Alumina Microparticles Research Articles

Multi-nationality epoxy adhesives on trial for future nanocomposite developments

Epoxy adhesives are prone to brittle failure and thermal degradation. Nanotechnology allows for developing advanced epoxy adhesives, but attempt to design high-performance epoxy adhesives must be made by starting inexpensive trials in micron scales by the use of recycled and waste materials. Phenolic resin, recycled tire powder, and alumina microfillers were systematically mixed here as epoxy toughening agent and modulus/strength modifier, respectively. Incorporation of phenolic resin to epoxy compensated for low thermal stability. Taguchi experimental design was used to study the main effects of waste tire powder, alumina microparticles, and phenolic resin contents on tensile, single-lap joint and thermogravimetric properties of epoxy adhesive. The results suggest that addition of 40 wt. % alumina microparticles, 15 wt. % recycled tire powder, and 30 wt. % phenolic resin to epoxy led to a drastic rise of ca. 80% in the lap shear strength with respect to the neat epoxy. Microscopic analyses unraveled blocking mechanism for cracking, as evidenced by a deviation in crack growth pathway at the vicinity of alumina microparticles. A considerable increase of ca. 34 °C in degradation peak temperature of epoxy was also noticeable. The outcome of this work enlightened future perspective on nanostructured epoxy adhesives.

Transport Properties of Flow-through Electrodes with Varying Composition and Particle Dimension for Electrochemical Desalination

The growing need for energy-efficient desalination has motivated research into cation intercalation as a technology to remove salt ions from water. However, Prussian Blue analogues (PBAs), a promising class of intercalation compounds with high capacity and cycle life, demonstrate low electronic conductivity [1]. A common technique to increase electronic conductivity is the use of additives such as carbon black, [2,3] however adding conductive particles reduces active particle volume fraction and overall energy density. In addition to electronic conductivity, MacMullin number and hydraulic permeability affect energy consumed by ionic conduction and electrolyte pumping, respectively. These factors can be improved through the use of macroscopic pores to increase ion transport and fluid flow at the cost of removing active material to form the pores and lowering areal capacity [4,5]. Developing practical desalination technology requires the selection of conductive additives to facilitate the electron transport with simultaneous ion transport and fluid permeation. The present work studies how the volume fraction of either C45 or Ketjen Black conductive additive affects electrodes that incorporate either insulative nanoparticles or microparticles. Here, alumina particles are chosen here as a surrogate for insulative redox-active particles. Based on electronic conductivity measurements, smaller carbon black particles were found to form a percolating path through the electrode microstructure at lower volume fractions, increasing the electrode’s bulk electronic conductivity without sacrificing active material loading. The use of smaller alumina particles showed a similar effect, as electrodes made with nanoparticles possessed orders of magnitude higher conductivity at lower carbon black volume fractions (Fig. 1). A new application of the four-point probe technique was developed to measure the in-plane MacMullin number, which showed a weak decline with increasing carbon black content. Hydraulic permeability was also measured by applying a hydraulic head onto the cross-section of an electrode. Electrodes made with smaller particles (either conductive or insulative) were less permeable due to the particles’ ability to form smaller pores at similar porosities. Particle radii and inter-particle forces played a key role in electrode solidification, an idea supported by simulations of materials used in Li-ion batteries [6]. The van der Waals forces between the carbon black particles and alumina are generally weaker than those between carbon particles themselves, and this difference is enhanced for more numerous particles of smaller radii, allowing the carbon to percolate more easily. The three transport properties were also used to predict theoretical power requirements and find the attainable area-specific adsorption rate for a given specific energy consumption in a desalination cell, as faster adsorption is expected to require more energy [7]. The size of both conductive and insulative particles correlate with these properties and determine the rate and energy cost of salt removal. Electrodes composed of similar volume fractions of conductive and insulative material but different particle sizes display dramatically different electronic conductivity, ionic conductivity, and hydraulic permeability. Applying these lessons to the fabrication of porous electrodes could reduce energy consumption and lead to efficient desalination technology. Figure 1: A) Conductivity values at varying volume fractions of carbon black for the four combinations of C45 and Ketjen Black mixed with alumina microparticles and nanoparticles. B) MacMullin Numbers for the same electrodes. C) Results of permeability tests for the four particle mixtures.

