- Email: [email protected]
Effect of denucleating glass composition on undercooling of Fe83Ga17 alloy melts
Journal of Alloys and Compounds 467 (2009) 179–181
Effect of denucleating glass composition on undercooling of Fe83Ga17 alloy melts Jiankun Zhou, Jianguo Li ∗ School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai, PR China Received 1 November 2007; received in revised form 29 November 2007; accepted 30 November 2007 Available online 8 December 2007
Abstract Adopting glass fluxing combined with superheating cycling method, the undercooling and its stability of Fe83 Ga17 alloy melts were investigated using different kinds of denucleating glass: B2 O3 , 90% NaSiCa + 10% B2 O3 (simplified as Na–Si–Ca–Al–B) and 70% Na–Si–Ca–Al–B + 30% Na2 B7 O4 . The results showed that different glass has different denucleating mechanism. The purification of B2 O3 glass is only a physical process, by which the stable bulk undercooling cannot be obtained during superheating–cooling cycles. While taking Na–Si–Ca–Al–B glass as purifying agent, its denucleating mechanism is a comprehensively physicochemical process. But the stability of undercooling is still undesirable because of the separation between melt and glass during cooling process in superheating cycling. A stable bulk undercooling can be obtained by physicochemical denucleating process in the case of 70% Na–Si–Ca–Al–B + 30% Na2 B7 O4 molten glass owing to its suitable viscosity. © 2007 Elsevier B.V. All rights reserved. Keywords: Undercooling; Denucleating glass; Viscosity
1. Introduction Textured Fe100−x Gax (13 ≤ x ≤ 23) alloys have attracted much attention due to their potential application as magnetostriction materials [1–4]. It has recently been reported that the large magnetostriction up to −1300 ppm was obtained in the near [1 0 0] textured melt-spun Fe85 Ga15 ribbons [5]. Furthermore, the rapid directional solidification method by triggering the undercooled melt was introduced as a new approach to prepare bulk Fe80 Ga20 rods with [1 0 0] preferred orientation [6]. Unfortunately, the technique of rapid directional solidification by triggering the undercooled melt was greatly limited due to the unstability of melts undercooling. Various experimental techniques, such as emulsification [7], electromagnetic levitation [8], microgravity [9], drop tube [10], glass fluxing [11] and superheating cycling [12] methods, have been developed to extend the range of undercooling mainly by elimination of crucible-induced nucleation and by separation of heterogeneous nucleants from the melt. Among them, the glass fluxing combined with superheating cycling method was mostly used due to its facility and effectivity. Generally, both B2 O3 and ∗
Corresponding author. E-mail address: [email protected] (J. Zhou).
0925-8388/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2007.11.145
Na–Si–Ca–Al–B glasses have good purification effect for Febased alloys melts [6,13,14]. But the obtained undercooling and its stability for FeGa melts still varies from different kinds of glasses. However, most of the previous investigations on undercooled melts are focused on basic researches of solidification behaviors and microstructure evolution [13–16]. In contrast, little has been reported about the undercooling and its stability of FeGa alloy melts which is crucial for fabricating bulk textured FeGa alloys through rapid solidification by triggering the undercooled melt. Therefore, in this paper we conduct the effect of composition and structure of different denucleating glasses on the undercooling ability and its stability during superheating–cooling cycles of Fe83 Ga17 melts. 2. Experimental High-purity elemental materials (Fe 99.99% and Ga 99.99%) were alloyed to form a master ingot of Fe83 Ga17 by arc-melting under an argon atmosphere. The master ingot, after being cut into small pieces, was cleaned acoustically in acetone for 30 min and then placed in a quartz crucible with denucleating glass inside. Compositions of the three kinds of denucleating glasses used in this paper are: B2 O3 , 90% NaSiCa + 10% B2 O3 (simplified as Na–Si–Ca–Al–B) and 70% Na–Si–Ca–Al–B + 30% Na2 B7 O4 . B2 O3 and Na2 B7 O4 were made from analytical reagents, while NaSiCa glass was a commercial standard substance which consists of 74.0% SiO2 , 15% (Na2 O + K2 O), 7% CaO, 2% Al2 O3 , 1.8% MgO and 0.2% Fe2 O3 .
