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AFPG-D1-10

Analysis of bubble gas composition by Raman spectroscopy（blank line）
Kimiyasu Okumura*, Yasushi Kii, Noriyuki YoshidaEvaluation Div., Research & Development Gr., Nippon Electric Glass Co., Ltd., Shiga, JAPAN（blank line）*Corresponding Author: (kokumura@neg.co.jp)
Keywords: (Bubble, Defect, Gas, Fining, Raman spectroscopy)（blank line）
1. Introduction
Bubbles in glass products are one of the major defects in glass manufacturing. The technology forremoving bubble defects has been advanced day by day. At the same time, the demand for higher glassquality is increasing. Therefore, reducing bubble defects has been a long-standing problem for glass
engineers. One way for reducing bubble defects is analyzing bubble gas composition and optimize theconditions of glass manufacturing process based on the results. So, it is essential technique for glass
manufacturing engineers to identify the bubble gas composition.
2. Analyzing the bubble gas composition by mass spectrometry
Generally, the bubble gas composition is analyzed quantitatively by mass spectrometry. This analysis
method is that gas in a bubble is released by breaking the bubble in a vacuum chamber, and the gas isdetected by a mass spectrometer. However, the analysis method is not suitable for tiny bubbles. One ofthe reasons is that it is extremely difficult to break a tiny bubble in the chamber. In general, the diameterof a bubble that can be broken is about 50 µm. Another reason is that the amount of gas released froma tiny bubble is very small. The gas volume of a bubble is proportional to the cube of the diameter.
Therefore, as the bubble becomes smaller, it becomes difficult to detect the released gas by a mass
spectrometer drastically. In addition, a part of the released gas is adsorbed on the fracture surface of a
glass sample and on the inner surface from the bubble breaking chamber to the detector.
3. Analyzing the bubble gas composition by Raman spectroscopy
In order to solve these problems, we analyzed a gas composition of tiny bubbles using a Raman
spectrophotometer. Analysis of bubble gas composition in glass by Raman spectroscopy has been
attempted for decades and it has reached a practical level due to the recent improvement of the analysis
apparatus. Raman spectroscopy is a non-destructive analysis. Therefore, it solves the problems ofbubble gas analysis related to breaking a tiny bubble and gas adsorption on active fracture surface bymass spectrometry. We succeeded in analyzing the gas composition of the bubble with a diameter ofabout 25 µm by Raman spectroscopy (Figure 1).

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Figure 1. Raman spectrum of bubbles with a diameter of about 25 µm and the gas composition ratio.
4. Bubble gas change experiment using Raman spectroscopy
One of the advantages of Raman spectroscopy is non-destructive analysis. Therefore, analysis morethan once can be performed on a same bubble. Heat treatment and analysis were carried out repeatedly
for specific bubbles in soda lime glass. We will introduce the results of the gas composition change andthe bubble size change during the heat treatment (Figure 2). Information on changes in the gas
composition and diameter of bubbles in the glass melt is very useful for estimating the source of bubbles.

Figure 2. Changes in gas composition and size of a bubble in soda lime glass with a heat-treatment at
1250 °C.