• Korean Journal of Metals and Materials
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• v.48 no.6
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• pp.506-513
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• 2010

The composite coatings of $(ZrO_2-8Y_2O_3)$/(Ni-22Cr-10Al-1Y) were prepared by the air plasma spraying method. They consisted of (Ni,Cr)-rich regions,$(ZrO_2-Y_2O_3)$-rich regions, and $Al_2O_3$-rich regions that were formed by oxidation of Al from (Ni-22Cr-10Al-1Y) during spraying. The coatings corroded at 800 and $900^{\circ}C$ in NaCl-$Na_2SO_4$ molten salts up to 50 hr. Ni, Cr and Al oxidized to NiO, $Cr_2O_3$ and ${\alpha}-Al_2O_3$, respectively. These oxides and $(ZrO_2-Y_2O_3)$ were dissolved off into the molten salts during hot corrosion, which resulted in the ever-lasting corrosion of the composite coatings. Chromium diffused out from the (Ni,Cr)-rich regions and oxidized to $Cr_2O_3$, which was most frequently found as surface scales. Aluminum retained in the (Ni,Cr)-rich regions were similarly diffused out.

• Journal of the Korean Ceramic Society
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• v.46 no.4
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• pp.405-412
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• 2009

In high temperature ceramic glazes, a stable range of pink-red colors that produced $Cr_2O_3-SnO_2-CaO-SiO_2$ pigments were factored by Cassiterite($SnO_2$) and Malayaite($CaSnSiO_5$) by $Cr_2O_3$. The experiment examined the influence of $CrCl_3$, a Sn-Cr substitution added with a mineralizer ($H_3BO_3$), as a chromophore in pigments. The experiment also studied the effect of $H_3BO_3$ (2 wt%) when added to malayaite($CaSnSiO_5$) to see if the crystalline reaction will increase. $Cr_2O_3$ was also substituted with $CrCl_3$ in order to prove how much influence $CrCl_3$ had on the $H_3BO_3$. Malayaite and cassiterite were the basic compound materials and the experiment was conducted both with and without mineralizers (2 wt% of $H_3BO_3$). Each compound was synthesized at 800, 1000, 1200, 1300, 1400, $1500^{\circ}C$ for 2 h. Synthesized pigments were analyzed by XRD, FT-IR and UV-Vis. The temperature variation produced two crystal phases that showed the different engaging effects of Cr oxidation. $CrCl_3$ produced a better effect on the malayaite crystal phase, resulting in a more defined pigmentation of the pink-red coloration compared to $Cr_2O_3$.

• Journal of the Korean Ceramic Society
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• v.46 no.4
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• pp.372-378
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• 2009

The coloring agents $Cr_2O_3$ and $CrCl_3$ were manipulated in this study to synthesize ZnO-$Al_2O_3-Cr_2O_3$ system pigments by changing their mixing ratio. The addition of varying amounts of mineralizer was also tested to obtain better color development of the pink pigment. In the synthesis of ZnO- $Al(OH)_3-Cr_2O_3-CrCl_3$ pigments, the best composition is $Cr_2O_3$-0.1 mole and $CrCl_3$-0.2 mole when $Cr_2O_3$ is partially substituted with $CrCl_3$ to synthesize them. Among the $ZnAl_{1.6-x}Cr_{0.2+x}O_4$ compositions to which a mineralizer was not added, ZnO-1mole, $Al(OH)_3$-1.7 mole, $Cr_2O_3$-0.075 mole, and $CrCl_3$-0.15 mole showed a desirable pink hue. The measurements of pigments $L^*$, $a^*$ and $b^*$, were $L^*$ 81.81, $a^*$ 16.65 and $b^*$ 0.45, and when the synthesized pigments were applied to a zinc glaze, the measurements were $L^*$ 60.41, $a^*$ 28.39, and $b^*$ 16.97. When adding a mineralizer, a 2 wt% addition resulted in the most favorable pink color. The composition for the most favorable result that included a mineralizer was $Al(OH)_3$-1.8 mole, $Cr_2O_3$-0.05 mole, and $CrCl_3$-0.1 mole, and the calcination temperature was $1250^{\circ}C$. The pigment color analysis showed $L^*$ 82.52, $a^*$17.14 and $b^*$-1.18, and the measurements of $L^*$, $a^*$ and $b^*$ in the glaze were $L^*$ 60.97, $a^*$ 28.77 and $b^*$ 13.72.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.07a
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• pp.399-402
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• 2000

