Journal
NANOSCALE RESEARCH LETTERS
Volume 3, Issue 11, Pages 421-426Publisher
SPRINGER
DOI: 10.1007/s11671-008-9172-y
Keywords
FTIR spectroscopy; Raman spectroscopy; Carbon nanoparticles; Oxide matrices
Funding
- CSIR-National Laser Centre
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Coatings of carbon nanoparticles dispersed in SiO2, ZnO and NiO matrices on aluminium substrates have been fabricated by a sol-gel technique. Spectrophotometry was used to determine the solar absorptance and the thermal emittance of the composite coatings with a view to apply these as selective solar absorber surfaces in solar thermal collectors. Cross-sectional high resolution transmission electron microscopy (X-HRTEM) was used to study the fine structure of the samples. Raman spectroscopy was used to estimate the grain size and crystallite size of the carbon clusters of the composite coatings. X-HRTEM studies revealed a nanometric grain size for all types of samples. The C-SiO2, C-ZnO and C-NiO coatings contained amorphous carbon nanoparticles embedded in nanocrystalline SiO2, ZnO and NiO matrices, respectively. Selected area electron diffraction (SAED) showed that a small amount of Ni grains of 30 nm diameter also existed in the NiO matrix. The thermal emittances of the samples were 10% for C-SiO2, 6% for the C-ZnO and 4% for the C-NiO samples. The solar absorptances were 95%, 71% and 84% for the C-SiO2, C-ZnO and C-NiO samples, respectively. Based on these results, C-NiO samples proved to have the best solar selectivity behaviour followed by the C-ZnO, and last were the C-SiO2 samples. Raman spectroscopy studies revealed that both the C-ZnO and C-NiO samples have grain sizes for the carbon clusters in the range 55-62 nm and a crystallite size of 6 nm.
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