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Zirconia fiber via biotemplate synthesis route
Materials Letters 101 (2013) 13–16
Contents lists available at SciVerse ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Zirconia fiber via biotemplate synthesis route M. Biswas, S. Bandyopadhyay n CSIR-Central Glass & Ceramic Research Institute, 196, Raja S.C. Mullick Road, Kolkata 700032, India
art ic l e i nf o
a b s t r a c t
Article history: Received 12 December 2012 Accepted 11 March 2013 Available online 21 March 2013
Monoclinic zirconia fiber was fabricated through a novel chemical synthesis route using economically cheap biotemplate and aqueous zirconyl oxychloride. Zirconyl oxychloride gets converted through various steps as follows: hydroxylation to remove Cl−, nitrate addition and subsequently further hydroxylation. The process of green fiber formation lies on the reaction between hydroxyl groups of biotemplate and zirconium ion on the cell walls of biotemplate. With heat treatment at 1200 1C for 2 h, the deposited hydroxide converts to oxide in the form of sintered fiber. Fibers are handleable, 1–10 cm long and 7–10 mm wide. The fibers are made of monoclinic nanocrystals with crystallite size ranging mostly between 40 and 100 nm (compared to 32–34 nm as calculated from the Scherrer equation) with discrete ones as large as 400 nm. & 2013 Elsevier B.V. All rights reserved.
Keywords: Ceramics Structural Fiber technology
1. Introduction
2. Experimental
Fracture toughness of a material can be improved by introducing secondary discontinuous phases in material's matrix. Fiber as secondary phase is a good option for toughening materials. The improvement occurs following various mechanisms such as crack bridging, crack deflection, fiber pull-out, etc. [1]. Many of these mechanisms can be employed by incorporating zirconia grains and fibers in ceramic matrix composites [2]. In addition to the effect of grain morphology, zirconia may also offer phase transformation induced toughening caused by its reversible monoclinic–tetragonal phase transformation. Synthesis of zirconia fiber is therefore important and a simple approach using aqueous zirconyl chloride has been attempted in this study. Templating is a universal method for synthesis of fibers and various porous materials with a controlled and ordered structure using collagen materials, polypropylene hollow fibers, etc. [3,4]. Until recently, not much attention has been paid for the formation of monoclinic zirconia fibers using cheap bio-templates like jute, etc. In the present research work, a new chemical route has been tried using an economically cheap and widely available biotemplate, jute, which is used for brooming floor.
Aqueous zirconyl chloride (ZrOCl2 8H2O, Sigma-Aldrich) was dissolved in minimum amount of water for complete dissolution of the solid. For Cl− removal, Zr4 þ ions were precipitated as hydroxide using ammonia solution followed by subsequent washing the precipitate with distilled water. The presence of Cl− ion was confirmed with the silver nitrate test. The washed precipitate was dissolved in minimum amount of nitric acid to form zirconium nitrate. A bunch of jute fibers were soaked in this zirconium nitrate solution for one day for complete impregnation of zirconium nitrate molecules inside the cells of jute fibers. The soaked fibers were dried for 12 h for removal of excess zirconium nitrate and water. The impregnated nitrates were hydrolyzed through the addition of ammonia solution, which facilitates reaction between the hydroxyl groups and Zr4 þ ; this reaction leads to the deposition of zirconium hydroxide on jute cells; the fibers were kept undisturbed for one day. The jute fibers were dried for handling purpose and fired at 1200 1C for 2 h for fiber formation. The sintered materials were characterized through x-ray diffractometry (Philips PW-1730 Philips Corporation, Netherlands) using CuKα radiation (1.5406 Å) in the angular region of 201–801, field-emission scanning electron microscopy (Supra 35VP Carl Zeiss, Germany), scanning electron microscopy (LEO S430i, UK) and transmission electron microscopy (TECNAI G2 30ST, FEI, Netherlands). 3. Results and discussion
n
Corresponding author. Tel.: þ91 33 2473 3469; fax: þ 91 33 2473 0957. E-mail addresses: [email protected], [email protected] (S. Bandyopadhyay). 0167-577X/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.matlet.2013.03.056
Fibers in majority cases are clustered, handleable, 1–10 cm long and 7–10 mm wide. Typical SEM images of a portion of the as-
14
M. Biswas, S. Bandyopadhyay / Materials Letters 101 (2013) 13–16
Fig. 1. (a) SEM image of long zirconia fiber, (b) an amplified view of cluster of zirconia fiber; inset: image of single fiber and (c) further amplified image (FESEM) of single fiber.
