And Micro-Sized Mgal2o4 Spinel by Combustion Method
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Journal of Advanced Ceramics 2017, 6(3): 187–195 ISSN 2226-4108 https://doi.org/10.1007/s40145-017-0230-8 CN 10-1154/TQ Research Article Technical aspect for oxidation of magnesium and aluminum nitrates to manufacture nano- and micro-sized MgAl2O4 spinel by combustion method Shiva SALEM* Faculty of Chemical Engineering, Urmia University of Technology, 57166-17165, Urmia, Iran Received: March 09, 2017; Revised: April 19, 2017; Accepted: May 06, 2017 © The Author(s) 2017. This article is published with open access at Springerlink.com Abstract: In the present investigation, the nano- and micro-sized powders were synthesized by stoichiometric contents of magnesium and aluminum nitrates using combustion–oxidation method. The study was conducted over a wide range of operating conditions, in terms of fuel ratio and calcination temperature. The characteristics of magnesium aluminate powders were studied by differential thermal analysis and thermogravimetry (DTA–TG), Brunauer–Emmett–Teller (BET), X-ray diffraction (XRD), and transmission electron microscopy (TEM) techniques. The thermal stability of powders was evaluated by calcination at different temperatures. Differences of the specific surface areas were related to the composition and crystallite size. The importance of fuel ratio and calcination temperature to achieve the nano- and micro-sized oxide was discussed in detail. The fuel ratio of 0.56 and calcination at 800 ℃ provided the conditions to achieve the nano-scale magnesium aluminate powders, smaller than 20 nm. The application of presented algorithm can be an important tool for control of particle size in the nano- and micro-scale. Keywords: magnesium aluminate spinel; oxidation; nano-crystallite; combustion; calcination 1 Introduction (9106 (℃)1 between 30 and 1400 ℃), and high thermal shock resistance [1]. Several applications were Recently, magnesium aluminate (MgAl2O4), which is a reported for magnesium aluminate, and numerous ceramic composition, is employed at different technologies were developed for manufacturing spinel engineering fields. The important properties that make powders depending on application. The control of magnesium aluminate as a superior material are high particle size plays an important role in the application melting point (2135 ℃), relatively low density demand. The major applications of this composition can (3.58 g/cm3), excellent transmittance in the wavelength be summarized as: (i) catalyst support especially for of 0.25–5.0 m, high bending strength (180 MPa) and high temperature reactions [2,3]; (ii) fabrication of Vickers hardness (16 GPa), inertness in acidic refractory [4,5]; (iii) manufacture of optical devices and environments, low thermal expansion coefficient sensors [6,7]; (iv) advance applications such as electrochemical fields, dentistry, and reinforcing fibers [6]. * Corresponding author. MgAl2O4 is crystallized in the cubic form in which E-mail: [email protected] the oxygen atoms are arranged in a cubic close-packed www.springer.com/journal/40145 188 J Adv Ceram 2017, 6(3): 187–195 lattice [8]. Different techniques were developed for environmental risk due to generation of nontoxic gases. production of MgAl2O4 particles. High energy ball Glycine, which is one of the simple amino acids, is milling process is the oldest technology for the direct known to act as a complexing agent for a number of fabrication of magnesium aluminate spinel in the metal ions [30], because it contains a carboxylic acid micro-scale [9–12]. In general, the wet-chemical group at one end and amino group at the other end. process [6], precipitation method [13], sol–gel route Moreover, glycine molecules can effectively maintain [14–16], polymerized complex method [17], the compositional homogeneity among the microwave [18,19], and pyrolysis [20] techniques were constituents. reported as processes for the preparation of spinel. The calcination of precursor yields dense particles Depending upon the method used, particles with the with high crystallinity, while the initial powders contain various morphology, stoichiometry, and level of amorphous phase. On the other hand, the increment in crystallinity have been produced. These factors calcination temperature increases the rate of grain essentially affect the quality of final product through the growth and consequently affects the crystalline influence on the thermal behavior, mechanical structure of material. The morphology and particle size characteristics, and electrical and optical properties. of spinel should be considered in calcination of Although, the sol–gel method using polyvinyl precursor to achieve nano-sized particles. The alcohol for polymerizing was developed for the optimization of