J. Aride

Chemical and electrochemical inhibition studies of corrosion and hydrogen surface embrittlement. I. Fe0.78B0.13Si0.09 amorphous alloy in molar HCl

Diorthoaminophenoldisulfane (DOAPD) was synthesized for use as a corrosion inhibitor and in order to test its effect on the hydrogen surface embrittlement of Fe0.78B0.13Si0.09 alloy. Results of electrochemical and gravimetric measurements were consistent and confirmed the beneficial role of this inhibitor. The amorphous state of the alloy was confirmed by X-ray measurements and differential thermal analysis. The maximum inhibition of corrosion was attained in the presence of 10−4 M DOAPD. This inhibitor concentration also gave rise to a diminution of metal hydrogenation. A mechanism explaining the mixed role of the disulfane was confirmed.

The optical properties of lanthanides in theLn2BaZnO5 area of the mixed oxide systemLnBaZnO

Abstract The absorption spectrum of neodymium is investigated at 4.2 K in the tetragonal phase Ln 4−2x Ba 2+2x Zn 2−x O 10−2x (Ln =La, Nd) (0 ɤ x ɤ 0.25) . There is evidence for a single site for which the 4f 3 energy levels are given. The fluorescence spectra of Eu 3+ is analyzed in the orthorhombic phase Y 2 BaZnO 5 . There are two sites for the europium ions. The energy levels of 4f 6 are given and the crystal field parameters are determined for one of the sites. The fourth-order parameters are large. The absorption spectra of the two neodymium sites in the doped orthorhombic phases along the rare-earth series show a pronounced nephelauxetic effect (shift to the red).

Electropolymérisation de monomère 3-amino-1,2,4-triazole sur une électrode de cuivre et effet du polymère sur la corrosion de l'électrode en milieu NaCl 3 %

RésuméLelectropolymérisation dun nouveau polymére a partir de 3-amino-triazole (ATA) est réalisée. Lélectrolyte support était de Leau distillée avec un mélange de méthanol et de KOH. Le microscope électronique à balayage (MEB), la voltammétrie cyclique et le chronoampérométrie ont été utilisées pour caractériser le nouveau polymere. Ces mêmes techniques ont été employees pour étudier la nature du mécanisme dinhibition de la corrosion du cuivre en milieu NaCl 3% par suite de la formation du polymere. Lélectropolymérisation in situ du monomére donne lieu à un polymère isolant. Le traitement thermique du polymère améliore son homogénéité et son adhérence à lélectrode. Un mécanisme de la formation du poly-ATA est proposé. La formation du polymere aboutit à une diminution des courants cathodique et anodique. Les vitesses des réactions de réduction de lóxygène et de dissolution du cuivre ont été remarquablement diminuées.AbstractThe electrochemical polymerization of a new polymer is described. The monomer used was 3-amino-1,2,4-triazole (ATA) and the supporting medium was distilled water/methyl alcohol containing KOH. Scanning electronic microscopy (SEM), cyclic voltammetry and chronoamperometry were used, to characterize the new polymer. The same techniques were also used to study the nature of corrosion inhibition processes caused by the formation of the polymer on copper in NaCl 3%. The in-situ electropolymerization of the monomer gives an insulating polymer. Heat treatment of the polymer improves its homogeneity and adherence to the copper electrode on which it is formed. A mechanism for the formation of the poly-ATA is proposed. The formation of the polymer gives rise to a decrease in both anodic and cathodic currents. The rates of oxygen reduction and copper dissolution reactions are considerably decreased.

The aragonite-type neodymium borate NdBO3 : energy levels, crystal field, and paramagnetic susceptibility calculations

Abstract Optical absorption spectra of NdBO3 single crystals were measured between 3900 and 31,700 cm−1 at liquid helium to room temperature. The derived energy level scheme with 119 levels was simulated according to the crystal field theory including free ion effects yielding a rms deviation of 15 cm−1. The 14 free ion and 14 crystal field parameters allowed by the Cs symmetry of the neodymium site were calculated. The derived wavefunctions were used in calculating the paramagnetic susceptibility and its variation with the temperature between 4.2 and 500 K by the van Vleck formula. Experimental and calculated values are in good agreement.

