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Effect of residual stress on azo dye degradation capability of Fe-based metallic glass
Journal of Non-Crystalline Solids xxx (xxxx) xxx–xxx
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Journal of Non-Crystalline Solids journal homepage: www.elsevier.com/locate/jnoncrysol
Effect of residual stress on azo dye degradation capability of Fe-based metallic glass Shuang-Qin Chen, Yang Shao, Meng-Ting Cheng, Ke-Fu Yao⁎ School of Material Science and Engineering, Tsinghua University, Beijing 100084, PR China
A R T I C L E I N F O
A B S T R A C T
Keywords: Fe-based metallic glass Residual stress Azo dye Degradation
Fe-based metallic glasses (MGs) are among the most interesting in the area of MG materials, due to their superior properties such as high degradation capability of azo dyes. However, the ways that factors influence the degradation capability of MGs towards azo dyes are still unclear. From this reason, the effect of residual stress on degradation capability of Fe-based MG was investigated. (Fe73.5Si13.5B9Nb3Cu1)91.5Ni8.5 as-cast MG ribbons and annealed MG ribbons were prepared and subjected to degrade Orange II solutions. The as-cast ribbons completely degrade the azo dye within 60 min, the ribbons annealed at 673 K take 120 min, although the annealed ribbons still sustain metastable glassy state. Surface morphology and magnetic domain pattern of the ribbons were characterized carefully. The results demonstrate that the inhomogeneous residual stress could contribute to high degradation capability of the as-cast MG ribbons by generating stress gradient cell and increasing active sites. Therefore, increasing residual stress can be a novel clue to enhance degradation capability of materials.
1. Introduction Metallic glass alloys (MGs), are disordered materials that lack the periodicity of crystals but behave mechanically like solids [1]. The most common way of making a MG is by cooling a viscous metallic liquid fast enough to avoid crystallization [1]. Their superior properties and field applications have been attracting increasing attention from lots of researchers [2]. For example, the fracture strength of (Co0.535Fe0.1Ta0.055B0.31)98Mo2 MG reaches as high as 5545 MPa [3]. Ni59Zr20Ti16Si2Sn3 MGs are employed in coating materials as a result of their superior corrosion resistance and wear resistance [2,4]. Fe-based MGs are utilized as magnetic cores of transformers and sensors due to their excellent soft magnetic properties [5–8]. Moreover, MGs are highly reactive owing to their metastable structure and they undergo solid-state reaction frequently more easily than their crystalline counterparts [9]. Since the high efficiency of (Fe0.99Mo0.01)78Si9B13 MG ribbons in degrading Direct Blue 2B was reported in 2010, the application of MGs in dying wastewater treatment has attracted extensive interests [10]. In 2012, J.Q. Wang etc. [11,12] reported that Fe73Si7B17Nb3 and Mg73Zn21.5Ca5.5 MG powders showed excellent capability in degrading azo dyes. Commercial Fe78Si13B9 MG ribbons with high reactivity in degrading azo dye solutions were studied by Y. Tang etc. [13] in 2015. Recently, Z. Jia etc. [2] investigated the degradation efficiency of the photo-enhanced Fenton-like process of BR3B-A dye in aqueous solution by using Fe78Si9B13 MG alloy.
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Most studies reported in the literatures focused on investigating the degradation capability of MGs in degrading azo dyes, while works on the mechanism of high degradation capability of MGs are rare [2,11–16]. Understanding the mechanism is important for rational design and fabrication of useful MGs for the purification of azo dye wastewater. In general, MGs' superior degradation capability can be attributed to: (i) the metastable nature compared to crystalline alloys, endows MGs with higher Gibbs free energy [2,11,12]; (ii) large residual stress inside MGs can also elevate their Gibbs free energy state and therefore promote reactivity [12]; (iii) more unsaturated coordination sites than their crystalline counterparts, can provide more active sites for the degradation reaction [9,17]; (iv) high reactivity with azo dye but low reactivity with water, can enhance their reusability in wastewater treatment [12]; (v) a possibly large quantity of nano-galvanic cells originating from nanoscale chemical inhomogeneous of MGs is expected with a strong affinity for donating electrons to the reaction [15]. However, what species are involved in the degradation process of azo dyes have not been elucidated. In this study, we focus on the effect of residual stress on degradation capability of (Fe73.5Si13.5B9Nb3Cu1)91.5Ni8.5 MG ribbons in degrading of Orange II. 2. Materials and methods Alloy ingots with a nominal composition of (Fe73.5Si13.5B9Nb3Cu1)91.5Ni8.5 (at. %) were prepared by induction
Corresponding author. E-mail address: [email protected] (K.-F. Yao).
http://dx.doi.org/10.1016/j.jnoncrysol.2017.07.030 Received 22 March 2017; Received in revised form 26 July 2017; Accepted 27 July 2017 0022-3093/ © 2017 Elsevier B.V. All rights reserved.
