Nickel Powder Particles Research Articles

Monitoring bridge bearings based on rubber-based composite materials

To improve the real-time monitoring capability of bridge structure safety, intelligent bridge bearings were prepared based on rubber based composite materials. The study selected T4/3-5 intelligent rubber bearings and conducted a systematic experimental analysis on their response characteristics under different loading speeds and holding states. By measuring the displacement and resistance changes of the intelligent bearings under various load conditions, their sensitivity and stability were evaluated. These experiments confirmed that the T4/3-5 intelligent rubber bearings exhibited a total creep deformation of approximately 1 mm and 1.5 mm under loads of 60 kN and 45 kN, respectively. This suggests that the molecular chains reach a relatively stable configuration under high loads and are not prone to further changes. Moreover, the resistance reduction ratio under a load of 60 kN is approximately 0.57, while under a load of 45 kN it is approximately 0.62, indicating that nickel powder particles in the composite material form a more stable conductive network after molecular rearrangement. At different loading rates, the displacement-load and load-resistance curves of the bearings show consistent trends, and the creep and resistance relaxation behaviors exhibit certain regularity with the concentration of load size. Through the analysis of these data, the study elucidated the resistance change mechanism in the bearings and validated the feasibility of intelligent bearings as a real-time load monitoring tool.

Current rate flash sintering of nickel at ambient temperature in <1 min

AbstractWe show that powder pressed specimens of nickel can be sintered to 99.96% density by injecting electrical current, without the use of a furnace. Full sintering could be accomplished in 10 to 52 s by changing the current rate from 5 to 1 A/s. In all instances, the samples sintered abruptly at a current density of ∼20 A mm−2. The grain size of the sintered samples was somewhat larger than the nickel powder particle size (∼60 μm vs. 40 μm). Tensile testing yielded a yield strength of 98 MPa, ultimate tensile stress of 323 MPa, and ductility of ∼17%. Four in‐operando measurements are reported: (i) sintering, (ii) the change in resistance with current density, (iii) the temperature, and (iv) electroluminescence. The change in resistance during flash sintering exhibited a high peak followed by a steep decline in resistance; the transient is attributed to the breakdown of particle–particle interface resistance. The same cycle repeated with the flash‐sintered, dense sample, did not show the spike, and gave reproducible results. The resistance data for these latter cycles, when viewed as a function of temperature exhibited sigmoidal behavior: initially lower, and then higher than the literature values. This unusual behavior reflects the influence of defects generated during flash. We have also measured the endothermic enthalpy, expressed by the difference between the in situ input electrical energy and the radiation, convection, and specific heat losses. Dividing by the formation energy of Frenkel pairs yields the concentration of defects, estimated to be 0.3–0.4 mol %. These concentrations are far above thermal equilibrium; it is concluded that flash of metals is a far from equilibrium phenomenon.

POROSITY OF A HEAT-RESISTANT ALLOY MADE BY SPARK PLASMA SINTERING OF NICKEL POWDER OBTAINED BY ELECTRODISPERSING THE ZHS6U ALLOY IN WATER

Metallographic studies are required to expand the scope of practical application of powder materials obtained from waste of the ZhS6U alloy. The purpose of this work was to study the porosity of a heat-resistant alloy produced by spark plasma sintering of nickel powder obtained by electrodispersing the LC6U alloy in water. The work is based on the task of obtaining a heat-resistant nickel alloy with improved physical and mechanical properties and low cost. The alloy under study is obtained by spark plasma sputtering of nickel powders obtained by electroerosive dispersion of waste of the alloy ZhS6U in distilled water. The waste of heat-resistant alloy of the brand ZhS6U was used in the work, which was crushed by the method of electroerosive dispersion in distilled water at the original installation. Parameters of the installation during the disposal of waste ZhS6U: voltage at the electrodes 190–210 V; capacitance of the condenses 55–60 UF; pulse repetition frequency 180–200 Hz. As a result of local exposure to short-term electrical discharges between the electrodes, the alloy waste was destroyed with the formation of heat-resistant nickel powder particles. Sintering of heat-resistant nickel powder was carried out in the SPS 25-10 "Thermal Technology" system (USA) at a temperature of 1300 °C, a pressure of 40 MPa and a holding time of 10 min. It has been experimentally established that new heat-resistant alloys produced by spark plasma sintering of an electroerosive charge have a porosity of about 0.52 %. The practically nonporous structure of heat-resistant alloys is explained by the presence of particles of different fractions in the electroerosion charge, which ensures tight packing and the so-called "spark discharge plasma effect" during spark plasma fusion.

