• Title/Summary/Keyword: %24Al_2O_3%24 powder

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Phase Formation and Physical Properties of SiAlON Ceramics Fabricated by Gas-Pressure Reactive Sintering (가스압 반응소결로 제조된 SiAlON 세라믹스의 상형성과 물리적 특성)

  • Lee, Soyul;Choi, Jae-Hyeong;Han, Yoonsoo;Lee, Sung-Min;Kim, Seongwon
    • Journal of Powder Materials
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    • v.24 no.6
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    • pp.431-436
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    • 2017
  • SiAlON-based ceramics are some of the most typical oxynitride ceramic materials, which can be used as cutting tools for heat-resistant super-alloys (HRSA). SiAlON can be fabricated by using gas-pressure reactive sintering from the raw materials, nitrides and oxides such as $Si_3N_4$, AlN, $Al_2O_3$, and $Yb_2O_3$. In this study, we fabricate $Yb_{m/3}Si_{12-(m+n)}Al_{m+n}O_nN_{16-n}$ (m=0.3, n=1.9, 2.3, 2.7) ceramics by using gas-pressure sintering at different sintering temperatures. Then, the densification behavior, phase formation, microstructure, and hardness of the sintered specimens are characterized. We obtain a fully densified specimen with ${\beta}$-SiAlON after gas-pressure sintering at $1820^{\circ}C$ for 90 min. under 10 atm $N_2$ pressure. These SiAlON ceramic materials exhibited hardness values of ~92.9 HRA. The potential of these SiAlON ceramics for cutting tool application is also discussed.

Synthesis of Metal Oxide-Coated Conductive Metal Powders and Their Application to Front Electrodes for Solar Cells (산화물이 코팅된 전도성 금속 분말의 제조 및 태양전지 전면 전극으로의 응용)

  • Park, Jin Gyeong;Lee, Young-In
    • Korean Journal of Materials Research
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    • v.24 no.9
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    • pp.502-507
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    • 2014
  • Recently, improvement in the conversion efficiency of silicon-based solar cells has been achieved by decreasing emitter doping concentration, because the lightly doped emitter can effectively prevent the recombination of electrons and holes generated by solar light irradiation. This type of emitter is very thin due to the low doping concentration, thus conductive materials (i.e., silver) used for front electrodes can easily penetrate the emitter during a firing process because of their large diffusivity in silicon. This results in junction leakage currents which might reduce cell efficiencies. In this study, $Al_2O_3$-coated Ag powders were synthesized by an ultrasonic spray pyrolysis method and applied to the conductive materials of the front electrode to control the junction leakage current. The $Al_2O_3$ shell obstructs the Ag diffusion into the emitter during the firing process. The powder is spherical with a core-shell structure and the thickness of the $Al_2O_3$ shell is tens of nanometers. Solar cells were fabricated using pure Ag powders or the $Al_2O_3$-coated Ag powder as front electrode materials, and the conversion efficiency and junction leakage current were compared to investigate the role of the $Al_2O_3$ shell during the firing processes.

Effect of $B_{2}O_{3}$ addition on mechanical strength and microstructure of a porous $LiAlO_{2}$ electrolyte support for molten carbonate fuel cells (용융 탄산염 연료전지용 gamma $LiAlO_{2}$ 전해질 지지체의 미세구조 및 기계적 강도 변화에 대한 $B_{2}O_{3}$ 첨가의 영향)

  • Ham, Hyung-Chul;Yoon, Sung-Pil;Hong, Seong-Ah
    • New & Renewable Energy
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    • v.3 no.1 s.9
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    • pp.54-59
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    • 2007
  • A sintering aid, $B_{2}O_{3}$ have been included into a $LiAlO_{2}$ electrolyte support by a tape casting method in order to reinforce mechanical strength of the support for molten carbonate fuel cells [MCFCs). Starting idea originates from the low melting point of $B_{2}O_{3}$ ($450^{\circ}C$), which can provide the low temperature consolidation of ceramic materials. The mechanical properties and the microstructure changes of the $B_{2}O_{3}$-included electrolyte support were examined by scanning electron microscope, mercury porosimetry, X-ray powder diffraction [XRD], high temperature differential scanning calorimeter and three-point bending strength measurement. The mechanical strength was clearly improved by addition of $B_{2}O_{3}$. The increase of mechanical strength results from the neck growth of a new $LiAlO_{2}$ phase between $LiAlO_{2}$ particles by the liquid phase sintering. Average pore size and porosity of the electrolyte support reinforced by addition of the sintering aid, $B_{2}O_{3}$, was $0.24{\mu}m$ and 59%, respectively which were suitable microstructure of a matrix for an application of MCFCs.