Please cite this article as: Chen, S.-Q., Journal of Non-Crystalline Solids (2017), http://dx.doi.org/10.1016/j.jnoncrysol.2017.07.030
Journal of Non-Crystalline Solids xxx (xxxx) xxx–xxx
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Fig. 1. DSC curve of the as-cast (Fe73.5Si13.5B9Nb3Cu1)91.5Ni8.5 ribbon, where Tg, Tx1 and Tx2 are the temperature of glass transition, first crystallization transition and second crystallization transition, respectively.
Fig. 2. XRD patterns of the as-cast (Fe73.5Si13.5B9Nb3Cu1)91.5Ni8.5 ribbon and the annealed (Fe73.5Si13.5B9Nb3Cu1)91.5Ni8.5 ribbons.
corresponding XRD patterns, indicating that the structure of the ribbons are in the glassy state [8,18,19]. Orange II, a typical azo dye, was used to examine degradation capability of the as-cast ribbons and the annealed ribbons. The concentration of Orange II in the solution was characterized by UV–vis spectrophotometer, as the intensity of characteristic absorbance peak at 484 nm is proportional to the concentration of Orange II. Fig. 3 illustrates UV–vis spectra of the Orange II solutions treated by the as-cast ribbons and the annealed ribbons. The intensity of the characteristic peak at 484 nm decreases gradually with the treatment time. After 60 min, the characteristic absorbance peak is invisible for the as-cast ribbons and the ribbons annealed at 573 K in the Fig. 3a and b, respectively. However, there is an obvious characteristic absorbance peak at 484 nm for the ribbons annealed at 673 K in the Fig. 3c. These results suggest that the degradation capability of the (Fe73.5Si13.5B9Nb3Cu1)91.5Ni8.5 MG ribbons deteriorate after annealing treatment, although the XRD results (Fig. 2) show that there is no obvious structural change of the annealed ribbons. Fig. 4 shows the progressive color change in Orange II dye at different time intervals during degradation. As shown in Fig. 4a and b, the solutions are almost colorless after 60 min for the as-cast ribbons and the ribbons annealed at 573 K; whereas a longer time is required for solutions degraded by the ribbons annealed at 673 K (Fig. 4c) to achieve the same clarity. These results also demonstrate the as-cast ribbons show the highest degradation capability, which is consistent with the results of UV–vis spectra. Since the intensity of the characteristic absorbance peak at 484 nm arising from the azo chromophore is proportional to the concentration of Orange II, curves of the normalized concentration versus the treatment time are derived from the UV–vis spectra. The degradation curve of 300 mesh Fe0 powders is also presented in the graph for comparison. As shown in Fig. 5, degradation rates of the MG ribbons are much higher than that of conventional Fe0 powders. The Orange II solution is completely degraded by the as-cast ribbons within 60 min, but it takes 120 min for the ribbons annealed at 673 K. For conventional Fe0 powders, it takes as long as 660 min to completely degrade the Orange II solution. The results demonstrate that the Fe-based MG ribbons, especially the as-cast ribbons, show much higher degradation capability than conventional Fe0 powders. The degradation of azo dyes is a surface-mediated process. Thus surface morphologies of the ribbons after degradation were examined carefully by OM and SEM. Fig. 6 shows OM images of the surfaces of the (Fe73.5Si13.5B9Nb3Cu1)91.5Ni8.5 MG ribbons after degradation experiment. As shown in Fig. 6a, amounts of circular main reacted regions distribute on the surface of the as-cast ribbon after degradation. The amount of circular main reacted regions on the surfaces of the annealed
melting Fe-B master alloys (B: 17.57, Al: 0.032, Si: 0.39, C: 0.18, P: 0.028, S: 0.002, Mn: 0.24, in wt%) and Si, Fe, Ni, Cu, Nb purity (99.5% ~ 99.9%) elements. Ribbons were produced by melt-spinning in the air. For degradation experiments, the ribbons were cut into pieces of size 10 mm × 10 mm. Cut ribbons were put into quartz tubes and annealed at temperatures of 573 and 673 K, respectively, for 300 s in argon protection environment. The annealing temperatures are below the glass transition temperature of 725 K on the DSC (differential scanning calorimetry, NETZSCH STA 409C/CD) curve at a heating rate of 20°C/ min, as shown in Fig. 1. Structural identification of the ribbons were carried out by X-ray diffraction (XRD, Rigaku D/max-RB) with Cu Kα radiation. Surface morphologies of the ribbons after degradation experiments were characterized by optical microscope (OM, ZEISS Axio). The cleaned surfaces of the ribbons after degradation experiments and removing degradation products were also observed. Magnetic domain patterns of the ribbons were examined by magneto-optic microscope based on the magnetooptic Kerr effect (MOKE, ZEISS Axio). The viewed surface was always the free surface in the original melt-spinning process, because this surface is smooth