Effect of iron and copper during scale suppression by threshold compounds

When a plant is run on threshold agents of the polyacrylic type, the resultant high brine pH can cause iron, if present, to precipitate on heat transfer surfaces as Ca(Mg_0.67Fe_0.33)(CO₃)₂ (ferroan dolomite), or as Mg₆FeCO₃(OH)₁₃·4H₂O (brugnatellite). Both deposits severely inhibit heat transfer. The soluble iron contributing to these formations can be complexed by adding agents such as the phenol-substituted ethylenediamine diacetic acids. Above concentrations of 0.2 to 0.4 ppm, copper will precipitate the polymers onto heat transfer surfaces; this too can be alleviated by chelating agents. Such treatment can be costly, but fortunately only temporary where the metal ions emanate from the internal corrosion associated with acid treatment. Supersaturation of calcium carbonate and magnesium hydroxide by threshold agents will raise brine recycle pH to more than 9, eliminate carbonic acid attack and thus drastically reduce corrosion rates of copper and ferrous alloys in one to two days. Thus, the principal objective of such specific metal treatment is to “hold off” the negative effects of dissolved metals until corrosion subsides in the brine circuit.     

Tribological behaviour of W‐alloyed carbon‐based coatings in dry and lubricated sliding contact

Carbon‐based coatings with different W contents were deposited by direct current magnetron sputtering in reactive and non‐reactive atmospheres. All deposited coatings have compact morphologies with amorphous (tungsten‐free) or nanocrystalline structures (tungsten‐doped). The latter one was indicated by very broad peaks in X‐ray Diffraction spectra in the position of tungsten carbide suggesting W‐carbide nanoparticles embedded in an amorphous carbon matrix. The hardness increased from 10 to 15 GPa with increasing W content. The coatings were tribological tested at dry and lubricated conditions with increasing temperature in a coating/steel configuration. In dry sliding, the friction coefficient increases with the increase of the temperature reaching values higher than 1.0. The friction is significantly lower in lubricated contact using three different oils: poly‐alpha‐olefin, paraffin and olive oil. The olive oil shows promising lubricating properties at the temperature lower than 70°C; however, at higher temperature, the coatings were quickly worn through. Copyright © 2014 John Wiley & Sons, Ltd.     

Analysis and insights from a dynamical model of nuclear plant safety risk

In this paper, we expand upon previously reported results of a dynamical systems model for the impact of plant processes and programmatic performance on nuclear plant safety risk. We utilize both analytical techniques and numerical simulations typical of the analysis of nonlinear dynamical systems to obtain insights important for effective risk management. This includes use of bifurcation diagrams to show that period doubling bifurcations and regions of chaotic dynamics can occur. We also investigate the impact of risk mitigating functions (equipment reliability and loss prevention) on plant safety risk and demonstrate that these functions are capable of improving risk to levels that are better than those that are represented in a traditional risk assessment. Next, we analyze the system response to the presence of external noise and obtain some conclusions with respect to the allocation of resources to ensure that safety is maintained at optimal levels. In particular, we demonstrate that the model supports the importance of management and regulator attention to plants that have demonstrated poor performance by providing an external stimulus to obtain desired improvements. Equally important, the model suggests that excessive intervention, by either plant management or regulatory authorities, can have a deleterious impact on safety for plants that are operating with very effective programs and processes. Finally, we propose a modification to the model that accounts for the impact of plant risk culture on process performance and plant safety risk. We then use numerical simulations to demonstrate the important safety benefits of a strong risk culture.     

The nanostructure and microstructure of steels: Electrochemical Tafel behaviour and atomic force microscopy

The influence of chemical composition and heat treatment on a low-carbon steel, chromium steel and high speed steel has been examined by polarisation curves and electrochemical parameters deduced from the Tafel plots. The electrochemical corrosion resistance, which is small between the as-received steels become greater after heat treatment, following the order: carbon steel < chromium steel high speed steel. To explain these differences, the nano- and microstructure of the steels has been characterized by the ex situ techniques of atomic force microscopy and optical microscopy, before and after surface etching with Nital (a solution of 5% HNO₃ in ethanol). This causes preferential attack of the ferrite phases showing the carbide phases more clearly. From these nanostructural studies it was possible to better understand why the passive films formed on chromium steel and high speed steel have superior protective properties to those formed on carbon steel.     

Effect of notch-root radius on the fracture toughness of composite Si3N4 ceramics

In-situ silicon nitride and a whisker-reinforced silicon nitride-silicon nitride composite, densified via gas pressure sintering and hot pressing, respectively, were evaluated using the single-edge V-notched beam (SEVNB) fracture toughness technique. The mean value ofK _IC for each material was 5.7 and 7.9 MPa·m^1/2, respectively, and the toughness was influenced by the presence of the elongated Si₃N₄ grains in the microstructure. The notch radius was observed to have the same effect as a sharp crack when notch-root radius was smaller than 10 μm, which was considered to be a realK _IC for these materials.     

Effect of venlafaxine on the pharmacokinetics of terfenadine

Prediction of the drug level in the volume of distribution was made using a numerical model taking into account the following facts: the kinetics of drug release out of the dosage form along the gastrointestinal tract, the kinetics of absorption in the blood compartment and the kinetics of elimination. Various parameters intervene significantly for a given dosage form. Some emphasis was placed upon the rate of elimination of the drug which appears to be the main characteristic for the drug, especially when it is delivered through controlled release dosage forms. The rate of release of the drug out of the dosage form, as well as the dose frequency and the gastrointestinal transit time were also considered. The drug level in the plasma was expressed by the amount of drug as a fraction of the amount of drug initially located in the dosage form.