Rapid one-step preparation of SrZrO3 using Zr4+ gel and SrSO4 ore under alkaline hydrothermal conditions

Abstract

SrZrO3-structured perovskite particles were prepared under hydrothermal conditions in a KOH (5M) solution using Zr-gel and SrSO4 mineral precursors. The treatments were conducted between 150 and 240°C for different reaction intervals (1–96h), and the KOH solution volume varied between 7.5 and 30mL. To evaluate the effect of the Zr-gel precursor, the treatments were preliminarily conducted with a coprecipitated pasty Zr-gel (Zr(OH)4·9.64H2O) and subsequently with a lyophilized Zr-gel Zr(OH)4 powder. Generally, SrZrO3 particles were produced by a single-step reaction following the simultaneous bulk dissolution of the Zr4+ gel precursor and the SrSO4 powder. However, in the preliminary experiments, a dehydration reaction of the pasty Zr-gel preceded the ultimate single-step reaction, resulting in complete SrZrO3 particle formation taking place over a longer interval of 96h at 240°C. In contrast, when using the dried Zr-gel powder, complete feedstock dissolution occurred more rapidly, producing SrZrO3 particles at 200°C over 48h. The SrZrO3 particle sizes varied significantly depending on whether the pasty gel or dried powder Zr precursor was used. Particles prepared with the pasty gel exhibited a bimodal size distribution with mean particle sizes of 25 and 65μm with pseudocubic and star-shaped cuboidal morphologies, respectively. In contrast, particle growth resulting from the rapid dissolution of solid powder feedstock produced cubic-shaped particles, monomodally distributed with an average particle size of 10μm. Furthermore, byproduct (SrCO3) formation occurred predominantly under earlier stages together with SrZrO3 particle irrespective of the 5M KOH filling volume; however, at a volume of 15mL spontaneously achieved in situ the SrCO3 dissolution at intermediate stages of reaction. This reaction pathway did not proceed at small (7.5mL) and large (30mL) volumes of the alkaline fluid. A kinetic study indicated that the activation energy required to produce the SrZrO3 cubic-shaped particles was low in both cases, i.e., 15.05 and 22.27kJmol−1 between the powder and pasty Zr4+ precursors, respectively.