THE EFFECT OF Mg-Al Wt% FOR PHASE FORMATION OF SPINEL MgAl2O4 PRODUCED BY METAL DISSOLVED METHOD

<p class="Abstract">Synthesis of magnesium aluminate spinel powder (MgAl₂O₄, abbreviated as MA) were prepared by the liquid mixing method. The synthesis of MA involved Mg powders with various weight compositions (4.8; 10; 20; 30; 40; and 60%) and Al powders (95.2; 90; 80; 70; 60 and 40%) as the raw materials, which were independently dissolved in 37% HCl to form MgCl₂ and AlCl₃ solutions. Both solutions were then mixed and stirred for 5 hours and dried to a temperature of about 100-105°C to produce powders with different weight compositions. Each powder resulted from drying was characterized using DTA-TGA, and then calcined at 650 °C; 750 °C and 850 °C for 1 hour. The calcined powder was characterized by XRD to qualitative and quantitative analyses using Rietica. It was found that MA samples contained only MgAl₂O₄ and MgO as the impurity phase. The relative weight fraction of MgAl₂O₄ increased up to 99% for 95.2 wt% Al. Using an extrapolative approach to determine the Mg-to-Al composition, nearly pure MA, as high as 99%, was achieved at 95.2% Al and 4.8% Mg.</p>

Structure and Electrochemical Properties of Li4Ti5O12 Prepared via Low-Temperature Precipitation

This work aimed to prepare the spinel phase Li4Ti5O12 by a combination of the low-temperature precipitation technique and assisted calcination step. X-ray diffraction (XRD) revealed that the intermediated phase was Li2TiO3, and the spinel phase could be evidently formed at 700°C for 12 to 20 hours. The morphology of spinel powder, determined by SEM and TEM, exhibited a good distribution at the submicrometric scale that promoted a fast kinetic of Li migration and an excellent performance at the high-rate cycling test. The stable performances were achieved in the charge-discharge test at different current densities: 80 mA/g (165 mAh/g), 320 mA (160 mAh/g), and 1600 mA (145 mAh/g) upon 100 cycles. Moreover, we observe a capacity retention of 48% (corresponding 80 mA/g) at a high rate of 5000 mAh/g. The cyclic voltammetry measurement displayed a reversible system and revealed the lithium diffusion coefficient of 1.15 × 10−11 cm2/s.

Preparation of High-Purity Magnesium Aluminate Spinel Powder by Thermal Decomposition Method

A precursor was obtained after dissolution, drying and cooling using MgSO4·7H2O and NH4Al (SO4)2·12H2O as raw materials. Then the high-purity magnesium aluminate (MgAl2O4) spinel powder was synthesized via the thermal decomposition process of the precursor calcined at different temperatures. The phase, morphology and particle size of the powder obtained at different calcining temperatures were characterized by X-ray diffraction, scanning electron microscopy and laser particle size analyzer. And also the purity of the powder was tested by inductively coupled plasma-atomic emission spectrometry (ICP-AES). The results show that the powder exhibits better crystalline shape and bigger crystalline size with the calcining temperature increasing. The calculated grain size is below 30 nm according to Scherrer formula. The particle size of the powder is below 35μm, the particle size distribution is relatively wide and some particles reunite to be bigger ones with the calcining temperature rising. The powder appears to be plate-shaped and the morphology of the grain is irregular particle. The purity of the powder is relatively high. Especially, the purity of the powder obtained at 1150 °C is 98.88%.

Homogeneous Precipitation Synthesis and Sintering of Magnesium Aluminate Spinel Nanoparticles

A wide application of magnesium aluminate spinel powder has attracted a number of studies concerning the preparation of magnesium aluminate spinel powder. In this study, a precursor for magnesium aluminate spinel was synthesized by a homogeneous precipitation method using urea as a precipitant. The precursor and the calcined powders were characterized by X-ray diffractometry, Fourier transform infrared spectroscopy, scanning electron microscopy, and transmission electron microscopy. After precipitation, the precursor was magnesium aluminium hydrate carbonate compound. By calcining, the precursor decomposed to MgO and an amorphous phase after calcining at 600°C. The formation of magnesium aluminate spinel via a reaction between MgO and the amorphous phase was observed after calcining over 800°C. The equiaxed magnesium aluminate spinel nanoparticles with particle size of 20-40 nm were obtained after calcining at 1100°C for 2 hours. Sinterability of the obtained magnesium aluminate spinel nanoparticles was also investigated by sintering compacts of magnesium aluminate spinel nanoparticles in the temperature interval of 1300-1650°C. Sintering temperature of 1600°C allowed the fabrication of dense magnesium aluminate spinel ceramics with relative density >95%.