Gamma phases in Cu-Al alloys and the influence of a square shaped phase in the electrochemical behavior of a Cu-13.6wt% Al alloy

The electrochemical behavior of Cu-xAl alloys, with 11 wt%less than or equal to x less than or equal to 15wt%, in 0.5 M H2SO4 was studied by means of open-circuit potential decay measurements, quasi-stationary and fast cyclic voltammetry, and electrochemical impedance spectroscopy. Some of the alloys (x less than or equal to 14%), when quenched formed martensitic structures. Alloys with greater than or equal to 13% showed a little square-shaped phase when quenched from temperatures around 800 degrees C. It was observed that in sulfuric medium, these formations were dealuminized differently than the martensitic phase. The values of the rest potentials are more influenced by the heat treatment rather than by the alloy composition. An anodic Tafel slope of ca. 60 mV/decade was observed for all the alloys, independently of the heat treatment. This is explained in terms of a competition between two processes: copper oxidation and copper(I) deproportionation. In the cyclic voltammetric experiments it was observed an anodic current peak, related with copper oxidation with a possible formation of some interfacial species, and a cathodic current peak during the reverse potential scan, associated with the reduction of soluble species and/or of the film. The AC Impedance data were interpreted in terms of electric equivalent circuits.

Interaction between nitroheterocyclic compounds with beta-cyclodextrins: Phase solubility and HPLC studies

Chagas disease is a serious health problem for Latin America. Nitrofurazone (NF) and Hidroxymethylnitrofurazone (NFOH) are active against Trypanosoma cruzi. The effect of beta-cyclodextrin (beta-CD) and dimethyl-beta-cyclodextrin (DM-beta-CD) complexation on the UV absorption and retention time of nitrofurazone (NF) and its hydroxymethylated analog (NFOH) were studied in solution. The retention behavior was analyzed on a reversed phase C(18) column and the mobile phase used was acetonitrile-water (20/80 v/v), in which cyclodextrins (beta-CD or DM-beta-CD) were incorporated as a mobile phase additive. The decrease in the retention times of NF (or NFOH) with increasing concentration of HP-beta-CD enables the cleternnination of the complex stability constants by HPLC. A phase-solubility Study was performed. according to the method reported by Higuchi and Connors, to evaluate the changes of NF/NFOH in the complexation state, and the diagrams obtained suggested that it forms complexes with a stoichiometry of 1 : 1. This is an important Study for the characterization of potential formulations to be used as therapeutic options for the treatment of Chagas disease. (c) 2008 Elsevier B.V. All rights reserved.

Quantitative Phase Analyses Through The Rietveld Method with X-Ray Powder Diffraction Data of Heat-Treated Carbamazepine Form III

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Metallurgical evaluation of a copper-based alloy for dental castings.

The present study was designed to evaluate the metallurgical properties of an experimental, low-cost copper-zinc-aluminum-nickel alloy for dental castings. Some specimens were subjected to heat treatment after induction casting. The extent of corrosion was determined by measuring weight loss of specimens stored in a sodium sulfite solution. In the as-cast specimens, tests demonstrated the presence of three phases: the first consisted of copper-zinc-aluminum, the second was similar but lower in copper and aluminum, and the third consisted of an intermetallic compound of manganese-nickel-phosphorus. After heat treatment, the first phase remained relatively constant, the second was converted to Cu3Al, and the third increased in volume. The weight loss from the as-cast specimens was eight times that of the heat-treated specimens. It was concluded that the heat treatment substantially changed the microstructure and improved the corrosion resistance of the experimental alloy.

Thermal decomposition and stability in a series of tetrafluorborate copper(I) complexes

Tetrafluorborate copper(I) complexes containing acetonitrile, triphenylphosphine, 1,10-phenanthroline, 2,2′-bipyridine and 2-quinolinethiol have been prepared in order to study their thermal stabilities as a function of the ligands present. The characterization of the above compounds was carried out by elemental analysis and IR spectroscopy. Their thermal behaviour has been investigated and the final products were identified by X-ray powder diagrams. © 1995.

