The effect of milling time and sintering temperature on

22 downloads 0 Views 1017KB Size Report
Erlina Yustanti, Mas Ayu Elita Hafizah, and Azwar Manaf. Citation: 1788, 030099 (2017); doi: 10.1063/1.4968352. View online: http://dx.doi.org/10.1063/ ...
The effect of milling time and sintering temperature on formation of nanoparticles barium strontium titanate Erlina Yustanti, Mas Ayu Elita Hafizah, and Azwar Manaf

Citation: 1788, 030099 (2017); doi: 10.1063/1.4968352 View online: http://dx.doi.org/10.1063/1.4968352 View Table of Contents: http://aip.scitation.org/toc/apc/1788/1 Published by the American Institute of Physics

The Effect of Milling Time and Sintering Temperature on Formation of Nanoparticles Barium Strontium Titanate Erlina Yustanti1,2), Mas Ayu Elita Hafizah1), Azwar Manaf 1,a) 1

2

Department of Physics, FMIPA University of Indonesia, Depok 16424, Indonesia Department of Metallurgy, Faculty of Engineering, University of Sultan Ageng Tirtayasa, Cilegon 42435, Indonesia a)

Corresponding author: [email protected]

Abstract. Nanoparticles of barium strontium titanate (BST) or Ba0.3Sr0.7TiO3 were synthesized by mechanical alloying and successive ultrasonic irradiation treatment. This research attempted to reduce the particles obtained through mechanical milling of mechanically alloyed powders to the particles with sizes in nanometer scale. The effectiveness of milling time on the synthesis of BST nanoparticles was confirmed by mean particle size evaluation which showed that a milling duration up to 60 h was required to bring down gradually the mean particle from 5.7 into 2.4 μm. The broadening lines of XRD pattern of the ultrasonically treated samples were analyzed using a high score plus (HSP) and a whole powder pattern modeling (WPPM) software to obtain the crystallite size distribution. The mean crystallite size of the treated particles was found 49 nm which is about 60 times lower than its mean particle size. It is shown that mechanical alloying through the sintering process followed by ultrasonic destruction will promote the formation of nanoparticles.

INTRODUCTION It is well known widely that nanoparticles are of great interest among researchers all over the world since the nano-scale size dependent properties of nano-crystalline materials are often observed in contrary to the conventional microcrystalline materials. The latter has un-change properties regardless of its size. Whereas in the former type microstructure materials, the large surface to volume ratio of crystallites in the materials often brings some unexpected properties as properties raise from surfaces dominate the contribution of final properties of bulk materials [1]. In the course of our research activities which are directed towards the synthesis of nanoparticles for magnetic and dielectric based compounds, we found that mechanical alloying [2] coupled with ultrasonic irradiation treatments can be an alternative route for the preparation of fine and homogeneous powder materials leading to nanoparticle-based materials [3]. There were several methods to obtain nanoparticles barium strontium titanate (BST), such as thin films, excellent dielectric and electrical properties obtained by a low-temperature process make the BST thin film a good candidate for above-IC integration in communication applications [4]. The electrochemical synthesis enabled the production of small nanoparticles (grain sizes 200 nm) at temperatures lower than 60qC in a short synthesis time 2 hours [5]. Barium titanate powders with well-developed crystallinity and good morphology could be synthesized at 120qC 12 hours comparatively lower than the normal sol–gel route [6]. Homogeneous Ba0.6Sr0.4TiO3 thin films as well as spatially inhomogeneous BST thin films exhibiting artificial gradients in composition normal to the growth surface were deposited. Both up and down-graded BST films were fabricated by depositing successive layers with Sr mole fraction x ranging from x=0.5 to x=0.3 [7]. Fine-grained BaTiO3 ceramics were obtained at a low sintering temperature of 900qC within a short sintering period by means of a new sintering method-spark plasma sintering [8], Sub-micrometric BaTiO3 particles were obtained by hydrothermal synthesis at 180 oC using titanium isopropoxide or titanium dioxide, and barium hydroxide as precursors. Uniaxially pressed powders were sintered at 1250qC retaining the sub-micrometric grain size. Samples showed ferroelectric behavior and tetragonal to cubic transition temperatures between 120 and 123qC [9]. Barium titanate powder was formed by heat treating the polymeric International Conference on Engineering, Science and Nanotechnology 2016 (ICESNANO 2016) AIP Conf. Proc. 1788, 030099-1–030099-6; doi: 10.1063/1.4968352 Published by AIP Publishing. 978-0-7354-1452-5/$30.00

