An Independent Method for Data Selection of Long-life Radionuclides (Actinides and Fission Products) in the Geosphere

Henry, Marc; Merceron, Thierry

doi:10.1524/ract.1994.6667.s1.57

Cited by 1 publication

(1 citation statement)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…An electrostatic energy calculation study based on a “partial charge” approach has been carried out by Taulelle et al , A case study has been examined, the formation of microporous AlPO 4 −CJ2 in a fluoride medium at neutral pH by in situ multinuclear NMR. Calculations support the assumption that the coordination change is due to a loss of a water molecule between the six- and five-coordinated Al species.…”

Section: Discussionmentioning

confidence: 99%

In Situ NMR of SAPO-34 Crystallization

et al. 2003

View full text Add to dashboard Cite

SAPO-34 (SAPO: silicoaluminophosphate) has been synthesized and examined by in situ multinuclear high-resolution NMR under hydrothermal conditions (170 °C) in the presence of HF, using morpholine as the structure-directing agent. Four routes have been examined: (a) from a SAPO gel with HF (triclinic SAPO-34), (b) from a SAPO gel without HF (trigonal SAPO-34), (c) from an AlPO4 gel with HF (triclinic AlPO4-34), and (d) from a slurry containing the layered AlPO4F prephase (triclinic AlPO4-34). In situ 13C, 19F, 27Al, and 31P NMR have uncovered the main steps of the reaction. The gel dissolves into small units condensed to no more than 4-rings (4R). The next steps are formation of a layered intermediate (the prephase), redissolution of the prephase into 4R building units of different types depending on the fluoride contents and aluminum coordination, and the subsequent nucleation and crystallization of triclinic AlPO4/SAPO-34. The initial fast process leads to the formation of the prephase made of an alternating stacking of 4R type-II units. When approaching 170 °C, this phase redissolves in 4R type-III units with aluminum in five-coordination. With additional defluorination, 4R type-IV units transform into 4R type-V units and both types connect in a chabazite topology. One 4R type-IV unit clips two fluorine atoms into the bridging position in the 4-ring and subsequently shapes the network topology into its crystalline order. The mechanism provided can now be subjected to further chemical testing for purposes of syntheses optimization.

show abstract

Section: Discussionmentioning

confidence: 99%