• Journal of Powder Materials
• /
• v.24 no.5
• /
• pp.406-413
• /
• 2017

A Nanosized $WO_3$ and CuO powder mixture is prepared using novel high-energy ball milling in a bead mill to obtain a W-Cu nanocomposite powder, and the effect of milling time on the structural characteristics of $WO_3-CuO$ powder mixtures is investigated. The results show that the ball-milled $WO_3-CuO$ powder mixture reaches at steady state after 10 h milling, characterized by the uniform and narrow particle size distribution with primary crystalline sizes below 50 nm, a specific surface area of $37m^2/g$, and powder mean particle size ($D_{50}$) of $0.57{\mu}m$. The $WO_3-CuO$ powder mixtures milled for 10 h are heat-treated at different temperatures in $H_2$ atmosphere to produce W-Cu powder. The XRD results shows that both the $WO_3$ and CuO phases can be reduced to W and Cu phases at temperatures over $700^{\circ}C$. The reduced W-Cu nanocomposite powder exhibits excellent sinterability, and the ultrafine W-Cu composite can be obtained by the Cu liquid phase sintering process.

• Journal of Powder Materials
• /
• v.7 no.4
• /
• pp.228-236
• /
• 2000

An investigation was carried out on the possibility whether the ball-milling process of low energy could successfully improve the packing density and flowability for MIM application in W-20wt%Cu system. In this study, W-20wt%Cu powder mixture was prepared by ball-milling. W powder was not fractured by low mechanical impact energy used in the present work during the critical ball-milling time, but the ductile Cu powder was easily deformed to the 3 dimensional equiaxed shape, having the particle size similar to that of W powder. The ball-milled mixture of W-20wt%Cu powder had the more homogeneous distribution of each component and the higher amount of powder loading for molding than the simple mixture of W-Cu powder with an irregular shape and a different size. Accordingly, the MIM W(1.75)-20wt%Cu powder compacts were able to be sintered to the relative density of 99% by sintering at $1400^{\circ}C$ for one hour.

• Proceedings of the Korean Powder Metallurgy Institute Conference
• /
• 2006.09b
• /
• pp.948-949
• /
• 2006

An infiltration technique using W-Cu composite powder has been developed to enhance microstructural uniformity of W-Cu pseudo-alloy. W-Cu composite powder, manufactured by reduction from $WO_3$ and CuO powder mixtures, were blended with W powder and then cold iso-statically pressed into a cylindrical bar under 150 MPa. The pressed samples were pre-sintered at $1300^{\circ}C$ for 1 hour under hydrogen to make a skeleton structure. This skeleton structure was more homogeneous than that formed by using W and Cu powder mixtures. The skeleton structures were infiltrated with Cu under hydrogen atmosphere. The infiltrated W-Cu pseudo-alloy showed homogeneous microstructure without Cu rich region

• Journal of Powder Materials
• /
• v.25 no.4
• /
• pp.322-326
• /
• 2018

The hydrogen reduction behavior of $MoO_3-CuO$ powder mixture for the synthesis of homogeneous Mo-20 wt% Cu composite powder is investigated. The reduction behavior of ball-milled powder mixture is analyzed by XRD and temperature programmed reduction method at various heating rates in Ar-10% $H_2$ atmosphere. The XRD analysis of the heat-treated powder at $300^{\circ}C$ shows Cu, $MoO_3$, and $Cu_2MoO_5$ phases. In contrast, the powder mixture heated at $400^{\circ}C$ is composed of Cu and $MoO_2$ phases. The hydrogen reduction kinetic is evaluated by the amount of peak shift with heating rates. The activation energies for the reduction, estimated by the slope of the Kissinger plot, are measured as 112.2 kJ/mol and 65.2 kJ/mol, depending on the reduction steps from CuO to Cu and from $MoO_3$ to $MoO_2$, respectively. The measured activation energy for the reduction of $MoO_3$ is explained by the effect of pre-reduced Cu particles. The powder mixture, hydrogen-reduced at $700^{\circ}C$, shows the dispersion of nano-sized Cu agglomerates on the surface of Mo powders.

• Journal of the Korean institute of surface engineering
• /
• v.36 no.2
• /
• pp.194-199
• /
• 2003

Polarization measurements were peformed to investigate the electrochemical behavior of copper ions and limiting current density in waste rinse water from copper electroplating processes. A newly designed cyclone type electrolyzer was tested to recover the copper powder. Synthetic solutions were prepared using analytical grade $CuSO_4$ to the desired waste water concentration and pH was adjusted with $H_2$$SO_4$. Electrowinning was peformed at room temperature and the solution was cycled with a pump. Results showed that more than 99 percent of Cu was recovered and the size of the recovered Cu powder ranges from 0.1 - $0.5\mu\textrm{m}$. The chemical composition of the Cu powder mainly consists of $Cu_2$O and Cu and can be easily reduced to pure Cu powder.

