Showing papers in "Journal of Materials Science Letters in 1992"

Influence of additives on the γ-to-α transformation of alumina

Abstract: Some metal ions are known to affect the γ to α transformation temperature. Comparison of the influence of a variety of additives , particularly those forming a liquid phase, at relatively low concentrations (1 and 5 mol%), by means of differential thermal analysis, X-ray diffraction and sintering dilatometry studies.

The static and dynamic moduli of auxetic microporous polyethylene

Abstract: In this letter the elastic constants of an auxetic form of microporous ultra high molecular weigth polyethylene (UHMWPE) are reported

Zinc oxide thin films prepared by chemical vapour deposition from zinc acetate

Abstract: These thin films were prepared by a low temperature atmospheric pressure CVD method without using an oxygen method. At a reaction temperature above 180°C, c-axis oriented polycristalline thin films were obtained

Synthesis and physicochemical characterization of cobalt aluminium hydrotalcite

Abstract: Hydrotalcite-like compounds, otherwise referred to as layered double hydroxides, possess the brucite network [Mg(OH)2], in which the divalent ion is substituted by the trivalent ion resulting in an increased positive charge density of the layer, and this is compensated by the occupation of anion and water molecules in the interlayer positions. These compounds are represented by the general formula

Crystal growth of SiC whisker from the SiO(g)-CO system

Abstract: The growth of SiC whisker is carried out and the effects of th partial pressure of SiO(g) and CO(g) and deposition temperature on the morphology of SiC deposits were investigated

Deposition of tantalum nitride thin films from ethylimidotantalum complex

Abstract: Croissance de couches minces de TaN sur un support Si par la methode LPCVD en utilisant des melanges d'ethyliminoethyl(C,N)tris(diethylamido)tantale et d'ethylimidotris(diethylamido)tantale

Kinetics of wetting and spreading of Cu−Ti alloys on alumina and glassy carbon substrates

Abstract: On etudie la mouillabilite de l'alumine et du carbone vitreux par des alliages Cu-Ti a l'aide de la methode de la goutte sessile. On examine la cinetique du mouillage et de l'etalement, qui est importante pour la comprehension des phenomenes fondamentaux du mouillage.

Phase transformation around indentations in zirconia

Abstract: On etudie la forme et l'etendue des transformations et la presence de fissurations aux alentours des indentations Vickers dans des ceramiques Y-TZP et Ce-TZP.

Decomposition and interfacial reaction in brazing of SiC by copper-based active alloys

Abstract: On decrit les phenomenes de decomposition de SiC par Cu et par un alliage fondu Cu-5at%Ti ainsi que les reactions interfaciales de Ti avec SiC dans le cas de l'alliage.

Low-temperature sintering of calcium-carbonate by a hydrothermal hot-pressing technique

Abstract: We deal with the binding process among particles of calcium carbonate under hydrothermal hot-pressing (HHP) conditions

Epitaxial deposition of silicon nitride during post-sintering heat treatment

Abstract: On montre qu'il se produit une precipitation epitaxique lors du traitement thermique du nitrure de silicium fritte en presence de Yb 2 O 3 . Il existe une correlation entre le developpement de la microstructure et une modification de la composition due a la formation d'une phase secondaire cristalline transitoire apres frittage, qui est convertie en deux phases stables de silicate d'ytterbium plus une couche epitaxique de Si 3 N 4 deposee lors du traitement thermique.

Composition and lattice parameters of a new aluminium-rich borocarbide

Abstract: High-strength and low-weight composite materials or cermets have been prepared by reinforcing an aluminium-base matrix with boron carbide particles or with boron carbide-coated boron fibres [1-3]. In the former case boron carbide (B4C) is the strengthening agent, whereas in the latter the role of B4C coating is to protect the fibres against a too severe attack by aluminium during processing or use of the composites. Recently B4C-coated carbon fibres have been produced on a pilot plant in our laboratory [4, 5]. A general study is now in progress with the aim of employing these treated fibres for the manufacture of aluminium-base matrix composites. The development of such materials and improvement of their performances require, however, a thorough understanding of the metal-carbide interface chemistry and, primarily, a detailed description of the phases likely to be formed by chemical reaction in the A1-B-C system. In a general study on the processing of B4C-A1 cermets, Halverson et al. observed the formation of a new ternary compound, which they called phase X, at every temperature between 800 and 1400 °C [1]. Attempts were made by Sarikaya et al. [6] to characterize that phase by electron diffraction and energy-loss spectroscopy: those authors proposed a hexagonal symmetry with the lattice parameters a 0 = 0.3520 nm and Co = 0.5820 nm and the chemical formula A14BC. This letter reports the composition and lattice parameters of an aluminium-rich borocarbide that was prepared by direct synthesis from the elements and discusses the possible relationship between this compound and the foregoing phase X. Commercial powders of aluminium (purity 99.8 wt %, grain size d < 50 txm, Alfa Ventron), boron (99.4 wt %, d < 250/xm, Alfa Ventron) and carbon (spectrographic grade, d < 25/xm, Le Carbone Lorraine) were ball-mixed in a steel mortar at the atomic ratio AI:B :C = 80:10:10 and cold-pressed under 272 MPa into small rods (dimensions 4 m m x 6 m m x 3 0 m m and weight about 2g). These rods were placed on an alumina boat and heated for 160 h at 1273 K in a closed silica tube under atmospheric-pressure purified argon. Under these conditions the weight losses were <5%. After air-cooling the resultant samples were characterized by X-ray powder diffraction (XRD), using standard Philips equipment: a PW1720 generator, PW1390 channel-control unit and PW1050/25 two-circle goniometer supplied with a step-scanning motor

Oxidation resistance of boron carbide-based ceramics

Abstract: On etudie l'effet de la teneur en composes de Si et Al (de 10 a 50% en poids) sur l'oxydation de ceramiques a base de B 4 C dans l'air jusqu'a 1500°C.