FR2954318A1 - POLYMETALLOSILAZANE FOR THE PREPARATION OF NANOCOMPOSITES WITH DECORATIVE PROPERTIES, WHICH CAN BE PRESENTED IN THE FORM OF MASSIVE OBJECTS - Google Patents

Abstract

The present invention relates to a modified polymetallosilazane, characterized in that it is capable of being obtained according to a process comprising the following successive steps: a) reaction of a polysilazane with a molecular entity comprising at least one transition metal and at least one a carbonaceous group, to obtain a polymetallosilazane type polymer and b) ammonolysis reaction by ammonia action of the polymetallosilazane obtained to at least partially remove the carbon groups, and a process for preparing a nanocomposite material from such a modified polymetallosilazane and nanocomposite materials in the form of bulk object obtained.

Description

The present invention relates to the field of nanocomposites. More specifically, the present invention relates to a novel precursor of the modified polymetallosilazane type, making it possible to obtain the preparation of nanocomposites with decorative properties, which can be in the form of solid objects. The invention also relates to a process for preparing a nanocomposite material from such a modified polymetallosilazane and the nanocomposite materials in the form of massive objects obtained. A nanocomposite can be defined as an assembly of two materials: a filler or reinforcement of which at least one of the dimensional parameters is of the order of one nanometer (typically 1 to 100 nm), and a matrix in which these nano-reinforcements are distributed. Numerous studies relate to nanocomposites based on nitride and in particular based on three components N, Si and M with M transition metal. The nanocomposites of the type ne-MN / a-Si3N4 and nc-MN / c-Si3N4 (in which M is a transition metal, symbolizes a phase "nanocrystals", has an amorphous matrix and c a crystalline matrix) are essentially used. for their property of extreme hardness and fall into the category of "super hard materials" (of the English "super hardness materials"). They therefore find a large number of applications as protective coatings. Indeed, the introduction of these nanocomposites of ternary composition in cutting tool protection applications under severe conditions of use or as a protective agent vis-à-vis the external mechanical attacks has notably contributed to the replacement of the laboratory scale of hard-coated tools such as TiN (titanium nitride). These were introduced in the 1980s to improve the wear resistance of heavily loaded surfaces. Nanocomposite coatings are much harder and more wear-resistant than conventional coatings. In addition to a high hardness, coatings combining, for example, titanium nitride (TiN) and silicon nitride (Si3N4) phases, ie, Si-Ti-N nanocomposites, exhibit better resistance to elevated temperatures. easily reach 800 ° C during turning, milling or drilling. With the encapsulation of tiny grains of TiN in a thin envelope of Si3N4 resistant to oxidation, these coatings oxidize twenty times more slowly than conventional coatings and that while having a hardness as high as that of sapphire. Among the most interesting technological advances in recent years, nanocomposite coatings of Si-Ti-N type, with extremely high hardness (40-100 GPa measured by nano-indentation) have been prepared for machining and intensive machinery . These nanocomposites are also characterized by their excellent performance as a diffusion barrier. In the form of coatings on silicon substrates, they are, for example, known to prevent the inter-diffusion of copper and its reaction with the silicon substrate in integrated circuits (X.-Z. Liu, et al. Am.Chem.Soc. 123, 2001, 8011). In these applications, these Si-Ti-N coatings tend to gradually replace the metal nitrides such as titanium nitride (TIN). Obtaining this unusual combination of features comes from the nanostructure of the materials used. The manufacturing process is directed in such a way that the grain size of TIN does not exceed a few nanometers. For physical reasons, grains as small as these can not deform and can only slide on each other. This slippage is, however, hampered by the envelope of Si3N4 surrounding the grains. As a result, nc-TiN-a-Si3N4 nanocomposites are harder than their individual components alone. These materials also find application as decorative coatings. The color is brought by the presence of the nanocrystals of metal nitride which then gives the nanocomposite a multifunctional character (S.M. Aouadi, et al., Surf Coatings Tech., 201, 2006, 418 and EP 1614764). In summary, nanocomposites such as Si-Ti-N are highly desirable materials for a large number of applications, due to their remarkable properties such as: • Very high hardness. • A high melting point. • Chemical inertness. • Good thermodynamic stability. • Decorative properties. Many design techniques are employed to design such nanocomposites. The majority of these techniques are used to produce coatings or deposits on substrates, for example to protect cutting tools. In this case, the methods used are, in particular, chemical vapor deposition (CVD), reactive magnetron sputtering (Reactive magnetron sputtering), plasma-assisted chemical vapor deposition, electrodeposition (Ion plating), the hypersonic deposition of plasma particles (Hypersonic plasma particle deposition), or else the deposition by arc (Arc deposition). In the context of the invention, the inventors have turned to a completely different route that uses a chemical method, using preceramic polymers. Such a route has been used by J. Loffellholz, et al. in Z. Anorg. Al / g. Chem., 626, 2000, 963, but to lead to materials very different from those obtained in the context of the invention. This publication describes the production of Si-M-N nanocomposites. In the study carried out, the authors implement a non-oxide sol-gel process by coammonolysis of molecular precursors of alkylamides type of silicon (Si), titanium (Ti), boron (B) and / or tantalum ( Ta) to prepare polymetallosilazanes. In this publication, the authors describe obtaining, from polytitanosilazanes, Si-Ti-N ceramic powders whose structure is described textually by the authors as a combination of an amorphous phase and a partially crystallized nanocomposite. More generally, they report in this article the formation of a composite composed of a nanocrystalline binary phase in titanium nitride (TiN) or tantalum nitride (TaN), ie, nanocrystals, immersed in an amorphous ternary phase or in nitride silicon and titanium either silicon nitride and tantalum, ie, matrix. No color other than black and dark gray is mentioned. Riedel et al. (Appt.Organomet.Chem., 15, 2001, 879 and Mater Chem Phys 81, 2003, 195) also disclose the preparation of a TiCXNi_X crystalline material containing silicon by pyrolysis of polymeric titanium carbodiimide. Here again, the material obtained is composed of a ternary nanocrystalline titanium carbonitride phase immersed in an amorphous ternary silicon carbonitride phase. In the context of the invention, the inventors have chosen to use a very particular type of polymetallosilazane, as a preceramic polymer. The term "polymetallosilazane" is used extensively in the literature and refers to a wide variety of polymers containing the elements Si, M, C, H, N and optionally O. In general, polymetallosilazanes, with in most cases M = Ti, ie, polytitanosilazanes, are obtained, according to the prior art, according to two methods consisting of a single step: The first is to react titanium tetrachloride TiCl4 with a polysilazane or with bis (trimethylsilyl) carbodiimide (CH3) 3Si-N = C = N-Si (CH3) 3. However, chlorinated residues can be found in the polymer and in the decomposition products. The second method consists in reacting polysilazanes or silazanes or bis (trimethylsilyl) carbodiimide (CH 3) 3 Si-N = C = NSi (CH 3) 3 with molecular precursors containing the metallic element such as metal alkoxides or dimethylamide. titanium Ti [N (CH 3) 2] 4 optionally under a reducing atmosphere. Thus, the polymetallosilazanes prepared by reaction between an Si [NHCH 3] 4 type silazane and Ti [N (CH 3) 2] 4 titanium dimethylamide (J. Loffellholz, et al., Supra) are described in US Patent 5,567,832 by US Pat. same authors to develop amorphous ceramics around ternary systems such as Si-Ti-N and Si-Zr-N, white or black, but not for the development of nanocomposites. These polymers are thermosetting and insoluble when the polymerization is carried out under ammonia. On the contrary, they become thermoplastic and soluble in the usual solvents, when the polymerization is carried out with primary amines. The polymers are then shaped to design particular geometries of materials such as fibers, coatings. No examples are given of these particular shapes of amorphous materials. No massive object type geometry is mentioned and these materials are not qualified as decorative. Other publications detailed below describe or use polymetallosilazanes prepared in a single step by condensation of the metal precursor and polysilazane, but none of these publications describe their use for the preparation of nanocomposites consisting of binary phase nanocrystals in a single phase. alpha binary phase amorphous or crystalline matrix (a: hexagonal shape / P63 / m gap group) and / or beta (j3: hexagonal shape / P31c gap group). Ziegler et al. (Adv Mater., 7, 1995, 380) uses polytitanosilazanes to prepare amorphous materials of composition Si, Ti, C and N. These polymetallosilazanes prepared by reaction between polysilazanes and titanium dimethylamide Ti [N (CH 3) 2] 4 can be used to develop amorphous coatings of materials as described in US Patent 6,544,657. Zirconium coatings are also prepared. Moreover, the materials are obtained around the quaternary system Si-M-C-N. The publication J. Ceram. Soc. Jp., 114, 2006, 502, for its part, mentions obtaining Si-Ti-N materials in which the silicon nitride is in the crystalline state while the second phase is silicon. These materials are prepared from polytitanosilazanes synthesized by reactions of titanium dialkylamides with perhydridopolysilazane. In US Patent 5,436,398, polymetallosilazanes are also used to prepare particular shapes of ceramics such as discs or coatings. These polymetallosilazanes such as polytitanosilazanes and polyzirconosilazanes are obtained by reaction of polysilazanes with metal alkoxides and are used to obtain amorphous ceramics and in no way nanocomposites. Furthermore, it is important to emphasize that none of the documents of the state of the art mentioned above which describe the preparation of nanocomposites or of a nanocrystalline phase dispersed in an amorphous phase mention a possibility of shaping the preceramic polymers employed and / or nanocomposites obtained from these polymers. Moreover, in these documents, obtaining nanocomposites which combine a nanocrystalline binary phase of metal nitride and an amorphous or crystalline binary matrix of silicon nitride is not mentioned. Moreover, none of these documents describes the formation of a polymetallosilazane-type polymer in the M-Si-N system (M = Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W) capable of combining a low temperature thermoplastic behavior and a high ceramic yield to make nanocomposite type solid objects. Finally, the articles mentioned above do not evoke the possibility of controlling the color of the nanocomposites whether in the form of micropowders or massive objects.

