Showing papers on "Nickel published in 1971"

The Magnetization of Pure Iron and Nickel

Abstract: The saturation magnetizations of very pure iron and nickel have been measured absolutely by a force method at room temperature. The values are 217.6 and 55.1 emu/g (217.6 and 55.1 J T -1 kg -1 ) respectively. The theory and reliability of the force method are investigated and discussed. New measurements have also been made by a relative method on the same materials at temperatures ranging from 4 K to above the respective Curie temperatures of iron and nickel. Reduced magnetization, temperature data have been derived and are compared with those already available for face centred cubic cobalt.

Mechanisms of formation of diffusion aluminide coatings on nickel-base superalloys.

Abstract: Studies on microstructures and compositions of model diffusion aluminide coatings coupled with existing information on diffusion in nickel-aluminum intermetallic compounds indicate that only two basic types of these coatings can be formed on nickel-base superalloys. The first type is formed by inward diffusion of aluminum from coating media of sufficiently high aluminum activity to cause formation of the δ (Ni2Al3) phase. Subsequent stabilizing heat treatments required for practical use of this type of coating cause some outward diffusion of nickel to form a three-zone β(NiAl) coating. The second type is formed by outward diffusion of nickel from the substrate alloy to react with aluminum of suitable activity to stabilize that β(NiAl) phase of composition through which only nickel motion can occur. This process produces a two-zone β(NiAl) coating. It follows that the structural type of coating to be expected from any given coating process can, in principle, be predicted from knowledge of the aluminum activity present during formation of the coating. The initial stages of diffusional degradation of these coatings involve continued outward diffusion of nickel from the substrate through the β(NiAl) coating with the resultant dilution of aluminum content of the coating; little inward diffusion of aluminum occurs.

Diffusivity and solubility of hydrogen as a function of composition in Fe-Ni alloys

Abstract: An electrochemical method has been used to determine the permeability,P, diffusion coefficient,D, and solubility,c, of hydrogen in alloys of the Fe-Ni system The heats of activation for diffusion and the heats of solution have been derivedD falls from ≃10−4 sq cm per sec for pure iron to ≃10−10 sq cm per sec for 40 wt pct of Ni in the alloy Thereafter it rises slightly to that for pure nickel,c rises by about 103 between pure iron and 40 wt pct Ni, then remains constant up to pure nickel The resultantP doubles at 5 wt pct Ni and then falls by 103 times up to 40 wt pct Ni, afterwards rising slightly to that for pure nickel Between 0 and 40 wt pct Ni the dominant factor in controlling the value ofP is the fall of the mole fraction of the α phase in the alloy This hypothesis gives a reasonable quantitative calculation of theP-composition relation Between 40 and 100 wt pct, the crystallographic phase is allγ and the major effect is the bonding of hydrogen in the alloy, the small changes noted being reasonably calculable The negligible change of solubility in this region reflects the negligible change ind character of the alloy from 40 to 100 wt pct Ni The hydrogen permeability of Fe-Ni (5 wt pct) is greater than that of palladium atT > 200°C The corrosion rate and hydrogen permeability (hence, susceptibility to hydrogen embrittlement) pass through a minimum at about 50 wt pct Ni A remarkable parallelism exists between corrosion rate and hydrogen permeation in Fe-Ni alloys An interpretation is suggested

Thermodynamics of the Fcc Fe−Ni−C and Ni−C alloys

Abstract: The activity of carbon in the fcc solid solution of the Fe−Ni−C system has been measured at 800°, 1000°, and 1200°C by comparison with observed values in the Fe−C binary by equilibration with methane-hydrogen mixtures. Defining the lattice ratioz C≡n C/(n Fe+n Ni−n C), the activity coefficient ΨC≡a C/z C has been determined as a function of temperature and composition. At infinite dilution log ΨC goes through a maximum at about 70 pct Ni in agreement with Smith. The partial molar free energy of carbon in the dilute solution referred to graphite is not a linear function of the base alloy composition, but has a large deviation with maximum at about 60 pct Ni. Similar maxima occur in both ΔH C ° and ΔS C ° . Linear equations are derived for the activity coefficient of carbon in three composition ranges of Fe−Ni−C alloys; a simplified equation applicable to nickel steels is included. The solubility of graphite in nickel has been determined. The marked deviation from linearity is ascribed to the existence of iron atoms in two electronic states, γ1 and γ2 which differ in energy and are antiferromagnetic and ferromagnetic, respectively.

