• Title/Summary/Keyword: Eutectic silicon

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Electrochemical Reduction of SiO2 Granules to One-Dimensional Si Rods Using Ag-Si Eutectic Alloy

  • Lee, Han Ju;Seo, Won-Chul;Lim, Taeho
    • Journal of Electrochemical Science and Technology
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    • v.11 no.4
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    • pp.392-398
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    • 2020
  • Producing solar grade silicon using an inexpensive method is a key factor in lowering silicon solar cell costs; the direct electrochemical reduction of SiO2 in molten salt is one of the more promising candidates for manufacturing this silicon. In this study, SiO2 granules were electrochemically reduced in molten CaCl2 (850℃) using Ag-Si eutectic droplets that catalyze electrochemical reduction and purify the Si product. When Ag is used as the working electrode, the Ag-Si eutectic mixture is formed naturally during SiO2 reduction. However, since the Ag-Si eutectic droplets are liquid at 850℃, they are easily lost during the reduction process. To minimize the loss of liquid Ag-Si eutectic droplets, a cylindrical graphite container working electrode was introduced and Ag was added separately to the working electrode along with the SiO2 granules. The graphite container working electrode successfully prevented the loss of the Ag-Si eutectic droplets during reduction. As a result, the Ag-Si eutectic droplets acted as stable catalysts for the electrochemical reduction of SiO2, thereby producing one-dimensional Si rods through a mechanism similar to that of vapor-liquid-solid growth.

The Effect of Sr Addition and Mold Preheating Temperature on the Solidification and Microstructure of Al-7wt%Si-0.3wt%Mg Alloy (Al-7wt%Si-0.3wt%Mg 합금의 응고 및 미세조직에 미치는 Sr 첨가와 금형예열온도의 영향)

  • Kwon, Il-Soo;Kim, Kyoung-Min;Yoon, Eui-Pak
    • Journal of Korea Foundry Society
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    • v.17 no.6
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    • pp.608-614
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    • 1997
  • The effect of mold preheating temperature on the microstructure such as grain size, eutectic silicon morphology was investigated for the Al-7wt%Si-0.3wt%Mg alloy. Microstructural variations have been characterized as a function of Sr addition and cooling rate during solidification. Microstructures were correlated with cooling rate, local solidification time and eutectic nucleation temperature, etc. In this study, Sr addition caused increase of local solidification time, undercooling and reduction of eutectic plateau temperature. In logarithmic scale, local solidification time was in inverse proportion to cooling rate. Eutectic nucleation temperature was in inverse proportion to cooling rate of logarithmic scale. Increasing the cooling rate refined dendrite arm spacing and eutectic silicon. Dendrite arm spacing was logarithmically in inverse proportion to cooling rate. Without modifier addition, eutectic silicon was modified at cooling rate of $7^{\circ}C/s$ or higher.

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The Effect of Electromagnetic Vibration on Eutectic Si Size in Hypoeutectic Al-Si alloys (아공정 Al-Si합금에 있어서 공정 Si크기에 미치는 전자기진동의 영향)

  • Choi, Jung-Pyung;Yoon, Eui-Pak;Nam, Tae-Woon
    • Journal of Korea Foundry Society
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    • v.24 no.2
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    • pp.79-84
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    • 2004
  • In this study, the electromagnetic vibration is adopted for modifying eutectic Si phase and reducing its size. The higher the current density and frequency of electromagnetic vibration(EMV), the finer the size of eutectic Si phase. The tensile strength and elongation of EMVed alloy were highly improved. Measured twin probability of EMVed alloy at a frequency of 1000 Hz was approximately six times as high as that of the normal alloy. The mechanism for the increase in twin density due to EMV during solidification could be supposed from the fact that the preferential growth along <112> in silicon was suppressed by preventing Si atom from attaching to the growing interface of Si phase and by changing the solid/liquid interfacial energy of silicon. According to the result of UTS test, because of modification of eutectic Si, UTS and elongation are highly increased.

