• 한국기계가공학회지
• /
• 제19권8호
• /
• pp.56-63
• /
• 2020

The heat transfer phenomenon in the vicinity of the irradiated region of a focused laser beam of a DMT process greatly affects both the deposition characteristics of powders on a substrate and the properties of the deposited region. The goal of this paper is to investigate the heat transfer characteristics of a single bead deposition of Inconel 718 powders on S45C structural steel using a laser-aided direct metal tooling (DMT) process. The finite element analysis (FEA) model with a Gaussian volumetric heat flux is developed to simulate a three-dimensional transient heat transfer phenomenon. The cross-section of the bead for the FEA is estimated with an equivalent area method using experimental results. Through the comparison of the results of the experiments and those of the analysis, the effective beam radius of the bottom region of the volumetric heat flux and the efficiency of the heat flux model for different powers and travel speeds of the laser are predicted. From the results of the FEA, the influence of the power and the travel speed of the laser on the creation of a steady-state heat transfer region and the formation of the heat-affected zone (HAZ) in the substrate are investigated.

• 한국결정성장학회지
• /
• 제27권6호
• /
• pp.303-308
• /
• 2017

여러 가지 금속을 에칭하기 위하여 사용된 $FeCl_3$ 폐용액은 유가금속인 니켈을 함유하고 있다. 본 연구에서는 염화철을 재생하고 남은 니켈 함유 에칭폐액으로부터 니켈을 고순도의 탄산니켈 결정분말로 회수하고자 하였다. 5 % NaOH 수용액을 이용하여 pH 4의 조건에서 1차적으로 철 성분의 불순물을 약 97 % 제거하고 추가적으로 남은 불순물을 제거하기 위하여 용매추출제 D2EHPA(Di-(2-ethylhexyl) phosphoric acid)를 사용하여 불순물로서 존재하는 금속이온들을 약 99% 제거하였다. 그 후 불순물이 제거된 염화니켈 용액에 탄산나트륨과의 반응을 통하여 99.9 % 이상의 순도를 가진 탄산니켈분말을 얻을 수 있었다.

• 한국재료학회지
• /
• 제21권8호
• /
• pp.468-475
• /
• 2011

[ $LaMeO_3$ ](Me = Cr, Co) powders were prepared using the polymeric precursor method. The effects of the chelating agent and the polymeric additive on the synthesis of the $LaMeO_3$ perovskite were studied. The samples were synthesized using ethylene glycol (EG) as the solvent, acetyl acetone (AcAc) as the chelating agent, and polyvinylpyrrolidone (PVP) as the polymer additive. The thermal decomposition behavior of the precursor powder was characterized using a thermal analysis (TG-DTA). The crystallization and particle sizes of the $LaMeO_3$ powders were investigated via powder X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and particle size analyzer, respectively. The as-prepared precursor primarily has $LaMeO_3$ at the optimum condition, i.e. for a molar ratio of both metal-source (a : a) : EG (80a : 80a) : AcAc (8a) inclusive of 1 wt% PVP. When the as-prepared precursor was calcined at $700^{\circ}C$, only a single phase was observed to correspond with the orthorhombic structure of $LaCrO_3$ and the rhombohedral structure of $LaCoO_3$. A solid-electrolyte impedance-metric sensor device composed of $Li_{1.5}Al_{0.5}Ti_{1.5}(PO_4)_3$ as a transducer and $LaMeO_3$ as a receptor has been systematically investigated for the detection of NOx in the range of 20 to 250 ppm at $400^{\circ}C$. The sensor responses were able to divide the component between resistance and capacitance. The impedance-metric sensor for the NO showed higher sensitivity compared with $NO_2$. The responses of the impedance-metric sensor device showed dependence on each value of the NOx concentration.

• 자원리싸이클링
• /
• 제11권4호
• /
• pp.44-50
• /
• 2002

분쇄, 자력선별을 통하여 철 성분을 제거한 폐망간전지 분말을 대상으로 침출제 농도, 온도, 고액비, 교반속도 등을 변화시키면서 황산용액에서 아연과 망간의 침출실험을 수행하였다. 침출시료의 X선 회절분석 결과 아연은 금속아연과 아연산화물, 망간은 이산화망간과 +3가 망간산화물로 존재하고 있어 황산에 의한 아연의 선택침출이 어렵다는 것을 확인하였다. 폐망간전지의 분쇄산물을 대상으로 황산침출을 행한 결과 고액비 1:10, 황산농도 1 M, 반응온도 $60^{\circ}C$, 교반속도 200 r.p.m에서 60분간 침출하였을 때 아연과 망간의 침출율은 각각 92%, 35%로 나타났으며, 반응 후 침출용액의 pH는 0.75, 침출용액 중 아연 및 망간의 농도는 각각 19.5 g/l, 7.8 g/l 이었다. 폐망간전지 분말의 황산침출시 망간의 침출율을 향상시키기 위해서는 환원제의 사용이 필요함을 알 수 있었다.

