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Synthetic calcite single crystals for optical device
Ping. Crystal Growth and Charact. 1991, Vol. 23, pp. 341-367 Printedin Great Britain.All rightsreserved
0146-3535/91 $0.OO+ .50 © 1992 PergamonPress Ltd
SYNTHETIC CALCITE SINGLE CRYSTALS FOR OPTICAL DEVICE S. Hirano, T. Yogo and K. Kikuta Department of Applied Chemistry, School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-01, Japan
1. INTRODUCTION Calcite is one of the c o m m o n minerals in nature and its t r a n s p a r e n t crystals are k n o w n as Iceland spar. Recently the d e m a n d for calcite and rutile single crystals with a large birefringence h a s been increasing b e c a u s e of application for polarized optical devices. The synthesis of calcite single crystals h a s received the great attraction with the development of the laser devices s u c h as a n optical isolator, since n a t u r a l resources have b e e n depleted. Calcite occurs in n a t u r e as minerals with a chief constituent of all kinds of limestone and marble as well as alternated veins and ore deposits. High quality natural calcite crystals have been considered to be grown hydrothermally and occurred mainly in Mexico and Brazil (1). The synthesis of calcite single crystals with optical grade h a s b e e n required for the optical applications, since no high quality n a t u r a l calcite crystals have occurred in J a p a n . Calcite dissociates at a b o u t 900°C u n d e r a t m o s p h e r i c p r e s s u r e and fuses at 1290°C u n d e r a p r e s s u r e of 170 b a r s of C02. Many a t t e m p t s have been made to grow calcite single crystals. Much work concerning the artificial growth of calcite h a s b e e n done using the high t e m p e r a t u r e flux method. Czochralski and travelling solvent zone melting m e t h o d s produce a calcite boule from a CaCO 3Li2CO ~ melt at 700-800°C by consulting with the p h a s e diagram of the CaCO 3Li2CO 3 s y s t e m as shown in Fig. 1 (2). The top seeded solution growth (TSSG) and the traveling solvent zone melting (TSZM) are the m e t h o d s to be employed for the crystal growth (3-7). These methods, however, include some difficulties in producing a high quality single crystal of calcite owing to large thermal stress, CO 2 dissociation, and alkaline c a r b o n a t e flux inclusions causing serious defects and c o n t a m i n a t i o n s by metal ions. The h y d r o t h e r m a l method is one of the promising techniques for growing u n s t a b l e crystals s u c h as a carbonate compound, with the advantage of s u p p r e s s i n g the dissociation of CO 2 and yielding high quality crystals in a
341
342
S. Hirano et at
h o m o g e n e o u s ambient at relatively low temperatures. This review describes mainly our recent results of the hydrothermal crystal growth and the characterization of the growth features of calcite single crystals with an emphasis on the proper selection of solvents.
1100 _ 18~7' 1000 Liquid ?
E
® I,-
/iii'0
900
800
700
Pco2= 5.3 xlO-3
+ Liquid
Li2CO3
.
.
20 .
/
1.1
CaCO3
~/664°C .
.
...... 6'o
40 WT
Fig. 1.
8.0
'
8'o
'
CaCO3
%
Phase diagram of CaCO3-Li2CO3 system
Optical Properties of Calcite
The space group of calcite belongs to R3C. The crystal exhibits the perfect {I0]'1} cleavage with extreme diversity of habit, being often rhombohedral in aspect. The optical property is characterized by the extremely strong birefringence, uniaxial character as shown in Table 1 compared with those of a-quartz and rutile. The CO 3 group is responsible for the birefringence in the structure, where the CO 3 groups are perpendicular to the threefold axis of calcite. This optical character has been utilized as optical prisms and isolators.
Table I
Optical Properties of Crystals no
ne
n
Transmission wave region (pm)
Calcite (CaCO 3)
1.65836
1.48641
- 0.17195
0.20 - 5.5
Quartz
{SiO2}
1.54425
1.55336
+ 0.00911
0.16 - 4.0
Rutile
(TiO2)
2.6124
2.8893
+ 0.2869
0.43 - 6.2
Synthetic calcite single crystals
343
In a birefringent crystal like a calcite, light waves travel through the crystal with different velocities depending on the vibration plane of electric vector relative to the crystallographic axis. The unpolarized incident light separates into two rays, the ordinary (o) ray and the extraordinary (e) ray. Nicol prism is designed using a polished calcite crystal with a Canada balsam (nb;refractive index) as shown in Fig. 2. As the order of the refractive index is no>nb>n e, only a n ordinal ray does reflect completely at the interface between calcite and Canada balsam crystals.
Optic \
axis
\ \A
C
'
1
J ,,~=
', :
', : ~ E
B/ 0
68 °
Fig. 2.
Nicol prism using Canada balsam
Calcite crystal is superior to others in order to produce linearly polarized ray, which is of importance for the design of an optical isolator providing the stabilized laser light. A simple set-up of the optical isolator is shown in Fig. 3. An incident laser light passes through a polarizer to be a linearly polarized ray, which then proceeds to a magneto-optic YIG crystal. The traveling ray rotated by 45 ° in the crystal transmits to an analyzer. If the traveling ray be reflected in a n optical fiber or at junctions, the reflected light travels back to the YIG crystal and is cut by the polarizer to isolate from the incident light. The crystals in the system are required to be highly perfect without absorptions or scattering.
Lens
LD
~
-
~
"\
" Reflected
I
Polarizer
YIG
Fig. 3. Alignment of optical isolator
light
Analyzer
344
S. Hirano et al.
1.2
Hydrothermal Synthesis
Many natural crystals are considered to be grown from m a g m a reacted or altered with mineralizers u p o n crystallizing. Water is the most c o m m o n and important mineralizer in n a t u r e and should also be considered to be a low-melting point or volatile constituent in a system, in that it can lower the liquidus temperature of a compound. In this sense, the term "hydrothermal" is appropriate in the category of "hlgh-temperature and pressure solutions." All hydrothermal crystal growth are carried out in the presence of active water or in solution above 100°C in a pressure vessel. Thus, a suitable combination of solution (solvent), pressure and temperature m u s t be discovered where calcite is thermodynamically stable and has sufficient solubility to give a reasonable supersaturation, leading to the proper convection circulation with temperature gradient along a pressure vessel. Hydrothermal growth of calcite single crystals has been studied by employing chloride, hydroxide and carbonate solvents. Ikornikova firstly investigated NaCl and other chloride solutions, but did not mention the details of crystal growth and the quality of the grown calcite crystals (8, 9). Balascio et al. and Kinloch et al. reported that K2CO 3 solution was an effective solvent to grow calcite crystals on a cleaved seed (10, 11). In order to protect the pressure vessel from corrosion by alkali solvent above 400°C, silver was used as a liner. Recently carbonic acid solvent was employed for the growth of calcite u n d e r elevated pressures by Higuchi et al. (12). The a u t h o r s discovered that nitrate solutions were the new effective solvent for the growth of calcite single crystals (13-15). It was confirmed that nitrate solvents are more effective t h a n chloride solvents from the viewpoint of solubilities of calcite (16, 17). Both carbonate and nitrate ions possess a similar structure containing triangular arrangement of atoms, which might lead to the advantage for calcite growth avoiding the contamination of alkali metal inclusions and allowing low-temperature growth conditions. Rhombohedral calcite crystals spontaneously grew in NH4NO 3 solvent even at 150°C. The following is the detail of the growth and dissolution behavior of calcite single crystal in hydrothermal solutions.
2. SOLUBILITY AND DISSOLUTION BEHAVIOR IN HYDROTHERMAL SOLUTIONS 2. i Selection of solvent The selection and comparison of the hydrothermal solvents were made on the basis of the stability and morphology of the calcite crystals. Experiments were carried out at c o n s t a n t conditions of 500°C (200°C only in NH4NO 3) and 100 MPa for 3 days with reagent grade powder of calcite. The results are shown in Table 2. Xray diffraction analysis of the crystals grown in these solutions indicated that calcite did not change to any other phase or c o m p o u n d except when the solution contained 3m Na2CO 3 (m, molality). In this case, the calcite changed to an u n k n o w n c o m p o u n d which was neither pirssonite nor gaylussite. This might be attributable to the high carbonate ion concentration and the close ionic radius of Na + to Ca 2÷.
Synthetic calcite single crystals Table 2
345
Results of hydrothermal treatment of calcite in several solutions
Solution
Crystal form
XRD
3m
NaCl
Polyhedral
Calcite
2m
KCI
Polyhedral
Calcite
3m
NaOH
Dendritic
Calcite
2m
KOH
Dendritic
Calcite
3m
Na2CO 3
3m
NaNO 3
Polyhedral
Calcite
2m
KNO 3
Polyhedral
Calcite
1.5m Ca(NO3) 2
Polyhedral
Calcite
3m
Polyhedral
Calcite
NH4NO 3 *
500°C, I 0 0 MPa, 3 days
---
Unknown c o m p o u n d
°200°C, 100 MPa, 3 days
Dendric crystals were grown in NaOH and KOH solutions, It was very difficult to grow the bulk crystals bounded by fiat surfaces i n these alkali hydroxide solutions. These hydroxide solutions are strong basic solvent and corrosive to the pressure vessel as is the same in K2CO 3 solutions. These results in Table 2 indicate that the anion group in the salt solution is a more dominant factor t h a n is the type of cation in the solvent used for the growth of calcite single crystals. It h a s been confirmed that both alkali chloride and nitrite solutions were useful for growing calcite crystals as the single phase.
2.2 Solubility The solubility of calcite in the solution was determined by the weight loss method. Both reagent grade calcite powder or highly pure natural single crystals were sealed with solution in a gold capsule as the specimen container, which then placed in the pressure vessel. Solubility r u n s were maintained, u n d e r each condition, for 3 days, which had been confirmed previously to be long enough to bring the system to equilibrium. Following a run, the pressure vessel was quenched with cold water. A stainless steel filler rod was also placed in the space above the capsule so as to reduce convection and to achieve thermal uniformity of the capsule.
