A thermodynamic study of digenite solid solution (Cu2-δS) at 600 to 1000°C and a statistical thermodynamic critique on general nonstoichiometry

A very accurate experimental method to determine the composition of metal-saturated sulfides has been developed and applied to Cu_2-δS. The technique consists of using a high-sensitivity thermobalance which operates in a controlled atmosphere of H₂-H₂S gas. By this method it was shown that Cu-saturated Cu_xS is stoichiometric(x= 2.0000 ± 0.0002) between 700 and 1000°C. The free energy of formation for Cu₂S was found to be: 2Cu(s) + 1/2 S₂(g) = Cu_2.0000S(s), ΔG⁰ = -30,610 + 6.80T (cal/mole). The sulfur partial pressure was determined over nonstoichiometric Cu_2-δS for sulfur contents up to 21 pct. From the result, thermodynamic functions such as activity of copper, heats and entropies of solution were calculated as a function of nonstoichiometric composition. It was thermo-dynamically demonstrated that previous models dealing with nonstoichiometric oxides (or sulfides) based on the law of mass action,i.e., δ = const ie 67 01 (or ie 67 02), are inconsis-tent as they fail to satisfy the Gibbs-Duhem relation and also fail to account for the dis-sociation pressure over the stoichiometric composition. To resolve this dilemma, a sta-tistical thermodynamic method of constructing the grand partition function was introduced. Stoichiometry and nonstoichiometry of the Cu_2-δS were then explained by postulating an ionic crystal consisting of Cu⁺, Cu²⁺, Cu⁰ and neutral vacancies in the copper sublattice and S²⁻ and neutral vacancies in the sulfur sublattice. Formerly Postdoctorate Fellow, National Research Council of Canada, Ottawa, Ontario     

Kinetics of the Lime Enhanced Reduction of Cu2S With Carbon

Abstract

The rate of reduction of Cu₂S with carbon in the presence of lime was investigated in the temperature range of 900 to 1050 °C by means of thermogravimetric analysis.

The composition of the gas phase evolving during the reduction of Cu₂S was determined. The effects of temperature, the amount of carbon and the amount of CaO on the reduction rate were also determined. The results indicate that reduction of Cu₂S to Cu proceeded through the gaseous intermediates of CO and CO₂. The controlling step of the overall kinetics was the oxidation of carbon by CO₂. Temperature had the largest influence on the reduction rate. An energy of activation of 363 kJ/mol was calculated for the reduction of Cu₂S with carbon in the presence of CaO within the temperature range of 900 to 1050 °C.

On a étudié le taux de réduction du Cu₂S par le carbone, en présence de chaux, dans la gamme de température allant de 900 à 1050 °C, au moyen d'analyse thermogravimétrique.

On a déterminé la composition de la phase gazeuse dégagée lors de la réduction du Cu₂S. On a également déterminé l'effet de la température et de la quantité de carbone et de CaO sur le taux de réduction. Les résultats indiquent que la réduction du Cu₂S en Cu passait par les intermédiaires gazeux CO et CO₂. L'étape de contrôle de la cinétique était l'oxydation du carbone par le CO₂. La température avait la plus grande influence sur le taux de réduction. On a calculé une énergie d'activation de 363 kJ/mole pour la réduction du Cu₂S par le carbone, en présence de CaO, dans la gamme de température de 900 à 1050 °C.     

Kinetics of the chlorination of Cu2S with Cl2 gas

Abstract

When Cu₂S is chlorinated with Cl₂ gas, CuS, CuCl and CuCl₂ are observed at various stages of the reaction. It is proposed that CuCl₂ and CuS are the first products, which then react to produee CuCl and elemental sulphur. The elemental sulphur is then chlorinated to S₂Cl₂, which acts as a liquid bridge for the transport of dissolved sulphur away from the reaction interface. CuCl₂ forms only when all of the sulphide has been eliminated, and the partial pressure of chlorine in the CuCl₂ layer can exceed that for the stability of CuCl. The activation energy proposed for the diffusion of sulphuralong the gradient in a pore filled with S₂Cl₂ is 8.6 ± 0.5 kcal.

