Synthesis and Characterization of Nano Structured Silicon Carbide by High Energy Ball Milling

Transcription

1 International Synthesis Journal and Characterization of Power Elecronics of Nano and Technology Structured Silicon Carbide by High... January-June 2011, Volume 1, Number 1, pp Synthesis and Characterization of Nano Structured Silicon Carbide by High Energy Ball Milling B Nooka Raju 1, G J Catherin 2, D Venkata Rao 3, and J Babu Rao 4 1,2,4 Department of Metallurgical Engineering, Andhra University, Visakhapatnam , India 3 Sri Chundi Ranganayakulu Engg. College, Chilakaluripet, Guntur (Dist) , India baburaojinugu@yahoo.com ABSTRACT: In this paper, an attempt has been made to convert the micro sized Silicon Carbide into nano structured silicon carbide by using High Energy Ball Mill under wet medium condition The smooth, glassy and an inert surface of the silicon carbide can be altered to a rough and more reactive by this technique. Ball milling was carried out for the total duration of 50hours. The sample was taken out after every 5 hours of milling for characterizing.the nano structured silicon carbide was characterized for its crystallite size, lattice strain, lattice parameter and percentage of crystallinity by using X-Ray Diffractometer. It was found that for the 50 hrs, milling the crystallite size was reduced from 0.12?m to nm and the percentage crystallinity was reduced from 74% to 49%. The size, shape and texture of initial and nano-structured silicon carbide were studied using Scanning Electron Microscopy(SEM). The initial silicon carbide particles are mostly angular in shape. The shape of the 50hrs particles is irregular and the surface morphology is rough. The SiC phase is the maximum sufferer during milling; with increasing the milling time SiC peaks shifts slightly to the lower angles and also broadening of the diffraction pattern occurs. Keywords: Nano structured powder, Planetary Milling, X-ray and SEM analysis. 1. INTRODUCTION Nanoscience and nanotechnology has become the buzzword in recent years since its inception in 1990 s. It literally means any technology performed in the nanoscale down to molecular level. 17

2 International Journal of Power Elecronics and Technology Nanotechnology encompasses the production and application of physical, chemical and biological systems at scales ranging from individual atoms or molecules to submicron level as well as integration of the resulting nano structure to larger systems [1]. Nanomaterial is defined as the materials with the microstructure having at least one dimension in nanometer range. It has appeal of miniaturization; also, it imparts enhanced electronic, magnetic, optical and chemical properties to a level that cannot be achieved by conventional materials [1, 2]. The key characteristics of nanomaterials are its small size, narrow size distribution, low levels of agglomeration and high dispersability [2]. A variety of ways have been reported to synthesize nano level materials such as plasma arcing, chemical vapor deposition, electro deposition, sol-gel synthesis, high intensity ball milling etc [3]. Among these methods high energy milling has advantages of being simple, relatively inexpensive to produce, applicable to any class of materials and can be easily scaled up to large quantities [4]. In this mechanical treatment, powder particles are subjected to a severe plastic deformation due to the repetitive compressive loads arising from the impacts between the balls and the powder. The high concentration of defects and the continuous interfaces renewal, associated with the milling induced enhanced atomic mobility, promote different phenomena depending on the materials being milled [5-7]. This produces novel crystalline and amorphous materials with crystallite sizes at the nanometer scale [5]. 2. MATERAILS AND METHODS 2.1. High Energy Ball milling The reduction in particle size of Silicon Carbide from micron level to the nano level was carried out using a high-energy planetary ball mill (Model: Retsch, PM 100, Germany) in a stainless steel chamber using tungsten carbide and zirconia balls of 10 mm Φ and 3 mm Φ ball sizes respectively. The total duration of milling was 50 hours. The rotation speed of the planet carrier was 200 rpm. The ball mill was loaded with ball to powder weight ratio (BPR) of 10:1. Toluene 18

