Powder Grains Research Articles

Discrete-element simulations of comminution in rotating drums: Effects of grinding media

By means of Discrete-Element simulations with Bonded-Cell method for particle breakage, we investigate the evolution of crushable granular materials in a 2D rotating drum partially filled with heavy balls and powder grains. The grinding process with balls of different sizes or numbers is analyzed in terms of grain size and specific surface. The grinding rate is an increasing function of the number of balls, but, as a result of increasing energy dissipation by inelastic collisions between the balls, the process becomes energetically less efficient for larger number of balls. When the total volume of balls is kept constant, the ball size has generally little influence on particle breakage. We also introduce a model for the evolution of three size classes by accounting for the cushioning effect and transition rates between the classes. This model predicts an exponential decrease of the volume of large particles at the beginning of the process.

Role of trapped water on electroresponsive characteristic of silica-graphene oxide composite microspheres

Electroresponsive microspheres containing nanosilica and graphene oxide (GO) sheets have been achieved by the one-step evaporation induced assembly of mixed colloids using spray drying. The interlocking of the nanostructured constituents by the attractive capillary force during drying of dispersion droplets results in the formation of powder grains with correlated nanoparticles and nanosheets. The presence of GO sheets arrests the buckling of the drying droplets during evaporative assembly and results in well-defined spherical shaped grains. Interestingly, this approach of random jamming in colloidal droplets is capable of preventing the spontaneous stacking of the GO sheets and, therefore, facilitates a way to confine the atomic-thick GO sheet in the solid matrix. A plausible mechanism for the formation of silica-GO binary composite microspheres is elucidated. Microspheres dispersed in insulating oil show interesting electroresponsive characteristics where the microspheres form a chainlike percolation path under the applied electric field. It has been established that the adsorbed water in the microspheres plays a profound role as far its electroresponsive behavior is concerned. GO sheets in the microspheres allow for tuning of electroresponse strength owing to the increased interaction of water molecules to the oxygen-containing functional groups anchored on the GO sheets.

X-ray peak broadening on microstructure, and structural properties of titanium and Ti-6Al-4V alloys

In this present work, the effect of milling duration on the microstructure and structural properties of titanium and Ti-6Al-4V alloy powders were investigated. Ti and Ti-6Al-4V alloy powders were mechanically alloyed using high energy planetary ball mill for different milling durations (AR, 10 and 20 h) at room temperature. The milled powders were characterized by XRD and HR-SEM analysis. Structural properties such as Crystal size, lattice strain, dislocation density and lattice parameter were examined by using X-ray peak broadening analysis in Williamson hall method i.e., Uniform Deformation Model (UDM). XRD peaks for different milled powders showed significant peak broadening and grain refinement. The Microstructure and size distribution of powder particles, grain size and morphology of Ti and Ti-6Al-4V alloy milled powders were characterized using High Resolution Scanning Electron Microscope (HR-SEM).

Low-cost cultivation and sporulation of alkaliphilic Bacillus sp. strain AK13 for self-healing concrete.

The alkaliphilic, calcium carbonate precipitating Bacillus sp. strain AK13 can be utilized in concrete for self-repairing. A statistical experimental design was used to develop an economical medium for its mass cultivation and sporulation. Two types of screening experiment were first conducted to identify substrates that promote the growth of the AK13 strain: the first followed a one-factor-at-a-time factorial design and the second a two-level full factorial design. Based on these screening experiments, barley malt powder and mixed grain powder were identified as the substrates that most effectively promoted the growth of the AK13 strain from a range of 21 agricultural products and by-products. A quadratic statistical model was then constructed using a central composite design and the concentration of the two substrates was optimized. The estimated growth and sporulation of Bacillus sp. strain AK13 in the proposed medium were 3.08 ± 0.38 × 108 and 1.25 ± 0.12 × 108 CFU/ml, respectively, which meant that the proposed low-cost medium was approximately 45 times more effective than the commercial medium in terms of the number of cultivatable bacteria per unit price. The spores were then powdered via a spray-drying process to produce a spore powder with a spore count of 2.0 ± 0.7 × 109 CFU/g. The AK13 spore powder was mixed with cement paste, yeast extract, calcium lactate, and water. The yeast extract and calcium lactate generated the highest CFU/ml for AK13 at a 0.4:0.4 ratio compared to 0.4:0.25 (the original ratio of the B4 medium) and 0.4:0.8. Twenty-eight days after the spores were mixed into the mortar, the number of vegetative cells and spores of the AK13 strain had reached 106 CFU/g within the mortar. Cracks in the mortar under 0.29 mm were healed in 14 days. Calcium carbonate precipitation was observed on the crack surface. The mortar containing the spore powder was thus concluded to be effective in terms of healing micro-cracks.

