Alumina Particles Research Articles

Measurement of the temperature of burning aluminum particles using multi-spectral pyrometry

ABSTRACT Aluminum is used in the composition of many high explosives and contributes to their blast effect. This work focuses on the study of the combustion of a single isolated particle of size between 30 and 100 µm in an arbitrary atmosphere, whose pressure and composition are chosen to be close to those encountered in a high-explosive fireball. This gaseous atmosphere is still largely unreferenced, and this work aims to provide a better understanding of combustion in this environment. The use of an electrostatic levitator coupled with multi-spectral pyrometric diagnostics enables us to select a single particle and measure its temperature during combustion. Photomultipliers (PMs) are used to follow the temporal evolution of the particle’s light emission during combustion. In this work, we also used PMs as pyrometric devices to measure temperature. The diagnostic allows us to determine the temporal evolution of the integrated temperature of the condensed phase during combustion of the aluminum particle. By way of example, a temperature of 3300K was obtained for the combustion of Al in air at 1 bar. The data collected will also be used to verify the assumptions made in the combustion models (e.g. temperature stability during combustion).

Performance investigation of the artificial aggregate by integrally recycling incineration bottom ash and fly ash

The potential expansion risks caused by the reaction of metallic aluminum and glass particles in incineration bottom ash (IBA) in high-alkalinity environments limit its use as an aggregate in concrete applications. This study aims to develop artificial aggregates (AAs) by integrating IBA with a low-alkalinity binder comprising incineration fly ash (IFA) and blast furnace slag (GGBS). The synergetic effects of using IBA with IFA-GGBS binders in AAs are investigated and compared to integrating IBA with IFA-OPC binders. The impacts of IFA and IBA contents on physico-mechanical properties and mineralogical characteristics of AAs are also assessed. The results show that AAs achieve a loose bulk density ranging from 890 to 1072 kg/m3, with the highest strength of 5.7 MPa recorded for GGBS-based aggregates with 40 % IBA. The pozzolanic reaction of GGBS-IFA contributes to a robust binder that facilitates interlocking within the system. The relatively low alkalinity associated with the pozzolanic reaction between GGBS and IFA suppresses the potential expansion reaction, ensuring the safe application of AAs in concrete. Moreover, the internal curing of GGBS-based AAs and their interaction with the cement matrix densify the microstructure of the interface transition zone, resulting in excellent compressive strength of AAs-contained concrete (>45 MPa), which surpasses that of conventional concrete.

Thermal Conductivity of AlSi12/Al2O3-Graded Composites Consolidated by Hot Pressing and Spark Plasma Sintering: Experimental Evaluation and Numerical Modeling

Functionally graded metal matrix composites have attracted the attention of various industries as materials with tailorable properties due to spatially varying composition of constituents. This research work was inspired by an application, such as automotive brake disks, which requires advanced materials with improved wear resistance on the outer surface as combined with effective heat flux dissipation of the graded system. To this end, graded AlSi12/Al2O3 composites (FGMs) with a stepwise gradient in the volume fraction of alumina reinforcement were produced by hot pressing and spark plasma sintering techniques. The thermal conductivities of the individual composite layers and the FGMs were evaluated experimentally and simulated numerically using 3D finite element (FE) models based on micro-computed X-ray tomography (micro-XCT) images of actual AlSi12/Al2O3 microstructures. The numerical models incorporated the effects of porosity of the fabricated AlSi12/Al2O3 composites, thermal resistance, and imperfect interfaces between the AlSi12 matrix and the alumina particles. The obtained experimental data and the results of the numerical models are in good agreement, the relative error being in the range of 4 to 6 pct for different compositions and FGM structure. The predictive capability of the proposed micro-XCT-based FE model suggests that this model can be applied to similar types of composites and different composition gradients.

