Formation and Dehydration Enthalpy of Potassium Hexaniobate

Sulata K. Sahu, Lynn A. Boatner, Alexandra Navrotsky, W. K. Wong-Ng

Research output: Contribution to journalArticlepeer-review

2 Scopus citations

Abstract

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 K4Nb6O17·3H2O (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. The loss of this water near 100°C on heating is consistent with the weak bonding of water.

Original languageEnglish (US)
Pages (from-to)304-311
Number of pages8
JournalJournal of the American Ceramic Society
Volume100
Issue number1
DOIs
StatePublished - Jan 1 2017
Externally publishedYes

Keywords

  • multilayers
  • photocatalysis
  • thermodynamics

ASJC Scopus subject areas

  • Ceramics and Composites
  • Materials Chemistry

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