ISSN:
1662-9779
Source:
Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
Topics:
Physics
Notes:
Electric discharge assisted mechanical milling using a 50 Hz power supply has been usedto produce a range of fine and nanostructural products, including nanocrystalline aglomerates andindividual nano-particles and nano-fragments. Processing variables include; starting powder samplesize; electric arc parameters such as arc length and arc voltage/current; mechanical millingparameters; gas atmosphere and ionized gas species present. We describe results of an experimentalprogram underway to investigate phase transformations and/or particle fragmentation duringdischarge milling using a new pulsed power supply working at frequencies in the kHz range. Theaims of this preliminary investigation were to determine processing parameters required for thesynthesis of potentially useful high surface area particles, nanostructural powders and nanoparticles,and to compare products with those synthesised by Hz frequency discharge milling.Microstructural, morphological, and phase changes induced by kHz discharge milling werecharacterised by x-ray diffractommetry and transmission electron microscopy. Results were found todepend on the often competing processes of fragmentation into nano-particles, agglomeration ofpowder particles, particle melting and/or sintering, and chemical reaction induced by mechanoprocessingin the presence of a particular type of plasma. Discharge milling of graphite underAr/4%H2 resulted in a range of products including; graphite nanostructures, carbon nanotubes andother exotic nanofragments. It was found that, compared with processing at 50 Hz, high frequency(kHz) electric discharge assisted mechanical milling of graphite resulted in higher yields of carbonnanotubes. hematite resulted in partial reduction to magnetite and FeO,and the formation ofnanostructural oxide nanorods and nanorod clusters. Discharge milling of Co-WC resulted inproducts including; micron and submicron fracture products, nanostructural regions of Co and WC,and carbon rich nanorods and nanotubes
Type of Medium:
Electronic Resource
URL:
http://www.tib-hannover.de/fulltexts/2011/0528/02/22/transtech_doi~10.4028%252Fwww.scientific.net%252FSSP.114.277.pdf
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