In this context, one of the objectives of the present invention is to provide new polymetallosilazanes which offer a possibility of direct or indirect shaping on the nanocomposites obtained from these polymers. Another object of the present invention is to provide novel polymetallosilazanes which can lead to nanocomposites having decorative properties. For this the inventors have chosen to develop new polymetallosilazanes which can lead to nanocomposites comprising a nanocrystalline metal nitride binary phase and an amorphous or crystalline matrix of silicon nitride. Such a structure, with respect to the material of the prior art which comprises a ternary nanocrystalline phase and / or a ternary matrix, makes it possible to control the color of the materials obtained, and thus obtain materials which have decorative properties, depending on the choice metal nanocrystals of metal nitride. Also, one of the objectives of the present invention is to provide novel polymetallosilazanes which, depending on their composition, make it possible to modulate and control the color of the nanocomposites that can be obtained from these polymetallosilazanes. Another objective of the present invention is to provide novel polymetallosilazanes which make it possible to lead to nanocomposites which have satisfactory mechanical properties, and in particular improved with respect to the materials of the prior art which comprise amorphous nanoparticles of ternary form. Another object of the present invention is to provide novel polymetallosilazanes which make it possible to lead to nanocomposites in the form of solid objects. In the context of the invention, the term "solid object" means a self-supporting object of at least one millimeter in thickness and, preferably, of simple geometry such as a cylinder or a parallelepiped. Another object of the present invention is to provide novel polymetallosilazanes which will be able to combine low temperature thermoplastic behavior and high ceramic yield to make nanocomposite solid objects. In the context of the invention, the inventors propose to use new polymetallosilazanes. Also, the present invention relates to modified polymetallosilazanes, characterized in that they are capable of being obtained according to a process comprising the following successive steps: a) reaction of a polysilazane with a molecular entity comprising at least one transition metal and at least one carbon group, to obtain a polymetallosilazane polymer and b) ammonolysis reaction of the polymetallosilazane obtained to at least partially remove the carbon groups, while increasing the degree of crosslinking of the polymer.

According to a particular embodiment, step b) may be followed by hot shaping of the modified polymetallosilazane obtained making it possible to obtain a densified form of the polymer by plastic deformation.

In the context of the invention, the inventors have planned to add to the second method previously described used in the prior art for the synthesis of polymetallosilazanes, a second ammonolysis step so that the synthesized polymetallosilazanes can combine plastic behavior and high ceramic yield, to allow, in particular, the preparation of massive objects. The post-polymerization ammonolysis step leading to the modified polymetallosilazanes according to the invention makes it possible to optimize the compactability of the polymer obtained, as well as the ceramic yield obtained with this polymer. Moreover, it gives the polysilazane polymer obtained a good morphological behavior, once the latter is shaped during its transformation into nanocomposites. The subject of the invention is also nanocomposite materials in the form of a solid object comprising a matrix composed of an amorphous or crystalline binary form of silicon nitride, in which nanocrystals of at least one metal nitride of nanoparticles are distributed. transition of binary form. According to another of its aspects, the invention also relates to a process for preparing a nanocomposite comprising a matrix composed of an amorphous or crystalline silicon nitride binary form, in which nanocrystals of a nitride of silicon metal are distributed. binary structure transition, in the form of particles, continuous micrometric fibers, nanofibers or nanotubes, a coating, a composite of infiltration of a fibrous preform or in the form of an object massive characterized in that it implements a pyrolysis step of a polymetallosilazane according to the invention.

According to an alternative embodiment of the method, especially adapted to the preparation of solid objects, the latter comprises a compaction shaping step, after the pyrolysis step. For example, this shaping step is performed by sintering, optionally with a plasma treatment. According to another variant of implementation, especially adapted to the preparation of solid objects, the latter comprises a compacting shaping step, before the pyrolysis step. For example, this compacting shaping step is carried out at a temperature in the range of from 20 to 400 ° C, preferably from 50 to 150 ° C. The description below provides a better understanding of the invention. Step a) leading to the polymetallosilazane according to the invention is carried out in a conventional manner. The polysilazane used is synthesized, according to the techniques used in the prior art previously described, from haloalkylsilane, such as dichloromethylsilane. For example, a silazanolysis reaction of a haloalkylsilane with hexamethyldisilazane (HMDS) or an ammonolysis is carried out or, preferably, an ammonolysis reaction, by action of lithium amide (LiNH 2) or preferably of ammonia, a haloalkylsilane, is carried out in a solvent such as toluene or xylene, for example at a temperature of 0 ° C. The polysilazane used is in liquid form at room temperature or in solid form and will then be solubilized in a suitable solvent in step b). The polysilazane is, for example, a perhydropolysilazane, a polymethylsilazane, a polydimethylsilazane, a polymethylvinylsilazane, a polyvinylsilazane, or a copolysilazane, polymethylsilazane being preferred. As an example of a transition metal that can be used and incorporated into the carbon-based molecular entity used in step a), mention may be made of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo and W. The molecular entity comprising at least one transition metal and at least one carbon group is preferably chosen from alkylamides of formula M (NR 2) x and alkoxides of formula M (OR) x in which M represents a metal of transition, the same or different represents an alkyl chain of the methyl and / or ethyl type and x is equal to 3, 4, 5 or 6 depending on the coordination of the metal M. As an example of molecular entities comprising at least one transition metal and at least one carbon group, mention may be made of Ti [N (CH 3) 2] 4, TI [N (CH 2 CH 3) 2] 4, Zr [N (CH 3) 2] 4, Zr [N (CH 2 CH 3) 2] 4, Zr [N (CH 2 CH 3) (CH 3)] 4 Hf [N (CH 3) 2] 4, Hf [N (CH 2 CH 3) 2] 4, Hf [N (CH 2 CH 3) (CH 3)] 4, Ti [O (CH2CH3)] 4i Zr [O (CH2CH3)] 4 • The molar ratio polysilazane / molecular entity containing the transition metal is typically selected in the range from 0.5 to 15. This molar ratio which will determine the Si / M ratio in the composite material, which will be subsequently obtained, has an influence on the synthesis yield, on the ammonolysis, on the plasticity and the ceramic yield of the modified polymetallosilazane which will be obtained, on the nanocomposite production temperature as well as on their physical properties. At this stage, it is possible to simultaneously introduce a single molecular entity containing a transition metal or several kinds, for example two kinds, of molecular entities each containing a different transition metal, so as to have several metals within the same polymer. The reaction between the polysilazane and the molecular entity comprising at least one transition metal and at least one carbon group is, for example, carried out at a temperature of 65 to 120 ° C. for 48 to 120 hours. The reaction time depends on the coordination of the metal element under consideration. It is possible to use a catalyst, such as butyl lithium, which increases the reaction rate between the polysilazane and the molecular precursor containing the metal element, as well as the degree of crosslinking of the polymer. The choice of solvent depends on the polysilazane used. This reaction is preferably carried out in a solvent in which the starting polysilazane and the polymetallosilazane obtained are soluble. By way of example, mention may be made of tetrahydrofuran (THF) and toluene and diethyl ether. The reaction is then conducted at the reflux temperature of the selected solvent. After reaction at the reflux temperature of the solvent, the solution obtained is, for the most part, cooled under an argon stream and the solvent is evaporated under dynamic reduced pressure at a temperature of between 25 and 150 ° C., and preferably between 50 and 100 ° C to generate an intermediate polymer. The polymer obtained provides a color that varies with the nature of the metal element incorporated in the molecular precursor containing the metal element but also with the Si / M ratio previously fixed. The ammonolysis reaction of step b) is carried out under the action of ammonia. The purpose of the ammonia is to promote nucleophilic reactions and thus to replace part of the groups initially present around the metal M (for example dimethylamino) with NH 2 and / or NH groups. The ammonia must be in direct contact with the polymer to ensure the reaction. For example, when cold, the ammonia is introduced directly into a solution of polymers in an anhydrous solvent. The reaction time depends on the temperature and the dimethylamino and alkoxide content of the mixture. The reaction is, for example, carried out at a temperature in the range of -50 to 400 ° C, preferably in the range of -40 to 200 ° C. Ammonolysis at low temperature, for example at a temperature below 0 ° C. and for example of the order of -40 ° C., represents a good compromise between reactivity and cost / ease of implementation of the ammonolysis step. / properties of the modified polymetallosilazane obtained. The reaction time is, for example, 24 to 120 hours. Most often, the reaction is maintained until a color change occurs. This reaction is preferably carried out in a solvent in which the starting polymetallosilazane and the modified polymetallosilazane obtained are soluble. By way of example, mention may be made of tetrahydrofuran (THF) and toluene. The synthesis of the polymetallosilazanes carried out in step a) must be carried out under a controlled atmosphere because of the sensitivity of these products with respect to oxygen and especially moisture. Their preparation may be carried out under any type of inert atmosphere, argon or nitrogen type. The ammonolysis reaction carried out in step b) can be carried out under an ammonia atmosphere or under a controlled argon or nitrogen atmosphere containing the amount of ammonia required. In general, polymetallosilazanes are defined by a three-dimensional network of crosslinked polysilazane chains via bridging groups incorporating the transition metal. In other words, the polymetallosilazanes may be defined as an assembly of polysilazane type chains: ## STR2 ## in which: M is a transition metal, for example selected from Ti, Zr, Hf, V, Nb, Ta , Cr, Mo and W, - a and b correspond to the Si / M molar ratio fixed during the reaction of step a), - RI and R2, which are identical or different, each represent, independently of one another, an atom of hydrogen, an alkyl or alkenyl group, or aminoalkyl, preferably a hydrogen atom or a -CH3 group, - CH = CH2 or -N (H) R4 with R4 which represents a hydrogen atom or a silicon atom of another polysilazane chain, - R3 represents: - either a crosslinking group incorporating the metal element of the type -M (R5) Z with z which depends on the degree of coordination (coordination) of the metal M and R5 which represents either a group derived from the starting molecular entity comprising the transition metal, for example an amino group, alkylamino, arylamino, alkoxide (saturated or unsaturated), alkyl, aryl and more generally any leaving group based on C, N, H, O, P or S, it being understood that R5 can not be a halogen atom (Cl , Br, I, F), or the nitrogen atom of another polysilazane chain, - or a nitrogen atom of another polysilazane chain. According to an alternative embodiment, different transition metals can be introduced into the same polymetallosilazane in order to optimize the physical and decorative properties of the nanocomposites subsequently obtained.

