• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2007년도 하계학술대회 논문집 Vol.8
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• pp.375-375
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• 2007

In the conventional crystallization method, thepoly-Si TFTs show poor device-to-device uniformity because of the random location of the grain boundaries. However, our new crystallization method introduced in this paper employed substrate-embedded seeds on the highly ordered anodic alumina template to control both the location of seeds and the number of grain boundaries intentionally. In the process of excimer laser crystallization (ELC), a-Si film deposited on the anodic alumina by low pressure chemical vapor deposition (LPCVD) is transformed into fine poly-Si grains by explosive crystallization (XC) prior to primary melting. At the higher energy density, the film is nearly completely melted and laterally grown by super lateral growth (SLG) from remained small part of the fine poly-Si grains as seeds at the Si/anodic alumina interface. Resultant grain boundaries have almost linear functions of the number of seeds in concavities of anodic alumina which have a constant spacing. It reveals the uniformity of. device can be enhanced prominently by controlling location and size of pores which contains fine poly~Si seeds under artificial anodizing condition.

• 한국세라믹학회지
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• 제29권3호
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• pp.211-215
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• 1992

Crack free PbTiO3 ceramics were produced by sol-gel processing using alkoxide, which has not been reported to be successful. The PbTiO3 gels were prepared from Ti alkoxide and lead acetate without any dopants. They were calcined at $600^{\circ}C$ and miled to produce fine PbTiO3 powder. It was pressed into discs and they were sintered at 110$0^{\circ}C$ for a few hours. The sintered ceramics were relativley hard and dense as having about 96% of theoretical density of PbTiO3. Fabrication of pure PbTiO3 ceramics by sol-gel processing is possibly due to their small grain size and uniform distribution of residual stress created during cubic-tetragonal transition over large number of small grains in fine grain PbTiO3 ceramics.

• Journal of Welding and Joining
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• 제31권3호
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• pp.17-21
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• 2013

Sn whiskers are one of the serious causes of the failure of electronics. Sn whiskers grow spontaneously from Sn-based, lead-free finished surfaces, even at room temperature. A primary factor of these Sn whiskers growth is compressive stress, which enhances the diffusion of Sn or other elements. The sources of compressive stress are the growth of non-uniform large intermetallic compounds along the interface between the Sn grain boundary and Cu substrate. Recent studies revealed the methods for reducing Sn whisker growth. This paper gives an overview about recent researches for mitigation methods of Sn whisker growth during nearly room temperature storage.

• 한국세라믹학회지
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• 제26권4호
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• pp.493-498
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• 1989

High purity, submicron BaTiO3 powder was prepared by a hydrothermal technique using Ba(OH)2.8H2O, TiCl4 and NH4OH as starting raw materials. The submicron BaTiO3 powder was synthesized at 130~23$0^{\circ}C$ for 2.5h to yield highly crystalline particles with a narrow particle distribution. The mole ratio of Ba(OH)2.8H2O/TiO(OH)2 was 1.5. It is possible to obtain BaTiO3 with Ba : Ti=1.00$\pm$0/01. The samples densified well at 13$25^{\circ}C$, showing a uniform and fine grain structure. The grain size ranged between 0.3 and 0.5${\mu}{\textrm}{m}$. The products obtained by hydrothermal treatment at various temperatures from 130 to 23$0^{\circ}C$ were characterized by XRD, DTA, BET and SEM etc.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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• pp.654-655
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• 2006

This is about the effects deoxidization, carbonization and alloying preparation on fine grain W, WC, and grade YG8 powder reduced by "yellow tungsten oxide" and "blue tungsten oxide". The result indicates that yellow tungsten has single composition and blue tungsten oxide has complex composition. With this feature, yellow tungsten oxide got better uniformity and concentration distribution on fine particle size W and WC powder than blue tungsten oxide's. The grade alloy YG8 that made of this W or WC powder has uniform alloy construction, concentrated WC grain distribution and better alloy properties.

• 한국표면공학회지
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• 제33권4호
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• pp.273-280
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• 2000

Silver was deposited on glass by electroless plating and electroplating. Surface properties were investigated using the AFM. Crystal structure of deposit layers was confirmed by TEM and XRD. Electroplating is performed by DC plating and pulse plating, respectively. This study resulted in followings, first, deposit of electroless plating showed fine grain and was similar to the amorphous structure. Second, electrodeposit on the electroless layer was revealed following results ; (1) more uniform layer and finer grains were obtained with increasing frequency (2) more isotropic structure was obtained with increasing frequency (3) finer grains at 25% duty cycle was obtained (4) grain size and roughness of the silver deposit was decreased with increasing frequency.

