Study On The Preparation MgAl₂O₄ Nanoparticles By Sol-gel Self-combustion Method And Their Optical Properties

Wide band gap oxide nanopowder material has the characteristics of high temperature resistance,corrosion resistance and high whiteness.As the main component of high reflectivity thermal control coating,it has important applications in aerospace,transparent ceramics,energy saving buildings,petrochemical industry and other fields.Common highly reflective oxide materials include Ti O₂,Al₂O₃,Ba SO₄,Mg Al₂O₄,etc.Among them,cubic spinel Mg Al₂O₄nanopowder has the characteristics of stable structure,strong radiation resistance and high reflectivity,which has become one of the hot spots in the research field of thermal control powder materials.At present,the preparation methods of Mg Al₂O₄ powder mainly include solid-state sintering and sol-gel method,but its application is limited due to the low purity and high energy consumption of the product,which affects the reflection performance.Therefore,it is necessary to study the preparation technology and its influence on defects in powder.In this paper,magnesium aluminate nanopowder with high reflectivity（ultraviolet near infrared）was prepared by sol-gel self-combustion method.The effects of sintering temperature,grinding time,Mg/Al atomic ratio and Gd³⁺doping on the microstructure,defect properties,photoluminescence and light reflectivity of Mg Al₂O₄ nano-powder were studied,which is of great significance to improve the reflectivity of Mg Al₂O₄ nanopowder and expand its application scope owner.（1）Preparation of Mg Al₂O₄ nanopowder and its physical properties by sol-gel self-combustion method.Firstly,the process conditions of preparing Mg Al₂O₄ nanoparticles by sol-gel self combustion method were studied,and the self combustion reaction pro cess was quantitatively studied by thermogravimetric differential thermal characterizatio n method.By adjusting sintering temperature（800-1400℃）and milling time（0.5-2 h）,the structure and optical properties of Mg Al₂O₄ nanopowder were optimized.It was fou nd that the reflectance of the powder increased with the increase of sintering temperat ure,and the increase of milling time also enhanced the reflectance of Mg Al₂O₄ nanop owder.After calcination at 1400℃for 4 h and ballmilling for 1.5 h,spherical nanopar ticles with an average reflectance of more than 80%in the range of 200-2600 nm w ere obtained.（2）Studied the control of Mg/Al composition on the structure of Mg Al₂O₄ nanopowder and its optical properties.Mg Al₂O₄/Al₂O₃ composite nanopowders were prepared by adjusting the Mg/Al atomic ratio in the precursor.The law of change of powder reflectance with Mg/Al atomic ratio was studied by diffuse reflectance and photoluminescence spectroscopy.It was found that the reflectance of nanopowders gradually increased with the increase of Al atomic ratio,and the luminous intensity of defect states gradually increased XRD and TEM confirmed that when the Mg/Al atomic ratio was 1:4,the interface of the formed Mg Al₂O₄/Al₂O₃composite core-shell structure had a scattering enhancement effect,which significantly enhanced the full-band reflectivity.（3）Prepared Mg Al₂O₄:Gd nanopowder by sol-gel self combustion method and researched its optical properties;Mg Al₂O₄:Gd nanopowders were prepared by adding Gd（NO₃）₃·6H₂O to the reaction precursor,and the doping concentration of Gd³⁺was adjusted（0.1%-0.7%）;researched the law of change of the reflectance of Mg Al₂O₄:Gd nanopowder with doping concentration.The UV-VIS-NIR characterization found that the reflectance increased first and then decreased with the increase of doping concentration.Compared with the undoped sample,the reflectance of that with 0.3%doping concentration in the ultraviolet visible band increased by more than 20%,and the near-infrared band increased by 10%.Photoluminescence spectroscopy（PL）confirmed that Gd³⁺doping could adjust the reflectivity of the powder by controlling the concentration of defect states.