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Crystallography and crystal growth of the (Na,Ca)(P,Si)O3 compound
Journal of Crystal Growth 94 (1989) 357—364 North-Holland, Amsterdam
357
CRYSTALLOGRAPHY AND CRYSTAL GROWTH OF THE (Na,Ca)(P,Si)03 COMPOUND Feng-Huei UN and Min-Hsiung HON Department of MaterEals Engineering, National Cheng-Kung University, Tainan, Taiwan, Rep. of China Received 25 August 1988
Recent investigation on the crystallization of the Na20—CaO—P205—Si02 glass-ceramics system has revealed the evolution of a unhiown compound. Electron probe microanalysis (EPMA), X-ray diffraction (XRD) and transmission electron microscopy (TEM) have allowed identification of the phase as (Na011,Ca059)(P011,Na059)03 with a triclinic PT structure. The lattice parameters were also calculated from the X-ray powder diffracion; they were in agreement with the results of the transmission electron microscopy. A series of nucleation and crystal growth processes of the glass ceramics was observed by optical microscopy, SEM and TEM.
1. Introduction The use of glass and ceramics as prosthetic materials in biological bodies has been the subject of rapidly expanding research. Abe [1] studied the phosphate glass-ceramics for use as artificial bones and made considerable progress. Permot [2] has reviewed in detail the preparation and application of artificial bones Kokubo et al [3] investigated the apatite-containing bioglass-ceramics and their surface properties. A series of studies in this laboratory have been concerned with the system of Na20—CaO—Si02— ~~205 bioglass-ceramics. In an earlier report, Ca2P207 and Na6Ca3Si6O18 have been formed as the main crystallized phases in the glass-ceramics with the composition of Na20 12%, CaO 28%, Si02 50% and P205 10%. It is well known that calcium-phosphate-containing materials are potentially important for medical implants because they are usually bioactive. Therefore, it is expected to have more calcium phosphate in the glass-ceramics if more CaO and P205 are added to the batch materials [4,5]. During a recent study on the crystallization characteristics of such a system of glasses with composition of Si02 39%, Na20 8.4%, CaO 40.6% and P205 12%, an unknown compound was crystallized. The composition, crystallography, nucleation and crystal growth of the this compound are bein treated in the present paper.
2. Experimental procedures 2.1. Materials preparation Glass specimens were made by melting a batch of approximately 100 g in a platinum crucible in the temperature range of 1350—1400°C. The batches consisted of well-mixed and dried powder of Si02, CaCO3 and Ca3 2• Tricalciumphosphate Ca3(P04)2 was normally used as the source of P205. The nominal composition of the glass was Si02 39%, Na20 8.4%, CaO 40.6% and P205 12%. After keeping it in the molten state for 1 h, the melt was poured onto a stainless steel plate and pressed into a plate approximately 10 mm thick. The glass plate was placed on a platinum sheet and heated up to various temperatures at a rate of 5°Cmin’ in the furnace. They were taken out at the appropriate temperature and allowed to cool in a furnace for annealing. The glass was given a two-stage heat-treatment at 800 °Cfor nucleation and at 890—1050°Cfor development of the crystal.
2.2. Measurements The DTA of the glass powder was measured with a Rigaku thermoflex TG 8110 at a rate of 5°C mm The crystallized phases precipitated in the heat-treatment were identified by a powder
0022-0248/89/$03.50 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
‘.
358
F H. Lin, M.H. Hon
/ Crystallography and growth of (Na, Ca)(P,Si)03
X-ray diffractometer with solid detector and using nickel filtered Cu Ka radiation. The 29 angular resolution was typically better than 0.05° and silicon powder was used as an internal standard. The specimen for TEM was sliced from a massive sample with a diamond blade saw and polished with diamond abrasive to a thickness of 30 ,.tm
LU
i I.-
and then thinned by ion-beam milling. The microstructure of these specimens was investigated by OM and TEM, in a Nikon AFX-IIA and Hitachi-700 STEM operating at 175 kV respectively. The electron diffraction pattern from the selected area was recorded with a photographic plate. Tilting of the crystal from one orientation to another was carried out in the selected area diffraction mode using a double tilt holder. Calculation of structure factor, and determination of diffraction patterns, angles between directions and interplanar spacings were executed by computer programs.
