Active-passive behaviour and stress corrosion cracking of A516 steel in Bayer solution

The susceptibility of A516 steel to stress corrosion cracking (SCC) is essentially restricted to the active-passive range and it increases with the presence of AlO ₂ ^– ions or other impurities of Bayer solution in the electrolytes. The application of anodic protection for preventing SCC does not completely eliminate the danger of cracking, particularly in caustic aluminate and Bayer solutions. The formation of an Fe₃O₄ layer in the active-passive zone and Fe₂O₃ in the passive zone is very likely. In the presence of AlO ₂ ^– ions, an amorphous film of Fe_3–xAl_xO₄ (x2) is observed on the electrode surface and leads very probably to an increased susceptibility to embrittlement. The corrosion behavior diagram (CBD) method, as well as the critical and passive current densities, the corrosion rates and the activation energy support strongly that passivation is easier, but less protective, against SCC in the presence of AlO ₂ ^– ions and impurities in Bayer solution than in pure NaOH. The calculated activation energy suggests that the mechanism of dissolution-controlle cracking is the principal process in SCC of A516 in these studied solutions.     

Multi-dimensional analysis of soil moisture dynamics in trickle irrigated fields. I: Mathematical modelling

An approach is presented to model soil moisture dynamics in irrigated fields. A generalised conceptual model is proposed for moisture transfer in response to hydraulic and thermal gradients. A model to stimulate moisture extraction by roots is presented, based on a philosophy related to fundamental physical principles and recent experimental evidence. The combined models are interpreted numerically by the finite element method and a number of numerical techniques are developed to treat time-dependent, nonlinear and moving boundary conditions. The approach is sufficiently general and is independent of the method of water application being considered. Its benefits are particularly magnified in studies of localised irrigation, where complex soil-water distribution patterns evolve.     

HPLC determination of ochratoxin A in high consumption Tunisian foods

Samples (180) of high consumption food commodities from various regions of Tunisia were analysed to determine ochratoxin A contamination levels. A high performance liquid chromatography method for ochratoxin A determination was optimized. Samples were extracted with acetonitrile/water (80:20, v/v) solution and purified by immunoaffinity column. Average recoveries at 0.5 and 2 ng/g levels ranged from 84 ± 3.1 to 94 ± 1.2% with a between-day coefficient of variation (RSDR) of 3.8%. The method detection limit was 0.1 ng/g and ochratoxin identity was confirmed by methyl ester formation. The whole procedure was simple and fast if compared with other existing procedures. Performed analysis indicates that 45% of monitored samples were contaminated with levels ranging from 0.11 to 33.9 ng/g. The most contaminated commodities were barley, sorghum and wheat.     

A Clothing Ventilation and Heat Loss Electric Circuit Model with Natural Convection for a Clothed Swinging Arm of a Walking Human

This work aims to develop a computationally effective electric circuit model to estimate the ventilation and heat transfer for walking human in the presence of natural convection. The ventilation circuit includes flow resistance, inductance, and electromotive force elements. It is coupled to an electric resistance circuit of heat flows to adjust the temperature difference inducing natural convection flow. The coupled ventilation and heat circuit models predicted both the segmental ventilation rate and heat loss from the arm at different walking and wind speeds. The developed model of the segmental ventilation and heat transfer from the clothed human segment was validated by performing experiments on a walking thermal manikin using tracer gas method. Good agreement was observed between the model predictions and the experiment at a maximum relative error of 10% lying within the standard deviation range. Results showed that the simplified ventilation-heat circuit models succeeded in estimating the natural convection effect at low computational cost. Moreover, it was shown that the effect of natural convection is more significant in walking at no wind than in windy condition. Accounting for natural convection effect increases the segmental ventilation and heat loss at low air permeability (0.02 m/s) by 68% and 20%, respectively.     

Preparation and properties of CdS thin films prepared on cold substrate as a window layer for solar cells

CdS films, usually, prepared on hot substrate at temperature range from 180 to 220°C. The electrical properties of the films are dependent on many parameters such as film thickness, deposition rate, film structure and substrate temperature. To control all these parameters to get film resistivity suitable for manufacturing solar cells, it needs a lot of precautions. CdS prepared on cold substrate could be the solution for this problem. Evaporation of CdS film at constant evaporation rate, then annealed in open air up to 600°C according to the film thickness. The resultant film have been studied. The properties of the films were comparable to the films prepared by the other methods with less control complexity.     

