Complex multilayer carbon structures for green energetics

The authors greatly acknowledge the IMIS2 project of the National Reform Programme of Latvia for financial support. The publication costs of this article were covered by the Estonian Academy of Sciences and the University of Tartu.We investigated a promising material for hydrogen storage and sensing. The material was obtained by exfoliating recycled graphite waste and simultaneously modifying the product with metal impurities (Bi, V, Cu). As a result, graphene sheet stack (GSS) powder was obtained. The material was further processed by hydrothermal annealing and reduction. Raman spectra of the GSS materials are provided to show the presence of graphene-like structures and defects in the exfoliated material. The synthesized graphene material has good semiconductor properties with a low electrical resistance for hydrogen sensing applications.Tartu Ülikool, Eesti Teaduste Akadeemia, Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

An Experimental and Numerical Study of Low Velocity Impact of Unsaturated Polyester/Glass Fibre Composite

In this paper validation of experimental and numerical results of low-velocity impact tests of unsaturated polyester/glass fibre composite laminate has been carried out. Impact response of composite laminates was experimentally studied with drop-tower Instron 9250HV determining impact force, energy absorption and deflection. In addition, quasi-static testing equipment Zwick Z100 has been used to determine material mechanical properties to ensure good input data for numerical predictions. Numerical model has been created with the finite element commercial code ANSYS/LS-DYNA to simulate impact response of composite laminate. Also non-destructive ultrasonic B- and C- scan imagining with USPC&nbsp;3010 system has been used to identify the deformation regions in the specimens and compare to simulation results. During the impact test all samples were perforated, showing brittle response followed by matrix cracking and delamination. Overall good agreement between experimental and simulation results was achieved, comparing impact characterizing parameters as load, energy and deflection. Discrepancy has been observed between ultrasonic scanning and simulation code ANSYS/LS-DYNA results of rupture and delamination. Simulation shows less uniform and larger deformation than it was experimentally observed.http://dx.doi.org/10.5755/j01.ms.17.4.773</p

(Neuroscience and material science joins efforts to create a new type of artificial tactile sensors)

Brain-Machine-Interfaces and mind controlled manipulators are no longer science fiction. It is time to go even further. The functionality of hand prosthesis and manipulators is limited by the availability of sensory information about features of grasped object and manipulative forces. Artificial sensors, which could match functionality of human tactile receptors, currently are not available. The aims of this study are: 1. Using neurophysiological knowledge about functional properties of human tactile afferents and use of sensory information in sensorimotor transformations during object manipulation acknowledge obstacles which have precluded engineers from developing highly efficient artificial sensors; 2. Define requirements crucial for building artificial tactile sensors mimicking biological prototype; 3. To test mechanical features and evaluate stimulus-response characteristics of unique mechanosensitive conductive rubber material developed by our material science team. Mechanosensitive conductive rubber was manufactured by blending polyisoprene caoutchouc with highly structured nano–size carbon black (Degussa Printex XE2), Cyclohexyl-Benzothiazole-Sulfenamide, zinc oxide and sulphur. Mechanosensitive conductive rubber demonstrated high sensitivity to deformation, feature stability across relevant environmental conditions and ability to respond to fast dynamic stimuli in the frequency range of up to 50 Hz, which matches features of biological type of receptors involved in signalling frictional information. Frictional information is the key parameter required to control grip forces during object manipulation. Our mechanosensitive conductive rubber demonstrated unique combination of features like sensitivity to deformation (bending and stretch) and softness which makes it exceptionally suitable for manufacturing artificial tactile sensors to be used in intelligent hand prosthesis and robotic manipulators

BTEX detection with composites of ethylenevinyl acetate and nanostructured carbon

By using a solvent-based method composites of ethylenevinyl acetate copolymer and carbon black (EVA–CB) were synthesized for sensing BTEX (benzene, toluene, ethylbenzene and xylene) vapours. The composites were characterized using atomic force microscopy (AFM) in an electroconductive mode. Gas sensing results show that EVA-CB can reproducibly detect BTEX and that the response increases linearly with vapour concentration. Compared to gas-sensing measurements of gasoline vapours, the responses with toluene and ethylbenzene are different and can be explained by varying side chains of the benzene ring

Grain growth in Na0.5Bi0.5TiO3-based solid solutions

This paper discusses effects of different dopants, sintering technique and parameters on microstructure and properties of pure and Yb, Er-doped Na0.5Bi0.5TiO3 (NBT). All stoichiometric compositions follow the abnormal grain growth mechanism (AGG) and exhibit a bimodal grain size distribution. Bi over-stoichiometry, two step sintering and hot pressing are effective inhibitors of AGG. Microstructure of sintered NBT greatly influences such properties as dielectric permittivity and depolarization temperature.Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

Electrical conduction and rheological behaviour of composites of poly(epsilon-caprolactone) and MWCNTs

Two mechanisms of conduction were identified from temperature dependent (120 K–340 K) DC electrical resistivity measurements of composites of poly(ε-caprolactone) (PCL) and multi-walled carbon nanotubes (MWCNTs). Activation of variable range hopping (VRH) occurred at lower temperatures than that for temperature fluctuation induced tunneling (TFIT). Experimental data was in good agreement with the VRH model in contrast to the TFIT model, where broadening of tunnel junctions and increasing electrical resistivity at T > Tg is a consequence of a large difference in the coefficients of thermal expansion of PCL and MWCNTs. A numerical model was developed to explain this behavior accounting for a thermal expansion effect by supposing the large increase in electrical resistivity corresponds to the larger relative deformation due to thermal expansion associated with disintegration of the conductive MWCNT network. MWCNTs had a significant nucleating effect on PCL resulting in increased PCL crystallinity and an electrically insulating layer between MWCNTs. The onset of rheological percolation at ∼0.18 vol% MWCNTs was clearly evident as storage modulus, G′ and complex viscosity, |η*| increased by several orders of magnitude. From Cole–Cole and Van Gurp-Palmen plots, and extraction of crossover points (Gc) from overlaying plots of G′ and G″ as a function of frequency, the onset of rheological percolation at 0.18 vol% MWCNTs was confirmed, a similar MWCNT loading to that determined for electrical percolation

Dynamic- and Thermo- mechanical Analysis of Inorganic Nanotubes/elastomer Composites

We present dynamic mechanical analysis (DMA) and thermomechanical analysis (TMA) measurements of a new type of polyurea elastomer nanocomposites based on inorganic MoS2 nanotubes and Mo6S2I8 nanowires. The addition of a small amount of nanoparticles (<1 wt-%) leads to an increase of the glass transition temperature Tg as compared to the pure elastomeric matrix. A second peak observed in tand in the pure and mixed elastomer is attributed to a second glass transition occurring in regions near the hard nanodomains of the microphase separated polyurea system. It is also found that the small amount of nanoparticles leads to an increase in the Young´s modulus of up to 15 % in the whole measured temperature range (from -130 °C to 20 °C). The thermal expansion of doped samples is considerably larger above Tg. Below Tg, this difference vanishes completely. A very similar behaviour was also found in measurements of polyisoprene/multiwall carbon nanotube (MWCNT) composites

PROCEDES, ENERGETIQUE

codirigée par « Leonids / BULIGINS