• 연구논문집
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• 통권34호
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• pp.11-19
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• 2004

An Experimental study on the characteristics of high pressure gas quenching system was carried out in the present study. The characteristics of gas quenching system have been studied with high pressure gas chamber and specimen for various gas pressure and velocity which are the design parameter of quenching system. The quenching gas was used compressed air which properties are very similar with Nitrogen gas usually used in industrial gas quenching system. The result shows that the quenching rate of mid surface of specimen is lower than each ends of them which are close to low temperature quenching surface. And to increases the quenching intensity, the increment of quenching gas pressure is more efficient than the increment of quenching gas velocity at the point of reducing the circulation fan power.

• Design & Manufacturing
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• 제8권2호
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• pp.23-29
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• 2014

Salt bath heat treatment is usually used but recently vacuum heat treatment is increased for the heat treatment of hot work die steels. The differences in two heat treatment processes were compared by testing the mechanical properties of heat treated products. With two different features of processes, mechanical properties such as hardness, tensile strength and impact strength of products show very different results. In this study salt bath heat treated products showed higher tensile strength and impact strength than vacuum heat treated products but hardness was not much different. These lower mechanical properties of vacuum heat treated products are due to differences in heating and quenching process.

• 열처리공학회지
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• 제25권3호
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• pp.115-120
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• 2012

It has been known that the ferritic stainless steel can be changed to martensitic stainless steel when nitrogen is added. However the high hardness of martensitic stainless steel prevents the plastic deformation. In this study, instead of martensite, the surface microstructure was changed into nitrogen pearlite to increase the plastic deformation easily by isothermal heat treatment after high temperature gas nitriding (HTGN) the AISI 430 ferritic stainless steel. The isothermal treatment was carried out at $780^{\circ}C$ for 4, 6, and 10 hrs, respectively, after HTGN treatment at $1100^{\circ}C$ for 10 hrs. The surface layer of isothermal-treated steel appeared nitrogen pearlite composed with fine chromium nitride and ferrite. Hence, the interior region that was not affected by nitrogen permeation exhibited ferrite phase. When quenching the isothermal treated steel at 1100oC, martensitic phase formed at the surface layer. The hardness of surface layer of isothermal-treated steel and quenched steel measured the value of 150~240 Hv and 630 Hv, respectively.

• 열처리공학회지
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• 제26권1호
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• pp.7-13
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• 2013

Vacuum heat treatment(indirect heating method) has long exposure time at high temperature and low quenching rate. Contrarily salt bath heat treatment (direct heating method) has short exposure time at high temperature and fast cooling rate. With these different features of processes, mechanical properties such as hardness, tensile strength and impact strength of products show very different results. In this study, Salt bath heat treated products showed higher tensile strength and impact strength than vacuum heat treated products but hardness was not much different. These lower mechanical properties of vacuum heat treated products are due to differences in heat process and secondary hardening with high temperature tempering process. Consequently, It indicates that salt bath heat treatment is better way than vacuum heat treatment for product to have high mechanical properties.

• 한국결정성장학회지
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• 제4권4호
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• pp.370-377
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• 1994

비이송식DC 플라즈마 토치를 제작하고 이를 이용하여 질화규소 분말을 제조하였다. Ar 가스를 사용하여 플라즈마를 발생시켯으며, 발생된 플라즈마 flame으로 반응가스 및 reactive quenching 가스를 도입하였다. 토치의 하단부에 2개의 slit를 장착하여 가스의 도입 위치를 변화시킬 수 있게 하였다. $SiCl_4와 NH_3$를 출발원료로 하여 질화규소 분말을 제조하였다. 얻어진 분말은 무정형이었으며, 반응부산물을 제거하고 $1420^{\circ}C$에서 질소 분위기하에서 가열함으로써 결정화된 질화규소 분말을 얻었다. XPD pattern 및 IR 스펙트럼으로부터 질화규소 분말을 확인하였고, TEM을 사용하여 전후의 형상을 관찰하였다.

