• Title/Summary/Keyword: 2D nucleation

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The Application of TiO2 Hollow Spheres on Dye-sensitized Solar Cells

  • Cho, H. J.;Jung, D.
    • Bulletin of the Korean Chemical Society
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    • v.32 no.12
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    • pp.4382-4386
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    • 2011
  • $TiO_2$ hollow spheres were fabricated by using $SiO_2$ as an inorganic template. Spherical $SiO_2$ particles were coated by $TiO_2$ through the nucleation process, and then the core $SiO_2$ part was eliminated by using HF solution. Finally, $TiO_2$ hollow spheres were obtained. The size of the $TiO_2$ hollow spheres was about 300-400 nm and the thickness of the hollow wall was about 20-30 nm. The hollow has several holes whose diameters were within 100-200 nm. Dye-sensitized solar cells fabricated by using the $TiO_2$ hollow spheres were characterized. The solar conversion efficiency of the cell was 8.45% when $TiO_2$ hollow spheres were used as a scattering material, while it was 4.59% when $TiO_2$ hollow spheres were used as a normal electrode material.

Synthesis of Potassium Hexatitanate with Non-Fibrous Shape as a Raw Material for Friction Material in Brake System (자동차 브레이크 마찰재용 비침상형 육티탄산칼륨의 합성 연구)

  • Lee, Jung Ju;Lee, Na-Ri;Pee, Jae-Hwan;Kim, Jong-Young;Kim, Jeong-Joo
    • Korean Journal of Materials Research
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    • v.27 no.3
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    • pp.132-136
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    • 2017
  • We synthesized potassium hexatitanate, ($K_2Ti_6O_{13}$, PT6), with a non-fibrous shape, by acid leaching and subsequent thermal treatment of potassium tetratitanate ($K_2Ti_4O_9$, PT4), with layered crystal structure. By controlling nucleation and growth of PT4 crystals, we obtained splinter-type crystals of PT6 with increased width and reduced thickness. The optimal holding temperature for the layered PT4 was found to be ${\sim}920^{\circ}C$. The length and width of the PT4 crystals were increased when the nucleation and growth time were increased. After a proton exchange reaction using aqueous 0.3 M HCl solution, and subsequent heat treatment at $850^{\circ}C$, the PT4 crystal transformed into splinter-type PT6 crystals. The frictional characteristics of the friction materials show that as the particle size of PT6 increases, the coefficient of friction (COF) and wear amounts of both the friction materials and counter disc increase.

Behavior of boiling heat transfer at coated heating surface(In the range of subatmosptheric pressure) (피복된 전열면에서의 비등특성(대기압 이하의 압력에서))

  • Moon D.Y;Oh S.C.;Yim C.S
    • The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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    • v.6 no.1
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    • pp.1-8
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    • 1977
  • This paper describes an experimental investigation which has been carried out with distilled water with the range of heat flux and pressure covering 7,400-28,000kcal/$m^2/h$ and 0.42-1.0332kg/$cm^{2}abs$, respectively. In this experiment, Nickel coated mirror surface heater of 5 cm O.D. was used as a heating source. The conclusions summerized as follows;1. The useful correlation of the test data for the heat transfer coefficient is presented as a function of the pressure. $$a/a_{s}=c{\times}p\;0.18$$ where a is the heat transfer coefficient and $a_s$ is the heat transfer coefficient at atmospheric pressure and p is the pressure, C is constant. 2. The bubble diameter near the heating surface and rising velocity increased with the heat flux. 3. A decrease in pressure results in the decrease of the number of nucleation sites and the increase of the bubble volume. 4. Bubble rising velocity differences are incrased maximumly up to $200\%$ of that at atmopheric pressure.

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열분해 반응기 내에서의 Si 오염입자에 관한 수치해석적 연구