Résumé

Quand Cu₂S est chloruré par Cl₂ gaz, on observe CuS, CuCl et CuCl₂ à divers stades de la réaction. L’hypothèse proposée est que le CuCl₂ et le CuS sont les premiers produits formés qui réagiront ensuite pour produire CuCl et S. Le soufre élémentaire est ensuite chloruré en S₂Cl₂, et agit alors comme un pont liquide pour éloigner le S dissout de l’interface de réaction. CuCl₂ se forme quand tout le sulfure a été éliminé, et la pression partielle de Cl₂ dans la couche de CuCl₂ peut excéder celle correspondant àCuCl stable. L’énergie d’activation proposée par la diffusion du soufre dans S₂Cl₂est 8.6 ± 0.5 kcal.     

Study of the mechanism of anodic dissolution of Cu2S

The anodic dissolution of Cu₂S in sulfuric acid solutions was studied under galvanostatic and potentiostatic conditions. The anodic products were studied by mineralogical and X-ray diffraction methods. In every case, the formation of a digenite Cu_1-8S layer is observed at the surface of Cu₂S according to 5Cu₂S → 5Cu_1.8S + Cu⁺⁺ + 2e A copper concentration gradient appears through the digenite layer whose thickness remains constant as soon as a Cu_1.1S layer appears at its own surface according to 3Cu_1.8S → 4Cu_1.1S + Cu++ + 2e If the electrolysis conditions are such that the anodic potential remains low, the next reaction to occur is 10Cu_1.1S → HCu⁺⁺ + 10S + 22e But if under galvanostatic conditions, the current density is high enough at a given temperature to reach the sharp rise in anodic potential, or if under potentiostatic conditions the potential is kept high, two other reactions are possible: 10Cu_1.1S → 10CuS + Cu⁺⁺ + 2e followed by CuS → Cu⁺⁺ + S + 2e Moreover, at high anodic potential, the following reaction occurs also to some extent CuS + 4H₂O ? Cu⁺⁺ + SO₄ ⁼ + 8H⁺ +8e resulting in a decrease in anodic current efficiency for the copper dissolution. From a more practical point of view, it was shown that it is possible to deplete virtually completely the copper content of the anode (residue at less than 0.5 pct Cu)keepingthe electrode potential at a low value (less than +650 mV/ENH). Providing the temperature is high enough (75°C at least), the mean current density remains near to 2 A/dm², a suitable value to obtain good cathodic deposits.     

Hardening mechanism in melt-quenched Al-Zn-Mg-(Cu) alloys

The effect of various hardening factors on the mechanical properties of melt-quenched high-strength Al-Zn-Mg and Al-Zn-Mg-Cu alloys is considered. Alloys with zirconium and Group VIIIA metals are shown to have high mechanical properties. The high strength of these materials is achieved due to the precipitation of Al₃Zr (Ll₂) metastable phase particles and to a pronounced aging effect in materials alloyed with cobalt and nickel. High-strength melt-quenched 01949 (Al-Zn-Mg), 01959, and 01979 (Al-Zn-Mg-Cu) alloys containing zirconium, cobalt, and nickel are developed using these phenomena.     

Gd_5Si_(1.8)Ge_(1.8)Sn_(0.4)合金的高温相变

为认识合金的高温相变,采用热分析技术对Gd5Si1.8Ge1.8Sn0.4合金可能的高温相变进行了定性研究,并利用高温XRD研究了合金在200～400℃之间的相结构。研究结果表明:升温过程中,Gd5Si1.8Ge1.8Sn0.4合金在200～300℃之间发生了由Gd5Si2Ge2-型单斜结构向Gd5Si4-型正交结构的转变。从而为探索材料方便快捷的制备工艺提供技术支持。     

Active site-directed inhibitors of Rhodococcus 20 S proteasome. Kinetics and mechanism

We have studied the mechanism of inhibition of the recombinant Rhodococcus proteasome by four different chemical classes of active site-directed small molecule inhibitors. Clasto-lactacystin beta-lactone is a time-dependent inhibitor of the Rhodococcus proteasome's ability to hydrolyze Suc-Leu-Leu-Val-Tyr-AMC, a substrate for this proteasome's single type of active site, and proceeds with a kinact/[I] of 1,700 M-1 s-1. Using peptide mapping of tryptic digests, LC/MS, and amino acid sequence analysis, we have established that the Ogamma of the hydroxyl group on the N-terminal threonine of the beta-subunit is the sole modification made by the beta-lactone. Active site titrations of the Rhodococcus proteasome with reversible peptide aldehydes show the expected stoichiometry of one inhibitor molecule per beta-subunit. Prior modification with beta-lactone completely abrogates the binding of peptidyl boronic acid inhibitors, suggesting that these inhibitors also inactivate the enzyme by reacting with the Ogamma moiety on Thr1. High performance liquid chromatography analysis of peptidyl vinyl sulfone-modified intact Rhodococcus proteasome beta-subunit and its tryptic peptides suggests that the peptidyl vinyl sulfone modifies a residue in the N-terminal 20 amino acids. This modification is also blocked by prior treatment with beta-lactone.     

