Synthesis, Crystal Structure, and Enthalpies of Formation
of Churchite-type REPO4·2H2O (RE = Gd to
Lu) Materials
Version 2 2019-07-16, 14:11Version 2 2019-07-16, 14:11
Version 1 2019-07-15, 13:03Version 1 2019-07-15, 13:03
Posted on 2019-07-16 - 14:11
Monazite
(REPO4; RE = La to Gd) and xenotime (REPO4;
RE = Tb to Lu & Y) materials have been proposed as host
matrices for the immobilization of actinides. Aqueous alteration of
monazite and xenotime minerals could result in the formation of rhabdophane
(REPO4·0.667H2O; RE = La to Dy) and churchite
(REPO4·2H2O; RE = Gd to Lu & Y) phases,
respectively. Among these structure types, the structure and properties
of churchite materials are not well-understood, and this study aims
to bridge this gap by providing a comprehensive insight into the structure
and thermochemical properties of churchite materials. Churchite materials
(REPO4·2H2O; RE = Gd to Lu) were synthesized
by a low-temperature precipitation route, and their crystal structures
were determined by powder X-ray diffraction (XRD). Examination of
the powder XRD data showed that the churchite materials crystallize
in the monoclinic crystal system (space group C2/c). The enthalpies of formation (ΔH°f,ox) of churchite-type REPO4·2H2O (RE = Gd to Yb) determined by high-temperature oxide melt
solution calorimetry are more negative than their anhydrous counterparts
(i.e., xenotime structure) and indicate that the formation of churchite
is more exothermic than the xenotime phase. However, the churchite
materials are likely to have a more negative entropy of formation
(ΔS°f,ox) due to the presence
of water molecules, resulting in a less negative Gibbs free energy
of formation (ΔG°f,ox) than
the xenotime structure. Therefore, churchite materials are expected
to be stable at lower temperatures. For the unique case of GdPO4 and GdPO4·nH2O materials, which could adopt all the above-discussed structure
types, the ΔG°f,ox of monazite
from oxides was observed to be more negative than those of xenotime,
rhabdophane, and churchite thereby suggesting the following order
of stability: Gd-churchite < Gd-rhabdophane < Gd-xenotime <
Gd-monazite.
CITE THIS COLLECTION
DataCite
DataCiteDataCite
3 Biotech3 Biotech
3D Printing in Medicine3D Printing in Medicine
3D Research3D Research
3D-Printed Materials and Systems3D-Printed Materials and Systems
4OR4OR
AAPG BulletinAAPG Bulletin
AAPS OpenAAPS Open
AAPS PharmSciTechAAPS PharmSciTech
Abhandlungen aus dem Mathematischen Seminar der Universität HamburgAbhandlungen aus dem Mathematischen Seminar der Universität Hamburg
ABI Technik (German)ABI Technik (German)
Academic MedicineAcademic Medicine
Academic PediatricsAcademic Pediatrics
Academic PsychiatryAcademic Psychiatry
Academic QuestionsAcademic Questions
Academy of Management DiscoveriesAcademy of Management Discoveries
Academy of Management JournalAcademy of Management Journal
Academy of Management Learning and EducationAcademy of Management Learning and Education
Academy of Management PerspectivesAcademy of Management Perspectives
Academy of Management ProceedingsAcademy of Management Proceedings
Academy of Management ReviewAcademy of Management Review
Subramani, Tamilarasan; Rafiuddin, Mohamed Ruwaid; Shelyug, Anna; Ushakov, Sergey; Mesbah, Adel; Clavier, Nicolas; et al. (2019). Synthesis, Crystal Structure, and Enthalpies of Formation
of Churchite-type REPO4·2H2O (RE = Gd to
Lu) Materials. ACS Publications. Collection. https://doi.org/10.1021/acs.cgd.9b00524