• Title/Summary/Keyword: Bulk Material

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Preparation of YBa2Cu3O7-y Superconductor Using Melt Method (용융법에 의한 YBa2Cu3O7-y 초전도체 제작)

  • Lee, Sang Heon
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.35 no.6
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    • pp.622-625
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    • 2022
  • YBa2Cu3O7-y bulk as a high temperature oxide superconducting conductor has the high critical temperature of 92 K. YBa2Cu3O7-y bulk superconductors have been fabricated by a seeded melting growth. Magnetic properties were studied by using superconductor of melted YBa2Cu3O7-y oxides. It was demonstrated that Y2BaCuO5 particles acts as a pinning center which plays an important role on the magnetic properties. The thickness of the upper and lower pellets of the YBa2Cu3O7-y bulk was formed at 40 mm with 55 g of the composition, and the YBa2Cu3O7-y superconductor was manufactured through a heat treatment process. Manufacturing the superconducting bulk, it is possible to improve the pore density of the superconducting bulk by providing a path through which oxygen could be emitted.

Asbestos Content in Friable Sprayed-on Surface Material and Airborne Fiber Concentrations in Commercial Buildings (대형건물내 비고형 석면함유 건축자재에 의한 기중 석면오염 및 관리실태)

  • Kim, Hyunwook
    • Journal of Korean Society of Occupational and Environmental Hygiene
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    • v.5 no.2
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    • pp.137-146
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    • 1995
  • Twenty(20) large commercial buildings located in Seoul with friable sprayed-on surface insulation material on ceilings were investigated for asbestos content in bulk material by polarized light microscopy and for airborne fiber concentrations in buildings by phase contrast microscopy. In addition, such building-related variables as building age, numbers of traffic, airflow, surface conditions of the ceiling, temperature, and humidity were studied for any correlation with airborne fiber concentrations. The results were as follows: 1. Chrysotile asbestos was found in two bulk samples with 3-5% content and with <1%in one sample out of total 20 bulk samples collected. Glass fiber and mineral wool were the two major constituents of the bulk samples. 2. The ceiling surfaces were very friable in 16 buildings and were relatively hard in 4 buildings. The friability of the surface material was dependent upon the type and the amount of binder that had been mixed with the sprayed-on surface material. 3. Airborne fiber concentrations were log-normally distributed and the geometric mean(geometric standard deviation) fiber concentrations in the underground parking lots, inside buildings, and outdoor ambient air were 0.0063(1.97)f/cc, 0.0068(2.29)f/cc, and 0.0033(2.36)f/cc, respectively. 4. No significant relationship of airborne fiber concentrations and all building-related variables studied except humidity was found. The results of this study suggest that the sprayed-on surface insulation material found in some commercial buildings may possibly be contaminated with asbestos. Since most of the ceiling surfaces surveyed were very friable and poorly maintained and the airborne fiber concentrations were relatively high, there is a possibility of asbestos fiber contamination in these buildings, particularly at those buildings with asbestos-contaminated surface material. Since poorly maintained surface conditions were thought to be a source of high airborne fiber concentrations, there is a urgent need of a systematic operation and maintenance program. Further study of non-occupational asbestos exposure in general population utilizing advanced analytical technique such as transmission electron microscopy is highly recommended.

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Method of Material Constants Extraction in Thin-Film Bulk Acoustic Resonator(FBAR) using Genetic Algorithm (유전자 알고리즘을 이용한 압전 박막 음향 공진기에서의 물질 상수 추출 기법)

  • 이정흠;정재용;김형동
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
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    • v.14 no.4
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    • pp.323-329
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    • 2003
  • In this paper, the method of material constants extraction in a thin-film bulk acoustic resonator(FBAR) using a genetic algorithm(GA) is proposed. The material constants are extracted from the input impedance of a FBAR by a GA optimizer. The characteristics of the FBAR input impedance affected by the material constants were studied to decide the fitness function for GA. As a result, the fitness was estimated by the series- and parallel -resonance frequencies and the FBAR bandwidth, as determined from the input impedance of the FBAR. A flowchart for the GA and a procedure fur the proposed extraction method are explained in detail, and the results of the material constants extraction are presented.

Fabrication of Bulk High-Tc Superconductor (벌크형 고온 초전도 합성)

  • Lee, Sang Heon
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.34 no.5
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    • pp.333-336
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    • 2021
  • Oxide YBCO bulk superconductors are manufactured using the melt process. Because seed crystal growth method utilizes a slow-spreading layer-by-layer reaction, a long-term heat treatment is required to manufacture a single-crystal specimen of several cm. In this study, the melt process method was applied to compensate for the shortcomings of the seed crystal growth method. The thickness of the upper and lower pellets of the YBCO bulk was molded to 40 mm, and YBCO superconductor was produced by heat treatment. The measurement results of capture magnetism was in line with the literature. This results in a relationship that the higher the growth of Y211 particle in the YBCO, the higher the superconducting properties. We analyzed the YBCO superconductor, focusing on the Y2BaCuO5 particle distribution.

