Kinetics and mechanism of chromium electrodeposition from formate and oxalate solutions of Cr(III) compounds

Kinetics of multistep reaction of Cr(III) ions discharge to metal was studied on a stationary electrode and on a rotating disk electrode from the solutions containing formic acid or oxalic acid. The electroreduction of Cr(III) complex ions in aqueous solutions is shown to proceed via the formation of relatively stable intermediates—Cr(II) compounds which are partially removed into bulk solution. The effect of pH, organic ligand concentration and disk rotation velocity on the partial current density of chromium electroplating was demonstrated. The kinetic equations of the studied process were derived and compared with the experimental data. Kinetic parameters for the discharge of Cr(II) ions were calculated. The mechanism of chromium electrodeposition reaction was proposed. The electrodeposition of chromium from formate bath is suggested to proceed with the participation of hydroxocomplexes of bivalent chromium. The oxalate complexes of bivalent chromium directly discharge in the electrolytes containing oxalic acid. The partial polarization curves of chromium electrodeposition exhibit a current peak which may be caused by blocking the electrode surface with poorly soluble Cr(III) hydroxide.     

Anisotropy of Wetting and Spreading in Binary Cu-Pb Metallic System: Experimental Facts and MD Modeling

Contact angle for millimeter-size drops of lead on {100} and {110} surfaces of monocrystalline copper and on polycrystalline copper was determined by means of dispensed drop technique at 450 °C under He-H₂ atmosphere. It was demonstrated that the wetting anisotropy (a difference between contact angles on differently oriented substrates) is not exceed a few degrees. Spreading kinetics was found to be different for the first and second drops deposited on each substrate. This result was interpreted as an effect of a lead precursor film formation on the substrate surface. Molecular dynamics simulations of the lead drop spreading over {111}, {100}, and {110} surfaces of monocrystalline copper confirm the weak anisotropy of equilibrium contact angle and a formation of lead precursor film on copper surface in front of wetting line.     

Thermodynamics and kinetics of dissolutive wetting of Si by liquid Cu

Wetting of Si single crystals by pure copper has been studied using the dispensed drop technique under high vacuum at 1100 °C. At this temperature copper dissolved large quantities of Si during spreading. CuSi droplets presaturated in silicon were also used to obtain non-reactive spreading. From the results obtained the different contributions to “dissolutive wetting” were determined. Moreover, a simple analytical model was formulated for analysing the influence on wetting of the interfacial atomic processes and of Si transport in the liquid. It is seen that, under our experimental conditions, solute transport by Marangoni convection controls the spreading kinetics.     

Capillary interactions between molten silicon and porous graphite

The capillary properties (wetting, infiltration) of the reactive Si/porous graphite system are studied by the sessile drop technique that enables the spreading and infiltration dynamics to be monitored in situ. The experiments are performed by varying the temperature, the type of graphite (porosity, grain size) and the vapour phase (inert gas or high vacuum). Further experiments are performed in order to quantify the influence of the exothermic reaction between Si and graphite on the temperature field close to the infiltration front. The effects of Si–graphite interactions on graphite mechanical integrity are also evidenced.     

Investigation of cellulose acetates by the optical rotatory dispersion method

Conclusions -- The optical activity of cellulose acetates having various contents of functional groups depends primarily on the change in asymmetry of the glucopyranose unit.-- The existence of several factors which simultaneously affect the optical activity of cellulose acetates prevents use of the Drude equation to calculate the constantsA and ₀.-- The use of the optical rotatory dispersion method to study the molecular structure of cellulose acctates is possible only in combination with other methods.Translated from Khimicheskie Volokna, No. 5, pp. 8–10, September–October, 1990.     

Finite size scaling in grain boundary wetting

Experimental studies of grain boundary invasion by a wetting fluid give clear evidence for a size dependence. In order to get a better numerical insight into grain boundary (GB) wetting as a percolation process, we have investigated size effects during gallium penetration into quasi-2D zinc polycrystalline strips of various width and during water penetration into 3D cylindrical NaCl polycrystals. Both systems are likely to be good objects for studying percolation effects because of a random distribution of wettable GB’s. Computer simulation on the square lattice, with a “wetting” probability p = 0.60 close to the number of experimental points (several dozens), shows a striking resemblance between both sets of data. Making more runs (about 10⁵) demonstrates consistency of our model with an earlier reported work by Marrink and Knackstedt describing finite size effects in elongated lattices. Using their approach, an excellent agreement can be obtained between the experimental and simulated data, as well as between the latter and theoretical predictions.     

LCD applications of thin‐crystal‐film polarizers

Abstract— We have developed a new technique for the production of thin crystal film (TCF) by deposition, molecular alignment, and the drying of water‐based lyotropic‐liquid‐crystal (LLC) materials. TCF exhibits high optical anisotropy and birefringence. This paper presents liquid‐crystal‐display (LCD) applications and opportunities for TCF plastic sheet polarizers, retarders, and color‐correction films as well as LCD designs with TCF internal polarizers.     

Changes in the Cardiotoxic Effects of Lead Intoxication in Rats Induced by Muscular Exercise

Exposure to lead is associated with an increased risk of cardiovascular diseases. Outbred white male rats were injected with lead acetate intraperitoneally three times a week and/or were forced to run at a speed of 25 m/min for 10 min 5 days a week. We performed noninvasive recording of arterial pressure, electrocardiogram and breathing parameters, and assessed some biochemical characteristics. Electrophoresis in polyacrylamide gel was used to determine the ratio of myosin heavy chains. An in vitro motility assay was employed to measure the sliding velocity of regulated thin filaments on myosin. Isolated multicellular preparations of the right ventricle myocardium were used to study contractility in isometric and physiological modes of contraction. Exercise under lead intoxication normalized the level of calcium and activity of the angiotensin-converting enzyme in the blood serum, normalized the isoelectric line voltage and T-wave amplitude on the electrocardiogram, increased the level of creatine kinase-MB and reduced the inspiratory rate. Additionally, the maximum sliding velocity and the myosin heavy chain ratio were partly normalized. The effect of exercise under lead intoxication on myocardial contractility was found to be variable. In toto, muscular loading was found to attenuate the effects of lead intoxication, as judged by the indicators of the cardiovascular system.     

Wetting of W by liquid Pb and PbLi alloys and surface interactions

Wetting of W by Pb and Pb–17 at.%Li in the range 400–900 °C is studied by the dispensed drop technique. Experiments are performed using different furnace atmospheres (high vacuum, reducing gas) and different heat treatments to achieve W deoxidation. A simple pairwise model is used to explain the relation between surface interaction, which is responsible for wetting, and bulk interactions determining miscibility.