346
S. Hiranoet al.
s,sO
soo i
4so/oc i
3.0
T
~
2.0
o~ o -0.5
1.0
-1.0
o 3;0 4~o 4~o 5~o s~o
I
I
I.
1.2
1.3
14
T-~/10-3K-1
Temperature/°C
Fig. 4. S o l u b i l i t y of CaCO 3 i n 3 m NaCI s o l u t i o n a s a f u n c t i o n of t e m p e r a t u r e a t 100 MPa
Fig. 5. Log S (solubility) of CaCO 3 a s a f u n c t i o n of 1 / T i n 3 m NaCI
5.0 IOOMPa 4-01
500
I
i
r~! /
450
400
350 (°C)
0.5
I
/
3m NAN03/ T
0
~3.0
u') r-
-I
~2.0 . "C]../,.[~'~m
NaCI
-0.5
1.0
3~0 450 4~0 s~o s~o Temperature, °C
Fig. 6. S o l u b i l i t y of CaCO 3 i n 3 m NaNO 3 s o l u t i o n a s a f u n c t i o n of t e m p e r a t u r e a t 100 MPa
1.3
1.4
1.5 1.6 1/T (xlO -3 K -1)
Fig. 7. Log S (solubility) of CaCO 3 a s a f u n c t i o n of 1 / T i n 3 m NaNO 3
347
Synthetic calcite single crystals
Figure 4 shows the solubility in the 3m NaCl solution as a function of the temperature at 100 MPa. The solubility increased remarkably with increasing temperature above 400°C and amounted to 2.0 g/1 at 500°C. The solubility value is acceptable practically for the hydrothermal growth above 400°C. Figure 5 shows a plot of log S (Solubility) vs. 1/T in order to confirm the van't Hoff relation. The enthalpy of the solution, AH, was calculated to be about 46 k J / m o l , m u c h larger t h a n tLH°=-12kJ/mol in CaCO3-H20 system u n d e r ordinary condition (18). This fact indicates that the state of dissolved species u n d e r hydrothermal conditions is quite different from that u n d e r ordinary conditions at atmospheric pressure. The solubility of calcite in 3m NaNO 3 is given in Fig. 6, being compared with that in 3m NaCl. The solubility in 3m NaNO3 increased abruptly with increasing temperature and it amounted to 2.2 g/l a t 450°(3. This solubility is acceptable for the growth of calcite single crystal b y the hydrothermal technique. Since the value of the solubility in 3m NaNO 3 is about twice that for 3m NaCl, NaNO 3 solutions were Judged to be suitable for the growth at lower temperatures. Figure 7 shows the plot of the log S (solubility) versus 1/T. The data reveal that the van't Hoff law is not obeyed in this system. This fact suggests that the state of the dissolved species m a y change with increasing temperature.
4.0
100MPa
//~ //
/ii II ~iiiil/l/
3.0 7 O~
2.o O
(/)
~:~
/
b
1.0
0
i
350
Fig. 8.
|
I
400 450 Temperature ,
!
500 °C
Solubility of CaCO 3 in 1.5m Ca(NO3) 2 and 3m NaCl soluUons as a funcUon of temperature;(a) in 1.5m Ca(NO3) 2 solution;(b) in 3m NaCl solution
348
S. Hirano et al.
T T~
~5.0 ..Q
"5 oo
0
I
i
I
I
140
160
180
200
Temperature, Fig. 9.
°C
S o l u b i l i t y of c a l c i t e in 3 m NH4NO 3 s o l u t i o n a s a f u n c t i o n of t e m p e r a t u r e
T h e s o l u b i l i t y of c a l c i t e in 1 . 5 m Ca(NO3) 2 a n d 3 m NH4NO 3 s o l u t i o n s a r e s h o w n in Figs. 8 a n d 9. T h e c o n c e n t r a t i o n of s o l u t i o n s is a d j u s t e d to t h e s a m e a n i o n c o n c e n t r a t i o n a s NO3-. T h e s o l u b i l i t y in 1.5m Ca(NO3) 2 s o l u t i o n i n c r e a s e d w i t h i n c r e a s i n g t e m p e r a t u r e a n d t h e s o l u b i l i t y is a b o u t twice a s m u c h a s t h a t for 3 m NaC1 in t h i s t e m p e r a t u r e r a n g e . T h e r e s u l t s i n d i c a t e t h a t Ca(NO3} 2 is m o r e effective t h a n t h e NaCl or KC1 s o l u t i o n s . T h e s o l u b i l i t y c u r v e of c a l c i t e in 3 m NH4NO 3 a t 100 M P a ( F i 9) s h o w s t h a t NH4NO 3 s o l u t i o n is t h e m o s t effective s o l v e n t e v e n a t t e m p e r a t u r e s b e l o w 200°C. T h e s o l u b i l i t y a t 200°C is 8.1 g / l . T h i s s o l u t i o n , h o w e v e r , c a n n o t serve a s a s o l v e n t a t t e m p e r a t u r e s a b o v e 300°C, d u e to t h e i n s t a b i l i t y of NH4NO 3. A r r h e n i u s p l o t s w e r e m a d e from t h e s o l u b i l i t y m e a s u r e m e n t s , a s s h o w n in Fig, 10 a n d 1 1. It is c l e a r l y c o n f i r m e d t h a t t h e v a n ' t Hoff r e l a t i o n h o l d s in all t h e s e s y s t e m . T a b l e 3 s u m m a r i z e s t h e e n t h a l p y of d i s s o l u t i o n c a l c u l a t e d f r o m Figs. 5, 10 a n d 11. T h e e n t h a l p y v a l u e in NH4NO 3, w h i c h is s m a l l e r t h a n t h o s e in t h e o t h e r s o l u t i o n s , s u g g e s t s t h a t t h e c h e m i c a l s p e c i e s d i s s o l v e d in NH4NO 3 s o l u t i o n had a stronger chemical bonding,
Synthetic calcite single crystals
1.0 a
U~ 0
\\Xx\ k\\ b,\
\ \ \
\
\ \ \ \
-1.0 I
1.2
I
I
/
1.3
1.4
1.5
1/T ,
Fig. 10.
10-3 K ' I
Log S {solubility) of CaCO 3 and a function of l / T ; (a) 1 . 5 m Ca{NOa) 2 ; (b) 3 m NaCl
-3.0
-3.5
¢]) e-
-
-4.0
-4.5
I
2.1
Fig. 11.
I
2.2 1/T ,
I
I
2.3 2.4 10"3K -1
Log S (solubility) of CaCO 3 and a function of 1 / T in 3 m NHcNO 3
349
350
S. Hirano et al.
Table 3
D i s s o l u t i o n e n t h a l p y of calcite Solvent 3m
1.5m 3m
Dissolution e n t h a l p y (AH} k J / m o l
NaCI
46
Ca(N03) 2
43
NH4NO 3
31
F i g u r e s 12 a n d 13 show the effect of c o n c e n t r a t i o n of the solvent on the solubility. In the case of Ca(NO3) 2 solvent, the solubility rises g r a d u a l l y u p to 3.5m a n d t h e n d e c r e a s e s slightly. The r e s u l t s s u g g e s t t h a t a Ca 2÷ c o n c e n t r a t i o n above 3.5m s u p p r e s s e d t h e f u r t h e r d i s s o l u t i o n of calcite. The solubility in NH4NO 3 solvent i n c r e a s e s with the concentration, a n d c o n t i n u e s to i n c r e a s e in this c o n c e n t r a t i o n range. The r e s u l t s indicate t h a t a r a t h e r dilute NH4NO 3 solution is a d e q u a t e to a d j u s t the s u p e r s a t u r a t i o n for the growth of calcite crystals.
2.0
T
e~
¢~1.0
/
/
1 O0 MPa
400 °C I
0
Fig. 12.
1
!
I
I
1 2 3 4 5 C o n c e n t r a t i o n of s o l v e n t ,
m
Solubility of CaCO 3 as a function of c o n c e n t r a t i o n of Ca(NO3) 2 solution at 400°C a n d I 0 0 MPa
Synthetic calcite single crystals
351
10
o)
~5 .o o
100 MPa 2 0 0 °C I
I
I
0 1 2 3 Concentration of solvent, m
Fig. 13.
2.3
Solubility of CaCO a as a function of concentration of NH4NO 3 solution at 200°C and 100 MPa
Dissolution behavior in nitrate solutions
The pH values of calcium nitrate were measured as a function of temperature. Figure 14 shows the changes of the pH curves in 1.5m Ca(NO3) 2 solvent with and without calcite crystals in the hydrothermal system. The pH value increased gradually with increasing temperature and a significant difference is found between these two curves, which reflects the dissolution behavior of calcite. It was already confirmed that the solubility of calcite started to increase at 300°C as mentioned above. These data indicate that calcite crystals can be recognized as a basic salt. In the case of a m m o n i u m nitrate solvent, however, the pH value of a pure solvent decreased abruptly with the increase in temperature as shown in Fig. 15. It t u r n s out from this fact that the decomposition of a m m o n i u m nitrate takes place to give nitrogen oxide and water, which turn the solution to be acidic. Calcite crystals dissolve in this acidic solution u n d e r these conditions to keep the pH value at a r o u n d 7.
352
S. Hirano et al.
100 MPa
1.5m Ca(NO3)2 +Calcite /
/ / ~
-
t"
~; 0
50
,
.
300
.
.
.
400
500
Temperature , Fig. 14.
°C
pH v a l u e s of 1 . 5 m Ca(NO3) 2 s o l v e n t a s a f u n c t i o n of t e m p e r a t u r e
1OO MPa
3mN
+Calcite
~5 \
\
\
\
3m NH4NO3
I
100
i
200 Temperature , °C
Fig. 15.
