Partial Reaction Orders Research Articles

Aluminosilicate colloidal gels: from the early age to the precipitation of zeolites.

Aluminosilicate hydrogels are often considered to be precursors for the crystallisation of zeolites carried out under hydrothermal conditions. The preparation of mechanically homogeneous aluminosilicate gels enables the study of these materials through bulk rheology and observation of the aging dynamics until the precipitation of crystalline zeolites. The first part of this study deals with the establishment of ternary state diagrams, in order to identify the range of chemical formulations that enable preparation of single-phase homogeneous gels. Then, by studying the viscoelastic moduli during the gelation reaction, and by yielding the gel under large deformation, we propose an empirical law considering the partial order of reaction on each chemical element, to predict the gelation time according to the chemical formulation. The scaling behavior of the elastic properties of this colloidal gel shows a transition from a strong link behavior to a weak link regime. Long term aging results in the shrinkage of the gel, accompanied by syneresis of interstitial liquid at the surface. Zeolites precipitate through crystallisation by a particle attachment mechanism, when thermodynamic equilibrium is reached. The stoichiometry of the precipitated zeolites is not only consistent with the concentration of the remaining species in the supernatant but, surprisingly, it is also very close to the partial order of the reaction of the chemical elements involved in the determination of the critical gel point. This indicates a strong correlation between the morphology of the soft amorphous gel network that is formed at an early age and those of the final solid precipitated crystals.

A comprehensive assessment of ammonia synthesis reaction kinetics and rate equations

In this study, the ammonia formation analytical rate equations were described well at pressures from 107 to 320 atm and different flow rates. The surface adsorption and desorption of nitrogen over iron-type catalysts were investigated according to the reaction kinetics of ammonia synthesis. The kinetic reaction rate equations of Temkin & Pyzhev, Langmuir–Hinshelwood, Ozaki et al., and the power rate law predicted the behaviour of the system and evaluated closeness to the experimental data. The microkinetic model rate (I and II) results were compared with other analytical and experimental rate equations. All proposed models showed excellent fits with experimental data. This result implies that the rate equation correlates to the overall dissociation rate of adsorbed nitrogen and the equilibrium constant for all ammonia formation reaction steps. The Temkin & Pyzhev rate results showed deficiencies at low ammonia synthesis operating pressures. Also, the nitrogen partial pressure reaction order was highly influenced by the power rate law results. The rate results from microkinetic models I and II were nearly the same. In addition, the Ozaki et al. rate equation could be used to predict the ammonia synthesis rate. The rapid computation time of the ammonia synthesis rate requires a simple rate equation. Therefore, calculating the rate based on the Temkin & Pyzhev and power rate laws is appropriate for fitting experimental measurements.

Определение частных порядков реакции восстановления перманганата калия этанолом в различных средах

A spectrophotometric kinetic study of the reaction of the potassium permanganate reduction by excess ethanol in acidic, neutral and alkaline environments was performed. The reaction mixtures were prepared from the solutions of potassium permanganate of different concentrations (0.0004, 0.001 and 0.002 М) and either the solutions of sulphuric acid (1, 3 and 10 %), water, or the solutions of sodium hydroxide (0.01, 0.04 and 0.1 М). The kinetic curves were recorded with the spectrophotometer at the wavelengths of 525 nm (in acidic environment), 400 nm (in neutral environment) and 605 nm (in alkaline environment). The initial reaction rates were determined from the slopes of the initial linear parts of the kinetic curves. Using the differential van’t Hoff method, the partial reaction orders were determined. It was shown that in the acidic environment the partial reaction order with respect to permanganate is close to 1.5, and that with respect to hydrogen ions is close to 0.6. In the neutral and alkaline environments the reaction obeys the first partial order with respect to permanganate, and the partial order of the reaction in alkaline environments with respect to hydroxyl-ions is close to 0.8. It was also shown that the effective rate constants of the reaction in acidic and alkaline environments are significantly higher than that in neutral environment

Kinetic regularities of hydrometallurgical recycling of spent displays: behavior of indium

