Kinetics of high temperature oxidation of chromium rich HfC reinforced cobalt based alloys

Mostly known to improve the high temperature oxidation resistance of superalloys, hafnium may also form carbides. Several per cents of Hf allow developing a dense carbide network to mechanically strengthen alloys. Here, the high temperature oxidation behaviour of three HfC containing cobalt alloys was characterised at all steps of a thermogravimetry test: heating, isothermal stage and cooling, compared with two Co–Cr–C model alloys. The five alloys were heated in synthetic air, maintained at 1200°C during 50 h and then cooled. The mass gains were plotted versus time or according to (m×dm/dt?=?Kp–m×Kv) to specify the isothermal kinetic constants, or versus temperature to determine how oxidation acts during heating and oxide spallation occurs during cooling. Compared to the ternary alloys, the oxidation of the HfC reinforced alloys starts earlier but leads to lower mass gains during heating, the isothermal oxidation is faster and oxide spallation occurs later.     

Freeform texture representation and characterisation based on triangular mesh projection techniques

Texture characterisation for freeform non-Euclidean surfaces is becoming increasingly important due to the widespread of the use of such surfaces in different applications, e.g. the additive manufacturing. Four main steps are required to analyse and characterise those surfaces which include new surface representation, surface filtration and decomposition, texture representation methods and finally the calculation of the surface parameters. Recently, the representation, as well as the filtration and decomposition, of freeform surfaces have been investigated and some algorithms have been proposed. This paper, however, shed the light on how to represent the texture of freeform non-Euclidean surfaces before calculating the parameters. A novel model for freeform surface parameterisation is introduced; this new model proposes the use of a projection algorithm before the actual calculation of the parameters. Different projection algorithms have been adopted from the mesh projection techniques found in the field of computer graphics. The results of applying those algorithms to represent the texture of both simulated and bio-engineering surfaces are shown, also a comparison between those algorithms has been carried out. Furthermore, examples of calculating some of the surface parameters for freeform surfaces are given.     

Influence of surface pre-treatments on disturbed rolled-in subsurface layers of aluminium alloys

Rolling is known to alter the surface properties of aluminium alloys and to introduce disturbed subsurface layers. These layers are characterised by a refined grain structure, rolled-in oxide particles, a fine distribution of intermetallic particles, various voids and cracks.In this study, the effects of some surface pre-treatments, i.e., alkaline etching at various temperatures and chemical cleaning with Nabuclean and CrO₃/H₃PO₄, on these rolled-in layers are investigated by means of surface analytical techniques. The changes in composition and morphology of the (sub)surface are studied with scanning electron microscopy/energy dispersive X-ray analysis and backscattered electron imaging (SEM/EDX + BEI). The presence of incorporated oxide particles is evaluated by measuring the total reflectance. The (re-)distribution of alloying, impurity and trace elements upon these surface treatments is investigated with radiofrequency glow discharge optical emission spectrometry (rf-GDOES).     

Composite hydrogeological investigation and characterisation methods applied at a nuclear power plant site in Taiwan

Drawing from the lessons learnt from the Fukushima nuclear disaster in Japan, the assessment of subsurface environmental hazard around nuclear power plants has emerged as a critical task. Consequently, aiming to better understand the possible environmental impact of radiation leaks into the groundwater, a prescreening programme was initiated in 2011 by the Taiwanese government. As part of this programme, this study conducted various borehole prospecting techniques to identify in situ hydrogeological characteristics at Chin‐Shan Nuclear Power Plant. Borehole electrical log, sonic log and temperature/conductivity log were conducted to explain the regional lithologic conditions and permeability of the formation. In conjunction with this, the interwell tracer and pumping test was carried out to simultaneously determine the hydraulic parameters. In our opinion, the implementation of such in situ end‐to‐end investigations is essential in interpreting in situ fluid and solute transport dynamics prior to programming any numerical scheme for early warning, vulnerability assessment and regular monitoring of a nuclear power plant site.     

Substrate characterisation for a subsurface reactive barrier to treat colliery spoil leachate

Subsurface permeable reactive barriers (PRB) have been used to successfully treat acidic mine drainage in Canada and offer great potential for doing the same in the United Kingdom. A PRB for the treatment of colliery spoil leachate from a site near Newcastle upon Tyne, UK, has been designed. The selection of the reactive media to be used is of paramount importance, with particular reference to permeability and reactivity. A number of reactive media mixtures containing varying proportions of cattle slurry screenings, green waste compost, calcite limestone chips and pea gravel were prepared and their respective permeabilities and reactivities were investigated. Media mixtures containing 50% 10 mm grade calcite limestone chips showed better alkalinity addition and metals removal than a blank containing 50% pea gravel. A media mixture containing 50% limestone chips and 50% green waste compost showed a 24 h period to achieve maximum addition of alkalinity and maximum removal of acidity and metals. Mixtures containing 25% green waste compost and 25% slurry screenings achieved maximum addition/removal in 4 h. The likely presence of iron sulphide in samples drawn from test vessels during both test runs indicates that bacterial sulphate reduction is occurring in this composite.     

