DEPOSITION OF ALUMINA (ALUMINUMOXIDE) NANOLAYER USING PLASMA TORCH

Transcription

1 DEPOSITION OF ALUMINA (ALUMINUMOXIDE) NANOLAYER USING PLASMA TORCH *Yousefzadeh M. 1, Sobhanian S. 2 and Naghshara H. 3 1 Department of Physics, East Azarbaijan Sience and Research Branch, Islamic Azad University, Tabriz, Iran 2 Department of Physics, Tabriz Branch, Islamic Azad University, Tabriz, Iran 3 Department of Solid State Physics, University of Tabriz, Tabriz, Iran *Author for Correspondence ABSTRACT A DC atmospheric plasma torch is designed and manufactured for deposition of refractory ceramic oxides (Al 2O 3, SiO 2, and ZrO 2). Coatings prepared by materials with high melting points have found wide applications in material science, medical physics research, especially in refractory material industries. The proper operation of the designed torch is tested by observation of alumina, silicate and kaolin layers on given substrates. In this research some metallic and non-metallic oxides are deposited on stainless- steel substrates using nitrogen and oxygen as the working gas. Results obtained with alumina nano powder injected in nitrogen carrying gas differs greatly from the case where pure metallic Al powders are fed to oxygen plasma jet. XRD spectra confirm the formation of alumina layer in both cases. Also, SEM images show the deposition of micro and nanometer sized alumina macromolecules on the substrate. Keywords: Plasma Torch, Alumina, Deposition INTRODUCTION Surface modification by thin film deposition has found numerous industrial and research applications (Reec, 2001). In plasma spraying method a high temperature plasma jet is used for layer deposition. The plasma produced by electric discharge may have high temperatures ( ~ K ) (Hippler et al., 2001). Because of this high temperature, the plasma jet is used for melting refractory and resistant materials (Al 2O 3, SiO 2, TiO 2, and ZrO2) (Virjay et al., 2009; Qi et al., 2011). In the process of plasma spray method which is developed since 1970 decade, the material to be sprayed is introduced inside the plasma jet, melted there and accelerated towards the substrate. Atmospheric pressure plasmas are used normally for the production of alumina, TiO 2, SiO 2 and ZrO 2 coatings (Irisawa and Matsumoto, 2006; Morks, 2010). Nanostructures are also identified on the deposited layer (Marcinauskas, 2010; Chen et al., 2009). Also grained micro and sub micrometric coatings have been reported by (Pawlowski, 2008). The main advantage of the plasma torch technology is the possibility of obtaining high temperatures ( K) using it. Surface coating by ceramic and also nanostructured ceramic oxides has found wide applications in refractory surface production as well as in advanced research in material science. Aluminum oxide films are also used in insulating and wear resistant coatings due their high resistance against the corrosion and erosion and dielectric strength. Formed in the crystalline polymorphic phase, α Al 2O 3 is known as mineral corundum. Among other refractory oxides, we will present specially the results concerning the formation of alumina layer. In section 2, the experimental device, especially the details of atmospheric plasma torch will be explained and in section 3, a brief conclusion and the results of plasma spray deposition with two different gases will be presented and discussed. Experiment An atmospheric plasma torch is designed and manufactured for refractory material layer deposition. It consists of a3. 6 kw power supply (I 60A) and the main body of the torch with nozzle electrode. The electrodes are cooled by water in order to prevent them from erosion caused by the heat flux. Nitrogen and oxygen are used as the carrying plasma gas. The input gas pressure must be at least 5 bars. A regulator placed in the system can reduce this pressure from 5 bars to fixed 4 bars. Al 2O 3 or other working powders Copyright 2014 Centre for Info Bio Technology (CIBTech) 1557

2 are introduced inside the plasma through a vibrating funnel placed on the upper part of the nozzle electrode. Stainless steel substrates cut in 2cm 2cm plates are cleaned properly by ultrasonic cleaner before being placed on the substrate holder. The substrate holder distance from the nozzle exit is adjustable and is fixed during the experiment in an optimum distance. The general view of the torch is shown in figure (1). The main parts of the torch including the internal parts of the torch head and nozzle electrode are shown in figure (2). Figure 1: General view of the torch Figure 2: Detailed structure of the nozzle hed The torch operation was tested by examining the formation of Al 2O 3, SiO 2 and kaolin layers on stainless-steel substrates Here we present as example only the results obtained with alumina. In order to melt alumina, plasma temperature should be higher than alumina melting point(~ K). Considering difficulties related to direct measurement of plasma flare temperature with sufficient precision, we used here the method mentioned in ref. (Akdogane et al., 2006; Marcinauskas and Valatkevicius, 2010) for rough estimation of the plasma jet temperature. According to this method the temperature of nitrogen plasma at the exit of the anode nozzle may be estimated through the following empirical formula: T f = (I 2 / G d) Where I is the plasma current in A, G is the rate of the input gas flux in Kg/S and d is the anode diameter in meter and T f is the mean temperature of the plasma outgoing from the nozzle given in 0 K. Using I = 60 A and the nitrogen gas flux rate of G=0.024 Kg/S and having d= 10-3 m T f is obtained around 2544 K 0 which is sufficiently high for melting alumina (melting point: C) and silicate(melting point : Five experiments are being reported as the followings a) Sample No: 1 alumina nano powder fed to nitrogen plasma jet. b) Sample No: 2 alumina powder fed to oxygen plasma jet. c) Sample No: 3 metallic aluminum powder fed to nitrogen plasma jet. d) Sample No: 4 SiO2 powder fed to nitrogen plasma jet. e) Sample No: 5 Kaolin powder fed to nitrogen plasma jet. As stated earlier, the quality of the coating especially its roughness and granule sizes depends on different system parameters as the input power, the substrate distance from the nozzle and its temperature. We tried to choose the optimum conditions in our experiments. RESULTS AND DISCUSSION XRD pattern of the irradiated samples are taken by X-ray facility of Tabriz University. Comparison of these XRD spectra with the standard Al 2 O 3, silicate, aluminum and kaolin spectra confirms the formation of the corresponding films on stainless-steel substrates. Copyright 2014 Centre for Info Bio Technology (CIBTech) 1558