Corrosion and hydrogen surface embrittlement inhibition of amorphous FeBSiC alloy in molar HCl by diorthoaminodiphenyldisulphane (DOAPD)

The mode of corrosion inhibition of amorphous alloys due to diorthoaminodiphenyldisulphane (DOAPD) in molar HCl is studied through solution analysis and electrochemical steady state and transient measurements. DOAPD acts on the cathodic reaction without changing the mechanism of the hydrogen reduction reaction on the surface of the amorphous alloy electrode. The efficiency of corrosion inhibition depends on both the concentration of DOAPD and the potential of the electrode. The addition of 10−4m DOAPD to 1m HCl increases the impedance and decreases the capacity of the double layer. From the comparison of results with those obtained using other organic compounds, it is shown that DOAPD is the best inhibitor. A correlation between the efficiency of corrosion inhibition of DOAPD and its molecular structure is established. A schematic representation of the surface coverage due to different action modes of DOAPD cations is presented. Evidence is revealed for a double rôle of DOAPD in the decrease of corrosion and in hydrogen penetration. The schematic representation proposed explains why the mechanism of hydrogen reduction reaction is the same in the absence and in the presence of DOAPD.

Comparative study of the optical spectra of Er3+ in Er2BaCuO5 and Er2BaZnO5

Abstract Optical absorption spectra of the two compounds Er 2 BaZnO 5 and Er 2 BaCuO 5 having the same crystallographic structure of the ‘green phase’ have been measured in a wide spectral range. The spectra of both compounds are similar, which points to a similarity of the crystal field around the erbium ion. The crystal field is, however, somewhat stronger for the copper compound. The calculations have been performed using the crystal field parameters obtained earlier for the two sites of Eu 3+ in Y 2 BaZnO 5 . The calculated overall splittings of J-manifolds and the distribution of levels are in agreement with the experiment. The high-resolution infrared spectra of Er 2 BaZnO 5 revealed a fine structure of absorption lines which has been attributed to the Davydov splitting.

Emission spectra and crystal field calculation of europium-doped C-type In2O3 oxide

Abstract The luminescent properties of the trivalent europium ion in the C-type indium oxide with two sites for the Eu3+ ion have been analysed. Because of the selection rules almost all emission arises from the C2 point symmetry site, since the S6 site does not allow electric dipole transitions. The energy level scheme of the 21 7 F J (J = 0–4) levels is well reproduced with an r.m.s. deviation of 3.9 cm−1 with 14 crystal field parameters allowed for the C2 site symmetry. A comparison with the Y2O3:Eu3+ emission spectra was also carried out.

Energy levels and crystal field calculations of Nd3+ in the REBMO5 phases (RE=rare earth, M=Ge, Si)

Abstract The optical properties of mixed oxides from the RE 2 O 3 –B 2 O 3 –MO 2 chemical system (RE=rare earth; M=Ge, Si) with general formula REBMO 5 have been analyzed. The energy level scheme of the Nd 3+ ion in the two structural types NdBGeO 5 and NdBSiO 5 have been deduced from the absorption and emission spectra recorded at different temperatures between 4.2 and 300 K. The simulation has been carried out on the 109 energy levels found for NdBGeO 5 and 125 for NdBSiO 5 . The phenomenological crystal field parameters have been determined assuming a C 2v point symmetry for the rare earth in NdBGeO 5 and C 2 or C s in NdBSiO 5 . The r.m.s. standard deviation is 17.5 cm −1 for NdBGeO 5 and 18.1 cm −1 for NdBSiO 5 , indicating a satisfying agreement between the calculated and experimental levels.

Optical study of europium-doped garnet Sr3 Y2 Ge3 O12

Abstract The optical emission spectrum of a europium structural probe replacing the yttrium in the garnet Sr3Y2Ge3O2 has been recorded at liquid nitrogen temperature. Only the 5 D o → 7 F 1 magnetic transition was observed. This is consistent with the octahedral position occupied by the rare earth element in that structure. No evidence for multisite occupation was found, in contrast with other garnets.

Mechanical properties of internally oxidized silver alloys

Abstract An increase in strength and a decrease in strain have been observed in Ag-0.4at.%Mg and Ag-0.2at.%Cu alloys during internal oxidation at 420 °C under 1 atm oxygen. This phenomenon, more pronounced in Ag-Mg alloy, is explained by a difference in coalescence degree: small precipitates are found in Ag-Mg (diameter about 1.5 nm) and voluminous precipitates in Ag-Cu (diameter about 10 3 nm). A correlation between mechanical properties and gravimetric studies shows that the most important modifications of these properties occur when a maximal oxygen quantity is stored in irregular and non-compact clusters. This amount is higher than the quantity required for stoichiometric oxide, MgO. Moreover, these clusters evolve towards a more compact structure by a release of oxygen and a small evolution of mechanical properties. In Ag-Mg alloys the grain boundary segregation of magnesium induces a small grain size (about 15 μm); when oxygen penetrates this matrix, the size increases to about 40 μm, allowing an increase in plastic deformation. During internal oxidation of Ag-Mg alloys a high concentration of dislocations in observed, contributing to the strengthening of the material.