Jar-Myung Koo

Effect of Initial Silicon Scrap Size on Powder Refining Process During High Energy Ball Milling (HEBM)

Silfine. Co., LTD, 374-2, Shinsuri, Eumbongmyeon, AsanCity, Chungnam, 336-862, Korea(Received May 7, 2010, Revised May 27, 2010, Accepted June 8, 2010)Abstract In this research, the optimal manufacturing conditions of fine Si powders from Si scrap were inves-tigated as a function of different initial powder size using the high-energy ball milling equipment, which producesthe fine powder by means of an ultra high-energy within a short duration. The morphological change of the pow-ders according to the milling time was observed by Scanning electron microscopy (SEM). With the increasingmilling time, the size of Si powder was decreased. In addition, more energy and stress for milling were requiredwith the decreasing initial powder size. The refinement of Si scrap was rapidly carried out at 10min ball millingtime. However, the refined powder started to agglomerate at 30 min milling time, while the powder size becameuniform at 60 min milling time.Keywords : Microstructure, High energy milling, Si, Silicon scrap, Refinement

The Effect of Milling Conditions for Dissolution Efficiency of Valuable Metals from PDP Waste Panels

In this study, the microstructure and valuable metals dissolution properties of PDP waste panel powders were investigated as a function of milling parameters such as ball diameter size, milling time, and rotational speed during high-energy milling process. The complete refinement of powder could achieved at the ball diameter size of 5 mm due to sufficient impact energy and the number of collisions. With increasing milling time, the average particle size was rapidly decreased until the first 30 seconds, then decreased gradually about at 3 minutes and finally, increased with presence of agglomerated particles of at 5 minutes. Although there was no significant difference on the size of the particle according to the rotational speed from 900 to 1,100 rpm, the total valuable metals dissolution amount was most excellent at 1,100 rpm. As a result, the best milling conditions for maximum dissolving amount of valuable metals (Mg: 375 ppm, Ag 135 ppm, In: 17 ppm) in this research were achieved with 5 mm of ball diameter size, 3min of milling time, and 1,100 rpm of rotational speed.

Synthesis and Characterization of (AgSbTe 2 ) 15 (GeTe) 85 Thermoelectric Powder by Gas Atomization Process

In this study, p-type : TAGS-85 compound powders were prepared by gas atomization process, and then their microstructures and mechanical properties were investigated. The fabricated powders were of spherical shape, had clean surface, and illustrated fine microstructure and homogeneous + GeTe solid solution. Powder X-ray diffraction results revealed that the crystal structure of the TAGS-85 sample was single rhombohedral GeTe phase, which with a space group . The grain size of the powder particles increased while the micro Vickers hardness decreased with increasing annealing temperature within the range of 573 K and 723 K due to grain growth and loss of Te. In addition, the crystal structure of the powder went through a phase transformation from rhombohedral () at low-temperature to cubic () at high-temperature with increasing annealing temperature. The micro Vickers hardness of the as-atomized powder was around 165 Hv, while it decreased gradually to 130 Hv after annealing at 673K, which is still higher than most other fabrication processes.

A Basic Study on the Fabrication of W-M(M

For the purpose of obtaining basic information on the development of lead-free materials, a high density composites (a) W-Cu, (b) W-Sn (c)W-Cu-Sn and (d) W-Cu-Ni were fabricated by the P/M method. The particle size of used metal powders were under 325 mesh, inner size of compaction mould was mm, and compaction pressure was 400 MPa. A High density composite samples were sintered at a temperature between and for 1 hour under Ar atmosphere. The microstructure, phase transformation and physical properties of the sintered samples were investigated. As the results, the highest relative density of 95.86% (10.87 g/) was obtained particularly in the sintered W-Cu-Sn ternary system sample sintered at 450 for 1hr. And, Rockwell hardness (HRB) of 70.0 was obtained in this system.

Analysis of the Aluminum Extrusion Process Equipped with the Continuous Heat Treatment System

In this study, the heat flow of the plant scale aluminum extrusion process was investigated to establish optimum continuous heat treatment conditions. During the extrusion of 6061 aluminum alloy, processing parameters such as the extrusion pressure, speed and temperature histories of billets were logged as a function of time. The surface temperature of the billets increased at constant ram speed, while it decreased with decreases of the ram speed. In order to maintain the billet temperature within a solutionizing temperature range prior to the succeeding water quenching step, the ram speed or the temperature of the blower should be controlled. The temperature histories of the billets during the extrusion and hot air blowing processes were successfully simulated by using the velocity boundary model in ANSYS CFX. The methodology to design an optimum process by using a commercial simulation program is described in this study on the basis of the metallurgical validation results of the microstructural observation of the extrudates. The developed model allowed the advantages of taking into account the motion of the extrudate coupled with the temperature change based on empirical data. Calculations were made for the extrudate passing through the isothermal chamber maintained at appropriate temperature. It was confirmed that the continuous heat treatment system is beneficial to the productivity enhancement of the commercial aluminum extrusion industry.

Densification of TiO 2 Nano Powder by Magnetic Pulsed Compaction

In this research, fine-structure TiO2 bulks were fabricated in a combined application of magnetic pulsed compaction (MPC) and subsequent sintering and their densification behavior was investigated. The obtained density of bulk prepared via the combined processes increased as the MPC pressure increased from 0.3 to 0.7 GPa. Relatively higher density (88%) in the MPCed specimen at 0.7 GPa was attributed to the decrease of the inter-particle distance of the pre-compacted component. High pressure and rapid compaction using magnetic pulsed compaction reduced the shrinkage rate (about 10% in this case) of the sintered bulks compared to general processing (about 20%). The mixing conditions of PVA, water, and nano powder for the compaction of nano powder did not affect the density and shrinkage of the sintered bulks due to the high pressure of the MPC.