For improvement of B constant in $CaMnO_3$-$CaTiO_3$ perovskite type thermistors, effect of $Cr_2$$O_3$ addition ranged from 0.0wt% to 5.0wt% on electrical properties were investigated with contents and sintering temperatures in the view of crystal and microstructures. The solubility limit of Cr$_2$O$_3$was up to 0.5wt% judging from the result of lattice parameter. The grain size was decreased and the resistance at room temperature and B constant were increased with the addition of $Cr_2$$O_3$.On particular, B constant of$CaMnO_{3-x}$$Cr_2$$O_3$ system was increased greatly from 1574k to 2598k at 0.5wt% $Cr_2$$O_3$addition. Further addition of $Cr_2$$O_3$, however, resulted in the decrease of the resistance and B constant due to the $Cr_2$$O_3$ precipitation on the grain boundary. As the$CaTiO_3$contents increased in the $CaMnO_3$-$CaTiO_3$ system, the resistance at room temperature and B constant were highly changed.

• Journal of the Korean Society for Heat Treatment
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• v.6 no.2
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• pp.89-97
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• 1993

An improvement in corrosion resistance of various types of Zn-coated steel sheets is thought to be possible with the addition of fine oxide powder to the coating. In this study the corrosion resistance of the $Al_2O_3$ dispersed Zn-Co-Cr electroplated steel sheet has been investigated and the results were as follows : The corrosion resistance of $Al_2O_3$ dispersed Zn-Co-Cr electroplated steel sheets was improved by increasing the contents of Co and Cr ions, and also $Al_2O_3$ powders in the bath because of the increased amount of Co, Cr and $Al_2O_3$ in deposits. In the $Al_2O_3$ dispersed Zn-Co-Cr electroplated steels sheet, the structure of deposits was changed from fine microstructure as observed in high Co containing deposits to coarse microstructure as in high Cr and $Al_2O_3$ containing deposits. By cold rolling of the $Al_2O_3$ dispersed Zn-Co-Cr electroplated steel sheets to about 2 percent, thr corrosion resistance was improved further.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2011.05a
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• pp.33-35
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• 2011

Films of CrAlN and CrZrN were deposited on a steel substrate by closed field unbalanced magnetron sputtering, and their oxidation behaviors were investigated. CrAlN films consisted of dense, polycrystalline CrN and AlN fine columns. The formed oxides consisted primarily of crystalline $Cr_2O_3$ incorporated with $Al_2O_3$. The oxide layers were thin and compact so as to make CrAlN films more protective than CrN films. In case of CrZrN films, Zr atoms were dissolved in the CrN phase. Zr atoms advantageously refined the columnar structure, reduced the surface roughness, and increased the micro-hardness. However, the addition of Zr did not increased oxidation resistance, mainly because Zr was not a protective element. All the deposited films displayed relatively good oxidation resistance, owing to the formation of the highly protective $Cr_2O_3$ on their surface. The $Cr_{40}Zr_9N$ and $Cr_{31}Zr_{16}N$ films oxidized to $Cr_2O_3$ as the major phase and ${\alpha}-ZrO_2$ as the minor one, whereas the CrN film oxidized to $Cr_2O_3$.