Effects of Thickness, Base Element and Additive to Inoculant on the Number of Eutectic Cells and Chill Depth of Thin-Section Gray Cast Iron (박육주철의 공정 셀 수와 칠 깊이에 미치는 두께, 기본 원소 및 접종제 첨가 원소의 영향)

  • Kim, Tae-Hyeong;Lee, Woo-Jong;Kwon, Hae-Wook
    • Journal of Korea Foundry Society
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    • v.32 no.6
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    • pp.261-268
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    • 2012
  • The effects of thickness, base element and additive to inoculant on the number of eutectic cells and chill depth of thin-section gray cast iron were investigated. Meanwhile the number of eutectic cells increased by inoculation, chill depth decreased. The former decreased and the latter increased by holding the melt at the temperature range between 1,450 and $1,500^{\circ}C$. The former was more for the thinner casting with the thickness of 5 mm than the other. The result of thermal analysis coincided well with the change of macrostructure. The former increased and the latter decreased with the increased contents of carbon, silicon and the silicon content by inoculation. The former decreased and the latter increased with increased manganese content. The number of eutectic cells decreased as the amounts of rare earth and the bismuth added to this inoculant increased. With the addition of sulfur of 0.10 wt% of the weight of this inoculant, the maximum number of eutectic cells was obtained.

Molecular Dynamics Simulation of Nano-Deformation Behavior of the Grain-Size Controlled Rheology Material (분자동력학을 이용한 결정립 제어 레오로지 소재의 나노 변형거동 전산모사)

  • Kim J. W.;Youn S. W.;Kang C. G.
    • Transactions of Materials Processing
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    • v.14 no.4 s.76
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    • pp.319-326
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    • 2005
  • In this study, the nano-deformation behavior of semi-solid Al-Si alloy was investigated using a molecular dynamics simulation as a part of the research on the surface crack behavior in thixoformed automobile parts. The microstructure of the grain-size controlled Al-Si alloy consists of primary and eutectic regions. In eutectic regions the crack initiation begins with initial fracture of the eutectic silicon particles and inside other intermetallic phases. Nano-deformation characteristics in the eutectic and primary phase of the grain-size controlled Al-Si alloy were investigated through the molecular dynamics simulation. The primary phase was assumed to be single crystal aluminum. It was shown that the vacancy occurred at the zone where silicon molecules were.

Microstructural Characteristics of SiC Particle Reinforced Aluminum Alloy Composite by Squeeze Casting (Squeeze Casting에 의한 SiC 입자강화 Al합금기 복합재료의 미세조직 특성)

  • Kim, Sug-Won;Woo, Kee-Do;Han, Sang-Won
    • Journal of Korea Foundry Society
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    • v.15 no.6
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    • pp.566-573
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    • 1995
  • In this study, the microstructural characteristics such as primary silicon, eutectic silicon, $SiC_p$ dispersion behavior, compound amount and Si solubility in $Al/SiC_p$ composite fabricated by the squeeze casting under various conditions were investigated systematically. As applied pressure(MPa) increases, cooling rate and compound amount are increased. In gravity casting, the cooling rate of hypereutectic composite is slower than of hypoeutectic composite by exothermic reaction of primary Si crystallization. But the cooling rate of hypereutectic composite is faster than that of hypoeutectic composite fabricated by same applied pressure, because amount of primary Si crystallization in hypereutectic composite was decreased, on the contrary, primary ${\alpha}-Al$ in hypoeutetic composite was increased due to increase of Si solubility in matrix by applied pressure. The crystalized primary silicon in hypereutectic composite fabricated by squeeze casting become more fine than that in non-pressure casting This is because mush zone became narrow due to increase of Si content of eutectic composition by pressure and time for growth of primary silicon got shorter according to applied pressure. It is turned out that eutectic temperature and liquidus are decreased by the increasing of squeeze pressure in all the composite due to thermal unstability of matrix owing to increasing of Si solubility in matrix by the increasing of applied pressure, as indicated in thermal anaiysis(DSC) results.

