Geoscience Reference
In-Depth Information
knowledge of stability and yield diagrams calculated for hydrothermal systems
involving ceramic materials. Repetitive application of the model for different input
concentrations of the different precursors as well as pH-adjusting agents (minerali-
zers) makes it possible to construct stability and yield diagrams. Stability diagrams
show the ranges of equilibrium conditions for which various aqueous and solid spe-
cies are stable in the hydrothermal system. Equilibrium conditions include the total
molality of a selected aqueous metal precursor, solution pH, and temperature. The
total molality of the aqueous metal precursor is the sum of the equilibrium concen-
trations of all dissolved metal species and does not include the species that precipi-
tate from the solution as solids. While the stability diagrams provide information
about the conditions for incipient precipitation of various solid phases, they do not
specify the reaction conditions required for an assumed yield of reaction product. To
accomplish this goal, the idea of yield diagram was conceived
[121]
. The reader can
get more valuable information in the works
[108,109]
. The theoretical predictions are
validated through selected experiments using the calculated stability and yield dia-
grams as a guide. The hydrothermal reactions are performed to investigate whether
the location of the various stability and yield regions agrees with the experimental
findings.
Figure 4.16
shows calculated yield of lead zirconate titanate (PbZr
0.6
Ti
0.4
O
3
)at
433 K with the ratio of lead acetate to a sum of titanium and zirconium dioxide
equal to 1.1. Phase-pure can form in a relatively wide region of input precursor and
0
0.5
1
1.5
2
2.5
3
0
0
PZT + unreacted ZrO
2
and TiO
2
T
= 433 K
Yield = 0.99
Pb/(Ti+Zr) = 1.1
-0.8
-0.8
PbO
PbZr
0.60
Ti
0.40
O
3
-1.6
-1.6
-2.4
-2.4
PZT + unreacted ZrO
2
and TiO
2
-3.2
-3.2
-4
-4
0
0.5
1
1.5
2
2.5
3
3.5
m (M
e
4
NOH)
Figure 4.16 Calculated yield diagram of PbZr
0.6
Ti
0.4
O
3
at 433 K. PbAc
2
, TiO
2
, and ZrO
2
are used as starting materials for the calculations
[108]
.
