Available online at www.sciencedirect.com
ScienceDirect Procedia Engineering 148 (2016) 243 – 248
4th International Conference on Process Engineering and Advanced Materials
Fabrication of Superconducting YBCO Nanoparticles by Electrospinning S. E. Jasima,b, M. A. Jusoha,*, M. Hafiza and Rajan Josea b
a Faculty of Industrial Sciences & Technology, Universiti Malaysia Pahang, UMP, Kuantan-26300, Pahang, Malaysia Electrical dept., Technical Institute/Al Haweejah, Northern Technical University, Al Haweejah-36007, Kirkuk, Republic of Iraq
Abstract High temperature superconductor YBa2Cu3O7-δ (HTS YBCO) nanoparticle was successfully prepared by electrospinning and sol-gel techniques. The sol-gel containing a homogeneous solutions of the precursor of Y-Ba-Cu acetate and Poly (vinyl pyrrolidone) PVP. The critical transition temperature (Tc) of the samples have been found using four point probe technique. By optimizing electrospinning, sol-gel process and heat treatment procedure, YBCO nanoparticle with a transition temperature of 78 K was obtained. The surface area measurements of YBCO samples showed, high surface area 2.0 m2/g for nanoparticle, in comparison with block sample 1.0 m 2/g. The structural Characterizations of YBCO samples demonstrated that, the YBCO nanoparticles have single phase orthorhombic structure which typical crowd nanoparticles diameter were 388 nm. The Individual nanoparticle diameter were found between 20 and 50 nm. The calcination temperature at 950 oC does not affect to decrease the surface area of YBCO samples. Electrospinning in combination with a sol-gel techniques are an effective routes to realize different nanostructure morphologies of YBCO superconductor. Production of HTS YBCO nanoparticle by these process promising practical applications.
© Publishedby byElsevier ElsevierLtd. Ltd. This is an open access article under the CC BY-NC-ND license © 2016 2016 The The Authors. Authors. Published (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of ICPEAM 2016. Peer-review under responsibility of the organizing committee of ICPEAM 2016 Keywords: Electrospinning; High Temperature; Nanoparticle; Superconductor; YBCO;
1. Introduction Superconducting YBa2Cu3O7-δ (YBCO) amongst other 1:2:3 ceramic materials became more popular, because of its outstanding properties, like high transition temperature, current density, magnetic field, and chemical stability[1, 2]. Furthermore, it is easy to fabricate from metal oxides, acetate and nitrite [1-4]. Besides their components are non-toxic, non-volatile, less anisotropic, relatively low cost and capable to have single phase. HTS YBCO has been widely explored to be the most promising cuprate [2, 3]. In point of fact, YBCO is by this time being examined in power transmission [5-7], transformers, motors, generators and extraordinary frequency electronics applications [8-10]. HTS YBCO was successfully fabricated to realize 1D nanostructure with single crystal structure, high performance and uniform, by employing various techniques. Techniques such as Pulsed Laser Deposition (PLD), Citrate Pyrolysis Technique and Soft Chemical Route, were demonstrated to fabricate HTS BCO nanoparticle [4, 11-13].
