• Title, Summary, Keyword: MgO

Search Result 7,420, Processing Time 0.052 seconds

Calculation of the Secondary Electron Emission Coefficients of MgO, MgBeO, MgCaO, MgSrO and MgBaO Induced by Auger Neutralization of He+, Ne+, Ar+ and Xe+ Ions

  • Lee, Jong Wan
    • New Physics: Sae Mulli
    • /
    • v.68 no.9
    • /
    • pp.939-944
    • /
    • 2018
  • In previous experiments, the secondary electron emission (SEE) coefficients, ${\gamma}^{\prime}s$, for MgO, MgSrO and MgCaO thin films deposited by using electron beam evaporation were investigated using a gamma focused-ion-beam system. The order of the SEE coefficients of the thin films was ${\gamma}^{MgO}$ < ${\gamma}^{MgSrO}$ < ${\gamma}^{MgCaO}$. We theoretically calculated the SEE coefficients of MgO, MgBeO, MgCaO, MgSrO and MgBaO induced by Auger neutralization of $He^+$, $Ne^+$, $Ar^+$ and $Xe^+$ ions by using the Mathematica code, wihch was developed to calculate those coefficients. In order to get the width of the valence band and the band gap of the materials, we performed a first-principles quantum-mechanical calculation. The calculated order of the ${\gamma}^{\prime}s$ was ${\gamma}^{MgBeO}$ < ${\gamma}^{MgO}$ < ${\gamma}^{MgCaO}$ < ${\gamma}^{MgSrO}$ < ${\gamma}^{MgBaO}$ for all ions. The SEE coefficients of MgCaO and MgSrO were greater than that of MgO. MgCaO and MgSrO, however, showed reverse order. This may be due to the fact that the MgCaO thin film has a polycrystalline structure whereas MgSrO has no crystalline structure.

Sputtering Yield and Secondary Electron Emission Coefficient(${\gamma}$) of the MgO, $MgAl_2O_4$ and $MgAl_2O_4/MgO$ Thin Film Grown on the Cu Substrate by Using the Focused Ion Beam (Cu 기판위에 성장한 MgO, $MgAl_2O_4$$MgAl_2O_4/MgO$ 박막의 집속이온빔을 이용한 스퍼터링수율 측정과 이차전자방출계수 측정)

  • Jung K.W.;Lee H.J.;Jung W.H.;Oh H.J.;Park C.W.;Choi E.H.;Seo Y.H.;Kang S.O.
    • Journal of the Korean Vacuum Society
    • /
    • v.15 no.4
    • /
    • pp.395-403
    • /
    • 2006
  • It is known that $MgAl_2O_4$ has higher resistance to moisture than MgO, in humid ambient MgO is chemically unstable. It reacts very easily with moisture in the air. In this study, the characteristic of $MgAl_2O_4$ and $MgAl_2O_4/MgO$ layers as dielectric protection layers for AC- PDP (Plasma Display Panel) have been investigated and analysed in comparison for conventional MgO layers. MgO and $MgAl_2O_4$ films both with a thickness of $1000\AA$ and $MgAl_2O_4/MgO$ film with a thickness of $200/800\AA$ were grown on the Cu substrates using the electron beam evaporation. $1000\AA$ thick aluminium layers were deposited on the protective layers in order to avoid the charging effect of $Ga^+$ ion beam while the focused ion beam(FIB) is being used. We obtained sputtering yieds for the MgO, $MgAl_2O_4$ and $MgAl_2O_4/MgO$ films using the FIB system. $MgAl_2O_4/MgO$ protective layers have been found th show $24{\sim}30%$ lower sputtering yield values from 0.244 up to 0.357 than MgO layers with the values from 0.364 up to 0.449 for irradiated $Ga^+$ ion beam with energies ranged from 10 kV to 14 kV. And $MgAl_2O_4$ layers have been found to show lowest sputtering yield values from 0.88 up to 0.109. Secondary electron emission coefficient(g) using the ${\gamma}$- FIB. $MgAl_2O_4/MgO$ and MgO have been found to have similar g values from 0.09 up to 0.12 for indicated $Ne^+$ ion with energies ranged from 50 V to 200 V. Observed images for the surfaces of MgO and $MgAl_2O_4/MgO$ protective layers, after discharge degradation process for 72 hours by SEM and AFM. It is found that $MgAl_2O_4/MgO$ protective layer has superior hardness and degradation resistance properties to MgO protective layer.

