Porous ceramic infiltrated by metals and polymers
Mikołaj Szafran*, Gabriel Rokicki*, Wojciech Lipiec*, Katarzyna Konopka**, Krzysztof Kurzydłowski** *Politechnika Warszawska, Wydział Chemiczny, ul. Noakowskiego 3, 00-664 Warszawa **Politechnika Warszawska, Wydział Inżynierii Materiałowej, ul. Wołoska 141, 02-507 Warszawa
Annals 2 No. 5, 2002 pages 313-317
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abstract In this paper, preliminary results of studies of ceramic-metal and ceramic-polymer composites obtained via infiltration of porous ceramic matrix are reported. Ceramic-metal composites based on porous ceramic material are usually obtained employing the method in which melted metal at high temperature is infiltrated into open pores of ceramic under pressure lower than 50 MPa. This type of composites amalgamates properties of both materials: hardness and elasticity. The image of Al2O3-Fe composite, presented in Figure 1 reveals the interlayer consisting of FeAl2O4. The presence of this interlayer between ceramic and metallic phases, which is formed at high temperature leads to the composite exhibiting mechanical strength higher than that of both metal and ceramic material. It is known that mechanical strength, especially compressive and tensile strengths of some human as well as animal bones is unexpectedly high. The bones are natural inorganic-organic composites. Thus, human and animal bones are examples of ceramic- polymer composites, in which the intercellular matrix of bone is bonded with the natural polymer - fibrous proteins of molecular weight up to several million. These two components are intimately bound, with the mineral crystals wrapped around and embedded among the protein. The hard mineral crystals provide great compressive strength, making bone an excellent load-bearing material. The protein fibers add elasticity and high tensile strength, enabling bone to withstand tension forces. The heat treatment of bones at temperature, at which the organic material is decomposed and removed, leads to the porous ceramic material, mainly consisting of hydroxyapatite, and additionally indicating the porosity gradient. The SEM picture of an animal bone after firing at 700°C is presented in Figure 2. Ceramic-polymer composites mimicking bones were prepared via introducing of monomer or reactive resin into pores of porous ceramic material and subsequent the monomer polymerization and resin curing. It was shown that the mechanical properties of resulting composites depend on a kind of monomer and reactive resin used as an organic material (Table 1). The problem of the composite preparation is the residual open porosity due to polymerization shrinkage which is immanent for polymerization process as well as crosslinking of reactive resins (Fig. 3). However, it is possible to use special monomers exhibiting low shrinkage or even the volume expansion during polymerization, which can result in an additional strengthen of the composite. Closing a flammable polymer in the porous structure of the ceramic material additionally can reduce ignition and flame susceptibility of the polymer. It is especially true for the ceramics-polymer composites, characterized by porosity gradient.