Freeze drying of a porous Cu-Sn alloy with unidirectionally aligned pore channels was accomplished by using a composite powder of CuO-SnO2 and camphene. Camphene slurries with CuO-SnO2 content of 3, 5 and 10 vol% were prepared by mixing with a small amount of dispersant at 50˚C. Freezing of a slurry was done at -25˚C while the growth direction of the camphene was unidirectionally controlled. Pores were generated subsequently by sublimation of the camphene during drying in air for 48 h. The green bodies were hydrogen-reduced at 650˚C and then were sintered at 650˚C and 750˚C for 1 h. XRD analysis revealed that the CuO-SnO2 powder was completely converted to Cu-Sn alloy without any reaction phases. The sintered samples showed large pores with an average size of above 100μm which were aligned parallel to the camphene growth direction. Also, the internal walls of the large pores had relatively small pores. The size of the large pores decreased with increasing CuO-SnO2 content due to the change of the degree of powder rearrangement in the slurry. The size of the small pores decreased with increase of the sintering temperature from 650˚C to 750˚C, while that of the large pores was unchanged. These results suggest that a porous alloy body with aligned large pores can be fabricated by a freeze-drying and hydrogen reduction process using oxide powders.

Freeze drying for porous Mo was accomplished by using MoO3 powder as the source and camphor-naph- thalene eutectic system as the sublimable material. Eutectic composition of camphor-naphthalene slurries with the initial MoO3 content of 5 vol%, prepared by milling at 55o C with a small amount of oligomeric dispersant, was frozen at -25o C. The addition of dispersant showed improvement of dispersion stability in slurries. Pores were generated subse- quently by sublimation of the camphor-naphthalene during drying in air for 48 h. To convert the MoO3 to metallic Mo, the green body was hydrogen-reduced at 750o C, and sintered at 1100o C for 2 h. The sintered samples, frozen by heated Teflon cylinder, showed large pores with the size of about 40 µm which were aligned parallel to the sublimable vehicles growth direction. The formation of unidirectionally aligned pores is explained by the rejection and accumulation of solid particles in the serrated solid-liquid interface.

Porous Ti-systems with unidirectionally aligned channels were synthesized by freeze-drying and a heat treatment process. TiH2 powder and camphene were used as the source materials of Ti and sublimable vehicles, respectively. Camphene slurries with TiH2 content of 10 and 15 vol% were prepared by milling at 50˚C with a small amount of oligomeric polyester dispersant. Freezing of the slurry was done in a Teflon cylinder attached to a copper bottom plate cooled at -25˚C while unidirectionally controlling the growth direction of the camphene. Pores were generated subsequently by sublimation of the camphene during drying in air for 48 h. The green body was heat-treated at 1100˚C for 1 h in a nitrogen and air atmosphere. XRD analysis revealed that the samples composed of TiN and TiO2 phase were dependent on the heat-treatment atmosphere. The sintered samples showed large pores of about 120 mm which were aligned parallel to the camphene growth direction. The internal wall of the large pores had relatively small pores with a dendritic structure due to the growth of camphene dendrite depending on the degree of nucleation and powder rearrangement in the slurry. These results suggest that a porous body with an appropriate microstructure can be successfully fabricated by freeze-drying and a controlled sintering process of a camphene/TiH2 slurry.

In the DBC (direct bonding of copper) process the oxygen partial pressure surrounding the AlN/Cu bonding pairs has been controlled by Ar gas mixed with oxygen. However, the direct bonding of Cu with sound interface and good adhesion strength is complicated process due to the difficulty in the exact control of oxygen partial pressure by using Ar gas. In this study, we have utilized the in-situ equilibrium established during the reaction of + 1/2 by placing powder bed of CuO or around the Cu/AlN bonding pair at . The adhesion strength was relatively better in case of using CuO powder than when powder was used. Microstructural analysis by optical microscopy and XRD revealed that the interface of bonding pair was composed of , Cu and small amount of CuO phase. Thus, it is explained that the good adhesion between Cu and AlN is attributed to the wetting of eutectic liquid formed by reaction of Cu and .

In order to fabricate the porous Mo with controlled pore characteristics, unique processing by using powder as the source and camphene as the sublimable material is introduced. Camphene-based 15 vol% slurries, prepared by milling at with a small amount of dispersant, were frozen at . Pores were generated subsequently by sublimation of the camphene during drying in air for 48 h. The green body was hydrogen-reduced at , and sintered at for 1 h. After heat treatment in hydrogen atmosphere, powders were completely converted to metallic W without any reaction phases. The sintered samples showed large pores with the size of about which were aligned parallel to the camphene growth direction. Also, the internal wall of large pores and near bottom part of specimen had relatively small pores due to the difference in the camphene growth rate during freezing process. The size of small pores was decreased with increase in sintering temperature, while that of large pores was unchanged. The results are strongly suggested that the porous metal with required pore characteristics can be successfully fabricated by freeze-drying process using metal oxide powders.