180
J. Zhou, J. Li / Journal of Alloys and Compounds 467 (2009) 179–181
Fig. 1. Sketch of the apparatus for undercooling experiments. Undercooling experiments were performed in an apparatus schematically shown in Fig. 1. The temperature of Fe83 Ga17 melts and undercooling were measured by an infrared pyrometer calibrated with a standard PtRh30–PtRh6 thermocouple, which possesses a relative accuracy of 5 K with a response time less than 1 ms. The typical experimental procedure may be summarized as follows: (1) Put the cleaned small piece of ingot into a quartz crucible with denucleating glass surrounded. (2) Evacuate to a pressure of 1 × 10−2 Pa and back fill to 0.06 MPa with Ar. Then inductive heat to 1273 K and keep 2 min to degas the molten glass. (3) Superheat to 1873 K (about 150 K above the liquidus temperature of Fe83 Ga17 ) and keep 2 min, then conduct the cycling process of solidifying–remelting–superheating, during which the cooling curve is recorded.
3. Results The degrees of undercooling of Fe83 Ga17 melts during the superheating–cooling cyclings using different denucleating agents are presented in Fig. 2. For B2 O3 as denucleating glass (Fig. 2(a)), the maximum undercooling is less than 100 K. The obtained undercooling changes randomly during the superheating–cooling cycles. While for Na–Si–Ca–Al–B glass (Fig. 2(b)), the obtained degree of undercooling during the cycles is much higher than that for B2 O3 glass. The maximum degree of undercooling obtained is 297 K. It should also be noted that the maximum value of the degree of undercooling can be achieved in the first cycle. In spite of this, the undercooling decreases gradually in the remelting process during the next several superheating–cooling cycles. However, for 70% Na–Si–Ca–Al–B + 30% Na2 B7 O4 (Fig. 2(c)), the undercooling obtained can be stable in about 300 K during all of the superheating–cooling cycles. 4. Discussions According to the studies by Powell [11] and Drehman et al. [12], there are two functions of glass fluxing technique for achieving high undercooling. On one hand, the molten glass can protect the surface of metal melts against atmosphere and crucible which avoid the formation of metal oxides and container-wall induced nucleation. On the other hand, the metal oxides which serve as the main heterogeneous nucleants can be separated from the melts through physical absorption and chemical reaction between molten glass and metal oxides. Similar to that, superheating cycling is introduced to dissolve and vaporize the heterogeneous nucleants which will result in high undercooling.
Fig. 2. Undercoolings obtained during the superheating–cooling cyclings by different denucleating agents. (a) B2 O3 ; (b) Na–Si–Ca–Al–B (90% NaSiCa + 10% B2 O3 ); (c) 70% Na–Si–Ca–Al–B + 30% Na2 B7 O4 .
Based on the Random Network Model [17], pure B2 O3 glass can be regarded as layer or chain network structure composed of disordering linked [BO3 ] triangles. Since ferrous oxide and gallium oxide cannot change the structure of [BO3 ] triangles when they are absorbed into the molten glass, B2 O3 glass purifies Fe83 Ga17 melts simply by physical viscous absorption in high temperature instead of chemical reaction effect. The arrangement of the oxide impurity which serves as nucleants among the molten glass can be described by a Poisson distribution [15]. For this case the nucleant free fraction, X is represented by X = exp(−mv) where m is the average number of nucleants per volume and v the volume. However, the oxide impurity absorbed in the layers and chains of [BO3 ] triangles is easy to be desorbed by the following electromagnetic stirring effect because the layers and chains are linked by intermolecular forces. In this case, only one randomly distributed metal oxide appearing in the interface of Fe83 Ga17 alloy melt and molten B2 O3 glass can work
J. Zhou, J. Li / Journal of Alloys and Compounds 467 (2009) 179–181
181
glass. On the other hand, the composition of [BO3 ] triangles in the glass network increases with the addition of Na2 B7 O4 which improves the dissolving effect of metal oxides for 70% Na–Si–Ca–Al–B + 30% Na2 B7 O4 glass. As a result, bulk undercooling up to 300 K can be achieved stably during all of the superheating–cooling cycles. 5. Conclusions
Fig. 3. Structural model of Na2 O–B2 O3 –Al2 O3 –SiO2 denucleating glass system [17] (0 < ξ * < 1).
