文章信息/Info

Title:

Dissolution of molybdate anions in borosilicate glasses for nuclear waste vitrification use

作者:

譚盛恒; Russell J HAND

英國謝菲爾德大學材料科學與工程系

Author(s):

TAN Shengheng;  Russell J HAND

Immobilisation Science Laboratory, Department of Materials Science and Engineering, University of Sheffield,

關鍵詞:

核廢料玻璃化; 鉬; 堿土金屬; 拉曼光譜; 電鏡

DOI:

10.7502/j.issn.1674-3962.2016.07.03

文獻標志碼:

A

摘要:

在英國和法國的很多高放核廢料中都含有大量的鉬。鉬在核廢料玻璃中的溶解度很低，過量的鉬會導致玻璃產生鉬酸鹽分相從而影響核廢料玻璃化的效率和安全。本文主要研究鉬酸鹽在硼酸鹽玻璃中的溶解度與玻璃中堿土金屬元素的關系以及鉬酸鹽的溶解對玻璃的結構和性質的影響。在其它玻璃組分不變的情況下，玻璃中的堿土金屬（由鎂至鋇）進行等摩爾量替換。結果發現，當堿土金屬為鈣時鉬酸鹽的溶解度最高，為2.84 mol%。XRD結果顯示除了明顯分相的玻璃外其它均一玻璃均為無定形態。SEM結果顯示玻璃基體內的分相大多為球狀/水滴狀并呈隨機分布；其尺寸與鉬酸鹽的過量程度有關，但直徑都小于1微米。對鈣硼硅酸鹽玻璃中析出相的EDX分析表明其中富含鉬和鈣，而TEM結果證明這些析出相為晶體相且符合鉬酸鈣的電子衍射特征。含鉬玻璃有兩個強烈的拉曼峰（分別位于320和910 cm–1附近）：其強度隨玻璃中鉬含量的增加而增加，其位置隨玻璃中堿土金屬元素變化而偏移。此外，鉬的加入也會導致玻璃的玻璃轉變溫度降低以及玻璃密度增加。

Abstract:

MoO3 is one of the challenging oxides in nuclear waste vitrification in the UK. It has a poor solubility in the conventionally used nuclear waste glasses and its excess presence may cause the formation of “yellow phase” which is highly detrimental to vitrification process. This work investigates the compositional dependence of MoO3 solubility in borosilicate glasses with varying alkaline earth species as well as the effects of MoO3 addition on glass structure and properties. Among all alkaline earths Ca is the best in terms of MoO3 solubility, with 2.84 mol% in calcium borosilicate glass (CBS) without causing any visible phase separation. Magnesium borosilicate glass (MBS) has the lowest MoO3 solubility (≤1 mol%). XRD results indicate that, while the visibly homogeneous glasses all remain amorphous nature, the visibly heterogeneous glasses contain tiny molybdate crystals. According to SEM results, the separated particles forming within glass matrices are mostly spherical, submicron in diameter and randomly dispersed; the size of these particles are dependent on the extent to which MoO3 addition is excessive. Compositional analysis for separated phases in CBS glass with excess MoO3 suggests that the phases are rich in Mo and Ca, while TEM results prove the crystallinity of separated particles whose electron diffraction patterns are in accordance with those of CaMoO4. Two Raman bands are observed due to addition of MoO3 in glass; the bands are assigned to bending and stretching vibrations of MoO42– and their intensities increase with MoO3 addition. The positions of these bands shift with alkaline earth species in glass, indicating that the local environment of MoO42– is closely associated with alkaline earth cations in glass network. MoO3 addition to glass also results in decreased glass transition temperature Tg, which suggests a depolymerized network due to MoO42– incorporation. Glass density is increased with the increase amount of MoO3 in glass as long as the glass remains homogeneous.