Zinc(II) oxide stability in alkaline sodium phosphate solutions at elevated temperatures
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}{sup {minus}} {r_reversible} NaZnPO{sub 4}(s) + H{sub 2}O or 2 ZnO(s) + H{sub 3}PO{sub 4}(aq) {r_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, and 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. Based on 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 {minus}1510.6 kJ/mol, respectively; similar values for Zn{sub 2}(OH)PO{sub 4} (tarbuttite) were 235.9 J/mol-K and {minus}1604.6 kJ/mol. Additions of sodium sulfite and sulfate did not alter the above reactions.
- Research Organization:
- Knolls Atomic Power Lab., Schenectady, NY (United States)
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- DOE Contract Number:
- AC12-76SN00052
- OSTI ID:
- 10194886
- Report Number(s):
- KAPL--4762; ON: DE94003316
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
152001
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201
AQUEOUS SOLUTIONS
CHEMICAL AND PHYSICOCHEMICAL PROPERTIES
CHEMICAL REACTION YIELD
CHEMICAL REACTIONS
CORROSION
ENTROPY
EXPERIMENTAL DATA
FORMATION FREE ENERGY
Geothermal Legacy
LATTICE PARAMETERS
PROPERTIES OF AQUEOUS SOLUTIONS
SODIUM PHOSPHATES
STABILITY
TEMPERATURE DEPENDENCE
THERMODYNAMIC PROPERTIES
THERMODYNAMICS
X-RAY DIFFRACTION
ZINC OXIDES