• 한국재료학회지
• /
• 제23권12호
• /
• pp.722-726
• /
• 2013

Freeze drying of a porous Cu-Sn alloy with unidirectionally aligned pore channels was accomplished by using a composite powder of CuO-$SnO_2$ and camphene. Camphene slurries with CuO-$SnO_2$ content of 3, 5 and 10 vol% were prepared by mixing with a small amount of dispersant at $50^{\circ}C$. Freezing of a slurry was done at $-25^{\circ}C$ while the growth direction of the camphene was unidirectionally controlled. Pores were generated subsequently by sublimation of the camphene during drying in air for 48 h. The green bodies were hydrogen-reduced at $650^{\circ}C$ and then were sintered at $650^{\circ}C$ and $750^{\circ}C$ for 1 h. XRD analysis revealed that the CuO-$SnO_2$ powder was completely converted to Cu-Sn alloy without any reaction phases. The sintered samples showed large pores with an average size of above $100{\mu}m$ which were aligned parallel to the camphene growth direction. Also, the internal walls of the large pores had relatively small pores. The size of the large pores decreased with increasing CuO-$SnO_2$ content due to the change of the degree of powder rearrangement in the slurry. The size of the small pores decreased with increase of the sintering temperature from $650^{\circ}C$ to $750^{\circ}C$, while that of the large pores was unchanged. These results suggest that a porous alloy body with aligned large pores can be fabricated by a freeze-drying and hydrogen reduction process using oxide powders.

• 한국결정성장학회지
• /
• 제22권6호
• /
• pp.279-285
• /
• 2012

BCP, Mg-BCP, Si-BCP 분말을 공침법(co-precipitation process)을 이용하여 합성하였다. 제조된 분말을 X-선 회절 분석(XRD), 적외선분광분석(FTIR)을 이용하여 특성을 분석하였다. Ca/P 몰 비율이 1.602인 칼슘 결손 아파타이트 공침물을 제조하여 $1000^{\circ}C$ 열처리 과정을 통하여 HAp와 ${\beta}$-TCP 상이 혼재된 BCP, Mg-BCP, Si-BCP을 합성할 수 있었다. 제조된 분말의 생체활성 거동을 평가하기 위하여 Hanks' Balanced Salt Solution(HBSS)에 침적시켜 시간에 따라 형상의 변화 및 결정상을 분석한 결과, BCP 분말에 비하여 금속 이온이 치환된 BCP 분말에서 빠른 생체활성을 관찰할 수 있었다. MTT assay를 통한 세포 성장률 평가에서모든 분말에서 시간 경과에 따라 독성을 나타내지 않았으며, 세포의 활성이 증가하였다.

• 자원리싸이클링
• /
• 제1권1호
• /
• pp.44-50
• /
• 1992

소규모공장 규모의 알카리 및 산공정법에 의해 철강의 산세 폐액으로부터 $\alpha$-FeOOH를 제조하였으며, 이 때 합성된 분체를 TEM, SEM, TG-DTA, XRD, VSM 및 화학분석으로 물성을 조사하였다. 실험결과에 의하면, $\alpha$-FeOOH의 제조에 있어서 알카리 공정의 반응 시간이 짧으며, 제조된 분체는 약 $0.5\mu\textrm{m}$의 크기로 침상을 나타내었다. 또한 제조 방법에 따라 $\alpha$-FeOOH 와 $\alpha-Fe_2O_3$가 생성되며 이들은 미려한 황색 및 적색을 띠고 있었고 $\alpha-Fe_2O_3$를 $370^{\circ}C$의 수소 분위기에서 1시간 환원하면 367(Oe) 및 86.7 (emu/g)의 자성을 갖는 $Fe_3O_4$ 가 얻어질 수 있었다.

