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Phase Formation in the System Na 2 O · Al 2 O 3 ‐CaO · A1 2 O 3 ‐Al 2 O 3 at 1200°C in Air
Author(s) -
VERWEIJ H.,
SARIS C.M.P.M.
Publication year - 1986
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.1986.tb04708.x
Subject(s) - phase diagram , tetragonal crystal system , phase (matter) , x ray crystallography , analytical chemistry (journal) , sodium oxide , crystallography , solid solution , materials science , quenching (fluorescence) , oxide , chemistry , diffraction , crystal structure , metallurgy , physics , organic chemistry , chromatography , optics , fluorescence , quantum mechanics
Phase relations in the system Na 2 O · Al 2 O 3 ‐CaO· Al 2 O 3 ‐Al 2 O 3 at 1200°C in air were determined using the quenching method and high‐temperature X‐ray diffraction. The compound 2Na 2 O · 3CaO · 5Al 2 O 3 , known from the literature, was reformulated as Na 2 O · CaO · 2Al 2 O 3 . A new compound with the probable composition Na 2 O · 3CaO · 8Al 2 O 3 was found. Cell parameters of both compounds were determined. The compound Na 2 O · CaO‐2Al 2 O 3 is tetragonal with a = 1.04348(24) and c = 0.72539(31) nm; it forms solid solutions with Na 2 O · Al 2 O 3 up to 38 mol% Na 2 O at 1200°C. The compound Na 2 O · 3CaO · 8Al 2 O 3 is hexagonal with) a = 0.98436(4) and c = 0.69415(4) nm. The compound CaO · 6Al 2 O 3 is not initially formed from oxide components at 1200°C but behaves as an equilibrium phase when it is formed separately at higher temperatures. The very slow transformation kinetics between β and β ”‐Al 2 O 3 make it very difficult to determine equilibrium phase relations in the high‐Al 2 O 3 part of the diagram. Conclusions as to lifetime processes in high‐pressure sodium discharge lamps can be drawn from the phase diagram.