STUDIES OF THE STABILITY OF HIGH TEMPERATURE RESISTANT CERAMIC COATING GLASSES. Report No. 82
Chemical and physical mechanisms were studied which were believed responsible for the instabilities of the glassy phase of composite glass-metal systems when subjected to elevated temperatures over prolonged periods of time. Two prominent types of glass devitrification behavior were indicated by x-ray- diffraction analysis of a series of glass-metal composite speco- mens which had been heat treated up to 200 hours at 870 C. (1) The cyclic development, disappearance amd reappearance of various diffraction peaks which indicated considerable crysinllinc activity, (2) For certain glasses the early development of diffraction peaks which persisted throughout the heat treating period. This behavior indicated an equilibrium between the products of devitrification amd the residual glass. A simple barium borosilicate glass was compared with a complex glass which was composed of 70 per cent by weight of the simple glass plus five modifying oxides. When identically heat treated, it was found that the simple glass devitrified more rapidly than the complex glass, although the same crystalline products were formed. Heat treatments on composite glass-metal spe;imens with glasses intermediate in composition between the sismple and complex glasses revealed that at temperatures of 815 and 870-C all of the glasses devitrified in a short time. However, at 760 C some of these glasses resisted initial devitrification for over 50 hours. Single oxide additions of CaO, ZnO, TiO/sub 2/, Bi/sub 2/O/sub 3/, and Ceo/sub 2/to the simple glass all delayed to some extent the initial appearamce of the devitrification products found in the simple glass. On firing to form the composite glass-metal specimens ceria crysinls precipitated from the ceria containing glasses, and these remained as a separate phase during subsequent heat treating. As determined by microscopic examination, ceria additions to the simple glass had two principal effectua (l) At lower heat treating temperatures an outside layer of crystalline cerin developed. (2) Relatively low temperature melting glasses werc formed which permitted the development of recogniable crystalline modifications of silica and barium disilicate at lower heat treating temperatures than the original simple barium borosilicate glass required. (auth)
- Research Organization:
- Illinois. Univ., Urbana
- DOE Contract Number:
- AF18(603)-28
- NSA Number:
- NSA-13-001347
- OSTI ID:
- 4327604
- Report Number(s):
- AFOSR-TN-58-828; AD-202913
- Resource Relation:
- Other Information: Orig. Receipt Date: 31-DEC-59
- Country of Publication:
- United States
- Language:
- English
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