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Chapter 2 Experimental Methodology CHAPTER 2 Chapter 2 Experimental Methodology 2.1 Introduction 2.2 Synthesis of nanomaterials. 2.2.1 DC arc plasma reactor setup for material processing 2.2.2 Microwave processing of materials 2.2.2.1 Microwave Induced Plasma processing System setup 2.2.2.2 Multimode Microwave setup 2.3 Analytical techniques for characterization nanophase powders 2.3.1 X- ray diffraction study 2.3.2 X-Ray photoelectron spectroscopy 2.3.3 Surface area measurement (BET method) 2.3.4 Electron Microscopy (SEM and TEM) 2.3.4.1 Scanning electron microscopy (SEM) 2.3.4.2 Transmission Electron Microscopy (TEM) 2.3.5 DTA&TGA 2.3.6 Vibrating sample magnetometer (VSM) 2.3.7 Ultraviolet visible spectroscopy (UV/vis) 2.3.8 Raman spectroscopy 2.3.9 Photoluminescence spectroscopy 2.4 Conclusion 2.5 References. 36 CHAPTER 2 Chapter 2 Experimental Methodology 2.1 Introduction This chapter provides the detailed description of the experimental setups for (i) DC arc plasma (reactor) & (ii) microwave processing systems used for the synthesis of nanophase materials and (iii) other analytical-measuring methods such as of X-ray diffraction, X-ray photoelectron spectroscopy, surface area using BET method, scanning and transmission electron microscopy (SEM / TEM), UV-Visible absorption spectroscopy, thermal analysis (DTA / TGA), vibrating sample magnetometer (VSM), Raman and Photoluminescence spectroscopy. 2.2 Synthesis of nanomaterials 2.2.1 DC arc plasma reactor setup for material processing The experimental DC arc plasma setup used for the synthesis of various nano­ materials is as shown in figure 2.1 (a). The plasma reactor consisted of a multi port stainless steel chamber (12 inch in diameter) with a multiple gas inlet facility providing various mixtures of gases, which can be incorporated as plasma forming gas. For inserting the arcing electrodes two opposite ports were used with ceramic bushes for insulation purpose. The electrodes were fabricated in such a way that they could be easily moved linearly along the arcing direction. The aluminum flange was used for covering this reactor from the top. The DC power supply (Keje Electric Co.) used in the synthesis process has specifications of open circuit voltage of 70 Volt and short circuit current of 200 Ampere. This got fitted on a separate trolley. After carrying out series of experiments another modified setup was developed. The modified setup is shown in the figure 2.1 (b). 37 CHAPTER 2 Figure 2.1 Open arc plasma reactor (a) original set up and (b) modified setup. The modified setup consisted of water cooled dome for collecting the nanopowders. The arc reactor was a stainless steel chamber (with a diameter = 28 cm and height = 53 cm). It has number of ports of different sizes for providing various facilities as follows: 1. Separate ports for anode and cathode. The Cathode is mounted at an angle of 40° with respect to the vertical axis. 38 CHAPTER 2 2. Two ports with 25 mm diameter each with feed-through, which are kept at a distance of 22.5 cm from the arc zone for the in-situ measurements of thermal and electrical parameters 3. A view port of 25 mm diameter for observation of the arc plasma process 4. Port for different gas inputs and a port for evacuation 5. A port with special quartz window for coupling the emission spectrometer for emission characteristics studies 6. The present chamber is demountable into two sections. Bottom and top sections hold the anode and cathode assemblies respectively 7. A separate water cooling arrangements for both the sections. Further, the top chamber has a provision to cool the collector dome using liquid nitrogen. It helps in getting better powder yield during the synthesis. 8. The cathode assembly is cooled using argon gas shroud The mass flow meters having measurement capacity from 2.5 to 40 lit / min are connected for monitoring and maintaining the flow of different gases like air, nitrogen, oxygen and argon. A rotary vacuum pump (of 100 liters capacity) can be connected for evacuation of the chamber which can lower the reactor chamber pressure up to 5 x 10"3 torr. The anode holder was made up of copper cup (diameter = 6 cm & thickness = 2.5 cm) which was kept in contact with a stainless steel co-axial tube. Inlet and outlet tubes for water flow into it were fitted. The metal to be evaporated was placed in the copper cup and tightened with screws so that anode cannot get lifted up with the cathode when it does get fused occasionally. The anode is metal slab (or rod / block/ foil) of interest preferably having dimensions: diameter = 5 cm and thickness = 2 cm. For a cathode there are hollow co-axial tubes (2 nos.) with gas flow arrangement. The end of co-axial tube has a special provision for mounting the cathode element, which is generally a tungsten rod (diameter = 2 mm & length = 7 cm). A graphite (a good electron emitter) cathode can also be used with rod (diameter = 6 mm & length = 5 cm). Figure 2.2 (a) and (b) show the schematic diagram and the photograph for the experimental setup of the DC arc plasma system respectively. 