as heterogeneity which results in the solidification of the melt. Consequently, the obtained undercooling changes randomly and unstably during the superheating–cooling cycles by using B2 O3 glass. While for Na–Si–Ca–Al–B glass, the denucleating mechanism is much more complex. According to Gan’s [17] report, the relation between structure and composition of boro-aluminosilicate glasses formation process is expressed as ξ∗ =
C(Na2 O) − C(Al2 O3 ) , C(B2 O3 )
(1)
where C is molar composition of glass component. When ξ * 1, Al2 O3 –glass network intermediate and B2 O3 –glass network former will enter into [SiO4 ] network of quartz glass in the form of [AlO4 ]− and [BO4 ]− tetrahedrons which are surrounded by the metal cations of Na+ and Ca2+ . In this case, the metal oxides yielded in the melting of Fe83 Ga17 can only be physically absorbed into the molten Na–Si–Ca–Al–B glass, otherwise it results in electronegative unbalance of the molten glass. When 0 < ξ * < 1, the metal cations cannot transform all of Al2 O3 and B2 O3 into [AlO4 ]− and [BO4 ]− tetrahedrons whereas part of B2 O3 enters into glass network in the form of neutral [BO3 ] triangle (Fig. 3). In this case, the metal oxides absorbed in the interface of Fe83 Ga17 alloy melt and molten Na–Si–Ca–Al–B glass is dissolved into the glass which results in the formation of new glass structure. The denucleating mechanism turns into a comprehensively physicochemical process in this way. For Na–Si–Ca–Al–B (90% NaSiCa + 10% B2 O3 ) glass used in this paper, ξ * ≈ 0.89, which means few heterogeneous nucleants can exist in the interface of alloy melt and molten glass. Consequently, the undercoolings obtained are much higher than using B2 O3 glass. Unfortunately, the interface of alloy melt and molten glass is easy to be separated during the superheating–cooling cycles due to the high viscosity of Na–Si–Ca–Al–B glass. Therefore, the undercooling decreases gradually in the remelting process during the next several superheating–cooling cycles as a result of oxidation of Fe83 Ga17 melt. Hence, to improve and stable the denucleating effect, 30% Na2 B7 O4 is added to decrease the viscosity of Na–Si–Ca–Al–B
(1) Bulk undercoolings can be obtained in Fe83 Ga17 melts by glass fluxing combined with superheating cycling method for different denucleating glass: B2 O3 , 90% NaSiCa + 10% B2 O3 (simplified as Na–Si–Ca–Al–B) and 70% Na–Si–Ca–Al–B + 30% Na2 B7 O4 . (2) For B2 O3 glass, the purification mechanism is only a physical process by which stable bulk undercooling cannot be obtained during superheating–cooling cycles. (3) For Na–Si–Ca–Al–B glass, high undercooling up to 297 K can be achieved in the first cycle. The denucleating mechanism is a comprehensively physicochemical process. But the stability of undercooling is still low due to its high viscosity. (4) For 70% Na–Si–Ca–Al–B + 30% Na2 B7 O4 glass, stable bulk undercooling of about 300 K can be obtained by physicochemical denucleating effect because of its appropriate viscosity. Acknowledgement The authors are grateful to the financial support of the National Natural Science Foundation of China (Grant No. 50574058). References [1] A.E. Clark, J.B. Restorff, M. Wun-Fogle, T.A. Lograsso, D.L. Schlagel, IEEE Trans. Magn. 36 (2000) 3238. [2] A.E. Clark, M. Wun-Fogle, J.B. Restorff, T.A. Lograsso, J.R. Cullen, IEEE Trans. Magn. 37 (2001) 2678. [3] J.R. Cullen, A.E. Clark, M. Wun-Fogle, J.B. Restorff, T.A. Lograsso, J. Magn. Magn. Mater. 