• 자원리싸이클링
• /
• 제7권4호
• /
• pp.64-75
• /
• 1998

본 연구의 목적은 분무배소법에 의해 조성과 입도분포가 매우 균일하고 고순도인 Fe 산화물과 Mn 산화물의 복합산화물 또는 Mn 페라이트 분말을 제조하는데 있다. 본 연구에서는 우선 염산 용액에$SiO_2$, P, Al, Ca, Na 등의 불순물들을 다량 함유하고 있는 Fe와 Mn 성분을 정해진 조성으로 용해시킴으로써 분무배소의 원료용액을 제조하였다. Na와 Ca를 제외한 대부분의 불순물들은 원료 산 용액의 pH를 약 3이상으로 유지시킴으로써 공침현상에 의해 효과적으로 제거되었으며 Na와 Ca 성분은 분말제조 후 수세에 의해 제거가 가능하였다. 반면 PVA, resin amine 등의 고분자 응집제들은 불순물 제거에 거의 효과가 없는 것으로 확인되었다. 본 연구에서는 불순물들이 효과적으로 제거된 정제된 산 용액을 노즐을 이용하여 고온의 배소로 내로 분무시킴으로써 Fe 산화물과 Mn 산화물의 복합 산화물 또는 Mn 페라이트 분말을 제조하였다. 이때 생성된 분말들은 매우 균일하게 혼합되어 있었으며, 배소로 내에서의 반응온도가 증가할수록 생성된 분말의 입도는 증가하였다.

• 대한치과기공학회지
• /
• 제29권1호
• /
• pp.121-131
• /
• 2007

A preparation process's conditions of aqueous sol which contains anatase-type nano titania particles with photocatalyic properties was established by using Yoldas process, so called, DCS(Destabilization of Colloidal Solution) process in this study. And crystal size change and phase transformation of titania particles in aqueous titania sol depending on reaction conditions was investigated by a light scattering method and XRD analysis of frozen dried powders, respectively. This sol with photo catalytic nano titania particles was used to the following hydrophilic hybrid coating film's fabrication and its properties was evaluated. Subsequently, for coating film using the above mentioned aqueous titania sol, non-aqueous titania sol was prepared without any chemical additives and its time stability according to aging time was investigate. By using the above mentioned aqueous titania sol and non-aqueous sol, a complex oxide coating sol for metal and ceramic substrate and a organic-inorganic hybrid coating sol for polymer substrate was prepared and it's hydrophilicity depending on UV irradiation conditions was evaluated. As a conclusions, the following results were obtained. (1)Aqueous titania sol The average particle size of titania in formed aqueous titania sol was distributed between 20$\sim$90nm range depending on reaction conditions. And the crystal phase of titania powders obtained by frozen drying method was changed from amorphous state to anatase and subsequently transformed to rutile crystal phase and it is attributed to concentration gradient in aqueous sol. (2)Non-aqueous titania sol Non-aqueous titania sol was prepared using methanol as a solvent and a little distilled water for hydrolysis and nitric acid as a catalyst were used. The obtained non-aqueous titania sol was stable at room temperature for 20 days. Additionally, non-aqueous titania sol with addition of chealating reagent such as acethylaceton and ethylene glycol prolonged the stability of sol by six months. (3)Complex sol and hybrid sol with super hydrophilicity The above mentioned aqueous titania sol as a main photocataylic component and non-aqueous titania sol as a binder for coating process was used to prepare a complex sol used for metal, ceramic and wood material substrate and also to prepare the organic-inorganic hybrid sol for polymer substrate such as polycarbonate and polyethylene, in which process APMS(3-Aminopropyltrimethoxysilane), GPTS(3-Glycidoxypropyl-trimethoxysilane) as a hydrophilic silane compound and HEMA(2-Hydroxyethyl methacrylate) as a forming network in hybrid coating film were used. The hybrid coating film such as prepared through this process showed a superhydrophilicity below 1$10^{\circ}$ depending on processing conditions and a pencil's hardness over 6 H.

• 한국분말재료학회지
• /
• 제25권2호
• /
• pp.137-143
• /
• 2018

In this study, two types of SKD61 tool-steel samples are built by a selective laser melting (SLM) process using the different laser scan speeds. The characteristics of two kinds of SKD61 tool-steel powders used in the SLM process are evaluated. Commercial SKD61 tool-steel power has a flowability of 16.68 sec/50 g and its Hausner ratio is calculated to be 1.25 by apparent and tapped density. Also, the fabricated SKD61 tool steel powder fabricated by a gas atomization process has a flowability of 21.3 sec/50 g and its Hausner ratio is calculated to be 1.18. Therefore, we confirmed that the two powders used in this study have excellent flowability. Samples are fabricated to measure mechanical properties. The highest densities of the SKD61 tool-steel samples, fabricated under the same conditions, are $7.734g/cm^3$ (using commercial SKD61 powder) and $7.652g/cm^3$ (using fabricated SKD61 powder), measured with Archimedes method. Hardness is measured by Rockwell hardness testing equipment 5 times and the highest hardnesses of the samples are 54.56 HRC (commercial powder) and 52.62 HRC (fabricated powder). Also, the measured tensile strengths are approximately 1,721 MPa (commercial SKD61 powder) and 1,552 MPa (fabricated SKD61 powder), respectively.