Cyclic oxidation processes during anodizing of Al-Cu alloys

The influence of copper on the morphologies of porous anodic alumina has been investigated under current and voltage control using a sputtering-deposited Al-2.7 at.% Cu alloy and a commercial AA 2024-T3 aluminium alloy anodized in either sulphuric acid electrolyte or the same electrolyte but with addition of tartaric acid. The findings indicate that film development involves repeated formation of embryo cells of anodic alumina at the metal/film interface. During the initial stages of anodizing at constant voltage, cell formation is accompanied by current peaks in the current-time response. The porosity of the resultant films has a lateral aspect due to the layering of embryo cells. The thickness of individual layers is proportional to the formation voltage, with a ratio of the order 1 nm V⁻¹. The cell formation is accompanied by enrichment of copper in the alloy, incorporation of copper species into the anodic film, in low amounts relative to the alloy, and evolution of oxygen. These processes disrupt the formation of the classical pore morphology, characteristic of high purity aluminium, due to continuous formation of fresh embryo cells and re-direction of pores. The main effect of the tartaric acid addition to the sulphuric acid was to reduce the rate of anodizing of the alloys at constant voltage by about 10-20%.     

Effect of seed maturity on seed oil,fatty acid and crude protein content of eightCuphea species

Thirty-six lots of eightCuphea species grown at nine geographical locations from 1983 to 1985 were analyzed for seed weight, oil percentage, fatty acid and crude protein content. Twenty-two samples were separated into two distinct seed maturity groups and also analyzed. Seed maturity varied widely but had little effect on oil percentage, even though mature seeds were significantly heavier than less mature seeds. Lauric acid content generally increased and capric acid decreased with increasing seed maturity. Crude protein of whole seeds and defatted seed meal increased with increasing seed maturity. The net effect of harvestingCuphea wrightii seeds at full maturity in comparison with that for less mature seeds was to increase seed weight by 12%, decrease capric acid by 3%, increase lauric acid by 2% and increase crude protein of whole seeds and defatted meal by 5% and 4%, respectively. Seed oil content was decreased by a statistically nonsignificant 1%. The effect of seed maturity was comparable for the other four lauric acid- and three capric acid-rich species, even though distinct species differences in all factors were measured. Location and environment contributed to some quantitative and qualitative changes, but these factors are not considered to be major sources of variation. It is concluded that variation in seed maturity does not present a major constraint to commercialization ofCuphea as a new, alternative source of lauric and other medium-chain fatty acids. The ultimate significance of these minor changes will depend upon relative yields, demands and values of the various seed components.     

Rheology studies of polyethylene/chemical blowing agent solutions within an injection molding machine

An in‐line capillary rheometer nozzle equipped to a conventional reciprocating 55‐ton injection molding machine was used to study the viscosity of single phase low density polyethylene (LDPE)/chemical blowing agent (CBA) solutions under high shear rate in the concentration range of 0 to 5 wt%. The steady shear viscosity of LDPE with endothermic and exothermic chemical blowing agents was measured for shear rates ranging from 170 to 200,000 s^?1 and under pressure conditions up to 36 MPa. Pressure‐volume‐temperature (pvT) measurements were determined to account for the pressure effects and the changes of the free volume during processing. The viscosity reduction of the polymer‐CBA solution was found to be dependent on the concentration of the chemical blowing agent and melt pressure. A model based on a simplified Cross‐Carreau model, incorporating the pvT behavior of LDPE, and the free volume concept was proposed to estimate the viscosity reduction resulting from the addition of a chemical blowing agent. The model employs a scaling method based on concentration‐dependent and pressure‐dependent shift factors to collapse the viscosity measurement to a master curve at each temperature. POLYM. ENG. SCI., 45:1108–1118, 2005. © 2005 Society of Plastics Engineers     

Testing a short-term feeding trial to assess compositional and histopathological changes in hearts of rats fed vegetable oils