Influence of stirring conditions on hard anodising of aluminium A6061-T6 shapes

Hard anodising is used to produce relatively thick and adherent coatings in order to improve the hardness, abrasion and corrosion resistance of aluminium components. In typical industrial conditions, the local variation of anodic oxide film thickness is often significant and it affects the dimensional tolerances and reliability of coating thickness. Electrolyte stirring is a simple and effective way to improve the uniformity of the oxide layer thickness. However, very little practical information is available in the literature to guide industry in this regard. In this work, extruded A6061-T6 specimens were anodised in industrial conditions. To reduce the thickness variability of the coating, three methods of electrolyte stirring were studied and compared. Air bubble stirring showed the best coating thickness uniformity and improved control over anodising parameters. However it did not reduce the variability due to metal forming texture.

On utilise l’anodisation dure afin de produire un revêtement d’oxyde épais et adhérent à la surface de pièces en alliage d’aluminium. Ce revêtement accroît la dureté, la résistance à l’abrasion et la résistance à la corrosion des composantes. En milieu industriel, l’épaisseur de la couche d’oxyde a tendance à varier en fonction de la position dans la cellule et même d’un endroit à l’autre sur une pièce, ce qui réduit la précision dimensionnelle. L’agitation de l’électrolyte dans la cellule est un moyen simple et efficace d’améliorer l’uniformité de l’épaisseur du revêtement. Toutefois, très peu d’information est disponible dans la littérature pour guider les industriels et déterminer dans quelle mesure l’agitation permet de réduire cette variabilité. Dans ce travail, des composantes extrudées en alliage A6061-T6 ont été anodisées en milieu industriel. Afin de réduire la variabilité de l’épaisseur de la couche anodisée, trois types d’agitation d’électrolyte dans la cellule ont été étudiés et comparés. L’agitation par bulles d’air a permis d’obtenir la meilleure uniformité de l’épaisseur de la couche anodisée et le meilleur contrôle sur les paramètres d’anodisation. Toutefois, les résultats montrent aussi que l’agitation accentue la différence d’épaisseur de la couche anodisée occasionnée par la texture de laminage ou d’extrusion.     

Corrosion par piqûres des alliages d'aluminium 5083-H321 et 6061-T651

Résumé Le comportement des alliages d'aluminium 5083-H321 et 6061-T651 en milieux aqueux avec deux concentrations de l'ion chlore en' présence et en absence de l'ion sulfate a été étudié par voie électrochimique. Les études potentiocinétiques ont permis de déterminer le potentiel de piqûres, tandis que les études potentiostatiques ont précisé davantage l'agressivité du milieu. Trois zones de pH ont été étudiées avec les deux techniques mentionnées, soit: 1–4, 4–9 et 9–12. Une étude morphologique au moyen de la microscopie électronique à balayage combinée par la méthode d'analyse de surface EDAX a été effectuée.

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The behaviour of aluminium alloys 5083-H321 and 6061-T651 in aqueous media containing two different concentrations of chloride ion, in the presence and in the absence of sulphate ion has been studied by electrochemical means. The potentiodynamic studies have permitted determination of the pitting potential, while the potentiostatic studies yielded information on the aggressiveness of the medium. The three regions of pH, studied with the two techniques are: 1–4, 4–9 and 9–12. A morphological study by scanning electron microscopy combined with (EDAX) analysis has been carried out.

     

Hybrid hexahedral element for solids,plates, shells and beams by selective scaling

A robust two-field hexahedral element capable of handling plate/shell, beam and nearly incompressible material analyses without locking are presented. Starting with the assumed stress element of Pian and Tong,⁷ parasitic strain components leading to locking in plate, shell and beam analyses are first identified. Locking can be alleviated by scaling down selectively the parasitic strain components in the leverage matrix. Unfortunately, the element then fails the patch test. However, patch test correction and reduction in computation can be achieved by the recently proposed admissible matrix formulation. The resulting element is lock-free and very efficient. All matrices involved in constructing the stiffness matrix can be derived explicitly. The accuracy of the element is tested by popular bench-mark problems.     

Deep and Handcrafted Feature Fusion for Automatic Defect Detection in Quadratic Frequency Modulated Thermal Wave Imaging

Russian Journal of Nondestructive Testing - Recent advancements of nondestructive testing and evaluation (NDT&E) with machine learning, artificial intelligence, and the internet of things...