• Title/Summary/Keyword: Crystalline Silica

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Synthesis and Electrochemical Characterization of Silica-Manganese Oxide with a Core-shell Structure and Various Oxidation States

  • Ryu, Seong-Hyeon;Hwang, Seung-Gi;Yun, Su-Ryeon;Cho, Kwon-Koo;Kim, Ki-Won;Ryu, Kwang-Sun
    • Bulletin of the Korean Chemical Society
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    • v.32 no.8
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    • pp.2683-2688
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    • 2011
  • Silica-manganese oxides with a core-shell structure were synthesized via precipitation of manganese oxides on the $SiO_2$ core while varying the concentration of a precipitation agent. Elemental analysis, crystalline property investigation, and morphology observations using low- and high-resolution electron microscopes were applied to the synthesized silica-manganese oxides with the core-shell structure. As the concentration of the precipitating agent increased, the manganese oxide shells around the $SiO_2$ core sequentially appeared as $Mn_3O_4$ particles, $Mn_2O_3+Mn_3O_4$ thin layers, and ${\alpha}-MnO_2$ urchin-like phases. The prepared samples were assembled as electrodes in a supercapacitor with 0.1 M $Na_2SO_4$ electrolyte, and their electrochemical properties were examined using cyclic voltammetry and charge-discharge cycling. The maximum specific capacitance obtained was 197 F $g^{-1}$ for the $SiO_2-MnO_2$ electrode due to the higher electronic conductivity of the $MnO_2$ shell compared to those of the $Mn_2O_3$ and $Mn_3O_4$ phases.

Quantitative X-ray Diffraction Analysis of Synthetic Mineral Mixtures Including Amorphous Silica using the PONKCS Method (PONKCS 방법을 이용한 비정질 실리카 함유 인공광물혼합시료의 정량 X-선회절 분석)

  • Chon, Chul-Min;Lee, Sujeong;Lee, Sung Woo
    • Journal of the Mineralogical Society of Korea
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    • v.26 no.1
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    • pp.27-34
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    • 2013
  • X-ray powder diffraction is one of the most powerful techniques for qualitative and quantitative analysis of crystalline compounds. Thus, there exist a number of different methods for quantifying mineral mixtures using X-ray diffraction pattern. We present here the use of Rietveld and PONKCS (partial or no known crystal structure) methods for quantification of amorphous and crystallized mineral phases in synthetic mixtures of standard minerals (amorphous silica, quartz, mullite and corundum). Pawley phase model of amorphous silica was successfully built from the pattern of 100 wt% amorphous silica and internal standard-spiked samples by PONKCS approach. The average of absolute bias for quantities of amorphous silica was 1.85 wt%. The larger bias observed for lower quantities of amorphous silica is probably explained by low intensities of diffraction pattern. Averages of absolute bias for minerals were 0.53 wt% for quartz, 0.87 wt% for mullite and 0.57 wt% for corundum, respectively. The PONKCS approach achieved improved quantitative results compared with classical Rietveld method by using an internal standard.

X-ray diffraction analysis on sapphire wafers with surface treatments in chemical-mechanical polishing process (사파이어 웨이퍼 연마공정에서의 표면처리효과에 대한 X-선 회절분석)

  • 김근주;고재천
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.11 no.5
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    • pp.218-223
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    • 2001
  • The chemical-mechanical polishing process was carried out for 2"-dia. sapphire wafer grown by horizontalBridgman method on the urethane lapping pad with the silica sol. The polished wafer shows the full-width at halfmaximum of 200~400 arcsec in double-crystal X-ray diffraction, indicating that the slicing, grinding and lapping processes before the polishing process affected the crystalline structural property of the wafer surface by the mechanical residual stress. For the inclusion of surface treatments after chemical-mechanical polishing such as the thermal annealing at the temperature of $1,200^{\circ}C$for 4 hrs. and chemical etching, the crystalline quality was sigdicantly enhanced with the reduced full-width at half maximum up to 8.3 arcsec.arcsec.

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Synthesis and Characterization of Zeolite Composite Membranes (I):Synthesis of ZSM-5 Type Zeolites (제올라이트 복합 분리막의 합성 및 특성화(I): ZSM-5계 제올라이트의 합성)

  • 현상훈;김준학;송재권
    • Journal of the Korean Ceramic Society
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    • v.33 no.9
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    • pp.1064-1072
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    • 1996
  • The synthetic conditions and characteristics of ZSM-5 type zeolites (ZSM-5/silicalite) for the preparation of the zeolite composite membranes for gas separation were investigated. ZSM-5 zeolites could be synthesized by the hydrothermal treatment of the mixture of colloidal silica sol aluminum nitrate sodium hydroxide and TPABr at a temperature range of 150-17$0^{\circ}C$ in the autoclave. Silicalties were done from the solution of water glass water and TPABr. Their crystalline structures transformed from orthorhombic to monoclinic from and their pore structures of three-dimensional channels were opened as TPABr filling channels was burned off at the calcination temperature of 50$0^{\circ}C$. The specific surface area of the calcined zeolite was about 360 m3/g and its surface property was hydrophobic. Crystal sizes of ZSM-5 and silicalite were 0.5-1.0${\mu}{\textrm}{m}$ and 8-10${\mu}{\textrm}{m}$ respectively having no change due to the calcination. In particular the shape and the size of the ZSM-5 type zeolite were sensitively varied with silica sources and concentrations of reaction solutions/sols.