• 한국세라믹학회지
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• 제29권4호
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• pp.253-258
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• 1992

ZnO varistors were prepared by the organochemical method which used citric acid and ethylene glycol as gelling agents. The microstructure of the sintered specimens exhibited small grains, uniform grain size distribution, and few intragranular pores. Thermal decomposition of the organic resin formed during the powder preparation process was completed around 450$^{\circ}C$. No significant changes were observed in microstructure and current voltage characteristic with respect to calcination temperatures. A major advantage of the organochemical method used in this experiment is a possible uniform mixing of trace amounts of dopants. Therefore, this powder preparation method seems promising in investigating the effect of Li or In ion, which is added in ppm level to ZnO varistors, on the pulse respose characteristic.

• Journal of Magnetics
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• 제1권1호
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• pp.31-36
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• 1996

An externally applied magnetic field during heat treating the $Nd_2Fe_{14}B/Fe_3B$ based spring magnet was found to enhance the exchange coupling between the hard and soft magnetic grains. More than 30% increase in $M_r/M_s$ values for melt-spun $Nd_2Fe_{73.5}Co_3$$(Hf_{1-x}Ga_x)B_{18.5}$ (x=0, 0.5, 1) alloys was resulted from a uniform distribution of $Fe_3B, \alpha-Fe$ and $Nd_2Fe_{14}B$ phases, and also from a reduced grain size of those phases by 20%. The externally applied magnetic field induced a uniform distribution of fine grains. A study of Mossbauer effect also report that the enhancement of total magnetization of nanocomposite $Nd_2Fe_{14}B/Fe_3B$ alloys is attributed to an increased formation of $Fe_3$B after magnetic annealing.

• 소성∙가공
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• 제28권5호
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• pp.257-265
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• 2019

Multi-axial forging (MAF), a severe plastic deformation technique, is known to be difficult to obtain materials with homogeneous microstructures. Recently, multi-axial diagonal forging (MADF) process has been developed to solve this problem. In this study, in order to compare the microstructural and mechanical homogeneities of the MAFed and MADFed samples, oxygen-free copper (OFC) cubes measuring 25 mm in length were deformed through MAF and MADF processes and the average grain size and hardness were measured at the edge, face, and center regions of the samples. In the MAFed samples, ultrafine grains were formed at the center region, but a considerable amount of coarse grains remain at the face region. Therefore, the MAFed samples showed a high inhomogeneity in regards to grain size and hardness. On the contrary, in the case of the MADFed sample, the grain sizes at the edge, face, and center regions were similar and the hardness in all the regions are almost similar. This indicates that the MADFed sample has a homogeneous microstructure and uniform mechanical properties, which can be attributed to the homogeneous distribution of the effective strain throughout the material. The results of this study suggests that the MADF is a suitable process in the fabrication of high-strength copper materials with a homogeneous and ultrafine grain structure.

• Journal of Biosystems Engineering
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• 제15권1호
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• pp.1-13
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• 1990

Aerodynamic property is the most important factor in designing the pneumatic separator and handling equipment for grains and seeds. Particularly the correct information about the terminal velocities of the corresponding grains and seeds is indispensible. However, a few studies with relation to the terminal velocities of grains and seeds were conducted in this country, even though the terminal velocities of the domestic grains and seeds are required to design those equiments which can be used for the domestic grains and seeds having specific aerodynamic properties. In this study, the terminal velocities for four varieties of varley and six varieties of paddy were investigated by means of two different methods, the suspension method and the drop method in an upward current of air. For measuring the terminal velocities, the vertical wind tunnel which had been examined about the uniform air flow in the previous study was used. In addition, the effect of the size of grains and the moisture content of grain kernel on the terminal velocity was examined. The following conclusions were derived from the study : 1. The different terminal velocities of grains are resulted from the different measuring methods. The terminal velocity measured by the drop method is smaller than that by the suspension method. It is considered that the difference in the terminal velocities is caused by the difference in the projection area of grain which is faced to the air stream. 2. The terminal velocity of grain increases as the size and the moisture content of the kernel increase. 3. The linear regression equations for the terminal velocities of grains were derived in terms of the moisture content of grains by the variety of grains and the measuring method. Also, the linear regression equations for the terminal velocity, based on the weighted size of grains, were derived in terms of the moisture contents of granis.