Dependence of the freeze-drying process condition on microstructure of porous W and pore formation mechanism were studied. Camphene slurries with contents of 10 vol% were prepared by milling at with a small amount of dispersant. Freezing of a slurry was done in Teflon cylinder attached to a copper bottom plate cooled at . Pores were generated subsequently by sublimation of the camphene during drying in air for 48 h. The green body was hydrogen-reduced at for 30 min, and sintered in the furnace at for 1 h. After heat treatment in hydrogen atmosphere, powders were completely converted to metallic W without any reaction phases. The sintered samples showed large pores with the size of about which were aligned parallel to the camphene growth direction. Also, the internal wall of large pores and near bottom part of specimen had relatively small pores with dendritic structure due to the growth of camphene dendrite depending on the degree of nucleation and powder rearrangement in the slurry.

An attempt was made to evaluate creep reliability of two commercial Ni-based superalloys by using ultrasonic wave. The materials include fine-grained PM alloy fabricated by mechanical alloying and subsequent hot isostatic pressing, and IN738LC cast alloy with a grain size of a few cm. Microstructural parameters (fraction of creep cavity and size of precipitates) and ultrasonic parameters (velocity, attenuation) were measured to try to find relationships between them. Ultrasonic velocity decreased with creep cavity formation in PM alloy. On the other hand, no distinct changing trend of ultrasonic velocity was observed for IN738LC alloy. Ultrasonic attenuation was found to have a linear correlation with the size of precipitates and was suggested as a potential parameter for monitoring creep reliability of IN738LC alloy.

Porous W with controlled pore characteristics was fabricated by a freeze-drying process. WO3 powder and camphene were used as the source materials of W and sublimable vehicles, respectively. Camphene slurries with WO3 contents of 10 and 15 vol% were prepared by milling at 50˚C with a small amount of oligomeric polyester dispersant. Freezing of a slurry was done in a Teflon cylinder attached to a copper bottom plate cooled at -25˚C while the growth direction of the camphene was unidirectionally controlled. Pores were generated subsequently by sublimation of the camphene during drying in air for 48 h. The green body was hydrogen-reduced at 800˚C for 30 min and sintered in a furnace at 900˚C for 1 h under a hydrogen atmosphere. Microstructural observation revealed that all of the sintered samples were composed of only W phase and showed large pores which were aligned parallel to the camphene growth direction. The porosity and pore size increased with increasing camphene content. The difference in the pore characteristics depending on the slurry concentration may be explained by the degree of powder rearrangement in the slurry. The results strongly suggest that a porous metal with the required pore characteristics can be successfully fabricated by a freeze-drying process using metal oxide powders.

In order to fabricate the porous metal with controlled pore characteristics, unique processing by using metal oxide powder as the source and camphene as the sublimable material is introduced. CuO powder was selected as the source for the formation of Cu metal via hydrogen reduction. Camphene-based CuO slurry, prepared by milling at with a small amount of dispersant, was frozen at . Pores were generated subsequently by sublimation of the camphene. The green body was hydrogen-reduced at for 30 min, and sintered at for 1 h. Microstructural analysis revealed that the sintered Cu showed aligned large pore channels parallel to the camphene growth direction, and fine pores are formed around the large pore. Also, it showed that the pore size was controllable by the slurry concentration.

The optimum route to fabricate nano-sized Fe-50 wt% Co and hydrogen-reduction behavior of calcined Fe-/Conitrate was investigated. The powder mixture of metal oxides was prepared by solution mixing and calcination of Fe-/Co-nitrate. A DTA-TG and microstructural analysis revealed that the nitrates mixture by the calcination at 300˚C for 2 h was changed to Fe-oxide/Co3O4 composite powders with an average particle size of 100 nm. The reduction behavior of the calcined powders was analyzed by DTA-TG in a hydrogen atmosphere. The composite powders of Fe-oxide and Co3O4 changed to a Fe-Co phase with an average particle size of 40 nm in the temperature range of 260-420˚C. In the TG analysis, a two-step reduction process relating to the presence of Fe3O4 and a CoO phase as the intermediate phase was observed. The hydrogen-reduction kinetics of the Fe-oxide/Co3O4 composite powders was evaluated by the amount of peak shift with heating rates in TG. The activation energies for the reduction, estimated by the slope of the Kissinger plot, were 96 kJ/mol in the peak temperature range of 231-297˚C and 83 kJ/mol of 290-390˚C, respectively. The reported activation energy of 70.4-94.4 kJ/mol for the reduction of Fe- and Co-oxides is in reasonable agreement with the measured value in this study.

