- Synthesis of nanocrystalline CrN from Cr[OC(NH2) 2]6Cl3 coordination compound
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Nanocrystalline chromium nitride (CrN) particles were prepared by the pyrolysis of Cr[OC(NH2)2]6Cl3 coordination compound in ammonia gas. The compound was characterized by infrared spectrum analysis and thermogravimetry-differential scanning calorimetry (TG-DSC). X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used to investigate the phase and morphology of the CrN powders. The CrN particle size obtained at 600°C was as small as 7nm. The influence of reaction temperature and time on particle sizes was also studied. The formation of CrN nanoparticles was proposed following nucleation and growth mechanism on the basis of the experimental results.
- Qiu, Yu,Gao, Lian
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- Use of chlorination for chromite upgrading
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The chlorination of a chromite concentrate was studied between 600 and 1000°C. The reaction products were analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD), and chemical analyses. Chlorination of a chromite concentrate at about 700°C allowed the extraction of about 50% of the iron, thus doubling the Cr/Fe ratio in the treated concentrate. Aluminum chloride was tested as a chlorinating agent in the presence of a reducing atmosphere. The effect of temperature on the kinetics of chromite chlorination was studied between 900 and 1040°C using thermogravimetric analysis (TGA). Temperature effects changed significantly with reaction extent. The initial stage of the chlorination was characterized by an apparent activation energy of about 112 kJ/mol, while a value of about of 269 kJ/mol was found for reaction extents greater than 0.4. (C) 2000 Elsevier Science B.V.
- Kanari,Gaballah,Allain
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- Enthalpy of formation of chromium(III) chloride
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Subjecting a chromium sample (mass fraction of impurities 2 x 10-4) to chlorination in a calorimetric bomb with a microfurance for sample heating made it possible to determine the standard molar change of energy at 298.15 K for the reaction: Cr(cubic) + 1.5Cl2(g) = CrCl3(hexagonal).The standard molar enthalpy of formation of CrCl3(hexagonal) at 298.15 K was calculated to be -(544.4 +/- 1.4) kJ.mol-1.Here and in the paper uncertainties are given for a 95 per cent confidence interval.)
- Timofeyev, B. I.,Yuldasheva, V. M.
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- An overview study of chlorination reactions applied to the primary extraction and recycling of metals and to the synthesis of new reagents
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Energy intensive classical metallurgical processes, the depletion of high-grade ores and primary sources push the scientific and technical communities to treat lean and complex ores as well as secondary metal resources for the recovery of valuable metals.
- Kanari,Allain,Joussemet,Mochón,Ruiz-Bustinza,Gaballah
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- Oxidation Kinetics of Chromium(III) Chloride
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The kinetic behaviour of anhydrous chromium(III) chloride pellets in oxygen in the temperature range 350-630 deg C has been examined by isothermal and temperature-programmed thermogravimetry and scanning electron microscopy.The reaction starts at ca. 400 deg C under non-isothermal conditions and exhibits a deceleratory rate.Cr2O3 is usually the only solid product detected, although CrO2Cl2 or CrOCl may form under extreme experimental conditions.Isothermal thermogravimetric curves are fitted to a number of kinetic expressions, and statistical analyses are used to identify the rate equation that best describes the experimental data.The examination, by scanning electron microscopy, of cross-sections of partially reacted samples supports the conclusion that the reaction is under chemical control, and occurs at a linearly advancing interface between the reactant and product.The reaction kinetics can best be described by a contracting-geometry rate expression.
- Sole, Kathryn C.,Moolman, Michael B.,Brown, Michael E.
