DS0305 - Nanomatériaux et nanotechnologies pour les produits du futur

New class of functional silicon carbonitride-based ceramic fibers from organometal compound-modified polysilazanes – Carbofibers

New generation of non-oxide ceramic fibers bearing multifunctionality

Non-oxide ceramic fibers prepared from organometal compound-modified polysilazane to offer particular functions to the materials while the cost remains relatively limited in comparison to silicon carbide fibers produced from polycarbosilane

Raise issues on the design of non-oxide ceramic fibers in comparison to silicon carbide fibers

The main objective is to raise issues on the design of non-oxide ceramic fibers in comparison to more conventional silicon carbide fibers (SiC) via experimental and theoritical approaches. The combination of these approaches should help us to decrease the cost of these materials while proposing high performances. The first objective is focused on the design of ceramic fibers around ternary Si-C-N and quaternary Si-B-C-N/Si-Al-C-N systems through a detailed investigation of the synthesis and characterization of preceramic polymers used as fiber precursors (polysilazanes), their spinning and the polymer-to-ceramic conversion. These materials are in particular used for their thermostructural properties. The second objective will consist to modify preceramic polymers with organometal compounds (metal being nickel (Ni), Iron (Fe), Platinum (Pt) and paladium (Pd)) at molecular scale in order to offer functionality to Si-C-N fibers, i.e., electrical, magnetic and catalytic properties. The third objective will investigate the reproducibility of the elaboration process and of the fiber performance, in particular by coupling experimental and numerical approaches.

The experimental method investigated in Carbofibers is focused on the synthesis of preceramic polymers from commercially available or home made molecular precursors (step 1). The chemistry (elemental composition and polymer network architecture) and the reactivity (thermal and chemical) of preceramic polymers can efficiently be controlled and tailored to supply after melt-spinning (step 2) and pyrolysis (step 3 ceramics with the desired phase distribution and homogeneity (Si-C-N, Si-B-C-N/Si-Al-C-N).

The first 18 months have been focused on the preparation of large diameter fibers (with hollow core, French partner) and low diameter fibers (french and german partners) in good agreement with the GANTT diagram. In France, we successfully demonstrated the possibility to synthesize melt-spinnable boron-modified polysilazane to prepare large diameter Si-B-C-N fibers with a hollow core after pyrolysis to 1000°C under nitrogen. The polymers could be mixed with PMMA sphere to develop the porosity and open application as electrode materials and membrane supports. In parallel, a series of co-polymers have been synthesized to prepare thin SiBCN fibers to be used as reinforcing agent. After melt-spinning co-polymers with an appropriate ratio of functional groups(NH/NCH3/SiCH3), the curing treatment under ammonia atmosphere efficiently rendered the green fibers infusible before their subsequent pyrolysis under nitrogen at 1000 °C to generate Si-B-C-N ceramic fibers. Besides the development of new Si-C-N spinnable precursors, German partners performed some preliminary tests regarding the functionalization of fibers. The mixture of polysilazane and iron compound was successfully spun into green fibers via melt-spinning, could be cured in infusible fibers and converted into iron containing Si-C-N fibers.

In agreement with the GANTT diagram, we are optimizing the production of Si-C-N (Germany) and Si-B-C-N (France) fibers as well as their performance, in particular mechanical properties. The synthesis of polysilazanes modified by organoiron compounds will be studied in detail and extended to other metals in order to produce high performance and functional materials. Furthermore, a numerical approach will be developped to be focused on the pyrolysis process of fibers

A. Viard, L. Gottardo, D. Lopez-Ferber, A. Soleilhavoup, C. Salameh, S. Samal, Y. Gueguen, T. Rouxel, G. Motz, F. Babonneau, C. Gervais, and S. Bernard «Molecular Design of Melt-Spinnable Co-Polymers as Si-B-C-N Fiber Precursors«, submitted to Dalton Trans, July 2017.

Research and development efforts on high-temperature ceramic matrix composites (CMCs) in United-States (General Electric) and Europe (SGL, Safran, …) over recent years have focused on using silicon carbide (SiC) fibers as reinforcing agent of these materials. SiC fibers are extremely resistant to wear and high temperatures and are designed to allow for much higher operating temperatures in industrial applications than oxide ceramic fibers. Therefore, SiC fibers represent the best candidate to reinforce CMCs in the next generation of nuclear energy conversion power plants and they are more and more applied in brake technologies, as airplane or steam turbines, thereby boosting system efficiency. However, the production of SiC fibers is dominated by companies from Japan (Nippon Carbon Co., Ltd; Ube Corporation) which renders them very expensive. Motivated by the increasing demand in SiC fibers to be used in CMCs, especially in Europe, the present proposal led by two institutes in France (IEM) and Germany (CME) with expertise on polymer-derived non-oxide ceramic fibers that completes each other is concerned with the design, processing and properties of cost-effective silicon-based non-oxide ceramic fibers. The project is seen to allow Europe to be one of the leaders on this thematic and reinforce its expertise gained in the nineties. The materials proposed here are prepared in the silicon-containing carbonitride (Si-(B/Al)-C-N) systems to maintain durability in aggressive and adverse environments while achieving functionalities through the modification of the precursors with organometal compounds with metals being nickel and iron. The proposed materials are expected to be used as reinforcing agents in CMCs for high-temperature and lighter-weight engine components. This project is located at the frontiers of materials chemistry, processing, ceramic science and physics. To reach our objectives, the project is shared into five interconnected scientific tasks (Ta1?Ta5). The first task (Ta1) is focused on the synthesis and characterization of preceramic polymers (polycarbosilazanes which can be modified by boron and/or aluminum) and their metal-containing analogs. Detailed investigation of their molecular chemistry will be achieved. The second task (Ta2) consists in the polymer spinning and investigation of rheological phenomena that take place during the spinning process. Rheology of preceramic polymers in shear and extension will be studied based on the structural information obtained in Ta1 in order to optimize the melt-spinning process to produce green fibers. The task 3 (Ta3) is focused on the ceramic conversion of green fibers prepared in Ta2 into the desired final nanostructures and compositions. Detailed investigation of polymer-to-ceramic conversion will be performed through different characterization tools to propose our targeted materials without loss of fiber cohesion. The task 4 (Ta4) is dedicated to the characterization of ceramic fibers with a particular attention on the thermostructural, mechanical, electrical and magnetic properties. The task 5 (Ta5) is focused on the development and optimization of the elaboration process of fibers through modeling approaches to improve the fiber performance and the reproducibility of their performance and elaboration. It should be mentioned that metals selected in the present study may provide other functions such as catalytic that could be investigated in the present project as a preliminary study. The present project is built to elaborate materials that are expected to lead to benefits for the advancement of science, industry and society and should allow Europe to be in place on this growing thematic.

Project coordinator

Monsieur Samuel Bernard (Institut Européen des Membranes)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

IEM Institut Européen des Membranes
CME Ceramic Materials Engineering
IEM Institut Européen des Membranes

Help of the ANR 228,960 euros
Beginning and duration of the scientific project: November 2015 - 36 Months

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