Research On Microstructure Control And Compressibility Of Porous Silicon Nitride Ceramics With Directional Pore Structure

There are about 4 million joint replacement operations in the world due to trauma,infection,and tumors each year.The amount of autologous bone grafts is limited and cannot meet the demand.Silicon nitride has good biocompatibility,antibacterial properties,stability and mechanical properties,and is expected to become a long-life bone replacement material.The difference in elastic modulus between the dense silicon nitride and the main bone is huge,which leads to stress concentration at the interface of the implant and the implant fails.Porous silicon nitride ceramics can solve the above-mentioned problems,so that the mechanical properties of the silicon nitride graft material are matched with the main bone.In this paper,the effects of porosity and pore size on the elastic modulus and strength of porous silicon nitride ceramics with directional pore structure were studied by ABAQUS finite element analysis software,And the porous silicon nitride ceramics with different pore structures were prepared by freezing casting method,the related mechanical properties were studied,and compared with simulation results.Based on the characteristics of bone structure-with the characteristics of directional connected pore structure,a porous material model is established.Using finite element method to systematically study the effect of pore size and porosity on the compression behavior of the model.The results show that as the pore size and porosity increase,the elastic modulus and compressive strength of porous silicon nitride decrease.The finite element analysis shows that the introduction of directional pore structure in silicon nitride is expected to achieve the matching of the elastic modulus of porous silicon nitride and the natural bone elastic modulus,while meeting the strength requirements of implanted bone.The Freeze casting method can prepare porous structure materials with wide porosity and directional holes.The pore structure of porous silicon nitride can be controlled by studying the influence of slurry preparation,directional freezing process and sintering process on the pore structure of porous silicon nitride.The freeze casting method is used to prepare porous silicon nitride materials.It is necessary to prepare a stable and well-dispersed suspension for injection molding and the preparation of a uniform green body.the effect of p H,dispersant content,solid phase content and ball milling time on the rheology and suspension stability of silicon nitride slurry were studied and the best preparation process was selected.the results show that tetramethylammonium hydroxide can improve the dispersion of the suspension.When the p H is 13 and the dispersant content is 1.8wt%,the dispersion effect is the best.the viscosity of the slurry increases with the increase of the solid phase content.the best ball milling time is 24 h.Using the above process to prepare porous silicon nitride materials,the effects of binder content,solid content,freezing temperature,sintering aid content,and sintering temperature on the pore structure of homogeneous porous silicon nitride were studied.the results show that gelatin affects the growth of ice crystals during low-temperature freezing,which makes the pore diameter distribution more concentrated;with the increase of solid content,the pore wall gradually thickens,the pore diameter gradually decreases,the linear shrinkage and porosity decrease,and the density increases.As the freezing temperature decreases,the pore diameter gradually decreases,and the pore diameter distribution becomes more concentrated.the compressive strength increases from 31.8 MPa to 47.1 MPa;the sintering temperature should be 1850 ?;as the content of the sintering aid increases,the glass phase Y10Al2Si3O18N4 increases.the glass phase makes part of the small pores in the ceramic body disappear,the pore size distribution becomes narrower and more concentrated,the porosity is reduced,and the density and linear shrinkage are increased.Comparing the finite element analysis and the experimental test,the finite element result is far better than the experimental test.This is because the original model is inaccurate.After the improved finite element model,its mechanical properties have dropped significantly,indicating that uneven pore size and hole defects affect its mechanical properties.