3 Synthesis and Characterization of Nano Structured Silicon Carbide by High... was used as the medium with an anionic surface active agent to avoid agglomeration. The milled sample powder was taken out at a regular interval of every 5 hours of milling. Then this powder was dried by drier and used for further characterization with an X-Ray Diffractometer (Model: 2036E201; Rigaku, Ultima IV, Japan). JADE software was used to investigate the structural changes and phase transformations of powders occur during mechanical milling. The X-ray diffraction measurements were carried out with the help of a Goniometer model 2036E201 using Cu K α radiation (K α = Aº) at an accelerating voltage of 40 kv and a current of 20 ma. The samples were scanned in the range from 20 to 900, 2-θ and analyzed for crystallite size, peak height, percentage of crystallinity and also amount of induced strains in the milled Silicon Carbide. Scanning electron microscopy (Model: SEM - Quanta 400, EI -Netherlands) was used in order to evaluate the morphological changes and the elemental analysis of certain phases observed in the nano structured Silicon Carbide powder particles. Table 1 The Experimental Details of Milling Process (Total Duration of Milling: 50hrs.) Milling Duration of Type of Rotational Dia. of Balls to medium Milling, hrs Balls of Balls(rpm) the Balls Powder Ratio(BPR) Wet (Toluene) 30 Tungsten mm 10:1 carbide Wet (Toluene) 20 Zirconia 150 3mm 10:1 3. RESULTS & DISCUSSION 3.1. Crystallite size and Lattice strain igure 1 shows the scanning electron micrograph of the fresh Silicon Carbide. rom this figure it is evident that majority of the Silicon Carbide particles are angular in nature. The X-ray diffraction (XRD) pattern of Silicon Carbide in initial stage is shown in igure 2, which shows the phases present in the Silicon Carbide and are largely Silicon Carbide (SiC), Moissanite (3C-SiC) and Quartz (SiO 2 ). 19

4 International Journal of Power Elecronics and Technology igure 1: SEM Micrograph of Initial Silicon Carbide used in the Study igure 2: X-ray Diffractogram of Initial Silicon Carbide The average crystallite size was calculated from the full width at half maximum (WHM) of the X-ray diffraction peak using Scherer s equation [19-24]. D = (k λ)/(b cos θ) 20

5 Synthesis and Characterization of Nano Structured Silicon Carbide by High... Where D is the particle diameter, λ is the X-Ray wave length, B is the WHM of the diffraction peak, K is the diffraction angle and K is the Scherer s constant of the order of unity for usual crystals. The existence of stress in the materials results in lattice distortions of crystals; consequently, the diffraction peaks of the crystals are broadened. The relationship between the half width of the broadened diffraction peaks, Bd and the distortion of lattice, ( d/d) was described by Qiaoqin et. al [25]. The lattice distortion ( d/d) can be obtained from the following equation. ( d/d) = B d /(4 tanθ) Where B d, is half width of the broadened diffraction peaks, θ is half of the diffraction angle. igure 3: Variation of Crystallite size and Relative Strain as unction of Milling Time igure 3 illustrates the variation in crystallite size and lattice strain of the Silicon Carbide with the milling time. A steady decrease in the crystallite size is observed and it was found that the crystallite size get reduced from nm to nm for 50h milling time. The relative lattice strain is increasing with increasing the duration of milling time. This lattice strain was increased from 0.15% to 0.278% for as received and 50 h milled Silicon Carbide respectively. During ball milling the intense mechanical deformation experienced by the Silicon Carbide powder leads to generation of lattice strains, crystal defects and this plus the balance between cold welding and fracturing operations among the powder particles is expected to 21

6 International Journal of Power Elecronics and Technology affect the structural changes in the powder. The measurement of crystallite size and lattice strain in the mechanically milled powders is very important since the phase constitution and transformation characteristics appear to be critically depending on them. igure 4: The Scanning Electron Microscope Photographs of Initial and Ball Milled Silicon Carbide.(a) Initial Silicon Carbide (b) Ball Milled Silicon Carbide for 15 h (c) Ball Milled Silicon Carbide for 30 h (d) Ball Milled Silicon Carbide for 50 h. The size, shape and texture of the initial as well as nano structured Silicon Carbide were studied using Secondary Electron Imaging mode of Scanning electron microscopy (SEM). igure 4 (a) shows the SEM image of initial Silicon Carbide. The initial Silicon Carbide particles are mostly angular in shape. igure 4 (b) shows the SEM image of 15h ball milled Silicon Carbide. Here the angular 22