Frequency Characteristics of a FBAR using ZnO Thin Film (ZnO 압전박막을 이용한 FBAR의 주파수 응답특성)

  • Do, Seung-Woo;Jang, Cheol-Yeong;Choi, Hyun-Chul;Lee, Yong-Hyun
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2003.08a
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    • pp.94-97
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    • 2003
  • This study uses ZnO thin film as a piezoelectric material and Pt as bottom electrode for FBAR (film bulk acoustic resonator) device. ZnO thin film and Pt were deposited by RF-magnetron sputtering method. ZnO thin film and Pt were oriented to c-axis. Top electrode Al was deposited by thermal evaporation. The membrane was formed of bulk micromachining. The FBAR was evaluated by XRD, SEM and electrical characterization. The resonant frequency was measured by HP 8753C Network Analyzer. A fabricated FBAR device exhibited a resonant frequency of 700 MHz ~ 1.5 GHz. When bottom electrode and top electrode thickness were fixed, the resonant frequency was increased as decreasing ZnO thin film thickness.

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The bounds for fully saturated porous material

  • Yoon, Young-June;Jung, Jae-Yong;Chung, Jae-Pil
    • The Journal of Korea Institute of Information, Electronics, and Communication Technology
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    • v.13 no.5
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    • pp.432-435
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    • 2020
  • The elasticity tensor for water may be employed to model the fully saturated porous material. Mostly water is assumed to be incompressible with a bulk modulus, however, the upper and lower bounds of off-diagonal components of the elasticity tensor of porous materials filled with water are violated when the bulk modulus is relatively high. In many cases, the generalized Hill inequality describes the general bounds of Voigt and Reuss for eigenvalues, but the bounds for the component of elasticity tensor are more realistic because the principal axis of eigenvalues of two phases, matrix and water, are not coincident. Thus in this paper, for anisotropic material containing pores filled with water, the bounds for the component of elasticity tensor are expressed by the rule of mixture and the upper and lower bounds of fully saturated porous materials are violated for low porosity and high bulk modulus of water.

Fabrication of the Bulk Superconductor by Thermal Diffusion Process (열확산 프로세스에 의한 초전도 벌크 합성)

  • Lee, Sang Heon
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.34 no.6
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    • pp.461-465
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    • 2021
  • A diffusion heat treatment process for YBa2Cu3O7-y bulk superconductor in a Gd2O3 powder was attempted. As a result of measuring the critical temperature of the superconducting bulk, there was no change in the superconducting transition temperature as the Gd particles diffused into the YBa2Cu3O7-y lattice, resulting in dense microstructure. As a result of measuring the critical current, the critical current density (Jc) of the superconducting bulk having treated by the Gd thermal diffusion treatment at 0 T increased to 3×104 A/cm2 at 0 T, which was higher than that of the superconducting bulk without thermal diffusion treatment. The surface magnetic force of the superconducting bulk with Gd thermal diffusion treatment was observed at the center of the superconducting bulk with the maximum trapped magnetic force (Hmax) of 1.51 kG. This result means that the Gd thermal diffusion treatment contributes to improving the critical current density Jc of YBa2Cu3O7-y, and it is believed that Gd particles migrating into the superconducting bulk through thermal diffusion either fill the surface pores of YBa2Cu3O7-y superconductors or act as a flux pinning center.

A Study on the Properties of Jumchi Hanji for Application as Shroud Materials (수의용 소재로 활용을 위한 줌치한지의 물성에 관한 연구)

  • Jeon, Yang Bae;Kim, Ki Hoon;Lim, Hyun A
    • Journal of the Korean Society of Clothing and Textiles
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    • v.38 no.3
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    • pp.397-403
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    • 2014
  • In this study, various types of Jumchi Hanji were made to develop shroud materials as a new use for Hanji. The properties of Hanji (basis weight, thickness, apparent density, bulk, tensile strength, wet tensile strength, elongation ratio, tear strength, bursting strength, and folding endurance) are measured. In all cases, Jumchi Hanji had a higher thickness, lower apparent density and higher bulk than Hanji because pores in the intervals of mulberry fiber are composed of bulk. So, it is considered to carry a value as a textile material. As for the results of the strength analysis of Jumchi Hanji, Jumchi technique enhances 25% of elongation ratio, which is regarded the most important role in textiles and 35% of bulk. Moreover, it was shown that it enhanced overall strength. In conclusion, it implies the possibility of applying it as a shroud material. Jumchi Hanji is thought to have enough potential to be developed as a material to carry the characteristics of Hanji in the textile market.

Study for the Bragg Detuning Effects on the Transmission Holograms and the Reflection Holograms (투과형 홀로그램과 반사형 홀로그램에서의 Bragg detuning 현상에 대한 연구)

  • Kwon, Yun-Young;Kim, Kun-Yul;Park, Joo-Youn
    • Transactions of the Society of Information Storage Systems
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    • v.2 no.3
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    • pp.189-195
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    • 2006
  • Bragg detuning effect if, one of the serious problems if the photopolymer is used for the recording material of holography memories. And the critical reasons of that are known as the bulk refractive index change and shrinkage of recording material. However, the trials for analyzing the effect are mainly on the K-sphere and biased on the transmission hologram. So, we approached Bragg detuning effect numerically and applied the method to the transmission holograms and the reflection holograms all together. We simulated it with MATLAB. As a result, the bulk refractive index change causes+Bragg detuning effect on the transmission holograms and the reflection holograms. But the shrinkage leads to+Bragg detuning effect on the transmission hologram and-Bragg detuning effect on the reflective hologram. Compared to experimental result, the bulk refractive index change(${\fallingdotseq}4{\times}10^{-4}$) and the ratio of shrinkage to the thickness of the material(${\fallingdotseq}1.67{\times}10^{-3}$) could be matched with Bragg detuning effect on the transmission hologram and the reflection hologram.

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