Electrochemical behaviour of Alloy 600 tubing in thiosulphate solution

Electrochemical and surface properties of passive films formed on Alloy 600 in a thiosulphate solution were studied. Oxide films formed at various passive potentials contained a bilayer oxide, whose composition changed as a function of the applied potential resulting in a change in the impedance behaviour. Destabilisation of the oxide film at potentials within the passive region was observed, which was due to the breakdown of the oxide film and coincided with the loss of Cr within the passive film. In contrast, a higher degree of corrosion protection was obtained when the Cr content within the oxide film was elevated.     

A classification of studies on properties of foam concrete

Though foam concrete was initially envisaged as a void filling and insulation material, there have been renewed interest in its structural characteristics in view of its lighter weight, savings in material and potential for large scale utilization of wastes like fly ash. The focus of this paper is to classify literature on foam concrete in terms of constituent materials (foaming agent, cement and other fillers used), mix proportioning, production methods, fresh and hardened properties of foam concrete. Based on the review, the following research needs have been identified: (i) developing affordable foaming agent and foam generator, (ii) investigation on compatibility between foaming agent and chemical admixtures, use of lightweight coarse aggregate and reinforcement including fibers, (iii) durability studies, and (iv) factors influencing foam concrete production viz., mixing, transporting and pumping.     

Cyclic voltammetric study of zinc and zinc oxide electrodes in 5.3 M KOH

The behaviour of zinc and zinc oxide in 5.3 M KOH in the presence of alkaline earth oxides, SnO, Ni(OH)₂ and Co(OH)₂ was examined by cyclic voltammetry. The influence of the alkaline earth oxides was compared with additives of established effects (Bi₂O₃, LiOH, Na₂CO₃ and CdO). The alkaline earth oxide each exhibits a distinct behaviour towards zincate. Whereas, a single process of interaction with zincate was shown by CaO; two modes of reaction were obtained with SrO and BaO. Solid solution formation was noticed with BeO and MgO. The other additives forming solid solution with ZnO were CdO, SnO. The ionic sizes of Ni(OH)₂ and Co(OH)₂ allow solid solution formation with Zn(OH)₂. Both Bi₂O₃ and Na₂CO₃ enter into complexation with zincate. LiOH forms two distinct zincates, of which one is an oxo zincate leaching the `hydroxyl' functionality. Cyclic voltammetry revealed the deposition of the oxide/hydroxide additives as metal prior to the onset of zinc deposition and the potential range for this additive metal deposition is almost the same for different additives (SnO, CdO, Ni(OH)₂). The beneficial action of these additives to zinc alkaline cells is associated with a substrate effect. The implication of this electrocatalytic deposition of metals on a zinc oxide electrode is also discussed.     

Estimation of impact-induced damage in CFRR laminates through ultrasonic imaging

Ultrasonic C-scans are used frequently to detect defects in composite components caused during fabrication and damage resulting from service conditions. Evaluation and characterization of defects and damage require experience and good understanding of the composites. Under low-velocity impact loading delamination is observed to be a major failure mode. In this paper, the results of extensive experimental work on damage of carbon fiber reinforced plastic (CFRP) laminates due to low-velocity impact are presented. The study was carried out on 10 different layups over four different thickness. Both drop-weight and projectile impacts simulating practical conditions like tool-drop and runway debris, respectively, were carried out at energy levels varying from 3 to 30 J. The ensuing delamination damage was determined by ultrasonic: C-scans using the pulse-echo immersion method for both projected and layer-wise distribution. While projected delamination was obtained by placing a gate over the backwall echo, layerwise distribution was obtained by successive time delay from the frontwall to the backwall echo covering each interface. Delamination areas were quantified accurately by processing the raw image data using a digital image processing technique. Based on the data obtained an empirical relation was established between the delamination area and the impact energy.     

Blank design optimization on deep drawing of square shells

A numerical scheme for improving the drawability in the deep drawing of square shells by blank design optimization is presented. The numerical scheme is formulated as an optimization problem whose objective is to maximize the drawability, subject to the constraint that fracture failure and draw-in failure do not occur. Appropriate blank design parameters are used as the design variables of the formulation. To enable the numerical scheme to work models predicting the onset of fracture failure and draw-in failure are required. Numerical models simulating the onset of these failures under the given process conditions are thus discussed. Optimal designs for three cases are then presented. Finally, by considering both the drawability and the non-uniformity of the final flange profile it is shown that the circular profile can be considered to be the optimal blank shape for square cup drawing.     

Comparison of the clinical efficacy of three perivascular techniques for axillary brachial plexus block

BACKGROUND AND OBJECTIVES: This study compared the efficacy of three perivascular techniques of axillary block. METHODS: In group 1, all of the local anesthetic was injected after advancing the needle through the axillary artery (back of artery, n = 20); in group 2, after withdrawing slightly from the artery (front of artery, n = 20); and in group 3, half of the anesthetic was injected after advancing through and half after withdrawing from the axillary artery (half and half, n = 20). The local anesthetic used for the axillary block was 50 ml of 1.5% mepivacaine with epinephrine 1:200,000. RESULTS: The groups did not differ significantly in the incidence of analgesia or anesthesia expected in the median nerve distribution, where there was a significantly lower incidence of anesthesia in the back of the artery group. This group also had a slower onset of anesthesia for the median and the medial antebrachial cutaneous nerves. CONCLUSIONS: There was no significant difference in the number of patients requiring supplementation, with five patients in the back group (25%), three patients in the front group (15%), and one patient in the half and half group (5%) requiring supplementation for the surgical procedure.     

Three-Dimensional Numerical Modeling of Mixing at River Confluences

Lateral mixing of a pollutant is considered as a slow process that is usually complete within 100–300 river widths. Recent studies on flow dynamics at river confluences revealed that lateral mixing can be markedly enhanced when the tributary channel is shallower than the main channel. This study uses a three-dimensional model to examine mixing processes immediately downstream of confluences as well as further downstream in the mainstream. Simulations are presented for a concordant and discordant laboratory junction and a field confluence for a low and a high flow condition. The decrease in standard deviation at a cross section of a tracer over a distance of 5 channel widths is 30% for discordant beds but only 10% for concordant beds in the laboratory simulation. At the natural site, bed discordance is more important at the low flow than at the high flow with corresponding decreases in the standard deviation of 31 and 18% over 3.5 channel widths. Mixing is completed after a distance of 25 and 37 channel widths for the low and high flow conditions, respectively. Further downstream, mixing is mainly affected by planform curvature of the channel.