Graded evolution of anisotropic microstructure during sintering from crystal‐oriented powder compact

AbstractAnisotropic sintering, including shrinkage and grain growth, was examined for c‐axis‐oriented (Sr,Ca)2NaNb5O15 (SCNN) ceramics, which were prepared by colloidal processing under a magnetic field. In the c‐axis‐oriented SCNN powder compact, shrinkage and grain growth along the c‐axis were higher than those along the a‐axis. The anisotropic microstructural development was clearly associated with anisotropic sintering shrinkage. X‐ray diffraction, scanning electron microscopy, and energy back scattering diffraction showed that the grain growth of oriented particles by including random grains contribute to the development of the oriented microstructure. Finally, the highly crystal‐oriented SCNN ceramics with a densified microstructure were obtained through anisotropic sintering. These results clearly showed the potential to develop a well‐defined anisotropic microstructure during sintering by designing and controlling the particle packing structure in a powder compact.

Using Mechanoluminescent Materials to Visualize Interparticle Contact Intensity in Granular Media

Mechanoluminescent materials have the property of emitting light when they are mechanically deformed. The paper deals with the potential use of these active substances to reveal interparticle contact force networks in granular media under mechanical loading. Preliminary uniaxial tensile tests were first performed on two types of longitudinal specimens for comparison purposes: pure epoxy resin and epoxy resin containing mechanoluminescent powders. Stress-strain curves showed that the powder acted as a reinforcement, but fractographic analysis by SEM revealed that debonding occurred between the epoxy matrix and powder grains during mechanical loading. Various two-dimensional cohesionless granular systems were then studied, using mechanoluminescent cylinders subjected to compression. Whereas uniaxial tensile tests featured homogeneous light emission, localized mechanoluminescence intensities were revealed in the contact zones between cylinders. The study shows that mechanoluminescent materials open perspectives for the identification of interparticle contact intensities in granular media.

Influence of Nickel Powders on Corrosion Resistance of Cold Sprayed Coatings on Al7075 Substrate

The influence of the size and structure of nickel powder grains on the corrosion resistance of nickel coatings on an Al7075 substrate in an acidic chloride solution was investigated. The Ni coating was produced by the cold spraying (CS) method. The surface and microstructure of specimens were observed by a scanning electron microscope (SEM). The corrosion test of the materials was carried out by using the electrochemical method. It has been found that the size of Ni powders has a significant effect on the corrosion resistance of nickel coatings. The porosity of nickel coatings on the Al7075 alloy increases with the increasing size of nickel powders. The corrosion rate of nickel coatings in the chloride environment decreases as the diameter of the nickel powders decreases. On the other hand, the highest corrosion resistance of nickel coatings was obtained using the Ni powders of the irregular spherical or dendritic structure. Moreover, the large particles of nickel powder cause strong residual stress (compared to small grains) in the depth of the nickel coatings.

INTERCONNECTION OF MATERIALS SCIENCE, 3D PRINTING AND MATHEMATIC IN INTERDISCIPLINARY EDUCATION

The substantial advantage of 3D printing is the ability to fabricate complex shapes objects from liquid molecules or powder grains which joins or solidifies using computer design files (CAD) to produce a three-dimensional object with material being added together layer by layer. This process is considered as an industrial technology. The most-commonly used 3D printing procedure is a material extrusion technique called fused deposition modelling. The producers of 3D printers have already developed prototypes for education purposes. The importance of the incorporation this printing method in schools is the fact. The learning experience for digital media is becoming a priority in school education. The practical application of this technique can be incorporated into a wide variety of school subjects to simplify the sophisticated theoretical concepts. 3D printing is the example of cooperation within material science and mathematics but this platform is very often not supported by the high school curriculum, but latest trends propose different approaches and make education close to the science achievements and contemporary life. Building lessons plans and project could help students to learn more contemporary achievement in this field. It is new trend to support enthusiastic teachers who want to implement this method of additive manufacturing in education. This paper provides an overview of 3D printing methods and highlights the possibility of their implementation in educational techniques.

Additive Manufacturing of WC-Co Cutting Tools for Gear Production

This article presents results relating to the production of a WC-Co gear cutting tool via selective laser melting (SLM). The influence of powder grain geometry and chemical composition on SLM process outcomes are firstly investigated by producing and testing simple cylindrical specimens, from which optimal process parameters and scanning strategies are establish for both the component itself and supporting structures. These parameters are then utilised to produce a real cutting tool that is subsequently employed for internal automotive gear fabrication.