030099-1

precursor in air at 500–900qC. The thermal decomposition of (Ba, Ti) polymeric precursor was studied by thermal analysis [10]. BST with x=0.25; 0.35; 0.40; 0.50; 0.60; 0.75; 0.90 were prepared by sintering method from BaCO 3, SrCO3, and TiO2 of high purity (99.98%). The solid-state reaction was employed to obtain pure and doped BST ceramic samples. The sintering treatment was performed in the temperature ranging from 1200 to 1260qC, for 2 hours [11]. Most mechanical alloying and milling processes, in order to obtain fine powders, required a long time, even up to hundred hours. In some cases, there were found in any unwanted material that contaminates the final product. To prepare fine powders with homogeneous particle size distribution, alternative processes necessary to reduce the duration of milling time and prevents the presence of contamination. Mechanical alloying and sintering processes encouraged crystallization of quasi-crystalline materials, particle size reduction, enhanced through high power ultrasonic destruction. This research discussed the average characterization of crystallite size and particle size.

EXPERIMENTAL METHODS Stoichiometry quantities of the analytical grade of BaCO3, SrCO3, TiO2 powders from Sigma-Aldrich with a purity better than 99% were mixed and milled in a planetary ball mill apparatus and milled into powder up to 60 hours with a speed of 160 rpm. Materials which resulted from mechanical milling were compacted into a cylindrical die of 25 mm diameter under 10 tons load force. The green compact was then sintered at 1200qC for 4 hours leading to crystalline bulk samples. Phase analysis of crystalline BST samples was carried out using Empyrean X-ray diffractometer (XRD). Crystalline BST powders were obtained through hand grinding and re-milling the bulk sample under the same apparatus for 20 hours, which then analyzed by the particle size analyzer (PSA). Further particle size reduction of the BST powders was performed under a Qsonica sonicators Q700, at a frequency 20 kHz and 60 μm transducer amplitude. Nonionic surfactant with a concentration of 0.1% was added to produce monodisperse particles. Data of the diffraction pattern of BST results from ultrasonic treatments was refined using the high score plus (HSP) and the whole powder pattern modeling (WPPM) software.

RESULTS AND DISCUSSION Figure 1 showed values of the average particle size of powder mixture BaCO 3, SrCO3, and TiO2 precursors after processed through mechanical alloying which were plotted against the length of milling time. It shows an increase in the mean size of the initial milling period, which associated with the occurring of cold welded precursor’s particle, resulted in bigger particle sizes. The average particle size of 5.7 μm at initial milling time reached a maximum value 14.9 μm after 6 hours, after which the mean size gradually decreased to 2.4 μm at 60 hours milling time. Result as shown in Fig. 1 can be best described as the following; the increase of mean size must be due to welding of particle’s precursors at the initial milling time. The continuous mechanical treatments, experiencing by particles through ball impact during the milling process increased the internal stress of the particles, which resulted in an increase of brittleness in the particles. The increasing of milling time on brittle particles will reduce the average particle size through fragmentation of the particles, which generally results in a high crystal defect due to heavy deformations [12]. In the current case, milling the precursors up to 60 hours produced particles of BST with the average particle size 2.4 μm. In addition, with an increase in duration of milling time caused broadening of the diffraction peaks which followed by decreasing in intensity. It was shown in Fig. 1 (inset plot of Fig.1), enlargement of peak 2-theta 27 to 28.5o for crystalline powders milled for 20 hours is being compared with that of 60 hours. Hence, crystallite size reduction is evidenced by the broadening of full-width half maximum (FWHM) values. [13] reported a similar study on the effect of milling period to the mean particles and the crystallites size of strontium titanate. Referring to the report, it was required 60 hours to obtain the mean same size for strontium titanate. The different in mechanical properties like the ductility for the two types of materials determined the length of milling duration.

