CERAMICS DERIVED FROM METALS AND WOOD

By infiltrating molten metals and alloys into porous ceramics you can make materials with a higher fracture toughness than that of the ceramic material itself. In addition these materials possess the conducting properties of metals. A combination of certain materials which results in a set of properties which the individual materials do not possess is called a composite. The entire chapter 14 is devoted to these materials. During and after the mentioned infiltration an exchange reaction can take place, e.g. 

In this example, the porous titanium (III) oxide is infiltrated by liquid aluminium. Depending on the reaction circumstances, the formed composite can be composed of titanium(III) oxide and aluminium, but also of aluminium oxide and aluminium titanide. In addition, intermediate compositions are also possible, for example all four components from the equation. 

There is an increasing interest in these kinds of composites for the development of durable components of, for example, high-quality braking systems for vehicles which are exposed to high temperatures and extreme mechanical strains. 

Wood is built up of parallel columns of cells. Around these cells, cellulose embedded in lignin is wrapped. If wood is heated to temperatures above 600 °C (the exact temperature depends on the type of wood) in an inert atmosphere, then the polyaromatic biopolymers are broken down and what remains is a carbon skeleton with the anatomy of wood, both at a microscopic and macroscopic level. This skeleton facilitates the infiltration of, for instance, silicon and the reaction to silicon carbide. 

Like wood, wood-derived composites also have anisotropic properties. For instance, the bending strength of a certain SiC ceramic with a density of 2.5 g/cm3 varies from 2000 to 120 MPa, depending on the direction of the load in relation to the growth rings of the wood. 

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Ceramics derived from metals and wood Clay balls (found in Turkey, but archeologists have no clue as to what their purpose is)... 

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