Atomized Copper Powder Research Articles

Influence of porogen type and copper powder morphology on property of sintering copper porous materials

Copper porous materials have been manufactured by the method of powder metallurgy. Electrolytic copper powders and atomized copper powders are used as matrix material. Methylcellulose and paraffin are used as porogen. The influence of porogen type and copper powder morphology on the property of copper porous materials is investigated as well. The results show that copper porous materials with paraffin as porogen have lower porosity and permeability compared with materials using methylcellulose as porogen, due to the different pore-forming mechanisms. The pore forming mechanism of methylcellulose is thermal decomposition, while the pore forming mechanism of paraffin is melting–evaporation. The morphology of copper powders affects the contact state between adjacent powders, which further influence the sintering shrinkage. The porous materials using arborescent copper powders as matrix have lower porosity, smaller pore size and lower permeability, compared with materials with atomized copper powders as matrix.

Permeability model of sintered porous media: analysis and experiments

In this paper, the permeability of porous media fabricated from copper powder sintering process was modeled and measured, aiming the use of the porosity as input parameter for the prediction of the permeability of sintering porous media. An expression relating the powder particle mean diameter with the permeability was obtained, based on an elementary porous media cell, which is physically represented by a duct formed by the arrangement of spherical particles forming a simple or orthorhombic packing. A circular duct with variable section was used to model the fluid flow within the porous media, where the concept of the hydraulic diameter was applied. Thus, the porous is modeled as a converging–diverging duct. The electrical circuit analogy was employed to determine two hydraulic resistances of the cell: based on the Navier–Stokes equation and on the Darcy´s law. The hydraulic resistances are compared between themselves and an expression to determine the permeability as function of average particle diameter is obtained. The atomized copper powder was sifted to reduce the size dispersion of the particles. The porosities and permeabilities of sintered media fabricated from powders with particle mean diameters ranging from 20 to 200 microns were measured, by means of the image analysis method and using an experimental apparatus. The permeability data of a porous media, made of copper powder and saturated with distilled water, was used to compare with the permeability model. Permeability literature models, which considers that powder particles have the same diameter and include porosity data as input parameter, were compared with the present model and experimental data. This comparison showed to be quite good.

Contamination during the high-energy milling of atomized copper powder and its effects on spark plasma sintering

Mechanical milling is a suitable technique to enhance various properties of copper by the severe plastic deformation involved during the process. Contamination from milling media is one of the major problems of mechanical alloying. In this study, the behaviour of copper powder during mechanical milling was investigated in order to minimize iron and chromium contaminations. Hence, three different parameters have been studied to highlight the high influence of ball milling parameters on the final products. The parameters included the type of process control agent (none, toluene or stearic acid), the ball-to-powder weight ratio (33:1 or 10:1) and finally, a change in the milling cycle (interrupted or continuous) in an interactive procedure according to the experimental results. As a result, the best morphology and contamination level combination was observed in powder milled with stearic acid; it was 10:1 for the ball to powder ratio when using a continuous milling cycle. Once the best milling conditions were determined, the resulting samples were exposed to spark plasma sintering (SPS). The sintering parameters were selected based on a previous thermal gravimetrical measurement of the milled powders to avoid residual porosity. The final density of all of the samples is very good, 99%, confirming an effective densification process and sintering activated by severely strain-hardened and nanostructured particles.

Powder Geometry Based Models for Sintered Media Porosity and Effective Thermal Conductivity

In this paper, the porosities of porous media fabricated from a copper powder sintering process were modeled and measured, aiming for use of the porosity as an input parameter for the prediction of the effective thermal conductivity of sintering porous media. An expression relating the porosity and the powder particle mean diameter, based on the arrangements of contacting spheres joined by necks, was obtained. The particle size distributions of the powders employed in this study were statistically analyzed. The atomized copper powder was sifted to reduce the size dispersion of the particles. The porosities of sintered media fabricated from powders with particle mean diameters ranging from 20 to 200 microns were measured by means of the image analysis method. Results from porosity literature models were compared with the present model and experimental data. A model to predict the effective thermal conductivity from the mean particle diameter was developed, based on an elementary porous media cell, which is physically represented by two metallic hemispheres in contact, surrounded by a thin film of liquid. The electrical circuit analogy is employed to determine the heat leaving the top and reaching the bottom of the cell. The effective thermal conductivity in a porous media, made of copper powder and saturated with distilled water, was used to compare with the effective thermal conductivity model. This comparison showed to be quite good.

