New covalent salts of the 4+ V class for Li batteries

There is urgent action required for replacing LiPF₆ as a solute for Li-ion batteries electrolytes. This salt, prone to highly Lewis acidic PF₅ release and hydrolysis to HF is responsible for deleterious reaction on carbonate solvents, corrosion of electrode materials leading to safety problems then release to toxic chemicals. A major advantage of LiPF₆ is that it passivates aluminium. Most attempts to replace LiPF₆ with hydrolytically-stable salts have been unsuccessful because of Al corrosion.We present here two “Hückel” type salts, namely lithium (2-fluoroalkyl-4,5-dicyano-imidazolate); fluoroalkyle = CF₃ (TDI), C₂F₅ (PDI) with high charge delocalization. These thermally stable salts give both appreciably conductive solutions in EC/DMC (>6 mS cm⁻¹ at 20 °C) with a lower decrease with temperature than LiPF₆. Non fluorinated lithium (4,5-dicyano-1,2,3-triazolate) is comparatively less than half as conductive. The lithium transference number T₊ measured by PFG-NMR is also higher. Voltammetry scans with either platinum or aluminium electrodes show an oxidation wall at 4.6 V versus Li⁺:Li°. These two salts are thus the first examples of strictly covalent, non-corroding salts allowing 4+ V electrode material operation. This is demonstrated with experimental Li/LiMn₂O₄ cells as beyond the third cycles, the fade of the three electrolytes were quasi-identical, though LiPF₆ had a sharper initial decrease.     

Tolerance modelling of vibrations of thin functionally graded plates

A problem of a modelling of vibrations of thin plates with a functionally graded macrostructure and a tolerance-periodic microstructure in planes parallel to the plate midplane is analysed. The proposed model, based on the Kirchhoff plate theory assumptions and additional hypothesis of the tolerance averaging technique [Wo?niak et al., editors. Thermomechanics of heterogeneous solids and structures. Tolerance averaging approach. ?ód?, University Press, Technical University of ?ód?; 2008], describes the effect of the microstructure size on dynamic behaviour of the plate. In this paper, as an example there are analysed free vibration frequencies of a functionally graded plate band. These frequencies are obtained in the framework of two proposed models—the tolerance model and the asymptotic model, using the known Ritz method.     

Semi-empirical model of efficiency of wire electrical discharge machining of hard-to-machine materials

In this study, the efficiency of wire electrical discharge machining of hard-to-machine materials was investigated experimentally. Uncoated brass wire, 0.25 mm diameter, zinc oxide coated brass wire and brass CuZn20 coated brass CuZn50 wire were utilized in the conducted research. The following variables were chosen as important WEDM parameters: discharge time t_on, average working voltage U. The following properties of machined materials, such as: melting point T_t, electrical conductivity σ, thermal conductivity K, thermal expansion coefficient k, density ρ, heat capacity c_p, were selected to develop the semi-empirical model of volumetric efficiency of WEDM. The variation of the WEDM efficiency in cutting different materials and applying different wire electrodes and different process parameters was modelled semi-empirically by employing dimensional analysis.     

Zinkacrylat und andere feste Monomere als Vernetzungsmittel für ungesättigte Polyester

The peroxide-initiated copolymerisation of an unsaturated polyester with zinc acrylate, diallyl phthalate prepolymer and a solid vinyl ester resin was investigated. The curing was followed by means of gelation curves and differential scanning calorimetry. The studies showed that zinc acrylate has the highest reactivity.     

Novel composite polymeric electrolytes with surface-modified inorganic fillers

Surface-modified inorganic powders were applied as additives to plain salt-in-polymer polymeric electrolytes in order to enhance their properties and make them applicable in all-solid-state Li-polymer primary and secondary cells. These fillers consisted of alumina and titania powders (coarse and nano-sized) with superacidic groups introduced onto their surface. Then they were added to low and high molecular weight poly(ethylene oxide) (PEODME 500 and PEO 4,000,000) together with lithium perchlorate (LiClO₄, lithium tetraoxochlorate(VII)). In this way several different composite electrolytes were obtained that exhibited excellent stability versus lithium metal electrode and high lithium transference number. Herein the preparation procedure is described and preliminary results given.     

On intuitionistic fuzzy sub-hyperquasigroups of hyperquasigroups

The notion of intuitionistic fuzzy sets was introduced by Atanassov as a generalization of the notion of fuzzy sets. In this paper, we consider the intuitionistic fuzzification of the concept of sub-hyperquasigroups in a hyperquasigroup and investigate some properties of such sub-hyperquasigroups. In particular, we investigate some natural equivalence relations on the set of all intuitionistic fuzzy sub-hyperquasigroups of a hyperquasigroup.     

Hermite polynomial smoothing in beam-to-beam frictional contact

In this paper a smoothing procedure is suggested for the 3D beam-to-beam contact. A smooth segment is defined basing on current position vectors of three nodes limiting two adjacent finite elements. The approximated fragment of a beam axis as a 3D curve spans between the centre points of these elements. The curve is described parametrically using three Hermite polynomials. The four boundary conditions necessary to determine the coefficients for each of these polynomials involve co-ordinates and slopes at the curve ends. The slopes are defined in terms of the element nodal co-ordinates, too. There is no dependence on nodal rotations so this formulation can be embedded in a beam analysis using any type of beam finite element. This geometric representation of the curve is incorporated into the 3D beam-to-beam frictional contact model with the penalty method used to enforce contact constraints. The residual vector and the corresponding tangent stiffness matrix are determined for the normal part of contact and for the stick or slip state of friction. A few numerical examples are presented to show the performance of the suggested smoothing procedure in the cases featuring large frictional sliding.     

Stress singularities in a periodically layered composite near interface crack tips

The paper deals with the asymptotic analysis of stresses near interface crack tips in the periodically two-layered elastic composites. The problem is investigated for the plane state of strain within the framework of the homogenized model with microlocal parameters. The angular dependence of stresses at the crack tip is presented for different mechanical and geometrical properties of the composite.     

New melamine–formaldehyde–ketone polymers. III. Coatings from melamine and reactive solvents based on cyclohexanone

The conditions and methods of preparing novel melamine–formaldehyde–cyclohexanone coatings are presented. The coatings were prepared by dissolving melamine in reactive solvents based on formaldehyde and cyclohexanone. The latter were prepared at different molar ratios of the components. The water resistance of the resulting coatings was measured. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1083–1092, 2006     

The reactions of formation of selected gas products during coal pyrolysis

Pyrolysis examinations conducted under non-isothermal conditions as well at low heating rate can show that the processes of hydrogen and methane formation are the result of several constituent reactions. In the presented paper a number of these reactions has been determined separately for each of the above mentioned gaseous products. The kinetic parameters of the reactions as well as the yields of products have also been calculated. It has been found that, during coal pyrolysis, methane is formed as a result of six constituent reactions and hydrogen is produced as a result of five constituent reactions. The values of activation energy and frequency factor for the reactions in question were determined. These values fall within the range, which is typical of chemical reactions.