The influence of nano boehmite on spinel formation in the alumina-magnesia system at low temperatures

H. R. Zargar,F. Golestani Fard,H. R. Rezaie 한양대학교 세라믹연구소 2008 Journal of Ceramic Processing Research Vol.9 No.1

The effect of nano boehmite on the formation of spinel at low temperatures (T<1000oC) in the alumina-magnesia system via a solid-state route is investigated. The homogeneity of prepared mixtures was studied carefully by X-ray diffraction, FTIR1 and SEM/EDX. This clarified that the formation of spinel was encouraged in the presence of nano boehmite. It was also found that the primary spinel formed via a solid-state reaction was in the nano size range and possessed a cubic morphology. The importance of the present study is explained with an emphasis on refractory applications. The effect of nano boehmite on the formation of spinel at low temperatures (T<1000oC) in the alumina-magnesia system via a solid-state route is investigated. The homogeneity of prepared mixtures was studied carefully by X-ray diffraction, FTIR1 and SEM/EDX. This clarified that the formation of spinel was encouraged in the presence of nano boehmite. It was also found that the primary spinel formed via a solid-state reaction was in the nano size range and possessed a cubic morphology. The importance of the present study is explained with an emphasis on refractory applications.

Phase and microstructural evolution of high TiO₂-containing Iranian bauxite at high temperatures in different atmospheres

R. Naghizadeh,H. R. Rezaie,F. Golestani-fard 한양대학교 세라믹연구소 2008 Journal of Ceramic Processing Research Vol.9 No.4

Calcined bauxite is one of the components of alumina-magnesia-carbon refractories for steelmaking applications when in these refractories two types atmosphere at the surface and inside of the refractories exist in service conditions. In this study, Iranian bauxite powders were pressed with and without graphite additions, fired at 1300 oC and 1600 oC in air or reducing atmospheres. The phase evolution of samples was investigated using X-ray diffraction. It was shown that the samples fired at 1600 oC in an air atmosphere, contain corundum, 3 : 2 mullite, tialite, rutile and in a reducing atmosphere corundum, alumina-rich mullite (Al1.7Si0.15O2.85), rutile and a reduced form of titanium oxide (Ti2O3) and titanium nitride (TiN) were present. For an explanation of alteration the 3 : 2 mullite to alumina-rich mullite and decomposition of tialite into the parent oxides, the microstructures of samples fired at 1600 oC were investigated. Also the effect of a reducing atmosphere at high temperatures on high purity TiO2 and a mixture of high purity TiO2 plus Al2O3 in the stoichiometric ratio of tialite were inspected. From these results, a new explanation for the mechanism of the alteration 3 : 2 mullite to alumina-rich type and decomposition of tialite were established. Calcined bauxite is one of the components of alumina-magnesia-carbon refractories for steelmaking applications when in these refractories two types atmosphere at the surface and inside of the refractories exist in service conditions. In this study, Iranian bauxite powders were pressed with and without graphite additions, fired at 1300 oC and 1600 oC in air or reducing atmospheres. The phase evolution of samples was investigated using X-ray diffraction. It was shown that the samples fired at 1600 oC in an air atmosphere, contain corundum, 3 : 2 mullite, tialite, rutile and in a reducing atmosphere corundum, alumina-rich mullite (Al1.7Si0.15O2.85), rutile and a reduced form of titanium oxide (Ti2O3) and titanium nitride (TiN) were present. For an explanation of alteration the 3 : 2 mullite to alumina-rich mullite and decomposition of tialite into the parent oxides, the microstructures of samples fired at 1600 oC were investigated. Also the effect of a reducing atmosphere at high temperatures on high purity TiO2 and a mixture of high purity TiO2 plus Al2O3 in the stoichiometric ratio of tialite were inspected. From these results, a new explanation for the mechanism of the alteration 3 : 2 mullite to alumina-rich type and decomposition of tialite were established.