enough to allow domain observation by the MOKE technique with no need of surface preparation. Let the x-axis be along the ribbon width, the y-axis along the ribbon length, and the z-axis normal to the ribbon plane. The azo dye (Orange II, C16H11N2NaO4S) was purchased from Sinopharm Chemical Reagent Beijing Co., Ltd. (Beijing, China). Orange II solution with the initial pH value of 6 and the initial concentration of 25 mg/L was prepared. The ribbons and the 300 mesh zero-valent Fe (Fe0) powders with a weight of 2.5 g were immersed, respectively, into a 250 mL Orange II solution, which was stirred at a fixed speed of 180 rpm and held at temperature of 25 °C during the degradation process. At fixed time intervals, a 4 mL solution was extracted by syringe and filtered with 0.22 μm membrane. The solutions were scanned by UV–vis spectrophotometer (UnicoUV-2802PC) to obtain its absorbance spectrum. Each degradation experiments were performed at least three times to determine the random errors and systematic errors. 3. Results and discussion Since the as-cast MG ribbons were prepared by melt-spinning at a cooling rate up to 105–106 K/s, there will be considerable residual stress within the as-cast ribbons. To investigate the influence of residual stress on the degradation capability, the as-cast ribbons were subjected to annealing treatment at temperatures below the glass transition temperature of 725 K (Fig. 1). Fig. 2 shows XRD patterns of the as-cast and also the annealed (Fe73.5Si13.5B9Nb3Cu1)91.5Ni8.5 ribbons. All the ribbons exhibit a broad diffuse diffraction peak at 2θ = 40–50° on the 2
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Fig. 4. Visible color variation of the Orange II solutions at different degradation time for (a) as-cast ribbons, (b) the ribbons annealed at 573 K for 300 s and (c) the ribbons annealed at 673 K for 300 s.
Fig. 3. UV–vis spectra of Orange II solutions at different degradation time for (a) as-cast ribbons, (b) the ribbons annealed at 573 K for 300 s and (c) the ribbons annealed at 673 K for 300 s.
ribbons gradually decreases with the annealing temperature, as shown in Fig. 6b and c. An enlarged main reacted region of the as-cast ribbon is shown in Fig. 6d. There are some cracks in the center of the reacted region and amounts of sediments on its periphery. OM images of the ribbons after removing the sediments are also shown in Fig. 6e–g. It is more easy to identify the reacted regions in these images. Before crystallization, annealing treatment of MGs mainly contributes to structural relaxation, leading to residual stress relaxation. Magnetic domain patterns of the ribbons were characterized by MOKE technique to reflect the residual stress status of the ribbons. In MG ribbons, magnetic domain patterns are particularly sensitive to stress because of generally high elastic limits, homogeneous atomic structure and the absence of magnetocrystalline anisotropy [20]. The magnetostriction and the elastic properties of MGs are assumed to be isotropic, and domain patterns are dominated by sample's geometric form and internal residual stress. Fe-based MG ribbons should have parallel domain pattern along the width direction or the length direction during uniaxial loading in the plane [20,21]. Results of magnetic domain characterization are presented in Fig. 7. As can be seen in Fig. 7a, magnetic domain pattern of the as-cast ribbon is irregular with varying orientation, indicating that its stress state is inhomogeneous [20]. In this case, amounts of localized corrosion such as galvanic corrosion result from the so-called stress gradient cell, in which the higher stress locations become anodic to the lower stress
Fig. 5. The normalized concentration of Orange II as a function of treatment time for the as-cast ribbons, the annealed ribbons and the conventional Fe0 powders.
locations, may occur on the ribbon with a stress gradient [22]. It is consistent with the result of surface morphology of the as-cast ribbon after degradation (Fig. 6a). After annealing treatment at 573 K, the size of magnetic domain increases and the domain pattern approach being parallel to the ribbon width, as shown in Fig. 7b. Further increasing the 3
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Fig. 6. OM images of the original surfaces of (a) the as-cast ribbon, (b) the ribbon annealed at 573 K and (c) the ribbon annealed at 673 K after degradation experiment with degradation products on top. (d) is a SEM image of an enlarged reacted region of the as-cast sample. OM images of the cleaned surfaces of (e) the as-cast ribbon, (f) the ribbon annealed at 573 K and (g) the ribbon annealed at 673 K after degradation experiment and removing degradation products.
Fig. 7. Magnetic domain patterns of (a) the as-cast ribbon, (b) the ribbon annealed at 573 K for 300 s and (c) the ribbon annealed at 673 K for 300 s.