3 a b c Figure 3: XRD spectra for samples No:1 (a), No: 2(b) and No: 3 (c) Copyright 2014 Centre for Info Bio Technology (CIBTech) 1559

4 Here in Figure 3 we give only the XRD spectra of the samples No: 1, No: 2 and No: 3, related to the formation of Al 2O 3. The surface morphology of the sprayed samples are characterized by the scanning electron microscope (SEM) of Tabriz university (Model Mira 3 TESCAN, HV= 10kV). Figures (4),(5) and (6) show SEM pictures of alumina layer deposited by nitrogen and oxygen plasma jets. Especially it is observed that in the case of using metal aluminum powders with oxygen plasma jet some composite of aluminum-alumina is formed on the substrate. Actually the rod shaped on SEM pictures are signs of composite formation. Composite formation is observed from fig (6) and also from XRD spectrum. Figure 4: SEM pattern of alumina nanoparticles deposited by oxygen plasma jet Figure 5: SEM pattern of alumina nanoparticles deposited by nitrogen plasma jet Figure 6: SEM pattern of alumina-al composite nanoparticles deposited by oxygenn plasma jet Copyright 2014 Centre for Info Bio Technology (CIBTech) 1560

5 Also the effectiveness of oxygen plasma compared with nitrogen one in the case of using aluminum powders is demonstrated. In the case of sample No: 5, the XRD and SEM results show the alumina which is a non-metallic material with physico-chemical properties different from the metallic aluminum has been deposited. The formation of Al-Al 2O 3 composite is due to the fact that the coatings are formed by fully or partially melted granules. The average size of the alumina Nano particulates is about 80 nm in our experiment. Furthermore the results show that using metallic aluminum powder injected into the oxygen plasma results in decrease in the grain size. In short the SEM images of alumina granules show different irregular shapes of sizes ( m ). Beside the micro sized particles, many nano-sized particles and agglomerated nanoparticle clusters of 5-50 μm sizes could be identified. Histograms of the granules size distributions are given in Figure (7), (8) and (9) for three torch powers of 3.2, 3.4 and 3.6 kw. It is seen from these histograms that the mean size of deposited granules decreases with the increase of the torch power. Table 1 shows the variation of this parameter with operation condition of the torch. Figure 7: Histogram of deposited particlulate size distribution for 3.2 kw torch power Figure 8: Histogram of deposited particlulate size distribution for 3.4 kw torch power Figure 9: Histogram of deposited particlulate size distribution for 3.6kW torch power Copyright 2014 Centre for Info Bio Technology (CIBTech) 1561

6 Table 1:??? Operation condition of the torch Current of deposited particulates (nm) I (A) Voltage (V) Power (kw) Mean size(nm) ACKNOWLEDGEMENT The authors would like to thank Tabriz Branch of Islamic Azad University for supporting the present research work. REFERENCES Akdogane E, Cokelier D, Valicius V and Valatkevicius P (2006). A new methd for immunosensor preparation: Atmospheric plasma Torch. Surface and Coatings Technology Chen H, Gou G, Tu M and Liu Y (2009). Characteristics of Nano Particles and Their Effect on the Formation of Nanostructures in Air Plasma Spraying WC-17Co Coating. Surface and Coatings Technology Hippler R, Pfau S, Schmidt M and Schoenbach KH (2001). Low Temperature Plasma Physics (Fundamentals Aspects and Applications) (Wiley- VCH) Berlin. Irisawa T and Matsumoto H (2006). Thermal shock resistance and adhesion strength of plasma-sprayed alumina coating on cast iron. Thin Solid Films Marcinauskas L (2010). Deposition of Alumina Coatings from Nanopowders by Plasma Spraying. Marcinauskas L and Valatkevicius P (2010). The effect of Plasma Torch Power on The microstructure and Phase composition of alumina coatings. Material Science Materials Science (Medžiagotyra) Morks MF (2010). Plasma Spraying of Zirconia-Titanium Silica Bio-Ceramic composite Coating for implant Applications. Material Letters Pawlowski L (2008). Finely grained nanometric and submicrometric coatings by thermal spraying: A Review. Surface and Coatings Technology Qi Min Wanga B, Jun Gonga, Chao Suna, Hyung Woo Leeb and Kwang Ho Kimb (2011). ZrO 2 and Y2O3-stablized ZrO 2 coatings deposited using an arc ion plating technique. Journal of Ceramic Processing Research Reec Roth J (2001). Industrial Plasma Engineering (IOP Publishing) London. Virjay M, Selvarajan V, Yugeswaran S, Ananthapadmanabhan PV and Sreekumar KP (2009). Effect of Spraying Parameters on DepositionEfficiency and Wear Behaviour of plasma Sprayed Alumina-Titania composite coatings. Plasma Science and Technology Copyright 2014 Centre for Info Bio Technology (CIBTech) 1562