Influence of the Strain Rate, Particle Size, and Equivalence Ratio on the Combustion of the Premixed Air–Aluminum Microparticle Mixture with a Counterflow Structure

The effects of the strain rate, equivalence ratio, and particle diameter on the combustion of a mixture of aluminum microparticles with air under fuel-lean conditions are studied in the counterflow configuration with an approximate analytical perturbation method. The flame structure is assumed to consist of three zones: preheating, flame, and post-flame zones. Reasonable agreement between the current results and experimental data is obtained in terms of the flame temperature. The dimensionless ignition and ultimate flame temperatures, place of the flame starting point, and flame thickness are obtained as functions of the strain rate for different particle diameters and equivalent ratios. The results indicate that the ignition and ultimate flame temperatures and also the flame thickness decrease with increasing strain rate. With a decrease in the strain rate, the length of the preheating zone increases. With increasing particle diameter, the flame thickness increases, whereas the ignition and ultimate flame temperatures decrease. An increase in the equivalence ratio causes an increase in the ultimate flame temperature and reduction of the preheating zone and flame thickness.

Numerical simulation of the suppression of cellular detonation by inert particles

The simulation of a cellular detonation wave propagating along a hydrogen-air mixture with a cloud of alumina microparticles was carried out. The gas dynamics was modeled by the system of Navier-Stokes equations describing the motion of a viscous compressible heat-conducting gas, with allowance for multicomponent nature of the gas mixture and chemical kinetics. A methodology has been developed for calculating detonation currents in ANSYS Fluent using the reduced kinetics. The reduced kinetics was verified by the size of the detonation cell. The interaction with inert particles with a diameter of 0.3÷100 μm and volume fraction of 10−4÷10−2 was investigated using a continuum approach. Values of the volume fraction resulting in a change of the detonation cell size, weakening of the detonation wave, and detonation suppression have been obtained.

Effect of aluminum micro- and nanoparticles on ignition and combustion properties of energetic composites for interfacial bonding of metallic substrates

In this study, the effect of micro- and nanoscale energetic materials in the formulation of aluminum microparticles (Al MPs)/aluminum nanoparticles (Al NPs)/iron oxide nanoparticles (Fe2O3 NPs) as a heat energy source for melting solder microparticles (SAC 305 MPs) on the interfacial bonding properties of Cu metallic substrates, is investigated. The optimized mixing ratio is Al MP:Al NP:Fe2O3 NP = 30:30:40 wt%, which generates a maximum total exothermic energy of ∼2.0 kJ g−1. The presence of Al NPs is essential to make stable ignition and initiation of Al MPs, which enable to attain relatively long combustion duration. The use of highly reactive Al NPs/Fe2O3 NPs can improve the aluminothermic reaction, while the addition of Al MPs to the Al NPs/ Fe2O3 NPs is also required to maintain their high thermal energy for a longer duration. An energetic material (EM) layer composed of Al MP/Al NP/Fe2O3 NP composites is employed as a heat source between solder material (SM) layers composed of SAC305 MPs. The SM/EM/SM multilayer pellets are assembled and ignited between interfacial Cu substrates for bonding. Thus, interfacial bonding between the Cu substrates is successfully achieved, and the resulting maximum mechanical strength for the bonded Cu substrates using the SM/EM/SM multilayer pellets increases by ∼40% compared to that when using a pure SM layer pellet. Hence, EM layers can act as both an effective heat energy generation source and a mechanical reinforcing medium, while the interfacial bonding process using SM/EM/SM multilayer pellets demonstrated herein provides an easy and versatile means of welding and jointing for industrial applications.

Wear Behavior of Al-Based Nanocomposites Reinforced with Bimodal Micro- and Nano-Sized Al2O3 Particles Produced by Spark Plasma Sintering

Abstract Spark Plasma Sintering (SPS) has been recognized, in the recent past, as a very useful method to produce metal matrix composites with enhanced mechanical and wear properties. Obviously, the material’s final properties are strongly related to the reinforcement types and percentages and the particles’ distribution, as well as to the processing parameters employed during synthesis. The present article analyzes the effect of microscopic and nanometric alumina particles, blended to pure aluminum in different combinations, on the final properties of metal matrix composites produced via SPS. A strong variation in the microstructural behavior, mechanical, and wear properties has been observed by varying the nano- to micro-alumina particles’ percentage and the distribution of the ceramic particles blended with aluminum ones.

THE CRYSTALIZATION REGULARITY OF POLYMER MICROCOMPOSITE MATERIALS IN DIFFERENT METHODS OF THEIR PREPARATION

The results of patterns studies of structure formation during the crysta- llization of a polymer microcomposite based on polyethylene filled with aluminum microparticles are presented. The data of a comparative analysis of the structure formation mechanisms in the use of different methods for the preparation of composites.