Roughness affects the response of human fibroblasts and macrophages to sandblasted abutments

BackgroundA strong seal of soft-tissue around dental implants is essential to block pathogens from entering the peri-implant interface and prevent infections. Therefore, the integration of soft-tissue poses a challenge in implant-prosthetic procedures, prompting a focus on the interface between peri-implant soft-tissues and the transmucosal component. The aim of this study was to analyse the effects of sandblasted roughness levels on in vitro soft-tissue healing around dental implant abutments. In parallel, proteomic techniques were applied to study the interaction of these surfaces with human serum proteins to evaluate their potential to promote soft-tissue regeneration.ResultsGrade-5 machined titanium discs (MC) underwent sandblasting with alumina particles of two sizes (4 and 8 μm), resulting in two different surface types: MC04 and MC08. Surface morphology and roughness were characterised employing scanning electron microscopy and optical profilometry. Cell adhesion and collagen synthesis, as well as immune responses, were assessed using human gingival fibroblasts (hGF) and macrophages (THP-1), respectively. The profiles of protein adsorption to the surfaces were characterised using proteomics; samples were incubated with human serum, and the adsorbed proteins analysed employing nLC–MS/MS. hGFs exposed to MC04 showed decreased cell area compared to MC, while no differences were found for MC08. hGF collagen synthesis increased after 7 days for MC08. THP-1 macrophages cultured on MC04 and MC08 showed a reduced TNF-α and increased IL-4 secretion. Thus, the sandblasted topography led a reduction in the immune/inflammatory response. One hundred seventy-six distinct proteins adsorbed on the surfaces were identified. Differentially adsorbed proteins were associated with immune response, blood coagulation, angiogenesis, fibrinolysis and tissue regeneration.ConclusionsIncreased roughness through MC08 treatment resulted in increased collagen synthesis in hGF and resulted in a reduction in the surface immune response in human macrophages. These results correlate with the changes in protein adsorption on the surfaces observed through proteomics.

Comparison of the Shear Bond Strength Using Primers with Different Application Numbers on Dental Zirconia.

This study examined the effect of the number of phosphate-containing primer applications on the shear bond strength (SBS) of zirconia to resin cement. 315 square specimens (10 × 10 × 4 mm3) were manufactured from Cercon ht presintered zirconia blocks. Alumina particles were used to sandblast zirconia specimens. These specimens were randomly divided into six primer-based groups: No primer application (NP), CLEARFIL CERAMIC PRIMER (C), PANAVIA V5 Tooth Primer (T), M&C PRIMER (MC), Monobond N (MN), and Z-PRIME plus (Z), and then separated into application number (1-4) groups (excluding NP). Each specimen was bonded with resin cement. The SBS was measured using a universal testing machine. The debonded surface was examined with a stereomicroscope. The SBSs were analyzed using two-way analysis of variance. Applying the primer twice exhibited the highest SBSs in each group, with significant differences in the T, MN, and Z groups. However, the SBS in the MC group was significantly lower on the second application. One-hundred percent adhesive failure was observed in all groups. Within the limitations of this study, prior to cementation, the sandblasted zirconia surface should be applied twice with a phosphate-containing primer other than MC to maximize the SBS at the zirconia-resin cement interface.

Atomic Force Microscopy of Transfer Film Development

Atomic force microscopy (AFM) provides the opportunity to perform fundamental and mechanistic observations of complex, dynamic, and transient systems and ultimately link material microstructure and its evolution during tribological interactions. This investigation focuses on the evolution of a dynamic fluoropolymer tribofilm formed during sliding of polytetrafluoroethylene (PTFE) mixed with 5 wt% alpha-phase alumina particles against 304L stainless steel. Sliding was periodically interrupted for AFM topography scans. The average film roughness, the average friction coefficient, and polymer wear rate based on sample height recession were recorded as a function of increasing sliding cycles. Topographical maps suggested tribofilm nucleates in grooves of the steel countersample, spreads, and develops into a uniform film through sliding. Prominent nanoscale features were visible around 10,000 sliding cycles and thereafter. Scanning electron microscopy and energy-dispersive X-ray spectroscopy showed good correlations between these features and aluminum-rich domains, suggesting the presence of alumina particles on the surface.

