Raman spectra of hot-pressed boron suboxide

Machaka, Ronald; Mwakikunga, Bonex W.; Manikandan, E.; Derry, T.E.; Sigalas, Iakovos

doi:10.5185/amlett.2010.9167

Cited by 11 publications

(7 citation statements)

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“…Asymmetrical broadening is ascribed to phonon confinement [12], a phenomenon that results from reduction of particle sizes. This phenomenon is observed in particles with diameter between 5 nm and 20 nm [13][14][15][16][17][18][19]. The spectra confirm that the NiO particles are indeed nanosized probably less than 20 nm in diameter.…”

Section: Raman Spectroscopy Before and After Thermal Ageingsupporting

confidence: 52%

Effect of Accelerated Thermal Ageing on the Selective Solar Thermal Harvesting Properties of Multiwall Carbon Nanotube/Nickel Oxide Nanocomposite Coatings

Roro

Mwakikunga

Tile

et al. 2012

International Journal of Photoenergy

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Varying amounts of dispersed multiwalled carbon nanotubes in NiO have been used to develop composites that absorb the solar energy very well but lose very little through emission. Determination of absorptance,αsol, and emissivity,εther, from such selective solar absorbers shows that the optimum efficiency of 71% can be attained when about 10 mg of MWCNTs are composited with NiO. One such absorber was subjected to thermal ageing tests. The performance criterion (PC) limit for passing the test when simulated for 25 years is(−Δα+0.25Δε)≤0.05. It was found that the typical absorber had a PC value of −0.01. This value is much better than the passing limit. Raman spectra of the typical absorber before and after the thermal ageing test showed a reduced intensity in the D and G bands of disordered and graphitic carbon, respectively but an enhancement of the NiO bands indicating loss of carbon atoms due to thermal ageing tests. Simple equations are derived determining the proportion of carbon atoms that are lost and the proportion of carbon atoms that remains in the absorber; both of these are in agreement with the original carbon composition before the thermal ageing test. It is reported that the typical absorber will retain 63% of the carbon after 25 years.

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Section: Raman Spectroscopy Before and After Thermal Ageingsupporting

confidence: 52%

Effect of Accelerated Thermal Ageing on the Selective Solar Thermal Harvesting Properties of Multiwall Carbon Nanotube/Nickel Oxide Nanocomposite Coatings

Roro

Mwakikunga

Tile

et al. 2012

International Journal of Photoenergy

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“…B 6 O powder was prepared by the reaction of B and B 2 O 3 as detailed by Andrews et al in [9] that were uniaxially hotpressed in hBN pots under argon environment at 1800 • C and 50 MPa for 20 minutes. The hot-pressed compacts were then metallographically prepared using a method prescribed by Machaka et al in [10]. The density of the hot-pressed compacts measured 2.44 g/cm 3 .…”

Section: Materials and Experimental Methodsmentioning

confidence: 99%

Analysis of the Indentation Size Effect in the Microhardness Measurements inB₆O

Machaka

Derry

Sigalas

et al. 2011

Advances in Materials Science and Engineering

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The Vickers microhardness measurements of boron suboxide (B6O) ceramics prepared by uniaxial hot-pressing was investigated at indentation test loads in the range from 0.10 to 2.0 kgf. Results from the investigation indicate that the measured microhardness exhibits an indentation load dependence. Based on the results, we present a comprehensive model intercomparison study of indentation size effects (ISEs) in the microhardness measurements of hot-pressed B6O discussed using existing models, that is, the classical Meyer's law, Li and Bradt's proportional specimen resistance model (PSR), the modified proportional specimen resistance model (MPSR), and Carpinteri's multifractal scaling law (MFSL). The best correlation between literature-cited load-independent Vickers microhardness values, the measured values, and applied models was achieved in the case of the MPSR and the MFSL models.

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“…The G1 band comprises vibrational modes observed below 600 cm À1 , G2 shows modes between 600 cm À1 and 950 cm À1 , and G3 comprises modes between 950 cm À1 and 1200 cm À1 . According to results reported in [24], the G1 group of Raman peaks is attributed to vibrational modes involving oxygen atoms. In particular, the Raman peak observed at 375 cm À1 , which is characteristic of the O-O chain vibration, has very weak intensity and is barely visible.…”

Section: Characterization Of the Combustion Productsmentioning

confidence: 61%