Investigation into Electrospun LaMnO 3 Nanofibres

Transcription

1 Universities Research Journal 2011, Vol. 4, No. 4 Investigation into Electrospun LaMnO 3 Nanofibres Zin Min Myat 1, Than Than Win 2 and Yin Maung Maung 3 Abstract This paper aims to prepare nanofibres by electrospinning utilizing sol-gel precursors. Thermal analysis of fibres were studied by Thermogravimetry and Simultaneous Different Thermal Analysis (TG-DTA). The crystal structure of LaMnO 3 nanofibres were examined by X-ray Diffraction (XRD). Scanning Electrons Microscopy (SEM) analysis was carried out to examine the fibre diameter and morphological properties. The electrospinning can potentially be used as a straightforward and cost-effective means for the assembly of one-dimensional nanostructures for building integrated nanodevices for various applications, such as transistors, sensors, diodes, and to develop photodetectors. Introduction Nanotechnology is the experimental process of manipulating matter on an incredibly minute scale (one thousandth of a millimeter and smaller) in order to create new products and materials or delivery systems. Nanofibres are an exciting new class of material used for several value added applications such as medical, filtration, barrier, personal care, composite, garments, insulation and energy storage. [Nano Technology and Non woven.com]. Electrospinning makes it relatively easy to spin continuous nanofibres from many different polymers. The electrospinning process is driven by the electrical forces on free charges on the surface or inside a polymeric liquid. In conventional spinning, the fibre is subject to tensile, rheological, gravitational, inertial and aerodynamic forces. [Jinxian W et al 2009] Mechanical formation of polymer crystals often produces fibres which are observed in electron micrographs of feature surfaces, for example such fibres typically have diameters of a few tens of nanometers and lengths up to a few micrometers. Many images of polymer nanofibres exist in the literature that deals with polymer morphology, but in almost all cases the nanofibres were observed incidentally to other features of the polymer [Geil PH 1963]. The sol-gel process is a versatile solution process for making ceramic and glass materials. In general, the sol-gel process involves the transition of a system from a liquid sol into a solid gel 1. Demonstrator, Department of Physics, Dagon University 2,3. Lecturer, Department of Physics, University of Yangon, Myanmar

2 246 Universities Research Journal 2011, Vol. 4, No. 4 phase. In a typical sol-gel process, the precursor is subjected to a series of hydrolysis and polymerization reactions to form a colloidal suspension or a sol [Sol-gel Technology.com]. Nanofibres can be made of Lanthanum Manganite (LaMaO 3 ) by electrospinning technique. In order to obtain these fibres, LaMnO 3 powder is required and is proposed mainly from the Lanthanum chloride, manganese chloride and ammonium carbonate used as the starting materials. LaMnO 3 has attracted much interest recently due to their specific electrical and catalytic properties. A few methods on the preparation of LaMnO 3 nanocrystalline materials are reported [Dong HT et al 1994]. Experimental Procedure In this study, the experimental procedure was depicted in a flow chart as shown in figure (1). LaMnO 3 nanofibres were formed by calcinating the precursor PVA/LaMnO 3 composite fibre. For the preparation of composite fibres, sol-gel process was used g of LaMnO 3 was dissolved in 10 g of Poly Vinyl Alcohol (PVA). The mixtures of these were dissolved in distilled water. The mixture was stirred by magnetic stirrer for 3 hour to form a homogeneous solution. Finally, that solution was determined by measuring its viscosity. After stirring, the temporary solutions were mixed at room temperature for 24 hours to get a uniform solution. The solution was expected to be viscous enough for electrospinning. The local-made electrospinning apparatus contains a needle or spinneret, high voltage power supply and the grounded collector. Horizontal experimental Set-up was chosen for electrospinning process.the precursor solution was taken in a syringe with hypodermic needle ( mm). The hypodermis syringe needle was connected to the positive terminal of a high DC voltage generator that produced maximum voltage 27 kv and the negative terminal of the powder supply was connected to the collector (Aluminium foil) opposite to the syringe needle with a distance about 9 cm. Al-substrate was then stuck on the collector. Before supplying the power, glass tube was created as vacuum condition by using vacuum pump and also tested by vacuum tester. The high electrical potential overcomes the surface tension of the solution in the syringe needle and the jet of charged precursor solution was ejected out from the collector. The precursor solution was deposited on Al substrate by electrospinning method. And then it was heat-treated at 800 ºC for 6 hours. Possible formation mechanism of LaMnO 3 fibres was found at 800 ºC. The