Effective thermal conductivity of sintered porous media: Model and experimental validation

A model to estimate the effective thermal conductivity of sintered porous media for heat pipes is proposed in this paper. An elementary cell of a porous media is physically modeled as two metallic hemispheres in contact with a fluid film around them. The electrical circuit analogy is employed to determine the heat leaving the top and reaching the bottom of the cell. The thermal circuit consists of two parallel resistance paths, one for the solid spheres in contact and the other for the heat transfer in the fluid. A literature model is employed to calculate the thermal resistance within the hemispherical particles. Also, literature models are used for the determination of the geometry of the neck produced between particles during the sintering process. The neck dimensions are used to estimate the neck thermal resistance, which is in series with the hemisphere resistances. Effective thermal conductivity experimental data were obtained for porous materials produced with atomized copper powder, with particle diameters ranging from 20 to 50μm. The comparison between present model and data is good. Statistics of the particle size distribution is employed to determine average particle dimensions. The porosity and permeability of the material tested was characterized in the laboratory. The samples were tested in three conditions: vacuum and saturated with distilled water or methanol. Literature models for the effective thermal conductivity for bed packed (not sintered) porous media were also compared with the present model and data results.

Effect of molecular interaction on the strength of green compacts

Modern approaches to calculating the strength of green compacts by van der Waals forces (σVW) are reviewed. Respective components (σVW) are calculated and green tensile strength (σtl.av) is experimentally determined for test powders of metals (Al, Zn, Cu, Ni, and Mo) and one nonmetal (FeSi). Comparison of σtl.av/σVW ratios shows that σtl.av and σVW are of one order for the atomized zinc powder, and σVW is greater than σtl.av for the atomized copper powder, though σtl.av is greater than σVW by two to three orders for most powders with irregular shape of particles. This difference can be attributed to the effect of shape and mechanical interlocking or seizure of particles when compacted. To predict the green strength, it is necessary to take into account both the shape of particles (or relative apparent density of the powder) and the forming temperature.

Confinement and aspiration of dust and gas in the production of atomized copper powders

A system for the confinement and aspiration of dust and gas emissions is developed. A movable casing installed on an induction crucible furnace prevents air contamination when melt is prepared and atomized to produce copper powders and alloys. The content of harmful admixtures in air at workplaces does not exceed the threshold limit value. The research has provided input data to develop aspiration and dust separation systems for the production of copper powders and alloys.

Investigation of the Sintering of Heterogeneous Powder Systems by Synchrotron Microtomography and Discrete Element Simulation

Collective particle behavior such as interparticle coordination and particle rearrangement plays a significant role in the sintering of heterogeneous powder systems. Those phenomena have been investigated by in situ X‐ray microtomography and discrete element simulation (DEM). In situ 3D images of sintering copper‐based systems have been obtained at the European Synchrotron Research Facilities. The sintered systems comprise a dense packing of atomized copper powder with a size range of 0–63 μm and the same powder including artificial pores. Quantitative analysis of these images provided valuable data on local strain, coordination number, and particle movement. The sintering of the same systems has been simulated with the discrete element code dp3D. From this set of information, the importance of collective behavior on densification and microstructural evolution is assessed and the relevance of DEM to describe it is discussed.

