Hydrothermal Synthesis and Crystal Growth of Fluorides, Sulfides, Tungstates, Molybdates, and Related Compounds (Coordinated Complex Crystals, Part II) - Hydrothermal Technology - page 550

of above dependencies allows the inference of the reactions responsible for the dis-
solution of HgS, ZnS, and ZnSe, at different solvent concentrations:

HS 2 ! Þ 2 C NaHS ,

HgS HgS ð HS 1M ð 8 : 26 Þ

1

2 2

2HS 2 ! HgS 1 HgS ð HS Þ C NaHS . 1M ð 8 : 27 Þ

OH 2 ! Þ 2 C KOH #

ZnS Zn ð S ; OH 1M ð 8 : 28 Þ

1

Þ 2 1

2 4 1

HS 2 C KOH .

ZnS 3 ð OH H 2 O ! Zn ð OH Þ 1M ð 8 : 29 Þ

1

ZnSe H 2 O ! Zn ð H ; Se Þ OH C KOH , 0 : 1M ð 8 : 30 Þ

1 2

Þ 2 ZnSe H 2 O OH 2 ! Zn ð H ; Se Þð OH 0 : 1m

, C KOH ,

0 : 5M ð 8 : 31 Þ

1 1

2 3

ZnSe H 2 O 2 ð OH Þ! Zn ð H ; Se Þð OH Þ C KOH . 0 : 5M ð 8 : 32 Þ

1 1

It can be concluded that the dissolution of HgS (in HgS a NaHS a H 2 Osystem)is
described by reactions, just as ZnS (in ZnS

H 2 O system) is dissolved by a
reaction at a low solvent concentration and a reaction at a higher one. As a result,
the transfer of HgS and ZnS (in low concentrated solutions) takes place in the form
of heterocomplexes, and ZnS is transferred in higher concentration solutions by the
separated ions (Zn OH

a KOH a

ð Þ 2 2 and HS 2 ). These differences are displayed in the kinetics
of crystal growth. Figure 8.27a and b gives examples of the growth rate of HgS and
ZnS and its dependence on the solvent concentration [101,102] . From Figure 8.27b ,
one can see that V (III) of ZnS hardly depends on the solvent concentration and
remains practically unchanged at C KOH . 20 wt%. The solubility of ZnS under such

conditions comes up to approximately 1.5 wt%. The authors associate the unusual

V (mm/day)

V (mm/day)

(0001)

0.04

0.2

(1010)

(111)

×

× ×

0.02

0.1

×

×

×

5 10 15 20 10 20 30

C NaHS (wt%) C KOH (wt%)

Figure 8.27 Growth rate of HgSd and ZnS and its dependence on the solvent
concentration [101,102] .