Fraction presenc
50 40 30 20 10
0
0
24
22
0
0 20
0
18
0
16
14
80 10 0 12 0
40 60
20
0
Grain Size (μm) Fig. 2. (a) TEM images of fiber grains; inset: SAED pattern, (b) grain size distribution, (c) TEM image of an elongated large grain; inset: SAED pattern and (d) EDS of the elongated grain in Fig. 2b.
M. Biswas, S. Bandyopadhyay / Materials Letters 101 (2013) 13–16
prepared fibers are presented in Fig. 1a and b. These were further viewed for enlarged microstructure; almost smooth single fiber is observed in intermediate magnification (Fig. 1b-inset) whereas a tentatively rough surface is detected under still higher magnification (FESEM), revealing a good extent of sintering in the material. Sintered fiber in general consisted of 40–200 nm sized grains (Fig. 1c). Therefore, it can be concluded that the obtained fibers are made of grains with a wide range of size distribution. TEM has been carried out on the ground powder of sintered fibers. The grains were seen to appear apparently in hexagonal shapes (Fig. 2a). SAED patterns reveal the fact that the grains are oriented randomly and there is no preferred single orientation. The highest population of grain size distribution lies in the region between 40 and 100 nm. The size distribution is tentatively estimated from five TEM photographs and is represented in Fig. 2b. Few larger grains were studied and one such (400 nm length) has been presented in Fig. 2c. The SAED pattern (Fig. 2cinset) of this grain indicates that it is single crystalline. Therefore, it can be concluded that single crystals with considerable growth could be generated through this process. The EDS pattern (Fig. 2d) shows that the fibers are made of only elemental components of zirconia without any other impurity ions (the peak of Cu being arising from Cu grid). The fiber is composed of phase pure monoclinic zirconia (matched with JCPDS file no. 83-0944), as evidenced by XRD profile (Fig. 3). The peaks observed in XRD profile are broad which indicates that the crystallites are very fine. The crystallite sizes
15
were determined using the Scherrer relation: D¼0.94λ/βcos θ, where D is the crystallite size, λ is the wavelength of CuKα radiation (1.5406 Å), λ is full width at half maxima (FWHM) of the broadening of the diffraction line and θ is half the angle of diffraction [5]. The crystallite size has been estimated to be 32–34 nm which is close to the lower limit of the observed values under TEM. Possible mechanism of formation is schematically represented in Fig. 4. Jute fibers are basically lignocellulogic materials made with hydroxyl group (OH−) and other oxygen containing groups [6,7]. These groups attract water by hydrogen bonding [8,9]. Following this property, heavy metals have been attempted to be removed by using plant fibers like jute [10]. Literature [11] reports that the lignin in jute may be highly effective in binding and removing heavy metal ions through (hydrogen) bonding them with the cells [12]. The absorptive capabilities of jute materials are dependent on the pH of solution. A series of materials have already been removed using lignocellulogic materials at pH levels above about 5.5. This process is highly effective in removing heavy metal ions like nickel (Ni) or heavier than Ni, but is ineffective in case of lighter cations such as sodium or magnesium [11]. Since, zirconium (Zr) is heavier than Ni, similar phenomenon can be expected with it. Upon soaking of jute fibers in aqueous zirconium nitrate solution, the cells of jute swell due to its moisture absorption capacity till saturation [12]. The layer of Zr4 þ ion gets primarily be attached with the existing OH− of the lignocellulogic structure [7] and the ion deposition takes the form of an elongated layer on the jute cell walls. With subsequent addition of ammonia, the nitrate gets fully converted to hydroxide and thus the hydroxide layer coats the fiber. Upon heat treatment, the lignocellulogic structure burns out, leaving the fiber shaped hydroxide layer to convert to oxide followed by sintering.
4. Conclusion
Fig. 3. XRD pattern of obtained zirconia fiber.