This article discusses the physicochemical regularities of indium leaching from the surface of glass plates of used displays in various acids. The glass of used displays was pre-cleaned from polarizers and crushed. Their base is comprised of silicon and aluminum oxides. Indium is presented in the form of In2O3·SnO2. Indium content in the material obtained is 174.8 mg/kg. Individual solutions of sulfuric, hydrochloric and methanesulfonic acids were used as leaching agents. The influence of concentrations of the mentioned acids (0.1–1.0 N), leaching duration (10–60 min), temperature (298–353 K) and liquid-to-solid ratio (L : S = (7.5÷15.0): 1 cm3/g) on the degree of indium extraction into solution has been determined. Partial orders of reaction in terms of CH3SO3H, H2SO4, HCl are 0.69, 0.67 and 1.10, respectively. In the course of experiments an intensive increase in indium concentration was observed in the first 20–40 min f leaching in H2SO4 and HCl solutions. The process rate then decreased and indium extraction actually did not increase, due to a fall in the amount of non-reacted indium. During leaching in 0.1–0.4 N in CH3SO3H solutions, the rate of indium dissolution did not change throughout the experiment, since the amount of non-reacted indium gas decreased insignificantly. The acids considered here can be ranked in the following ascending order of their efficiency for indium dissolution: CH3SO3H, H2SO4, HCl, which corresponds to the growth of strengths of these acids. An increase in the temperature led to a significant increase in indium extraction. The apparent activation energies of In2O3 dissolution in CH3SO3H, H2SO4, HCl solutions have were calculated as equal to 51.4, 51.2, 43.4 kJ/mole, respectively. It was established that with the use of HCl as leaching agent, the increase in the fraction of liquid phase in the slurry from 7.5 : 1 to 15 : 1 cm3/g lead to fall in indium extraction by 2.4 times and the initial leaching rate by 3.2 times. It was demonstrated that an increase in L : S during indium dissolution in CH3SO3H (from 7.5 : 1 to 15 : 1 cm3/g) and H2SO4 (from 10 : 1 to 15 : 1 cm3/g) is accompanied by insignificant changes in extraction and initial leaching rate. Therefore, the studies performed demonstrated that indium leaching from glasses of spent displays flows in mixed mode upon the use of HCl and in kinetic mode in H2SO4 and CH3SO3H solutions.

Crying Wulff on vapor–solid distributions of crystallogen chemical vapor deposition via p-block element hydride thermal decomposition

Chemical vapor deposition is key in silicon device manufacturing. Surprisingly, crystallogen thin film deposition is executed without adequate knowledge of vapor–solid distributions. To address the issue, classical thermodynamics is applied to the determination of vapor–solid distributions for Si1-xCx, Si1-xGex and Ge1-xSnx depositions via a hydride route. The enthalpy of formation is substituted with a X – H bond dissociation energy which stands for the surface energy. Theory and experiments are in reasonable agreements. Indeed, the surface energy drives the solid growth, in line with Wulff’s principle. And the thermal decomposition of a covalent hydride is a quasistatic process. Chemical vapor deposition and thermal decomposition are unified with thermodynamics. Growth Rate, partial reaction order n = 1/2 and activation energy E fingerprint an interface chemistry consistently across covalent precursors. E is often found equal to a fraction of either X – H or H – H bond dissociation energy, i. e., E = n BDE, where n is a partial reaction order, and 1/n an integer matching the molecular hydrogen stoichiometric coefficient. Thus, p-Block elemental deposition mechanism is elucidated. Three sequential deposition mechanisms are identified. In the first mechanism, the growth rate is controlled by the dissociation of a X – H bond. In the second mechanism, a H – H bond dissociation is controlling the growth rate. The H – H path is triggered by a near complete surface hydrogenation. Finally, in the third mechanism, the deposition turns out amorphous from the lack of vacant lattice sites, as the H – H breaking energy is exhausted, and once more complete surface hydrogenation is achieved.

