Showing papers in "Materials Transactions Jim in 1975"

Dissolution of Hydrous Chromium Oxide in Acid Solutions

Abstract: It has been considered that the corrosion of passive metals and alloys is not caused by the active metal-dissolution but the dissolution of a nonporous passive oxide film in aqueous solution. The corrosion current density of iron(1)(2), chromium(3) and their alloys(4) is independent of the potential in all the range of passivity, although depending upon the pH of solution. Vetter(1) explained such a corrosion behavior by assuming that the dissolution rate of the passive oxide film is electrochemically controlled by the potential difference at the filmsolution interface, which is determined soley by the pH of solution. Recent studies of passivated stainless steels in acid solutions by means of X-ray photo electron spectroscopy(5) and Auger electron spectroscopy(6) have proved the high enrichment of chromium component in the passive oxide film, which seems to explain the high corrosion resistivity of stainless steels in acid solutions. The passive oxide film has an amorphous structure with a chemically bound water (7). Hydrous chromium oxide prepared by precipitation in aqueous solution according to the X-ray diffraction data(8), has also an amorphous structure. Therefore it is expected that the structure of hydrous chromium oxide is similar to that of the passive chromium oxide on stainless steels. In this study, hydrous chromium oxide prepared by precipitation is adopted as a model material of the passive oxide film on stainless steels and the dissolution of hydrous chromium oxide in acid solutions is investigated and the dissolution mechanism is discussed from the electrochemical point of view.

Phenomenological Consideration on the Compositional Deviation from Equilibrium at the bcc ⁄ fcc Interface in Fe: Cr Diffusion Couples

Abstract: interface in Fe:Cr diffusion couples is not equal to the equilibrium value even if the coupies are heated for a long time more than 100 hr. In a diffusion experiment Eifert et al.(2) reported a systematic deviation from the equilibrium composition at the bcclfcc interface in Cu:Al diffusion couples. Such deviations have also been detected in the two-phase diffusion couples of Au:Co by Braun et al.(3) and those of Ni:Cr by the present authors(4). Furthermore, Oikawa et al.(5) suggested the occurrence of a deviation in carbon concentra-

Antiferromagnetic Characteristics of Cr–Sn and Cr–Fe Alloys, and Nonferromagnetic Cr–Fe–Sn Invar Alloys

Abstract: Invar alloys are widely used as materials for precision instruments. The practical Invar alloys are all ferromagnetic, and the ferromagnetism of these alloys often limits the scope of their application. In recent years, therefore, considerable attention has been directed to the research and development of nonferromagnetic Invar alloys. Cr is an antiferromagnetic material and its physical properties such as thermal expansivity and electrical resistivity change anomalously near the Neel temperature. These properties are sensibly modified by the addition of other elements. The present authors investigated the temperature dependence of the physical properties for some Cr-base primary solid solution alloys. With the addition of Sn, the Neel temperature of Cr increases up to 2.0% Sn and then decreases gradually, and the thermal expansion coefficient below the Neel temperature becomes smaller. The Neel temperature in the Cr-Fe system decreases with increasing Fe concentration, while the thermal expansivity does not show any regular dependences on temperature and concentration. Taking the above-mentioned results into consideration, the thermal expansivity and the magnetic susceptibility of the Cr-Fe-Sn alloys in the range of the primary solid solution have been measured. The results show that the alloys are of the antiferromagnetic Invar type and their magnetic susceptibility is negligibly small.

Activity Measurements of the Binary Mn-Base Molten Alloys by the TIE Method

Abstract: Metals of 99.9 to 99.9999% purities were employed for the alloy and standard electrodes, and fluorides and manganese carbonate of high-purity reagent grade were used for the electrolytes. The cell design employed is illustrated in Fig. 1. The electric furnace used for the measurements was a siliconite resistance furnace and temperature measurements were carried out with a 13% Pt-Pt¥Rh thermocouple. The Mullite tube (I. D. 42mm) sealed at the bottom by isolite brick is inserted in the furnace.