Preparation And Properties Of Si₃N₄ Ceramics Via Digital Light Processing Using Si₃N₄ Powder Coated With Sintering Additives

Silicon nitride ceramics with high temperature resistance and high strength are playing a more and more important role in many high-tech fields like aviation,machinery,biomedical.However,traditional methods limited by the mold are difficult to form complex structures,which restrict the application of Si₃N₄ceramics.Although digital light processing（DLP）can fabricate ceramic parts with complex structures,Si₃N₄ceramics are difficult to be formed by DLP technology because of the high refractive index and ultraviolet absorption of Si₃N₄powder.In this paper,Si₃N₄ceramics were directly prepared by DLP technology using Si₃N₄powder coated with sintering additive as raw materials.The effects of coating amount of sintering additives and solid loading of ceramic slurry on the properties of Si₃N₄ceramic slurry,Si₃N₄ceramic green parts and Si₃N₄ceramics were systematically studied.The main conclusions are as follows:（1）Si₃N₄ceramic slurry with low viscosity and high curing depth was prepared for DLP technology.The formulation was as follows:the content of dispersant was 1.5 wt%,the mass ratio of photosensitive resin was HDDA:TMP3EOTA=3:1,and the content of photoinitiator was 4.0 wt%.Sintering additivies（Al₂O₃and Y₂O₃）were coated on Si₃N₄powder via chemical coprecipitation method,and the UV absorptivity of the coated Si₃N₄powder was about 18%lower than that of the uncoated Si₃N₄powder.When Al（NO₃）₃and Y（NO₃）₃solution was added in an amount of 20 m L/100 g Si₃N₄,the curing depth of the slurry prepared by coated Si₃N₄powder is about 13%higher than that of the uncoated Si₃N₄powder.（2）Si₃N₄ceramics with good quality and clear outline were prepared by DLP technology with different amounts of sintering additives.The relative density and flexural strength of Si₃N₄ceramics fabricarted by DLP technology first increased and then decreased with the increase of the amount of sintering additives.When Al（NO₃）₃and Y（NO₃）₃solution was added in an amount of 20 m L/100 g Si₃N₄,the maximum relative density and flexural strength of the Si₃N₄ceramics with solid loading of 35.0 vol%were 85.4%and 149.2 MPa,respectively.（3）Si₃N₄ceramics with better properties were prepared by DLP technology with different solid loading of the ceramic slurry.When the solid loading of the ceramic slurry was lower than 40.0 vol%,the viscosity of the slurry at shear rate of 30 s^-1was less than 2Pa·s,which could be used for DLP technology.The relative density and flexural strength of Si₃N₄ceramics fabricarted by DLP technology increased first and then decreased with the increase of the solid loading of ceramic slurry.The maximum relative density and flexural strength of Si₃N₄ceramics with solid loading of 37.5 vol%were 89.8%and 162.5 MPa respectively,which were 10%and 16%higher than those of the sample with solid loading of32.5 vol%.In this paper,Si₃N₄ceramics were prepared by optimization of ceramic slurry properties and coating modification of Si₃N₄powder.The research has laid a certain experimental foundation for the DLP of Si₃N₄and other non-oxide ceramics,which has important research significance.