3 Universities Research Journal 2011, Vol. 4, No schematic diagram of electrospinning Set-up is shown in figure 2. The crystal structure and thermal analysis of fibres were characterized by TG- DTA and XRD measurement. The morphology and size of the fibres were observed with Scanning Electron Microscope. [SEM] Typical range of operating parameters used for this experiment is shown in Table 1. Polymer Solution LaMnO 3 Syringe capacity 20 cc Electrodes spacing 9 cm Capillary Diameter 0.65 mm High voltage power supply (DC) ~ 30 kv Working high voltage power supply (DC) ~ 27 kv Running time 20 min Cooling Time 10 h Annealing Temperature 800 C Annealing Time 6 h

4 248 Universities Research Journal 2011, Vol. 4, No. 4 LaCl 3.7H 2 O (NH 4 ) 2 CO 3 MnCl 2.4H 2 O calcinated at 1000ºC for 30 min Distilled water LaMnO 3 powder PVA Stirred vigorously about 3 h LaMnO 3 sol-gel Absorbed by syringe Electrosprinning Set-up Applied high voltages (~ 27 kv) Fibres on Al substrate annealed at 800 ºC for 6 h LaMnO 3 nanofibers TGA-DTA XRD SEM Fig. 1 Schematic flow diagram of investigation into LaMnO 3 fibres

5 Universities Research Journal 2011, Vol. 4, No Fig. 2 Schematic diagram of electrospinning Set-up Results and Discussion TG-DTA Analysis TG and DTA curves of the PVA/[LaCl 3 +MnCl 2 +(NH 4 ) 2 CO 3 ) composite fibres were indicated in figure 3(a) and (b). It was noted that the DTA of the LaMnO 3 of mixed carbonate showed four district endothermic peaks in fig 3(a). The first endothermic peak at 170 ºC may be due to the loss of moisture from the LaMnO 3 composite sample. The endothermic peak at 170 ºC corresponds to do the decomposition taking place in three steps corresponding to the endothermic peaks at 170 ºC, 260 ºC and 400 ºC which finally results in MnO 3 formation. It may be inferred that the endothermic peak around 400 ºC represented the decomposition of LaCO 3 as well as the initial stage of MnCO 3 decomposition. In figure 3(b), there were two further distinct steps in TGA analysis. The major weight loss completed at approximately 440 ºC. The TGA analysis of the LaMnO 3 was in agreement with the DTA peaks showing distinct regions mentioned in the DTA.

6 250 Universities Research Journal 2011, Vol. 4, No C 260 C 400 C Fig.3 (a) DTA analysis of LaMnO 3 powder 350 C 440 C Fig.3 (b) TGA analysis of LaMnO 3 powder X-ray Diffraction Analysis The X-ray diffraction pattern of Lanthanum manganite nano powders are shown in figure 4(a). The XRD measurement showed that all peaks of LaMnO 3 are consistent with that LaMnO 3 standard (JCPDS) powder having a orthorhombic structure. The broad peaks in XRD patterns indicate fine crystallite size of the LaMnO 3 powder. The crystallite size was calculated from the XRD peak broadening of the (020) peak using Scherrer s formula. The strongest peak was examined at (020) reflection as

7 Universities Research Journal 2011, Vol. 4, No the 5 th peak for all fabricated powders. The crystallite size of LaMnO 3 powders were in the range of nm. From XRD measurement, it was found that the orthorhombic phase of LMO powder was obtained at this temperature range 800 ºC to 1200 ºC. In order to investigate the lowest crystallizing temperature and the variety of phases, the PVA/ [LaCl 3 + MnCl 2 +(NH 4 ) 2 CO 3 composite fibres and samples on Al substrate obtained by calcining the composite fibres at different temperature for 6 h were characterized by XRD as indicated in Figure 4(b). According to this figure, a broad peak was located around 23º, it was the typical peak of the amorphous polymer indicating that the composite fibres were amorphous in structure. The polycrystalline LaMnO 3 nano fibres with single phase were synthesized when calcinations temperature was in the range of 500 ºC-900 ºC, the d (spacing between crystallographic plane) values and relative intensities of LaMnO 3 were consistent with those of JCPDS standard card and the crystal structure of the prepared LaMnO 3 nano fibres were orthorhombic system with space group Pb nm. Table 2 Show the structural properties of LaMnO 3 Sample LaMnO 3 Sample Structural Properties powder fibre Lattice Parameter, a ( Å) Lattice Parameter, b ( Å) Lattice Parameter, c ( Å) Bond-length FWHM (deg) Crystallite-size (nm)

