Preparation Of Medical ZrO₂ Ceramics Based On 3D Printing

Zirconia bioceramics have good biocompatibility and superior mechanical properties compared with hydroxyapatite and calcium phosphate bioceramics.The 3D printing method has unique advantages in that it is able to design the shape and internal pore structure of the material,so as to design personalized bone repair scaffolds for patients.However,the pore sizes designed by this method are all macroporous structures,it is impossible to design microporous structures.Pore-forming method is often used to prepare microporous structure.The advantage of pore-forming method in preparing porous ceramics is that it can introduce a large number of pores into the ceramics,but the disadvantage is that the connectivity rate is low.With deionized water as the solvent,dispersant,binder and plasticizer were added.Through the test and analysis of viscosity and stability of the slurry,the ceramic slurry meeting the requirements of 3D printing was obtained.The drying and debinding process of the green body was studied,and a ceramic body with complete morphology was obtained.The effects of sintering temperature on the phase,relative density,porosity and microstructure of zirconia ceramics were investigated.The porous zirconia ceramic with macroporous/microporous structure prepared by adding starch as a pore-forming agent,and it was characterized and analyzed.Finally a porous zirconia bioceramic with high porosity and high strength was obtained.The main findings are as follows:(1)In the experiment,3 mol%of yttria-stabilized zirconia was used as a raw material,citric acid was used as a dispersant,polyvinyl alcohol was used as a binder,and polyethylene glycol was used as a plasticizer.The green body of the macroporous structure was formed by a 3D printing method.A complete blank was obtained by optimizing the drying and debinding process.The effects of the type and content of dispersant,binder,solid content and plasticizer content on zirconia ceramic slurry were studied.The results showed that the zirconia ceramic slurry prepared with citric acid content of 0.4 wt.%,polyvinyl alcohol content of 0.6 wt.%,polyethylene glycol content of 0.25 wt.%,and solid content of 44 vol%had better stability and lower viscosity.During the extrusion of the slurry in the 3D printing process,the slurry was uniformly extruded in a filament form without cracking.The debinding system was formulated as follows:from 25?to 200?,the heating rate was 3?/min,from 200?to 600?,the heating rate was 1?/min and held at 600?for 2 h.(2)The effects of sintering temperature on the phase,bulk density,relative density,porosity,shrinkage and microstructure of porous zirconia ceramics were investigated.The results showed that the sintering temperature increased from 1400?to 1500?,the tetragonal phase content increased and the monoclinic phase decreased.When the sintering temperature was at 1550?,the monoclinic phase was relatively increased,but the amount of increase was small.With the increase of sintering temperature,the bulk density,relative density and shrinkage of zirconia ceramics gradually increased,and the porosity decreased.When the sintering temperature was 1500?,the ceramic bulk density was 5.93 g/cm~3 and the relative density was 97.2%.The shrinkage rate was 18.3%,the porosity was 2.78%,and the sintering temperature was increased to 1550?,and the amounts of change were small.With the increase of sintering temperature,the zirconia ceramic samples had uniform grain distribution and narrow pores.However,when the sintering temperature was at 1550°C,the number of large crystal grains increased remarkably,and the over-burning phenomenon was particularly obvious.When the sintering temperature was at 1500°C,the sintering effect was better.(3)The effects of different starch additions on the bulk density,porosity,shrinkage and pore size distribution of zirconia ceramics were investigated,and their mechanical properties and microstructure were characterized.The results showed that the amount of starch added increased from 10 wt.%to 50 wt.%,and the porosity of the sintered porous zirconia ceramics increased gradually,the bulk density decreased,and the shrinkage rate gradually increased.When the amount of starch added reached 50 wt.%,the porosity of the porous ceramic reached 57.03%,the bulk density was 2.62 g/cm~3,the shrinkage rate was23.82%,and the flexural strength can reach 14.5 MPa.The prepared porous zirconia ceramic had a uniform pore distribution and the pore size was equivalent to the starch particle size.By controlling the amount of starch added,the microporous porosity and pore size distribution of zirconia ceramics can be effectively controlled,and porous zirconia bioceramics with macroporous and microporous structures with pore design can be prepared.