7 Synthesis and Characterization of Nano Structured Silicon Carbide by High... structure of initial Silicon Carbide has been destroyed; and in this 15h, milling stage the Silicon Carbide is in cold welding condition hence the particles appears like enlarged flakes. The large flake shaped particles are further crushed by intense impacts of the balls; hence the decrease in particle size occurs with increasing milling time as shown in igure 4 (c &d), the SEM images for 30h and 50h ball milling times respectively. The shape of the particles is angular and the surface morphology is rough. The X-Ray diffractograms of the initial as well as ball milled Silicon Carbide were shown in igures 2 and 5. rom these figures clearly observed that the intensity of the sample got reduced and the peak broadening increased as the duration of milling increases. Three major phases were identified for all the milling times; which is Silicon Carbide (SiC), Moissanite (3C-SiC) and Quartz (SiO 2 ). Silicon Carbide phase exhibits strong peaks at º, º, º and º 2θ values of (110) plane (d spacing of , , and Aº) Moissanite(3C-SiC) phase shows strong peaks at º, º, º and º 2θ values of (111) (d spacing of , , and Aº). Quartz phase shows a peaks at º, º º and º 2θ values of (101) plane (d spacing of , , and Aº). igure 5: X- Ray Diffraction Patterns of Initial and Ball Milled Silicon Carbide at Different Milling Times 23

8 International Journal of Power Elecronics and Technology 3.2. Crystallinity Crystallinity refers to the degree of structural order in a solid. Crystallinity is usually specified as a percentage of the volume of the material that is crystalline. The decrease in crystallinity of Silicon Carbide with ball milling hours is shows in the igure 6. This decrease was observed from 74% to 49% for Silicon Carbide and 50h ball milled powder respectively. While increasing the milling time decreases the crystallinity of the Silicon Carbide, thus increasing the amorphous domains in it. This change is beneficial for the applications such as particulate nano filler in polymeric or metallic matrices. igure 6: Variation in % Crystallinity with Milling Time 3.3. Lattice Parameter Diffraction peak positions are accurately measured with XRD, which makes it the best method for characterizing homogeneous and inhomogeneous strains are shifts the diffraction peaks positions. rom the shift in peak positions, one can be calculate the change in d-spacing, which is the result of the change of lattice constants under a strain. Inhomogeneous strains vary from crystallite to crystallite or within a single crystallite and this cause a broadening of the diffraction peaks that increase with sin θ [3]. The displacement of SiC (111) XRD peaks during ball milling process is represented in igure 7. It indicating that with increasing the milling time SiC peaks shifts slightly to the lower angels. The SiC phase is the maximum sufferer during milling hence lead to the decreasing crystallite size with broadening of the diffraction pattern. SiC lattice parameter was 24

9 Synthesis and Characterization of Nano Structured Silicon Carbide by High... evaluated from the precise parameter measurements described in [24] using five XRD peaks. igure 8 shows the variation of lattice parameter of silicon carbide (SiC) after different milling times for (111) plane. As plotted the silicon carbide lattice parameter is decreases from Aº to Aº for 50h milling time with slight variations on the parameter due to intense impact of the balls and converting this powder into the lower sizes i.e nano crystallite sizes. igure 7: Displacement of SiC (111) XRD at Different Milling Times igure 8: Lattice Parameter Changes with Peaks Milling Time for the (111) Plane of SiC 25