LU
i~tJ 600
o
1000
TEMPERATU RE ( °CI Fig. 1. DTA curve of the glass powder: (A) annealing point; (B) exothermic peak due to formation of crystal phase; (C) exothermic peak for recrystallization; (D) endothermic peak due to first melting.
Fig. 3 shows optical micrographs of the crystallized (Na,Ca)(P,Si)03 compound. Selected area electron diffraction patterns (fig. 4) showing a single phase are present in the sample. From the electron diffraction patterns for the compound shown in fig. 4, it is likely that the lattice of the new compound is a triclimc system. All electron diffraction patterns were successfully indexed to a tricinic lattice with a 0.80 ±0.01 nm, b 0.72
3. Results and discussion 3.1. Composition and crystallography The DTA curve for investigating the phase transformation of the glass specimen in heating is shown in fig. 1. During the heating, the samples were taken out at different temperatures for X-ray diffraction. It was found that the glass was devitrified at 830°C and a transition phase was formed. Thereafter, most of the constituents transformed into a (Na,Ca)(P,Si)03 compound. When the temperature was raised to 990°C, the (Na,Ca)(P,Si)03 compound recrystallized and an exothermic reaction was observed. At 1150°C, the glass powder reached the first melting temperature and the endothermic peak appeared. The results of X-ray diffraction analysis for different temperatures and 2 h duration are shown in fig. 2. Curve a (750°C) appears to have no characteristic diffraction peak, implying that this sample is still in the glassy state. In curve b (830°C) several small peaks are found; it might be thought as a begin ning of crystallization. The peaks shown in curves c and d indicate that the (Na,Ca)(P,Si)03 compound is the major phase present in the samples.
800
=
~
=
b
-____________________________________________ D~RACTION
APV3LE
2~
Fig. 2. X-ray diffraction curves of glass samples heating at: (a) 7500 C; (b) 8300 C; (c) 8900 C; (d) 10500 C.
FH. Lin, M.H. Hon
/
Crystallography and growth of (Na, Ca) (P,Si)0
3
359
—
J~~*;-~ I
~oi~s
Fig. 3. Optical micrographs of the glass-ceramics nucleated at 8000 C and crystallized at 10500 C. Marker represents 15 pm.
±0.02nm, c=0.69±0.01 nm, a=9O°±0.5, $ 95.03°±0.02 and y 104.32°±0.5. Fitting to detailed X-ray powder diffraction scans of the specimens (see fig. 2), the lattice parameters were determined to be a 0.79 nm, b 0.71 nm, c 0.69 nm, a 90.03°,$ 95.34°and y 103.45 =
L
=
=
=
=
=
=
=
°,
Fig. 5. Electron probe microanalysis for (Na0 11,Ca0 89)(P011, Si0 ~9)O3 compound precipitated in the glass ceramics
010 90
:00
011
001
110
001
100
10
100
~
Fig. 4. Electron diffraction patterns of the (Na0 11,Ca089)(P01~,Si059)O3compound with double tilt specimen holder in the direction of: (a) [100];(b) [0101;(c) [001].
360
F.H. Lin, M.H. Hon
/
Crystallography and growth of (Na, Ca)(P,Si)0
in agreement with the above results. This structure belongs to the P1 space group, and is isomophic with CaSiO3 [6]. From the results of EPMA, as shown in fig. 5, and the calculation of the atomic percent, the formula of the compound is determined to be (Na011,Ca089)(P011,Si089)03. In the glassy state, Si04 and P04 are the network-forming oxides that play a similar structural roles in the glass, whereas Na and Ca atoms are the modifiers [7]. During the formation of the compound, it is possible to accommodate the Na and P atoms in the CaSiO3 cells in the following way: P atom replaces Si atom in tetrahedral chains and Na atom substitutes Ca atom in octahedral sites (see fig. 6) which 5± are= related the coupled Ca2~+by Si4t. In this substitution Na’~ +p arrangement the excessive charge of + 1 associated with the P atom replacement serves to neutralize the excessive charge of 1 associated with Na atom substitution. It can achieve electroneutrality in the crystal structure. Similar substitutions exist in many other compounds, such as feldspathoid minerals and members of plagioclase feldspar [8]. Under such condition, the formula of the compound should be of the type of (Nay, Ca 1 )(P~,Si1 )0~,which is in close agreement with the results of EPMA with x 0.11. It is interesting to investigate the replacement of Na Ca and P Si as a disorder substitution —
—
.
