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3LiBO 2 1
2H 3 BO 3 !
Li 3 B 5 O 8 ð
OH
Þ 2 1
2H 2 O
ð
7
:
28
Þ
Water is considered as the hard base and strongly acts upon the dissolution of
the solvanted particles of LiBO 2 and determines the solubility of the final resultant
acid
base complex, i.e., Li 3 B 5 O 8 (OH) 2 . It must have been formed through several
intermediate stages of solvation and formed several stable and unstable ions
through an active interaction between the solute and solvent depending upon the
dissolution energy of various cations and donors. Usually when HCOOH is taken
as a mineralizer, LiOH forms LiHCOO which later forms LiBO 2 and interacts with
H 2 BO 3 . Since the system studied is a quarternary system, it becomes extremely
difficult to assess the exact stage and nature of crystallization. The reactions given
are more or less hypothetical without much speculation. It is possible that the inter-
mediate solvated complexes like LiHCOO and LiBO 2 interact with each other
because of their weak ionic bonding or very low charge in order to give a
stable coordinated compound with a high lattice energy and a relatively strong ionic
bonding, Li 3 B 5 O 8 (OH) 2 .
The experimental conditions in the hydrothermal synthesis of Li 3 B 5 O 8 (OH) 2 are
given in Table 7.29 . The size varies up to 15 mm and the crystals are good in quality
( Figure 7.89 ). The present study also shows that Li 3 B 5 O 8 (OH) 2 crystallizes within a
narrow region in the system Li 2 O
H 2 O( Figure 7.82 ). The crystals were occa-
sionally twinned and are transparent. Since, Li 3 B 5 O 8 (OH) 2 crystals of size 15 mm
could be obtained in an experimental run of 8
a
B 2 O 3 a
10 days, a careful study of growth
parameters and an introduction of the seed will enable one to grow bigger crystals.
Li 4 B 7 O 12 Cl. In the recent years, boracites have attracted attention of materials
scientists owing to their variety of applications in modern technology, particularly
after the successful application of transitional metal rare earth borates—
NdAl 3 (BO 3 ) 4 , Nd(Al, Cr) 3 (BO 3 ) 4 , Nd(Ga, Cr) 3 (BO 3 ) 4 , etc.—as miniature laser
materials [343] . Almost at the same time, high ionic conductivity was observed in
lithium boracite (Li 4 B 7 O 12 Cl) [366] . This compound was successfully synthesized
in 1972 [367] . Later the structure of the compound was reported in 1973 [368] . This
compound has been reported to be obtained earlier by two techniques: (1) through
sublimation and (2) hydrothermally. Although the hydrothermal technique has been
successfully adopted to the synthesis of this compound, the PT conditions were quite
high and crystal size was too small and less then 1 mm. Byrappa et al. [369] selected
the suitable composition region in the phase diagram where Li 4 B 7 O 12 Cl could be
crystallized in the presence of Cl under hydrothermal condition. They took chlorine
in the starting mixture as HCl with a varying molarity. Figure 7.82 shows the crys-
tallization boundary for this compound, Li 4 B 7 O 12 Cl. The crystallization field is
rather narrow and any slight change in the composition will give rise to other varie-
ties of lithium borates like Li 2 B 4 O 7 , LiB 3 O 5 , and Li 3 B 5 O 8 (OH) 2 . Therefore, one has
to be extremely cautious in selecting the nutrients. The experiments were taken in a
Teflon liner, which was placed inside the autoclave. The capacity of the autoclave
was 30
50 ml. These autoclaves are normally provided with a safety blowout disk.
The percent filling of the liners and the experimental temperatures were used in
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