소결형 고체탄탈 축전기의 제조조건과 전기적 특성

윤용구,이동녕 대한금속재료학회(대한금속학회) 1972 대한금속·재료학회지 Vol.10 No.2

固體탄탈 蓄電器의 제조에 있어서 燒結조건이 化成速度와 신틸레이숀 전압에 미치는 영향 및 熱分解와 에이징 (aging) 조건이 蓄電器의 전기적 성질에 미치는 영향을 중점적으로 연구하였다. 이 燒結體의 誘電酸化皮膜은 燐酸水溶液에서 化成하여 형성시켰고 이 酸化層위에다 窒酸망간을 含浸하여 熱分解시켜 二酸化망간層을 입혔다. 熱分解 과정과 熱分解 과정중 생긴 결함을 고치기 위한 再化成을 여러번 되풀이 하였다. 250볼트 이상의 신틸레이숀 전압을 얻기위하여는 2,000℃ 이상에서 眞空燒結 해야 했다. 熱分解와 에이징 과정중 誘電體의 tanδ_f의 증가와 容量의 周波數에 대한 변화가 증가 하는 것은 酸化皮膜內의 擴散層의 중가 때문인 것으로 분석되었다. Fabrication variables of tantalum solid electrolytic capacitors were studied in relation to their electrical properties. Emphasis was placed on investigating effects of sintering conditions on anodization rates and scintillation voltage, and effects of pyrolysis and aging conditions on electrical properties of tantalum capacitors. The dielectric oxide layer on the surface of sintered porous anode pellets was formed by anodizing in phosphoric acid solution. The solid electrolyte was applied on the dielectric oxide layer by impregnating the anodized pellets with manganese nitrate and then by its pyrolysis. The application of the solid electrolyte and reanodization at a reduced voltage were repeated several times. Vacuum sintering of tantalum pellets at a temperature above 2,000 ℃ was required to achieve the scintillation voltage above 250 volts. The increases in tanδ_f and in frequency dependence of capacitance of the dielectric oxide layer during Pyrolysis and aging process are attributed to increasing diffusion layer of the dielectric oxide layer.

응력이 지르칼로이-4 의 산화막 성장과 산화후의 크리프변형에 미치는 영향

윤용구,임상호 대한금속재료학회(대한금속학회) 1986 대한금속·재료학회지 Vol.24 No.4

Effects of compressive stress generated in the oxide layer and its subsequent relief on oxidation rate and post-oxidation creep characteristics of Zircaloy-4 were investigated by oxidation studies in steam with and without applied tensile stress and by creep testing at 700℃ in high purity argon. The thickness of oxide layer increased with the magnitude of tensile stress applied during oxidation at 650℃ in steam whereas similar phenomenon was not observed during oxidation at 800℃. Zircaloy-4 specimens oxidized at 600℃ in steam without applied stress exhibited higher creep strain than that shown by unoxidized specimens when creep-tested in argon. Zircaloy-4 specimens oxidized at 600℃ steam under the applied stress of 8.53MPa and oxidized at 800℃ under the applied stress of 0 and 8.53MPa exhibited lower strain than that shown by unoxidized specimen. The above experimental results were accounted for on the basis of interactions among applied stress during oxidiation, compressive stress generated in the oxide layer and elasticity of Zircaloy-4 matrix.

