Nickel foil, polycrystalline

The 3 mm disc was covered by a 3 pm thick polycrystalline nickel foil, then a polycrystalline molybdenum disc was placed on top of the nickel foil. This composite sandwich was placed between two alumina supports and heated for 30 min at 1350°C. The cross-sections used for microanalysis were prepared by cutting with a wire saw in a direction perpendicular to the grain boundary, then mechanically and chemically polished. 

In this account of work in progress, we report that the kinetics of CH4 production over initially clean Ni(lOO) are in excellent agreement with previous data for polycrystalline nickel foil and high-area-supported nickel catalysts. Traces of surface impurities such as iron act as poisons, causing a marked lowering of the reaction rate. 

The values of Nch4 determined in the present work are plotted in Arrhenius form in Figure 3 the activation energy determined from the slope of this line is 24.6 kcal/mol. For comparison, the values of Nch4 measured for both polycrystalline nickel foil and high-area-supported nickel catalysts are also shown. The rates are all normalized to a 4 1 H2 C0 mixture at a total pressure of 120 Torr. Generally speaking, a... 

Massaro TA, Petersen EE. Bulk diffusion of carbon-14 through polycrystalline nickel foil between 350 °C and 700 °C. J Appl Phys 1971 42 5534-9. 

Fig. 7. Polycrystalline ferric oxide sphere sintered to a single crystal of magnesium oxide at 1090°C for 51 hr. The sphere was held in position by nickel foil visible in the upper part of the photograph. Polarized light, 100 x.

It can be seen that the activities of the amorphous alloys are lower than those of the polycrystalline catalysts. Formation of the corresponding diol was not observed on the amorphous catalysts, while the crystalline catalysts either produced the diol selectively, or a mixture of the diol and the hydroxy ketone was formed. The fundamental reason for the lower activity and higher selectivity of the amorphous alloys is their rather small surface area. Of the amorphous alloys studied, Ni-B and Ni-P alloy powders prepared by chemical reduction exhibited higher activities than those of Ni-P alloys prepared by electrolytic reduction or rapid quenching. This difference in activity can be attributed to an oxide layer covering the surface of m-P foils [Ij. It is necessary to point out, however, that the comparison of activities is based on unit catalyst weight. Obviously, this comparison does not take into account the real surface area of the nickel samples, nor active site densities. 

The nickel aluminide NijAl - known as the y phase - crystallizes with the cubic LI2 structure (CujAu-type) which results from the fc.c. structure by ordering (see Fig. 1). Deviations from stoichiometry are accommodated primarily by antisite defects (Lin and Sun, 1993). The density of NijAl is 7.50 g/cm (see Liu et al., 1990) and thus is only slightly lower than that of the superalloys (see Table 2) which, however, is still of interest. The elastic constants have been studied experimentally and theoretically by various authors (e.g. Davies and Stoloff, 1965 Dickson et al., 1969 Kayser and Stassis, 1969 Foiles and Daw, 1987 Wallow et al., 1987 Yoo and Fu, 1991, 1993 Yasuda et al., 1991a, 1992). Young s modulus of cast polycrystalline NijAl at room temperature is about the same as that of pure Ni with a weaker temperature dependence (Stoloff, 1989),... 

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