• Elastomers and Composites
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• v.40 no.1
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• pp.45-52
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• 2005

Synthesis or fullerene oxides[$C_{60}(O)_n$] ($n=1{\sim}4$ or n=1) by fullerene[$C_{60}$] and several oxidants such as 3-chloroperoxy benzoic acid, benzoyl peroxide, trichloroisocyanuric acid, and chromium(VI) oxide took place under microwave irradiation. The reactivity in solid state of fullerene[$C_{60}$] with various oxidants under same microwave rendition increased in order or 3- chloroperoxy benzoic acid > benzoyl peroxide > trichloroisocyanuric acid $\simeq$chromium(VI) oxide. The MALDI-TOF-MS, UV-visible spectra and HPLC analysis confirmed that the products of fullerene oxidation were [$C_{60}(O)_n$] ($n=1{\sim}4$ or n=1).

• Elastomers and Composites
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• v.39 no.4
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• pp.309-317
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• 2004

Synthesis of fullerene oxides [$C_{70}O_n$] ($n=1{\sim}3$ or n=1) in solid state by fullerene [$C_{70}$] and several oxidants such as 3-chloroperoxy benzoic acid, chromium(VI) oxide, benzoyl peroxide, and trichloroisocyanuric acid was taken place under microwave irradiation. The reactivity in solid state oi fullerene [$C_{70}$] with various oxidants under same microwave condition increased in the order of 3-chloroperoxy benzoic acid > chromium(VI) oxide > trichloroisocyanuric acid ${\simeq}benzoyl$ peroxide. The MALDI-TOF-MS, UV-visible spectra and HPLC analysis confirmed that the products of fullerene oxidation were [$C_{70}O_n$] ($n=1{\sim}3$ or n=1).

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.280-281
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• 2006

Powder grades pre-alloyed with 1.5-3 wt% chromium can be successfully sintered at the conventional temperature $1120^{\circ}C$ although well-monitored sintering atmospheres are required to avoid oxidation. Mechanical properties of the Cr-alloyed PM grades are enhanced by a higher sintering temperature in the range $1120-1250^{\circ}C$, due to positive effects from pore rounding, increased density and more effective oxide reduction. Astaloy CrM (Fe-3 wt% Cr-0.5 wt% Mo) with 0.6 wt% graphite added obtains an ultimate tensile strength of 1470 MPa and an impact strength of 31 J at density $7.1\;g/cm^3$, after sintering at $1250^{\circ}C$ followed by cooling at $2.5^{\circ}C/s$ and tempering.

• The Journal of Korean Academy of Prosthodontics
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• v.35 no.1
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• pp.78-94
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• 1997

The purpose of this experiment was to determine the effects of various treatments on denture base resin to metal bond for cobalt-chromium alloy. The metal surface was treated as follows. Group 1 : Sandblasted with $50{\mu}m$ aluminum oxide. Group 2 : Sandblasted with $250{\mu}m$ aluminum oxide. Group 3 : Sandblasted with $250{\mu}m$ aluminum oxide and followed by silicoating. Group 4 : Electrochemically etched. Group 5 : treated with oxidizing solution. Group 6 : Beaded with $200{\mu}m$ retention structure and followed by silicoating. All specimens were applied with 4-META resin and were thermocycled 1000 times at temperature of $5^{\circ}C$ to $55^{\circ}C$. The effects of various surface treatments on the bond strength between 4-META resin and metal interface were measured by using the universal testing machine. All specimens were observed with SEM. The results were as follows 1. The bond strength of 4-META resin were significantly higher to Co-Cr alloy. 2. The bond strength decreased in the following orders : group 6, group 3, groups 1 and 2, group 4, group 5 and there was no statistically significant difference in bond strength among groups 1 and 2.(p>0.05) 3. The bond strength of cobalt-chromium alloy to 4-META resin were not significantly different.(p>0.05) 4. The treated surface of groups 1, 2 and 3 has more fine undercut than that of groups 4 and 5 with SEM. 5. Stable adhesion can be achieved when mechanically roughened metal surface by sandblasting than treating in an electrochemical etching and an oxidizing solution with potassium manganate.

• Applied Biological Chemistry
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• v.41 no.1
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• pp.89-94
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• 1998

Various Mn-oxides can oxidize Cr(III) to Cr(VI). Behaviors of chromium species in the oxidation system, especially on the oxide surface, are expected to control the reaction. During Cr(III) oxidation by birnessite and pyrolusite, Cr species in the reaction system were determined to elucidate their effects on the oxidation. Capacities of Cr oxidation of the two Mn-oxides were quite different. Solution pH and initial Cr(III) concentration also had significant effects on the Cr(III) oxidation by Mn-oxides. Chromium oxidation by pyrolusite was less than 5% of the oxidation by birnessite. The high crystallinity of pyrolusite could be one of the reasons and the difficulty of Cr (III) diffusion to the positive pyrolusite surface and Cr(VI) and Cr(III) adsorption seems to be other controlling factors. At pH 3, adsorption or precipitation of Cr species on the surface of birnessite were not found. Small amount of Cr(VI) adsorption was found on the surface of pyrolusite, but arty Cr precipitation on the oxide surface was not found. Therefore Cr(III) oxidation at pH 3 seems to be controlled mainly by the characteristics of Mn-oxides. Chromiun oxidation by Mn-oxides is thermodynamically more favorable at higher solution pH. However as solution pH increased Cr oxidation by birnessite was significantly inhibited. For Cr oxidation by pyrolusite, as pH increased the oxidation increased, but as Cr(III) addition increased the reaction was inhibited. Under these conditions some unidentified fraction of Cr species was found and this fraction is considered to be Cr(III) precipitation an the oxide surface. Chromium(III) precipitation on the oxide surface seems to play an important role in limiting Cr(III) oxidation by armoring the reaction surface on Mn-oxides as well as lowering Cr(III) concentration available for the oxidation reaction.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.11a
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• pp.409-414
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• 1999

