"The chemical durability of phosphate glasses in general can be improved by the incorporation of chemically dissolved nitrogen and/or addition of oxides such AI2O3.
Over 100 oxide and oxynitride glass compositions were evaluated. The general compositions investigated were the following:
2. MPO3 where M = K, Na, Ag
3. M2O-AI2O3-P2O5, where M = K, Na and Ag
4. 30K2O-10M2O3-60P2O5, where M = Al, Ga, In, La, B, Fe and Bi
5. Glasses of general composition M2O-MO-M2O3-P2O5, where M2O stands for K2O, Na2O, Li2O and Ag2O, MO for BaO, CaO, ZnO and PbO, and M2O3 for Al2O3, B2O3Fe2O3 etc.
6. Oxynitrides of the above compositions
7. Other glass compositions such as PbO containing glasses
These glasses were investigated for the purposes of (a) identifying phosphate glasses whose thermal expansion and chemical durability make them suitable for sealing to high expansion metals like aluminum alloys and stainless steels, (b) learning more about how the dissolution of nitrogen in a glass can be affected by the processing conditions and glass compositions, (c) gaining more fundamental information for the structural role of nitrogen in phosphorus oxynitride glasses and its correlation with the properties of by oxynitride glasses, (d) investigating how oxide addition is compared to nitrogen dissolution in a glass in terms of chemical durability, thermal expansion and glass forming characteristics.
The maximum nitrogen content achievable in phosphate glasses nitrided in ammonia depended not only on the time and temperature of remelting in ammonia, but also on the melt composition and the water content of the nitriding atmosphere. The presence of MO, M2O3 oxides, especially M2O3 oxides, in a glass melt limits the maximum nitrogen dissolution in the melt. The nitrogen content of some PONH glasses obtained from nitriding ammonium phosphate reached 17.8 wt%, while a glass containing ~ 10 mole% Al2O3 typically had a nitrogen content 1-3 wt%. Glasses containing Ag2O, PbO, Bi2O3 and Fe2O3 were not nitridable in dry ammonia. Metallic Ag, Pb and Bi were formed after nitriding in ammonia at 750-800°C for only 30 min.
Many glass compositions in the system M2O-MO-M2O3-P2O5 had a thermal expansion coefficient > 180x10-7/°C and a dissolution rate in deionized water at 30°C < 10-8gm/cm2·min and at 70°C < 10-7gm/cm2·min. Some of these compositions appeared suitable for sealing to stainless steels.
Oxides like P2O5, Al2O3 , Ag2O and PbO played important roles in optimizing the compositions in terms of achieving low melting and high expansion glasses with a good chemical durability. Ag2O oxide, when partially substituted for Na2O or K2O in phosphate glasses, improved the chemical durability without lowering the thermal expansion coefficient like MO or M2O3 oxides. This beneficial effect was apparent when only a few mole percent of Ag2O was present in a phosphate glass. PbO was partially substituted for BaO and alkali oxides (mainly K2O), since it lowered the melting and softening point temperature and improved the chemical durability. A P2O5 content higher than 50 mole% improved glass formation, lowered the softening temperature and increased the chemical durability.
The change in properties after nitrogen is chemically dissolved can be explained by the presence of > N- and = N- nitrogen species in the structure. These species increase the cross-linking in the phosphate chain structure.
The effect of MO, M2O3 oxides on the glass properties and the nitrogen dissolution is related to their structural role in phosphate glasses. M2+ cations and large M3+ cations tends to be located between the chains. Small M3+ cations, particularly Al3+ and Fe3+ cations can be tetrahedrally or octahedrally coordinated depending on their content in the glass. Coordinations of Fe3+ can even be affected by temperature"--Abstract, pages iii-v.
Day, D. E.
Ownby, P. D.
Moore, Robert E., 1930-2003
Lorey, G. Edwin
Materials Science and Engineering
Ph. D. in Ceramic Engineering
University of Missouri--Rolla
Journal article titles appearing in thesis/dissertation
- Preparation and Properties of PONxHy Glasses
- Nitrogen Dissolution in Phosphate Glasses Containing M2O, MO and M2O3
- High Thermal Expansion Phosphate Glasses, I
- High Thermal Expansion Phosphate Glasses, II
- Optimizing Batch Calculation on Personal Computers
v, 157 pages
© 1990 Yongren Benjamin Peng, All rights reserved.
Dissertation - Restricted Access
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Electronic access to the full-text of this document is restricted to Missouri S&T users. Otherwise, request this publication directly from Missouri S&T Library or contact your local library.http://merlin.lib.umsystem.edu/record=b2303400~S5
Peng, Yongren B., "High thermal expansion phosphorus oxide and oxynitride glasses" (1990). Doctoral Dissertations. 769.
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