Papers by Author: Rahim Naghizadeh

Abstract: Hematite widely used since ancient times as a pigment but its chemical and thermal stability at high temperatures application is not enough. In this study, hematite nanoparticles were included into the zircon matrix and its stability was increased. Fe₂O₃ ZrSiO₄ nanocomposite with Fe/Zr molar ratio of 5 to 30% was synthesized from Si and Zr alkoxides by sol-gel method. The products of the solgel method were calcined in the 1200°C /2.5 h. The structural and morphological characteristics of nanocomposite are determined by X-ray diffraction (XRD), simultaneous thermal analysis (STA) and scanning electron microscopy (SEM) investigations. The results indicate that formation of zircon promoted with iron addition. Finally, colorimetric parameters of the glazed ceramic samples were measured by the CIE colorimetric method. It was found that the samples withe 20% molar Fe has the highest red shade and is the best color according to the a* parameter.

Abstract: Aluminum titanate (Al2TiO5) is an engineering ceramic with low thermal expansion coefficient, excellent thermal shock resistance, good refractoriness and non-wetting with most metals. In this work the use of colloidal silica and nano boehmite mixture in proper stoichiometry of mullite in aluminum-titanate (tialite) has been studied. Analytical structural evaluations including XRD, TEM and SEM have been used to characterize the influence of these additives on phase transformation, sintering process and microstructure. The results show that the presence of nano size silica and boehmite enhanced the densification leads to fine microstructure, mullite phase formation and improve the tialite ceramics properties.

Abstract: Full formation of aluminum titanate compound at low temperatures was obtained by solgel method. With addition of various amount of Fe2O3 additive to tialite composition formation and decomposition of tialite phase have been investigated. X-ray diffraction (XRD), simultaneous thermal analysis (STA) and scanning electron microscopy (SEM) analysis showed that the formation of nano tialite at low temperatures (around 950oC) was improved at the presence of additive and decomposition rate of aluminum titanate to α-Al2O3 and TiO2 (Rutile) in sample with 5%wt Fe2O3 was controlled with formation of Al2TiO5-Fe2TiO5 solid solution.

Abstract: The formation of in-situ spinel in Al2O3-MgO-C refractories along with different antioxidants occurs at different atmospheres in surface and inner of refractories. Then the types and microstructures of established phases have become increasingly important in these refractories. In the present work, reactions on firing Al2O3-MgO samples with added graphite, Al, Si and SiC in air or coke bed atmosphere at 1300°C and 1600°C have been studied. The results showed that with the addition of graphite and Al especially at 1600°C in coke bed, high alumina-rich spinel (Mg0.866Al1.83O3.611) was increased and in the microstructure were appeared high amount porosity. In silicon and silicon carbide additive samples after firing at 1600°C in coke bed, sapphirine phase were revealed.

Abstract: Aluminum-titanate (tialite) based ceramics have found widespread applications due to their good thermal shock resistance and low thermal expansion. Tialite is presently used in automotive industry, thermal processing technology, metallurgy and glass industry. Eutectoid decomposition in to the initial oxides and low mechanical strength limit the well-known properties of aluminum-titanate. In the present work, good stabilizing behavior was achieved by addition of talc in micron size and appropriates properties were obtained by adding nano boehmite and colloidal silica that results mullite phase formation. The effect of mullite phase in the densification of tialite has been studied. XRD, DTA and SEM have been used to characterize the influence of these additives on phase transformation, sintering process and microstructure.