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Adaptation of an Existing Raman Spectrometer for In Situ Real-Time Composition Analysis of Gaseous Bubbles in Glass Melts, 20-9144

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Principal Investigators
Vijay Jain (Todd Mintz)
Darrell S. Dunn

Inclusive Dates: 06/25/99 - Current

Background - Increasingly stringent quality standards tolerate fewer defects in glass products. Many glass product defects are in the form of bubbles. The formation of bubbles in glass melts can be attributed to processes such as gases originally introduced physically in the batch (porosity), gases released during decomposition of batch materials (carbonate salts), gases released due to reactions at the glass-refractory interface, and gases released due to redox conditions in the glass (reboil). The determination of gas components within bubbles is a useful approach for diagnosing a fining problem or identifying the origin of a specific defect. In addition, verification and validation of mathematical models for the identification of defects require experimental data on gas bubble composition and size. Compositional analyses of gas bubbles have been performed using gas chromatography and mass spectrometry. Both techniques require extensive set up and sample preparation time, and neither can analyze all gases.

Approach - In this project, an existing fiber Raman spectrometer with a 532-nm laser was used to collect high-temperature spectra and to analyze gas constituents in the bubbles. The main advantages of Raman spectroscopy as an in situ analytical tool are its abilities to be used remotely with long lead optical fibers and to probe complex, corrosive liquid and gaseous environments, obtaining quantitative information regarding molecular or ionic composition. While Raman spectroscopy cannot distinguish all gaseous species, the separation in Raman peaks for O2, N2, CO, CO2, SO2 and H2 are sufficient for differentiation. Initially, gas bubbles were introduced in glass and were analyzed at room temperature. Following the initial determination of maximum temperature at which Raman spectra can be collected without black body radiation, gas bubbles were introduced into glass melts and analyzed.

Accomplishments - Preliminary data have demonstrated that spectra can be collected using Raman spectroscopy at temperatures ranging from room temperature to 700° C. Black body radiation, which interferes with Raman spectra, increases with temperature. Current study demonstrates, as shown in the illustration, that black-body radiation becomes significant at 800° C. Thus, this temperature is the maximum at which the existing 532-nm Raman system can be used without significant black-body radiation interference. Study also indicates that CO2 introduced in the melt can be detected by Raman spectroscopy at room temperature but required precise focusing on the bubble. Longer focal length probes suitable for focusing through the furnace for in situ measurements lacked precision. Work is continuing to demonstrate that Raman spectra from bubbles can be collected at higher temperatures. To study bubble formation at temperatures higher than 800° C will require a continuous wave 425-nm laser.

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Raman spectra of green sodium silicate glass at temperatures ranging from 25 to 800° C

Materials Research and Structural Mechanics Program
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