Electrochemical studies of copper-aluminum-silver alloys in 0.5 M H2SO4

The electrochemical behavior in 0.5 M H2SO4 at 25 degreesC of a Cu-Al(9.3 wt%)-Ag(4.7 wt%) alloy submitted to different heat treatments and an annealed Cu- Al(9.7 wt%)-Ag(34.2 wt%) were studied by means of open circuit potential (E-mix) measurements, potentiodynamic polarizations and cyclic voltammetry. SEM and EDX microanalysis were used to examine the changes caused by the electrochemical perturbations. The steady state potentials observed for the studied samples were correlated in terms of the phases present in the alloys surface. The resulting E/I potentiodynamic profiles were explained in terms of the potentiodynamic behavior of pure copper and pure silver. The presence of aluminum decreased the extent of copper oxidation. In the apparent Tafel potential region, two anodic Tafel slopes were obtained: 40 mV dec(-1) in the low potential region and 130 mV dec(-1) in the high potential region, which were related with the electrochemical processes involving copper oxidation. (C) 2001 Elsevier B.V. Ltd. All rights reserved.

WC-CoCr coatings sprayed by high velocity oxygen-fuel (HVOF) flame on AA7050 aluminum alloy: electrochemical behavior in 3.5% NaCl solution

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

Prospecting sugarcane genes involved in aluminum tolerance

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

Clustering of rare earth in glasses, aluminum effect: experiments and modeling

Luminescent spectra of Eu3+-doped sol-gel glasses have been analyzed during the densification process and compared according to the presence or not of aluminum as a codoping ion. A transition temperature from hydrated to dehydroxyled environments has been found different for doped and codoped samples. However, only slight modifications have been displayed from luminescence measurements beyond this transition. To support the experimental analysis, molecular dynamics simulations have been performed to model the doped and codoped glass structures. Despite no evidence of rare earth clustering reduction due to aluminum has been found, the modeled structures have shown that the luminescent ions are mainly located in aluminum-rich domains. The synthesis of both experimental and numerical analyses has lead us to interpret the aluminum effect as responsible for differences in structure of the luminescent sites rather than for an effective dispersion of the rare earth ions. (C) 2004 Elsevier B.V. All rights reserved.

Coating residual stress effects on fatigue performance of 7050-T7451 aluminum alloy

The tendency of the aircraft industry is to enhance customer value by improving performance and reducing environmental impact. In view of availability, aluminum alloys have a historically tendency to faster insertion due to their lower manufacturing and operated production infrastructure. In landing gear components, wear and corrosion control of many components is accomplished by surface treatments of chrome electroplating on steel or anodizing of aluminum. One of the most interesting environmentally safer and cleaner alternatives for the replacement of hard chrome plating or anodizing is tungsten carbide thermal spray coating, applied by the high velocity oxy fuel (HVOF) process. However, it was observed that residual stresses originating from these coatings reduce the fatigue strength of a component.An effective process as shot peening treatment, considered to improve the fatigue strength, pushes the crack sources beneath the surface in most of medium and high cycle cases, due to the compressive residual stress field induced. The objective of this research is to evaluate a tungsten carbide cobalt (WC-Co) coating applied by the high velocity oxy fuel (HVOF) process, used to replace anodizing. Anodic films were grown on 7050-T7451 aluminum alloy by sulfuric acid anodizing, chromic acid anodizing and hard anodizing. The influence on axial fatigue strength of anodic films grown on the aluminum alloy surface is to degrade the stress-life performance of the base material. Three groups of specimens were prepared and tested in axial fatigue to obtain S-N curves: base material, base material coated by HVOF and base material shot peened and coated.Experimental results revealed increase in the fatigue strength of Al 7050-T7451 alloy associated with the WC 17% Co coating. on the other hand, a reduction in fatigue life occurred in the shot peened and coated condition. Scanning electron microscopy technique and optical microscopy were used to observe crack origin sites, thickness and coating/substrate adhesion. (c) 2007 Elsevier B.V. All rights reserved.