4. Conclusion
annealing temperature to 673 K, wide domains, separated by 180° walls lying parallel to the ribbon width, are observed. Thus, there is an essentially weak uniaxial stress, producing uniaxial magnetic symmetry and wide parallel domains [20], which means the irregularly inhomogeneous residual stress relaxation and the elimination of stress gradient. Hence, the preferred reactive corrosion locations reduce, leading to the decline of active sites and the degradation capability of the annealed ribbons decline with the annealing temperature. After degradation experiment, the surfaces of the annealed ribbons also show less main reacted regions compared with the as-cast ribbons (Fig. 6). In previous works, the superior degradation capability of MGs is attributed dominantly to their metastable structure. However, after annealing at 673 K for 300 s, the ribbons take twice as much time as the as-cast ribbons to completely degrade the Orange II solution, although the annealed ribbons is still MG. The current results suggest a significant effect of residual stress or strain towards the reaction activity in MGs, which is well known in crystalline materials [23]. Thus by increasing the residual stress, the reaction activity of both crystalline materials and MGs will be also enhanced. Since the MGs can be fabricated by different methods, such as J-quenching, copper mold casting, melt-spinning, and so on. The melt-spinning that could provide cooling rate as high as 105–106 K/s and therefore more residual stress inside MGs, will be more preferred to fabricate MGs in wastewater treatment or even catalytic fields.
The as-cast (Fe73.5Si13.5B9Nb3Cu1)91.5Ni8.5 MG ribbons, the annealed ribbons and the conventional Fe0 powders were used to degrade Orange II solutions, respectively. Among these samples, the as-cast ribbons show the highest degradation capability. The magnetic domain pattern of the as-cast ribbon is irregular with varying orientation, indicating its inhomogeneous internal residual stress state. After degradation experiment, the surface of the as-cast ribbon shows amounts of main reacted regions which should correspond to the residual stress concentration regions. Results suggest that the high degradation capability of the as-cast ribbons could be attributed to inhomogeneous residual internal stress which gives rise to stress gradient cells and increases active sites. From this point, it could be a novel clue for enhancing the degradation capability of reagents by increasing residual stress. Acknowledgements This work was supported by the National Natural Science Foundation of China (NSFC, Grand No. 51571127) and National Key Basic Research and Development Programme (Grant No. 2016YFB0300502). References [1] P.G. Debenedetti, F.H. Stillinger, Supercooled liquids and the glass transition,
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S.-Q. Chen et al. Nature 410 (2001) 259–267. [2] Z. Jia, W.C. Zhang, W.M. Wang, D. Habibi, L.C. Zhang, Amorphous Fe78Si9B13 alloy: an efficient and reusable photo-enhanced Fenton-like catalyst in degradation of cibacron brilliant red 3B-A dye under UV–vis light, Appl. Catal. B Environ. 192 (2016) 46–56. [3] A. Inoue, B.L. Shen, C.T. Chang, Fe- and Co-based bulk glassy alloys with ultrahigh strength of over 4000 MPa, Intermetallics 14 (2006) 936–944. [4] J. Jayaraj, D.J. Sordelet, D.H. Kim, Y.C. Kim, E. Fleury, Corrosion behaviour of Ni–Zr–Ti–Si–Sn amorphous plasma spray coating, Corros. Sci. 48 (2006) 950–964. [5] B.L. Shen, M. Akiba, A. Inoue, Excellent soft-ferromagnetic bulk glassy alloys with high saturation magnetization, Appl. Phys. Lett. 88 (2006) 131907. [6] F.L. Kong, C.T. Chang, A. Inoue, E. Shalaan, F. Al-Marzouki, Fe-based amorphous soft magnetic alloys with high saturation magnetization and good bending ductility, J. Alloys Compd. 615 (2014) 163–166. [7] J.F. Li, X. Liu, S.F. Zhao, H.Y. Ding, K.F. Yao, Fe-based bulk amorphous alloys with iron contents as high as 82at%, J. Magn. Magn. Mater. 386 (2015) 107–110. [8] J.H. Zhang, C.T. Chang, A.D. Wang, B.L. Shen, Development of quaternary Fe-based bulk metallic glasses with high saturation magnetization above 1.6 T, J. Non-Cryst. Solids 358 (2012) 1443–1446. [9] A. Baiker, Metallic glasses in heterogeneous catalysis, Faraday Discuss. 