Sh. Masoumi, Hosein Sarpoolaky, B. Eftekhari Yekta , M. Soltanieh,
Volume 33, Issue 2 (3-2015)
Abstract
Hercynite, FeAl2O4, was synthesized via molten salt synthesis method in the coke bed at 800°C with 3h of holding time. It was synthesized by reacting stoichiometric compositions of Al2O3 and FeCl2.4H2O in eutectic compositions of alkaline chlorides NaCl-KCl-LiCl. The reactant to salt ratio was 1 to 3. The phase formation, and morphology of these synthesized powders after washing and filtration were characterized via X-ray diffraction (XRD), and scanning electron microscopy (SEM). Differential thermal analysis (DTA) and thermogravimetric analysis (TGA) were performed at temperatures up to 1000 °C at a heating rate of 10 °C/min in argon atmosphere, to elucidate the different reaction mechanisms in the synthesis of Hercynite by the molten-salt method. The effects of processing parameters including the temperature and holding time on the formation of FeAl2O4 were investigated. The results demonstrated that the formation of FeAl2O4 spinel could be initiated at 700°C. By increasing the temperature to 900 °C and holding time, the amounts of FeAl2O4 particles in the resulting powder increased at
the expense of Hematite and Al2O3. Morphology of the synthesized powder was cubic and tetragonal, increased by increasing the holding time and temperature.
H. Ahmadi, S. Otroj, M. R. Nilforushan, A. Dehghani Varnamkhasti,
Volume 36, Issue 2 (9-2017)
Abstract
In this study, the composition of magnesium aluminate spinle and the converter mud were used as raw materials to in-situ formation of hercynite phase in magnesite-hercynite refractory bricks. The pressed samples were sintered at 1400 and 1500℃ and then, the phase composition of bricks was evaluated after firing at 1400℃. Besides, the effect of nano-magnesia particles addition on the properties of magnesia-hercynite refractory bricks was examined. Hence, the physical peroperties, thermal shock resistance and microstructure of refractory bricks were evaluated. The phase composition results showed that hercynite is well-formed in the refractory matrix, which leads to bonding formation and its increase between magnesia particles. The evaluation of results indicated that the addition of nano-magnesia particles can reduce the porosity of brick via increasing particles packing. In this relation, 1 wt. % nano-magnesia addition was determined as optimum content. Further addition of nano-magnesia leads to increasing of porosity via agglomeration of particles. Due to the high surface area of used nano-magnesia particles, the adequate sintering of refractory brick containing nano-magnesia take places at 1400℃. This leads to increasing of particles bonding and then, increasing mechanical strength, but it can not affect the thermal shock resistance of refractory bricks. The microstructural evaluations showed the lower porosity and further particles bonding with addition of nano-magnesia optimum content.
