Sliding performance of polymer composites in liquid hydrogen and liquid nitrogen

Outstanding features favour the application of polymers and polymer composites in low-temperature technology. The booming hydrogen technology is a challenge for these materials, which are considered as seals and bearings in cryogenic pumps. In the present study, three types of thermoplastics, i.e., polyetheretherketone (PEEK), polyetherimide (PEI) and polyamide 6,6 (PA6,6), and one epoxy were considered as matrix materials. Micron-sized fillers, i.e., short carbon fibres, graphite flakes, and PTFE powders, were incorporated into these polymers together with nano-sized TiO₂ particles. Optimised compositions of each matrix were selected from our previous works at room temperature in order to be studied at very low temperature conditions. In particular, frictional tests were carried out with polymer composite pins against polished steel surfaces under constant load over a certain distance in liquid hydrogen and liquid nitrogen. Afterwards, worn surfaces were analysed by using scanning electron microscopy (SEM). It was found out that the tribological properties in liquid hydrogen are dominated by the matrix materials, in particular thermoplastics perform generally slightly better than thermosetting resins.     

Method for Characterization of Solvents for Physical Absorption Processes

A method for solvent screening and searching for additives in the field of physical absorption processes is presented. A model based on the concept of virtual components and on the concept of a simplified abstract flow sheet is created. An estimation procedure for thermodynamically consistent property sets for the virtual component is developed. The model is implemented into MATLAB®. Its application is demonstrated in two studies including a study for a solvent additive. Potential candidates can be characterized and ranges for properties of the solvent or additive are found by means of the model. Conclusions obtained from the model support the screening process by a reduction of the number of further investigated components.     

The Effect of Mn-rich Precipitates on the Strength of AZ31 Extrudates

The commercial magnesium alloy AZ31 has been subjected to a range of solution treatment regimes. These have then been extruded and their microstructure, texture, and precipitate populations characterized along with their mechanical properties. During the solution treatment, Mn-enriched particles develop and these remain largely unchanged throughout subsequent processing steps. A direct link between grain size and texture has been found, with coarser-grained specimens showing sharper textures. VPSC modeling has been used to quantify the effect of texture on the tensile yield strength, and it has been found that sharper textures have larger tensile yield strengths. Since coarser grain sizes have reduced Hall–Petch hardening, but have an additional texture-strengthening component, a region on the Hall–Petch plot for tension has been identified in which there is an insensitivity of strength to grain size. This has been quantitatively modeled and a texture-modified Hall–Petch plot for tension has been developed. The Mn-rich particles have also been shown to provide precipitate strengthening to the alloy of up to 40 MPa. The compressive behavior was clearer, with the compressive yield strength being directly correlated to grain size and unaffected by texture or precipitation hardening.     

Radio‐opaque fecal impaction and pseudo‐occlusion in a dialyzed patient taking lanthanum carbonate

Lanthanum therapy is an efficient therapy of hyperphosphoremia by chelating phosphore in the digestive tract. Lanthanum is a silvery white metallic element that belongs to group 3 of the periodic table. This drug is lightly absorbed and has low water solubility. It should be borne in mind that abdominal X‐rays of patients taking lanthanum carbonate may have a radio‐opaque appearance typical of imaging agents. This characteristic is suggested to confirm adherence of the patient by doing an abdominal X‐ray. We describe in our case a particular good compliant patient with slow digestive transit, which ends by pseudo‐occlusion.     

Lime production in a MAK-90 sintering machine

The production of lime by bed roasting in a MAK-90 sintering machine is considered. The thermal and material balances of the process are analyzed. The thermal system of the sintering machine is modernized so as to permit lime production, with reduction in the power consumption and considerable decrease in dust emission.     

Influence of mesostasis in volcanic rocks on the alkali-aggregate reaction

Mesostasis material present in the interstices of volcanic rocks is the main cause of the alkali-aggregate reaction (AAR) in concretes made with these rock aggregates. Mesostasis often is referred to as volcanic glass, because it has amorphous features when analyzed by optical microscopy. However, this study demonstrates that mesostasis in the interstitials of volcanic rocks most often consists of micro to cryptocrystalline mineral phases of quartz, feldspars, and clays. Mesostasis has been identified as having different characteristics, and, thus, this new characterization calls for a re-evaluation of their influence on the reactivity of the volcanic rocks. The main purpose of this study is to correlate the characteristics of mesostasis with the AAR in mortar bars containing basalts and rhyolites.     

Molecular dynamics investigation of the effect of the interatomic potential on steady‐state crack propagation

Abstract

We present molecular dynamics simulations examining the effect of the interatomic potential on steady‐state mode I crack propagation in a two‐dimensional triangular lattice as a function of applied strain. The interatomic potential is the Morse potential whose failure strain exhibits linear variation with its exponential parameter. The limiting crack speed is defined to be the steady‐state crack velocity observed at the onset of instability in steady‐state crack propagation leading to dislocation nucleation or crack branching. For all systems studied, the limiting crack speed is observed to be less than one third the Rayleigh wave speed. The fastest crack propagation in these ideal systems is associated with a material's long‐wavelength elastic properties being dominated by the strength of the nearest‐neighbor bond.     

Coal flotation by ozonized spent motor oil

The influence of ozonization on the composition and flotation properties of spent motor oil is investigated. Preliminary ozonization increases the proportion of low-boiling components in the spent oil, reduces its viscosity, and improves its flotation properties in the enrichment of coking coal.