Preparation of Nano Powders by Sintering Process for Nanomaterials

Transcription

1 International Journal of Pure and Applied Physics ISSN Volume 6, Number 4 (2010), pp Research India Publications Preparation of Nano Powders by Sintering Process for Nanomaterials K. Raji 1 and Alfred Cecil Raj 2 1 Associate Professor of Physics Holy Cross College (Auto), BARD University, Tiruchirappalli, T.N., India 2 Associate Professor of Physics St. Josephs s College (Auto), BARD University, Tiruchirappalli, T.N., India Abstract Nanospace Technologies is an industry leading Nano crystalline materials innovator and also manufacturing the integrated family using nanomaterial technologies. The entire preparation and commercial manufacturing of nanopowder Metal oxides i.e. Aluminium Oxide, Zinc Oxide, Calcium Oxide, Titanium Di oxide and several, having main focus on Nanophase of Nanotechnology. Nanophase produces the nano material products for a variety of markets like anti microbial products, ultra-fine polishing applications, semiconductors wafers, hard disk drives, optics, wood preservation, antifouling, fuel cells, UV attenuation and resistant coatings etc. but still Nanotechnology oriented markets are constantly developing. The main aim is to provide the understanding of procedure at the nanoscale. Focus lies on methods that enable to understand the problems on 1) the Nanoscale mechanical behaviour of materials 2) the mechanical behaviour of nanostructures. Keywords: Mixture, sintering, compaction, porosity. Introduction Mechanical properties of materials largely depend on the stressed state 1 formed in the course of testing and therefore on the nature of the test being made. Tests may be generally divided into two classes 1) attempt is made to stimulate suitable service condition 2 ) designed to study the behavior of metals under the specified conditions not necessarily related to specific service or fabrication e.g. tensile hardness and impact tests. All is chemically active metal that owes its stability and corrosion resistance to an ever present protective film of oxide.

2 496 K. Raji and Alfred Cecil Raj Experiment One of the advantages of P/M is, metals and alloys in any proportion can be mixed together to manufacture articles of any desired shape and various steps involved are shown in the flow chart of Fig : 1. in this respect this process is not governed by the phase rule which is applicable to alloys manufactured by melting. Process involved is 1. Admixing the metal powders 2 into the desired proportions. 2. Sintering the prepared powder in Muffle Furnace Compacting the metal powders into the desired shapes in suitable dies at specified pressures Sintering the compacted components in furnace provided with controlled atmospheres. 5 Powder Mixing Powder mixing is an important process in material science and it influences the effectiveness of materials. When two or more varieties of powders are used, these powders are mixed well and in efficient way in order to obtain a homogeneous mixture. A 3%to 10% of copper powder is mixed with aluminium powder in a pot mill for the investigation. When aluminium is alloyed with appreciable amount of copper it becomes nobler. Sintering The mixed powder ratio is sintered at a temperature of 550 o C. These alloys are made by sintering aluminum oxide (Al 2 O 3) in surface layers. In the sintered state, aluminum forms a cellular matrix in which disperse particles of Al 2 O 3 form inclusions in the strengthening phase 7. Al 2 O 3 particles do not react with the metallic matrix nor coagulate during heating, because of which the strength properties of the alloy vary only slightly with increasing temperature. The metallic matrix provides fair plasticity to the alloy. 8 Nanostress Stress is the internal force set up in a material by the action of an external force. TABLE: 1 is depicting the amount of the external force applied on the powder composition because it is the intensity of the force within a body which resists a change in shape. It is normally calculated on the basis of the original cross-sectional dimensions. From a practical point of view, the principal change in the metal during recovery is the reduction of macro, micro and nano stress is resulting from rearrangement of the dislocations introduced during deformation 9. Macro stresses refer to elastic stresses existing the balanced one and the unbalanced is distributed as distortion.micro stresses also needed in balanced state but on so small scale or so localized in exist that they can not cause a change of dimensions upon machining of the metal and are detectable by X-Ray diffraction or comparable methods. Nano stresses in nano structures, and CNS in particular, exhibits a strong spatial non homogeneity and a larger number of elementary resonances. Reducing the size of