Electroplating of aluminium microparticles with nickel to synthesise reactive core-shell structures for thermal joining applications

Reactive particles represent a promising alternative for effectively joining components with freeform surfaces and different material properties. While the primary application of reactive systems is combustion synthesis for the production of high-performance alloys, the highly exothermic reaction can also be used to firmly bond thermosensitive joining partners. Core-shell structures are of special interest, since they function as separate microreactors. In this paper, a method to synthesise reactive nickel-aluminium core-shell structures via a two-step plating process is described. Based on an electroless process, the natural oxide layer of the aluminium particles is removed and substituted with a thin layer of nickel. Subsequently, the pre-treated particles are electroplated with nickel. The high reactivity of aluminium and the oxide layer play a significant role in adjusting the process parameters of the Watts bath. Additionally, the developed experimental set-up is introduced and the importance of process control is shown. In order to achieve reproducible results, the electroplating process was automated. Ignition tests with electromagnetic waves demonstrated that the particles undergo an exothermic reaction. Therefore, they can be used as a heat source in thermal joining applications.

ВОДОГРІЙНІ КОНДЕНСАЦІЙНІ ТЕПЛОУТИЛІЗАТОРИ ІЗ ЗАСТОСУВАННЯМ НАНОКОМПОЗИЦІЙНИХ МАТЕРІАЛІВ ДЛЯ ГАЗОСПОЖИВАЛЬНИХ ОПАЛЮВАЛЬНИХ КОТЛІВ

Викладено результати досліджень ефективності використання в теплоутилізаційних технологіях газоспоживальних опалювальних котельних установок із глибоким охолодження їхніх відхідних газів водогрійного теплоутилізаційного устаткування різного типу. Розглянуто устаткування, теплообмінні поверхні якого компонувались з пучків поперечно-оребрених труб двох видів та гладкотрубних пучків. Визначено для різних режимів роботи котельних установок протягом опалювального періоду такі відносні характеристики даних поверхонь, як теплопродуктивність на одиницю маси цієї поверхні та її об'єм на одиницю теплопродуктивності. Виконано порівняльний аналіз зазначених характеристик при використанні для поверхонь теплообміну традиційних матеріалів і полімерних мікро- і нанокомпозитів з різними коефіцієнтами теплопровідності. За значеннями робочих температур теплообмінної поверхні із мікро- і нанокомпозитів визначено її полімерну матрицю, а за величиною теплопровідності - необхідний склад наповнювачів полімеру, якими можуть слугувати мікрочастки алюмінію або вуглецеві нанотрубки. Показано, що для опалювальних котельних установок водогрійне теплоутилізаційне устаткування із вказаних нанокомпозиційних матеріалів за питомою теплопродуктивністю має істотні переваги над традиційно застосовуваними аналогами цього призначення.

Study of the morphology and structure of porous composites obtained from Na–CMC suspensions with aluminum micro-particles and boehmite nanoparticles

It is found that adding boehmite nanoparticles to a sodium–carboxymethyl cellulose suspension with glycerin and aluminum powder allows the formation of films with ordered pores (cells of 1200–600 μm in size). X-ray diffraction and infra-red spectroscopy reveal no changes in the chemical composition of films upon their solidification. The surface porosity of the films is established to be 65%. The developed porous composites are shown to be promising in the fabrication of antifriction coatings.

Synthesis of new metal-matrix Al–Al2O3–graphene composite materials

The mechanism of formation of ceramic microparticles (alumina) and graphene in a molten aluminum matrix is studied as a function of the morphology and type of precursor particles, the temperature, and the gas atmosphere. The influence of the composition of an aluminum composite material (as a function of the concentration and size of reinforcing particles) on its mechanical and corrosion properties, melting temperature, and thermal conductivity is investigated. Hybrid metallic Al–Al2O3–graphene composite materials with up to 10 wt % alumina microparticles and 0.2 wt % graphene films, which are uniformly distributed over the metal volume and are fully wetted with aluminum, are synthesized during the chemical interaction of a salt solution containing yttria and boron carbide with molten aluminum in air. Simultaneous introduction of alumina and graphene into an aluminum matrix makes it possible to produce hybrid metallic composite materials having a unique combination of the following properties: their thermal conductivity is higher than that of aluminum, their hardness and strength are increased by two times, their relative elongation during tension is increased threefold, and their corrosion resistance is higher than that of initial aluminum by a factor of 2.5–4. We are the first to synthesize an in situ hybrid Al–Al2O3–graphene composite material having a unique combination of some characteristics. This material can be recommended as a promising material for a wide circle of electrical applications, including ultrathin wires, and as a structural material for the aerospace industry, the car industry, and the shipbuilding industry.

