Synthesis of nanocrystalline titanium carbide by spark erosion
Interest in nanocrystaJline ceramic powders is due to their attractive processing and mechanical properties. The disadvantages of conventional ceramics, such as large internal flaws, negligible ductility, hightemperature processing, can possibly be eliminated or minimized by starting with finegrained powders. A previous study on the sinterability of nanocrystalline ceramic powders showed that high densities can be achieved at lower temperatures, both with and without the’ application of pressure [ 11. In addition, it is remarkable that superplastic behavior has been reported in nanocrystalline ceramics at room temperature [2]. One of the novel methods for nrenaring nanocrvstalline ceramic powders is reactive spark erosion [3-51. An important feature of this method is the-capability to synthesize new materials by reacting the eroded particles with the dielectric liguid. This technique utilizes two metal or conducting electrodes sparked in a suitable dielectric liquid that reacts with the pa&les to produce the desired ceramic powders. The high temperature provided by the spark results in vaporization of the electrodes and the surrounding dielectric liquid; the reaction products formed between the various vapor species are quenched in the liquid and produce spherical particles. The aim of the present note is to report on the titanium carbide particle formation in a carbonic dielectric liquid (pentane) with titanium electrodes and charges. The nanocrystalline titanium carbide was produced in a wide range of particle size distribution and in the form of single phase spheres.
Processing of porous GaAs at low frequency sparking
We report on the preparation of photoluminescent porous GaAs by the application of high voltage spark discharges at low repetition rates (20 Hz) in air and in argon atmospheres. The spark-processed porous (spp) samples were characterized by the observation of their visible photoluminescence (PL) when illuminated with UV monochromatic radiation. In contrast to previous work on spp-GaAs at high sparking frequencies we find that the PL of samples prepared at low sparking frequency is highly reproducible from sample to sample. Important differences are observed in the initial PL spectra of the spp-GaAs according to the atmosphere of preparation under similar conditions. After prolonged air exposure both the spp-GaAs prepared in air and in argon show two similar broad peaks at energy positions 2.5 and 3.1 eV. Raman results indicate that the PL might not be associated to any size dependent mechanism. We present evidence that oxygen compounds formed by the exposure to air of the samples play a role in the PL exc...
Atomic structure of amorphous particles produced by spark erosion
The atomic structure of amorphous particles of composition ${\mathrm{Fe}}_{75}$${\mathrm{Si}}_{15}$${\mathrm{B}}_{10}$ produced by spark erosion was studied by the energy-dispersive x-ray diffraction technique and was compared to that of the amorphous ribbon of the same composition produced by melt spinning. It was found that the nearest-neighbor Fe-Fe correlation is almost identical for the ribbon and the particles of different sizes, whereas the second peak of the radial distribution function shows considerable differences among the samples. The result is consistent with decreased metal-metalloid compositional short-range order in the particles compared to that in the ribbon sample.