• Journal of Welding and Joining
• /
• 제22권1호
• /
• pp.71-76
• /
• 2004

In the standpoint of the arc pressure, the effects of the filler wire feed rate on the penetration was investigated in this study. The pure Ar gas was used as a shield gas and the parameters investigated were the welding current and the filler wire feed rate. By making the experiment on the arc pressure, we could know that the arc pressure was fluctuated as the depth-into-arc of the tungsten rod. Instead of the filler wire, the tungsten rod was supplied into the molten pool to make this experiment. Because the filler wire melted in arc and then we couldn't measure the arc pressure. So, the tungsten rod - the highest melting point - was used. According to the depth-into-arc of the tungsten rod, the arc pressure could be measured by using the manometer. It was proved that the arc pressure got higher as the wire feed rate was slow. It is reported the arc pressure is proportion to welding voltage and the square of welding current. But, in the filler wire TIG welding, we could blow that arc pressure was fluctuated as the depth-into-arc of filler wire was changed. We could measure the arc pressure by the variation of the filler wire feed rate and could verify that it affected bead shape and penetration.

• 한국재료학회지
• /
• 제29권10호
• /
• pp.592-602
• /
• 2019

Feasibility is investigated for reduction of chromium ore by Si sludge with mixed silicothermic and carbothermic reaction. The reduction behavior of chromium ore using Si sludge is investigated precisely to determine the effects of carbon addition, reaction time, and reaction temperature. The pellets are dropped into the furnace after temperature stabilized. As the amount of C addition increases, the amounts of CO and $CO_2$ gas generation increase. After the dropping of the pellets, the pellets are heated and the reaction starts at about 1,573 K or higher. The pellets maintain their shape until 10 min after the drop, and then melted. As the holding time increased, the size of the reduced metal particles increased. The chromium ore is rapidly reduced by the Si sludge, and the slag penetrated into the chromium ore and reduction progressed inside. As the reduction temperature increased, the reaction initiation time is shortened and the reaction fraction of the reduction reaction increased. As the reaction temperature increased, agglomeration of reduced ferrochrome metal is promoted.

• 약학회지
• /
• 제39권5호
• /
• pp.487-494
• /
• 1995

Solid lipid microspheres (SLMs) were prepared using various lipids and solidifying agents, in order to enhance the gastrointestinal absorption of Cyclosporine A (Cs A) which is a practically water-insoluble drug with low systemic bioavailability. Egg lecithin and HCO-60 (polyoxyethylated 60 mol, hydrogenated castor oil) were used as lipids. Stearic acid and stearyl alcohol were used as solidifying agents. Emulsion concentrates containing Cs A were prepared by mixing the melted lipid and solidifying agent with water, employing bile salts as a cosurfactant. SLMs were obtained by dispersing the warm emulsion concentrate in cold distilled water under mechanical stirring, followed by freeze drying. Physical characteristics of each SLM were investigated by particle size analysis, optical microscopy and scanning electron microscopy. Mean particle size of SLMs was in the range of 30 to 40.mu.m. The SLMs were in good appearance with spherical shape before freeze drying, but were deformed partially after freeze drying. Drug loading efficiencies of SLMs were observed as high as 80 to 90% in average. The systemic bioavailability of Cs A from different SLM formula was investigated in rats following oral administration. Cs A in whole blood was extracted and assayed by HPLC. SLMs revealed the higher bioavailabilities than the standard formula based on the marketed product. SLMs might have several advantages over standard formula for enhanced gastrointestinal absorption, controlled release properties, high loading capacity of the water-insoluble drug, and feasibility of solid dosage forms with better stability in storage.

• 열처리공학회지
• /
• 제12권2호
• /
• pp.145-156
• /
• 1999

The distribution of the second phase, the change of transformation temperature and mechanical properties with thermomechanical treatment conditions were investigated by metallography, calorimetry, EDS, tensile test and fractography in a Cu-Al-Ni-Ti-Mn alloy. The cast structure revealed Ti-rich precipitates($X_L$ phase) between dendrite arms, which have been identified as $(Cu,Ni)_2TiAl$ intermetallic compounds. By homogenizing above $900^{\circ}C$, the $X_L$ phase was melted in the matrix, while the Xs phase was precipitated in matrix and the volume fraction of it was increased. When hot-rolled specimen was betatized below $750^{\circ}C$, recrystallization could not be observed. However, the specimen betatized above $800^{\circ}C$ was recrystallized and the grain size was about $50{\mu}m$, while Xs phase was precipitated in matrix. With raising betatizing temperature, $M_s$ and $A_s$ temperatures were fallen and transformation hysteresis became larger. The strain of the specimen betatized at $800^{\circ}C$ was 8.2% as maximum value. The maximum shape recovery rate could be obtained in the specimen betatized at $800^{\circ}C$ but it was decreased due to the presence of Xs phase with increasing betatizing temperature.