87 (1989) 239–251. [10] C.Q. Zhang, H.F. Zhang, M.Q. Lv, Z.Q. Hu, Decolorization of azo dye solution by Fe–Mo–Si–B amorphous alloy, J. Non-Cryst. Solids 356 (2010) 1703–1706. [11] J.Q. Wang, Y.H. Liu, M.W. Chen, G.Q. Xie, D.V. Louzguine-Luzgin, A. Inoue, J.H. Perepezko, Rapid degradation of azo dye by Fe-based metallic glass powder, Adv. Funct. Mater. 22 (2012) 2567–2570. [12] J.Q. Wang, Y.H. Liu, M.W. Chen, D.V. Louzguine-Luzgin, A. Inoue, J.H. Perepezko, Excellent capability in degrading azo dyes by MgZn-based metallic glass powders, Sci Rep 2 (2012) 418. [13] Y. Tang, Y. Shao, N. Chen, X. Liu, S.Q. Chen, K.F. Yao, Insight into the high
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reactivity of commercial Fe-Si-B amorphous zero-valent iron in degrading azo dye solutions, RSC Adv. 5 (2015) 34032–34039. X.D. Qin, Z.W. Zhu, G. Liu, H.M. Fu, H.W. Zhang, A.M. Wang, H. Li, H.F. Zhang, Ultrafast degradation of azo dyes catalyzed by cobalt-based metallic glass, Sci Rep 5 (2015) 18226. S.H. Xie, P. Huang, J.J. Kruzic, X.R. Zeng, H.X. Qian, A highly efficient degradation mechanism of methyl orange using Fe-based metallic glass powders, Sci Rep 6 (2016) 21947. P.P. Wang, J.-Q. Wang, H. Li, H. Yang, J.T. Huo, J.G. Wang, C. Chang, X.M. Wang, R.W. Li, G. Wang, Fast decolorization of azo dyes in both alkaline and acidic solutions by Al-based metallic glasses, J. Alloys Compd. 701 (2017) 759–767. C.Q. Zhang, Z.W. Zhu, H.F. Zhang, Z.Q. Hu, Rapid reductive degradation of azo dyes by a unique structure of amorphous alloys, Chin. Sci. Bull. 56 (2011) 3988–3992. Z.L. Long, C.T. Chang, Y.H. Ding, Y. Shao, P. Zhang, B.L. Shen, A. Inoue, Corrosion behavior of Fe-based ferromagnetic (Fe, Ni)–B–Si–Nb bulk glassy alloys in aqueous electrolytes, J. Non-Cryst. Solids 354 (2008) 4609–4613. X.D. Fan, B.L. Shen, Crystallization behavior and magnetic properties in High Fe content FeBCSiCu alloy system, J. Magn. Magn. Mater. 385 (2015) 277–281. J.D. Livingston, Stresses and magnetic domains in amorphous metal ribbons, Phys. Status Solidi A 56 (1979) 637–645. M.H. Phan, H.X. Peng, Giant magnetoimpedance materials: fundamentals and applications, Prog. Mater. Sci. 53 (2008) 323–420. H.-Q. Yang, Q. Zhang, S.-S. Tu, Y. Wang, Y.-M. Li, Y. Huang, Effects of inhomogeneous elastic stress on corrosion behaviour of Q235 steel in 3.5% NaCl solution using a novel multi-channel electrode technique, Corros. Sci. 110 (2016) 1–14. H. Wang, S. Xu, C. Tsai, Y. Li, C. Liu, J. Zhao, Y. Liu, H. Yuan, F. Abild-Pedersen, F.B. Prinz, J.K. Norskov, Y. Cui, Direct and continuous strain control of catalysts with tunable battery electrode materials, Science 354 (2016) 1031–1036.
Contents lists available at ScienceDirect
Journal of Non-Crystalline Solids journal homepage: www.elsevier.com/locate/jnoncrysol
Effect of residual stress on azo dye degradation capability of Fe-based metallic glass Shuang-Qin Chen, Yang Shao, Meng-Ting Cheng, Ke-Fu Yao⁎ School of Material Science and Engineering, Tsinghua University, Beijing 100084, PR China
A R T I C L E I N F O
A B S T R A C T
Keywords: Fe-based metallic glass Residual stress Azo dye Degradation
Fe-based metallic glasses (MGs) are among the most interesting in the area of MG materials, due to their superior properties such as high degradation capability of azo dyes. However, the ways that factors influence the degradation capability of MGs towards azo dyes are still unclear. From this reason, the effect of residual stress on degradation capability of Fe-based MG was investigated. (Fe73.5Si13.5B9Nb3Cu1)91.5Ni8.5 as-cast MG ribbons and annealed MG ribbons were prepared and subjected to degrade Orange II solutions. The as-cast ribbons completely degrade the azo dye within 60 min, the ribbons annealed at 673 K take 120 min, although the annealed ribbons still sustain metastable glassy state. Surface morphology and magnetic domain pattern of the ribbons were characterized carefully. The results demonstrate that the inhomogeneous residual stress could contribute to high degradation capability of the as-cast MG ribbons by generating stress gradient cell and increasing active sites. Therefore, increasing residual stress can be a novel clue to enhance degradation capability of materials.