\ \\
\
\
\
\
I
300
pH v a l u e s of 3 m NH4NO 3 s o l v e n t as a f u n c t i o n of t e m p e r a t u r e
Table 4 s u m m a r i z e s the effects of h y d r o t h e r m a l s o l v e n t o n c r y s t a l l i z a t i o n of calcite. At 20(YC, calcite d o e s d i s s o l v e in the a m m o n i u m nitrate s o l v e n t w i t h a release of a m m o n i a . T h i s p h e n o m e n o n is quite s i m i l a r to t h e c a s e of t h e other a m m o n i u m
Synthetic calcitesingle crystals
353
solvents. A m m o n i u m sulfate and a m m o n i u m fluoride solutions react with calcite to form insoluble calcium salts, e.g. CaSO 4 and CaF 2, and ammonia. At elevated temperature, NH4NO3 is not effective as a hydrothermal solvent for the growth of calcite single crystal due to its decomposition.
Table 4
Effects of hydrothermal solvent on the crystallization of calcite
HT solvent
Temperature (°el
Effect of solvent
Remarks
0. i m NH4NO3
200
Good
Ammonia odor
0.02m NH4NO3
250
Slight
--
0.02m NH4NO3
300
No
--
Im
(NH4)2SO4
200
No
Ammonia odor, CaSO 4
Im
NH4F
200
No
Ammonia odor, CaF 2
lm
(NH4)2COS
200
No
Ammonia odor, powder nutrient
0. l m NH4NO 3 +0.00 lm(NH4)2HPO4
200
No
0. l m NH4NO3 +0.001 m(NH4)2SO 4
200
No
0. l m NH4NO3 +0.001 mNa2B407
200
No
0. l m NH4NO3 +0.003mEG
200
No
0. l m NH4NO 3 +0.1 mNaNO 3
200
No
FT-IR spectra of the solvent were analyzed with a ZnSe single crystal ATR cell. Figure 16 shows the FT-IR spectra before and after the experiment in NH4NO3 solution. In the solution before the growth run, the absorption at a r o u n d 3400 cm -l is observed, which is ascribed to stretching vibrations of NH4÷ and OH-, and at a r o u n d 1600 cm -I due to OH-. The remarkable difference in the spectra before and after the dissolution of CaCO 3 is the absorption assigned to HCO3"at around 2350 cm I . This absorption b a n d became considerably stronger after the dissolution of C a C O 3. These results suggest that calcite dissolves into the solvent below 200°C as follows;
354
S. Hirano et al.
CaCO3 + NH4NO3 + H 2 0
:c >
Ca2+ + HCO3- + NO3- + NH4+ + OH-,
C a C O 3 + 2NH4F + H 2 0
< "~
CaF24,
+ HCO 3" + 2NH4 + + O H ,
C a C O a + (NH4)2SO 4 + H 2 0 ~
CaSO4. ~, + H C O a- + 2NI--I4* + OH-,
C a C O a + (NH4)2CO 3 + 2 H 2 0 ~
C a 2+ + 2 H C O a- + 2NH4 ÷ + 2OH-.
/
H C O 3-
/
before
after
i
4000
i
Wavenumber,
Fig. 16.
i
.
3000
i
2000 c m -1
C h a n g e of FT-IR s p e c t r a of c a l c i t e b y t r e a t m e n t in NH4NO a (a)before t r e a t m e n t ; (b)after t r e a t m e n t .
(NH4)2CO 3 s o l u t i o n h a s n o effect a s a s o l v e n t for g r o w i n g c a l c i t e c r y s t a l s . The r e s u l t r e v e a l s t h a t t h e h i g h HCO 3- c o n c e n t r a t i o n d u e to a h y d r o l y s i s of (NH4)2CO 3 c a n s u p p r e s s t h e f u r t h e r d i s s o l u t i o n of c a l c i t e in t h e h i g h p r e s s u r e s y s t e m . In f l u o r i d e a n d s u l f a t e s o l u t i o n s , l e s s - s o l u b l e s a l t s of C a F 2 a n d C a S O 4 f o r m s to p r o c e e d t h e r e a c t i o n s , a n d p r o d u c e a m m o n i a w h i c h is c o n f i r m e d b y odor. It w a s a l s o c o n f i r m e d t h a t a s m a l l a m o u n t of a d d i t i v e s s u c h a s p h o s p h a t e , s u l f a t e , b o r a t e a n d e t h y l e n e glycol effectively a r r e s t e d t h e g r o w t h of c a l c i t e s i n g l e c r y s t a l s a s s h o w n i n T a b l e 4. A m o n g t h e s e a d d i t i v e s , s u l p h a t e i o n m a y o f t e n c o e x i s t a s a c o m m o n t r a c e i m p u r i t y in t h e c h e m i c a l r e a g e n t . T h e r e s u l t s c l e a r l y e x h i b i t t h a t t h e s e i m p u r i t i e s m u s t b e r e m o v e d c a r e f u l l y f r o m a h y d r o t h e r m a l solvent.
Synthetic calcite single crystals
355
3. HYDROTHERMAL GROWTH 3.1
Morpholo&W of grown calcite single crystals
Some growth experiments were carried out with highly pure Iceland spar as the starting material to s t u d y the morphological change. Calcite single crystals of sizes u p to 1.0 m m were grown spontaneously on the inner wall of the capsule. There were two kinds of crystal habits in NaCl solution. The morphologies of grown crystals were found to be strongly influenced by the growth temperature. Platelike calcite crystals bounded by well developed {0001] faces could form mainly at elevated temperatures above 500°C. Associated with the crystals (Fig. 17a), a few polyhedral crystals were grown as shown in Fig. 17b. The variation of crystal habits showed a good agreement with the occurrence in nature. Sunagawa et al. showed that the plate-like {0001] calcite crystal might occur at elevated temperatures in the first stage of the precipitation of Iceland spar (19). Euhedral crystals bounded by [10~1] faces were also prepared at 450°C and I00 MPa (Fig. 18). This fact suggests that the Iceland spar in nature might occur in a hydrothermal solution at a relatively lower temperature. In Ca(NOaJ 2 solution, spontaneously grown crystals usually showed a rhombohedral form bounded by {10TI] faces. Figure 19 shows a photomicrograph of calcite crystals prepared in 3m NH4NO 3 at 200°C, ~T=I2°C and 100 MPa for 10 days. These opaque crystals were large in size, b u t showed a lot of growth steps on surfaces. As mentioned above, the supersaturation u n d e r this condition is too high to grow a high quality t r a n s p a r e n t calcite single crystals, indicating that the concentration of the solvent m u s t be lowered below lm.
Fig. 17.
Calcite single crystals grown in 3m NaCl solution at 500°C and I00 MPa for 10 days : (a) Plate-like crystals; (b) Polyhedral crystals
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S. Hirano et aL
Fig. 18.
Calcite single crystals grown in 3m NaC1 solution at 450°C a n d 100 MPa for 10 days
Fig. 19.
Calcite single crystals grown in 3m NH4NO 3 solution at 200°C and 100 MPa for 10 days
Synthetic calcite single crystals
357
Euhedral crystals shown in Fig. 20 could be actually grown in a 0.1 m NH4NO3 solution u n d e r the s a m e conditions. Natural calcite crystals occur in various forms, while the crystals grown in NH4NO 3 solution below 200°C are b o u n d e d by {i011} faces b u t not by the other faces s u c h as {0001] in this experiment.
Fig. 20.
Calcite single crystals grown in 0.1m NH4NO3 solution at 200°C and 100 MPa for 10 days
Fig. 21.
Calcite single crystals grown in quartz glass capsule from NH4NO3 solution (a) 0.5m. 150°C. 1 week; (b) 0.5m, 120°C. 1 week; (c) 3m, 100°C, 1 week.
S. Hirano et al.
35B
Nutrient calcite and NH4NO 3 solvent were also sealed in quartz glass capsules so as to investigate the growth feature. After a run, the capsule could be directly examined by the naked eye (Figs. 21a-21c). Calcite single crystals had been grown on the inner wall of the capsules even at temperatures as low as 120°C. The pressure inside the capsule in this r u n was estimated to be a few MPa. These conditions were advantageous to avoid the contamination due to corrosion of the pressure vessel and to reduce the cost of crystal growth. It is necessary to grow a single crystal on a seed for the industrial scale production. A Grayloc type-hydrothermal a p p a r a t u s was used with Ti liner set inside the pressure vessel to avoid the contamination from vessel materials (Fig. 22). Both spherical and rhombohedral seeds were s u s p e n d e d in the u p p e r portion of the vessel.
II
I
Ti
i
--/
Seed
j z~T
sheath
//
Baffle plate Nutrient
"l
f i
Fig. 22.
Grayloc type hydrothermal a p p a r a t u s with Ti liner and baffle plates
In 3m NaC1 solution at 400°C and 100 MPa, the thickness of the rhombohedral seed increased by 0.087 m m while keeping for 2 weeks. On the other hand, spherical seeds were observed to be completely covered with fiat s m o o t h surfaces and the steps of a grown calcite crystal (Fig. 23). The fiat plane is identified to be {101-1} faces, axial s y m m e t r y perpendicular to which symmetry is confirmed to be two fold by back-reflection Laue photographs. The {10]-1} faces form by b u n c h i n g of steps and have the slowest growth rate. This result reveals that it would be possible to accelerate the growth rate on the seed by a proper selection of the seed morphology s u c h as {1150}.
Synthetic calcite single crystals
Fig. 23.
359
Calcite single crystals (a) Spherical seed crystals; (b) Grown calcite layer on the seed at 4000C and 100 MPa for 14 days
NH4NO 3 solution shows a higher solubility for calcite t h a n others. The concentration of NH+NOs solution in the growth experiment was selected in the range of 0 . 0 0 5 m - 0.02m to avoid a heterogeneous nucleation. Growth of calcite single crystals was carried out first u n d e r a large t e m p e r a t u r e gradient condition of a b o u t 20°C without a baffle plate. The results are s u m m a r i z e d in Table 5. Calcite crystals grew on the {1011] plane of the seed crystal while holding its orientation, on which m a n y m a c r o s t e p s were observed as s h o w n in Fig. 24. The surface of the {0001] seed crystal was completely covered with (1011} steps. The r and e faces of calcite are recognized to be inherently stable F (fiat) planes. Thus, it is k n o w n t h a t the growth rate is lowered on developing the {1011] face. F u r t h e r i m p r o v e m e n t s could be achieved by using a baffle plate a n d b a n d heaters to control the t e m p e r a t u r e gradient and the t r a n s p o r t behavior. In this case, the t h e r m a l gradient was lowered to 10°C to s u p p r e s s the strong convection. Figures 25a and 25b illustrate the highly t r a n s p a r e n t growth on the {1011} seed crystals. The thickness of the grown crystals u n d e r these conditions increased to a b o u t 0.01 m m / d a y . Seed crystal of {0001] faces tended to be covered with steps b y the grown {10T1} faces. No corrosion of Ti liner was detected during the growth run.