On the growth kinetics, texture, microstructure, and mechanical properties of tungsten carbonitride deposited by chemical vapor deposition

Tungsten carbonitride [W(C,N)] was deposited on cemented carbide substrates by chemical vapor deposition (CVD) in a hot-wall reactor using tungsten hexafluoride (WF6), acetonitrile (CH3CN), and hydrogen (H2) as precursors. Tungsten carbides and nitrides with a hexagonal δ-WC type structure are generally difficult to obtain by CVD. Here, it was found that the combination of WF6 and CH3CN precursors enabled the deposition of W(C,N) coatings with a δ-WC type structure and columnar grains. A process window as a function of the deposition temperature and precursor partial pressures was determined to establish the conditions for the deposition of such coatings. Scanning electron microscopy, x-ray diffraction, electron backscatter diffraction, and elastic recoil detection analysis were used for the investigation of the coating thickness, microstructure, texture, and composition. From the investigation of the kinetics, it was concluded that the growth was mainly controlled by surface kinetics with an apparent activation energy of 77 kJ/mol, yielding an excellent step coverage. The partial reaction orders of the reactants together with their influence on the microstructure and coating composition was further used to gain a deeper understanding of the growth mechanism. Within the process window, the microstructure and the texture of the W(C,N) coatings could be tailored by the process parameters, enabling microstructural engineering with tuning of the mechanical properties of the W(C,N) coatings. The nanoindentation hardness (36.6–45.7 GPa) and elastic modulus (564–761 GPa) were found to be closely related to the microstructure.

High-pressure cell to study the catalytic behavior of bulk samples and surface deposited mass-selected nanoclusters at atmospheric conditions

A high-pressure reaction cell was developed to study the catalytic activity of supported subnanometer catalysts under atmospheric conditions. With the help of a capillary, the gas composition in the vicinity of the catalyst surface can be analyzed. First, the mean residence time of the gaseous components in the capillary was determined. The dependence of the partial pressures of the reactants on the vertical distance between the capillary and the catalyst was then characterized with the aid of a polycrystalline Pt sample. A Pt(111) surface was then used to validate the experimental setup concerning the CO oxidation under oxygen-rich conditions at a total pressure of 1000 mbar. The partial orders of reaction for CO and O2 agree with values from the literature. The change in the reaction mechanism, which was also described in the literature, could be observed from the temperature-dependent investigation of the CO oxidation. The obtained turn-over frequency and the activation energy at about 660 K agree well with the values obtained in the high-pressure CO oxidation studied in a batch reactor. The efficiency of the experimental setup is demonstrated by examining supported Pt10 clusters since the site density was reduced by a factor of 15 compared to the bulk samples. Taking the Pt site density into account, the sample with the decamers is approximately 5–6 times more active than the Pt(111) surface at a temperature of 673 K. Accordingly, the activation energy for the CO oxidation of 106 kJ mol−1 significantly decreased compared to the value of 132 kJ mol−1 for Pt(111). This finally proves that the high-pressure cell enables the systematic investigation of the size-dependent catalytic behavior of nanoclusters with low degrees of coverage in the future.

Photochemical study of interaction of chromium (III) with EDTA reaction kinetics: a chemical kinetics laboratory experiment

Abstract: The kinetics of the complex ion of chromium (III) with EDTA formation reaction in a water solution was studied. The possibility of simultaneous determination of partial reaction orders with respect to all reactants was shown. The influence of temperature and hydrocarbonate-ions as a catalyst on the reaction rate was studied. It was shown that this reaction is very suitable for the experimental demonstration of formal kinetics regularities and can be used in a university laboratory practice course. The methodical instructions for students were developed.

Kinetics of the low-pressure chemical vapor deposited tungsten nitride process using tungsten hexafluoride and ammonia precursors

