Hydrothermal growth of single crystals of cinnabar (red HgS)

Mat. R e s . Bull. Vol. 4, pp. 8 9 7 - 9 0 4 , 1969. in the United S t a t e s .

Pergamon Press,

Inc.

Printed

H Y D R O T H E R M A L GROWTH OF SINGLE CRYSTALS OF C I N N A B A R (RED HgS)*

S. D. Scott** and H. L. Barnes D e p a r t m e n t of G e o c h e m i s t r y and M i n e r a l o g y The P e n n s y l v a n i a State University University Park, Pa., 16802

( R e c e i v e d O c t o b e r 3, 1969; C o m m u n i c a t e d by R. Roy) ABSTRACT Single crystals of cinnabar up to 2 mm in diameter and free of foreign, contaminating, solvent anions were grown h y d r o t h e r m a l l y from aqueous sodium bisulfide solutions in a rocking autoclave at 26 ° to 200°C. Of the conditions tested, optimum results were obtained when both the solubility and solubility gradient, controlled by the composition of the bisulfide solution and temperature, were highest. Stoichiometry of the cinnabar crystals is controlled by fixing temperature and f--s~ z during growth, f_s2 being dependent on pH and bisulflde concentration.

Introduction Single needed

crystals

of red, hexagonal mercuric

for studies of their electrical

for several

industrial

applications.

ments have been made on natural Attempts

to synthesize

from the vapor phase peratures bar

metacinnabar

isometric HgS) inverts

and

Until recently most measure-

cinnabar or on highly doped HgS.

have been unsuccessful

that are high enough

(black,

and optical properties

large crystals of high-purity

(1,2)

sulfide are

cinnabar

because

at tem-

for transport to occur, m e t a c i n n a -

is the stable phase.

to cinnabar

Upon cooling,

and the accompanying

decrease

* C o n t r i b u t i o n no. 69-11, College of Earth and Mineral The P e n n s y l v a n i a State University, University Park, Pa. ** Now at the D e p a r t m e n t of Geology, Toronto 5, Canada.

897

in

Sciences,

U n i v e r s i t y of Toronto,

898

SINGLE CRYSTALS OF CINNABAR

molar volume

(AV=l.753cm

For this r e a s o n stability

3

cinnabar

field,

below

Cinnabar

; 3) causes crystals

the c r y s t a l s

transition

of m m d i m e n s i o n s

low the t r a n s i t i o n

temperature

phere

(5) and h y d r o t h e r m a l l y

at 2 7 0 - 2 8 0 ° C

In this p a p e r we d e s c r i b e crystals

of fixed

in aqueous

bisulfide

essentially relatively

solutions.

Because

uously

resulting

w e r e grown

operates crystals

are

saturating

Method

and S t e m p r o k

of HgS

of c o n d i t i o n s crystals

elevated

by w h i c h

the p r o c e s s

equilibrium,

Romberger

the s o l u b i l i t y

cinnabar

technique

(6).

free of i m p e r f e c t i o n s .

Barnes,

a variety

(4).

in an argon atmos-

up to 2 m m in d i a m e t e r

Hydrothermal

measured

at 344°C

in 2 m HCI at 320°C

a hydrothermal

at t h e r m o d y n a m i c

their own

have been g r o w n be-

by s u b l i m a t i o n

stoichiometry

to fracture.

m u s t be grown w i t h i n

the r e p o r t e d

crystals

Vol. 4, No. iZ

in aqueous

up to 200°C.

could be s y n t h e s i z e d an a p p r o p r i a t e

temperature

(7) have r e c e n t l y solutions

T h e i r data suggests hydrothermally

aqueous

and p r e c i p i t a t i n g

sulfide

under

that

by c o n t i n -

s o l u t i o n w i t h HgS at

single

crystals

at a lower

temperature. The g r o w t h lined h y d r o t h e r m a l which

solids,

tamination. assembly

experiments

pressure

liquids,

is r o c k e d

two ways. recess this

coolant pressure

steel o u t e r

vessel.

to be the b e t t e r

solution

was

control

and the finger

with

without

con-

and the entire

to aid the e q u i l i b r a -

A detailed

was p r o d u c e d

However,

description

of

in the v e s s e l

in

the t e m p e r a t u r e

finger,

and an inner

circulated,

consisting

of a

tube t h r o u g h w h i c h

was

inserted

a

into the

at the tip of the finger was

a thermocouple.

coolant

of

k n o w n and could not be r e a d i l y

a cold

The t e m p e r a t u r e

monitored

sensitive

runs

jacket

(air or water)

continuously

more

In s u b s e q u e n t

axis

into

w e r e g r o w n on a cold spot in a

cold spot was not a c c u r a t e l y

stainless

found

gradient

crystals

capacity

(8).

in the head of the vessel.

controlled.

in a furnace

in the vessel.

is g i v e n by B a r n e s

At first,

in a c h r o m i u m -

can be i n t r o d u c e d

is h e a t e d

A temperature

conducted

of i.i litre

about a h o r i z o n t a l

tion of the m a t e r i a l s the a p p a r a t u s

vessel

and gases

The v e s s e l

were

as it a l l o w e d

of t e m p e r a t u r e

Compressed a wider

gradients

than did w a t e r w h i c h

range

between

tended

air was and

the

to o v e r c o o l

Vol. 4, No. IZ

SINGLE

CRYSTALS

OF CINNABAR

899

the finger. The c i n n a b a r crystalline

lumps was

(7) in t h e i r thermally

in the f o r m of p o l y -

that u s e d by B a r n e s ,

solubility

by h e a t i n g

tion a one

starting material

experiments.

