Electrochemical corrosion behavior of Al<Subscript>18</Subscript>B<Subscript>4</Subscript>O<Subscript>33</Subscript>w/Al composite

The effects of the volume fraction of alumina borate (Al₁₈B₄O₃₃) whisker and the scan rate of potentiodynamic technique on the localized corrosion behaviors of Al₁₈B₄O₃₃w/Al composite were investigated. Potentiodynamic polarizations and cyclic polarizations were performed to examine the electrochemical corrosion behavior of the composites. The surface morphologies of the as-cast composite were observed by optics microscopy and the surface morphologies of the composite after corrosion tests were observed by scanning electronic microscopy (SEM). The results of electrochemical measurement indicated that the anodic passive region reduced with the increasing in the volume fraction of Al₁₈B₄O₃₃ whisker in the composites (at the same scan rate), and the anodic passive region reduced with the decreasing in the scan rate of potentiodynamic technique (in the same volume fraction of whisker). The results of cyclic polarization indicated that increase in the volume fraction of Al₁₈B₄O₃₃ whisker in the composites results in a significant decrease of protection potential and an increase of the area of cyclic hysteresis loop.     

Effect of surface morphology on atmospheric corrosion behaviour of Fe-based metallic glass,Fe<Subscript>67</Subscript>Co<Subscript>18</Subscript>Si<Subscript>14</Subscript>B<Subscript>1</Subscript>

The nature of atmospheric corrosion behaviour of an as-cast metallic glass, Fe₆₇Co₁₈Si₁B₁₄ ribbon, was evaluated. The wheel side surface of the ribbon was more corroded than the air side surface, due to the higher density of air pockets present. The phases present in atmospheric rust were analysed by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) to be goethite, lepidocrocite, magnetite, cobalt oxide and cobalt hydroxide phases. Goethite and lepidocrocite were in amorphous form. The nature of rusting was understood by scanning electron microscopy (SEM). Nucleation of rust started at preferred locations on the surface and grew along the surface in certain directions.     

Enhanced electrochemiluminescence behavior of C,N quantum dots embedded g-C<Subscript>3</Subscript>N<Subscript>4</Subscript> nanosheets and its sensing application for copper (II)

Electrochemiluminescence (ECL) is a very sensitive method for trace analysis because of its background interference and high signal-to-noise ratio. In the past decade, the determination of Cu²⁺ in environment has attracted considerable attention since it plays an essential role in many physiological processes. Herein, a novel ECL sensor based on C,N quantum dots embedded g-C₃N₄ nanosheets (C,N-QDs@NSs) was constructed for the detection of Cu²⁺. The nanocomposite was rapidly obtained via the oxidation of normal g-C₃N₄ in H₂O₂ solution using sonochemical synthesizing method. Due to the abundant surface defects on C,N-QDs@NSs, the ECL intensity was magnified 2.5 times for using a C,N-QDs@NSs electrode in comparision to a g-C₃N₄ modified electrode. Besides, C,N-QDs@NSs could accelerate the rate of electron transfer in ECL reaction and thus resulted in the lower cathodic peak potential. Significantly, Cu²⁺ could effectively quench the ECL of C,N-QD@NSs, which endowed C,N-QD@NSs with a great advantage in the ECL detection of Cu²⁺. under optimum conditions, C,N-QDs@NSs modified electrode exhibited a linear detection range from 5 × 10^?4 to 10 µM with a detection limit of 2 × 10^?4 µM (S/N?=?3) for Cu²⁺, and was finally applied to detect Cu²⁺ in real samples with satisfactory results.     

Characterization and corrosion protection properties of cerium conversion coating on Gr<Subscript>(f)</Subscript>/Al composite surface

The aim of this work is to investigate corrosion protection properties of Ce conversion coating on the graphite fiber-reinforced aluminum matrix (Gr_(f)/Al) composite surface by electrochemical measurements, and microstructure of the Ce conversion coating was studied by scanning electron microscopy (SEM), energy dispersive X-ray (EDX), and X-ray photoelectron spectroscopy (XPS). It is found that the coating covers the whole surface of Gr_(f)/Al composites as oxidized islands, since there are some micro-cracks on the coating. The Ce conversion coating consists of Ce-rich nano-particles, and the contact sites between particles have some porosity. The porosity is not obvious during initial deposition, however, as deposition time prolonged development apparently. Moreover, some severe cracks may appear during the drying process, since evaporation of water molecules would cause shrinkage and large stress is induced. In addition, pretreatment of surface has an effect on the formation of cracks. Ce conversion coating has the composition of Ce³⁺ and Ce⁴⁺. Deposition of Ce-rich coating on Gr_(f)/Al composite surfaces shifts the polarization curves toward lower current density values. Electrochemical impedance spectroscopy (EIS) data show that Ce conversion coating improved corrosion resistance as compared with samples that have no coating.     

