Study On Preparation And Piezoresistive Characteristics Of SiBCN Polymer Derived Ceramics

In the aerospace field,pressure measurement is relatively extensive,For example,it is used to measure the pressure on the fairing during the launch of the spacecraft,The pulsating pressure of the engine cascade,Airflow pressure distribution of helicopter wings,Test the dynamic distortion of the engine air intake,and the jitter of the wing.At the same time pressuremeasurement is also complicatedTransforming difficult-to-measure mechanical quantities into easy-to-measure electrical quantities of piezoresistive materials will do more with less.The material of the current pressure sensor is usually single crystal silicon,but it can withstand a relatively low temperature.Therefore,it is very important to find a new pressure sensor material.The polymer derived ceramic materials studied in recent years have excellent high temperature resistance,corrosion resistance and ablation resistance,and have a high piezoresistive coefficient,so it may become the most promising material for the preparation of pressure sensors in the aerospace field.The polymer derived ceramic material is formed of an amorphous silicon substrate and free carbon.Free carbon has a high electrical conductivity and becomes the conductive phase of the precursor ceramic,which is very important for the piezoresistive properties of the precursor ceramic.This topic is mainly to control the free carbon of the polymer derived ceramics through two aspects of process and materials.First: adjust the form of the free carbon by changing the cracking temperature during the preparation of the polymer derived ceramics;second: the precursor of the preparation materials The body is modified to regulate the free carbon content.Further study the effect of cracking temperature and free carbon content on the piezoresistive properties of polymer derived ceramics.According to the research results,the process was improved,and the polymer derived ceramic material with the highest piezoresistive properties was finally prepared.First: The effect of cracking temperature on the piezoresistive properties of polymer derived ceramic.First,silicon boron carbonitride polymer derived ceramic with cracking temperatures of 1000?,1100?,1200?,1300? and 1400? were prepared.Secondly,the silicon boron carbonitride polymer derived ceramics with different cracking temperatures are characterized.The results show that the polymer derived ceramics prepared at each temperature are amorphous,and the volume of the polymer derived ceramics has shrunk at 1000 ?.High,the free carbon in the precursor ceramic changes from sp3 to sp2,and the conductivity of the precursor ceramic gradually increases.Finally,the piezoresistive properties of the polymer derivedceramics prepared at different cracking temperatures were tested,and the results showed that the silicon boron carbonitride polymer derived ceramics prepared at various temperatures had very stable piezoresistive properties.As the applied load increases,the electrical resistance of the material decreases significantly.The piezoresistive coefficient of Si BCN polymer derived ceramics prepared at the cracking temperature of 1300 ? is the highest.Then : The effect of free carbon content on the piezoresistive properties of polymer derived ceramics.First,the Si BCN precursor was modified so that the Si BCN precursor and different proportions of tetravinylsilane(TVS)hydrosilation reaction.Secondly,on the basis of the first part,the cracking temperature was selected to be 1300 ?,and Si BCN polymer derived ceramics with different free carbon contents were prepared through crosslinking cracking and other steps.Finally,the piezoresistive characteristics of the polymer derived ceramics with different free carbon content were tested.The results showed that the free boron content of silicon boron carbonitride polymer derived ceramics had very stable piezoresistive characteristics,and the piezoresistive coefficients were not very different.Last: Explore the mechanism of piezoresistive properties of Si BCN polymer derived ceramics.Si BCN polymer derived ceramics have very excellent piezoresistive properties,and their piezoresistive coefficient can reach 4000-5000,which is the ceramic material with the highest piezoresistive coefficient in the world so far.On the one hand: after the pressure is applied,the distance between the free carbon of the conductive phase becomes smaller,and even the phases between the conductive phases will conduct,forming an effective conductive network inside the precursor ceramic,which reduces the resistance of the ceramic.On the other hand: after applying pressure,the distance between the free carbon of the conductive phase becomes smaller,but the conductive phases are not in contact with each other.Due to the macroscopic quantum tunneling effect,electrons tend to transfer from one conductive phase to another conductive phase,Making the transfer of electrons easier than before without applying a load,and the ceramic resistance will also be reduced at this time.