Influence of Aluminum Content and Agglomerates Initial Velocity on Erosion in Solid Rocket Motor

Abstract Despite the aluminized propellants offering a high specific impulse, the challenge of nozzle erosion adversely impacts the rocket's performance and its potential for reusability. This study presents a numerical model aiming to predict the mechanical erosion of the propulsion chamber nozzle. The model employs an Eulerian/Lagrangian approach to simulate the complexity of the flow field within the rocket combustion chamber and the interactions between the continuous phase and particles. The model also includes a simplified representation of the aluminum particle combustion process, besides the consideration of secondary breakup phenomena in liquid droplets. Experimental and numerical data from the literature were used to validate the numerical model. Subsequently, the model was utilized to explore the impacts of increasing propellant aluminum content and varying particles' injection velocities on the nozzle mechanical erosion. The outcomes indicated that higher aluminum content leads to a 4-10% increase in nozzle erosion compared to the 15% content case. Furthermore, the aluminum particles tend not to fully burn within the combustion chamber and contribute to nozzle erosion. Lastly, particles with higher initial velocity at the inlet of the combustion chamber increase the nozzle mechanical erosion despite the observed decrease in incident mass flux.

Understanding the explosion risk presented by ammonium nitrate and aluminium home-made explosives detonated as surface charges in hexahedral main charge containers

Ammonium nitrate and aluminium (AN–Al) has been used as a typical homemade explosive (HME) by non-state actors since the turn of the century. Despite the regulation applied to ammonium nitrate above 16% nitrogen content and an aluminium particle size below 200 µm, their use has been widespread in Afghanistan, Columbia, Iraq, Syria and Yemen. Containers used to utilise AN–Al as a man-portable improvised explosive device (IED) are typically hexahedral in shape, not the spherical or hemispherical geometries used to theorise risk mitigation. This is particularly important in post-blast investigation where explosives of a non-ideal nature are often used in non-spherical containers.Given the breadth of HME available to criminals, the explosion performance of forty hexahedral containers filled with AN–Al of unknown manufacture is examined. Performance of the AN–Al is determined through the surface detonation of these containers on alluvial soil, with apparent crater volume compared to theoretical calculations for spherical charges of TNT detonated in that same medium. A conversion factor for hexahedral main charges to spherical charges is then established to achieve more accurate predictions of the explosion risk using Kingery-Bulmash and Bowen curves. The paper provides worked examples for practical application and a methodology by which predictions of charge mass in other mediums such as asphalt can be determined.

In situ preparation of aluminum-copper pentafluorobenzoate energy microspheres: Enhancing aluminum combustion properties in composite propellants

Aluminum powder is the main metal fuel in composite propellants, and upgrading the proportion of aluminum powder loaded in solid propellants is currently one of the most effective means of increasing propellant energy. Nonetheless, the substantial disparity in boiling points between the core aluminum particles and the alumina layer enveloping their surfaces often results in reduced reactivity, inadequate combustion, and combustion agglomeration during the combustion process of the aluminum powder. Herein, copper pentafluorobenzoate (CuPF) interfacial layer was established on the surface of aluminum powder through the self-assembly coordination reaction between pentafluorobenzoic acid and copper ions, and Al-CuPF energy microspheres were successfully prepared. A comprehensive examination was carried out to scrutinize the surface morphology, elemental composition, and distribution of the Al-CuPF energy microspheres. Furthermore, meticulous studies were conducted on the ignition and combustion properties of these Al-CuPF energy microspheres under various atmospheric conditions. It was found that the Al-CuPF interfacial layer within the Al-CuPF energy microspheres plays a pivotal role in enhancing ignition initiation and acting as a catalyst to facilitate the more efficient combustion of aluminum powder. Moreover, the combustion behavior of Al-CuPF energy microspheres when integrated into composite propellants has been exhaustively researched. Notably, composite propellants incorporating Al-CuPF energy microspheres exhibit heightened burning temperatures and an increased burning rate. Additionally, the combustion and agglomeration dynamics of Al-CuPF energy microspheres on the propellant burning surface were meticulously documented using a high-speed camera. The findings revealed that Al-CuPF energy microspheres spend a significantly shorter duration on the propellant burning surface and notably mitigate the occurrence of aluminum agglomeration issues thereon. This research contributes fresh insights into the application of innovative aluminum-based fuels within the realm of composite propellants.

