Various multilayer coatings on silicon carbide basis, deposited by chemical vapor deposition (CVD), are discussed as oxidation protection for carbon-carbon composites (CFC) at high temperatures. Graded carbon to silicon carbide layers (C. SiC) are derived from methyltrichlorosilane/hydrogen (MTS/H2) mixtures in a one step process at 1050°C varying the H2MTS ratio. the oxidation resistance of the multilayer systems is determined in a thermobalance under dynamic conditions (650°–1500°C, heating rate 2 K/min) as well as thermocyclic conditions (10 cycles between 1050° and 1500°C) in air flow. As a result, two multilayer combinations are proposed as promising candidates for oxidation protection of CFC in different temperature ranges: SiCIgraded C. SiC/SiC for temperatures above 1000°C and TiN/graded C. SiC/SiC for temperatures between 650° and 1500°C.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
Abstract Durch unterschiedliche Oxidationsverfahren wird die Oberfläche der Kohlenstoffasern physikalisch und chemisch verändert. Der Einfluß dieser modifizierten Oberflächen auf den Verstärkungseffekt der Fasern in Epoxidverbundkörpern wird untersucht. Es wurde festgestellt, daß die Gesamtmenge an Oberflächenoxiden, die die Benetzbarkeit der Faseroberfläche mit polaren Substanzen bestimmt, die entscheidende Rolle für die Haftungsverbesserung in Epoxidverbunden spielt. Den höchsten Verstärkungseffekt zeigen die mit KNO 3 oxidierten und anschließend mit Schwefelsäure nachbehandelten Kohlenstoffasern.
Abstract The kinetics of the CVD of boron nitride from trimethoxyborane (TMOB) and ammonia (NH 3 ) under atmospheric pressure was investigated by varying the following process parameters: temperature, residence time of the reactants, molar fraction of TMOB, and the NH 3 /TMOB ratio, γ. A kinetic power law equation was derived, that describes the experimental results with good accuracy. The reaction order with respect to TMOB is found to be 0.9 and – 0.2 with respect to NH 3 . Between 800 °C and 950 °C, the deposition rate is controlled by the surface reaction kinetics with apparent activation energy of 115.1 kJ mol –1 . The deposited BN films were characterized by IR spectroscopy, Raman spectroscopy, and X‐ray diffraction (XRD). The microstructure of the deposits depends on the nature of the substrates used. Turbostratic boron nitride (t‐BN) was deposited on graphite, and hexagonal boron nitride (h‐BN) on alumina substrates. X‐ray photoelectron spectroscopy (XPS) analyses show nearly stoichiometric BN films for deposition temperatures in the range 850–950 °C for high amounts of ammonia (100 < γ < 150) in the feed gas.
Abstract Anodic surface treatment of high tensile-carbon fibres under galvanostatic conditions has been performed in diammonium hydrogen phosphate solution, containing an addition of ammonium rhodanide. The oxidized fibres have been characterized by monofilament tensile strength, XPS measurements and surface energetic analysis. Additionally, the acid-base interactions have been evaluated by wetting with aqueous solutions of different pH values. An addition of ammonium rhodanide to the diammonium hydrogen phosphate anodization bath affects the oxidation of carbon fibres in terms of decreasing both the amounts of the surface oxides as well as that of degradation by-products. At the optimal treatment conditions (I = 100 mA) no changes in the tensile strength or BET-surface area of the fibre have been observed. The rise in ILSS values of amine cured epoxy composites is not dependent on Ols/Cls ratio or surface free energy of the reinforcing fibres, but on the acidic as well as nitrogen functional groups on their surface. Key Words: carbon fibresanodic oxidationdiammonium hydrogen phosphate solutionammonium rhodanide additionadhesion
