Micro-Raman study of copper hydroxychlorides and other corrosion products of bronze samples mimicking archaeological coins

Three bronze samples created by CNR-ISMN (National Research Council—Institute of Nanostructured Materials) to be similar to Punic and Roman coins found in Tharros (OR, Sardinia, Italy) were studied to identify the corrosion products on their surfaces and to evaluate the reliability of the reproduction process. Micro-Raman spectroscopy was chosen to investigate the corroded surfaces because it is a non-destructive technique, it has high spatial resolution, and it gives the opportunity to discriminate between polymorphs and to correlate colour and chemical composition. A significant amount of green copper hydroxychlorides (Cu₂(OH)₃Cl) was detected on all the coins. Their discrimination by Raman spectroscopy was challenging because the literature on the topic is currently confusing. Thus, it was necessary to determine the characteristic peaks of atacamite, clinoatacamite, and the recently discovered anatacamite by acquiring Raman spectra of comparable natural mineral samples. Clinoatacamite, with different degrees of order in its structure, was the major component identified on the three coins. The most widespread corrosion product, besides hydroxychlorides, was the red copper oxide cuprite (Cu₂O). Other corrosion products of the elements of the alloy (laurionite, plumbonacrite, zinc carbonate) and those resulting from burial in the soil (anatase, calcite, hematite) were also found. This study shows that identification of corrosion products, including discrimination of copper hydroxychlorides, could be accomplished by micro-Raman on valuable objects, for example archaeological findings or works of art, avoiding any damage because of extraction of samples or the use of a destructive analytical technique.     

Pulsed electrochemical deposition of nickel oxides on multi-walled carbon nanotubes from EDTA alkaline solutions: a SEM,XPS, and voltammetric characterization

A study regarding the electrodeposition of nickel oxide particles on the activated multi-walled carbon nanotubes from 2 M NaOH solution containing Ni(NO₃)₂ and EDTA was carried out. The electrodeposition process was carried out using an optimized double-pulse sequence of potentials: E ₁ = ?0.2 V vs. SCE (t ₁ = 0.3 s) and E ₂ = 0.7 V vs. SCE (t ₂ = 0.03 s). Spectroscopic XPS investigations and SEM analysis were used in order to characterize the surface and morphology of the studied modified electrode. Cyclic voltammetry and chronoamperometry were used in order to evaluate the electrochemical/amperometric performance of the GC/MWCNT-Ni electrode toward the oxidation of some aliphatic alcohols in strong alkaline medium.     

Electrochemical synthesis of oxide nanotubes on Ti6Al7Nb alloy and their interaction with the simulated body fluid

The aim of the present work was to investigate electrochemical behavior of the Ti6Al7Nb alloy in the simulated body fluid (SBF) containing Ca²⁺, HCO₃ ^?, and HPO₄ ^2? ions. At first, optimal conditions necessary for oxide nanotube formation were determined. The experiments were conducted in the 1 M (NH₄)₂SO₄ with 0.5 wt% NH₄F electrolyte at room temperature. Anodization of the alloy samples was carried out under variable external voltage U in the range from 10 to 40 V at room temperature. Obtained surface morphology was examined by SEM and X-ray techniques. Nanotube diameter was calculated and correlated with the imposed voltage. Having control over the size of nanotubes, samples with the obtained nanostructures of a chosen diameter were immersed into SBF solution with pH = 7.4 for a fixed period of time. Then, they were removed from the fluid and subjected to the electrochemical investigation. Corrosion current and corrosion potential were determined, and it was found that the best anticorrosion properties were obtained for heat-treated nanotube layer: i _corr = 39 nA/cm² and E _corr = ?0.236 V vs Ag/AgCl. Finally, the interaction between the oxide surface and the solution was studied using polarization and electrochemical impedance spectroscopy (EIS) techniques.     

