦粉末焼結法によるポーラスアルミニウム板の作製

Multi-pass friction powder sintering process was proposed for fabricating a large plate of porous aluminum by the sintering and dissolution process. In this process, sintering of a powder mixture of aluminum and NaCl was achieved only the rotating tool plunged into the die filled with the powder mixture was made to traverse as in the case of multi-pass friction stir processing. In this study, porous aluminum plates of 60 mm × 30 mm × 5 mm with porosity of 70% were successfully fabricated by multi-pass friction powder sintering process. From measurements of temperature and torque, it was found that the entire sample had almost same sintering condition during the multi-pass friction powder sintering process. From X-ray computed tomography (CT) and scanning electron microscopy (SEM) observations of the pore structures of the fabricated porous aluminum plates, it was found that the entire sample had almost same pore shape and porosity that was similar to the NaCl morphology and proportion. From compression tests of the fabricated porous aluminum plates, it was found that entire sample exhibited a similar stress-strain curve to that of the previous work regardless of the position. This is considered to be attributed to the good bonding between aluminum particles during friction powder sintering process. From these results, it was indicated that multi-pass friction powder sintering process had a potential to fabricate the porous aluminum plate that was similar to the size of the tool traversing area.

Investigation on the reactions sequence between synthesized ilmenite and aluminum

Fe–Al2O3/TiC composites have features of which we can refer to: good strength, toughness, wear resistance, high temperature strength and light weight. It can also be used as cutting tools. Some researchers have used ilmenite, aluminum and carbon to produce these composites. However the formation mechanism and reaction sequences are not clear enough. In this research, the first step of reactions was investigated by studying the binary phase between aluminum and ilmenite. At first, ilmenite was synthesized, and then the critical temperatures due to the reactions occurring in the ilmenite–aluminum powder mixture were determined by DTA. The milled and pressed samples of synthesized ilmenite and aluminum with molar ratio of 1:2 were heat treated at 740°C for 3, 12, 15, 24 and 72h and at 1000°C for 24h. The final products were analyzed with XRD, SEM and EDS. The results show that after the melting of aluminum, the reaction between ilmenite and molten aluminum starts, leading to formation of Fe and TiO2. It is found that the tendency of FeO to reduce with aluminum is more than TiO2. Therefore, FeO reduces to Fe while the TiO2 remains unchanged. By consumption of the raw materials, Fe and TiO2 react with remained aluminum, resulting in the formation of spherical Fe2Ti in the TiO2 and Al2O3 matrix.

Application of Layered Double Hydroxide Membranes as Phosphate-Sensitive Electrodes

GRAPHICAL ABSTRACT

Formation of Metal-Intermetallic Laminate Composites by Spark Plasma Sintering of Metal Plates and Powder Work Pieces

Laminate composites with an intermetallic component are some of the most prospective constructional and functional materials. The basic formation method of such materials consists in heating a stack composed of metallic plates reacting at elevated temperatures to form intermetallic phases. The temperature of the process is usually approximately equal to a melting point of a more easily fusible component. In this study, an alternative technology of producing a titanium – titanium aluminide composite with a laminate structure is suggested. It consists in combining metallic (titanium and aluminum) powder mixtures pre-sintered at 400 оС with titanium plates, alternate stacking of these components and subsequent spark plasma sintering (SPS) of the fabricated workpieces. Applying this technology allowed for the fabrication of metal-intermetallic laminate (MIL) materials with an inhomogeneous structure of intermetallic interlayers. The phases revealed in the composite by X-Ray diffraction (XRD) were α-Ti, Al, Al3Ti and Al2Ti. Moreover, the results of the energy-dispersive analysis gave the evidence of the formation of Ti-enriched phases in powder layers after SPS. A small number of voids were observed between the structural components of the intermetallic layers. Voids were also detected at “metal-intermetallic” interfaces; however, the quality of connection between different layers in the composite was very high. The microhardness of an intermetallic layer formed in the composite was comparable to the microhardness of the Al3Ti compound. The microhardness of titanium was equal to 1600 MPa.