Tungsten nitride (WNx) is a hard refractory material with low electrical resistance that can be deposited using multiple methods. This study focuses on the microstructrual development of low pressure chemical vapor deposition grown WNx coatings. Also, the growth kinetics is studied and discussed in terms of the resulting microstructures. Samples of WNx were deposited using WF6, NH3, and Ar at 592–887 K in a hot-wall reactor with variable gas mixture compositions (NH3:WF6 = 0.5–25). The coatings were nitrogen-rich (x ∼ 1.65) and oxygen-free as determined by time-of-flight-elastic recoil detection analysis. X-ray diffraction showed that the coatings transformed from being amorphous to crystallizing as β-W2N at 641–690 K. The morphologies changed with deposition temperature. Being very fine grained and nodular at deposition temperatures 740 K and below, increasing the deposition temperature to 789 K while employing a NH3:WF6 molar ratio of 1, large disc-shaped protrusions were formed. When increasing the NH3:WF6 molar ratio to 25, striped facets became increasingly dominant. Investigating the latter by transmission electron microscopy, a microstructure of smaller ridges formed by twinning, oriented as <211> in the out-of-plane direction, was revealed across the facet surfaces. Transmission Kikuchi diffraction confirmed that <211> was the texture of these coatings. The partial reaction order of WF6 and NH3 at 740 K was determined to be close to 1/6 and 1/2, respectively. The apparent activation energy ranged from 82 to 12 kJ/mol corresponding to deposition temperatures from 592 to 887 K.

Hydrogenation of CO2 to Methanol with Mn‐PNP‐Pincer Complexes in the Presence of Lewis Acids: the Formate Resting State Unleashed

AbstractThe hydrogenation of CO2 to methanol was achieved using a catalytic system comprising metal complexes of the form [Mn(CO)2[N(C2H4PR2)] (R=iPr/Ph, [HN(C2H4PPh2)2]=MACHO−Ph) together with Lewis acid additives. Mechanistic studies suggest initial CO2 insertion into a Mn−H bond leads to a formate complex as resting state. By systematically balancing the interaction between the acidic additive and the catalyst, the formate ligand could be removed through esterification to unleash the full catalytic potential. The reaction conditions were optimized on basis of the partial reaction order of relevant compounds. The combination of MACHO−Ph and Ti(OiPr)4 was identified as the most active system with a TON of 160 (p(CO2)=5 bar, p(H2)=160 bar, T=150 °C). Using methanol as solvent and co‐reagent allows the catalytic conversion of CO2/H2 in a liquid phase process comprising only the substrates and products.

Сравнительные кинетические исследования химического осаждения PbSe селеносульфатом натрия и селеномочевиной с установлением влияния их природы на состав и морфологию пленок

After analyzing the literature, one can note the increased interest in lead selenide in the thin-film state, used in various fields: from microelectronics to solar energy converters. There are physical and chemical methods for producing PbSe films, each of which has its own advantages and disadvantages. However, researchers prefer chemical deposition from aqueous media, which eliminates the need for complex, expensive equipment, heating to high temperatures and creating high pressures. The Ural school of thin-film synthesis has developed and tested a kinetic-thermodynamic method for predicting the chemical deposition of metal chalcogenides. The thermodynamic assessment carried out in our previous publication indicated only the principal possibility of the formation of lead selenide when using selenocarbamide СSe(NH2)2 and sodium selenosulfate Na2SeSO3. For a more complete understanding of this process, a comprehensive approach is necessary, taking into account the patterns of the deposition of the solid phase of PbSe in time, depending on thermodynamic factors - temperature and concentration of reagents. Therefore, in this work, we studied the kinetics of the chemical deposition of lead selenide with selenourea and sodium selenosulfate from solutions containing lead acetate, sodium citrate, ammonium hydroxide and iodide, in the temperature 303 -353 K under conditions of spontaneous nucleation of the solid phase. As a result of the studies, the partial kinetic reaction orders for chalcogenizers were determined, amounting to 0.86 (СSe(NH2)2) and 0.78 (Na2SeSO3), as well as the activation energy of the formation of lead selenide, which amounted to 45.1 and 25.07 kJ/mole, respectively. Hydrochemical deposition of selenocarbamide and sodium selenosulfate produced PbSe films on substrates of sitall and glass with a thickness of 200-300 nm. Energy dispersive analysis and scanning electron microscopy showed the influence of the nature of the substrate, type chalcogenizer on the morphology, particle size distribution and elemental composition of lead selenide layers. An elemental analysis showed that PbSe films precipitated with sodium selenosulfate contain an excess of lead compared to selenium (Pb/Se = 1.25-1.32), and the stoichiometric composition ensures the use of selenocarbamide (Pb/Se = 0.99-1.05).