Evaluation of subsurface dentin microhardness after Er : yttrium-aluminum-garnet and Nd : yttrium-aluminum-garnet laser irradiation

Background and objectives: To assess the microhardness of dentin subsurface after Er:yttrium-aluminum-garnet (YAG) and Nd:YAG laser irradiation. Study design/materials and methods: Twenty-four bovine incisors, without pulp, were used. The vestibular surface was worn out until the dentin was reached and divided in mesial and distal regions. The samples were divided into two groups: GI-distal, irradiated by Er: YAG laser, and GII-distal, irradiated by Nd: YAG laser. The mesial area was protected so as to not receive the laser irradiation. The measurements were made on Vickers digital microhardmeter. Results: For GI-there was no significant statistical difference, Cl(-4.59 to 0.78), between the values of irradiated (55.61 +/- 4.38) and unirradiated (57.51 +/- 4.00) areas. For GII-the values were higher for the irradiated (62.21 +/- 6.48) compared to the unirradiated (57.82 +/- 5.42) area, CI(1.65 +/- to 7.13). Conclusions: There was an increase of dentin microhardness when the Nd: YAG was used, but the Er: YAG did not cause significant alterations in dentin microhardness. (c) 2007 Laser Institute of America.

Mapping QTLs for aluminum tolerance in maize

Aluminum toxicity is one of the major constraints for plant development in acid soils, limiting food production in many countries. Cultivars genetically adapted to acid soils may offer an environmental compatible solution, providing a sustainable agriculture system. The aim of this work was to identify genomic regions associated with Al tolerance in maize, and to quantify the genetic effects on the phenotypic variation. A population of 168 F-3:4 families derived from a cross between two contrasting maize inbred lines for Al tolerance was evaluated using the NSRL and RSRL parameters in nutrient solution containing toxic level of aluminum. Variance analyses indicated that the NSRL was the most reliable phenotypic index to measure Al tolerance in the population, being used for further QTL mapping analysis. RFLP and SSR markers were selected for bulked segregant analysis, and additional SSR markers, flanking the polymorphisms of interest, were chosen in order to saturate the putative target regions. Seven linkage groups were constructed using 17 RFLP and 34 SSR markers. Five QTLs were mapped on chromosomes 2, 6 and 8, explaining 60% of the phenotypic variation. QTL(4) and marker umc043 were located on chromosomes 8 and 5, close to genes encoding for enzymes involved in the organic acids synthesis pathways, a widely proposed mechanism for Al tolerance in plants. QTL(2) was mapped in the same region as Alm2, also associated with Al tolerance in maize. In addition, dominant and additive effects were important in the control of this trait in maize.

Mullite whiskers grown from erbia-doped aluminum hydroxide-silica gel

Mullite whiskers and anisotropic grains that were derived from erbia-doped aluminum hydroxide-silica gel were studied. Firing 3.0-mol%-erbia-doped isostatically pressed pellets at 1600 degrees C for 1.0-8.0 h resulted in a high surface concentration of mullite whiskers. Their c-axes were aligned preferentially along the pellet surface; the maximum length was 50 mu m, and the maximum aspect ratio was 23. The pellet surface was fully covered by mullite whiskers, and small anisotropic grains with a low aspect ratio were observed in the bulk. The voids that were observed in the fracture surfaces were covered fully by mullite whiskers. The large number of voids resulted in an apparent density of 1.60 g/cm(3) in the sintered pellets. The molar ratio of alumina to silica in the whiskers was in the range of 1.30-1.45 tan average value of 1.31), regardless of whether the alumina/silica powder compositions were mixed in a 3:2 or 2:1 ratio.

Mutagenic activity in waste from an aluminum products factory in Salmonella/microsome assay

The mutagenic activity of waste material originating from an aluminum products factory was determined by the Salmonella/microsome assay, using the bacterial strains TA100, TA98 and YG1024. The material was obtained by sweeping the factory floor at the end of the work shift. Organic compounds were extracted by ultrasound for 30 min in dichloromethane or 70% ethanol. After evaporation of solvent, these extracts were dissolved in dimethylsulfoxide, and tested for the mutagenic activity at varying concentrations. All the extracts from the factory had mutagenic activity, especially in the YG1024 strain, suggesting the presence of aromatic amines, later confirmed by chemical analysis. The TA98 strain also showed mutagenic activity, though it did not exhibit the highest mutagenicity index observed with the YG1024 strain. In TA100, mutagenic activity was not observed. This study should serve as an alert to management and those who are occupationally exposed, and as a warning that this type of waste should not be discarded in the environment without any control. (C) 2004 Elsevier Ltd. All rights reserved.

INHIBITION OF BOVINE BRAIN ACETYLCHOLINESTERASE BY ALUMINUM

We report the in vitro inhibitory effect of very low concentrations of aluminum salts (IC50 = 4.1 X 10(-12)M) on bovine brain acetylcholinesterase (AChE). The enzymatic assays were performed using acetylcholine bromide in a buffered pH 7.4 solution at 37 degrees C. The relevant enzyme interacting species is the Al3+ ion, whose concentrations were fixed at pM levels by a citrate metal ion buffer system. The IC50 demonstrates that Al3+ is a potent inhibitor of AChE.