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- The thermodynamic characteristics of sublimation of chromium trichloride
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The sublimation of stoichiometric chromium trichloride was experimentally studied by the static method of vapor pressure measurements. The main reaction was found to be CrCl3(cr) = CrCl3(g). The enthalpy and entropy of this reaction
- Titov,Grinberg
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- Vapor complexation in the ACl-CrCl3 (A = Li, Cs) system up to 1400 K and the tetrahedral ligand field states of chromium (III)
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Electronic absorption spectroscopy is used in the temperature range 800-1400 K, to study the vapor species, over molten CrCl3-ACl (A = Li, Cs) mixtures and solid CrCl3. The observed Vis/near IR bands are assigned to d ← d transitions of Cr3+ in distorted tetrahedral coordination (CrCl4-). Spectra of octahedral CrCl63 - in molten alkali chlorides were also measured and used to estimate the spectroscopic constants (Dq, B, C) of Cr3+ in all chloride tetrahedral and octahedral environments. Composition and temperature-dependent measurements suggest that the predominant vapor species is the 1:1 monomer ACrCl4 and that an equilibrium is established: ACrCl4 (g) ? CrCl3 (g) + ACl (g)Due to vapor complexation the apparent vapor pressure of CrCl3 increases. The volatility enhancement is higher for the LiCl-CrCl3 than the CsCl-CrCl3 system reaching values near 60, at ~950 K. Based on the preferential octahedral ligand field stabilization energy of Cr(III) it is argued that dimeric and/or trimeric 1:1 species may be also present as minor components in the vapor phase. Finally, the vapor complexation and volatility enhancement for the MX3-AX (M = rare earth, Cr; X = halide) systems are discussed and correlated to the melt structure of the corresponding binary melts.
- Papatheodorou
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- The mechanochemical reduction of AgCl with metals : RRRRevisiting an experiment of M. Faraday
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Faraday induced the mechanochemical reduction of AgCl with Zn, Sn, Fe and Cu in 1820, using trituration in a mortar. This experiment is revisited, employing a mortar-and-pestle and a ball mill as mechanochemical reactors. The reaction kinetics depends both on the thermochemical properties and the hardness of the reactants. When using Zn as the reducing agent, Faraday likely observed a mechanically induced self-sustaining process (MSR), or at least he came very close to doing so.
- Takacs
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- Solubility properties of the systems chromium salts-amino acids-water
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Solubility properties of the ternary systems of Cr(NO3) 3-His-H2O, Cr(NO3)3-Met-H 2O, and CrCl3-His-H2O (His - histidine, Met - methionine) have been investigated in t
- San-Ping, Chen,Sheng-Li, Gao,Qi-Zhen, Shi
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- Synthesis and crystal structure of [Cr(thd)2(OEt)]2
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The mixed-ligand complex [Cr(thd)2(OEt)]2 [(thd) - = anion of H(thd) = C11H20O2 = 2,2,6,6-tetramethylheptane-3,5-dione] appears as by-product when EtOH/H 2O is used as solvent during preparation of Cr(thd)3. [Cr(thd)2(OEt)]2 can be difficult to separate from Cr(thd)3 by sublimation, but separation is easily accomplished by extracting Cr(thd)3 with acetone. A detailed account for the sublimation behavior of [Cr(thd)2(OEt)]2/Cr(thd) 3 mixtures is advanced. Good yields of [Cr(thd)2(OEt)] 2 are obtained when CrCl3, H(thd), and Na(EtO) react in absolute EtOH. [Cr(thd)2(OEt)]2 is obtained in the form of green needle-shaped crystals by recrystallization from toluene. The crystal structure is triclinic [a = 10.2919(15), b = 10.6686(16), c = 14.194(3) A, α = 106.559(2), β = 107.869(2), and γ = 98.326(2)° at 295 K; space group P1. The complex contains two crystallographic equivalent chromium atoms, which are bridged by two cis-configured ethoxy groups, the four remaining sites in the octahedral coordination around each chromium atom being occupied by oxygen atoms from two thd ligands. The bond lengths and angles concur with the findings for related molecular complexes. The temperature dependence of the magnetic susceptibility of [Cr(thd)2(OEt)] 2 follows Curie-Weiss law with Weiss constant θ ≈ -65 K and μp = 3.87 μB. Copyright
- Ahmed, Mohammed A. K.,Fjellvag, Helmer,Kjekshus, Arne,Wragg, David S.,Sen Gupta, Nalinava
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- A study of chloropentaamminechromium(III) tetrachloroplatinate(II)
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The double complex salt [Cr(NH3)5Cl][PtCl 4] (I) was synthesized and structurally characterized. Crystal data: a = 16.5178(19) ?, b = 8.1086(9) ?, c = 9.4401 (11) ?, V = 1264.4(3) ?3, space group Pnma, Z = 4, ρcalcd = 2.677 g/cm3, R = 0.0304. Complex I is isostructural to the compounds [M(NH3)5Cl] [M′X4] (M = Co, Rh, Ir; M′ = Pt, Pd; X = Cl, Br) studied previously. Thermolysis of I in hydrogen and helium was studied. The products of the thermolysis in hydrogen are solid solutions CrxPt1-x with a different degree of order, which depends on the experimental conditions.