Male, female and castrated rats, three wk of age, were fed a low-fat diet for 14 wk followed by high-fat diets (20% by weight) for one wk containing graded levels of erucic acid from 1 to 50%, to evaluate the effect of short-term feeding and interaction of male sex hormones on formation of heart lesions. Some rats within each group were returned to the low-fat diet for one wk after the test period. For comparison, one group of three-wk-old male rats was fed the high fat 50% erucic acid diet for 15 wk. Erucic acid depressed growth rate and food consumption and increased cardiac lipidosis and triglycerides proportional to the erucic acid content of the diet. There were no sex differences, and the effects disappeared once rats were returned to the low-fat diet for one week. There was a significance (P<0.05) in the incidence of myocardial necrosis among male rats fed increased levels of erucic acid for one week, but the response was not linear to the increase in dietary erucic acid. Furthermore, the response was much less than in males fed the 50% erucic acid diet continually for 15 weeks. These results suggest that the short-term model is not a suitable substitute for the long-term feeding trial to test the cardiopathogenicity of a vegetable oil. The significantly lower incidence in myocardial lesions in female and castrated male rats compared with male rats suggests involvement of sex hormones. However, the process appears to be long term, since changes in cardiac lipids and their fatty acid pattern between sexes became evident after one wk on diet but was significant only after long-term feeding. Deceased.     

Quantitating heart lipids: Comparison of results obtained using the Iatroscan method with those from phosphorus and gas chromatographic techniques

The precision and accuracy of the Iatroscan method was evaluated by comparing the results obtained with established phosphorus and gas chromatographic techniques. A complete lipid class analysis of rat heart lipids was chosen in order to evaluate the performance of the Iatroscan method for biological samples which contained both neutral lipids and phospholipids. A partial scan and repeat development with chloroform/methanol/water (68.5∶29∶2.5) was introduced to achieve consistently good separations of the phospholipids on the Chromarods in the Iatroscan method. The results showed that the precision of the Iatroscan method for some lipid classes was comparable to that of phosphorus or gas chromatographic techniques, while for other lipid classes it was lower. Compared to the data obtained using the phosphorus method, the Iatroscan data were generally similar, while the gas chromatographic method generally gave lower values. These findings, together with the advantages of time required for analysis, size of sample, and universality of detection, suggest that the Iatroscan is a valuable complementary method for complex lipid analyses.     

Defense Suppression through Interplant Communication Depends on the Attacking Herbivore Species

In response to herbivory, plants emit volatile compounds that play important roles in plant defense. Herbivore-induced plant volatiles (HIPVs) can deter herbivores, recruit natural enemies, and warn other plants of possible herbivore attack. Following HIPV detection, neighboring plants often respond by enhancing their anti-herbivore defenses, but a recent study found that herbivores can manipulate HIPV-interplant communication for their own benefit and suppress defenses in neighboring plants. Herbivores induce species-specific blends of HIPVs and how these different blends affect the specificity of plant defense responses remains unclear. Here we assessed how HIPVs from zucchini plants (Cucurbita pepo) challenged with different herbivore species affect resistance in neighboring plants. Volatile “emitter” plants were damaged by one of three herbivore species: saltmarsh caterpillars (Estigmene acrea), squash bugs (Anasa tristis), or striped cucumber beetles (Acalymma vittatum), or were left as undamaged controls. Neighboring “receiver” plants were exposed to HIPVs or control volatiles and then challenged by the associated herbivore species. As measures of plant resistance, we quantified herbivore feeding damage and defense-related phytohormones in receivers. We found that the three herbivore species induced different HIPV blends from squash plants. HIPVs induced by saltmarsh caterpillars suppressed defenses in receivers, leading to greater herbivory and lower defense induction compared to controls. In contrast, HIPVs induced by cucumber beetles and squash bugs did not affect plant resistance to subsequent herbivory in receivers. Our study shows that herbivore species identity affects volatile-mediated interplant communication in zucchini, revealing a new example of herbivore defense suppression through volatile cues.