• 암석학회지
• /
• 제10권1호
• /
• pp.1-12
• /
• 2001

경상분지 통남부에 위치하는 울산 철-사문암광산 지역에는 유일하게 국내에서는 초염기성암과 탄산염 암체가 공간적으로 연관성을 가지고 소규모로 분포하고 있다. 야외지질조사, 광상시추코아자료, 안정동위원소 분선 등의 연구결과는 울산의 탄산염암체는 용융체에서 형성된 카보내타이트의 가능성이 큰 것으로 나타났으며, 산출상태는 관입암상의 특징임을 반영하고 있다. 이번 연구에 의한 이곳의 지질은 중생대 퇴적암과 화산암, 이를 관입하고 있는 화강암류, 화강암을 관입하고 있는 초염기성암, 이 초염기성암을 관입하고 있는 카보내타이트로 이루어진다. 탄산염암체는 지표 상에서는 초염기성암과 함께 동심원상의 타원형으로, 수직단면도에서는 깔때기형태로 산출되고 있다. 탄소, 산소 안정동위원소비는 전형적인 맨틀기원의 카보내타이트로서의 특징이라기보다는 특이한 이원성형태(bimodal pattern)를 나타내었으며, 이는 울산의 카보내타이트를 형성한 마그마가 맨틀에서 직접적으로 상승한 마그마라기보다는 지각 내에서 형성된 2차적 카보내타이트 마그마임을 지시하는 것으로 해석된다. 즉, 초염기성암 마그마가 상승하면서 지각 내에 있던 석회질암이 용융되어, 탄산염마그마를 형성하고, 심부의 파쇄대가 발달한 현재의 장소에 사문암체를 형성한 초염기성 마그마와 그 뒤를 이어 탄산염마그마가 관입한 것으로 여겨진다. 또한 울산 철-사문암광산 지역은 심부파쇄대가 발달된 것이며, 탄산염암체내의 유체포유물의 유형, 안정동위원소의 패턴, 초염기성암과의 공간적 관계 등은 울산의 탄산염암체가 카보내타이트로 해석되는 것을 지지해주고 있다.

• 한국안전학회지
• /
• 제27권2호
• /
• pp.7-12
• /
• 2012

This paper describes electrical fire on electric pad caused by defect of hot wires. We analyzed two type electric pad using by carbon type hot wire and magnetic shielded type hot wire. First, a carbon type hot wires electric pad is virtually impossible to connect hot wire as a method of electrical welding or soldering. In order to connect between hot wires, that has to splice carbon type material connector. If junction of hot wires was occurrence of poor connection on electric pad, it increase contact resistance on this junction point. With increasing contact resistance, junction of hot wires on electric pad generates local heating and finally leads to electrical fire. An electric pad using by a magnetic shielded type hot wire happened local heating on signal wire for sensing temperature-rise caused by applying current for magnetic shielded. With increasing local heating of signal wire, insulated coating of hot wire was melted. Finally the magnetic shielded type hot wire electric pad lead to electrical fire with breakdown between signal wire and hot wire. In this paper, we analyzed shape of damage in hot wire caused by electrical local heating and investigated fire cause on electric pad due to defect of hot wires.

• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2012년도 제43회 하계 정기 학술대회 초록집
• /
• pp.376-376
• /
• 2012

Semiconductor nanowires (NWs) are future building block for nano-scale devices. Especially, Ge NWs are fascinated material due to the high electrical conductivity with high carrier mobility. It is strong candidate material for post-CMOS technology. However, thermal stability of Ge NWs are poor than conventional semiconductor material such as Si. Especially, when it reduced size as small as nano-scale it will be melted around CMOS process temperature due to the melting point depression. Recently, Graphene have been intensively interested since it has high carrier mobility with single atomic thickness. In addition, it is chemically very stable due to the $sp^2$ hybridization. Graphene films shows good protecting layer for oxidation resistance and corrosion resistance of metal surface using its chemical properties. Recently, we successfully demonstrated CVD growth of monolayer graphene using Ge catalyst. Using our growth method, we synthesized Ge/graphene core/shell (Ge@G) NW and conducted it for highly thermal stability required devices. We confirm the existence of graphene shell and morphology of NWs using SEM, TEM and Raman spectra. SEM and TEM images clearly show very thin graphene shell. We annealed NWs in vacuum at high temperature. Our results indicated that surface melting phenomena of Ge NWs due to the high surface energy from curvature of NWs start around $550^{\circ}C$ which is $270^{\circ}C$ lower than bulk melting point. When we increases annealing temperature, tip of Ge NWs start to make sphere shape in order to reduce its surface energy. On the contrary, Ge@G NWs prevent surface melting of Ge NWs and no Ge spheres generated. Furthermore, we fabricated filed emission devices using pure Ge NWs and Ge@G NWs. Compare with pure Ge NWs, graphene protected Ge NWs show enhancement of reliability. This growth approach serves a thermal stability enhancement of semiconductor NWs.