The pressureless sintering behavior of /Cu powder mixtures, prepared from /CuO and /Cu-nitrate, has been investigated. Microstructural observation revealed that powders with nano-sized Cu particles could be synthesized by hydrogen reduction method. The specimens, pressureless-sintered at for 4 min using infrared heating furnace with the heating rate of /min, showed the relative density of above 90%. Maximum hardness of 16.1 GPa was obtained in /MgO/Cu nanocomposites. The nanocomposites exhibited the enhanced fracture toughness of 4.3-5.7 , compared with monolithic . The mechanical properties were discussed in terms of microstructural characteristics

The calcination and hydrogen-reduction behavior of Fe- and Ni-nitrate have been investigated. /NiO composite powders were prepared by chemical solution mixing of Fe- and Ni-nitrate and calcination at for 2 h. The calcined powders were hydrogen-reduced at for 30 min. The calcination and hydrogen-reduction behavior of Fe- and Ni-nitrate were analyzed by TG in air and hydrogen atmosphere, respectively. TG and XRD analysis for hydrogen-reduced powders revealed that the /NiO phase transformed to phase at the temperature of . The activation energy for the hydrogen reduction, evaluated by Kissinger method, was measured as 83.0 kJ/mol.

Through the electrostatic interaction between the poly-diallydimethylammonium chloride (PDDA) modified Multi-walled carbon nanotube (MWNT) and SnO2 suspension in 1mM NaNo3 solution, MWNT-SnO2 nanocomposites (MSC) for anode electrodes of a Li-ion battery were successfully fabricated by colloidal heterocoagulation method. TEM observation showed that most of the SnO2 nanoparticles were uniformly deposited on the outside surface of the MWNT. Galvanostatic charge/discharge cycling tests showed that MSC anodes exhibited higher specific capacities than bare MWNT and better cyclability than unsupported nano-SnO2 anodes. Also, after 20 cycles, the MSC anode fabricated by heterocoagulation method showed more stable cycle properties than the simply mixed MSC anode. These improved electrochemical properties are attributed to the MWNT, which adsorbs the mechanical stress induced from volume change and increasing electrical conductivity of the MSC anode, and suppresses the aggregation between the SnO2 nanoparticles.

Multi-walled carbon nanotube (MWNT)/SnO2 nano-composite (MSC) for the anode electrode of a Li-ion battery was prepared using a homogeneous precipitation method with SnCl2 precursors in the presence of MWNT. XRD results indicate that when annealed in Ar at 400˚C, Sn6O4(OH)4 was fully converted to SnO2 phases. TEM observations showed that most of the SnO2 nanoparticles were deposited directly on the outside surface of the MWNT. The electrochemical performance of the MSC electrode showed higher specific capacities than a MWNT and better cycleability than a nano-SnO2 electrode. The electrochemical performance of the MSC electrode improved because the MWNT in the MSC electrode absorbed the mechanical stress induced from a volume change during alloying and de-alloying reactions with lithium, leading to an increase in the electrical conductivity of the composite material.

The sintering behavior and mechanical property of Mo nanopowder was investigated as a function of various sintering condition. Mo oxide nanopowders were milled using a high energy ball-milling process. After the ball milling for 20h, the crystalline size of was about 20 nm. The nanopowders were reduced at the temperature of without holding time in atmosphere. The sinterability of Mo nanopowder and commercial Mo powder was investigated by dilatometric analysis. Mo nanopowder and commercial Mo powder were sintered at for 1 hand for 3 h, respectively. In both specimens the measured relative density was about 95%. But the measured hardness values were 2.34 GPa for nanopowder and 1.87 GPa for commercial powder. Probably due to finer grain size of the sintered body prepared from Mo nanopowder than that prepared using commercial Mo powder. The mean grain sizes were measured to be about 1.4 mm and 6.2 mm, respectively.

Oxidation behavior and microstructural characteristics of nano-sized Sn powder were studied. DTA-TG analysis showed that the Sn powder exhibited an endothermic peak at and exothermic peak at with an increase in weight. Based on the phase diagram consideration of Sn-O system and XRD analysis, it was interpreted that the first peak was for the melting of Sn powder and the second peak resulted from the formation of phase. Microstructural observation revealed that the powder, heated to under air atmosphere, consisted of agglomerates with large particle size due to the melting of Sn powder during heat treatment. Finally, fine SnO2 powders with an average size of 50nm can be fabricated by controlled heat treatment and ultrasonic milling process

The microstructure and mechanical properties of hot-pressed composites with a different sintering temperature have been studied. The size of matrix grain and Cu dispersion in composites increased with increase in sintering temperature. Fracture toughness of the composite sintered at high temperature exhibited an enhanced value. The toughness increase was explained by the thermal residual stress, crack bridging and crack branching by the formation of microcrack. The nanocomposite, hot-pressed at , showed the maximum fracture strength of 707 MPa. The strengthening was mainly attributed to the refinement of matrix grains and the increased toughness.