Aluminum Powder Mixtures Research Articles

Shock-induced reaction in a flake nickel + spherical aluminum powder mixture

Mixtures of flake-shaped nickel and spherical aluminum powders have been subjected to shock-loading up to 6 GPa to investigate the occurrence of shock-induced chemical reactions. The high-pressure Hugoniot state is determined through time-resolved measurements of the input stress and shock transit time through the specimen. An increase in shock velocity is observed above stress levels of 3.5 GPa, suggesting the initiation of an ultrafast shock-induced chemical reaction and formation of Ni-Al compound(s) occurring in the time scale of the high-pressure shock state.

Al–Ti powder produced through mechanical alloying for different times

A powder mixture of aluminum, 10 wt% titanium, and 1.5 wt% of a wax acting as process control agent (PCA), has been attrition-milled for 2–20 h. Titanium powder had been previously ground to a lower particle size to make it similar to the as-received aluminum particle size. The overall aim of this work was to achieve a metastable titanium solution in the aluminum matrix. Changes with milling time of particle size and shape, microstructure, hardness and other powder characteristics have been studied. Given the used experimental-conditions, a process time of 10 h has been selected for the mechanical alloying (MA) of Al–10Ti powder, attaining a compromise between uniform microstructure development and a not so long processing time. At this milling time aluminum dissolves about 9 wt% Ti, increasing its Vickers microhardness (202 VH20) more than 10 times with reference to the starting Al powder (20 VH20). Milled particle size is smaller than the starting one (17 vs. 44 μm). Increasing milling for longer times, up to 20 h, does not produce important changes in powders structure.

Surface characterization of alumina reinforced with niobium carbide obtained by polymer precursor

Active filler controlled pyrolysis of polymers (AFCOP) is a recent method for obtaining near-net shaped ceramic bodies. Alumina based composites have been developed for use as cutting tools, so knowledge of the surface composition is extremely important because it is directly related to the hardness and wear resistance Samples containing a fixed concentration of 60 wt. (%) of polysiloxane and a mixture of metallic niobium and alumina powder were homogenized, uniaxially warm pressed at 80 °C and subsequently pyrolyzed in flowing argon at 1200, 1400 and 1500 °C. Analysis of the surface composition was carried out by X ray photoelectron spectroscopy, infrared spectroscopy, X ray diffraction and scanning electron microscopy. The results have indicated that the formation of the phases on the surface depends strongly on the niobium/carbon ratio in the raw materials.

Formation of TiAl intermetallics by heat treatment of cold-sprayed precursor deposits

Cold spray is a rapidly developing coating and manufacturing technology in which metal particles are deposited at velocities of over 700 ms −1 without significant melting. The severe plastic deformation of the particles on impact produces a deposit that is very dense, with low oxide content and no thermally induced tensile stresses. In this study, solid shapes of precursor material were made by the cold spray process using titanium and aluminium powder mixtures and then converted to titanium aluminide with suitable heat treatments. Such heat-treated material has been characterised using differential scanning calorimetry to trace the kinetics of the phase transformation, X-ray diffraction to determine the phases present and scanning electron microscopy with microprobe analysis to observe the microstructure and measure the chemical composition. It was found that the first intermetallic phase to form with heat treatment was TiAl 3. The desirable set of intermetallic phases (TiAl 3, r-TiAl 2, TiAl and Ti 3Al) was obtained by varying heat treatment conditions. While the porosity in the as-sprayed precursor deposits was about zero, significant porosity developed during heat treatment and the sources for this are discussed.

Alon-based materials prepared by SHS technique

The aim of the presented paper was preparation of the highly reactive in the sintering powders in the Al–O–N system by SHS method. Combustion reactions of metallic aluminium and corundum powder mixtures (from 15% Al–85% Al 2O 3 to 50% Al–50% Al 2O 3) were performed in nitrogen atmosphere. The obtained powders were ground and hot-pressed at 1750, 1850 and 1950 °C for 1 h under 25 MPa in nitrogen flow. In contrast to conventional methods, which require 24 h of the precursor heat treatment at 1200 °C our studies, showed that it is possible to prepare almost pure γ-alon materials using SHS reaction. Sintering of the powders led to obtained dense materials composed of pure γ-alon or γ-alon–AlN composites. The phase composition of the sintered bodies was controlled by the chemical composition of the starting mixture and the sintering temperature.

