The mechanical properties of oxide scales at high-temperature were studied in order to improve the surface quality of commercial Sicontaining high strength steels. Specific oxides of Fe 2 O 3 , Fe 3 O 4 , FeO and Fe 2 SiO 4 were synthesized by powder metallurgy. The Vickers hardness, thermal expansion coefficient and thermal conductivity were measured at high-temperatures. A series of measurements confirmed that the physical properties of the synthesized oxides were different each other. From the Vickers hardness measurements, it was verified that the hardness of each synthesized oxide was identical with the naturally-formed iron oxide, as observed in the cross-section of oxide scales on steels. The influence of the Fe 2 SiO 4 formed on Si-containing steels on the scale adhesion at high temperature and the surface property is discussed on the basis of the physical properties of the oxides.
a b s t r a c tVarious Mn-based oxides have been screened to find a suitable all-solid-state gas-insensitive referenceelectrode (RE) for yttria-stabilized zirconia (YSZ)-based potentiometric oxygen sensor. The experimental observation of tubular YSZ-based sensors attached with each of the outer Mn-based oxide sensing electrodes (SEs) and the inner Pt-RE revealed that Mn 2 O 3 -SE was insensitive to all gases including oxygen at operating temperatures below 550 • C. Thus, the planar-like rod-type YSZ-based sensor using Pt-SE, Au-SE and Mn 2 O 3 -RE was then fabricated and its sensing performances were evaluated at 550 • C. As a result, the planar sensor using a couple of Pt-SE and Mn 2 O 3 -RE exhibited excellent responses to oxygen in the concentration range of 0.05-21 vol.% obeying Nernst equation and gave negligible responses to other co-existing gases. Close similarity of the results for tubular and planar sensors operated in a wide range of air/fuel (A/F) ratio indicated that the tubular YSZ-based sensor using the inner Pt-RE could be successfully miniaturized to the planar one using Mn 2 O 3 -RE without sacrificing its performance.
The rate constants for internal oxidation of Si containing steels (Fe-Si alloys) at 850 C were calculated in order to clarify the formation mechanism of fayalite scale, which can form as a ''sub-scale'' in Si containing steels. The diffusion coefficient of oxygen in the oxide layer, D O , and the oxygen concentration at specimen surface, N O (s) , which are constituents of the internal oxidation rate constant, (
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.