Effect of Reaction Time on Surface Nano-Structure of TiN Oxide Nanofilm by Hydrothermal Method

Dye-sensitized solar cells have better development prospects than silicon cells, and the main structural components of nanoporous semiconductor films are particularly important. In this experimental study, we used tin dioxide film and investigated the effect of preparing this film on dye-sensitized solar cells under different conditions. Furthermore, SnO2 powder was prepared through hydrothermal method, and an experiment was conducted through a controlled variable method. The properties of the obtained tin dioxide powder were characterized by SEM, 3D ultradepth microscopy, and XRD. An XRD peak is displayed as tetragonal-phase rutile-type SnO2, and the SEM indicates that the powder grain size is several nanometers. With the increase in reaction time, the film gradually became flat and uniform from only a small amount of powder coating. At the reaction time of 8 days, the integrity and flatness of the film were optimal, and the pore size was uniform. Moreover, the specific surface area was large. In summary, the reaction time of 8 days is suitable for membrane growth.

A mechanism study on influence of strong external magnetic field on fracture properties of a ferromagnetic steel

For some ferromagnetic metallic materials, measurable influence of strong external magnetic field on their fracture properties has been observed experimentally, i.e., an external magnetic field of large intensity can promote the propagation of the crack. In order to clarify the mechanism of this phenomenon, a fracture model is put forward in this paper based on reversal magnetic domain theory and minimum free energy algorithm and verified through observations of magnetic domains structure. Compact tensile (CT) specimens which were stretched in strong magnetic field are adopted to observe their magnetic domains structure with the powder grain method in practice. It is found that the crack in the CT specimen propagated mainly along the magnetic domain wall rather than passing through the domain body. Together with the experimental results, the fracture model for the rupture and propagation mechanism under strong magnetic field was discussed.

Natural Rubber Powder Production from Latex

Natural rubber-based products are widely used in everyday life. There are three types of upstream processed natural rubber, that are crumb rubber, conventional rubber, and concentrated latex. Latex is easily damaged by clotting and contains 35-40% w/w of water so that the packaging volume is relatively large and inefficient in transportation. Latex also contains ammonia as an anti-clotting agent so the packaging must be special to prevent unpleasant odour. This study aims to create a pilot plant of the spray drying latex from simulation results then test the performance, evaluate the performance test results, as well as making improvements to the production of rubber powder. The steps of this research are data collection for spray dryer design, design verification, construction of spray dryer, spray dryer appliance testing, and characterization of rubber powder produced. The heating system used in the spray dryer is LPG gas-fired furnace. Testing is done by varying the spray dryer drying air temperature of 120°C, 150°C, and 180°C, the water content of the feed latex 70% and 80% w/w, as well as non-stick material such as talc powder and MgO. Rubber powder characterized by water content with digital tools moisture meter and analysed spectra with Fourier Transform Infrared Spectroscopy (FTIR). The results showed the optimum operating conditions for the production of natural rubber powder is drying air temperature of 150°C and the water content of the feed latex 80% w/w. Natural rubber powder produced contains 10 to 13% w/w water but still sticky so that the powder grains stick to each other. The FTIR spectrum analysis of natural rubber powder products show similarity with bonding group of polyisoprene natural rubber compound. Natural rubber powder product can also be used as a substitute for crumb rubber.

Powder metallurgy of the porous Ti-13Nb-13Zr alloy of different powder grain size

ABSTRACTThe objective of the present project was to determine the effects of powder granulation (fraction of grain size) for the Ti-13Nb-13Zr alloy, produced by powder metallurgy, on its porosity, grain cohesion, compressive strength, and Young`s modulus. Two powder fractions, 45–105 µm, and 106–250 µm were applied. The 50 mass pct of NH4HCO3 was added as a space holder. The specimens were in compaction stage uniaxially pressed at pressure 625 MPa for 120 s. The brown bodies were sintered at a temperature 1150°C for 3.5 h. The well-joined grains were observed for both powder granulations. The increase in powder granulation resulted in an increase of porosity from 51% to 59%, and it was only 30% with no space holder used. The compressive strength increased with decreased porosity from 57 to 236 MPa. Young`s modulus was measured as 4.8 GPa for finer powder and 0.9 GPa for coarser powder. It is evident from the results obtained that the applied process parameters, the space holder and its fraction, and the use powder granulation between 45 and 105 µm bring out the porous material fulfilling mechanical and biological requirements specific of load-bearing titanium implants.