Thermal stability and crystallization kinetics of ternary Se–Te–Sb semiconducting glassy alloys

This paper presents the results of kinematical studies of glass transition and crystallization in glassy Se_85?x Te₁₅Sb _x (x = 2, 4, 6 and 8) using differential scanning calorimetry (DSC). From the dependence on heating rates of, the glass transition temperatures (T _g), and temperature of crystallization (T _p) the activation energy for glass transition (E _g) and the activation energy for crystallization (E _c) are calculated and their composition dependence can be discussed in term of the average coordination number and cohesive energy. The thermal stability of Se_85?x Te₁₅Sb _x was evaluated in terms of criterion ΔT = T _c ? T _g and kinetic criteria K(T _g) and K(T _p). By analyzing the crystallization results, the crystallization mechanism is characterized. Two (two- and three-dimensional growth) mechanisms are working simultaneously during the amorphous–crystalline transformation of the Se₈₃Te₁₅Sb₃ alloy while only one (three-dimensional growth) mechanism is responsible for the crystallization process of the chalcogenides Se_85?x Te₁₅Sb _x (x = 4, 6 and 8) glass. The phases at which the alloy crystallizes after the thermal process have been identified by X-ray diffraction.     

Investigation of ferromagnetic layer dissolution characteristics during pulse electrodeposition of FeCoNiCu/Cu multilayers

Minimization of interface roughness of electrodeposited metallic multilayers with nanometer thick sublayers during pulse electrolysis largely depends on the choice of potential pairs and electrolyte. In this study, a systematic effort has been made to identify the different origins of less noble ferromagnetic (FM) layer dissolution during two pulse potentiostatic electrochemical deposition (ECD) of FeCoNiCu/Cu multilayers and its subsequent minimization. Detailed investigations by employing cyclic voltammetry and chronoamperometry, it was established that the FM layer dissolution not only depends on copper layer discharge potential (E _Cu) but also on FM layer discharge potential (E _FM) and Cu²⁺ concentrations. Both the cell capacitance effect and galvanic displacement reactions are accountable for corrosion of FM layer. It was found that potentials, E _FM = ?2.3 V vs. SCE and E _Cu = ?0.6 vs. SCE are the optimum pair for growth of FeCoNiCu/Cu multilayers with minimum dissolution of FM layer.     

Application de la radiopolarographie a l'étude dequelques éléments à l'échelle des indicateurs

Basic equations of classical polarography are transposed and tested withmanganese and europium at tracer scale. Using the previously presented automatic system, standard dispersion for experimental points is about 3% and residual activity before the wave 3±2% compared with diffusion activity A_d. Results with manganese in 10^?3M ≤[LiCl]≤10^?1M and 2≤pH≤4 solutions, give an experimental yield about 100%, E_1/2=?1.47 V/SCE and α?0.85. The last values agree with results achieved at a weighable scale. For potentials <?2.00 V/SCE a screening effect with supporting electrolyte ions is observed. The screening effect influence on the diffusion coefficient is taken into consideration and results for europium (R?100%, E_1/2??1.95 V/ECS, α=1 at pH 2.7) are in good agreement with the literature. Radiopolarograms for Mn and Eu and mixtures of both are similar. Thus the range of polarographic analysis is enlarged.     

Investigation into the crystal structure of bis(pyridine)-bis(trichloroacetato) copper(II) and its electrophotochemical properties

A novel chained Cu(II) complex was synthesized from trichloroacetato copper(II) and pyridine in ethanol solvent, and characterized by elemental analysis and infrared (IR) spectroscopy. The special crystal structure of the Cu(II) complex was determined by X-ray single-crystal diffraction. The results indicate that a chained structure of the Cu(II) complex formed through intermolecular hydrogen bonds. Cu(CCl₃COO)₂(C₅H₅N)₂(H₂O) was monoclinic, with unit cell P21/c and cell parameters as follows: a = 14.389(3) Å, b = 7.1911(14) Å, c = 23.107(8) Å, V = 2,257.5(10) Å³, Z = 4, M _r = 564.51, D _c = 1.661 mg/m³, T = 293(2) K, F(000) = 1,124, μ(Mo K_α) = 1.704 mm^?1, R = 0.0984, and ωR = 0.2791. The electrochemical behavior of the Cu(II) complex on a glassy carbon working electrode determined by cyclic voltammetry showed the electrochemical activity of the title compound at 0.2 to ?0.3 V (versus SCE) in NH₃–NH₄Cl buffer solution (pH 9.2), and the redox peak current of the complex had a good linear relationship with the square root of the scan rate in the range 0.02–0.2 V/s.     