다공질 크롬도금에 관한 연구

윤용구,오룡기 대한금속재료학회(대한금속학회) 1970 대한금속·재료학회지 Vol.8 No.3

Porous chromium plating is used in the automobile parts industry for plating engine cylinders or cylinder liners, and piston rings. Porous chromium plating with oil retaining characteristics makes the automobile parts more corrosion-and wear-resistant. The mast conventional process for porous chromium plating is electrochemical etching after chromiumplating. The present study was undertaken to investigate effects of bath composition, plating temperature ancnd ent density on the type of porous plating achieved, surface condition, current efficiency, hardness and crack size. The change of porosity ratio was also examined with regard to etching and honing. Major results obtained can be summarized as follows: 1. The current efficiency decreased with a rise of bath temperature and sulfate ratio but decreased with a rise of current density. 2. The crack size increased with a rise of bath temperature and sulfate ratio but slightly decreased with a rise of current density. 3. The optimum conditions for obtaining pit-type, intermediate-type and channel-type porousplating were the current density of 50 A/d㎡ at 50℃, the current density of 50∼60 A/d㎡ at 55℃ and the current density of 60 A/d㎡ at 60℃, respectively. 4. A fluosilicate self-regulating solution for porous chromium plating that is stable and is of high current efficiency was developed by controlling the solubility of sodium fluosilicate. When this plating solution was used, pit-type and intermediate-type porousplating were obtained at 50℃ and 60℃, respectively. 5. The etching process after chromium plating had to he adjusted, depending on plating thickness, honing thickness and type of porous plating.

SmCo5 영구자석의 소결단계에 관한 연구

윤용구,나종갑 대한금속재료학회(대한금속학회) 1980 대한금속·재료학회지 Vol.18 No.6

SmCo_5영구자석의 소결중 Sm함량이 60wt%인 Sm-Co계 소결첨가제의 역할을 규명하기 위하여 조대한 소결첨가제(약 200 ㎛크기)와 미세한 Smco_5분말(약 5㎛크기)의 혼합분말과 역으로 조대한 SmCo_5분말과 미세한 소결첨가제의 혼합분말을 소결하는 소결시험을 하였다. 또한 미세한 Sm-Co계 혼합분말의 총 Sm함량 및 소결시간의 변화에 따른 밀도변화를 측정하여 SmCo_5균질영역의 Sm과다상분말의 소결을 규명하였다. 위 실험결과 Sm-Co계 혼합분말은 아래의 3단계를 거쳐 소결되는 것으로 생각된다. 1) Sm-Co계 혼합분말의 소결에 있어서 초기단계에 소결첨가제는 액상으로 변하여 주위 SmCo_5분말에 빨려 들어가 균일하게 퍼진다. 2) 액상과 SmCo_5분말이 접촉하면 제 2단계로 두상사이에 상간반응과 Sm, Co함량차에 의한 상호확산이 일어나 새로운 조성의 상인 SmCo₃상과 Sm₂Co_7상이 석출되며 계속 소결하면 액상, SmCo₃상, Sm₂Co_7 상 순으로 소멸되어 Sm-Co계 혼합분말은 평형상인 SmCo_5균질영역의 Sm과다상으로 변한다. 3) SmCo_5균질영역의 Sm과다상분말은 마지막 단계로 Sm과다상중에 포함되어있는 Co-vacancy에 의한 고상소결로 치밀화된다. Sm-Co계 혼합분말의 소결시간에 따른 밀도변화의 관계를 측정하여 기존의 소결이론 및 실험결과와 연관시켜 해석하였다. Sintering studies of the mixture of a coarse 60wt% Sm-Co additive (about 200㎛ size) and a fine SmCo_5 powder (about 5㎛ size) and the mixture of a coarse SmCo_5 powder and a fine additive were made to understand the role of the liquid additive during sintering of the SmCo_5 permanent magnets. The density change of the fine powder mixtures was also studied, varying their total Sm content and sintering time, to understand the sintering of a Sm-rich phase powder of the SmCo_5 homogeneity region. The results showed that the mixture of the SmCo_5 powder and the 60wt% Sm-Co additive was sintered through three stages; 1) Upon melting of the Sm-Co additive, the liquid phase immediately permeated through the SmCo_5 powder during the first stage. 2) As the liquid phase was brought to contact with the SmCo_5 powder, new phases, SmCo₃ and Sm₂Co_7 were formed by interphase reaction and interdiffusion of Sm and Co atoms between the liquid phase and the SmCo_5 powder. On continued sintering, the liquid phase, the SmCo₃ and the Sm₂Co_7 phase disappeared successively in the order of listing, while an equilibrium phase of the powder mixture, that is, a Sm-rich phase of the SmCo_5 homogeneity region was formed during the second stage. 3) During the last stage, solid state sintering of the Sm-rich phase of the SmCo_5 homogeneity region occurred by diffusion of Co-vacancies that were believed to exist in the Sm-rich phase. The experimentally observed relationship between density change of sintered magnets and sintering time was discussed in relation to the theories and experimental results reported previously.

