Fabrication and mechanical properties of porous brittle materials

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Inorganic non-metallic porous materials are necessary for many applications where they must combine a functional property, which is improved by porosity (e.g. bone substitutes, thermal insulators, catalytic supports, filtration devices, fuel cells...), with a structural role, i.e. they must possess sufficient mechanical properties. The latter, however, are strongly affected by porosity ; in addition these materials are by nature very brittle, i.e. they fail in the elastic regime with no deformation.

Typical fracture of a brittle material in compression

Our works intend to:

• Understand the relations between porosity (amount, size, distribution, morphology...) and mechanical properties.
• Propose original routes to produce porous structures.
• Fabricate optimised materials for specific applications.

Current research includes:

• Biomaterials: Biphasic Calcium Phosphate (BCP) ceramics and Calcium Phosphate Cements (CPC) for bone substitution, in collaboration with LIOAD (Nantes).
• Mesoporous silica (SBA-15) for thermal insulation, in collaboration with UHA (Mulhouse).

	Macroporous CPC obtained by the addition of porogenic mannitol particles during fabrication
Macroporous inorganic-organic composite CPC obtained by a foaming process during the cement paste preparation

 There is also a search to produce less brittle materials by providing them with a certain tolerance to damage. This can be achieved, for instance, by the fabrication of composite materials through the incorporation of organic polymers.
   

	The toughening (reinforcing) effect comes from a mechanism of crack bridging by plastically deforming polymer ligaments.
Tolerance to damage of an inorganic-organic CPC. The addition of a polymer (blue curve) allows the material withstanding a certain amount of deformation before failure, compared to the purely inorganic cement (red curve).
Evolution of the fracture toughness of CPC with porosity. The inorganic-organic composite cements (non-circled symbols) exhibit higher mechanical properties than purely inorganic cements ("control": circled symbols).