Carbon-bonded materials are widely used in refractory applications because of their unique chemical, physical, and mechanical properties at high temperatures. The mechanisms of their high-temperature ...deformation are, however, unclear. The present study reveals new results from mechanical testing of both fine-grained, carbon-bonded alumina and graphite (ISEM 8) observed at temperatures of up to 1500 °C in an inert atmosphere. The results were achieved by means of microstructural investigations by scanning electron microscopy. For Al2O3-C, a pronounced maximum strength vs. testing temperature occurred at 1300–1400 °C, with a change from brittle to ductile behavior. In contrast, graphite showed an increase in strength until 1500 °C and no evidence of ductile deformation. A model based on the differences in the coefficients of thermal expansion of the components is presented to explain this phenomenon. In addition, Raman spectroscopy revealed the formation of graphitic structures due to testing at 1500 °C.
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Open cell ceramic foam filters are used for metal melt filtration to enhance the quality of cast products by reducing non-metallic inclusions and generating calm mold fill with less turbulences. A ...new generation of filters made of carbon-bonded alumina show an increased thermal shock resistance but a lower strength. The filters have to withstand high thermal and mechanical loads due to the filtration process, whereas a temperature dependent mechanical characterization of the bulk material is required.
This contribution concentrates on the influence of carbon content and coking temperature, which are two important manufacturing process parameters. In the ball on three balls test miniaturized disk-shaped specimens are loaded with a spherical tipped punch at temperatures up to 1500∘C until failure occurs. The fracture stress is calculated and used to analyze the material strength by means of Weibull distribution.
Two different mechanisms are identified, which change the micro-structure and therewith the strength of the material. Additionally, Raman spectroscopy supports the interpretation of the achieved results of the mechanically tested specimens.
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New carbon-bonded alumina filters for steel melt filtration were developed. The carbonaceous matrix was based on a new, environmental friendly binder system based on lactose and tannin. The filter ...preparation was analogous to the production of conventional foam filters according to the Schwartzwalder process. The processing as well as the rheology of the slurries was investigated. An addition of n-Si increased the carbon yield and the cold crushing strength (CCS) of the samples. Higher values of CCS were obtained after coating of the filters with alumina. The material was characterized by scanning electron microscopy, X-ray diffraction and Raman spectroscopy. The applicability of these new filters was assessed in impingement tests with a steel melt, in which three out of four recipes survived the thermal shock.
•Ripples obtained on carbon films after irradiation with visible ps laser pulses.•Amorphous carbon was transformed in nanographite following irradiation.•Ripples had a complex morphology, being made ...of islands of smaller ripples.•Hydrophilic carbon films became hydrophobic after surface structuring.
Thin films of carbon were synthesized by ns pulsed laser deposition in vacuum on silicon substrates, starting from graphite targets. Further on, the films were irradiated with a picosecond laser source emitting in visible at 532nm. After tuning of laser parameters, we obtained a film surface covered by laser induced periodical surface structures (LIPSS). They were investigated by optical, scanning electron and atomic force microscopy. It was observed that changing the irradiation angle influences the LIPSS covered area. At high magnification it was revealed that the LIPSS pattern was quite complex, being composed of other small LIPSS islands, interconnected by bridges of nanoparticles. Raman spectra for the non-irradiated carbon films were typical for a-C type of diamond-like carbon, while the LIPSS spectra were characteristic to nano-graphite. The pristine carbon film was hydrophilic, while the LIPSS covered film surface was hydrophobic.
•Thin polycrystalline SiC films grown by the pulsed laser deposition technique were irradiated by 800keV Ar ions at a dose of 2.6×1014at/cm2.•The SiC films hardness and Young modulus values ...significantly decreased after irradiation.•Glancing X-ray diffraction investigations showed a partial transformation of the SiC hexagonal phase into the cubic phase.•Smooth PLD grown thin films are excellent for radiation effects investigations using XRR, GIXRD and nanoindentation techniques.
The effects of 800keV Ar ion irradiation on thin nanocrystalline SiC films grown on (100) Si substrates using the pulsed laser deposition (PLD) technique were investigated. On such PLD grown films, which were very dense, flat and smooth, X-ray reflectivity, glancing incidence X-ray diffraction and nanoindentation investigations were easily performed to evaluate changes induced by irradiation on the density, surface roughness, crystalline structure, and mechanical properties. Results indicated that the SiC films retained their crystalline nature, the cubic phase partially transforming into the hexagonal phase, which had a slightly higher lattice parameter then the as-deposited films. Simulations of X-ray reflectivity curves indicated a 3% decrease of the films density after irradiation. Nanoindentation results showed a significant decrease of the hardness and Young's modulus values with respect to those measured on as-deposited films. Raman and X-ray photoelectron spectroscopy investigations found an increase of the CC bonds and a corresponding decrease of the SiC bonds in the irradiated area, which could explain the degradation of mechanical properties.
Raman scattering in orthorhombic CuInS2 nanocrystals Dzhagan, V. M.; Litvinchuk, A. P.; Valakh, M. Ya ...
Physica status solidi. A, Applications and materials science,
01/2014, Volume:
211, Issue:
1
Journal Article
Peer reviewed
We report the results of non‐resonant and resonant Raman scattering in orthorhombic nanocrystalline CuInS2 semiconductor, supported by density functional first principle lattice dynamics ...calculations. A larger number of dominant phonon modes in comparison with standard tetragonal CuInS2 phases is shown to be associated with peculiarities of cation sublattice ordering and is the “fingerprint” of the corresponding structural polymorph. Good overall agreement is found between theoretical and experimental phonon mode frequencies.
Single crystals of Mott-Hubbard insulator LaVO3 exhibit spin and orbital ordering along with a structural change below ≈140 K. The occurrence of orbital ordering in epitaxial LaVO3 films has, ...however, been little investigated. By temperature-dependent Raman scattering spectroscopy, we probed and evidenced the transition to orbital ordering in epitaxial LaVO3 film samples fabricated by pulsed-laser deposition. This opens up the possibility to explore the influence of different epitaxial strain (compressive vs. tensile) and of epitaxy-induced distortions of oxygen octahedra on the orbital ordering, in epitaxial perovskite vanadate films.
Vapor deposition of perfluorinated phthalocyanines with bulky perfluorpropyl groups (F
64Pc) yielded intensely colored thin films (20–100 nm) despite the large molecular weight.
In situ electrical ...conduction and optical transmission measurements revealed an almost negligible extent of intermolecular electronic coupling. Such quasi-independent character of molecules in solids was confirmed by detailed spectroscopic ellipsometry. The influence of the bulky peripheral groups on the packing in the films and on the electronic and optical properties of the films as well as potential applications of this class of strong electron acceptors are discussed.
We have studied the vibrational properties of perfluoropentacene (PFP) thin films on highly oriented pyrolytic graphite (HOPG) substrates by high-resolution electron energy loss spectroscopy (HREELS) ...and Raman spectroscopy. The HREELS spectra showed slight but clear increase in the vibrational energies with increasing film thickness as well as with decreasing temperature of the multilayer films. In the polarization-dependent Raman spectra of a multilayer film, the depolarization ratios of all detected vibrations with the Ag irreducible representation were found to be larger than 1, indicating that the molecular structure is distorted in the multilayer. Both results suggest that there is a fairly strong intermolecular interaction in PFP multilayer films.
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