A thermoanalytical study of the oxidation of chalcocite

A sample of chalcocite of particle size 45–75 μm, has been oxidised in a TG-DTA apparatus at a heating rate of 10 deg·min⁻¹ and the products at various temperatures characterised by XRD, SEM, FTIR and EPMA. This has enabled the events in the TG-DTA record to be assigned to specific chemical reactions, as well as the development of a full reaction scheme for the oxidation of chalcocite. Only minor reactions occurred up to 430°C, but above this temperature there was significant oxidation which resulted in an exotherm and mass gain. These events were due primarily to the oxidation of sulfide to copper(I) oxide, and the formation of copper(II) sulfate. The reaction then slowed, but melting commenced at 490°C which permitted further oxidation to take place with the appearance of a second exotherm and mass gain. By 570°C, sulfide oxidation was complete, but solid-solid reactions took place between Cu₂O and CuSO₄ to produce CuO·CuSO₄. Some conversion of Cu₂O had occurred. By 775°C, CuO and CuO·CuSO₄ were the only phases detected. Above this temperature the latter phase was unstable and decomposed to the end product CuO. In celebration of the 60^th birthday of Dr. Andrew K. Galwey     

Preparation and Crystal Structure of Copper(I) Carbonyl Hydrogensulfate,obtained by Carbonylation in Sulphuric Acid

The hydrogensulfato‐carbonyl derivative [Cu(CO)(SO₄H)]_n, as obtained from the Cu₂O/ H₂SO₄/CO system and recrystallized from H₂SO₄/(CH₃O)₂SO₂ has been shown to possess a crystal structure organised in infinite chains built up by corner sharing of {CuO₃(CO)} and {S(OH)O₃} tetrahedra. The chains are connected by hydrogen bonds in layers, with CO groups leaning out on both sides. The absorption of CO by CuSO₄/Cu or by Cu₂O in sulfuric acid was quantified as a function of concentration. The CuSO₄/Cu system in water absorbs carbon monoxide (CO/Cu molar ratio = 1.0).     

Quantitative determination of phases present in oxidised chalcocite

A sample of chalcocite (Cu₂S) of particle size 45–75 m was heated in air at 10°C min^–1 in a simultaneous TG-DTA apparatus. The phase compositions of the products at various temperatures were quantitatively determined by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and wet chemical analyses. Copper(II) sulfate, of amount 1.7% by mass, was observed at 435°C and increased rapidly in concentration to 56% at 570°C. From 570–670°C, there was a rapid decrease in CuSO₄ content to 9.8% as the phase converted to CuSO₄·CuO, with the CuSO₄ not being detected at 775°C. From 435–570°C, Cu₂O formed, but at a rather slower rate, reaching 47% at 570°C. The Cu₂O level then decreased to 38% over the range 570–670°C. CuSO₄·CuO was first detected at 570°C by FTIR, although it was not detected by XRD at this temperature. The content of this species reached 41% at 670°C, decreased to 24% at 775°C, and was not detected at 840°C. CuO first appeared at 670°C and rose steadily in concentration until at 840°C it was the only compound present.Dedicated to Prof. Menachem Steinberg on the occasion of his 65th birthday     

Solid-state reactions in the system Cu—Sb—O; Formation of a new copper(I) antimony oxide

The solid-state reactions in the system Cu—Sb—O were investigated by thermogravimetry and X-ray diffraction. Equimolar mixtures of CuO and Sb₂O₃ form Cu(II)Sb₂O₆ when slowly heated in air up to 1000°C. The firt step in this reaction is the oxidation of Sb₂O₃ to Sb₂O₄ at 380–500°C, followed by further oxidation of Sb₂O₄ and the formation of CuSb₂O₆ at 500–1000°C. Thermal decomposition of CuSb₂O₆ in a flowing nitrogen atmosphere occurs in three stages; the first, with an activation energy of 356 kJ mole^?1, results in the formation of a new copper(I) antimony oxide, with a composition of Cu₄SbO_4.5, as determined by atomic absorption analysis and X-ray fluoresecence. Confirmation of predominantly monovalent copper and pentavalent antimony in the new compound was by ESR and ESCA, respectively. Two forms of Cu₄SbO_4.5 have been distinguished; one of these (form II) has a structure of lower symmetry, and decomposes when heated in air at 600°C to a mixture of CuO and another new copper antimony oxide, as yet uncharacterized. On further heating to 1100°C in air, Cu₄SbO_4.5 (form I) gradually reforms. Details of these reactions are summarized and X-ray powder data presented for Cu₄SbO_4.5.     