* Corresponding author. Tel.: +609-5492314; fax:+609-5492766. E-mail address:
[email protected]
1877-7058 © 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of ICPEAM 2016
doi:10.1016/j.proeng.2016.06.595
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Electrospinning process appears as an efficient technique, versatile, simple, controlled parameters and cheapest incorporation with other techniques [14, 15]. Electrospinning is a powerful technique, generally used in combination with the sol - gel technique followed by calcination process at high temperature [16, 17]. The typical sol-gel solution used with the electrospinning technique consists of a precursor of the desired materials plus polymer and a relative volatile solvent [1, 18]. The solvent is utilized to control the product solution viscosity, conductivity and morphology. Solvents like water, methanol, isopropanol, ethanol and others are widely used as a solution parameters [14, 19]. Although, several researchers have synthesized HTS YBCO with different morphologies in nanoscale diameter and individually by electrospinning technique in combination with sol-gel [13, 14, 16, 17]. Morphology of HTS YBCO like nanofibres, nanotube and nanowires have been demonstrated via electrospinning and sol-gel [3]. However, morphologies of HTS YBCO nanoparticles are still not realized up to now by electrospinning. This work presents a practical experiment and process routes to fabricate and characterize HTS YBCO nanoparticles with intrinsic properties by electrospinning the sol-gel solutions followed by heat treatment techniques [19, 20]. The superconducting properties of YBCO nanoparticle samples are experimentally depending on the solution parameters of sol-gel, electrospinning process and heat treatment conditions [14, 21]. 2. Experimental 2.1. Materials Poly (vinyl pyrrolidone), PVP [Mw = 160,000 g/mole] were purchased from Adrich,. Yttrium (III) acetate tetrahydrate [99.9% (REO), powder Y(OOCCH3)3.4H2O], Barium acetate [ACS 99.0%, crystalline Ba(OOCCH3)3] and Copper (II) acetate monohydrate [powder C4H6CuO4.H2O] were purchased from Alfa Aesar. Solvents were used Propionic acid (C3H6O2), Acetic acid (C2H4O2) and Methanol (CH4O) used (purity, 99%) supplied commercially. All the material were used without any purification. 2.2 Sample preparation The sample was prepared by dissolving 4.0 g of Y-Ba-Cu acetate and 3.0 g of PVP powder in 25.0 ml mixture of propionic acid, acetic acid and methanol. The propionic acid utilized successfully to dissolve metallic acetate of (Y, Ba and Cu) [3, 16]. The addition of Acetic acid was very important to avoid any hydrolysis of the polymers [2, 3, 16]. Moreover, Acid medium was suitable to create a stabilization of the solution and to prevent the hydrolysis of the sol–gel precursor. Finally, Methanol was added as a Polymer solvent and to tune the viscosity [3]. 2.3 Sol-gel method The sol-gel solution was conducted by dissolving separately the polymer and precursor acetate solutions. The polymer solution was prepared by melting 3.0 g of PVP polymer in 10 ml of methanol and then stirred at 70 oC for 1 h in a closed beaker. The precursor solution of metal acetate was made by dissolving the components of Y-Ba-Cu acetate with a stoichiometric ratio of 1:2:3 molar mass among acetate in 10 ml of propionic acid. Then the result stirred at room temperature in a covered beaker for 12 h. The two solutions were collected with the addition 5.0 ml of acetic acid, then stirred at room temperature for 12 h. The addition of polymer and adjustment of viscosity was maintained to achieve the nanostructure shapes [2, 3, 14]. The viscosity of the solutions were controlled by the addition of polymer and solvent. Different weight ratio and solvents quantity could be adopted to change the viscosity, leading to a new results. Both viscosity and conductivity were determined to be consistent with the literature of electrospinning process [15, 22]. 2.4 Electrospinning The electrospinning processes set up are supported by a syringe (14 cm diameter, 5 ml volume), needle (20 gauge, stainless steel), ground collector (10 cm diameter, 30cm length, stainless steel and controlled speed), high power supplier and controlled injection pump [14, 19, 21]. The resultant sol-gel solutions were loaded by a syringe and electrospun at 20 kV with 16 cm tipcollector distance, 1 ml/h flow rate injection and collector speed at 1200 rpm. All the electrospun samples were deposited on flat LaAl2O3 (100) substrate and aluminium foil covered the collector, in order to remove it easily from the collector. The electrospinning process was carried out at room temperature and closed environment. All samples produced by the electrospinning were placed in a closed desiccator to dry for 48 h. 2.5 Heat treatments The heat treatment process was divided in two steps, the first was to burn out the polymer and the second was to carry out the single structure of HTS YBCO nanoparticle. The electrospun sample was firstly transferred to the box furnace (Nabertherm, 303000 oC) and heated from room temperature up to 500 oC for 3 h at a heating rate of 50 oC/h. The second heat treatment was