• 한국HCI학회:학술대회논문집
• /
• 한국HCI학회 2008년도 학술대회 1부
• /
• pp.813-816
• /
• 2008

본 연구에서는 주물의 유통해석결과를 3차원 모델로 복원하여 가상현실 디스플레이 상에 가시화 하는 방법을 제안한다. 먼저 기존 CAE 해석 소프트웨어를 사용하여 유한차분법 기반 열유동 수치해석을 수행한다. 이 과정에서는 주물의 설계모델은 그 형태가 규칙적인 사각형 격자에 근사되며 용탕을 주형에 주입하는 것을 시작으로 충전이 완료될 때까지 사전에 정의된 단계수만큼 반복적으로 전체 복셀에 대한 충전도와 온도수치가 기록된다. 다음 단계에서는 그 결과별 입력으로 하여 복셀 단위로 주울 형태를 복원한다. 이 때 유통진행에 따른 각 단계에서 각 복셀의 충전여부와 온도수치를 색상에 대응시켜 복셀의 색상을 결정한다. 복원 모델은 수평형 가상현실 디스플레이 장치인 Projection Table 상에서 가시화 하였으며 액티브 스테레오 방식으로 입체화면을 제공한다.

• 열처리공학회지
• /
• 제33권3호
• /
• pp.99-106
• /
• 2020

Selective laser melting (SLM) is an additive manufacturing process by melting metallic powders and stacking into layers, and can product complex shapes or near-net-shape (NNS) that are difficult to product by conventional processes. Also, SLM process is able to raise the efficiency of production by creating a streamlined manufacturing process. For manufacturing in SLM process using Ti-6Al-4V powder, analysis of microstructural evolution and evaluation of mechanical properties are essential because of rapid melting and solidification process of powders according to high laser power and rapid scan speed. In addition, it requires a post-processing because the soundness and mechanical properties are degraded by defects such as pore, un-melted powder, lack-of-fusion, etc. In this study, hot isostatic press (HIP) was conducted as a post-processing on SLM-printed Ti-6Al-4V alloy. Microstructure of post-processed Ti-6Al-4V alloy was compared to as-built Ti-6Al-4V, and the evolution of quasi-static (Vickers hardness, room temperature tensile characteristic) and dynamic (high-cycle fatigue characteristic) mechanical properties were analyzed.

• 한국건설순환자원학회논문집
• /
• 제5권2호
• /
• pp.83-90
• /
• 2010

As a reinforced fabric, asbestos has been utilized as a fire-resistant material as it has a superior flexural stiffness and heat resistance up to $1500^{\circ}C$. However, due to its harmfulness, its use has been prohibited recently and the even the installed asbestos materials are being repaired or supplemented if there is a concern about flying. Asbestos is mainly used for construction panels as a reinforced fabric and coating materials to ensure the fire-resistance of steel frames. Asbestos was used as fire-resistant materials for steel frames until 1991 and then prohibited as Act on Industrial Safety and Health limits the concentration of asbestos in the air. Classified as a designated waste according to Act on Waste Control, asbestos must be buried if there is no possibility of flying (panel-type materials) or cement-solidified and then buried if there is a possibility of flying (spray coating material) In general, it is required that a new waste landfill include a certain landfill facility for designated waste, but in reality there is an absolute storage of landfill facilities for designated waste as they only install facilities of the size required by the regulations. This could result in the 2nd environmental pollution as they cannot process asbestos wastes which will be generated in large volume in the future. This study explores a method that melts asbestos wastes at $700^{\circ}C$ rather than cement-solidifying the waste asbestos from construction sites, especially asbestos-containing spray coating. The study results showed that there was no change in the composition and shape even though asbestos wastes was melted at $1300^{\circ}C$, but there was a change for the specimen which was process in advance for low temperature melting and then melt at $900^{\circ}C$.