Chemical and electrochemical behavior of metallic technetium in acidic media

The chemical and electrochemical properties of technetium metal were studied in 1–6 M HX and in 1 M NaX (pH 1 and 2.5), X = Cl, NO₃. The chemical dissolution rates of Tc metal were higher in HNO₃ than in HCl (i.e. 8.63 × 10^?5 mol cm^?2 h^?1 in 6 M HNO₃ versus 2.05 × 10^?9 mol cm^?2 h^?1 in 6 M HCl). The electrochemical dissolution rates in HNO₃ and HCl were similar and mainly depended on the electrochemical potential and the acid concentration. The optimum dissolution of Tc metal was obtained in 1 M HNO₃ at 1 V/AgAgCl (1.70 × 10^?3 mol cm^?2 h^?1). The dissolution potentials of Tc metal in nitric acid were in the range of 0.596–0.832 V/AgAgCl. Comparison of Tc behavior with Mo and Ru indicated that in HNO₃, the dissolution rate followed the order: Mo > Tc > Ru, and for dissolution potential the order: E _diss(Ru) > E _diss(Tc) > E _diss(Mo). The corrosion products of Tc metal were analyzed in HCl solution by UV–Visible spectroscopy and showed the presence of TcO₄ ^?. The surface of the electrode was characterized by microscopic techniques; it indicated that Tc metal preferentially corroded at the scratches formed during the polishing and no oxide layer was observed.     

Corrosion inhibition investigations of 3-acetylpyridine semicarbazone on carbon steel in hydrochloric acid medium

The corrosion inhibition efficiency of 3-acetylpyridine-semicarbazide (3APSC) on carbon steel (CS) in 1.0 M HCl solution has been investigated using weight loss measurements, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization studies. The results show that inhibition efficiency on metal increases with the inhibitor concentration. 3APSC exhibited marked inhibition towards carbon steel in HCl medium even at low concentrations. The adsorption of inhibitor on the surfaces of the corroding metal obeys the Langmiur isotherm and thermodynamic parameters (K _ads, ?G _ads ⁰ ) were calculated. Activation parameters of the corrosion process (E _a, ?H* and ?S*) were also calculated from the corrosion rates. Polarization studies revealed that 3APSC act as a mixed-type inhibitor. Surface analysis of the metal specimens was performed by scanning electron microscopy.     

Synthesis,structure and electrochemical properties of some thiosemicarbazone complexes of iridium

Reaction of thiosemicarbazones of salicylaldehyde and 2-hydroxyacetophenone (H₂L¹ and H₂L²) with [Ir(PPh₃)₃Cl] affords complexes of type [Ir(PPh₃)₂(L)(H)] (L = L¹ or L²) in ethanol. A similar reaction carried out in toluene affords the [Ir(PPh₃)₂(L)(H)] complexes along with complexes of type [Ir(PPh₃)₂(L)Cl], where a chloride is coordinated to iridium instead of the hydride. The structure of the [Ir(PPh₃)₂(L²)(H)] and [Ir(PPh₃)₂(L²)Cl] complexes has been determined by X-ray crystallography. Crystal data for [Ir(PPh₃)₂(L²)(H)]: space group, P2₁/c; crystal system, monoclinic; a=12.110(2) Å, b=17.983(4) Å, c=18.437(4) Å, β=103.42(3)°, Z=4; R ₁=0.0591, wR ₂=0.1107. Crystal data for [Ir(PPh₃)₂(L²)Cl]: space group, P2₁/c; crystal system, monoclinic; a=17.9374(11) Å, b=19.2570(10) Å, c=24.9135(16) Å, β=108.145(5)°, Z=4; R ₁=0.0463, wR ₂=0.0901. In all the complexes the thiosemicarbazones are coordinated to the metal center as dianionic tridentate O, N, S-donors and the two triphenylphosphines are trans. The complexes are diamagnetic (low-spin d? ⁶, S=0) and show intense MLCT transitions in the visible region. Cyclic voltammetry on all the [Ir(PPh₃)₂(L)(H)] and [Ir(PPh₃)₂(L)Cl] complexes shows a quasi-reversible Ir(III)–Ir(IV) oxidation within 0.55–0.78 V vs. SCE followed by an irreversible oxidation of the thiosemicarbazone within 0.91–1.27 V vs. SCE. An irreversible reduction of the thiosemicarbazone is also observed within ?1.10 to ?1.23 V vs. SCE.     

