480658 Characterization of Amber Colored Aluminum Doped Silica Glass

Monday, November 14, 2016
Grand Ballroom B (Hilton San Francisco Union Square)
Alvin Chang, Yujuan He and Chih-hung Chang, School of Chemical, Biological, and Environmental Engineering, Oregon State University, Corvallis, OR

Silica with an aluminum doped framework has been widely utilized as biosensors,1-3 encapsulation matrices,4-7 adsorption and separation devices,8-10 and catalysts11-15due to its ion exchange ability, high surface area, and extraordinary physical and chemical resistance.

In this paper we followed Rai’s procedures16 to fabricate silica xerogel with aluminum nitrate nonahydrate. Upon the drying/densification step of the xerogel from 25 to 550° C, a color transition of transparent to amber in the silica glass was observed. This phenomenon has been perceived and recorded in previous literatures as the glass is heated from 200-400° C17but the reason for the color was barely discussed. After densification through a heating step up to 650° C, our glass returned to become clear and transparent in the visible range. This transformation is apparent even after the adjusting of aluminum concentration and heating rates.

Upon further inspection of the amber glass, TEM images show a porous nanostructure within the glass that may be responsible for the amber color. As the temperature increased from 550 to 650° C, the porosities of glass were transformed into condensed amorphous structure in a direction from the outer edge to the center. The amber color vanished along with the disappearance of pores within the glass. TGA data indicates that the carbonization of organics was completed before 400° C which revealed the amber color can hardly be attributed to the burning of organic residuals. Thus, we hypothesize that the color transition is related to the porosity of the glass as the amorphous array of air pores with short-range order in the silica glass results in noniridescent colors18. By controlling the pore size and the distance among pores, color modification of glass is able to be achieved.

In our study, the color transition of aluminum doped silica glass was also investigated by altering parameters such as aluminum concentration, heating rate, and pH of the sol to adjust porosity features, and therefore locate the sources of the color. The components of the sol-gel will be further inspected to confirm our hypothesis.

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