8 252 Universities Research Journal 2011, Vol. 4, No. 4 Fig.4(a) XRD patterns of LaMnO 3 powders, annealing temperature at 1000 C

9 Universities Research Journal 2011, Vol. 4, No Fig. 4(b) XRD Patterns of LaMnO 3 fibres, annealing temperature at 800 C SEM Analysis The SEM images of LaMnO 3 samples were shown in figure 5 and 6. The SEM behaviour of surface morphology of LaMnO 3 nanofibres were found. It was observed that with the increase in annealing temperature the diameter of the fibres also decreased and that were approached to nanometer (nm) range. In order to study the morphology and size of the assynthesized fibres, the prepared fibres were investigated by SEM, as shown in figure 5. As seen from figure 6, the morphology and size of the fibres varied strongly with the increase of calcination temperature. The surface of the PVA/[LaCl 3 +MnCl 2 +(NH 4 ) 2 CO 3 composite fibres was about 50 nm. From SEM results, the diameter of the LaMnO 3 fibres at 500 ºC were not examined to reach the nanoscales but the diameter of LaMnO 3 fibres was about 50 nm at 800 ºC. Therefore, it was investigated that LaMnO 3 nano fibres became good morphology with the increase of calcinations temperature.

10 Universities Research Journal 2011, Vol. 4, No nm 50 nm Fig. 5 SEM Images of Lanthanum Manganite Fibres 800 C

11 Universities Research Journal 2011, Vol. 4, No Fig. 6 SEM Images of Lanthanum Manganite Fibres 500 C Conclusion In conclusion, the investigation of PVA/[LaCl 3 +MnCl 2 +(NH 4 ) 2 CO 3 composite nanofibres were fabricated by electrospinning technique. The electrospinning process took place in the cylindrical shape of glass tube that had very limited exposure to external conditions to the tube. Polycrystalline LaMnO 3 nanofibres were synthesized by calcining the relevant composite fibres at 800 ºC. The crystal structure of LaMnO 3 nanofibres were orthorhombic system. According to TGA curve, LaMnO 3 was thermally stable and final weight loss was completed at about 440 ºC. The endothermic peak was formed at about 440 ºC on DTA curve. Therefore the combined TGA-DTA data indicated that slow heating resulted in transformation of the inorganic compounds nanofibres could be obtained at 440 ºC. SEM images indicated that the surface of the prepared composite fibres were smooth and the diameters of the composite nanofibres were

12 256 Universities Research Journal 2011, Vol. 4, No. 4 about 50 nm at 800 ºC. Therefore the surface morphology of the LaMnO 3 nanofibres became coarse with the increase in calcinations temperatures. Therefore LaMnO 3 ultra-fine fibres were successfully formed by electrospinning technique. The nanofibres should be useful for some potential application of electronic devices, separation membrane, biomedical applications structural elements in artificial organs, nanocomposites and protective clothings. Acknowledgements The authors would like to thank Professor Dr Khin Mar Kyu PhD (Head of Department of Physics), Dagon University for her kind permission to carry out this research work. References W, Jinxian. et al. (2009). Synthesis of LaMnO 3 Nanofibres via Electrospinning Applied Physics Research 1 (2) 30. Geil, PH (1963). Polymer Single Crystals. New York: Inter science Dong, HT et al. (1994). Study of Synthesis and electrical conductivity of LaMnO 3 ultrafine powders 23 (2) 60. Zin Min Myat, Taw Taw, Sabai Aye, Than Than Win, Yin Maung Maung et al Proceedings of the Second International Conference on Science and engineering http;// Technology and Non woven.com pedia. Org/wiki/ Polymerization Technology.com