Characterization of a new magnesium hydrogen orthophosphate salt, Mg 3.5H 2(PO 4) 3, synthesized in supercritical water

Abstract

Beige crystals of a new magnesium hydrogen orthophosphate salt, Mg 3.5H 2(PO 4) 3, as well as nanoparticles of an amorphous, non-Mg-containing phosphate material, Fe 1− y K y PO 4 (0 < y < 1), have been produced by hydrothermal reactions in supercritical water (SCW) of equivalent quantities of aqueous MgCl 2·6H 2O (2 M), and K 4P 2O 7 (1 M) in concentrated HCl in a stainless-steel batch reactor at 400–450 °C and 25–32 MPa. The new salt has been characterized by single-crystal X-ray diffraction and IR and Raman spectroscopies. It crystallizes in the triclinic space group Pī, Z = 2 with the following unit-cell parameters: a = 6.438(1), b = 7.856(1), c = 9.438(1) Å; α = 104.57(1), β = 108.61(1), γ = 101.28(1)°, V = 739.99 Å 3. The effects of the SCW conditions on the nature of the products and their yields and morphologies have been studied by IR and Raman spectroscopies, X-ray powder diffraction, X-ray energy dispersive analysis, scanning electron microscopy, transmission electron microscopy and inductively coupled plasma analysis.