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made after graining the powder and performed by using tube furnace (Nabertherm, 30-3000 oC), sample was heated and cooled from the room temperature up to 900 oC for 4 h with a rate of 250 oC/h, followed by 25 oC/h heating rate from room temperature up to 950 oC for 3 h inflow of oxygen. Actually, there were two procedures of heat treatments are followed by graining the powder to get the right single structure of YBCO. One by calcination 900 oC and the second by annealing in oxygen atmosphere at 950 oC, separately. 2.6 Measurements The viscosity and conductivity of the sol-gel solution was determined by using high resolution lab Viscometer (Brook Field, model: LVDV -11+P) and digital conductivity meter respectively, at room temperature. The thermogravimetric analyzer (Mettler Toledo, TGA DSC) was used to examine the thermal analysis of the electrospun (Y–Ba–Cu acetates) sample. The crystal structure of the sample was analyzed from 5 to 85o angle with a count speed of 1 degree per minute using X-ray diffractometer (Rigaku, model: Miniflex II) operating at 30 kV, 15 mA. The morphology of the sample was observed by Field Emission Scanning Electron Microscope (FESEM, JEOL, model: JSM–7600) operating with 5.0 kV, LED. The transition temperatures (Tc) of superconducting YBCO samples were measured via a closed cycle of liquid helium refrigeration systems and the four-probe technique. A comparison measurements were conducted between Tc and resistance of YBCO nanoparticle thin film and thick samples. Surface area measurements for both thick and electrospun nanoparticle thin film samples were investigated using BET Surface Area and Porosity Analyzer (Micrometrics, model: ASAP 2020), degas temperature at 400 oC for 7 h. 3. Results and discussion The measured viscosity was found to be in a range of 135 to 175 cps, while the conductivity results in the range of 162 to 184 mS/cm at room temperature. The results of conductivity measurements indicated high conductivity in comparison with the work of Edgar et al (2014) which is the conductivity is around 12.7 µS/cm [3]. High conductivity and lower viscosity are desired for easy transformation of the charged jet solution between the nozzle tip and collector in electrospinning process [14, 23]. X. M. Cui et al 2006 [16] studied the relation between the viscosity of Y-Ba-Cu acetate solutions and the diameter of the nanofibres produced by electrospinning. The diameter of fibers were increased slightly by increasing the viscosity from 200 to 400 cps and simultaneously increased gradually by increasing the viscosity from 500 to 700 cps [16]. The electrospun precursor transformation to the final product nanoparticle sample could be clarified by the thermal analysis data. Thermogravimetric analysis (TGA) and simultaneously differential scanning calorimeter (DSC) curves versus temperature for the jalousie specimen of YBCO nanoparticle, is presented in Fig. 1. After drying the electrospun sample over 48 h by desiccator, it was heated from room temperature up to 1100 oC. The two curves of TGA and DSC shows that, about 20% weight gradual losses between 220 and 250 oC due to the solvent evaporation. As reported in literature the sequences exothermic peak existed at 250 and 450 oC related to decomposition of organic acetate groups and burnout the polymer and other intermediate component. Finally, the trend of increasing the temperature above 820 oC indicates the beginning of YBCO crystallization [1, 3, 16]. Thus weight losses of sample from room temperature up to 850 °C was 56%. According to the data and previous literature [3], nanoparticle sample transferred from electrospinning could be obtained by two heat treatment process. The first heat treatment was assigned to remove out the polymer at temperature between 450-500 °C. The second heat treatment was desired for phase crystallization of YBCO and form the final pure product nanoparticle sample. The transformation to single crystal orthorhombic structure was maintained by annealing the YBCO nanoparticle sample with flow of oxygen yielding high stability and high transition temperature due to the high oxygen content [1-3].
Fig. 1. TGA and DSC of electrospun YBCO nanoparticle samples.