Кинетика фотовосстановления меди(II) в композициях на основе ацетата меди и тетрафторпропианата меди

In the technology of manufacturing printed circuit boards by additive method, photoselective activation of dielectric materials is widely used. In order to obtain a given circuit pattern on the surface and in the holes of the printed circuit board it is necessary to form catalytically active centers for further chemical metallization. The aim of the work was to study the physical and chemical patterns of the photoactivation process of dielectric materials. Copper acetate (CuAc2) and copper tetrafluoropropyanate (Cu(TFP)2) having sufficiently high spectral sensitivity to UV radiation and good solubility in water were added to the analysed photosensitive compositions as copper-containing compounds (photopromotors). Chemical sensitizer in analysed photosensitive compositions is water-soluble organic compound – disodium salt of anthraquinone-2,6-disulfonic acid (Na2AS), acting as optical sensitizer in processes of photochemical reduction of copper(II). The process of photochemical reduction of copper(II) in the presence of sensitizers is possible with the presence of secondary reducing agents – alcohols. Such compounds are sorbitol and ethyl alcohol. In comparison with solutions, the study of the process of photo recovery of copper(II) in the dry layer of the photoactivator under the influence of ultraviolet radiation requires a special approach. A quantitative evaluation of the photochemical process was chosen to pass the photosensitive layer. On the transmission spectra of the photosensitive layer, it is clearly possible to distinguish a maximum at a wavelength of 520 nm, from the change of which during ultraviolet irradiation it is possible to judge the progress of photochemical transformation in the dry layer of photocomposition. The kinetics of the photochemical process were monitored by the transmission spectra of the 520 nm samples, which were taken immediately after irradiation. Survey of spectra was carried out on spectrophotometer of grade СF-18 in visible region of spectrum relative to chromatographic paper FN-5 without photoactivator. Mercury-quartz lamp of DRT-1000 grade was used as radiation source. Exhibiting carried out on GG-2258 installation in a special vacuum frame at distance 40 cm from a radiation source A phenomenological description is given of the process of photo-recovery of copper(II) in solid phase in compositions based on copper acetate and copper tetrafluoropropionate in form of kinetic equations. Fractional partial reaction orders by components of the photocomposition indicate the complexity of the process in the systems studied. It has been found that, depending on the kind of copper-containing compound, the process of copper photo-recovery is described by different kinetic equations, suggesting a different mechanism of copper(II) photo-recovery. It has been shown that complicating the composition of the photosensitive composition results in a slight change in the reaction order of the main components. The description of the kinetics of the photochemical process by means of mathematical equations will allow to determine in advance the time by which the specified degree of conversion of the substance will be achieved.

Promoting effect of AuCu alloying on Au-Cu/CeO2-catalyzed CO oxidation: A combined kinetic and in situ DRIFTS study

Reduced Au-Cu/CeO2 catalysts (Cu/Au = 1, 3) are more efficient towards the preferential oxidation of CO (PROX) than their calcined counter-parts. They exhibit lower activation energies and CO partial reaction orders (αCO), and even more interestingly, significantly higher O2 partial reaction orders (βO2). For the stoichiometric composition in particular (Au1Cu1/CeO2-R), the partial pressure of oxygen has a higher impact on the reaction rate than the partial pressure of CO (βO2 > αCO), which is unprecedented in low temperature catalysis involving gold and a reducible oxide support. DRIFTS studies further show (1) that Au1Cu1/CeO2-R contains electron-deficient, alloyed Cu atoms (Au-Cu+) and (2) that the formation of CO2 is enhanced by the preadsorption of O2 rather than the preadsorption of CO. This suggests that CO oxidation proceeds via a Langmuir-Hinshelwood-type, bifunctional mechanism, involving CO adsorbed on Au0 sites and oxygen adsorbed on electron-deficient, gold-alloyed copper sites. This alloy-mediated oxygen activation could be the key to the superior PROX activity of Au1Cu1/CeO2-R.