Further tailoring of material properties in non-equimolar aluminium titanate ceramic materials

The authors started their R&D activities related to aluminium titanate (AT) ceramics in the early 1990s by addressing the critical problems of aluminium titanate, such as thermodynamical instability and micro-cracking. After that, their focus has permanently been on improving, optimizing and tailoring the properties of the aluminium titanate ceramic materials produced by reaction-sintering of equimolar mixtures of alumina and titania powders. This paper presents their latest investigations on AT ceramics produced by reaction-sintering of non-equimolar mixtures of the two main components. The objective of these investigations has been to emphasize the effects of excesses of either alumina or titania on the internal stresses build up in these materials and the consequences these internal stresses could have on some material properties which are most important for the industrial applications of AT ceramics. The ways and the extent in which these internal stresses could be controlled/managed were investigated, with the ultimate goal of expanding the possibilities for further tailoring the thermo-mechanical properties of the aluminium titanate ceramics, so that they meet specific application requirements.

ANN model for prediction of powder packing

A multilayer feed forward backpropagation (MFFB) learning algorithm was used as an artificial neural network (ANN) tool to predict packing of fused alumina powder mixtures of three different sizes in green state. The data used in model construction were collected by mixing and pressing powders with average particle sizes of 350, 30 and 3 μm and with narrow particle size distributions. The data sets that were composed of green densities of cylindrical pellets were first randomly partitioned into two for training and testing of the ANN models. Based on the training data an ANN model of the packing efficiencies was created with low average error levels (3.36%). Testing of the model was also performed with successfully good average error levels of 3.39%.

Combined shock-wave synthesis of noble spinel and laves cubic phase

The paper described the shock-wave synthesis of high-pressure high-temperature mineral MgAl2O4 with the parameter a = 8.085(3) A and the Laves phase MgCu2 with a = 7.076(2) A from a mixture of MgO and aluminum powder placed into a copper insert inside a steel conservation ampoule. Spinel MgAl2O4 with a smaller lattice parameter a = 8.0798 A has been formed in an aluminum insert cup.

Use of nano-composite component to improve the conductivity and mechanical properties of Li 2SO 4–Al 2O 3 solid electrolyte

The microstructure, density, and conductivity of Li 2SO 4 ion-conducting membranes incorporating nano-composite Li 2SO 4–Al 2O 3 prepared using a sol–gel technique are superior to membranes having the same bulk composition prepared from mixtures of lithium sulfate and fine alumina powder. Properties of membranes made from the nano-composite material depend on both the overall composition and the preparative parameters. The relationships between preparative parameters, microstructure, and properties have been determined, from which we have found the optimum lithium sulfate content and thermal treatment parameters for manufacture of membranes with minimum gas permeability and maximum ionic conductivity.

Thermal behavior of aluminum powder and potassium perchlorate mixtures by DTA and TG

In this work the thermal decomposition characteristics of micron sized aluminum powder + potassium perchlorate pyrotechnic systems were studied with thermal analytical techniques. The results show that the reactivity of aluminum powder in air increases as the particle size decreases. Pure aluminum with 5 μm particle size has a fusion temperature about 647 °C, but this temperature for 18 μm powder is 660 °C. Pure potassium perchlorate has an endothermic peak at 300 °C corresponding to a rhombic–cubic transition, a fusion temperature around 590 °C and decomposes at 592 °C. DTA curves for Al 5/KClO 4 (30:70) mixture show a maximum peak temperature for thermal decomposition at 400 °C. Increasing the particle size of aluminum powder increases the ignition temperature of the mixture. The oxidation temperature increased by enhance in the aluminum content of the mixture.

Pressureless sintering of particle-reinforced metal–ceramic composites for functionally graded materials: Part I. Porosity reduction models

There is a need to fabricate particle-reinforced metal–ceramic composites through pressureless sintering for functionally graded materials (FGMs) for use in a variety of high-temperature and energy-absorbing applications. However, the pressureless sintering behavior of these composites over wide volume fraction ranges has not been modeled. In this investigation, metal–ceramic composites were prepared by sintering mixtures of nickel and alumina powders. The changes in porosity and shrinkage were measured, and models were developed to understand both the nature of the porosity during sintering and the sintering behavior of the composites. In Part I of the investigation, the development of porosity reduction models is described to understand microstructural effects on the sintering behavior. These models indicate that there is significant porosity associated with the agglomeration of particles. Particle agglomeration and porosity are confirmed by direct observation of the microstructure. The porosity reduction models can be used to assess the quality of particle-reinforced metal–ceramic composites formed by pressureless sintering and to predict changes that can be achieved in the porosity reduction through engineering of the particle dispersion for the processing of FGMs.