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Synthesis of Powder of the System Si-Al-O-N from Alkoxides I. Synthesis of Si3N4 and $\beta$-Sialon Ultrafine Powders from Alkoxides (알콕사이드로부터 Si-Al-O-N계 분말합성 I. 알콕사이드로부터 Si3N4와 $\beta$-Sialon 초미분말 합성)

  • 이홍림;유영창
    • Journal of the Korean Ceramic Society
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    • v.24 no.1
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    • pp.23-32
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    • 1987
  • Synthesis of high purity ultrafine Si3N4 and ${\beta}$-Sialon powders was investigated via the simultaneous reduction and nitriding of amorphous SiO2, SiO2-Al2O3 system prepaerd by hydrolysis of alkoxides, using carbonablack as a reducing agent. In Si(OC2H5)4-C2H5 OH-H2 O-NH4OH system, hydrolysis rate increased with increasing reaction temperature and pH. Pure ${\alpha}$-Si3N4 was formed at 1350$^{\circ}C$ for 5 hrs in N2 atmosphere. In Si(OC2H5)4-Al(OC3H7)3-C6H6-H2 O-NH4OH system, weight loss increased as Si/Al ratio decreased. Single phase ${\beta}$-Sialon consisted of Si/Al=2 was formed at 1350$^{\circ}C$ in N2 and minor phases of ${\alpha}$-Si3N4, AIN, and X-phase were existed besides theSialon phase at other Si/Al ratios. The Si3N4 and Sialon powders synthesized from alkoxides consisted of uniform find particles of 0.05-0.2$\mu\textrm{m}$ in diameter, respectively.

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Solid State Reduction of Haematite by Mechanical Alloying Process (기계적 합금화법에 의한 헤마타이트의 고상환원)

  • 이충효;홍대석;이만승;권영순
    • Journal of Powder Materials
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    • v.9 no.1
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    • pp.25-31
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    • 2002
  • The efects of mechanical aloying conditions and the type of reducing agent on the solid state reductionof haematite $Fe_2O_3$ have been investigated at room temperature. Aluminium titanium zinc and copper were used as reducing agent. Nanocomposites of metal-oxide in which oxide particles with nano size were dispersed in Fe matrix were obtained by mechanical alloying of $Fe_2O_3$ with aluminium and titanium respectively However the reduction of $Fe_2O_3$ by coppe was not occurred Composite materials of iron with $Al_2O_3$ and $TiO_2$ were obtained from the system of $Fe_2O_3-Al$ and $Fe_2O_3-Ti$ after ball milling for 20 hrs and 30 hrs respectively. And the system of $Fe_2O_3-Zn$ resulted in the formationof FeO with ZnO after ball milling of 120 hrs. The final grain sizes of iron estimated by X-ray diffraction line-width measurement were in the ranges of 24~33 nm.

High Temperature Oxidation Behavior of Ni based Porous Metal (Ni계 다공체 금속의 고온 산화 거동)

  • Choi, Sung-Hwan;Yun, Jung-Yeul;Lee, Hye-Mun;Kong, Young-Min;Kim, Byoung-Kee;Lee, Kee-Ahn
    • Journal of Powder Materials
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    • v.18 no.2
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    • pp.122-128
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    • 2011
  • This study investigated the high temperature oxidation behavior of Ni-22.4%Fe-22%Cr-6%Al (wt.%) porous metal. Two types of open porous metals with different pore sizes of 30 PPI and 40 PPI (pore per inch) were used. A 24-hour TGA test was conducted at three different temperatures of $900^{\circ}C$, $1000^{\circ}C$ and $1100^{\circ}C$. The results of the BET analysis revealed that the specific surface area increased as the pore size decreased from 30 PPI to 40 PPI. The oxidation resistance of porous metal decreased with decreasing pore size. As the temperature increased, the oxidation weight gain of the porous metal also increased. Porous metals mainly created oxides such as $Al_2O_3$, $Cr_2O_3$, $NiAl_2O_4$, and $NiCr_2O_4$. In the 40 PPI porous metal with small pore size and larger specific surface area, the depletion of stabilizing elements such as Al and Cr occurred more quickly during oxidation compared to the 30 PPI porous metal. Ni-Fe-Cr-Al porous metal's high-temperature oxidation micro-mechanism was also discussed.