Вплив діаметру частинок порошку нікелю на їх швидкість і температуру при холодному газодинамічному напилюванні

To deposit coatings in cold gas-dynamic spraying (CS), a high-speed gas flow is used to accelerate and heat particles. Therefore, first of all, it is necessary to consider the general laws of the gas flow and the movement of particles in the flow, as well as its interaction with the substrate. Due to the CS process depends primarily on the particle velocity, it is important to understand the effect of the process parameters (pressure and temperature at the nozzle inlet), the characteristics of the powder particles (material density, shape, and size), and the geometry of the nozzle. The gas velocity limits the particle velocity that can be achieved with the CS process. Utilization of high gas pressure, long nozzles, and small particles lead to the fact that the particles move at a velocity close to the velocity of the gas, which can be increased by using gases with low molecular weight, as well as heating it. As a result of the analysis of theoretical and experimental methods for studying the cold spraying process, it was found that for coating formation velocity of powder particles needs to obtain a certain value (critical velocity), which depends on particle temperature at the impact, and density of the particle material. Numerical simulation of gas dynamics of a two-phase flow in CS nozzle and at the outlet from it for the range of air temperatures from 573 K to 873 K and constant pressure of 1,0 MPa has been carried out. The influence of the diameter of nickel powder particles on their temperature and velocity at impact was investigated. Numerical simulations were performed for a range of particle diameters from 5 to 30 μm. In the future, the results obtained can be used to find the optimal size of the powder particles under certain spraying conditions, to calculate the critical particle velocity, and also to develop the window of deposition. This will make it possible to select the optimal parameters of the gas flow at the nozzle inlet (pressure and temperature), which are guaranteed to ensure the adhesion of particles to the substrate and the formation of coatings. Also, the results obtained can be used to predict the properties of coatings, as well as to achieve maximum deposition efficiency of the CS process.

Influence of Nickel Powder Particle Size on the Microstructure and Densification of Spark Plasma Sintered Nickel-Based Superalloy

This study aims to investigate the effects of powder particle size on the densification and microhardness properties of spark plasma sintered superalloy. Three particles size ranges of nickel were used in this study, namely, (3-44, 45-106 and 106-150 μm), and this is the matrix in the IN738LC superalloy composition (powder), used in the study. The effects of the particle size were examined at a specific applied temperature and pressure. The transitioning stages during the sintering process of the green powders to the formation of the sintered alloy were analyzed and given as the particle rearrangement stage, the localized deformation stage and the neck formation/grain growth stage. There was the formation of γ, γ' and a solid solution within the microstructure of the sintered alloys. The effect of particle size was more pronounced on the grain sizes obtained, while the phases formed is the same for the three alloys. The results indicate that the nickel particle size (>60% of the total composition) has a significant influence on the densification, porosity, grain size and hardness properties of the IN738LC sintered alloy. Finer nickel particle size resulted in a sintered product with smaller grain size (9 µm), reduced percentage porosity (3.9%), increased relative density (96.1%) and increased hardness properties (371 Hv).

Effect of Particle Sizes of Nickel Powder on Thermal Conductivity of Epoxy Resin-Based Composites under Magnetic Alignment.