Effects of Temperature and Anion on the Copper(II) Complexes based on 2‐(Carboxyphenyl)iminodiacetic Acid and 1,10‐Phenanthroline

Using Cu(NO₃)₂ as metal salt, [Cu₃(cpida)(phen)₂(H₂O)₅] · 3NO₃ · 2H₂O ( 1 ) and {[Cu₂(cpida)(phen)(NO₃)] · 2H₂O}_n ( 2a ) were synthesized from an identical starting mixture with 2‐(carboxyphenyl)iminodiacetic acid (H₃cpida) and 1,10‐phenanthroline (phen) at 5 °C and 25 °C, respectively. Additionally, complexes 2b – 2d , which are isostructural to 2a , were obtained using Cu(ClO₄)₂, Cu(BF₄)₂, and Cu(CF₃SO₃)₂ instead of Cu(NO₃)₂ in the temperature range 0–65 °C. 1 is characterized by a V‐shaped trinuclear Cu^II monomer, whereas 2a – 2d features a one‐dimensional (1D) Δ Cu^II chain. Abundant hydrogen bonds constructed by the nitrate anion are observed in 1 . A structural transformation study was undertaken and revealed that 1 could completely transform into 2a from the reaction solution at 25 °C and the temperature plays a crucial role in the process. Magnetic measurements revealed that 1 exhibits dominant antiferromagnetic behavior, whereas 2a presents dominant ferromagnetic behavior.     

Thermochemical production of hydrogen

Copper oxychloride, Cu₂OCl₂, was synthesized from CuCl, or CuCl₂·2H₂O in a tubular furnace in a dry air atmosphere between 325 and 400?°C. Thermal gravimetric and gas analysis of the reaction products were used to follow the decomposition of Cu₂OCl₂ in both dry air and argon environments. The thermograms show the release of chlorine and oxygen gases, the volatilization of CuCl, and a residue, identified as CuO, of ~17 to 25% which varies as the conditions of the run. A mechanism of reaction able to describe the experimental results has been proposed and used to explain other published data.     

Spectrophotometric and thermal analytical studies on the dehydration of copper(II) sulfate and its double salts

Spectrophotometric (diffuse reflection) and TG-DTA data on the dehydration of CuSO₄ · 5H₂O, Na₂Cu(SO₄)₂ · 2H₂O, M₂Cu(SO₄)₂ · 6H₂O(M⁺ = K⁺, Rb⁺, Cs⁺ and NH⁺₄) and Co₂Cu(SO₄)₃ · 18H₂O are given. Although complete dehydration of CuSO₄ · 5H₂O brings about a striking color change from blue to white, it was found that there is only a slight decrease in the v?_max. of its d-d band in the course of this change, and the total light absorption in the visible-UV region increases at the same time. The dehydration of the alkali metal and ammonium double salts, most of which contain [Cu(OH₂)₆]²⁺ aquo ions (in contrast to the [Cu(OH₂)₄]²⁺ in CuSO₄ · 5H₂O), occurs generally more easily than that of CuSO₄ - 5H₂O, and their v?_max. increases slightly in the change, leading to blue or green anhydrous products, although the formation of a white modification was observed with the potassium salt. It was also found that the v?_max. of the Cu²⁺ ion in the dehydrated cobalt(II) double salt is still lower than that in anhydrous CuSO₄, i.e., the ligand field and/or tetragonality around it is decreased by the presence of Co²⁺ ions.     

