Advanced Materials Research Vol. 1115 (2015) pp 378-381 © (2015) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/AMR.1115.378
Submitted: 2015-02-12 Accepted: 2015-03-26 Online: 2015-07-20
Effect of Dispersants on Microstructures of Nano Alpha Alumina Developed from Aluminium Dross Waste S. Anis Sofia 1, a, N. Samat2, b and M. S. Meor Yusoff 3, c 1, 2
Department of Manufacturing and Materials Engineering, Faculty of Engineering, International Islamic University Malaysia, Jalan Gombak 53100, Kuala Lumpur, Malaysia
3
Material Technology Group, Industrial Technology Group, Malaysian Nuclear Agency, Bangi 43000, Kajang, Selangor Darul Ehsan, Malaysia a
[email protected],
[email protected],
[email protected]
Keywords: Nano Alpha Alumina; Dispersants; Particle Size; Crystallite Size; Morphology.
Abstract. This paper compares the effect of dispersants which are Sodium Laureth Sulfate (SLS) and distilled water (DW) on the crystallization, particle size distribution and morphological behavior of nano alpha Alumina (α-Al2O3) synthesized from Aluminium (Al) dross waste. The synthesizing of nano α-Al2O3 via wet milling method was performed using a planetary mill for 4 hours at a speed of 550 rpm. The nano α-Al2O3 powders with dispersants were characterized with xray diffraction (XRD), particle size analyzer (PSA) and transmission electron microscopy (TEM). XRD analysis shows the broadening and shifting of peaks after the sample was calcined at 1300 ̊C, indicating high crystallinity. The crystallite size of α-Al2O3 milled with SLS is also smaller than the α-Al2O3 milled with DW. These results are consistent with the PSA analysis in which the graphs displayed a symmetrical trend. Then, the PSA analysis is validated with TEM observation up to 100000x magnification, particularly for α-Al2O3 milled with SLS. Introduction Alumina (Al2O3) is ceramics material that frequently used as an abrasive tools and refractory. The excellent chemical and physical properties like high resistance to heat and wear, high specific strength and good oxidation resistance makes Al2O3 amongst the highly demand of mineral particles in industrial sectors. The production of Al2O3 from aluminium (Al) refining process also produces a byproduct that lead to environmental problem. It is known as Al dross and this waste is produced almost five million tonnes every year from worldwide Al industry. Since it is classified as a schedule waste in Malaysia, thus its storage, transportation and disposal activities must be carried out by licensed contractors [1]. Although many methods had been introduced in synthesizing Al2O3, the process is yet still quite expensive. Consequently, the production of Al2O3 from Al dross waste by the Aluminium recycling technology has been applied ever since. The extraction of Al2O3 from Al drosses are carried out through certain processes [2]. It has been reported that [3] the wet milling method is one the best technique in producing nano-sized powder. This method provides an aqueous environment which results in less agglomeration of produced particles. Thus, this study is to compare the effect of Sodium Laureth Sulfate (SLS) and distilled water (DW) as a dispersant media in wet milling method. The produced α-Al2O3 particles are characterized in term of particle size distribution, crystallization and morphological behavior. Materials and Experimental Procedure Materials Preparation. White Aluminium (Al) dross was obtained from a local aluminium smelting company located in Penang. The crystalline phase and morphology of the Al dross was characterized using PANalytical, BW 2040/60 X’Pert PROMPD XRD machine. The employment
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of Sodium Laureth Sulfate (SLS) and distilled water (DW) into the α-Al2O3 nanoparticles functioned as dispersing agents. Both SLS and DW were obtained from Sigma-Aldrich Company and Malaysian Nuclear Agency laboratory respectively. Sample Preparation. The thermal decomposition method was used to produce α-Al2O3 from Al dross. The furnace was set up to 1300 ̊C for calcination, breaking the compound into simpler compound or element [4]. The α-Al2O3 produced via wet milling process employed a Fritsch Pulverisette 7 planetary mill with maximum milling speed of 600 rpm. Milling Process. 50 ml distilled water was added into 9 g of α-Al2O3 particles while 45 ml distilled water was mixed with 0.5 g of SLS prior to added into 9 g of α-Al2O3 particles. These two different mixtures were then placed into the zirconium container. 150 of small zirconium balls (weight per ball ± 0.0038 g) were rotated at a speed of 550 rpm for 4 hours during the milling process. After milling, these samples were filtered and dried for overnight at 70 ̊C in an oven. Characterization on Crystallography and Morphology. The dried samples were taken for XRD observation at temperature of 25 ̊C, operated using Cu κα1 with λ = 1.54060 Å radiation source. The analysis was done to determine the crystallite size of the milled samples while the morphology was analyzed by JEOL-JEM 2100 transmission electron microscope (TEM) at 160 kV. Particle size analysis was performed by the laser diffraction Honeywell, MICROTRAC X-100 instrument. Results and Discussion X-Ray Diffraction (XRD) Analysis. Before the calcination process the diffractogram spectrum of Al dross (Fig.1a) shows very high and sharp peaks at 18 ̊ 2θ peak position indicating high crystallinity of this compounds [5]. This spectrum fits well with the ICSD diffractogram reference for gibbsite (98-001-73260) [1] which suggests that the Al dross comprises of a single gibbsite phase with a monoclinic crystal system. After calcination at 1300 ̊C, the peaks of Al dross were shifted to 16 ̊ 2θ as seen in Fig.1b. This signifies the gibbsite phase had transformed to α phase Al2O3 where the peaks became sharper and more intense. The rhombohedral crystal system exhibited by the compound at this α phase indicates no further phase changing occurrence since Al2O3 had reached high stability [6].
Fig. 1 XRD diffractograms of Al dross (a) before and (b) after calcinations.
