Preparation And Properties Of Photocurable 3D Printed Silicon Carbide-based Ceramics Based On Polysilicone Acetylene

The organosilicon precursor has been widely studied because it has the advantages of designing molecular structure,convenient processing,and easy formation of complex components,which overcome the difficulty of preparing non-oxide ceramics by traditional powder sintering.The combination of photocurable 3D printing technology and precursor has realized the preparation of non-oxide ceramics with complex shapes,but the types of liquid silicone precursor polymers that can be photocurable still need to be enriched.At the same time,the high shrinkage rate after pyrolysis,low ceramic yield and poor mechanical properties of precursor polymers also limit their application.In this paper,a new type of low viscosity precursor vinyl polysiloxylene（PVSA）containing photocurable groups was synthesized,and PVSA,γ-methacryloxypropyltrimethoxysilane（KH570）and acrylic monomer were prepared into a photosensitive resin system with high ceramic yield and low curable shrinkage.By using the photocurable 3D printing technology,the preparation of complex shape precursor ceramic structure was realized.The mechanical properties of the precursor ceramics were improved and the shrinkage was reduced by optimizing the formula of the precursor photosensitive resin system.In order to further improve the mechanical properties and reduce the shrinkage of precursor ceramics,the composite ceramics were prepared by adding fillers（such as particles,whiskers,graphene oxide GO and h-BN,etc.）to precursor ceramics,which realized the preparation of precursor ceramics with high performance,low shrinkage and complex shape.This study not only provides a feasible method to improve the ceramic yield and forming accuracy of the precursor photosensitive resin and the integrated preparation of the structure and function of the precursor ceramic,but also expands the application field of the photocuring 3D printing of the precursor ceramic.The main research conclusions and achievements are as follows:The introduction of KH570 in the PVSA photosensitive resin system reduced the curing shrinkage rate of the photosensitive resin and increased the ceramic yield of the photosensitive resin.When the PVSA precursor content was 50 wt%and KH570 content was 41 wt%,the X-axis shrinkage and bending strength of the sample after pyrolysis were30.2%and 44.2MPa,respectively.In order to improve the activity of photocuring groups in the PVSA precursor and increase the content of PVSA in the PVSA photosensitive resin,PVSA with different average molecular weight was synthesized.The effects of average molecular weight on the photocuring properties of the photosensitive resin and the precursor ceramics were studied.By controlling the number and average molecular weight of the precursor,the formula of the precursor photosensitive resin had been optimized,and the bending strength of the precursor ceramics had been improved to a certain extent and the linear shrinkage had been reduced.The X-axis shrinkage and bending strength of Si CO ceramics produced by pyrolysis were 27.2%and 61.5±3.7MPa,respectively.The effect of zero（one）dimension filler in the precursor photosensitive resin system on the properties of composites prepared,including Si CO microspheres,Si C whiskers and Si COFe microspheres,had been studied.When microspheres or whiskers with different mass fractions were added into the precursor photosensitive resin system,the slurry viscosity was low and the fluidity was good.With the increase of microsphere or whisker mass fraction,the absorbance value of the slurry increased,the curing depth deteriorated,the linear shrinkage rate of the photocured 3D printing sample after pyrolysis decreased,and the ceramic yield and bending strength increased.When the additive amount of Si CO powder increased from 0 wt%to 10 wt%,the X-axis shrinkage of ceramics decreased from 32.9%to 26.4%,the ceramics yield increased from 50.0%to 58.1%,and the bending strength increased from 43.9 MPa to 79.8 MPa.When the content of Si C whiskers in the PVSA photosensitive resin was 5 wt%,Si C whiskers are relatively evenly dispersed in the Si CO ceramic matrix,and the bending strength and fracture toughness of the pyrolytic sample reached the highest of 260.1±49.7 MPa and 3.2±0.1 MPa·m^1/2,respectively.Meanwhile,the introduction of Si COFe microspheres and Si C whiskers had improved the absorbing properties of Si CO ceramics and laid the foundation for the structure-function integrated preparation of Si CO composite ceramics.The influence of PVSA content in the photosensitive resin system on the performance of Si CO ceramics had been explored,and the formula of the photosensitive resin had been further optimized.Based on the introduction of two-dimensional fillers,GO/h-BN and PVSA photosensitive resin had good wettability,the slurry prepared had low viscosity and good fluidity,showing the characteristics of Newtonian fluid.With the increase of GO/h-BN content in photosensitive resin,the absorbance value of slurry increased,curing depth deteriorated,and thermal conductivity increased.The bending strength and fracture toughness values of Si CO ceramics first rised and then declined.The bending strength and fracture toughness of Si CO ceramics reach their maximum value when GO content was 5 wt%or h-BN content was 1 wt%.When the GO content of PVSA photosensitive resin was 5 wt%,the bending strength and fracture toughness of the photocured 3D printing sample after pyrolysis were 203.3±9.8MPa and 2.3±0.04MPa·m^1/2,respectively,and the linear shrinkage of the X-axis was 19.2%.When the h-BN content of PVSA photosensitive resin was 1 wt%,the bending strength and fracture toughness of the sample after pyrolysis reached 252.4±12.2 MPa and 2.7±0.2MPa·m^1/2,respectively,and the linear shrinkage of X-axis was 22.4%.