Magnetically oriented three-phase composite systems of epoxy resin, aluminum nitride, and nickel have been prepared, the thermal conductivity of composites filled with nickel powder with different particle sizes and content under different applied magnetic fields was studied. The vibrating scanning magnetometer (VSM) and scanning electron microscopy (SEM) were applied to investigate the dispersion of nickel powder in the composites. The results showed that the anisotropic thermal conductivity of the composites treated by applied magnetic field forming chain structure is obtained. The epoxy resin-based composites filled with 30 vol% aluminum nitride with particle size of 1 μm and 2 vol% nickel powder with particle size of 1 μm and aligned with vertical magnetic field have the highest thermal conductivity (1.474 W/mk), which increases the thermal conductivity of the composites by 737% and 58% compared to the pure epoxy resin (0.2 W/mk) and the composites filled with 30 vol% aluminum nitride (0.933 W/mk). In addition, we simulated the influence of nickel powder particles with different particle sizes and arrangements on the thermal conductivity of the composite material in COMSOL Multiphysics software, and the results were consistent with the experimental results.

Effect of nickel powder particle size on the microstructure and thermophysical properties of spark plasma sintered NiCrCoAlTiW-Ta superalloy

The spark plasma sintering technique (SPS) was used to consolidate admixed elemental powder in order to fabricate NiCrCoAlTiW-Ta superalloy. Nickel which is the key element that formed the matrix powder particle size was varied in the range of 3-44, 45-106 and 106-150 μm. The effect of varying the starting powder particle size, on the formation of intermetallic phases was investigated. Also, important thermophysical properties in the development of superalloys for high temperature applications were investigated by using laser flash machine, in the range of 100-800 °C. The constituents of the microstructure for the sintered alloy includes, the gamma (γ) matrix phase (Ni), precipitated intermetallic gamma prime (γ’) phase Ni3(Al, Ti) and the precipitated solid solution strengthening elements (Cr and W). There was an increase in the density with decreasing powder particle size. Also, the averave grain size increased with increasing powder particle size. The thermophysical properties obtained, which include thermal conductivity and diffusivity increase with increasing temperature. Non-linear behaviour and inflection points were observed as the temperature increases due to short range order and disorder phenomenon which is associated with superalloys. The powder particle size has little or no significant effect of the thermophysical behaviour as the pattern observed were almost the same.

Reduction crystallization of heavy metals from acid treated phosphogypsum effluent utilizing hydrazine as a reducing reagent

Phosphogypsum is a by-product generated from phosphoric acid production processes. Due to the negative impact posed to the environment by the material, a chemical treatment process was developed to reduce the hazardous constituents in the material and render the final product useful for other applications. The treatment of phosphogypsum produced an effluent laden with contaminants such as copper, iron, manganese and thallium. This study was conducted to investigate the use of hydrazine as a reducing agent to remove and reduce Cu, Fe, Mn and TI from effluent, applying a reduction crystallization process. Nickel powder a base substrate was utilised as a seeding material. A feasibility study was carried out to test the efficiency and find the optimum operating conditions for the process. The predominant detected components in the feedstock were 71% Fe, 14% Tl, 5.1% Mn, 4.12% Cu and 2.4% Zn. The results obtained indicate that hydrazine can effectively remove up to 99.8% of metals from the effluent at the optimum pH of 10.5. Growth of the nickel powder particles was evident indicating a reduction and adsorption of contaminants on the surface of the powder. The treated solution was within South African acceptable limits for effluent discharge, which stipulates a concentration of 20 mg/l of copper, iron, manganese and thulium.