• 청정기술
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• 제24권3호
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• pp.233-238
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• 2018

급속열분해를 통한 바이오-오일 생산 공정은 무산소 조건에서 바이오매스를 급속열분해하여 얻어진 열분해가스를 급속 냉각 시켜 열분해오일을 생산한다. 이에 공정 내부의 산소 농도를 0 ~ 3% 이하로 유지하기 위해 캐리어 가스로 질소를 사용한다. 그러나 공정의 규모가 커질수록 질소의 사용량이 증가하고, 이는 공정 운전비용 증감 및 지속적인 질소 가스 충전을 위한 설비비 증감 할 수밖에 없다. 이에 본 연구에서는 팜 부산물 열분해에서 질소 사용량 감소를 위해 미응축가스 재순환 공정을 적용하여, 가스재순환율에 따른 질소 사용량과 미응축가스의 가연성 성분의 농도 변화를 측정하고 이에 따른 바이오-오일의 품질 수율 변화를 측정하여 가스재순환 공정의 활용 가능성을 연구하였다.

• 한국재료학회지
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• 제21권2호
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• pp.106-110
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• 2011

A high thermal conductive AlN composite coating is attractive in thermal management applications. In this study, AlN-YAG composite coatings were manufactured by atmospheric plasma spraying from two different powders: spray-dried and plasma-treated. The mixture of both AlN and YAG was first mechanically alloyed and then spray-dried to obtain an agglomerated powder. The spray-dried powder was primarily spherical in shape and composed of an agglomerate of primary particles. The decomposition of AlN was pronounced at elevated temperatures due to the porous nature of the spray-dried powder, and was completely eliminated in nitrogen environment. A highly spherical, dense AlN-YAG composite powder was synthesized by plasma alloying and spheroidization (PAS) in an inert gas environment. The AlN-YAG coatings consisted of irregular-shaped, crystalline AlN particles embedded in amorphous YAG phase, indicating solid deposition of AlN and liquid deposition of YAG. The PAS-processed powder produced a lower-porosity and higher-hardness AlN-YAG coating due to a greater degree of melting in the plasma jet, compared to that of the spray-dried powder. The amorphization of the YAG matrix was evidence of melting degree of feedstock powder in flight because a fully molten YAG droplet formed an amorphous phase during splat quenching.

• 한국표면공학회지
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• 제47권4호
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• pp.192-197
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• 2014

Red-emitting nitride phosphors recently attracted considerable attention because of their high thermal stability and high color rendering index properties. For excellent phosphor of white light-emitting-diode, ternary nitride phosphor of $Sr/SmSi_5N_8:Eu^{2+}$ with different $Eu^{2+}$ ion concentration were synthesized by solid state reaction method. In this work, red-emitting nitride $Sr/SmSi_5N_8:Eu^{2+}$ phosphor was successfully synthesized by using multi-step high frequency induction heat treatment. The effects of molar ratio of component and experimental conditions on luminescence property of prepared phosphors have been investigated. The structure and luminescence properties of prepared $Sr/SmSi_5N_8:Eu^{2+}$ phosphors were investigated by XRD and photoluminescence spectroscopy. The excitation spectra of $Sr/SmSi_5N_8:Eu^{2+}$ phosphors indicated broad excitation wavelength range of 300 - 550 nm, namely from UV to visible area with distinct enhanced emission peaks. With an increase of $Eu^{2+}$ ion concentration, the peak position of emission in spectra was red-shifted from 613 to 671 nm. After via multi-step heat treatment, prepared phosphor showed excellent luminescence properties, such as high emission intensity and low thermal quenching, better than commercial phosphor of $Y_3Al_5O_{12}:Ce^{3+}$. Using $Eu_2O_3$ as a raw material for $Eu^{2+}$ dopant with nitrogen gas flowing instead of using commercial EuN chemical for $Sr/SmSi_5N_8:Eu^{2+}$ synthesis is one of characteristic of this work.