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Title: Formation and dehydration enthalpy of potassium hexaniobate

The formation energetics of hydrous and dehydrated potassium hexaniobates are investigated using high-temperature oxide melt solution calorimetry. The enthalpies of formation of K4Nb6O17 and K4Nb6O17•3H2O from oxides are (–864.42 ± 10.63) and (–899.32 ± 11.48) kJ/mol, respectively. The formation enthalpy of K4Nb6O17 from elements is (–7289.64 ± 12.50) kJ/mol, and of K4Nb6O17•3H2O is (–8181.94 ± 13.24) kJ/mol. The enthalpy of dehydration (ΔHdehy) for the reaction K4Nb6O173H2O (xl, 25 °C) = K4Nb6O17 (xl, 25 °C) + 3H2O (l, 25 °C) is endothermic and is 34.60 ± 7.56 kJ/mol. The ΔHdehy per mole of water, 11.53 ± 2.52 kJ/mol, indicates the water molecules in K4Nb6O17•3H2O are not just physically adsorbed, but loosely bonded in the K4Nb6O17 phase, presumably in specific interlayer sites. As a result, the loss of this water near 100 °C on heating is consistent with the weak bonding of water.
 [1] ;  [2] ;  [3]
  1. Univ. of California, Davis, CA (United States); Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
  2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  3. Univ. of California, Davis, CA (United States)
Publication Date:
OSTI Identifier:
Grant/Contract Number:
Accepted Manuscript
Journal Name:
Journal of the American Ceramic Society
Additional Journal Information:
Journal Name: Journal of the American Ceramic Society; Journal ID: ISSN 0002-7820
American Ceramic Society
Research Org:
Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
Sponsoring Org:
USDOE Office of Science (SC)
Country of Publication:
United States
36 MATERIALS SCIENCE; 37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY thermodynamics; multilayers; photocatalysis; Layered hexaniobates; K4Nb6O17; K4Nb6O17.3H2O; calorimetry; formation enthalpy; dehydration enthalpy