     

Generation of copper nanoparticles during alkaline etching of an Al-30 at.%Cu alloy

A mechanism of formation of copper nanoparticles is proposed for alkaline etching of a sputtering-deposited Al-30 at.%Cu alloy, simulating the equilibrium θ phase of 2000 series aluminium alloys. Their formation involves enrichment of copper in the alloy beneath a thin alumina film, clustering of copper atoms, and occlusion of the clusters, due to growth of alumina around the clusters, to form nanoparticles. The proposed mechanism is supported by medium energy ion scattering, Rutherford backscattering spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy of the alloy following immersion in the sodium hydroxide solution, which disclose the enrichment of copper and the generation of the nanoparticles in the etching product of hydrated alumina. The generation of the nanoparticles is dependent upon the enrichment of copper in the alloy in a layer of a few nanometres thickness, with no requirement for bulk de-alloying of the alloy.     

The effect of copper content and heat treatment on the hydrogen embrittlement of 7050-type alloys

The effect of copper content (0.01 and 2.1%) and microstructure on the intrinsic hydrogen embrittlement susceptibility of unl nercially-processed AI---6Zn---2Mg---XCu alloys was investigated. (The alloy with 2.1 Cu corresponds to 7059). Hydrogen was introduced into the alloys using cathodic charging, both with and without concurrent plastic straining. The copper-free alloy in both the under-aged and peak-aged conditions was embrittled by hydrogen and the effect was enhanced by concurrent plastic strain. The copper-containing alloy (7050) was susceptible to hydrogen embrittlement when under-aged, but once the peak-strength microstructure had been developed, the alloy in the longitudinal direction showed no embrittlement even under severe hydrogen-entry conditions. Similar beneficial effects have been reported for copper additions in imparting resistance to humid air and stress-corrosion cracking for high strength AI-Zn-Mg alloys, and the results are discussed with emphasis on the parallel nature of the phenomena of stress-corrosion cracking and hydrogen embrittlement.     

Grain orientation effects on copper enrichment and oxygen generation during anodizing of an Al-1at.%Cu alloy

Anodizing of solid-solution Al-1at.%Cu alloy in ammonium pentaborate electrolyte is shown to develop two distinct types of amorphous film. On alloy grains of {1 0 0} orientation, the alumina film is of uniform thickness and relatively featureless. For other grains, the film is of non-uniform thickness and contains oxygen bubbles. In both cases, copper species are distributed throughout the film. Copper is enriched in the alloy to ∼5.8×10¹⁵ Cu atoms cm⁻² for bubble-free grains, with similar or slightly lower levels for other grains. Evidently, copper enrichment alone does not lead to generation of oxygen. Other factors suggested to be involved, each dependent upon grain orientation, are the structure of the enriched alloy layer, the cyclic nature of the oxidation of copper, and the generation of modulated film compositions.     

Initial stages of plasma electrolytic oxidation of titanium

The initial stages of oxide growth on titanium are examined in a recently developed commercial alkaline pyrophosphate/aluminate electrolyte of interest for plasma electrolytic oxidation of light metal alloys. Constant current anodizing was employed, with resultant films examined by scanning and transmission electron microscopies and Rutherford backscattering spectroscopy. The initial film is relatively uniform and composed of TiO₂, with low concentrations of aluminium and phosphorus species incorporated from the electrolyte. With increase in voltage the film breaks down locally, and regions of original and modified film develop simultaneously, with the latter occupying more of the surface as the voltage rises. Porous regions due to dielectric breakdown also become increasingly evident. At 240 V, sparking commences, and the surface reveals extensive, relatively uniform porosity, with the coating now containing much enhanced concentrations of aluminium and phosphorus species compared with the coating at lower voltages. The films develop at low efficiency due to generation of oxygen. The oxygen is produced within the original film material and at sites of dielectric breakdown. The former type of film develops a two-layered morphology, with an outer layer of amorphous TiO₂ and an inner layer with numerous fine and course cavities. The cavities are due to the generation of oxygen that may be associated with the formation of anatase in the inner layer.