Subsequently, the polymetallosilazane thermoplastic polymers according to the invention can lead, by thermo-chemical decomposition, to obtain nanocomposites. This thermochemical decomposition leads to the in situ generation of metal nitride nanocrystals in binary form within an amorphous or crystalline matrix of Si3N4 silicon nitride. These nanocomposites are obtained by thermal treatment of the pyrolysis type, with or without a shaping step, depending on the type of nanocomposite desired. In the context of the invention, the polymetallosilazanes are prepared so as to generate nanocomposites, for example in the form of micropowders or solid objects with intrinsic color and / or hardness properties specifically adapted to multiple applications. Examples of applications that may be mentioned include watchmaking or jewelery applications, applications in the field of cutting and finishing tools, and 15 in the field of electronics and structural materials (composite materials). . In the context of the invention, the nanocomposites obtained comprise a matrix comprising an amorphous or crystalline binary form of silicon nitride, in which are distributed nanocrystals of at least one transition metal nitride of binary structure. In the context of the invention, the nanocomposites obtained are preferably composed exclusively of a matrix comprising an amorphous or crystalline binary form of silicon nitride Si 3 N 4, in which nanocrystals of at least one transition metal nitride of nanoparticles are distributed. binary structure. By "exclusively constituted" is meant in particular that the binary silicon nitride matrix and the binary metal nitride nanocrystals represent at least 97% of the total mass of the nanocomposite material obtained. In particular, less than 2% by weight of oxygen is present within the nanocomposite material obtained. Preferably, the nanocomposites according to the invention consist exclusively of either a matrix consisting exclusively of an amorphous binary form of silicon nitride (a-Si3N4), in which nanocrystals of a single metal nitride are distributed. of transition of binary structure or crystals of a transition metal nitride of binary structure and crystals of a nitride of another transition metal of binary structure (nc-MN) (called nc - MN / a -Si3N4), or a matrix consisting exclusively of a crystalline binary form of silicon nitride (c-Si3N4), in which are distributed nanocrystals of a single or more transition metal nitride (s) of binary structure (nc-MN), (called nc-MN / c-Si3N4), with M representing a transition metal such as Ti, Zr, Hf, V, Nb, Ta, Cr, Mo or W. These materials have a color adaptable according to the nature of the metal and the experimental conditions. The nanocrystals have, most often, a larger size in the range of 1 to 100 nm. The nanocrystals are distributed homogeneously within the matrix. The nanocomposite materials according to the invention have a homogeneous color which accounts for the homogeneous distribution of the nanocrystals. The structural and morphological properties of the composite materials according to the invention are also homogeneous. Moreover, the silicon nitride constituting the matrix is thermally stable. When the silicon nitride matrix is crystalline, the crystalline form of the silicon nitride is the alpha phase (a: hexagonal shape / space group P63 / m) and / or beta (R: hexagonal shape / space group P31c ) and varies according to the temperature and the nature of the precursor containing the metal element. These nanocomposites can be in various forms, in particular in the form of particles, continuous micrometric fibers, nanofibers or nanotubes, a coating, a composite infiltration of a fibrous preform or in the form of a massive object, of the monolith type. Nanocomposites in the form of massive objects form an integral part of the invention. The polymetallosilazanes according to the invention can be used for designing solid objects without the addition of binding agents or sintering additives. Such materials have an excellent relative density.

When formatting is necessary, two strategies are possible. According to the first strategy (also called strategy 1), the polymetallosilazane may be shaped prior to its thermo-chemical decomposition, carried out by pyrolysis. In this case, hot forming of the polymer is carried out. The hot shaping step can be carried out at a temperature in the range of room temperature (typically 20 ° C) to 400 ° C, and preferably in the range of 50 to 150 ° C.

The shaping step is a function of the shape that one wishes to give the nanocomposite. In the case of a massive object, a simple compaction step in a mold corresponding to the chosen shape can be performed. The solid object of nanocomposite type can be obtained indifferently in the form of a workpiece of simple geometry (eg cylinder) machinable or in the form of a more complex piece of architecture, controlled geometry, requiring very little machining post-synthesis and this by means of appropriate molds. For example, the polymer can be compacted by means of a uniaxial press and a heating mold at a temperature in the range of room temperature (typically 20 ° C) to 400 ° C, and preferably in the range ranging from 50 to 150 ° C, the whole being arranged in a chamber under a nitrogen atmosphere protecting the polymer from humidity and ambient air. Compaction can be carried out at a pressure in the range of 25 to 500 MPa and preferably in the range of 25 to 150 MPa. The holding time at the compaction temperature is advantageously at least 30 minutes. In the case of an infiltration nanocomposite of a fibrous preform, the fibrous preform will be infiltrated beforehand with the modified polymetallosilazane according to the invention. To form continuous micrometric fibers, the modified polymetallosilazane according to the invention will be extruded. To form nanotubes or nanowires, a step of impregnating a pore network with the modified polymetallosilazane according to the invention may be provided. According to this first strategy, the polymetallosilazane is crosslinked by heat treatment to be compacted into a densified form by plastic deformation of the polymer. This crosslinking / compaction step is generally preceded by a grinding step of the polymetallosilazane, optionally followed by a step of homogenizing the size of the polymetallosilazane particles obtained, for example by sieving. The compacted polymer obtained can then be converted by pyrolysis. The densified polymer form by hot compaction is then pyrolyzed at between 800 and 1800 ° C. to generate the desired structures comprising a nanocrystalline binary phase of metal nitride and an amorphous or crystalline matrix of silicon nitride as a function of the temperature of the ammonia process and under nitrogen or argon and the nature of the precursor containing the metal element. It is possible according to this method to obtain any type of shapes such as continuous micrometric fibers, nanofibers or nanotubes, coatings, infiltration composites of a fibrous preform and, in particular, massive objects nanocomposites.

