Utralow coefficient of thermal expansion in a spheroidized natural flake graphite based isotropic graphite

Abstract

With the development of high-temperature gas-cooled reactors, the coefficient of thermal expansion (CTE) of nuclear-grade graphite plays an increasingly important role in reactor design. A lower CTE enhances both the integrity of the graphite core structure and reactor efficiency. In this paper, we present a new isotropic graphite grade with a low CTE, utilizing spheroidized natural flake graphite (SFG) as a filler material. The ultralow isotropic CTE of 2.6–2.9 × 10⁻⁶ K⁻¹ in the SFG-based graphite, owing to the ability of the slit-shaped pores within the SFG particles to accommodate cross-plane thermal expansion. To enhance the baking performance of the SFG-based graphite, hybrid fillers of SFG/coke or SFG/microcrystalline graphite (MG) were used to prevent cracking of the green bodies. In particular, the addition of MG prevents cracking without changing the low CTE value of the SFG-based graphite. This research contributes to the development of new graphite materials with low CTE that can be used in nuclear engineering, the semiconductor industry, and other high-temperature environments.