High thermal expansion phosphorus oxide and oxynitride glasses

<p>"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.</p> <p>Over 100 oxide and oxynitride glass compositions were evaluated. The general compositions investigated were the following:<br />1. P₂O₅·xH₂O<br />2. MPO₃ where M = K, Na, Ag<br />3. M₂O-AI₂O₃-P₂O₅, where M = K, Na and Ag<br />4. 30K₂O-10M₂O₃-60P₂O₅, where M = Al, Ga, In, La, B, Fe and Bi<br />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.<br />6. Oxynitrides of the above compositions<br />7. Other glass compositions such as PbO containing glasses</p> <p>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.</p> <p>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.</p> <p>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.</p> <p>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.</p> <p>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.</p> <p>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.</p>

Name thesis:degree_name

Ph. D. in Ceramic Engineering

Grantor

University of Missouri--Rolla

Year dc:date.available

2016

Author dc:creator

• Peng, Yongren B.

• Ceramic Materials

Repository record dc:identifier

https://scholarsmine.mst.edu/doctoral_dissertations/769

OAI identifier oai:identifier

oai:scholarsmine.mst.edu:doctoral_dissertations-1771