FABRICATION, STRUCTURE, AND MAGNETIC PROPERTIES OF CARBON/NICKEL - PDF document

18 TH INTERNATIONAL CONFERENCE ON COMPOSITE MATERIALS FABRICATION, STRUCTURE, AND MAGNETIC PROPERTIES OF CARBON/NICKEL FERRITE (NiFe 2 O 4 ) COMPOSITE NANOFIBERS S. Nilmoung 1 , S. Rugmai 1,2 , S. Maensiri 1,  1. School of Physics, Institute of Science, Suranaree University of Technology, Nakhon Ratchasima, Thailand, 30000. 2. Siam Photon Laboratory Synchrotron Light Research Institute (Public Organization), Nakhon Ratchasima, Thailand, 30000. * Corresponding author (santimaensiri@g.sut.ac.th) Carbon/NiFe 2 O 4 composite nanofibers have been successfully fabricated by electrospinning method using a solution that contained polyacrylonitrile (PAN) in N,N’ dimethylformamide (DMF) solvent as polymer sources and 10 wt.% of Ni and Fe nitrates solution as alternative metal sources. The as-spun and carbonized PAN/NiFe 2 O 4 composite samples were characterized by TG-DTA, XRD, SEM, TEM, Raman spectroscopy and SAXS, respectively. It has been found that, the morphologies and the crystal size were influenced by the stabilization time and the carbonization temperature. A full phase of NiFe 2 O 4 embedded carbon fibers was formed after carbonization in argon atmosphere at 1000 ºC. The shrinkage diameter and porous surface were present after carbonization. The average crystallite sized (D) were found to be 30.9 and 30.1 nm for the samples stabilized at 280 0 C for 0.5 h and 2 h, respectively. The magnetic properties of the prepared samples were measured at room temperature by a vibrating sample magnetometer. Both samples stabilized for 0.5 and 2 h exhibit ferromagnetism having saturation magnetizations of 0.36 and 3.40 emu/g, respectively. Keywords : NiFe 2 O 4 , Carbon nanofibers, Magnetic/carbon composite, Magnetic properties . 1 Introduction The structure and morphologies of the composite samples were characterized by thermogravimetric- Carbon nanofibers (CNFs) composited with soft magnetic elements have received much attention due differential thermal analysis (TG-DTA), X-ray diffractometer (XRD), scanning electron microscopy to their unusual properties, including large surface to (SEM), transmission electron microscopy (TEM), volume ratio, chemical and thermal stability, high thermal and electrical conductivity and high Raman spectroscopy and small angle X-ray scattering (SAXS). Magnetic properties of the mechanical strengths. Especially, nanocrystalline samples were also measured at room temperature by ferrites with the general formula of MFe 2 O 4 (M = vibrating sample magnetometer (VSM). Co, Cu, Mn, Ni, or Zn) are very important magnetic materials because of their high saturation magnetization and high permeability. Therefore, the 2 Experimental carbon/magnetic composite nanofibers have been received much attention for numerous applications, PAN/NiFe 2 O 4 composite nanofibers were prepared by electrospinning using a 10 wt.% PAN solution in such as in electromagnetic shielding coating [1], catalyst [2], super-capacitor [3], and rechargeable DMF. Nickel ferrite embedded PAN fibers were batteries [4, 5]. obtained by using a composite solution of 10 wt.% of Ni(No 3 ) 2 .6H 2 O and Fe(NO 3 ) 3 .9H 2 O dispersed into In the present work, we report the fabrication of carbon/nickel ferrite (NiFe 2 O 4 ) composite nanofibers PAN solution in DMF. The solution was electrospun using electrospinning technique followed by at room temperature in an ambient air atmosphere using our home-made electrospinning system, under stabilization and carbonization process, respectively. Electrospinning is a simple and efficient method for the following conditions: applied voltage of 17 kV, preparing polymer fibers and ceramic fibers with flow rate of solution at 0.5 ml/h, distance from both solid and hollow interiors that are exceptionally syringe nozzle to collector of 15 cm. After the long in length, uniform in diameter ranging from PAN/NiFe 2 O 4 composite is formed into fibers, it tens of nanometers to several micrometers. must then be stabilized to prevent the fibers from

