Sintering behavior of nano alumina powder shaped by pressure filtration M. Aminzare a , Mehdi Mazaheri b, * , F. Golestani-fard a , H.R. Rezaie a , R. Ajeian c a Department of Materials and Metallurgical Engineering, Iran University of Science and Technology, Tehran, Iran b Institute of Physics of Complex Matter, Swiss Federal Institute of Technology Lausanne (EPFL), SB-IPMC-LNNME, PH D2 434 (Baˆtiment PH), Station 3 (Boı ˆte A), CH-1015 Lausanne, Switzerland c Department of Physics, Iran University of Science and Technology, Tehran, Iran Received 16 December 2009; received in revised form 27 January 2010; accepted 12 June 2010 Available online 3 August 2010 Abstract In the present study, the sintering behavior of a commercial nano alumina powder with an initial particle size of 100 nm was investigated. The shrinkage response of the powder formed by pressure filtration (PF) during non-isothermal sintering was measured in a laser assisted dilatometer at three different heating rates of 2, 10 and 25 8C min 1 up to 1400 8C. In order to calculate the activation energy of sintering, constant rate of heating (CRH) was employed and the activation energy was found to be 608  20 kJ mol 1 for iso-density method. The heating rate was demonstrated to have a vital role on densification behavior and final grain size. The mean grain size of the full dense specimens decreased from 875 to 443 nm when the heating rate increased from 2 to 25 8C min 1 . # 2010 Elsevier Ltd and Techna Group S.r.l. All rights reserved. Keywords: A. Sintering; D. Al 2 O 3 ; Activation energy; Dilatometry 1. Introduction Sintering, defined a complicated process consists of different transport mechanism for densification of powder and microstructure enhancement. Powder characteristics including composition, agglomeration tendency, and particle size distribution, sintering methods and forming technique all have significant role in sintering behavior of materials [1–4]. Conditions such as time, temperature and atmosphere are crucial in a typical sintering procedure; hence, it has been investigated widely to optimize these parameters. To bring about a predictable situation for sintering behavior, final density and the domination of a special mechanism have been studied for decades. Computer simulations have been taken into consideration to provide predictable models for sintering stages [5,6]. These methods were not successful in as much as they just focused on one stage of sintering out of three stages, which were: (1) neck forms; (2) neck growth and make a continuous network of pores; (3) pore channels destroyed and grain coarsening happened. Master sintering curve (MSC) is one of the inspiring and useful approaches to predict and control sintering presented by Su and Johnson [7], based on the combined stage sintering model [8]. Description of sintering behavior for a given powder and prediction of microstructure evolution are possible by using the MSC theory [9–11]. In addition, sinter-ability of different powders also can be compared with the MSC [12]. In the MSC theory, two equal functions (Eq. (3)) are introduced: F(r), which is function of density (Eq. (1)) and Q(t,T(t)), which is as a function of temperature and time (Eq. (2)): FðrÞ¼ k gVD 0 Z r r 0 ðG ðrÞ Þ n 3rG ðrÞ (1) Qðt; T ðtÞÞ ¼ Z T 0 1 T exp Q RT   dt (2) FðrÞ¼ Qðt; T ðtÞÞ (3) where Q is apparent activation energy for sintering, R gas constant, T absolute temperature, t time, g specific surface energy, V atomic volume, k Boltzmann constant, G mean grain diameter, D 0 pre-exponential term for the diffusion coefficient, www.elsevier.com/locate/ceramint Available online at www.sciencedirect.com Ceramics International 37 (2011) 9–14 * Corresponding author. Tel.: +41 21 693 3389; fax: +41 21 693 4470. E-mail addresses: mehdi.mazaheri@epfl.ch, mmazaheri@gmail.com (M. Mazaheri). 0272-8842/$36.00 # 2010 Elsevier Ltd and Techna Group S.r.l. All rights reserved. doi:10.1016/j.ceramint.2010.07.027