Laser Ablation and Low-Pressure Helium-ICP-MS for the Analysis of Alumina Powder Dispersed in Glycerol

A combined method of laser ablation (LA) and ICP-MS has gained much attention as a direct analytical method for solid samples. The determination of some elements, however, is seriously disturbed by isobaric interferences, mainly caused by argon and ambient air constituents. The use of low-pressure helium-ICP is a promising solution of the problem. A 1:1 mixture of alumina powder and glycerol was deaerated and irradiated with a pulsed laser beam (150 mJ) for 10 s. The sample aerosol was transported to the ICP with a stream of helium. Indium was used as an internal standard for correcting the ablated sample amount. Calibration curves were prepared from glycerol containing high-purity alumina, trace metals and indium. The detection limits for Cr, Mn, Fe, Co, Ni, and Cu approached the fractional ppm levels. The proposed method was successfully applied to the analysis of different alumina samples (99 - 99.995% purity).

Chemical reaction of in-situ processing of NiAl/Al2O3 composite by using thermite reaction

NiAl/Al2O3 composite were synthesized by thermite reaction of nickel oxide and aluminum powder mixtures. The phase, the microstructure of the composite, as well as the thermite reaction mechanism, were investigated by X-ray diffractometry (XRD), scanning electron microscopy (SEM) combined with differential scanning calorimetry (DSC). The experimental results show that the thermite reaction leads to the interpenetrating network structure of NiAl/Al2O3 at 1223K for 60 min and the chemical reaction apparent activation energy is Eap=166.960±13.496 kJ·mol−1 in the NiO/Al system.

Fabrication of Al2O3-based composites by indirect 3D-printing

A powder mixture of alumina and dextrin was used as a precursor material for fabrication of porous alumina preforms by indirect three-dimensional printing. Post-pressureless infiltration of the fabricated preforms with copper alloys resulted in dense composites with interpenetrating microstructure. The fabrication procedure involves four steps: a) freeze-drying of Al2O3/dextrin blends, b) three-dimensional printing of the green bodies, c) drying, dextrin decomposition and sintering of the printed bodies and d) post-pressureless infiltration of Cu-alloy into as-fabricated Al2O3 porous preforms. As result of the dextrin decomposition and Al2O3 sintering an average linear shrinkage of 17.7% was measured. After sintering the Al2O3 preforms with ∼36 vol.% porosity were obtained. A post-infiltration with copper alloy at 1300 °C for 1.5 h led to formation of dense Al2O3/Cu parts. X-ray analysis showed the presence of α-Al2O3, Cu and Cu2O only. Al2O3/Cu composite exhibits a fracture toughness of ∼5.5 MPa m1/2 and bending strength of ∼236 MPa. Fractographic analysis showed that crack bridging by plastically deformed metal phase may control the fracture toughness of this composite.

Highly crystalline AlN particles synthesized by SHS method

Aluminium nitride (AlN) powders were prepared by self-propagating high-temperature synthesis (SHS). Aluminium and AlN powder mixtures with weight ratios of about 60:40, in the absence and in the presence of 3-wt.% NH4F and 3-wt.% NH4F+3-wt.% carbon powders as additives were ignited in a nitrogen atmosphere of 8 MPa. Highly crystalline AlN particles with regular hexagonal morphology were obtained in the presence of 3-wt.% NH4F+3-wt.% carbon. The microstructure development during the reaction and the influence of these additives were determined by SEM/EDS and XRD analysis of the resulting products. A mechanism for the formation of AlN with a regular hexagonal morphology has been suggested.