In this first strategy, it is preferable that the polymer is solid, plastic by heating and strongly crosslinked, which is obtained thanks to the preliminary shaping step, to limit the volume shrinkage of the part during the polymer conversion. ceramic. After compaction in the plastic state and pyrolysis, it is possible to obtain massive objects of dense ceramic type which are free of cracks. This method thus has several advantages: it avoids the synthesis of ceramic powders at high temperatures, low temperatures (800.degree.-1400.degree. C.) are sufficient for the production of a dense ceramic, and no sintering additive is required. necessary for densification, • the production of materials with an amorphous or crystalline matrix is possible. According to a second strategy (also called strategy 2), it is also possible to carry out the shaping or compacting step on the final nanocomposite material, after the pyrolysis step. In this case, the polymetallosilazane polymer is not subjected to shaping but is thermally decomposed into a ceramic powder, which is then post-synthesis shaped by conventional sintering, optionally with a plasma treatment. Polymetallosilazane therefore undergoes directly a thermo-chemical decomposition, carried out by pyrolysis, without prior shaping. This pyrolysis step is generally preceded by a step of grinding the polymetallosilazane, optionally followed by a step of homogenizing the size of the polymetallosilazane particles obtained, for example by sieving. A nanocomposite powder of micrometric size is then generated and can be used later to develop solid objects, by sintering. The sintering can be carried out conventionally (uniaxial pressing) or by isostatic pressing or by plasma-assisted sintering (SPS) of the English language "Spark Plasma Sintering". For this, the micropowders are, for example, introduced into a graphite mold. A heating cycle with heating up to a temperature of at least 1200 ° C with a step of about 5 minutes can be provided. Whatever the strategy adopted (strategy 1 or 2), or even when no shaping step is desired, the pyrolysis step of the polymetallosilazane is preferably carried out in two steps: a first treatment step thermal ammonia, preferably at a temperature greater than or equal to 800 ° C and a second heat treatment step under nitrogen or argon, preferably at a temperature greater than or equal to 1200 ° C. An example of pyrolysis conditions, on a laboratory scale, is detailed below: the polymetallosilazane to be pyrolyzed is placed in a nacelle of boron nitride, carbon or alumina which is introduced directly, for example into a tubular furnace made of silica without contact with air. The oven is then isolated and placed under dynamic vacuum (10-2 bar / 22 ° C) in order to evacuate the nitrogen previously introduced. Ammonia is introduced to atmospheric pressure and the whole is heated under gas flushing. The gas flow rate can be between 0 and 1000 ml.min-1, and preferably between 50 and 200 ml.min-1. The temperature ramp can be between 10 and 600 ° Ch-1, and preferably between 20 and 60 ° Ch-1 for the compacted polymers (first strategy) and between 100 and 300 ° Ch-1 for the ground and sieved polymers in micropowders (second strategy) .The maximum temperature of heating or temperature of bearing is at least 800 ° C. The temperature of the furnace is maintained for a predetermined period at its maximum value The time during which the temperature is maintained at its maximum value, or dwell time, is a parameter which influences the degree of crystallinity nanocrystalline phase and therefore in fine on the physical properties of nanocomposites and will be adapted by those skilled in the art.For example, a time of less than 2 hours is fixed.The descent in temperature is controlled and can be between 3 0 and 600 ° C.h "1, and preferably between 60 and 100 ° C.h-1 for compacted polymers (first strategy) and between 300 and 600 ° C.h" 1 for the ground and sieved polymers in micropowders (second strategy). After this first thermal treatment with ammonia, the product obtained in the nacelle is, for example, introduced into a furnace to the graphite resistors to undergo a thermal treatment under nitrogen flushing to a plateau temperature of at least 1200 °. C by means of a temperature ramp of between 10 and 600 ° C.h_1, and preferably between 40 and 100 ° Ch "1 for the compacted polymers (first strategy) and between 300 and 600 ° Ch" 1 for the ground and sieved polymers in micropowders (second strategy). The temperature of the oven is maintained for a predetermined period at its maximum value. The time during which the temperature is maintained at its maximum value, or dwell time, is again a parameter that has a significant influence on the degree of crystallinity of the nanocrystalline phase and therefore ultimately on the physical properties of the nanocomposites and will be adapted by the skilled person. For example, a time limit of about 2 hours is fixed. The heating is then stopped and the experimental system is cooled to room temperature. The cooling rate is controlled and may be between 30 and 600 ° C-1, and preferably between 60 and 100 ° C-1 for compacted polymers (first strategy) and between 300 and 600 ° C-1 for polymers crushed and screened into micropowders (second strategy). The process according to the invention which makes it possible to prepare nanocomposites from the above-described specific polymetallosilazanes has numerous advantages over prior art, particularly in view of the ability to shape the composition of polymetallosilazanes in a temperature-stable manner. structure according to the invention. In addition, the density of nanocrystals of metal nitride in the matrix, as well as their degree of crystallization, can be controlled by the Si / M ratio previously fixed in the polymer and by the heat treatment conditions (final temperature, treatment time, ...). The density and crystallization state of the nanocrystals in the matrix make it possible to adjust some of the properties of the resulting nanocomposites (color, density, etc.). The examples which follow with reference to the appended figures serve to illustrate the invention but are not limiting in nature.

Figure 1 shows the UV-Visible spectrum of the nanocomposite powders prepared from the polytitanosilazane (Si / Ti = 3.6) of Example 1. Figure 2 shows the ATM curve used in Example 2 of the polytitanosilazane (Si / Ti = 3.6) of Example 1.

FIG. 3 shows the diffractogram of the nanocomposite powders resulting from the polytitanosilazane (Si / Ti = 3.8) of Example 3. FIG. 4 shows the ATM Curve used in Example 5 of the polytitanosilazane (Si / Ti = 2.5 ) of Example 1. Figure 5 shows the ATM curve used in Example 7 of the polytitanosilazane (Si / Ti = 2.6) of Example 6.

Figure 6 shows the diffractogram of the nanocomposite powders prepared from the polyzirconosilazane (Si / Zr = 5) of Example 8. Figure 7 shows the diffractogram of the nanocomposite powders prepared from the polyzirconosilazane (Si / Zr = 5) of the Example 9

FIG. 8 shows the UV-Visible spectrum of the nanocomposite powders prepared in Example 10 from the polyzirconosilazane (Si / Zr = 5) of Example 9. FIG. 9 shows the diffractogram of nanocomposite powders resulting from polyzirconosilazane (Si / Zr = 2.5) of Example 11.

The synthesis of the polymetallosilazanes is carried out under a controlled atmosphere of argon by using Schlenk type glassware and mixed vacuum-argon ramps to carry out these syntheses. In the context of the examples, the shaping of the polymers (channel (a)) is carried out by hot compaction by means of an automatic and programmable uni-axial hydraulic press and heated molds of geometry adapted to that desired for the final material. The assembly is placed in an enclosure under nitrogen flow due to the sensitivity of the polymers vis-à-vis the humidity of the air. The heat treatment is carried out, taking into account the available equipment, in two stages by means of a silica tube furnace (for treatments up to at least 800 ° C), then of a resistive graphite furnace with opening frontal (for treatments up to 1800 ° C). Furnaces are systematically inerted by dynamic vacuum heat treatment (10-2 bar / 600 ° C) before use. The temperature rise ramp, the duration of the bearing as well as the cooling rate are controlled by means of an electronic regulator. Flow meters allow the control of the gas flow rates at the inlet of each furnace. Regarding the sintering of the micropowders (lane (b)), this is carried out by plasma-assisted sintering (SPS, Spark Plasma Sintering) under nitrogen. The sample preparation is carried out in a glove box and the inner surface of the graphite molds used for this sintering is covered with a Papyex film thus avoiding any adhesion of the powder to be sintered with the mold.

Material handling is carried out in a glove box (Jacomex BS521) under argon. The chamber is dehydrated with phosphorus pentoxide (P205). Ammonia and nitrogen are electronic quality gases.

Thermogravimetric analysis is performed with Setaram equipment (TGA 92 16 18). The experiments are carried out under ammonia at 5 ° C / min up to 1000 ° C by placing the polymer in a silica nacelle. The chemical analyzes of the polymers are done at the Central Microanalysis Service of the CNRS (Vernaison, France). The infrared spectra of the polymers are recorded from pellets (polymer mixture + KBr) by means of a Nicolet analyzer (Nicolet Magna 550 Fourier transform-infrared spectrometer). The 1 H NMR data in solution was obtained with a Bruker apparatus (Bruker AM 300 spectrometer) in CDCI3 operating at 300 MHz.

The density measurements of the massive objects are carried out at room temperature under helium using an AccuPyc 1330 analyzer (Helium pycnometer from Micromeritics). The X-ray diffraction (XRD) diffractograms of the micropowders are obtained from a Philips analyzer (Philips PW 3040/60) ('Pert PRO diffractometer) operating at 30 mA and 40 kV. The micropowders and nanocomposite-type parts are placed on a PVC substrate. The composition of the micropowders was determined during the observation of scanning electron microscopy (EDX system (EDAX Genesis 4000) coupled with a Hitachi S-800 microscope). Infrared spectroscopy is performed on nanocomposite powders with Nicolet equipment (Nicolet 380 FT-IR spectrometer) coupled with ATR (Attenuated Total Reflectance) accessory. Raman spectrometry was performed on a Renishaw microscope (Renishaw mode) RM 1000 Raman microscope) operating at a wavelength λ = 514.5 nm. A measure of the intensity of the total reflectance (measured on the Kubelka-Munk transformation) over a range of UV-Visible (190-1100 nm) is carried out on powder with a Parkin-Elmer apparatus (Parkin-Elmer UV / Visible spectrophotometer lambda 35). The uniaxial compacting press for polymers according to (a) is an Atlas Auto T8 from Specac. The sintering system SPS is of type 5 FCT (HPD25).

EXAMPLE 1 Two-step synthesis of a polytitanosilazane (Si / Ti = 3.6) and obtaining the nanocomposite nc-TiN / a-Si3N4 in the form of micropowder A first step is carried out by reaction between the polymethylsilazane [HSiCH 3 NH] n and Ti [N (CH 3) 2] 4 titanium dimethylamide in toluene at its reflux temperature. 7.4 ml (7 g, 31 mmol) of titanium dimethylamide Ti [N (CH 3) 2] 4 are added under argon to a solution of polymethylsilazane [HSiCH 3 NH] n (9.3 g, 157.25 mmol) under stirring in toluene (200 ml) placed in a knit-type glassware (500 ml) surmounted by a water-cooled condenser and an argon inlet. The addition of Ti [N (CH 3) 2] 4 is by means of a micro-syringe previously purged under argon at room temperature. A black solution is formed instantly. The reaction mixture is left at room temperature with stirring for 15 h. The raising of the temperature to the reflux temperature of toluene is progressively carried out at a rate of 30 ° C./h with stirring. The mixture is maintained at this temperature for 72 hours with stirring and then the whole is cooled to room temperature under argon flow. After returning to ambient temperature, the solvent is removed under reduced pressure at 100 ° C. using a distillation bridge and a recovery Schlenk placed in the liquid air. A soluble light brown compound is obtained. Infrared spectroscopy (KBr / cm-1): 3373, 2954-2773, 2125, 1460-1370, 1255, 1173, 1000-800.

