• Title, Summary, Keyword: $CrO_4^{2-}$

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Solid Solution and Defect Structure of LiCrO2 in the Pseudo-binary Systems : Li2Cr2O4-MgAl2O4 (의사이성분계, Li2Cr2O4-MgCr2O4와 Li2Cr2O4-MgAl2O4에서의 LiCrO2 고용체 형성과 결합구조)

  • 정영서;오근호;김호기
    • 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.

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Kinetic Studies on the Oxidation of Oxalatoaquamolybdenum(IV) Trimer by Hydrogen Chromate Ion (수소크롬산 이온에 의한 옥살라토아쿠아몰리브덴(IV) 삼합체의 산화반응)

  • Chang-Su Kim;Chang-Yong Kwon
    • 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.

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Humidity-Sensitive Characteristics of MgO and $TiO_2$ Addition on $ZnCr_2O_4$ Ceramic Thick-Film Humidity Sensors (MgO 및 $TiO_2$가 첨가된 $ZnCr_2O_4$ 세라믹 후막 습도센서의 감습 특성)

  • Yoon, Sang-Ok;Kim, Kwan-Soo;Jo, Tae-Hyun;Shim, Sang-Heung
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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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$$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.

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Kinetic Studies on the Oxidation of Oxalate Complex of Oxomolybdenum (V) of Hydrogen Chromate Ion (수소크롬산 (VI) 이온에 의한 몰리브덴 (V) 의 옥살산착물의 산화반응)

  • Chang-Yong Kwon;Chang-Su Kim
    • 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.

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Investigation of Electronic Structures of TCr2O4 (T = Fe, Co, Ni) Spinel Oxides by Employing Soft X ray Synchrotron Radiation Spectroscopy (연 X선 방사광 분광법을 이용한 TCr2O4(T = Fe, Co, Ni) 스피넬 산화물의 전자구조 연구)

  • Kim, Hyun Woo;Hwang, Jihoon;Kim, D.H.;Lee, Eunsook;Kang, J.S.
    • 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).

A Study of Cathodic Reduction of Chromate Ion on Platinum (백금전극에서 크롬산염이온의 음극환원반응에 관한 연구)

  • Hwang, Kum-Sho
    • 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.

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Effect of Chrome Substitution on Coloration Characteristics of Black Ceramic Pigments (크롬 치환에 따른 흑색 세라믹 안료의 발색 특성 연구)

  • Lee, Ji-Hyeon;Hwang, Hae-Jin;Kim, Jin-Ho;Hwang, Kwang-Taek;Han, Kyu-Sung
    • Journal of the Korean Ceramic Society
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    • v.51 no.5
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    • pp.505-510
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    • 2014
  • The properties of black ceramic pigments including thermal and glaze stability were systematically investigated so that these pigments could be used to decorate porcelain products. Various compositions of $(Ni,Mn)(Fe,Cr,Mn)_2O_4$ and $Co(Fe,Cr)_2O_4$ powders were synthesised using a solid state reaction method. The obtained $Co(Fe,Cr)_2O_4$ and $(Ni,Mn)(Fe,Cr,Mn)_2O_4$ powders showed single phases of spinel structure after calcination processes at $1000^{\circ}C$ and $1200^{\circ}C$, respectively. CIE $L^*a^*b^*$ colourimetric parameters of glazed $Co(Fe,Cr)_2O_4$ and $(Ni,Mn)(Fe,Cr,Mn)_2O_4$ pigments were analyzed according to the different amounts of Cr substitution. In addition, the amount of $Cr^{+6}$ remaining in the $Co(Fe,Cr)_2O_4$ and $(Ni,Mn)(Fe,Cr,Mn)_2O_4$ pigments was also measured.

Synthesis of ZnO-Al2O3-Cr2O3 System Pigments with CrCl3

  • Choi, Soo-Nyong;Lee, Byung-Ha
    • 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.

Depletion Kinetics of the Ground State CrO Generated from the Reaction of Unsaturated Cr(CO)x with O2 and N2O

  • Son, H.S.;Ku, J.K.
    • 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.

Spectroscopic and Thermal Studies of [Cr2(NH2)2(H2O)2(SO4)2]·2H2O,[Cr(NCO)3(H2O)]·3H2O and [Fe O(OH)]·0.2H2O Compounds Formed by the Reactions of Urea with Cr2(SO4)3, Cr(CH3COO)3 AND Fe2(SO4)3

  • Sadeek, S.A.;Refat, M.S.;Teleb, S.M.
    • 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.