  • U, Dae-Gwang;Kim, Tae-Seong
    • Proceedings of the Korean Vacuum Society Conference
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    • 2011.02a
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    • pp.363-363
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    • 2011
  • 열분해 반응기 내에서 실리콘 필름을 성장시키는 것은 반도체/디스플레이, 태양전지, 신소재 등 다양한 분야에서 중요한 공정이다. 더욱이 반도체 소자 선폭이 줄어들면서 나노입자의 오염 제어가 더불어 중요해지고 있다. 생산 공정 기술의 집적화에 따라 패턴 사이 거리가 작아지고, 이에 불과 수 십 나노미터크기의 오염입자에 의해서 패턴불량이 발생하고 생산수율을 감소시킨다. 일반적으로 반도체 공정 중 발생한 오염입자는 반응기 내의 가스가 물리/화학적 공정에 의해 핵생성(nucleation)이 일어나 핵(nuclei)이 생성되고, 이 때 표면반응 및 응집(coagulation)에 의해 성장하게 된다. 이에 본 연구에서는 열분해 반응기 내에서 사일렌(SiH4) 가스를 열분해하여 발생되는 실리콘 오염입자의 핵생성과 성장 모델을 정립하고, 생성된 오염입자의 거동과 전달 현상을 이론적으로 고찰하였다. 열분해 반응기와 같은 기상공정(Gas to particle conversion)에서 오염입자가 생성될 때, 그 성질과 크기 등에 물리/화학적 영향을 주는 요소는 전구체/이송기체의 농도 및 유량, 작동 압력, 작동 온도와 반응기 고유 특성 등이 있다. 수치해석의 정당성과 빠른 계산을 위해 단순화시킨 0D 모델인 Batch 반응기와 1D모델인 plug flow 반응기 등에서 SiH4 가스의 열분해 과정시 생성되는 Si cluster를 상용코드인 CHEMKIN 4.1.1을 이용하여 계산하였으며, 2D모델인 Shear flow 반응기로 확장시켜 Si 오염입자가 생성특성을 연구하였다.

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Enhancement of Density and Piezoelectric Properties of 0.96(K0.456Na0.536)Nb0.95Sb0.05-0.04Bi0.5(Na0.82K0.18)0.5ZrO3 Lead-Free Piezoelectric Ceramics through Two-Step Sintering Method (Two-Step 소결법을 통한 0.96(K0.456Na0.536)Nb0.95Sb0.05-0.04Bi0.5(Na0.82K0.18)0.5ZrO3 무연 압전 세라믹의 밀도 및 압전 특성 향상)

  • Il-Ryeol Yoo;Sang-Hyun Park;Seong-Hui Choi;Kyung-Hoon Cho
    • Korean Journal of Materials Research
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    • v.34 no.2
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    • pp.116-124
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    • 2024
  • In this study, we investigated the microstructure and piezoelectric properties of 0.96(K0.456Na0.536)Nb0.95Sb0.05-0.04Bi0.5(Na0.82K0.18)0.5ZrO3 (KNNS-BNKZ) ceramics based on one-step and two-step sintering processes. One-step sintering led to significant abnormal grain (AG) growth at temperatures above 1,085 ℃. With increasing sintering temperature, piezoelectric and dielectric properties were enhanced, resulting in a high d33 = 506 pC/N for one-step specimen sintered at 1,100 ℃ (one-step 1,100 ℃ specimen). However, for one-step 1,115 ℃ specimen, a slight decrease in d33 was observed, emphasizing the importance of a high tetragonal (T) phase fraction for superior piezoelectric properties. Achieving a relative density above 84 % for samples sintered by the one-step sintering process was challenging. Conversely, two-step sintering significantly improved the relative density of KNNS-BNKZ ceramics up to 96 %, attributed to the control of AG nucleation in the first step and grain growth rate control in the second step. The quantity of AG nucleation was affected by the duration of the first step, determining the final microstructure. Despite having a lower T phase fraction than that of the one-step 1,100 ℃ specimen, the two-step specimen exhibited higher piezoelectric coefficients (d33 = 574 pC/N and kp = 0.5) than those of the one-step 1,100 ℃ specimen due to its higher relative density. Performance evaluation of magnetoelectric composite devices composed of one-step and two-step specimens showed that despite having a higher g33, the magnetoelectric composite with the one-step 1,100 ℃ specimen exhibited the lowest magnetoelectric voltage coefficient, due to its lowest kp. This study highlights the essential role of phase fraction and relative density in enhancing the performance of piezoelectric materials and devices, showcasing the effectiveness of the two-step sintering process for controlling the microstructure of ceramic materials containing volatile elements.

Measurement of Hydrogenation Characteristics of Pd Film by Using Electrical Resistivity Measurement Technique (전기저항 측정법을 이용한 Pd박막의 수소화 특성 측정)

  • Cho, Young-Sin;Lee, Ho-Jae;Lee, Jong-Suk
    • Journal of Hydrogen and New Energy
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    • v.7 no.2
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    • pp.173-180
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    • 1996
  • 4-probe resistivity measurement technique was used to study kinetics of hydrogen absorption-desorption on Pd film($520{\AA}$ thick) at room temperature upto 1 bar. Kinetics data are fitted well to 1st order kinetics equation in ${\alpha}$ and ${\alpha}^{\prime}$ phases. In ${\alpha}+{\alpha}^{\prime}$ phase, absorption kinetics was very complicated, but it could be explained partially with nucleation and growth process. Ln(dR/dt) vs. time plot gives rate constant k value(R is resistance of sample, t is time). k value for absorption is $4^{-6}{\times}10^{-4}/sec$ in ${\alpha}$ phase. k is increasing upto $4^{\times}10^{-2}/sec$ as hydrogen pressure increasing in ${\alpha}^{\prime}$ phase. k is proportional to ln(Pop/Peq), where Peq is equilibrium plateau pressure and Pop is the opposing pressure. In contrast to bulk sample k value was decreasing with increasing number of A-D cycling in ${\alpha}^{\prime}$ phase absorption.