Evolved gas analyses on a mixed valence copper(I,II) complex salt with thiosulfate and ammonia by in situ TG-EGA-FTIR and TG/DTA-EGA-MS

Thermal decomposition of a mixed valence copper salt, Na₄[Cu(NH₃)₄][Cu(S₂O₃)₂]₂·0.5NH₃ (1) prepared from pentahydrates of sodium thiosulfate and copper sulphate of various molar ratios in 1:1 v/v aqueous ammonia solution, has been studied up to 1,000 °C in flowing air by simultaneous thermogravimetric and differential thermal analysis coupled online with quadrupole mass spectrometer (TG/DTA-MS) and FTIR spectrometric gas cell (TG-FTIR), in comparison. Compound 1 releases first but very slowly some of the included ammonia till 170 °C, then simultaneously ammonia (NH₃) and sulphur dioxide (SO₂) from 175 to 225 °C, whilst the evolution of SO₂ from thiosulfate ligands continues in several overlapping stages until 410 °C, and is escorted by explicit exothermic heat effects at around 237, 260, 358 and 410 °C. The former two exothermic DTA-peaks correspond to the simultaneous degradation and air oxidation processes of excess thiosulfate anions not reacted by formation of copper sulfides (both digenite, Cu_1.8S and covellite, CuS, checked by XRD) and sodium sulfate, while the last two exothermic peaks are accompanied also by considerable mass gains, as the result of two-step oxidation of copper sulfides into various oxosulfates. The mass increase continues further on until 580 °C, when the sample mass begins to decrease slowly, as a continuous decomposition of the intermediate copper oxosulfates, indicated also by re-evolution of SO₂. At 1,000 °C, a residual mass value of 64.3% represents a stoichiometric formation of Cu^IIO and anhydrous Na₂SO₄.     

Effect of heating on speciation of copper in Si/Al/Ca-based environmental matrices

X-ray absorption spectroscopy is used to investigate the speciation of sorbed copper in heated fly ash. CuO and Cu(OH)₂ are determined to be the principal copper species in the Cu-sorbing fly ash heated at 500 °C for 2 h. Heating the Cu-sorbing fly ash to 900 °C or 1100 °C can result in the formation of CuSO₄, representing 41% and 32% of the total copper, respectively. Ash sintering and/or co-melting at 900 and 1100 °C occur, thereby triggering chemical reaction between CuO/Cu(OH)₂ and sulfur compounds.     

Untersuchungen zur Kinetik der thermischen Dissoziation von Nickel-, Kupfer- und Zinksulfat

The rates of decomposition and the energies of activation were determined for the thermal dissociation of NiSO₄, CuSO₄, Cu₂(SO₄)O, ZnSO₄and Zn₃(SO₄)₂O. Linear, parabolic and logarithmic rate laws were found. Kinetics are largely determined by the rate of energy transfer. The reasons for the formation of basic sulfate intermediates are discussed.     

Catalytic wet air oxidation of 2-nitrotoluidine and 2,4-dinitrotoluene

The rates of wet air oxidation of 2-nitrotoluidine and 2,4-dinitrotoluene in the presence of excess oxygen and at different temperatures and oxygen pressures was investigated. Oxidation experiments were carried out at temperatures between 180 and 225^oC and oxygen partial pressures of 1,0-3,0 MPa, in a 280 mL glass vessel-inserted stainless steel reactor. Copper sulfate (CuSO₄ .5H₂O) was used as a catalyst, and the effect of catalyst loading was studied by varying the concentration: 0.75, 2.5 and 25 mg/L as Cu²⁺. Addition of Cu²⁺ ions in the reaction media accelerated 2-nitrotoluidine oxidation nearly ten times even if it exists in trace amount in the reaction medium (0.75 ppm Cu²⁺). Unfortunately copper did not show catalytic effect for the oxidation of 2,4-dinitrotoluene. This revised version was published online in August 2006 with corrections to the Cover Date.     

Wet-air oxidation of p-nitrophenol

Summary Wet air oxidation rates of p-nitrophenol in the presence of excess oxygen, at different temperatures and oxygen pressures conditions were investigated. The experiments were carried out at between 120 and 200^oC and at 1.0-3.0 MPa partial pressures of oxygen, in a glass vessel inserted in a stainless steel reactor. Initial p-nitrophenol concentration was 3.59x10^-4 mol/L. Copper sulfate (CuSO₄.5H₂O) was used as a catalyst. Presence of Cu²⁺ ions in the reaction medium accelerated oxidation reaction slightly. Oxidation kinetics have also been investigated with respect to p-nitrophenol disappearance and TOC results.     

