• Journal of the Korean Ceramic Society
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• v.25 no.1
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• pp.35-41
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• 1988

In the system of Li2O-MgO-Al2O3-Cr2O3, the crystalline solid solution of LiCrO2 along the pseudo-binary join between rocksalt structure(LiCrO2) and spinel structure(MgCr2O4 or MgAl2O4) have been investigated by x-ray diffraction techniques. In this study, order-disorder phase transition of LiCrO2 was observed and the unit cell of the disordered LiCrO2 structure has been established. It has been found that LiCrO2 makes a solid solution over a wide range with MgAl2O4, while not with MgCr2O4. This difference was explained as being due to the ability of oxygen lattice distortion which depended on the relative sizes and chemical bonding characteristics of the substituted ions.

• Journal of the Korean Chemical Society
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• v.30 no.1
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• pp.57-62
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• 1986

Oxidation of $[Mo_3O_4(C_2O_4)_3(H_2O)_3]^{2-}$ with HCr$O_4^-$ yields the molybdenum(Ⅳ) complex, $[Mo_2O_5(C_2O_4)_2(H_2O)_2]^{2-}$. Stoichiometry for the reaction of $[Mo_3O_4(C_2O_4)_3(H_2O)_3]^{2-}$ with HCr$O_4^-$ are expressed as $2Mo_3^{IV} + 4Cr^{VI} {\to} 3Mo_2^{VI} + 4Cr^{III}$. Observed rate constants are dependent on hydrogen ion concentration. The kinetic data are consistent with a mechanism in which three successive single-electron steps convert $Cr^{VI}$to $Cr^{III}$ by way of intermediate $Cr^V$ and $Cr^{IV}$. Detailed mechanisms are presented and discussed.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.07b
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• pp.898-901
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• 2004

[ $ZnCr_2O_4$ ]를 모물질로 하고 MgO, $TiO_2$를 몰비로 2:1, 4:1, 6:1, 및 8:1이 되게 정량적으로 조합한 후, 조사하였다. $ZnCr_2O_4$-MgO와 $ZnCr_2O_4-TiO_2$를 X-선 분석한 결과 Spinel 결정구조를 형성하였으며, 또한 SEM과 EDX 분석결과 각각 $Li_2CrO_4$와 $Li_3VO_4$의 형성으로 인하여 저항 특성이 나타나는 것을 알 수 있었다. $ZnCr_2O_4-MgO$, $ZnCr_2O_4-TiO_2$에서 MgO의 양이 증가할수록 저항값은 약간 감소하는 반면, $TiO_2$의 양이 증가할수록 저항값이 급격히 증가하는 특성을 나타내었고, 감습 특성에서도 M??보다 TiO2가 더 높게 나타내었다. 습에 따른 복원 특성의 경우 $700^{\circ}C$에서 소결한 ($ZnCr_2O_4:MgO=4:1$)과 ($ZnCr_2O_4:TiO_2=6:1$) 조성의 센서가 가장 양호하였다.

• Journal of the Korean Chemical Society
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• v.30 no.2
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• pp.231-236
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• 1986

Oxidation of $[Mo_2O_4(C_2O_4)_2(OH_2)_2]^{2-}$ with hydrogen chromate yields the molybdenum (VI) complex, $[Mo_2O_4(C_2O_4)_2(OH_2)_2]^{2-}$. Stoichiometry for the reaction of $[Mo_2O_4(C_2O_4)_2(OH_2)_2]^{2-}$ with hydrogen chromate are expressed as ${3Mo_2}^V+2Cr^{VI}\;{\rightleftharpoons}\;{3Mo_2}_{VI}+2Cr^{III}$. Observed rate constants are dependent on $[H+]^2$. The kinetic data are consistent with a mechanism in which three successive single-electron steps convert $Cr^{VI}$to $Cr^{III}$ by way of intermediate Cr^V$ and $Cr^{IV}$. Mechanism of the reaction are presented and discussed.

• Journal of the Korean Magnetics Society
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• v.23 no.5
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• pp.149-153
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• 2013

The electronic structures of $TCr_2O_4$ (T = Fe, Co, Ni) spinel oxides have been investigated by employing synchrotron radiation-based soft X ray absorption spectroscopy (XAS). The measured 2p XAS spectra of transition-metal ions reveal that Cr ions are trivalent ($Cr^{3+}$), and all the T (T = Fe, Co, Ni) ions are divalent ($Fe^{2+}$, $Co^{2+}$, $Ni^{2+}$). It is also found that most of T (T = Fe, Co, Ni) ions occupy the A sites under the tetrahedral symmetry, while Cr ions occupy mainly the B sites under the octahedral symmetry. These findings show that the structures of $TCr_2O_4$ (T = Fe, Co, Ni) are very close to the normal spinel structures. Based on these findings, it is expected that Jahn-Teller (JT) effects are important in $FeCr_2O_4$ and $NiCr_2O_4$. In contrast, $CoCr_2O_4$ maintains the cubic structure without having the JT distortion since both $Cr^{3+}$ and $Co^{2+}$ ions are non-JT ions. This work suggests that the antiferromagnetic interaction between $Cr^{3+}$ and $T^{2+}$ ions plays an important role in determining the magnetic properties of $TCr_2O_4$ (T = Fe, Co, Ni).