3
Table 1 Experimental and calculated d-spacings and relative intensities for (Na011,Ca089)(P011,Si089)03
___________________________________________ (exp) (nm) 0.79790 0.55345 0.38835 0.35309 0.33359 0.32639 0.31078 0.29857 0.28823
I/I,/ exp)
hkl
I/10(calc)
30 4 98 55 100 4 40 60 9
100 101 200 201 ~O2 201 210 220 221
26 1 80 50 100 5 37 40 2
d(calc) (nm) 0.78549 0.55340 0.38469 0.35309 0.33359 0.32522 0.31078 0.29857 0.28116
0.27218 0.26727 0.26345 0.25686 0.24926 0.23540 0.23074 0.21892
8 54 31 23 18 23 28 20
202 310 300 022 202 222 103 222
10 85 45 15 15 20 24 12
0.27281 0.26573 0.26270 0.25686 0.24926 0.23540 0.23074 0.21892
0.19918 0.19239 0.18717
5 8 15
302 400 322
3 5 25
0.20256 0.19239 0.18717
in the crystal. The structural factor F is given by
—
—
IF
I=
exp [2~i(hu
+ kv + 1w)],
—*
where 2~asin 29)_2
is the reflection angle, a is the atomic radius, and h, k, 1 and u, v, w represent the Miller indices of the reflection planes and atomic positions, respectively. The calculated d-spacing and intensities are
~
-.
S
compared with the experimental X-ray powder diffraction data in table 1, within empirical agreement. Thus, the authors deduced that the Na—Ca and P~Sisubstitutional pairs should be a disorder substitution in the compound [9]. 3.2. Nucleation and crystal growth
For the achievement of the desired microstrucFig. 6. Ideal structure of (Na0~1,Ca0s9)(P01i,Si059)O3compound. Si and P are in the tetrahedral chains and Na and Ca in the octahedral sites,
ture to improve the mechanical property of the glass, it is necessary to ensure that a high density
FH. LEn, M.H. Hon
/ Crystallography and
growth of (Na, Ca)(P,Si)0
3
361
B
~‘r:
~•
B
~
Fig. 7. Glass-in-glass separation of a P,O~-richdroplet phase in the glass matrix. Scanning electron micrograph of the speciment nucleated at 800°Cfor 1 h. Marker represents 0.5 pm.
of nuclei should arise with in the material. The technique for producing fine and uniform-grained glass-ceramics is to generate nuclei in the glass at the temperatures below those at which major crystalline phases could grow at a significant rate [101.Thus, the parent glass must contain a suitable nucleating agent. Fortunately, phosphorus pento-
Fig. 8. Transmission electron micrograph of the specimen nucleated at 800 0 C for 1 h and heat-treated at 1050 0 C for 2 h. A and B represent the “precipitate” areas and “matrix” areas, respectively. Marker represents 4 pm.
xide, P205, added as a suitable phospl’ ate, has long been known to act as a nucleating agent in the formation of glass-ceramics [11]. After nucleating treatment at 800°C for lh, the parent glass revealed a fine spherical glass-in-glass phase-separation structure that was based on the incompati-
U. 101
101
0
Fig. 9. Selected area electron diffraction patterns for: (a) A area; (b) B area.
00
362
FH. LEn, M.H. Hon
/ Crystallography
and growth of (Na. Ca)(P,Si)O,
______
bility of different types of network-forming structural groups between P04 and SO4, as shown in
~fl
fig. 7 [11].