Selective synthesis of acetonitrile by reaction of ethanol with ammonia over Ni/Al2O3 catalyst

A highly selective synthesis of acetonitrile was carried out by the reaction of ethanol with ammonia on a 10 wt% Ni/Al2O3 catalyst. The conversion of ethanol and selectivity to acetonitrile, ethylene, and monoethylamine were examined by varying experimental parameters such as ammonia partial pressure, reaction temperature, and space time. The increase in the ammonia partial pressure led to a considerable decrease in the conversion and small increase in the acetonitrile selectivity up to a molar ratio of NH3/ethanol of 3, followed by almost constant values. The partial reaction order of ethanol obtained by controlling the space time was one, while that of ammonia was negative, −0.4. The deactivation behavior of the catalyst after 100 h on stream reaction at 230 °C was analyzed by X-ray photoelectron spectroscopy and temperature programmed oxidation of the catalyst used. The catalyst deactivation was attributed to the gradual formation of nickel carbonitride on the catalyst surface.

Carbon Dioxide Absorption into Aqueous Potassium Salt Solutions of Arginine for Post-Combustion Capture

The mass transfer and kinetics of CO2 absorption into aqueous potassium argininate (ArgK) solutions were investigated using a wetted-wall column at concentrations ranging from 0.26 to 1.23 M and temperatures from 298 to 333 K. Absorption rates of CO2 were compared by the absorption flux and a fall-in-pressure method among basic amino acid salts (AAS) and two amine standards for capture technology. Results showed that ArgK has comparable kinetics toward CO2 with the standard monoethanolamine (MEA) but lower kinetics than piperazine (PZ). The kinetic results were interpreted using two models based on zwitterion mechanism and termolecular mechanism for the reactive absorption of CO2. It was found that the partial reaction orders vary from 1.25 to 1.60 with respect to ArgK. Under the pseudo-first-order regime, the overall reaction rate constants were obtained and the individual reaction rate constants in these models were derived. The calculated values from two models agree well with the experimental data wit...

Reaction kinetics of carbon dioxide absorption into aqueous potassium salt of histidine

Aqueous amino acid salts are attractive absorbents for carbon dioxide (CO2) capture due to low volatility and resistance to oxidative degradation. The kinetics of CO2 absorption into aqueous solutions of potassium histidinate (HisK) was investigated using a wetted wall column at concentrations ranging from 0.26 to 2.07M and temperatures from 298 to 333K. Density, viscosity of aqueous HisK and physical solubility of N2O in these solutions were measured. A temperature dependant ion parameter hHis− was correlated to estimate Henry׳s constants of CO2. The zwitterion and termolecular mechanisms as well as ionic strength effect on reaction rate were applied to interpret the absorption rate of CO2 in non-ideal systems. Under the pseudo-first-order regime, the overall reaction rate constants increase strongly with the increasing HisK concentration and temperature. HisK shows comparable chemical reactivity toward CO2 with the industrial standard monoethanolamine (MEA). The partial reaction order with respect to HisK was found to be an average value of 1.26. Zwitterion deprotonation by water and HisK should be the rate-determining step. Two proposed models from zwitterion and termolecular mechanisms could successfully predict the experimental data within 12% AAD. The activation energy was calculated to be approximately 25.0kJmol−1.

DFT-based modeling of benzene hydrogenation on Pt at industrially relevant coverage

A fundamental kinetic model for the catalytic hydrogenation of benzene over Pt(111) has been constructed based on periodic DFT calculations using the PW91 and optPBE vdW-DF functional. In contrast to traditional quantum chemical calculations at low to medium surface coverage, the calculations have been performed at a hydrogen coverage of 0.44 in order to account for the strong lateral interactions between the surface intermediates at industrial hydrogenation conditions (pB=0.1–0.6bar; pH2=0.5–6bar; T=400–500K). The destabilization of the surface species at increased hydrogen coverage results in rate coefficients that are several orders of magnitude larger than at low hydrogen coverage, caused by not only reduced activation barriers, but also a one-order of magnitude increase of the pre-exponential factors. Accounting for coverages representative for industrial conditions in the ab initio calculations is crucial for a correct modeling of the hydrogenation kinetics. Using the given methodology, the turnover frequency (TOF), temperature dependence of the TOF, and the partial reaction orders of benzene and hydrogen are in quantitative agreement with experimental results.

