However, the machining technologies aiming to achieve high shape accuracy and surface quality on PMAS are still restricted by its poor machinability and limited endeavours to survey. The spinel phase emerges at 450 °C and the perfect crystalline structure emerges at 600 °C. Magnesium aluminate (MgAl 2O 4) spinel (MAS) is a synthetic material with cubic crystal structure and excellent chemical, thermal, dielectric, mechanical and optical properties. Magnesium aluminate (MgAl 2 O 4) spinel (MAS) is a synthetic material with cubic crystal structure and excellent chemical, thermal, dielectric, mechanical and optical properties. However, because of the basic nature of the spinel surface, surface modification is essential and part of the study during aqueous slip or gel casting process. The particle surface is made up of laminated structure and it grows bigger with the increase of hydrothermal temperature and hydrothermal time. In this regard, further explorations of improving machining performance with advanced machining technologies and enhancing the machinability through optimising sintering strategies are expected in the outlook.The spinel sintering methods are systematically classified with its parameters governing the material properties outlined.Progression and advancements for PMAS are comprehensively reviewed from synthesis to machining in the processing chain.Current efforts to study the material removal mechanism and machining technologies of spinel are critically summarised.ScienceDirect ® is a registered trademark of Elsevier B.V.Unique mechanical properties and poor machinability of spinel brought by its intrinsic crystal structure are highlighted. The percent of MgAl2O4 spinel goes up with the increase of heat treatment temperature. The spinel has a large BET surface area and its special surface area diminishes continuously from 245.68 m2/g to 58.65 m2/g when the calcinating temperature increases from 500 °C to 1200 °C. It was synthesized using aluminum tri-sec-butoxide and magnesium nitrate hexahydrate as precursors, in an acid medium at 80 °C.
The fundamental material properties of PMAS including the crystal structure, mechanical properties and damage mechanisms are systematically discussed. Magnesium aluminate (MgAl2O4) spinel (MAS) is a synthetic material with cubic crystal structure and excellent chemical, thermal, dielectric, mechanical and optical properties. Transparent polycrystalline magnesium aluminate spinel (PMAS), owing to its high optical transparency with acceptable mechanical properties and chemical stabilities, exhibits great potential for optical applications under extreme environments and operating conditions. Xiaoyan Xiang, Wentang Xia and Wenqiang Yang, Effect of Compound Additives on Synthetic Magnesium Aluminate Spinel under Low Temperature, 7th International Symposium on High-Temperature Metallurgical Processing, 10.1007/978-3-319-48093-0_55, (443-451), (2016). These properties made MAS an indispensable material for optically transparent windows, domes and armours, and for certain refractory applications. The spinel has wormlike porous structures and these structures grow smaller and better distributed at Hexadecyl trimethyl ammonium Bromide (CTAB) condition. The sample also exhibited a marginally higher density and hardness in comparison to conventional SPS-processed samples and transmission of 81–85% in the 3–5 μm region.Linear shrinkage of the slip cast spinel specimens during sintering at heating rates of 5, 10, and 20 °C/minA schematic of hot isostatic pressingHIPed sample along with transmission patternThermal decomposition of ammonium carbonatesAll the specimens processed through different routes are designated as S-SHIP for spinel-sinter + HIP, S-SPS for spinel-spark plasma, S-FS for spinel-flash sintering, and S-FHIP for spinel-flash sintering + HIP. The first stage of preparing highly transparent PMAS is attainable with the rapidly maturing sintering technology. Transparent magnesium aluminate (MgAl2O4) spinel is a material of special interest due to its optical properties coupled with excellent mechanical properties. The magnesium aluminate spinel powders synthesized by hydrothermal process were characterized by scanning electron microscope, transmission electron microscope, X-ray diffraction and N2 adsorption-desorption isotherms. The green ceramic parts formed through these processes are exposed to sintering temperature which results in the densification and final components with desired properties. Synthesis of dense magnesium aluminate spinel using a single stage solid oxide reaction is difficult owing to volume expansion associated with spinel formation. Outlooks are outlined to improve the spinel processability in conjunction with its sintering strategy optimisation.Transparent polycrystalline magnesium aluminate spinel (PMAS), owing to its high optical transparency with acceptable mechanical properties and chemical stabilities, exhibits great potential for optical applications under extreme environments and operating conditions.