Stillwellite, a New Rare-Earth Mineral from Queensland

McAndrew, John; Scott, T. R.

doi:10.1038/176509b0

Cited by 27 publications

(11 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…According to the crystallization results that will be presented below, it is important to note that two forms have been reported in the literature for LaBO3 (La-orthoborate): a hightemperature form (HT) and a low-temperature form (LT) that all consist of isolated BO3 units ((BO3) 3-) bearing three non-bridging oxygen atoms (NBOs) [30,31,32]. All the crystalline phases reported in literature are indicated in the SiO2-B2O3-La2O3 ternary diagram shown in Stillwellite REBSiO5 (RE2O3.B2O3.2SiO2) was first discovered in an Australian ore deposit [33], with major RE being Ce, and has since been synthesized and studied for different REs (La, Ce, Pr, Nd, Sm) [34,35], using either solid-state reaction or hydrothermal synthesis. The crystalline structure belongs to the trigonal crystal system (space group P31) [36,37].…”

Section: Crystalline Phasesmentioning

confidence: 99%

Exploration of glass domain in the SiO2-B2O3-La2O3 system

Trégouët

Caurant

Majérus

et al. 2017

Journal of Non-Crystalline Solids

View full text Add to dashboard Cite

The existence of a relatively wide glass domain has been put in evidence in the SiO2-B2O3-La2O3 ternary system, using a melt-quenching method. This domain extends from a region surrounding the lanthanum metaborate (LaB3O6) composition in the B2O3-La2O3 binary system to ternary compositions bearing up to 39 mol% SiO2. Outside this domain, phase separation phenomena and/or crystallization of La-rich borate (LaBO3) and borosilicate (La3Si2BO10) phases are observed during quenching. The evolution of glass transition temperature (Tg) with composition in the glassy domain has been studied and discussed according to structural changes put in evidence by 11 B MAS NMR. Moreover, the evolution of the thermal stability of a series of glasses derived from a lanthanum metaborate glass by substituting B2O3 by increasing amount of SiO2 (up to 36 mol% SiO2) was studied by DTA and thermal treatments followed by characterization by XRD and Raman spectroscopy. In spite of silica-enrichment along the glass series, the first phases crystallizing during heating were always lanthanum borates (LaB3O6, LaBO3) according the following sequence when SiO2 content increases:

show abstract

Section: Crystalline Phasesmentioning

confidence: 99%

Exploration of glass domain in the SiO2-B2O3-La2O3 system

Trégouët

Caurant

Majérus

et al. 2017

Journal of Non-Crystalline Solids

View full text Add to dashboard Cite

show abstract

“…Natural stillwellite [1,2] is a rare earth mineral, which accepts a very wide range of substitutions, described by the general formula (Ln +3 ,M +2 )B(Si,Ge,Al,P)(O,OH,F) 5.0 where Ln=La, Ce, Pr, or Nd. Among these, LaBGeO 5 (LBG) can be taken as a prototype to represent the series of the larger rare-earth borogermanate stillwellite compounds.…”

Section: Introductionmentioning

confidence: 99%

Structural, electronic, vibrational, and dielectric properties of LaBGeO5 from first principles

Shaltaf

Juwhari

Hamad

et al. 2014

Journal of Applied Physics

View full text Add to dashboard Cite

Structural, electronic, vibrational and dielectric properties of LaBGeO5 with the stillwellite structure are determined based on ab initio density functional theory. The theoretically relaxed structure is found to agree well with the existing experimental data with a deviation of less than 0.2%. Both the density of states and the electronic band structure are calculated, showing five distinct groups of valence bands. Furthermore, the Born effective charge, the dielectric permittivity tensors, and the vibrational frequencies at the center of the Brillouin zone are all obtained. Compared to existing model calculations, the vibrational frequencies are found in much better agreement with the published experimental infrared and Raman data, with absolute and relative rms values of 6.04 cm −1 , and 1.81%, respectively. Consequently, numerical values for both the parallel and perpendicular components of the permittivity tensor are established as 3.55 and 3.71 (10.34 and 12.28), respectively, for the high-(low-)frequency limit.

show abstract

“…Only qualitative X-ray analytical data are available for the phase, which showed concentrations of La, Nd, and Ce, in roughly the proportions contained within the initial glass. Stillwellite was first identified by McAndrew and Scott (1955) from the uranium deposit at Mary Kathleen, Queensland, Australia where it occurs with allanite, garnet, and uraninite as a metasomatic replacement of metamorphosed calcareous sediments. It has since been reported as occurring in nepheline syenite pegmatite dykes with feldspar, nepheline, zircon, fluorite, aegirine, pyrophanite, and pyrochlore (Neumann et al, 1966); in a magnetite ore (Klemic and Loferski, 1979); and has also been synthesized hydrothermally in the temperature range 150-500 ~ by Nekrasov and Nekrasova (1972).…”

Section: Resultsmentioning

confidence: 99%

Hydrothermal crystallization of a radioactive waste storage glass

1985

View full text Add to dashboard Cite

ABSTRACT. A borosilicate glass, containing 25 wt. % of simulated high-level radioactive waste has been reacted with water at 350 ~ and 500 bars for 14 and 48 days using large-volume 'cold-seal' high-pressure equipment. Under these conditions the glass crystallizes a suite of mineral phases including: albite, NaA1Si3Os; aegirine, NaFeSi206; riebeckite, Na2Fez(Fe,Mg)aSisOE2(OH)2; zektzerite, LiNaZrSirOls; barium strontium molybdate, (Ba,Sr) MOO4; stillwellite, (Nd,Ce,La)BSiOs; willemite, ZnzSiO4; smectite; a lithium-sodium borosilicate hydrate; melilite (fikermanite), Ca2MgSi20 7. A description of the morphology of these phases is given, together with a number of chemical analyses. The implications of the incorporation of waste species in these mineral phases to the disposal of high-level radioactive waste is discussed. K E V W O R D S:radioactive waste, borosilicate glass, albite, aegirine, riebeckite, zektzerite, stillwellite, willemite, smectite, melilite.

show abstract

Stillwellite, a New Rare-Earth Mineral from Queensland

Cited by 27 publications

References 0 publications

Exploration of glass domain in the SiO2-B2O3-La2O3 system

Exploration of glass domain in the SiO2-B2O3-La2O3 system

Structural, electronic, vibrational, and dielectric properties of LaBGeO5 from first principles

Hydrothermal crystallization of a radioactive waste storage glass

Contact Info

Product

Resources

About