226 (2001) 948. [4] R.A. Kellogg, A.B. Flatau, A.E. Clark, M. Wun-Fogle, T.A. Lograsso, J. Appl. Phys. 91 (2002) 7821. [5] G.D. Liu, L.B. Liu, Z.H. Liu, M. Zhang, J.L. Chen, J.Q. Li, G.H. Wu, Y.X. Li, T.S. Chin, Appl. Phys. Lett. 84 (2004) 2124. [6] W. Ma, H. Zheng, M. Xia, J. Li, J. Alloys Compd. 379 (2004) 188. [7] D. Turnbull, R.E. Cech, J. Appl. Phys. 21 (1950) 804. [8] D. Turnbull, J. Appl. Phys. 21 (1950) 1022. [9] R. Jansen, et al., Mater. Sci. Eng. A 65 (1984) 199. [10] W.H. Hofmeister, M.B. Robinson, R.J. Bayuzick, Appl. Phys. Lett. 49 (1986) 1342. [11] G.L.F. Powell, Aust. Inst. Met. 10 (1965) 223. [12] A.J. Drehman, et al., Appl. Phys. Lett. 41 (1982) 716. [13] Y.Z. Chen, G.C. Yang, F. Liu, H. Xie, Y.H. Zhou, J. Cryst. Growth 282 (2005) 490. [14] C.L. Yang, G.C. Yang, F. Liu, et al., Physica B 373 (2006) 136. [15] J.H. Perepezko, Mater. Sci. Eng. A 226–228 (1997) 374. [16] D.M. Herlach, J. Gao, D. Holland-Moritz, T. Volkmann, Mater. Sci. Eng. A 375–377 (2004) 9. [17] F.X. Gan, Modern Glass Science and Technology, Science and Technology Press, Beijing, 1986, pp. 39–42.
Effect of denucleating glass composition on undercooling of Fe83Ga17 alloy melts Jiankun Zhou, Jianguo Li ∗ School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai, PR China Received 1 November 2007; received in revised form 29 November 2007; accepted 30 November 2007 Available online 8 December 2007
Abstract Adopting glass fluxing combined with superheating cycling method, the undercooling and its stability of Fe83 Ga17 alloy melts were investigated using different kinds of denucleating glass: B2 O3 , 90% NaSiCa + 10% B2 O3 (simplified as Na–Si–Ca–Al–B) and 70% Na–Si–Ca–Al–B + 30% Na2 B7 O4 . The results showed that different glass has different denucleating mechanism. The purification of B2 O3 glass is only a physical process, by which the stable bulk undercooling cannot be obtained during superheating–cooling cycles. While taking Na–Si–Ca–Al–B glass as purifying agent, its denucleating mechanism is a comprehensively physicochemical process. But the stability of undercooling is still undesirable because of the separation between melt and glass during cooling process in superheating cycling. A stable bulk undercooling can be obtained by physicochemical denucleating process in the case of 70% Na–Si–Ca–Al–B + 30% Na2 B7 O4 molten glass owing to its suitable viscosity. © 2007 Elsevier B.V. All rights reserved. Keywords: Undercooling; Denucleating glass; Viscosity
1. Introduction Textured Fe100−x Gax (13 ≤ x ≤ 23) alloys have attracted much attention due to their potential application as magnetostriction materials [1–4]. It has recently been reported that the large magnetostriction up to −1300 ppm was obtained in the near [1 0 0] textured melt-spun Fe85 Ga15 ribbons [5]. Furthermore, the rapid directional solidification method by triggering the undercooled melt was introduced as a new approach to prepare bulk Fe80 Ga20 rods with [1 0 0] preferred orientation [6]. Unfortunately, the technique of rapid directional solidification by triggering the undercooled melt was greatly limited due to the unstability of melts undercooling. Various experimental techniques, such as emulsification [7], electromagnetic levitation [8], microgravity [9], drop tube [10], glass fluxing [11] and superheating cycling [12] methods, have been developed to extend the range of undercooling mainly by elimination of crucible-induced nucleation and by separation of heterogeneous nucleants from the melt. Among them, the glass fluxing combined with superheating cycling method was mostly used due to its facility and effectivity. Generally, both B2 O3 and ∗
Corresponding author. E-mail address: [email protected] (J. Zhou).