1. Introduction Metallic glass alloys (MGs), are disordered materials that lack the periodicity of crystals but behave mechanically like solids [1]. The most common way of making a MG is by cooling a viscous metallic liquid fast enough to avoid crystallization [1]. Their superior properties and field applications have been attracting increasing attention from lots of researchers [2]. For example, the fracture strength of (Co0.535Fe0.1Ta0.055B0.31)98Mo2 MG reaches as high as 5545 MPa [3]. Ni59Zr20Ti16Si2Sn3 MGs are employed in coating materials as a result of their superior corrosion resistance and wear resistance [2,4]. Fe-based MGs are utilized as magnetic cores of transformers and sensors due to their excellent soft magnetic properties [5–8]. Moreover, MGs are highly reactive owing to their metastable structure and they undergo solid-state reaction frequently more easily than their crystalline counterparts [9]. Since the high efficiency of (Fe0.99Mo0.01)78Si9B13 MG ribbons in degrading Direct Blue 2B was reported in 2010, the application of MGs in dying wastewater treatment has attracted extensive interests [10]. In 2012, J.Q. Wang etc. [11,12] reported that Fe73Si7B17Nb3 and Mg73Zn21.5Ca5.5 MG powders showed excellent capability in degrading azo dyes. Commercial Fe78Si13B9 MG ribbons with high reactivity in degrading azo dye solutions were studied by Y. Tang etc. [13] in 2015. Recently, Z. Jia etc. [2] investigated the degradation efficiency of the photo-enhanced Fenton-like process of BR3B-A dye in aqueous solution by using Fe78Si9B13 MG alloy.
⁎
Most studies reported in the literatures focused on investigating the degradation capability of MGs in degrading azo dyes, while works on the mechanism of high degradation capability of MGs are rare [2,11–16]. Understanding the mechanism is important for rational design and fabrication of useful MGs for the purification of azo dye wastewater. In general, MGs' superior degradation capability can be attributed to: (i) the metastable nature compared to crystalline alloys, endows MGs with higher Gibbs free energy [2,11,12]; (ii) large residual stress inside MGs can also elevate their Gibbs free energy state and therefore promote reactivity [12]; (iii) more unsaturated coordination sites than their crystalline counterparts, can provide more active sites for the degradation reaction [9,17]; (iv) high reactivity with azo dye but low reactivity with water, can enhance their reusability in wastewater treatment [12]; (v) a possibly large quantity of nano-galvanic cells originating from nanoscale chemical inhomogeneous of MGs is expected with a strong affinity for donating electrons to the reaction [15]. However, what species are involved in the degradation process of azo dyes have not been elucidated. In this study, we focus on the effect of residual stress on degradation capability of (Fe73.5Si13.5B9Nb3Cu1)91.5Ni8.5 MG ribbons in degrading of Orange II. 2. Materials and methods Alloy ingots with a nominal composition of (Fe73.5Si13.5B9Nb3Cu1)91.5Ni8.5 (at. %) were prepared by induction
Corresponding author. E-mail address: [email protected] (K.-F. Yao).
http://dx.doi.org/10.1016/j.jnoncrysol.2017.07.030 Received 22 March 2017; Received in revised form 26 July 2017; Accepted 27 July 2017 0022-3093/ © 2017 Elsevier B.V. All rights reserved.
Please cite this article as: Chen, S.-Q., Journal of Non-Crystalline Solids (2017), http://dx.doi.org/10.1016/j.jnoncrysol.2017.07.030
Journal of Non-Crystalline Solids xxx (xxxx) xxx–xxx
S.-Q. Chen et al.
Fig. 1. DSC curve of the as-cast (Fe73.5Si13.5B9Nb3Cu1)91.5Ni8.5 ribbon, where Tg, Tx1 and Tx2 are the temperature of glass transition, first crystallization transition and second crystallization transition, respectively.
Fig. 2. XRD patterns of the as-cast (Fe73.5Si13.5B9Nb3Cu1)91.5Ni8.5 ribbon and the annealed (Fe73.5Si13.5B9Nb3Cu1)91.5Ni8.5 ribbons.