Copper injection molding using a thermoplastic binder based on paraffin wax

In this work the processing steps for producing copper parts by means of metal injection molding technique were investigated. Different feedstocks were prepared from gas atomized copper powder and a thermoplastic binder based on paraffin wax. The optimum formulation of 95 / 5 wt/wt (copper powder / binder) was selected from rheological investigation and then the suitable feedstock was injected successfully at low pressure. The molded specimens were debinded by solvent debinding followed by thermal debinding methods and were sintered under argon atmosphere. It was observed that injection molding of a feedstock containing 66% by volume of copper powder was possible at low pressure and the sintered parts were free from defects and dimensional shrinkage was nearly the same in three dimensions.

Resistance Sintering of Copper-Graphite Powder Mixture under Pressure

Resistance sintering characteristics of electrolytic and atomized copper powders mixed with graphite powder in steps of 10vol% up to 50vol% were experimentally investigated. In the experiments electrifying voltage and time, and applied pressure were varied. Post-electrification pressurization and insertion of low thermal conductive austenitic stainless steel discs between the sintering powder cake and electrodes were attempted to promote the sintering. The effects of the operational parameters including the two devices on sintering performance are discussed. Sintering strength of the resistance-sintered composites is also discussed.

Correlation of the microstructure and mechanical properties of oxide-dispersion-strengthened coppers fabricated by internal oxidation

This study was aimed at the correlation of the microstructure and mechanical properties of oxide-dispersion-strengthened (ODS) coppers fabricated by internal oxidation. Atomized copper powders mixed with Cu2O oxidant powders were internally oxidized and then hot extruded to fabricate ODS coppers without defects. In order to sufficiently oxidize copper powders, oxidant powders should be added in amounts 30 pct in excess of the stoichiometrically calculated amount. In the extruded ODS coppers, very fine Al2O3 dispersoids of 10 nm in diameter were homogeneously distributed inside copper grains of 1 µm in size. The volume fraction of Al2O3 dispersoids increased as the Al content in atomized copper powders increased. With increasing volume fractions of Al2O3 dispersoids, the yield and tensile strengths increased, while the elongation and electrical conductivity decreased, and all the properties of the ODS coppers were sufficiently above the required properties of electrode materials for spot welding. To understand the mechanism responsible for the improvement of the yield strength of the ODS coppers, yield strength was interpreted using the Orowan’s strengthening model, which was fairly consistent with the experimental results.

Sintering of gas and water atomized copper powders : J. Piszcek. (Inst. Metal. Niezelaznych, Gliwice, Poland), Metal. Proszkow, vol 27, no 3/4, 1994, 8–13. (In Polish)

Sintering of gas and water atomized copper powders : J. Piszcek. (Inst. Metal. Niezelaznych, Gliwice, Poland), Metal. Proszkow, vol 27, no 3/4, 1994, 8–13. (In Polish)

Influence of superheat temperature on particle size and shape of gas atomized copper powders: S. Özbilen et al, (Imperial Coll, London, UK Powder Metallurgy, Vol 34, No 1 1991, 53–61

Influence of superheat temperature on particle size and shape of gas atomized copper powders: S. Özbilen et al, (Imperial Coll, London, UK Powder Metallurgy, Vol 34, No 1 1991, 53–61

Influence of alloying on the properties of water atomized copper powders: J.J. Dunkley et al, (Davy McKee (Sheffield) Ltd, Sheffield, UK)

The catalytic properties of Ni-25 at% Al (Ni25Al) nanoparticles fabricated by arc plasma evaporation toward methanol decomposition were studied at temperatures ranging from 513 to 753 K. The Ni25Al nanoparticles showed much higher activity than gas atomized Ni25Al powders. They showed a high degree of selectivity for methanol decomposition into H2 and CO. Side reactions such as methanation and water-gas shift reaction were suppressed to a high temperature of 673 K, which is hardly achieved for common Ni catalysts. Detailed characterization of the Ni25Al nanoparticles showed that they were composed of Ni, Ni3Al, and Al2O3 phases with Ni and Al oxides on the surface of the Ni and Ni3Al phases. The Ni oxides were reduced to Ni phase by a hydrogen reduction prior to methanol decomposition, while the Al oxides remained unchanged. It is supposed that the Ni phase provided the active sites for methanol decomposition, and the Ni3Al and Al2O3 phases acted as supports for the Ni phase. Probably the Ni3Al and Al2O3 phases provided good resistance to agglomeration of the Ni phase during the reaction, which might contribute to maintain the high catalytic performance of the nanoparticles for methanol decomposition.

