Investigations on thermal reactivity of Si/C/N nanopowders produced by laser aerosol or gas interactions

Abstract

Ultrafine SiCN particles with various compositions, synthesised by laser pyrolysis in interaction either with gaseous or liquid reactant, were heat treated at temperatures between 300 and1773 K. Thermogravimetric measurements performed under inert (helium) atmosphere, showed that the best thermal stability was exhibited by nanopowders prepared from gaseous precursors (SiH 4 , CH 3 NH 2 , NH 3 ). Mass spectrometry analysis data revealed that nanopowders derived from a mixture with ammonia and hexamethyldisilazane (HMDS) contained more N-H and C-N groups than those obtained without ammonia. The loss of hydrogen clearly dominated amongst the observed losses in all the examined samples at all temperatures. This study indicates that thermal degradation of such silicon based systems is not a single reaction but the net result of a number of reactions.

Synthesis of SiCNAl(O) pre-alloyed nanopowders by pyrolysis of an aluminosilazane aerosol

“…12 Moreover, the in situ introduction of gaseous precursors of heteroelements (like Al) in the synthesized powders was not demonstrated, maybe due to the high difficulty to handle the precursors, and to the complexity of the reactions induced. To explain the differences between these two methods, the residence time and the cooling rate can be mentioned, as it was previously seen for the particle size.…”

“…The efficiency of an ammonia addition in the pyrolysis atmosphere to reduce the final carbon content was shown in several previous investigations. 12,44,50 So ammonia was added to the carrier gas (NH 3 /Ar = 25/75 vol.%) with a total flow rate of 3 L min −1 in the aerosol generator device, for a pyrolysis at 1400 • C of an aluminosilazane with a ratio Si/Al = 15. To discuss these results, the chemical compositions of powders issued from similar precursors pyrolysed under argon or Ar/NH 3 mixtures with two heating techniques are summarized in Table 7.…”

“…7 On an other hand, nanostructured materials can be fabricated if an ultrafine multielement powder method is used. Several teams have worked and are still working on this route, [8][9][10][11][12][13] mainly using the laser-pyrolysis process, but their investigations concern mixtures of non-miscible precursors. They did not realize an unique hybrid precursor containing metallic elements needed for sintering.…”

Synthesis under NH3 and thermal behaviour of SiCNAlO polymer-derived nanopowders

“…Different previous studies, dealing with polysilazane and polycarbosilane pyrolysis, showed that the introduction of ammonia into the pyrolysis atmosphere leads to a decrease of the final carbon content. [25][26][27][28][29] In this work, pyrolysis experiments were carried out in a reactive atmosphere (Ar/NH 3 ), with different amounts of ammonia: 5, 10, 15 and 25 vol.%. All the batches were fabricated with the same aluminum content, corresponding to a Si/Al molar ratio of 15 in the starting aluminosilazane (nomenclature in Fig.…”

Thermodynamics of the Au-Si-O System: Application to the Synthesis and Growth of Silicon-Silicon dioxide Nanowires

“…The decomposition of metastable SiO needs two steps, the first one being the breaking of the Si=O bonding, and the second one, the condensation of gaseous Si. [31,32] Between the two steps, Si exists in the gaseous phase under a potential higher than Si gaseous in equilibrium with the solid and this excess of chemical potential is enough to trigger the nanowiresÕ crystallization.…”