Prebreakdown current and DC breakdown strength of alumina-filled poly(ethylene-co-butyl acrylate) nanocomposites: Part II - prebreakdown currents

Pre-breakdown currents through the poly (ethylene-co-butyl acrylate) (EBA) nanocomposites filled with spherical alumina particles were studied as a function of particle coating and moisture content. The nanocomposites were prepared from a mixture of EBA formulations (13 wt% butyl acrylate groups content) and alumina powder. Two kinds of alumina nanoparticles were used: NA (25 nm in diameter) and ND (45 nm in diameter). The particles were either unmodified or surface-treated with aminopropyltriethoxy silane or octyltriethoxy silane. Two different relative humidities of air were used for conditioning the samples prior to testing: 0 % RH (dry case) and 86 % RH (samples were saturated with moisture). The pre-breakdown current measurements were performed with a DC ramp of 1.2 kV/s. Twenty samples were tested for each material formulation - ten of which were tested in dry conditions and ten were tested after conditioning in humid environment. Results were compared to the reference unfilled EBA samples. The measured currents were analyzed under the assumption of space charge limited conduction. As expected, conditioning materials in humid environment caused an increase in pre-breakdown currents. This effect was more pronounced for nanocomposite materials, while the reference unfilled material was least affected.

Research of Formulation and Processing of Hydroxyl-Terminated Polybutadiene (HTPB) Propellants

Solid composite propellants are extensively used for propulsion of rockets, missiles and space applications. The composite propellant is a polymeric matrix in which the oxidizer and fuel particles are embedded in a polymeric binder. Different composite propellant mixtures have been prepared using ammonium-perchlorate (ratio 70:30) as oxidant and mixture of aluminium powder (ratio 50:50) as metal component. In the present work, RDX (Cyclotrimethylene trinitramine) has been used in successive increments replacing AP (Ammonium Perchlorate) in number of batches by varying the percentage of solid loading, and studied their different properties such as viscosity build-up, mechanical and ballistic properties.

Convective burning of an aluminum-water mixture

The burning of a stoichiometric mixture of aluminum (PAP-2 powder) with water in a constant-volume bomb is studied. It is shown that, depending on the charge diameter and igniter-generated pressure, three situations can arise: the mixture does not burn, burns slowly (in the layer-by-layer mode), or burns rapidly in the convective mode. The characteristics of the rapid burning, such as the effect of the igniter-generated burning, charge length, and initial charge density, are in general similar to those of the convective burning of mixtures of aluminum powder with an oxidizing agent (AP or PA), described in the literature. The difference lies in the fact that, due to a relatively low water activity as an oxidant, the convective burning of aluminum-water mixtures is harder to initiate, and it proceeds at a much lower velocity.

Structure and properties of a nanoscaled composition modulated metallic glass

The aim of this study was to evaluate the possibilities offered by severe plastic deformation to prepare nanoscaled composites based on a bulk metallic glass. High pressure torsion was applied to a mixture of aluminium and metallic glass powders to process a composite at the nanoscale. Ultimate mixing of the two phases was achieved for a very large level of deformation resulting in a fully amorphous structure. Using analytical scanning transmission electron microscopy, nanoscaled chemical gradients were clearly exhibited. The very high strength (HV ~ 700) of the final metallic glass is attributed to this unique nanoscaled composition modulated structure. The role of shear bands both in the partial mixing and in the amorphization mechanism is discussed on the basis of a simple geometrical model.

Rapid synthesis of bulk Ti3AlC2 by laser melting

The Mn+1AXn phase ternary layered compound Ti3AlC2 samples had been successfully synthesized by laser melting using titanium, aluminum, and titanium carbide powder mixtures with a molar ratio of 1:1.2:2 as the starting materials. Microstructure of the samples was examined by X-ray diffraction (XRD), scanning electron microscope (SEM) and X-ray energy dispersive spectrometer (EDS). Ti2AlC and TiC were the main impurities in the formation process of Ti3AlC2. The synthesis was extremely fast because the migration of solute mainly depended on the convection mixing of molten pool caused by intense laser beam which was far faster than the solid state diffusion by traditional sintering methods.

Magnetic Property of Iron-Dust Cores With Mixture of Ferromagnetic Ferrite Powder and Alumina Powder

Iron-dust cores are produced from insulated iron particles by using the powder metallurgy pressure forming process. These dust cores are suitable for small motor cores because of their high shape flexibility; however, the iron loss of iron-dust cores is larger than conventional laminated cores. Generally, the insulation material between the iron particles degrades the magnetic property of the core. In this paper, the magnetic property of the iron-dust core in which the resin, which is usually used as insulation material, is replaced by the soft magnetic Mn-Zn ferrite or alumina is examined. We have found that the iron-dust core mixed with alumina particles shows higher space factor, 10% lower iron loss, and 30% higher permeability. Contrary to expectation, the magnetic properties of the iron-dust core deteriorate by mixing with soft magnetic Mn-Zn ferrite.

