Papers by Author: Zófia Vértesy

Abstract: The deformation of ceramic matrix composites (CMC) is controlled by several processes occurring in the matrix, in the enforcing phase, at the interfaces between different phases and at the surface of the body. The main tool to study morphology features of CMC-s is high resolution scanning electron microscopy (SEM). In this study destructive chemical methods such as chemical etching and burning of combustible phases were used to prepare samples for SEM investigations from three types of materials. I. SiC skeletons of C/C-SiC structures prepared of 2D woven fabric and chopped fiber bodies were produced by chemical elimination of the constituents: Si, reinforcing C- fibers and amorphous carbon. II. Silicon-nitride reaction bonded silicon-carbide samples with finishing surface oxide films – as produced and aged - were handled by HF etchants. Etching revealed cristobalite crystallites at the interface between ceramics and oxide film, and cracks in the glassy surface layer. III. Microstructure and pore structure of Si3N4 ceramics, carbon nanotube reinforced Si3N4 (CNT/Si3N4), and C/Si3N4 with graphite and carbon black addition were examined by HF etching.

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.

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.

Abstract: Ownvkycnn" ectdqp" pcpqvwdg" tgkphqtegf" uknkeqp" pkvtkfg" eqorqukvgu" jcxg" dggp" tgcnkugf" d{" jqv"kuquvcvke"rtguukpi0"Qrvkokucvkqp"qh"vjg"ocpwhcevwtkpi"rtqeguugu"jcu"dggp"eqpfwevgf"vq"rtgugtxg" vjg" ectdqp" pcpqvwdgu" kp" eqorqukvgu" cpf" vq" cxqkf" fcocig" fwtkpi" jkij" vgorgtcvwtg" *3922̇E+" cpf" jkij"pkvtqigp"icu"rtguuwtg"*42"ORc+"rtqeguukpi0"Cu"ujqyp"d{"uecppkpi"cpf"vtcpuokuukqp"gngevtqp" oketqueqr{"ectdqp"pcpqvwdgu"jcxg"iqqf"cfjgtgpeg"vq"vjg"uknkeqp"pkvtkfg"itckpu."cu"qdugtxgf"hqt"nqy" cpf"jkij"rtguuwtg"rtqeguukpi"cu"ygnn0"Oqtgqxgt."ectdqp"pcpqvwdgu"jcxg"dggp"hqwpf"vq"dg"nqecvgf" pqv" qpn{" cv" itckp" dqwpfct{" uwthcegu." dwv" oc{" dg" kpeqtrqtcvgf" fktgevn{" kpvq" uknkeqp" pkvtkfg" itckpu0" Eqorqukvgu"ykvj"jkijgt"uvtgpivju"ecp"dg"qdvckpgf"d{"kpetgcukpi"vjg"pkvtqigp"icu"rtguuwtg0""""

Abstract: This work is focusing on exploring preparing processes to tailor the microstructure of carbon nanotube (CNT) reinforced silicon nitride-based ceramic composites. Samples with different porosity’s and different amount (1, 3 or 5 wt%) of carbon nanotubes have been prepared by using gas pressure sintering or hot isostatic pressing. In comparison, composites with 1wt%, 5wt% or 10wt% carbon black and graphite have been manufactured. We measured the room temperature mechanical and electrical properties, examined the micro and nano structure by X-ray diffraction and electron microscopy. It was found that it is possible to develop CNT-silicon nitride composite for applications where a decent electric conductivity and good mechanical properties are required.