corresponding XRD patterns, indicating that the structure of the ribbons are in the glassy state [8,18,19]. Orange II, a typical azo dye, was used to examine degradation capability of the as-cast ribbons and the annealed ribbons. The concentration of Orange II in the solution was characterized by UV–vis spectrophotometer, as the intensity of characteristic absorbance peak at 484 nm is proportional to the concentration of Orange II. Fig. 3 illustrates UV–vis spectra of the Orange II solutions treated by the as-cast ribbons and the annealed ribbons. The intensity of the characteristic peak at 484 nm decreases gradually with the treatment time. After 60 min, the characteristic absorbance peak is invisible for the as-cast ribbons and the ribbons annealed at 573 K in the Fig. 3a and b, respectively. However, there is an obvious characteristic absorbance peak at 484 nm for the ribbons annealed at 673 K in the Fig. 3c. These results suggest that the degradation capability of the (Fe73.5Si13.5B9Nb3Cu1)91.5Ni8.5 MG ribbons deteriorate after annealing treatment, although the XRD results (Fig. 2) show that there is no obvious structural change of the annealed ribbons. Fig. 4 shows the progressive color change in Orange II dye at different time intervals during degradation. As shown in Fig. 4a and b, the solutions are almost colorless after 60 min for the as-cast ribbons and the ribbons annealed at 573 K; whereas a longer time is required for solutions degraded by the ribbons annealed at 673 K (Fig. 4c) to achieve the same clarity. These results also demonstrate the as-cast ribbons show the highest degradation capability, which is consistent with the results of UV–vis spectra. Since the intensity of the characteristic absorbance peak at 484 nm arising from the azo chromophore is proportional to the concentration of Orange II, curves of the normalized concentration versus the treatment time are derived from the UV–vis spectra. The degradation curve of 300 mesh Fe0 powders is also presented in the graph for comparison. As shown in Fig. 5, degradation rates of the MG ribbons are much higher than that of conventional Fe0 powders. The Orange II solution is completely degraded by the as-cast ribbons within 60 min, but it takes 120 min for the ribbons annealed at 673 K. For conventional Fe0 powders, it takes as long as 660 min to completely degrade the Orange II solution. The results demonstrate that the Fe-based MG ribbons, especially the as-cast ribbons, show much higher degradation capability than conventional Fe0 powders. The degradation of azo dyes is a surface-mediated process. Thus surface morphologies of the ribbons after degradation were examined carefully by OM and SEM. Fig. 6 shows OM images of the surfaces of the (Fe73.5Si13.5B9Nb3Cu1)91.5Ni8.5 MG ribbons after degradation experiment. As shown in Fig. 6a, amounts of circular main reacted regions distribute on the surface of the as-cast ribbon after degradation. The amount of circular main reacted regions on the surfaces of the annealed
melting Fe-B master alloys (B: 17.57, Al: 0.032, Si: 0.39, C: 0.18, P: 0.028, S: 0.002, Mn: 0.24, in wt%) and Si, Fe, Ni, Cu, Nb purity (99.5% ~ 99.9%) elements. Ribbons were produced by melt-spinning in the air. For degradation experiments, the ribbons were cut into pieces of size 10 mm × 10 mm. Cut ribbons were put into quartz tubes and annealed at temperatures of 573 and 673 K, respectively, for 300 s in argon protection environment. The annealing temperatures are below the glass transition temperature of 725 K on the DSC (differential scanning calorimetry, NETZSCH STA 409C/CD) curve at a heating rate of 20°C/ min, as shown in Fig. 1. Structural identification of the ribbons were carried out by X-ray diffraction (XRD, Rigaku D/max-RB) with Cu Kα radiation. Surface morphologies of the ribbons after degradation experiments were characterized by optical microscope (OM, ZEISS Axio). The cleaned surfaces of the ribbons after degradation experiments and removing degradation products were also observed. Magnetic domain patterns of the ribbons were examined by magneto-optic microscope based on the magnetooptic Kerr effect (MOKE, ZEISS Axio). The viewed surface was always the free surface in the original melt-spinning process, because this surface is smooth enough to allow domain observation by the MOKE technique with no need of surface preparation. Let the x-axis be along the ribbon width, the y-axis along the ribbon length, and the z-axis normal to the ribbon plane. The azo dye (Orange II, C16H11N2NaO4S) was purchased from Sinopharm Chemical Reagent Beijing Co., Ltd. (Beijing, China). Orange II solution with the initial pH value of 6 and the initial concentration of 25 mg/L was prepared. The ribbons and the 300 mesh zero-valent Fe (Fe0) powders with a weight of 2.5 g were immersed, respectively, into a 250 mL Orange II solution, which was stirred at a fixed speed of 180 rpm and held at temperature of 25 °C during the degradation process. At fixed time intervals, a 4 mL solution was extracted by syringe and filtered with 0.22 μm membrane. The solutions were scanned by UV–vis spectrophotometer (UnicoUV-2802PC) to obtain its absorbance spectrum. Each degradation experiments were performed at least three times to determine the random errors and systematic errors. 3. Results and discussion Since the as-cast MG ribbons were prepared by melt-spinning at a cooling rate up to 105–106 K/s, there will be considerable residual stress within the as-cast ribbons. To investigate the influence of residual stress on the degradation capability, the as-cast ribbons were subjected to annealing treatment at temperatures below the glass transition temperature of 725 K (Fig. 1). Fig. 2 shows XRD patterns of the as-cast and also the annealed (Fe73.5Si13.5B9Nb3Cu1)91.5Ni8.5 ribbons. All the ribbons exhibit a broad diffuse diffraction peak at 2θ = 40–50° on the 2
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Fig. 4. Visible color variation of the Orange II solutions at different degradation time for (a) as-cast ribbons, (b) the ribbons annealed at 573 K for 300 s and (c) the ribbons annealed at 673 K for 300 s.