Influence of silver additions on the structure and phase transformation of the Cu-13 wt % Al alloy

The influence of silver additions on the structure and phase transformation of the Cu-13 wt % Al alloy was studied by differential thermal analysis, X-ray diffraction, scanning electron microscopy and energy dispersive analysis of X-rays. The results indicate that the presence of silver modifies the phase-stability field, the transition temperature and the structure of the alloy. These effects are more pronounced for silver concentrations up to 8 wt %.

Lead- and copper-complexing extracellular ligands released by Kirchneriella aperta (Chloroccocales, Chlorophyta)

The freshwater planktonic alga Kirchneriella aperta was grown in batch cultures to stationary growth phase. Copper and lead complexation properties of the exudate from stationary and exponential growth phases were determined by titrations monitored by ion-selective electrodes. Molecular weight fractionation dialysis) and analysis of the titration data (Scatchard Plot) revealed that K. aperta releases metal-complexing ligands. Copper is associated with low and high molecular weight compounds, whereas lead forms complexes with only high molecular weight compounds. Gas-liquid chromatography showed that mannose and rhamnose make up 74% of the total high molecular weight organic material, with uronic acids present at 19%.

Copper complexation by Cyanophyta and Chlorophyta exudates

Several freshwater phytoplanktonic species (eukaryotic and prokaryotic) were grown in batch cultures up to stationary phase and quantified by chlorophyll a analysis. The complexation properties (conditional stability constant and total ligand concentration) of their exudates were investigated by complexometric titrations of the culture media using either copper or lead ion-selective electrodes. For most algae, Scatchard plot analysis of the titration data revealed two classes of copper-complexing ligands, one weaker and the other stronger. Strong copper-complexing agents were produced by Cyanophyta mainly in stationary growth phase. During exponential phase, ligand concentrations and the affinity for copper were similar for both Chlorophyta and Cyanophyta. Complexation parameters for Chlorophyta exudates were similar for both growth phases: exponential and stationary. In contrast, ligand concentrations were similar for Cyanophyta, but the conditional stability constants (the strength of association between ligand and metal) were different. Weak lead-complexing ligands were produced exclusively by two Chlorophyta.

Minimization of lead and copper interferences on spectrophotometric determination of cadmium using electrolytic deposition and ion-exchange in multi-commutation flow system

A new strategy for minimization of Cu2+ and Pb2+ interferences on the spectrophotometric determination of Cd2+ by the Malachite green (MG)-iodide reaction using electrolytic deposition of interfering species and solid phase extraction of Cd2+ in flow system is proposed. The electrolytic cell comprises two coiled Pt electrodes concentrically assembled. When the sample solution is electrolyzed in a mixed solution containing 5% (v/v) HNO3, 0.1% (v/v) H2SO4 and 0.5 M NaCl, Cu2+ is deposited as Cu on the cathode, Pb2+ is deposited as PbO2 on the anode while Cd2+ is kept in solution. After electrolysis, the remaining solution passes through an AG1-X8 resin (chloride form) packed minicolumn in which Cd2+ is extracted as CdCl4/2-. Electrolyte compositions, flow rates, timing, applied current, and electrolysis time was investigated. With 60 s electrolysis time, 0.25 A applied current, Pb2+ and Cu2+ levels up to 50 and 250 mg 1-1, respectively, can be tolerated without interference. For 90 s resin loading time, a linear relationship between absorbance and analyte concentration in the 5.00-50.0 μg Cd 1-1 range (r2 = 0.9996) is obtained. A throughput of 20 samples per h is achieved, corresponding to about 0.7 mg MG and 500 mg KI and 5 ml sample consumed per determination. The detection limit is 0.23 μg Cd 1-1. The accuracy was checked for cadmium determination in standard reference materials, vegetables and tap water. Results were in agreement with certified values of standard reference materials and with those obtained by graphite furnace atomic absorption spectrometry at 95% confidence level. The R.S.D. for plant digests and water containing 13.0 μg Cd 1-1 was 3.85% (n = 12). The recoveries of analyte spikes added to the water and vegetable samples ranged from 94 to 104%. (C) 2000 Elsevier Science B.V.