spinel preparation and calcination synthesis of high surface area MgAl2O4 spinel conditions promises the direction to obtain nano-sized precursors, this technique involved quite long particles. Although different fuels were employed for processing time. As the contrary solution, combustion production of MgAl2O4, the effect of fuel ratio on synthesis has emerged as a simple, fast, and crystallite size, morphology, and purity of product was economically viable procedure to prepare pure and not studied fundamentally. The compromise between nano-structured powders. This quick, straightforward fuel ratio and calcination temperature should be taken process can be used to synthesize homogeneous, into account in production of spinel. In this article, the high-purity crystalline powders including ultrafine effects of above factors on technical characteristics of particles with a broad range of particle size. In this powders were investigated to optimize the procedure technique, an aqueous solution containing the desired for achieving pure nano-sized particles. metal ions and a suitable fuel is prepared. A viscous gel is obtained during the heat treatment and exothermic reaction which take place rapidly, leading to formation 2 Experimental procedure of fluffy powders. The calcination of autoignition product increases the crystallinity of spinel. The 2. 1 Materials and powder preparation combustion technique is an inexpensive method that Magnesium nitrate, Mg(NO ) ·3H O, and aluminum allows the preparation of highly purified, nano-sized 3 2 2 nitrate, Al(NO ) ·9H O, both manufactured by crystalline powders at lower calcination temperatures in 3 3 2 Sigma-Adrich Company, were used as starting significantly shorter time [21–30]. materials. The purity of nitrate salts was above 99 wt%. Urea–formaldehyde [21], urea and Glycine, NH CH COOH (produced by the same triethylenetetramine mixture [22], sugar–urea [23], 2 2 company, 99.5 wt%), was applied as fuel. 61.2 g glycine [24], starch [25], alanine [14], citrate [26–28], magnesium nitrate and 227.2 g aluminum nitrate were and polyacrylamide [29] were used as fuels in the dissolved in 300 mL de-ionized water, and the molar combustion synthesis of nano-scale MgAl O powders. 2 4 ratio of Mg/Al was considered to be 0.50. Generally, in the combustion process, a thermally Mg(NO ) 3H O 2Al(NO ) 9H O induced redox reaction takes place between cations and 32 2 33 2 2+ 3+ fuel. The metal nitrates act as cation sources, whereas Mg Al 8NO32 21H O (1) organic compounds are employed as fuels. Although The lean and rich contents of glycine were MgAl2O4 spinel with high surface area was produced considered to evaluate the effect of fuel amount on at relatively low temperature by urea–formaldehyde, technical characteristics of final product. The the fuels like glycine and starch can be economically appropriate amounts of glycine were added to the applied for production of nano-sized spinel which is prepared solution for adjusting the fuel/NO3 molar ratio not only cost-effective, but it also reduces the at levels of 0.56 and 0.75, corresponding to 4.5 and 6.0 www.springer.com/journal/40145 J Adv Ceram 2017, 6(3): 187–195 189 moles of glycine, respectively. After stirring for 30 min 2. 2 Powder characterizations and considering the industrial feasible condition, the pH In order to investigate the effect of fuel ratio on thermal of solutions was controlled at level of 7.0 by slowly decomposition of viscous precursors, the dropping ammonia and continuously stirring by thermo-analytical measurements were carried out with magnetic mixer. The homogeneous solutions were simultaneous differential thermal analysis and heated at 110 ℃ on a hot plate to form viscous thermogravimetry (DTA–TG) instrument (Model 409, precursors. The temperature of the obtained precursors Netzsch, Germany). The heating rate was fixed at ℃ was raised to 300 by electrical furnace. The 10 ℃/min and air was used as purge gas. Approximate smoldering-type ignition causes the decomposition, 10 mg of each precursor was placed in a ceramic pan generating a large volume of gas. The combustion and the thermal treatment was performed from room occurs as flaming, gas phase reaction, or smoldering, temperature to 600 ℃. In order to better evaluate the solid–gas reaction. The flaming-type combustion can ignition of fuel after calcination, the residual hydrogen, endure for seconds or maximum 1 min, while the carbon, and nitrogen amounts were determined by smoldering type is extinguished in a few seconds. elemental analysis (Carlo Erba, Model EA 1110, Italy). During the smoldering-type combustion, the material The synthesized powders were characterized by underwent foaming followed by decomposition and it X-ray diffraction (XRD) technique (X’PERT PRO, lasted for almost 7 min, but in flaming-type