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Prospects of the relationship between liquid-phase separation and crystallization in glass
Journal ol Non-Crystalline North-Holland, Amsterdam
Solids
87 (1986)
387
387-391
PROSPECTS OF THE RELATIONSHIP SEPARATION AND CRYSTALLIZATION LI Jiazhi and FANG Shmghu~
Ittstrrrr~e
BETWEEN LIQUID-PHASE IN GLASS *
Chih-yao
of Ceramrcs.
Academia
Sinicu,
Shmghoi.
Chiuu
The past half century has seen the publication of a large number of studies dealing with liquid-phase separation in glass-forming systems. In contrast to the abundance of studies on thermodynamics. kinetics of liquid phase separation as well as its effect on crystallization and properties of glass. relatively few applications have been known directly utilizing this phenomenon. There is some experimental evidence that liquid-phase separation exerts an important influence both on the properties of glass ceramics and the striking properties of ruby glasses. It is possible to utilize knowledge available and more fully understand liquid-phase separation and its relation with crystallization for improving the properties of glass ceramics and developing new glass materials with promising properties. Thus, much work remains to be done. The objective of this paper is to emphasize the relationship between liquid-phase separation and the crystallization behavior of glass.
Liquid-phase separation exists commonly in many glass-ceramic systems. As glass ceramics were discovered and developed, interest in the phase separation and control of crystallization of glasses further increased, The prior liquid-phase separation may produce two liquid compositions, one of which has a greater tendency to crystallize than initial non-separated glass. This shift in composition probably caused changes in the nucleation barrier of thermodynamics and kinetics as well as the change in thermodynamic driving force and in atomic mobility which in turn influence the nucleation rate and the crystallization course including the kind of primary crystalline phase, the amount of final crystalline phase and the microstructure of the material. We can predict if the effect of liquid phase separation on the crystallization process of glass can be fully understood and controlled, that new glass ceramics of desired properties could be developed. In our work on MgO-Al,O,-SiO,-TiO, [l], ZnO-Al,O,-SiO, [2] and ZnO-Al,Os-SiO,-ZrO, [3] glass-ceramic systems, we found in all glasses which exhibit a great degree of liquid-phase separation, a tendency to decrease the crystallization temperature, i.e. the primary crystalline phase with complicated composition can be precipitated at lower temperature as compared to the non-phase-separated composition [4]. The MgO-A1203--SiOz-TiO, system exhibited a great liquid-phase separation; a magnesium-alumino-titanate * Paper presented Kreidl), Vienna,
at the Symposium on Glass July 1984, but not published
Science and Technology in the Proceedings.
0022-3093/86/$03.50 0 Elsevier Science Publishers (North-Holland Physics Publishing Division)
B.V
(in honour
o/ Norherr
J.
388
Li Jiozhi.
Fung Chih,vao
660
/ Liquid-phase
680
700
720
Temperature
Fig.
1. The
effect
of pre-heat
seporution
740
760
of pre-heat
treatment on the thermal MgO-A1203-Si02-Ti02.
and uystollizotiotl
780
800
treatment
expansion
820
in glass
840
I”CI
of coefficient
of glass-ceramics
crystal may be precipitated at a temperature 90°C lower than that in the composition not tending to liquid-phase separation. In the ZnO-Al,O,-SiO, system, the crystallization temperature of p-willemite solid solution may also be decreased by 60°C. In addition, prior liquid-phase separation exerts a strong influence on the amount of final crystalline phase in glass ceramics. This may be due to the fact that liquid-phase separation promotes the nucleation of crystal. Thus, the properties of the material will be greatly changed. In the MgO-Al ,O,-SiO,-TiO, system tending to liquid-phase separation, the glass-ceramic sample with given composition pre-heated at different temperature may have quite different properties [5]. Figure 1 shows the effect of a different pre-heated schedule on thermal expansion of the coefficient of glass ceramics. As seen from fig. 1, thermal expansion of the coefficient of 11-13 x 10-‘/O C could only be obtained for the prethermal treatment at a 700-760° C temperature range. The specimens which were preheated at 650°C for 10 h have a modulus of rupture of 2000 kg/cm2, the glass-ceramic specimens preheated at 750°C for 10 h have a modulus of rupture of 400 kg/cm2. While both specimens were heated to 800°C and then quenched in cold water, the modulus of rupture for the former was almost decreased one order of magnitude but that for the latter remained unchanged. Figure 2 shows the
Fig. 2. (a) Scanning electron micrograph of specimen heat-treated at 650°C/10 h (X 10000); Scanning electron micrograph of specimen heat-treated at 75O”C/lO h ( X 10000).
