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A Study of Natural Metamict Yttrium Niobate as Analogue of Actinide Ceramic Waste Form

Published online by Cambridge University Press:  01 July 2014

Cao Qiuxiang
Affiliation:
East China Institute of Technology, Guanglan Road, 418, 330013, Nanchang, Jiangxi, China Saint-Petersburg State University, Universitetskaya emb. 7/9, 199034, St.-Petersburg, Russia
Anton I. Isakov
Affiliation:
Saint-Petersburg State University, Universitetskaya emb. 7/9, 199034, St.-Petersburg, Russia V.G. Khlopin Radium Institute, 2-nd Murinskiy Ave. 28, 194021, St.-Petersburg, Russia
Liu Xiaodong
Affiliation:
East China Institute of Technology, Guanglan Road, 418, 330013, Nanchang, Jiangxi, China
Sergey V. Krivovichev
Affiliation:
Saint-Petersburg State University, Universitetskaya emb. 7/9, 199034, St.-Petersburg, Russia
Boris E. Burakov
Affiliation:
V.G. Khlopin Radium Institute, 2-nd Murinskiy Ave. 28, 194021, St.-Petersburg, Russia
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Abstract

Natural metamict mineral found as large (1-3 cm in size) homogeneous grains (as assumed, former single crystals), was investigated by X-ray powder diffraction (pXRD), high-temperature pXRD, scanning electron microscopy (SEM) and electron microprobe analysis (EMPA). The average chemical composition obtained by EMPA is (wt. %): Nb2O5 – 42.6; Ta2O5 – 4.4; TiO2 – 9.2; UO3 – 4.4; ThO2 – 1.0; MnO – 1.3; FeO – 19.4; Y2O3 – 16.6.

The untreated (original) sample is X-ray amorphous. The sample remained amorphous after annealing at 400 °C for 1 hour. The sample became almost fully crystalline after annealing at 700 °C for 1 hour with an X-ray diffraction pattern similar to that of Fe-columbite (ICCD: 01-074-7356). Further annealing at 1000 °C and higher temperatures caused changes in the phase composition of the sample. It was proposed that under self-irradiation a single-phase U-Th-bearing solid solution, based on monocrystalline Y-niobate, became metamict but remained homogeneous without evidence of solid solution destruction. However, this metamict solid solution is unstable under thermal treatment and recrystallization.

Type
Articles
Copyright
Copyright © Materials Research Society 2014 

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References

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