Kwang-Taek Hwang

Decomposition Mechanism of Waste Hard Metals using by ZDP (Zinc Decomposition Process)

Decomposition promoting factors and decomposition mechanism in the zinc decomposition process of waste hard metals which are composed mostly of tungsten carbide and cobalt were evaluated. Zinc volatility amount was suppressed and zinc valatilization pressure was produced in the reaction graphite crucible inside an electric furnace for ZDP. Reaction was done for 2 h at 650℃, which 100 % decomposed the waste hard metals that were over 30 ㎜ thick. As for the separation-decomposition of waste hard metals, zinc melted alloy formed a liquid composed of a mixture of γ-β₁ phase from the cobalt binder layer (reaction interface). The volume of reacted zone was expanded and the waste hard metal layer was decomposed-separated horizontally from the hard metal. Zinc used in the ZDP process was almost completely removed-collected by decantation and volatilization-collection process at 1000℃.

Preparation and characterization of CoAl 2 O 4 blue ceramic nano pigments by attrition milling

Cobalt aluminate () is a highly stable pigment with excellent resistance to light, weather, etc., which has resulted in widespread use as a ceramic pigment. Due to the unique optical characteristics, is generally used as a coloring agent to decorate porcelain products, glass, paints and plastics. Here, pigments were synthesized by polymerized complex method and solid state reaction. Then pigment were grinded using the attrition milling with 1 mm size zirconia ball for 3 hours. The attrition milling process was performed at the constant speed of 800 rpm and ball to powder weight ratio (BPR) was 100 : 1. The characteristics of synthesized pigment were analyzed by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), particle size analyser (PSA) and CIE . The XRD patterns of show single phase spinel structure. The particle size of measured by FE-SEM, TEM and PSA analysis was in the range of 100~200 nm. The blue color of obtained pigments could be confirmed through CIE measurement.

Recovery of Metallurgical Silicon from Slurry Waste

Metallurgical grade silicon was recovered from slurry waste for ingot sawing process by acid leaching and thermal treatment. SiC abrasive was removed by gravity concentration and centrifugation. Metal impurities were removed by the acid leaching using HF/HCl. The remaining SiC was separated by the thermal treatment at 1600℃ in an inert atmosphere by the difference in melting points. The purity of the obtained silicon was found to be around 99.7%.

Synthesis of porous nano-sized AlN by chemical vapor synthesis

We report the synthesis of AlN powders by the chemical vapor synthesis of an AlCl3–NH3–N2–H2 system. The starting material was gasified AlCl3, generated using a preheating system. AlCl3 gas was transported to a tube furnace in NH3–N2–H2 atmosphere. We synthesized highly crystalline AlN at over 900  °C. The average size of the spherical AlN particles decreased from 250 to 40 nm with increasing reaction temperature in the tube furnace. Porous nano-sized particles synthesized at high reaction temperatures have low oxygen contents and high thermal stability.

Synthesis of Nano-size Aluminum Nitride Powders by Chemical Vapor Process

Aluminum nitride (AlN) powders were prepared by the chemical vapor synthesis (CVS) process in the system. Aluminum chloride () as the starting material was gasified in the heating chamber of . Aluminum chloride gas transported to the furnace in atmosphere at the gas flow rate of 200-400ml/min. For samples synthesized between 700 and , the XRD peaks corresponding to AlN were comparatively sharp and also showed an improvement of crystallinity with increasing the reaction temperature. In additions, the average particle size of the AlN powders decreased from 250 to 40 nm, as the reaction temperature increased.

Effect of Bi and Zr addition on yellow colour properties of environment-friendly ceria-based pigments

Inorganic pigments have been received a great attention for various applications including paint, glazed ceramic ink, art tile, and building exterior due to their excellent thermal and chemical stability. Traditionally, the compositions of , CdS and CdSe have been widely used as a yellow inorganic pigment. However, the use of these compositions has been restricted in recent years, because they contain harmful elements such as Cd, Cr, Pb and Se. In this study, new environment-friendly ceria-based pigment was synthesized using solid state reaction. Crystal structure and morphology of the obtained yellow pigment were analyzed using XRD and SEM, respectively. Substitutional effect of Zr and Bi on the pigment color was analyzed using UV-vis. spectrophotometer and CIE analysis. The crystal structure of the obtained pigments was dependent on the calcination temperature. The color characteristics and absorption band of the pigments were dependent on the calcination temperature and Zr, Bi contents. As a result, all the obtained yellow pigments showed the effective absorption ranged from ultraviolet to visible light, and (x

Synthesis of boehmite powder from aluminum etching solution

Boehmite (AlOOH) powder was synthesized using waste aluminium etching solution. In waste solution, precipitated phase was gibbsite (), and boehmite (AlOOH) phase was obtained at pH of 7 and 8 controlled by addition of acid. Boehmite powder was obtained by washing process to remove the Na ion in precipitated solution. Mean particle size of obtained powder was 40 nm. Boehmite phase transformed to phase via , , and .

플라이애시 첨가에 따른 세라믹 벽타일 소지의 물성변화

Recently, there have been many efforts to establish suitable processes for recycling fly ash, which is produced in thermal power plants and which poses serious environmental problems. Use of fly ash as a major ingredient of ceramic tiles can increase fly ash utilization, as well as reduce the cost of raw materials in ceramic tile production. In this study, the effects of fly ash addition on ceramic tile properties such as bending strength, water absorption and porosity were investigated. A manufacturing process of ceramic tile was developed for utilization of fly ash with high carbon content. In this approach, it is important to hold the ceramic tiles at a temperature that is sufficient for carbon oxidation, before the pores supplying oxygen to the inside of the ceramic tile are sealed. Ceramic wall tiles were manufactured with 0-40wt% of fly ash addition. The water absorption and porosity of the fired body were slightly changed with increasing fly ash content up to 30wt% and decreased with greater amounts of fly ash addition. The bending strength of ceramic tile including 10wt% fly ash increased, reaching a level comparable to that of ceramic tile without fly ash.

Sintered body characteristics of LAS by addition of CaCO 3 and ZrO 2 using a solid-state reaction

LAS () ceramics were sintered by a solid-state reaction. and were added to the -spodumene () composition of the LAS system for enhancement of sintering behavior and mechanical strength, respectively. We have investigated the sintering characteristics, microstructures, mechanical properties and thermal expansion characteristics according to the change of the amount of additive and sintering temperature of the -spodumene. At 0.1 mol% , the densification of -spodumene was significantly improved. At 0.04 mol% , the strength of -spodumene was also improved. For all the selected all compositions, the thermal expansion coefficient was measured by a dilatometer, which revealed 1.2 to .

Fabrication and Characterization of Silica Coated Fe 3 O 4 Nanoparticles in Reverse Micro Emulsion

The silica coated Fe3O4 nanoparticles have been synthesized using a micro-emulsion method. The Fe3O4 nanoparticles with the sizes 6 nm in diameter were synthesized by thermal decomposition method. Hydrophobic Fe3O4 nanoparticles were coated silica using surfactant and tetraethyl orthosilicated (TEOS) as a SiO2 precursor. Shell thickness of silica coated Fe3O4 can be controlled (11~20 nm) through our synthetic conditions. The Fe3O4 and silica coated Fe3O4 nano powders were characterized by transmission electron microscopy (TEM), x-ray diffraction (XRD) and vortex magnetic separation (VMS).