• 한국세라믹학회지
• /
• 제31권4호
• /
• pp.443-447
• /
• 1994

Compacts of mixed SiO2-Si powder were liquid phase sintered at 145$0^{\circ}C$ for up to 60 min in a hydrogen atmosphere. In contrast to the conventional microstructures of liquid phase sintered materials, the specimens showed that the solid phase of SiO2 formed a matrix while the liquid phase of Si was the dispersed in the solid matrix. The dispersion of liquid Si pockets was attributed to the high wetting angle of liquid Si on solid SiO2. Because of relatively high solubility of SiO2 in liquid Si at 145$0^{\circ}C$, SiO2 particles accommodated their shape via a solution-reprecipitation process. The liquid Si pockets grew by coalescing with their neighbour pockets. In the latter stage of the sintering, plate-shape grains appeared in the liquid Si pockets. The grains were SiO2 phase precipitated from the liquid Si which was oversaturated with oxygen during cooling to room temperature. By the formation and subsequent removal of the gaseous SiO phase due to the reaction between SiO2 and Si, the specimens became porous.

• 한국재료학회지
• /
• 제18권11호
• /
• pp.604-609
• /
• 2008

The sintering behavior of zircon with silica was investigated. Zircon with 5 vol% of sedimentation $SiO_2$ resulted in the apparent density of $4.45\;g/cm^3$, the diametral tensile strength of $12.125\;kgf/cm^2$, and the micro Vickers hardness of 1283 HV. The dissociation temperature and mechanical characteristics of the $ZrSiO_4$ were changed with different kinds of $SiO_2$. $SiO_2$ addition prevented dissociation of $ZrSiO_4$. Zircon with 5 vol% of sedimentation $SiO_2$ and with 5 vol% of fused $SiO_2$ resulted in increased diametral tensile strength and increased micro Vickers hardness by suppression of $ZrSiO_4$ dissociation and low temperature liquid $SiO_2$ formation. Zircon with fumed $SiO_2$ and quartz $SiO_2$ resulted in decreased diametral tensile strength and decreased micro Vickers hardness because of cristobalite and quartz phase formation and high temperature liquid $SiO_2$ formation. Zircon with 10 vol% of $SiO_2$ resulted in decreased diametral tensile strength and decreased micro Vickers hardness because of weak particle coupling due to excess formation of liquid $SiO_2$.

• Journal of Electrochemical Science and Technology
• /
• 제11권4호
• /
• pp.392-398
• /
• 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.

• 한국세라믹학회지
• /
• 제44권6호
• /
• pp.319-324
• /
• 2007

The structural properties of $SiO_2$ liquid at finite temperatures have been investigated by molecular dynamics (MD) simulations utilizing the Tersoff interatomic potential. During cooling process, the $SiO_2$ liquid structure quenched with a cooling rate of $1.0{\times}10^{11}K/sec$ shows the traditional properties observed in the experiments. The coordination defects of system decrease with decreasing temperature up to 17%. The $SiO_2$ glass quenched up to 1600 K contains defects consisting of the fivefold coordination of Si, and the threefold coordination of O atoms. The calculated diffusion coefficients which are calculated by monitoring. the mean-square displacement of atoms drop to almost zero below 3000 K ($<10^{-6}\;cm^2/sec$) but has a fluctuations at low temperature. The structure properties of $SiO_2$ liquid shows a significant dependence on the temperature during cooling process. Bond-angle distribution at around $120^{\circ}$ originate from the O and Si atoms consisting of the over-coordinated O atoms.

• 한국결정성장학회지
• /
• 제11권3호
• /
• pp.127-131
• /
• 2001

산화물계의 액상소결시 액상량을 변수로 하여 입자형성이 입자성장 거동에 미치는 영향을 고찰하였다. 산화물계 모델로 구형입자의 경우는 MgO$CaMgSiO_{4}$계를 선택하였으며, 각진입자의 경우는 $Al_{2}O_{3}$/ $CaAl_{2}Si_{2}O_{8}$계를 선택하였다. 구형입자인 MgO의 경우 액상량 증가에 따라 입자크기가 감소하였으나,각진입자인 $Al_{2}O_{3}$ 입자의 경우는 계면지배과정에 의해 성장하는 반면, 거친 고상/액상계면을 지닐 것으로 예상되는 구형 MgO입자의 경우는 확산지배과정에 의해 성장하였다.

• 한국세라믹학회지
• /
• 제52권3호
• /
• pp.215-220
• /
• 2015

Phase evolution, microstructure, and microwave dielectric properties of $Li_2O$ and $Al_2O_3$ doped $Zn_{1.9}Si_{1.05}O_4$, i.e., $Zn_{1.9-2x}Li_xAl_x-Si_{1.05}O_4$, ceramics (x = 0.02 ~ 0.10) were investigated. The ceramics were densified by $SiO_2$-rich liquid phase composed of the Li-Al-Si-O system, indicating that doped Li and Al contributed to the formation of the liquid. As the secondary phase, ${\beta}$-spodumene solid solution with the composition of $LiAlSi_3O_8$ was precipitated from the liquid during the cooling process. The dense ceramics were obtained for the specimens of $$x{\geq_-}0.06$$ showing the rapid densification above $1000^{\circ}C$, implying that a certain amount of liquid is necessary to densify. The specimen of x = 0.06 sintered at $1050^{\circ}C$ exhibited good microwave dielectric properties; the dielectric constant and the quality factor ($Q{\times}f_0$) were 6.4 and 11,213 GHz, respectively.