When the temperature was raised to 1050°C for 2 h, the (Na,Ca)(P,Si)03 compound crystallized. Investigated by optical microscope, the material exhibited a fine and uniform-grained microstructure with 10 ~tm mean grain size (see fig. 3). The same material which was observed by a bright field image of TEM displayed a different microstructure, where “precipitate” areas (mdi cated A) and “matrix” areas (indicated B) were demonstrated in fig. 8. The electron diffraction patterns of areas A and B in fig. 8 are shown in figs. 9a and 9b, respectively, where the crystal orientations of these two areas correspond exactly with each other. However, the “precipitate” area possesses a perfect diffraction pattern but the “matrix” area has a blurred and broadened sport pattern. From the orientation relationship of the two areas, the whole image of fig. 8 may be considered as an equivalent to a single grain which might be equivalent to a grain of fig. 3. The difference in spot patterns between areas A and B arose due to a locally varying strain field or a small misfit in the grain which was associated with the crystal growth. The authors suggest that the “precipitates” in fig. 8 were the original nucleating sites and consider that the crystal growth of the material may go through the following three steps. First step: a nucleus formed and dispersed in the parent glass as shown in fig. 7. Second step: during the nucleus expanding, small precipitates with a spherical strain field arising from volume misfit give rise to these lobes of contrast (see fig. lOa) and subgrains formed while the growth continued. Third step: it might occur that the combi nation of subgrains or subgrain coalescence reduced the excessive energy by means of eliminat-
ing subgrain boundaries. Thus, a crystal deformation formed between subgrains resulted from the small misfit. The contour of crystal deformation image was clearly observed between subgrains, as shown in figs. lOb and lOc, during subgrain cornbination or coalescence. Under such conditions, the subgrains should be a perfect crystal, as shown in fig. 8a and fig. 9a, and the “inter-subgrain”
..,,.
0
_____________
-______
‘~j~’TT~~
____
_____ ~-
_______
-______
..
I’ ig. ift I ran~,nassion electron micro~raph~ol the ~la’.~ nucleated at 110(1 C for I h and heat-treated at 1050 ( br: (a) 10 mm; (h) 31) mm: (c) 60 mm. Markers represent: (a) (1.2 pm; (b) I pm; (c) 1 pm.
area (see fig.8, area B) had the same crystal orientation with subgrains but was locally deformed as a result of misfit during the combination. This process is shown schematically in fig. 11.
F H. LEn, M.H. Hon
/
Crystallography and growth of (Na, Ca)(P,Si)0
3
363
orininal nucleation nucleation site
Parent glass
aite or subgrdins
1. Nucleation 2. Nucleation growth P205—rich glass and suhgrain phase separation precipitation
3. ~iubgrain comnination and crystal growth
Fig. 11. Schematic crystallization process of the glass ceramics.
p
rotation direct ion
__
__
Fig. 12. Optical micrographs of the glass-ceramics. The grains demonstrated the wave extinction property as the stage of the OM was rotated. EP in the micrographs is the extinction position. Marker represents 15 ~sm.
364
F.H. Lin, M.H. Hon
/
Crystallography and growth of(Na,Ca)(P,Si)0
On closer examination of fig. 3, the grain demonstrated an inconsistent extinction while the stage of the OM was rotated. A perfect crystal displayed a consistent extinction under OM cross nicols; however, a deformed crystal always has a wave extinction property, which could identify the deformed crystal as shown in fig. 12 [121.The extinction position of the grain changed as the stage of the OM was rotated.
3
subgrain coalescence. The grain was deformed as the result of small misfit between subgrains.
References [1] Y.Abe, Japan Kokai 73 (1976) 19. [2] F. Permot, J. Mater. Scm. 14 (1979) 1694.
4. Conclusion It has been demonstrated that the glass-ceramics with composition of Na2O 8.4%, CaO 40.6%, Si02 39% and P205 12% may form a (Nay, Ca1~)03 compound with x 0.11.. The crystal structure is . the P1 space group with lattice parameters of a = 0.79 nm, b = 0.71 nm, c = 0.69 nm, a = 90.03°, /3 = and y = 103.45°. During the compound formation, the Na,Ca and P,Si are substitutional pairs and may have a disorder substitution in the crystal. The crystal growth of the compound was proposed to go through nucleation, precipitation and —
—
95~340
[3] T. Kokubo, S. Ito and S. Sakaa, J. Mater. Sci. 21(1986) [4] F.H. Lin and M.H. Hon. J. Mater. Sci. Letters 5 (1987) 331 [5] F.H. Lin and M.H. Hon. J. Med. Eng. ROC 4. No. 5 (1985) 33. [6] H. Matsueda, Mineral. J. Japan 7 (1973) 180. [7] P.W. Macmillan. Glass Ceramics, 2nd ed. (Chapman and Hall, London, 1984) pp. 9—16. [8] R.G. Cawthorn and K.D. Collerson, Am. Mineralogist 59 (1974) 1203. [9] Y. Ohashi and LW. Finger, Am. Mineralogist 63 (1978) 274. [10]R.W. Douglas, Phys. Chem. Glasses 1 (1967) 19. [11] R.R Shaw and D.R. Uhlmann, J. Non-Crystalline Solids 1 (1969) 4~l4. [12]A. Smakula, Opt. Acta 9 (1962) 205.