0925-8388/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2007.11.145
Na–Si–Ca–Al–B glasses have good purification effect for Febased alloys melts [6,13,14]. But the obtained undercooling and its stability for FeGa melts still varies from different kinds of glasses. However, most of the previous investigations on undercooled melts are focused on basic researches of solidification behaviors and microstructure evolution [13–16]. In contrast, little has been reported about the undercooling and its stability of FeGa alloy melts which is crucial for fabricating bulk textured FeGa alloys through rapid solidification by triggering the undercooled melt. Therefore, in this paper we conduct the effect of composition and structure of different denucleating glasses on the undercooling ability and its stability during superheating–cooling cycles of Fe83 Ga17 melts. 2. Experimental High-purity elemental materials (Fe 99.99% and Ga 99.99%) were alloyed to form a master ingot of Fe83 Ga17 by arc-melting under an argon atmosphere. The master ingot, after being cut into small pieces, was cleaned acoustically in acetone for 30 min and then placed in a quartz crucible with denucleating glass inside. Compositions of the three kinds of denucleating glasses used in this paper are: B2 O3 , 90% NaSiCa + 10% B2 O3 (simplified as Na–Si–Ca–Al–B) and 70% Na–Si–Ca–Al–B + 30% Na2 B7 O4 . B2 O3 and Na2 B7 O4 were made from analytical reagents, while NaSiCa glass was a commercial standard substance which consists of 74.0% SiO2 , 15% (Na2 O + K2 O), 7% CaO, 2% Al2 O3 , 1.8% MgO and 0.2% Fe2 O3 .
180
J. Zhou, J. Li / Journal of Alloys and Compounds 467 (2009) 179–181
Fig. 1. Sketch of the apparatus for undercooling experiments. Undercooling experiments were performed in an apparatus schematically shown in Fig. 1. The temperature of Fe83 Ga17 melts and undercooling were measured by an infrared pyrometer calibrated with a standard PtRh30–PtRh6 thermocouple, which possesses a relative accuracy of 5 K with a response time less than 1 ms. The typical experimental procedure may be summarized as follows: (1) Put the cleaned small piece of ingot into a quartz crucible with denucleating glass surrounded. (2) Evacuate to a pressure of 1 × 10−2 Pa and back fill to 0.06 MPa with Ar. Then inductive heat to 1273 K and keep 2 min to degas the molten glass. (3) Superheat to 1873 K (about 150 K above the liquidus temperature of Fe83 Ga17 ) and keep 2 min, then conduct the cycling process of solidifying–remelting–superheating, during which the cooling curve is recorded.
3. Results The degrees of undercooling of Fe83 Ga17 melts during the superheating–cooling cyclings using different denucleating agents are presented in Fig. 2. For B2 O3 as denucleating glass (Fig. 2(a)), the maximum undercooling is less than 100 K. The obtained undercooling changes randomly during the superheating–cooling cycles. While for Na–Si–Ca–Al–B glass (Fig. 2(b)), the obtained degree of undercooling during the cycles is much higher than that for B2 O3 glass. The maximum degree of undercooling obtained is 297 K. It should also be noted that the maximum value of the degree of undercooling can be achieved in the first cycle. In spite of this, the undercooling decreases gradually in the remelting process during the next several superheating–cooling cycles. However, for 70% Na–Si–Ca–Al–B + 30% Na2 B7 O4 (Fig. 2(c)), the undercooling obtained can be stable in about 300 K during all of the superheating–cooling cycles. 4. Discussions According to the studies by Powell [11] and Drehman et al. [12], there are two functions of glass fluxing technique for achieving high undercooling. On one hand, the molten glass can protect the surface of metal melts against atmosphere and crucible which avoid the formation of metal oxides and container-wall induced nucleation. On the other hand, the metal oxides which serve as the main heterogeneous nucleants can be separated from the melts through physical absorption and chemical reaction between molten glass and metal oxides. Similar to that, superheating cycling is introduced to dissolve and vaporize the heterogeneous nucleants which will result in high undercooling.