1H Nuclear Magnetic Resonance (CDCl3 / ppm): 5.5-4.4, 3.3-2.4, 1, 0.3. In a second synthesis step, the intermediate compound previously synthesized is dissolved in toluene in a knitted flask (500 mL) surmounted by a refrigerant cooled to -40 ° C. and an argon / ammonia inlet immersed in the solution. The solution is cooled to -40 ° C and an ammonia flow is then sent directly into the solution with stirring. The addition is done until the ammonia is condensed in the refrigerant. A color change occurs during the addition of ammonia. After condensation of the ammonia in the refrigerant, the solution is kept stirring for 3 days at -40 ° C. and then is naturally heated under argon. The solvent is removed under reduced pressure at 100 ° C. using a distillation bridge and a recovery Schlenk placed in the liquid air. An insoluble yellow / green polytitanosilazane is obtained.

Elemental analysis: Si / Ti = 3.6 (Si = 26.4 m%, Ti = 12.3 m%) Infrared spectroscopy (KBr / cm 1): 3386, 2958-2779, 2132, 1410, 1257, 1180, 1000-800. Thermogravimetric analysis, ceramic yield (1000 ° C (5 ° C / h), NH3): 71% The polytitanosilazane is ground and then sieved (63 μm) in an argon glove box. The powder is placed in a boron nitride boat for pyrolysis (300 ° C / h) in ammonia (120 ml / min) at 1000 ° C (2 h of step) in a silica furnace connected to a glove box under nitrogen before cooling to room temperature at 600 ° C / h. The pyrolysis product is then heated to 1500 ° C (300 ° C / h) under nitrogen (200 ml / min) and maintained 2 hours at 1500 ° C before cooling to 600 ° C / h at room temperature to produce micropowder blue / violet color in which nanocrystals of titanium nitride in the cubic phase (TiN) are dispersed in an amorphous phase of silicon nitride (Si3N4).

Infrared spectroscopy (IR-ATR; cnf-1): 700-1100 cm-1 (Ti-N, Si-N) Raman (cm-1): Ti-N bands: 150-300 cm-1 (acoustic transition LA and YOUR); 390-650 cm-1 (LO and TO optical modes); 840 cm-1 (A + 0) and 1070 cm-1 (20). XRD: TIN diffraction peaks (cfc crystal structure, Fm-3m gap group) (36.44 °, 42.41 °, 61.99 °, 73.31 and 77.8 °) FIG. 1 shows the UV-Visible (nm) of the resulting nanocomposite powder.

EXAMPLE 2 Hot Compaction of the Polytitanosilazane of Example 1 to Generate a Solid Nanocomposite Decorative Object The polytitanosilazane of Example 1 was ground and then sieved (63 μm) to form homogeneous microparticles. The polymer is uniaxially pressed at room temperature to test its hot plasticity by thermomechanical analysis (ATM). The ATM was used in compression mode on the polymer by heating under nitrogen up to 300 ° C at a heating rate of 5 ° C / min, according to the curve shown in Figure 2. The flow rate of the gas is 15 ml / min and the applied force is 0.9 N. 45 mg of polymer are used to prepare a pellet of 5 mm in diameter. After a slight swelling up to 135 ° C., the polytitanosilazane (Si / Ti = 3.6) undergoes a dimensional change highlighting its ability to plastically deform under the action of a load from 135 ° C. . To prepare the bulk objects, 250 mg of milled and sieved polymers (63 μm) are uniaxially compacted as a cylindrical piece 13 mm in diameter using a uniaxial compaction press placed in a nitrogen glove box and applying a pressure of 74 MPa at room temperature. The rise in temperature is carried out under load at a heating rate of 10 ° C / min to 135 ° C. Once the temperature of 135 ° C reached, it is maintained for 30 min under load. After the bearing, the charge is released slowly and the cooling is at a rate of 1 ° C / min.

The cylindrical piece is placed in a boron nitride pod for pyrolysis (20 ° C / h) in a silica furnace connected to an ammonia glove box (120 ml / min) at 1000 ° C (2 h of step ) before cooling to room temperature at 30 ° C / h. The pyrolysis product is then heated at 1500 ° C. (60 ° C./h) under nitrogen (200 ml / min) and maintained for 2 hours at 1500 ° C. before cooling at 60 ° C./h up to 800 ° C. at 100 ° C / hr to room temperature to produce a mass-dyed solid object (blue / violet) in which nanocrystals of titanium nitride in the cubic phase (TiN) are dispersed in an amorphous phase of silicon (Si3N4). The material obtained has a relative density of 91% (dpoudre = 3,1916 and dpièce = 2,904).

EXAMPLE 3 Two-step synthesis of a polytitanosilazane (Si / Ti = 3.8) and preparation of the nanocomposite nc-TiN / a-Si3N4 in powder form A first step is carried out by reaction between the polymethylsilazane [HSiCH3NH] n and Titanium ethoxide C8H2808Ti in toluene at its reflux temperature. 1.5 ml (1.65 g, 7.23 mmol) of titanium ethoxide C 8 H 20 O 4 Ti are added under argon to a solution of polymethylsilazane [HSiCH 3 NH] (2.1 g, 35.5 mmol) in toluene (50 g). ml) with stirring in a knit-type glassware (500 ml) surmounted by a water-cooled condenser, and an argon inlet containing. The addition of titanium ethoxide C8H2O04Ti is by means of a micro syringe 25 previously purged under argon at room temperature. A clear yellow solution is formed instantly. The reaction mixture is left at room temperature with stirring for 15 h. The raising of the temperature to the reflux temperature of toluene is progressively carried out at a rate of 30 ° C./h with stirring. The mixture is kept at this temperature for 3 days with stirring and then the whole is cooled to room temperature under argon flow. After returning to ambient temperature, the solvent is removed under reduced pressure at 100 ° C. using a distillation bridge and a recovery Schlenk placed in the liquid air. A viscous compound of soluble burgundy color is obtained. Infrared Spectroscopy (KBr / cm-1): 2972, 1644-1618, 1460-1370, 1271, 767-532.

1H Nuclear Magnetic Resonance (CDCl3 / ppm): 5.8-4.6, 3.66, 3.3-2.7, 1.15-1.22, 0.3. In a second synthesis step, the intermediate compound previously synthesized is dissolved in toluene in a Tricol flask (500 mL) surmounted by a refrigerant cooled to -40 ° C. and an argon / ammonia inlet immersed in the solution. The solution is cooled to -40 ° C. and an ammonia flow is then sent directly into the stirred solution until the ammonia is condensed in the refrigerant. A color change occurs during the addition of ammonia. After condensing the ammonia in the refrigerant, the solution is kept stirring for 72 hours at -40 ° C. and then is naturally heated under argon. The solvent is removed under reduced pressure at 100 ° C. using a distillation bridge and a recovery Schlenk placed in the liquid air. An insoluble yellow / green polytitanosilazane is obtained. Elemental analysis: Sil = 3.8 (Si = 28.4 m%, Ti = 12.8 m%) Infrared spectroscopy (KBr / cm i): 3437, 2973-2927, 1631, 1460-1370, 1272, 1239, 770-516. Thermogravimetric analysis, ceramic yield (1000 ° C (5 ° C / h), NH3): 67% The polytitanosilazane is ground and then sieved (63 μm) in glove box under argon. The powder is placed in a boron nitride boat for pyrolysis (300 ° C / h) in ammonia (120 ml / min) at 1000 ° C (2 h of step) in a silica furnace connected to a glove box under nitrogen before cooling to room temperature at 600 ° C / h. The pyrolysis product is then heated to 1700 ° C (300 ° C / h) under nitrogen (200 ml / min) and maintained for 2 hours at 1700 ° C before cooling to 600 ° C / h at room temperature to produce micropowder in gold color in which nanocrystals of titanium nitride in the cubic phase (TiN) are dispersed in an amorphous phase of silicon nitride (Si3N4). Infrared spectroscopy (IR-ATR; cm-1): 700-1100 cm-1 (Ti-N, Si-N) Raman (cni-2): Ti-N bands: 150-300 cm-1 (acoustic transition LA and 5 TA); 390-650 cm-1 (LO and TO optical modes); 900 cm-1 (A + 0) and 1100 cm-1 (20). Si-N: 1355 cm -1. XRD: TiN diffraction peaks (cfc crystal structure, Fm-3m gap group) (36.5 °, 42.57 °, 61.84 °, 74.07 °, 77.89 °). The powder diffractogram is shown in FIG. 3. EXAMPLE 4 Two-step synthesis of a polytitanosilazane (Si / Ti = 2.5) and preparation of the nc-TiN / a-Si3N4 nanocomposite in the form of a powder A first step is carried out by reaction between polymethylsilazane [HSiCH3NH] n and titanium dimethylamide Ti [N (CH3) 214 in toluene at its reflux temperature 8 ml (7.58 g, 33.8 mmol) of titanium dimethylamide Ti [N ( CH 3) 2] 4 are added under argon to a solution of polymethylsilazane [HSiCH3NH] n (5 g, 84.54 mmol) in toluene (100 ml) with stirring in a Tricol glassware (500 ml) surmounted by a coolant cooled with water and an argon inlet. The addition of tetrakis (dimethylamido) titanium Ti [N (CH 3) 2] 4 is by means of a micro-syringe previously purged under argon at room temperature. A black solution is formed instantly. The reaction mixture is left at room temperature with stirring for 15 hours. The raising of the temperature to the reflux temperature of toluene is progressively carried out at a rate of 30 ° C./h with stirring. The mixture is maintained at this temperature for 72 hours with stirring and then the whole is cooled to room temperature under argon flow. After returning to ambient temperature, the solvent is removed under reduced pressure at 100 ° C. using a distillation bridge and a recovery Schlenk placed in the liquid air. An orange-brown compound is obtained.

