The Effect of Firing Temperature and Molarity on the Structural and Electrical Properties of Nano Particles Ofnickel- Cobalt Oxide
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ECO-CHRONICLE 163 ECO-CHRONICLE VOL. 1, No. 4. DECEMBER 2006, 163 - 170 THE EFFECT OF FIRING TEMPERATURE AND MOLARITY ON THE STRUCTURAL AND ELECTRICAL PROPERTIES OF NANO PARTICLES OFNICKEL- COBALT OXIDE. Nisha J. Tharayil1, R. Raveendran1 and Alexander Varghese Vaidyan2 1Department of Physics, Sree Narayana College, Kollam, Kerala. 2Department of Chemistry, St.Stephen’s College, Pathanapuram, Kerala. ABSTRACT Nano particles of Nickel-Cobalt Oxide were prepared by chemical co-precipitation method by decomposition of their respective metal chlorides, sodium carbonate and Ethylene Diamene Tetra acetic Acid (EDTA).The metal chlorides were taken in different molar ratios but the total molarity remains the same as 0.5M. The influences of molarity on the formation of nano particles of Nickel- Cobalt oxide were analyzed. The heat treatment of the ground precursor powders at their respective decomposition temperatures and beyond, resulted in the evolution of heat from the combustion of the residual carbonaceous material. This facilitated the reaction among the constituent metal ions and the formation of the desired oxide phase at low temperature. The average particle size was determined from X-ray diffraction line broadening and the diffractogram was compared with JCPDS data to identify the crystallographic phase of the particles. The shift in the d-value due to the nano nature was also analyzed. The effect of sintering on the particle size was also analyzed. The low temperature DC conductivity studies of the samples were carried out and it was seen that for Spinel structure, the activation energy was found to be 0.14552eV for the temperature range 100K-250K and 0.09030eV for the temperature range 250K-350K and for the cubic structure, it was found to be 0.5145eV for the temperature range 100K-245K and 0.5836eV for the range 245K-350K. The conductivity in the temperature range 250K-350K was much larger than in the range 100K-250K. Key words: Nano particles, Chemical co-precipitation, Thermogravimetric analysis, SEM, Low temperature DC conductivity Thus these types of compounds can display INTRODUCTION many complicated chemical and physical properties (Dimitar et. al., 2003). Nickel-Cobalt Nano crystalline materials are solids composed Oxide is one of the transparent conducting of crystallites with characteristic size (at least on oxides. It is a P-type conducting material and a one dimension) of a few nanometers (Richard promising infrared transparent conducting oxide and Earl, 2005). The discovery of these materials because of its infrared transparency, stability in by Gleiter can be viewed as one of the most oxygen, ease of preparation, phase purity and fascinating ones of the past decades. Research high conduction. Nickel doped cobalt oxide into the synthesis and properties of nano scale shows p-type semi conducting behavior, similar materials has exploded over the past decade to intrinsic spinel cobalt oxide (Tareen, 1989). due to their unique size dependent properties Spinel nano crystals are important technological that often differ considerably from their bulk phase materials because they have a wide range of materials. Research in the field of fine grain applications ranging from ultra high magnetic mixed oxide systems have gained immense data storage, magnetic resonance imaging, importance because of their potential sorbents, drug delivery, battery materials, applications in many areas of technology (Slick, catalysts, biosensing to nano electronic 1980). The present study deals with the materials etc. (Zhang and Chen, 2006). In this preparation and characterization of mixed spinel paper, investigations were carried out primarily oxide systems with the general formula AB O 2 4 with the following objectives in mind. where A and B represent divalent or trivalent cations such as Ni and Co respectively. The ions a. In synthesizing Nickel - Cobalt Oxide by at both A and B sites can be tetrahedrally and chemical co-precipitation method, the effect of octahedrally co-ordinated by the oxygen atoms. molarity of Nickel Chloride solution and Cobalt 164 ECO-CHRONICLE Chloride solution on the formation of Nickel- 40KV and 100mA at a scanning rate of 80minute- Cobalt Spinel Oxide. 1 from 2 =50to 800 . The SEM photographs of the b. The effect of sintering temperature on the samples were recorded with a Hitachi Model S- formation of Nickel - Cobalt Oxide. 