Zinc(II) oxide stability in alkaline sodium phosphate solutions at elevated temperatures
- Knolls Atomic Power Lab., Schenectady, NY (United States)
Zinc oxide (ZnO) is shown to transform into either of two phosphate-containing compounds in relatively dilute alkaline sodium phosphate solutions at elevated temperatures via ZnO(s) + Na[sup +] + H[sub 2]PO[sub 4]- [l reversible] NaZnPO[sub 4](s) + H[sub 2]O or 2ZnO(s) + H[sub 3]PO[sub 4](aq) [l reversible] Zn[sub 2](OH)PO[sub 4](s) + H[sub 2]O. X-ray diffraction analyses indicate that NaZnPO[sub 4] possesses an orthorhombic unit cell having lattice parameters a = 8.710 [+-] 0.013, b = 15.175 [+-] 0.010, c = 8.027 [+-] 0.004 [angstrom]. The thermodynamic equilibria for these reactions were defined in the system ZnO-Na[sub 2]O-P[sub 2]O[sub 5]-H[sub 2]O for Na/P molar ratios between 2.1 and 3. On the basis of observed reaction threshold values for sodium phosphate concentration and temperature, the standard entropy (S[degrees]) and free energy of formation ([delta]G[sub f][degrees]) for NaZnPO[sub 4] were calculated to be 169.0 J/(mol K) and -1510.6 kJ/mol, respectively; similar values for Zn[sub 2](OH)PO[sub 4] (tarbuttite) were 235.9 J/(mol K) and -1604.6 kJ/mol. Additions of sodium sulfite and sulfate did not alter the above reactions. 26 refs., 5 figs., 7 tabs.
- OSTI ID:
- 7019810
- Journal Information:
- Chemistry of Materials; (United States), Vol. 6:4; ISSN 0897-4756
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
SODIUM PHOSPHATES
CHEMICAL REACTIONS
ZINC OXIDES
EQUILIBRIUM
FORMATION HEAT
ALKALI METAL COMPOUNDS
CHALCOGENIDES
ENTHALPY
OXIDES
OXYGEN COMPOUNDS
PHOSPHATES
PHOSPHORUS COMPOUNDS
PHYSICAL PROPERTIES
REACTION HEAT
SODIUM COMPOUNDS
THERMODYNAMIC PROPERTIES
ZINC COMPOUNDS
400201* - Chemical & Physicochemical Properties