Korelacija izmedju orijentacije kristala i morfologije elektrolitički proizvedenih praškastih čestica - analiza graničnih slučajeva

Lead and nickel powder particles were produced by the processes of electrolysis and characterized by scanning electron microscope (SEM). The X-ray diffraction (XRD) analysis of the produced particles was done. Morphologies of Pb and Ni particles were correlated with their crystal structure at the semi quantitative level by determination of 'Texture Coefficients' (TC) and 'Relative Texture Coefficient' (RTC). The two dimensional (2D) dendritic particles of lead of different degree of ramification were obtained by the potentiostatic regime of electrolysis from the nitrate, acetate and hydroxide electrolyte. The spongy-like particles of nickel constructed from holes formed of the detached hydrogen bubbles and surrounded by cauliflower-like agglomerates of approximately spherical grains (the honeycomb-like structure) were obtained by the galvanostatic regime of electrolysis from the chloride electrolyte. Although crystallites were dominantly oriented in the (111) plane in both Pb and Ni particles, analysis of the XRD data showed different preferred orientation of the formed particles. All types of Pb dendritic particles showed the strong (111) preferred orientation, while crystallites of Ni in the spongy-like particles were almost random oriented. The obtained results were discussed following Winand's classification of metals on the normal, intermediate and inert metals based on their values of the exchange current density, melting point and overpotential for hydrogen evolution reaction.

Study on Nickel Nanopowders Prepared by Arc Plasma

In order to prepare the nickel nano-metal with high purity and uniform particle size , the arc plasma method was used. The nano-Ni was got under a constant current , voltage , barometric pressure, hydrogen and argon gas . The nickel nanopowders were tested through the Scan Electron Microscope (SEM ), X-ray diffraction (XRD), Laser Sizer Analysis (LSA). The results indicated that the feature of the nickel nanopowders were mainly spherical, smooth surface. The nickel powder particle distribute from 40 to 80nm. And average particle size is 60nm. Nanocrystals had a better internal crystallinity. The crystal structure is face-centered cubic FCC structure, the same as ordinary nickel nanoparticles .

Comparison between Microwave and Microwave Plasma Sintering of Nickel Powders

The objective of this study is to investigate the use of microwave plasma treatments as a processing technology for the sintering of metal powders. The volumetric heating process achieved with microwaves is considerably more efficient compared with resistance heating. The sintering study was carried out on 20 mm diameter by 2 mm thick compacted discs of nickel powder, with mean particle size of 1 µm. The discs were fired in a 5 cm diameter microwave plasma ball, under a hydrogen atmosphere at a pressure of 2 kPa. There was an increase in fired pellet transverse rupture strength (TRS) with plasma treatment duration. The mechanical properties of the sintered nickel discs were compared based on TRS, Rockwell hardness tests and density measurements. The morphology of the sintered discs was compared using microscopy and SEM. Comparison disc sintering studies were carried out using both a non plasma microwave and tube furnace firing. Using the microwave plasma sintering process full sintered disc strength of ≈1000 N (based on 3-point bend tests) was achieved after a 10 minute treatment time. In contrast the sintering time in the tube furnace treatment involved total processing time of up to 6 hours. The non plasma microwave system involved intermediate treatment periods of 2 hours. The degree of sintering between the individual nickel powder particles can be precisely controlled by the duration of the treatment time in the plasma.

Effects of the content level and particle size of nickel powder on the piezoresistivity ofcement-based composites/sensors

To explore the effects of the content level and particle size of spikyspherical nickel powder on electrical conductivity and piezoresistivity, threetypes of spiky spherical nickel powder with different particle sizes (3–7 µm, 2.6–3.3 µm and2.2–2.8 µm) were dispersed into the cement–matrix to fabricate the nickel powder filled cement-basedcomposites/sensors. Experimental results indicate that a high content level and a smallpractical size are beneficial for the improvement of electrically conductivity. Thepiezoresistive sensitivities of composites/sensors with 20, 24 and 22 vol% of nickelpowder increase orderly when nickel powder particle size is in the range of 3–7 µm. The piezoresistive sensitivities of composites/sensors with different particle sizes of nickelpowder decrease with an increase of nickel powder particle sizes at 24 vol% of nickel powdercontent level. The piezoresistive sensitivity is highly dependent on the conductive networkin the composites, which is dominated by the content level and the particle size of the spikyspherical nickel powder.

