Papers by Author: Orsolya Koszor

Abstract: We have investigated the influence of the milling time on the structure and mechanical properties of the nanocomposite, as well as the effect of grain size on the sintering kinetics (α to β silicon nitride phase transformation). As we observed, by increasing the milling time the mechanical properties of the ceramics may be improved. The reason of this improvement is partly due to the α-Si3N4 to β-Si3N4 transformation facilitated by the smaller grain size, on the other hand it is due to the better dispersion of the carbon nanotubes. The X-ray measurements confirmed that in the case of samples milled for 5 hours, even when sintered at 1700°C, low nitrogen pressure (2MPa) and without holding time, a faster phase transformation occurs, resulting in improved mechanical properties.

Abstract: Thermophysical and tribological measurements have been performed on carbon nanotube added silicon nitride composites. Higher thermal conductivity values were observed in the case of the sample with CNT than for the reference sample. As was observed from tribological measurements, nanocomposite Si3N4 without carbon nanotubes shows a higher friction coefficient than carbon nanotube - Si3N4. The results of wear study indicate that the Si3N4 ball (used as static partner) was more damaged with MWCNTs addition nanocomposite than with pure Si3N4 ceramic. A pronounced difference was observed in the wear rate: there was a much higher wear for carbon nanotube - Si3N4 than for Si3N4 without MWCNTs.

Abstract: There is a continuous need to develop structural and functional components to sustain fusion plasma under the very severe environment such as intense radiation or high temperature in fusion reactors. The reference Si3N4 and novel Si3N4 based nanocomposites with carbon nanotube, graphene or carbon black additions were irradiated in a controlled-temperature irradiation rig inside the Budapest Research Reaktor (BRR) at a temperature of 270 °C. In the irradiation channel of BRR the 1,5×1013 n/cm2 fluence can be reached in 700 hours. The effect of the neutron radiation on the mechanical properties of Si3N4 based nanocomposites with different carbon additives was investigated. In the case of 3-point bending test graphene and carbon nanotube added samples showed an increase in strength ~100-300 MPa after irradiation. 4-point bending strength measurements resulted in a significant increase of strength in the case of reference samples ~200-400 MPa and carbon nanotube added composites ~200-300 MPa after irradiation. Other samples showed no change in strength after irradiation.

Abstract: Silicon nitride based composites with 3wt% of single wall carbon nanotubes and exfoliated graphite have been prepared. Optimisation of the manufacturing processes has been conducted to preserve the carbon nanotubes and exfoliated graphite in composites and to avoid damaging during high temperature processing. The first results show that carbon nanotubes and exfoliated graphite have a good contact to the surface of silicon nitride grains. In the case of increase of sintering pressure an increase of bending strength was achieved. It was found that microstructure features achieved by properly designed sintering parameters are the main responsible factors for the strength improvements.