Influence of sulphide ions on the cathodic behaviour of copper in 0.1 M borax solution

The presence of sulphide ions in solution greatly influences the cathodic behaviour of copper in borax solutions (pH9.2), even when this contaminant is in low concentration. Cyclic voltammograms, polarisation curves and Tafel plots are compared for polluted and unpolluted solutions. Prereduced and aged copper electrodes are investigated. The presence of sulphide ions in solution increases the rate of oxygen reduction on copper, thus having a detrimental effect on the global corrosion process. The transformation of the surface film into one with better conductive properties is suggested.     

Rheo-optical investigations of highly concentrated polyurethane solutions for industrial processing into elastic fibres

On a large industrial scale, segmented polyurethanes are processed from solution in the dry spinning process to produce textile fibres. Rheo-optical investigations of the flow behaviour of polyurethane solutions enable new material functions to be determined and provide important information for processing. Proportional increases with shear rate were observed for the flow birefringence, Δn', and the orientation, ϕ. The polymer segments were more easily aligned in the direction of the shear field in more concentrated solutions than in dilute solutions. The same tendency was observed for samples with differing molar masses. An ideal standardisability for the temperature (in a window of 20 K) was found over the entire range of shear rate and, hence, the change in the Newtonian and non-Newtonian flow behaviour was also observed to be completely identical. Using the stress-optical rule, it was possible to determine the first normal stress difference. The stress-optical coefficient, C, was 2.6·10^–9 Pa^–1. The normal stress values lie in the range of accessible shear rates below the shear stress, but do, however, rapidly approach this value as the strain increases. Even at a shear rate of 100 s^–1 the viscoelasticity of a 17 wt.-% polyurethane solution is already significant. At a high shear rate the Weissenberg number, We, which is a measure of the viscoelasticity, has a constant limiting value that only depends on the power law exponent, n. Its values in the range of high shear rates mostly lie between 2 and 3 and are rarely (for the smallest n) above 3.     

Possible time-dependent effect of ions and hydrophilic surfaces on the electrical conductivity of aqueous solutions

The purpose of this work was to determine the influence of mechanical and electrical treatment on the electrical conductivity of aqueous solutions. Solutions were treated mechanically by iteration of two steps: 1:100 dilution and vigorous shaking. These two processes were repeated until extremely dilute solutions were obtained. For electrical treatment the solutions were exposed to strong electrical impulses. Effects of mechanical (as well as electrical) treatment could not be demonstrated using electrical conductivity measurements. However, significantly higher conductivity than those of the freshly prepared chemically analogous solutions was found in all aged solutions except for those samples stored frozen. The results surprisingly resemble a previously observed weak gel-like behavior in water stored in closed flasks. We suggest that ions and contact with hydrophilic glass surfaces could be the determinative conditions for the occurrence of this phenomenon.     

Experimental study on the burning behaviour of Pinus halepensis needles using small‐scale fire calorimetry of live,aged and dead samples

Limited research has been conducted on the burning characteristics of live fuels, which are commonly assumed to behave like moist dead fuels. We use small‐scale laboratory calorimetric experiments to investigate the differences in fire dynamics between live and dead Pinus halepensis needles. The study includes laboratory‐aged samples and different moisture conditions (fresh or oven dry). A series of ten fire behaviour parameters are extracted from the measurements to identify and quantify differences. The main parameters are the following: time to ignition; flaming time; mass loss pre‐ignition, during flaming, and during smouldering; peak power; effective heat of combustion; mean and peak CO/CO₂; and radiative fraction. Using these parameters, we show that the most flammable samples are fresh dead and aged needles, followed by dry dead and dry live needles. The least flammable is fresh live needles. Live needles ignite about four times slower, and burn with ~60% lower power and ~50% lower heat of combustion than dead needles. Aged needles resemble most closely the behaviour of dead needles, but many fire behaviour parameters were significantly different. The results confirm the importance of moisture content in the burning behaviour of pine needles, but the differences between live and dead samples cannot be explained solely in terms of moisture but require consideration of plant chemistry and sample drying. © 2015 The Authors. Fire and Materials published by John Wiley & Sons Ltd.     

