Study On The Structure Optimization And Properties Of AlN And AlN/C Composites Prepared By Gelcasting

In this paper,Al N ceramic and Al N/C composite were prepared by gelcasting and pressureless sintering method with the surface hydration resistance of modified Al N powder and C powder as the main raw material,environmental protection nontoxic curdlan as gel system.Study on the rheological property of slurry by viscometer,the curing mechanism of curdlan gel system by infrared spectrum analyzer,analysis of the ceramic body and sintered materials.The phase composition and microstructure were characterized by using XRD diffraction,scanning electron microscopy,transmission electron microscopy,mechanical properties of green body and sintered body was tested by the three point bending method,the thermal resistance of thermal detector materials were studied.The effects of dispersant content,p H value,curdlan content,solid phase content,C content and sintering aids content on the properties of slurry,the mechanical and thermal conductivity and microstructure of sintered body were investigated.The experimental results show that the system of curdlan gel injection molding of Al N ceramic and Al N/C composite body is prepared,curdlan at an elevated temperature,due to the formation of hydrogen bond and alkaline conditions inside the spiral and annular structure,forming a three-dimensional network structure in the molecules,raw material powder curing.The increasing of curdlan content,solid content and C content increase the viscosity of slurry,and influence the density,flexural strength,thermal conductivity and microstructure of sintered body.The introduction of sintering aids(Ca F2+Y2O3)enables liquid phase sintering of materials,accelerates the densification process of materials,and improves the mechanical and thermal properties of materials.The microstructure of Al N ceramic body is homogeneous and there is a certain pore.After sintering,the densification of the billet increased.Through TEM,it is found that there are different degrees of voids and second phases in the material,and there are dislocation in the Al N grains,and there are pores in the grains.The dislocation in Al N will cause phonon scattering.The larger the density of dislocation is,the more serious the scattering phenomenon is.The mean free path of phonons decreases,and the thermal conductivity of materials decreases.When curdlan was 0.5 wt.%,the solid content of 50 vol.% and sintering additive content of 7 wt.%,Al N ceramics and Al N/C composite,the maximum bending strength,highest thermal conductivity,the flexural strength can meet the following machining requirements,the density is the main factors affecting the thermal conductivity of Al N ceramics.The introduction of the C sheet,the whole material density decreased slightly,and because the C itself belongs to the low ductile material,when the amount reaches a certain value,Al N/C composite microstructure uniformity and stability decreased,have a certain influence on the mechanical properties and thermal conductivity rate.