In the current study, the effects of particle size on compaction behavior of water-atomized pure iron powders are investigated. The iron powders are assorted into three groups depending on the particle size; 20-45 , 75-106 , and 150-180 for the compaction experiments. The powder compaction procedures are processed with pressure of 200, 400, 600, and 800 MPa in a cylindrical die. After the compaction stage, the group having 150-180 of particle size distribution shows the best densification behavior and reaches the highest green density. The reason for these results can be explained by the largest average grain size in the largest particle group, due to the low plastic deformation resistance in large grain sized materials.
W-ZrC and W-HfC composite powders were fabricated by the Plasma Alloying & Spheroidization (PAS) method and the powders were sprayed into hybrid coating layers by using Low Vacuum Plasma Spray (LVPS) process, respectively. Microstructure, mechanical properties, and ablation characteristics of the fabricated coating layers were investigated. The LVPS process led to successful production of W-Carbide hybrid coatings, approximately 400 or above in thickness. As the substrate preheating temperature increased from to , the hardness of the W-ZrC coating layer increased due to decreased porosity. Vickers hardness showed higher value (about 108.4 HV) in W-ZrC hybrid coating material compared to that of W-HfC while adhesive strength was found to be similar in both coating layers. The plasma torch test revealed good ablation resistance of the W-Carbide hybrid coating layers. The relatively high performance W-ZrC coating layer at the elevated temperature is thought to be attributed to both the strengthening effect of ZrC particle remained in the layer and the formation of ZrO2 phase with high temperature stability.
Al/AlN composites were synthesized by mechanical alloying using process control agents(PCAs). Three different PCAs which contain N element, were examined to see the effectiveness of ball-milling and the nitridation during sintering. Among examined PCAs, was the most effective to facilitate ball-milling and to form nitrides during a subsequent sintering. By a proper control of ball-milling and sintering, we could obtained surface-hardened Al-based composites.
Spherical nanosized cobalt powder with an average size of 150-400 nm was successfully prepared at room temperature from cobalt sulfate heptahydrate (). Wet chemical reduction method was adopted to synthesize nano cobalt powder and hypophosphorous acid () was used as reduction agent. Both the HCP and the FCC Co phase were developed while concentration ranged from 0.7 M to 1.1 M. Secondary phase such as and were also observed. Peaks for the crystalline Co phase having HCP and FCC structure crystallized as increasing the concentration of , indicating that the amount of reduction agent was enough to reduce . Consequently, a homogeneous Co phase could be developed without second phase when the ratio exceeded 7.
The potential application of ultrafine cerium oxide (ceria, ) as an oxygen gas sensor has been investigated. Ceria was synthesized by a thermochemical process: first, a precursor powder was prepared by spray drying cerium-nitrate solution. Heat treatment in air was then performed to evaporate the volatile components in the precursor, thereby forming nanostructured having a size of approximately 20 nm and specific surface area of 100 . After sintering with loosely compacted samples, hydrogen-reduction heat treatment was performed at 773K to increase the degree of non-stoichiometry, x, in . In this manner, the electrical conductivity and oxygen-response ability could be enhanced by increasing the number of oxygen vacancies. After the hydrogen reduction at 773K, was obtained with nearly the same initial crystalline size and surface. The response time measured at room temperature was extremely short at 4 s as compared to 14 s for normally sintered . We believe that this hydrogen-reduced ceria can perform capably as a high-performance oxygen sensor with good response abilities even at room temperature.
In order to make a (CZTSe) sputtering target sintered for solar cell application, synthesis of CZTSe compound by solid state reaction of Cu, Zn, Sn and Se mixed powders and effects of ball milling condition on sinterability such as ball size, combination of ball size, ball milling time and sintering temperature, was investigated. As a result of this research, sintering at after ball milling using mixed balls of 1 mm and 3 mm for 72 hours was the optimum condition to synthesis near stoichiometric composition of and to prepare sintered pellet with high density relatively.
