Daniel Caurant

Publications (74) View all

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  Available from: Daniel Caurant

  Dataset: Structural Characterization of Nd-Doped Hf-Zirconolite Ceramics Ca1-xNdxHfTi2-xAlxO7 (0 <x <0.2)

  Daniel Caurant, Isabelle Bardez, Pascal Loiseau
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  ABSTRACT: Because of its high incorporation capacity and of the high thermal neutron capture cross-section of hafium, Hf-zirconolite (CaHfTi2O7) ceramic can be envisaged as a potential waste form for minor actinides (Np, Am, Cm) and plutoniumimmobilization. In this work, Nd-doped Hf-zirconolite Ca1-xNdxHfTi2-xAlxO7 (x = 0; 0.01 and 0.2) ceramics have been prepared by solid state reaction. Neodymium has been used as trivalent actinide surrogate. The ceramic samples structure has been studied by X-ray diffraction and refined by the Rietveld method. This revealed that Nd3+ ions only enter the Ca site, whereas part of Hf4+ ions substitute titanium into Ti(1) sites and Al3+ions mainly occupy the Ti(2) split sites and Ti(3) sites of the zirconolite structure. Using various spectroscopic techniques (electron spin resonance, optical absorption and fluorescence), the environment of Nd3+ cations in Hf-zirconolite has been studied and compared with that of Nd3+cations in Zr-zirconolite (CaZrTi2O7). Different local environments of Nd3+cations have been detected in Hf-zirconolite that can be attributed to the existence of an important disorder around Nd in the Ca site probably due to the statistical occupancy of the next nearest cationic site of neodymium (a split Ti site) by Ti4+ ,Al3+ cations and vacancies. No significant differences were observed concerning Nd3+ cations environment and distribution in Hf- and Zr-zirconolite ceramics.
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  Available from: Thibault Charpentier

  Dataset: Structural investigations of borosilicate glasses containing MoO3 by MAS NMR and Raman spectroscopies

  Daniel Caurant, Odile Majérus, Edouard Fadel, Marion Lenoir, Christel Gervais, Thibault Charpentier, D. R. Neuville
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  ABSTRACT: igh molybdenum concentration in glass compositions may lead to alkali and alkaline-earth molybdates crystallization during melt cooling that must be controlled particularly during the preparation of highly radioactive nuclear glassy waste forms. To understand the effect of molybdenum addition on the structure of a simplified nuclear glass and to know how composition changes can affect molybdates crystallization tendency, the structure of two glass series belonging to the SiO2–B2O3–Na2O–CaO–MoO3 system was studied by 29Si, 11B, 23Na MAS NMR and Raman spectroscopies by increasing MoO3 or B2O3 concentrations. Increasing MoO3 amount induced an increase of the silicate network reticulation but no significant effect was observed on the proportion of image units and on the distribution of Na+ cations in glass structure. By increasing B2O3 concentration, a strong evolution of the distribution of Na+ cations was observed that could explain the evolution of the nature of molybdate crystals (CaMoO4 or Na2MoO4) formed during melt cooling.
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  Available from: Daniel Caurant

  Article: Crystallization of CaHf1−xZrxTi2O7 (0 ≤ x ≤ 1) zirconolite in SiO2–Al2O3–CaO–Na2O–TiO2–HfO2–ZrO2–Nd2O3 glasses

  Daniel Caurant, Isabelle Bardez, Pascal Loiseau
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  ABSTRACT: Glass-ceramics containing (Hf,Zr)-zirconolite crystals (nominally CaHf1−x Zr x Ti2O7 with 0≤x≤1) were envisaged to immobilize minor actinides and plutonium. Such materials were prepared in this study by controlled crystallization of glasses belonging to the SiO2–Al2O3–CaO–Na2O–TiO2–HfO2–ZrO2–Nd2O3 system. Neodymium was used as trivalent actinides surrogate. The effect of total or partial substitution of ZrO2 by HfO2 (neutron poison for fission reactions) on glass crystallization in the bulk and near the surface is presented. It appeared that Hf/Zr substitution had not significant effect on nature, structure, and composition of crystals formed both on glass surface (titanite+anorthite) and in the bulk (zirconolite). This result can be explained by the close properties of Zr4+ and Hf4+ ions and by their similar structural role in glass structure. However, strong differences were observed between the nucleation rate IZ of zirconolite crystals in glasses containing only HfO2 and in glasses containing only ZrO2. Hf-zirconolite (CaHfTi2O7) crystals were shown to nucleate only very slowly in comparison with Zr-zirconolite (CaZrTi2O7) crystals. Composition changes - by increasing either HfO2 or Al2O3 concentration or by introducing ZrO2 in parent glass - were performed to increase IZ in hafnium-rich glasses. The proportion of Nd3+ ions incorporated in the zirconolite phase was estimated using ESR.
  Journal of Materials Science 04/2012; 42(24):10203-10218. · 2.02 Impact Factor
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  Available from: Daniel Caurant

