Determination of Anisotropic Factors of Pyrolytic Carbon by Electron Diffraction

The preferred orientation of pyrolytic carbon coating is an important performance parameter for the safe use of artificial mechanical heart valve.In this paper,the selected area electron diffraction(SAED) analysis of pyrolytic carbon coating samples of artificial heart valve was carried out by transmission electron microscopy(TEM), and the experimental method of characterizing the preferred orientation of pyrolytic carbon by electron diffraction spectrum, namely bacon anisotropy factor(BAF), was described,and the orientation angle and BAF corresponding to the electron diffraction spectrum were measured.The results show that the BAF value can directly reflect the anisotropy of pyrolytic carbon in the selected area. The BAF value range is from 1 to infinity, and the higher the preferred orientation is, the greater the value is. The BAF value decreases exponentially with the increase of orientation angle. When the pyrolytic carbon tends to be isotropic, the orientation angle tends to 180 and the BAF value tends to 1.