Quantitative Analysis of Phases Formed During The Oxidation of Covellite (CuS)

A sample of covellite of particle size 45–90 μm was heated in air at 20°C min^–1 in a simultaneous TG-DTA apparatus. The phase compositions of the products at various temperatures were determined quantitatively by XRD and FTIR. By 500°C, 5.8% of Cu₂ O had formed, and this increased to a maximum of 44.8% at 585°C after which it decreased to zero by 750°C. 10% of CuO had formed by 680°C, and then steadily increased to 83.6% at 1000°C. 5.9% of CuO⋅CuSO₄ was found at 610°C, and increased to a maximum value of 79% after which it decomposed completely by 820°C. This revised version was published online in July 2006 with corrections to the Cover Date.     

X-ray crystal and molecular structure of sulphato aquotris(benzotriazole) copper(II)benzotriazole

The complex “Cu(SO₄)(btaH)₄·2H₂O” (btaH = benzotriazole) deposited as deep blue crystals from aqueous CuSO₄·5H₂OH₂SO₄btaH solutions been shown by X-ray diffraction methods to be a monohydrate [Cu(SO₄)(H₂O)(btaH)₃·btaH]. The crystals contain five-coordinate, tetragonal pyramidal Cu(SO₄)(H₂O)(btaH)₃ units and bridging btaH molecules linked together by a three-dimensional array of H-bonding interactions.     

Crystal Structure and Properties of Strontium Phosphate Apatite with Oxocuprate Ions in Hexagonal Channels

Strontium phosphate apatites containing different amounts of copper were prepared by a solid state reaction at 1100 °C or by arc melting above 1600 °C in air. The samples were characterized by X‐ray diffraction, ICP analysis, scanning electron microscopy, IR spectroscopy, MAS—¹H—NMR, diffuse reflectance spectroscopy, and SQUID magnetometry. X‐ray crystal structure determination was carried out for a single crystal obtained from the melt. The compound is formulated as Sr₅(PO₄)₃(CuO₂)_1/3 and has an apatite structure (space group P6₃/m, a = 9.7815(4)Å, c = 7.3018(4)Å, Z = 2) with linear CuO₂^3— ions occupying hexagonal channels. For solid state synthesized samples, Rietveld refinement of powder XRD patterns was performed. The samples obtained at 1100 °C acquire the composition Sr₅(PO₄)₃Cu_xOH_y, with x changing from 0.01 to 0.62 and y < 1—x. The copper content can be increased to x = 0.85 by annealing in argon at 950 °C. The compounds represent a hydroxyapatite in which part of the protons is substituted by Cu⁺ and Cu²⁺ ions. The ions form linear O—Cu—O units which are progressively condensed creating the Cu—O—Cu bridges on increasing copper content. IR and NMR data testify existence of OH groups, non‐disturbed and disturbed by neighboring Cu atoms. In the electron spectra, the samples exhibit absorption bands at 7800‐7900, 14200‐14500 and 17500‐17550 cm^—1, which were assigned to Cu²⁺ d‐electron transitions. By annealing the sample with x = 0.1 in oxygen at 800 °C copper is fully oxidized while retaining in channels in unusual for Cu²⁺ linear coordination.     

Studies on mechanism and kinetics of reaction of CuSO4 with Cu2SO2

The reaction of CuSO₄ with Cu₂SO₂ to give Cu₂SO₄ was studied. The influence of the degree of reaction, the initial mixture composition and the temperature upon the reaction rate and the product composition was discussed. It was found that the reaction starts above 710 K and pure Cu₂SO₄ can be obtained under strictly defined conditions.     

Zur Kenntnis eines neuen Kupfermolybdats: Cu4Mo5O17

About a New Copper Molybdate: Cu₄Mo₅O₁₇ Single crystals of Cu₄Mo₅O₁₇ were prepared by solid state reaction of Cu₂O and MoO₃ in the absence of oxygen. Single crystal X-ray investigations lead to triclinic symmetry (space group P1, a = 6.782, b = 9.573, c = 10.948 Å; α = 107.03, β = 88.40, γ = 111.02°, Z = 2). Cu₄Mo₅O₁₇ shows crystal chemical differences in respect to the Cu^II-oxomolybdates. The differences concern the coordination of Mo⁶⁺. Cu⁺ formes not a linear O? Cu? O group but is surrounded by oxygen tetrahedrally and octahedrally. The crystal structure is described and discussed.     