• Journal of the Korean Chemical Society
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• v.48 no.4
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• pp.358-366
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• 2004

The bridged disulphato complex $[Cr_2(NH_2)_2(H_2O)_2(SO_4)_2]{\cdot}2H_2O$, terminal triisocyanato $[Cr(NCO)_3(H_2O)]{\cdot}3H_2O$ complex and limonite, $[FeO(OH)]{\cdot}0.2H_2O$ compound were prepared by the reaction of $Cr_2(SO_4)_3{\cdot}xH_2O, Cr(CH_3COO)_3$ and $Fe_2(SO_4)_3$, respectively, with urea in aqueous media at $80^{\circ}C$. The infrared spectra of the products indicate that the absence of the bands of urea, but shows the characteristic bands of coordinated amide, water, bridged sulphato and isocyanato groups. Thermogravimetric (TG) and differential thermal analysis (DTA) measurements on the complexes are also recorded. The data obtained agree quite well with the expected structures. A general mechanisms describing the formation and its thermal decomposition of the complexes are suggested.

• Journal of the Korean Ceramic Society
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• v.34 no.1
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• pp.88-94
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• 1997

The oxidation behavior of the NiCrAlY bond coat and thermal fatigue failure in the plasma-sprayed thermal barrier coating system, ZrO2.8wt%Y2O3 top coat/Ni-26Cr-5Al-0.5Y bond coat/Hastelloy X superalloy substrate, in commercial use for finned segment of gas turbine burner were investigated. The main oxides formed in the bond coat were NiO, Cr2O3, and Al2O3. It divided the oxide distribution at this interface into two types whether an Al2O3 thin layer existed beneath ZrO2/bond coat interface before operation at high temperature or not. While a continuous layer of NiO was formed mainly in the region where the Al2O3 thin layer was present, the absence of it resulted in the formation of mixture of Cr2O3 and Al2O3 beneath NiO layer. Analyses on the fracture surface of specimen spalled by thermal cycling showed that spalling occurred mainly along the ceram-ic coat near ZrO2/bond coat oxide layer interface, but slightly in the oxide layer region.

• Journal of the Korean Ceramic Society
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• v.22 no.5
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• pp.71-75
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• 1985

This study deals with sintering and corrosive behavior of sintered zircons mixed with 5wt% of clay $Cr_2O_3$ $CrO_3-MgO$ aqueous solution and $CrO_3-Mg(OH)_2$ aqueous solution. Measurements were conducted by firing specimens at 135$0^{\circ}C$ 145$0^{\circ}C$ and 155$0^{\circ}C$ 1$650^{\circ}C$ for 3hrs in oxidized and reduced atmospheric conditions. Following results were obtained. 1. Sintered zircon with 5 wt% clay showed that highest compressive strength and the lowest apparent porosity and the other showed less positive result than above specimen in order of zircon with $CrO_3-MgO$ aqueous solution $CrO_3-Mg(OH)_2$ aqueous solution and $Cr_2O_3$. 2. The more firing temperature increased the more its strength improved and porosity decreased and specimen which was fired over 155$0^{\circ}C$ and in reduced atmospheric condition showed better results. 3. Zircon with additives which was fired over 155$0^{\circ}C$ showed the evidence of thermal dissociation but it was not rebonded completely during cooling. 4. Zircon with $CrO_3-MgO$ aqueous solution and $CrO_3-Mg(OH)_2$ aqueous solutiion showed more corrosive resistance than zircon itself and zircon-clay system.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2014.11a
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• pp.21-21
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• 2014

$CrN/Al_2O_3/CrN$ 다층 코팅을 HIPIMS와 ALD간 하이브리드 코팅법을 통해 형성하였다. ALD를 통해 CrN 층에 도입한 $Al2O_3$층의 두께 및 위치가 $CrN/Al_2O_3/CrN$ 다층 코팅층의 미세구조, 표면 거칠기, 기계적 특성 및 화학적 특성에 미치는 영향에 대해 조사하였다. 전체 공정시간은 거의 변화시키지 않고도, ALD를 이용한 $Al2O_3$층의 삽입에 의하여 기계적/화학적 특성이 크게 개선될 수 있음을 확인하였으며, 개선된 특성에 대한 원인에 대해 조사하였다.