Copolymerization of polyurethane macromer with 2-hydroxyethyl methacrylate: NMR kinetic study

Summary The copolymerization kinetics of Polyurethane containing a vinylic bond with 2-hydroxyethyl methacrylate in solution was investigated. The reaction was studied using a JEOL-PS-100 spectrometer at various temperatures and concentration conditions. The a and b exponents in the equation for the overall polymerization rate, R_p=const[M]^a[I]^b were determined. The reaction products were analyzed by means of ¹H-NMR and turbidimetric titration.     

The comparison of galvanostatic and potentiostatic copper powder deposition on platinum and aluminium electrodes

Experiments have been carried out on copper powder electrodeposition by constant overpotential and constant current on aluminium, graphite, platinum and copper electrodes. It is shown that for one and the same quantity of electricity, electrode material, electrode surface area, electrolyte, temperature and time of deposition, different particle size distribution curves, current efficiency and specific energy consumption are obtained in galvanostatic and potentiostatic deposition.     

Analysis of catalyst effectiveness in trickle-bed reactors processing volatile or nonvolatile reactants

The problem of diffusion and first-order reaction in catalyst pellets whose exterior surface is partially wetted, as encountered in trickle-bed reactors; is formulated to account for all cases of interest such as gas or liquid limiting reactants, finite or negligible external surface resistance, and volatile or nonvolatile liquids. It is shown that the problem of evaluating catalyst effectiveness for a slab, cylindrical, or spherical shape results in a general dual-series equation which for a given geometry may be reduced to a variety of cases of interest by proper assignment of Biot numbers for dry and wetted surfaces. The catalyst effectiveness factor is given by a simple expression that depends solely on the Thiele modulus and first series coefficient which is found by numerical solution of the dual-series using the method of weighted residuals. A comparison between effectiveness factors predicted by approximate formulas to those given by the more accurate numerical solutions suggests that these former expressions underestimate the catalyst effectiveness and consequently are safe to employ for initial design estimates. The opposite effect of contacting efficiency on catalyst effectiveness for nonvolatile liquid limiting and gas or volatile liquid limiting reactants is illustrated and quantified. Possible pitfalls of employing reaction studies to determine contacting are also discussed.     

On the determination of rat constants for hydration processes in cement pastes

A procedure has been developed to evaluate the actual rate constants for the hydration of individual phases in polysize cementitious systems. The evaluation is based on the comparison between observed and calculated degrees of hydration, the latter being obtained by taking into account the particle size distribution of the original sample and the effects of possible overlapping of different rate-determining processes. The determination of rate constants for C₃S-hydration is described in order to illustrate the proposed procedure.     

The prediction of failure strain for Zircaloy-4 subjected to non-stationary loading conditions

A modified Monkman-Grant relationship (MMG) is applied to predict — as far as the life time is known — the failure strain of Zry-4 subjected to tensile rupture test at load as well as temperature ramp conditions, respectively. As the analysis has shown in the first case, a simple relationship exists between the minimum creep rate and the stress rate. Thus, this quantity appearing in the MMG is phenomenologically connected with the test conditions. For failure strain predictions in temperature ramp tests the introduction of an effective temperature has shown to be advantageous. As compared to the peculiarities of the problem, the agreement between experiments and calculations is encouraging.     

The tensile properties of mixtures of cohesive powders

The theory of tensile stress proposed by Cheng has been extended to deal with binary and three-component mixtures of powders by means of an equation which relates the tensile strength to the particle size parameters and the composition of the mixtures and also to the interparticle force. The interparticle force is expressed in terms of a “strength” parameter ε₀ and a range parameter to by applying the law of corresponding states.By means of ε₀, the tensile strength of the mixtures can be compared relative to the strength of an arbitrarily chosen (single) material.The modified equation has been used in combination with the law of corresponding states to predict the tensile strengths of binary and three-component mixtures with an accuracy of about ± 20%.     

Some observations on the properties of zinc electrodeposited from alkaline zincate solutions

Zinc has been electrodeposited from alkaline zincate solutions onto steel substrate and its properties investigated as a function of overpotential of deposition. The ratio of disperse to compact deposit could be estimated from the results of anodic stripping coulometry. Electron microscopy, stereo-scanning electron microscopy and X-ray diffraction have been used to study the morphology, crystal orientation and lattice parameters, while the bet method rendered information about the specific surface area of the disperse part of the deposit. The yield and degree of dispersion of the disperse (dendritic) deposit have been found to increase with overpotential. The lattice parameters indicate residual stress in the compact part of the deposit. In one and the same deposit the orientation of the compact part was found to be <0001> while that of the dendrites was <10$\text{1}$0> or <11$\text{2}$0>. This selectivity of the two types of growth for particular types of crystal nuclei is explained in terms of a much faster growth on the (10$\text{1}$0) or (11$\text{2}$0) plane than on the (0001) plane, favoured by the structure of the plane at which continuous formation of new layers is possible by the mechanism of unidimensional nucleation.     

The effect of foreign atoms on the properties of electrolytic zinc powders

Kinetic and morphological studies have been made of the deposition of zinc powder on steel substrate, from pure alkaline zincate electrolytes and with small amounts of lead and tin ions in the electrolyte. The rate of co-deposition of hydrogen has been followed volumetrically and the current efficiency of zinc deposition calculated as a function of potential.The addition of lead and tin was found to have a profound effect on the properties of the powder. The dendritic powder, obtained from pure zincate solutions, changes with the addition of lead into a mossy deposit consisting of very small crystallites. Both additives increase the specific surface area of the powder and the average lattice parameters. Hydrogen evolution per unit real surface area and hence the corrosion of the powder are somewhat inhibited by both additives.Reported at the Symposium on Electrocrystallization, 140th Meeting of the Electrochemical Society, Cleveland, Ohio, October 1971.