THE INFLUENCE OF THE ELECTROCHEMICAL TREATMENT ON CU-AL-AG ALLOYS IN DEAERATED 0.5M NAOH

The effect of consecutive cyclic polarization in de-aerated 0.5 M NaOH solutions on the surface microstructure of mechanically polished Cu-Al-Ag alloys of different compositions and heat treatments has been studied using optical microscopy, SEM and EDS. The current peaks of the cyclic polarization curves do not depend on the alloy composition in the composition range studied. The repetitive potential scans between H2 and O2 evolution in alkaline media lead to preferential dissolution of aluminium, the roughness and phase composition of the surface of the alloys changing significantly. The quasistationary I-E curves of the different Cu-Al-Ag alloys studied consist in the superposition of the quasistationary I-E curves of high-purity Cu and Ag, the EDS microanalysis showing that aluminium is not present on the surface of the alloy in these conditions.

Upconversion luminescence in transparent glass ceramics containing beta-PbF2 nanocrystals doped with erbium

Frequency upconversion luminescence in erbium-doped PbGeO3-PbF2-CdF2-based transparent glass ceramics (TGC) under 980 nm infrared excitation is investigated. Upconversion emission signals around 410, 525, 550, 660, and 850 nm were generated and identified as due to the H-2(9/2) H-2(11/2), S-4(3/2), and F-4(9/2) transitions to the I-4(15/2) ground-state, and S-4(3/2)-I-4(13/2), respectively. The erbium ions excited-state emitting levels were populated via a combination of stepwise ground-state absorption (GSA), excited-state absorption (ESA), and cross-relaxation processes. The results also disclosed that both blue (410 nm) and red (660 nm) upconversion emission signals in the transparent glass ceramic sample presented twice as much intensity as compared to its vitreous counterpart. (C) 2003 Elsevier B.V. All rights reserved.

Precipitation of rare earth phosphates from H3PO4 solutions

A study of several factors has been carried out in order to determine their influence on rare earth phosphates precipitation from H3PO4 solutions obtained after the treatment of the Kola phosphate rock.

Kinetics of eutectoid decomposition in Cu-Al and Cu-Al-Ag alloys

The kinetics of eutectoid decomposition beta(1)' --> gamma(2) + (alpha + gamma(2)) in Cu-12.86 wt% Al and Cu-12.84 wt% Al-1.98 wt% Ag alloys was studied by hardness measurements, using the Johnson-Mehl-Avrami equation. The results indicate that the presence of silver seems to influence the nucleation rate and the activation energy of the reaction.

Thallium-arene contacts in a rare yttrium tris(pyrazolyl)hydroborate ate complex

A salt elimination reaction between [YCl3(THF)(3.5)] and 1 or 2 equiv. of Tl(Tp(Ms*)) [Tp(Ms*) = HB(3-mesitylpyrazolyl)2(5-mesitylpyrazolyl)(-)] leads in both cases to single metathesis, giving a mixture of the mono-Tp(Ms*) complex [YCl3(Tp(Ms*))Tl] (1) and another complex, [YCl2(Tp(Ms* *))] (2) [Tp(Ms* *) = HB(3-mesitylpyrazolyl)(5-mesitylpyrazolyl)(2)(-)], that results from the transfer of a second mesityl group to the 5-position of the pyrazolyl ring. The solid-state structure of 1 shows a unique ate dimeric structure with the TV cations coordinated by two mu(2)- and two mu(3)-bridging Cl atoms as well as two eta(3)-mesityl ligands. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004).

