New Crystalline Phases in the System Chromium(III) Oxide—Water<sup>1</sup>

Laubengayer, A. W.; McCune, H. W.

doi:10.1021/ja01129a054

Cited by 60 publications

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“…In supercritical water of density 0.7 g cm-3 at 440 "C, CrO(0H) reacts with stainless steel to produce a spinel (Fe,Ni)Cr,O, (a trace of copper was also present in this spinel, because the strongly adhesive copper-graphite lubricant used on the threaded parts apparently accidentally contaminated the internal vessel walls). This experiment suggests that the "cubic Cr203" of Laubengayer and McCune (21), which was produced in the same way except that the CrO(0H) was contained in a platinum experiments is ascribed to its limited chemical contact with the stainless steel vessel walls, via the supercritical aqueous fluid through leaks or openings in the platinum container. The reported conversion of the "cubic Cr203" to a-Cr203 by heating in air at 800 "C (21) may result from aerial oxidation of FeCr204 to a solid solution of a-Fe203 in a-Cr203 (22), whose X-ray diffraction pattern is similar to that of a-Cr20,.…”

Section: Reaction Oj' Aqueous Chromium(iii) With Metalsmentioning

confidence: 95%

The Aqueous Chemistry of Chromium(III) above 100 °C: Hydrothermal Synthesis of Chromium Spinels

Swaddle¹,

Lipton²,

Guastalla³

et al. 1971

Can. J. Chem.

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The hydrothermal deposition of CrO(OH) from aqueous chromium(III) chloride, nitrate, and perchlorate, and of Cr3(SO4)2(OH)5•H2O and Cr(OH)SO4•2H2O(?) from aqueous chromium(III) sulfate, has been investigated. Aqueous chromium(III) is oxidized to chromium(VI) by 0.4 M perchloric acid above 225 °C, and by molecular oxygen above 250 °C. Aqueous chromium(III) can react at 300 °C with iron or steel, cobalt, and copper to produce FeCr2O4, CoCr2O4, and Cu2Cr2O4, respectively. CrO(OH) reacts with type 316 stainless steel at 440 °C in supercritical water of density 0.7 g cm−3 to yield (Fe,Ni)-Cr2O4, which is the "cubic Cr2O3" of Laubengayer and McCune. The spinels MCr2O4 (M = Mg, Mn, Fe, Co) can be made hydrothermally at ca. 300 °C from Cr(OH)3 and M(OH)2. This information is relevant to corrosion phenomena, and the possible hydrothermal origin of chromite deposits in serpentinized rocks.

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Section: Reaction Oj' Aqueous Chromium(iii) With Metalsmentioning

confidence: 95%

The Aqueous Chemistry of Chromium(III) above 100 °C: Hydrothermal Synthesis of Chromium Spinels

Swaddle¹,

Lipton²,

Guastalla³

et al. 1971

Can. J. Chem.

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“…Earlier, a measured refractive index of approximately 2.0 ±0.1 was given by Shafer and Roy (1954). For the density Douglass (1957) reported 4.11 ±0.03 gcm~3 as a measured value and calculated 4.10 from X-ray data; even earlier, Laubengayer and McCune (1952) reported 4.12 gem-3 (measured value). No optical data were reported for CrOOH (mcconnellite), but Ys (2 w + e) can be calculated as 2.29 by the Gladstone-Dale formula, using the measured density 5.49 gem-3 (calculated, 5.609 gem-3 ) of Dannhauser and Vaughan (1955).…”

Section: Physical Propertiesmentioning

confidence: 95%

“…CrOOH AND CrOOCu Laubengayer and McCune (1952) prepared rhombohedral CrOOH hydrothermally at 145°C, and Shafer and Roy (1954) cite Simon and others (1930) as having first prepared crystalline chromium oxyhydroxide hydrothermally at 200°C and 15 atm. Shafer and Roy (1954) prepared crystalline CrOOH from a gel at 230°C and 4 atm for 322 hr.…”

Section: Previous Syntheses Of Rhombohedralmentioning

confidence: 99%

Merumite; a complex assemblage of chromium minerals from Guyana

Milton¹,

Appleman²,

Appleman³

et al. 1976

Professional Paper

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TABLE 3. Spectrographic analyses (in percent) of four merumite samples _ 9 4. X-ray powder patterns of merumite (eskolaite 37 percent, guyanaite 63 percent), merumite approaching eskolaite (Guyana), guyanaite (Guyana, four strongest lines), eskolaite (Finland), and Cr2O8 9 5. Cell constants of guyanaite (from Guyana and Finland), and of CrOOH, ScOOH, and InOOH 11 6. Analyses of guyanaite ______________________-_ __________ ______________ ____ _____ _ 12 7. X-ray powder data of (Cr, Al, Fe, Ti, Mn)02 from guyanaite, and CrO2 from CrOOH _ 8. X-ray powder data of (Cr, Al, Fe, Ti Mn) 2O8 ____-_ _ 9. X-ray powder data of guyanaite (from Guyana and Finland), "merumite" and synthetic guyanaite CrOOH 10. Analysis of merumite containing 70 percent bracewellite and 30 percent eskolaite ______ _____ __ _ 11. Spectrographic analysis of merumite containing 70 percent bracewellite and 30 percent eskolaite _ ______ 12. Electron-probe analysis (in percent) of seven crystals of bracewellite and two merumite fragments ______ 13. X-ray powder data for bracewellite, goethite, and eskolaite ___________ __ __ __ __ _ ___ 14. Chemical analysis of grimaldiite-mcconnellite polycrystals _______ _________________ ____ __ ___ 18 15. Microspectrographic analysis of grimaldiite-mcconnsllite polycrystals _____ __ _ _ __ __ ____ _ 16. X-ray powder pattern of grimaldiite and mcconnellite ___________ __ __ __ __ _ ____ __ 17. Cell constants of grimaldiite, mcconnellite, and related substances ______ ______ __ _____ ___ 18. X-ray powder patterns of 7-CrOOH and lepidocrocite ________ _____________ 19. Cell constants of 7-CrOOH and related compounds ___ __ __ ______ ______________ _ ____ ___ 20. X-ray powder data for chromian gahnite Zn(Al0.7, CrOo.sHOi from Guyana and synthetic spinels ________ 23 21. Gold and silver in six fragments of merumite ___ ____ ____ ____ _ 22. X-ray powder data for topaz _____________________________________ __ 23. Analysis of topaz _________________________________________________ ______ 26 24. Crystallographic relationship of the CrOOH compounds and other metallic hydroxides _____ ______ 27 MERUMITE A COMPLEX ASSEMBLAGE OF CHROMIUM MINERALS FROM GUYANA

