Quaternary diffusion in the Cu−Ni−Zn−Mn system at 775°C

Quaternary diffusion was investigated in the α (fcc) region of the Cu−Ni−Zn−Mn system at 775°C with solid-solid diffusion couples assembled with alloys characterized by similar concentrations of one of the components. The concentration profiles of the quaternary couples were examined on the basis of a relative concentration variable for each component; the profiles for any given couple exhibited a common cross-over composition. The interdiffusion fluxes of the components were calculated directly from the concentration profiles. Interdiffusion of each component up its own concentration gradient was observed in several couples, while the zero-flux planes for the individual components were identified in selected couples. The common cross-over composition reflected the relative diffusion depths in the terminal alloys of the single-phase quaternary diffusion couples. The quaternary diffusion paths were presented on the basis of relative concentration variables for the individual components.     

Diffusion studies in Ag-Zn alloys

Diffusion studies were made in the alpha and beta phases of the silver-zinc system at 600°C with vapor-solid and solid-solid diffusion couples in order to determine intrinsic diffusion coefficients and interdiffusion coefficients. Intrinsic diffusion coefficients, D_Zn and D_Ag, determined experimentally for bothα andβ alloys, were compared with those predicted from the models of Darken, Manning, and Dayananda with the aid of thermodynamic and single crystal tracer diffusion data. The experimental values of D_zn were close to those predicted by the models of Darken and Manning, while the experimental D_Ag values were higher than those determined by both models. The experimental values of the ratio, D_Zn/D_Ag, were found to be lower than those predicted by either Darken’s or Manning’s relations. Also, Dayananda’s model was found to be inapplicable with the available tracer diffusion data. This disagreement is considered to reflect the inadequacy of the single crystal tracer diffusivities in the analysis of intrinsic diffusion in polycrystalline Ag-Zn alloys.     

Kinetics of dissolution of aluminum in bismuth and zinc in mercury

The kinetics of dissolution of rotating aluminum cylinders in liquid bismuth and zinc single crystal disks in mercury were investigated under controlled hydrodynamic conditions, and solution rate constants were evaluated with the aid of the Nernst-Brunner relation. Dissolution of aluminum in bismuth was studied in the temperature range from 300° to 600°C over the range of Reynolds numbers from 13,500 to 54,000; the experimental results obeyed the Eisenberg correlation and indicated a diffusion-controlled corrosion process. On the other hand, zinc single crystal disks dissolved in the geometry of a rotating disk in nearly-saturated zinc amalgams at 50°C showed that the rate of crystal attack was independent of hydrodynamic conditions in the range of Reynolds numbers from 20,000 to 30,000 and that the overall dissolution process was surface-controlled. T. L. SRI KRISHNA, formerly Graduate Student, School of Materials Science and Metallurgical Engineering, Purdue University, Lafayette, Ind.     

Zero-flux planes and flux reversals in the Cu- Ni- Zn System at 775 °C

Ternary diffusion in the Cu-Ni-Zn system was investigated at 775 °C for the development of zero-flux planes (ZFP) and flux reversals of the individual components. ZFP’s, where the interdiffusion flux of either Cu, Ni, or Zn goes to zero, were identified in several series of single phase and multiphase solid-solid diffusion couples assembled with a (fcc),β (bcc), or γ (cubic) Cu-Ni-Zn alloys and characterized by terminal alloys of similar thermodynamic activity for one of the components. Profiles of interdiffusion fluxes were directly determined from concentration profiles. The diffusion path for a single phase couple with a ZFP was experimentally found to be invariant with diffusion time. The locations of ZFP’s within the diffusion zone of a couple corresponded to sections where the activity of a component was the same as its activity in either of the terminal alloys of the couple. Couples developing ZFP’s showed regions where a component diffused up its own activity gradient. The diffusional interactions among the components described by the ratios of cross to main ternary interdiffusion coefficients were determined directly from the slopes of the diffusion paths at various ZFP compositions. In several multiphase couples, discontinuous flux reversals for the components were also identified at theβ/a and γ/β interfaces. A discontinuous flux reversal for a component was observed at a planar interface, when the activity of the component at the interface corresponded to its activity in one of the terminal alloys of the couple.     

Ternary Diffusion in a RuAl-NiAl Couple

A ternary diffusion couple assembled with NiAl and RuAl disks and annealed at 1100 °C was examined by scanning electron microscopy and analyzed for concentration profiles by electron microprobe analysis. Complete mutual solid solubility with continuous variations in compositions was observed between the binary B2 aluminides. Ternary interdiffusion coefficients were determined with the aid of a program called MultiDiFlux over two composition ranges, one Ru-rich and the other Ni-rich, within the diffusion zone. The interdiffusion coefficient, varies little with variation in composition, but the interdiffusion coefficient, decreases by an order of magnitude from the Ni-rich region to the Ru-rich region. is larger than in the Ni-rich region by an order of magnitude. The cross coefficients, and , are both positive. is comparable in magnitude to the main coefficient in the Ni-rich region; hence, Ni interdiffusion flux is enhanced down a Ru concentration gradient but decreased against it. Similarly, Ni interdiffusion is reduced down Al gradients. Characteristic depth parameters calculated for Ni and Ru are larger on the NiAl side than on the RuAl side. Approximate calculations of cumulative intrinsic diffusion fluxes past a Kirkendall plane suggest that the atomic mobility of Ni is larger than that of Ru.     

Nutritive values of Nepalese edible wild fruits

Summary The nutritive values of forty edible wild fruits of Nepal were determined in terms of total dry matter, sugar, protein, total ash and sodium, potassium, magnesium and calcium. It was concluded that most of the wild fruits are comparable to cultivated fruits in nutritive values and, therefore, may be considered as suitable for cultivation.

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Nährwert der eßbaren Wildfrüchte von Nepal

Zusammenfassung Der Nährwert von 40 eßbaren Wildfrüchten von Nepal wurde bestimmt. Die Werte der meisten wilden Früchte sind vergleichbar mit denen von kultivierten Früchten. Einige der Wildfrüchte können zur Kultivierung empfohlen werden.

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This work was sponsored by the Research Division, Rector's office, Tribhuvan University     

An analysis of concentration profiles for fluxes,diffusion depths,and zero-flux planes in multicomponent diffusion

Concentration profiles developed during isothermal, multicomponent diffusion for a single-phase, solid-solid diffusion couple are expressed on the basis of a relative concentration variable for each component and analyzed for the determination of interdiffusion fluxes. The individual concentration profiles intersect at a common cross-over composition where the relative concentrations of all components are identical. New relations are developed for describing internal consistency among the concentration profiles of the various components. A link is made between the cross-over composition and the depths of the diffusion zone on either side of the Matano plane for a diffusion couple. The cross-over composition is interpreted as the average relative concentration of each component over the diffusion zone. The identification of a zero-flux plane from concentration profiles is also described. The analysis offers several advantages in presenting as well as checking the self-consistency of results as illustrated with a single phase Cu-Ni-Zn diffusion couple annealed at 775 °C.