The influence of ion beam energy and reactive oxygen partial pressure on the electrical and crystallographic characteristics of transition metal oxide compound(Cr0x) film was studied in this paper. Chromium oxide films were prepared onto the coverglass using Ion Beam Sputter Deposition(1BSD) technique according to the processing conditions of the partial pressure of reactive oxygen gas and ion beam energy. Crystallinity and grain size of as-deposited films were analyzed using XRD analysis. Thickness and Resistivity of the films were measured by $\alpha$-step and 4-point probe measurement. As results, according to the XRD, XPS and resistivity measurement, the deposited films were the cermet type films which has a crystal structure including amorphous oxide(a-oxide) phase and metal Cr phase simultaneously. The increasernent of the ion b m energy during the deposition process happened to decreasernent of metal Cr grain size and the rapid change of resistivity above the critical $O_2$ partial pressure.

• Transactions of Materials Processing
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• v.6 no.2
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• pp.95-101
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• 1997

The thermal fatigue and wear properties of high speed steel roll which was recently developed were investigated by observing microstructure, by measuring mechanical and physical properties, by conducting thermal fatigue testing, and by measuring the amount of wear in actual mill. High speed steel roll had better thermal fatigue testing, and by measuring the amount of wear in actual mill. High speed steel roll had better thermal fatigue life than high chromium iron roll, which was due to lower carbide content, higher strength, and higher thermal conductivity. The amount of wear of high speed steel roll was nearly the same as that of high chromium iron roll in the first finishing stand, which was due to the oxide formation on the roll surface. However, in the third finishing stand, the wear resistance of high speed steel roll was 2~3 times as good as that of high chromium iron roll because the former had higher hardness at high temperature.

• Bulletin of the Korean Chemical Society
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• v.16 no.3
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• pp.214-216
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• 1995

Passive films formed on chromium surface in citrate buffer solution were investigated by means of three-parameter ellipsometry. The citrate buffer was found to be a suitable medium in which oxide film on chromium could be removed by cathodic treatment, providing a reference surface for the optical study. The passive film effectively protecting the chromium surface from corrosion was found to have thicknesses in the range 0.65 to 1.25 nm depending on the potential in the range of -0.20 to 0.60 V (0.1M KCl calomel electrode). The complex refractive index of the passive film did not show significant potential-dependent changes, indicating that the composition of the film material does not depend on potential.

• Resources Recycling
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• v.13 no.2
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• pp.9-15
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• 2004

A large tons of spent iron oxide catalyst come from the Styrene Monomer(SM) production company. It is caused to pollute the land and underground water due to the high alkali contents in the catalyst by burying them in the landfill. In order to recycle the spent catalyst, a basic study on the recovery of chromium ion from metal plating wastewater with the spent catalyst was carried out. The iron oxide catalyst adsorbed physically $Cr^{+6}$ in the lower pH 3.0, that is the isoelectric point of the spent catalyst. It was found that the iron oxide catalyst reduced the $Cr^{+6}$ into Cr+3 by the oxidation of ferrous ion into ferric ion on the surface of catalyst, and precipitated as $Cr(OH)_3$ in the higher than pH 3.0. The $Cr^{+6}$ was recovered 2.0∼2.3g/L catalyst in the range of pH 0.5∼2.0, but it was recovered 1.5 g/L catalyst at pH 3.0 of wastewater. The recovery of Cr was increased as the higher concentration in the continuous process, but the flowrates were nearly affected on the Cr recovery.

• Proceedings of the Korea Association of Crystal Growth Conference
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• 1998.09a
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• pp.97-102
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• 1998

Transition metal Cr3+ and Fe3+ ion was diffused in white sapphire {0001}, {1010} crystal plane which were grown by the Verneuil method. It enhanced and changed the physical, electrical and optical properties of sapphires. After mixing the metallic oxide and metal powder, it were used for diffusion. Metallic oxide was synthesized by precipitation method and it's composition was mainly alumina which doped with chromium or ferric oxide. In case using metallic oxide, the dopping was slowly progressed and it needed the longer duration time and higher temperature, relatively. Metallic powder was vapoured under 1x10-4 torr of vacuum pressure at 1900(iron metal) and 2050(chromium)℃, first step. Diffusion condition were kept by 6atm of N2 accelerating pressure at 2050∼2150℃. Each surface density of sapphire crystal are 0.225(c) and 0.1199atom/Å2(a). The color of the Cr-doped sapphires was changed to red. Dopping reaction was come out more deep in th plane of {1010} than {0001}. It was speculated that the planar density was one of the factors to determine diffusion effect.