360
S. Hirano et al.
Table 5
No.
Results of h y d r o t h e r m a l growth of single crystals in NH4NO 3 solution
Experimental conditions
Seed
Thickness (mm) Before
Seed surface
After
Without baffle plate 1
(10T1)
0.02m, 100 MPa, 170°C AT=20°C, 10 days
1.745
2.798 (+ 1.053)
2
(0001)
0.02m, 100 MPa, 170°C AT=20°C, 10 days
2.901
3
(10-11)
0.005m, 100 MPa, 200°C 10 days
2.331
2.600 (+0.269)
Rough
--
Rough
Rough
With baffle plate 4
(10~1)
0.01m, 50 MPa, 170°C AT=10°C, 30 days
0.883
1.155 (+0.272)
Flat
5
(1011)
0.02m, 50 MPa, 200°C AT=10°C, 20 days
1.442
1.852 (+0.410)
Flat
Fig. 24.
Calcite single crystal after the growth experiment (AT=20°C)
Synthetic calcite single crystals
Fig. 25.
3.2
361
Calcite single crystal grown in NH4NO 3 solution by using baffle plate (AT=10°C)
Characterization of ~rown calcite single crystals
Qualities of grown single crystals were analyzed in terms of dislocation density, infra-red absorption. Etch pits were observed on crystals chemically etched with 20% NH¢CI solution. The etch pits exhibit the crystallographic symmetry of calcite. Dislocation density reflects the grade of optical transparency. Single crystals grown in NaCl solution showed the dislocation density of around 106 c m -2, while crystals grown in nitrate solutions had the dislocation density of the order of 104 c m -2 which is the same order of high quality of natural single crystals. In general, it has been considered that the up-take of OH- be disadvantageous in hydrothermal crystal growth, causing the optical absorption of the crystals especially in the infra-red region. Infra-red spectra of the single crystals grown in NaNO 3 solution showed that they were identical to highly perfect natural calcite crystals with a stretching vibration a r o u n d 3500 cm -I, due to trace OH- {Fig. 26). The up-take of OH" in these hydrothermally grown crystals is not considered to be serious, compared with high quality natural calcite single crystals which are useful for optical devices, The comparisons of the infra-red absorption of the grown crystals are illustrated in Fig. 27. A low quality natural calcite (a) shows the strong absorption at 2400 cm -I assigned to I-ICO 3- impurity. The IR spectra of single crystals grown i n Ca(NO3) 2 (c) and in NH4NO3(d) are completely identical to those of high quality natural crystals (b). The OH- absorption shows a comparable trace uptake of O H between the grown crystals and the high quality natural Iceland spar crystal. The absorption due to NO 3- alSO cannot be detected in these spectra.
362
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(a)
¢J
¢.¢0 t. I-I
3 0' 2 'o Wavenumber
Fig. 26,
15' 1'o /xlO2cm-~l
'
IR spectra of calcite single crystals: (a) hydrothermally grown crystal in NaNO 3 solution; (b) natural Iceland spar crystal
I
I
3200
Fig. 27.
2400 Wavenumber
,
1600 cm-1
800
FT-IR spectra of calcite single crystal: (a) natural single crystal (low quality); (b) natural single crystal (high quality); (c) artificial single crystal grown in Ca(NO3)2; (d} artificial single crystal grown in NH4NO 3 solution.
Synthetic calcite single crystals
363
4. CONCLUSIONS NaCI a n d nitrate solutions are found to be more effective solvent for calcite growth. The results in NaCl solution indicate that the natural calcite crystals h a d been grown by the h y d r o t h e r m a l condition as in n a t u r a l quartz crystals. Plate-like single crystals, b o u n d e d by {0001] faces, could be prepared at elevated t e m p e r a t u r e s above 500°C, which indicates good agreement with the mineralogical a p p e a r a n c e of n a t u r a l Iceland spar. Ca(NO3) 2 and NI-14NO3 solutions are the m o s t effective solvent a m o n g various solvents. Considering the changes in pH of solutions and IR spectra before and after the growth run, the solvent action might originate from the interaction between Ca 2+ and NOa. Highly perfect calcite single crystals can be hydrothermally grown in newly discovered NH4NO 3 solution even at 150°C. The results of this work suggest t h a t NH4NO a solvent can offer operative conditions to synthesize calcite single crystals at t e m p e r a t u r e s below 200°C in industrial scale. Some inorganic salts and organic compound act as a n inhibitor to the crystallization of calcite and m u s t be removed from the nutrient and hydrothermal solvents. Calcite crystals dissolved into the NH4NO 3 hydrothermal solution a c c o m p a n i e d b y the evolution of ammonia. This reaction increases the dissolution of calcite in the h y d r o t h e r m a l solution, which gives a n advantage of lowering both the growth t e m p e r a t u r e and pressure conditions in NH4NO3 solution. This moderate growth condition allows us to employ a Teflon liner for the pure a t m o s p h e r e to grow the optical grade of calcite single crystals. The quality of grown single crystals is identical to the high optical grade of natural Iceland s p a r crystals in t e r m s of dislocation density and optical absorption. HCO 3" and NO a- ions in the crystals cannot be detected as impurities with a comparable trace u p t a k e of O H in the grown crystals.
5. REFERENCES I. 2. 3. 4. 5. 6. 7. 8. 9. 10, 11. 12. 13. 14.
L.G.Berry and B.Mason, Mineralogy, Freeman, San Francisco (1959), W.Eitel and W.Skalisks, Z. anorg, allgerru Chem., 183, 268 (1929). J.F.Nester and J.B.Schroeder, Am. Mineral., 52, 276 (1967). J . J . B r i s s o t and C.Belin. J. Cryst. Growth, 8, 213 (1971). C.Berlin. J . j , B r i s s o t and R.E.Jesse, J. Cryst. Growth, 13/14. 597 (1972). J.F.Balascio and W.B.White, J. Cryst, Growth, 23, I01 (1974). C.Belin, J. Cryst. Growth, 34, 341 (1976). N.Yu.Ikornikova, Soviet Phys. Cryst., 5. 726 (1961]. N.Yu.lkornikova, Growth of Crystals, 3, 297 (1962). J.F.Balascio and W.B.White, Mat. Res. Bull., 7, 1461 (1972). D.R.Kinloch, R.F.Belt and R.C.Puttbach, J. Cryst. Growth, 2 4 / 2 5 , 610 (1974). M.Higuchi, A.Takeuchi and K.Kodaira, J. Cryst. Growth, 92. 341 (1988). S.Hirano and K.Kikuta, J. Cryst. Growth, 79, 223 (1986). S.Hirano a n d K.Kikuta, J. Cryst, Growth, 94, 351 (1989).
S. Hirano et at
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K.Kikuta and S.Hirano, J. Cryst. Growth, 99, 895 (1990). S.Hirano and K.Kikuta, Chem. Lett., 1985, 1613 (1985). S.Hirano and K.Kikuta, Bull. Chem. Soc. Japan, 60, 1109 (1987]. C.F.Bell and K.A.K.Lott, Modem Approach to Inorganic Chemistry, Butterworth (1972). 19. I.Sunagawa, N.Morimoto and A.Miyashiro, Kobutsugaku, lwanami-shoten, (1975). 15. 16. 17. 18.
Acknowledgement This work was supported by the Asahi Glass Foundation for Industrial Technology,
Synthetic calcite single crystals
Dr. Shin-ichi Hirano Shin-ichi Hirano is Professor in the Dept. of Applied Chemistry, School of Engineering, Nagoya University, Nagoya 464, Japan. He earned his B.S. in 1965, M.S. in 1967, and Dr. of Eng. in 1970, all in applied chemistry from Nagoya University. Hirano was with Tokyo Institute of Technology as a research associate during 1970-76 and as an associate professor during 1976-78.
He also joined with the Penn. State Univ. from
1971-72. He was appointed to an associate professor at Nagoya Univ. in 1978 and was named full professor in 1983. He has been contributing to chemical processing and characterization of advanced ceramics. He was presented the Tokai Chemical Engineering Society Award in 1980, the Academic Award of the J a p a n Society of Powder and Powder Metallurgy in 1984, the Academic Award of the Ceramic Society of J a p a n in 1986, and the Academic Award of the Chemical Society of J a p a n in 1989.
In 1986 he was a recipient of the Richard M. Fulrath Award and a
Fellow of the American Ceramic Society from 1989.
365
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Dr. Toshinobu Yogo Toshinobu Yogo is an Associate Professor in the Dept. of Applied Chemistry, School of Engineering, Nagoya University. He earned his B.E. in 1974, M.E. in 1976 in synthetic chemistry from Nagoya University, and Dr. of Eng. in 1980 in applied chemistry from Hokkaido University.
Yogo worked for Nagoya Univ. as a research associate
during 1980-90 and as an associate professor from 1990. He also joined with the Univ. Washington from 1986-87. His
contribution
characterization.
to
ceramics
science
is
chemical processing
and
He was presented the Academic Award of the Nagai Science
and Technology Foundation in 1986.
Dr. Ko-ichi Kikuta Ko-ichi Kikuta is a Research Associate in the Dept. of Applied Chemistry, School of Engineering, Nagoya University. He earned his B.E. in 1984, M.E. in 1986, and Dr. of Eng. in 1989, all in applied chemistry from Nagoya University.
Kikuta has been with Nagoya
Univ. from 1989. He has been contributing to crystal growth, and chemical processing and
Synthetic calcite single crystals
characterization of advanced ceramics.
He was a recipient of the Academic
Award of the Nagai Science and Technology Foundation in 1989.