음향 방출에 의한 인코넬 600 합금의 응력 부식 균열 거동 평가

윤용구,김인섭,성게용 韓國非破壞檢査學會 1996 한국비파괴검사학회지 Vol.16 No.3

본 연구에서는 인코넬600 합금을 열처리 상태 및 변형속도 등이 서로 다른 SCC 발생 조건하에서 정변형 속도 시험법으로 인장시켜 그때 발생되는 AE신호와 균열 거동을 비교하므로서 SCC 발생 및 진전을 AE로서 적절히 탐지할 수 있는가를 연구하였고, AE로 탐지 가능한 초기의 최소 균열 크기를 측정하므로서 비파괴시험법으로서의 적용성을 평가하고자 하였다. 실험결과, IGSCC에서 발생되는 AE amplitude 준위는 연성파괴 및 기계적인 변형에서 발생되는 것들보다 큰 것으로 나타났으며, 이것은 AE amplitude 준위가 AE발생원을 식별할 수 있는 중요한 변수가 될 수 있음을 의미한다. IGSCC 미소균열의 성장 및 주균열의 형성으로부터 주균열의 성장으로 전환되는 시점을 AE로 적절히 감시할 수 있음을 보였으며, AE로 탐지 가능한 최소 균열 크기는 길이 200∼400㎛, 깊이 100㎛ 이하의 균열인 것으로 나타났다. 결론적으로 AE기술은 입계 응력 부식 균열의 진전을 조기 탐지할 수 있는 유용한 방법으로 평가되며 비파괴시험법으로서의 실제 적용 가능성도 높을 것으로 판단된다. Acoustic emission(AE) response during stress corrosion cracking(SCC) of Inconel 600 alloy has been monitored to study the AE detectability of crack generation and growth by comparing the crack behavior with AE parameters processed, and to evaluate the applicability as a nondestructive evaluation(NDE) by measuring the minimum crack size detectable with AE. Variously heat-treated specimens were tensioned by constant extension rate test(CERT) in various extension rate to give rise to the different SCC behavior of specimens. The AE amplitude level generated from intergranular stress-corrosion cracking(IGSCC) is higher than those from ductile fracture and mechanical deformation which means the AE amplitude can be a significant parameter for distinguishing the AE source. AE can also provide the effective means to identify the transition from the small crack initiation and formation of dominant cracks to the dominant crack growth. Minimum crack size detectable with AE is supposes to be approximately 200 to 400㎛ in length and below 100㎛ in depth. The test results show that AE technique has a capability for detecting the early stage of IGSCC growth and the potential for practical application as a NDE.

규소강판 (硅素鋼板) 의 자기특성에 미치는 야금학적 요인

윤용구,이택동 대한금속재료학회(대한금속학회) 1968 대한금속·재료학회지 Vol.6 No.3

탄탈양극 산화피막의 결함과 화성중 신틸레이숀과의 관계

윤용구,이동녕 대한금속재료학회(대한금속학회) 1973 대한금속·재료학회지 Vol.11 No.2

탄탈박막을 인산수용액에서 양극산화 시켰을 때 생기는 산화피막의 새로운 결함의 모양을 소개하고, 그 발생기구를 제시하였다. 화성용액에 따라 화성중 신틸레이숀 양상이 다르며, 화성중 산화피막에 발생하는 결정은 β-Ta₂O_5 이었다. 탄탈양극산화 피막에 이산화망간을 피복한 다음 재화성을 할 때의 신틸레이숀의 대소는 양극산화피막의 결함 및 응력과 밀접한 관계가 있었다. 즉, 양극산화피막의 결함이 많을수록 응력이 클수록 신틸레이숀 전압이 낮아졌다. Flaws of a new shape in anodic Ta₂O_5 films on tantalum foils formed in aqueous solutions of phosphoric acid were observed by electron microscopy. A mechanism for the formation of the flaws is proposed by the present study. Modes of scintillation were dependent upon anodizing solutions used. Crystals formed during anodization of tantalum foils were identified as β-Ta₂O_5. Scintillation voltages at reanodization after MnO₂ application were closely related to flaws and stresses in the anodic oxide films. Namely, scintillation voltages decreased with increasing number of flaws and increasing stresses in the films.