(b)
Li Jimhi.
Fuug Chih-wo
/ Liquid-phase
separurion
und qarollizaliotl
in glass
389
SEM microphotographs of glasses undergoing these different pre-heating treatments and different extents of liquid-phase separation. After glass-phase separation, the composition of each separated phase will diversify according to the ionic field strength of cations. For example in MgO-Al,O,-SiO,-TiO,, two liquid phases, silica-rich as well as titania- and magnesia-rich, and in ZnO-Al ,O,-SiO,, two liquids, silica-rich and zinc-rich, can be formed. The greater the degree of phase separation, the more beneficial to richening in magnesium and titanium ions or zinc ions in respective phases, i.e. in subsequent crystallization process of glasses, the more beneficial to crystallize magnesium aluminium titanate or j%willemite solid solution and gahnite in these phases respectively. This makes them crystallized at a lower temperature. From this point of view, the kinds of initial crystalline phase, crystallized from the phase-separated glass, depend on the composition of two or more liquid phases rather than the original glass composition. Of course, they are also different from those of original glass composition in the phase diagram. However, the final crystalline phase crystallized from the liquid-phase separated glass depends on the original glass compositions. Different degrees of liquid-phase separation do not affect the final crystalline phase, but change their amounts only because of a different crystallization process. Another interesting aspect is the influence of liquid-phase separation on optical absorption of ruby glasses. Copper ruby and silver ruby glasses have been known since the Middle Ages. Although the complex colloid chemistry of these glasses has already been elucidated, the selection of their base glasses still requires unusual experience, so that their manufacture has been confined to a few glass compositions. Little glass literature has been offered concerning the composition of ruby glasses. The formation of the ruby colour is basically a problem of chemical thermodynamics in the glass melt and the kinetics of the precipitation of phase in which the melt is supersaturated. Indeed, the striking process of ruby glass is a course of nucleation and growth of colloidal crystals. The optical absorption of these ruby glasses is proportional to the amount and size of colloidal particles. In our work on copper ruby and silver ruby [6], we made a study of the influence of liquid-phase separation on copper ruby and silver ruby formation. We chose two similar soda-boron-silica glass compositions as base glasses, one of which exhibits liquid-phase separation, the other is non-phase separated. The experimental results show that the most desirable and most intense colours of copper ruby and silver ruby are obtained in liquid-phase separated base glasses. Figures 3 and 4 show absorption spectra of copper ruby and silver ruby glasses. At the same striking temperature, phase separated copper ruby glass gives a deeper red colour than non-phase separated copper ruby glass. Liquid-phase separation exerts a stronger influence on the striking of silver ruby. The heat
390
Li Jiarhi,
800
1200
Fung
1600 Wavelength
Chih-yoo
2000
/ Liquid-phase
2400
sepuratiorl
und ctystalliration
in glass
2800
“m
Fig. 3. (a) Absorption spectra of liquid-phase separation copper ruby glass. A, 470°C for 4 h; B. 490°C for 4 h; C, 53O’C for 4 h; D. 550°C for 4 h. (b) Absorption spectra of non-liquid phase separated copper ruby glass. A, 470°C for 4 h; B, 490°C for 4 h; C, 530°C for 4 h; D. 550°C for 4 h.
treatment at 490°C for 4 h gives liquid-phase separated silver ruby a deep yellow colour; however, non-phase separated silver ruby does not strike until 610°C. At a temperature of 53O”C, phase-separated silver ruby glass has developed a deep red colour which means the colloidal particles have grown to a larger size. The effect of liquid-phase separation on the striking features of silver ruby and copper ruby glasses might also be attributed to the marked influence of liquid-phase separation on the course of crystallization of metallic particles in ruby glass. These observations could also be explained in terms of the composition shif )f the matrix during liquid-phase separation. 100
a
80
I
20
2800
Wavelength
Fig. 4. (a) Transmission spectra of liquid-phase separated B,490oCfor4h;C,5100Cfor4h;D,5300Cfor4h;E.5500Cfor4h.
nm
silver
ruby
glass.
