Viscoelastic behaviour of poly(methyl methacrylate) and polystyrene.

Poly(methyl methacrylate) (PMMA) and polystyrene (PS), which are fully amorphous polymers, have been extensively studied for over a decade to discover how their mechanical behaviours vary with temperatures and strain rates. In this study, Mechanical tests were carried out at a range of strain rates and temperatures using a Hounsfield H50KM Test Machine wluch provides quasi- static rates (10-4 - 10-3 S-l) and low strain rates (10-2 - 10-1 S-l), and an in-house built Dropweight Machine which provides high strain rates (102 - 103 S-l) Mechanical tests were also performed in a high-speed photographic system, which provides high strain rates (103 S-l), to visualise the deformation of the polymers at a range of temperatures. An aluminium-heating block was built to heat up the samples to the required temperature. Strain limited tests were carried out at a range of strain rates and temperatures. Differential Scanning Calorimetry (DSC) was employed to study the glass transition temperatures and the specific heats of the samples. Dynamic Mechanical Thermal Analysis (DMTA) was adopted to study the transitions in the samples and the change of moduli with temperature densities of samples before and after high strain rate compression at certain strain were measured using a Six Column Density Apparatus The polarising microscope was used to study the orientation of the polymer chains at a range of temperatures, strains and strain rates. Eyring's theory of viscous flow was applied on yield point, 20% and 30% strain to relate the activation energy and volume with strain rate and temperature from the thermodynamic perspective. Temperature rise was calculated for high strain rate data to fit into the isothermal curve for the application of Eyring's theory and to obtain the actual smnple temperature at which the deformation took place. PMMA and PS showed ductile behaviour when tested at quasi-static and low strain rates at temperatures below their ductile-brittle transition temperatures. The densities of samples were not found to increase at different strains. The orientations of polymer chains did not influence the increase at Yield stress at high strain rates. The interpretation of activation energy and volume provided information of how the flows of chains took place at different temperatures and strain rates

Pumping of concrete and Mortar - state of the art

-The pumpability of concrete, or its ability to move through pipes and hoses by the help of a pump while maintaining its fresh and hardened properties, can be quantified as being better the lower the necessary pressure to obtain a given flow in a specific configuration and set-up (pump type, -capacity, pipes/hoses, –diameter/length etc). The practical pumping process including the principles of piston- and screw pumps show that for a wide range of concretes the flow in a given set-up is approximately proportional to pump-frequency whereas resulting pressure depends on concrete technological parameters (concrete composition, rheology). Based on review and some preliminary pumping trials in the NTNU concrete laboratory we propose concrete pressure gradient over the pipe length as a measure of pumpability for a given pump set-up. We then present some results on flow measurements in experiments on commercial premix products and open lab concretes and mortars. Measurements of rheological parameters in the BML-viscometer, concrete pressure in pipe , concrete flow and energy in an instrumented full-scale pump-set up with a screw pump indicate that plastic viscosity is the main rheological parameter affecting pumpability. Analysis of the degree of plug flow indicates a wide variety of flow profiles. A simplified 2D FEM analysis with Navier Stokes equation using Papanastasious solution for Bingham fluid gives convergent flow with similar plug flow profiles as the analytical Buckingham Reiner equation. An analytical slip layer model was developed applying the Bingham model. It can be fitted to plug flow but more experiments are needed on what the boundary flow looks like. Continued research should study plug flow, slip layers and concrete rheology effects (admixtures, matrix volume and –properties) on pumpability including effects of pump frequency, increasing vs decreasing flow, hose characteristics (material, diameter, length, height etc). This could also be used in form filling experiments. A reliable numerical model must describe both flow through the pump and pipes/hoses as well as the form filling satisfactorily

Effects of Mott–Schottky Frequency Selection and Other Controlling Factors on Flat-Band Potential and Band-Edge Position Determination of TiO₂

The use of titanium dioxide for tackling environmental pollution has attracted great research interest recently. The potential of a photocatalyst in removing contaminants depends mainly on its conduction and valence-band edges relative to the standard potential of reactive oxygen species. One of the methods used in determining these band-edge positions is via the Mott–Schottky analysis. Thus, the aim of this work was to investigate the influence of the Mott–Schottky frequency and different electrochemical conditions on flat-band potential values and band-edge positions of pure anatase or Degussa P25, calcined or uncalcined in a 0.2 M Na2SO4 solution. The results showed that the shift in the flat-band potential was not so frequency-dependent in the Mott–Schottky analysis, however, other reasons, such as immersion duration leading to thenardite Na2SO4 salt deposition on the surface, irradiation of sources and the change in the pH of the solution (in the range of 1.64–12.11) were also responsible for it. In general, both the calcined anatase and P25 had a less negative value of the flat-band potential compared to the uncalcined. On the other hand, the calcined anatase had a tendency to have a less negative value of the flat-band potential than the calcined P25. From this study, the frequency range for obtaining the flat-band potential within one standard deviation in the Mott–Schottky at a single-frequency analysis was found to be between 200 and 2000 Hz. The energy difference between the Fermi level and the conduction band edge for anatase and P25, either calcined or uncalcined, was 0.097–0.186 and 0.084–0.192 eV, respectively. On the other hand, the band-edge position of anatase or P25 tended to shift upwards when it was repeatedly used in the photoelectrochemical analysis

