Mechanism of carbothermal reduction of iron, cobalt, nickel and copper oxides

A new scheme of thermal dissociation which is based on the dissociative evaporation of the reactant with simultaneous condensation of the low-volatile product has been invoked to interpret the kinetics of reduction of FeO, CoO, NiO and Cu₂O by carbon. A critical analysis of literature data and their comparison with theoretical calculations has shown that the main kinetic characteristics of carbothermal reduction, including the initial decomposition temperature and activation energy are in full agreement with the proposed mechanism of decomposition. Condensation of the low-volatile product (metal vapour) in the reaction zone and partial transport of condensation energy to the oxide account for the features which are typical of solid state reactions and manifest themselves in the appearance of periods of induction and acceleration in the course of the process. Carbon fulfils the role of buffer in this process. This is supported by an appearance of metals in the condensed phase and a higher than equilibrium partial pressure of oxygen in high-vacuum experiments with Knudsen cells.     

Thermal analysis of cobalt,nickel and copper complexes of 2-aminothiazole

The thermal decomposition of 2-aminothiazole (2-amt) complexes of general formula M(2-amt)₂X₂ [M = Co(II) and Cu(II)] and Ni(2-amt)₄X₂ [X = Cl and Br] have been studied in air and argon by TG and DTG as well as by DTA in nitrogen; end products from the decompositions in air have been characterised by X-ray powder diffraction. Decomposition stoichiometries have been proposed and factors governing the thermal decomposition have been discussed.     

Chelate formation of ammonium aurintricarboxy-late with bivalent copper : Physico-chemical investigation of the composition,structure and stability

The formation of a coloured chelate, having λmax at 540 mμ, between cupric ions and ammonium aurintricarboxylate has been reported. It has been concluded that only one complex having metal : reagent ratio of 1:2 is formed in solution. The method adopted for investigation has been the continuous variation method, using spectrophotometric and electrical conductance measurements. It has been observed that there is an increase in acidity on mixing the reactants, which shows that hydrogen ions are liberated as a result of chelation It has been suggested that chelation occurs between the phenolic oxygen and the adjacent carboxylic oxygen.A method has been presented for the calculation of formation constant from spectrophotometric data and the value of K in the case of the chelate investigated has been calculated to be 6.45.10⁸. The free energy of formation works out to be —14.6 kcal at 25°C.     

Syntheses,equilibrium, and structural studies of copper(II) and nickel(II) complexes with a tripodal alanine-based ligand

A heptadentate ligand, tris[(L)-alanyl-2-carboxamidoethyl]amine (H₃trenala), has been synthesized as its tetrahydrochloride salt; its protonation constants and the stability constants of the copper(II) and nickel(II) chelates have been determined by potentiometry. Mononuclear species with protonated, neutral, or deprotonated forms of the ligand, [Cu(H₅trenala)]⁴⁺, [M(H₄trenala)]³⁺, [M(H₃trenala)]²⁺, [M(H₂trenala)]⁺, and [M(Htrenala)] (M?=?Cu²⁺ and Ni²⁺) have been detected in all cases, while only Cu²⁺ gives dinuclear [Cu₂(H₂trenala)]²⁺, [Cu₂(Htrenala)]²⁺, [Cu₂(trenala)]⁺, and [Cu₂(trenala)(OH)] species. Two dinuclear copper(II) complexes have been prepared and characterized by spectroscopic techniques (IR, UV-Vis, mass electro-spray) and thermogravimetric analysis.     

Complexes of nitrilotrimethylphosphonic acid with cobalt, nickel, copper and zinc

Substances of the types MH₄ntmp, Mg₃[M(Hntmp)]₂, M₂H₂ntmp and Mg[M₂(Hntmp)]₂, where M = Co, Ni, Cu, Zn and H₆ntmp = N[CH₂PO(OH)₂]₃ were prepared. The sodium and cesium salts of the [Co(Hntmp)]³⁻ complexes were also prepared. The IR and electronic spectra and the experimental magnetic susceptibilities indicate that these are high-spin complexes. The coordination surroundings of the central atom consist of a highly distorted octahedron of the ligand oxygen atoms. The nitrogen atom is not coordinated to the central atom.     

Theoretical and molecular modelling studies on organic transition metal complexes,II. Calculation of the stability constants of bidentate ligands in relation to theIrving-Williams order

The bidentate chelates of the transition elements Mn to Zn with salicylaldoxime, 8-hydroxyquinoline and 8-mercaptoquinoline have been constructed using molecular graphics and the stability constants derived from the calculated reaction enthalpies using an extended CNDO/2 method. The results generally follow theIrving-Williams order except for the mercaptoquinoline where large entropy effects are known to be present experimentally. The influence of substituents on the stability constant of salicylaldoxime is reflected in the calculated value particularly for electron-withdrawing groups.

