Preparation Of Transparent Y₂O₃-MgO Nanocomposite For Ceramic Window Applications

Infrared window materials that applied to infrared guidance mostly use ceramics such as MgF2,ZnS etc.or sapphire single crystal at present.As the optical window of high-speed aircraft,those materials have a poor mechanical strength and thermal performance,that they can not meet the material requirements of infrared detection window.The window is easy to crack because of aerodynamic forces and thermal stress during high-speed flight.Because of the aerodynamic heat,materials have a high background radiation which will hinder the detection accuracy.On the other hand,Y2O3-MgO nanocomposite ceramic has an excellent infrared transmission,high temperature mechanical properties,thermal shock resistance and extremely low thermal emissivity.Therefore,it become the best candidate for future infrared detection windows of high-speed aircraft.In this paper,Y2O3-MgO nanocomposite powder was prepared by sol-gel method.The optimum calcination process of xerogel was studied.The precursor xerogel foam was calcined at 500℃ for 10 hours.After ball-milling,drying and sieving,the porous foam-like high activity nanocomposite powder was obtained.The powder has a fine crystalline size(～9 nm),high BET surface area(110 m2/g),light aggregation and good dispersion.In addition,the experiment results proved that adding the ammonium nitrate solution in the sol-gel reaction can improve phase distribution in powder.And then the phase distribution and phase size samples were optimized in the hot-pressed sinteringThe better fluidity powder which can be directly applied to hot-pressing sintering without forming was prepared at 200 MPa isostatic pressing followed by grinding and sieving.A diameter of 30 mm and thickness of 5 mm nanocomposite ceramic was prepared by HP sintering at 1375℃ for 30 minutes.The near completely compact ceramic has an average grain size of 200 nm.After being grinded and polished,the 2.5 mm thick sample has an 80%transmittance in the mid-infrared wave band.The infrared transmittance of the ceramics prepared by powder after isostatic pressing or green-body after molding is not much difference.There are no significant difference in transmittance and average grain size between the ceramic prepared by iso static pressed powder and the ceramic prepared by molding green body.As a comparison,the ceramic prepared by original powder is not densified completely in the same sintering conditions.The large quantities Y2O3-MgO nanocomposite powder with fine grain size,uniform phase distribution and good sintering activity was prepared through the large volume oil-bath reactor.The dome-shaped green body was consolidated in stainless steel mold at 80 MPa using the original powder.The dome-shaped Y2O3-MgO nanocomposite ceramic with a size of Φ72 mm×5 mm was fabricated at 1375℃ and 45 MPa by HP sintering.The completely compact center of dome-shaped ceramic,with a～160 nm average grain size,has a transmittance up to 80%(thickness of 3 mm).But the homogeneity of each part of ball-shaped ceramic still needs to be improved.