Thermal analysis study on the simultaneous grain refinement and modification of 380.3 aluminum alloy

In this research, effect of integrated Al–10Sr–1Ti–2B master alloy has been studied on the microstructure and solidification characteristics of 380.3 aluminum alloy. Thermal Analysis has been used as a technique to study the cooling curves and first derivative curves during solidification of the alloy. Effect of integrated grain refiner and modifier on solidification parameters such as α-Al dendrite growth temperature (T _G,α), α-Al dendrite recalescence undercooling (?T _R,α), aluminum–silicon eutectic growth temperature (T _G,E), and eutectic recalescence undercooling (?T _R,E) has been determined. By increasing master alloy content, T _G,α and ?T _R,E have been increased, but, ?T _R,E has been decreased, and T _G,E increases first and then decreases. Aluminum–silicon eutectic depression temperature ( $ \Updelta T_{\text{G,E}}^{{{\text{Al}} - {\text{Si}}}} $ ) can be used as a parameter to control the modification of eutectic silicon. The results of this research indicate that the optimum level of Al–10Sr–1Ti–2B master alloy for the simultaneous grain refinement and modification of 380.3 alloy is about 0.5 mass%.     

Chemical-epigenetic method to enhance the chemodiversity of the marine algicolous fungus, Aspergillus terreus OUCMDZ-2739

Four new meroterpenoids identified as (R)-4-((2,2-dimethylchroman-6-yl)methyl)-3-(4-hydroxyphenyl)-5-methoxyfuran-2(5H)-one (1), 1-(2,2-dimethylchroman-6-yl)-3-(4-hydroxyphenyl)propan-2-one (2), (R,E)-3-(2,2-dimethylchroman-6-yl)-4-hydroxy-5-((2-(2-hydroxypropan-2-yl)-2,3-dihydrobenzofuran-5-yl)methylene)furan-2(5H)-one (3), methyl (R)-2-(2-(2-hydroxypropan-2-yl)-2,3-dihydrobenzofuran-5-yl) acetate (4), along with nine known compounds (5–13) were isolated from a chemical-epigenetic culture of Aspergillus terreus OUCMDZ-2739 with 10 μM trichostatin A (TSA). Under the same condition without TSA, A. terreus OUCMDZ-2739 produced different compounds (14–20), supporting that the chemical-epigenetic modification of fungi could enrich the chemodiversity of the fungal products. The cytotoxicity was observed for compound 8 against K562 cell, 9 against MCF-7 and K562 cells and 12 against MCF-7 cell with IC₅₀ values of 9.5, 10.1, 13.0 and 8.5 μM, respectively. Compounds 3, 8 and 17 exhibited stronger α-glucosidase inhibition than 1-deoxynojirimycin and acarbose (positive controls) with IC₅₀ values of 24.8, 1.2, 61.6, 191.7 and 555.1 μM, respectively. The enzyme kinetics study further indicated that compound 8 was an anticompetitive inhibitor with K_i value of 1.42 μM.     

