Study Of Composites With Controllable Thermal Expansion

The spatial light machine requires its own with higher accuracy and better dimensional stability,preparation of composites with controllable thermal expansion can be good regulation and control of the material thermal expansion properties of composite materials.In this paper,with a carbon fiber woven pieces to enhance the body,using two different precursor,by PIP process for preparing C_f/SiC and C_f/Si-C-N composites,by adding negative thermal expansion material ZrW₂O₈ to fiber and matrix interface,analyze their complex affect to material properties,in addition to the fiber interface modifier,analyze the impact of the interfacial stress of thermal expansion properties.C_f/Si-C-N Composites was prepared by polysilazane.polysilazane at a temperature above 800? pyrolysis into amorphous Si-C-N ceramics,the ceramic yield is of 70.8% at 1200?,so polysilazane is a good ceramics precursor.The density of the composites after 16 cycles is 1.85g·cm-3,and the corresponding bending strength and specific strength is 407 MPa,2.2×105N·m·kg-1,respectively,The thermal expansion coefficient measured from 15? to 25? is 0.03×10-6K-1.The property illustrate polysilazane has a strong advantage in the preparation of zero-expansion material.Coating modified interface with C_f/SiC composites,at the same coating thickness,the density of 3D3 d smaller than 3D5d;3D5d mechanical properties of woven composites is superior to 3D3 d woven structure.With increasing coating time,the coating thickness is increased,the mechanical properties of the two woven structure has downward trend.Longitudinal thermal expansion coefficient of C coating of 3D3 d structure over time increase first and then decrease.The thermal expansion coefficient of 3D5 d woven structure is of deposition with time increased,to reduce the thermal expansion coefficient of the SiC coating of 3D3 d woven structure over time also increases first and then decrease,the thermal expansion coefficient of 3D5 d woven structure is decreasing with the coating thickness increased.When deposition 5h,C fiber of two weave C coating C_f/SiC composites receive compressive stress,when 10 h C fiber receive tensile stress;3D3d woven structure SiC coating Raman peak position offset G law and is similar with C coating,is first skewed to the right,then go to the left with the deposition time increases;But after the thermal expansion coefficient of the composite material is now increased and then decreased.3D5 d woven structure SiC coating Raman G peak position is slightly skewed to the left and then the right side.Using solid phase chemical reactions prepared ZrW₂O₈ material.The material is heated in a box furnace at 1200? for 24 h by liquid nitrogen cooling.miscellaneous peak of ZrW₂O₈ is less prepared,purity is high,Zr W₂O₈ phase??-phase?transition from order to disorder occurs near 160 ?,and get??-phase?,the thermal expansion coefficient of ? phase is-9.97×10-6K-1,and the thermal expansion coefficient of ? phase is-4.85×10-6K-1.Also draw the conclusion that the thermal expansion propert of HfW₂O₈ is extremely similar with ZrW₂O₈.Using furnace cooling and liquid nitrogen cooling in two ways to prepare ZrW_2-xMo_xO₈.ZrW_2-xMo_xO₈ has a crystal structure of ?-ZrW₂O₈,weight loss began at 900?,emiting a lot of heat at 1000?,indicating that the accession of MoO3 can strength temperature resistance than ZrW₂O₈,and also can reduce the transition temperature of ?-? phase,liquid nitrogen cooling ?-? phase transition temperature point is significantly higher than by the furnace cooling.The thermal expansion properties of ZrW_2-xMo_xO₈ by furnace cooling can achieve the same effect with the preparation by liquid nitrogen cooling,saving the energy in this method.The ZrW_2-xMo_xO₈ was added to the impregnating solution of polycarbosilane?PCS?,polysilazane?PSZ?.In the vacuum box furnace at 800 ? treatment found massive ZrW2-x MoxO8 can stably coexistence with polysilazane immersion liquid,while the ZrW2-x MoxO8 powder was added to polycarbosilane?PCS?impregnation liquid mixture was decomposed after high temperature treatment.Because WO 3,MoO3 can easily react with C which is the pyrolysis products of polysilazane?PSZ?or polycarbosilane?PCS?,lose oxygen and then becomes more WO 2 and MoO2.So the plan of adding ZrW_2-xMo_xO₈ to prepare composites with controllable thermal expansion is not feasible,But also to the preparation of composites with controllable thermal expansion provides more ideas and thoughts.