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High Temperature Reaction Behaviors of Oxide Materials with Carbon for Refractory Application (내화물 응용을 위한 산화물 재료들과 탄소와의 고온 반응거동)

  • Choi, Do-Mun;Lee, Jin-Seok;Kim, Nam-Hoon;Choi, Sung-Churl
    • Journal of the Korean Ceramic Society
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    • v.44 no.6 s.301
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    • pp.331-337
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    • 2007
  • High temperature reaction behaviors of various oxide materials (such as bauxite, pyrophyllite, mullite and fused silica powders) used in the refractory materials for tap-hole plugging of blast furnace were investigated with varying temperature in the carbon surrounding. Kinetics of carbothermal reduction of $SiO_2$ for forming SiC with high corrosion resistance were strongly dependent on it's crystalline phase. SiC generation yield increased with increasing catalyst amount in oxide regardless of generated SiO gas amount at temperature of $<1500^{\circ}C$. However, in case of fused silica over $1500^{\circ}C$, SiC generation yield was dominantly influenced by SiO amount without catalyst effect. Bauxite showed the most effective carbothermal reduction reaction, since bauxite have a large amount of catalyst and well-dispersed $SiO_2$ phase in oxide matrix.

The concentrations of airborne dust in non-metallic products factories and problems associated with the application of the occupational exposure limits (비금속광물 제품제조업에서 발생하는 분진 농도와 분진 노출기준 적용에 따른 문제점 고찰)

  • Kim, Hyunwook;Phee, Young Gyu;Won, Jung Il;Ko, Won Kyung;Roh, Young Man;Shin, Chang Sub
    • Journal of Korean Society of Occupational and Environmental Hygiene
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    • v.10 no.1
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    • pp.104-114
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    • 2000
  • This study was carried out to estimate current status of dust concentrations in the factories producing non-metallic products in Korea. Data were gathered from the environmental monitoring reports by 40 workplace environmental monitoring institutes and the questionnaire designed for the study by the authors. A total of 1838 dust samples from 368 plants were obtained from the reports and were analyzed with no data modifications. But data on asbestos, rock wool, and welding fumes were excluded in this evaluation. The factories were classified into eight groups according to the standard industrial classification scheme in Korea. The results of this study were as follows; 1. The factories included were glass, non-refractory ceramic, refractory ceramic ware, structural non-refractory clay and ceramic, cement and lime, articles of concretes, and stone. Mean(geometric mean) concentrations of total dust samples ranged from $1.75(0.84)mg/m^3$ to $5.87(2.84)mg/m^3$. Statistically significantly higher dust concentrations were found in the cement and lime industries compared with other industries. 2. The non-compliance rates were 15.2% in glass and 20.6% in other non-metallic mineral products industries. Although all institutions surveyed utilized the identical sampling and classification scheme for dusts as specified in the current occupational exposure limits, wide discrepancies were found in collecting samples and classifying dusts. Further problems were discovered in classifying dusts. A dust sample collected could be classified into any of the three groups regardless of silica content. The results of this study showed that dust concentrations in the non-metallic products industries varied widely. Also discovered was classification errors of dust types among workplace monitoring institutes. These errors could adversely affect the results of exposure assessments and the true nature of dust hazards. Further, no institutions performed respirable dust sampling and analysis of crystalline silica. In order to correct these malpractices, current standards of occupational exposure limits should be revised and tight supervision by the Ministry of Labour be suggested.

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Structural Properties of MO-SiO$_2$(M=Zn, Sn, In, Ag, Ni) by Sol-Gel Method (졸겔법으로 제조된 MO-$SiO_2$(M=Zn,Sn,In,Ag,Ni)의 구조특성)

  • Sin, Yong-Uk;Kim, Sang-U
    • Korean Journal of Materials Research
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    • v.11 no.7
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    • pp.603-608
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    • 2001
  • $MO-SiO_2$ (M = Zn, Sn, In, Ag, Ni) binary silica gels were synthesized by sol-gel method and their structural change with the kind of metal ions was characterized by XRD, FT- IR and $^{29}$Si-NMR. Although X-ray analysis showed partial recrystallization of $AgNO_3$ in $Ag-SiO_2$gel, crystalline phase formed by the bonding between metal ion and the silica matrix didn't appear in all $MO-SiO_2$ gels. The FT-IR analysis showed that Zn, Sn and in partially formed Si-O-M bonding in silica matrix and made an shift of absorption peak to by Si-O-Si symmetrical vibration. In addition, $^{29}Si-NMR$ studies showed that Zn, Sn and In didn't affect sol-gel process of silica and were linked with non-bridging oxygen of the linear silica structure, which formed imperfect network because of low temperature sol-gel process. Ag and Ni make a role of catalysis on sol-gel process, resulting in densifying the silica network structure.

