Nanophase alumina synthesis in thermal arc plasma and characterization: correlation to gas-phase studies
| Autor: | Sudha V. Bhoraskar, V.K. Rohatgi, S. Badrinarayanan, N. D. Sali, P. Madhu Kumar, C. Balasubramanian |
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| Rok vydání: | 1999 |
| Předmět: |
Materials science
Absorption spectroscopy Band gap Mechanical Engineering Analytical chemistry Infrared spectroscopy Condensed Matter Physics Electron diffraction X-ray photoelectron spectroscopy Mechanics of Materials Transmission electron microscopy Phase (matter) Zeta potential General Materials Science |
| Zdroj: | Materials Science and Engineering: B. 63:215-227 |
| ISSN: | 0921-5107 |
| DOI: | 10.1016/s0921-5107(99)00038-0 |
| Popis: | Nanophase alumina (Al2O3) was synthesized in a d.c. arc plasma reactor under isochronal oxygen flow conditions. Transmission electron microscopy revealed spherical particles (50 nm) and the corresponding electron diffraction showed a δ-Al2O3 phase. Structural morphology by X-ray diffraction (XRD) evidenced the phase changes. These measurements confirmed the existence of the nanophase structure. X-ray photoelectron spectrsocopy (XPS) of the core levels of as-deposited, and calcined powders were carried out for comparative study. Zeta potential as determined from electrophoretic mobility measurements, at a pH value of 4, indicated a high value (+42.7 mV) for the nanophase alumina as compared to that for the commercial alumina (−14.1 mV). This is a measure of the state of agglomeration, which is higher for the nanophase alumina. Fourier transform infrared spectra of the alumina powder revealed a broad band from 500 to 1000 cm−1, indicative of the complex Al–O vibration due to interactions of the octahedral and tetrahedral coordination groups. The FTIR spectra also revealed the intermediate route leading to alumina formation, as seen from the presence of gas-phase type sub-oxide bands. In addition the presence of a strained surface vibrational mode retaining itself even after complete transformation to α-Al2O3 is confirmed. Optical absorption spectroscopy was studied yielding a band gap for the nanophase alumina of >5 eV. The Infrared and the absorption spectrum is characteristic of a gas-phase type of reaction. Thus a dimensional evolution starting from a gas-phase precursor, which is molecular in nature, leads to a collisionally quenched structure resulting in very fine particulates condensing from the plasma. |
| Databáze: | OpenAIRE |
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