Polymeric compounds in activated sludge supernatant -- Characterisation and retention mechanisms at a full-scale municipal membrane bioreactor

In this study, for the first time a full-scale membrane bioreactor (MBR) was investigated with focus on organic compounds in activated sludge over a period of approximately 2 years. Soluble extracellular polymeric substances (EPS) in the sludge supernatant and permeate as well as bound EPS extracted from fouled membranes were determined photospectrometrically and revealed a typical composition of three main components in the order metals>humic acids>carbohydrates>proteins. Results showed an important influence on membrane fouling by soluble humic substances and carbohydrates in complexes with metal cations. It was found that Fe(2+) and Fe(3+) play a decisive role in natural organic matter (NOM) complexation and subsequent membrane blockage. The determination of molar mass distribution in supernatant and permeate by size exclusion chromatography (SEC) revealed a significant retention of macromolecular compounds by the porous membranes in the range of 10-50%.     

Permeability of low molecular weight organics through nanofiltration membranes

The removal of natural organic matter (NOM) using nanofiltration (NF) is increasingly becoming an option for drinking water treatment. Low molecular weight (LMW) organic compounds are nevertheless only partially retained by such membranes. Bacterial regrowth and biofilm formation in the drinking water distribution system is favoured by the presence of such compounds, which in this context are considered as the assimilable organic carbon (AOC). In this study, the question of whether NF produces microbiologically stable water was addressed. Two NF membranes (cut-off of about 300 Da) were tested with different natural and synthetic water samples in a cross-flow filtration unit. NOM was characterised by liquid chromatography with organic carbon detection (LC-OCD) using a size-exclusion column in addition to specific organic acid measurements, while AOC was measured in a batch growth bioassay.Similarly to high molecular weight organic compounds like polysaccharides or humic substances that have a permeability lower than 1%, charged LMW organic compounds were efficiently retained by the NF membranes tested and showed a permeability lower than 3%. However, LMW neutrals and hydrophobic organic compounds permeate to a higher extent through the membranes and have a permeability of up to 6% and 12%, respectively. Furthermore, AOC was poorly retained by NF and the apparent AOC concentration measured in the permeated water was above the proposed limit for microbiologically stable water. This indicates that the drinking water produced by NF might be biologically unstable in the distribution system. Nevertheless, in comparison with the raw water, NF significantly reduced the AOC concentration.     

Compressive Viscoplastic Response of 6082‐T6 and 7075‐T6 Aluminium Alloys Under Wide Range of Strain Rate at Room Temperature: Experiments and Modelling

Abstract: In this work, the viscoplastic behaviour of 6082‐T6 and 7075‐T6 aluminium alloys is examined over a wide range of strain rates. Three different testing techniques were applied to this investigation: low‐rate experiments were performed using a regular servo‐hydraulic testing machine, high‐rate tests were conducted using a split Hopkinson bar apparatus and very‐high‐rate experiments were carried out using a miniaturised direct impact test arrangement. The latter testing set‐up allowed for the characterisation of material flow at strain rates up to . These experimental results showed a sharp increase in the rate sensitivity of the materials once a threshold loading rate of is exceeded. This behaviour may be attributed to the presence of viscous drag on high‐velocity dislocation motion. In addition, the thermo‐viscoplastic behaviour of the 6082‐T6 and 7075‐T6 aluminium alloys was analytically described using the extended Rusinek–Klepaczko model of viscous drag effects. Satisfactory correlation was observed between the experiments and the constitutive model results over the entire range of strain rates studied,      

Epitaxial growth and interface strain coupling effects in manganite film/piezoelectric-crystal multiferroic heterostructures

We constructed multiferroic structures by epitaxially growing colossal magnetoresistive La_0.7Sr_0.3MnO₃ (LSMO) thin films on piezoelectric single-crystal substrates of composition 0.67Pb(Mg_1/3Nb_2/3)O₃–0.33PbTiO₃ (PMN-PT). Due to the efficient elastic coupling at the interface, the electric-field-induced piezoelectric strain (?_piezo) in the PMN-PT substrate is effectively transferred to the LSMO film, giving rise to a remarkable modulation of the lattice strain, resistivity, and Curie temperature T_C of the LSMO film. Particularly, it was found that the magnetic field has an opposite effect on the strain-tunability of resistivity above and below T_C. Moreover, we found that the resistivity of the film is most sensitive to ?_piezo near T_C and becomes less sensitive to ?_piezo when the temperature is lower or higher than T_C. These, together with the well fitted resistivity data into a phenomenological model based on coexisting phases, demonstrate that the phase separation is crucial to understand the strain-mediated multiferroic properties in manganite film/PMN-PT structures.