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The x-ray diffraction pattern result of HTS YBCO nanoparticle sample was intense inescapably and consistent with literature [2, 3]. Fig. 2, shows the optimum XRD pattern obtained for YBCO nanoparticle after the heat treatment process of the electrospun sample. All indicated peaks could be seen under the YBCO indexed correspond to the d-spacing. The sample structure showed a single, pure phase and orthorhombic symmetry. As the dimension of lattice parameter was determined using Braggs Law (2d sin θ = nλ), Miller indices and d-spacing. The lattice parameters were unequal (a ≠ b ≠ c), a = 3.897 Å, b = 3.8889 Å, c = 11.707 Å, V = 177.4064 Ǻ3 and consistent with literature, which is well known as perovskites structure [11]. The morphology of HTS YBCO nanoparticle was tested via field emission scanning electron microscope (FESEM) operating at 5.0 kV, with the sample examined after the first and second heat treatments. The powder of nanoparticle sample placed on a tape at regular distribution and dried. The FESEM image of the sample taken for various areas, directions and enlargement. Fig. 3, shows the FESEM images of HTS YBCO nanoparticle after heat treatments.
Fig. 2. X-ray diffraction pattern of the HTS YBCO nanoparticle after the heat treatments in air at 900 °C and annealed at 950 °C for 3 h.
Fig. 3. FESEM images of HTS YBCO nanoparticle (a), (b) after first heat treatment, and (c), (d) after second heat treatment.
The Tc of samples were measured in order to prove the superconductivity of YBCO nanoparticle thin films and block samples.
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The YBCO nanoparticle thin film sample was deposited on LaAl 2O3 substrate by electrospinning. The block sample was prepared by using sol-gel precursor solution and solid state reaction method. All the samples were treated under the same heat treatment conditions, and the Tc measurements were done using four probe technique via a closed cycle of liquid helium refrigeration system with a constant 200 mA current. The YBCO samples (thin film and thick pellet) resistance could be determined from the slope of relationship between the current-voltage curved. Fig. 4, illustrates the Tc measurements, from the resistance-temperature relations for nanoparticle thin film and pellets of YBCO samples. The block sample shows zero resistance transition temperature at 85 K, with sharp transition width of 6 K. On the other hand, the nanoparticle thin film sample exhibit zero resistance at 78 K, and semi sharp transition width of 13 K. The reduction in the transition temperature correlated with the reducing in energy gap due to the minimization of sample dimensions [24]. The transition temperature result of YBCO nanoparticle thin film and pellet samples inconsistent with previous work by Shen z. et al [2].
Fig. 4. Tc measurements of HTS YBCO, (a) thin film nanoparticle Tc = 78 K, (b) the block sample Tc = 85 K.
Physically, BET surface area measurements for both thick and electrospun thin film YBCO nanoparticle samples were 1.0 m2/g and 2.0 m2/g respectively. Both samples were heated and annealed by 900 °C and 950 °C respectively in oxygen atmosphere. G. E. Shter et al.[23], Studied the interrelation between the surface area and the calcination temperature. The results showed a decrease in surface area of the YBCO powder from 2.36 to 0.46 m 2/g by increasing the calcination temperature from 750 °C to 910 °C. However, G. E. Shter and G. S. Grader [24], found the surface area of YBCO powder with 1.7 m2/g could be obtained when calcined at 780°C for 12 h, while calcining YBCO at 920 °C lead to decrease in the particle size to submicron and surface area equal to 0.3 m2/g. On the other hand, this work presented unexpected result to prove that, the surface area of YBCO nanoparticle is not affected by the high calcination temperature. This result due to the small size diameter of YBCO nanoparticle, which lead to increase the surface area [25]. 4. Conclusion The electrospinning and sol-gel techniques are very competitive to obtain several nanostructured shapes of high porosity small volume with respect to the high surface area and controlled diameter. This work present a novel and excellent procedure to synthesis the superconducting YBCO nanoparticle by electrospinning process. The electrospinning technique used a sol-gel of polymer and precursor of metal acetate solutions, which is followed by a complex heat treatment processes. The transition temperature of YBCO nanoparticle thin film showed zero resistance at 78 K, with semi sharp transition width of 13 K. while, block sample indicated zero resistance at 85 K, and sharp transition width of 6 K. The diameter and morphology of the YBCO nanoparticle sample depends on the viscosity of the solution and electrospinning process. Typical nanoparticle diameter between 20 and 50 nm, and agglomerated nanoparticles about 388 nm were obtained. The measured surface area of YBCO nanoparticle was greater than for block sample, and not influenced by the calcination temperature. Reference [1] [2] [3] [4] [5]
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