Preparation of Ultra Fine Alumina Powder Via Ammonium Aluminium Carbonate Hydroxide (AACH 를 이용한 고순도 알루미나 분말 제조)

  • Tun, Zhu;Shin, Kun-Chul
    • Journal of Industrial Technology
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    • v.24 no.B
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    • pp.65-71
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    • 2004
  • The ultra fine gamma-alumina powder was prepared via ammonium aluminium carbonate hydroxide (AACH). The XRD, SEM, BET, thermal analysis were used to characterize the samples. The effects of various reaction parameters as concentration, of solution, anion on specific area, PH, aging time and thermal decomposition condition on the produced AACH and alumina were discussed.

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Study on the Corrosion Characteristics in the Slag Line of SEN Oxide Refractory (산화물계 SEN내화물의 슬래그 라인부 침식특성 연구)

  • Sung, Young Taek;Son, Jeong Hun;Lee, Sung Seok;Bae, Dong Sik
    • Korean Journal of Materials Research
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    • v.24 no.1
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    • pp.53-59
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    • 2014
  • The corrosion resistance of submerged entry nozzle (SEN) materials were investigated for high-class steel manufacturing. Composite samples were fabricated by mixing $ZrO_2$, $Al_2O_3$, MgO, mullite, spinel, and carbon. The raw materials were mixed with attrition milling, compacted in a uniaxial pressure of 200MPa and calcined at $1000^{\circ}C$ for 3 h in $N_2$ atmosphere. The bulk density and apparent porosity of the calcined samples were measured by the liquid displacement method in water using Archimedes's principle. The corrosion resistance of the samples were measured by cup test with mold powder at $1550^{\circ}C$ for 2 h. The microstructure and elemental analysis of samples were observed by scanning electron microscopy (SEM), energy dispersive spectrum (EDS), and X-ray diffraction pattern (XRD). The XRD result shows that the starting raw materials were crystalline phase. The microstructure of fabricated specimen was investigated before and after corrosion tests at $1000^{\circ}C$ and $1550^{\circ}C$ for 2h. $ZrO_2$-C composite showed good resistance in the slag corrosion test. Among the composite oxide materials, $ZrO_2-Al_2O_3$-C and $ZrO_2$-MgO-C showed better resistance than $ZrO_2$-C in the slag corrosion test. The diameter variation index of $ZrO_2$-C refractory was 16.1 at $1000^{\circ}C$ for 2 h. The diameter variation index of the $ZrO_2-Al_2O_3$-C refractory was larger than that of the $ZrO_2$-C refractory at $1550^{\circ}C$ for 2 h.

Synthesis of $\alpha$-Sialon from Kimcheon Quartzite (김천규석으로부터 $\alpha$-Sialon의 합성)

  • 이홍림;서원선;조덕호;이경원
    • Journal of the Korean Ceramic Society
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    • v.24 no.5
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    • pp.491-499
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    • 1987
  • Silicon nitride powder synthesized from Kimcheon quartzite and commercial reagents, AlN and Y2O3 powders were used to prepare the partially and fully stabilized Y-${\alpha}$-Sialon ceramics by the pressureless sintering at 1800$^{\circ}C$ for 2 hours in N2 atmosphere. Good mechanical properties of the prepared Y-${\alpha}$-Sialon ceramics were found over 0.4∼0.6 of the Yttrium solubility range, X, in the equation Yx(Si12-4.5x, Al4.5x)(O1.5x, N16-1.5x). The properties of these prepared Y-${\alpha}$-Sialon ceramics were compared with those prepared in the same way from a commercial Toshiba Si3N4 powder.

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The Effect of SiO2 addition on Oxidation and Electrical Resistance Stability at High-temperature of P/M Fecralloy Compact (P/M Fecralloy 성형체의 고온산화 및 전기저항 안정성에 미치는 SiO2 첨가 효과)

  • Park, Jin-Woo;Ok, Jin-Uk;Jung, Woo-young;Park, Dong-kyu;Ahn, In-Shup
    • Journal of Powder Materials
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    • v.24 no.4
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    • pp.292-297
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    • 2017
  • A metallic oxide layer of a heat-resistant element contributes to the high-temperature oxidation resistance by delaying the oxidation and has a positive effect on the increase in electrical resistivity. In this study, green compacts of Fecralloy powder mixed with amorphous and crystalline silica are oxidized at $950^{\circ}C$ for up to 210 h in order to evaluate the effect of metal oxide on the oxidation and electrical resistivity. The weight change ratio increases as per a parabolic law, and the increase is larger than that observed for Fecralloy owing to the formation of Fe-Si, Fe-Cr composite oxide, and $Al_2O_3$ upon the addition of Si oxide. Si oxides promote the formation of $Al_2O_3$ and Cr oxide at the grain boundary, and obstruct neck formation and the growth of Fecralloy particles to ensure stable electrical resistivity.