Photocatalytic degradation of ethidium bromide over titania in aqueous solutions

The photocatalytic degradation of ethidium bromide (EtBr), a DNA intercalating pollutant, by TiO₂-based catalysts has been analyzed. Three different titanium dioxide samples synthesized by sol–gel within reverse microemulsions at different pH and thermal treatments were characterized and studied for the photocatalytic degradation of EtBr by oxygen in aqueous solutions. A commercial titania, Degussa P25, was also examined as a reference material for comparative purposes. Appreciable differences in the final structural and surface properties of these titania samples are observed which include disparities in the anatase/rutile proportions, optical absorption characteristics, EtBr chemisorption and acid–base properties. EtBr photodegradation results suggest that catalytic acid–base properties are the most relevant to explain EtBr chemisorption and play an important role in their final photocatalytic behaviour. It is stressed that photocatalysis can be an interesting alternative to other chemical or biological methods for mineralization of EtBr diluted in aqueous solutions.     

Physical Ageing in Polymethylmethacrylate — A Dielectric Investigation

Abstract

Polymethylmethacrylate aged for various times at temperatures below the glass transition temperature, T_g, were studied using dielectric spectroscopy. The study uses dipole relaxation as a probe for the physical ageing process. Isothermal measurements indicate that the dominant changes occurring in the dielectric loss spectrum at temperatures between the T_g and the side chain (β) relaxation process are associated with changes in the dipole relaxation distribution and the ionic charge mobility. Differences between the spectra for aged and unaged samples are used to assess the nature of the changes occurring at a molecular level. The rate of change of dielectric loss was estimated as a function of the ageing temperature and the observed behaviour was found to be similar in form to that observed from creep and structural relaxation.     

Electrochemical characterization of polymer precoated lithium electrodes

The electrochemical behaviour of lithium electrodes in contact with solutions of propylene carbonate is investigated as a function of different polymer precoating materials (poly-(2-vinylpyridine) and poly-(ethylene oxide)). Impedance and polarization measurements show that the electrochemical behaviour of the surface is influenced markedly by precoating due to a modification of the passivating layer. Such information is important for lithium electrodes in batteries with organic electrolytes.     

Structural characterization and electrocatalytic properties of Au30Zr70 amorphous alloy obtained by rapid quenching

The present work describes the characteristics of Au₃₀Zr₇₀ amorphous alloy as a precursor of a catalyst for hydrogen evolution both in acid and in basic environments and for oxidation of methanol and formaldehyde in alkaline solutions. Amorphous Au–Zr ribbons were prepared by melt spinning methods and were characterized by X-ray diffraction, optical and scanning electron microscopy. In order to obtain an active electrocatalyst, the surface of the amorphous ribbons was treated by immersion in 1 M HF solution. The results of electrocatalytic tests were compared to those obtained with untreated ribbons and also with electrodes made in polycrystalline pure gold. Moreover, some untreated samples were aged in air for 30 days before the electrochemical measurements, in order to investigate the effect of surface oxidation on the electrochemical behaviour of the alloys. The HF treatment yielded a porous structure rich in nanocrystalline gold particles which had better electrocatalytic activity than untreated ribbons or polycrystalline gold electrodes. Ageing in air produced a duplex phase structure, comprising of ZrO₂ scales and nanocrystalline gold which had also improved electrocatalytic activity.     

Structure–property relationship in aging acrylic latex films

We have used environmental scanning electron microscopy (ESEM) and mechanical testing to study the effect of aging parameters (temperature, T and relative humidity, RH) on the structure–property relationship of aged specimens from two acrylic latex compositions, referred to as ‘standard’ and ‘novel’. It was found that the tensile strength of the novel system increases as a function of aging time, whereas the tensile strength of the standard specimens remains almost unchanged. This was attributed to the formation of salt dendrites in the aged novel samples. It was also found that humidity does not have a significant effect on the microstructures observed. However, it was found that aging at lower temperatures results in decreased rate of dendritic formation, which is suggested to be due to decreased diffusion of the species taking part in the crystallisation process. Further examination of fractured surfaces of the studied latex systems revealed features indicative for a more ductile behaviour of the standard specimens and a more brittle behaviour for the novel latex samples.     

Use of Nb2O5 as nickel passivating agent: characterisation of the Ni/Nb2O5/SiO2 system

Niobia-modified silica was used as support for nickel-based catalysts. Catalysts with different nickel loading were prepared by successive incipient-wetness impregnation of toluenic nickel octanoate solutions. The samples were characterised after both calcination and reduction by TEM-EDX techniques and tested in the ethane hydrogenolysis. Their catalytic behaviour was compared to that of related silica-supported nickel catalysts. A high suppression of hydrogenolysis activity (93–99%) was determined for the niobia-modified silica-supported nickel catalysts which do not show nickel particles on silica.     