Electrodeposition of Zn Alloys with Cu and Sn from Citrate Electrolytes

Zinc alloys with copper and tin are of interest for a variety of applications,1–3 and due to their disparate equilibrium potentials are often electrodeposited with complexing agents, such as cyanide, to shift their potentials more closely together. Other more environmentally friendly alternative complexants have been examined, such as citrate, and conditions demonstrated to achieve electrodeposited Cu-Zn4 and Sn-Zn-Cu5 alloys. Several models of the Zn reduction mechanism have been proposed and involve of an adsorbed intermediate in Zn reduction.6-8In this study, the influence of codepositing Cu (or Sn) on the Zn partial current density and reaction order is reported. Experimental Due to the inherent low current efficiency expected in zinc and zinc alloy deposition an upward facing rotating disk electrode was used. Polarization data was obtained for Cu, Sn, Zn, CuZn, and SnZn using a Pt counter electrode and a silver/sliver chloride reference. The aqueous electrolytes contained 10 mM CuSO4, ZnSO4 or SnSO4 , 60 mM sodium citrate, 500 mM Na2SO4 and 1 mM hydroquinone. Three different ZnSO4 concentrations were examined to assess the reaction order of Zn when deposited as an elemental deposit, and when Zn is codeposited with CuZn, and SnZn, where the metal:citrate ratio was maintained at value of 0.5. The pH was adjusted to 2 using sulfuric acid and electrolytes were at room temperature. Deposits were fabricated at constant potential of -1.25 V vs Ag/AgCl for 30 min, and the composition characterized using X-ray fluorescence spectroscopy. Ohmic drop was measured with electrochemical impedance spectroscopy (EIS). EIS was also used to characterize the deposition of CuZn and SnZn with a frequency range from 0.1 to 100K Hz. Results Table 1 provides a sample of the alloy composition at 900 rpm at a constant potential deposition. There is non-linear increase in the Zn deposit content with the addition of zinc ions in the electrolyte. From the composition data, the Zn partial current density and reaction order were determined for the three electrolytes Zn, CuZn, and SnZn. There was a decrease in the Zn partial current density when codeposited with Cu (or Sn) at low Zn concentration and an increase in the Zn apparent reaction order was observed when Zn was codeposited with Cu (or Sn). This increase in the Zn partial current density and the change in the Zn apparent reaction order when codeposited with Cu or (Sn) is attributed to the presence of an anodic contribution by the less noble Zn. The influence of the codepositing noble elements on the Zn partial current density can be accounted for in the Zn rate expression by including the mole fraction of the deposit Zn concentration to estimate the activity of the solid state. Conclusions The current-potential behavior of Zn deposited alone or codeposited with Cu (or Sn) in an agitated environment showed that the total current density was lowered with increasing Zn concentration, due to a decrease in the Zn partial current density itself. The Zn partial current density could be described by a rate expression that includes the Zn mole fraction of the solid state. Acknowledgements The authors wish to acknowledge support by the Embassy of United Arab Emirates in Washington DC, USA Y. Fujiwara and H. Enomoto, Surf. Coatings Technol., 35, 101–111 (1988).M. Arici, H. Nazir, and M. L. Aksu, J. Alloys Compd., 509, 1534–1537 (2011).P.-Y. Chen, M.-C. Lin, and I.-W. Sun, J. Electrochem. Soc., 147, 3350–3355 (2000).F.L. G. Silva, D.C. B do Lago, E. D'Elia, L.F. Senna, J. Appl. Elecctrochem 40 2013 (2010)M. Slupska and P. Ozga, Electrochem. Acta 141 149 (2014).M. G. Lee and J. Jorne, J. Electrochem. Soc., 139, 2841–2844 (1992).I. Epelboin, M. Ksouri, E. Lejay, and R. Wiart, Electrochim. Acta, 20, 603–605 (1975).I. Epelboin, M. Ksouri, and R. Wiart, J. Electrochem. Soc., 122, 1206–1214 (1975). Figure 1