Mechanism of the Electrocrystallization of Nickel and Cobalt in Acidic Solution

Abstract: This mechanism is studied by means of the analysis of the polarization characteristic and of the cathodic impedance. The results, obtained from an acidic solution of the Watts type, strongly support the hypothesis that the cathodic reaction occurs in several steps probably involving an adion . In the case of nickel, the results can be accounted for by a mechanism implying two successive transfer reactions in which acts as an intermediate compound and not as a catalyst. The presence in the electrolyte of either sodium benzenesulfonate or 2‐butyne 1,4‐diol (two inhibitors commonly used for the electrocrystallization of nickel) specifically modifies the kinetic parameters of transfer reactions and diminishes the capacity of the electrochemical double‐layer. This capacity is defined thanks to a least‐squares analysis of the cathodic impedance.

Electronic Spectra of Square-Planar Bis(tertiary phosphine)dialkynyl Complexes of Nickel(II), Palladium(II), and Platinum(II)

Abstract: Electronic spectra of trans-[L2M(C≡CR)2], (L=tertiary phosphine or tertiary stibine, and M=Ni, Pd or Pt) have been studied in solution from 220 mμ to 360 mμ. Nickel and platinum complexes showed three intense absorption bands. The lowest energy band was particularly sensitive to substituents of alkynyl groups. This band was assigned empirically to the transition between the molecular orbitals involved in metal-alkynyl bonds. The possibility of π-interaction between the two alkynyl groups through central metal was discussed in relation to the influence of R.

Diffusion of nickel in alloys based on the intermetallic compound Ni3Al(γ

Abstract: The diffusion of nickel in the intermetallic compounds Ni3Al and Ni3(AlTi) has been measured as a function of temperature and composition. The diffusion coefficient is insensitive to both titanium additions and deviations from stoichiometry. La diffusion du nickel dans les composes intermetalliques Ni3Al et Ni3(AlTi) a ete measuree en fonction de la temperature et de la composition. Le coefficient de diffusion est insensible aux additions du titane et aux deviations stoichiometriques.

Surface tension measurements on pure liquid iron and nickel by an oscillating drop technique

Abstract: A novel experimental technique for the measurement of surface tension of molten metals has been developed. It is based on the Rayleigh equation which relates frequency and surface tension for an oscillating drop. A systematic study has shown this equation to be valid for a liquid metal droplet levitated electromagnetically in an inert flowing gas with no prior calibration required. It is, therefore, an absolute method. The frequencies of oscillation of droplets of pure iron and nickel in a 6 pct H2-He gas mixture were measured by high speed cinematography. Surface tensions were obtained for temperatures of 1550° to 1780°C for iron and 1475° to 1650°C for nickel.

Temper embrittlement in a Ni-Cr steel containing phosphorus as impurity

Abstract: Phosphorus segregates to prior austenite grain boundaries in ferrite during embrittling treatments (below 1000°F) and contributes to temper embrittlement of a Ni-Cr-C-P steel. The phosphorus is confined to a width of 5 to 10A, at a very high concentration of approximately 5 wt pct (0.1 monolayer) in the vicinity of the grain boundaries; segregation of nickel is also observed to a lesser degree and spread over a distance somewhat larger than 50a. Nickel segregation to the grain boundaries appears to be of minor consequence either in terms of its own effect or in terms of its interaction with phosphorus. Fracture appearance transition temperatures of the various samples are directly correlatable to the phosporous content at grain boundaries through a linear plot. Deembrittlement of the steel is found to consist of reversing the boundary segregation and driving the phosphorus and nickel away from the prior austenite boundaries. The amount of phosphorus segregated at grain boundaries of the embrittled Ni-Cr-C-P steel is found to be compatible with an equilibrium segregation model.

Studies on the magnetic cross-over in five-co-ordinate complexes of iron(II), cobalt(II), and nickel(II). Part II

Abstract: The new terdentate ligand 2,6-di(diphenylphosphinomethyl)pyridine forms a series of crystalline complexes, MLX2, with iron(II), cobalt(II), and nickel(II) halides and thiocyanates. Distorted square pyramidal structures are suggested on the evidence of their electronic spectra and other physical properties. Magnetic susceptibility measurements as a function of temperature classify the cobalt and nickel compounds as low-spin, high-spin, or as having an anomalous temperature-dependence. For the latter group a low-spin ⇌ high-spin equilibrium is suggested. All the iron complexes are fully high-spin over the temperature range studied. The suggested magnetic cross-over in these compounds is discussed in relation to that in previously reported compounds having a distorted trigonal bipyramidal structure.