39 CHAPTER 2 i'tium ajaigc (a) IT - -^ Figure 2.2 (a) Schematic diagram and (b) photograph of the modified DC arc reactor. Both the anode and cathode are movable over a distance of 7.5 cm. The cathode is oriented at an angle of 60° with respect to the anode. Thermocouples are connected inside the chamber which enables the measurement of the temperature inside the reactor. The detail 40 CHAPTER 2 description of the method of synthesis of nanophase oxide powders of aluminum, iron and zinc using different plasma parameters, is given in the Chapter No.3 2.2.2 Microwave processing of materials 2.2.2.1 Microwave Induced Plasma Processing [MIPS] System setup The rectangular waveguide (RWG), designated as WR-430 [11], in the S-Band [12] was fabricated indigenously using the design details and specifications as found elsewhere [13]. The phosphor-bronze (M.P. = 1010°C and having composition 90 % Cu + 10 % Sn) material was used for the fabrication of RWG. The RWG was fabricated using the standard casting techniques in a single piece. They were milled and polished to a fine accuracy. The RWG was fabricated in following three sections as shown figure 2.3 (a). (i) TEJO3 applicator with three screw tuner facility (ii) Input guide (magnetron coupling) and (iii) An adjustable short circuit (a) N F P j-^Hr^-a QS- IK 5? tfl D2-45 GHz 750 W MICROWAVE GENERATOR {Magnetron) Figure 2.3 (a) MIPS setup 41 CHAPTER 2 (b) Figure 2.3 (b) photograph for complete MIPS processing setup An isolator was added to protect the magnetron (microwave source, frequency 2.45 GHz, power = 750 W) from excessive reflected power. The entire set up has been identified as Microwave Induced Plasma System [MIPS] is as shown in figure 2.3 (a). An adjustable choke coupling is placed Ag/4 from the end with incorporation of the quartz sintering tube. The photograph for complete setup of MIPS processing is shown in figure 2.3 (b). The Quartz resonating tube The double walled quartz tube was used for the processing purpose. The outer wall of tube is provided for flowing helium gas which was used as a coolant gas. A special aluminum head attachment was designed incorporating a novel quartz hanger. This is used for easy sample translation and rotation. This was suspended within the TE103 applicator. The complete assembly was designed to work up to a pressure of 1 militorr. The quartz tube was placed at a distance of lg /4 (wavelength of guide = Xg) from the end, this was to ensure the maximum E-field penetration. The sample diameter was chosen to be < (kg 12), so that the E- field does not vary too much across the sample length. The technical details evaluated from the literature [11] are given in table 2.1 for understanding of the wave guide. 42 CHAPTER 2 Table 2.1 Technical specifications of RWG S.No. Parameter Specification 1. Guide wavelength Xg -15.3 cm 2. Free space wavelength h, = 12.24 cm at f0 = 2.45 Hz 3. Width a =10.922 cm 4. Height b = 5.461 cm 5. Wall thickness = 5 mm 6. Comer radius <= 1mm 7. Three screw tuner placed at distance 3Xg/8 8. Resonator length (LR) 3 (kg 1 2) = 22.95 cm 9. Xc (TEio) Cutoff = 2a 10. Distance of the quartz sintering tube from the end = V4 11. Skin depth (for phosphor bronze) c = 3.29xl0"4cm 12. Attenuation conductor loss Oc = 0.1846 Np/m 13. Skin Resistance (for phosphor bronze) R = 0.032 £2 The magnetron was coupled to the RWG in such a way that there is complete grounding between the body of magnetron and the RWG for safety precautions so that there are no leakages of microwaves. The tuning is properly adjusted by characterizing the RWG with a standard Vector network analyzer coupled to the S-parameter test set. The temperature in the reactor tube was measured using the optical pyrometer (CHINO, Pyrostar model IR-U, China) by with and without detuning the plasma. In some cases, a single wall quartz rube was used for processing of different materials. The detail description for the synthesis of carbon n:. v\ubes and processing of materials by using Microwave Induced Plasma System [MIPS] is given in the Chapter No.4. 2.2.2.2 Multimode Microwave setup In some material processing experiments, convection domestic microwave oven [KENSTAR, Model No.: OM-29ECF) with grill was used.
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