Dynamics and extreme plasticity of metallic microparticles in supersonic collisions

Metallic microparticles can acquire remarkable nanoscale morphologies after experiencing high velocity collisions, but materials science regarding the extreme events has been limited due to a lack of controlled experiments. In this work, collision dynamics and nonlinear material characteristics of aluminum microparticles are investigated through precise single particle collisions with two distinctive substrates, sapphire and aluminum, across a broad range of collision velocities, from 50 to 1,100 m/s. An empirical constitutive model is calibrated based on the experimental results, and is used to investigate the mechanics of particle deformation history. Real-time and post-impact characterizations, as well as model based simulations, show that significant material flow occurs during the impact, especially with the sapphire substrate. A material instability stemming from plasticity-induced heating is identified. The presented methodology, based on the use of controlled single particle impact data and constitutive models, provides an innovative approach for the prediction of extreme material behavior.

Analysis of production parameters of single-lap bonds adhesive bonded with composites based on aluminium filler

In the area of bonding of sheets of metals, mainly in construction of transport and agricultural machines, single-lap bonds are used. In manufacturing corporations focused on bonding of the metal sheets the technologies such as riveting, welding and adhesive bonding are particularly used. These methods are frequently combined. The aim of the research was the evaluation of lap length of alloy AlCu4Mg adhesively bonded using two component epoxy adhesive, which is commonly used in construction of machines and its modification based in addition of filler in form of aluminium microparticles. The secondary aim of the research was to ascertain the influence of microparticle volume of aluminium filler on mechanical properties of polymer particle composite. Strength of adhesively bonded joint depends on the thickness of the bonded material. Strength of the adhesively bonded joint is dependent on the lapping length of adhesively bonded material. The highest values of strength of adhesively bonded joint were reached with the coefficient of the proportional length 0.27 ± 0.01. The assumption about negative effect of filler on tensile strength during the experiments was not confirmed.

Preparation of a disperse Fe–Al–Mo system and production of bulk materials on its base

We show the feasibility to prepare a disperse Fe–Al–Mo polymetal system by contact exchange in chloride-containing aqueous solutions. Reaction schemes are suggested to describe the processes that proceed on aluminum microparticles in aqueous solutions where the relevant metal ions are contained. The system is shown to be a precursor for intermetallic compounds, which are generated by high-temperature processes, e.g., spark plasma sintering (SPS).

Effects of Aluminium Microparticles and Surface Treatment of AlCu4Mg on Mechanical Properties of Adhesive Bond Strength

The aim of the research was to evaluate the lapping length, the adhesive bonded surface treatment and the influence of the filler in the form of the aluminium microparticles on the adhesive bond strength. The alloy AlCu4Mg was the adhesive bonded material bonded by means of a two-component epoxy adhesive used in construction of machines. The filler in a form of aluminium microparticles was added into the adhesive. Laboratory experiments were performed on normalized testing samples of alloy AlCu4Mg prepared under standard CSN EN 1465. Within the research three various treatments of the adhesive bonded surface were evaluated, i.e. without the surface treatment (WT), mechanical treatment of the surface (MT) and mechanical and chemical treatment of the surface (MCHT). The adhesive bonds without the adhesive bonded surface treatment (marked as WT) reach the smallest adhesive bond strength. When adding the filler in the form of aluminium microparticles (10 vol. %) the adhesive bond strength was increased of about 12%.

Impact Strength of Filled Polymer Materials

Polymers rank among a significant group of technical materials. One of requirements for this constructional material is to have enough resistance to a dynamic loading. Especially in the area of connecting the materials reactoplastics are used, which are distinguished for a low resistance to the dynamic loading. One solution for increasing an impact strength is filling the reactoplastics, i.e. a formation of polymer composites. The aim of the research was to evaluate an impact strength of various polymer materials (composites filled with different types of a filler, structural two-component epoxies, mixed recycled plastics, PPO – polyphenyle oxide and PS – polystyrene). The Dynstat method CSN 64 0611 was chosen for the evaluation of the impact strength. Reactoplastics matrix on the basis of two-component epoxy adhesive with high liquidity and an increased speed of a hardening GER reaches low values of the impact strength (2.54 ± 0.30 kJ·m-2). It is evident from the experimental results the positive effect of aluminium microparticles GER MFAI (3.26 ± 0.35 kJ·m-2), glass beads GR B134 (2.83 ± 0.29 kJ·m-2) and microfibres of polyamide from the process of tyre recovery GER MPA (3.92 ± 0.25 kJ·m-2) on the impact strength. The results of this experiments show the possibility of the modification of the relative fragile epoxy resin with the filler, which increases the impact strength.