Numerical modeling of heat transfer behavior for two-phase flow in a nozzle considering phase change

The heat transfer and phase change of alumina particles in the gas-particle flow of the nozzle plays an important role in solid rocket motors (SRM) due to the coupling between the heat transfer and two-phase flow. However, it lacks precise modeling of the heat transfer behaviors of condensed particles in the nozzle, especially the phase change effect. In this article, we determine that the Drake model has the highest accuracy in calculating the convective heat flux between two phases, and propose a correlation to obtain radiative heat flux between the particle and walls. Then, a one-dimensional two-phase non-equilibrium model is established to consider the effects of heat transfer and solidification of particles on the two-phase flow in the nozzle. The results show that considering the phase change of particle improves the outlet thrust of the nozzle, but such increment decreases with the gas inlet temperature. When the supercooling phenomenon is considered, the nozzle thrust is reduced by 1.14% compared with that considering no supercooling. As the particle size increases, the outlet temperature of the particle phase rises and can even surpass the solidification temperature of particles and the velocity of the particle phase decreases significantly.

Effects of Aluminum/Carbon and Morphology on Optical Characteristics and Radiative Forcing of Alumina Clusters Emitted by Solid Rockets in the Stratosphere

Alumina (Al2O3) particles, the primary combustion products of solid rockets, can accumulate in the stratosphere, changing the global radiative balance. These Al2O3 particles were usually treated as homogeneous spheres. However, they contain impurities and may form clusters during the combustion process. Models representing Al-containing and C-containing Al2O3 clusters were developed, denoted as Al2O3 shell model (ASM) and Al2O3 core model (ACM), respectively. The superposition T-matrix method (STMM) was applied to examine their optical characteristics. Subsequently, a method to obtain the top-of-atmosphere flux was proposed by integrating the models with the moderate resolution atmospheric transmission code (MODTRAN). With the addition of Al/C, the absorption cross-section enhances by several orders of magnitude at 0.55 μm and increases slightly at 10 μm. The equivalent sphere models will weaken their scattering ability. A 4Tg mass burden of Al2O3 produces radiative forcing of −0.439 Wm−2. However, the addition of Al and C reduces the forcing by up to 15% and 12%, respectively. In summary, the optical characteristics and radiative forcing of Al2O3 clusters are sensitive to Al/C and morphology models. While our findings are impacted by various uncertainties, they contribute valuable insights into the radiative forcing of Al2O3 particles, potential climatic changes by space activities.

Influence of the Glycidyl Azide Polymer on the Energy Release of Aluminum Sub-Micron Particles under Ultrafast Heating Rates Stimulated by Electric Explosion and Solid Laser

Glycidyl azide polymer (GAP)-coated sub-micron aluminum (sub-mAl@GAP) particles exhibit higher heat release than their uncoated counterparts under low heating rates. However, their application in explosives has been hindered due to a lack of understanding of their energy release characteristics under heating rates of detonation levels. To address this problem, the energy release performances of sub-mAl@GAP particles under ultrafast heating rates stimulated by an electric explosion of wire and high-energy laser were studied. The results showed that the reaction of sub-mAl@GAP particles was more violent than that of an uncoated counterpart under an electric explosion stimulus. Additionally, the reaction time of the former was 0.4 ms shorter than that of the latter. In addition, the propagations of shock waves of the sub-mAl@GAP and sub-mAl were analyzed. The propagation distances of shock waves of the sub-mAl@GAP were all longer than those of sub-mAl under laser fluences of 0.5 J/cm2, 1.2 J/cm2, and 2.4 J/cm2. The distance difference gradually increased with the decrease in the laser fluence. Under a laser fluence of 0.5 J/cm2, the velocity and distance differences of the sub-mAl@GAP and sub-mAl were both the largest due to the energy contribution from the GAP. In conclusion, the fast decomposition rate of the GAP and its energy contribution would benefit the energy release of sub-mAl under ultrafast heating rates.

