Purification effect of the methods used for the preparation of the ultra-high purity graphite

The purification effect of a high temperature and high temperature thermochemical purification methods on some of the major impurity elements (B, Mg, Al, Si, Ca, Ti, V, Mn, Fe and Ni) has been studied for comparison, and ultra-high purity graphite was prepared. The content of impurity elements in the purified graphite was determined using glow discharge mass spectrometry. From the results obtained from various impurity elements during the analysis of graphite, the high temperature purification method can appreciably decrease the content of impurity elements with the exception of boron and was inapplicable toward the preparation of high purity graphite with low-boron content. In comparison, the high temperature thermochemical purification method can significantly decrease the content of boron to <0.01 ppm and can be used to realize the preparation of ultra-high purity graphite. The relatively poor purification effect of the high temperature purification method on boron may be related to the high reactivity between boron and the graphite matrix, while the introduction of ecological fluorine will obstruct the reaction between boron and the graphite matrix, which is beneficial toward the removal of boron when the high temperature thermochemical purification method is used.