Influence of Thermal Treatments on the Evolution of Conductive Paths in Carbon Nanotube-Al2O3 Hybrid Reinforced Epoxy Composites.

The conductive path formed by carbon nanotubes (CNTs) in a polymer matrix is one of the most attractive topics for developing multifunctional nanocomposites. In this article, we studied the evolution of conductive paths and interactions in the interfacial regions in epoxy-based composites reinforced by an urchinlike hybrid of CNTs and alumina microparticles (μAl2O3). A homogeneous dispersion of CNTs in the epoxy matrix was achieved thanks to the core-shell structures of CNTs-μAl2O3 hybrids, resulting in the interpenetrated epoxy's cross-linking network that strongly bonds with CNTs. Furthermore, thermal treatments at different temperatures around the glass-transition temperature (Tg) were conducted under vacuum on composites near the percolation threshold. It was found that the dielectric behavior and the Tg were shifted in spite of the constant CNT mass fraction used. This was mainly due to the fact that thermal treatment generated the adjustment of the cross-linking network of epoxy, and the distances between adjacent CNTs were reduced gradually. This study can provide insight into the evolution of conductive paths in the interfacial regions from a more straightforward perspective.

Copper and aluminium deposition by cold-plasma spray on wood surfaces: effects on natural weathering behaviour

Atmospheric pressure plasma was used to deposit thin layers of copper and aluminium micro-particles on the surface of Scots pine sapwood (Pinus sylvestris L.) boards. Three different loadings of metal particles were established. Additional wood boards were topcoated with a commercial acrylic binder. Boards were exposed to natural weathering for 18 months. Discolouration of copper-treated boards was slowed down, and the treatment at highest loading displayed the best appearance. Aluminium treatment was not sufficient to prevent or reduce discolouration. The application of an acrylic binder as topcoating enhanced the general appearance of metal-treated boards. Evaluation of treated boards did not reveal any reduction in crack formation or water uptake due to the particle deposition. Infrared spectroscopy suggested that copper does not protect lignin from photo-degradation. Nevertheless, copper treatment reduced fungal infestation on wood; at highest copper loading, blue stain did not penetrate through the treated surface.

Micro- and Nanoscale Energetic Materials as Effective Heat Energy Sources for Enhanced Gas Generators.

In this study, we systematically investigated the effect of micro- and nanoscale energetic materials in formulations of aluminum microparticles (Al MPs; heat source)/aluminum nanoparticles (Al NPs; heat source)/copper oxide nanoparticles (CuO NPs; oxidizer) on the combustion and gas-generating properties of sodium azide microparticles (NaN3 MPs; gas-generating agent) for potential applications in gas generators. The burn rate of the NaN3 MP/CuO NP composite powder was only ∼0.3 m/s. However, the addition of Al MPs and Al NPs to the NaN3 MP/CuO NP matrix caused the rates to reach ∼1.5 and ∼5.3 m/s, respectively. In addition, the N2 gas volume flow rate generated by the ignition of the NaN3 MP/CuO NP composite powder was only ∼0.6 L/s, which was significantly increased to ∼1.4 and ∼3.9 L/s by adding Al MPs and Al NPs, respectively, to the NaN3 MP/CuO NP composite powder. This suggested that the highly reactive Al MPs and NPs, with the assistance of CuO NPs, were effective heat-generating sources enabling the complete thermal decomposition of NaN3 MPs upon ignition. Al NPs were more effective than Al MPs in the gas generators because of the increased reactivity induced by the reduced particle size. Finally, we successfully demonstrated that a homemade airbag with a specific volume of ∼140 mL could be rapidly and fully inflated by the thermal activation of nanoscale energetic material-added gas-generating agents (i.e., NaN3 MP/Al NP/CuO NP composites) within the standard time of ∼50 ms for airbag inflation.

Improvement of synthesis conditions of dispersed polymetallic Fe–Al–Mo systems in aqueous solutions

Kinetic dependences describing the processes occurring on aluminum microparticles in aqueous solutions containing iron and molybdenum ions were determined. It was shown that the samples obtained contain iron, molybdenum, and aluminum in the elementary state in the absence of an oxide phase.