Communication should be sent to S. Hirano, Department of Applied Chemistry, School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-01, Japan.
367
0146-3535/91 $0.OO+ .50 © 1992 PergamonPress Ltd
SYNTHETIC CALCITE SINGLE CRYSTALS FOR OPTICAL DEVICE S. Hirano, T. Yogo and K. Kikuta Department of Applied Chemistry, School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-01, Japan
1. INTRODUCTION Calcite is one of the c o m m o n minerals in nature and its t r a n s p a r e n t crystals are k n o w n as Iceland spar. Recently the d e m a n d for calcite and rutile single crystals with a large birefringence h a s been increasing b e c a u s e of application for polarized optical devices. The synthesis of calcite single crystals h a s received the great attraction with the development of the laser devices s u c h as a n optical isolator, since n a t u r a l resources have b e e n depleted. Calcite occurs in n a t u r e as minerals with a chief constituent of all kinds of limestone and marble as well as alternated veins and ore deposits. High quality natural calcite crystals have been considered to be grown hydrothermally and occurred mainly in Mexico and Brazil (1). The synthesis of calcite single crystals with optical grade h a s b e e n required for the optical applications, since no high quality n a t u r a l calcite crystals have occurred in J a p a n . Calcite dissociates at a b o u t 900°C u n d e r a t m o s p h e r i c p r e s s u r e and fuses at 1290°C u n d e r a p r e s s u r e of 170 b a r s of C02. Many a t t e m p t s have been made to grow calcite single crystals. Much work concerning the artificial growth of calcite h a s b e e n done using the high t e m p e r a t u r e flux method. Czochralski and travelling solvent zone melting m e t h o d s produce a calcite boule from a CaCO 3Li2CO ~ melt at 700-800°C by consulting with the p h a s e diagram of the CaCO 3Li2CO 3 s y s t e m as shown in Fig. 1 (2). The top seeded solution growth (TSSG) and the traveling solvent zone melting (TSZM) are the m e t h o d s to be employed for the crystal growth (3-7). These methods, however, include some difficulties in producing a high quality single crystal of calcite owing to large thermal stress, CO 2 dissociation, and alkaline c a r b o n a t e flux inclusions causing serious defects and c o n t a m i n a t i o n s by metal ions. The h y d r o t h e r m a l method is one of the promising techniques for growing u n s t a b l e crystals s u c h as a carbonate compound, with the advantage of s u p p r e s s i n g the dissociation of CO 2 and yielding high quality crystals in a
341
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S. Hirano et at
h o m o g e n e o u s ambient at relatively low temperatures. This review describes mainly our recent results of the hydrothermal crystal growth and the characterization of the growth features of calcite single crystals with an emphasis on the proper selection of solvents.
1100 _ 18~7' 1000 Liquid ?
E
® I,-
/iii'0
900
800
700
Pco2= 5.3 xlO-3
+ Liquid
Li2CO3
.
.
20 .
/
1.1
CaCO3
~/664°C .
.
...... 6'o
40 WT
Fig. 1.
8.0
'
8'o
'
CaCO3
%
Phase diagram of CaCO3-Li2CO3 system
Optical Properties of Calcite
The space group of calcite belongs to R3C. The crystal exhibits the perfect {I0]'1} cleavage with extreme diversity of habit, being often rhombohedral in aspect. The optical property is characterized by the extremely strong birefringence, uniaxial character as shown in Table 1 compared with those of a-quartz and rutile. The CO 3 group is responsible for the birefringence in the structure, where the CO 3 groups are perpendicular to the threefold axis of calcite. This optical character has been utilized as optical prisms and isolators.
Table I
Optical Properties of Crystals no
ne
n
Transmission wave region (pm)
Calcite (CaCO 3)
1.65836
1.48641
- 0.17195
0.20 - 5.5
Quartz
{SiO2}
1.54425
1.55336
+ 0.00911
0.16 - 4.0
Rutile
(TiO2)
2.6124
2.8893
+ 0.2869
0.43 - 6.2
Synthetic calcite single crystals
343
In a birefringent crystal like a calcite, light waves travel through the crystal with different velocities depending on the vibration plane of electric vector relative to the crystallographic axis. The unpolarized incident light separates into two rays, the ordinary (o) ray and the extraordinary (e) ray. Nicol prism is designed using a polished calcite crystal with a Canada balsam (nb;refractive index) as shown in Fig. 2. As the order of the refractive index is no>nb>n e, only a n ordinal ray does reflect completely at the interface between calcite and Canada balsam crystals.
Optic \
axis
\ \A
C
'
1
J ,,~=
', :
', : ~ E
B/ 0
68 °
Fig. 2.
Nicol prism using Canada balsam
Calcite crystal is superior to others in order to produce linearly polarized ray, which is of importance for the design of an optical isolator providing the stabilized laser light. A simple set-up of the optical isolator is shown in Fig. 3. An incident laser light passes through a polarizer to be a linearly polarized ray, which then proceeds to a magneto-optic YIG crystal. The traveling ray rotated by 45 ° in the crystal transmits to an analyzer. If the traveling ray be reflected in a n optical fiber or at junctions, the reflected light travels back to the YIG crystal and is cut by the polarizer to isolate from the incident light. The crystals in the system are required to be highly perfect without absorptions or scattering.
Lens
LD
~
-
~
"\
" Reflected
I
Polarizer
YIG
Fig. 3. Alignment of optical isolator
light
Analyzer
344
S. Hirano et al.
1.2
Hydrothermal Synthesis
Many natural crystals are considered to be grown from m a g m a reacted or altered with mineralizers u p o n crystallizing. Water is the most c o m m o n and important mineralizer in n a t u r e and should also be considered to be a low-melting point or volatile constituent in a system, in that it can lower the liquidus temperature of a compound. In this sense, the term "hydrothermal" is appropriate in the category of "hlgh-temperature and pressure solutions." All hydrothermal crystal growth are carried out in the presence of active water or in solution above 100°C in a pressure vessel. Thus, a suitable combination of solution (solvent), pressure and temperature m u s t be discovered where calcite is thermodynamically stable and has sufficient solubility to give a reasonable supersaturation, leading to the proper convection circulation with temperature gradient along a pressure vessel. Hydrothermal growth of calcite single crystals has been studied by employing chloride, hydroxide and carbonate solvents. Ikornikova firstly investigated NaCl and other chloride solutions, but did not mention the details of crystal growth and the quality of the grown calcite crystals (8, 9). Balascio et al. and Kinloch et al. reported that K2CO 3 solution was an effective solvent to grow calcite crystals on a cleaved seed (10, 11). In order to protect the pressure vessel from corrosion by alkali solvent above 400°C, silver was used as a liner. Recently carbonic acid solvent was employed for the growth of calcite u n d e r elevated pressures by Higuchi et al. (12). The a u t h o r s discovered that nitrate solutions were the new effective solvent for the growth of calcite single crystals (13-15). It was confirmed that nitrate solvents are more effective t h a n chloride solvents from the viewpoint of solubilities of calcite (16, 17). Both carbonate and nitrate ions possess a similar structure containing triangular arrangement of atoms, which might lead to the advantage for calcite growth avoiding the contamination of alkali metal inclusions and allowing low-temperature growth conditions. Rhombohedral calcite crystals spontaneously grew in NH4NO 3 solvent even at 150°C. The following is the detail of the growth and dissolution behavior of calcite single crystal in hydrothermal solutions.
2. SOLUBILITY AND DISSOLUTION BEHAVIOR IN HYDROTHERMAL SOLUTIONS 2. i Selection of solvent The selection and comparison of the hydrothermal solvents were made on the basis of the stability and morphology of the calcite crystals. Experiments were carried out at c o n s t a n t conditions of 500°C (200°C only in NH4NO 3) and 100 MPa for 3 days with reagent grade powder of calcite. The results are shown in Table 2. Xray diffraction analysis of the crystals grown in these solutions indicated that calcite did not change to any other phase or c o m p o u n d except when the solution contained 3m Na2CO 3 (m, molality). In this case, the calcite changed to an u n k n o w n c o m p o u n d which was neither pirssonite nor gaylussite. This might be attributable to the high carbonate ion concentration and the close ionic radius of Na + to Ca 2÷.
Synthetic calcite single crystals Table 2
345
Results of hydrothermal treatment of calcite in several solutions
Solution
Crystal form
XRD
3m
NaCl
Polyhedral
Calcite
2m
KCI
Polyhedral
Calcite
3m
NaOH
Dendritic
Calcite
2m
KOH
Dendritic
Calcite
3m
Na2CO 3
3m
NaNO 3
Polyhedral
Calcite
2m
KNO 3
Polyhedral
Calcite
1.5m Ca(NO3) 2
Polyhedral
Calcite
3m
Polyhedral
Calcite
NH4NO 3 *
500°C, I 0 0 MPa, 3 days
---
Unknown c o m p o u n d
°200°C, 100 MPa, 3 days
Dendric crystals were grown in NaOH and KOH solutions, It was very difficult to grow the bulk crystals bounded by fiat surfaces i n these alkali hydroxide solutions. These hydroxide solutions are strong basic solvent and corrosive to the pressure vessel as is the same in K2CO 3 solutions. These results in Table 2 indicate that the anion group in the salt solution is a more dominant factor t h a n is the type of cation in the solvent used for the growth of calcite single crystals. It h a s been confirmed that both alkali chloride and nitrite solutions were useful for growing calcite crystals as the single phase.
2.2 Solubility The solubility of calcite in the solution was determined by the weight loss method. Both reagent grade calcite powder or highly pure natural single crystals were sealed with solution in a gold capsule as the specimen container, which then placed in the pressure vessel. Solubility r u n s were maintained, u n d e r each condition, for 3 days, which had been confirmed previously to be long enough to bring the system to equilibrium. Following a run, the pressure vessel was quenched with cold water. A stainless steel filler rod was also placed in the space above the capsule so as to reduce convection and to achieve thermal uniformity of the capsule.
346
S. Hiranoet al.
s,sO
soo i
4so/oc i
3.0
T
~
2.0
o~ o -0.5
1.0
-1.0
o 3;0 4~o 4~o 5~o s~o
I
I
I.