Microstructural Characterization of Slurry Aluminide Diffusion Coatings

Commercially pure aluminium powder and a mixture of aluminium and silicon powders, both in a liquid amyl acetate-based organic binder, were sprayed onto the surface of Inconel 713LC nickel base superalloy. A two-stage heat treatment process in an argon atmosphere flow was designed and applied to produce nickel aluminide diffusion coatings. Two coating systems composed of different layers with gradual changes in chemical composition and phase quantities were formed. Scanning electron microscope, scanning electron microscope/focused ion beam, both equipped with energy dispersive microanalyzers, were utilized to characterize the microstructure and chemical composition of the coatings.

Size Effect on Functionally Graded Material Fabrication by Sedimentation

AbstractA simple, economic, and scalable material manufacturing method of sedimentation has been used to fabricate functionally graded materials for solar roofing panels. This paper investigates the size effect of aluminum powder on the material gradation in the depth direction when only aluminum powder or the mixture of aluminum and high-density polyethylene (HDPE) powder is uniformly dispersed in ethanol and then subjected to sedimentation for a certain period, respectively. A Stokes’ law–based model is developed to simulate the sedimentation process, in which the concentration of aluminum and HDPE particles temporally and spatially changes in the depth direction due to the nonuniform motion of particles. The concentration variation further changes the effective viscosity of the suspension, and thus affects the drag force of particles. The numerical simulation demonstrates the effect of manufacturing parameters for sedimentation and predicts the graded microstructure of deposition in the depth direction...

Large-scale aluminum foam plate fabricated by enhanced friction powder compaction process based on sintering and dissolution process

An enhanced friction powder compaction (FPC) process was proposed for fabricating a large plate of aluminum foam by the sintering and dissolution process. In this process, the rotating tool plunged into the die filled with a powder mixture of aluminum and NaCl during the FPC process was made to traverse perpendicularly to the direction of plunging as in the case of friction stir welding. In the enhanced FPC process, no external heat source, such as an electric furnace or a spark plasma sintering, was necessary for fabricating aluminum foam, except for the friction heat generated by traversing the rotating tool. It was found that a long plate of aluminum foam can be fabricated with a length equal to the tool traversing length. By X-ray computed tomography (CT) and scanning electron microscopy (SEM) observations of the pore structures of the fabricated aluminum foam, it was found that the entire sample had a pore structures that was similar to the NaCl morphology, regardless of the position along the traversing direction. The fabricated aluminum foam had a similar stress–strain curve to that of aluminum foam fabricated by spark plasma sintering and exhibited ductile fracture. This is considered to be attributed to the good bonding between aluminum particles in the entire sample. The fabricated aluminum foam exhibited almost the same plateau stress regardless of the position along the traversing direction.

Formation mechanism and synthesis of Fe–TiC/Al2O3 composite by ilmenite, aluminum and graphite

Al2O3/TiC composites are used as cutting tools for machining gray cast iron and steels. The addition of iron improves the toughness of Al2O3/TiC composites. Ilmenite, aluminum and graphite can be used to produce in-situ Al2O3/TiC–Fe composites. However the formation mechanism and reaction sequences of the system are not clear enough. Therefore, the present research is designed to determine the formation mechanism and the reaction sequences of the foresaid system.In this research, ilmenite was synthesized to prevent the presence of impurities in the system and then the critical temperatures of ilmenite, aluminum and graphite powder mixture were determined by DTA analysis. The milled and pressed samples, prepared from this mixture, were heat treated at the critical temperatures. The final products were analyzed with XRD. It was found that at the first exothermic peak of DTA curve (720°C), aluminum reacts with FeTiO3, forming Fe, TiO2, Al2O3 and Fe2Al5. Further increase in the temperature, up to 930°C, results not only in the transformation of TiO2 to Ti2O3 and TiO, but also in the conversion of Fe2Al5 to FeAl. Moreover, titanium carbide will also be formed. With the rise in temperature, Ti2O3, TiO and iron aluminides disappear and TiC, Al2O3 and Fe will be the final compounds.

Exothermic surface reactions in alumina–aluminum shell–core nanoparticles with iodine oxide decomposition fragments

A pre-ignition reaction (PIR) once thought to be unique to aluminum (Al) and fluorine-based oxidizer reactions is observed for aluminum and an iodine-containing oxidizer. This PIR is exothermic and precedes the main exothermic reaction corresponding to aluminum combustion. For the aluminum and iodine oxide system, exothermic surface chemistry was recently predicted for I–O fragments forming bridge bonds with the alumina passivation shell using first principle calculations, but now has been observed experimentally. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TG) were used to assess aluminum and iodine pentoxide (I2O5) powder mixtures. Various equivalence ratios were examined and found to affect the PIR onset temperature. Prior to this work, the PIR was attributed solely to surface reactions of the halogen with the Al2O3 surface, but, results shown here indicate that both the alumina surface and aluminum core contribute to a PIR and a minimum activation energy is necessary for PIR production.