Bérangère Toury

Boron Nitride Fibers Prepared from Symmetric and Asymmetric Alkylaminoborazines

The thermolysis of 2,4,6-[(CH3)2N]3B3N3H3 (1), 2,4-[(CH3)2N]2-6-(CH3HN)B3N3H3 (2), and 2-[(CH3)2N]-4,6-(CH3HN)2B3-N3H3 (3) led to polyborazines 4, 5, and 6 respectively. The polymers display direct B–N bonds between borazinic B3N3 rings and, in addition, a proportion of –N(CH3)– bridges for 5 and 6, as clearly underlined by 13C NMR spectroscopy. Melt-spinning of these three polymeric precursors exemplified that their ease of processing increases in the order 4 < 5 < 6. Nevertheless, polyborazine filaments could be prepared from each of them and a subsequent thermal treatment up to 1800 °C resulted in the formation of crystalline hexagonal boron nitride fibers, which were characterized by X-ray diffraction analysis, Fourier transform infrared (FTIR) spectroscopy, and Raman spectroscopy. Scanning electron microscopy (SEM) images showed that the ceramic fibers are circular and dense without major defects. The mechanical properties for 4-derived fibers could not be measured because of their brittleness, whereas measurements on 5- and 6-derived fibers gave tensile strength σR = 0.51 GPa, Young’s modulus E = 67 GPa, and σR = 0.69 GPa, E = 170 GPa, respectively. The improvement in mechanical properties for ceramic fibers prepared respectively from 4, 5, and 6 could be explained to a large extent by the improvement of the processing properties of the preceramic polymers. This evolution could be related to the increased ratio of bridging –N(CH3)– groups between the B3N3 rings within the polymers 4, 5, and 6 and therefore to the functionalities of the starting monomers 1, 2, and 3.

Boron nitride matrices and coatings from boryl borazine molecular precursors

Thermal treatment of 2,4,6-[(NHPr i ) 2 B(NPr i )] 3 B 3 N 3 H 3 in vacuo led to a polyborazine in which the borazine rings are mainly linked by –N–B–N– bridges. Pyrolysis of up to 1400 °C resulted in the formation of high crystallinity hexagonal boron nitride which has been characterised by ESCA, powder X-ray diffraction and FTIR spectroscopy. Precursor has been used to prepare carbon fibres/BN microcomposites by dipping bundles of fibres into a solution of followed by pyrolysis up to 1200 °C. Optical micrographs and SEM analysis have shown that the BN matrices were compact and displayed good adherence properties onto graphite substrates. By contrast, BN coatings obtained from a polymer derived from B(NHPr i ) 3 displayed poor adherence properties. These results are related to the hydrocarbon chain ratio of each preceramic polymer. The effectiveness of the BN protective coatings in preventing oxidation has been measured by isothermal gravimetry in air. As expected, by considering the quality of the coatings, those obtained from showed the most interesting properties.

A Study on the Chemistry of Epitaxial Ti3SiC2 Formation on 4H-SiC Using Al-Ti Annealing

In order to form Ti3SiC2 on 4H-SiC(0001) 8°-off, 200 nm of Ti30Al70 was deposited onto SiC substrates by magnetron sputtering from pure Ti30Al70 targets. The samples were then annealed at 1000°C for 10 min under Ar atmosphere in a Rapid Thermal Annealing (RTA) furnace. Structural analyses reveal the formation of epitaxial hexagonal Ti3SiC2 (0001) oriented. Elemental analyses show that high amount of Al and O elements are present inside the deposit. Obviously, the formation of Ti3SiC2 is accompanied by parasitic Al oxide, probably due to some unwanted oxygen residual in the RTA chamber. By using proper backing steps before the annealing, the deposit is not anymore composed of only Ti3SiC2 but accompanied with other compounds (Al3Ti, and Al). On the oxide-free sample, the specific contact resistance ρc of the Ti3SiC2 based contact on p-type 4H-SiC (having Na= 2×1019 cm-3) was measured to be as low as 6×10-5 Ω.cm2.

X-Ray structureof 1,2'-diborazine-2,6-dichloro-4,4', 6'-tri(diisopropylamino) toluene solvate

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. X-RAY STRUCTUREOF 1,2-DIBORAZINE-2,6DICHLORO-4,4-TRI(DIISOPROPYLAMINO) TOLUENE SOLVATE David Cornu, Bérangère Toury, Sylvain Lecocq, Claude Bavoux, Philippe Miele