Kinetics and equilibrium of Cu(II) adsorption onto chemically modified orange peel cellulose biosorbents

A series of orange peel cellulose biosorbents has been specifically prepared by different chemical modifications to understand the mechanism of copper adsorption from chloride solutions. The different biosorbents and raw orange peels were characterized using elemental analysis and Fourier transform infrared spectroscopy (FTIR). The acidic and basic sites and pH of zero charge were also determined. The influences of pH, contact time, initial copper concentration and solid/liquid ratio on copper removal were examined. The maximum adsorption capacity of copper was 1.22 mol/kg, using orange peel esterified by 0.6 mol/L citric acid at 80 °C after 0.1 mol/L NaOH saponification. A comparison of different isotherm models revealed that the combination of Langmuir and Freundlich (L–F) isotherm model fitted the experimental data best. Results indicate that the chemically modified orange peel cellulose can provide an efficient and cost-effective technology for eliminating copper from aqueous solution.     

Fe_固-Sn_液反应过程中FeSn_2及FeSn生长动力学研究

本文研究了在350～600℃间,Fe_固与Sn_液间的反应扩散及金属化合物FeSn_2和FeSn的生长动力学,确定出FeSn_2及FeSn形成的温度范围分别为350～520℃和520～600℃,二者均按抛物规律生长。求出了抛物常数和扩散激活能,并研究了FeSn_2及FeSn的形貌。     

Kinetics and mechanism of the cleavage of the peptide bond next to asparagine

The spontaneous cleavage reaction of the tetra-peptide Piv-Gly Asn-Sar-Gly-NHtBu to the C-terminal dipeptide and N-terminal succinimide dipeptide proceeds through pre-equilibrium deprotonation of the amide group of the asparagine side chain, followed by intramolecular nucleophilic attack of nitrogen on the peptide carbonyl carbonyl carbon atom. General acid-catalyzed breakdown of the intermediate then gives the products. According to this mechanism, the reaction rate strongly increases with pH and buffer concentration.     

Kinetics of Cu(II) cementation on a pure aluminum disc in acidic sulphate solutions

Abstract

The rates of copper cementation on pure aluminum discs were studied as a function of (a) initial copper ion concentration, (b) temperature, (c) initial hydrogen ion concentration, and (d) the effect of the peripheral velocity of the Al disc.

At low initial copper ion concentration (1 × 10^?4M), there are two rate-controlling processes: ionic diffusion control at temperatures. above 40°C, and surface reaction control at temperatures below 40° C. At higher initial copper ion concentrations (5 × 10^?3 M), the rate is controlled by a chemical (surface) reaction.

When the-hydrogen ion concentration is increased to 0.7 M, the cementation rate increases. The pH remains constant during the reaction.

The cemented deposit is pure copper. The structure. of the deposit is dependent on both temperature and the initial copper ion concentration. At high initial copper ion concentration (5 × 10^-3 M) and at high temperatures (75° C), the rate, which was constant initially, increases with increasing deposition.

Résumé

Les taux de cémentation du cuivre sur des disques d'aluminium pur ont été étudié en fonction (a) de la concentration initiale des ions cuivres, (b) de la température, (c) de la concentration initiale des ions hydrogene et (d) de l'effet de la vitesse tangentielle du disque d'aluminium.

Pour une faible concentration initiale d'ions cuivre (1 × 10^?4 M) il y a deux processus régulateurs : à des températures supérieures à 40°C un côntrale de diffusion ionique et à moins de 40°C un côntrale de la réaction de surface. Pour des concentrations d'ions cuivre plus élevées (5 × 10^?3 M), le taux est contrôlé par une réaction chimique (de surface).

Quand la concentration des ions hydrogène est augmentée à 0.7M Ie taux de cémentation augmente, lp. pH demeure constant pendant la réaction.

Le dépôt est du cuivre pur et sa structure dépend à la fois de la température et de la teneur initiale en ions cuivre. A haute concentration initiale d'ions cuivre (5 × 10^-3M) et à haute temperature (75°C), le taux, constant du début, augmente quand le dépôt augmente.