3 Preparation of Nano Powders by Sintering Process for Nanomaterials 497 the objects to nanometer scale to physically manipulate the electronic or structural properties and it offers a fabrication challenge with a large pay off. 10 Compaction Compaction of the mixed powder is another important step in P/M method. This process is performed by pouring a measured amount of the appropriate powder in to the die cavity and then introducing one or more plungers to press the metal powder into a coherent mass. An ideal pressed compact will be having the desired shape. Nearly 15 compacts are prepared for further investigation. The characteristics of 5% of Cu O in Aluminum are Apparent density of the above combination= gm /cc. Theoretical density of the above combination =2.786 gm /cc. Height of the compact = mm Diameter of the compact =15.80 mm Lubrication of the die walls is helpful for the powder to minimize the friction 11 and reducing pressure gradients with in the compact. Compact Sintering Sintering of the compacts of different mixing ratios carried in batches. The atmosphere surrounding the work should be capable of preventing oxidation of the powder surfaces and should reduce any surface oxides 12 that are present. More care was taken during this process. Because heat treatment is used to change the mechanical properties of metal by suitable alteration of its metallurgical structure. The primary purpose is to increase the strength of metal while retaining some toughness or ductility. Essential Conditions for the Preparation of Miniature Size Product Figure 1: Product Process.

4 498 K. Raji and Alfred Cecil Raj Table 1: External force against nano stress in powder. Load tonnes Height of Powder mm ρ co / ρ the Percentage of Porosity ρ co is defined as Density of the compact. ρ the is defined as theoretical density of composition. Conclusion Al is chemically active metal that owes its stability and corrosion resistance to an ever present protective film of oxide. Porosity is calculated either to accept or to reject the component. Reduction in porosity GRAPH: 1 shows good result of the mixing proportion. During powder compaction it reveals that the coarse pores get closed earlier than the smaller pores. A small slug of copper placed on top of the component melts during sintering and it is drawn into the pores by capillary action.al and Al matrix composites offer lower density, improved strength, stiffness and wear resistance. The characteristics like plasticity and ability to be cold pressed are greatly influenced by the nano structure of the powder (GRAPH: 1). The miniature size testing specimen providing the required mechanical properties which will be helpful for the deformations applications like Aluminium pipes, rods, rivets, aircrafts wing spars, propeller blades, frames etc. Graph 1

5 Preparation of Nano Powders by Sintering Process for Nanomaterials 499 Acknowledgement The author thanks all the teachers and skilled assistants who helped to complete the project and also thanks the UGC funding agency. References [1] Yu.A.Geller, A.G. Rakhshtadt, Science of Materials Methods of Analysis Laboratory Exercises And Problems Translated from the Russian by V. Afanasyev Mir Publications Moscow 1977, p58. [2] R.M Brick., Structure and properties of Alloys, 1998 Chapter 4 K6.31. [3] Barett C.S. Structure of Metals, McGraw Hill Book Company, 1976, p67. [4] Dieter G.E. Mechanical Metallurgy, McGraw Hill Book Company, New York 1961, p9. [5] Lin CB, Chang,R.J.,Weng,W.P., A study on process and tribological behaviour of Al alloy/gr(p) composite, Wear 217 (1998) p [6] Lepper K., James M., Chashechkina., J., Rigney, D.A., Sliding behaviour Of selected aluminium alloys, Wear 203 (1997) p [7] Pathak, J. P., Torabian, H., Tiwari, S. N., Anti seizure and antifriction characteristics of Al-Si-Ph alloys, Wear 202(1997) p [8] G.S. Upadhyaya, Sintered Metallic and Ceramic Materials, J.Wiley, New York, NY, (1999), P21. [9] Yih A.A, Chung D.D.L, Titanium diboride Copper matrix composites, Journal of Material Science, 32 (1997), p [10] V.Sivaraj, Engineering Metallurgy VK Publishers, Bangalore, India, p 62. [11] W.J Dawson, Hydrothermal Synthesis of Advanced Ceramic Powders Am. Cream. Soc. Bull., Vol.67, No. 10, 1998, p [12] R.M.Anklekar, K. Bauer, D.K. Agrawal and R.Roy, Improved mechanical Properties and Microstructural development of microwave Sintered Copper and nickel steel PM parts, Powder Metallurgy 2005 Vol. 48 No.1.

6 500 K. Raji and Alfred Cecil Raj