Laser weld: microstructure and corrosion study of Ag-Pd-Au-Cu alloy of the dental application

The laser Welding process was introduced into dentistry by the end of the 1980s, resulting on a great impulse to that area with the development of cheaper and smaller equipment, using simpler technique. This allowed greater use of that process on the confection of prostheses compared to the brazing process since the heat source for that process is a concentrated light beam of high power, which minimizes distortion problems on the prosthetic pieces. Ag-Pd-Au-Cu alloy used on the confection of dental implant prostheses was observed before and after subjection to the laser welding process. The microstructure was analyzed with the. use of optic microscopy and the corrosion resistance was studied by the traditional electrochemical techniques and by electrochemical impedance, under environmental conditions simulating the aggressiveness found in the mouth cavity. A structural change was detected on the weld area, which presented a refined microstructure deriving from the high-speed cooling. The base metal out of the weld area presented a fusion coarse microstructure. The electrochemical essays showed differences on the potentiodynamic polarization behavior in both weld and metal base areas, indicating superior corrosion resistance in the weld area. The impedance spectra were characterized by capacitive distorted components, presenting linear impedance in the low frequencies area. (C) 2002 Elsevier B.V. B.V. All rights reserved.

Direct determination of Al, As, Cu, Fe, Mn, and Ni in fuel ethanol by simultaneous GFAAS using integrated platforms pretreated with W-Rh permanent modifier together with Pd plus Mg modifier

A method is proposed for the simultaneous determination of Al, As, Cu, Fe, Mn, and Ni in fuel ethanol by electrothermal atomic absorption spectrometry (ETAAS) using W-Rh permanent modifier together with Pd(NO3)(2) + Mg(NO3)(2) conventional modifier. The integrated platform of a transversely heated graphite atomizer (THGA) was treated with tungsten, followed by rhodium, forming a deposit containing 250 mug W + 200 mug Rh. A 500-muL, volume of fuel ethanol was diluted with 500 muL, of 0.14 mol L-1 HNO3 in an autosampler cup of the spectrometer. Then, 20 muL, of the diluted ethanol was introduced into the pretreated graphite platform followed by the introduction of 5 mug Pd(NO3)(2) + 3 mug Mg(NO3)(2). The injection of this modifier was required to improve arsenic and iron recoveries in fuel ethanol. Calibrations were carried out using multi-element reference solutions prepared in diluted ethanol (1 + 1, v/v) acidified to 0. 14 mol L-1 HNO3. The pyrolysis and atomization temperatures of the heating program were 1200degreesC and 2200degreesC, respectively, which were obtained with multielement reference solutions in acidic diluted ethanol (1 + 1, v/v; 0. 14 mol L-1 HNO3). The characteristic masses for the simultaneous determination in ethanol fuel were 78 pg Al, 33 pg As, 10 pg Cu, 14 pg Fe, 7 pg Mn, and 24 pg Ni. The lifetime of the pretreated tube was about 700 firings. The detection limits (D.L.) were 1.9 mug L-1 Al, 2.9 mug L-1 As, 0.57 mug L-1.Cu, 1.3 mug L-1 Fe, 0.40 mug L-1 Mn, and 1.3 mug L-1 Ni. The relative standard deviations (n = 12) were 4%, 4%, 3%, 1.5%, 1.2%, and 2.2% for Al, As, Cu, Fe, Mn, and Ni, respectively. The recoveries of Al, As, Cu, Fe, Mn, and Ni added to the fuel ethanol samples varied from 81% to 95%, 80% to 98%, 97% to 109%, 85% to 107%, 98% to 106% and 97% to 103%, respectively. Accuracy was checked for the Al, As, Cu, Fe, Mn, and Ni determination in 10 samples purchased at a local gas station in Araraquara-SP City, Brazil. A paired t-test showed that at the 95% confidence level the results were in agreement with those obtained by single-element ETAAS.