Comportement des lits fluidisés en milieu viscoélastique

The flow of various fluids of different rheological behaviour has been studied in both fixed and fluidized beds. These fluids were water and aqueous solutions of glycerin, Carbopol and Separan AP-30. For small Deborah numbers, the flow of Carbopol and Separan AP-30 solutions thorough fixed beds is well described by the Ergun relation using the generalized Reynolds number of Christopher and Middleman (1965). Deviations from this behaviour are observed in fluidized beds as preferential flow paths easily occur near the distributor. These deviations are small for Newtonian fluids but take more importance with non-Newtonian solutions and are increased by viscoelasticity.     

Experimental study on the availability of polyurethane foam used as compressible layers in subsea tunnels

The yielding support comprising a compressive layer is considered as a solution to the time-dependent damage of the lining in squeezing tunnels. The feasibility of the use of polyurethane foam (PUF) as the compressible layers in subsea tunnels was investigated in this study. Confined compression tests were conducted to investigate the compression performance degradation of PUF immersed in artificial seawater for 400 days. The yield strength and elastic modulus of PUF decreased within 180 days but then increased to over 80% of their initial values within the subsequent following 220 days, the degradation rate and strengthening rate of these parameters are of the same order of magnitude. The degradation rate of the yield strength and elastic modulus can be significantly inhibited by ions in artificial seawater, thus causing samples immersed in low-salt-concentration solutions to exhibit worse compression performance than those of samples immersed in a high-salt-concentration solution. The stress at the end of the yielding plateau and yielding plateau strain range were slightly affected by hydrolysis aging. The shape of the yielding plateau stage of the aged samples changed from a horizontal line to an inclined line owing to the variation in the yield strength. Even after immersion for 400 days, all the aged samples still exhibited compression failure and neither crumbled into pieces nor fractured into parts. The strengthening effect, unchanged failure mode, and almost constant yielding plateau strain range guarantee the safe utilization of PUF in marine environments.     

The action of some aggressve solutions on Portland, pozzolanic and blastfurnace slag cement mortars

An account of the results of a systematic investigation on the effects of percolation by solutions of magnesium sulphate and magnesium chloride of the same normality, respectively, through mortar samples manufactured with different types of cement is given by the Authors. The aim of the investigation is the comparative evaluation of the behaviour of the single cements under the attack from the two aggressive solutions, as well as the search for possible relationships between the manifold factors responsible, to a different extent, for the lowering of the mechanical strength of the resultant mortars.     

Comparative study of conventional and microwave sintered mullite fibres: structural study

Mullite fibres were synthesised from a mixture of aluminium, aluminium chloride and acidic silica solutions as monophasic salts using a sol–gel technique. The viscosity and rheological behaviour of the mullite precursor sol were examined. Mullite fibres were synthesised using both conventional and microwave sintering techniques. The samples were characterised by X-ray diffraction and scanning electron microscopy. Pure mullite fibres were synthesised by microwave sintering at a relatively low temperature of 1200°C. The grain size of the fibre samples sintered using the microwave technique was finer than that produced by conventional sintering. These results show that microwave sintering is a promising technique for processing mullite fibres.     

Newtonian behaviour of sheared aqueous carboxymethylcellulose solution on aging

The effects of microbiological attack on the rheological properties of sodium carboxymethylcellulose (NaCMC) solutions are described. The effect of aging on the viscosity of aqueous NaCMC solution was studied by means of a Brookfield viscometer. An aqueous NaCMC solution was allowed to age and was subjected to shearing at different time intervals. Dilatant rheological properties were observed in contrast to the usually pseudoplastic behaviour of a normal NaCMC solution. This is attributed to the effect of shear-induced recombination of NaCMC macromolecular crystallites produced as a result of chain scission of NaCMC molecules during aging. The recombination of the crystallites gives higher values of viscosity at higher shear rates. A five months aged sample when subjected to shearing for a period of 20 h exhibits different behaviour. After prolonged post-shearing of this sample, the viscosity measured at shear speeds of 10 rpm and 20 rpm at 72 h and 102h approaches a common value for post-shearing period. The approach to the Newtonian character is attributed to the shear-stress-induced breakdown of the crystalline aggregates. These studies reveal that the aging effects on NaCMC solution have a drastic influence on the rheological properties.     