The Study on Solid-State Reaction Between MgO Single Crystal and $Fe_2O_3$ Powder (단결정 MgO와 분말 $Fe_2O_3$간의 고상 반응 연구)

  • 김성재;박재우
    • Journal of the Korean Ceramic Society
    • /
    • v.32 no.2
    • /
    • pp.234-238
    • /
    • 1995
  • MgFe2O4 formation, grain growth in Fe2O3, Fe solid-solution limit in MgO for MgO-Fe2O3 mixture were studied by means of investigating the distribution of phases and compositions in reaction area between MgO and Fe2O3. The reaction area at equlibrium was composed with MgO-FexO matrix and MgFe2O4 precipitation, MgFe2O4 was formed by precipitating from MgO-FexO matrix dependent on oxygen partial pressure. Fe contents was exponentially decreased with diffusion distance in MgO single crystal, and thus Fe solid-solution limitation in MgO was about 4mol%. The grain growth rate in Fe2O3 base was increased with Mg contents diffused from MgO single crystal.

  • PDF

LEED I/V Curve Analysis of O/Fe(100) and MgO/Fe(100) System (O/Fe(100) and MgO/Fe(100) 계의 LEED I/V curve 분석)

  • Seo, J.K.;Kim, S.H.
    • Journal of the Korean Vacuum Society
    • /
    • v.16 no.1
    • /
    • pp.1-6
    • /
    • 2007
  • We have analyzed the atomic structure of O/Fe(100) and interface atomic structure of MgO deposited on Fe(100) surface using LEED I/V curve analysis. As the O adsorption on the Fe(100) surface, the first substrate interlayer distance is expanded by up to 16%. For 1ML MgO deposited on Fe(100) surface, the oxygen ions of MgO are located on-top of the Fe atoms, the interlayer distance at the MgO/Fe interface are expanded. From the AIA(average intensity mixing approximation) calculation, we find the interface structure of monolayer MgO on Fe(100) system has the two interface structure with MgO/FeO/Fe(100) and MgO/Fe(100). This supports the results of EELS experiment that shown existence of stretched FeO layer and coexistance of MgO/FeO/Fe(100) and MgO/Fe(100) structure.

Wear Mechanism of MgO-C Refractory with Thermite Reaction Products of MgO and Al (MgO와 Al의 테르밋 반응생성물이 첨가된 MgO-C계 내화재료의 용손 기구)

  • 최태현;전병세
    • Journal of the Korean Ceramic Society
    • /
    • v.33 no.7
    • /
    • pp.832-838
    • /
    • 1996
  • Thermite reaction products of MgO and Al were added to MgO-C refractory to improve the properties of corrosion against the attack of slag, oxidation and mechanical spalling. Corrosion rate of MgO-C-MgAl2O4 spinel refractory at the ratio of 3.3(CaO/SiO2) slag was smaller than that of MgO-C and MgO-C-Al refractory. The excellent corrosion resistance of the MgO-C-MgAl2O4 spinel refractory against the slag attack was appeared by Al and MgAl2O4 spinel with high melting point and corrosion resistance and the high thermal conductivity and low thermal expansion of AIN. Hot M.O.R at 140$0^{\circ}C$ and the resistance of oxidation weight loss at 90$0^{\circ}C$ were 210kg/cm2 and -12% respectively.