10 International Journal of Power Elecronics and Technology 4. CONCLUSIONS The size reduction of Silicon carbide from micrometer level to nano meter levels has been achieved by high energy ball milling for the period of 50hrs. The percentage of crystallinity reduces from 74% to 49%. The silicon carbide becomes more amorphous and the crystallite size reduces drastically. The lattice strain was increased with increasing the milling time. The SiC phase is the maximum sufferer during milling; hence with increasing the milling time SiC peaks shifts slightly to the lower angles and also broadening of the diffraction pattern occurs. The lattice parameter was initially rapidly decrease then further milling it was decreased slowly due to lattice distortion of 50hr milled powder. The further TEM study needs to be carried out to explain the role of the lattice parameter with milling time. Currently the author is utilizing this nano structured silicon carbide for synthesis of Aluminium-Silicon Carbide metal matrix nano composites (MMNC) [11-14]. The work is on progress and the results will be presented in the next publication. ACKNOWLEDGEMENTS The authors thank the Center for Nano Technology and Department of Metallurgical Engineering, Andhra University College of Engineering, Visakhapatnam, India for providing necessary support in conducting the experiments and also to Dr. K Siva Prasad, Dept of Materials and Metallurgical Engg, NIT- Tirchy, India for support in SEM studies. REERENCES [1] Bhushan B, Hand Book of Nanotechnology Springer Verlag, NewYork, [2] Kohlar M, ritzsche W, Nanotechnology-An Introduction to Nano Structuring Techniques Wiley -VCH -Verlag, Germany, [3] Guozhong Cao, Nanostructures and Nano Materials- Synthesis, Properties and Applications-Imperial College Press, USA, [4] Marie Isabelle baraton, Synthesis, unctionalization and Surface Treatment of Nano Particles, Aerican Scientific Publication, USA, [5] Carl C Koch, Nano Structured Materials Processing, Properties and Applications William Andrew Inc.-New York,USA,

11 Synthesis and Characterization of Nano Structured Silicon Carbide by High... [6] Akio. K, Atsushi. O, Toshiro. Hiroyuki. K.T, J Jpn.Inst.Light Met, 1999: 49: [7] Mussert.K.M, Vellinga.W.P, Bakker.A, VanDrtZwaag.S," J.Material Science,"2002:37: [8] J.N. ridlyander, Ed., Metal Matrix Composite, Chapman & Hall, London, [9] T.W. Clyne and P.J. Withers, An Introduction to Metal Matrix Composites, Cambridge University Press, [10] W.S. Miller and.j. Humphreys, Strengthening Mechanism in Metal Matrix Composites, undamental Relationships Between Microstructure and Mechanical Properties of Metal Matrix Composites, P.K. Liaw and M.N. Gungor, Ed., The Minerals, Metals & Materials Society, [11] L. Lu, M.O. Lai, and C.W. Ng, Enhanced Mechanical Properties of an Al Based Metal Matrix Composite Prepared Using Mechanical Alloying, Mater. Sci. Eng, A, 252, 1998, pp [12] R.D. Evans and J.D. Boyd, Near-Interface Microstructure in a SiC/Al Composite, Scr. Mater., 49, 2003, p [13] P.N. Bindumadhavan, H.K. Wah, and O. Prabhakar, Assessment of Particle- Matrix Debonding in Particulate Metal Matrix Composites Using Ultrasonic Velocity Measurements, Mater. Sci. Eng, A, 323, 2002, pp [14].Y.C. Boey, Z. Yuan, and K.A. Khor, Mechanical Alloying for the Effective Dispersion of Sub-Micron Sicp Reinforcements in Al-Li Alloy Composite, Mater. Sci. Eng, A, 252, 1998, pp [15] L. Lu and M.O. Lai, Mechanical Alloying, Kluwer Academic Publishers, [16] C. Suryanarayana, Mechanical Alloying and Milling, Prog. Mater. Sci., 46, 2001, pp [17] D.L. Zhang, Processing of Advanced Materials Using High-Energy Mechanical Milling, Prog. Mater. Sci., 49, 2004, pp [18] K. Mahadevan, K. Raghukandan, B.C. Pai. & U.T.S. Pillai, Experimental Investigation on the Influence of Reinforcement and Precipitation Hardening Parameters of AA 6061-SiCp Composites., Indian Journal of Engineering & Materials Sciences, 14, August 2007, pp [19] B.D. Cullity & S.R. Stock, Elements of X-Ray Diffraction, 3rd Ed., Prentice- Hall Inc., 2001, pp [20] R. Jenkins & R.L. Snyder, Introduction to X-ray Powder Diffractometry, John Wiley & Sons Inc., 1996, p [21] H.P. Klug & L.E. Alexander, X-Ray Diffraction Procedures, 2nd Ed., John Wiley & Sons Inc., 1974, pp [22] B.E. Warren, X-Ray Diffraction, Addison-Wesley Publishing Co., 1969, pp [23] P. Scherrer, Göttinger Nachrichten Gesell., 2, 1918, pp. 98. [24] A.L. Patterson, The Scherrer ormula for X-Ray Particle Size Determination Phys. Rev. 1939, 56 (10):