Research On Structure And Properties Variation Of Low Temperature Isotropic Pyrocarbon

Artificial heart valves that is mainly composed of low temperature isotropic pyrocarbon aredesigned for patients with heart valve diseases, which are devices instead of the function of humanheart valves with lesions. Isotropic pyrocarbon is prepared by using a fluidized bed chemical vapordeposition method, as it has a good anti-clotting properties, biocompatibility and excellentmechanical properties in the human physiological environment, so which is considered to be thebest material for the manufacture of artificial mechanical heart valves. Density, hardness and porestructure are the mainly statistics for the material of pyrocarbon. And they have a direct influenceon the material of abrasion performance, Young modulus and breaking tenacity.In this paper, low temperature isotropic pyrocarbon that was considered the factors of depositionwas deposited using steady-state fluidized bed chemical vapor deposition process. The depositionwas at different temperatures and concentrations of propane gas. The structural properties of thedeposited low temperature isotropic pyrocarbon were investigated by densimeter,microhardness tester, scanning electron microscope, transmission electron microscope and mercuryinjection apparatus.Combining above results, the changed structure and properties of pyrocarbon that were preparedunder different deposition conditions were investigated, and its model diagram were also drawn.Themain contents and conclusions are as follows:（1）The changed density of low temperature isotropic pyrocarbon has been studied. Resultsshow that a lower deposition temperature and concentrations of propane can obtain a higher densityisotropic pyrocarbon, as the deposition temperature and the concentration of propane gas increased,the density of pyrocarbon is gradually decreased, for low concentration (25%~40%) of propanegas, the deposition temperature has a greater impact than propane on the density of pyrocarbon,however, high temperature (1350~1450℃) and high concentration (60%) of propane gas cansignificantly reduce the density of pyrocarbon.（2）The pore structure of high density low temperature isotropic pyrocarbon that is used inartificial mechanical heart valves was investigated. Results show that the pore in high densityisotropic pyrocarbon is mainly composed of the larger pores of about0.83μm and the mediumpores of about62nm between particles in sphere-like structure and the micro-pores derived ofentangled structure in spherical particles.（3）The relationship of density and pore structure for pyrocarbon were investigated. Results show that pyrocarbon with similar density have different pore structure; Distribution of poresbetween growth characteristics have a greater impact on the density of pyrocarbon with highdensity.（4）The changed micro-hardness of low temperature isotropic pyrocarbon has been studied.Results show that the higher deposition temperature and propane gas concentration are, the lowerpyrocarbon micro-hardness have; Lower deposition temperature and low concentrations of propanecan get pyrocarbon with higher hardness; For low concentration (25%~40%) of propane gas, thedeposition temperature has a greater impact than propane on the micro-hardness of pyrocarbon.However, high temperature (1350~1450℃) and high concentration (60%) of propane gas cansignificantly reduce the micro-hardness of pyrocarbon.（5）The deposition mechanism of low temperature isotropic pyrocarbon that was prepared byfluidized bed chemical vapor deposition under different conditions was studied. Results show that atthe low temperature with low propane concentration, the structure of isotropic pyrocarbon isuniform and dense. While at the low temperature with high propane concentration, pyrocarbon iscomposed of spherical-like carbon particles with the diameter more than1.5μm and large pores.When the deposition conditions is controlled at high temperature, most of spherical-like carbonparticles are less than0.5μm in the diameter, and among the particles there exists a lot of pores,what is more, carbon black is formed at the same time.