Kinetics of martensitic phase decomposition in the Cu-10wt.%Al alloy with Ag additions

The study of the kinetics of martensitic phase decomposition in the Cu-10wt.%Al alloy with Ag additions showed that the presence of Ag retarded the eutectoid decomposition reaction and enhanced martensite stabilization. This stabilization effect was attributed to Ag atoms redistribution as structure defects, increase in the numbers of Cu-Al pairs due to Ag-Al interaction and the Al atoms redistribution around one Cu atom at the sub-lattice of the martensitic crystal. © 2008 Trans Tech Publications.

On the electrochemical behavior of Cu-16%Zn-6.5%Al alloy containing the β'-phase (martensite) in borate buffer

In this work, the electrochemical behavior of Cu-16(wt.%)Zn-6.5(wt.%)Al alloy containing the β'-phase (martensite) was studied in borate buffer solution (pH 8.4) by means of open-circuit potential (EOC), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The alloy EOC was -0.29 V vs. Hg/HgO/OH-, similar to that of pure copper in this medium, indicating that the processes which occur on the alloy surface are mainly governed by copper. EIS response was related to the dielectric and transmission properties of the complex oxide layer. The CVs showed peaks concerning the redox reactions for copper and zinc. These peaks were assigned to the formation and reduction of copper and zinc species. Furthermore, they showed that the copper oxidation was suppressed by the presence of zinc and aluminum in the alloy composition. The copper and zinc oxidation to form complex oxide layers and the reduction of the different metallic oxides generated in the anodic potential scan suggest that a solid state reaction could determine the metallic oxide formation. © 2013 Elsevier Ltd. All rights reserved.

XAS/WAXS time-resolved phase speciation of chlorine LDH thermal transformation: Emerging roles of isovalent metal substitution

The XAS/WAXS time-resolved method was applied for unraveling the complex mechanisms arising from the evolution of several metastable intermediates during the degradation of chlorine layered double hydroxide (LDH) upon heating to 450 °C, i.e., Zn2Al(OH)6·nH2O, ZnCuAl(OH)6·nH2O, Zn2Al 0.75Fe0.25(OH)6·nH2O, and ZnCuAl0.5Fe0.5(OH)6·nH2O. After a contraction of the interlamellar distance, attributed to the loss of intracrystalline water molecules, this distance experiences an expansion (T > 175-225 °C) before the breakdown of the lamellar framework around 275-295 °C. Amorphous prenucleus clusters with crystallo-chemical local order of zinc-based oxide and zinc-based spinel phases, and if any of copper-based oxide, are formed at T > 175-225 °C well before the loss of stacking of LDH layers. This distance expansion has been ascribed to the migration of Zn II from octahedral layers to tetrahedral sites in the interlayer space, nucleating the nano-ZnO or nano-ZnM2O4 (M = Al or Fe) amorphous prenuclei. The transformation of these nano-ZnO clusters toward ZnO crystallites proceeds through an agglomeration process occurring before the complete loss of layer stacking for Zn2Al(OH)6· nH2O and Zn2Al0.75Fe0.25(OH) 6·nH2O. For ZnCuAl(OH)6·nH 2O and ZnCuAl0.5Fe0.5(OH)6· nH2O, a cooperative effect between the formation of nano-CuO and nano-ZnAl2O4 amorphous clusters facilitates the topochemical transformation of LDH to spinel due to the contribution of octahedral CuII vacancy to ZnII diffusion. © 2013 American Chemical Society.

Writing saturated holograms in LiNbO3 crystals through phase control and double diffraction

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Determination of tetramethylthiuram disulfide (thiram) for residual analysis in food using spectrophotometry coupled with a solid-phase reactor (SPR) in a flow system

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Estudo da deformação heterogênea no ensaio do anel de atrito

The plastic deformation is widely used in the metallurgical market due to its positive factors such as low prices and high speed production. Forming process products are obtained in high quality, both surface quality and mechanical properties. Friction is an importante factor in metal forming. Friction study in metal forming can be accomplished indirectly, such as the ring test of friction. Two samples of different materials being mild steel and copper alloy were used. The results showed the influence of friction in the flow behavior of the deformation of the second phase, as evidenced by standard metallography. It is observed that in the outer regions of the ring, plastic deformation occured in the radial direction. In the central region of the disc deformation occured in the direction of compression and the inner region of the ring flux lines showed a significant deformation in the radial direction towards the center of the ring