Walter Wilhelm Focke

Conduction mechanisms in polyaniline (emeraldine salt)

Abstract The conductive emeraldine salt form of polyaniline features a partially filled valence band. Conduction parameters can therefore be evaluated from linear sweep voltammetry data on the further assumption that charge transport occurs via a hopping mechanism. From cyclic voltammograms the density of states at the Fermi level is estimated at 0.6 states/(eV polaron). Similarly the mobility is of the order of 0.2 m 2 V −1 s −1 . This low value indicates that the electronic states are localized, consistent with the assumption of a hopping mechanism. This localization may be the result of structural and dynamic disorder inherent in the polyaniline system. Proton exchange with absorbed moisture and proton tautomerism represent forms of dynamic disorder affecting conductivity.

Flow visualization in parallel-plate ducts with corrugated walls

For flow visualization o-cresolphthalein was found to be superior to thymol blue as an electrode-activated pH indicator because its slower reverse reaction results in better colour retention; its poor solubility was overcome by using a 50:50 water-ethanol mixture. The method revealed unknown flow patterns in plate heat-exchanger configurations with the corrugations on opposite walls abutting. The main flow is along the furrows on each wall. The interaction between these criss-crossing flows causes spiralling in the flow along a furrow. At angles between corrugations and the duct axis of at least up to 45°, the furrow flow is reflected only at the sidewalls of the duct, whereas at high angles, e.g. at 80°, there are intermediate ‘reflections’ at the nodes where the crests of opposite walls meet.

Assessment of the effect of nanomaterials on sediment-dwelling invertebrate Chironomus tentans larvae

Studies were conducted to determine the effects of a panel of seven nanomaterials (NMs), namely: α-alumina, γ-alumina, precipitated silica; silica fume, calcined silica fume, colloidal antimony pentoxide (Sb(2)O(5)), and superfine amorphous ferric oxide (Fe(2)O(3)), on sediment dwelling invertebrates Chironomus tentans under controlled laboratory conditions. Percentage survival, enzyme activities, growth development, and DNA fragmentation parameters were studied as acute, biochemical, and physiological toxicities of NMs, respectively. Quantitation of catalase and peroxidase enzyme activity demonstrated that toxicant stress of the NMs increased enzyme activity in a concentration dependent fashion across all treatments. The percentage growth length of the test specimens exposed to different NMs was significantly reduced compared to the negative control while only five concentrations were not in the toxic range, namely; Fe(2)O(3) (5 μg/kg); silica fume (5 μg/kg, 50 μg/kg); Sb(2)O(5) (5 μg/kg) and calcined silica fume (5 μg/kg). Genotoxic stress assessed by use of DNA laddering showed complementary findings to the other ecotoxicological endpoints tested in this study--the percentage survival and growth length inhibition.

A revised equation for estimating the vapour pressure of low-volatility substances from isothermal TG data

Previous investigators have used the Langmuir vaporisation relation to estimate the vapour pressures of low-volatility compounds from thermogravimetric data. However, this equation is strictly valid for evaporation into a vacuum only. For measurements conducted at finite pressures, molecular diffusion must be taken into account. A revised equation is proposed: dmA/dt8MAPADAB/T. It is also shown that the proportionality between vapour pressure and vaporisation rate is very general. It arises from the assumptions of ideal gas behaviour, Raoults law and a negligible concentration of the sample compound far from the sample surface.

INTRODUCTION TO VAPOUR PHASE CORROSION INHIBITORS IN METAL PACKAGING

Abstract For a compound to be classified as a volatile corrosion inhibitor (VCI), it must possess two basic properties: volatility and ability of the vapour to retard the corrosion rate. VCIs can be used in cases where other protection methods are not feasible or when protection could be very expensive. Usually, most organic compounds giving inhibitive action against corrosion of metals have one or more electronegative atoms (e. g. oxygen, nitrogen, sulphur) in the form of functional groups and/or have an unsaturated bond. Inhibitors for atmospheric corrosion can be used economically only in enclosed spaces. When metal items are in transit, the following protection methods should be considered: protective oils, water or oil based formulations and/or protective packaging. In the manufacture and use of corrosion inhibitors and their products (e.g.VCI paper), workers are occupationally exposed to various chemicals, noise and elevated air temperatures. The concentrations of chemicals in workplace air are dependent on the manufacturing process and equipment used. It is recommended that any plant processing VCIs should have good processing equipment and ventilation. Workers should wear protective clothing, safety glasses and gloves when handling VCI products.

Degradation of insecticides used for indoor spraying in malaria control and possible solutions.

