Authors: Mihail Chubarov, Henrik Pedersen, H. Högberg, Magnus Garbrecht, Zsolt Czigány, Sven G. Andersson, Anne Henry
Abstract: We give here an overview of our recent work on growth of rhombohedral boron nitride (r-BN) thin films on SiC substrates by chemical vapor deposition (CVD). We demonstrate the growth of twinned r-BN on various SiC polytypes at 1500 °C, using H2 as carrier gas and triethyl boron and ammonia as precursors with an N/B ratio of ~ 640. The epitaxial relation with various substrates is determined from XRD and TEM. Adding Si to the gas phase stabilizes the r-BN phase but does not alter the electric properties of the material which remains electrically insulating.
990
Authors: Peter Kun, Orsolya Tapasztó, Zsolt Czigány, Csaba Balázsi
Abstract: As graphene nanomaterials present exceptional mechanical, thermal and electric properties therefore it can be an excellent reinforcement material for ceramic composites. The research of ceramic composites incorporated with carbon-based fillers has focused on carbon nanotubes until now. In this work silicon nitride-based nanocomposites have been prepared with different ammount (1 and 3 wt%) of multilayer graphene (MLG) made by mechanical milling-based method as well as exfoliated graphite nanoplatelets (xGnP) and nanographene platelets (Angstron) in comparison. The morphology and microstructure of the sintered samples were studied by scanning electron microscope and transmission electron microscope. Phase compositions were determined by X-ray diffractometer. The bending strength and elastic modulus of MLG-silicon nitride composites showed enhanced values compared to the other graphene reinforced silicon nitride ceramic composites.
252
Authors: E. Broitman, A. Furlan, Gueorgui K. Gueorguiev, Zsolt Czigány, H. Högberg, L. Hultman
Abstract: The inherent resiliency, hardness and relatively low friction coefficient of the fullerene-like (FL) allotrope of carbon nitride (CNx) thin solid films give them potential in numerous tribological applications. In this work, we study the substitution of N with P to grow FL-CPx to achieve better cross- and inter-linking of the graphene planes, improving thus the material’s mechanical and tribological properties. The CNx and CPx films have been synthesized by DC magnetron sputtering. HRTEM have shown the CPx films exhibit a short range ordered structure with FL characteristics for substrate temperature of 300 °C and for a phosphorus content of 10-15 at.%. These films show better mechanical properties in terms of hardness and resiliency compared to those of the FL-CNx films. The low water adsorption of the films is correlated to the theoretical prediction for low density of dangling bonds in both, CNx and CPx. First-principles calculations based on Density Functional Theory (DFT) were performed to provide additional insight on the structure and bonding in CNx, CPx, and a-C compounds.
581
Authors: Csaba Balázsi, Zsolt Czigány, Ferenc Wéber, Zoltán Kónya, Zófia Vértesy, László Péter Biró, Imre Kiricsi, Péter Arató
Abstract: Multiwall carbon nanotube reinforced silicon nitride composites have been prepared by
hot isostatic pressing. A manufacturing process has been worked out to avoid the damage of
nanotubes during sintering. This method provides their preservation even in severe circumstances at
temperature 1700°C and gas pressure 20 MPa. As shown by scanning and transmission electron
microscopy after low and high pressure processing, carbon nanotubes have good adherence to the
silicon nitride grains. Moreover, carbon nanotubes have been found to be located not only at grain
surfaces, but in several cases they are well integrated with the silicon nitride grains. Composites
with higher strengths can be obtained by increasing the nitrogen gas pressure.
123
Authors: Dóra Janovszky, Jenő Sólyom, András Roósz, Zsolt Czigány
Abstract: The devitrification of the Fe-Ni-B-Si amorphous ribbon was investigated by the
differential scanning calorimetry (DSC) with scanning and isothermal methods. The
devitrification of rapidly quenched ribbons is a multilevel process. On the basis of DSC
investigations it was determined that crystallization occurs in three processes up to 700°C in
the Fe40Ni40B16Si4 alloy. In the present work the first and second steps have been discussed.
The first crystallization step involves the segregation of the Fe-Ni crystalline solid solution
from the amorphous matrix. During the second crystallization phase, in addition to austenite,
nickel silicide and two types of iron borides crystallize as well. The ribbons were relaxed at
380°C for 2 hours, following the pre-annealing at different temperatures. Pre-annealing was
performed in the DSC within the temperature range elapsing from 395°C to 420°C. The preannealing
at temperatures below the first exothermal DSC peak has an effect on the
crystallization processes. After the pre-annealing the samples were investigated by DSC. The
DSC peak of the first crystallization step shifts to higher temperatures and decrease its
enthalpy. The scanning DSC measurements, applied after the isothermal pre-annealing, were
performed in order to determine the fraction of the ribbon transformed in the primary
crystallization step. The second DSC peak shifts to lower temperatures with a maximum of
4°C. The X-ray diffraction (XRD) analyses reveal that the lattice constant changes with the
pre-annealing temperatures. Such observation was also supported by the circumstance that the
composition of the Fe-Ni solid solution undergoes certain modifications.
185
Authors: Csaba Balázsi, Zsolt Czigány, Ferenc Wéber, Zsuzsanna Kövér, Zoltán Kónya, Zófia Vértesy, László Péter Biró, Imre Kiricsi, Péter Arató
Abstract: Ownvkycnn" ectdqp" pcpqvwdg" tgkphqtegf" uknkeqp" pkvtkfg" eqorqukvgu" jcxg" dggp" tgcnkugf" d{"
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cpf"jkij"rtguuwtg"rtqeguukpi"cu"ygnn0"Oqtgqxgt."ectdqp"pcpqvwdgu"jcxg"dggp"hqwpf"vq"dg"nqecvgf"
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97
Authors: László S. Tóth, Béla Pécz, Zsolt Czigány, K. Amimer, A. Georgakilas
999
Authors: Zsolt Czigány, D. Mademann, P. Weissbrodt, E. Hacker
233
Authors: Zsolt Czigány, György Z. Radnóczi
235