Controlled structure preparation of low thermal conductivity Bi ₄ B ₂ O ₉ foams

Abstract In this contribution, Bi ₄ B ₂ O ₉ foam ceramics with porosity of 76.6%–85.8% and thermal conductivity of .062–.092(W/(m·K)) were successfully prepared for the first time by the foam casting method using bismuth oxide and boric acid as the main raw materials and gelatin as the gel forming agent. The effects of additive content and solid loading on the slurry, pore size, and distribution as well as mechanical and thermal properties of porous ceramics were investigated. The addition of gelatin led to the stable arrangement of the liquid‐gas interface, which eventually resulted in a foam with a stable pore structure. The sintered ceramics have a highly spherical morphology with typical micropores and cell window, which may also contribute to the low thermal conductivity of Bi ₄ B ₂ O ₉ foams. Bi ₄ B ₂ O ₉ foam with tailored properties and graded pore structure by adjusting the process parameters can be used as a high‐performance nuclear reactor insulation material.