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Digitale Medien

Application of photoelectron spectroscopy to molecular properties. Part 22. Electronic structure of group 14 (.eta.4-metallole)tricarbonyliron complexes (1985)

Guimon, C. ; Pfister-Guillouzo, G. ; Dubac, J. ; [weitere]

s.l. : American Chemical Society

Organometallics 4 (1985), S. 636-641

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ISSN: 1520-6041

Quelle: ACS Legacy Archives

Thema: Chemie und Pharmazie

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1021/om00123a004

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Digitale Medien

Composition-microstructure-property relationships in ceramic monofilaments resulting from the pyrolysis of a polycarbosilane precursor at 800 to 400 °C (1991)

Bouillon, E. ; Mocaer, D. ; Villeneuve, J. F. ; [weitere]

Springer

Journal of materials science 26 (1991), S. 1517-1530

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ISSN: 1573-4803

Quelle: Springer Online Journal Archives 1860-2000

Thema: Maschinenbau

Notizen: Abstract A 15 μm monofilament was extruded from a Yajima's type molten polycarbosilane, stabilized by addition of oxygen and heat-treated at 800 to 1400 °C under an argon atmosphere. Two important phenomena occur during pyrolysis. At 500 to 750 °C, an organic-inorganic state transition takes place with a first weight loss. It yields an amorphous material stable up to about 1100 °C. At this temperature, its composition is close to Si4C5O2. It can be described as a continuum of SiC4 and/or SiC4−x Ox tetrahedral species (and possibly contains free carbon), with a homogeneity domain size less than 1 nm. The amorphous filament exhibits a high strength and semi-conducting properties. Above 1200 °C, a thermal decomposition of the amorphous material takes place with an evolution of gaseous species thought to be mainly SiO and CO, an important cross-section shrinkage and the formation of 7 to 20 nm SiC crystals which are surrounded with a poorly organized turbostratic carbon. The amorphous-crystalline state transition results in a drop in the tensile failure strength and an increase, by four orders of magnitude, in the electrical conductivity which becomes temperature independent. The former effect is due to the crystallization of the filament and the latter to a percolation phenomenon related to the intergranular carbon. The low stiffness is also due to the presence of carbon. It is anticipated that this transition is mainly related to the decomposition of the silicon oxycarbide species. Finally, a 40 to 50 nm layer of turbostratic carbon is formed at the filament surface at 1200 to 1400 °C whose origin remains uncertain. It is thought to be mainly responsible for the formation of the carbon interphase in the high-temperature processing of ceramic matrix composites.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00544661

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XPS study of BN thin films deposited by CVD on SiC plane substrates (1990)

Guimon, C. ; Gonbeau, D. ; Pfister-Guillouzo, G. ; [weitere]

Chichester [u.a.] : Wiley-Blackwell

Surface and Interface Analysis 16 (1990), S. 440-445

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ISSN: 0142-2421

Schlagwort(e): Chemistry ; Polymer and Materials Science

Quelle: Wiley InterScience Backfile Collection 1832-2000

Thema: Physik

Notizen: BN films deposited from a BF3—NH3 precursor, under chemical vapour infiltration conditions, on plane sintered α-SiC substrates were analysed by XPS. The films are non-stoichiometric with an N/B atomic ratio of 〈1. They also contain significant amounts of oxygen atoms, homogeneously distributed in the film and thought to replace partly the nitrogen atoms in the turbostratic hexagonal network. As a result, ternary BNxOy species are formed locally. Near the BN/SiC interface, the oxygen concentration increases owing to the occurrence of ternary SiNxOy species, thought to be the result of an oxinitriding reaction on the substrate surface with the gas phase containing residual oxygen, at the very beginning of the BN deposition process.

Zusätzliches Material: 7 Ill.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1002/sia.740160191

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Study of the bulk and surface acidity of protonated Y zeolites by TPD and XPS (1994)

Guimon, C. ; Boreave, A. ; Pfister-Guillouzo, G.

Chichester [u.a.] : Wiley-Blackwell

Surface and Interface Analysis 22 (1994), S. 407-411

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ISSN: 0142-2421

Schlagwort(e): Chemistry ; Polymer and Materials Science

Quelle: Wiley InterScience Backfile Collection 1832-2000

Thema: Physik

Notizen: The combined use of temperature programmed desorption (TPD) of nitrogened bases (ammonia, pyridine) and x-ray photoelectron spectroscopy (XPS) was applied to the study of acidity of HY zeolites with different molar Si/Al ratios (∼ 2.7, 5.8, 24).N1s binding energies of probe molecules showed two types of sites (Brönsted and Lewis) whose relative proportions varied with pretreatment and desorption temperatures, and a dissociative adsorption of NH3 for dehydroxylated zeolites.The TPD curves and the XPS quantitative analyses of probe molecule concentration in Zeolites allowed the determination of acid sites distribution in term of strength for the real surface of crystals and for a sub-surface partially freed of extra-framework species that cover it. These data showed that the acid sites located in sodalite units are mostly strong and Brönsted type sites.

Zusätzliches Material: 4 Ill.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1002/sia.740220188

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