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“…After the furnace was cooled, the Pt WE was surrounded by green precipitates whose X-ray diffraction peaks indicates a cubic chromium oxide. According to Laubengayer and McCune [25] who first identified this X-ray pattern, the cubic chromium oxide is a metastable phase above about 420C, and is probably a monotrope, similar to the spinel y-Fe203, of the rhombohedra1 Crz03 oxide. Therefore the insulation of the electrochemical cell resulted from the deposition of this poorly conductive oxide on the electrode.…”

Section: Dynamic Polarization For Mildly Acidic Cr2(s04)3-na2s0solutionmentioning

confidence: 99%

Electrochemical studies of Na₂CrO₄‐Na₂So₄ melts at 1200 K

Shi¹,

Rapp

1990

Materials & Corrosion

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The electrochemical response of Na2S04-Na2Cr04 solutions at a Pt working electrode was established by cyclic voltammetry and chrono-potentiometry measurements at 1200 K. Experiments were made under conditions of controlled and electrochemically measured values of melt basicity for basic, neutral, and acidic melts. Despite the thermodynamic stability of chromite ions under reducing conditions, a direct conversion of chromate to chromite upon cathodic polarization was not observed. Rather, the cathodic reduction of chromate ions proceeds by a reversible one-electron charge transfer to an electroactive intermediate species formed through an equilibrium between Cr0;-and oxide ions in the solution.An irreversible chemical reaction reduces the chromium solute species further to precipitate a solid. As a solute in a corrosive fused salt film, a chromate to chromite transition would not be expected to stabilize the oxidation state and basicity. However, chromate ions do provide a reduction reaction more favorable than sulfate reduction to sulfide; chromate reduction leads to the precipitation of solid NaCrOz or CrzO3 in basic or neutral solutions, respectively. A large shift in melt basicity can only occur for mildly acidic solutions with high chromate solute.Das elektrochemische Verhalten von Na2S04-Na2Cr04-Losungen an einer Arbeitselektrode aus Platin wurde mittels zyklischer Voltammetrie und durch chronopoteniometrische Messungen bei 1200 "C untersucht. Dabei wurde unter kontrollierten elektrochemisch gemessenen Werten der Schmelzbasizitat fur basische, neutrale und saure Schmelzen gearbeitet. Trotz der thermodynamischen Stabilitat von Chromitionen unter reduzierenden Bedingungen konnte keine direkte Umwandlung von Chromat in Chromit nach kathodischer Polatisation beobachtet werden. Die kathodische Reduktion von Chromat verlauft vielmehr uber einen reversiblen Einelektronenladungsubergang an eine elektroaktive Zwischenform, die in einem Gleichgewicht zwischen Chromat-und Oxidionen in der Losung entsteht.Eine irreversible chemische Reaktion vemngert den Chromgehalt in der Losung soweit, daB eine feste Substanz ausfallt. Wenn Chromat in einem aggressiven geschmolzenen Salzfilm gelost ist , ist zwar nicht zu erwarten, dal3 der Ubergang von Chromat zu Chromit den Oxidationszustand und die Basizitat stabilisiert , doch ermoglichen Chromationen eine Reduktionsreaktion, die gunstiger als die Reduktion von Sulfat zu Sulfit ist; die Reduktion von Chromat fuhrt namlich zur Ausfallung von festem NaCrOz bzw. Crz03 in basischen bzw. neutralen Losungen. Eine starkeverschiebung der Basizitat der Schmelze kann nur im Falle von schwach sauren Losungen mit hohem Chromatgehalt auftreten.

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New Crystalline Phases in the System Chromium(III) Oxide—Water¹

Cited by 60 publications

References 0 publications

The Aqueous Chemistry of Chromium(III) above 100 °C: Hydrothermal Synthesis of Chromium Spinels

The Aqueous Chemistry of Chromium(III) above 100 °C: Hydrothermal Synthesis of Chromium Spinels

Merumite; a complex assemblage of chromium minerals from Guyana

Electrochemical studies of Na₂CrO₄‐Na₂So₄ melts at 1200 K

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New Crystalline Phases in the System Chromium(III) Oxide—Water1

Cited by 60 publications

References 0 publications

The Aqueous Chemistry of Chromium(III) above 100 °C: Hydrothermal Synthesis of Chromium Spinels

The Aqueous Chemistry of Chromium(III) above 100 °C: Hydrothermal Synthesis of Chromium Spinels

Merumite; a complex assemblage of chromium minerals from Guyana

Electrochemical studies of Na2CrO4‐Na2So4 melts at 1200 K

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New Crystalline Phases in the System Chromium(III) Oxide—Water¹

Electrochemical studies of Na₂CrO₄‐Na₂So₄ melts at 1200 K