• 한국결정성장학회지
• /
• 제10권1호
• /
• pp.30-35
• /
• 2000

부상응고법은 액상 받침 재료 위에 용융 재료를 띄워서 응고시키는 방법으로 판유리 제조가 대표적이며, 이러한 방법을 이용하여 Si 판재를 얻기 위한 실험을 하였다. 본 연구에서는 액상받침재료에 요구되는 물리 화학적인 성질을 고려하여 3원계 산화물 상태도를 조사한 후, 적절한 액상받침재료로 50 wt% $SiO_2$- 2l wt% $A1_2$$O_3$-29 wt% MnO를 이용하였다. 실험결과 본 연구에서 이용한 받침재료는 온도와 밀도, Si의 반응성 면에서 적절한 성질을 나타내었으나, 유동도 및 계면 장력면에서 문제점을 나타내었다.

• Current Research on Agriculture and Life Sciences
• /
• 제4권
• /
• pp.1-6
• /
• 1986

수도(水稻) 생육초기(生育初期)에 규산(珪酸)을 처리(處理)할 때 유묘(幼苗)의 엽선단(葉先端)으로부터 배출(排出)되는 일액량(溢液量)과 일액(溢液)을 통(通)해 어느 정도((程度) 규산(珪酸)이 외부(外部)로 배출(排出)되며, 일액중(溢液中)의 규산(珪酸)과 엽소(葉燒)와의 관계(關係)를 구명(究明)하고저 다수계(多收系) 품종(品種) 삼강벼와 일반계품종(一般系品種) 낙동벼를 공시(供試)하여, 온도범위(溫度範圍)가 $29{\sim}33^{\circ}C$인 실내(室內) 자연광하(自然光下)에서 $50cm{\times}150cm{\times}70cm$인 vinyl 상자(箱子)로 밀폐(密閉)하여, 수경(水耕) 재배(栽培)한 수도(水稻) 유묘(幼苗)에서 채취(採取)한 일액중(溢液中)의 규산(珪酸)을 분절(分折) 조사(調査)하여던 바 결과(結果)를 요약(要約)하면 다음과 같다. 1. 규산(珪酸) 처리(處理) 농도(濃度)가 200ppm까지 증가(增加)할수록 일액량(溢液量)은 증가(增加)하였으며, 규산(珪酸) 처리(處理) 농도(濃度)가 200ppm 일때 일액량(溢液量)은 낙동벼 4.30mg/plant, 삼강벼 4.34mg/plant이었으며, 250ppm이상(以上)에서는 일액량(溢液量)이 감소(減少)하였다. 2. 규산(珪酸) 처리(處理) 농도(濃度)가 높을수록 일액량(溢液量) 함유(含有)되어 있는 규산(珪酸)의 농도(濃度)는 증가(增加)하였으며, 일액중(溢液中) 규산(珪酸)의 농도(濃度) 대(對) 규산(珪酸) 처리(處理) 농도(濃度) 비(比)는 100ppm 이상(以上)에서는 감소(減少)하였다. 3. 처리(處理)된 규산(珪酸)은 단시간(短時間)에 수도근(水稻根)으로 흡수(吸收)되어 일액(溢液)을 통(通)해 배출(排出)되며 처리(處理) 후(後) 12시간(時間)에 배출(排出)된 일액(溢液)에 규산(珪酸)의 함량(含量)이 가장 많았으며, 규산(珪酸) 처리(處理) 300ppm에서의 일액중(溢液中) 규산(珪酸)의 농도(濃度)는 낙동벼 $SiO_2$ 172.6ppm/cc, 삼강벼 $SiO_2$ 199.8ppm/cc이었다. 4. 일액중(溢液中)에 함유(含有)되어 있는 규산(珪酸)의 농도(濃度)와 엽소(葉燒)의 정도(程度)는 정(正)의 상관(相關)(낙동벼 $r=0.97^{**}$, 삼강벼 $r=0.97^{**}$)이 있었다.

• 한국세라믹학회지
• /
• 제23권5호
• /
• pp.47-54
• /
• 1986

The structures of crystalline vitreous and liquid $SiO_2$ were Monte carlo simulated employing the potential energy function comprising Lennard-Jones 2-body and Axilrod-Teller 3-body potentials. Although the Si-O-Si angular distribution functions obtained in the simulation appear to be higher than the experimental results the other simulation results including SiO, O-O and Si-Si radial distribution functions and O-Si-O anglular distribution functions agree well with experimental data within acceptable limits. Themost important outcome in this study is that various $SiO_2$forms were successfully reproduced with the same potential energy function.

• 한국해양공학회지
• /
• 제22권4호
• /
• pp.59-64
• /
• 2008

The mechanical properties of liquid phase sintered (LPS) SiC materials, with the addition of oxide powder, were investigated, in conjunction with a detailed analysis of their microstructures. LPS-SiC materials were fabricated at a temperature of 1820 $^{\circ}C$ under an argon atmosphere, using three different starting sizes of SiC particles. The sintering additive for the fabrication of the LPS-SiC materials was an $Al_2O_3-Y_2O_3$ mixture with a constant composition ratio ($Al_2O_3/Y_2O_3$: 1.5). The particle sizes of the commercial SiC powderswere 30 nm, 0.3 $\mu$m, and 3.0 $\mu$m. The flexural strength of the LPS-SiC materials was also examined at elevated temperatures. A decrease in the starting size of the SiC particles led to an increase in the flexural strength of the LPS-SiC materials, accompanying a highly dense morphology with the creation of a secondary phase. Such a secondary phase was identified as $Y_3Al_2(AlO_4)2$. The flexural strength of the LPS-SiC materials greatly decreased with an increase in the test temperature, due to the creation of a large amount of pores.