The crystal structure of α-copper vanadate

The crystal structure of α-copper vanadate has been determined and refined by full-matrix least-squares procedures using automatic diffractometer data to a residual R = 0.050 (R_w = 0.059). The space group is rhombohedral, $\text{R}\text{3}$, with hexagonal unit cell a = 12.857(3) and c = 7.161(2) Å (a_R = 7.797(2) Å and α = 111.06(1)°). On the basis of the detailed structural analysis the contents Cu_7?xV₆O_19?x with x = 0.22 are proposed for the rhombohedral cell. Copper is in the divalent and vanadium in the quadrivalent state. The structure is based on a cubic close-packed array of oxygen ions with the vanadium ion occupying an octahedral site, one copper in a partially occupied octahedral site and the other copper in a tetrahedral site. The latter is one of the few examples of tetrahedrally coordinated copper.     

The electrochemical synthesis of poly(o-phenylenediamine) on stainless steel and its corrosion protection ability in 3.5 % NaCl solution

In this study, electrochemical synthesis of poly(o-phenylenediamine) (PoPDA) on 316L stainless steel and its corrosion inhibition effect were studied. Electropolymerization of o-phenylenediamine (oPDA) was carried out by a potentiodynamic method using 0.5 M H₂SO₄ solution containing 0.05 M oPDA monomer. The corrosion protection ability of the PoPDA in 3.5 % NaCl was investigated by potentiodynamic polarization, electrochemical impedance spectroscopy, and change of open circuit potential with immersion time (E_OCP ? t). The results showed that PoPDA acted as a protective layer on stainless steel against corrosion in 3.5 % NaCl solution.     

Thermal analysis, decomposition kinetics, and molecular modeling of transition metal (Fe, Co) surfactant complexes

A detailed thermal analysis of iron and cobalt surfactant complexes of the type [M(CH₃COO)₄]^2?[C₁₂H₂₅NH₃ ⁺]₂ has been carried out using Thermogravimetric (TG) analysis at different heating rates (i.e., 5, 10, 15, and 20 °C min^?1). It has been observed that iron complex decomposes by a different mechanism compared to other transition metal complexes. Metal is the final product instead of metal oxide. Combining the results from our previous study, first row transition metal complexes exhibit an order of stability in agreement with the famous Irving Williams series, i.e., the apparent activation energy, E for thermal decomposition varies as: E _Fe > E _Co < E _Ni < E _Cu > E _Zn (exception being iron because of different decomposition mechanism). Thermal decomposition parameters have been measured and compared using the multiple heating rate method of Flynn–Wall–Ozawa. Further, molecular modeling calculations have been carried out to compare the experimental TG data with theoretical computations for the synthesized metal surfactant complexes. Minimum energy optimized structures for the complexes have been obtained using Gaussian software.     

Electrochemical properties of LaY2Ni9 hydrogen storage alloy,used as an anode in nickel-metal hydride batteries

The electrochemical properties of LaY₂Ni₉ alloy used as an anode in nickel-metal hydride batteries were investigated at ambient and at different temperatures. Several techniques, such as the galvanostatic charging and discharging, the constant potential discharge, and the potentiodynamic polarization, were applied to characterize these electrochemical properties. The discharge capacity of the LaY₂Ni₉ alloy increases to reach 258 mAh g^?1 after 5 cycles and decreases to 140 mAh g^?1 after 100 cycles then stabilizes around this same value indicating good cycling held. The hydrogen diffusion coefficient D _H in the bulky alloy is estimated to be (1.02?±?0.11)?×?10^?11 cm² s^?1 correlated with the good stability of electrochemical capacity after 100 cycles. The evolution of the ratio \( \frac{D_{\mathrm{H}}}{a^2} \) and the corrosion current density and potential are correlated with the evolution of the electrochemical capacity during the activation and for a long cycling. The enthalpy, the entropy, and the apparent activation energy of the LaY₂Ni₉ hydride formation are evaluated. The calculated results show that the enthalpy change, the entropy change, and the activation energy are (?42.64?±?1.08), (56.85?±?2.11), and (14.84?±?0.35)?kJ mol^?1, respectively.     

