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Bekhta P.,National University of Forestry and Wood Technology of Ukraine | Sedliacik J.,Technical University In Zvolen
International Wood Products Journal | Year: 2015

The aim of this work was to study the bondability of birch (Betula verrucosa Ehrh.) veneer subjected to different surface treatments (chemical treatment, short term thermo-mechanical densification, and combination of these two processes) using phenol-formaldehyde (PF) resin with the aim of improving bonding during the production of plywood. Four chemical agents (hydrogen peroxide, aluminium potassium sulphate, potassium carbonate, and potassium permanganate) were used for chemical treatment of the veneer surface. The veneer samples were thermo-mechanically densified between heated plates of a laboratory press. The results revealed that short term thermo-mechanical densification and combined chemical and thermo-mechanical pre-treatment of the veneer surface prior to the resin application reduced the glue spread (a 33% reduction) and improved the bondability of the veneer. The obtained shear strength values for all of the studied treatments exceeded the standard requirements (1.0 MPa), and the properties of the plywood samples satisfied the European standard EN 314-2. © 2015 IWSc. Source

Reshak A.H.,University of South Bohemia | Reshak A.H.,University Malaysia Perlis | Reshak A.H.,Czestochowa University of Technology | Kityk I.V.,Czestochowa University of Technology | And 6 more authors.
Journal of Alloys and Compounds | Year: 2013

The influence of crystallochemical affinity for crystals ZrGa2 and ZrGa3 on the optical properties was studied. We have calculated dispersion of optical constants ε2average(ω). We have established that application of different exchange correlation potentials XC has no significant effect on the optical constant dispersion. Moreover, use of LDA, GGA and EVGGA has an insignificant effect on the corresponding optical features. The crystallochemical transformation between the two titled compounds leads to a spectral shift of the whole ε2average(ω) structure: for ZrGa 3 it leads to higher energy shift with respect to ZrGa2. Moreover, one can see that the first spectral peak of ε2average(ω) for ZrGa2 which situated at around 0.5 eV becomes very small for ZrGa3 but still situated in the same location. The first right hand side hump in ε2average(ω) - ZrGa2 which is located at around 1.5 eV becomes pronounced and situated at around 2.2 eV in ε2average(ω) - ZrGa3. For more complete information we have calculated dispersions of the electronic loss function, reflectivity and the optical conductivity. © 2012 Elsevier B.V. All rights reserved. Source

Reshak A.H.,University of South Bohemia | Reshak A.H.,University Malaysia Perlis | Lakshminarayana G.,Los Alamos National Laboratory | Ebothe J.,University of Reims | And 5 more authors.
Journal of Alloys and Compounds | Year: 2013

Using FP-LAPW Method we have performed calculations of the band structure of the ZrGa2 and ZrGa3 crystals. The all-electron full potential linearized augmented plane wave method was used to solve the Kohn Sham DFT equations. We have explored different approximations using three kinds of exchange-correlation potentials on the electronic structure and we concluded that there is insignificant influence on the band structure and the density of states. It is clear that there exists a difference in the band dispersion with one move from ZrGa2 to ZrGa3 that is attributed to the fact that ZrGa2 has four formula per unit cell (Z = 4) while ZrGa3 has two formula per unit cell (Z = 2). Despite some similarity in the crystallochemistry of ZrGa2 to ZrGa3 some differences are observed in the band structure dispersion. There is a strong hybridization between the states. The interaction of charges between Zr and Ga atoms is due to the strong hybridization, and the covalent bond arises due to the degree of hybridization. Hence, there is a strong covalent bonding between these atoms. We have obtained a space electron charge density distribution in the average unit cell by calculations of the electron charge density distribution. The space electronic charge density contour distribution is illustrated in (1 0 0) and (1 1 0) planes. © 2012 Elsevier B.V. All rights reserved. Source

Sichevych O.,Max Planck Institute for Chemical Physics of Solids | Sichevych O.,National University of Forestry and Wood Technology of Ukraine | Krellner C.,Max Planck Institute for Chemical Physics of Solids | Krellner C.,University of Cambridge | And 3 more authors.
Journal of Physics Condensed Matter | Year: 2012

Single crystals of the new ternary compound Ce 2Ga 12Ptwere prepared by the self-flux technique. The crystal structure with the space group P4/nbm was established from single crystal x-ray diffraction data and presents a derivative of the LaGa 6Ni 0.6 prototype. Magnetic susceptibility measurements show CurieWeiss behaviour due to local Ce 3+ moments. At high temperatures, the magnetic anisotropy is dominated by the crystal-electric-field (CEF) effect with the easy axis along the crystallographic c direction. Ce 2Ga 12Ptundergoes two antiferromagnetic phase transitions at T N,1=7.3K and T N,2=5.5K and presents several metamagnetic transitions for the magnetic field along c. Specific-heat measurements prove the bulk nature of these magnetic transitions and reveal a doublet CEF ground state. The 4f contribution to the resistivity shows a broad maximum at T max85K due to Kondo scattering off the CEF ground state and excited levels. © 2012 IOP Publishing Ltd. Source

Bryn O.,National University of Forestry and Wood Technology of Ukraine
26th International Conference on Wood Science and Technology, ICWST 2015: Implementation of Wood Science in Woodworking Sector - Proceedings | Year: 2015

The possibility of applying conventional flame retardants usually used to improve fire behaviour of wood was evaluated in this study for the production of fire-resistance plywood panels. For making plywood the birch (Betula verrucosa Ehrh.) veneer and commercial phenol-formaldehyde glue resin were used. Five different standardized fire-retardants (-1110, -11, C-13, M-11, C-11) were chosen for veneer impregnation. Firstly, veneer sheets were treated by immersion in 20% aqueous solution of each fire-retardant. Diffusive and capillary methods were evaluated to select the most effective treatment of veneer. Afterwards, five-layer plywood panels were prepared from impregnated and non-impregnated veneers in laboratory press at the following pressing parameters: pressure of 2.0 MPa, temperature of 130°C, time of 10 min, and glue spread of 120 g/m2. Shear strength and fire resistance of plywood were determined. It was found that diffusive method of impregnation of moist veneer, in comparison with capillary method of impregnation of dry veneer, is characterized by the less salting-out of fire-retardants on the veneer surface and their more homogeneous distribution in middle of veneer. It was also found that using of conventional wood fire-retardants for plywood allows to transfer plywood from the group of increased flammability materials to the group of hard inflammable materials. But unfortunately, investigated fire-retardants don't provide the necessary shear strength of plywood panels. Source

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