- Uncton of the 
From Conventional Ceramics to Bioactive Coatings: Trends in Ceramography 
H. Schubert, Technische Universitit Berlin, Institut fiir Nichtmetallische Werkstoffe, Fachgebiet 
Keramik 
The development of ceramic materials and components is undergoing a significant change in the 
past years. While the development of new materials with new microstructure was main target in the 
eighties and early nineties, this development is more or less finished. The most interesting materials 
are identified and have been developed to a high state of maturity. As a consequence, there are well 
established recipes for material's preparation and visualisation [1,2]. Since the reaction of ceramics 
is sluggish on thermal treatment, as compared to metallic systems, less variation in microstructural 
changes. Thus, ceramography is usually allied for quality assurance, mainly focussed on homgeneity 
and the inspection of defects. 
Functional ceramics are mainly applied for electronic industry and they are typically manufactured 
in multilayer structures of 5 to 100 um in thickness. The task for ceramography can be described as 
a industrial quality assurance. One wants to identify homogeneity of electrode contact areas, 
potential sites of a dielectric breakdown and residual porosity. Analogously to structural ceramics, 
functional materials are developed to a very high state of maturity and consequently the most 
ceramographic recipes are well established. 
A clear trend in material's development is increasing use of ceramic coatings. Ceramic materials 
have very interesting properties but their manufacturing is quite expensive. Thus, the use of ceramic 
coatings is a straight forward engineering approach of many developments. Figure 1 shows a 
schematic representation of various applications versus the characteristic thickness of the coating. In 
05 samples structural application like tribo-coatings, abradable coatings (in turbine systems), thermal barrier 
coatings (in turbines and engines), and corrosion resistant coatings for chemical apparatus are 
sarameters sich typically suffering a complex mechanical, thermal and corrosive load. The thickness varies from a 
mount of te few pm up to a few cm. There are various types of characteristic processing technology supplied. 
The ceramographic task is focused on the quality assurance of the coating but also on the quality of 
the interface between coating and substrate as well as on changes of the materials during service. In 
contrast, functional coatings are typically thinner and been manufactured by typical film 
ne a technologies like tape casting, sol-gel coating, CVD- and PVD-coating. The spectrum reaches from 
iy deni 100 um down to a thickness of a few atoms. Again the quality of the interface is a main task, but 
since the microstructure of thin films are different from monolithic materials especially textures, 
gradients and micro stresses are of great interest for the understanding of properties. 
A new field of research are bioactive materials, coatings and surfaces. Typical examples are be 
medical implants, bio-sensors or scaffolds for bio-reactors. In all of these examples, the surfaces of 
the materials are in contact with the biological system. This interface can be understood as a 
ld sequence material-protein-human cells. The quality of such a coating is not only determined by the 
ls OH microstructure but even more by the ability to undergo a positive interaction with human proteins 
coupling to human cells. Cells usually grow in a confluent layer requiring the protein interaction 
vi with neighbour cells and the underlaying tissue. All artificial components such as the implants in a 
ied deff way need to imitate this situation, i.e. surface roughness, chemistry, grain size, corrosion 
resistance/solubility etc. need to be designed according to the type of human cells. 
ml The development of this type of materials is certainly a very fascinating interdisciplinary work 
combining natural and engineering science with biology, medicine and related disciplines (cf Figure 
ah CS 2). In order to judge on the quality of a bioactive surface, investigations reaching from physical, 
chemical and engineering testing via in vitro to in vivo testing, finally to clinical experiment in a 
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