3000H scanning electron microscope. Pellets c. To check whether molarity change affect the of nano particles of Nickel-Cobalt Oxide of low temperature DC conductivity of the sample. diameter 13 mm and thickness 1-2 mm were made by applying a pressure of 4 tones in a MATERIALS AND METHODS hand operated hydraulic press. Using these pellets, the low temperature conductivity was Nano particles of Nickel-Cobalt Oxide were measured using a computer controlled TSC prepared by arrested precipitation from analytical apparatus in the temperature range 100K- 350K. grade Cobalt Chloride, Nickel Chloride and Sodium Carbonate using Ethylene Diamene RESULTS AND DISCUSSION Tetra acetic Acid (EDTA) as the capping agent, the details of which are given elsewhere (Jose Thermal analysis et. al., 2001). The samples were prepared from 0.5M solution. The choice of selection of 0.5M is The precursor on heating decomposes to form a compromise between quantity and quality. If Nickel-Cobalt Oxide. Thermo gravimetric we go for low molarities, the quantity obtained analysis of the carbonate precursor was carried will be very small; on the other hand high out to determine the decomposition temperature molarities will increase the size of the nano and the rate of decomposition. The TGA analysis particles. The metal carbonate precipitate was was performed in the temperature range from separated from the reaction mixture and washed 28o C to 800oC at a heating rate of 15oC/minute several times with alcohol and then with distilled under nitrogen atmosphere. The TGA curve of water to remove impurities, including the traces the carbonate precursor, together with the of EDTA and the original reactants if any. The wet corresponding derivative thermo gravimetry curve precipitate was dried and thoroughly ground is as shown in Figs. 1. a & b. using an agate mortar to obtain the metal carbonate precursor in the form of fine powder. The decomposition temperatures were found to On heating to the required temperature, the metal lie between 3000c and 3500c. Thus the heat carbonate precursor decomposed to form metal treatment of the ground precursor powders at oxide. In this process the particle size is their respective decomposition temperature and governed by the solution concentration, rate of beyond, resulted in the evolution of heat from precipitation and calcination temperature the combustion of the residual carbonaceous (Ashuthosh Sharma et. al., 2004). In the present material. This facilitates the reaction among the study, two combinations were taken, which are constituent metal ions and the formation of the defined as: desired oxide phase at a relatively low external a. Nickel Chloride in 0.4 molarity of the solution temperature. The decomposition temperature in and the Cobalt Chloride in 0.1 molarity and the both cases were found to be at 3500 C . sample formed out of this is denoted from here onwards by the code CN. XRD analysis b. Nickel chloride in 0.1 molarity of the solution and Cobalt Chloride in 0.4 molarity of the solution The precursor powders of CN and CoNi were and the sample formed out of this is denoted calcined at temperatures 3000 C, 5000C, 7000C from here onwards by the code CoNi. and 9000C for 3 hours each. All the XRD patterns revealed that the Nickel - Cobalt Oxide prepared Characterization of the sample were crystalline. The XRD patterns of the calcined samples are shown in Figs. 2. a & b. The calcination temperature of the carbonate precursor was determined from TGA and DTA The XRD studies revealed that the nano particles analysis. The TGA and DTA of the samples were of mixed oxide formed by chemical method were taken using Perkin- Elmer, diamond TG/DTA. crystalline. The fine particle nature of the mixed The XRD study was carried out by using an oxide was reflected in the X-ray line broadening. ‘X’pert pro model X-ray diffractometer employing The relative crystalline sizes were determined Cu K radiation (PAN analytical, Netherlands) at from the XRD line broadening, using the Scherrer ECO-CHRONICLE 165 Fig. 1a TGA of CoNi Fig.1b TGA of CN equation d = 0.9 / cos (Cullity, 1978). The adjusted by controlling the temperature of the particle size for various calcination temperatures reaction. are as shown in Table 1. From the Table it is clear that with the increase in sintering The XRD analysis of CoNi, when compared with temperature, particle size also increased. This JCPDS (File No 40-1191) revealed the presence indicated that the size of the crystallites can be of a cubic phase. The lattice parameter was calculated as a = 8.12nm ( 0.003) A0, which Table 1. was found to be in agreement with JCPDS value. Sintering Particle size Particle size In the diffractometer, the angle (d-spacing) and temperature in nm for CoNi in nm for CN intensities of the high angle reflected beams served as a finger print for the crystal structure. As prepared 17 ± 5 15±5 The XRD pattern, when compared with JCPDS 5000 C 24 ± 5 33±5 revealed the structure as Spinel Oxide. The most 7000 C 34 ± 5 34±5 intense peak (intensity 100) was from the (311) 9000 C 35 ± 5 39±5 plane which correspond to an angle of 2 = 36. 692890 . 166 ECO-CHRONICLE The XRD analysis of CN, when compared with The cell parameter of the NiO within this JCPDS (File No 40-1191) also revealed the temperature range changed little and remained presence of a cubic phase. The lattice parameter close to the literature value of 4.176A0, indicating was calculated as a = 8.12nm ( 0.003) A0, which little structural interaction between the two was found to be in agreement with JCPDS value.