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Crystallization of sodium molybdate-phosphate and tungstate-phosphate glasses

Authors: Koudelka Ladislav | Kupetska Oksana | Kalenda Petr | Mošner Petr | Montagne Lionel | Revel Bertrand

Year: 2018

Type of publication: článek v odborném periodiku

Name of source: Journal of Non-Crystalline Solids

Page from-to: 42-48

Titles:

Language	Name	Abstract	Keywords
cze	Krystalizace molybdáto-fosfátových a wolframáto-fosfátových sodných skel.	Transformace skel na krystalickou fázi byla studována u dvou skel o složení 25Na(2)center dot O.50MoO(3)center dot 25P(2)O(6) a 25Na(2)O center dot 50WO(3)center dot 25P(2)O(5). Při zahřívání skel došlo k jejich transformaci na krystalické sloučeniny NaMoO2PO4 a NaWO2PO4. Pomocí DTA byly stanoveny jejich body tání jako 695 +/- 2 °C pro NaMoO2PO4 and 858 +/- 2 °C pro NaMoO2PO4. NMR spektroskopie jader 31P ukázala na stejnou lokální koordinaci ve skelné i krystalické fázi a na dvě různé koordinace fosforu v krystalických sloučeninách ve shodě s literárními údaji.	fosfátová skla; krystalizace; Ramanova spektra; NMR spektra; oxid wolframový; oxid molybdenový
eng	Crystallization of sodium molybdate-phosphate and tungstate-phosphate glasses	The glass to crystal transformation was studied for two glasses with composition 25Na(2)center dot O.50MoO(3)center dot 25P(2)O(6) and 25Na(2)O center dot 50WO(3)center dot 25P(2)O(5). During the heat treatment process, two crystalline compounds were formed, NaMoO2PO4 and NaWO2PO4, respectively. Physico-chemical properties of the corresponding glasses and crystals were compared, as well as their Raman and P-31 MAS NMR spectra. Differential thermal analysis revealed crystallization peaks at 483 degrees C for the Mo-containing glass and at 624 degrees C for the W-containing glass; melting points of crystalline compounds were determined as 695 +/- 2 degrees C for NaMoO2PO4 and 858 +/- 2 degrees C for NaMoO2PO4. Sodium tungstate-phosphate glass has lower solubility in comparison with the sodium molybdatephosphate glass. The study of the crystallization mechanism showed a prevailing surface nucleation. P-31 MAS NMR spectra of the two glasses revealed the same shape and almost the same width, which reflects a similar local environment for P in these glasses. The position of the resonance for W-containing glass at a more negative chemical shift than the Mo-containing one is attributed to the different electrical field strength of W atoms than Mo atoms. P-31 MAS NMR spectra of crystals revealed two resonances at + 17 and -0.5 ppm for the Mo glass and at -0.1 and -1.9 ppm for the W glass, reflecting the presence of two different phosphorus short range environments, in agreement with their crystal structure. Raman spectra showed similarity in structural features for Mo and W glasses and their isomorphic compounds. Splitting of the dominant Raman bands in the crystal spectra reflects a distortion of MoO6 and WO6 octahedra. Raman spectra also suggested the breaking of Mo-O-Mo and WOW linkages during crystallization.	Phosphate glasses; Crystallization; Raman spectra; NMR spectra; Tungsten oxide; Molybdenum oxide