Synthesis Of Zirconium Diboride And Its Coating Preparation

Zirconium diboride is one of the representative materials in transition metal borides.Due to its special crystal structure,it has excellent comprehensive properties,such as high melting point,good abrasion resistance and thermochemical stability.Zirconium diboride materials have been used in many fields such as high temperature resistant materials,special electrode materials,coating materials and nuclear control materials.The main content of this thesis focuses on the preparation of zirconium diboride coatings.As a highperformance structural material,carbon fiber has unique properties,such as low density,low thermal expansion coefficient,and excellent thermal shock resistance.However,carbon fiber has poor oxidation resistance in high temperature environments(>500?).In order to improve the oxidation resistance of carbon fibers/carbon fiber fabrics,a zirconium diboride coating was prepared on their surface by solution impregnation combined with carbothermic reduction.X-ray diffractometer,scanning electron microscope and thermogravimetric differential thermal analysis were used to evaluate the morphology and performance of the samples.This paper mainly focused on the following contents:(1)A sol-gel combined carbothermal reduction process was used to prepare zirconium diboride powder.Raw materials include zirconium n-propoxide,boric acid and sucrose.In the experiment,the influencing factors such as the molar ratio of zirconium to boron,the atmosphere of the calcination environment and the holding time were explored.The influence of different experimental conditions on the synthesis products was explored.A synthesis scheme of zirconium diboride powder suitable for the experimental conditions was obtained.The experimental results show that a pure phase zirconium diboride can be obtained by the sol-gel combined with carbothermal reduction process,where a zirconium diboride precursor with a zirconium-boron molar ratio of 1:9 was at first prepared,and then calcined in argon atmosphere at 1450? for 4 hours.(2)By adjusting the preparation scheme of the zirconium diboride precursor in the sol-gel method,a precursor impregnation solution suitable for three-dimensional braided carbon fibers was obtained.The impregnation process and high-temperature calcination process of preparing zirconium diboride coating on the surface of carbon fiber fabrics were studied.Based on the experimental results,the final coating preparation scheme was obtained:the zirconium-boron molar ratio of the zirconium diboride coating precursor impregnation solution is 1:20,the zirconium-carbon molar ratio is 1:25,and the hightemperature calcination conditions is samples kept at 1450? for 4 hours in carbon-boron mixture under an argon atmosphere.(3)Analysis of microscopic morphology and anti-oxidation test of three-dimensional braided carbon fiber loaded with zirconium diboride coating,the results show that the coating preparation process used in this research can prepare a uniform and continuous zirconium diboride coating on the surface of carbon fiber fabrics.The oxidation resistance of the zirconium boride coated samples was significantly improved compared with the blank carbon fiber fabric.