• Journal of Powder Materials
• /
• v.9 no.4
• /
• pp.235-244
• /
• 2002

The effects of residual impurities on solid state sintering of the powder injection molded (PIMed) W-15wt%Cu nanocomposite powder were investigated. The W-Cu nanocomposite powder was produced by the mech-ano-chemical process consisting of high energy ball-milling and hydrogen reduction of W blue powder-cuO mixture. Solid state sintering of the powder compacts was conducted at $1050^{\circ}C$ for 2~10 h in hydrogen atmosphere. The den-sification of PIM specimen was slightly larger than that of PM(conventional PM specimen), being due to fast coalescence of aggregate in the PIM. The only difference between PIM and PM specimens was the amount of residual impurities. The carbon as a strong reduction agent effectively reduced residual W oxide in the PIM specimen. The $H_2O$ formed by $H_2$ reduction of oxide disintegrated W-Cu aggregates during removal process, on the contrary to this, micropore volume rapidly decreased due to coalescence of the disintegrated W-Cu aggregates during evolution of CO.It can be concluded that the higher densification was due to the earlier occurred Cu phase spreading that was induced by effective removal of residual oxides by carbon.

• Korean Journal of Materials Research
• /
• v.30 no.3
• /
• pp.149-154
• /
• 2020

A powder-in-sheath rolling method is applied to the fabrication of a carbon nano tube (CNT) reinforced copper composite. A copper tube with outer diameter of 30 mm and wall thickness of 2 mm is used as sheath material. A mixture of pure copper powder and CNTs with a volume content of 3 % is filled in a tube by tap filling and then processed to an 93.3 % reduction using multi-pass rolling after heating for 0.5 h at 400 ℃. The specimen is then sintered for 1h at 500 ℃. The relative density of the 3 vol%CNT/Cu composite fabricated using powder in sheath rolling is 98 %, while that of the Cu powder compact is 99 %. The microstructure is somewhat heterogeneous in width direction in the composite, but is relatively homogeneous in the Cu powder compact. The hardness distribution is also ununiform in the width direction for the composite. The average hardness of the composites is higher by 8Hv than that of Cu powder compact. The tensile strength of the composite is 280 MPa, which is 20 MPa higher than that of the Cu powder compact. It is concluded that the powder in sheath rolling method is an effective process for fabrication of sound CNT reinforced Cu matrix composites.

• Journal of Powder Materials
• /
• v.21 no.3
• /
• pp.191-195
• /
• 2014

This study reports a simple way of fabricating the porous Cu with unidirectional pore channels by freeze drying camphene slurry with Cu oxide coated Cu powders. The coated powders were prepared by calcination of ball-milled powder mixture of Cu and Cu-nitrate. Improved dispersion stability of camphene slurry could be achieved using the Cu oxide coated Cu powders instead of pure Cu powders. Pores in the frozen specimen at $-25^{\circ}C$ were generated by sublimation of the camphene during drying in air, and the green bodies were sintered at $750^{\circ}C$ for 1 h in $H_2$ atmosphere. XRD analysis revealed that the coated layer of Cu oxide was completely converted to Cu phase without any reaction phases by hydrogen heat treatment. The porous Cu specimen prepared from pure Cu powders showed partly large pores with unidirectional pore channels, but most of pores were randomly distributed. In contrast, large and aligned parallel pores to the camphene growth direction were clearly observed in the sample using Cu oxide coated Cu powders. Pore formation behavior depending on the initial powders was discussed based on the degree of powder rearrangement and dispersion stability in slurry.

• Journal of Powder Materials
• /
• v.5 no.4
• /
• pp.258-264
• /
• 1998

The initial sintering behaviour of the powder injection molded (PIMed) W-l5wt%Cu nanocomposite powder was investigated. The W-Cu nanocomposite powder was produced by the mechanochemical process consisting of high energy ball-milling and hydrogen reduction of W blue powder-CuO mixture. Solid state sintering of the powder compacts was conducted at $1050^{\circ}C$ for 2~10 hours in hydrogen at mosphere. The sintering behaviour was examined and discussed in terms of microstructural developments such as W-Cu aggregate formation, pore size distribution and W grain growth. The volume shrinkage of PIM specimen was slightly larger than that of PM(conventional PM specimen), being due to fast local densification in the PIM. Remarkable decrease of carbon and oxygen in the PIM enhanced local densification in the early stage of solid state sintering process with eliminating very fine pores less than 10 nm. In addition, such local densiflcation in the PIM is presumably responsible for mitigating of W-grain growth in the initial stage.

• Journal of Powder Materials
• /
• v.5 no.3
• /
• pp.220-226
• /
• 1998

W-12.8wt%Cu-7.2%Pb powders were milled at room temperature and $-100^{\circ}C$ to investigate the mechanical alloying behavior of immiscible W-Cu-Pb system and the effect of milling temperature on the extent of alloying and microstructural refinement. W-Cu-Pb powder reached steady state after further extended milling due to Pb addition, compared to the W-Cu system. The cryomilling at $-100^{\circ}C$ caused the more refinement of powder particle size, and enhanced the solubility of Cu or Pb in W, compared with milling at room temperature. In W-12.8wt%Cu-7.2%Pb powder cryomilled at $-100^{\circ}C$, the monotectic temperature of Cu-Pb as well as the melting temperature of Cu was decreased by refinement of Cu crystalline size, and the most amorphization was occurred after milling for 150 h.