Powder catchment in laser metal deposition

Laser metal deposition (LMD) of Inconel 718 using a coaxial nozzle is investigated by high-speed imaging. The interaction of individual powder grains with the laser induced melt pool surface and, finally, their catchment in the LMD track is observed. Powder catchment trends are explained by interpreting physical phenomena, such as the melt flow and surface tension. Distinct zones for powder catchment are categorized depending on the position of initial interaction between powder grains and the melt pool. Particles are introduced outside the melt pool ricochet and do not attach to the clad. Particles arriving outside the laser spot, onto the solidifying skin of the melt pool, are caught, and may incorporate. Some particles may remain on the clad surface as surface roughness on the built part. Particles interacting with the laser-irradiated region of the melt pool tend to move toward its center and readily incorporate into the melt. Quantitative analyses of high-speed videos are carried out to measure incorporation time of powder grains in the melt pool, their velocity, and distance traveled.

Duplication of uniqueness: electrotyping in nature printing and its application in contemporary art

The nature printing technique was designed for the electrotyping reproduction of leaves and other natural products. Authentic impressions could be performed by inserting leaves between two lead plates or pressing leaves into the lead plate by a press. The impression obtained in the soft lead plate could then be further reproduced by copper electroplating. Electrochemically deposited copper is hard-wearing and therefore very suitable for the production of printing plates. However, depending on the technical implementation and the choice of the materials used, decisive differences in the faithfulness of reproductions of original motifs may occur during the electrochemical deposition. A central topic in electroforming of printing plates is the choice of the conductive layer on the mould. In the present study, it has been shown that graphite powder represents a conductive phase on the siloxane mould superior to silver and copper powder. The grain size of the copper electrodeposit depended on the powder grain size. The copper plate deposited on graphite powder showed the lowest grain size (5–20 µm) and the highest homogeneity of the print background. Hand polishing of the printing plate resulted in a much better faithfulness of the motif details than that of the machine polished version. However, the background of the print derived from the machine polished plate was the most homogeneous. Electrochemical investigation showed that remnants of the silver powder could result in local elements that could enhance corrosion and thus impair the durability of the printing plates. This phenomenon was negligible with the conductive layers consisting of graphite and copper.

Grain size effects of tungsten powder on the micro-structure and mechanical properties of tungsten-based alloys

Bulk W-0.5 wt% ZrC (WZC) plates were fabricated using tungsten powders with different powder grain sizes of 0.2 μm, 0.5 μm and 2.8 μm, respectively. The different grain sizes resulted in completely different micro-structures and mechanical properties of as-rolled WZC plates. For the tungsten plate prepared from the initial powder with grain size of 0.5 μm (0.5WZC), more excellent mechanical properties were achieved than those of plates made of powders with grain sizes of 0.2 μm (0.2WZC) and 2.8 μm (2.8WZC). In the as-rolled 0.5WZC, the ductile-brittle transition temperature is as low as 150 °C and ultimate tensile strength is as high as 932 MPa at 150 °C, respectively. Moreover, the 0.5WZC plate has the most outstanding high-temperature stability with a recrystallization temperature of 1500 °C. Micro-structure analysis indicates that the second-phase particles are uniformly distributed in the 0.5WZC, but serious particle aggregation occur in the 2.8WZC. The possible micro-mechanisms have been proposed.

Characterisation of carbon fibre (Cf) - Poly Ether Ketone (PEK) composite powders for laser sintering

Laser sintering (LS) of composites is an attractive prospect for industries with an interest in complex structures of enhanced mechanical performance. Unfortunately, dry blends of carbon fibre (Cf) and polymeric powders are known to lead to poor mechanical properties. This paper brings evidence that Cf incorporated within the polymer grains (referred in the paper as composite grain powder) can enhance mechanical performance and highlights areas within the powder preparation stages where careful powder examination is critical. An in-depth powder analysis was performed on a dry blend of Cf/PEK powder and several composite grain powder grades obtained from milling, both at 30 wt% of Cf. The results showed that characterisation of the milling fraction is very important and only certain composite grain grades maintain expected powder properties for LS as well as wt% of Cf. The SEM images of laser sintered films provided a clear insight into what happens in the laser sintering of dry blends versus composite grain powders. The complex moduli (E*) obtained from the DMTA tests presented an increase in the samples manufactured using composite grain powders over the dry blend powder and approximately double values when compared with plain polymer HP3 PEK.