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Theoretische und Molekülmodellierungs-Studien von organischen Übergangsmetallkomplexen, 2. Mitt.: Berechnung der Stabilitätskonstanten von zweizähnigen Liganden in Relation zurIrving-Williams-Ordnung

Zusammenfassung Die zweizähnigen Chelate der Übergangsmetalle Mn bis Zn mit Salicylaldoxim, 8-Hydroxychinolin und 8-Mercaptochinolin wurden unter Verwendung von molekulargraphischen Methoden und den Stabilitätskonstanten aus den mittels einer erweiterten CNDO/2-Methode ermittelten Reaktionsenthalpien konstruiert. Die Ergebnisse folgen generell derIrving-Williams-Ordnung, mit Ausnahme von 8-Mercaptochinolin, von dem bekannt ist, daß experimentell große Entropieeffekte auftreten. Der Einfluß von Substituenten auf die Stabilitätskonstanten der Salicylaldoximkomplexe spiegelt sich besonders für elektronenabziehende Gruppen in den berechneten Werten deutlich wider.

     

Thermal investigation of cobalt, nickel and copper complexes with 8-aminoquinoline

Complexes of Co(II), Ni(II) and Cu(II) with 8-aminoquinoline were prepared and characterized, and their thermal behaviour and decomposition pathways were studied. The thermal stabilities are discussed in terms of ionic radii, crystal field splitting energy and steric hindrance. The effective roles of the counter-ions (Cl^? and NO ₃ ^? ) on the decomposition temperatures and the final products were also clarified. The energies of activation (E _a ) and the orders of some decomposition reactions were determined. Light is shed on the nature of the interaction of the water of crystallization and the polymorphic transformation phenomenon.     

Simultaneous spectrophotometric determination of traces of cobalt,nickel and copper with dithio-oxamide

The cobalt, nickel and copper complexes of dithio-oxamidc have been characterized in terms of color, effect of pH, structure in solidion, order of addition of reagents, adherence to Beer's law and sensitivity. The reactivity of the reagent to other ions has been reported. A method for the simultaneous spectrophotometric determination of cobalt, nickel and copper has been developed. the results of the application of this procedure to synthetic samples and to several National Bureau of Standards Samples are given.     

Simultaneous spectrophotometric determination of cobalt, nickel and copper with 2,3-quinoxaline- dithiol

In aqueous ethanol cobalt(II), nickel(II) and copper(I) react instantaneously with 2,3-quinoxalinedithiol at pH 2 to form strongly coloured complexes exhibiting absorption maxima at 510, 606 and 665, and 625 nm, respectively. At pH 6 the reaction of copper can be virtually eliminated, while the cobalt and nickel reactions show only small decreases in sensitivity. This behaviour has been made the basis of a rapid method for the simultaneous determination of these three elements. The absorbances of the complexes have been found to be additive for all combinations of these elements in which the individual concentrations have been varied from approximately 0.1 to 1 ppm. A least-squares estimate of the concentration of any of the elements may be readily obtained by using a simple linear equation based on the absorbance readings and a set of constants derived from the spectrophotometric data. The analyses of seven synthetic solutions and four NBS Standard Reference Materials yielded a maximum error of 6.0% and an average error of 1.6%.     

Dissociation constants of some Schiff bases and stability constants of their copper,cobalt, nickel and zinc complexes

The stoichiometry and stability constant of metal complexes with 4-(3-methoxy-salicylideneamino)-5-hydroxynaphthalene-2,7-disulfonic acid monosodium salt (H₂L) and 4-(3-methoxysalicylideneamino)-5-hydroxy-6-(2,5-dichlorophenylazo)-2,7-naphthalene disulfonic acid monosodium salt (H₂L¹) were studied by potentiometric titration. The stability constants of H₂L and H₂L¹ Schiff bases have been investigated by potentiometric titration and u.v.–vis spectroscopy in aqueous media. The dissociation constants of the ligand and the stability constants of the metal complexes were calculated pH-metrically at 25 °C and 0.1 m KCl ionic strength. The dissociation constants for H₂L were obtained as 3.007, 7.620 and 9.564 and for H₂L¹, 4.000, 6.525, 9.473 and 10.423, respectively. The complexes were found to have the formulae [M(L)₂] for M = Co(II), Ni(II), Zn(II) and Cu(II). The stability of the complexes follows the sequence: Zn(II) < Co(II) < Cu(II) < Ni(II). The high stability of H₂L¹ towards Cu(II) and Ni(II) over the other ions is remarkable, in particular over Cu(II), and may be of technological interest. Concentration distribution diagram of various species formed in solution was evaluated for ligands and complexes. The formation of the hydrogen bonds may cause this increased stability of ligands. The pH-metric data were used to find the stoichiometry, deprotonation and stability constants via the SUPERQUAD computer program.     