3
)a
A, non-heat
treatment;
Li J&hi,
Fang Chih-yao
0
400
/ Liquid-phuw
800
1200
sepamion
1600
Wavelength
Fig. 4. (b) Transmission
2000
and cryslallizatiott
2400
2800
in glass
391
3000
nm
spectra of non-liquid phase separated and530°Cfor4h;B,5500Cfor4h;C,610”Cfor4h.
silver
ruby
glass. A. 490°C,
510°C
One practical implication of the experimental results above is that for many glass-ceramic systems, the effect of different heat treatment prior to crystal nucleation treatment is particularly striking. Various degrees of liquid-phase separation do appear to have a very significant effect on the crystallization course and microstructure of glass ceramics. Many factors can possibly affect the properties of glass ceramics; among them crystallinity, crystal size and the microstructure of material are of obvious importance. A need exists to investigate in greater detail the correlation of prior liquid-phase separation with crystallization course and microstructure in order to trace a path of controlling the properties of glass ceramics and developing new glass ceramics. The main effect of liquid-phase separation on optical absorption of ruby glass appears to be a lowering of the striking temperature and an increase of intensity of ruby glass, This has practical importance for ruby glass. The base glass with liquid-phase separation is most desirable for striking of ruby glass. From this point of view, in future the main effort should also be directed towards correlation of liquid-phase separation with the striking properties of ruby glass. Once the effect of this is fully known, glass scientists could take advantage of this to guide the exploration of a new type of colloidally coloured glasses and give valuable reference to research on photochromic glasses, photosensitive glasses and so on. References [l] [2] [3] [4] [5] [6]
Shari Ying, Li Jiazhi, De Zequn and Zhou Xueqin, J. Chin. Silicate Sot. 9 (1981) 403. Li Jiazhi, Shan Ying and Hu Guanging, J. de Phys. 43 (1982) 231. Shan Ying, Li J&hi, Deng Zequn and Zhou Xuqin, J. Non-Cryst. Solids 52 (1982) 275. Li Jiazhi and Shari Ying, Glastechn. Ber. 56K (1983) 800. Bao Zhiqin, Li Jiazhi and Shen Chongde, J. Chin. Silicate Sot. 9 (1981) 1. Fang Chib-yao and Li J&hi, to be published.
Solids
87 (1986)
387
387-391
PROSPECTS OF THE RELATIONSHIP SEPARATION AND CRYSTALLIZATION LI Jiazhi and FANG Shmghu~
Ittstrrrr~e
BETWEEN LIQUID-PHASE IN GLASS *
Chih-yao
of Ceramrcs.
Academia
Sinicu,
Shmghoi.
Chiuu
The past half century has seen the publication of a large number of studies dealing with liquid-phase separation in glass-forming systems. In contrast to the abundance of studies on thermodynamics. kinetics of liquid phase separation as well as its effect on crystallization and properties of glass. relatively few applications have been known directly utilizing this phenomenon. There is some experimental evidence that liquid-phase separation exerts an important influence both on the properties of glass ceramics and the striking properties of ruby glasses. It is possible to utilize knowledge available and more fully understand liquid-phase separation and its relation with crystallization for improving the properties of glass ceramics and developing new glass materials with promising properties. Thus, much work remains to be done. The objective of this paper is to emphasize the relationship between liquid-phase separation and the crystallization behavior of glass.
Liquid-phase separation exists commonly in many glass-ceramic systems. As glass ceramics were discovered and developed, interest in the phase separation and control of crystallization of glasses further increased, The prior liquid-phase separation may produce two liquid compositions, one of which has a greater tendency to crystallize than initial non-separated glass. This shift in composition probably caused changes in the nucleation barrier of thermodynamics and kinetics as well as the change in thermodynamic driving force and in atomic mobility which in turn influence the nucleation rate and the crystallization course including the kind of primary crystalline phase, the amount of final crystalline phase and the microstructure of the material. We can predict if the effect of liquid phase separation on the crystallization process of glass can be fully understood and controlled, that new glass ceramics of desired properties could be developed. In our work on MgO-Al,O,-SiO,-TiO, [l], ZnO-Al,O,-SiO, [2] and ZnO-Al,Os-SiO,-ZrO, [3] glass-ceramic systems, we found in all glasses which exhibit a great degree of liquid-phase separation, a tendency to decrease the crystallization temperature, i.e. the primary crystalline phase with complicated composition can be precipitated at lower temperature as compared to the non-phase-separated composition [4]. The MgO-A1203--SiOz-TiO, system exhibited a great liquid-phase separation; a magnesium-alumino-titanate * Paper presented Kreidl), Vienna,
at the Symposium on Glass July 1984, but not published
Science and Technology in the Proceedings.
