Study On Preparation And Properties Of MgF₂Infrared Transparent Ceramics

As a kind of MWIR window/fairing materials used very maturely,hot-pressingmagnesium fluoride is still applied most widely, but the limitation on the aspects suchas hardness,thermal shock resistance also confines its application in the high-speedflight environment.Infrared transparent ceramic is a sort of newly developed infraredoptical materials.Due to its high density, wide transmission band range, high hardness,high temperature resistance, infrared transparent ceramic has wide use in the field ofinfrared imaging guidance technology.This study intends to substitute magnesiumfluoride infrared transparent ceramic prepared using hot-pressing sintering technologyfor hot-pressing polycrystalline magnesium fluoride. It can guarantee high opticaltransmission of magnesium fluoride materials, and improve its hardness and thermalshock performance at the same time, so as to further broaden its application domain.To a large extent, the ceramic materials’ microstructure depends on the performanceof the precursor powder, therefore, it’s a key to synthesize precursor powder withexcellent performance for preparing high quality ceramic materials. The magnesiumfluoride powders were firstly synthesized and the influences of different reactionconditions and rare earth doping on their microstructure were studied systematically.Then MgF2infrared transparent ceramics were prepared by hot-pressing sintering, theinfluences of process parameters on the ceramic microstructure were studied, and thesame like its optical and physical properties such as hardness.In this paper, the mainresearch contents, methods and results are listed as follows:1. This paper firstly adopting direct precipitation method synthesized pure MgF2powders, and using different analysis methods such as XRD, FESEM and particlesize analyzer and infrared spectrometer studied effects of different reaction conditionson its microstructure, surface morphology, particle size, and the infrared absorptionspectroscopy. The results indicated that the optimum aging time was3h, and powderssynthesized at the concentration of1mol/L were with moderate grain size,gooddispersion and the lowest content of impurities.2.The microporous structure of powders doped with rare earth ions wasobviously improved, and their grain size presented a trend of decrease.Calcination could eliminate residual moisture in the powder effectively, promote crystallizationand improve powders sintering character.3. This paper studied the effects of sintering temperature on the performance ofceramic samples and drew a conclusion by the contrast analysis: ceramic samplesobtained at900℃completed sintering with integrity crystal grain.We could hardly seemicropore in sintered body with a high density of98.74%and hardness of5.55GPa.Therefore,900℃is a more appropriate sintering temperature of pure magnesiumfluoride particles.4. With double sides polished, the ceramic sample prepared at900℃presented ahigh translucence in the visible light.The analysis of different range transmissionspectra of the sample showed that it can’t transmit in the ultraviolet spectral range;itstransmittance increased with the increase of wavelength in visible light range, but itcan only appear as translucency with the highest transmittance less than20%.Withinthe infrared spectral range, it keep higher transmittance during3.5-6μm and thehighest value was above87%.