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The Effects of Alloying Elements and Cooling Rates on the Formation of Phosphide Eutectics of Wear Resistance CV Graphite Cast Irons (내마모 CV흑연주철의 공정인화물 형성에 미치는 합금원소 및 냉각속도의 영향)

  • Park, Heung-Il;Kim, Myung-Ho
    • Journal of Korea Foundry Society
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    • v.9 no.4
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    • pp.311-319
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    • 1989
  • The effects of the alloying elements and cooling rates on the formation of phosphide eutectics of compacted vermicular graphite cast irons containing copper, tin, molybdenum for producing pearlitic matrix, and also containing phosphorus and boron for increasing wear resistance, were investigated. The liquidus phosphide eutectic was found to solidify as a pseudo-binary phosphide eutectic, but with increasing of the cooling rate non-equlibrium phosphide eutectic with needle type carbide could be formed. However, the liquidus phosphide eutectic containing both phosphorus and carbide-forming boron was found to solidify always as a non-equlibrium phosphide eutectic with coarse carbide, independent from the cooling rate. It was also confirmed that the tiny isolated phase observed by SEM was gamma iron solid solution with phosphorus, silicon, molybdenum and the matrix containing these tiny islands was phosphide phase containing manganese and molybdenum. The addition of copper was found to decrease the tendency of forming ledeburitic carbides in the phosphide eutectic.

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Behavior of Eutectic Si and Mechanical Properties of Sr Modified Al-7Si-0.35Mg alloy with Solid Solution Treatment for Sand Casting (Sr 개량처리된 사형주조 Al-7Si-0.35Mg 합금의 열처리에 따른 공정 Si상 변화거동 및 특성평가)

  • Kim, Myoung-Gyun;Hwang, Seok-Min
    • Journal of Korea Foundry Society
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    • v.38 no.1
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    • pp.1-8
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    • 2018
  • In this study, we focused on the correlation between the solidification structure, heat treatment and mechanical properties of the A356 alloy according to the conditions of Sr modification. The microstructural evolution of the eutectic Si and ${\alpha}-Al$ phase in the A356 alloy castings depending on the amount of Sr were investigated during solid solution heat treatment using an optical microscope, a scanning electron microscope and an image analyzer. In addition, tensile tests on the heat treated materials examined the relationship between the microstructure and the fracture surface. The as-cast A356 alloys under 40 ppm Sr showed an undermodified microstructure, but that of the added 60-80 ppm Sr had well modified structure of fine fibrous silicon. After solid solution treatment, the microstructure of the undermodified A356 alloy exhibited a partially spheroidized morphology, but the remainder showed the fragmentation of fibrous shaped silicon. The spheroidization of the eutectic silicon in the modified A356 alloys was completed during heat treatment, which was very effective in increasing the elongation. This is supported by the fracture surface in the tensile test.

Effects of Thickness, Base Element and Inoculants on the Number of Eutectic Cells and Chill Depth of Gray Cast Iron Plate Casting (회주철 판형 주조품의 공정 셀 수와 칠 깊이에 미치는 두께, 기본 원소 및 접종제의 영향)

  • Kim, Tae-Hyeong;Oh, Jung-Hyuck;Kwon, Hae-Wook
    • Journal of Korea Foundry Society
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    • v.31 no.3
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    • pp.137-144
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    • 2011
  • The effects of thickness, base element and inoculants on the number of eutectic cells and chill depth of gray cast iron plate casting were investigated. Meanwhile the number of eutectic cells increased by inoculation, chill depth decreased. The former decreased and the latter increased by holding the melt at the temperature range between 1,450 and $1,500^{\circ}C$. The former was more for the thinner casting with the thickness of 5 mm than the other. The result of thermal analysis coincided well with the change of macrostructure. The former increased and the latter decreased with the increased contents of carbon, silicon and the silicon content by inoculation. The former decreased and the latter increased with increased manganese content. The performance of the Superseed Extra was the best among 5 inoculants.

Effects of Thickness, Si and Mn Contents on the Mechanical Properties of 3.3 wt%C-0.1 wt%S Thin-Section Gray Cast Iron (3.3 wt%C-0.1 wt%S 박육 주철의 기계적 성질에 미치는 두께, 규소 및 망간의 영향)

  • Lee, Woo-Jong;Kim, Tae-Hyeong;Kwon, Hae-Wook
    • Journal of Korea Foundry Society
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    • v.32 no.5
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    • pp.211-218
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    • 2012
  • The effects of thickness, silicon and manganese contents on the mechanical properties of 3.3 wt%C-0.1 wt%S thin-section gray cast iron plates were investigated. The eutectic cell counts and volume fraction of pearlite in the matrix decreased with increased thickness and therefore the strength and hardness decreased with it. Even though the eutectic cell count increased with increased silicon content, the volume fraction of pearlite decreased and the strength and hardness decreased with it. The pearlite was refined more with increased manganese content and therefore the strength and hardness increased with it.