Will petroleum coke undergo partial graphitization during the calcination process?

Yes, but the extent is limited — it is “increased structural ordering” rather than true graphitization in the strict sense.

During calcination, petroleum coke is typically heated to 1200–1350 °C. This range is close to, but still below, the ~2500 °C threshold required for graphitization. Strictly speaking, petroleum coke does not undergo a complete graphitization transformation inside a calciner, but it does experience significant structural ordering (a carbonization / graphitization precursor reaction). The specifics are:

What happens at the micro-level: The carbon atomic layer sheets (crystallites) in petroleum coke gradually shift from disordered to ordered arrangements at high temperature. X-ray diffraction analysis shows that the d₀₀₂ interlayer spacing shrinks from about 0.344 nm in raw coke to 0.336–0.338 nm after calcination, and the crystallite dimensions La and Lc both increase. This means the carbon network planes are expanding and the layers are drawing closer — the very early steps of graphitization, academically referred to as “the ordering process of graphitizable carbon.”

Why it is not true graphitization: True graphitization requires carbon layers to fully rearrange into a three-dimensionally ordered graphite crystal structure, which is virtually impossible to complete spontaneously below 2500 °C. At calcination temperatures, petroleum coke completes at most 60–70 % of the ordering process; the remaining disordered carbon (turbostratic structure) is still abundant. Hence the product is called “calcined coke,” not “graphite.” Its true density rises from roughly 2.05–2.10 g/cm³ in green coke to 2.08–2.12 g/cm³, and its electrical conductivity and oxidation resistance improve noticeably — but it is still far from graphite’s true density of 2.26 g/cm³.

Practical significance: It is precisely this “incomplete graphitization” — the gain in ordering — that gives calcined coke its higher bulk density, lower porosity, higher electrical conductivity, and better thermal-shock resistance. That is the core value of the calcination process. To achieve actual graphitization, the material must be heated further to 2800–3000 °C in a dedicated graphitization step, which is an entirely separate operation.

One-sentence conclusion: Calcination takes petroleum coke “a long step toward graphite, but it does not reach the finish line.”