Enhancing Lithium‐Ion Battery Performance with Alumina‐Coated Separators: Exploring the Potential of Different Alumina Particle Sizes, Coating Techniques, and Calendering

AbstractA range of techniques for the coating of high purity alumina (HPA) on porous polypropylene battery separators has been investigated. A slurry was prepared by dispersion of the alumina powder in acetone solvent and poly (vinylidene fluoride‐co‐hexafluoropropylene) (PVdF‐HFP) as the binder to obtain an excellent adhesion to the membrane. Doctor blade, spin coating, and electro‐spin coating techniques were utilized to coat a thin layer of HPA on the separator that was followed up with a calendering step to improve compactness, decrease thickness and enhance adhesion. Furthermore, the effect of HPA particle size, distribution, and the use of a calendering step on coating thickness, compactness, and electrochemical performance were investigated using three HPA sources. The doctor blade technique was found to give the most uniform coating with the best mechanical properties and high‐temperature resistance. The coated separators were incorporated into lithium‐ion coin cells to evaluate the rate capability and long‐term cycling performance.

The investigation of the performance and exhaust emissions of the compression-ignition engine with a mixture of diesel and aluminum particles

In this study, aluminum particles were added to diesel fuel in amounts of 75 and 150 ppm, with a particle size of 15 micrometers and a purity of 98.95 %. A magnetic stirrer was used to achieve homogeneous mixing of aluminum particles in diesel. In order to prevent aluminum particles from settling, fuel mixtures were stirred for 45 minutes for every 2 kg of fuel mixture. Fuel mixtures prepared to prevent settling were used immediately to avoid affecting the experimental results. The experiments were conducted at torque values of 100, 150, and 200 Nm, with a constant 660 rpm. The experiments initially started with pure diesel. Then, they continued with diesel fuels containing 75 and 150 ppm of aluminum additives, respectively. Positive effects of aluminum addition on engine performance were observed. The highest efficiency was obtained with the fuel containing 75 ppm of aluminum additive. The fuel with 75 ppm of aluminum additive provided efficiency increases of 4.57 %, 2.90 %, and 2.23 % compared to pure diesel at torque values of 100, 150, and 200 Nm, respectively. Although the fuel with 150 ppm of aluminum additive showed less efficiency improvement compared to 75 ppm, it still provided efficiency improvement compared to pure diesel. Improvements in NOx, CO, and HC emissions were observed in experiments conducted with aluminum particle-added fuels. The aim of this study is to increase the efficiency of diesel engines and reduce exhaust emissions by using aluminum particle additives.

Polymeric advancements in innovating wax injection molds using aluminum-filled epoxy resin with face-cooled waterfall cooling channels

Aluminum-filled epoxy resin is a polymer composite material formed by adding aluminum particles to epoxy resin, which is widely used to make a rapid tool for developing new prototypes in the research and development department. A conformal cooling channel (CCC) facilitates the swift and even cooling process in injection molding. Nevertheless, the considerable drawback of CCC lies in the notable pressure drop along the cooling channels. This study introduces an inventive solution known as the waterfall cooling channel (WCC), which was proposed and fine-tuned through optimization using Moldex3D simulation software. Two sets of aluminum-filled epoxy resin injection molds were designed and employed, featuring distinct cooling channels. The cooling time for the injection molded part was assessed using a low-pressure wax injection molding machine. Experimental results regarding the cooling time were then juxtaposed with simulation outcomes obtained from Moldex3D software. It was found that a mesh size of 1 mm is the optimal decision for molding simulation based on both the cooling time of the injection molded part and the total computation time. The maximum flow velocity of the cavity insert can be increased by 9.7 % using WCC. A reduction in the coolant flow length of the WCC is about 29–50 % compared to CCC. A reduction in the pressure drop of the WCC is about 58–61 % compared to CCC. The difference in cooling efficiency for CCC is 6 %, while the difference in cooling efficiency for CCC is 4 %. The heat flux of WCC is about 21 times larger than that of CCC. Taking a water cup as an example, the experimental results confirmed that an aluminum-filled epoxy resin injection mold embedded with WCC can increase cooling efficiency by about 16.4 % compared to an aluminum-filled epoxy resin injection mold embedded with CCC.

