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Na 4 ZrSi 3 O 10 , belonging to the NASICON family. Figure 7.23 shows part of the
system Na 2 O
P 2 O 5 .Na 4 ZrSi 3 O 10 has been characterized as a mono-
clinic compound with lattice parameters which are quite similar to the monoclinic
low-temperature modification of NASICON.
In recent years, there has been a general trend to synthesize these zirconium sili-
cates under lower pressure
a
ZrO 2 a
SiO 2 a
temperature conditions Yong and Wenqin [102,103]
studied this system and obtained Na 4 Zr 2 (SiO 4 ) 3 at 290
300 C and further reduced
temperature conditions (250 C) using ZrOCl 2 ,Na 2 SiO 3 , and NaOH solution, and
the hydrothermal chemical reaction is given below:
2ZrOCl 2 1
3Na 2 SiO 3 1
2NaOH
!
Na 4 Zr 2 ð
SiO 4 Þ 3 1
4NaCl
H 2 O
ð
7
:
12
Þ
1
Clearfield and coworkers [93,94,104] have obtained a series of zirconium sili-
cates under mild hydrothermal conditions (180
190 C) and studied the influence
of the type of silicon-containing reagent, the molar ratio, and concentrations of
reagents in the reaction mixture on the yield of resultant products. These authors
have studied the formation of several different sodium zirconium silicate phases in
the systems: (i) Zr(OC 3 H 7 ) 4
silicic acid
NaOH
a
H 2 O; (ii) Zr(OC 3 H 7 ) 4 -silicon-
containing reagent
NaOH( 4 M)
H 2 O under mild hydrothermal conditions (T
5
180
190 C, pressure generated from 50% fill). These studies have yielded several
novel sodium zirconium silicates. According to these authors, the predominant
phase is hydrated sodium zirconium silicates in this system in contrast to mainly
anhydrous sodium zirconium silicate (Na 2 a
ZrSiO 5 ,Na 2 ZrSi 2 O 7 ,Na 4 Zr 2 Si 3 O 12 ,
etc.) while carrying out the reactions at much higher temperatures (300
550 C)
[95] . This suggests that a relatively low temperature of hydrothermal synthesis
P 2 O 5
ZrP 2 O 7
NaZr 2 (PO 4 ) 3
Na 5 Zr(PO 4 ) 3
ZrO 2
Na 3 PO 4
Na 2 ZrO 3
Na 4 Zr 2 (SiO 4 ) 3
Na 2 O
SiO 2
Figure 7.23 Part of the system Na 2 O a ZrO 2 a SiO 2 a P 2 O 5 [95] .
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