Measurement of the dielectric constants of metallic nanoparticles embedded in a paraffin rod at microwave frequencies

A cylindrical rod composed of a uniform mixture of metallic nanoparticles and alumina powder dissolved in paraffin was inserted in the center of a cylindrical microwave cavity. The real and imaginary parts of the complex dielectric constant of metallic nanoparticles at various microwave frequencies of the TM/sub 010/ mode can be determined from the resonant frequency and quality factor, respectively, of the transmission resonance spectrum. This method involves the protection of the sample from adsorbed moisture and prevents the rod from filling with air, thus making the experimental values more accurately and stably determined than they are by the dielectric double-cavity method. The real parts of the dielectric constants of metallic nanoparticles are negative and their magnitudes decrease as the particle size decreases. This finding is consistent with theory, which states that conduction becomes weaker as the particle size is reduced.

Nitride Formation during Combustion of Ultrafine Aluminum Powders in Air. I. Effect of Additives

This paper summarizes the results from studies of the effect of 17 additives on the process and products of ultrafine aluminum combustion in air. It is shown that the additives influence the temperature and duration of the combustion process and the structure of the end products, including the yield of aluminum nitride. The major factor determining the yield of aluminum nitride is the maximum temperature reached in combustion of mixtures of ultrafine aluminum powder with definite additives.

Zirconia–Mullite Composites Consolidated by Spark Plasma Reaction Sintering from Zircon and Alumina

Mullite–ZrO2 composites have been fabricated by attrition milling a powder mixture of zircon, alumina, and aluminum metal with MgO or TiO2 as sintering additives, heating at 1100°C to oxidize the aluminum metal, and consolidation by spark plasma sintering (SPS). The influence of the SPS temperature on the formation of mullite, and the density and the mechanical properties of the resulting composites have been studied. For the mullite–zirconia composites without sintering additives, the mullite formation was accomplished at 1540°C. In contrast, for the composites having MgO and TiO2, the formation temperature dropped to 1460°C. The composites without sintering additives were almost fully dense (99.9% relative density) and retained a larger amount of tetragonal zirconia. Those materials attained the best mechanical properties (E=214 GPa and KIC=6 MPa·m1/2). To highlight the advantages of using the SPS technique, the obtained results have been compared with the characteristics of a mullite–zirconia composite prepared by the conventional reaction‐sintering process.

Role of Constituent Configuration on Shock-Induced Reactions in a Ni+Al Powder Mixture

AbstractUltra-fast reactions initiated within or immediately behind the shock front in powder mixtures are of importance in the synthesis of high-pressure phases and next-generation energetic materials. Reactions in nickel and aluminum powder mixtures and the establishment of a reaction threshold have been the source of many studies over the last 20 years. Prior work has suggested that the criterion for reaction is most probably mechanochemical in nature, in which shock loading environment plays a larger role than absolute shock energy input. The mechanisms responsible for intimate mixing of fresh reactants are however still unclear. In this work we are investigating the role of particle size and morphology on the loading, mixing, and their subsequent shock-induced reaction behavior, by performing shock-compressibility experiments on equi-volumetric mixtures of nickel and aluminum powders, with variations in nickel particle size (micron and nano-scale) and shape (spherical and flake). Determination of shock states is accomplished through time-resolved in situ PVDF gauge measurements of input shock stress and shock propagation speed obtained from transit time through the thickness of powder mixture. The reaction product shock-compressibility state is also being calculated based on constant pressure approximations to allow correlation with measured states for inference of the occurrence of shock-induced chemical reactions. The results of this study suggest that powder configuration in the nickel-aluminum system can be modified to encourage or discourage reaction.

2933 硝酸アンモニウムを用いた爆発破砕に関する基礎研究(S82-2 衝撃力の解析と利用・設備管理,S82 安全のための新技術)

The experiments of destruction in high-speed strain rate area have been used explosive and the Hopkinson bar Method, etc. There is the gap in the range of a strain rate between cases with explosive (strain rate: more 10^4 s^<-1>) and Hopkinson bar Method (strain rate: below 10^3 s-1). Therefore, experiments in this range ofa strain rate (10^3〜10^4 s^<-1>) are needed dearly. The purpose of this study is the experiment on high-strain rate at about 10^3 s^<-1>. Then, The mixture of Ammonium Nitrate and Aluminum powder was used instead of explosive in the present experiment. From these results, it became possible to experiment at the high-strain rate of about 10^3 s^<-1>