Dissolution of uranium mixed oxides: The role of oxygen vacancies vs the redox reactions

While uranium-based mixed oxides are interesting materials for several concepts of nuclear reactors, the effects of trivalent elements in the fluorite structure and the redox reactions at the solid/solution interface during the dissolution of such compounds remain widely unknown. In order to underline the influence of those parameters, various dissolution experiments were carried out on different compositions (i.e. U0.75Ce0.25O2, U0.75Th0.25O2, Th0.75Nd0.25O1.875 and U0.75Ln0.25O1.875 with Ln = Nd, Gd). These tests were performed on sintered pellets in nitric acid solutions (from 10−2 M to 4 M) at different temperatures (22°C–90°C) under dynamic conditions. Therefore, a multiparametric study of the dissolution kinetics was then achieved in order to determine the partial order of dissolution reaction regarding to H3O+ activity and the activation energy. The obtained results gave evidence of the strong dependency of the dissolution rate with the nitric acid concentration. In fact, for concentrations higher than 2 M, the dissolution process is almost controlled by the oxidation of U(IV) to U(VI). On the contrary the effect of oxygen vacancies became predominant for acid concentrations lower than 0.5 M. Under these conditions, the systems containing trivalent elements exhibited the lowest chemical durability. The partial order of the reaction regarding to the H3O+ activity reached n = 2.1 for U0.75Th0.25O2 and was found to be constant over the entire acidity range. A variation of the partial order of the dissolution reaction regarding to H3O+ was observed along the nitric acid concentration range for U0.75Ln0.25O1.875 solid solutions, that underlines the predominance of different controlling reactions in the dissolution mechanism: surface-controlling reaction involving H3O+ at low pH (i.e. n < 1) for CHNO3 ≤ 0.5 M, and uranium oxidation (i.e. n > 1) for CHNO3 ≥ 1 M.

Qualitative and quantitative characterization of the arsenic‐binding behaviour of sulfur‐containing peptides and proteins by the coupling of reversed phase liquid chromatography to electrospray ionization mass spectrometry

Phenylarsenic-substituted cysteine-containing peptides and proteins were completely differentiated from their unbound original forms by the coupling of reversed phase liquid chromatography with electrospray ionization mass spectrometry. The analysis of biomolecules possessing structure-stabilizing disulfide bridges after reduction provides new insights into requirements concerning the accessibility of cysteine residues for reducing agents as well as for arsenic compounds in a spatial protein structure. Complementary binding studies performed using direct ESI-MS without chromatographic coupling in different solvent systems demonstrated that more than one binding site were activated for aprotinin and lysozyme in denaturing solvents because of a stronger defolding. From the intensities of the different charge states occurring in the mass spectra as well as from the LC elution behaviour, it can be deduced that the folding state of the arsenic-bound protein species resembles the native, oxidized conformation. In contrast, although the milk protein α-lactalbumin has several disulfide bridges, only one phenylarsenic moiety was bound under strongly denaturing conditions. Because of the charge state distribution in the ESI mass spectra, a conformational change to a molten globule structure is assumed. For the second considered milk protein ß-lactoglobulin, a noncovalent interaction with phenylarsine oxide was detected. In general, smaller apparent binding constants for the condensation reactions of the biomolecules with phenylarsine oxide leading to covalent arsenic-sulfur bindings were determined from direct injection ESI-MS measurements than from LC-ESI-MS coupling. The following order of binding affinities for one phenylarsenic group can be assumed from both ESI-MS and LC-ESI-MS: nonapeptide vasopressin > nonapeptide vasotocin > lysozyme > aprotinin > α-lactalbumin > thioredoxin. Kinetic investigations by LC-ESI-MS yielded a partial reaction order of 2 for vasopressin, Lys and α-lactalbumin and corresponding half-lives of 0.93, 2.56 and 123.5 min, respectively.