  • PDF

The hydration resistance improvement of MgO ceramics by $TiO_2$ addition ($TiO_2$ 첨가에 의한 MgO 세라믹스의 표현 수화 저항성 향상)

  • Ryu, Su-Chak;Kim, Jin-Kon;Hyun Cho
    • Journal of the Korean Crystal Growth and Crystal Technology
    • /
    • v.11 no.6
    • /
    • pp.269-273
    • /
    • 2001
  • The effect of $TiO_2$addition on the hydration reaction of MgO ceramics were studied after being heated at $1450^{\circ}C$. The pure MgO ceramics showed significant weight change after exposure to water due to the hydration reaction through the formation of $Mg(OH)_2$while $TiO_2$-added MgO ceramics did not. The $Mg_2TiO_4$phase were observed in the $TiO_2$-added MgO ceramics sintered at 145$0^{\circ}C$. Bulk density increased as the amount of $TiO_2$increased and the apparent porosity and water absorption decreased by $TiO_2$addition. The hydration resistance of MgO ceramics was found to be improved by $TiO_2$addition.

  • PDF

Effect of Hydration on Swelling Properties and Shear Strength Behavior of MgO-sand Mixture (수화 반응에 따른 MgO-모래 혼합물의 팽창 특성 및 전단 거동 변화)

  • Lee, Jihwan;Yoon, Boyoung;Choo, Hyunwook;Lee, Woojin;Lee, Changho
    • Journal of the Korean Geotechnical Society
    • /
    • v.36 no.11
    • /
    • pp.97-106
    • /
    • 2020
  • Swelling properties and shear strength behavior of MgO-Sand mixtures with hydration procese of MgO are compared according to different MgO contents (WMgO/WTotal=0, 30, 50, 70, 100%) in this study. The specimens are prepared by mixing with crushed MgO refractory bricks and silica sand. After hydration, the particle size and the specific gravity of MgO were decreases. Through microstructure observation and X-ray diffraction analysis, it is confirmed that MgO changes from the cubic structure of Periclase to the hexagonal cubic structure of Brucite after hydration. As the MgO content increases, both swelling rate and swelling pressure of the mixtures increase. WMgO/WTotal=30% specimen shows relatively low swelling pressure and swelling rate because produced Mg(OH)2 mainly fills the pores between sand particles. However, in the case of MgO more than 50%, swelling pressure and swelling rate increase significantly because Mg(OH)2 fills the pores of sand particles at first and then either pushes out sand particles or Mg(OH)2 particles after filling the pores. As a result of the direct shear test, before hydration, the mixtures show a dilative behavior on high MgO contents and a contractive behavior on low MgO contents. However, after hydration, the behavior of all mixtures changes to contractive behavior. The threshold fraction of fine (i.e., Mg(OH)2) contents of the hydrated MgO-Sand mixtures reveals approximately 60% compared with normalized shear strength.

A study on Electrical and Diffusion Barrier Properties of MgO Formed on Surface as well as at the Interface Between Cu(Mg) Alloy and $SiO_2$ (Cu(Mg) alloy의 표면과 계면에서 형성된 MgO의 확산방지능력 및 표면에 형성된 MgO의 전기적 특성 연구)

  • Jo, Heung-Ryeol;Jo, Beom-Seok;Lee, Jae-Gap
    • Korean Journal of Materials Research
    • /
    • v.10 no.2
    • /
    • pp.160-165
    • /
    • 2000
  • We have investigated the electrical and diffusion barrier properties of MgO produced on the surface of Cu (Mg) alloy. Also the diffusion barrier property of the interfacial MgO between Cu alloy and $SiO_2$ has been examined. The results show that the $150\;{\AA}$-MgO layer on the surface remains stable up to $700^{\circ}C$, preventing the interdiffusion of C Cu and Si in Si/MgO/Cu(Mg) structure. It also has the breakdown voltage of 4.5V and leakage current density of $10^{-7}A/\textrm{cm}^2/$. In addition, the combined structure of $Si_3N4(100{\AA})/MgO(100{\AA})$ increases the breakdown voltage up to lOV and reduces the leakage current density to $8{\tiems}10^{-7}A/\textrm{cm}^2$. Furthermore, the interfacial MgO formed by the chemical reac­t tion of Mg and $SiO_2$ reduces the diffusion of copper into $SiO_2$ substrate. Consequently, Cu(Mg) alloy can be applied as a g gate electrode in TFT /LCDs, reducing the process steps.

