Study On Fabrication Of MgO·nAl₂O₃（n=1²） Transparent Ceramics

MgO·nAl₂O₃ transparent ceramic material is a typical integration of structure and fuctional material with excellent optical performance,high mechanical strength and hardness,low dielectric constant and dielectric loss,good thermal stability and resistance.MgO·nAl₂O₃ transparent ceramic can be widely applied in transparent armor,infrared dome,high temperature windows,optical lens etc.In this study,pure MgO·nAl₂O₃ ceramic powders,which have uniform and fine particle size,were synthesized through the solid-state reaction.A two-step structural refinement procedure,including XRD Rietveld analysis by Fullprof software and further refinement by spinel solid solutions structure modeling program SIDR,was utilized to resolve the crystal structure of synthesized powders.Using the synthesized MgO·nAl₂O₃ ceramic powders,high performance transparent ceramic was fabricated by pressureless sintering and subsequent hot isostatic pressing sintering（HIP）.Solid reaction process was employed to prepare high purity fine-grained and homogeneous dispersed MgO·nAl₂O₃ powders of different composition,which can meet requirements for preparation of transparent ceramics.The crystal structure was determined by XRD Rietveld and analysis structure modeling program SIDR.The refinement results showed that the lattice parameters and anion location parameters decreases with the n increasing.Pressureless presintering under N₂ atmosphere and subsequent hot isostatic pressing sintering were adopted to prepare the MgO·nAl₂O₃ transparent ceramic.The samples were presintered under N₂ atmosphere at 1650℃and then subjected to180MPa argon at 1800℃for 5h to reach full density.The max in-line transmittance of sample n=1.5 in visible range reached as high as 60%,while the sample n=1 and n=1.25 showed lower optical performance.Better optical properties of transparent ceramics were achieved by optimizing the presintering temperature and atmosphere.The samples n=1.8 presintered under N₂ atmosphere at 1825℃demonstrated excellent optical properties,which showed the maximum transmittance 80%from the ultraviolet to middle-infrared wavelengths.While the sample n=1.5 also showed good optical properties with the maximum transmittance 65%in visible and 80%in infrared region,respectively.The material also exhibited good mechanical properties of Vickers hardness（12.75±0.12 GPa）and Young’s modulus（277 GPa）.