Dynamic recrystallization in the particle/particle interfacial region of cold-sprayed nickel coating: Electron backscatter diffraction characterization

Electron Backscatter diffraction was used to investigate the microstructural evolution of nickel powder particles during the high-velocity impact in the cold spray process. Ultrafine grains in the scale of 100–200 nm were observed in the particle bonding region. The formation of these nanometer-sized grains is interpreted in terms of dynamic recrystallization by lattice and subgrain rotation.

Experimental study on the contribution of the quantum tunneling effect to theimprovement of the conductivity and piezoresistivity of a nickel powder-filled cement-basedcomposite

The voltage–current characteristics of a nickel powder (NP)-filled cement-based composite(NPCC) and the variation of electrical resistivity of NPCC under compressionare studied by using a four-pole method based on embedded loop electrodes.The generation of conductivity and piezoresistivity in NPCC is investigated byexamining the morphology of NPCC by SEM and studying the variation ofdistance between NP particles under compression. Experimental results indicatethat the electrical conductivity of NPCC is ohmic when the voltage is below3.5 V. Although NP particles are dispersed in the cement matrix and they do notform a connected conductive network, NPCC has a low electrical resistivity of2.29 × 103Ω cm without loading. A decrease of 0.042% in the fractional change in volume of NPCC undercompression causes the tunneling distance to decrease 0.60–1.42 nm and the fractionalchange in electrical resistivity to reach 62.61%. It is therefore concluded that theimprovement of conductivity and piezoresistivity of NPCC is due to the quantum tunnelingeffect.

Kinetic modelling of nickel powder precipitation by high-pressure hydrogen reduction

The active mechanisms in the precipitation of nickel powder by hydrogen reduction were investigated by means of mathematical models based on the moment form of the population balance equation (PBE). The objective of the work was to establish the mechanisms involved in powder formation and how these are affected by the presence of impurities. The effects of two major impurities were considered namely; iron, inherently present as ferrous sulphate, and a morphology modifier, a polyacrylic acid derivative used as an additive. Experiments were conducted on a laboratory and pilot-plant scale using a 0.5 and 75 L stainless steel autoclave, respectively. Nickel powder samples were collected from the autoclaves after each successive batch reduction (densification) and the particle size distribution (PSD) analysed using a laser diffraction technique. The PSD data was then transformed into moments and the experimental values were compared with those simulated using different models based on the moment form of the PBE. Five models were tested namely: (a) aggregation-only; (b) aggregation and growth; (c) nucleation and aggregation; (d) nucleation and growth and (e) aggregation and breakage. Under standard operating conditions, the process was best simulated by a size-independent aggregation and growth model in the early stages of the cycle, with breakage and growth becoming significant in later stages of the cycle when large particles have been formed. Crystallisation in the presence of Fe was characterised by a size-independent aggregation and growth model with varying degrees of nucleation depending on the Fe concentration and the available surface area. At modifier dosages of 0.25 and 5 vol% the process was best modelled by a size-independent aggregation and growth model coupled with a constant breakage frequency model. Based on the mathematical modelling results and evidence from scanning electron micrographs, the spherically shaped nickel powder particles were proposed to be formed through the formation of a pre-cursor by secondary aggregation followed by spherulitic growth. The degree of compactness of the spherulites was proposed to be determined by the number of active growth sites on the nickel particle surface. The morphology modifier was found to act as a growth inhibitor, decreasing the number of growth sites leading to more open spherulites. Iron was found to induce surface nucleation, thus, creating more growth sites on the particle surface and leading to more compact spherulites.

