# 【8.2 参考资料 16】The 28th Japan-Korea International Seminar on Ceramics, GO-P-2, 2011 年 11 月, Okayama.

# Distribution of transition metal ions associated with phase separation in $ Na_{2}O-CaO-B_{2}O_{3}-SiO_{2} $ glass system

Manami Ohno $ ^{1} $ , Shinichi Sakida $ ^{2} $ , Yasuhiko Benino $ ^{1,*} $ , Tokuro Nanba $ ^{1} $

$ ^{1} $ Graduate School of Environmental Science, Okayama University,

$ ^{2} $ Environmental Management Center, Okayama University,

Okayama 700-8530, Japan

$ ^{*} $ benino@cc.okayama-u.ac.jp

Keywords: Glass, Phase separation, Distribution, Transition metal

### 1. Introduction

General wastes such as household garbage are currently emitted as molten slags which are glassy solid produced by high-temperature incineration furnaces. The waste treatment is effective for the decomposition of dioxin, volume reduction of wastes, and life extension of waste disposal sites. Moreover molten slags are also reused to asphalt pavement materials and concrete ingredients, because they have high chemical stability. The chemical components of molten slags are $ SiO_{2} $ , CaO, and $ Al_{2}O_{3} $ , which are the constituents of commercial glasses, such as cups and windows. In the authors' research group, a novel waste recycling method has been developed by using phase separation of borosilicate glass, in which alkali, alkali earth metal, and Fe ions are preferentially distributed into $ B_{2}O_{3} $ -rich phase [1,2]. Among transition metals, Ti indicated a different behavior; Ti ions were not incorporated into $ B_{2}O_{3} $ -rich phase after the phase separation. It was suggested that the distribution of transition metals was influenced by the nature of transition metals. Transition metals are widely used in the field of glass industry as a coloring agent, and in the recycling of inorganic wastes, therefore, it is very important to clarify the distribution behavior of transition metals due to phase separation of glasses.

In this study, various transition metals were introduced to the borosilicate glasses in the system of $ Na_{2}O-CaO-B_{2}O_{3}-SiO_{2} $ , and distribution behavior was investigated, obtaining the effect of glass composition, redox state of transition metal ions, and influence of co-existing additives on the distribution behavior of transition metal ions.

### 2. Experimental procedure

Glasses with the composition of (1) $ 6Na_{2}O\cdot4CaO\cdot30B_{2}O_{3}\cdot60SiO_{2} $ and (2) $ 10Na_{2}O\cdot30B_{2}O_{3}\cdot60SiO_{2} $ (mol%) were chosen as matrix glass, to which transition metal oxides, $ TiO_{2} $ , $ CrO_{1.5} $ , $ FeO_{1.5} $ , and ZnO equivalent of 1 mol% of main glass were added. The raw materials of reagent grade $ Na_{2}CO_{3} $ , $ CaCO_{3} $ , $ B_{2}O_{3} $ , $ SiO_{2} $ and a transition metal oxide were mixed thoroughly and melted in a platinum crucible in an electric furnace at $ 1400^{\circ}C $ for 1 h after calcination at $ 1000^{\circ}C $ for 30 min. The melts were quenched, obtaining glass plates with a thickness of 2 - 3 mm. Differential thermal analyses (DTA) were carried out in order to determine glass transition and crystallization temperatures.

According to the results, heat treatments for phase separation were carried out at 600 and $ 650^{\circ} $ C for 16, 32, and 48 h. After the heat treatment, the glasses were immersed in nitric acid of 1.0 N for 24 h, and the insoluble residues were recovered with vacuum filtration. The insoluble residues were dried in an oven, $ SiO_{2} $ -rich glasses were obtained.

Chemical composition of the acidic solutions was determined by an inductively coupled plasma (ICP) emission spectrometry, and that of the insoluble residues after acid treatment was by X-ray fluorescence analysis (XRF).

### 3. Result

As shown in Figs. 1 and 2, with increasing the time of heat treatment, transmittance decreases at shorter wavelength region, suggesting the development of phase separation. In the CaO-free glass system (2), significant shift of transmission curve is identified, even after the same heat treatment with