Romberger

It was

and S t e m p r o k

synthesized

hydro-

at 200 ° to 300°C in a s o d i u m b i s u l f i d e

to one m i x t u r e

of m e r c u r y

and sulfur,

solu-

b o t h of 9 9 . 9 9 9 + %

purity. All crystals were grown solutions.

The pH's,

temperature

gradients were

data

(7) w h i c h

neutral

the m e r c u r y

sodium bisulfide

of s o d i u m b i s u l f i d e

c h o s e n on the b a s i s

that the o p t i m u m

alkaline

bisulfide

tota£ activity In m o r e

concentrations

indicate

to w e a k l y

in a q u e o u s

pH's w i t h i n

complexes,

of d i s s o l v e d

acid H2S s o l u t i o n s

conditions

are n e a r -

the s t a b i l i t y

species

HgS e x h i b i t s

a f u n c t i o n of t e m p e r a t u r e w i t h i n

of the s o l u b i l i t y

fields

Hg(HS) 3 and H g S ( H S ) ~ - ,

sulfide

and

at a

(ZS) g r e a t e r

retrograde

the t e m p e r a t u r e

of

than

solubility

1.0. as

r a n g e of i n t e r e s t

(9). In a t y p i c a l run reagent grade NaOH required were

15 to 25 g m of HgS to give

s e a l e d into the p r e s s u r e

50 m i c r o n s . weighted tained

H2S

(99.5+%)

through

the d e s i r e d N a H S

v e s s e l w h i c h was

and d e g a s s e d ,

into the v e s s e l .

and the a m o u n t of concentration

then e v a c u a t e d

to

deionized water were

The s o d i u m b i s u l f i d e

s o l u t i o n was ob-

the r e a c t i o n H2S + N a O H + H20 + N a H S

w h i c h goes was

effectively

adjusted

amounts

at r o o m t e m p e r a t u r e

of N a H S

equilibrate

and H2S

were

in T a b l e

calculated

i.

The pH of e a c h

by c a r e f u l l y

in the vessel.

the s o l u t i o n The r a n g e

marized

to c o m p l e t i o n .

solution

balancing

The v e s s e l was

the rocked

to

and then heated.

in c o n d i t i o n s

of the e x p e r i m e n t s

The p H ' s w e r e

all n e a r n e u t r a l

are sum-

at 20°C and

f r o m the r e a c t i o n s NaHS = Na +

+ HS-

and

H2S = H + + HSfor w h i c h the r e s p e c t i v e e q u i l i b r i u m c o n s t a n t s are 5(10) and -6.88 i0 (ii). At the t e m p e r a t u r e of the e x p e r i m e n t s , the pH's were

slightly more

alkaline

than calculated

e f f e c t of t e m p e r a t u r e

on the i o n i z a t i o n

and on the s o l u b i l i t y

of H2S in w a t e r

at 20°C due to the

constants

(i0).

of H2S and N a H S

For e x a m p l e ,

the

900

SINGLE

calculated line

for run

relative

tions The

pH

within

solubilities

Romberger

OF CINNABAR

pH of 5.8.

the o p t i m u m

of HgS w e r e

solution

and the

and S t e m p r o k

cold

the

The b e s t

solubility

gradient

were

crystals

ranging

cess

the h i g h e s t

in the h e a d

finger

all of the s o l u -

at r u n

temperatures.

from

the d a t a

were

obtained

are

of B a r n e s ,

from run

runs.

vessel.

ger

euhedral

lined

Subsequent using

a re-

runs

were

the c o l d

for a v a r i e t y

solubilities ture

and

gradients of

tempera-

to study

the e f f e c t

~

variables

........ !i .....

In r u n

ii a d r u s e

stals,

1 m m thick,

were

cold

Cinnabar

within 0.5 m m

those

crystals from run S q u a r e s are 1 mm.

of s p o n t a n e o u s

the s o l u b i l i t y both

runs,

ed the

masses

surface

t i o n of

the

solubility

of the

gradient

for c r y s t a l and

in runs

crystals,

of HgS

were

1 clearly

growth

12 and

As

shown

finger

in

cry-

in d i a m e t e r , smaller

than

106 b u t

as w e l l

13 w e r e than

solution

solubility

that

of HgS

gradient.

coat-

reduc-

and of the

were

the b e s t

In

ii,

further

a n d no c r y s t a l s

demonstrates

solubility

in run

14,

the

by r e d u c i n g

unsuccessful.

those

in run

formed.

to c o n t r o l

finger

in the n u t r i e n t

too s e v e r e

are h i g h

a large

on the c o l d

smaller

finger.

solubility

Table

solution

of

coated

the m a s s

from run

equally

nucleation

gradient

of cry-

106. Attempts

amount

rates.

