The stability of zeolite/surfactant systems

The effect of various surfactants on the stability properties of zeolite dispersions has been studied in aqueous solutions. The results show a close relation between the structural properties of the interfacial solid/liquid region and the association equilibria in surfactant aqueous solutions.     

The use of microcrystalline cellulose to extract metals from lubricating oils

The effectiveness of macrocrystalline cellulose as an adsorber of trace amounts of metals from oils was investigated. Prepared samples and samples from engines were used. Samples were prepared by admixture of known amounts of metal-cyclohexyl butyrates of copper, lead, iron and aluminium. Microcrystalline cellulose moistened with aqueous HCl (0.2 ml g^?1) was added to a sample diluted with toluene. The mixture was heated to 60 °C and the adsorbed metal was removed by filtration and ashed. The metals present in the ash were separated and their concentration was determined by standard Chromatographic methods. The minimum time for sorbent and sample to remain in contact to ensure the complete extraction of contaminant metals was determined.     

ARARAT — A computer code for thermal design of cooling towers

A computer program is presented for thermal and hydraulic design of cooling towers. Options have been provided for the evaluation of cooling tower size and performance curves by applying a basic physical model of heat and mass transfer.The solution is conducted by multiple iteration, in which iteration loops are mutually inclusive. Both film and spray-filled cooling towers are considered with either induced or natural air circulation.Numerical solutions are presented to a number of natural draft cooling towers which serve present nuclear or conventional power plants.     

A comparison of lagrangian and serendipity mindlin plate elements for free vibration analysis

The performance of five Lagrangian and Serendipity (4,8,9,12 and 16 noded) isoparametric elements in the free vibration finite analysis of Mindlin plates is evaluated. The results are compared with well established analytical and numerical solutions based on Mindlin's thick plate theory and three dimensional elasticity solutions.     

Mathematical model and digital simulation of pulsating overpotential copper electrodeposition

The relationships between the effective current density and the effective overpotential in copper electrodeposition carried out by pulsating overpotential have been analysed experimentally and by digital simulation on the basis of a simple mathematical model. The agreement between the theoretical and experimental results was satisfactory. The quality of the electrodeposit was also studied.     

Time optimal electrodeposition of metals with a pulsating current

A method of input current shape synthesis, applied to the process of the electrodeposition of metals, is given. It is shown that the optimal control theory can be successfully applied to this kind of problem. Essentials of the mathematics of the method and the computer program flow chart are also given.Theory is checked using experiments on the electrodeposition of copper. The agreement between theoretical and experimental results is satisfactory.     

Deposition of zinc of foreign substrates

Initial stage of deposition of zinc from buffered zinc sulphate solution (pH = 3.55) was studied using platinum, gold and graphite as substrates. The phenomenon of underpotential deposition, noted by recording potential sweep voltammograms (PSV), was taken as a criterion of the existence and strength of interaction between a substrate and the depositing metal. Strong adhesive interactions (including alloy formation) were found in the case of platinum and gold with indication of the existence of multiple states of zinc atoms at the surface. Graphite exhibited no notable interaction and at cathodic overpotentials a characteristic surface growth loop was recorded in the PSV. The later was submitted to a semiquantitative interpretation assuming instantaneous 3-D nucleation and growth with overlap of growing centres.Kinetics of deposition was investigated under the same conditions using a specially design potential pulse sequence enabling separate estimate of zinc deposition and hydrogen evolution partial currents. Recorded current responses were in line with the hypothesis that the deposition at substrates exhibiting strong interactions proceeds without notable nucleation effects. In the absence of such interactions phenomena typical of three-dimensional nucleation and growth are observed.     

The effect of microstructure on the anodic behaviour of Cu-Be-Ni-Zr alloy system

The effect of heat treatment on the anodic behaviour of the Cu-Be-Ni-Zr alloy in 65% phosphoric acid has been investigated by the potentiostatic method. Different anode states obtained by quenching from temperatures of 900,950 and 1000°C were examined under the microscope. It was found that the position and shape of the polarization curves, especially in the active and passive parts, are dependent upon the quenching temperature and colling rate. For pre-quenching temperatures up to 950°C, at which there are no appreciable changes in microstructure, the polarization curves are similar. For higher pre-quenching temperatures up to 1000°C where substantial microstructural changes occur, the active part of the polarization curves becomes more negative, by almost 100 mV, while the passivation decreases.     

Dynamic control of manipulators using load-feedback

In the paper is proposed a procedure for introducing feedback with respect to forces, measured in the contact points between the manipulator gripper and working onject. Information about the dynamic reactions serve as data for the realization of a very efficient algorithm, which calculates the supplementary manipulator movements and the corresponding supplementary loads (driving forces) for their realizations. The problem of controlling the complete dynamic model in that way is solved without on-line calculations of the dynamics based on the complex system of differential equations.