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Want more information on graphite blocks? Feel free to contact us.
You have two problems.
1.) pencil lead graphite is actually a graphite-clay composite.
2.) carbon does not sustain burning easily unless it is held at very high temperatures.
Contact us to discuss your requirements of how to clean a crucible. Our experienced sales team can help you identify the options that best suit your needs.
Pencil lead will not burn effectively for the first reason as clay is non-combustible and smothers any fire load. If you did have pure graphite to burn, a simple flame wouldn't be hot enough to combust it. You need to sustain temperatures of around $1000\mathrm{-}2000~^\circ\mathrm{C}$ in order for pure carbon to burn.
If you are looking for more details, kindly visit carbon graphite block price.