melting or fusing together during the high observed at ~280 ºC and ~420 ºC, suggesting the temperature heat treatment required to form carbon thermal events related to the decomposition of Ni fibers of high strength and modulus. This step was and Fe nitrates along with the degradation of PAN carried out via heating rate of 5º C/min in air by dehydration on the polymer side chain, which atmosphere at 280 ºC for 0.5 and 2 h, respectively. was confirmed by a dramatic weight loss in TG If not assisted by chemical means, such as air or curve at the corresponding temperature range (270 - other oxidizing agents, stabilization can require 450 ºC). The plateau formed between 450 ºC and many hours. On the other hand, if an acrylic polymer 1200 ºC on the TG curve indicated the formation of is heated rapidly, a violent exotherm occurs, crystalline NiFe 2 O 4 as confirmed by XRD (Fig. 2). producing fragmentation of the chain into an Figs. 2 (a), (b), and (c) show the XRD patterns of the assortment of oligomers, as well as copious composite nanofibers after stabilization at 280 ºC for quantities of hydrogen cyanide and ammonia [6]. 2 h in air atmosphere and carbonization at 800, 900 The carbon/NiFe 2 O 4 composite nanofibers were and 1000 ºC, respectively, for 2 h in argon obtained by carbonized NiFe 2 O 4 /PAN nanofibers atmosphere. The full NiFe 2 O 4 phase was formed under an argon atmosphere via a heating rate of 10 after carbonization at 1000 ºC. The main peaks with 2θ values of about 18.37 º, 30.22º, 35.60º, 37.11º, ºC/min for 2 h at 800, 900, 1000 ºC, respectively. The as-spun PAN/NiFe 2 O 4 composite nanofibers 43.25º, 47.70º, 53.73º, 57.36º, 62.91º correspond to were subjected to thermogravimetric-differential the crystal planes (111), (220), (311), (222), (400), thermal analysis (TG-DTA, PerkinElmer Instrument, (331), (422), (511), (440) in the standard data (JCPD USA) for determining the temperatures of possible 80-0072) of crystalline NiFe 2 O 4 , respectively. No decomposition and crystallization of the as-spun foreign phases were detected, proving the phase nanofibers. The morphology and the structure of as- purity of the samples. A broad peak appears around 2θ = 26. 0º indicating the formation of graphite spun PAN/NiFe 2 O 4 and carbon/NiFe 2 O 4 composite nanofibers were investigated using a scanning structure [7]. This broad peak can be indexed to the electron microscopy (SEM, LEO 1450VP, UK), a peak (111) Bragg reflection derived from carbon transmission electron microscopy (TEM, TECNAI (JCPD 75-1621). In this work, since full NiFe 2 O 4 G 2 20 S-TWIN at 200 kV, Philips, Eindhoven, The phase was formed only at 1000 ºC, we tried to Netherlands) and a small angle X-ray scattering carbonize the composite fibers at the same (SLRI, BL 2.2). The phase of the carbonized temperature but the stabilization time was reduced samples were identified using a Philips X-ray from 2 h to 0.5 h. The result indicates that the diffractometer (XRD, PW3040, The Netherlands) NiFe 2 O 4 phase still appears as shown in Fig. 2 (d). with Cu K α radiation (λ =0.15406 nm). The structures of the CNFs and carbon/NiFe 2 O 4 400 composite nanofibers were investigated by Raman 0 Air spectroscopy (JOBIN-YVON T64000 Micro- 300 λ= 514.5 PL/Raman spectroscopy, nm). The -20 magnetic properties such as saturation magnetization TG 200 Weight loss (%) and coercivity of the carbonized samples were -40 DTA DTA (uV) examined at room temperature using a vibrating 100 sample magnetometer (VSM, Lake Shore VSM -60 7403, USA). 0 -80 3 Results and Discussion -100 -100 The TG curve in Fig. 1 show a minor weight loss steps from 30 ºC up to about 270 ºC and two major 0 200 400 600 800 1000 1200 weigh loss steps from 270 ºC to 450 ºC. No further O C) Temperature ( weigh loss was observed up to 1200 ºC. The minor weight loss was related to the loss of moisture and Fig. 1. TG-DTA curves of thermal decomposition of trapped solvent in the as-spun NiFe 2 O 4 /PAN the as-spun NiFe 2 O 4 /PAN composite nanofibers in composite nanofibers while the major weigh loss air atmosphere. was due to the combustion of organic PAN matrix. On the DTA curve, main exothermic peaks were