Infrared Spectroscopy (KBr / cm 1): 3381, 2959-2770, 2111, 1460-1370, 1255, 1173, 1000-800, 591. 1H Nuclear Magnetic Resonance (CDCl3, / ppm): 5.5-4.4, 3.3-2.4, 1, 0.3 In a second synthesis step, the intermediate compound previously synthesized is dissolved in toluene in a Tricol flask (500 mL) surmounted by a refrigerant cooled to -40 ° C. C and an argon / ammonia inlet plunging into the solution. The solution is cooled to -40 ° C. and an ammonia flow is then sent directly into the stirred solution until the ammonia is condensed in the refrigerant. A color change occurs during the addition of ammonia. After condensation of the ammonia in the refrigerant, the solution is kept stirring for 3 days at -40 ° C. and then is naturally heated under argon. The solvent is removed under reduced pressure at 100 ° C. using a distillation bridge and a recovery Schlenk placed in the liquid air. An insoluble yellow / green polytitanosilazane is obtained. Elemental analysis: Si / Ti = 2.5 (Si = 22.13 m%, Ti = 14.88 m%) Infrared spectroscopy (KBr / cm 1): 3381, 2955-2788, 2113, 1410, 1256, 1181, 1000-800, 621.

Thermogravimetric analysis, ceramic yield (1000 ° C (5 ° C / h), NH3): 69.5 The polytitanosilazane is ground and sieved (63 μm) in a glove box. The powder is placed in a boron nitride boat for pyrolysis (300 ° C / h) in ammonia (120 ml / min) at 1000 ° C (2 h of step) in a silica furnace connected to a glove box before cooling to room temperature at 600 ° C / h. The pyrolysis product is then heated to 1400 ° C (300 ° C / h) and maintained 2 h at 1400 ° C under nitrogen (200 ml / min) before cooling to 600 ° C / h at room temperature to produce micropowder of purple color with metallic luster in which nanocrystals of titanium nitride in the cubic phase (TiN) are dispersed in an amorphous phase of silicon nitride (Si3N4). EDX: Si / Ti = 1.9 (Si (33.57 at%) and Zr (17.34 at%)).

Infrared Spectroscopy (IR-ATR; cm i): 600-1100 cm-1 (Ti-N, Si-N). Raman (cni-i): Ti-N bands: 150-300 cc (acoustic transition LA and TA); 390-650 cm-1 (LO and TO optical modes); 840 cm -1 (A + 0) and 1090 cc (20).

XRD: TIN diffraction peaks (cfc crystal structure, Fm-3m gap group) (36.39 °, 42.44 °, 61.80 °, 73.78 °, 77.9 °). UV-Visible (nm): 2 = = 550 nm

EXAMPLE 5 Hot Compaction of the Polytitanosilazane of Example 4 to Generate a Solid Nanocomposite Decorative Object The polytitanosilazane of Example 1 is milled and then sieved (63 μm) to form homogeneous microparticles. The polymer undergoes uniaxial pressing at room temperature to test its hot plasticity by thermomechanical analysis (ATM). The ATM was used in compression mode on the polymer by heating under nitrogen up to 300 ° C / h at a heating rate of 5 ° C / min, according to the curve presented in Figure 4. The gas flow rate was 15 ° C / min. ml / min and the applied force is 0.9 N. 45 mg of polymer are used to prepare a pellet of 5 mm in diameter.

After a slight swelling up to 112 ° C, the polytitanosilazane (Sil = 2.5) undergoes a dimensional change highlighting its ability to plastically deform under the action of a charge from 112 ° C. To prepare the bulk objects, 250 mg of milled and sieved polymers (63 μm) are compacted in a uni-axial way in the form of a cylindrical piece 13 mm in diameter using a uniaxial compaction press placed in a glove box and applying a pressure of 74 MPa at room temperature. The rise in temperature is carried out under load at a heating rate of 10 ° C./min up to 112 ° C. Once the temperature of 112 ° C reached, it is maintained for 30 min under load. After the bearing, the charge is released slowly and the cooling is at a rate of 1 ° C / min.

The cylindrical piece is placed in a boron nitride pod for pyrolysis (20 ° C / h) in a silica furnace connected to an ammonia glove box (120 ml / min) at 1000 ° C (2 h of step ) before cooling to room temperature at 30 ° C / h. The pyrolysis product is then heated at 1400 ° C. (60 ° C./h) under nitrogen (200 ml / min) and maintained for 2 hours at 1400 ° C. before cooling at 60 ° C. to 800 ° C. and then 100 ° C. C / h 800 ° C at room temperature to produce a bulk dyed (purple) mass object in which nanocrystals of titanium nitride in the cubic phase (TiN) are dispersed in an amorphous phase of silicon nitride (Si3N4 ). The material obtained has a relative density of 95.6% (dpoudre = 3,1143 and dpièce = 2,9763).

EXAMPLE 6 Two step synthesis of a polytitanosilazane (Si / Ti = 2.6) and preparation of the nanocomposite no-TiN / a-Si3N4 in powder form A first step is carried out by reaction between perhydrosilazane [HSiHNH] n ( in solution in xylene) and titanium dimethylamide Ti [N (CH 3) 2] 4 in toluene at its reflux temperature 6.3 ml (5.97 g, 26.6 mmol) of titanium dimethylamide Ti [ N (CH 3) 2] 4 are added under argon to a solution of polyhydrosilazane [HSiHNH] n (3 g, 66.67 mmol) in toluene (100 ml) with stirring in a Tricol glassware (500 ml) surmounted by a coolant cooled with water and an argon inlet. The addition of tetrakis (dimethylamido) titanium Ti [N (CH 3) 2] 4 is by means of a micro-syringe previously purged under argon at room temperature. A black solution is formed instantly. The reaction mixture is left at room temperature with stirring for 15 h. The raising of the temperature to the reflux temperature of toluene is progressively carried out at a rate of 30 ° C./h with stirring. The mixture is maintained at this temperature for 72 hours with stirring and then the whole is cooled to room temperature under argon flow. After returning to ambient temperature, the solvent is removed under reduced pressure at 100 ° C. using a distillation bridge and a recovery Schlenk placed in the liquid air. A poorly soluble dark brown compound is obtained. Infrared Spectroscopy (KBR / cm-1): 3368, 2959-2770, 2148, 1460-1370, 1251, 1186, 1000-800, 600.

In a second synthesis step, the intermediate compound previously synthesized is dissolved in toluene in a Tricol flask (500 mL) surmounted by a coolant cooled to -40 ° C. and an argon / ammonia inlet immersed in the solution. The solution is cooled to -40 ° C. and an ammonia flow is then sent directly into the stirred solution until the ammonia is condensed in the refrigerant. A color change occurs during the addition of ammonia. After condensation of the ammonia in the refrigerant, the solution is kept stirring for 3 days at -40 ° C. and then is naturally heated under argon. The solvent is removed under reduced pressure at 100 ° C. using a distillation bridge and a recovery Schlenk placed in the liquid air. An insoluble yellow polytitanosilazane is obtained. Elemental analysis: Si / Ti = 2.6 (Si = 22.13 m%, Ti = 14.28 m%) Infrared Spectroscopy (KBR / cm-1): 3368, 2959-2770, 2148, 1542, 1460-1370 , 1186, 1000-800, 600.

Ceramic Yield (1000 ° C (5 ° C / h), NH3): 69.7 ° F The polytitanosilazane is ground and sieved (63 μm) in a glove box under argon. The powder is placed in a boron nitride boat for pyrolysis (300 ° C / h) in ammonia (120 ml / min) at 1000 ° C (2 h of step) in a silica furnace connected to a glove box under nitrogen before cooling to room temperature at 600 ° C / h. The pyrolysis product is then heated at 1400 ° C (300 ° C / h) under nitrogen and maintained for 2 hours at 1400 ° C before cooling to 600 ° C / hr at room temperature to produce purple-colored micropowder in which Nanocrystals of titanium nitride in the cubic phase (TiN) are dispersed in an amorphous phase of silicon nitride (Si3N4). Infrared spectroscopy (cm-1): 600-1100 cm -1 (Ti-N, Si-N) Raman (cm-r). Ti-N bands: 150-300 cm-1 (acoustic transition LA and TA); 390-650 cm-1 (LO and TO optical modes); 828 cm-1 (A + 0) and 1090 cm-1 (20). XRD: TiN diffraction peaks (cfc crystal structure, Fm-3m gap group) (36.45, 42.59, 61.85, 74.56 and 77.8 °).