- Plusnin,Shubin,Yusenko,Baidina,Korda,Korenev
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p. 1148 - 1153
(2008/10/09)
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- Multiplet splitting of core-electron binding energies in chromium compounds
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The multiplet structure of core-electron binding energies in Cr3s and Cr3p levels of CrCl3 and CrBr3 compounds is investigated by means of x-ray photoelectron spectroscopy. In Cr3s core levels a doublet splitting of about 4.3 eV is o
- Pollini I.
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- π-facial diastereoselection in the 1,2-addition of allylmetal reagents to 2-methoxycyclohexanone and tetrahydrofuranspiro(2-cyclohexanone)
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The stereochemical course of the 1,2-addition of several allylmetal reagents and of the Normant Grignard [ClMgO(CH2)3MgCl] to 2-methoxycyclohexanone and tetrahydrofuranspiro-(2-cyclohexanone) has been determined. In four of the six substrates examined, a 4-tert-butyl group is present to serve as a conformational anchor. The neighboring methoxyl substituent is shown to be capable of engaging effectively in chelation, although special circumstances can dictate otherwise. Experiments involving the allylindium reagent as the nucleophile in aqueous solution reveal that the presence of water does not inhibit the operation of chelation control, which often exceeds that attainable with the corresponding magnesium, cerium, and chromium reagents in anhydrous media by significant margins. The extent to which cooperation between the α-oxygen atom and control of π-facial nucleophilic attack reaches a maximum ( > 97:3) is when the system is conformationally rigid and the 2-methoxy and 4-tert-butyl groups are both oriented equatorially. As the steric bulk about the oxygen is increased, the ability of indium to anchor onto the heteroatom is significantly lessened. The results of competition experiments are detailed. The prospects for useful synthetic applications of indium catalysis in water or water/THF mixtures appear to be very promising.
- Paquette,Lobben
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p. 1917 - 1930
(2007/10/03)
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- Syntheses and Spectral Characterizations of Tricarbonylchromium Complexes of Calixarenes
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The 1:1 arene-tricarbonylchromium complexes were synthesized for the first time from four conformational isomers of 25,26,27,28-tetrapropoxycalixarene (14Pr) and Cr(CO)6.The 1:2, 1:3 and 1:4 complexes of cone-14Pr were also synthesized by increasing the ratio of Cr(CO)6 against cone-14Pr.The 1:2 complex was a mixture of two compounds, which were identified as distal and proximal isomers of cone-14Pr*2Cr(CO)3.The relative stability of the 1:1 complex was estimated via its oxidation by CuCl2.The pseudo-first-order rate constants appeared to be in the order of 1,3-alternate-14Pr > 1,2-alternate-14Pr > cone-14Pr > 2,6-dimethylanisole.The results indicate that the 14r*Cr(CO)3 complexes are less stable than the corresponding monomeric complex.The 1:1 complexes with partial-cone-14Pr and 1,2-alternate-14Pr were demonstrated to be a pair of racemates by 1H NMR spectroscopy using a chiral shift reagent (Pirkle's reagent).
- Iki, Hideshi,Kikuchi, Taketoshi,Shinkai, Seiji
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p. 205 - 210
(2007/10/02)
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