BackgroundThe insecticide dichloro-diphenyl-trichloroethane (DDT) is widely used in indoor residual spraying (IRS) for malaria control owing to its longer residual efficacy in the field compared to other World Health Organization (WHO) alternatives. Suitable stabilization to render these alternative insecticides longer lasting could provide a less controversial and more acceptable and effective alternative insecticide formulations than DDT.MethodsThis study sought to investigate the reasons behind the often reported longer lasting behaviour of DDT by exposing all the WHO approved insecticides to high temperature, high humidity and ultra-violet light. Interactions between the insecticides and some mineral powders in the presence of an aqueous medium were also tested. Simple insecticidal paints were made using slurries of these mineral powders whilst some insecticides were dispersed into a conventional acrylic paint binder. These formulations were then spray painted on neat and manure coated mud plaques, representative of the material typically used in rural mud houses, at twice the upper limit of the WHO recommended dosage range. DDT was applied directly onto mud plaques at four times the WHO recommended concentration and on manure plaques at twice WHO recommended concentration. All plaques were subjected to accelerated ageing conditions of 40°C and a relative humidity of 90%.ResultsThe pyrethroids insecticides outperformed the carbamates and DDT in the accelerated ageing tests. Thus UV exposure, high temperature oxidation and high humidity per se were ruled out as the main causes of failure of the alternative insecticides. Gas chromatography (GC) spectrograms showed that phosphogypsum stabilised the insecticides the most against alkaline degradation (i.e., hydrolysis). Bioassay testing showed that the period of efficacy of some of these formulations was comparable to that of DDT when sprayed on mud surfaces or cattle manure coated surfaces.ConclusionsBioassay experiments indicated that incorporating insecticides into a conventional paint binder or adsorbing them onto phosphogypsum can provide for extended effective life spans that compare favourably with DDTs performance under accelerated ageing conditions. Best results were obtained with propoxur in standard acrylic emulsion paint. Similarly, insecticides adsorbed on phosphogypsum and sprayed on cattle manure coated surfaces provided superior lifespans compared with DDT sprayed directly on a similar surface.

Modelling the Young's modulus of platelet reinforced thermoplastic sheet composites

Particulate reinforced polymers is a mature field and many models are available to predict the Youngs modulus of such composites. However, most existing models have a common flaw; they all predict that the composite modulus equals that of the reinforcing agent when the polymer content approaches zero. This implies, in this limit, a monolithic reinforcement whereas, in fact, it is composed of discrete particles with very little interaction. This is a serious drawback and therefore this study focussed on deriving an improved model for the prediction of the Youngs modulus. The porosity of the present samples was correlated with the volume fraction binder and the maximum packing density of the pure reinforcement. A theoretical model for Youngs modulus was derived along the lines of the Padawer and Beecher modified Cox model. However, it includes the effect of composite porosity on the composites mechanical properties. In contrast to other available models, it correctly predicts the loss of material stiffness and strength in the limit of zero binder content. Good agreement was found between the predictions of this model and experimental measurements.

Mixture Models Based on Neural Network Averaging

A modified version of the single hidden-layer perceptron architecture is proposed for modeling mixtures. A particular flexible mixture model is obtained by implementing the Box-Cox transformation as transfer function. In this case, the network response can be expressed in closed form as a weighted power mean. The quadratic Scheff K-polynomial and the exponential Wilson equation turn out to be special forms of this general mixture model. Advantages of the proposed network architecture are that binary data sets suffice for training and that it is readily extended to incorporate additional mixture components while retaining all previously determined weights.

ALTERNATIVE OXIDANTS FOR SILICON FUEL IN TIME-DELAY COMPOSITIONS

Antimony trioxide, lead chromate, and copper antimonite are suitable oxidants for silicon metal in time-delay compositions ignitable by shock tubing. Measured burn rates for these systems vary from 6 to 30 mm/s. Lead chromate mixtures burned fastest under comparable conditions. The latter two systems show a bimodal burn rate versus silicon content dependence with a local minimum in burn rate at about 35 mass% silicon. Addition of aluminium powder or fumed silica reduces burn rate. Copper antimonite–zinc antimonite coprecipitates provide for faster burning than neat copper antimonite–silicon mixtures.

Asymmetrically corrugated plate heat exchanger plates

Abstract Design flexibility for plate heat exchangers is a measure of the ability to adjust the characteristics of individual channels (semi-)independently to suit a particular application. Conventional plate heat exchangers with approximately sinusoidal corrugations have limited design flexibility since the channels for the two heat- exchanging streams are generally geometrically identical. Corrugations that are assymetrical in profile make it possible to construct physically different configurations from a set of identical plates: channels of different cross-sectional free flow area are feasible. Such plates used in various orientations with respect to each other were found to be less efficient than plates with sinusoidal corrugations because a lower heat transfer rate is obtained per unit of pumping power. However, when the flow rates or allowable pressure drops of the two streams exchanging heat differ greatly, such plates may be advantageous.