Synthesis and formation mechanism of submicrometer ZrB2 powders via the Pechini-type polymerizable complex route

Abstract

ZrB₂ powders were synthesized by a polymerizable complex method based on the Pechini-type reaction route, wherein a precursor solution of citric acid, glycerol, boric acid, and zirconium ions was prepared, and polymerized to form a semitransparent resin without any precipitation at 150 °C. The precursor solutions and the resulting resins were characterized by FT-IR and ¹³C NMR spectroscopy. The results show the formation of a hybrid polymer with zirconium and boron arrested within the polymeric chain by complexation. The submicrometer ZrB₂ powders (200–600 nm) are formed after pyrolysis of the polymeric precursor with 4 B/metal molar ratios at 1400 °C. Investigation of the formation mechanism of ZrB₂ powders indicates that ZrC is the intermediary phase and two reduction reactions determine the specific pathway leading to ZrB₂ formation: (1) ZrC formation, (2) the formed ZrC directly reacts with B₂O₃ to form ZrO₂ and ZrB₂. In the whole conversion process, ZrC formation by carbothermal reduction is a fast reaction, while the direct reaction of ZrC with B₂O₃ to form ZrO₂ and ZrB₂ is the rate-limiting step.