Synthesis and Crystal Structure of Maricite and Sodium
Iron(III) Hydroxyphosphate
John. N. Bridson
Sean E. Quinlan
Peter R. Tremaine
10.1021/cm9704847.s001
https://acs.figshare.com/articles/journal_contribution/Synthesis_and_Crystal_Structure_of_Maricite_and_Sodium_Iron_III_Hydroxyphosphate/3594963
Maricite and sodium iron hydroxyphosphate (SIHP) are recently
discovered iron(II) and
iron(III) compounds that play a major role in phosphate
“hideout” and corrosion in high-pressure boilers. This paper reports a novel method for
synthesizing maricite by thermally
decomposing the complex of aqueous iron(III) nitrilotriacetic acid
at 200 °C and methods
for the hydrothermal synthesis of SIHP from
Fe<sub>3</sub>O<sub>4</sub> or FePO<sub>4</sub>. The crystal
structure of
maricite is identical to the impure natural mineral (Le Page Y.; Donnay
G. <i>Can. </i><i>Mineral.</i>
<b>1977</b>, <i>15</i>, 518−521). The X-ray diffraction
pattern of SIHP is consistent with an orthorhombic
unit cell containing 8 units of formula
Na<sub>3</sub>Fe(PO<sub>4</sub>)<sub>2</sub>·(Na<sub>2(1</sub><sub>-</sub><i><sub>x</sub></i><sub>)</sub>H<sub>2</sub><i><sub>x</sub></i>O),
with <i>x</i> = 0.226 ± 0.025.
This is similar, but not identical, to the formula
Na<sub>4</sub>Fe(OH)(PO<sub>4</sub>)<sub>2</sub>·<sup>1</sup>/<sub>3</sub>NaOH
proposed by
Ziemniak and Opalka (<i>Proc. Sixth Int. Symp. on Environmental
</i><i>Degradation of Materials
in Nuclear Power </i><i>Systems</i><i>Water Reactors</i>;
Gold, R. E., Simonen, E. P., Eds.; Mater., Metals,
Minerals Soc., 1993; pp 929−935.). The main structural feature
is a chain of iron(III) ions
linked by bridging oxygens and phosphate bridges. The iron
phosphate chains are held
together by sodium ions in the ratio 3Na/Fe/2(PO<sub>4</sub>).
Charge balance with the O<sup>2-</sup>
bridge
between each iron ion is maintained by Na<sup>+</sup> and
H<sup>+</sup> ions located in a relatively open cage in
the phosphate lattice. The structure is significant in that it
explains the variable
stoichiometry observed in powder diffraction patterns, and it
identifies the stoichiometry of
H and O, which cannot be determined from solubility
studies.
1998-02-12 00:00:00
Crystal Structure
phosphate lattice
phosphate bridges
paper reports
SIHP
8 units
solubility studies
sodium iron hydroxyphosphate
FePO 4
powder diffraction patterns
synthesizing maricite
hydrothermal synthesis
Environmental Degradation
Sixth Int
Na
Charge balance
sodium ions
iron ion
Fe 3 O 4
iron phosphate chains
crystal structure
unit cell
novel method