THE DIFFUSION OF BORON IN CARBON
Preliminary experiments are performed on the diffusion of boron in graphite and investigations of the properties of the boron carbide obtained in this way. It is found that by the diffusion of boron in graphite alloys are obtained which show greater solidity and lower brittleness than boron carbide obtained by compression under heat. These alloys have semiconductor properties, and can be utilized for the preparation of high temperature thermocouples. By the diffusion of boron into the surface of graphite samples, their corrosion resistance becomes noticeably higher, particularly at higher temperatures. The purpose of this work is to investigate the mechanism of diffusion and to determine its parameters. The object investigated is a cylindrical sample of spectroscopically pure graphite onto whose surface a 2 mm thick layer of a paste of amorphous boron is applied. After the samples are dried at 150 deg C, they are enclosed in a graphite shell and preheated in an atmosphere of hydrogen at 700 to 800 deg C, for 60 to 80 min. After this treatment the samples are subjected to metallographic, chemical, and x-ray analyser. Further, the reverse process of diffusion of carbon in boron is investigated. For this purpose, boron samples of a porosity of 36% are employed. They are prepared by compression of boron powder and sintering at 1900 deg C. In this case there results a saturation of the carbon samples with carbon in 30 minutes in a vacuum oven at 1940 deg C. Experiments show that in similar conditions the boron penetrates deeper in carbon (1.4 to 1.6 mm) than carbon does in boron (0.6 to 0.8 mm). This indicates a remarkably higher mobility of boron atoms. The diffusion coefficients are calculated to be 6.2 - 10/sup -6/cm/sup 2//sec (B -- C) and 1.8 - 10/sup -6/cm/ sup 2//sec (C -- B). Numerical data for two samples showing boron content at different depths of the carbon sample (chemical analysis) are given. The boron concentration diminishes exponentially with depth. That a solid solution is formed due to diffusion, is shown by an x-ray analysis. Here the interplanar spacings of graphite lattice are measured as function of boron concentration. Further, the temperature dependence of diffusion of boron in graphite is investigated; D = 3.02 exp (-28625/T) is found to hold. (TCO)
- Research Organization:
- Inst. of Powder Metallurgy and Special Alloys, Academy of Sciences, Ukrainian SSR
- NSA Number:
- NSA-15-014767
- OSTI ID:
- 4050825
- Journal Information:
- Fiz. Tverdogo Tela, Vol. Vol: 2; Other Information: Orig. Receipt Date: 31-DEC-61
- Country of Publication:
- Country unknown/Code not available
- Language:
- English
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