Celsian crystal phases

Referring in particular to Ba++ and NH4, inasmuch as their anhydrous radii are the closest among those of the cations examined, to Rb+ and Tl+, it has been considered useful to investigate more widely on the phases synthesizable, when they are coupled with lithium (see experimental). Figures 3 and 4 report the respective crystallization fields, from which it is possible to notice that no cancrinite forms at any composition of the reaction system. The phases obtained refer to Li-A, ABW (A) and Li-K (K) (9) in both fields, Ba,Li-M, PHI (4) and Ba-P, analogous to celsian or cymrite (15) in Ba,Li field. Am denotes no crystallization. 

On heat treatment, both hexacelsian and monoclinic celsian phases crystallize in BAS glass [23-25]. Also, hot pressing of barium aluminosilicate (BAS) glass or its composites reinforced with large diameter silicon carbide SCS-6 monofilaments or small diameter multifilament Nicalon or Hi-Nicalon fibers resulted in the crystallization of both hexacelsian andmonoclinic celsian phases [12]. On doping BAS with 5 wt.% monoclinic celsian seeds or 10 wt.% strontium aluminosilicate (SAS), only the celsian phase was formed in hot pressed... 

Adachi T., Sakka S. Microstructural changes in sol-gel derived silica gel monolith with heating as revealed by the crack formation on immersion. J. Ceram. Soc. Jpn. 1989 97 203-207 Adachi T., Sakka S. Dependence ofthe elastic moduli of porous silica gel prepared by the sol-gel method on heat treatment. J. Mater. Sci. 1990 25 4732 737 Chen A., James P.F. Amorphous phase separation and crystallization in a lithium silicate glasses prepared by the sol-gel method. J. Non-Cryst. Solids 1988 100 353-358 Chen M., Lee W.E., James P.F. Preparation and characterization of alkoxide-derived celsian glass-ceramic. J. Non-Cryst. Solids 1991 130 322-325 Chen M., James P.F., Lee W.E. Densificaation and crystallization of celsian glass derived from alkoxide gel. J. Sol-Gel Sci. Tech. 1994a 2 233-237... 

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