Redox kinetics of iron in alkali silicate glasses exposed to ionizing beams: Examples with the electron microprobe

详细信息	查看全文 | 推荐本文 |

• 作者：Michel Fialin^a ; ^{michel.fialin@upmc.fr} ; Christiane Wagner^b ; ^c
• 关键词：Electron probe microanalysis ; Peak-shift method ; Alkali diffusion ; Oxygen outgassing ; Iron redox in glasses
• 刊名：Journal of Non-Crystalline Solids
• 出版年：2012
• 期刊代码：50_00223093
• 类别：ms
• 出版时间：1 July, 2012
• 卷：358
• 期：12-13
• 页码：1617-1623
• 文件大小：1056 K

摘要

We report herein on changes in the Fe³⁺/危Fe ratios induced by the electromigration of alkali ions (Alk⁺s) in natural alkali silicate glasses by measuring the shift of the Fe L伪 emission peak at the electron microprobe. The Fe³⁺ reduction to Fe²⁺ classically occurs by electron transfer (Fe³⁺ + e^{鈭?/sup> 鈫?#xA0;Fe2+). The inward diffusion (to the bulk) of Alk+s is correlated with the outward diffusion (to the surface) of electrons transferred from a Fe2+ site to a neighboring Fe3+ site. This reduction process is somewhat different when iron is found at low amounts in glasses. In the latter case, Fe3+ is an efficient electron trap and its reduction to Fe2+ occurs by direct capture of a free electron. The Fe2+ oxidation is induced by the formation and the outward diffusion of O2鈭?/sup> interstitial ions produced at the sites of paired nonbridging oxygens after the departure of the charge compensating Alk+s. The accumulation of free oxygens beneath the surface makes Fe3+-rich oxide phases to precipitate as separate nanometer sized particles. Outgassing of atomic oxygens as bubbles is also observed.}