Magnesium oxide nanopowder is synthesized using magnesium nitrate hexahydrate and oxalic acid as precursors via the sol-gel method. In order to investigate the effect of magnesia nanopowders on the physical properties of sintered alumina, 0.1, 0.3, and 0.5 wt% of MgO are added to alumina. The prepared specimens were sintered at 1570°C for 4 hours under an inert atmosphere. The morphology and size of nanopowders were characterized by transmission electron microscope (TEM) and scanning electron microscope (SEM). Structural analysis was investigated by means of Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD). Outcomes show that by increasing the percentage of MgO, spinel phase (MgAl2O4) has been formed in the structure of alumina. During the sintering process, spinel phase diffused through the grain boundaries and pinned the grain boundaries which led to decrease in grain sizes. So, by decreasing the grain size, the physical properties of sintered alumina have improved. 1. Introduction α-Al2O3 has the highest hardness and density among aluminum oxides that is formed by heating of other polymorphs of alumina or alumina hydrate at a high temperature. Additionally, α-alumina can be produced by melting process of alumina hydrate at up to more than 2000°C and subsequently its cooling and crushing [1]. Regarding formation of particulate or whisker-reinforced composites with good thermomechanical properties, alumina is compatible with other ceramics such as ZrO2, mullite, cordierite, SiC, B4C, and Si3N4. Due to the above versatility of its nature, alumina and its composites include more than 70% of structural ceramics [2]. Another reason alumina is significant compared to other engineering oxide ceramics is due to a lower sintering temperature which makes it economical. In recent years, nanomaterials attract more attention in comparison with micron size materials due to a high surface area which leads to its specific properties. For instance, particles with nanodimension can increase strength, ductility, and formation of ceramics. Moreover, nanoparticles are used for producing transparent coats. Nanoalumina powders are also applied to the production of ceramic parts with hardness and wear resistance as well as raw materials in the catalyst industry [3, 4]. Furthermore, alumina nanosize with regard to micron size alumina can reach a higher density at lower temperature; hence it is utilized as a raw material in the generation of alumina ceramic bodies. There are different methods to synthesize nanomaterials including mechanical alloying
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