Supercritical fluid: a potential route in the synthesis of cerate, zirconate and cerate-zirconate ceramics powder / Wan Zuliana Wan Zulkifli

A Supercritical fluid (SCF) is a processing technique which a fluid simultaneously heated and compressed above its critical temperature and pressure. A SCF is used to produce many types of materials since their properties can be varied with different reaction temperature (Treaction) and/or reaction pressure (Preaction). In this study, cerate and/or zirconate based ceramic powders of BaCe0.9Y0.1O2.95 (BCY), BaZr0.9Y0.1O2.95 (BZY) and BaCe0.54Zr0.36Y0.1O2.95 (BCZY) were synthesized by a high pressure-high temperature (HP-HT) batch wise reactor system using a SCF method. Ethanol was used to synthesize BCY and BZY powders at a constant Preaction (4 MPa) but a different in the Treaction ranging from 150 – 300 °C. Conversely, BCZY powder was synthesized using six different reaction media, namely ethanol, methanol, hexane, pentane, acetone and dichloromethane. Later, a SCF assisted sol-gel (SCF-SG) method was proposed by employment of Polyoxyethyle (10) oleyl ether (Brij97) as a surfactant to improve the properties of BCZY powder. In the synthesis of BCZY sample using a SCF-SG method, a gel was dried at temperature (Tdrying) of 150 – 325 °C. Then, it was subjected to HP-HT batch wise reactor system using a SCF at a constant Treaction (150 °C) and different Preaction ranging from 2 – 4 MPa. The prepared samples were characterized using Fourier transform infrared (FTIR) spectroscopy, X-ray diffractometry (XRD) and scanning electron microscope/energy dispersive X-ray (SEM/EDX). The presence of carbonate compound at ~800 cm-1 and metal-oxide (M–O) bond at 700 – 400 cm-1 in the BCY, BZY and BCZY after calcined at 1100 °C was confirmed by FTIR analysis. XRD result revealed that a single perovskite of BCY and BZY was formed at minimum calcination temperature of 800 °C and 1100 °C, respectively. The BCZY prepared by a SCF using ethanol as reaction medium at calcination temperature of 1100 °C showed the less secondary phases of BaCO3, BaCeO3, BaZrO3, CeO2, ZrO3, BaO2 and Ba(OH)2 compared to others medium. The formation of single perovskite phase of BCZY was only obtained after prepared via a SCF-SG at Preaction 2 MPa. The SEM results depicted that the particles of the single perovskite phase of BCY and BZY samples prepared by a SCF are respectively, cubical and spherical in shape. The employment of Brij97 in a SCF-SG produced homogeneous and fewer agglomerated particles with size ranging from 60 to 90 nm. As a conclusion, the used of surfactant in a SCF-SG method able to produce a single perovskite phase of BCZY ceramic powder with homogeneous and fine particles. Therefore, a study on significant parameter involved in a SCF and SCF-SG methods may contribute to a significant new knowledge in the synthesis of cerate, zirconate and cerate-zirconate ceramic powders at a relatively lower processing temperature.