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Structural Dependence of Nonlinear Optical Properties in $TeO_2-PbO-GeO_2$ ($TeO_2-PbO-GeO_2$계 유리 내 비선셩 광학 특성의 구조 의존성)

  • Kim, Weon-Hyo;Heo, Jong;Kim, You-Song;Ryou, Sun-Youn
    • Journal of the Korean Ceramic Society
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    • v.33 no.5
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    • pp.507-513
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    • 1996
  • Nonlinear optical properties of TeO2-PbO-GeO2 glasses were investigated and their correlation with struc-tural modification was investigated. Third-order nonlinear susceptibility $\chi$, ranged between 5.0$\times$10-13 esu and 10.7$\times$10-13 esu which are approximately 20-40 times larger than that of silica glass. The glass with a composition of 85(80TeO2-20PbO)-15GeO2(mol%) seemed to provide an optimum compromise between $\chi$and the stability against crystallization. Analyses of the Raman spectra suggested that these glasses are mainly composed of [TeO4] tbp, [TeO3]tp and [GeO4] tetrahedral structural units. It was concluded that the positive contribution of Pb2+ with high polarizability to $\chi$ in TeO2-PbO glasses overwhelmed the negative influence due to the structural modification of [TeO4]tbplongrightarrow[TeO3]tp. On the other hand addition of GeO2 in TeO2-PbO-GeO2 glasses resulted in the decrease of $\chi$ values. This behavior was attributed to the formation of [GeO4] polyhedra at the expense of [TeOn] polyhedra and Pb2+ ions which normally sowed a higher contribu-tion to $\chi$ than [GeO4] polyhedra.

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A Study on Physical Properties of Epoxy Resin Filled with Surface-treated Silica: I. Surface-treating of Silica and Properties of Mixtures (표면처리된 실리카를 충전한 에폭시 수지계의 물성에 관한 연구 I. 실리카의 표면처리 및 혼합 물성)

  • Hong, Suk-Pyo;Choi, Sang-Goo
    • Applied Chemistry for Engineering
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    • v.1 no.1
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    • pp.63-72
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    • 1990
  • Surface of crystalline silica was sequentially reacted with silane(A 187), liquid rubber(CTBNx8) and vinyl monomer(AA, MMA, 2-HEA, GMA) in existance of amines(TEA, CTMAB, BETAC) or peroxide(BPO). By mixing it with epoxy resin at a ratio 0~36%(volume %) of total component, liquid properties of mixtures was investigated experimentally. i) Coating ratio depended on quantity and sorts of catalyst. ii) Total coating of 2.5~5.8% was attained by using 0.1~2.0% of catalyst. iii) Treated surfaces represented each different features in according to sorts of treatment. iv) Silane/rubber or silane/rubber/vinyl represented lower viscosity and settling than non-treated or silane-treated.

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Preparation and characterization of CdS nanoparticle on the surface of silica nanoparticles (실리카 나노입자 표면에 CdS 나노입자의 제조 및 평가)

  • Kang, Yun-Ok;Choi, Seong-Ho;Gopalan, A.;Lee, Kwang-Pill
    • Analytical Science and Technology
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    • v.20 no.5
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    • pp.413-418
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    • 2007
  • Poly(vinylpyrrolidone) stabilized cadmium sulfide (CdS) nanoparticles were loaded onto the surface of silica ($SiO_2$) nanoparticles by using ${\gamma}$-irradiation. TEM micrograph reveals the presence of ~20nm sized CdS nanoparticles on the surface of $SiO_2$ nanoparticles. XRD patterns confirm the crystalline. PL spectra of the simple PVP-stabilized CdS nanoparticle and $SiO_2$@CdS composite confirm the differences in the emission characteristics between them. Two prominent emission peaks were noted around 550 nm and 600 nm for PVP-stabilized CdS nanoparticles). The emission peaks noted for the PVP-stabilized CdS nanoparticles were found to be blue shifted for $SiO_2$@CdS composites. Besides, an additional emission peak around 450 nm was noticed for the $SiO_2$@CdS composite. The presence of CdS nanoparticles influence the emission characteristics and induce quantum confinement effect.