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Preparation of Multiple‐Cation alpha‐SiAlON Ceramics Containing Lanthanum
Author(s) -
Mandal Hasan,
Hoffmann Michael J.
Publication year - 1999
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.1151-2916.1999.tb01750.x
Subject(s) - sialon , lanthanum , materials science , phase (matter) , ionic radius , sintering , mineralogy , cerium , crystallography , analytical chemistry (journal) , inorganic chemistry , chemistry , metallurgy , organic chemistry , ion
Until recently, it was accepted that Ce 3+ cations, with an ionic radius ( r ) of 1.03 Å, were too large to form an α‐SiAlON structure. However, more‐recent studies have shown that cerium cations can be incorporated into α‐SiAlON via quenching at a rate of 600°C/min, after sintering at 1800°C. Thus far, no α‐SiAlON formation has been observed for La 3+ cations with r = 1.06 Å. In the present work, the possibility of having the La 3+ species as a dopant cation in α‐SiAlON has been investigated by using La 2 O 3 alone or in equimolar mixtures with CaO or Yb 2 O 3 . The resulting materials have been heat‐treated at a temperature of 1450°C for up to 720 h to devitrify the grain‐boundary glass into crystalline phases and also to observe the α→β SiAlON transformation. X‐ray diffractometry on samples that were densified with single cations revealed that the La 3+ cation alone does not form an α‐SiAlON; rather, it forms the N‐phase (La 3 Si 8 O 4 N 11 ) with a ß‐SiAlON phase. In the case of multiple cations, α‐SiAlON was observed only as a matrix phase. Energy‐dispersive X‐ray measurements have proven that La 3+ cations can be accommodated into the α‐SiAlON structure and this structure also does not transform to β‐SiAlON at lower temperatures.