Energy-transfer frequency upconversion in neodymium-sensitized praseodymium-doped PbGeO3-PbF2-CdF2 glass excited at 810 nm

Visible frequency upconversion emission through resonant energy-transfer involving neodymium and praseodymium ions in PbGeO3-PbF2-CdF2 glass excited by a semiconductor laser at 8 10 nm is investigated. Luminescence emission centered around 485, 530, 610, and 645 nm, which correspond to the P-3(0) -> H-3(4), P-3(1) + I-1(6) -> H-3(5), P-3(0) -> H-3(6) and P-1(0) -> F-3(2) transitions of praseodymium ions, respectively, are observed. The upconversion excitation of the Pr3+ ions excited-state emitting levels was accomplished by means of an ion-pair interaction involving ground-state absorption, multiphonon relaxation, and excited-state absorption of pump photons at 8 10 nm by the Nd3+ (I-4(9/2) -> H-2(9/2), F-4(5/2); F-4(3/2) -> P-2(1/2)) and direct energy-transfer to Pr3+ ((4)G(11/2) + K-2(11/2), H-3(4) -> I-4(9/2), P-3(1) + I-1(6)). The dependence of the upconversion emission intensity upon the excitation power, and neodymium concentration are also examined. (c) 2004 Elsevier B.V. All rights reserved.

Optical characteristics of Er3+-Yb3+ doped SnO2 xerogels

Er3+ doped SnO2 xerogels have been obtained from aqueous colloidal suspensions. Emission and excitation spectra were obtained and allowed the identification of two main families of sites for Er3+. In the first one Er3+ substitutes for Sn4+ in the SnO2 cassiterite structure. In the second Er3+ are found adsorbed at the SnO2 particle surface. For the first family of sites the technological important infrared Er3+ emission about 1.5 mum is efficiently excited through absorption at the SnO2 conduction band at 3.8 eV. on the other hand the emission due to adsorbed ions appears inhomogeneously broadened by the statistical distribution of sites available for Er3+ ions at the surface of the particles. Moreover it is not excited by the host. The emission of this second family of sites could be also excited by an energy transfer mechanism involving Yb3+ ions also adsorbed a posteriori at particles surface. Results are compared with spectra obtained for Eu3+ doped samples. (C) 2002 Elsevier B.V. B.V. All rights reserved.

Effect of the bath pH on the electrodeposition of nanocrystalline Pd-Co alloys and their magnetic properties

The effect of the bath pH on the electrodeposition of nanocrystalline Pd-Co alloys and on their magnetic properties was studied. The pH practically did not affect the alloy composition. Conversely, the pH showed a significant influence on the shape and size of crystallites. Two different crystallites morphology were observed depending on the bath pH. A crystallite size ranging from 18.2 to 30 nm was obtained from X-ray diffractometry (XRD) patterns using the Scherrer's method. Also from the XRD patterns the lattice strain percentage was calculated and correlated with the residual stress, which probably originated during the film electrodeposition on the substrate. Some alloy magnetic properties showed small variations. In contrast, high and unexpected coercivities were obtained reaching a maximum of 1.69 kOe at pH 5.5. The high coercivity values were attributed to the presence of residual stress at the film-substrate interface, which increased as the bath pH and crystallite size decrease, both of them contributing simultaneously to increase in coercivity. (C) 2006 Elsevier B.V. All rights reserved.

The influence of residual stress and crystallite size on the magnetic properties of electrodepo sited nanocrystalline Pd-Co alloys

Nanocrystalline Pd-Co alloys were obtained by electrodeposition from an ammoniacal chloride bath. The influence of the crystallite size and the residual stress on the magnetic properties of the alloys was investigated. The residual stress increased as the applied current density was increased. It was associated to the high nucleation rate during electrodeposition and correlated to the lattice strain, estimated from the XRD patterns. Also from the XRD patterns the average crystallite size and the lattice constant were determined by Scherrer's and Rietveld's methods, respectively. Both parameters were directly influenced by the applied current density. Magnetic properties such as coercivity, remanence, saturation magnetization and squareness showed strong dependence on the residual stress and crystallite size. Coercivity higher than 1 kOe was achieved when a high current density was applied. High coercivity was attributed to the presence of residual stress and to the small crystallite size of deposits. (C) 2007 Elsevier B.V. All rights reserved.