Analysis of the Gradients of the Pore and Particle Size Distributions in Ceramic 
Materials 
M. Mangler, G. Tomandl, H. Baum, D. Stoyan; Freiberg University of Mining and Technology 
Abstract 
Materials with a graded microstructure become increasingly important for mechanical engineering 
one as well as for functional applications. The analysis of location-dependence microstructure 
parameters represents an essential requirement for the active manipulation of materials properties. 
Especially for high porosity ceramic layers with pore sizes of a few micrometers down to 
nanometer scale, methods are generated for preparation of cross section samples. The analysis of 
the microstructure are realised on the scanning microscope with field emission gun (FESEM). In 
order to receive high resolution images for the quantitative characterization of nanopores methods 
were developed for optimizing the contrast. Statistical models were worked out to determine the 
systematic change of the microstructure parameters in graded materials. 
Introduction 
Porous graded structures show some interesting properties which may be attractive for technical 
section showina applications in the fields of filtration, catalysis or humidity sensors. Ceramics have the advantage of 
' a higher chemical and temperature resistance compared to metals and polymer materials. These 
properties are essential for the wide range of applications as filtration membranes. Commercially 
available ceramic MF- and UF- membranes are usually assembled in layers. On a porous support 
mi with a median pore size of a few micrometers, a number of intermediate layers with decreasing 
SR particle sizes are deposited which are dried and sintered separately. Gradient membranes with a 
dk fins continuous transition of pore sizes can be produced in a single process step, for instance by 
centrifugal deposition as unsupported layers or deposited on a single or multi layer substrate. /1/ 
For the proof of the aimed effect it is necessary to conduct filtration experiments with test 
molecules /2/. The pore size distribution of the active sol-gel layer can be determined by nitrogen 
es nd adsorption (ASAP) using an unsupported membrane layer, processed under the same conditions as 
sit pla the supported membrane. As the result of these measurements we receive a volume cumulative or 
Bh frequency distribution averaged over the entire investigated specimen volume, but no evidence of 
the layered structure and the local dependence of the pore size distribution. /3/ Especially for 
continuous gradient membranes it is essential to determine the systematic change of pore sizes in 
the direction of the gradient. A method to determine the location dependence of the global 
parameters the volume fraction (V,) and the surface area density (S,) was described in /5/. 
ya) . 
Experimental 
For the investigations supported (a - Al,O,) membranes were used, which consist of several layers. 
On the last layer with 60 nm mean pore size a graded layer of TiO, was deposited by the method of 
centrifugal sedimentation with a suspension showing low solid content. The gradient is developed 
from a broad particle size distribution, which was achieved using a suspension of fine powder 
mixed with a sol./2/ In the second variant a homogenous layer of 5 nm pore size was prepared on 
this 60 nm basic layer. For both examples flat membranes with dimensions of 25 mm diameter and 
0.8 mm thickness were used. 
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