• 한국표면공학회지
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• 제38권2호
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• pp.83-87
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• 2005

We enhanced the color of blue sapphires and rubies successfully by using a oxygen-propane torch flame annealing, which had not been employed so far. We confirmed that about 1 mm-thick de-coloring of the corundum samples were available with 60 minutes flame annealing through eye evaluation, color coordination characterization, and methylene iodide immersion observation. We also suggest that the color centers such as $[Fe_{Al}^{\cdot}]$ may transform into transparent $[Fe_{Al}^{x}],\;[Cr_{A1}^{x}]$ sites with $[V_o^']$ generation at the elevated temperature in oxygen-rich atmosphere by diffusion mechanism. Our results implied that the longer diffusion time and the higher oxygen partial pressure might lead to the better de-coloring enhancement in corundum gem stones.

• Bulletin of the Korean Chemical Society
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• 제20권8호
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• pp.939-942
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• 1999

The tie lines delineating ion-exchange equilibria between NiFe2O4-NiCr2O4 spinel solid solution and Fe2O3-Cr2O3 corundum solid solution were determined at 900, 1000, and 1200 ℃ by electron microprobe and energy dispersive X-ray analysis of oxide phases, using the flux growth technique. Activities of the spinel components were calculated from the tie lines, assuming Temkin's ideal mixing in the corundum solid solution. The spinel phase could be expressed by a regular solution with negative deviations from ideality. The Gibbs free energies of mixing for spinel solid solution were discussed in terms of the cation distribution model, based on site preference energies and assuming random mixing on both tetrahedral and octahedral sites.

• Bulletin of the Korean Chemical Society
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• 제29권9호
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• pp.1827-1830
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• 2008

• Corrosion Science and Technology
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• 제3권4호
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• pp.140-147
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• 2004

High temperature oxidation of Fe-19Cr and Fe-19Cr-0.2Ti alloys is studied at 1173-1373 K in 16.5 kPa $O_2$ - balances $N_2$ atmosphere aimed at clarifying the effect of titanium addition. Oxidation rate of Fe-19Cr alloy was accelerated with titanium. For both alloys chromium rich $(Fe,\;Cr)_2O_3$ was formed as a major oxidation product. On Fe-19Cr-0.2Ti alloy, a thin layer composed of spinel type oxide and titanium oxide was also formed and an internal oxidation of titanium was observed. Titanium was concentrated at the oxide surface and internal oxidation zone but a small amount of titanium was also found in the intermediate corundum type $(Fe,\;Cr)_2O_3$ layer. Crystals of corundum type $(Fe,\;Cr)_2O_3$ formed on Fe-19Cr alloy are coarse but that formed on Fe-19Cr -0.2Ti alloys were fine and columnar. Reason for the difference in oxidation kinetics and crystal structure will be discussed relating to the distribution of aliovalent titanium in corundum type $(Fe,\;Cr)_2O_3$ oxide layer.

• 한국광물학회지
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• 제11권2호
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• pp.85-96
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• 1998

The sericite ore is formed by the hydrothermal alteration of rhyodacitic welded tuff. The alteration zone of the host rock can be classified into four types based on the mineral assemblages ; sericite, quartz-sericite, silicified and propylite zone. The sericite ore mainly occurs as vein types and fault clay along the fault plane in the quartz-sericite zone. Mineral components of the sericite ore are mainly sericite with minor diaspore, corundum and pyrite. The sericitic porcelaineous ore is mainly composed of quartz and sericite. Accessory minerals are muscovite, diaspore, sphene, corundum, pyrite, iron-oxides and etc. The chemical compositions of K2O, Al2O3, and ignition loss in the sericite ore increase largely than that of the host rock, while the compositions of SiO2, Na2O and Fe2O3 decrease. XRD patterns of the heat-treated sericite ores show the formation of mullite at $1,200^{\circ}C$. and the diaspore-bearing sericite ore forms mullite and corundum at $1,200^{\circ}C$. The differential thermal analysis of the sericite ores show small endothermic peak at 645~668$^{\circ}C$. and the diaspore-bearing sericite ore shows a strong endothermic peak at $517^{\circ}C$. It indicates that the decomposition of diaspore appear at lower temperature than that of sericite. The thermal expansivity of the sericite ores show the similar pattern. The sericite ores show the thermal expansivity of 3.3~4.7% at 900$^{\circ}C$ and 0.39~0.75% at 1,20$0^{\circ}C$, respectively. DTA-TG curves of the sericite ores show closely relations with the thermal expansivity.