Pumping of concrete and Mortar - State of the art

The pumpability of concrete, or its ability to move through pipes and hoses by the help of a pump while maintaining its fresh and hardened properties, can be quantified as being better the lower the necessary pressure to obtain a given flow in a specific configuration and set-up (pump type, -capacity, pipes/hoses, –diameter/length etc). The practical pumping process including the principles of piston- and screw pumps show that for a wide range of concretes the flow in a given set-up is approximately proportional to pump-frequency whereas resulting pressure depends on concrete technological parameters (concrete composition, rheology). Based on review and some preliminary pumping trials in the NTNU concrete laboratory we propose concrete pressure gradient over the pipe length as a measure of pumpability for a given pump set-up. We then present some results on flow measurements in experiments on commercial premix products and open lab concretes and mortars. Measurements of rheological parameters in the BML-viscometer, concrete pressure in pipe , concrete flow and energy in an instrumented full-scale pump-set up with a screw pump indicate that plastic viscosity is the main rheological parameter affecting pumpability. Analysis of the degree of plug flow indicates a wide variety of flow profiles. A simplified 2D FEM analysis with Navier Stokes equation using Papanastasious solution for Bingham fluid gives convergent flow with similar plug flow profiles as the analytical Buckingham Reiner equation. An analytical slip layer model was developed applying the Bingham model. It can be fitted to plug flow but more experiments are needed on what the boundary flow looks like. Continued research should study plug flow, slip layers and concrete rheology effects (admixtures, matrix volume and –properties) on pumpability including effects of pump frequency, increasing vs decreasing flow, hose characteristics (material, diameter, length, height etc). This could also be used in form filling experiments. A reliable numerical model must describe both flow through the pump and pipes/hoses as well as the form filling satisfactorily

Synergetic adsorption–photocatalysis process for water treatment using TiO2 supported on waste stainless steel slag

This study presents an economical and efficient method to decolourise dye wastewater using industrial waste stainless steel slag (SSS). Titanium dioxide was immobilised on SSS by a precipitation–calcination method. Samples with different TiO loadings (prepared using either titanium isopropoxide precursor or commercial TiO nanoparticles) were used to decolourise an organic contaminant (methylene blue) under dark and UV conditions in aqueous solution, and their adsorption and photocatalytic performances were compared. Samples with 15 and 25 TiO wt% prepared by the precursor method had normalised photocatalytic efficiencies per gram close to that of bare TiO; using an adsorption–photocatalysis process led to efficiencies 4.4 and 1.6 times higher than that of pure TiO. The improvement in catalytic performance (greater for samples with less than 50% TiO content) may be due to better UV absorption ability (related to with the improvement of TiO particle dispersion) and the close TiO support interaction, which can eventually cause a photocatalysis-enhancing shift towards more negative oxidation potentials. The SSS also acted as an efficient adsorption trap for organic compounds. The pollutant was thus transferred to the TiO surface and photodegraded more rapidly and efficiently. The outstanding synergetic adsorption–photocatalysis capacities of TiO waste stainless steel slag composites for dye water treatment made the proposed conversion approach have great potential in practical applications. Graphical abstract: [Figure not available: see fulltext.

Photoelectrochemical global approach to the behaviour of nanostructured anatase under different irradiation conditions

An anatase film electrode on FTO glass has been produced by a mix of commercial nanostructured anatase with water in a dispersion using a glass rod followed by calcination at 400 °C for one hour with the ramp of 20 °C per minute. The structural morphology of the resulting surface has been analysed by scanning electron microscopy (SEM) and its photoelectrochemical behaviour in the dark, at laboratory environment and under UVA light has been examined using different electrochemical techniques as open circuit photovoltage decay (OCP), linear sweep voltammetry (LSV), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and Mott-Schottky plot measurements allowing a global electrochemical approach. Analysis of the results has allowed a better understanding about its photoelectrochemical properties and charge transfer abilities in photocatalytic applications

Pitting corrosion induced on high-strength high carbon steel wire in high alkaline deaerated chloride electrolyte

Electrochemical response causing pitting corrosion of high-strength high carbon steel wire in deaerated electrolyte at pH 13.4 due to different chloride ion (Cl−) concentrations was investigated using open circuit potential, cyclic potentiodynamic polarization, and anodic potentiostatic application (APA) within the passive zone. Results showed that the higher the Cl− concentration, the more negative the corrosion potential becomes. In the high alkaline pH 13.4 without the presence of free oxygen gas the Cl− concentration could reach up to 1 M not showing pitting potential. An inverse relationship between anodic potentials (APs) and Cl− concentrations was found and the rate of corrosion within passive period was almost a constant, not influenced by the Cl− concentrations. Faraday´s law failed to predict the mass loss when active pitting corrosion occurred. Green rust and hydrogen gas were observed during active pitting corrosion under APA. Pitting corrosion mechanism in the deaerated high alkaline electrolyte was then proposed. This work deduces that in the deaerated electrolyte at pH 13.4 with the presence of Cl−, it is essential to apply the APs within the safety margin on the high-strength high carbon steel wire to avoid active pitting corrosion and hydrogen embrittlement