1.2
1.3
14
T-~/10-3K-1
Temperature/°C
Fig. 4. S o l u b i l i t y of CaCO 3 i n 3 m NaCI s o l u t i o n a s a f u n c t i o n of t e m p e r a t u r e a t 100 MPa
Fig. 5. Log S (solubility) of CaCO 3 a s a f u n c t i o n of 1 / T i n 3 m NaCI
5.0 IOOMPa 4-01
500
I
i
r~! /
450
400
350 (°C)
0.5
I
/
3m NAN03/ T
0
~3.0
u') r-
-I
~2.0 . "C]../,.[~'~m
NaCI
-0.5
1.0
3~0 450 4~0 s~o s~o Temperature, °C
Fig. 6. S o l u b i l i t y of CaCO 3 i n 3 m NaNO 3 s o l u t i o n a s a f u n c t i o n of t e m p e r a t u r e a t 100 MPa
1.3
1.4
1.5 1.6 1/T (xlO -3 K -1)
Fig. 7. Log S (solubility) of CaCO 3 a s a f u n c t i o n of 1 / T i n 3 m NaNO 3
347
Synthetic calcite single crystals
Figure 4 shows the solubility in the 3m NaCl solution as a function of the temperature at 100 MPa. The solubility increased remarkably with increasing temperature above 400°C and amounted to 2.0 g/1 at 500°C. The solubility value is acceptable practically for the hydrothermal growth above 400°C. Figure 5 shows a plot of log S (Solubility) vs. 1/T in order to confirm the van't Hoff relation. The enthalpy of the solution, AH, was calculated to be about 46 k J / m o l , m u c h larger t h a n tLH°=-12kJ/mol in CaCO3-H20 system u n d e r ordinary condition (18). This fact indicates that the state of dissolved species u n d e r hydrothermal conditions is quite different from that u n d e r ordinary conditions at atmospheric pressure. The solubility of calcite in 3m NaNO 3 is given in Fig. 6, being compared with that in 3m NaCl. The solubility in 3m NaNO3 increased abruptly with increasing temperature and it amounted to 2.2 g/l a t 450°(3. This solubility is acceptable for the growth of calcite single crystal b y the hydrothermal technique. Since the value of the solubility in 3m NaNO 3 is about twice that for 3m NaCl, NaNO 3 solutions were Judged to be suitable for the growth at lower temperatures. Figure 7 shows the plot of the log S (solubility) versus 1/T. The data reveal that the van't Hoff law is not obeyed in this system. This fact suggests that the state of the dissolved species m a y change with increasing temperature.
4.0
100MPa
//~ //
/ii II ~iiiil/l/
3.0 7 O~
2.o O
(/)
~:~
/
b
1.0
0
i
350
Fig. 8.
|
I
400 450 Temperature ,
!
500 °C
Solubility of CaCO 3 in 1.5m Ca(NO3) 2 and 3m NaCl soluUons as a funcUon of temperature;(a) in 1.5m Ca(NO3) 2 solution;(b) in 3m NaCl solution
348
S. Hirano et al.
T T~
~5.0 ..Q
"5 oo
0
I
i
I
I
140
160
180
200
Temperature, Fig. 9.
°C
S o l u b i l i t y of c a l c i t e in 3 m NH4NO 3 s o l u t i o n a s a f u n c t i o n of t e m p e r a t u r e
T h e s o l u b i l i t y of c a l c i t e in 1 . 5 m Ca(NO3) 2 a n d 3 m NH4NO 3 s o l u t i o n s a r e s h o w n in Figs. 8 a n d 9. T h e c o n c e n t r a t i o n of s o l u t i o n s is a d j u s t e d to t h e s a m e a n i o n c o n c e n t r a t i o n a s NO3-. T h e s o l u b i l i t y in 1.5m Ca(NO3) 2 s o l u t i o n i n c r e a s e d w i t h i n c r e a s i n g t e m p e r a t u r e a n d t h e s o l u b i l i t y is a b o u t twice a s m u c h a s t h a t for 3 m NaC1 in t h i s t e m p e r a t u r e r a n g e . T h e r e s u l t s i n d i c a t e t h a t Ca(NO3} 2 is m o r e effective t h a n t h e NaCl or KC1 s o l u t i o n s . T h e s o l u b i l i t y c u r v e of c a l c i t e in 3 m NH4NO 3 a t 100 M P a ( F i 9) s h o w s t h a t NH4NO 3 s o l u t i o n is t h e m o s t effective s o l v e n t e v e n a t t e m p e r a t u r e s b e l o w 200°C. T h e s o l u b i l i t y a t 200°C is 8.1 g / l . T h i s s o l u t i o n , h o w e v e r , c a n n o t serve a s a s o l v e n t a t t e m p e r a t u r e s a b o v e 300°C, d u e to t h e i n s t a b i l i t y of NH4NO 3. A r r h e n i u s p l o t s w e r e m a d e from t h e s o l u b i l i t y m e a s u r e m e n t s , a s s h o w n in Fig, 10 a n d 1 1. It is c l e a r l y c o n f i r m e d t h a t t h e v a n ' t Hoff r e l a t i o n h o l d s in all t h e s e s y s t e m . T a b l e 3 s u m m a r i z e s t h e e n t h a l p y of d i s s o l u t i o n c a l c u l a t e d f r o m Figs. 5, 10 a n d 11. T h e e n t h a l p y v a l u e in NH4NO 3, w h i c h is s m a l l e r t h a n t h o s e in t h e o t h e r s o l u t i o n s , s u g g e s t s t h a t t h e c h e m i c a l s p e c i e s d i s s o l v e d in NH4NO 3 s o l u t i o n had a stronger chemical bonding,
Synthetic calcite single crystals
1.0 a
U~ 0
\\Xx\ k\\ b,\
\ \ \
\
\ \ \ \
-1.0 I
1.2
I
I
/
1.3
1.4
1.5
1/T ,
Fig. 10.
10-3 K ' I
Log S {solubility) of CaCO 3 and a function of l / T ; (a) 1 . 5 m Ca{NOa) 2 ; (b) 3 m NaCl
-3.0
-3.5
¢]) e-
-
-4.0
-4.5
I
2.1
Fig. 11.
I
2.2 1/T ,
I
I
2.3 2.4 10"3K -1
Log S (solubility) of CaCO 3 and a function of 1 / T in 3 m NHcNO 3
349
350
S. Hirano et al.
Table 3
D i s s o l u t i o n e n t h a l p y of calcite Solvent 3m
1.5m 3m
Dissolution e n t h a l p y (AH} k J / m o l
NaCI
46
Ca(N03) 2
43
NH4NO 3
31
F i g u r e s 12 a n d 13 show the effect of c o n c e n t r a t i o n of the solvent on the solubility. In the case of Ca(NO3) 2 solvent, the solubility rises g r a d u a l l y u p to 3.5m a n d t h e n d e c r e a s e s slightly. The r e s u l t s s u g g e s t t h a t a Ca 2÷ c o n c e n t r a t i o n above 3.5m s u p p r e s s e d t h e f u r t h e r d i s s o l u t i o n of calcite. The solubility in NH4NO 3 solvent i n c r e a s e s with the concentration, a n d c o n t i n u e s to i n c r e a s e in this c o n c e n t r a t i o n range. The r e s u l t s indicate t h a t a r a t h e r dilute NH4NO 3 solution is a d e q u a t e to a d j u s t the s u p e r s a t u r a t i o n for the growth of calcite crystals.
2.0
T
e~
¢~1.0
/
/
1 O0 MPa
400 °C I
0
Fig. 12.
1
!
I
I
1 2 3 4 5 C o n c e n t r a t i o n of s o l v e n t ,
m
Solubility of CaCO 3 as a function of c o n c e n t r a t i o n of Ca(NO3) 2 solution at 400°C a n d I 0 0 MPa
Synthetic calcite single crystals
351
10
o)
~5 .o o
100 MPa 2 0 0 °C I
I
I
0 1 2 3 Concentration of solvent, m
Fig. 13.
2.3
Solubility of CaCO a as a function of concentration of NH4NO 3 solution at 200°C and 100 MPa
Dissolution behavior in nitrate solutions
The pH values of calcium nitrate were measured as a function of temperature. Figure 14 shows the changes of the pH curves in 1.5m Ca(NO3) 2 solvent with and without calcite crystals in the hydrothermal system. The pH value increased gradually with increasing temperature and a significant difference is found between these two curves, which reflects the dissolution behavior of calcite. It was already confirmed that the solubility of calcite started to increase at 300°C as mentioned above. These data indicate that calcite crystals can be recognized as a basic salt. In the case of a m m o n i u m nitrate solvent, however, the pH value of a pure solvent decreased abruptly with the increase in temperature as shown in Fig. 15. It t u r n s out from this fact that the decomposition of a m m o n i u m nitrate takes place to give nitrogen oxide and water, which turn the solution to be acidic. Calcite crystals dissolve in this acidic solution u n d e r these conditions to keep the pH value at a r o u n d 7.
352
S. Hirano et al.
100 MPa
1.5m Ca(NO3)2 +Calcite /
/ / ~
-
t"
~; 0
50
,
.
300
.
.
.
400
500
Temperature , Fig. 14.
°C
pH v a l u e s of 1 . 5 m Ca(NO3) 2 s o l v e n t a s a f u n c t i o n of t e m p e r a t u r e
1OO MPa
3mN
+Calcite
~5 \
\
\
\
3m NH4NO3
I
100
i
200 Temperature , °C
Fig. 15.
\ \\
\
\
\
\
I
300
pH v a l u e s of 3 m NH4NO 3 s o l v e n t as a f u n c t i o n of t e m p e r a t u r e
Table 4 s u m m a r i z e s the effects of h y d r o t h e r m a l s o l v e n t o n c r y s t a l l i z a t i o n of calcite. At 20(YC, calcite d o e s d i s s o l v e in the a m m o n i u m nitrate s o l v e n t w i t h a release of a m m o n i a . T h i s p h e n o m e n o n is quite s i m i l a r to t h e c a s e of t h e other a m m o n i u m
Synthetic calcitesingle crystals
353
solvents. A m m o n i u m sulfate and a m m o n i u m fluoride solutions react with calcite to form insoluble calcium salts, e.g. CaSO 4 and CaF 2, and ammonia. At elevated temperature, NH4NO3 is not effective as a hydrothermal solvent for the growth of calcite single crystal due to its decomposition.
