Study On Preparation And Sintering Mechanism Of Large-sized New Amorphous Oxide

Oxide glasses lacking network formers?i.e.,silicon,boron oxide and phosphorus pentoxide?have potentially broad application in the fields of laser light and imaging since they possess superior optical properties such as higher refractive index.But under the conditions of conventional melting-solidification methods,they are prone to crystallize due to low glass-forming ability.Through special processes such as containerless solidification,only small amorphous products within millimeter scale can be obtained,which severely limits the application of these new glasses.To solve this problem,we proposed a synthetic route to get large-sized glass via vacuum hot-press sintering of amorphous oxides at the temperatures in the kinetic window??T_x?.First,amorphous oxide was made by containerless solidification technology.Then,amorphous oxides were applied by the pressure in?T_x sintered under vacuum.The glass appeared superplastic in this temperature range,thus large-sized amorphous oxides with low content of SiO2 or without SiO2 were obtained.The compositions and microstructure properties were systematically studied by X-ray diffractometer?XRD?,diffrential scanning calorimeter?DSC?,the scanning electron microscope?SEM?,the SPEC ellipsometer and UV-VIS-NIR spectrophotometer.Finally,the effects of grain size,sintering pressure and temperature on the densification process were investigated.Meanwhile the sintering densification mechanism of amorphous powders was analyzed.The high-density La₂O₃-TiO₂-SiO₂ amorphous materials were fabricated by the addition of a small amount of SiO₂ in the La₂O₃-TiO₂ oxide system.SiO₂ could improve the glass-forming ability of La₂O₃-TiO₂.The raw powders made by aerodynamic levitation furnace were completely non-crystal,while the sintered samples had weak crystallization,which affected fully densification of sintered samples.There was a small amount of porosity in the high-density product made by vacuum hot press sintering.Finally,the optical property of hot pressed La₂O₃-TiO₂-SiO₂ material was investigated and it was found that it still kept high refractive index of above 2.2 in the visible light region.The high-density La₂O₃-TiO₂-ZrO₂ amorphous materials without traditional network formers were fabricated by hot-press sintering.ZrO₂ could improve the glass-forming ability of La₂O₃-TiO₂.The increase of the grain size of amorphous powder could accelerate the densification process,but it had no effect on sintering densification rate.The rising of both sintering temperature and pressure could promote the relative density of the sintered sample.The sintering densification mechanism of the La2O3-TiO2-ZrO2 amorphous powders was predominantly controlled by plastic flow.Compared with La₂O₃-TiO₂ amorphous powder,La₂O₃-Nb₂O₅ glass is more difficult to sinter.The samples have higher density and demonstrate significant densification between powders when the sintering pressure was improved from 60 MPa to 200 MPa.The shrinkage process consisted of three stages,including accelerating shrinkage,rapid shrinkage and shrinkage stagnation.