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Glass formation and crystallization in high-temperature glass-ceramics and si3n4
| Content Provider | NASA Technical Reports Server (NTRS) |
|---|---|
| Author | Drummond II, Charles H. |
| Copyright Year | 1991 |
| Description | The softening of glassy grain boundaries in ceramic matrix composites and Si3N4 at high temperatures reduces mechanical strength and the upper-use temperature. By crystallizing this glass to a more refractory crystalline phase, a material which performs at higher temperatures may result. Three systems were examined: a cordierite composition with ZrO2 as a nucleating agent; celsian compositions; and yttrium silicate glasses both in bulk and intergranular in Si3N4. For the cordierite compositions, a series of metastable phases was obtained. The crystallization of these compositions was summarized in terms of metastable ternary isothermal sections. Zircon formed at the expense of ZrO2 and spinel. In SiC composites, the transformations were slower. In celsian, two polymorphs were crystallized. One phase, hexacelsian, which always crystallized, even when metastable, had an undesirable volume change. The other phase, celsian, was very difficult to crystallize. In yttrium silicate bulk glasses, similar in composition to the intergranular glass in Si3N4, a number of polymorphs of Y2Si2O7 were crystallized. The conditions under which these polymorphs formed are compared with crystallization in Si3N4. |
| File Size | 893829 |
| Page Count | 16 |
| File Format | |
| Alternate Webpage(s) | http://archive.org/details/NASA_NTRS_Archive_19910022650 |
| Archival Resource Key | ark:/13960/t4km46j7x |
| Language | English |
| Publisher Date | 1991-08-01 |
| Access Restriction | Open |
| Subject Keyword | Solid-state Physics Grain Boundaries Ceramic Matrix Composites Nucleation Crystallization Glass Cordierite Crystallinity Silicates Softening Refractory Materials Spinel Metastable State Zirconium Oxides Silicon Nitrides Yttrium Oxides Ntrs Nasa Technical Reports Server (ntrs) Nasa Technical Reports Server Aerodynamics Aircraft Aerospace Engineering Aerospace Aeronautic Space Science |
| Content Type | Text |
| Resource Type | Article |