357
CRYSTALLOGRAPHY AND CRYSTAL GROWTH OF THE (Na,Ca)(P,Si)03 COMPOUND Feng-Huei UN and Min-Hsiung HON Department of MaterEals Engineering, National Cheng-Kung University, Tainan, Taiwan, Rep. of China Received 25 August 1988
Recent investigation on the crystallization of the Na20—CaO—P205—Si02 glass-ceramics system has revealed the evolution of a unhiown compound. Electron probe microanalysis (EPMA), X-ray diffraction (XRD) and transmission electron microscopy (TEM) have allowed identification of the phase as (Na011,Ca059)(P011,Na059)03 with a triclinic PT structure. The lattice parameters were also calculated from the X-ray powder diffracion; they were in agreement with the results of the transmission electron microscopy. A series of nucleation and crystal growth processes of the glass ceramics was observed by optical microscopy, SEM and TEM.
1. Introduction The use of glass and ceramics as prosthetic materials in biological bodies has been the subject of rapidly expanding research. Abe [1] studied the phosphate glass-ceramics for use as artificial bones and made considerable progress. Permot [2] has reviewed in detail the preparation and application of artificial bones Kokubo et al [3] investigated the apatite-containing bioglass-ceramics and their surface properties. A series of studies in this laboratory have been concerned with the system of Na20—CaO—Si02— ~~205 bioglass-ceramics. In an earlier report, Ca2P207 and Na6Ca3Si6O18 have been formed as the main crystallized phases in the glass-ceramics with the composition of Na20 12%, CaO 28%, Si02 50% and P205 10%. It is well known that calcium-phosphate-containing materials are potentially important for medical implants because they are usually bioactive. Therefore, it is expected to have more calcium phosphate in the glass-ceramics if more CaO and P205 are added to the batch materials [4,5]. During a recent study on the crystallization characteristics of such a system of glasses with composition of Si02 39%, Na20 8.4%, CaO 40.6% and P205 12%, an unknown compound was crystallized. The composition, crystallography, nucleation and crystal growth of the this compound are bein treated in the present paper.
2. Experimental procedures 2.1. Materials preparation Glass specimens were made by melting a batch of approximately 100 g in a platinum crucible in the temperature range of 1350—1400°C. The batches consisted of well-mixed and dried powder of Si02, CaCO3 and Ca3 2• Tricalciumphosphate Ca3(P04)2 was normally used as the source of P205. The nominal composition of the glass was Si02 39%, Na20 8.4%, CaO 40.6% and P205 12%. After keeping it in the molten state for 1 h, the melt was poured onto a stainless steel plate and pressed into a plate approximately 10 mm thick. The glass plate was placed on a platinum sheet and heated up to various temperatures at a rate of 5°Cmin’ in the furnace. They were taken out at the appropriate temperature and allowed to cool in a furnace for annealing. The glass was given a two-stage heat-treatment at 800 °Cfor nucleation and at 890—1050°Cfor development of the crystal.
2.2. Measurements The DTA of the glass powder was measured with a Rigaku thermoflex TG 8110 at a rate of 5°C mm The crystallized phases precipitated in the heat-treatment were identified by a powder
0022-0248/89/$03.50 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
‘.
358
F H. Lin, M.H. Hon
/ Crystallography and growth of (Na, Ca)(P,Si)03
X-ray diffractometer with solid detector and using nickel filtered Cu Ka radiation. The 29 angular resolution was typically better than 0.05° and silicon powder was used as an internal standard. The specimen for TEM was sliced from a massive sample with a diamond blade saw and polished with diamond abrasive to a thickness of 30 ,.tm
LU
i I.-
and then thinned by ion-beam milling. The microstructure of these specimens was investigated by OM and TEM, in a Nikon AFX-IIA and Hitachi-700 STEM operating at 175 kV respectively. The electron diffraction pattern from the selected area was recorded with a photographic plate. Tilting of the crystal from one orientation to another was carried out in the selected area diffraction mode using a double tilt holder. Calculation of structure factor, and determination of diffraction patterns, angles between directions and interplanar spacings were executed by computer programs.
LU
i~tJ 600
o
1000
TEMPERATU RE ( °CI Fig. 1. DTA curve of the glass powder: (A) annealing point; (B) exothermic peak due to formation of crystal phase; (C) exothermic peak for recrystallization; (D) endothermic peak due to first melting.
