Controlled coammonolysis of elementalkylamides in aprotic organic solvents at low temperatures have been shown to result in the formation of polyazanes. The synthetic procedure developed may be addressed as “sol‐gel‐route in the ammono system”. Pyrolysis of these novel polymer precursors gave access to multinary nitrides. For the model systems Si(NHMe)4/B(NMe2)3, Si(NHMe)4/Ti(NMe2)4, and Si(NHMe)4/Ta(NMe2)5 polymeric boro‐, titano and tantalosilazanes were obtained. Pyrolysis in ammonia at 1000 °C yielded amorphous silicon boron nitride, silicon titanium nitride and silicon tantalum nitride powders; further heating of the nitride powders at 1500 °C in nitrogen atmosphere led to the formation of partly crystalline composites of α‐Si3N4 and amorphous silicon boron nitride for the Si/B/N system, a composite of finely dispersed TiN and amorphous silicon titanium nitride for the Si/Ti/N system, and crystalline TaN and amorphous silicon nitride for the Si/Ta/N system. Furthermore, the structure and pyrolysis chemistry of the polymeric intermediates, as well as the morphology of the pyrolysis products, were studied by NMR, MAS‐NMR, FT‐IR, DTA‐TG‐MS, XRD, SEM, EDX and elemental analyses.

Communications ADVANCED hl ATE R I A LSbottom edge of the catalyst particle, leading directly to a nested cylindrical structure. This is quite different from the usual metal-catalyzed VGCF[36 -401 and metal catalyzed carbon nanotubes. [2'-241 The relationship between various crystals and the tip structures of the carbon nanotubes they catalyze is now being considered in detail. ExperimentalPitch carbon was obtained by the thermal decomposition of 3,4,9,10perylenetetracarboxylic dianhydride at 800 "C under a nitrogen atmosphere Hafnium dioxide (99.9% purity) was mixed with the pitch carbon in a weight ratio of 1 :4, and the mixture was thermally annealed at 900°C under vacuum. This produced hafnium carbide, a dark gray solid with a fine crystalline texture. After cooling, the mixture was pressed into a 7 mm hole drilled into a tubular graphite rod 10 mm in diameter (99.99 % purity). During the course of electrlc arc vaporization of the hafnium-composite graphite electrode, the inner pressure of a water-cooled chamber was maintained at 200 Torr and a DC current of 100 A was supplied across the electrodes.X-ray diffraction measurements were performed using a Rigaku RAD Ill-B diffractometer (Cu-Ka radiation, 1.5418 A), The Carbonaceous deposits were mechanically milled, moistened with ethanol, and set in a sample holder prior to the XRD measurements. TEM observations of the milled powder confirmed that the carbon nanotubes and gigantic fullerenes were not damaged by the mechanical action of the milling operation. The carbonaceous deposits formed on the negative electrode were removed by sonication in ethanol for 10 s. This solution was then spread onto a collodion mesh and the HREM observations were carried out using a JEOL JEM-2000FX TEM operated at 200 kV. The samples were not cooled during the observations.

X-ray photoelectron spectroscopy (XPS) and X-ray absorption near edge structure (XANES) spectroscopy at the K-edge of Si, N, and B are presented as techniques suited to determine structural units in amorphous SiBN(3)C. The measurements reported give evidence for the presence of tetrahedral (SiN(4))- and planar (BN(3))-groups. It is concluded that these structural elements dominate the atomic surroundings of B and Si, respectively. From the spectroscopic results we conclude that C is mainly bonded to N and is not present as a pure carbide.

Inorganic polymers are attractive precursors for high‐performance ceramics. A new method of producing the polymers via thermal polycondensation of volatile molecular precursors is presented which does not involve the use of catalysts and therefore avoids contamination of the polymers with the catalysts or with byproducts of the catalytic reaction. The example presented is the polycondensation of tetrakis(methylamino)silane, which is a readily available precursor for Si3N4/SiC ceramics.

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