The effect of different milling dispersants (DW and SLS) on α-Al2O3 phases is compared in Fig. 2. No foremost significant differences were noticed except for the two most intense peaks found, both at 35 ̊ and 44 ̊ of 2θ respectively in the Fig. 2(b). Even so, the 2θ peak position of 35 ̊ was assumed to perceive the broadening and shifting effect from the milling method due to its importance in the standard reference of α-Al2O3 XRD pattern ICSD (98-006-3945) [1]. The sharp and high intensity peaks in Fig. 2 were shown instead, presenting that the α-Al2O3 possesses high crystallinity [7].
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Fig. 2 XRD diffractograms of α-Al2O3 milled with (a) DW and (b) SLS
The crystallite size of four compounds was determined from XRD analysis. On the other hand, the mean particle size was obtained from particle size analyzer (PSA) at d50. Both results are shown in Table 1. It is noted that the phase transformation after calcination led to the decrease of crystallite size. Consequently, α-Al2O3 particles in nano meter range were formed. Clearly the influence of dispersing agent in reducing the crystallite size is displayed in Table 1. The crystallite size decreases significantly from 115.3 nm to 67.6 nm after milled for 4 hours with SLS. Conversely, the crystallite size of α-Al2O3 milled with DW is slightly larger than α-Al2O3 milled with SLS. This could be associated with the aggregation of particles that caused by the inefficient of DW as dispersant medium during milling compared to SLS. Table 1. Crystallite size and PSA results of the samples
Samples Al white dross α-Al2O3 α-Al2O3 milled with SLS α-Al2O3 milled with DW
XRD Crystallite Size, [nm] 115.3 71.2 67.6 93.3
PSA d50, [µm] 68.22 64.62 1.951 1.694
Particle Size Distribution. The particle distribution of the samples was validated with particle size analyzer (PSA). As shown in Fig.3, α-Al2O3 milled with SLS exposed a symmetrical pattern which indicates a very good distribution of particle size in the compound. Whilst α-Al2O3 milled with DW shows a trinodal shape of trend which verifies the presence of various types of particle size distribution and also particle agglomeration [8]. This suggests that the SLS is a better dispersant medium than DW since it can synthesize the nano α-Al2O3 particle with well distribution.
Fig. 3 Particle size distribution of milled sample with (a) SLS and (b) DW
Surface Morphology. TEM micrograph of four compounds is shown in Fig. 4(a-d). The morphology of Al dross (Fig. 4a) comprises of plate-shaped crystal structure. The change of the
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plate structure to smaller circular structure of α-Al2O3 after calcination process conforms to the micrograph shown in Fig. 4b. A similar finding was also reported by Meor et al. (2011). The positive influence of SLS on the reduction of particle size and homogeneous particle distribution is evident in Fig. 4c. This micrograph is also consistent with the graph of distribution in PSA (Fig. 3a). In contrast, the α-Al2O3 milled with DW (Fig.4d) shows a poor distribution due to the agglomeration of particles. Nonetheless, it also shows a very high crystalline structure when magnified to 100000x of magnification.
Fig. 4 (a) Al dross, (b) α-Al2O3, (c) α-Al2O3 milled with SLS and (d) α-Al2O3 milled with DW at 100000x, 100000x, 50000x and 100000x magnifications respectively
Conclusion The effect of different dispersants on the production of α-Al2O3 particle from Al dross was determined. The results showed that SLS is able to produce α-Al2O3 with smaller crystalize and particle size with less agglomeration as compared to DW. References [1] M.Y. Meor Sulaiman, M. Muslimin, W. Paulus, M. E. Mahmoud and P. Devi, Effect of Milling Time and Dispersant on Microstructures of Alpha Alumina Nanopowder Synthesized from Aluminum Dross Waste, Advanced Materials Research, Trans Tech Publication Vol. 576 (2011) [2] S.O. Adeosun, M. A. Usman, W. A. Ayoola and I.O. Sekunowo, Evaluation of the Properties of Polypropylene-Aluminum-Dross Composite, ISRN Polymer Science (2012) [3] P. Pourghami, E. Altin, M. R. Mallembakam, W. Peukert and E. Forssberg, Microstructural Characterization of Hematite during Wet and Dry Milling using Reitveld and XRD Line Profile Analyses, Powder Technology, 186 (2008), p. 9-21 [4] V. Isupov, L. Chupakhina, G. Kryukova and S. Tsybulya, Fine α-alumina with Low Alkali: New Approach for Preparation, Solid State Ionics, 141-142 (2001), p. 471-478 [5] W. Paulus, M. Y. Meor Sulaiman, M. Muslimin, M. E. Mahmoud, S. Mahat and P. Devi, XRD and SEM Characterization of Different Alumina Crystalline Forms from Aluminum White Dross Waste (2009), pp. 1-12 [6] P.S. Santos, H. S. Santos and S. P. Toledo, Standard Transition Aluminas Electron Microscopy Studies, Materials Research, Vol. 3, No. 4 (2000), p. 104-114 [7] J. Aquilar-Santillan, H. B. Ramirez and R. C. Brandt, Journal of Ceramic Processing Research, 5(3) (2004), pp. 196-202 [8] K. Abdelrazak and S.W. Kim, Mechanical Wet-milling and Subsequent Consolidation of Ultrafine Al2O3-(ZrO2+3%Y2O3) Bioceramics by using High-frequency Induction Heat Sintering, Trans Nonferrous Met. Soc. China 17 (2006), pp. 21-26
Advances in Manufacturing and Materials Engineering 10.4028/www.scientific.net/AMR.1115
Effect of Dispersants on Microstructures of Nano Alpha Alumina Developed from Aluminium Dross Waste 10.4028/www.scientific.net/AMR.1115.378
