Synthesis of a magnesium aluminum spinel by the burning method

Abstract

Synthesis of MgAl 2 O 4 from a stoichiometric mixture of aluminum and magnesium nitrates by its burning with urea, glycine, sugar, and mixtures of these as a fuel was studied.A transparent ceramic based on MgAl 2 O 4 is a good alternative to the expensive and diffi cultly reproducible single-crystal MgAl 2 O 4 spinel. Optical applications of the transparent ceramic includes IR windows and inert laser shutters [1]. It is known that good properties of a ceramic result from the adequate choice of synthesis method and sintering conditions, being also determined by favorable properties of the starting powder. It is impossible to obtain a good, homogeneous, pore-free ceramic suitable for optical applications without using a highly active, pure, and unagglomerated powder.It was shown in [2, 3] that the burning method is promising for production of highly pure homogeneous crystalline powders of the aluminomagnesium spinel at comparatively low temperatures with lower energy expenditure. In addition, powders produced by this method retain their nanostructure even upon sintering, which is highly important for fabrication of superelastic materials.A study of MgAl 2 O 4 synthesis in an electric furnace at 500°C in the course of 5 min with urea [2] demonstrated that parameters of the powder synthesized depend on the charge of the starting substances. For example, with the mass of the fi nal product raised from 2 to 100 g, the specifi c surface area of the powder decreases from 126 to 8.1 m 2 g -1 . This can be attributed to the high adiabatic temperature generated as a result of increasing accumulation of heat at larger single-portion charges.The goal of our study was to obtain Mg Al 2 O 4 by the burning method. EXPERIMENTALAs starting materials served magnesium nitrite Mg(NO 3 ) 2 ·6H 2 O, aluminum nitrite Al(NO 3 ) 3 ·9H 2 O, urea, glycine (all of analytically pure grade), and sugar. A mixture of the starting components to obtain 5-10 g of MgAl 2 O 4 was prepared by mixing of stoichiometric amounts of Al(NO 3 ) 3 ·9H2O and Mg(NO 3 ) 2 ·6H 2 O and a prescribed amount of the fuel in a Tefal household blender. The mixture was thermally treated in singleor double-stage modes: (1) by calcination in alundum crucibles in a muffl e furnace heated at a rate of 15 deg min -1 to 800°C in the course of 1 h and (2) by preliminary drying in glass vessels in a drying box at 300°C for 1 h, mixing in a blender, and calcination in a muffl e furnace under the same conditions.The phase composition of the powders was determined by X-ray phase analysis on a DRON-12 diffractometer (Cu Kα radiation and graphite monochromator), with a counter motion rate of 2 deg min -1 . The phases were identifi ed using the JCPDS database. The specifi c surface area of MgAl 2 O 4 powder samples was determined by the method of thermal desorption of nitrogen on a FlowSorb II 2300 laboratory electronic specifi c-surface-area and porosity meter. The average crystallite size was calculated by the Debye-Scherrer formula d = 0.94λ/ βcos θ, where λ for Cu K is 0.15406 nm;...

Effect of glycine–starch mixing ratio on the structural characteristics of MgAl2O4 nano-particles synthesized by sol–gel combustion

“…A thermally induced redox reaction occurs between an oxidant and fuel. Nitrate salts typically act as oxidants and cation sources, and organic compositions as fuels (Gromov, Tikhomirova, Lokshin, & Kalinnikov, 2012;Ianos & Lazau, 2009;Prabhakaran, Patil, Dayal, Gokhale, & Sharma, 2009). …”

“…Urea, sugar, and their mixtures are suitable fuels for preparing MAS from a stoichiometric mixture of aluminum and magnesium nitrates. Phase-pure MAS powder of crystallite size of 18.4 nm has been formed using sugar-urea as a fuel (Gromov et al, 2012).…”

Technical aspect for oxidation of magnesium and aluminum nitrates to manufacture nano- and micro-sized MgAl2O4 spinel by combustion method

“…The calcination of autoignition product increases the crystallinity of spinel. The combustion technique is an inexpensive method that allows the preparation of highly purified, nano-sized crystalline powders at lower calcination temperatures in significantly shorter time [21][22][23][24][25][26][27][28][29][30].…”

“…Urea-formaldehyde [21], urea and triethylenetetramine mixture [22], sugar-urea [23], glycine [24], starch [25], alanine [14], citrate [26][27][28], and polyacrylamide [29] were used as fuels in the combustion synthesis of nano-scale MgAl 2 O 4 powders. Generally, in the combustion process, a thermally induced redox reaction takes place between cations and fuel.…”

Application of autoignition technique for synthesis of magnesium aluminate spinel in nano scale: Influence of starting solution pH on physico-chemical characteristics of particles

“…It was demonstrated that urea, glycine, sugar, and mixtures of these materials are suitable fuels for synthesis of MAS from a stoichiometric mixture of aluminum and magnesium nitrates by the autoignition method. The single-phase MAS powder with crystallite size of 18.4 nm was obtained when sugar-urea was used as a fuel [24]. Nano-scale powders were successfully synthesized via combustion process using various mixtures of urea, glycine and starch.…”