Electrical Conductivity and Viscosity of 1-Hexyl-3-methylimidazolium Bis(trifluorosulfonyl)imide, [C<Subscript>6</Subscript>mim] [(CF<Subscript>3</Subscript>SO<Subscript>2</Subscript>)<Subscript>2</Subscript>N] (CAS-RN# 382150-50-7)

The electrical conductivity and viscosity of 1-hexyl-3-methylimidazolium bis(trifluorosulfonyl)imide, [C₆mim] [(CF₃SO₂)₂N], were measured at atmospheric pressure, between 270 K and 350 K, for samples with an amount of water not exceeding 200 ppm, as part of International Union of Pure and Applied Chemistry Project 2002-005-1-100. Water content was monitored before and after measurements, by coulometric Karl–Fisher titration. Special care was taken with ionic liquid manipulation in view of the measurement uncertainty budget. The uncertainties of the electrical conductivity measurements and of the viscosity measurements are estimated to be better than 2.0 % and 0.5 %, respectively. Results were compared with data from other authors, and all data were correlated as a function of temperature.     

Optical band gap in the system ZnO<Subscript>1 – <Emphasis Type="Italic">x</Emphasis></Subscript>S<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>. An experimental and quantum chemical study

The synthesis of single crystalline and polycrystalline material is reported in the system ZnO_{1 – x} S _x . Substitution of oxygen by sulphur yields hexagonal wurtzite-type mixed crystals in the range 0 ≤ x ≤ 0.05. The cubic zincblende structure is observed for oxygen incorporation into ZnS for 0.96 ≤ x ≤ 1. At intermediate compositions, the system is two-phase. For both types of anion substitution, the band gap energies, as determined from optical transmission and remission experiments, are found to decrease from the pure end members. Quantum chemical calculations at density functional level identify local structural changes as the main factor responsible for the reduction of band gap energies.     

Cesium and Its Analogs,Rubidium and Potassium,in Rhombohedral [NaZr<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> Type] and Cubic (Langbeinite Type) Phosphates: 1. Crystal-Chemical Studies

The published crystallographic data on cesium, rubidium, and potassium phosphates crystallizing in the NaZr₂(PO₄)₃ (NZP) and langbeinite structural types are summarized and correlated. The existence of new phosphates, analogs of langbeinite mineral, is predicted. The phosphates of the suggested compositions are prepared and studied by X-ray and neutron diffraction and by IR spectroscopy. Phosphates of the formulas A₂RM(PO₄)₃, A₂B_0.5Zr_1.5(PO₄)₃, and ABR₂(PO₄)₃ have a cubic cell, space group P2₁3. The unit cell parameters of the phosphates in these series vary only slightly with variation of the cationic composition. Variations in the bond lengths and bond angles in the langbeinite structure depending on the cation are estimated from the results of structural studies. Cesium can be incorporated in cubic framework phosphates in an amount of up to 38 wt %. The langbeinite structure is characterized by wide possibilities of isomorphous substitutions involving large alkali and alkaline-earth metal cations arranged in the framework voids and small cations of p, d, and f elements in oxidation states 2+, 3+, and 4+, arranged in the framework positions. A specific role of lanthanides in formation of the langbeinite-type framework is noted.__________Translated from Radiokhimiya, Vol. 47, No. 3, 2005, pp. 203–212.Original Russian Text Copyright © 2005 by A. Orlova, V. Orlova, Buchirin, Beskrovnyi, Kurazhkovskaya.     

Structural,Superconducting, and Magnetic Properties of Y<Subscript>1- <Emphasis Type="Italic">x</Emphasis></Subscript>Dy<Subscript>x</Subscript>Rh<Emphasis Type="Italic">4</Emphasis>B<Emphasis Type="Italic">4</Emphasis> Borides

Samples with nominal compositions Y_1-x Dy_xRh₄B₄ are prepared by argon-atmosphere arc melting. The phase composition of the samples and the elemental compositions of the individual phases present are determined by x-ray diffraction and electron-probe x-ray microanalysis. The results indicate that increasing the dysprosium content of the starting mixture increases the percentage of the magnetic phase and reduces that of the superconducting phase in the samples. The electrical resistivity, magnetic susceptibility, and magnetic moment of the samples are measured between 1.6 and 30 K (magnetic fields of up to 14 T). The magnetic phase present in the samples with 0.2 ≤ × ≤ is shown to undergo ferromagnetic ordering at T _magn ≃ 13–13.5 K. The samples with 0 ≤ × ≤ 0.6 contain a superconducting phase with T _c from 9.1 to 5.0 K. The superconducting and magnetic properties of the Y_0.6Dy_0.4Rh₄B₄ sample are examined in detail.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 6, 2005, pp. 676–681.Original Russian Text Copyright © 2005 by Burkhanov, Lachenkov, Kuz’micheva, Kovneristyi, Khlybov, Kostyleva, Tomilin.     

Influence of buffer surface preparation on the quality of Al<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Ga<Subscript>1-<Emphasis Type="Italic">x</Emphasis></Subscript>As/GaAs quantum wells studied by optical orientation experiments

Quantum well (QW) structures of Al _x Ga_1-x As/GaAs with x = 0.3 were characterized by photoluminescence spectroscopy (PL) with circularly polarized excitation at a temperature of 1.6 K. The samples contained three QWs with thickness of 7, 5, and 3 nm grown by molecular beam epitaxy (MBE) on a 500 nm thick buffer layer. Four samples with identical geometry but different surface treatments (in-situ etching the GaAs buffer with Cl₂ at different temperatures, and air-exposed buffer, respectively) were compared. The degree of circular polarization of the PL and its decrease in a magnetic field applied perpendicularly to the direction of propagation of light (Hanle effect) allows the determination of the interband lifetime τ and the spin lifetime τ _s of the electrons. These lifetimes were different in the different QWs and strongly depend on the growth procedure.