An evaluation on sol-gel chemical processing of refractory barium hexa aluminate fibrous structures

H.R. Rezaie,R. Naghizadeh,F. Arianpour,R. Ghasemzadeh,S. Eslami 한양대학교 세라믹연구소 2009 Journal of Ceramic Processing Research Vol.10 No.2

In this research barium hexa aluminate fibrous refractory products were produced by a chemical processing route. Boehmite was used as aluminum precursor while barium nitrate was used as barium precursor and the final solution had made according to stoichiometric BaO.6Al2O3 composition. It was found that two different gels could be obtained during this route. Mainly the secondary gel was trapped into the initial gel structure. Finally gels were heated at various temperatures (1350, 1650℃) to following the formation of the barium hexa aluminate in fibrous structure due to sintering. Then the crystallization of transitional phases such as 3BaO.Al2O3 and BaO.Al2O3 to BaO.6Al2O3 were followed at different sintering temperatures by X-ray diffractometry (XRD) and Fourier transform infrared (FTIR) spectroscopy. Also scanning electron microscopy (SEM) was used to study the microstructural changes and micrographies. The produced gels were characterized by thermo gravimetrical and differential thermal analysis (TG/DTA). The results showed that BaO.6Al2O3 was the major phase at higher temperatures and fibrous structure appeared in final samples. In this research barium hexa aluminate fibrous refractory products were produced by a chemical processing route. Boehmite was used as aluminum precursor while barium nitrate was used as barium precursor and the final solution had made according to stoichiometric BaO.6Al2O3 composition. It was found that two different gels could be obtained during this route. Mainly the secondary gel was trapped into the initial gel structure. Finally gels were heated at various temperatures (1350, 1650℃) to following the formation of the barium hexa aluminate in fibrous structure due to sintering. Then the crystallization of transitional phases such as 3BaO.Al2O3 and BaO.Al2O3 to BaO.6Al2O3 were followed at different sintering temperatures by X-ray diffractometry (XRD) and Fourier transform infrared (FTIR) spectroscopy. Also scanning electron microscopy (SEM) was used to study the microstructural changes and micrographies. The produced gels were characterized by thermo gravimetrical and differential thermal analysis (TG/DTA). The results showed that BaO.6Al2O3 was the major phase at higher temperatures and fibrous structure appeared in final samples.

Investigation of the formation of different phases in a frittic glaze at different temperatures and pressures

Z. Mahmoudi,H.R. Rezaie,H. Ghassai 한양대학교 세라믹연구소 2011 Journal of Ceramic Processing Research Vol.12 No.6

In this research, the influence of temperature and pressure on the phases formed in a defined glaze are investigated, so an initial batch including silicate, soda, calcium carbonate and boric acid with a defined seger formulation was prepared, and then it was divided into several samples. Some samples were fired at different temperatures and some of them were autoclaved at different pressures. Then the formation of different phases was investigated by X-ray diffraction. Also the microstructure of the samples was observed by scanning electron microscopy. The X-ray diffraction results showed that different phases were formed during firing and autoclaving where the firing process influenced the behavior of the solubility of the materials.

Investigation of the percentage crystallization in glass ceramics using an image analyzer method

S. Mahdavi,V. Madahi,M. Samedani,H.R. Rezaie 한양대학교 세라믹연구소 2011 Journal of Ceramic Processing Research Vol.12 No.1

Glass-ceramics are normally obtained by a controlled crystallization process of suitable glasses. Properties of glass-ceramics are affected by the amount of crystalline phases. In this paper, a new, fast, and simple method is investigated to measure the percentage crystallization in glass-ceramic samples. The most common method for measuring the percentage of crystalline phases is investigation of XRD patterns, but in this new method, image analysis (IA) is used for this purpose. Thus, SEM images of two cordierite-based glass-ceramics were investigated by image analyzer software and the variation in crystallization,which were obtained by two methods, were compared. A good correspondence between the results of the XRD patterns and SEM image analysis was achieved, and the difference between the results of these two methods was about 2%. Finally, it was shown that image analysis can be used to measure the percentage of crystalline phases in glass-ceramics with good accuracy.