Preparation And Properties Of Protective Coating On Carbon Materials Used In Czochraski Single Crystal Silicon Furnace

With the application of single crystal silicon in solar photovoltaic and the semiconductor industry more widely, carbon materials used as thermal field parts developed more quickly. But because the micro oxidizing atmosphere in CZ furnace makes carbon thermal field slow oxidation, generate carbon dioxide and carbon monoxide, these gas dissolved in silicon materials cause the silicon products carbon and oxygen settlement. In addition, in the process of pulling crystal, silicon material melt may produce silicon steam and molten silicon splash, cause carbon thermal field material surface silicification, seriously affecting the mechanical properties of carbon parts and service life. So, the antioxidant protection and corrosion protection of carbon thermal field material in monocrystalline silicon furnace is necessary, and coating technology is a necessary choice.This paper first studied carbon thermal field materials in oxidation environment and silicification corrosion cases failure mechanism. This study found that carbon materials matrix type, which structure, impurity content, surface finish effect the oxidation performance significantly. Due to the carbon fiber skin core structure, outer carbon atoms are arranged neat, reaction activity is relatively low, and in the oxidation process, oxidation reaction begin from carbon matrix began, the antioxidant performance of high fiber content carbon material is good. In addition, oxidation performance of carbon material with carbon atoms arranged neat, graphite crystallite complete is good, the higher graphitization degree, the higher antioxidant performance. Carbon materials internal metal impurity effectively reduces the carbon and oxygen element reaction activation energy, the carbon materials play a catalytic role in oxidation. Surface polishing treatment will reduce carbon material specific surface area, reduce carbon atoms and oxygen atom collision probability and improve the carbon material of oxidation resistance. For carbon materials for molten silicon silicification corrosion found that silicon elements on carbon material corrosion is mainly through the carbon material surface open pore and defect to material internal diffusion. For C/C composite material, cellulose exist between a large number of continuous pore, silicon mainly through these pore and matrix longitudinal defects. In addition with silicification corrosion the extension of time, the C/C composite material mechanics performance gradually declined, and graphite material silicification corrosion surface generation after continuous SiC, the mechanical properties of graphite materials for not silicification materials, but surface silicification seriously affect its service life.According to the carbon material oxidation erosion and silicification corrosion mechanism research, this paper designed a resin pyrolytic carbon coating and deposition pyrolytic carbon coating on carbon materials to protection oxidation and silicification. Based on two kinds of pyrolytic carbon coating phase structure and microstructure, because resin contracte in carbonized process, the surface of resin pyrolytic carbon coating has a lot of holes.Adding graphite powder as filler, restrain the the hole caused by resin shrinkage. After900℃static oxidation test and1600℃silicification corrosion test, resin pyrolytic carbon coating on carbon materials have some antioxidant protection ability, but after four hours of static oxidation, weight loss rate is still as high as60%. Antioxidant effect of CVD pyrolytic carbon coating is good,4hours oxidation weightlessness rate at about10%. After1600℃silicification corrosion, vapor deposition pyrolytic carbon has excellent silicification protection ability, and resin pyrolytic carbon coating corrosion resistance is better than that of silicide though without coating samples.Because of pyrolytic carbon coating inherent oxidation performance, makes the pyrolytic carbon coating as a protective coating of antioxidant effect is not good. In this paper, using embedding melt infiltration method and deposition method, we prepared the SiC coating. This study found that, along with the melt infiltration embedding for SiC coating time growth, SiC grain grew older, according to the XRD results, SiC coating is mainly beta SiC, and SiC grain grow up priority along the (311) crystal plane stacking direction. C/C composites matrix for embedding method for SiC coating effect is significant, SiC coating with carbon matrix coefficient of thermal expansion difference, causes micro crack generation in coating surface. Through the900℃,10h oxidation test found that SiC coating has good antioxidant protection ability, oxidation weightlessness rate at about4%.Through the SiC coating silicification corrosion test found that SiC coating surface microcrack exists, and be fused silicon to matrix internal diffusion channels. How to suppress the SiC surface micro crack generation, called SiC coating play antioxidant protection and resistance to silicification protection ability of the key.In order to alleviate the stress concentration caused by SiC coating and carbon material coefficient of thermal expansion mismatch, restrain SiC coating surface microcrack production, this paper designed a pyrolytic carbon coating for transition layer to SiC coating for external coating of composite protective system. Through the PyC transition layer test analysis found that, with the graphite powder add, coating internal exist a lot of grain boundary and defects existed, and these defects improve the transition layer of plastic. After1600℃processing PyC transition layer internal residual stress to less than900℃processing PyC transition layer, mainly because of the high degree of graphitization PyC transition layer can consume more energy thermal stress. After preparation SiC external coating found that characterization of SiC residual stress of Raman frequency shift and the equilibrium position basic balance, explain the existence of PyC transition layer for SiC coating ease most thermal stress, makes the SiC surface is less micro crack, more effective play SiC coating of antioxidant protection and resistance to silicification protective effect. Through the PyC toughening coating mechanism study found that PyC transition layer is actually into a layer of weak interface, in the weak interface internal there are many defects and micro crack, these defects and micro crack can be the main crack is dispersed, absorb the main crack energy, alleviate the main crack perpendicular to the direction of expansion coating, to avoid the penetrability micro crack generation.As furnace thermal field material in Czochralski silicon, the thermal radiation properties of carbon materials is very important. With the development of Czochralski silicon, the design and simulation of the thermal field in the furnace is particularly important, wherein the heat radiation performance of the thermal field of materials is one of the important parameters. This paper sdudied carbon substrate material and coating composite heat radiation performance analysis and found that the spectral emissivity of the C/C composites AC100and isostatic graphite G330high relative to other carbon materials, the spectral emissivity with wavelength variation smaller, the emission rate is relatively stable. C/C composites AC100and isostatic graphite G330graphite microcrystalline structure relative to the regularity of similar other materials is not high, the probability of the existence of the defect structure disorders cause localized vibrational mode structure of the carbon material to form a strong spectral radiation belts. Surface irregularities of the spectral emissivity of carbon materials, AC100surface smoothness of the rough surface caused by strong electromagnetic wave absorption scattering, strong spectral emissivity; graphite material surface uneven degree of difference is not obvious from the emission caused by the surface state of the rate change is not obvious. Thermal radiation properties of the protective coating of pyrolytic carbon composite materials in the test band is better than the base C/C composites, the performance of the vapor deposition of pyrolytic carbon coated composite thermal radiation, normal the basic spectral emissivity0.85-0.9range, to the total emission rate of0.89. Relative to the base C/C composites, silicon carbide heat protection coating composite spectral emissivity significantly improved in the test band embedding method Pyc/SiC coating the spectral emissivity basic higher than the vapor deposition coating, embedding composite coating, which can effectively improve the thermal radiation properties of carbon materials.