• 한국광물학회지
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• 제22권4호
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• pp.297-305
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• 2009

전남지역에서 산출되는 납석은 좁은 의미의 납석(pyrophyllite)뿐 아니라, 고령토, 백운모, 석영 등을 포함하는 저급으로서 상업적으로 도석으로 분류되는 비금속광석류까지 포함한다. 납석광체와 주변 암층에 대한 광물학적 연구를 통하여 비슷한 시기에 분출된 유사한 화산변질물도 지질조건에 따라 납석이 생성되거나, 혹은 고령토로도 될 수 있음을 확인하였다. 납석광상에서는 또 다른 부성분 광물로 다이어스포에 비해 강옥이 흔히 산출되며, 다이어스포는 고령토를 소량으로 포함하는 납석광상에서 좀더 흔하여 강옥으로 가는 중간산물로 추정된다. 납석광상과 달리, 고령토광상에서는 강옥과 다이어스포가 확인되지 않으나, 고령토광체의 상단부에서는 심화점토화작용에 의한 명반석(alunite)의 산출이 흔한 편이다. 연구 지역에서 최하부에 위치한 광체를 포함하는 응회암층은 최상단부에 저색 응회암을 협재하며, 상부로 가면서 규화대층, 담백색 미세 응회암층 및 암설 응회암층 등이 확인되며, 이들 각 암층의 광물조성은 뚜렷한 차이를 나타낸다. 즉, 지질시대가 젊어짐에 따라 납석/고령토함량이 감소하거나 거의 확인되지 않기도 하며, 백운모는 다소 증가하고, 사장석류와 석영은 상대적으로 양은 풍부하나 원래 암석에 포함된 것들이다. 전남지역의 납석/고령토광체는 대체적으로 층리가 뚜렷하여 연장 확인에 어려움이 없기도 하지만, 괴상으로 나타나는 지역에서의 효과적 탐사를 위해서는 암상과 연장성이 확실히 구분되는 지층(건충; key bed)의 선정이 필요하다. 납석/고령토광체의 상부에 오는 규화대층과 저색 응회암층은 야외조사에서 건층으로 이용될 수 있는 특징이 확실하다.

• 한국결정성장학회지
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• 제14권3호
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• pp.101-104
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• 2004

결정내부에 존재하는 인클루전의 구성성분 및 결정학적인 구조를 분석하기 위해서는 기존의 normal XRD 분석 장비에 비해, 수십 $\mu\textrm{m}$ 크기의 결정입자에 대해 X-선 빔을 포커싱(focusing)하여 높은 S/N비로 분석할 수 있는 MC-XRD(Multi-Channel Ray Diffractome)가 매우 유용하였다. 이러한 MC-XRD로 분석한 결과, 루틸로 알려져 있는 커런덤내에 함유된 침상내포물은 iron titanium oxide, iron oxide들로 이루어져 있었고, 각각은 $Fe_2TiO_4,\; Fe_2TiO_5,\; Fe_2O_3$와 같은 화학조성을 가짐을 알았다.

• Applied Science and Convergence Technology
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• 제25권6호
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• pp.120-123
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• 2016

The rotor of a turbomolecular drag pump is generally made of an aluminum alloy. Its surface finish is affected by various processes that the rotor itself undergoes during the manufacturing phase. The impact of different surface finishes on the pumping performances of a turbomolecular pump has been mainly investigated by Sawada et al [1]. The present work aims to broaden the previous bibliographic study to the drag stages of a turbomolecular pump by testing the impact of different surface finishes on the compression ratio of the pump. Experimental tests have been made focusing on two processes: the corundum sandblasting and the glass microspheres shot-peening. Both the processes flatten and/or physically remove EDM melted spheres; in particular, blasted surfaces obtained by glass shot-peening are generally smoother than surfaces obtained by corundum sandblasting. In order to characterize the surface texture left by such processes, preliminary surface roughness measurements have been made on the drag rotor disks of several pumps. The experimental tests conducted on both sandblasted and shot-peened rotors confirms previous results obtained on the turbo stages by Sawada et al. [1], showing that the average roughness of the surface has an impact on the compression ratio of the pump; in particular, an increment in the surface roughness causes a corresponding increment in the compression ratio of the pump and vice versa. For the tested pumps, the higher surface roughness gives a factor of increment of about 2 on the measured hydrogen maximum compression ratio of the pump.

