Synthesis of zinc ferrite nanopowders in an RF thermal plasma

Nanosized zinc ferrite spinel powders of various compositions were produced in an RF thermal plasma from oxide mixtures and from co-precipitated hydroxides. The products were characterised for bulk chemical (ICP-AES), and phase composition (XRD). In spite of the short residence time of the reagents in the plasma reactor considerable extent of spinel formation was achieved. Magnetization and Curie point measurements indicated that the spinel phases exhibited ferrimagnetic behaviour. Ferrites synthetized in the RF plasma reactor were compared to that produced by the conventional ceramic route

Atmospheric ageing of nanosized silicon nitride powders

Ambient oxidation of nanosized silicon nitride powder produced by the vapour phase reaction of silicon tetrachloride and ammonia has been studied in this work. Aliquots of the powder were stored in argon gas, in dry air and in air of 80% humidity, and changes in the bulk and surface properties were investigated against the ageing time. The powder samples were characterised by wet chemical analysis, XPS, TG-MS, FTIR, XRD and TEM methods. No significant changes were detected on storage in argon gas for 90 days. However, in samples stored in dry air and humid air, remarkable oxidation and formation of N-H species were found. The particulate powder tends to agglomerate in both dry and humid air, and this results in changes in the particle size and morphology. The nanosized silicon nitride powders therefore should be processed by excluding their contact with the oxygen and moisture containing ambient atmosphere

Synthesis of Zinc Ferrites in RF Thermal Plasma Reactor

Formation of nanosized zinc ferrite spinels was studied from iron- and zinc oxide powders and corresponding nitrate solutions, respectively in a radiofrequency thermal plasma reactor. From the viewpoint of applications, the research was motivated by the potential use of these materials in advanced magnetic devices on the one hand, and by their biomedical applications such as drug carriers or agents for cancer treatment by hyperthermia on the other. In this work effects of synthesis conditions on properties of products were studied in details. The products were characterised for chemical composition, phase conditions, particle size distribution, morphologies and saturation magnetisation. Most products exhibited ferrimagnetic behaviour. Correlations among domain- and particle sizes were also investigated. Conditions for the synthesis of nanosized, inverse zinc ferrites of high saturation magnetisation were established. It was proved that in thermal plasma conditions normal and inverse ferrites could be produced in a single step process

Synthesis of Spinel Ferrites in Radiofrequency Thermal Plasma Reactor

Formation of nanosized zinc-ferrites and nickel-zinc ferrites from iron- and zinc oxide powders and corresponding nitrate solutions, respectively, was studied in RF thermal plasma conditions. The products were characterized for chemical composition, phase conditions, particle size distribution, morphologies and saturation magnetization. Effects of synthesis conditions on properties of products were studied in details

Crystallite size distribution and dislocation density in nanocrystalline silicon nitride powders produced by two different procedures

Két különböző eljárással készült nanokristályos szilicium-nitrid por mikroszerkezetét vizsgáltuk röntgen vonalprofil analízissel. Az egyik mintát termikus plazmában SiCl(4) és NH(3) gőzfázisú szintézisével majd kristályosításával készítettük, míg a másik egy a kereskedelmi forgalomban kapható por, amit szilicium nitridálásával majd őrlésével állítottak elő. A porok szemcseméreteloszlását és diszlokációsűrűségét röntgen vonalprofil analízissel határoztuk meg. Megállapítottuk, hogy a nitridálással és őrléssel előállított por szemcséinek átlagos mérete kisebb, míg eloszlásuk szélesebb mint a plazmában előállított mintáé. Mindkét por diszlokációsűrűsége 10(14) és 10(15) m(-2) között volt. A röntgen diffrakciós mérésből meghatározott szemcseméret jól egyezik a fajlagos felületből számolt értékkel és az elektronmikroszkópos megfigyelésekkel. | Two silicon nitride powders were investigated by high resolution X-ray diffraction. The first sample was crystallized from the powder prepared by the vapor phase reaction of silicon tetrachloride and ammonia in thermal plasma while the second was a commercial powder produced by the direct nitridation of silicon and milling. Their crystallite size and dislocation density were obtained by the recently developed procedure of diffraction profile analysis. In this procedure assuming spherical shape and log-normal size distribution of crystallites, the Fourier coefficients of the measured physical profiles are fitted by the Fourier coefficients of well established ab initio functions of size and strain peak profiles. The anisotropic broadening of peak profiles is accounted for by the dislocation model of the mean square strain in terms of average dislocation contrast factors. The area-weighted average particle size calculated from nitrogen adsorption isotherms was in good agreement with that obtained from X-rays. The powder produced by silicon nitridation and milling has a wider crystallite size distribution with a smaller average size than the powder prepared by vapor phase reaction in thermal plasma and subsequent crystallization. The dislocation densities were found to be between 10(14) and 10(15) m(-2)

Nagydiszperzitású kerámiaporok és fullerén-származékok szintézise termikus plazmákban = Synthesis of highly-disperse ceramic powders and fullerene derivatives in thermal plasmas

A pályázat keretében bizonyítottuk, hogy a rádiófrekvenciás termikus plazmareaktorban hatékonyan és gyorsan lehet előállítani különleges tulajdonságú és morfológiájú mikro- és nanoporokat. Tisztáztuk a mikro- és nanoporok olvadék-gáz és gáz-gőzfázisú reakciókban történő előállításának több kémiai és kinetikai kérdését. Feltártuk az RF termikus plazmában végzett anyagszintézis körülményei és a reakciótermékek összetétel, szerkezete és tulajdonságai közötti kapcsolatok számos részletét. Megkezdtük azokat az alkalmazástechnikai kutatásokat, amelyek a jelen pályázat keretében szerzett új ismeretek és az itt előállított nanoanyagok gyakorlati hasznosításának előkészí-tésére irányulnak. | We proved in the project that the radiofrequency thermal plasma reactor is a suitable tool to produce micro- and nanopowders of special properties and morphology at high production rate. We answered several important chemical and kinetical questions related to the synthesis of micro- and nanopowders by high-temperature liquid-gas and vapor-phase reactions. We revealed some details of connections among conditions of materials synthesis in RF thermal plasma and the composition, structure and properties of reaction products. We started application tests aiming at practical implementation of knowledge acquired in the project and also at producing advanced functional materials from thermal plasma powders

Deposition of Silicon Carbide and Nitride Based Coatings by Atmospheric Plasma Spraying

In this work atmospheric plasma spraying of SiC and Si3N4 was investigated. Plasma spraying of these ceramics raises several problems since they would tend to decompose instead of melting at elevated temperatures during the process. To circumvent this problem the non-oxide ceramics were deposited as a composite powder mixed with non-oxide ceramic particles resulting in a ceramic/ceramic composite structure. Our findings were that using such a composite feedstock powder both oxidation and decomposition of the non-oxide particles could be avoided. A vitrified phase was also developed in the coating