0022-3093/86/$03.50 0 Elsevier Science Publishers (North-Holland Physics Publishing Division)
B.V
(in honour
o/ Norherr
J.
388
Li Jiozhi.
Fung Chih,vao
660
/ Liquid-phase
680
700
720
Temperature
Fig.
1. The
effect
of pre-heat
seporution
740
760
of pre-heat
treatment on the thermal MgO-A1203-Si02-Ti02.
and uystollizotiotl
780
800
treatment
expansion
820
in glass
840
I”CI
of coefficient
of glass-ceramics
crystal may be precipitated at a temperature 90°C lower than that in the composition not tending to liquid-phase separation. In the ZnO-Al,O,-SiO, system, the crystallization temperature of p-willemite solid solution may also be decreased by 60°C. In addition, prior liquid-phase separation exerts a strong influence on the amount of final crystalline phase in glass ceramics. This may be due to the fact that liquid-phase separation promotes the nucleation of crystal. Thus, the properties of the material will be greatly changed. In the MgO-Al ,O,-SiO,-TiO, system tending to liquid-phase separation, the glass-ceramic sample with given composition pre-heated at different temperature may have quite different properties [5]. Figure 1 shows the effect of a different pre-heated schedule on thermal expansion of the coefficient of glass ceramics. As seen from fig. 1, thermal expansion of the coefficient of 11-13 x 10-‘/O C could only be obtained for the prethermal treatment at a 700-760° C temperature range. The specimens which were preheated at 650°C for 10 h have a modulus of rupture of 2000 kg/cm2, the glass-ceramic specimens preheated at 750°C for 10 h have a modulus of rupture of 400 kg/cm2. While both specimens were heated to 800°C and then quenched in cold water, the modulus of rupture for the former was almost decreased one order of magnitude but that for the latter remained unchanged. Figure 2 shows the
Fig. 2. (a) Scanning electron micrograph of specimen heat-treated at 650°C/10 h (X 10000); Scanning electron micrograph of specimen heat-treated at 75O”C/lO h ( X 10000).
(b)
Li Jimhi.
Fuug Chih-wo
/ Liquid-phase
separurion
und qarollizaliotl
in glass
389
SEM microphotographs of glasses undergoing these different pre-heating treatments and different extents of liquid-phase separation. After glass-phase separation, the composition of each separated phase will diversify according to the ionic field strength of cations. For example in MgO-Al,O,-SiO,-TiO,, two liquid phases, silica-rich as well as titania- and magnesia-rich, and in ZnO-Al ,O,-SiO,, two liquids, silica-rich and zinc-rich, can be formed. The greater the degree of phase separation, the more beneficial to richening in magnesium and titanium ions or zinc ions in respective phases, i.e. in subsequent crystallization process of glasses, the more beneficial to crystallize magnesium aluminium titanate or j%willemite solid solution and gahnite in these phases respectively. This makes them crystallized at a lower temperature. From this point of view, the kinds of initial crystalline phase, crystallized from the phase-separated glass, depend on the composition of two or more liquid phases rather than the original glass composition. Of course, they are also different from those of original glass composition in the phase diagram. However, the final crystalline phase crystallized from the liquid-phase separated glass depends on the original glass compositions. Different degrees of liquid-phase separation do not affect the final crystalline phase, but change their amounts only because of a different crystallization process. Another interesting aspect is the influence of liquid-phase separation on optical absorption of ruby glasses. Copper ruby and silver ruby glasses have been known since the Middle Ages. Although the complex colloid chemistry of these glasses has already been elucidated, the selection of their base glasses still requires unusual experience, so that their manufacture has been confined to a few glass compositions. Little glass literature has been offered concerning the composition of ruby glasses. The formation of the ruby colour is basically a problem of chemical thermodynamics in the glass melt and the kinetics of the precipitation of phase in which the melt is supersaturated. Indeed, the striking process of ruby glass is a course of nucleation and growth of colloidal crystals. The optical absorption of these ruby glasses is proportional to the amount and size of colloidal particles. In our work on copper ruby and silver ruby [6], we made a study of the influence of liquid-phase separation on copper ruby and silver ruby formation. We chose two similar soda-boron-silica glass compositions as base glasses, one of which exhibits liquid-phase separation, the other is non-phase separated. The experimental results show that the most desirable and most intense colours of copper ruby and silver ruby are obtained in liquid-phase separated base glasses. Figures 3 and 4 show absorption spectra of copper ruby and silver ruby glasses. At the same striking temperature, phase separated copper ruby glass gives a deeper red colour than non-phase separated copper ruby glass. Liquid-phase separation exerts a stronger influence on the striking of silver ruby. The heat
390
Li Jiarhi,
800
1200
Fung
1600 Wavelength
Chih-yoo
2000
/ Liquid-phase
2400
sepuratiorl
und ctystalliration
in glass
2800
“m
Fig. 3. (a) Absorption spectra of liquid-phase separation copper ruby glass. A, 470°C for 4 h; B. 490°C for 4 h; C, 53O’C for 4 h; D. 550°C for 4 h. (b) Absorption spectra of non-liquid phase separated copper ruby glass. A, 470°C for 4 h; B, 490°C for 4 h; C, 530°C for 4 h; D. 550°C for 4 h.