• 한국광물학회지
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• 제3권1호
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• pp.1-6
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• 1990

Clacic amphiboles along the tremolite (Tr)-tschermakite(Ts) joint were synthesized using a piston-cylinder appratus. At 750-85$0^{\circ}C$and 12-2 kb, amphibole+corundum coexist with zoisite($\pm$talc, chlorite, and Mg-staurolite), but with anorthite($\pm$cholorite, spinel, pyroxenes, and sapphirine) at lower P. At 90$0^{\circ}C$, amphibole+corundum+clinopyroxene($\pm$anorthite, forsterite, sapphirine, and garnet) are stable over the P range 12-18 kb. These amphibole-bearing assemblages are replaced at high P by clcinopyroxene+talc+chlorite+zoisite at 650-75$0^{\circ}C$, and at higher temperatures by garnet+clinopyroxene($\pm$zoisite, orthopyroxene, and Mg-staurolite). Synthetic amphiboles with Ts>~45 mol% contain as much as 0.15 excess cations per formula unit(pfu) based on 23 oxygens(anhydrous formula), whereas less tschermakitic ones are deficient in cation occupancy by up to 0.18 pfu. This trend is attributed to the 야/trioctahedral substitution in Ca-amphiboles. Compositions of synthetic amphiboles display systematic changes with P and T governed by coexisting mineral assemblages. The Ts content (=[8-Si-Na]/2) increases with increasing T( Ts/ T=~0.1 nik% K-1) in the range 750-85$0^{\circ}C$, but remains nearly constant at 850-90$0^{\circ}C$. Pressure dramatically affects the Ts content of Ca-amphiboles:it increases with P at 8-12 kb( Ts/ T=2-3 mol% K-1), but significantly decreases at 12-21 kb( Ts/ P=-2.5 mol% Kb-1). Hence, the most tschermakitic amphiboles, containing 60$\pm$5 mol % Ts, or 1.2$\pm$0.1 tetrahedral Al, occur at 12 kb and 850-90$0^{\circ}C$. Compositions of Ca-amphiboles defined by a simple reaction, 3 Tr+2 zoisite+7 corundum+H2O=5 Ts, are reversed and used to estimate thermodynamic parameters of tschermakite assuming ideal mixing of Tr-Ts solid solutions. Predicted standard molal entropy and enthalpy of tschermakite are : S$^{\circ}$of Tr-Ts solid solutions. Predicted standard molal entropy and enthalpy of tschermakite are : S$^{\circ}$=566.9$\pm$13.7 J mol-1K, -1and H$^{\circ}$=-12518.36$\pm$15.17 kJ mol.-1

• 한국결정성장학회지
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• 제21권3호
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• pp.105-109
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• 2011

수정(quartz)과 다이아몬드(diamond)의 임계각을 $sin{\theta}=r_2/r_1$(r = 굴절률, $r_1$ > $r_2$)의 식에 의해 계산한 결과 수정(R.I. ${\fallingdotseq}$ 1.553)은 $40.09^{\circ}$, 다이아몬드(R.I. = 2.417)는 $24.26^{\circ}$로 계산되었다. 계산된 임계각에 따른 각각의 보석 내부의 빛의 경로를 고찰한 결과 수정과 다이아몬드의 휘광성은 각각 20.33%와 55.07%였다. 임계각과 관련된 이론을 팬시 형 브릴리언트 컷으로 연마된 보석내부에서의 빛의 경로에 적용시킴으로써 보타이(bow-tie) 현상의 원인을 규명하였다. 또한 수정과 커런덤을 굴절계로 굴절률 측정 시 헤미실린더에서의 임계각을 계산한 결과 각각 $59.1^{\circ}$와 $77.9^{\circ}$로 계산되었다.