Ti-Al-V 계 합금에서 Al 함량이 경도 및 조직에 미치는 영향

윤용구,정원용 대한금속재료학회(대한금속학회) 1982 대한금속·재료학회지 Vol.20 No.1

Effects of Al contents on the microstructure and hardness of Ti-Al-4V alloys were investigated after solution anneal and aging treatment of the alloys containing 4. 5, 6, 9 and 12% Al, respectively. The titanium alloys exhibited different α+ β⇔ βtransformation temperatures, and their hardness after solution anneal was influenced by the formation and decomposition of α' transformed from β, whereas the hardness after aging treatment was affected by the decomposition of α', agglomeration of βgrains and precipitation of α₂(Ti₃Al). It is believed that 4% V of the alloys kept fine α₂precipitates from growing and that the α₂, precipitates, in turn, retarded the agglomeration of β-grains. α₂precipitates of about 100Å were actually observed by transmission electron microscopy in Ti-9Al-4V and Ti-12Al-4V alloys after aging treatment whereas it was not possible to observe them in Ti-6Al-4V.

뫼스바우어 분광장치와 자화율 측정을 이용한 시효된 Fe-40wt.% Cr 합금의 상변태에 관한 연구

윤용구,박광석 대한금속재료학회(대한금속학회) 1993 대한금속·재료학회지 Vol.31 No.7

Phase transformation in Fe-40wt.%Cr binary alloy thermally aged at 475℃ was investigated by Mo¨ssbauer spectroscopy, superconductivity quantum interference device(SQUID) and vibrating sample magnetometer(VSM). Microhardness change accompanying its thermal aging was also studied. Microhardness of the binary alloy increased immediately and without saturation with aging up to 2000 hours. Specific saturation magnetization value(σ_s) measured at room temperature by VSM increased during the initial aging time of 2 hours to 1000 hours whereas it increased slowly during aging of 1000 to 2000 hours. Broadening of the six-line Mo¨ssbauer spectrum obtained at room temperature and additional appearance of paramagnetic peaks were observed for binary alloy specimens aged for a time range of 400 to 2000 hours. These observations indicate occurrence of phase separation into Fe-rich and Cr-rich region. Results of Curie temperature measurements for the Cr-rich region by SQUID indicate that the volume fraction and Cr concentration of the Cr-rich region increased with increasing aging time. These results lead to a conclusion that spinodal decomposition progresses during aging at 475℃ and the Fe-40wt.%Cr alloy and that gives rise to hardening of the alloy.

전기 화학적 방법을 이용한 이상스테인리스강의 시효 열화 진단에 관한 연구

김정식,윤용구,박준상 대한금속재료학회(대한금속학회) 1995 대한금속·재료학회지 Vol.33 No.8

Electrochemical methods were employed as nondestructive means of diagnosis of thermal aging embrittlement of cast duplex stainless steels of CF8 and CF8M grade. In polarization experiments conducted in 5wt% CH₃ COOH solution and the mixture of 0.5M H₂SO₄ and 0.01M KSCN, the anodic current density peak increased, with the aging time. SEM observations to investigate what gives rise to the increase of the anodic current density peak, however, indicated that such change was not related to the spinodal decomposition that was known to be the main cause of thermal aging embrittlement. In polarization experiments for CF8 grade specimens conducted in the mixture of 0.05M H₂SO₄ and 0.01M KSCN, two current density peaks, i_(peak1) and i_(peak2_ appeared. i_(peak1) was attributed to preferential dissolution of the ferrite phase and decreased by aging. The decrease of i_(paek1) was caused by the decrease of ferrite dissolution in aged specimens and reflected the degree of spinodal decomposition occurring in the ferrite phase. A correlation was established between the increase of ferrite hardness and Δi_(peak1)/ferrite%. It was suggested that thermal aging embrittlement of duplex stainless steels of CF8 grade could be evaluated nondestructively by electrochemical method.