In order to investigate the microstructure and mechanical properties of WC-10 wt% Co insert tool alloy fabricated by PIM (Powder Injection Molding) process, the feedstock of WC-10 wt% and wax used as a kind of binder were mixed together by two blade mixer. After injection molding, the debinding process was carried out by two-steps. First, solvent extraction, in which the binder was eliminated by putting the specimen into normal hexane for 24 hrs at , and subsequently thermal debinding which was conducted at and for 6 hrs in the mixed gas of , respectively. Meantime, in order to compensate the decarburization due to hydrogen, 1.2~1.8% of carbon was added to ensure the integrity of the phase. Finally, the specimens were sintered in vacuum under different temperatures, and the relative density of 99.8% and hardness of 2100 Hv can be achieved when sintered at , even the TRS is lower than the conventional sintering process.
The synthesis behavior of nanoporous silica aerogel in the macroporous ceramic structure was observed using TEOS as a source material and glycerol as a dry control chemical additive (DCCA). Silica aerogel in the macroporous ceramic structure was synthesized via sono-gel process using hexamethyldiazane (HMDS) as a modification agent and n-hexane as a main solvent. The wet gel with a modified surface was dried at under ambient pressure. The addition of glycerol appears to give the wet gel a more homogeneous microstructure. However, glycerol also retarded the rate of surface modification and solvent exchange. Silica aerogel completely filled the macroporous ceramic structure without defect in the condition of surface modification (20% HMDS/nhexane at 36hr).
[ ] a cathode material for lithium rechargeable batteries, was prepared using recycled . First, the cobalt hydroxide powders were separated from waste WC-Co hard metal with acid-base chemical treatment, and then the impurities were eliminated by centrifuge method. Subsequently, powders were prepared by thermal treatment of resulting . By adding a certain amount of and , the was obtained by sintering for 10 h in air at . The synthesized particles were characterized by X-ray diffraction (XRD) and Scanning Electron Microscope (SEM) analysis.
Magnesium hydroxide sulfate hydrate whiskers (, abbreviated 513 MHSH) were prepared using hydrothermal reaction with magnesium oxide (MgO) and magnesium sulfate () as the starting materials. The effects of the molar ratio of /MgO and amount of were studied. As a result, 513 MHSH whiskers co-existed with hexagonal plate at low concentration of . The molar ratio of /MgO was 7:1, uniform 513 MHSH whiskers were formed without impurity such as . Appropriate amount of has affected to formation of high quality MHSH. Their morphologies and structures were determined by powder X-ray diffraction (XRD) scanning electron microscopy (SEM) and thermo-gravimetric analyzer (TGA).
Titanium carbonitride is more perspective materials compared to titanium carbide. It can be used in tool industry and special products because of its higher strength, abrasive wear-resistance and especially its strong chemical stability at high temperatures. We produced STS+TiCxNy composite by the spark plasma sintering for higher strength and studied the characteristics. The planar and cross-sectional microstructures of the specimens were observed by scanning electron microscopy. Characterizations of the carbon and nitride phases on the surface of composite were carried out using an X-ray diffractometer. During annealing TiCxNy particles diffusion into STS 430 was observed. After annealing, sintering isolations between particles were formed. It causes decreasing of mechanical strength. In addition when annealing temperature was increased hardness increased. Heterogeneous distribution of alloying elements particles was observed. After annealing composites, highest value of hardness was 738.1 MHV.
Colloidal stability is one of crucial factors for many applications of nanodiamond. Despite recent development, nanodiamonds available on the market often exhibit a high impurity content, wide size distribution of aggregates and low resistance to sedimentation. In the current study, four commercial nanodiamond powders synthesized by detonation synthesis were surface modified and then separated with respect to the size into six fractions by centrifugation. The fractions were evaluated by zeta potential, particle size distribution and elemental composition. The results showed that the modified nanodiamonds form stable colloidal suspensions without sedimentation for a long time.