Ferric-oxalate-gluconate based redox mediated electrochemical system for vat dyeing

The voltammetric behaviour of the ferric-oxalate-gluconate system is investigated along with some electrochemical dyeing results. The results are compared with the conventional ferric-triethanolamine-gluconate system on a glassy carbon electrode. The ferric-triethanolamine redox system is stable and exhibits quasi-reversible redox behaviour in alkaline medium. The ferric-oxalate system undergoes hydrolysis and precipitates above pH 8. Vat dyeing requires the stability of the redox system in alkaline solutions. The ferric-oxalate redox system alone cannot satisfy this requirement. However, in the presence of excess gluconate, both systems exhibit stability in alkaline media. Mechanistic studies indicate the formation of ferrous-gluconate as the reducing agent for vat dyeing from these mediator systems. Electrochemical dyeing was also carried out in the mediator system under investigation. Colour depth was characterized by the Kubelka-Munk value (K/S) and CIE Lab-coordinates for the dyed fabrics and was found to be comparable with samples dyed using sodium dithionite as the reducing agent.     

EFFECT OF DEFORMATION SEQUENCE ON RHEOLOGICAL BEHAVIOUR AND MECHANICAL DEGRADATION OF POLYMER SOLUTIONS

The flow behaviour of polymer solutions of non-hydrolyzed polyacrylamide and Xanthan was investigated in two rectangular and similar plexiglas models containing 3 cylindrical enlargements of the same dimensions. These three enlargements were located successively at the mid point of the first model length, whereas they were equally spaced along the second one. Only non-hydrolyzed polyacrylamide polymer solutions have shown viscoelastic behaviour in these plexiglas models. However, the behaviour of these polymer solutions in the first model was different from that in the second one.

The multipass mechanical degradation of the non-hydrolyzed polyacrylamide polymer solutions was studied extensively in the two plexiglas models. It was shown that, at high flow rates, the multipass mechanical degradation was stronger in the second model than in the first one. The mechanical degradation in model 1 converges with that in model 2 as the flow rate decreases.

The difference in flow behaviour and mechanical degradation of the same polymer solutions in the used plexiglas models was ascribed to the different times allowed for polymer solutions to relax prior to extension in the tested flow fields.     

Analysis of the wetting behaviour of pigments and the effectiveness of surfactants

A new test method is introduced to analyse the wetting behaviour of pigments and the effectiveness of surfactants. The method involves the study of torque vs time curves obtained during the wetting of pigments by surfactant solutions. These curves provide valuable information regarding the wetting behaviour of pigments and the ability of the surfactant to wet the pigment. To study the wetting behaviour, two pigments which varied widely in their surface character are studied with the same surfactant, while, to study the effectiveness of the surfactant, different surfactants with differing polarity are studied using the same pigment. The results are found to be consistent with the theoretical expectations.     

Compressive strength and preliminary in vitro evaluation of gypsum and gypsum–polymer composites in protein-free SBF at 37 °C

Gypsum is a bioresorbable material that has been used in many applications such as tissue regeneration. Mechanical properties of gypsum have limited its applications to non-load bearing sites. The current study aimed at studying the compressive strength and behaviour of gypsum–polymer composites in protein-free simulated body fluids (SBF). Polymers studied were poly(vinyl alcohol) (PVA) and its copolymers with vinyl acetate and itaconic acid in addition to vinyl acetate and vinyl chloride. Composites with the highest compressive strength results were chosen for the preliminary in vitro evaluation in protein-free SBF solutions. Changes in the concentrations of Ca²⁺ and PO₄³⁻ ions, weight loss and morphology of the solid samples were monitored after soaking them in SBF and 1.5 SBF solutions. Results showed resorption of gypsum, concurrently with deposition of apatite in all composites, including polymer-free gypsum. Mechanical integrities of all samples were maintained, suggesting their stabilities when used as bone cements.     

Flow-modified permittivity of solutions of poly(n-butyl isocyanate) and poly(n-hexyl isocyanate)

The dielectric behaviour of solutions of poly(n-butyl isocyanate) and poly(n-hexyl isocyanate) in flow have been examined, including, for the latter polymer, fractions of differing molecular weight. The data are analysed in terms of established theories for changes in the permittivity of solutions of rigid macromolecules undergoing shear and are critically compared to dielectrically based information obtained from studies of still solutions. Rotational diffusion coefficients and dipole moments have been measured and the influence of heterogeneity in molecular weight on flow-modified permittivity is examined. The results obtained support the view that the theories for the flow-modified permittivity of rigid macromolecules are generally satisfactory in providing rotational diffusion coefficients and resolved dipoles, but that the influence of molecular shape on the effect is not simply obtained when polydisperse material is involved.