Phase formation of Mn-doped zinc silicate in water at high-temperatures and high-pressures

• Published in: The Journal of supercritical fluids 2007-12, Vol.43 (2), p.214-221
• Main Authors: Takesue, Masafumi, Shimoyama, Kenji, Murakami, Sachiko, Hakuta, Yukiya, Hayashi, Hiromichi, Smith, Richard L.
• Format: Article
• Language: English
• Subjects: Hydrothermal reaction; In situ observation; Phase formation; Supercritical water; Zinc silicate
• ISSN: 0896-8446; 1872-8162
• DOI: 10.1016/j.supflu.2007.04.014

Phase formation of Mn-doped zinc silicate (Zn 2SiO 4:Mn 2+, ZSM) in high-temperature and high-pressure water was studied by in situ observations with a hydrothermal diamond anvil cell (HDAC). Precursor was prepared with zinc oxalate dihydrate, manganese oxalate, and silica, where the Zn/Mn/Si molar ratio was 192/8/120 to 199/1/120. Conditions of particle formation were at temperatures up to 650 °C and at pressures up to 1250 MPa. Precursors dissolved at temperatures of 145–203 °C and needle-like particles formed through homogeneous nucleation at temperatures from 357 to 374 °C, close to the critical point of water. The needle-like particles grew at growth rates of 0.5–3.8 μm/s and were identified to be ZSM as evident from their green luminescence. ZSM synthesized in supercritical water (400 °C for 180 min) by batch reactions had comparable luminescence with that of ZSM produced by solid-state reaction (1200 °C for 240 min) using the same precursor. The key finding in this work is that the precursors can be made to dissolve in near-critical water and that this allows ZSM to form via a homogeneous nucleation process.