Preparation of ultra-fine copper–nickel bimetallic powders with hydrothermal–reduction method

Gray bimetallic copper–nickel powders were synthesized with hydrothermal–reduction method. Formic acid and glutin were employed as hydrothermal–reduction agent and dispersion agent, respectively. Nickelous carbonate, copper carbonate and sodium formate were carried out in a titanium material autoclave at 230 °C to obtain gray-black powders for 20 h. Scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersion X-ray (EDX), thermal analyzer and laser size distribution analyzer were applied to analyze particle behavior. Bimetallic copper–nickel particles with polyhedral shape and uniform size in the range of 0.5 ± 0.2 μm were formed in an optimal reaction condition. Influences of dispersing agent on size and shape of particles were obvious. The size of particles decreases as an increasing dosage of formic acid. Microanalysis and thermal behavior of nickel-rich Ni–Cu solid solution suggest that copper–nickel powder particle has a core–shell structure.

Effect of powder loading on the excitation temperature of a plasma jet in DC thermal plasma spray torch

Abstract A DC non-transferred mode plasma spray torch was fabricated for plasma spheroidization. The effect of powder-carrier gas and powder loading on the temperature of the plasma jet generated by the torch has been studied. The experiment was done at different input power levels; the temperature of the jet was within 5000–7000 K argon was used as plasma gas and powder-carrier gas. Nickel powder particles in the size range from 40 to 100 μm were processed. The temperature of the jet was estimated after flowing powder-carrier gas only into the plasma jet and with powder-carrier gas feeding powder into the flame. On introduction of powder-carrier gas and powder loading the temperature of the jet was found to decrease appreciably down to 11%. The temperature of the plasma jet was estimated using the Atomic Boltzmann plot method.

Plasma spheroidization of nickel powders in a plasma reactor

Thermal spray coatings of surfaces with metal, alloy and ceramic materials for protection against corrosion, erosion and wear is an intense field of research. The technique involves injection of the powder into a plasma flame, melting, acceleration of the powder particles, impact and bonding with the substrate. Feedstock powders of metals, alloys and ceramics for thermal spray applications have to meet several requirements. Particle shape, size and its distribution, powder flow characteristics and density are the important factors to be considered in order to ensure high spray efficiency and better coating properties. For smooth and uniform feeding of powders into plasma jet, the powder particles have to be spherical in shape. High temperatures and steep temperatures present in thermal plasma is exploited to spheroidize particles in the present investigation. Nickel powder particles in the size range from 40–100 μm were spheroidized using plasma processing. SEM and optical micrographs showed spherical shape of processed particles.

Experimental research on fatigue crack growth in powder composite nickel-bearing steels

Micromechanical aspects of fatigue crack growth propagation in powder heterogeneous materials such as porous composite nickel-bearing steels are discussed. It is found that the residual porosity of powder steels (usually 3-5%) is favourable to damage initiation under cyclic loading and damage growth due to fatigue crack propagation. High strength austenitic phases of powder composite steel generated by the sintering process because of microscale volumes rich in nickel are formed near nickel powder particles and these microscale austenitic volumes are favourable to fatigue damage growth. The powder nickel-bearing steel microstructure contains ferrite and austenite phases and pores in the iron-carbon-nickel base system. In addition, under cyclic loading, the meta-stable austenite phase is turned into a carbide-ferrite substructure, resulting in a change in the fatigue crack propagation process. Considering that the lifetime of functional materials in friction wearing parts or cutting tools is defined through the crack propagation time, the experimental research into fatigue crack resistance for powder nickel-bearing steels presented in this paper should have substantial practical importance.

Effect of process conditions on ultrafine nickel powder particle size : M. Udaka et al (Neturen Co Ltd, Hiratsuka, Japan), J. Japan Inst. of Metals, vol 58, no 6, 1994, 683–690. (In Japanese)

Effect of process conditions on ultrafine nickel powder particle size : M. Udaka et al (Neturen Co Ltd, Hiratsuka, Japan), J. Japan Inst. of Metals, vol 58, no 6, 1994, 683–690. (In Japanese)