Comprehensive modeling of ignition and combustion of multiscale aluminum particles under various pressure conditions

The ignition and combustion of aluminum particles are crucial to achieve optimal energy release in propulsion and power systems within a limited residence time. This study seeks to develop theoretical ignition and combustion models for aluminum particles ranging from 10 nm to 1000 μm under wide pressure ranges of normal to beyond 10 MPa. Firstly, a parametric analysis illustrates that the convective heat transfer and heterogeneous surface reaction are strongly influenced by pressure, which directly affects the ignition process. Accordingly, the ignition delay time can be correlated with pressure through the pb relationship, with b increasing from –1 to –0.1 as the system transitions from the free molecular regime to the continuum regime. Then, the circuit comparison analysis method was used to interpret an empirical formula capable of predicting the ignition delay time of aluminum particles over a wide range of pressures in N2, O2, H2O, and CO2 atmospheres. Secondly, an analysis of experimental data indicates that the exponents of pressure dependence in the combustion time of large micron-sized particles and nanoparticles are –0.15 and –0.65, respectively. Further, the dominant combustion mechanism of multiscale aluminum particles was quantitatively demonstrated through the Damköhler number (Da) concept. Results have shown that aluminum combustion is mainly controlled by diffusion as Da > 10, by chemical kinetics when Da ≤ 0.1, and codetermined by both diffusion and chemical kinetics when 0.1 < Da ≤ 10. Finally, an empirical formula was proposed to predict the combustion time of multiscale aluminum particles under high pressure, which showed good agreement with available experimental data.

Classification of pairing phase transition in metal clusters in vanadium and aluminum particles using Grossman theory

In this work, the phase transition from normal to superconductivity state of two metal clusters, vanadium and aluminum particles, are theoretically studied by changing size and resistance parameter. We obtained the heat capacity integral of Grossman's theory considering that the first zero of the partition functions is located in the complex temperature plane. Then, we used the experimental data of the heat capacity of aluminum metal clusters and vanadium particles to determine the unknown integral coefficients of the heat capacity of Grossman's theory. Based on the obtained coefficients, we discussed the classification of the phase transition of the aforementioned metal clusters. Also, the obtained coefficients have been used to plot the heat capacity of aluminum metal clusters and vanadium particles. Finally, we compared the obtained heat capacity with the experimental results. A good agreement between our results and the experimental data has been obtained.

Multi-objective optimization and thermodynamic assessment of a solar unit with a novel tube shape equipped with a helical tape

The performance of several heat transfer mechanisms, including solar energy sources, is being improved through optimization, which also effectively supports the most efficient feasible design. A numerical study has been done on a turbulator-enhanced flat plate solar collector (FPSC) while also introducing the utilization of a quad-lobed tube as a pioneering innovation in the system’s design. The incorporation of nanoparticles into the working fluid was implemented to enhance performance, with aluminum oxide particles selected for this purpose. Furthermore, assessing the second law and analyzing exergy generation was employed to discern irreversibility within the system. Optimization of both geometric and non-geometric elements has been accomplished through the integration of a multi-objective optimization (MOO) method with machine learning (ML). Random Forest (RF), LASSO Regression (LaR), and Support Vector Regression (SVR) are the machine learning models that were utilized in order to ascertain the correlations that exist between the system’s inputs and outputs. According to the findings, RF was found to be the most appropriate algorithm for capturing the impacts of parameter variations. This was demonstrated by the high coefficient of determination (R2) quantities that RF possessed, which were 0.95, 0.99, and 0.99 for friction factor (f), exergy loss (Xd), and second law effectiveness (ηII), respectively. However, the SVR and LaR algorithms showed significant deviations from the FPSC simulation results. The SVR algorithm achieved R2 values of 0.54 for f, 0.78 for Xd, and 0.84 for ηII, while the LaR algorithm achieved R2 values of 0.65 for f, 0.99 for Xd, and 0.98 for ηII. This research aims to find the optimal input parameters that minimize f and Xd while maximizing ηII. Therefore, to determine the Pareto optimal solutions the non-dominated sorting genetic algorithm (NSGA-II) has been utilized. The result was an illustration of the Pareto set, which stands for a collection of optimal solutions. Every solution in this collection achieved the desiredbalance, obtaining the best outcomes without compromising any objectives.