Fig. 3. UV–vis spectra of Orange II solutions at different degradation time for (a) as-cast ribbons, (b) the ribbons annealed at 573 K for 300 s and (c) the ribbons annealed at 673 K for 300 s.
ribbons gradually decreases with the annealing temperature, as shown in Fig. 6b and c. An enlarged main reacted region of the as-cast ribbon is shown in Fig. 6d. There are some cracks in the center of the reacted region and amounts of sediments on its periphery. OM images of the ribbons after removing the sediments are also shown in Fig. 6e–g. It is more easy to identify the reacted regions in these images. Before crystallization, annealing treatment of MGs mainly contributes to structural relaxation, leading to residual stress relaxation. Magnetic domain patterns of the ribbons were characterized by MOKE technique to reflect the residual stress status of the ribbons. In MG ribbons, magnetic domain patterns are particularly sensitive to stress because of generally high elastic limits, homogeneous atomic structure and the absence of magnetocrystalline anisotropy [20]. The magnetostriction and the elastic properties of MGs are assumed to be isotropic, and domain patterns are dominated by sample's geometric form and internal residual stress. Fe-based MG ribbons should have parallel domain pattern along the width direction or the length direction during uniaxial loading in the plane [20,21]. Results of magnetic domain characterization are presented in Fig. 7. As can be seen in Fig. 7a, magnetic domain pattern of the as-cast ribbon is irregular with varying orientation, indicating that its stress state is inhomogeneous [20]. In this case, amounts of localized corrosion such as galvanic corrosion result from the so-called stress gradient cell, in which the higher stress locations become anodic to the lower stress
Fig. 5. The normalized concentration of Orange II as a function of treatment time for the as-cast ribbons, the annealed ribbons and the conventional Fe0 powders.
locations, may occur on the ribbon with a stress gradient [22]. It is consistent with the result of surface morphology of the as-cast ribbon after degradation (Fig. 6a). After annealing treatment at 573 K, the size of magnetic domain increases and the domain pattern approach being parallel to the ribbon width, as shown in Fig. 7b. Further increasing the 3
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Fig. 6. OM images of the original surfaces of (a) the as-cast ribbon, (b) the ribbon annealed at 573 K and (c) the ribbon annealed at 673 K after degradation experiment with degradation products on top. (d) is a SEM image of an enlarged reacted region of the as-cast sample. OM images of the cleaned surfaces of (e) the as-cast ribbon, (f) the ribbon annealed at 573 K and (g) the ribbon annealed at 673 K after degradation experiment and removing degradation products.
Fig. 7. Magnetic domain patterns of (a) the as-cast ribbon, (b) the ribbon annealed at 573 K for 300 s and (c) the ribbon annealed at 673 K for 300 s.
4. Conclusion
annealing temperature to 673 K, wide domains, separated by 180° walls lying parallel to the ribbon width, are observed. Thus, there is an essentially weak uniaxial stress, producing uniaxial magnetic symmetry and wide parallel domains [20], which means the irregularly inhomogeneous residual stress relaxation and the elimination of stress gradient. Hence, the preferred reactive corrosion locations reduce, leading to the decline of active sites and the degradation capability of the annealed ribbons decline with the annealing temperature. After degradation experiment, the surfaces of the annealed ribbons also show less main reacted regions compared with the as-cast ribbons (Fig. 6). In previous works, the superior degradation capability of MGs is attributed dominantly to their metastable structure. However, after annealing at 673 K for 300 s, the ribbons take twice as much time as the as-cast ribbons to completely degrade the Orange II solution, although the annealed ribbons is still MG. The current results suggest a significant effect of residual stress or strain towards the reaction activity in MGs, which is well known in crystalline materials [23]. Thus by increasing the residual stress, the reaction activity of both crystalline materials and MGs will be also enhanced. Since the MGs can be fabricated by different methods, such as J-quenching, copper mold casting, melt-spinning, and so on. The melt-spinning that could provide cooling rate as high as 105–106 K/s and therefore more residual stress inside MGs, will be more preferred to fabricate MGs in wastewater treatment or even catalytic fields.
The as-cast (Fe73.5Si13.5B9Nb3Cu1)91.5Ni8.5 MG ribbons, the annealed ribbons and the conventional Fe0 powders were used to degrade Orange II solutions, respectively. Among these samples, the as-cast ribbons show the highest degradation capability. The magnetic domain pattern of the as-cast ribbon is irregular with varying orientation, indicating its inhomogeneous internal residual stress state. After degradation experiment, the surface of the as-cast ribbon shows amounts of main reacted regions which should correspond to the residual stress concentration regions. Results suggest that the high degradation capability of the as-cast ribbons could be attributed to inhomogeneous residual internal stress which gives rise to stress gradient cells and increases active sites. From this point, it could be a novel clue for enhancing the degradation capability of reagents by increasing residual stress. Acknowledgements This work was supported by the National Natural Science Foundation of China (NSFC, Grand No. 51571127) and National Key Basic Research and Development Programme (Grant No. 2016YFB0300502). References [1] P.G. Debenedetti, F.H. Stillinger, Supercooled liquids and the glass transition,
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