Table 4
Effects of hydrothermal solvent on the crystallization of calcite
HT solvent
Temperature (°el
Effect of solvent
Remarks
0. i m NH4NO3
200
Good
Ammonia odor
0.02m NH4NO3
250
Slight
--
0.02m NH4NO3
300
No
--
Im
(NH4)2SO4
200
No
Ammonia odor, CaSO 4
Im
NH4F
200
No
Ammonia odor, CaF 2
lm
(NH4)2COS
200
No
Ammonia odor, powder nutrient
0. l m NH4NO 3 +0.00 lm(NH4)2HPO4
200
No
0. l m NH4NO3 +0.001 m(NH4)2SO 4
200
No
0. l m NH4NO3 +0.001 mNa2B407
200
No
0. l m NH4NO3 +0.003mEG
200
No
0. l m NH4NO 3 +0.1 mNaNO 3
200
No
FT-IR spectra of the solvent were analyzed with a ZnSe single crystal ATR cell. Figure 16 shows the FT-IR spectra before and after the experiment in NH4NO3 solution. In the solution before the growth run, the absorption at a r o u n d 3400 cm -l is observed, which is ascribed to stretching vibrations of NH4÷ and OH-, and at a r o u n d 1600 cm -I due to OH-. The remarkable difference in the spectra before and after the dissolution of CaCO 3 is the absorption assigned to HCO3"at around 2350 cm I . This absorption b a n d became considerably stronger after the dissolution of C a C O 3. These results suggest that calcite dissolves into the solvent below 200°C as follows;
354
S. Hirano et al.
CaCO3 + NH4NO3 + H 2 0
:c >
Ca2+ + HCO3- + NO3- + NH4+ + OH-,
C a C O 3 + 2NH4F + H 2 0
< "~
CaF24,
+ HCO 3" + 2NH4 + + O H ,
C a C O a + (NH4)2SO 4 + H 2 0 ~
CaSO4. ~, + H C O a- + 2NI--I4* + OH-,
C a C O a + (NH4)2CO 3 + 2 H 2 0 ~
C a 2+ + 2 H C O a- + 2NH4 ÷ + 2OH-.
/
H C O 3-
/
before
after
i
4000
i
Wavenumber,
Fig. 16.
i
.
3000
i
2000 c m -1
C h a n g e of FT-IR s p e c t r a of c a l c i t e b y t r e a t m e n t in NH4NO a (a)before t r e a t m e n t ; (b)after t r e a t m e n t .
(NH4)2CO 3 s o l u t i o n h a s n o effect a s a s o l v e n t for g r o w i n g c a l c i t e c r y s t a l s . The r e s u l t r e v e a l s t h a t t h e h i g h HCO 3- c o n c e n t r a t i o n d u e to a h y d r o l y s i s of (NH4)2CO 3 c a n s u p p r e s s t h e f u r t h e r d i s s o l u t i o n of c a l c i t e in t h e h i g h p r e s s u r e s y s t e m . In f l u o r i d e a n d s u l f a t e s o l u t i o n s , l e s s - s o l u b l e s a l t s of C a F 2 a n d C a S O 4 f o r m s to p r o c e e d t h e r e a c t i o n s , a n d p r o d u c e a m m o n i a w h i c h is c o n f i r m e d b y odor. It w a s a l s o c o n f i r m e d t h a t a s m a l l a m o u n t of a d d i t i v e s s u c h a s p h o s p h a t e , s u l f a t e , b o r a t e a n d e t h y l e n e glycol effectively a r r e s t e d t h e g r o w t h of c a l c i t e s i n g l e c r y s t a l s a s s h o w n i n T a b l e 4. A m o n g t h e s e a d d i t i v e s , s u l p h a t e i o n m a y o f t e n c o e x i s t a s a c o m m o n t r a c e i m p u r i t y in t h e c h e m i c a l r e a g e n t . T h e r e s u l t s c l e a r l y e x h i b i t t h a t t h e s e i m p u r i t i e s m u s t b e r e m o v e d c a r e f u l l y f r o m a h y d r o t h e r m a l solvent.
Synthetic calcite single crystals
355
3. HYDROTHERMAL GROWTH 3.1
Morpholo&W of grown calcite single crystals
Some growth experiments were carried out with highly pure Iceland spar as the starting material to s t u d y the morphological change. Calcite single crystals of sizes u p to 1.0 m m were grown spontaneously on the inner wall of the capsule. There were two kinds of crystal habits in NaCl solution. The morphologies of grown crystals were found to be strongly influenced by the growth temperature. Platelike calcite crystals bounded by well developed {0001] faces could form mainly at elevated temperatures above 500°C. Associated with the crystals (Fig. 17a), a few polyhedral crystals were grown as shown in Fig. 17b. The variation of crystal habits showed a good agreement with the occurrence in nature. Sunagawa et al. showed that the plate-like {0001] calcite crystal might occur at elevated temperatures in the first stage of the precipitation of Iceland spar (19). Euhedral crystals bounded by [10~1] faces were also prepared at 450°C and I00 MPa (Fig. 18). This fact suggests that the Iceland spar in nature might occur in a hydrothermal solution at a relatively lower temperature. In Ca(NOaJ 2 solution, spontaneously grown crystals usually showed a rhombohedral form bounded by {10TI] faces. Figure 19 shows a photomicrograph of calcite crystals prepared in 3m NH4NO 3 at 200°C, ~T=I2°C and 100 MPa for 10 days. These opaque crystals were large in size, b u t showed a lot of growth steps on surfaces. As mentioned above, the supersaturation u n d e r this condition is too high to grow a high quality t r a n s p a r e n t calcite single crystals, indicating that the concentration of the solvent m u s t be lowered below lm.
Fig. 17.
Calcite single crystals grown in 3m NaCl solution at 500°C and I00 MPa for 10 days : (a) Plate-like crystals; (b) Polyhedral crystals
356
S. Hirano et aL
Fig. 18.
Calcite single crystals grown in 3m NaC1 solution at 450°C a n d 100 MPa for 10 days
Fig. 19.
Calcite single crystals grown in 3m NH4NO 3 solution at 200°C and 100 MPa for 10 days
Synthetic calcite single crystals
357
Euhedral crystals shown in Fig. 20 could be actually grown in a 0.1 m NH4NO3 solution u n d e r the s a m e conditions. Natural calcite crystals occur in various forms, while the crystals grown in NH4NO 3 solution below 200°C are b o u n d e d by {i011} faces b u t not by the other faces s u c h as {0001] in this experiment.
Fig. 20.
Calcite single crystals grown in 0.1m NH4NO3 solution at 200°C and 100 MPa for 10 days
Fig. 21.
Calcite single crystals grown in quartz glass capsule from NH4NO3 solution (a) 0.5m. 150°C. 1 week; (b) 0.5m, 120°C. 1 week; (c) 3m, 100°C, 1 week.
S. Hirano et al.
35B
Nutrient calcite and NH4NO 3 solvent were also sealed in quartz glass capsules so as to investigate the growth feature. After a run, the capsule could be directly examined by the naked eye (Figs. 21a-21c). Calcite single crystals had been grown on the inner wall of the capsules even at temperatures as low as 120°C. The pressure inside the capsule in this r u n was estimated to be a few MPa. These conditions were advantageous to avoid the contamination due to corrosion of the pressure vessel and to reduce the cost of crystal growth. It is necessary to grow a single crystal on a seed for the industrial scale production. A Grayloc type-hydrothermal a p p a r a t u s was used with Ti liner set inside the pressure vessel to avoid the contamination from vessel materials (Fig. 22). Both spherical and rhombohedral seeds were s u s p e n d e d in the u p p e r portion of the vessel.
II
I
Ti
i
--/
Seed
j z~T
sheath
//
Baffle plate Nutrient
"l
f i
Fig. 22.
Grayloc type hydrothermal a p p a r a t u s with Ti liner and baffle plates
In 3m NaC1 solution at 400°C and 100 MPa, the thickness of the rhombohedral seed increased by 0.087 m m while keeping for 2 weeks. On the other hand, spherical seeds were observed to be completely covered with fiat s m o o t h surfaces and the steps of a grown calcite crystal (Fig. 23). The fiat plane is identified to be {101-1} faces, axial s y m m e t r y perpendicular to which symmetry is confirmed to be two fold by back-reflection Laue photographs. The {10]-1} faces form by b u n c h i n g of steps and have the slowest growth rate. This result reveals that it would be possible to accelerate the growth rate on the seed by a proper selection of the seed morphology s u c h as {1150}.
Synthetic calcite single crystals
Fig. 23.
359
Calcite single crystals (a) Spherical seed crystals; (b) Grown calcite layer on the seed at 4000C and 100 MPa for 14 days
NH4NO 3 solution shows a higher solubility for calcite t h a n others. The concentration of NH+NOs solution in the growth experiment was selected in the range of 0 . 0 0 5 m - 0.02m to avoid a heterogeneous nucleation. Growth of calcite single crystals was carried out first u n d e r a large t e m p e r a t u r e gradient condition of a b o u t 20°C without a baffle plate. The results are s u m m a r i z e d in Table 5. Calcite crystals grew on the {1011] plane of the seed crystal while holding its orientation, on which m a n y m a c r o s t e p s were observed as s h o w n in Fig. 24. The surface of the {0001] seed crystal was completely covered with (1011} steps. The r and e faces of calcite are recognized to be inherently stable F (fiat) planes. Thus, it is k n o w n t h a t the growth rate is lowered on developing the {1011] face. F u r t h e r i m p r o v e m e n t s could be achieved by using a baffle plate a n d b a n d heaters to control the t e m p e r a t u r e gradient and the t r a n s p o r t behavior. In this case, the t h e r m a l gradient was lowered to 10°C to s u p p r e s s the strong convection. Figures 25a and 25b illustrate the highly t r a n s p a r e n t growth on the {1011} seed crystals. The thickness of the grown crystals u n d e r these conditions increased to a b o u t 0.01 m m / d a y . Seed crystal of {0001] faces tended to be covered with steps b y the grown {10T1} faces. No corrosion of Ti liner was detected during the growth run.