  • PDF

Fundamental Properties of Cement Composites Containing Lightly Burnt MgO Powders (저온 소성한 MgO 분말을 혼입한 시멘트 복합체의 기초 물성)

  • Jang, Bong-Seok;Kwon, Yong-Gil;Choi, Seul-Woo;Lee, Kwang-Myong
    • Journal of the Korea Concrete Institute
    • /
    • v.23 no.2
    • /
    • pp.225-233
    • /
    • 2011
  • The volume change in concrete takes place with changes in temperature and water content immediately after concrete casting. In the early age stage, the thermal and drying shrinkages can cause cracks that are very crucial to the durability of concrete. It was reported that when the cement with lightly-burnt MgO powder was used, the shrinkage of concrete can be reduced. This study investigates fundamental properties of cement composites with lightly burnt MgO powder by performing various experiments. The stability test results verified that MgO powder in cement composites does not cause any abnormal expansion. Also, the hydrate product analysis results obtained from MgO cement paste showed that MgO powder reduces the shrinkage at the longterm ages. In addition, the cement composites containing the proper amount of MgO powder could improve compressive strength. Finally, the shrinkage reduction from using MgO powder can be optimized by increasing MgO replacement level and curing temperature.

Effect of Core Morphology on the Decomposition of CCI₄ over the Surface of Core/Shell Structured Fe₂O₃/MgO Composite Metal Oxides

  • 김해진;강진;박동곤;권호진;Kenneth J. Klabunde
    • Bulletin of the Korean Chemical Society
    • /
    • v.18 no.8
    • /
    • pp.831-840
    • /
    • 1997
  • Core/shell structured composite metal oxides of Fe2O3/MgO were prepared by thermal decomposition of Fe(acac)3 adsorbed on the surface of MgO cores. The morphology of the composites conformed to that of the MgO used as the cores. Broad powder X-ray diffraction peaks shifted toward larger d, large BET surface area (∼350 m2/g), and the size of crystalline domains in nano range (4 nm), all corroborate to the nanocrystallinity of the Fe2O3/MgO composite which was prepared by using nanocrystalline MgO as the core. By use of microcrystalline MgO as the core, microcrystalline Fe2O3/MgO composite was prepared, and it had small BET surface area of less than 35 m2/g. AFM measurements on nanocrystalline Fe2O3/MgO showed a collection of spherical aggregates (∼80 nm dia) with a very rough surface. On the contrary, microcrystalline Fe2O3/MgO was a collection of plate-like flat crystallites with a smooth surface. The nitrogen adsorption-desorption behavior indicated that microcrystalline Fe2O3/MgO was nonporous, whereas nanocrystalline Fe2O3/MgO was mesoporous. Bimodal distribution of the pore size became unimodal as the layer of Fe2O3 was applied to nanocrystalline MgO. The macropores in a wide distribution which the nanocrystalline MgO had were absent in the nanocrystalline Fe2O3/MgO. The decomposition of CCl4 was largily enhanced by the overlayer of Fe2O3 on nanocrystalline MgO making the reaction between nanocrystalline Fe2O3/MgO and CCl4 be nearly stoichiometric. The reaction products were environmentally benign MgCl2 and CO2. Such an enhancement was not attainable with the microcrystalline samples. Even for the nanocrystalline MgO, the enhancement was not attained, if not with the Fe2O3 layer. Without the layer of Fe2O3, it was observed that the nanocrystalline domain of the MgO transformed into microcrystalline one as the decomposition of CCl4 proceeded on its surface. It appeared that the layer of Fe2O3 on the particles of nanocrystalline Fe2O3/MgO blocked the transformation of the nanocrystalline domain into microcrystalline one. Therefore, in order to attain stoichiometric reaction between CCl4 and Fe2O3/MgO core/shell structured composite metal oxide, the morphology of the core MgO has to be nanocrystalline, and also the nanocrystalline domains has to be sustained until the core was exhausted into MgCl2.

  • PDF