030099-2

FIGURE 1. Average particle size distribution of Ba0.3Sr0.7TiO3 during the milling process.

Generally, mechanical milling of crystalline precursors like a mixture of SrCO3, CaCO3, and TiO2 would no affect the crystal stability of respective precursors, but defects cannot be avoided. Hence, the diffraction pattern of the mixture of SrCO3, BaCO3, and TiO2 after milling process would consist of a mixture of the respective diffraction pattern. It is shown in Fig. 2(a) identification of milling result showed the diffraction pattern mix of SrCO 3, CaCO3, and TiO2 can be distinguished clearly.

(a)

(b)

FIGURE 2. Diffraction pattern a mixture of BaCO3, SrCO3 and TiO2 (a) Variation of milling time (b) Variation of sintering temperature

Figure 2(b) showed a diffraction pattern from BST characterization at the various sintering temperature. The sintering temperature at 500°C formed amorphous phase with diffraction intensity under 350 (cps). While at temperatures 900°C began forming solid state with the maximum peak around 1200 (cps), but precursor still be distinguished in 2-theta respectively 41.2o = SrCO3; 47o = BaCO3; 48.5o = BaCO3; 87.8o = SrCO3. At a temperature 1200o C solid state has been going perfectly, it can be seen by no presence of metastable phase. The diffraction

030099-3

pattern of BST single phase reached up to 9500 (cps) intensity, 11 peaks were confirmed very well with the inorganic crystal structure database (ICSD) no. 98-008-8532. Refinement data-fitting-residual with WPPM software [14-15] can analyze the average of crystallite size distribution from BST crystalline powder. WPPM is the most appropriate method for considering the damage due to fluctuations in stoichiometric crystal, dislocations, grain surface effects, instrumental profile and gradient concentration [14]. The BST sintering process continued by hand grinding to reduce the average of particle size and crystallite size before re-milling and ultrasonic destruction [16]. Figure 3 showed that the average of particle size BST powder after re- milling 2 hours was 2.1 μm and 1.1 μm after 20 hours. The Increasing of re-milling time can decrease the average crystallites size of BST, it can be seen by the broadening of FWHM re-milling 2 hours to 20 hours in the enlargement of peak 2-theta 31.8-32.30 (inset plot of Fig. 3). The increased of re-milling time from 2 hours up to 20 hours resulted in the decreased in an average of particle size and crystallite size.

FIGURE 3. Average particle size distribution of Ba0.3Sr0.7TiO3 during re–milling.

The reduction of crystallite size on barium strontium titanate observed each end of 3 hours ultrasonic process, each sample was added 0.1% non-ionic surfactant ultrasonic and continued for 5 minutes with amplitude 60 μm. The Powder results ultrasonic characterization by XRD continued refinement using software HSP and WPPM. In Figure 4 shown that the lowest concentration of 10 g/L value crystallite size smallest 22 nm, it is understandable given the growing concentrated particle concentration in the reactor, the process of the breakup of cavitation wave due to frequency ultrasonic waves did not optimally so that the particles can’t be reduced to the maximum.

FIGURE 4. Influence of particle concentration in the ultrasonic reactor Ba0.3Sr0.7TiO3 the reduction of the average size of crystallites.

To ensure that with increasing time of ultrasonic crystallite size reduction also occurred in the barium strontium titanate particles, it is necessary to continue the comprehensive analysis at a fixed concentration of 10 g/L.

030099-4

Crystallite size reduction was observed at the end of the ultrasonic process at the time variation of the ultrasonic varied at 0, 3, 6, 9 and 12 hours. At the end of the ultrasonic process, each sample was given a non-ionic surfactant 0.1% ultrasonic continued for 5 minutes with amplitude 60 μm. The Powder results in ultrasonic characterization by XRD and continued refinement using software HSP and WPPM to get the size distribution of the crystallites.

