The glass forming regions in the systems of Na
2O-Fe
2O
3-(SiO
2 or B
2O
3) and CaO-Fe
2O
3-(SiO
2, B
2O
3 or GeO
2) were determined.
(Na
2O or CaO)-Fe
2O
3-SiO
2 glasses were found to be capable of containing up to 30mole % Fe
2O
3, while (Na
2O or CaO)-Fe
2O
3-(B
2O
3 or GeO
2) glasses up to 20mole % Fe
2O
3. The glass forming region in the system (Na
2O or CaO)-Fe
2O
3-(SiO
2 or B
2O
3) was narrower than that in the system (Na
2O or CaO)-Al
2O
3-(SiO
2 or B
2O
3). Although the density of the CaO-Fe
2O
3-SiO
2 glasses increased linearly with Fe
2O
3 content when CaO/SiO
2 ratio was kept constant, the molar volume increased with Fe
2O
3 content. On the other hand at constant Fe
2O
3 content, the molar volume decreased with increasing CaO/SiO
2 ratio. This implies that Fe
2O
3 tends to loosen the glass structure and CaO to tighten the glass structure in the systems containing less than 40mole % SiO
2.
The dissolution ratio of Ca
2+ ions in water was almost constant for all the glasses studied, while that of Fe
3+ ions varied considerably. The dissolution ratio of Fe
3+ ions decreased when SiO
2 was replaced by CaO or Fe
2O
3, and it became 1/10 when Fe
2O
3 was partially replaced by CaO. Such changes were considered to be associated with the variation of the coordination number of Fe
3+ ions in the glass. The electrical conductivity of the CaO-Fe
2O
3-SiO
2 glasses changed from 10
-6 to 10
-11/ohm-cm, depending upon the Fe
2O
3 content. This variation may be explained by the change in interatomic distances of iron ions in the glass.
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