Phase pure monoclinic zirconia fibers have been successfully prepared using the biotemplate method. The green shaping of the fiber is possible through the attraction of Zr4 þ ions into the cell wall through existing structural OH− ions. Fired fibers are made of single crystalline grains, mostly 40–100 nm sized, with occasional larger ones.
Biotemplate Zirconium nitrate OH group ammonia
Biotemplate
Zirconium hydroxide Heat treatment at 1200°C for 2 hrs
Zirconia fiber in agglomerated stage Fig. 4. Schematic representation of fiber formation mechanism.
16
M. Biswas, S. Bandyopadhyay / Materials Letters 101 (2013) 13–16
Acknowledgment The first author (MB) conveys her sincere thanks to CSIR for financial assistance through the grant of research associate position. Sincere thanks are also due to the Director, Central Glass and Ceramic Research Institute, Kolkata, India for his encouragement. The help of service sections of CGCRI and other colleagues are gratefully acknowledged. References [1] Balasubramaniam R. Callister's materials science and engineering. New Delhi, India: John Wiley & Sons; 2010.
[2] [3] [4] [5] [6] [7] [8] [9]
Ruf H, Evans AG. J Am Ceram Soc 1928;6:328–32. Deng D, Liao X, Liu X, Shi B. J Mater Res 2008;23:3263–8. Xu L, Lee HK. Anal Chem 2007;79:5241–8. Culity BD. Elements of X-Ray diffraction. Reading, MA: Addison-Wesley; 1978. Banerjee K, Roy A. Nat Inst Sci 1941;7:376. Mwaikambo LY, Ansell MP. J Appl Polym Sci 2002;84:2222–34. Stamm A, Wood J. Cellulose science. New York: The Renold Press Co.; 1964. Rowell RM, Banks WB. USDA forest service general technical report FPL 50, FPL. Madison,WI; 1985. [10] Ngah WSW. Hanafiah MAKM. Bioresour Technol 2008;99:3935–48. [11] Harman G, Patrick R, Spittler T. Ind Biotechnol 2007;3:366–74. [12] Das S, Saha AK, Choudhury PK, Basak RK, Mitra BC, Todd T, et al. J Appl Polym Sci 2000;76:1652–61.
Contents lists available at SciVerse ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Zirconia fiber via biotemplate synthesis route M. Biswas, S. Bandyopadhyay n CSIR-Central Glass & Ceramic Research Institute, 196, Raja S.C. Mullick Road, Kolkata 700032, India
art ic l e i nf o
a b s t r a c t
Article history: Received 12 December 2012 Accepted 11 March 2013 Available online 21 March 2013
Monoclinic zirconia fiber was fabricated through a novel chemical synthesis route using economically cheap biotemplate and aqueous zirconyl oxychloride. Zirconyl oxychloride gets converted through various steps as follows: hydroxylation to remove Cl−, nitrate addition and subsequently further hydroxylation. The process of green fiber formation lies on the reaction between hydroxyl groups of biotemplate and zirconium ion on the cell walls of biotemplate. With heat treatment at 1200 1C for 2 h, the deposited hydroxide converts to oxide in the form of sintered fiber. Fibers are handleable, 1–10 cm long and 7–10 mm wide. The fibers are made of monoclinic nanocrystals with crystallite size ranging mostly between 40 and 100 nm (compared to 32–34 nm as calculated from the Scherrer equation) with discrete ones as large as 400 nm. & 2013 Elsevier B.V. All rights reserved.
Keywords: Ceramics Structural Fiber technology
1. Introduction
2. Experimental
Fracture toughness of a material can be improved by introducing secondary discontinuous phases in material's matrix. Fiber as secondary phase is a good option for toughening materials. The improvement occurs following various mechanisms such as crack bridging, crack deflection, fiber pull-out, etc. [1]. Many of these mechanisms can be employed by incorporating zirconia grains and fibers in ceramic matrix composites [2]. In addition to the effect of grain morphology, zirconia may also offer phase transformation induced toughening caused by its reversible monoclinic–tetragonal phase transformation. Synthesis of zirconia fiber is therefore important and a simple approach using aqueous zirconyl chloride has been attempted in this study. Templating is a universal method for synthesis of fibers and various porous materials with a controlled and ordered structure using collagen materials, polypropylene hollow fibers, etc. [3,4]. Until recently, not much attention has been paid for the formation of monoclinic zirconia fibers using cheap bio-templates like jute, etc. In the present research work, a new chemical route has been tried using an economically cheap and widely available biotemplate, jute, which is used for brooming floor.