FIGURE 5. Influence of ultrasonic time to reduction of the average of crystallites size from Ba0.3Sr0.7TiO3

In Figure 5, it is shown average crystallite size of Ba0.3Sr0.7TiO3 before ultrasonic is 70 nm and after process 12 hours ultrasonic became 23 nm. This shows the influence ultrasonic time at the first 3 hours ultrasonic were effective in reducing the size of the crystallites and further with increasing time of ultrasonic up to 12 hours, the size of crystallites tend not changed much. Ultrasonic irradiation for 12 hours by using Qsonica sonicators Q700 resulted in a reduction in particle size up to 49 nm. Nonionic surfactant was added at 0.1% effective in reducing agglomeration.

CONCLUSIONS This research was successfully synthesized of Ba0.3Sr0.7TiO3 nanoparticles by mechanical alloying through ultrasonic destruction. Milling until 60 hours was effective to reduce the average of particle size up to micrometer at 1200o C sintering temperature. Ultrasonic destruction 12 hours successfully obtained of Ba0.3Sr0.7TiO3 with average particle size up to 49 nm.

ACKNOWLEDGMENTS The author would like to thank you for the support and laboratory facilities of the Department of Physics, University of Indonesia. Research work is partially funded by the University of Indonesia under the research grant KOPIT with contract number: 1993/UN2.R12/HKP.05.00/2016. We also thank PT. DKSH Indonesia for access to use Particle Size Analyzer Malvern Zetanano ZS.

REFERENCES 1. 2. 3. 4. 5. 6. 7.

W. Jiang, X. Gong, Z. Chen, et al., J. Ultra. Son., 14, 208-212 (2007). C. Suryanarayana, Prog. Mater. Sci. 46, 1–184 (2001). A. Manaf and M. A. E. Hafizah, J. of Mat. Sci. Res., 1, 4 (2012). X. H. Zhu, et al., J. Eur. Ceram. Soc. 30, 471–474 (2010). G. O. S. Santos, et al., Ceram. Int. 40, 3603–3609 (2014). W. Wang, L. Cao, W. Liu, G. Su & W. Zhang, Ceram. Int. 39, 7127–7134 (2013). D. Czekaj, A. Lisińska-Czekaj, T. Orkisz, J. Orkisz & G. Smalarz, J. Eur. Ceram. Soc. 30, 465–470 (2010).

030099-5

8. 9. 10. 11. 12. 13.

W. Luan, L. Gao, H. Kawaoka, T. Sekino & K. Niihara, Ceram. Int. 30, 405–410 (2004). H. A. Avila, L. A. Ramajo, M. M. Reboredo, M. S. Castro & R. Parra, Ceram. Int. 37, 2383–2390 (2011). V. Vinothini, P. Singh & M. Balasubramanian, Ceram. Int. 32, 99–103 (2006). C. Berbecaru, H. V. Alexandru, C. Porosnicu & A. Velea, J. Thin Solid Film. 516, 8210–8214 (2008). L. Lii and M. O. Lai, Mechanical Alloying. Kluwer Academiac Publisher, 1998. R. D. Widodo, A. Manaf, R. R. V. Viktor, and D. H. Al-Janan, Int. J. Innov. Res. Adv. Eng., 2(12), 66–70 (2015) 14. M. Leoni, T. Confente & P. Scardi, Zeitschrift fur Krist. Suppl. 1, 249–254 (2006). 15. P. Scardi & M. Leoni, Acta Crystallogr. Sect. A Found. Crystallogr. 58, 190–200 (2002). 16. E. Yustanti, M. A. E. Hafizah & A. Manaf, "Synthesis of Strontium Substituted Barium Titanate Nanoparticles by Mechanical Alloying and High Power Ultrasonication Destruction," in The 3rd International Conference on Advanced Materials Science and Technology (ICAMST 2015), AIP Conference Proceedings 1725, edited by Sutikno et al. (American Institute of Physics, Melville, NY, 2016), pp. 020102–1 020102–6.

030099-6