Electrochemical studies with a Cu-5wt.%Ni alloy in 0.5 M H2SO4

The electrochemical behavior of the annealed Cu-5wt.%Ni alloy in 0.5 M H2SO4 was studied by means of open-circuit potential (E-OCP) measurements, cyclic voltammetry, electrochemical impedance spectroscopy (EIS), and quasi-stationary linear potential sweep. The hydrodynamics of the system was also studied. This material is constituted by a single a, phase. The anodic behavior of a Cu-Ni alloy in H2SO4 consists fundamentally on the electrodissolution of Cu, its main component, and the formation of a sulfur-containing passive layer. The presence of Ni decreases the rate of Cu oxidation, mostly at high positive potentials. The impedance spectra, obtained for the unrotating electrode, can be interpreted in terms of a simple charge-transfer reaction across a surface layer. When the electrode is rotated, the occurrence of an inductive loop evidenced the existence of an adsorbed layer. All the resistance estimated from the proposed equivalent circuits diminished with the electrode rotation rate, emphasizing the influence of ion transport in the overall electrode process. The system presented two anodic Tafel slopes: 40 mV dec(-1) for E < 255 mV and 67 mV dec(-1) for E > 275 mV. A Tafel slope of 40 mV dec(-1) evidences that copper dissolution can be interpreted in terms of the mechanism proposed by Mattsson and Bockris. The second Tafel suggests that at potentials more positive than 275 mV, copper dissolves according to a mechanism that considers the disproportionation of adsorbed Cu(1) species. (C) 2003 Elsevier Ltd. All rights reserved.

Use of diffusive gradients in thin films and tangential flow ultrafiltration for fractionation of Al(III) and Cu(II) in organic-rich river waters

Diffusive gradients in thin films (DGT) and tangential-flow ultrafiltration (TF-UF) were combined for fractionation of Al and Cu in river water containing high content of dissolved organic carbon. A procedure based on ultrafiltration data is proposed to determine diffusion coefficients of the analytes in water samples and model solutions containing both free metal (M) and complex (metal - humic substance). Aiming to evaluate the accuracy of the proposed approach, the DGT results were compared with those from a protocol for determination of labile Al and Cu based on solid phase extraction (SPE). Good agreement between data from DGT and SPE were attained for model solutions. For analysis of real organic-rich water samples, differences between DGT and SPE measurements were consistent with the time-scales of the techniques. The concentration of labile Al determined by DGT were lower than the total dissolved concentrations (determined by inductively coupled plasma mass spectrometry) and exceeded the ultrafiltered concentration, indicating that inorganic Al species (species small enough to pass through 1 kDa membrane) were minor species as compared with Al organic complexes. For both Al and Cu, there were species not measured by DGT as they are not sufficiently labile. (C) 2007 Elsevier B.V. All rights reserved.

A NEW CU-BASED SMA WITH EXTREMELY HIGH MARTENSITIC-TRANSFORMATION TEMPERATURES

A new series of high temperature copper based shape memory alloys has recently been patented. These alloys contain 8-20 wt% Al, 1-20 wt% Ag, 0-2 wt% of a minor element (preferably Co), balance copper. The martensitic start transformation temperatures of these alloys are above 200 degrees C and, in some cases, they have good high temperature stability and may be useful in commercial applications where higher operating temperatures than those obtained from Cu-Zn-Al and Cu-Al-Ni shape memory alloys are required.

Synthesis, characterization and thermal behavior of complexes of Cu(II), Zn(II) and Cd(II) with S,S '-methylenebis(cysteine)

Synthesis and characterization, including data on thermal decomposition, are reported for the complexes of S,S'-methylenebis(cysteine) (djenkolic acid) with copper(II), zinc(II) and cadmium(II): CuC(7)H(12)N(2)O(4)S(2) [I]; ZnC(7)H(12)N(2)O(4)S(2) [II] and CdC(7)H(12)N(2)O(4)S(2) [III] X-ray diffraction showed that the compounds are isostructural and belong to a monoclinic system. According to IR spectra, COO, NH(2) groups and bridging sulfur atoms are the main coordination sites.

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.

