Institute Advanced Ceramics

It is well known, that nature constructs hierarchically structured hard tissues out of a combination of a hard material such as hydroxyapatite or aragonite (CaCO3) and a very small amount of soft phase, e.g. proteins and water. These “natural composites” reveal good properties such as high stiffness, high hardness and high damage tolerance. Examples for these biomaterials are enamel, snail shells and seashells such as nacre.

The objective of the present project work is to mimic nature´s concept of combining different material systems on different length scales to obtain properties superior to their single constituents (see Figure 1).

Figure 1: schematic of hierarchical structure of ceramic/metal polymer composite

Inspired by their natural counterpart, artificial materials developed in this project will contain a hard phase, ceramic (and metal), and a polymer as the soft phase. These materials aim for a combination of good mechanical properties, e.g. hardness, fracture toughness by using an extremely small amount of polymer.

The freedom to choose different materials combinations on several hierarchical levels as well as low processing temperatures (200 – 300°C) give the opportunity for tailoring properties.

As a model material system for the first hierarchical level TiO2 and PMMA (a thermoplast) were chosen. The processing route was developed as following (Figure 2): Ceramic particles are coated with a small amount of polymer to get thin polymer layers. Subsequently the powders are pressed at elevated temperatures, to create a solid body. The latter has to be ground down for producing the second hierarchical level.

 
Figure 2: Compaction route to produce first hierarchical level

To evaluate microstructural and mechanical properties of the densified body, several investigations are being made. These include Scanning Electron Microscopy for optical characterization of the polymer-ceramic interaction. Thermogravimetric Analysis and Differential Scanning Calometrie are used for characterizing the amount of polymer and its thermal properties. Mechanical testing such as Four-Point-Bending, Nanoindentation, Vickers Microhardness or SEVNB is used to determine the mechanical properties on different hierarchical levels.

First experimental investigations with the SEM confirm coating of TiO2 by PMMA as can be seen in Figure 3. As porosity is still higher than 10%, further investigations on densification are underway.

 
Figure 3: Ceramic-polymer composite with low polymer content

Realization of the second hierarchical level will be done in cooperation with the Institute of Solids Process Engineering and Particle Technology.