Mechanical, physical properties and tribological behaviour of silicon carbide composites with addition of carbon nanotubes

Four types of silicon carbide/carbon nanotubes composites were prepared with the main aim to develop ceramics with enhanced electrical conductivity. The SiC/CNT composites were prepared by in-situ growth of CNT on the SiC powder grains. Three types of SiC/CNT composites, where the precursor SiC/CNT powder mixture was prepared by Catalytic Chemical Vapour Deposition (CCVD) method and different amounts of Fe catalytic nanoparticles (2.5, 5, 10 wt% Fe), were designed. In addition, one reference material containing 2.5 wt% Fe catalytic nanoparticles but without CCVD application, i.e. without CNT, was prepared in order to correctly assess the role of CNT. The experimental materials were compacted by hot pressing (1850 °C/Ar/60 min/40 MPa). Mechanical properties such as hardness and elastic modulus of experimental materials were determined. Electrical conductivity as a function of CNT content was measured. The effect of the CNT addition on tribological properties (coefficient of friction, wear) of SiC/CNT composites was also observed.Hardness of the reference sample was relatively high (HV1 = 24 GPa) and it decreased down to HV1 = 17–19.8 GPa with presence of CNT. Similarly, the fracture toughness decreased with presence of CNT from 4.99 MPa.m1/2 for the reference sample down to 3.4–4 MPa.m1/2 for the SiC/CNT composites. Nanoindentation showed that hardness HIT of reference sample without CNT was around 26 GPa and with increasing amounts of CNT it decreased down to 21 GPa. The composites had similar modulus of elasticity (EIT = 337–348 GPa), while for the reference sample it was EIT = 434 GPa. Electrical conductivity increased with amount of CNT (1.76 S/m for the reference sample, 484.3 S/m for the composite with 2.5 wt% Fe, and up to 2873.6 S/m for the composite with 10 wt% Fe). Specific wear rate increased with presence of CNT from 7.7 × 10−7 mm3/Nm for the reference sample to 2.4–2.9 × 10−6 mm3/Nm for the composites. Complex wear behavior common for all types of experimental materials was observed: mainly abrasion, mechanical wear (micro-fractures) and tribochemical reactions with created SiO2 layer. In the reference sample the dominant wear mechanism was abrasion, in SiC/CNT composites formation of transferred films in wear tracks consisting of oxides and carbon phases formed by crushing the CNT were observed.

Energetic Nanoparticles and Nanomaterials for Future Defense Applications

The integration of nanostructured materials in defense systems is expected to improve their performance in terms of power, safety, and reliability. That is why considerable research effort has been undertaken by major military powers worldwide in this domain. The first important step was to develop the production capacities of organic explosives in the state of fine powders with submicron to nanosized particle size distributions. The Spray Flash Evaporation (SFE) process, which is a unique method for producing such materials, was developed at industrial scale. Explosive nanopowders obtained by this process were subsequently mixed with nanosized pyrotechnic compositions such as nanothermites, to prepare hybrid detonating materials able to replace lead-based primary explosives. Composite propellants can also be prepared by SFE which allows mixing their components in a single step with better homogeneity. The ultimate challenge is to move from powder to object, in order to integrate energetic nanomaterials in operational systems. Although the research in this last domain is still in its infancy, several ways of preparation of objects from nanothermites have been recently reported in scientific literature. The focus will be on two examples studied in our laboratory. The first one is the preparation of nanothermites in the state of solid, porous foams; the second one is the use of nanothermites for coating grains of propulsive powder to change their combustion properties.

Compressive properties of magnetorheological elastomer with different magnetic fields and types of filler

Magnetorheological elastomer (MRE) specimens were prepared to find the optimum compressive characteristics using different types and amounts of iron powder. A magnetic field of up to 2 T was applied during vulcanization. Among the four types of iron powders, the specimen with round‐shaped carbonyl iron powder and small grain size shows higher magnetic effects than that with bigger and irregularly shaped electrolyte iron powder. However, the compressive modulus of the rubber with electrolyte iron powder is higher without magnetic treatment at a given amount. In general, the bigger and irregularly shaped iron particles tend to move slowly and produce nonuniform distribution when a magnetic field is applied. The experimental results show that the mechanical properties are better when applying a magnetic field of 1.5 T compared with 2.0 T during the specimen vulcanization. Applying a magnetic field of 300 mT during the compression test enhanced the compressive modulus by 12% to 15%. The rate of increase of the modulus decreased exponentially with prestrain.