Oxyde de neptunium(IV)

Oxyde de neptunium(IV)
Identification
No CAS 12035-79-9
No ECHA 100.031.651
SMILES
InChI
Apparence cristaux verts cubiques[1]
Propriétés chimiques
Formule NpO2
Masse molaire[2] 269 g/mol
Np 88,12 %, O 11,9 %,
Propriétés physiques
fusion 3 070 K (2 797 °C)
± 62 K[3]
Cristallographie
Système cristallin Cubique
Symbole de Pearson
Classe cristalline ou groupe d’espace Fm3m (no 225)
Structure type Fluorine
Précautions
Matériau radioactif
Composé radioactif

Unités du SI et CNTP, sauf indication contraire.

L'oxyde de neptunium(IV) ou dioxyde de neptunium est un composé chimique vert olive[4] de formule NpO2.

Production et purification

Le dioxyde de neptunium est produit industriellement par calcination de l'oxalate de neptunium(IV). L'oxalate de neptunium(IV) est préalablement obtenu par précipitation depuis une solution d'acide nitrique contenant le neptunium sous divers états d'oxydation traitée à l'acide ascorbique (pour que le neptunium(IV) prédomine) puis à l'acide oxalique[5].

Le dioxyde de neptunium peut également être produit à partir du peroxyde de neptunium(IV)[5].

Comme composant du combustible nucléaire usé, le dioxyde de neptunium peut être purifié par fluoration puis réduction par du calcium en excès en présence d'iode[6]. Cependant, la synthèse du dioxyde par calcination de l'oxalate conduit à un produit contenant moins de 0,3 % en masse d'impureté. Une purification ultérieure n'est donc généralement pas nécessaire[5].

Notes et références

  1. (en) D. R. Lide, Handbook of Chemistry and Physics 87 ed., CRC Press, (ISBN 0-8493-0594-2, lire en ligne), p. 471.
  2. Masse molaire calculée d’après « Atomic weights of the elements 2007 », sur www.chem.qmul.ac.uk.
  3. R. Böhler, M. J. Welland, F. De Bruycker, K. Boboridis, A. Janssen, R. Eloirdi, R. J. M. Konings et D. Manara, « Revisiting the melting temperature of NpO2 and the challenges associated with high temperature actinide compound measurements », American Institute of Physics, vol. 111, no 11,‎ , p. 113501 (DOI 10.1063/1.4721655, Bibcode 2012JAP...111k3501B).
  4. (en) Pradyot Patnaik, Handbook of Inorganic Chemical Compounds, McGraw-Hill Professional, , 1086 p. (ISBN 978-0-07-049439-8 et 0-07-049439-8), p. 271.
  5. a b et c (en) J. A. Porter, « Production of Neptunium Dioxide », Industrial & Engineering Chemistry Process Design and Development, vol. 4, no 3,‎ , p. 289–292 (DOI 10.1021/i260012a001).
  6. (en) Elmer J. Huber Jr et Charles E. Holley Jr, « Enthalpy of formation of neptunium dioxide », Journal of Chemical Engineering Data, vol. 13, no 4,‎ , p. 545–546 (DOI 10.1021/je60039a029).

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