Fig. 3 shows optical micrographs of the crystallized (Na,Ca)(P,Si)03 compound. Selected area electron diffraction patterns (fig. 4) showing a single phase are present in the sample. From the electron diffraction patterns for the compound shown in fig. 4, it is likely that the lattice of the new compound is a triclimc system. All electron diffraction patterns were successfully indexed to a tricinic lattice with a 0.80 ±0.01 nm, b 0.72
3. Results and discussion 3.1. Composition and crystallography The DTA curve for investigating the phase transformation of the glass specimen in heating is shown in fig. 1. During the heating, the samples were taken out at different temperatures for X-ray diffraction. It was found that the glass was devitrified at 830°C and a transition phase was formed. Thereafter, most of the constituents transformed into a (Na,Ca)(P,Si)03 compound. When the temperature was raised to 990°C, the (Na,Ca)(P,Si)03 compound recrystallized and an exothermic reaction was observed. At 1150°C, the glass powder reached the first melting temperature and the endothermic peak appeared. The results of X-ray diffraction analysis for different temperatures and 2 h duration are shown in fig. 2. Curve a (750°C) appears to have no characteristic diffraction peak, implying that this sample is still in the glassy state. In curve b (830°C) several small peaks are found; it might be thought as a begin ning of crystallization. The peaks shown in curves c and d indicate that the (Na,Ca)(P,Si)03 compound is the major phase present in the samples.
800
=
~
=
b
-____________________________________________ D~RACTION
APV3LE
2~
Fig. 2. X-ray diffraction curves of glass samples heating at: (a) 7500 C; (b) 8300 C; (c) 8900 C; (d) 10500 C.
FH. Lin, M.H. Hon
/
Crystallography and growth of (Na, Ca) (P,Si)0
3
359
—
J~~*;-~ I
~oi~s
Fig. 3. Optical micrographs of the glass-ceramics nucleated at 8000 C and crystallized at 10500 C. Marker represents 15 pm.
±0.02nm, c=0.69±0.01 nm, a=9O°±0.5, $ 95.03°±0.02 and y 104.32°±0.5. Fitting to detailed X-ray powder diffraction scans of the specimens (see fig. 2), the lattice parameters were determined to be a 0.79 nm, b 0.71 nm, c 0.69 nm, a 90.03°,$ 95.34°and y 103.45 =
L
=
=
=
=
=
=
=
°,
Fig. 5. Electron probe microanalysis for (Na0 11,Ca0 89)(P011, Si0 ~9)O3 compound precipitated in the glass ceramics
010 90
:00
011
001
110
001
100
10
100
~
Fig. 4. Electron diffraction patterns of the (Na0 11,Ca089)(P01~,Si059)O3compound with double tilt specimen holder in the direction of: (a) [100];(b) [0101;(c) [001].
360
F.H. Lin, M.H. Hon
/
Crystallography and growth of (Na, Ca)(P,Si)0
in agreement with the above results. This structure belongs to the P1 space group, and is isomophic with CaSiO3 [6]. From the results of EPMA, as shown in fig. 5, and the calculation of the atomic percent, the formula of the compound is determined to be (Na011,Ca089)(P011,Si089)03. In the glassy state, Si04 and P04 are the network-forming oxides that play a similar structural roles in the glass, whereas Na and Ca atoms are the modifiers [7]. During the formation of the compound, it is possible to accommodate the Na and P atoms in the CaSiO3 cells in the following way: P atom replaces Si atom in tetrahedral chains and Na atom substitutes Ca atom in octahedral sites (see fig. 6) which 5± are= related the coupled Ca2~+by Si4t. In this substitution Na’~ +p arrangement the excessive charge of + 1 associated with the P atom replacement serves to neutralize the excessive charge of 1 associated with Na atom substitution. It can achieve electroneutrality in the crystal structure. Similar substitutions exist in many other compounds, such as feldspathoid minerals and members of plagioclase feldspar [8]. Under such condition, the formula of the compound should be of the type of (Nay, Ca 1 )(P~,Si1 )0~,which is in close agreement with the results of EPMA with x 0.11. It is interesting to investigate the replacement of Na Ca and P Si as a disorder substitution —
—
.