Formation of cobalt, nickel and copper complexes with murexide in ethanol-water mixtures

The complexation reactions between murexide and Co²⁺, Ni²⁺ and Cu²⁺ in C₂H₅OH-H₂O mixtures have been investigated spectrophotometrically. The formation constants of the 1:1 complexes formed increase in the order Co²⁺ < Ni²⁺ < Cu²⁺ for all solvent mixtures studied, and log K_f is a linear function of the mole fraction of ethanol. The heat of complexation was determined calorimetrically for the nickel and copper complexes. The values of ΔH° and ΔS° are solvent-dependent, and all three complexes have negative ΔH° and positive ΔS° values.     

Gravimetric determination of cobalt and nickel,and their separations from copper with n-benzoylphenylhydroxylamine

N-Benzoylphenylhydroxylamine can be used for the gravimetric determination of cobalt and nickel. The precipitates can be weighed as such, or ignited and weighed as cobalt sulphate or nickclous oxide. Cobalt or nickel can be separated from copper with the reagent.     

Determination of copper,cobalt and nickel by circular thin-layer chromatography

Summary A method for the microdetermination of copper, cobalt and nickel from a mixture containing 40 metal ions by circular thin-layer Chromatographic technique is described. The procedure is simple; the chromatoplate takes about 2 minutes for its development and other metal ions do not interfere with the determination. The recovery of copper, cobalt and nickel is better than 98%. The apparatus for the concentration of test solution before TLC analysis is also described.

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Zusammenfassung Die Mikrobestimmung von Kupfer, Kobalt und Nickel in Gemischen von 40 verschiedenen Metallionen im Wege der zirkulären Dünnschichtchromatographie wurde beschrieben. Die Vorgangsweise ist einfach; die Entwicklung der Chromatogramme erfordert 2 Minuten, fremde Metallionen stören nicht. Die Ausbeute an Kupfer, Kobalt und Nickel ist besser als 98%. Ein Gerät für das Einengen der Probelösung vor der DC-Analyse wurde gleichfalls beschrieben.

     

Trace determination of iron,cobalt, nickel and copper in zirconium fluoride by substoichiometric radioactivation analysis

Trace amounts of transition elements (Fe, Co, Ni and Cu) in zirconium fluoride and NBS SRM's were determined by substoichiometric radioactivation analysis. The contents of impurities in sublimed sample were less than those of high-purity material and of reagent grade. The detection limits of these elements in zirconium fluoride were 10 ng/g for iron, 0.01 ng/g for cobalt, 1 ng/g for nickel and 0.1 ng/g for copper. The analytical results for iron, cobalt, nickel and copper in NBS SRM's were in good agreement with certified values.     

Coordination compounds of cobalt, nickel, copper and zinc with thiosemicarbazone and 3-phenylpropenal semicarbazone

Hydrates of 3-phenylpropenal thiosemicarbazone (HL·H₂O) and semicarbazone (HL′·H₂O) react in methanol with cobalt, nickel, copper, and zinc chlorides, nitrates, and acetates to form coordination compounds MX₂·2HL·nSolv [M = Co, Ni, Cu, Zn; X = Cl, NO₃; HL = C₆H₅CH=CH-CH=N-NHC(O)NH₂; n = 0–3; Solv = H₂O, CH₃OH], CuX₂·HL·nH₂O [M = Ni, Cu; n = 0, 1], ML₂·nH₂O and ML′·nH₂O [M = Co, Ni, Zn; HL′ = C₆H₅CH=CH-CH=N-NHC(O)NH₂; n = 0–3]. In the presence of amines (A = C₅H₅N, 2-CH₃C₅H₄N, 3-CH₃C₅H₄N, and 4-CH₃C₅H₄N) these reactions yield the complexes Cu(A)LCl·CH₃OH and M(A)LX·nH₂O [M = Cu, Ni; X = Cl, NO₃; n = 0–2]. The copper complexes with the amine ligands are of polynuclear structure, and other complexes are monomeric. Carbazones (HL and HL′) are included in the complexes as bidentate N,S-and N,O-ligands. The thermolysis of the complexes involves the stages of removing solvent crystallization molecules (70–90°C), deaquation (150–170°C), and full thermal decomposition (500–580°C).