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  • 1
    Electronic Resource
    Electronic Resource
    s.l. ; Stafa-Zurich, Switzerland
    Key engineering materials Vol. 132-136 (Apr. 1997), p. 1870-1873 
    ISSN: 1013-9826
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0044-2313
    Keywords: Phosphorus nitrides ; nitrido sodalites ; transition metals ; synthesis ; structure ; i.r. data ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Nitrido-Sodalites. II. Synthesis, Crystal Structure, and Properties of M(6+(y/2)-x)H2x[P12N24]Zy with M = Fe, Co, Ni, Mn; Z = Cl, Br, I; 0 ≤ x ≤ 4; y ≤ 2The nitrido sodalites M(6+(y/2)-x)H2x[P12N24]Zy with M = Fe, Co, Ni, Mn; Z = Cl, Br, I; 0 ≤ x ≤ 4; y ≤ 2 are obtained by the reaction of HPN2 or [PN(NH2)2]3 with the metal halogenide MZ2 (T = 700°C). The compounds are isotypic to Zn(7-x)H2x[P12N24]Cl2. An increase of the ionic radii of the cations or anions results in an expansion of the lattice which is caused by an increase of the P—N—P angle. The influence of the cation is more dominant than that of the anion. By reacting [PN(NH2)2]3 with metal halogenide (MZ2) hydrogen free, X-ray amorphous products are obtained. The formation of the chloride-containing P—N-sodalite in this reaction begins at temperatures below 450°C.
    Notes: Die Nitrido-Sodalithe M(6+(y/2)-x)H2x[P12N24]Zy mit M = Fe, Co, Ni, Mn; Z = Cl, Br, I; 0 ≤ x ≤ 4; y ≤ 2 wurden durch Umsetzung von HPN2 bzw. von [PN(NH2)2]3 mit dem jeweiligen Metallhalogenid MZ2 hergestellt (T = 700°C). Sie sind mit Zn(7-x)H2x[P12N24]Cl2 isotyp. Mit steigendem Ionenradius von Kationen oder Anionen findet man eine Aufweitung des Volumens. Dies ist mit einer Vergrößerung des P—N—P-Winkels verbunden. Der Einfluß der Kationen ist dabei stärker als jener der Anionen. Durch Reaktion von [PN(NH2)2]3 mit dem jeweiligen Metallhalogenid MZ2 werden wasserstofffreie P—N-Sodalithe als röntgenamorphe Pulver erhalten. Bei diesen Reaktionen setzt die Bildung der chlorhaltigen P—N-Sodalithe schon unterhalb von 450°C ein.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Applied Organometallic Chemistry 11 (1997), S. 181-194 
    ISSN: 0268-2605
    Keywords: synthesis ; silazanes ; polymer pyrolysis ; non-oxide ceramics ; Si3N4 ; SiC ; crystallization ; ceramic matrix composites ; Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The goal of this investigation was to optimize the synthesis of silazane-based polymers for processing fibre-reinforced ceramic matrix composites (CMCs). Liquid oligomeric silazanes were synthesized by ammonolysis of chlorosilanes and characterized spectroscopi- cally (FTIR, NMR) as well as by elemental analysis. The silazanes were obtained in high yield and purity. Different functional groups (system S1: Si - H, Si - CH3, Si - CH=CH2) and different degrees of branching in the Si - N backbone [system S2; Si(NH)3, Si(NH)2] were realized in order to study the properties of the silazanes that are dependent on the molecular structure.For processing ceramics via pyrolysis of pre-ceramic oligomers, molecular weight, rheological behaviour, thermosetting and ceramic yield were investigated systematically and correlated with the molecular structure of the silazanes. Low molecular weights (500-1000 g mol-1) as well as low viscosity values (0.1-20 Pa s) enable processing of the silazanes in the liquid phase without any solvent. Due to the latent reactivity of the functional groups, curing of the polymers via hydrosilylation is achieved.Structural changes and weight loss during polymer curing as well as the organic/inorganic transition were monitored by FTIR spectroscopy and differential thermogravimetric analysis. With increasing temperature (room temperature to 800 °C) the hydrogen content decreases from 7 to 〈 0.5 wt% due to the formation of gaseous molecules (NH3, CH4, H2). High ceramic yields up to 80% were reached by branching the oligomers, thus reducing the amount of volatile precursor fragments.Up to 1300 °C, ceramic materials remained amorphous to X-rays. At higher temperatures (1400-1800 °C) either SiC or SiC/Si3N4 composites were selectively crystallized, depending on the pyrolysis conditions. The utility of the optimized precursors for CMCs has been demonstrated by infiltration of fibre preforms and subsequent pyrolysis. © 1997 by John Wiley & Sons, Ltd.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
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