Glass - Back to the Future!



Presenting Author:
Radchada Buntem
<radchadab@yahoo.com>

article posted 16 Jan 2016


Asst. Prof. Dr. Radchada Buntem
Address : Department of Chemistry, Faculty of Science, Silpakorn University, Nakorn Pathom, 73000
E-mail : radchadab@yahoo.com
Education :
1. Ph.D. (Inorganic Chemistry), University of Cambridge, UK (1995).
2. B.Sc. (1st class Hons, Chemistry), Kasetsart University, Thailand (1991).
Research Interest : Glass Chemistry, hybrid materials






The investigation on colours and oxidation states of transition metal
ions in glass and sapphire

Radchada Buntem 1 *, Kamolwan Samkongngam 1 ,
Shohei Asaka 2 , Shuichi Kawaminami 2


The base composition of the sapphire is Al2O3. The dopants are Fe2O3, Cr2O3 and CoO. The sapphire was grown by flame-fusion method from mixed powder of Al2O3 and the dopant. Grown boules are heat treated at 1600 C for 20 hours under two different atmospheres, H2 (reduced) and O2 (oxidized). The samples obtained are Fe-sapphire (reduced), Fe-sapphire (oxidized), Cr-sapphire (reduced), Cr-sapphire (oxidized), Co-sapphire (reduced), Co-sapphire (oxidized).



While the base composition of the glass sample containing mixed transition metal ions is composed of SiO2 (from rice husk ash), Na2CO3, K2CO3, ZnO, H3BO3, CaO, Al2O3. The transition metal or transition metal oxide was added into the base composition and calcined at 1150 C for 3 hours in electrical kiln to obtain Fe-glass (reduced), Fe-glass (oxidized), Cr-glass (reduced), Cr-glass (oxidized), Co-glass (reduced) and Co-glass (oxidized). The optical spectra were studied by visible spectroscopy.



The colours of the doped sapphire are blue (Fe-reduced), pale blue (Fe-oxidized), red (Cr-reduced), red (Cr-oxidized), blue (Co-reduced) and green (Co-oxidized). While those of doped glass are blue (Fe-reduced), yellow (Fe- oxidized), green (both reduced- and oxidized-Cr), dark blue (both reduced- and oxidized-Co). The electronic transition depends on doped metal ion type, the coordination geometry and also the matrix type. The finger prints of the bond vibrations in sapphire and glass samples were studied using IR spectroscopy. While the oxidation states of the metal ions in the glass and sapphire matrices were investigated using X-ray absorption near edge structure (XANES). From the data, iron exist in the glass matrices in the form of Fe2+ (reduced) and Fe3+ (oxidized). However in the case of sapphire, the oxidation state of iron in both oxidized and reduced conditions is +3. Chromium (reduced and oxidized) in sapphire and glass exists in the form of Cr3+. Cobalt (reduced and oxidized) in sapphire and glass exists in the form of Co2+.



Institutions:

1 Department of Chemistry, Faculty of Science, Silpakorn University, Nakhon Pathom 73000, Thailand

2 Shinkosha Co., Ltd., 2-4-7 Kosugaya, Sakae-ku, Yokohama 247-0007, Japan.