For the image analysis one or more cuts are made from an agglomerate and the ratio of the void areas to the solid material fraction are determined. With the help of sequential cuts, the difference between open and closed pores can be seen. In addition, the distribution of the values and the forming area can be determined. From a single individual sectional drawing only the value distribution for the spherical pores can be calculated. The intermediate porosity areas agree well however with the total porosity.

The method suggested by Washburn 1921 can be used to determine the volumes of the pores and of the distribution of the pore radius. Mercury wets very badly and wraps itself around the agglomerates. The volume of the mercury, which is displaced from the agglomerate, is measured with a mercury porosity meter, as shown in the figure.

Figure: Mercury porosimeter

Through known solid densities, the agglomerate density yields corresponding to DIN 53193 or DIN 51057 from the displaced volume and the difference in mass. In dependence of the pressure needed, the mercury penetrates the small pores, corresponding to the Gauß-Laplace equation:

$$p = \frac{2\sigma \cos(\Theta)}{r} \tag{1}$$

with:

• p = pressure,
• s = surface tension of the mercury,
• Q = angle of contact of the mercury,
• r = radius of pore

With this equation the distribution of the pore radius lets itself be calculated. At higher pressures, the compressibility of the mercury must be considered.