When Lotus Leaves Prevent Metal from Melting — Biomimetic Surfaces for High Temperature Applications

Abstract

Functional properties of biological surfaces have gained increasing interest in the last two decades, especially with regard to wetting and self-cleaning. Here, biological surfaces of arthropods (Collembola) and plants (sacred Lotus) served as models for the principle design of high temperature resistant surfaces used in blast furnaces to prevent tuyeres from melting. Tuyeres are double-walled, watercooled pipes supplying the blast furnace with hot air to keep the reduction and melting process running. Tuyere failure is mainly caused by melting of the wall after direct contact with liquid iron, resulting in the partial shut down of the blast furnace and huge energy losses. As a new approach to avoid tuyere failure we developed a new type of tuyere surface with (i) defined cone shaped indentations and (ii) a heat resistant zirconium/corundum coating with “ferrophobic” properties i.e. it forms with liquid iron of 1500 °C a contact angle exceeding 130°. Theoretical considerations indicate that liquid iron infiltrates these indentations only partially if this contact angle and the aperture angle of the cone satisfy an inequality condition. Since heat conductivity of the remaining gas trapped inside the cones is by five orders of magnitude lower than in copper, the overall heat flow into the tuyere is substantially reduced and the outer walls are much less prone to melting.