360
S. Hirano et al.
Table 5
No.
Results of h y d r o t h e r m a l growth of single crystals in NH4NO 3 solution
Experimental conditions
Seed
Thickness (mm) Before
Seed surface
After
Without baffle plate 1
(10T1)
0.02m, 100 MPa, 170°C AT=20°C, 10 days
1.745
2.798 (+ 1.053)
2
(0001)
0.02m, 100 MPa, 170°C AT=20°C, 10 days
2.901
3
(10-11)
0.005m, 100 MPa, 200°C 10 days
2.331
2.600 (+0.269)
Rough
--
Rough
Rough
With baffle plate 4
(10~1)
0.01m, 50 MPa, 170°C AT=10°C, 30 days
0.883
1.155 (+0.272)
Flat
5
(1011)
0.02m, 50 MPa, 200°C AT=10°C, 20 days
1.442
1.852 (+0.410)
Flat
Fig. 24.
Calcite single crystal after the growth experiment (AT=20°C)
Synthetic calcite single crystals
Fig. 25.
3.2
361
Calcite single crystal grown in NH4NO 3 solution by using baffle plate (AT=10°C)
Characterization of ~rown calcite single crystals
Qualities of grown single crystals were analyzed in terms of dislocation density, infra-red absorption. Etch pits were observed on crystals chemically etched with 20% NH¢CI solution. The etch pits exhibit the crystallographic symmetry of calcite. Dislocation density reflects the grade of optical transparency. Single crystals grown in NaCl solution showed the dislocation density of around 106 c m -2, while crystals grown in nitrate solutions had the dislocation density of the order of 104 c m -2 which is the same order of high quality of natural single crystals. In general, it has been considered that the up-take of OH- be disadvantageous in hydrothermal crystal growth, causing the optical absorption of the crystals especially in the infra-red region. Infra-red spectra of the single crystals grown in NaNO 3 solution showed that they were identical to highly perfect natural calcite crystals with a stretching vibration a r o u n d 3500 cm -I, due to trace OH- {Fig. 26). The up-take of OH" in these hydrothermally grown crystals is not considered to be serious, compared with high quality natural calcite single crystals which are useful for optical devices, The comparisons of the infra-red absorption of the grown crystals are illustrated in Fig. 27. A low quality natural calcite (a) shows the strong absorption at 2400 cm -I assigned to I-ICO 3- impurity. The IR spectra of single crystals grown i n Ca(NO3) 2 (c) and in NH4NO3(d) are completely identical to those of high quality natural crystals (b). The OH- absorption shows a comparable trace uptake of O H between the grown crystals and the high quality natural Iceland spar crystal. The absorption due to NO 3- alSO cannot be detected in these spectra.
362
S. Hirano et al.
(a)
¢J
¢.¢0 t. I-I
3 0' 2 'o Wavenumber
Fig. 26,
15' 1'o /xlO2cm-~l
'
IR spectra of calcite single crystals: (a) hydrothermally grown crystal in NaNO 3 solution; (b) natural Iceland spar crystal
I
I
3200
Fig. 27.
2400 Wavenumber
,
1600 cm-1
800
FT-IR spectra of calcite single crystal: (a) natural single crystal (low quality); (b) natural single crystal (high quality); (c) artificial single crystal grown in Ca(NO3)2; (d} artificial single crystal grown in NH4NO 3 solution.
Synthetic calcite single crystals
363
4. CONCLUSIONS NaCI a n d nitrate solutions are found to be more effective solvent for calcite growth. The results in NaCl solution indicate that the natural calcite crystals h a d been grown by the h y d r o t h e r m a l condition as in n a t u r a l quartz crystals. Plate-like single crystals, b o u n d e d by {0001] faces, could be prepared at elevated t e m p e r a t u r e s above 500°C, which indicates good agreement with the mineralogical a p p e a r a n c e of n a t u r a l Iceland spar. Ca(NO3) 2 and NI-14NO3 solutions are the m o s t effective solvent a m o n g various solvents. Considering the changes in pH of solutions and IR spectra before and after the growth run, the solvent action might originate from the interaction between Ca 2+ and NOa. Highly perfect calcite single crystals can be hydrothermally grown in newly discovered NH4NO 3 solution even at 150°C. The results of this work suggest t h a t NH4NO a solvent can offer operative conditions to synthesize calcite single crystals at t e m p e r a t u r e s below 200°C in industrial scale. Some inorganic salts and organic compound act as a n inhibitor to the crystallization of calcite and m u s t be removed from the nutrient and hydrothermal solvents. Calcite crystals dissolved into the NH4NO 3 hydrothermal solution a c c o m p a n i e d b y the evolution of ammonia. This reaction increases the dissolution of calcite in the h y d r o t h e r m a l solution, which gives a n advantage of lowering both the growth t e m p e r a t u r e and pressure conditions in NH4NO3 solution. This moderate growth condition allows us to employ a Teflon liner for the pure a t m o s p h e r e to grow the optical grade of calcite single crystals. The quality of grown single crystals is identical to the high optical grade of natural Iceland s p a r crystals in t e r m s of dislocation density and optical absorption. HCO 3" and NO a- ions in the crystals cannot be detected as impurities with a comparable trace u p t a k e of O H in the grown crystals.
5. REFERENCES I. 2. 3. 4. 5. 6. 7. 8. 9. 10, 11. 12. 13. 14.
L.G.Berry and B.Mason, Mineralogy, Freeman, San Francisco (1959), W.Eitel and W.Skalisks, Z. anorg, allgerru Chem., 183, 268 (1929). J.F.Nester and J.B.Schroeder, Am. Mineral., 52, 276 (1967). J . J . B r i s s o t and C.Belin. J. Cryst. Growth, 8, 213 (1971). C.Berlin. J . j , B r i s s o t and R.E.Jesse, J. Cryst. Growth, 13/14. 597 (1972). J.F.Balascio and W.B.White, J. Cryst, Growth, 23, I01 (1974). C.Belin, J. Cryst. Growth, 34, 341 (1976). N.Yu.Ikornikova, Soviet Phys. Cryst., 5. 726 (1961]. N.Yu.lkornikova, Growth of Crystals, 3, 297 (1962). J.F.Balascio and W.B.White, Mat. Res. Bull., 7, 1461 (1972). D.R.Kinloch, R.F.Belt and R.C.Puttbach, J. Cryst. Growth, 2 4 / 2 5 , 610 (1974). M.Higuchi, A.Takeuchi and K.Kodaira, J. Cryst. Growth, 92. 341 (1988). S.Hirano and K.Kikuta, J. Cryst. Growth, 79, 223 (1986). S.Hirano a n d K.Kikuta, J. Cryst, Growth, 94, 351 (1989).
S. Hirano et at
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K.Kikuta and S.Hirano, J. Cryst. Growth, 99, 895 (1990). S.Hirano and K.Kikuta, Chem. Lett., 1985, 1613 (1985). S.Hirano and K.Kikuta, Bull. Chem. Soc. Japan, 60, 1109 (1987]. C.F.Bell and K.A.K.Lott, Modem Approach to Inorganic Chemistry, Butterworth (1972). 19. I.Sunagawa, N.Morimoto and A.Miyashiro, Kobutsugaku, lwanami-shoten, (1975). 15. 16. 17. 18.
Acknowledgement This work was supported by the Asahi Glass Foundation for Industrial Technology,
Synthetic calcite single crystals
Dr. Shin-ichi Hirano Shin-ichi Hirano is Professor in the Dept. of Applied Chemistry, School of Engineering, Nagoya University, Nagoya 464, Japan. He earned his B.S. in 1965, M.S. in 1967, and Dr. of Eng. in 1970, all in applied chemistry from Nagoya University. Hirano was with Tokyo Institute of Technology as a research associate during 1970-76 and as an associate professor during 1976-78.
He also joined with the Penn. State Univ. from
1971-72. He was appointed to an associate professor at Nagoya Univ. in 1978 and was named full professor in 1983. He has been contributing to chemical processing and characterization of advanced ceramics. He was presented the Tokai Chemical Engineering Society Award in 1980, the Academic Award of the J a p a n Society of Powder and Powder Metallurgy in 1984, the Academic Award of the Ceramic Society of J a p a n in 1986, and the Academic Award of the Chemical Society of J a p a n in 1989.
In 1986 he was a recipient of the Richard M. Fulrath Award and a
Fellow of the American Ceramic Society from 1989.
365
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S. Hirano et aL
Dr. Toshinobu Yogo Toshinobu Yogo is an Associate Professor in the Dept. of Applied Chemistry, School of Engineering, Nagoya University. He earned his B.E. in 1974, M.E. in 1976 in synthetic chemistry from Nagoya University, and Dr. of Eng. in 1980 in applied chemistry from Hokkaido University.
Yogo worked for Nagoya Univ. as a research associate
during 1980-90 and as an associate professor from 1990. He also joined with the Univ. Washington from 1986-87. His
contribution
characterization.
to
ceramics
science
is
chemical processing
and
He was presented the Academic Award of the Nagai Science
and Technology Foundation in 1986.
Dr. Ko-ichi Kikuta Ko-ichi Kikuta is a Research Associate in the Dept. of Applied Chemistry, School of Engineering, Nagoya University. He earned his B.E. in 1984, M.E. in 1986, and Dr. of Eng. in 1989, all in applied chemistry from Nagoya University.
Kikuta has been with Nagoya
Univ. from 1989. He has been contributing to crystal growth, and chemical processing and
Synthetic calcite single crystals
characterization of advanced ceramics.
He was a recipient of the Academic
Award of the Nagai Science and Technology Foundation in 1989.
Communication should be sent to S. Hirano, Department of Applied Chemistry, School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-01, Japan.
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