Pyrolysis mechanism of ZrC precursor and fabrication of C/C-ZrC composites by precursor infiltration and pyrolysis

C/C-ZrC composites were prepared by precursor infiltration and pyrolysis using the organic zirconium as precursor.The conversion mechanisms of the precursors such as the thermal behavior,structural evolution,phase composition,microstructure,composition of the precursors and products were analyzed by thermal gravimetric analyzer,Fourier transform infrared spectrometer,X-ray diffraction and scanning electron microscope.The results indicate that the ZrC precursor transforms to inorganic ZrO2 from room temperature to 1200 ℃,then reduces to ZrC at 1600 ℃ through the carbothermal reduction reaction.The microstructure of the C/C-ZrC composites was also investigated.The composites exhibit an interesting structure,a coating composed of ZrC ceramic covers the exterior of the composite,and the ZrC ceramic is embedded in the pores of the matrix inside the composite.

Processing and properties of 2D SiC/SiC composites by precursor infiltration and pyrolysis

Two-dimensional plain-weave silicon carbide fiber fabric reinforced silicon carbide(2D-SiC/SiC)composites were molded by stacking method and densified through precursor infiltration and pyrolysis(PIP)process.SiC coating was deposited as the fiber/matrix interphase layer by chemical vapor deposition(CVD)technique.Fiber/matrix debonding and relatively long fiber pullouts were observed on the fracture surfaces.Additionally,the flexural strength and elastic modulus of the composites with and without fiber/matrix interphase layer were investigated using three-point bending test and single-edge notched beam test.The results show that the fiber fraction and the porosity of 2D-SiC/SiC composites with and without coating are 27.2%(volume fraction)and 11.1%,and 40.7%(volume fraction)and 7.5%,respectively.And the flexural strength and elastic modulus of 2D-SiC/SiC composites with and without coating are 363.3 MPa and 127.8 GPa,and 180.2 MPa and 97.2 GPa,respectively.With a proper thickness,the coating can effectively adjust the fiber/matrix interface,thus causing a dramatic increase in the mechanical properties of the composites.

A novel mullite anti-gyroid/SiC gyroid ceramic metastructure based on digital light processing 3D printing with enhanced electromagnetic wave absorption and mechanical properties

Sic-based composites are widely used as electromagnetic wave absorbers due to their excellent dielectric properties.However,the constraints associated with structural design and the intricacies of the preparation process hinder their broader application.In this study,novel mullite anti-gyroid/SiC gyroid metastructures are designed to integrate the mechanical and electromagnetic wave(EMW)absorption properties of composite materials.Mullite anti-gyroid/SiC gyroid composites are fabricated utilizing a combination of digital light processing(DLP)three-dimensional(3D)printing and precursor infiltration and pyrolysis(PiP)processes.Through the modulation of structural units,the electromagnetic parameters can be effectively regulated,thus improving the impedance matching characteristics of the composites.The structural composites show outstanding EMW absorption properties,with a minimum reflection loss of-54 dB at a thickness of 1.9 mm and an effective absorption bandwidth of 3.20 GHz at a thickness of 2.2 mm.Furthermore,the PIP process significantly enhances the mechanical properties of the composites;compared with those of the mullite/SiC ceramics,the flexural strength of the composites is improved by 3.69-5.85 times(13.28±1.15 MPa vs.(49.05±1.07)-(77.78±3.72)MPa),and the compressive strength is improved by 4.59-13.58 times(8.55±0.90 MPa vs.(39.02±1.63)-(116.13±2.58)MPa).This approach offers a novel and effective method for fabricating structural composites with an expanded range of higher electromagnetic wave absorption properties and improved mechanical properties.

New route to synthesize preceramic polymers for zirconium carbide

A preceramic polymer, polyzirconosaal （PZSA）, was synthesized by the ligand-exchange reaction between polyzirconoxane （PZO） and salicyl alcohol （SA）. The precursor was air-stable and exhibited excellent solubility and rheology. These properties are useful for the processing of C/C-ZrC composites v/a precursor infiltration and pyrolysis （PIP） process. The polymer to ceramic conversion was investigated by TG, XRD and TEM. Nanosized ZrC was formed by pyrolysis of this precursor at 1300 ℃ in argon with ceramic yield of 57.8%.