  Article: Effect of Al2O3 concentration on zirconolite (Ca(Zr,Hf)Ti2O7) crystallization in (TiO2,ZrO2,HfO2)-rich SiO2–Al2O3–CaO–Na2O glasses

  Daniel Caurant, Pascal Loiseau, Isabelle Bardez, Christel Gervais
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  ABSTRACT: Glass-ceramic matrices containing zirconolite (nominally Ca(Zr,Hf)Ti2O7) crystals in their bulk that would incorporate high proportions of minor actinides (Np, Am, Cm) or plutonium could be envisaged for their immobilization. Zirconolite-based glass-ceramics can be prepared by controlled crystallization of zirconolite in glasses belonging to SiO2–Al2O3–CaO–Na2O–TiO2–ZrO2–HfO2 system. In this study, neodymium was used as trivalent actinides surrogate. Increasing Al2O3 concentration in glass composition had a strong effect on the nucleation rate I z of zirconolite crystals in the bulk, on the amount of neodymium incorporated in zirconolite phase and on the crystal growth rate of silicate phases (titanite+anorthite) from glass surface. These results could be explained by the existence of competition—in favor of aluminum—between Al3+ and (Ti4+, Zr4+, Hf4+) ions for their association with charge compensators cations to facilitate their incorporation in the glassy network. Differential thermal analysis (DTA) was used to study exothermal effects associated with bulk and surface crystallization. 27Al magic angle spinning nuclear magnetic resonance (MAS NMR) spectra showed that aluminum enters glasses network predominantly in 4-fold coordination. Neodymium optical absorption and fluorescence spectroscopies showed that the Al2O3 concentration changes performed in this study had not significant effect on Nd3+ ions environment in glasses.
  Journal of Materials Science 04/2012; 42(20):8558-8570. · 2.02 Impact Factor
• Article: Structural characterization of SiO2-Na2O-CaO-B2O3-MoO3 glasses

  Daniel Caurant, Odile Majérus, Edouard Fadel, Marion Lenoir, Christel Gervais, Thibault Charpentier, D. R. Neuville
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  ABSTRACT: Nuclear spent fuel reprocessing generates high level radioactive waste with high Mo concentration that are currently immobilized in borosilicate glass matrices containing both alkali and alkaline-earth elements [1]. Because of its high field strength, Mo6+ ion has a limited solubility in silicate and borosilicate glasses and crystallization of alkali or alkaline-earth molybdates can be observed during melt cooling or heat treatment of glasses [2-4]. Glass composition changes can significantly modify the nature and the relative proportions of molybdate crystals that may form during natural cooling of the melt. For instance, in a previous work we showed that CaMoO4 crystallization tendency increased at the expenses of Na2MoO4 when B2O3 concentration increased in a SiO2-Na2O-CaO-MoO3 glass composition [4]. In this study, we present structural results on two series (Mx, By) of quenched glass samples belonging to this system using 29Si, 11B, 23Na MAS NMR and Raman spectroscopies. The effect of MoO3 on the glassy network structure is studied and its structural role is discussed (Mx series). The evolution of the distribution of Na+ ions within the borosilicate network is followed when B2O3 concentration increased (By series) and is discussed according to the evolution of the crystallization tendency of the melt. For all glasses, ESR was used to investigate the nature and the concentration of paramagnetic species.
  04/2011;