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[en] Highlights: • Impact of environmental relative humidity on NCA based cell performance is investigated. • Higher environmental relative humidity impacts first discharge capacity and coulombic efficiency. • Higher environmental relative humidity has negligible impact on cycling stability of NCA cathode.
[en] Confined growth of crystals in porous building materials is generally considered to be a major cause of damage. We report on the use of X-ray diffraction under controlled conditions of temperature and relative humidity (RH-XRD) for the investigation of potentially deleterious phase transition reactions. An improved procedure based on rate measurements is used for the accurate and reproducible determination of equilibrium humidities of deliquescence and hydration reactions. The deliquescence humidities of NaCl (75.4 ± 0.5% RH) and Ca(NO3)2.4H2O (50.8 ± 0.7% RH) at 25 deg. C determined with this improved RH-XRD technique are in excellent agreement with available literature data. Measurement of the hydration of anhydrous Ca(NO3)2 to form Ca(NO3)2.2H2O revealed an equilibrium humidity of 10.2 ± 0.3%, which is also in reasonable agreement with available data. In conclusion, dynamic X-ray diffraction measurements are an appropriate method for the accurate and precise determination of equilibrium humidities with a number of interesting future applications
[en] A diffusion theory with a linear or a nonlinear coefficient of diffusivity is insufficient for the characterization of the drying behaviour of hydrated concrete slabs. A general mathematical model, based on nonequilibrium, irreversible flows of heat and mass, yields a set of nonlinear partial differential equations of parabolic type. Implicit finite difference calculations for a concrete slab yield moisture, temperature, and pressure histories as well as global average drying rates. Graphs show that during the pendular state of dessication, diffusion, capillary, and evaporation-condensation processes are the governing mechanisms in drying. (orig.)
[en] Highlights: • Shrinkage of concrete is measured with various temperature and humidity conditions. • The fib MC2010 shrinkage model is accurate for low RH and high T conditions. • The fib MC2010 shrinkage model slightly underestimate for other conditions. • The fib MC2010 creep model conservatively predicts creep strains. - Abstract: Creep and shrinkage of concrete is influenced by many factors including relative humidity and temperature. The combined effect of low relative humidity (<20%) and high temperature (38 °C) on creep and shrinkage of concrete is uncertain as limited tests have been conducted in this domain. Also unknown is the ability of the fib MC2010 model code in predicting the shrinkage and creep at the environment. This paper presents the results of experiments conducted in which concrete was cast and exposed to the aforementioned environmental conditions. The shrinkage and creep behaviour of the concrete was observed for 110 days, and experimental results were compared with predicted values using fib MC2010 model code.
[en] Selected test results concerning the creep of low strength concrete Bk 20 at elevated temperatures up to T=1300C are presented. Both drying specimens and those in a vapour saturated environment were investigated at transient temperatures. The quartzite concrete specimens were tested after curing periods of 28 and 365 d at load levels of 0 and 27% of the ultimate strength Rn of a 150 mm cube at ambient temperature. Besides short informations to the test techniques used this report summarizes the test results of creep behaviour including first observations on moisture transfer in sealed specimens during and after heating up. Finally some generalized conclusions are drawn. (orig./HP)
[en] In spite of extensive investigation and applications, influence of oxygen (O), and humidity on polyaniline (PANI) behaviour is not well understood. For this reason we have performed semi-empirical quantum mechanics, and ab-initio calculations of the pernigraniline base (PNB) PANI oligomers, of various lengths, before and after approach of H2O, O2 , and hydroxyl (OH −) group, and attachment of OH − and O to various molecular positions. Structure, charge and electrostatic potential distribution, relevant energies and enthalpies, infrared and electronic spectra of the PNB tetramer equilibrium conformation, and their changes induced by specific OH − , and O attachments are determined. These results provide identification of the most probable positions for O2 and H2O approach to PNB_PANI, enthalpies of OH − and O attachments to them, changes of molecular properties induced by the attachments, and infrared and electronic modes that are most suitable for the attachments detection. The results are compared to the existing experimental data, and the results of similar calculations, and implications for the PNB_PANI applications are notified. © 2019 Elsevier B.V.
[en] Concrete is a composite material with dense aggregates embedded in a porous matrix. Hence moisture transfer is limited to water and vapour movement through the porous system of hardened cement paste and along the interface. It is shown that it is reasonable to subdivide the structure of concrete into three different levels. This concept is now called the 3L-approach. The micro-level serves to describe moisture transfer mechanisms. The meso-level has been introduced to take the composite structure of concrete into consideration and finally the macrolevel is used to formulate realistic material laws. The reliability of this approach is underlined by an arbitrarely chosen example, i.e. drying of a concrete element. It is shown that the time-dependent moisture distribution can be obtained for variable relative humidities of the environment. (orig.)
[en] The paper deals with heat and moisture transfer in concrete in the temperture range between 20 and 800C with respect to thick-walled prestressed reactor pressure vessels. The measurements were carried out on concrete made with crushed limestone or natural gravel/sand aggregate and also on cement mortar and hardened cement paste. The programme included measurements of the transport phenomena on 6 model beams heated on their front sides during a period of 3 years, as well as determinations of porosity, compressive strength, thermal expansion, etc. Investigations on thermal conductivity and diffusivity were performed depending on temperature, moisture content and the age of concrete. (orig.)
[en] Highlights: • Triboelectric nanogenerator was prepared using force-assembled colloidal arrays. • The electrical performance was determined by the structures and colloidal size. • They displayed high electric output, stability, and humidity resistance. We introduce a novel, robust, cost-effective, and scalable approach for the preparation of a large-area force-assembled triboelectric nanogenerator (FTENG), which allows a stable and high electric output under a wide range of humidity conditions through its dual-sized morphology (i.e., microstructures and nanostructures). In this study, hexagonally packed colloidal arrays prepared by a force assembly approach rather than by conventional self-assembly were used as a mold for a triboelectric poly(dimethylsiloxane) (PDMS) replica with desired pattern shapes (intaglio and embossed structures) and sizes. The morphological size of the PDMS films was determined by the diameter of the force-assembled colloids. The electrical output performance of FTENGs composed of electrodes and a PDMS film increased substantially as the size of the micropores (for intaglio-structured PDMS) or embossed features (for embossed-structured PDMS) decreased. Furthermore, the triboelectric PDMS film with micro-/nanosized features (i.e., dual-embossed PDMS) displayed a remarkable electrical output of 207 V (open-circuit voltage under a compressive force of 90 N in relative humidity (RH) of 20%) and high hydrophobicity compared to that of PDMS films with flat, intaglio or embossed structures. This device maintained a high electric output even in a high-humidity environment (i.e., open-circuit output voltage ~175 V in RH 80%). Our approach using force-assembly and hierarchical surface morphology will provide a novel and effective framework for developing strong power sources in various self-powered electronics.
[en] The report gives information on the vapor release of thick concrete walls under thermal exposure, which has been determined experimentally. Concrete specimen of 1,0 m thickness and 12 000 kg of weight, with a steel-liner on the heated surface have been tested. The vapor release has been observed, using a special drainage system. The concrete surfaces were heated with different heating rates. With high heating rates (e.g. about 30 K/h) the evaporation of water exceeds sometimes 1,0 kg/m2h. The evaporation rates show some specific features due to the pore structure of concrete. The transport mechanism is quite different from the well-known moisture transport at temperatures below 1000C. A flow type transport model seems to be an appropriate assumption to explain the rapid moisture transport and high evaporation rates. (orig.)