Individual

considerably i.

these

on g r o w t h

the e n t i r e

stals

fin-

of

iii~!

a week.

both

solubility

red,

(Fig.l)

made

in

106 w h e r e

and the Deep

in d i a m e t e r

of the p r e s s u r e

summarized

solution

of all f i v e

1 to 2 m m

FIG.

of

and D i s c u s s i o n

in the a q u e o u s

from

alka-

for the t e m p e r a t u r e s

of the e x p e r i m e n t s

crystals

of HgS

pH r a n g e

1.3 u n i t s

12

(7).

The r e s u l t s i.

is

However,

calculated

Results

Table

Vol. 4, No.

ii at 150 ° is 7.1 w h i c h

to a n e u t r a l

remained

the a q u e o u s

CRYSTALS

grown.

conditions

in the n u t r i e n t

We w e r e

unable

to de-

Vol. 4, No. IZ

SINGLE CRYSTALS

crease sufficiently taneous

the spon-

OF CINNABAR

tl-4 , ~ O ~

nucleation of HgS on

C~

Lr~

I

the cold finger by manipulating the HgS solubility temperature gradient,

and

although

•

0 V

0

;--I

~0

O4

O -,-4 r./l I~-

seed crystals

L~

'

0 V

U? r..)

this problem might be overcome by attaching

Lrb

•

0

901

~

to

4J

C~

the cold finger.

0

Although our method of growing

q3

cinnabar crystals o.,-I

is more complicated

.~

than that

0

0

0

0

0

(1)

described by Rau and Rabenau

J

(6), there are two distinct advantages

~

0

of using sulfide

solutions•

First,

0

our cry-

04

stals are free of the potentially contaminating present

0 0

anions

Rabenau.

crystals

solutions

,-4m~ .,..t o ..Q ~-4 .,q ~o-w

it

o

to grow cinnabar

of different

hiometries

(1) d)

in aqueous because

~ 0

0

0

sulfur fu-

This principle

is explain-

ed with the aid of Figure

2.

A l t h o u g h growth conditions temperatures

and values of ZS different from those illustrated,

the

shape of the d i a g r a m

m

g

-,--I ~

4~ N ~ C) lalO

~ O -,-t 4~

• ~

O m

0 0

P~ ¢',1

',,0 C'q

L~ I.~

O a~

(1)~ ~ O

m

m

r~ Ca

r~

m O :>1 ~ m ~.~ .-C .~ ~J

~

m O

~ O L~

0 L~

0 ~

I.~ ~0

L~

~0 04o

~

4.-I ~.I

4-1

~.~

O

r~ ¢

~

- ,---t

,-4

,-.-t m

r.)

r..) >

L~ ::>I o ] 4.~ -;--.I

o,I

and indi-

cates the chemical relations

-,-t

0

0

0

0

0

~

~

00

o

,--I

remains u n c h a n g e d

.£1

.,--t

sulfide

tude as a function of f o 2 and

O rd ON O-~-t 4J

0

t~

(f_s2) can be varied

were at various

~ r~ 0

0

0 ;.--t

stoic-

over several orders of magni-

general

0 0 r.-I

r--I

<

More importantly,

is possible

pH.

0 L~

in the strong chloride

solutions used by Rau and

gacity

0 ~

Ord

of consequence here. ~0

~:~ O ,--4

~-t ~

~ ~

~ ~

~1~ ~

90Z

SINGLE CRYSTALS

OF CINNABAR

Vol. 4, No. IZ

-50

-40

o

-50 N

O %.

-.1

-60

-70

-80

2

4

6

6~

I0

P2

pH FIG.

2.

Distribution of predominant, sulfur-containing, aqueous ions and molecules at i00°C and ZS = 0.i. Fugacity of S 2 is contoured in atm. After Barnes and Kullerud (12).

Within buffered

the optimum pH range

and the solutions

and within

over ten orders

Thus it is expected

in sulfur

conditions

below the HS-/SO~-

the required

of magnitude

that cinnabar

acid end of the boundary

richer

S0~- + 4H 2 + H +

lie on or slightly

this boundary

continuously

more

growth ~O 2 is

by the reaction HS- + 4H20 ~

Along

for cinnabar

pH range f_s2 varies

as a function

crystals

and therefore

boundary.

of pH.

grown at the relatively at higher f_s2 will be

than those grown under relatively

more

alkaline

and lower -of~2"

Acknowledgement This study was supported Projects Materials

Agency,

Contract

Research

and by the National

DA-49-083,

Laboratory Science

by the Advanced OSA 3140,

through

of The Pennsylvania

Foundation

Research the

State University

with grant GP-2597.

Vol. 4, No. IZ

SINGLE

CRYSTALS

OF CINNABAR

903

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