In-Situ Synthesis and Characterization of Nanocomposites in the Si-Ti-N and Si-Ti-C Systems

Abstract

The pyrolysis (1000 °C) of a liquid poly(vinylmethyl-co-methyl)silazane modified by tetrakis(dimethylamido)titanium in flowing ammonia, nitrogen and argon followed by the annealing (1000–1800 °C) of as-pyrolyzed ceramic powders have been investigated in detail. We first provide a comprehensive mechanistic study of the polymer-to-ceramic conversion based on TG experiments coupled with in-situ mass spectrometry and ex-situ solid-state NMR and FTIR spectroscopies of both the chemically modified polymer and the pyrolysis intermediates. The pyrolysis leads to X-ray amorphous materials with chemical bonding and ceramic yields controlled by the nature of the atmosphere. Then, the structural evolution of the amorphous network of ammonia-, nitrogen- and argon-treated ceramics has been studied above 1000 °C under nitrogen and argon by X-ray diffraction and electron microscopy. HRTEM images coupled with XRD confirm the formation of nanocomposites after annealing at 1400 °C. Their unique nanostructural feature appears to be the result of both the molecular origin of the materials and the nature of the atmosphere used during pyrolysis. Samples are composed of an amorphous Si-based ceramic matrix in which TiNxCy nanocrystals (x + y = 1) are homogeneously formed “in situ” in the matrix during the process and evolve toward fully crystallized compounds as TiN/Si3N4, TiNxCy (x + y = 1)/SiC and TiC/SiC nanocomposites after annealing to 1800 °C as a function of the atmosphere.

From design to characterization of zirconium nitride/silicon nitride nanocomposites

“…As expected, FTIR spectroscopy tends to corroborate the involvement of NH and SiH groups in polysilazanes during the reaction of the latter with TDEAZr through the occurrence of the mechanism already identified during the reaction between PMSZ and tetrakis(dimethylamino) titanium (Ti[N(CH3)2]4) labelled TDMATi [14,23]: i) those involving -NH units in both polysilazanes and -N(CH2CH3)2 groups in TDEAZr to form -N-Zr-bonds releasing ethylamine according to the reaction (1) in Fig. 2.…”

“…In this work, we have exploited the advantage of producing TMN/ Si3N4 compounds [14,15,[21][22][23] by the PDC route [24][25][26][27][28][29][30][31][32][33][34][35][36][37] to design ZrN/Si3N4 nanocomposites where their structure can be well controlled from the precursor level. Our approach involves first the synthesis of zirconium (Zr)-modified polysilazanes from liquid polysilazanes as Si3N4 precursors, i.e., polymethylsilazane (PMSZ) and poly(vinyl-methyl-comethyl)silazane (PVMSZ), which are known to deliver Si-C-N ceramics [22,38,39].…”

Mechanistic Investigation of the Formation of Nickel Nanocrystallites Embedded in Amorphous Silicon Nitride Nanocomposites

“…This might be due to the systematically thermodynamically-controlled formation of metal nitride through the reaction of the metal cations chemically-bonded and/or physically-loaded to the polysilazane with ammonia (NH 3 ), which is used as extrinsic nitrogen source for the formation of Si 3 N 4 . This is well illustrated in the recent reports on Si 3 N 4 -based nanocomposites, such as titanium nitride (TiN)/Si 3 N 4 [ 29 , 30 ] and vanadium nitride (VN)/Si 3 N 4 [ 31 ]. However, we recently succeeded in the formation of cobalt (Co)/Si 3 N 4 nanocomposites through the PDCs route, using PHPS as amorphous Si 3 N 4 (labeled a-SiN) precursor coordinated with CoCl 2 as Co source [ 32 ], although it was not possible to isolate samples free of ammonium chloride at low temperature while keeping the Si 3 N 4 matrix amorphous, which is required for catalytic activity [ 27 ].…”

Ceramic nanocomposites prepared via the in situ formation of a novel TiZrN2 nanophase in a polymer-derived Si3N4 matrix

“…These characterization tools allowed demonstrating that PMZrTiSZ5 is obtained via reactions already identified in the literature [11][12][13][14]:…”

“…The synthesis of TMNs as nanoparticles or nanostructured materials, on the other hand, is challenging due to the high temperatures required for preparation and the difficulties in controlling the particle size distribution. The polymer-derived ceramics (PDCs) route can tackle these issues by providing a way to in situ generating nanosized TMNs into a robust and covalently-bonded nitride matrix such as silicon nitride (Si3N4) [1,3,4,[11][12][13][14][15]. Through a fundamental structure-property relationship, such TMN/Si3N4 nanocomposites can display totally new combinations of properties, especially by synergetic effect.…”