Growth Of Mg-Al Spinel Film On Sapphire Surface For Strengthening

Sapphire is one of the best infrared windows and domes materials used for 3~5μm mid-wave infrared waveband because of its excellent opticial and mechanical properties. However, the strength of sapphire decreases rapidly at elevated temperature and it can not satisfy the demand of applications on the high mach number missile.The most efficient way to solve the puzzle is to grow MgAl2O4 films on sapphire, and precipitate nano particles of Mg-Al spinel on sapphire matrix through high-temperature diffusion and quenching technology to meet its demand for high-speed and high temperature environment. MgAl2O4 films have excellent physical and chemical properties, and also have similar optical properties of sapphire crystal and quartz glass, which have good transmittance from the UV to the infrared wave band(0.2-6.5μm). And spinel structure has a special reaction mechanisms with alumina substrate. All of these characteristics make MgAl2O4 film is appropriate to enhance sapphire high temperature property. Now both the foreign and domestic have researched to enhance sapphire crystal high temperature strength using magnesium ion doping and magnesium ion implantation, but the study of MgAl2O4 nano particles precipitation to enhance sapphire high temperature strength in this area has not been reported. This paper investigated Mg-Al spinel thin film preparation technology and its microstructure.The precipitation process of MgAl2O4 nanoparticles by quenching is also discussed .By optimizing continually the experimental parameters of the sol-gel and the magnetron sputtering method, the MgO films and Mg films were prepared independently.The MgO films prepared by the sol-gel method are analyzed by XRD, XPS and SEM, which show that the MgO film remain amorphous structure after 800℃heat treatment, and the MgO films distribute densely and uniformly on the sapphire crystal surface.The Mg films prepared by the magnetron sputtering method are analyzed by XRD and SEM, which show that the Mg film deposition process have a high degree of crystallography orientation. The MgO films and the Mg films samples after annealing process are analyzed, the general rule is that the single crystal MgAl2O4 epitaxial films have grown on the sapphire crystal surface , and there are the rules of the equilateral triangle layered lines formed on the spinel surface.The Mg films samples after quenching process are analyzed, there are dispersive precipiting nano particles of Mg-Al spinel in sapphire matrix, these particles are strip, and distribute along the particular direction.The infrared transmittance of the coated and uncoated MgAl2O4 films sapphires are measured, which show that the infrared transmittance of the sapphires coated MgAl2O4 films have somewhat decreased, and the absorption edge has a"blue shift".