treatment at 490°C for 4 h gives liquid-phase separated silver ruby a deep yellow colour; however, non-phase separated silver ruby does not strike until 610°C. At a temperature of 53O”C, phase-separated silver ruby glass has developed a deep red colour which means the colloidal particles have grown to a larger size. The effect of liquid-phase separation on the striking features of silver ruby and copper ruby glasses might also be attributed to the marked influence of liquid-phase separation on the course of crystallization of metallic particles in ruby glass. These observations could also be explained in terms of the composition shif )f the matrix during liquid-phase separation. 100
a
80
I
20
2800
Wavelength
Fig. 4. (a) Transmission spectra of liquid-phase separated B,490oCfor4h;C,5100Cfor4h;D,5300Cfor4h;E.5500Cfor4h.
nm
silver
ruby
glass.
3
)a
A, non-heat
treatment;
Li J&hi,
Fang Chih-yao
0
400
/ Liquid-phuw
800
1200
sepamion
1600
Wavelength
Fig. 4. (b) Transmission
2000
and cryslallizatiott
2400
2800
in glass
391
3000
nm
spectra of non-liquid phase separated and530°Cfor4h;B,5500Cfor4h;C,610”Cfor4h.
silver
ruby
glass. A. 490°C,
510°C
One practical implication of the experimental results above is that for many glass-ceramic systems, the effect of different heat treatment prior to crystal nucleation treatment is particularly striking. Various degrees of liquid-phase separation do appear to have a very significant effect on the crystallization course and microstructure of glass ceramics. Many factors can possibly affect the properties of glass ceramics; among them crystallinity, crystal size and the microstructure of material are of obvious importance. A need exists to investigate in greater detail the correlation of prior liquid-phase separation with crystallization course and microstructure in order to trace a path of controlling the properties of glass ceramics and developing new glass ceramics. The main effect of liquid-phase separation on optical absorption of ruby glass appears to be a lowering of the striking temperature and an increase of intensity of ruby glass, This has practical importance for ruby glass. The base glass with liquid-phase separation is most desirable for striking of ruby glass. From this point of view, in future the main effort should also be directed towards correlation of liquid-phase separation with the striking properties of ruby glass. Once the effect of this is fully known, glass scientists could take advantage of this to guide the exploration of a new type of colloidally coloured glasses and give valuable reference to research on photochromic glasses, photosensitive glasses and so on. References [l] [2] [3] [4] [5] [6]
Shari Ying, Li Jiazhi, De Zequn and Zhou Xueqin, J. Chin. Silicate Sot. 9 (1981) 403. Li Jiazhi, Shan Ying and Hu Guanging, J. de Phys. 43 (1982) 231. Shan Ying, Li J&hi, Deng Zequn and Zhou Xuqin, J. Non-Cryst. Solids 52 (1982) 275. Li Jiazhi and Shari Ying, Glastechn. Ber. 56K (1983) 800. Bao Zhiqin, Li Jiazhi and Shen Chongde, J. Chin. Silicate Sot. 9 (1981) 1. Fang Chib-yao and Li J&hi, to be published.