Numerical study of Marangoni convective hybrid-nanofluids flow over a permeable stretching surface

This paper is discussing nanofluid flow with effect of radiation along a stretching sheet in a porous means. Also, magnetic field is applied uniformly. The hybrid nanofluid is blend of base fluid kerosine oil and suspending particles of Copper Aluminum Oxide (Cu − Al2O3). The Marangoni boundary condition is considered. The flow considered is mathematically modeled with suitable boundary conditions in partial differential equations. Similarity transformations applied and followed numerical computations with Runge–Kutta method of order 4th aided by shooting approach. The graphs for different flow control parameters plotted and analytical study carried with illustration of temperature and velocity fields. Heat transfer rate for hybrid-nanofluid falls with increasing Mass transfer, Wall parameter (fw)and Prandtl Number (Pr), and the reversed effect for same is seen for higher Radiation parameter values (R). The current study's relevance has numerous applications in the key fields of materials processing, industrial thermal control, and heat transfer optimization in energy-efficient systems.

TO HIGHLY PRODUCTIVE SYNTHESIS OF ALUMINUM NANOPARTICLES IN PLASMA FLOW AT ATMOSPHERIC PRESSURE

Purpose. To study the highly productive evaporation of aluminum micron powder in an atmospheric pressure plasma jet for the synthesis of nanoaluminum. Using special plasma technology, nanoparticles can be produced by rapid melting and evaporation of the initial micrometer particles and their subsequent re-nucleation. Research methods. Methods of mathematical and computer modeling of subsonic plasma turbulent jets at atmospheric pressure and experimental studies of two-phase processes during thermal plasma treatment using an arc plasma torch. Results. Based on computer modeling, a special reactor system was designed and developed, which includes a plasma-jet reactor with an electric arc plasma torch for the synthesis of aluminum nanoparticles. Numerical modeling makes it possible to determine the position of the melting point, evaporation and crushing of a molten particle, the evolution of the fractional composition of the dispersed phase, and find the speed and temperature of the particle in the area from its melting point to the crushing point. An experimental test of the operation of the reactor system was carried out using arc plasma torches with a power of 30 and 150 kW. It has been shown that intensifying the fragmentation of dispersed raw materials in a plasma jet can be useful in technologies for producing nanomaterials. The consequence of the fragmentation process is the redistribution of the fractional composition of the powder along the plasma jet and the accompanying changes in the dynamics of movement, heating and evaporation of particles. It has been determined that when the temperature of the largest aluminum particles reaches 2500 C, the total amount of evaporated mass is theoretically equal to 100%. The main parameters influencing the behavior of particles in a plasma jet are particle diameter, powder injection rate, flow rate, temperature and composition of the plasma gas. Taking these parameters into account will allow the process to operate at increased productivity. Scientific novelty. A mathematical description of the process of fragmentation a polydisperse powder, based on a continuum approach, has been obtained, which makes it possible to determine the position of the crushing point of a molten particle, the fractional composition of the dispersed phase, and find the speed and temperature of the particle in the area from its melting point to the point of crushing and evaporation. It was shown for the first time that it is possible to carry out a process in which complete evaporation of a molten drop is achieved due to the high enthalpy of the plasma before the end of mixing with steam. Practical value. A special reactor system has been designed and developed, which includes a plasma-jet reactor with an electric arc plasmatron for the synthesis of aluminum nanoparticles. The operating parameters of the reactor system have been determined, which will allow the synthesis of aluminum nanoparticles to be carried out with high productivity.