H. Buscail et al., THE INFLUENCE OF CERIA COATINGS ON THE MANGANESE SULFIDE TEXTURE, Journal de chimie physique et de physico-chimie biologique, 92(6), 1995, pp. 1257-1271
Ceria coatings applied by a sol-gel method, strongly modify the micros
tructure and texture of alpha-MnS scales grown on pure manganese in H2
S/H-2 environments at 700 degrees C. Under the imposed sulfidizing con
ditions, the manganese sulfide scale always exhibit the (111)-texture
when blank specimens were sulfidized, whereas, a (110)-texture was obs
erved for coated specimens. The (110) crystallographic orientation cor
responds to a fine grained sulfide scale, while, the (111) orientation
is associated with large grains expanding in the direction parallel t
o the interfaces (''lateral growth''), A small grain size is maintaini
ng an important grain boundary network in the scale. Kinetic results s
how that the scale growth mechanism, controlled by the bulk diffusion
in the sulfide scale for blank specimens, becomes limited by the exter
nal interfacial reaction for coated specimens. The benefic effect of c
eria coatings on adherence, is attributed : 1) to the posibility of ce
rium introduction into the manganese sulfide scale as the cerium sulfi
de compound beta-Ce2S3; 2) to the smaller sulfide grain size inducing
better mechanical properties; 3) to the vacancies coalescence in the c
erium sulfide rich area (which acts as vacancy sinks) instead of the v
acancy coalescence at the metal-scale interface.