EXAMPLE 7 Hot compaction of the polytitanosilazane of Example 6 to generate a nanocomposite solid decorative object The polytitanosilazane of Example 1 is milled and then sieved (63 μm) to form homogeneous microparticles. The polymer undergoes a uni-axial pressing at room temperature to test its hot plasticity by thermomechanical analysis (ATM). The ATM was used in compression mode on the polymer by heating under nitrogen up to 300 ° C. at a heating rate of 5 ° C./min, according to the curve shown in FIG. 5. The flow rate of the gas is 15 ml. / min and the applied force is 0.9 N. 45 mg of polymer are used to prepare a pellet of 5 mm in diameter. The polytitanosilazane (Si / Ti = 2.6) undergoes a dimensional change highlighting its ability to plastically deform under the action of a charge from 113 ° C. To prepare the bulk objects, 250 mg of crushed and screened polymers (63 μm) are compacted as a cylindrical piece 13 mm in diameter using a uniaxial compaction press placed in a glove box and applying a pressure of 74 mm. MPa at room temperature. The temperature rise is carried out under load at a heating rate of 10 ° C / min to 110 ° C. Once the temperature of 110 ° C reached, it is maintained for 30 min under load. After the bearing, the charge is released slowly and the cooling is at a rate of 1 ° C / min. The cylindrical piece is placed in a boron nitride boat 30 to undergo pyrolysis (20 ° C / h) in a silica furnace connected to an ammonia glove box (120 ml / min) at 1000 ° C (2 hr). bearing) before cooling to room temperature at 30 ° C / h. The pyrolysis product is then heated at 1400 ° C. (60 ° C./h) and maintained for 2 hours at 1400 ° C. before cooling at 60 ° C. to 800 ° C. and then at 100 ° C./h at 800 ° C. to room temperature to produce a mass-dyed solid object (Violet) in which nanocrystals of titanium nitride in the cubic phase (TiN) are dispersed in an amorphous silicon nitride (Si3N4) phase. The resulting material has a relative density of 92 ° (powder = 3.6459 and dp = 3,3434).

EXAMPLE 8 Two-step synthesis of a polyzirconosilazane (Si / Zr = 5) and preparation of the nanocomposite nc-ZrN / a-Si3N4 in powder form A first step is carried out by reaction between the polymethylsilazane [HSiCH3NH] n and the dimethylamide of zirconium Zr [N (CH 3) 2] 4 in toluene at its reflux temperature 2 g (33.81 mmol) of polymethylsilazane [HSiCH 3 NH] n diethylamide are added under argon to a solution of zirconium dimethylamide Zr [N (CH 3) 2 ] (1.8 g, 6.73 mmol) in toluene (50 ml) with stirring in a Tricol-type glassware (500 ml) surmounted by a water-cooled condenser, and an inlet of argon. The addition of the polymethylsilazane [HSiCH3NH] n is by means of a micro-syringe previously purged under argon at room temperature. A yellow solution is formed instantly. The reaction mixture is left at room temperature with stirring for 15 h. The raising of the temperature to the reflux temperature of toluene is progressively carried out at a rate of 30 ° C./h with stirring. The mixture is maintained at this temperature for 72 hours with stirring and then the whole is cooled to room temperature under argon flow. After returning to ambient temperature, the solvent is removed under reduced pressure at 100 ° C. using a distillation bridge and a recovery Schlenk placed in the liquid air. A soluble orange compound is obtained. Infrared Spectroscopy (KBR / cm 1): 3389, 2960-2789, 2125, 1258, 1180, 1000-800 and 466.

1H Nuclear Magnetic Resonance (CDCl3 / ppm): 4.9-3.1, 3.1-2.3, 2.7-2.08, 0.8-0.2, and O. In a second step of synthesis, the previously synthesized intermediate compound is dissolved in toluene in a Tricol flask (500 mL) surmounted by a coolant cooled to -40 ° C and an argon / ammonia inlet immersed in the solution. The solution is cooled to -40 ° C and an ammonia flow is then sent directly into the solution with stirring. The addition is done until the ammonia is condensed in the refrigerant. A color change occurs during the addition of ammonia. After condensation of the ammonia in the refrigerant, the solution is kept stirring for 3 days at -40 ° C. and then is naturally heated under argon. The solvent is removed under reduced pressure at 100 ° C. using a distillation bridge and a recovery Schlenk placed in the liquid air. An insoluble light yellow polyzirconosilazane is obtained. Elemental analysis: Si / Zr = 5.05 (Si = 27.19 m%, Zr = 17.5 m%). Infrared spectroscopy (KBR / cm-1): 3387, 2960-2790, 2131, 1259, 1181, 906 and 470. Ceramic yield (1000 ° C (5 ° C / h), NH3): 70% Polyzirconosilazane is ground then sieved (63 11m) in glove box under argon. The powder is placed in a boron nitride boat for pyrolysis (300 ° C / h) under ammonia (120 m / min) at 1000 ° C (2 h of stage) in a silica furnace connected to a glove box under nitrogen before cooling to room temperature at 600 ° C / h. The pyrolysis product is then heated to 1500 ° C (300 ° C / h) under nitrogen and maintained for 2 hours at 1500 ° C before cooling to 600 ° C / hr at room temperature to produce purple-colored micropowder in which Zirconium nitride nanocrystals in the cubic phase (ZrN) are dispersed in a silicon nitride phase (a-Si3N4).

Infrared spectroscopy (IR-ATR; cm 1): 750-1100 (Si-N asymtretched), 490 (Si-N) and 460 (Zr-N). Raman (cm-1); Zr-N strips: 150-300 cm -1 (acoustic transition LA and TA); 390-650 cm -1 (optical modes LO and TO); 645, 697 cm -1 (A + O) and 970 cm -1 (20) DRX: ZrN diffraction peaks (cfc crystal structure, Fm-3m space group) and a-Si3N4, as shown in Figure 6. UV-Visible (nm): A = 500 nm

EXAMPLE 9 Two-step synthesis of a polyzirconosilazane (SI / Zr = 5) and preparation of the nanocomposite nc-ZrN / a-Si3N4 in powder form A first step is carried out by reaction between polymethylsilazane [HSiCH3NH] n and diethylamide zirconium Zr [N (CH 2 CH 3) 2] 4 in toluene at its reflux temperature 12.5 ml (12.84 g, 33.8 mmol) of zirconium diethylamide Zr [N (CH 2 CH 3) 2] 4 are added under argon to a solution of polymethylsilazane [HSiCH3NH] n (10 g, 169.08 mmol) in toluene (200 mL) with stirring in a knit-type glassware (500 mL) surmounted by a water-cooled refrigerant, and an argon inlet. The addition of the tetrakis (diethylamido) zirconium Zr [N (CH 2 CH 3) z] 4 is by means of a micro-syringe previously purged under argon at room temperature. A black solution is formed instantly. The reaction mixture is left at room temperature with stirring for 15 h. The raising of the temperature to the boiling point of toluene is progressively carried out at a rate of 30 ° C./h with stirring. The mixture is maintained at this temperature for 72 hours and then the whole is cooled to room temperature under an argon stream. After returning to ambient temperature, the solvent is removed under reduced pressure at 100 ° C. using a distillation bridge and a recovery Schlenk placed in the liquid air. A soluble light yellow compound is obtained. Infrared Spectroscopy (KBR / cm-1): 3377, 2954-2773, 2129, 1460-1370, 1255, 1179, 1000-800 and 473.

1H Nuclear Magnetic Resonance (CDCl3 / ppm): 5.1-4.49, 3.4-2.7, 1, 0.3. In a second synthesis step, the intermediate compound previously synthesized is dissolved in toluene in a Tricol flask (500 mL) surmounted by a coolant cooled to -40 ° C. and an argon / ammonia inlet immersed in the solution. The solution is cooled to -40 ° C and an ammonia flow is then sent directly into the solution with stirring. The addition is done until the ammonia is condensed in the refrigerant. A color change occurs during the addition of ammonia. After condensation of the ammonia in the refrigerant, the solution is kept stirring for 3 days at -40 ° C. and then is naturally heated under argon. The solvent is removed under reduced pressure at 100 ° C. using a distillation bridge and a recovery Schlenk placed in the liquid air. An insoluble white polyzirconosilazane is obtained.

Elemental analysis: Si / Zr = 5.03 (Si = 27.19 m%, Zr = 17.55 m%). Infrared Spectroscopy (KBR / cni-1): 3379, 2962, 2862, 2130, 1546, 1258, 1178, 1000-800, 460 cm-1. Ceramic yield (1000 ° C (5 ° C / h), NH3): 71.5 The polyzirconosilazane is ground and sieved (63 μm) in an argon glove box. The powder is placed in a boron nitride boat for pyrolysis (300 ° C / h) in ammonia (120 ml / min) at 1000 ° C (2 h of step) in a silica furnace connected to a glove box under nitrogen before cooling to room temperature at 600 ° C / h. The pyrolysis product is then heated to 1500 ° C (300 ° C / h) under nitrogen and maintained for 2 hours at 1500 ° C before cooling to 600 ° C / h at room temperature to produce violet-colored micropowder in which Zirconium nitride nanocrystals in the cubic phase (ZrN) are dispersed in a silicon nitride phase (a-Si3N4). EDX: Si / Zr = 4.3 (Si (47.99% At) and Zr (11.08% At)).

