3.1. Porosity and microstructures
Fig. 1 shows the effect of valeric acid concentration on the
foaming capacity and hence the bulk density of sintered
specimens. All measurements were carried out in suspensions
containing 15 vol% PZT at pH 5.
As shown in Fig. 1, there is a distinct increase in the
foaming capacity (the ratio of foam volume to slurry volume)
from 1.68 to 2.93 with the increase of the valeric acid
concentration. When the concentration of valeric acid was less
than 30 mmol/L, the number of amphiphilic molecules was not
enough to adsorb to ceramic particles, which degraded directly
the hydrophobicity of colloidal particles and led to a relatively
low foaming capacity of the suspension. With increasing the
valeric acid concentration, there was a higher adsorption of
amphiphilic molecules onto particles, the hydrophobicity of
particles to adsorb to air–water interfaces was enhanced,
resulting in stable wet foams and an increasing foaming
capacity up to 2.93. Accordingly, the bulk density of porous
ceramics decreased almost linearly from 4.16 g/cm3 to 1.80 g/
cm3 in the range of valeric acid concentration, indicating that
the density could be easily tailored in a broad range.
3.1. Porosity and microstructures
Fig. 1 shows the effect of valeric acid concentration on the
foaming capacity and hence the bulk density of sintered
specimens. All measurements were carried out in suspensions
containing 15 vol% PZT at pH 5.
As shown in Fig. 1, there is a distinct increase in the
foaming capacity (the ratio of foam volume to slurry volume)
from 1.68 to 2.93 with the increase of the valeric acid
concentration. When the concentration of valeric acid was less
than 30 mmol/L, the number of amphiphilic molecules was not
enough to adsorb to ceramic particles, which degraded directly
the hydrophobicity of colloidal particles and led to a relatively
low foaming capacity of the suspension. With increasing the
valeric acid concentration, there was a higher adsorption of
amphiphilic molecules onto particles, the hydrophobicity of
particles to adsorb to air–water interfaces was enhanced,
resulting in stable wet foams and an increasing foaming
capacity up to 2.93. Accordingly, the bulk density of porous
ceramics decreased almost linearly from 4.16 g/cm3 to 1.80 g/
cm3 in the range of valeric acid concentration, indicating that
the density could be easily tailored in a broad range.
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