Aqueous zirconyl chloride (ZrOCl2 8H2O, Sigma-Aldrich) was dissolved in minimum amount of water for complete dissolution of the solid. For Cl− removal, Zr4 þ ions were precipitated as hydroxide using ammonia solution followed by subsequent washing the precipitate with distilled water. The presence of Cl− ion was confirmed with the silver nitrate test. The washed precipitate was dissolved in minimum amount of nitric acid to form zirconium nitrate. A bunch of jute fibers were soaked in this zirconium nitrate solution for one day for complete impregnation of zirconium nitrate molecules inside the cells of jute fibers. The soaked fibers were dried for 12 h for removal of excess zirconium nitrate and water. The impregnated nitrates were hydrolyzed through the addition of ammonia solution, which facilitates reaction between the hydroxyl groups and Zr4 þ ; this reaction leads to the deposition of zirconium hydroxide on jute cells; the fibers were kept undisturbed for one day. The jute fibers were dried for handling purpose and fired at 1200 1C for 2 h for fiber formation. The sintered materials were characterized through x-ray diffractometry (Philips PW-1730 Philips Corporation, Netherlands) using CuKα radiation (1.5406 Å) in the angular region of 201–801, field-emission scanning electron microscopy (Supra 35VP Carl Zeiss, Germany), scanning electron microscopy (LEO S430i, UK) and transmission electron microscopy (TECNAI G2 30ST, FEI, Netherlands). 3. Results and discussion
n
Corresponding author. Tel.: þ91 33 2473 3469; fax: þ 91 33 2473 0957. E-mail addresses: [email protected], [email protected] (S. Bandyopadhyay). 0167-577X/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.matlet.2013.03.056
Fibers in majority cases are clustered, handleable, 1–10 cm long and 7–10 mm wide. Typical SEM images of a portion of the as-
14
M. Biswas, S. Bandyopadhyay / Materials Letters 101 (2013) 13–16
Fig. 1. (a) SEM image of long zirconia fiber, (b) an amplified view of cluster of zirconia fiber; inset: image of single fiber and (c) further amplified image (FESEM) of single fiber.
Fraction presenc
50 40 30 20 10
0
0
24
22
0
0 20
0
18
0
16
14
80 10 0 12 0
40 60
20
0
Grain Size (μm) Fig. 2. (a) TEM images of fiber grains; inset: SAED pattern, (b) grain size distribution, (c) TEM image of an elongated large grain; inset: SAED pattern and (d) EDS of the elongated grain in Fig. 2b.
M. Biswas, S. Bandyopadhyay / Materials Letters 101 (2013) 13–16
prepared fibers are presented in Fig. 1a and b. These were further viewed for enlarged microstructure; almost smooth single fiber is observed in intermediate magnification (Fig. 1b-inset) whereas a tentatively rough surface is detected under still higher magnification (FESEM), revealing a good extent of sintering in the material. Sintered fiber in general consisted of 40–200 nm sized grains (Fig. 1c). Therefore, it can be concluded that the obtained fibers are made of grains with a wide range of size distribution. TEM has been carried out on the ground powder of sintered fibers. The grains were seen to appear apparently in hexagonal shapes (Fig. 2a). SAED patterns reveal the fact that the grains are oriented randomly and there is no preferred single orientation. The highest population of grain size distribution lies in the region between 40 and 100 nm. The size distribution is tentatively estimated from five TEM photographs and is represented in Fig. 2b. Few larger grains were studied and one such (400 nm length) has been presented in Fig. 2c. The SAED pattern (Fig. 2cinset) of this grain indicates that it is single crystalline. Therefore, it can be concluded that single crystals with considerable growth could be generated through this process. The EDS pattern (Fig. 2d) shows that the fibers are made of only elemental components of zirconia without any other impurity ions (the peak of Cu being arising from Cu grid). The fiber is composed of phase pure monoclinic zirconia (matched with JCPDS file no. 83-0944), as evidenced by XRD profile (Fig. 3). The peaks observed in XRD profile are broad which indicates that the crystallites are very fine. The crystallite sizes
