The influence of SiO2 doped concentration, temperature and pressure on the microstructure of Al2O3(SiO2)x bulk model

This paper looks at the influence of SiO2-doped concentration, temperature and pressure on the microstructure of the Al2O3(SiO2)x (ASx) bulk model using the Molecular Dynamics (MD) method with a Born-Mayer pair interaction potential and periodic boundary conditions.
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The influence of SiO2 doped concentration, temperature and pressure on the microstructure of Al2O3(SiO2)x bulk model JOURNAL OF SCIENCE OF HNUE DOI: 10.18173/2354-1059.2015-0046 Mathematical and Physical Sci., 2015, Vol. 60, No. 7, pp. 162-168 This paper is available online at http://stdb.hnue.edu.vn THE INFLUENCE OF SIO2 -DOPED CONCENTRATION, TEMPERATURE AND PRESSURE ON THE MICROSTRUCTURE OF Al2 O3 (SiO2 )x BULK MODEL Nguyen Trong Dung and Nguyen Chinh Cuong Faculty of Physics, Hanoi National University of Education Abstract. This paper looks at the influence of SiO2 -doped concentration, temperature and pressure on the microstructure of the Al2 O3 (SiO2 )x (ASx ) bulk model using the Molecular Dynamics (MD) method with a Born-Mayer pair interaction potential and periodic boundary conditions. The ASx model was created by changing the doping concentration (SiO2 )x with x = 1, x = 2 and x = 3 at a temperature of 3,500 K and a pressure of 25 GPa. When models with the most suitable concentration were obtained, we maintained a pressure of 25 GPa and reduced the temperature to 2,500 K, 1,500 K and 500 K, or kept the temperature unchanged and reduced the pressure to 20 GPa, 15 GPa, 10 GPa, 5 GPa and 0 GPa. The models were analyzed using radial distribution functions (RDF), the coordination number, the energy, the size and the length of couplings between atoms. Obtained results showed that there was an influence of doping concentration, temperature and pressure on the microstructure of Al2 O3 (SiO2 )x bulk model. Keywords: Microstructure, Al2 O3 .(SiO2 )x bulk model, Molecular Dynamics. 1. Introduction Oxide materials such as Al2 O3 , SiO2 , Fe2 O3 and GeO2 are widely used in many industries. In particular, the mixed oxide Al2 O3 (SiO2 )x (ASx ) is used in ceramic technology and petrochemical technology and this material is also the basic component of the earth’s crust. Research on Al2 O3 , SiO2 and ASx materials are of great interest today. Some works on Al2 O3 (SiO2 )2 (AS2 ) materials have shown that there was an influence of pressure on the microstructure [1] and an influence of the phase transition process on the mechanical properties [2]. In particular, studies on the influence of phase transition from one amorphous state to another one under pressure (from 14 GPa to 22 GPa [3] and from 8 GPa to 25 GPa [4]) at low temperature have found that the phase transition process occurred slowly [3]. Al atoms (molecules) have a complex structure so when they are linked to the Si-O tetrahedral lattice, the Al3+ ion has to be under a pressure which is great enough to form an AlO4 tetrahedral lattice with Al3+ and Si2+ ions that are linked together through O atoms. Some experimental methods such as Nuclear Magnetic Resonance (NMR) [5], X-ray diffraction, Raman spectrum [6] and Neutron Scattering [7] have shown that structural units 3, 4, 5 and 6 appeared in the material at 4,000 K [8]. Recently, some Received July 9, 2015. Accepted September 4, 2015. Contact Nguyen Trong Dung, e-mail address: dungntsphn@gmail.com 162 The influence of SiO2 -doped concentration, temperature and pressure... theoretical and simulation methods [9] have shown the role of O atoms in the coupling to form the composites Al2 O2 and AlSiO2 . The results showed that the length of the Al-O coupling is in the range of 1.8 - 1.9 A ˚ and the number of O atoms which are surrounded the Al atoms is in the range of 4.0 - 4.8. The structure of the AS2 system is made up of AlO4 tetrahedral and AlO8 octahedral blocks with the rate depending on the research methodology and procedures of experimental processes. P. Lamparter and his colleagues studied the microstructure of Al2 O3 using experimental methods (X-ray diffraction and neutron diffraction) and the Monte Carlo simulation method [10] and found that with 20% Al atoms, 3 were surrounded by O atoms, with 56% Al atoms 4 were surrounded by O atoms and with 22% Al atoms 5 were surrounded by O atoms. Until today, there has been no adequate explanation for the microstructure change in the AS2 model under the influence of temperature, pressure and SiO2 -doped concentration. There are still many problems to be studied in detail. In this paper, the influence of SiO2 -doped concentration, temperature and pressure on the microstructure (radial distribution function, coordination number, energy, size and the length of the couplings between pairs of atoms) of the ASx model was studied. 2. Content 2.1. Method of calculation The (Al2 O3 )(SiO2 )x (ASx ) bulk model is constructed with x = 1, x = 2 and x = 3, corresponding to AS1 , AS2 , AS3 models which have atomic numbers as shown in Table 1. ...