Fig. 2. Undercoolings obtained during the superheating–cooling cyclings by different denucleating agents. (a) B2 O3 ; (b) Na–Si–Ca–Al–B (90% NaSiCa + 10% B2 O3 ); (c) 70% Na–Si–Ca–Al–B + 30% Na2 B7 O4 .
Based on the Random Network Model [17], pure B2 O3 glass can be regarded as layer or chain network structure composed of disordering linked [BO3 ] triangles. Since ferrous oxide and gallium oxide cannot change the structure of [BO3 ] triangles when they are absorbed into the molten glass, B2 O3 glass purifies Fe83 Ga17 melts simply by physical viscous absorption in high temperature instead of chemical reaction effect. The arrangement of the oxide impurity which serves as nucleants among the molten glass can be described by a Poisson distribution [15]. For this case the nucleant free fraction, X is represented by X = exp(−mv) where m is the average number of nucleants per volume and v the volume. However, the oxide impurity absorbed in the layers and chains of [BO3 ] triangles is easy to be desorbed by the following electromagnetic stirring effect because the layers and chains are linked by intermolecular forces. In this case, only one randomly distributed metal oxide appearing in the interface of Fe83 Ga17 alloy melt and molten B2 O3 glass can work
J. Zhou, J. Li / Journal of Alloys and Compounds 467 (2009) 179–181
181
glass. On the other hand, the composition of [BO3 ] triangles in the glass network increases with the addition of Na2 B7 O4 which improves the dissolving effect of metal oxides for 70% Na–Si–Ca–Al–B + 30% Na2 B7 O4 glass. As a result, bulk undercooling up to 300 K can be achieved stably during all of the superheating–cooling cycles. 5. Conclusions
Fig. 3. Structural model of Na2 O–B2 O3 –Al2 O3 –SiO2 denucleating glass system [17] (0 < ξ * < 1).
as heterogeneity which results in the solidification of the melt. Consequently, the obtained undercooling changes randomly and unstably during the superheating–cooling cycles by using B2 O3 glass. While for Na–Si–Ca–Al–B glass, the denucleating mechanism is much more complex. According to Gan’s [17] report, the relation between structure and composition of boro-aluminosilicate glasses formation process is expressed as ξ∗ =
C(Na2 O) − C(Al2 O3 ) , C(B2 O3 )
(1)
where C is molar composition of glass component. When ξ * 1, Al2 O3 –glass network intermediate and B2 O3 –glass network former will enter into [SiO4 ] network of quartz glass in the form of [AlO4 ]− and [BO4 ]− tetrahedrons which are surrounded by the metal cations of Na+ and Ca2+ . In this case, the metal oxides yielded in the melting of Fe83 Ga17 can only be physically absorbed into the molten Na–Si–Ca–Al–B glass, otherwise it results in electronegative unbalance of the molten glass. When 0 < ξ * < 1, the metal cations cannot transform all of Al2 O3 and B2 O3 into [AlO4 ]− and [BO4 ]− tetrahedrons whereas part of B2 O3 enters into glass network in the form of neutral [BO3 ] triangle (Fig. 3). In this case, the metal oxides absorbed in the interface of Fe83 Ga17 alloy melt and molten Na–Si–Ca–Al–B glass is dissolved into the glass which results in the formation of new glass structure. The denucleating mechanism