• Journal of the Korean Chemical Society
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• v.18 no.2
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• pp.110-116
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• 1974

Reduction of chromate ion at the Pt-electrode was investigated in neutral unbuffered solutions, in buffered solutions of pH between 8 and 10, and in strongly alkaline medium. In buffered solutions of pH between 8 and 10, the number of electrons transfered in the reduction of chromate ion increased progressively with increasing pH. When chromate ion was reduced in 0.2 N sodium hydroxide medium the following mechanism was suggested: $CrO_4^=+H_2O+2e{\rightarrow}CrO_3^=+2OH^-,\;CrO_3^=3H_2O+e{\rightarrow}Cr(OH)_3+3OH^-$ When tetramethylammonium hydroxide (pH=13.5) was used as the supporting electrolyte, a second wave indicated strong adsorption. In unbuffered solutions of 0.1 N potassium chloride the linear sweep voltammogram consists of three or four distinct waves depending on the initial voltage and the voltage sweep rates, but the first wave was difficult to explain as a diffusion controlled wave.

• Bulletin of the Korean Chemical Society
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• v.23 no.2
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• pp.184-188
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• 2002

Unsaturated $Cr(CO)_x(1{\leq}x{\leq}5)$molecules were generated in the gas phase from photolysis of $Cr(CO)_6$vapor in He using an unfocussed weak UV laser pulse and their reactions with $O_2$ and $N_2O$ have been studied. The formation and disappearance of the ground state CrO molecules were identified by monitoring laser-induced fluorescence(LIF) intensities vs delay time between the photolysis and probe pulses. The photolysis laser power dependence as well as the delay time dependence of LIF intensities from the CrO orange system showed different behavior as those from ground state Cr atoms, suggesting that the ground state CrO molecules were generated from the reaction between $O_2/N_2O$ and photo-fragments of $Cr(CO)_6$ by one photon absorption. The depletion rate constants for the ground state CrO by $O_2$ and $N_2O$ are $5.4{\pm}0.2{\times}10^{-11}$ and $6.5{\pm}0.4{\times}10^{-12}cm^3molecule^{-1}s^{-1}$, respectively.

• Elastomers and Composites
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• v.50 no.1
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• pp.7-12
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• 2015

The $BaCrO_4$ nanoparticles were synthesized from a 0.1 M $K_2CrO_4$ and 0.1 M $BaCO_3$ solution with stirring for 10 h. The product was washed several times with acetone and heated to $700^{\circ}C$ for 6 h. At that time, the color of mixture was a greenish yellow. The graphene/$BaCrO_4$ nanocomposites were prepared with graphene and $BaCrO_4$ nanoparticles by stirring in tetrahydrofuran and heated in an electric furnace at $700^{\circ}C$ for 2 h. The $BaCrO_4$ nanoparticles, graphene/$BaCrO_4$ and heated graphene/$BaCrO_4$ nanocomposites were characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The graphene/$BaCrO_4$ nanocomposites and heated graphene/$BaCrO_4$ nanocomposites were evaluated as a photocatalyst and discussed about kinetics study for the degradation of organic dyes, such as methylene blue and rhodamine B under ultraviolet light irradiation at 254 nm.

• 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.19 no.4
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• pp.293-299
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• 1982

The effects of $MnO_2$ and $Cr_2O_3$ on the Piezoelectrictric properties of Pb(Mg1/2W1/2)0.3 Ti0.4 Zr0.3O3 Ceramics. Electromechanical properties in the system in connection with the sintering temperature and the effects of $MnO_2$ and $Cr_2O_3$ addition. The dielectric constant of the ceramics decreased with the additions of $MnO_2$ while the additions of $Cr_2O_3$ increased the value. The Planar coupling factor (Kp) of the ceramics with 0.2wt% $MnO_2$ and with 0.2wt% $Cr_2O_3$ gave the highest value of 0.52 and 0.513 as sintered at 106$0^{\circ}C$, 108$0^{\circ}C$, respectively. The value of mechanical Q-factor were in parallel with the fired density of the ceramics. The optical micrography of the sintered bodies showed that the additions of $MnO_2$ promoted the grain growth, while the additions of $Cr_2O_3$ retarded the grain growth.