Design And Preparation Of SiOC Porous Ceramics Via Additive Manufacturing Technology

SiOC ceramics exhibit the advantages of high strength,oxidation resistance,corrosion resistance,et al.Further,the SiOC ceramic with lattice structure also feature a specific light weight,heat insulation,wave and sound absorption,and so forth.It has many potential applications in the field of multiphase filtration,furnace,combustor,catalytic loading,biological tissue growth and interpenetration composites.With the evolution of miniaturization of ceramic devices,more and more ceramic components requst for higher precision and complexity.However,it is often difficult to obtain hard and brittle ceramic materials with lattice structure and complex structures.In this paper,we have used photosensitive polysiloxane as synthesized for direct ink writing,by the combination of Polymer-Derived-Ceramics technology and Additive Manufacturing technology.And successfully prepared the complex lattice structure with micron-scale shape and tunable porosity that can be designed and controlled.Besides,The effect of printing parameters on the structure forming and properties of the UV-assisted direct writing molding process was analyzed.The chemical conversion,crystal structure and micro-morphology of the porous ceramic precursor green body after photocuring during pyrolysis were systematically studied.The main research contents and results of this paper are as follows:The synthesis of SiOC precursors was studied:the photosensitive polysiloxane was synthesized by Hydrolysis of polysiloxane resin（MK）containing a certain amount of silicon methoxy and silicon hydroxyl groups withγ-methylacryloxypropyl trimethoxysilane（TMSPM）under acidic catalytic conditions.The effects of water content,TMSPM content and trimethyl-propane triacrylate（TMPTA）on the rheological properties and photocuring rate of synthetic resins were studied.The results show that the higher the water content,the higher the viscosity of the synthetic resin.The higher the TMSPM content,the lower the viscosity and photocuring rate.8wt%TMPTA can reduce the viscosity of resin and accelerate curing rate without significantly reducing transmittance of the resin.At the same time,the resin presents shear thinning characteristics,which meets the requirements of direct ink writing.The process of direct ink writing was studied:the synthetic photosensitive polysiloxane resin was subject to UV-assisted direct ink writing,and the effects of printing process parameters,regarding as printing rate,UV dosage,and noozle spacing,on the fineness and strength of the manufactured porous structure were studied.The results show that at a constant extrusion rate,as the printing rate increases,the smaller the filament diameter,the greater the porosity of the molded structure.Photocuring rate of the resin could be greatly affected by the intensity of UV.With the increase of UV intensity,the porous structure exhibits better resolution and fineness,but at the same time it will reduce the degree of fusion between the structures.The distance between the nozzles mainly affects the deposition path of the filaments.it increases the length of the filament from extrusion point to deposition point and the UV irradiation time,which increases the curing degree of filaments before deposition and reduces the degree of structural deformation.When the distance is too high or too low,it can affect the precision of the printed structure.The pyrolysis process of the ceramic precursor was studied:SiOC ceramics with tailored structure,and no-pores,and cracks-free were obtained after pyrolysis at high temperature.The evolution mechanism of microstructure of precursors in pyrolysis process was investigated.The precursor has a thermal crosslinking process at about 200℃according to the results of FTIR,DSC,TG,Raman,XRD,SEM,etc.,so that the structure further densifies.At 800℃,the precursor has completed the transformation from organic to inorganic.The structure of SiOC ceramics was amorphous at 1000℃,it begins to crystallize at 1200°C,andβ-Si C is formed at 1600°C.At this temperature,the carbothermic reduction reaction occurred,so the content of SiO₂ decreases.After pyrolysis,the surplus carbon in the structure exists in the form of carbon clusters,the main phase of carbon is disorder at 1000-1200°C.And the size of carbon clusters increases with the sintering temperature.