Contribution of the Guinier-Preston zones to the hardening of Al-5%Ag alloy and its photo-electrochemical protection in seawater using n-CdS

The contributions of the GP zones and the matrix to the alloy hardening have been studied in the alloy Al-5% at. Ag aging at 150 °C. They were determined separately using a method based on the hardness measurement which obeys the relation ΔHv_SS = 19.72x^2/3 + 0.218 (Gpa), where x is the means atomic concentration of the matrix. The GP zones follows the relationship (ΔHv _GP = 18.4 f_v^0.94 kg/mm²), f_v is the volume fraction of GP zones. In a second part, the photo-electrochemical properties of n-CdS were exploited for the cathodic protection of the alloy Al-5% at.Ag in one of the most corrosive environments namely seawater. The corroded surface was rough and the corrosion product contains divided particles. However, the corrosion was significantly hindered by contacting the alloy to n-CdS (E_g = 2.40 eV) irradiated by visible light with different intensities (42–103 mW cm^-2). Under illumination, the electrode potential of the alloy is cathodically shifted when short-circuited to n-CdS, indicating a photo cathodic protection while the corrosion current falls from 2.67 (in the dark) down to 1.73 mA cm^-2 under a light flux of 103 mW cm^-2. Conversely, when the alloy is short-circuited to p-type CuO (E_g = 1.46 eV), the corrosion current increased by 26% under illumination, due to the activated dissolution by photoholes.     

PANI–TiC nanocomposite film for the direct electron transfer of hemoglobin and its application for biosensing

A novel polyaniline and titanium carbide (PANI–TiC) nanocomposite was synthesized by an in situ chemical oxidative polymerization method, and a hydrogen peroxide (H₂O₂) biosensor was fabricated by PANI–TiC with hemoglobin (Hb)-modified glassy carbon electrode (GCE). Scanning electron microscope and energy dispersive X-ray spectroscopy showed the morphology and ingredient of PANI–TiC. Electrochemical investigation of the biosensor showed a pair of well-defined, quasi-reversible redox peaks with E _pa?=??0.318 V and E _pc?=??0.356 V (vs SCE) in 0.1 M, pH 7.0 sodium phosphate-buffered saline at the scan rate of 150 mV s^?1. Transfer rate constant (k _s) was 2.01 s^?1. The Hb/PANI–TiC/GCE showed a good electrochemical catalytic response for the reduction of H₂O₂ with the linear range from 0.5 to 285.5 μM and the detection limit of 0.2 μM (S/N?=?3). The apparent Michaelis–Menten constant (K _m) was estimated to be 1.21 μM. Therefore, the PANI–TiC as a novel matrix opened up a further possibility for study on the design of enzymatic biosensors with potential applications.     

Novel α-spirocyclic (alkyl)(amino)carbenes at the theoretical crossroad of flexibility and rigidity

Spirocyclic (alkyl)(amino)carbenes (CAACs) with reasonable conformations of cyclopropyl, cyclobutyl, cyclopentyl, and cyclohexyl substituents in the position α to the carbenic center are investigated at B3LYP/AUG-cc-pVTZ//B3LYP/6-31+G*. The singlet–triplet energy separations (?E _s?t), HOMO–LUMO energy gaps (?E _HOMO?LUMO), hydrogenation energies (?E _H), heats of methylene formation (?E) as well as philicity indices (N and ω) of these carbenes are compared and contrasted. The highest ?E _s?t is encountered for the cyclopropyl substituted CAAC (54.2 kcal/mol), while the other ones lay in a narrow range of 48.2–51.8 kcal/mol. Assignment of the barriers for ring inversions is carried out in order to probe the “flexible steric bulk” of cyclic substituents, showing negligible differences with those of the unsubstituted rings. The calculated N and ω indices indicate that in contrast to the popular belief, CAACs appear less electrophilic than N-heteorcyclic carbenes (NHCs).