Incipient formation of zircon and hafnon during glass alteration at 90°C

Abstract

Layered zircon and hafnon are observed at the surface of gels resulting from the complete alteration of Zr‐ or Hf‐bearing borosilicate glasses at 90°C and pH 1. The unusually low temperature of formation may arise from the similarity of the local structure around Zr in the gel (from the altered glasses), the leaching solution and the zircon structure, in particular, the majority eight‐coordination of Zr and the connectivity of Zr‐sites with their surroundings. Similar behavior is expected for Hf, which mimics Zr speciation in solution and hafnon structure. This work expands the known formation methods of zircon and hafnon at low temperature, underlining the importance of amorphous precursors to facilitate crystal growth under unusual conditions.

Raman spectra of gem‐quality variscite and metavariscite

“…The chemistry does not change much within samples of the same provenance . Minor substitution of Al by Cr 3+ and Fe 3+ is responsible for the green to blue color of these materials . There is no significant difference between different colored areas of the sample #2698, so possibly, the color variation in the same sample is only linked to microstructure, inducing light scattering.…”

“…Gem cabochons are opaque with a waxy to vitreous luster, depending on polish. Variscite beads, sometimes with remarkably bright green tint, have been discovered in several Neolithic archaeological sites around Europe . Objects made out of this material are commonly macroscopically mistaken for turquoise or ‘jade’, as well as lesser known gem materials .…”

“…Variscite and metavariscite are relatively rare in nature, and they form at low temperatures from the reaction of phosphate‐bearing surface solutions with aluminum‐rich rocks . Besides gems, variscite and metavariscite mineral group members are also used as trap for phosphorus emitted by plants as well as a zeolite‐like water absorbing material…”

Soft Hydrothermal Synthesis of Hafnon, HfSiO4

“…These conditions appear to be quite surprising, taking into account the possibility to prepare isostructural silicates, e.g., ZrSiO 4 , ,− CeSiO 4 , ,− ThSiO 4 , ,,− USiO 4 , ,,,− NpSiO 4 , PuSiO 4 , and AmSiO 4 under soft hydrothermal conditions (i.e., for T ≤ 250 °C). However, it may be also noticed that the formation of amorphous hafnon has been observed by alteration, in an aqueous solution, of Hf-bearing borosilicate glasses at 90 °C and pH = 1 . More specifically, we recently reported that modifications of the starting pH and elementary concentrations allowed for the decrease of the temperature of formation of ThSiO 4 and CeSiO 4 under hydrothermal conditions. , Therefore, the aim of this study was to determine an efficient way of synthesis allowing the formation of HfSiO 4 under soft hydrothermal conditions.…”

Recent Advances in Corrosion Science Applicable To Disposal of High-Level Nuclear Waste

“…By coupling experiments and simulations, the effects of ZrO 2 , V 2 O 5 , and Al 2 O 3 on glass structure and corrosion characteristics have been investigated. Even at low concentration, zirconia is known to significantly affect the glass chemical durability ,, and other properties such as viscosity and glass transition temperature . In particular, the addition of zirconia was found to decrease r 0 but increase r r by changing potentially protective properties of alteration layers such as porosity. , Lu et al studied the effects of ZrO 2 /SiO 2 substitution on ISG properties using classical MD simulations with the recently developed Deng–Du potential set .…”