Infrared spectroscopy (IR-ATR; cm-1): 800-1100 (Si-N), 480 (Si-N) and 456 (Zr-N) Raman (cm -1): Zr-N bands: 150-300 cm -1 1 (acoustic transition LA and TA); 390-650 cm-1 (LO and TO optical modes); 661, 700 cm-1 (A + 0) and 970 cm-1 (20). XRD: ZrN diffraction peaks (cfc crystal structure, Fm-3m gap group) and a-Si3N4 as shown in FIG. 7. UV-Visible: λ = 550 nm

EXAMPLE 10 Sintering of the Powders of Example 9 by Plasma-assisted Sintering (SPS) to Generate a Nanocomposite Decorative Massive Object The polyzirconosilazane of Example 9 is milled and then sieved (63 μm) in a glove box under argon. The powder is placed in a boron nitride boat for pyrolysis (300 ° C./hour) under ammonia (120 ml / min) at 1000 ° C. (2 h of stage) in a silica furnace connected to a box. gloves under nitrogen before cooling to room temperature at 600 ° C / h. The pyrolysis product is then heated at 1200 ° C (300 ° C / h) under nitrogen and maintained at 1200 ° C for 2 hours before cooling to 600 ° C / h at room temperature to produce yellow-green amorphous micropowder. The UV-Visible spectrum of the powder obtained is shown in FIG. 8. 600 mg of this powder are placed in a glove box in a graphite mold 10 mm in diameter whose walls have been previously covered with Papyex. The powder is then sintered under nitrogen (50 mI / min) at 1700 ° C (6000 ° C / hr, 5 min of bearing) applying a pressure of 50 MPa before cooling to room temperature to produce a solid object tinted in the purple mass in which zirconium nitride nanocrystals in the cubic phase (ZrN) are dispersed in a phase [3 of silicon nitride (R-Si3N4). The material obtained has a relative density of 91% (dusts = 4.1618 g / cm3 and dice = 3.7754 g / cm3).

EXAMPLE 11 Two-step synthesis of a polyzirconosilazane (Si / Zr = 2.4) and preparation of the nanocomposite nc-ZrN / a-Si3N4 in powder form A first step is carried out by reaction between perhydropolysilazane [HSiHNH] n and the zirconium diethylamide Zr [N (CH 2 CH 3) 2] 4 in toluene at its reflux temperature 9.9 ml (10.13 g, 26.67 mmol) of zirconium diethylamide Zr [N (CH 2 CH 3) 2] 4 are added under argon to a solution of perhydropolysilazane [HSiHNH] n (3 g, 66.67 mmol) in toluene (100 ml) with stirring in a Tricol glassware (500 ml) surmounted by a water-cooled refrigerant, and an argon inlet. The addition of the tetrakis (diethylamido) zirconium Zr [N (CH 2 CH 3) 2] 4 is by means of a micro-syringe previously purged under argon at room temperature. A black solution is formed instantly. The reaction mixture is left at room temperature with stirring for 15 h. The raising of the temperature to the boiling point of toluene is progressively carried out at a rate of 30 ° C./h with stirring. The mixture is maintained at this temperature for 72 hours and then the whole is cooled to room temperature under an argon stream.

After returning to ambient temperature, the solvent is removed under reduced pressure at 100 ° C. using a distillation bridge and a recovery Schlenk placed in the liquid air. A soluble yellow compound is obtained. Infrared Spectroscopy (KBR / cm-1): 2962-2927, 2861, 2142, 1457, 1376, 1000-800 and 485.

1H Nuclear Magnetic Resonance (CDCl3 / ppm): 4.56-4.16, 2.8-2.7, 1.22-0.8. In a second synthesis step, the intermediate compound previously synthesized is dissolved in toluene in a Tricol flask (500 mL) surmounted by a coolant cooled to -40 ° C. and an argon / ammonia inlet immersed in the solution. The solution is cooled to -40 ° C and an ammonia flow is then sent directly into the solution with stirring. The addition is done until the ammonia is condensed in the refrigerant. A color change occurs during the addition of ammonia. After condensation of the ammonia in the refrigerant, the solution is kept stirring for 3 days at -40 ° C. and then is naturally heated under argon. The solvent is removed under reduced pressure at 100 ° C. using a distillation bridge and a recovery Schlenk placed in the liquid air. An insoluble white polyzirconosilazane is obtained. Elemental analysis: Si / Zr = 2.4 (Si = 22.19 m%, Zr = 30.03 m%). Infrared Spectroscopy (KBR / cni-i): 3368, 2962-2857, 2131, 1464-1346, 1000-800 and 500.

Ceramic yield (1000 ° C (5 ° C / h), NH3): 70% The polyzirconosilazane is ground and sieved (63 μm) in an argon glove box. The powder is placed in a boron nitride boat for pyrolysis (300 ° C / h) in ammonia (120 ml / min) at 1000 ° C (2 h of step) in a silica furnace connected to a glove box under nitrogen before cooling to room temperature at 600 ° C / h. The pyrolysis product is then heated to 1500 ° C (300 ° C / h) under nitrogen and maintained for 2 hours at 1500 ° C before cooling to 600 ° C / h at room temperature to produce golden brown micro-powders in which nanocrystals of zirconium nitride in the cubic phase (ZrN) are dispersed in an amorphous phase of silicon nitride (Si3N4). Infrared spectroscopy (IR-ATR; cnf-1): 800-1100 (Si-N), 600-400 (Zr-N). Raman (cm 1): Zr-N strips: 150-300 cm-1 (acoustic transition LA and TA); 390-650 cm-1 (LO and TO optical modes); 648, 700 cm-1 (A + O) and 970 cm-1 (20) DRX: ZrN diffraction peaks (cfc crystal structure, Fm-3m gap group) as shown in Figure 9.

Claims (9)

CLAIMS 1-Polymetallosilazane modified, characterized in that it is capable of being obtained by a process comprising the following successive steps: a) reaction of a polysilazane with a molecular entity comprising at least one transition metal and at least one carbon group to obtain a polymetallosilazane type polymer and b) an ammonolysis reaction by ammonia action of the polymetallosilazane obtained to at least partially remove the carbon groups, while increasing the degree of crosslinking of the polymer. 2 - modified polymetallosilazane according to claim 1, characterized in that step b) is followed by hot shaping of the modified polymetallosilazane obtained making it possible to obtain a densified form of the polymer by plastic deformation. 15 3 - modified polymetallosilazane according to one of the preceding claims, characterized in that the transition metal (s) is (are) chosen from Ti, Zr, Hf, V, Nb, Ta, Cr, Mo and W. 4 - Polymetallosilazane modified according to one of the preceding claims, characterized in that it corresponds to the formula: - ([Si (R ') (R2) -NH] a [Si (RI) (R2) -N ( Wherein: M is a transition metal, for example selected from 11, Zr, Hf, V, Nb, Ta, Cr, Mo and W, - a and b correspond to the Si / molar ratio; During the reaction of step a), R 1 and R 2, which are identical or different, each represent, independently of one another, a hydrogen atom, an alkyl or alkenyl group or an aminoalkyl group, preferably an atom; of hydrogen or a group -CH3, -CH = CH2 or -N (H) R4 with R4 which represents a hydrogen atom or a silicon atom of another polysilazane chain, -R3 represents: - a grouping crosslinking agent incorporating the metal element of the type -M (R5) Z with z which depends on the degree of coordination (coordination) of the metal M and R5 which represents either a group derived from the molecular entity used in step a), p for example an amino, alkylamino, arylamino, alkoxide (saturated or unsaturated), alkyl, aryl and more generally any leaving group based on C, N, H, O, P or S, it being understood that R5 can not be a halogen atom (Cl, Br, I, F), the nitrogen atom of another polysilazane chain, or a nitrogen atom of another polysilazane chain. 5 - modified polymetallosilazane according to one of claims 1 to 4, characterized in that said polysilazane is a perhydropolysilazane, a polyhydrosilazane, a polymethylsilazane, a polydimethylsilazane, a polymethylvinylsilazane, a polyvinylsilazane, or a copolysilazane. 6 - Polymetallosilazane modified according to one of the preceding claims, characterized in that the molecular entity comprising at least one transition metal and at least one carbon group is chosen from the alkylamides of formula M (NR 2) X and the alkoxides of formula M (OR) X in which M represents a transition metal such as Ti, Zr, Hf, V, Nb, Ta, Cr, Mo or W, the identical or different R groups represent an alkyl chain of methyl or ethyl type and x is equal to 3, 4, 5 or 6 depending on the coordination of the metal M. 7 - Polymetallosilazane modified according to one of the preceding claims, characterized in that the molecular entity comprising at least one transition metal and at least one carbon group is selected from Ti [N (CH 3) 2] 4, Ti [N ( ## STR2 ## CH2CH3) 2] 4, Hf [N (CH2CH3) (CH3)] 4, Ti [O (CH2CH3)] 4, Zr [O (CH2CH3)] 4. 8 - Process for the preparation of a nanocomposite material comprising a matrix composed of an amorphous or crystalline binary form of silicon nitride, in which nanocrystals of a transition metal nitride of binary structure, in the form of of particles, continuous micrometric fibers, nanofibres or nanotubes, a coating, a composite of infiltration of a fibrous preform or even in the form of a massive object characterized in that it implements a pyrolysis step of a polymetallosilazane according to one of claims 1 to 7. 9 - Process according to claim 8 characterized in that it is implemented to obtain a nanocomposite in the form of a massive object. - Process according to claim 9 characterized in that it comprises a compaction forming step, after the pyrolysis step. 11 - Process according to claim 10 characterized in that the shaping step is carried out by sintering, optionally with a plasma treatment. 12 - Process according to claim 9 characterized in that it comprises a shaping step by compacting, before the pyrolysis step. 13 - Process according to claim 12 characterized in that the compacting shaping step is carried out at a temperature in the range of 20 to 400 ° C, preferably 50 to 150 ° C.