turns into a comprehensively physicochemical process in this way. For Na–Si–Ca–Al–B (90% NaSiCa + 10% B2 O3 ) glass used in this paper, ξ * ≈ 0.89, which means few heterogeneous nucleants can exist in the interface of alloy melt and molten glass. Consequently, the undercoolings obtained are much higher than using B2 O3 glass. Unfortunately, the interface of alloy melt and molten glass is easy to be separated during the superheating–cooling cycles due to the high viscosity of Na–Si–Ca–Al–B glass. Therefore, the undercooling decreases gradually in the remelting process during the next several superheating–cooling cycles as a result of oxidation of Fe83 Ga17 melt. Hence, to improve and stable the denucleating effect, 30% Na2 B7 O4 is added to decrease the viscosity of Na–Si–Ca–Al–B
(1) Bulk undercoolings can be obtained in Fe83 Ga17 melts by glass fluxing combined with superheating cycling method for different denucleating glass: B2 O3 , 90% NaSiCa + 10% B2 O3 (simplified as Na–Si–Ca–Al–B) and 70% Na–Si–Ca–Al–B + 30% Na2 B7 O4 . (2) For B2 O3 glass, the purification mechanism is only a physical process by which stable bulk undercooling cannot be obtained during superheating–cooling cycles. (3) For Na–Si–Ca–Al–B glass, high undercooling up to 297 K can be achieved in the first cycle. The denucleating mechanism is a comprehensively physicochemical process. But the stability of undercooling is still low due to its high viscosity. (4) For 70% Na–Si–Ca–Al–B + 30% Na2 B7 O4 glass, stable bulk undercooling of about 300 K can be obtained by physicochemical denucleating effect because of its appropriate viscosity. Acknowledgement The authors are grateful to the financial support of the National Natural Science Foundation of China (Grant No. 50574058). References [1] A.E. Clark, J.B. Restorff, M. Wun-Fogle, T.A. Lograsso, D.L. Schlagel, IEEE Trans. Magn. 36 (2000) 3238. [2] A.E. Clark, M. Wun-Fogle, J.B. Restorff, T.A. Lograsso, J.R. Cullen, IEEE Trans. Magn. 37 (2001) 2678. [3] J.R. Cullen, A.E. Clark, M. Wun-Fogle, J.B. Restorff, T.A. Lograsso, J. Magn. Magn. Mater. 226 (2001) 948. [4] R.A. Kellogg, A.B. Flatau, A.E. Clark, M. Wun-Fogle, T.A. Lograsso, J. Appl. Phys. 91 (2002) 7821. [5] G.D. Liu, L.B. Liu, Z.H. Liu, M. Zhang, J.L. Chen, J.Q. Li, G.H. Wu, Y.X. Li, T.S. Chin, Appl. Phys. Lett. 84 (2004) 2124. [6] W. Ma, H. Zheng, M. Xia, J. Li, J. Alloys Compd. 379 (2004) 188. [7] D. Turnbull, R.E. Cech, J. Appl. Phys. 21 (1950) 804. [8] D. Turnbull, J. Appl. Phys. 21 (1950) 1022. [9] R. Jansen, et al., Mater. Sci. Eng. A 65 (1984) 199. [10] W.H. Hofmeister, M.B. Robinson, R.J. Bayuzick, Appl. Phys. Lett. 49 (1986) 1342. [11] G.L.F. Powell, Aust. Inst. Met. 10 (1965) 223. [12] A.J. Drehman, et al., Appl. Phys. Lett. 41 (1982) 716. [13] Y.Z. Chen, G.C. Yang, F. Liu, H. Xie, Y.H. Zhou, J. Cryst. Growth 282 (2005) 490. [14] C.L. Yang, G.C. Yang, F. Liu, et al., Physica B 373 (2006) 136. [15] J.H. Perepezko, Mater. Sci. Eng. A 226–228 (1997) 374. [16] D.M. Herlach, J. Gao, D. Holland-Moritz, T. Volkmann, Mater. Sci. Eng. A 375–377 (2004) 9. [17] F.X. Gan, Modern Glass Science and Technology, Science and Technology Press, Beijing, 1986, pp. 39–42.