15
were determined using the Scherrer relation: D¼0.94λ/βcos θ, where D is the crystallite size, λ is the wavelength of CuKα radiation (1.5406 Å), λ is full width at half maxima (FWHM) of the broadening of the diffraction line and θ is half the angle of diffraction [5]. The crystallite size has been estimated to be 32–34 nm which is close to the lower limit of the observed values under TEM. Possible mechanism of formation is schematically represented in Fig. 4. Jute fibers are basically lignocellulogic materials made with hydroxyl group (OH−) and other oxygen containing groups [6,7]. These groups attract water by hydrogen bonding [8,9]. Following this property, heavy metals have been attempted to be removed by using plant fibers like jute [10]. Literature [11] reports that the lignin in jute may be highly effective in binding and removing heavy metal ions through (hydrogen) bonding them with the cells [12]. The absorptive capabilities of jute materials are dependent on the pH of solution. A series of materials have already been removed using lignocellulogic materials at pH levels above about 5.5. This process is highly effective in removing heavy metal ions like nickel (Ni) or heavier than Ni, but is ineffective in case of lighter cations such as sodium or magnesium [11]. Since, zirconium (Zr) is heavier than Ni, similar phenomenon can be expected with it. Upon soaking of jute fibers in aqueous zirconium nitrate solution, the cells of jute swell due to its moisture absorption capacity till saturation [12]. The layer of Zr4 þ ion gets primarily be attached with the existing OH− of the lignocellulogic structure [7] and the ion deposition takes the form of an elongated layer on the jute cell walls. With subsequent addition of ammonia, the nitrate gets fully converted to hydroxide and thus the hydroxide layer coats the fiber. Upon heat treatment, the lignocellulogic structure burns out, leaving the fiber shaped hydroxide layer to convert to oxide followed by sintering.
4. Conclusion
Fig. 3. XRD pattern of obtained zirconia fiber.
Phase pure monoclinic zirconia fibers have been successfully prepared using the biotemplate method. The green shaping of the fiber is possible through the attraction of Zr4 þ ions into the cell wall through existing structural OH− ions. Fired fibers are made of single crystalline grains, mostly 40–100 nm sized, with occasional larger ones.
Biotemplate Zirconium nitrate OH group ammonia
Biotemplate
Zirconium hydroxide Heat treatment at 1200°C for 2 hrs
Zirconia fiber in agglomerated stage Fig. 4. Schematic representation of fiber formation mechanism.
16
M. Biswas, S. Bandyopadhyay / Materials Letters 101 (2013) 13–16
Acknowledgment The first author (MB) conveys her sincere thanks to CSIR for financial assistance through the grant of research associate position. Sincere thanks are also due to the Director, Central Glass and Ceramic Research Institute, Kolkata, India for his encouragement. The help of service sections of CGCRI and other colleagues are gratefully acknowledged. References [1] Balasubramaniam R. Callister's materials science and engineering. New Delhi, India: John Wiley & Sons; 2010.
[2] [3] [4] [5] [6] [7] [8] [9]
Ruf H, Evans AG. J Am Ceram Soc 1928;6:328–32. Deng D, Liao X, Liu X, Shi B. J Mater Res 2008;23:3263–8. Xu L, Lee HK. Anal Chem 2007;79:5241–8. Culity BD. Elements of X-Ray diffraction. Reading, MA: Addison-Wesley; 1978. Banerjee K, Roy A. Nat Inst Sci 1941;7:376. Mwaikambo LY, Ansell MP. J Appl Polym Sci 2002;84:2222–34. Stamm A, Wood J. Cellulose science. New York: The Renold Press Co.; 1964. Rowell RM, Banks WB. USDA forest service general technical report FPL 50, FPL. Madison,WI; 1985. [10] Ngah WSW. Hanafiah MAKM. Bioresour Technol 2008;99:3935–48. [11] Harman G, Patrick R, Spittler T. Ind Biotechnol 2007;3:366–74. [12] Das S, Saha AK, Choudhury PK, Basak RK, Mitra BC, Todd T, et al. J Appl Polym Sci 2000;76:1652–61.