Production and handling of electrolytic powders

Norddeutsche Affinerie AG (NA) of Hamburg, Germany, one of the world's major copper producers, celebrates its 125th anniversary this year. The company's name is closely connected with the invention of electrolysis. In 1876 the first electrolytic refinery commenced production in Hamburg, and in the 1930s copper powder was added to NA's product family. Today, the company says that it is not only the largest European manufacturer of electrolytic copper powders, but also leads in the production of atomized copper powder and alloy powders. A new production plant for atomized copper powder is currently under construction. The following article deals with the present state of metal powder production by electrolytic methods.

Temperature distribution of bonded tools having atomized copper powder mixed with adhesive

Investigations of heat flow through bonded and brazed tools have shown that heat is not dissipated at the same rate in bonded tools as in brazed tools. Therefore temperature is higher in the bonded tool at the tool tip. In the present work, atomized copper powder was mixed with the adhesive in order to improve the thermal conductivity of bonded tools. The finite element technique has been used to assess the effect of mixing copper powder with adhesive on the temperature distribution of bonded tools when used both dry and with coolant. Here, the combined effect of coolant and copper powder on reducing the temperature of the bond line as well as the carbide tip has been assessed. It was found that the effect of coolant on the temperature distribution of bonded tools is more pronounced than the effect of copper powder mixed with the adhesive. Accordingly cutting fluids should always be used with bonded tools whether or not a metallic powder is mixed with the adhesive.

電解銅圧粉体の異方性膨張に及ぼす加圧・焼結条件の影響

The swelling of cylindrical compacts, 10 mm(d)×10 mm (h) in size, was measured with a micrometer during each production process; after pressing at 2-8 t/cm2 (196-784 MPa), after dewaxing at 500°C (773K) for 30 min, and after sintering at 900°C (1173 K) for 5-180 min.Compacts pressed under higher pressures (588-784 MPa) swelled during sintering, while those pressed under lower pressures (196-392 MPa) shrank. Both the swelling and the shrinkage of compacts pressed with die-wall lubrication and sintered in cracked ammonia gas were larger than those of compacts pressed with powder lubrication or sintered in argon gas. Dimensional change during sintering was larger in swelling or smaller in shrinkage, in the pressing direction than in the lateral direction.The sintering time for the swelling of electrolytic copper powder compacts in argon gas was longer than that of the compacts sintered in cracked ammonia gas or of the compacts made from atomized copper powder.

Application of atomized copper powder in obtaining copper-graphite contacts

The method of decomposing salts makes it possible to obtain materials which, by their tribotechnical and electrocontact properties, are not inferior to the standard materials for electric brushes brands MG, MGSOA. The oriented laminated structure of fine-grained copper in graphite causes the formation of surface layers that are characteristic of normal mechanochemical wear. This improves the wear resistance of the material and stabilizes its electrocontact characteristics.

Manufacture of small bearings from atomized powders

Processes have been developed for the manufacture of atomized copper, tin, and bronze powders suitable for the bearings of the electric motors of domestic air conditioners. A technique has been developed for the production of small instrument journal bearings possessing good operating characteristics.

Atomized copper powders

For the first time in the Soviet Union pilot-plant batches of copper powder have been produced by the method of atomization of melts with water under high pressure. The powder produced is characterized by increased apparent density and flowability. The best compressibility (2–6 tons/cm2) is exhibited by the powder after annealing. The compressibility of the powder in the as-atomized condition is slightly poorer (2–4 tons/ cm2), while that of the powder subjected to pickling amounts to 2–3 tons/cm2. The atomized powder can be successfully used for pressing in automatic presses, since it ensures stability of weights of batches and dimensions of parts and produces very little dust during pressing.