Stability of Ultradisperse Copper in a Sulfo Cation Exchanger Matrix

The recrystallization of ultradisperse copper chemically deposited onto a sulfo cation exchanger matrix was studied by the potentiometric method. The stationary value of the electrode potential of the copper-sulfo cation exchanger composite was established during a long period of time, which depended on the ionic form of the composite (H⁺, Cu²⁺, or Na⁺), solution composition (CuSO₄, H₂SO₄, and Na₂SO₄), and solution concentration. Recrystallization was favored by copper(II) counterions, which entered the composite as a result of ion exchange, nonexchange absorption of copper sulfate, or preliminary composite transformation into the Cu²⁺ form. In the quasi-equilibrium state, the concentration of copper(II) counterions was maintained at a high level by the Donnan interfacial potential. At all the copper(II) sulfate concentrations used, the potential of the Cu²⁺/Cu ion—metal pair in the ion-exchange matrix remained at virtually the same level, which was indicative of the stable state of copper particles. In the absence of an external source of copper ions, recrystallization was significantly hindered; therefore, the potential exhibited only a slight drift. Copper ions formed in the solution of small crystals were localized in the vicinity of ionogenic matrix centers, which decreased the mobility of these particles as counterions; therefore, the dispersity of particles remained unchanged.     

Untersuchungen zur Reaktivität in den Systemen A/Cu/M/O (A = Na–Cs und M = Co,Ni, Cu,Ag); Synthese und Kristallstrukturen von K3Cu5O4 und Cs3Cu5O4

Reactivity in the Systems A/Cu/M/O (A = Na–Cs and M = Co, Ni, Cu, Ag); Synthesis and Crystal Structures of K₃Cu₅O₄ und Cs₃Cu₅O₄ The systems A/Cu/M/O with A = Na–Cs and M = Co, Ni, Cu, Ag have been investigated with preparative, thermoanalytical and in situ X‐ray techniques to study the reactivity. For the redox reaction Co/CuO in the presence of Na₂O the intermediate, NaCuO, has been characterized. K₃Cu₅O₄ was obtained by annealing intimate mixtures of K₂O and CuO (molar ratio 1 : 1) in Ag containers at 500 °C. Cs₃Cu₅O₄ could be synthezised by reaction of KCuO₂ with Cs₂O (molar ratio 1 : 1) in Cu containers at 500 °C. Both compounds crystallize in the space group P2₁/c with Z = 4 isotypic to Rb₃Cu₅O₄ [IPDS data, Mo–Kα; K₃Cu₅O₄: a = 946.0(1), b = 735.61(6), c = 1401.3(2) pm, β = 107.21(1)°; 2249 F²(hkl), R₁ = 7.09%, wR₂ = 11.42%; Cs₃Cu₅O₄: a = 1027.7(1), b = 761.42(7), c = 1473.4(2) pm, β = 106.46(1)°, 1712 F²(hkl), R₁ = 6.04%, wR₂ = 14.22%]. Force constants obtained from FIR experiments for the deformation mode δ(O–Cu–O), the Madelung Part of the Lattice Energie, MAPLE, Effective Coordination Numbers, ECoN, calculated via Mean Effective Ionenradii, MEFIR, are given.     

Anion-induced assembly of two distinct copper(II) coordination polymers with a versatile multidentate N-donor ligand

Reaction of a ligand N-(3,5-di-2-pyrazinyl-4H-1,2,4-triazol-4-yl)-2-pyrazinecarboxamide (Hpztp) with CuSO₄ and Cu(acac)₂ (acac = acetylacetonate), respectively, yields two distinct Cu^II coordination polymers {[Cu₃(pztp)₂(SO₄)₂(H₂O)₂]·3H₂O} _n and {[Cu(pztp)(acac)]·0.5H₂O} _n . Both complexes have been structurally determined and also characterized by physicochemical and spectroscopic methods. The results reveal that by using different anions (SO₄ ^2? versus acac^?), the dimensionality (from 2D to 1D) of the resulting coordination architectures as well as conformations and binding fashions of the pztp ligand are significantly changed. That is to say, the selection of anions will play a key role in inducing the formation of the crystalline materials. The thermal stabilities of both complexes have also been explored and discussed.