Porosity and Microstructure of Thin Films of Al2 O 3 Formed from an Alumina Sol

Abstract

Thin films of porous alumina were formed from an alumina sol which was cured at 500~ in either air or oxygen. We have determined, from a simple RBS marker experiment, that alumina films made from this sol have a volume porosity of about 50%, which is substantially different from bulk structures formed from this material. Ellipsometric measurements were also carried out to determine the porosity of these films. Our analysis shows an excellent agreement between the two measurements. No change in film porosity was found to occur after annealing at 900~ for 60 min in oxygen. ABSTRACTAn alloy containing 41 weight percent Ni was reacted at temperatures of 793, 888, and 938 K with flowing H2/H2S/N2 gas mixtures corresponding to equilibrium sulfur partial pressures in the range from 2 • 10 -5 to 6 • 10 -1 Pa. At 793 K the reaction product consisted of an inner compact layer of (Fe, Ni)I_=S plus pentlandite overgrown by layers of pentlandite and Ni-rich sulfide whiskers. Morphologies at the higher temperatures were similar except that pentlandite was absent. At all temperatures increases in the H2S partial pressure led to a more compact scale morphology. The scale phases are shown to be consistent with local equilibrium, although the scale-gas interface is not exactly at equilibrium because H2S dissociation is slow. Reaction kinetics were irregular at 793 K, due to scale-alloy separation, but parabolic at higher temperatures. Growth kinetics of the compact (Fe, Ni)I-xS layer were parabolic and are shown to be consistent with DFe/ DNi = 0.4 and highly nonideal defect levels.) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 130.126.162.126 Downloaded on 2015-03-11 to IP