Flow injection AAS determination of Cd, Cu, and Pb at trace levels in wine using solid phase extraction

A comparative study is reported between C-18 bonded silica gel and powdered polyethylene (PE) as sorbent for Cd, Cu, and Pb determination using ammonium diethyldithiophosphate (ADTP) as the complexing agent in a flow injection system. The complexes were formed in 0.14 mol L-1 HNO3 and processed in a simple flow system comprising a peristaltic pump, a manual injector-commutator, and a sorbent-packed minicolumn. Ethanol was selected as the eluent and analytes in the eluate were determined by flame atomic absorption spectrometry. The optimum concentration of the complexing agent was 0.1% (m/v) ADTP for Cu and Pb determination using either C-18 or PE, and 0.25% (m/v) ADTP for Cd determination using PE. The sample loading flow rates were 5.0, 3.6, and 3.0 mL min(-1) for Cu, Pb, and Cd, respectively. The best elution flow rate was 6.5 mL min(-1). For a 60-sec preconcentration time, the sampling rate was 40 h(-1) and the enrichment factors of 33, 36, and 11 times (C-18) or 18, 22, and 23 times (PE) were obtained for Cu, Pb, and Cd, respectively. The limits of detection (LOD) were 1.6 mug L-1 Cu, 11 mug L-1 Pb, and 2.0 mug L-1 Cd using C-18 or 2.9 mug L-1 Cu, 19 mug L-1 Pb, and 1.0 mug L-1 Cd using PE, respectively. The relative standard deviations (n = 12) were typically <2%, <2%, and <6% for Cd, Cu, and Pb, respectively. The recoveries of Cd, Cu, and Pb added to wine samples varied from 96-99%, 97-102%, and 90-99%, respectively, using C-18 or PE. Accuracy was checked for Cd, Cu, and Pb determination in six wine samples digested by block digestor and open-vessel microwave-assisted digestion systems. The results revealed that C-18 was more efficient for Cu and Pb determination, while PE was the best sorbent for Cd.

Thermal behavior of alpha-(Cu-Al-Ag) alloys

Thermal behavior of alpha-(Cu-Al-Ag) alloys, i.e. alloys with composition less than about 8.5 mass% Al, was studied using differential scanning calorimetry (DSC), differential thermal analysis (DTA), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and X-ray diffractometry (XRD). The results indicated that the presence of silver introduces new thermal events ascribed to the formation of a silver-rich phase and, after addition higher amounts than 8 mass% Ag to the Cu-8 mass% Al alloy it is possible to observe the formation of the gamma(1) phase (Al4Cu9), which is only observed in alloys containing minimum of 9 mass% Al. These results may be attributed to some Ag characteristics and its interaction with Cu and Al.

Effect of Ag concentration on the thermal behavior of the Cu-10 mass% Al and Cu-11 mass% Al alloys

In this work the effect of Ag concentration on the thermal behavior of the Cu-10 mass% Al and Cu-11 mass% Al alloys with additions of 4, 6, 8 and 10 mass% Ag was studied using differential scanning calorimetry (DSC), in situ X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The results showed that for the Cu-10 mass% Al alloy Ag addition induce the beta'(1) phase formation and for the Cu-11 mass% Al alloy these additions increase the amount of martensite formed on quenching and decrease the stability range of this phase on heating.

Thermal behavior of the Cu-22.55 at.%Al alloy with small Ag additions

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

Completeness of beta-phase decomposition reaction in Cu-Al-Ag alloys

The completeness of beta-phase decomposition reaction in the Cu-11wt%Al-xwt%Ag alloys (x = 0, 1, 2, and 3) was studied using differential scanning calorimetry (DSC), X-ray diffractometry (XRD), and optical microscopy (OM). The results indicated that beta-phase transformations are highly dependent on cooling rate and on the presence of Ag. on slow cooling, the silver presence prevents the beta- and beta(1)-phase decomposition; thus, inducing the martensitic phase formation. After rapid cooling, a new thermal event is observed and the reverse martensitic transformation is shifted to lower temperatures.

SAE 1045 steel/WC-Co/Ni-Cu-Ni/SAE 1045 steel joints prepared by dynamic diffusion bonding: Microelectrochemical studies in 0.6 M NaCl solution

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

Paper-based diffusive gradients in thin films technique coupled to energy dispersive X-ray fluorescence spectrometry for the determination of labile Mn, Co, Ni, Cu, Zn and Pb in river water

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