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Structure and Properties of Hemispherical Grain LPCVD Polycrystalline Silicon Films (반구형 LPCVD 다결정 실리콘 박막의 구조 및 특성)

  • Park, Yeong-Jin;Jeon, Ha-Eung;Lee, Seung-Seok;Lee, Seok-Hui;U, Sang-Ho;Kim, Jong-Cheol;Park, Heon-Seop;Cheon, Hui-Gon;O, Gye-Hwan
    • Korean Journal of Materials Research
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    • v.1 no.2
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    • pp.77-85
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    • 1991
  • In this study we have investigated surface morphologies of as-deposited silicon films on the various deposition conditions using LPCVD(Low Pressure Chemical Vapor Deposition) System. The processing conditions such as deposition temperature, pressure and flow rate of $SiH_4$ gas were found to determine the surface morphology. The optimum temperature of maximum effective surface area increased with increasing the deposition pressure and the flow rate of $SiH_4$ gas, These experimental results were also in quite good agreement with the equation derived under the assumption that the maximum effective surface area is obtained on the condition of maximum nucleation rate.

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Analysis of the Inhibition Layer of Galvanized Dual-Phase Steels

  • Wang, K.K.;Wang, H.-P.;Chang, L.;Gan, D.;Chen, T.-R.;Chen, H.-B.
    • Corrosion Science and Technology
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    • v.11 no.1
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    • pp.9-14
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    • 2012
  • The formation of the Fe-Al inhibition layer in hot-dip galvanizing is a confusing issue for a long time. This study presents a characterization result on the inhibition layer formed on C-Mn-Cr and C-Mn-Si dual-phase steels after a short time galvanizing. The samples were annealed at $800^{\circ}C$ for 60 s in $N_{2}$-10% $H_{2}$ atmosphere with a dew point of $-30^{\circ}C$, and were then galvanized in a bath containing 0.2 %Al. X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) was employed for characterization. The TEM electron diffraction shows that only $Fe_{2}Al_{5}$ intermetallic phase was formed. No orientation relationship between the $Fe_{2}Al_{5}$ phase and the steel substrate could be identified. Two peaks of Al 2p photoelectrons, one from metallic aluminum and the other from $Al^{3+}$ ions, were detected in the inhibition layer, indicating that the layer is in fact a mixture of $Fe_{2}Al_{5}$ and $Al_{2}O_{3}$. TEM/EDS analysis verifies the existence of $Al_{2}O_{3}$ in the boundaries of $Fe_{2}Al_{5}$ grains. The nucleation of $Fe_{2}Al_{5}$ and the reduction of the surface oxide probably proceeded concurrently on galvanizing, and the residual oxides prohibited the heteroepitaxial growth of $Fe_{2}Al_{5}$.

A Study on the Preparation of a Linear Low Density Polyethylene particles by Thermally Induced Phase Separation (열유도 상분리에 의한 선형 저밀도 폴리에틸렌 입자 제조에 관한 연구)

  • Park, Keun-Ho;Jang, Young-Min
    • Journal of the Korean Applied Science and Technology
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    • v.28 no.4
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    • pp.386-392
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    • 2011
  • We are crystallized to the linear low density polyethylene(LLDPE) particles by a thermally induced phase separation(TIPS). TIPS process based on the phase separation mechanism was performed for the LLDPE system which undergoes liquid-solid phase separation. The linear low density polyethylene particle formation occurred by the nucleation and growth mechanism in the metastable region. Although the growth rates depended on the experimental conditions such as the polymer concentration and temperature, the particles were larger when the polymer concentration was higher or temperature was higher. The particles were observed by SEM. The LLDPE particle size distribution became broader when the polymer concentration was higher.

Carbide Grain Growth in Cemented Carbides

  • Mannesson, Karin;Agren, John
    • Proceedings of the Korean Powder Metallurgy Institute Conference
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    • 2006.09a
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    • pp.336-337
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    • 2006
  • During sintering of cemented carbides abnormal grain growth is often observed but cannot be understood from the classical LSW-theory. A model based on 2-D nucleation of new crystalline layers and a grain-size distribution function is formulated and the equations are solved numerically. Experimental studies and computer simulations show that the initial grain size distribution has a strong effect on the grain growth behavior. For example, a fine-grained powder can grow past a coarser powder.

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