3
Table 1 Experimental and calculated d-spacings and relative intensities for (Na011,Ca089)(P011,Si089)03
___________________________________________ (exp) (nm) 0.79790 0.55345 0.38835 0.35309 0.33359 0.32639 0.31078 0.29857 0.28823
I/I,/ exp)
hkl
I/10(calc)
30 4 98 55 100 4 40 60 9
100 101 200 201 ~O2 201 210 220 221
26 1 80 50 100 5 37 40 2
d(calc) (nm) 0.78549 0.55340 0.38469 0.35309 0.33359 0.32522 0.31078 0.29857 0.28116
0.27218 0.26727 0.26345 0.25686 0.24926 0.23540 0.23074 0.21892
8 54 31 23 18 23 28 20
202 310 300 022 202 222 103 222
10 85 45 15 15 20 24 12
0.27281 0.26573 0.26270 0.25686 0.24926 0.23540 0.23074 0.21892
0.19918 0.19239 0.18717
5 8 15
302 400 322
3 5 25
0.20256 0.19239 0.18717
in the crystal. The structural factor F is given by
—
—
IF
I=
exp [2~i(hu
+ kv + 1w)],
—*
where 2~asin 29)_2
is the reflection angle, a is the atomic radius, and h, k, 1 and u, v, w represent the Miller indices of the reflection planes and atomic positions, respectively. The calculated d-spacing and intensities are
~
-.
S
compared with the experimental X-ray powder diffraction data in table 1, within empirical agreement. Thus, the authors deduced that the Na—Ca and P~Sisubstitutional pairs should be a disorder substitution in the compound [9]. 3.2. Nucleation and crystal growth
For the achievement of the desired microstrucFig. 6. Ideal structure of (Na0~1,Ca0s9)(P01i,Si059)O3compound. Si and P are in the tetrahedral chains and Na and Ca in the octahedral sites,
ture to improve the mechanical property of the glass, it is necessary to ensure that a high density
FH. LEn, M.H. Hon
/ Crystallography and
growth of (Na, Ca)(P,Si)0
3
361
B
~‘r:
~•
B
~
Fig. 7. Glass-in-glass separation of a P,O~-richdroplet phase in the glass matrix. Scanning electron micrograph of the speciment nucleated at 800°Cfor 1 h. Marker represents 0.5 pm.
of nuclei should arise with in the material. The technique for producing fine and uniform-grained glass-ceramics is to generate nuclei in the glass at the temperatures below those at which major crystalline phases could grow at a significant rate [101.Thus, the parent glass must contain a suitable nucleating agent. Fortunately, phosphorus pento-
Fig. 8. Transmission electron micrograph of the specimen nucleated at 800 0 C for 1 h and heat-treated at 1050 0 C for 2 h. A and B represent the “precipitate” areas and “matrix” areas, respectively. Marker represents 4 pm.
xide, P205, added as a suitable phospl’ ate, has long been known to act as a nucleating agent in the formation of glass-ceramics [11]. After nucleating treatment at 800°C for lh, the parent glass revealed a fine spherical glass-in-glass phase-separation structure that was based on the incompati-
U. 101
101
0
Fig. 9. Selected area electron diffraction patterns for: (a) A area; (b) B area.
00
362
FH. LEn, M.H. Hon
/ Crystallography
and growth of (Na. Ca)(P,Si)O,
______
bility of different types of network-forming structural groups between P04 and SO4, as shown in
~fl
fig. 7 [11].
When the temperature was raised to 1050°C for 2 h, the (Na,Ca)(P,Si)03 compound crystallized. Investigated by optical microscope, the material exhibited a fine and uniform-grained microstructure with 10 ~tm mean grain size (see fig. 3). The same material which was observed by a bright field image of TEM displayed a different microstructure, where “precipitate” areas (mdi cated A) and “matrix” areas (indicated B) were demonstrated in fig. 8. The electron diffraction patterns of areas A and B in fig. 8 are shown in figs. 9a and 9b, respectively, where the crystal orientations of these two areas correspond exactly with each other. However, the “precipitate” area possesses a perfect diffraction pattern but the “matrix” area has a blurred and broadened sport pattern. From the orientation relationship of the two areas, the whole image of fig. 8 may be considered as an equivalent to a single grain which might be equivalent to a grain of fig. 3. The difference in spot patterns between areas A and B arose due to a locally varying strain field or a small misfit in the grain which was associated with the crystal growth. The authors suggest that the “precipitates” in fig. 8 were the original nucleating sites and consider that the crystal growth of the material may go through the following three steps. First step: a nucleus formed and dispersed in the parent glass as shown in fig. 7. Second step: during the nucleus expanding, small precipitates with a spherical strain field arising from volume misfit give rise to these lobes of contrast (see fig. lOa) and subgrains formed while the growth continued. Third step: it might occur that the combi nation of subgrains or subgrain coalescence reduced the excessive energy by means of eliminat-
ing subgrain boundaries. Thus, a crystal deformation formed between subgrains resulted from the small misfit. The contour of crystal deformation image was clearly observed between subgrains, as shown in figs. lOb and lOc, during subgrain cornbination or coalescence. Under such conditions, the subgrains should be a perfect crystal, as shown in fig. 8a and fig. 9a, and the “inter-subgrain”
..,,.
