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closer to the mineral baddeleyite. Figure 9.15 shows the photograph of ZrO 2 crystals
grown under hydrothermal conditions. Today, several variations in the hydrothermal,
solvothermal, and supercritical fluid growth of ZrO 2 crystals include thin films and
the nanosize crystals, for a variety of application have been proposed.
HfO 2
According to Kuznetsov [86] , the growth of HfO 2 does not differ much from that of
ZrO 2 . The crystallization of HfO 2 takes place at a higher temperature in KF and NaF
solutions and at still higher temperatures in NH 4 Fsolution(700 C). Again, the major
disadvantage is the higher temperature of crystallization and retrograde solubility.
Hence, in this case also, a horizontally disposed autoclave was used by Kuznetsov
and coworkers [82,86] . The autoclave had a transverse baffle in which the orifice
area was
15% of the internal cross-sectional area. Crystals up to 2
2
0.5 mm
B
3
3
Figure 9.15 ZrO 2 crystals grown under
hydrothermal condition.
Source: Courtesy of Kuznetsov [82] .
Figure 9.16 HfO 2 crystals.
Source: Courtesy of Kuznetsov [86] .
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