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Kim J.,Chungnam National University | Nersisyan H.,Rapidly Solidified Materials Research Center | Won C.,Chungnam National University
Korean Journal of Materials Research | Year: 2014

Zirconium boride is an artificial or which is rarely found in the nature. ZrB2 is popular in the hard material industry because it has a high melting point, excellent mechanical properties and chemical stability. There are two known methods to synthesize ZrB2. The first involves direct reaction between Zr and B, and the second is by reduction of the metal halogen. However, these two methods are known to be unsuitable for mass production. SHS(Self-propagating High-temperature Synthesis) is an efficient and economic method for synthesizing hard materials because it uses exothermic reactions. In this study, ZrB2 was successfully synthesized by subjecting ZrO2, Mg and B2O3 to SHS. Because of the high combustion temperature and rapid combustion, in conjunction with the stoichiometric ratio of ZrO2, Mg and B2O3; single phase ZrB2 was not synthesized. In order to solve the temperature problem, Mg and NaCl additives were investigated as diluents. From the experiments it was found that both diluents effectively stabilized the reaction and combustion regime. The final product, made under optimum conditions, was single-phase ZrB2 of 0.1-0.9 μm particle size. © Materials Research Society of Korea.


Choi S.-H.,Chungnam National University | Nersisyan H.,Rapidly Solidified Materials Research Center | Won C.,Chungnam National University
Korean Journal of Materials Research | Year: 2014

Due to their unique properties, tungsten borides are good candidates for the industrial applications where certain features such as high hardness, chemical inertness, resistance to high temperatures, thermal shock and corrosion. In this study, conditions were investigated for producing tungsten boride powder from tungsten oxide(WO3) by self-propagating hightemperature synthesis (SHS) followed by HCl leaching techniques. In the first stage of the study, the exothermicity of the WO3- Mg reaction was investigated by computer simulation. Based on the simulation experimental study was conducted and the SHS products consisting of borides and other compounds were obtained starting with different initial molar ratios of WO3, Mg and B2O3. It was found that WO3, Mg and B2O3 reaction system produced high combustion temperature and radical reaction so that diffusion between W and B was not properly occurred. Addition of NaCl and replacement of B2O3 with B successfully solved the diffusion problem. From the optimum condition tungsten boride(W2B and WB) powders which has 0.1~0.9 um particle size were synthesized. © Materials Research Society of Korea.


Kim S.J.,Chungnam National University | Won H.I.,Rapidly Solidified Materials Research Center | Won C.W.,Chungnam National University | Nersisyan H.,Rapidly Solidified Materials Research Center
Journal of the Korean Ceramic Society | Year: 2011

A red strontium aluminate phosphor (Sr 3Al 2O 6:Eu 3+, Eu 2+) is synthesized using a solid state reaction method in air and reducing atmosphere. The investigation of firing temperature indicates that a single phase of Sr 3Al 2O 6 is formed when the firing temperature is higher than 1300°C. The effect of firing temperature and doping concentration on luminescent properties are investigated. Sr 3Al 2O 6 phosphor exhibits the typical red luminescent properties of Eu 3+, Eu 2+.


Lee T.-H.,Chungnam National University | Joo S.-H.,Chungnam National University | Nersisyan H.H.,Chungnam National University | Nersisyan H.H.,Rapidly solidified Materials Research Center | And 5 more authors.
KONA Powder and Particle Journal | Year: 2016

A pyrometallurgical reduction process for the recovery of copper and zinc from brass secondary slag (BSS) was studied. Specifically, the effect of reduction temperature and time on the conversion to metallic phases was investigated. The brass secondary slag was characterized by X-ray diffraction, inductively coupled plasma-atomic emission spectrometry, automatic elemental analysis, thermogravimetric analysis, and field emission scanning electron microscopy. A two-step reduction of BSS was identified. The step 1 comprised the reduction of ZnO, while the step 2 featured the reduction of Zn0-Al203. Furthermore, the application of a first-order reaction model with Arrhenius analysis, indicated a conversion of ZnO to Zn(g) that had a rate constant increasing from 1.4 ±0.13 x 10-3s-1 at 900 °C to 2.18 ±0.15 x 10-2>s-1 at 1050 °C. This reaction had an activation energy of 233.2 ± 26.1 kJ/mol. Secondly, the conversion of Zn0-Al203 to Zn(g) and A1203 increased from 1.54 ± 0.21 x 10-5s-1 at 900 °C to 1.09 ±0.19 x 10-3s-1 at 1050 °C, and the activation energy was 376.7 ±22.4 kJ/mol. This reaction mechanism and its associated kinetic data can be applied to optimize the operation conditions of recycling processes for Cu-containing wastes. © 2016 Hosokawa Powder Technology Foundation.


Yoo H.H.,Chungnam National University | Nersisyan H.,Rapidly Solidified Materials Research Center | Won H.I.,Rapidly Solidified Materials Research Center | Won C.W.,Chungnam National University
Korean Journal of Materials Research | Year: 2011

Zn 2(1-x)Mn xSiO 4(0.07 ≤ × ≤ 0.15) green phosphor was prepared by solid state reaction. The first heating was at 900°C-1250°C in air for 3 hours and the second heating was at 900°C in N 2/H 2(95%/5%) for 2 hours. The size effect of SiO 2 in forming Zn 2SiO 4 was investigated. The temperature for obtaining single phase Zn 2SiO 4 was lowered from 1100°C to 1000°C by decreasing the SiO 2 particle size from micro size to submicro size. The effect of the activators for the Photoluminescence (PL) intensity of Zn 2SiO 4:Mn 2+ was also investigated. The PL intensity properties of the phosphors were investigated under vacuum ultraviolet excitation (147 nm). The emission spectrum peak was between 520 nm and 530 nm, which was involved in green emission area. MnCl 2·4H 2O, the activator source, was more effective in providing high emission intensity than MnCO 3. The optimum conditions for the best optical properties of Zn 2SiO 4:Mn 2+ were at x = 0.11 and 1100°C. In these conditions, the phosphor particle shape was well dispersed spherical and its size was 200 nm.


Kang J.Y.,Chungnam National University | Won H.I.,Rapidly Solidified Materials Research Center | Hayk N.,Rapidly Solidified Materials Research Center | Won C.W.,Chungnam National University
Korean Journal of Materials Research | Year: 2013

In this study, green barium strontium silicate phosphor (BaSrSiO4:Eu3+, Eu2+) was synthesized using a solid-state reaction method in air and reducing atmosphere. Investigation of the firing temperature indicates that a single phase of BaSrSiO4 is formed when the firing temperature is higher than 1400 °C. The effect of firing temperature and doping concentration on luminescent properties are investigated. The light-emitting property was the best when the molar content of Eu2O3 was 0.025 mol. Also, the luminescent brightness of the BaSrSiO4 fluorescent substance was the best when the particle size of the barium was 0.5 μm. BaSrSiO4 phosphors exhibit the typical green luminescent properties of Eu3+ and Eu2+. The characteristics of the synthesized BaSrSiO4:Eu3+, Eu2+ phosphor were investigated using X-ray diffraction (XRD) and scanning electron microscopy. The maximum emission band of the BaSrSiO4:Eu3+, Eu2+ was 520 nm. © Materials Research Society of Korea.

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