0
_____________
-______
‘~j~’TT~~
____
_____ ~-
_______
-______
..
I’ ig. ift I ran~,nassion electron micro~raph~ol the ~la’.~ nucleated at 110(1 C for I h and heat-treated at 1050 ( br: (a) 10 mm; (h) 31) mm: (c) 60 mm. Markers represent: (a) (1.2 pm; (b) I pm; (c) 1 pm.
area (see fig.8, area B) had the same crystal orientation with subgrains but was locally deformed as a result of misfit during the combination. This process is shown schematically in fig. 11.
F H. LEn, M.H. Hon
/
Crystallography and growth of (Na, Ca)(P,Si)0
3
363
orininal nucleation nucleation site
Parent glass
aite or subgrdins
1. Nucleation 2. Nucleation growth P205—rich glass and suhgrain phase separation precipitation
3. ~iubgrain comnination and crystal growth
Fig. 11. Schematic crystallization process of the glass ceramics.
p
rotation direct ion
__
__
Fig. 12. Optical micrographs of the glass-ceramics. The grains demonstrated the wave extinction property as the stage of the OM was rotated. EP in the micrographs is the extinction position. Marker represents 15 ~sm.
364
F.H. Lin, M.H. Hon
/
Crystallography and growth of(Na,Ca)(P,Si)0
On closer examination of fig. 3, the grain demonstrated an inconsistent extinction while the stage of the OM was rotated. A perfect crystal displayed a consistent extinction under OM cross nicols; however, a deformed crystal always has a wave extinction property, which could identify the deformed crystal as shown in fig. 12 [121.The extinction position of the grain changed as the stage of the OM was rotated.
3
subgrain coalescence. The grain was deformed as the result of small misfit between subgrains.
References [1] Y.Abe, Japan Kokai 73 (1976) 19. [2] F. Permot, J. Mater. Scm. 14 (1979) 1694.
4. Conclusion It has been demonstrated that the glass-ceramics with composition of Na2O 8.4%, CaO 40.6%, Si02 39% and P205 12% may form a (Nay, Ca1~)03 compound with x 0.11.. The crystal structure is . the P1 space group with lattice parameters of a = 0.79 nm, b = 0.71 nm, c = 0.69 nm, a = 90.03°, /3 = and y = 103.45°. During the compound formation, the Na,Ca and P,Si are substitutional pairs and may have a disorder substitution in the crystal. The crystal growth of the compound was proposed to go through nucleation, precipitation and —
—
95~340
[3] T. Kokubo, S. Ito and S. Sakaa, J. Mater. Sci. 21(1986) [4] F.H. Lin and M.H. Hon. J. Mater. Sci. Letters 5 (1987) 331 [5] F.H. Lin and M.H. Hon. J. Med. Eng. ROC 4. No. 5 (1985) 33. [6] H. Matsueda, Mineral. J. Japan 7 (1973) 180. [7] P.W. Macmillan. Glass Ceramics, 2nd ed. (Chapman and Hall, London, 1984) pp. 9—16. [8] R.G. Cawthorn and K.D. Collerson, Am. Mineralogist 59 (1974) 1203. [9] Y. Ohashi and LW. Finger, Am. Mineralogist 63 (1978) 274. [10]R.W. Douglas, Phys. Chem. Glasses 1 (1967) 19. [11] R.R Shaw and D.R. Uhlmann, J. Non-Crystalline Solids 1 (1969) 4~l4. [12]A. Smakula, Opt. Acta 9 (1962) 205.