Geoscience Reference
In-Depth Information
great detail
the hydrothermal crystallization mechanism of HNaMP
2
O
7
(where
M
Mn, Co, Ni, Zn, Cd, Pb) crystals.
Table 7.24
gives the experimental conditions
of the growth of these novel phosphates with very interesting structures. In all the
experiments, 85% H
3
PO
4
and NaOH solutions have been used as the solvents and
only in a very few experiments, other solvents like HNO
3
, HCl, H
2
SO
4
, and
HCOOH have been used.
The hard bases H
2
O, OH
2
,PO
2
3
5
NO
3
, and SO
2
4
act upon the dissolution of
the solvated complexes determining the solubility of the final resultant
stable complex
[293]
. The following reaction series can be proposed for the forma-
tion of HNaCoP
2
O
7
:
;
4
3NaOH
H
3
PO
4
!
Na
3
PO
4
1
3H
2
O
1
3Co
ð
NO
3
Þ
2
1
2H
3
PO
4
!
Co
3
ð
PO
4
Þ
2
1
3H
2
O
6NO
2
m
1
3
½
O
m
1
Zr
ð
NO
3
Þ
4
1
4NaOH
!
4NaNO
3
1
2H
2
O
1
ZrO
2
k
2H
3
PO
4
!
H
4
P
2
O
7
1
H
2
O
Na
3
PO
4
1
H
4
P
2
O
7
!
NaH
3
P
2
O
7
1
HNO
3
Na
3
PO
4
1
H
4
P
2
O
7
!
NaH
3
P
2
O
7
1
Na
2
HPO
4
Co
3
ð
PO
4
Þ
2
1
H
4
P
2
O
7
1
4H
2
O
!
H
2
CoP
2
O
7
1
2H
3
PO
4
1
2Co
ð
OH
Þ
2
Co
ð
NO
3
Þ
2
1
H
4
P
2
O
7
!
H
2
CoP
2
O
7
1
2HNO
3
Co
ð
NO
3
Þ
2
1
H
4
P
2
O
7
!
H
2
CoP
2
O
7
1
2HNO
3
NaOH
H
2
CoP
2
O
7
!
HNaCoP
2
O
7
1
H
2
O
1
Co
ð
OH
Þ
2
1
NaH
3
P
2
O
7
!
HNaCoP
2
O
7
1
2H
2
O
The formation of a stable complex, i.e., HNaCoP
2
O
7
at 250
C and 100 bar
pressure, must have undergone several intermediate stages of solvation, forming
stable and unstable solvated complexes like NaNO
3
, having very low values of
lattice energy constant, 755 kJ/mole, and Co, which has a desolvation energy
value around 15 eV, etc. that have further interacted with each other because of
their weak ionic bonding of very low charge to give a stable coordinated com-
pound with a very high of lattice energy constant and stronger ionic bonding.
But at temperatures around 250
C, the polymerization of the orthogroup of
phosphates to form the pyrogroup with higher lattice energy may be expected.
Also, the reaction between the alkali pyrophosphate complexes with metal com-
plexes results in the formation of stable complexes of pyrophosphate,
i.e.,
HNaCoP
2
O
7
.
