CRYSTAL STRUCTURE AND /ATOMIC PROPERTIES OF ALLOYS CONTAINING TRANSITION ELEMENTS.”
THE TRANSITION ELEMENTS.
According to Bohr, more than half the number of metallic elements belong to series within which a gradual consolidation of the inner electron groups of the atoms takes place. These metals-the so-called transition elements-consist of the series zlSc-28Ni, 39Y-@Pd, 57La-78Pt, 8gAc-92U. Bohr has marked them out by enclosing them in frames in his periodic table (Fig. I). The electronic configuration of the atoms of these elements seems to be of an easily changeable character, i.e. the steps between their energy levels are smaller than in other kinds of atoms. Because of this, their ions differ from those of other elements inasmuch as they have the capacity of absorbing in the visibIe part of spectrum. Their solutions are consequently colored. Further, owing to the assymetry of their ions they are in the ionic state generally not diamagnetic, like the normal elements, but instead are more or less distinctly paramagnetic.
To download the file click on the link below:
ALLOYS WITH NICKEL-ARSENIDE STRUCTURE.
When Aminoff and Al& (2, 3) several years ago determined the atomic grouping of the mineral nickehne, NiAs, they scarcely suspected that it was one of the most generally occurring structure types of the alloy phases that they had encountered. Soon afterwards Al&t (4) also found that pyrrhotite, FeS, as well as breithauptite, NiSb, and the synthetically produced compounds FeSe, NiS, NiSe and CoS all have the same atomic grouping as NiAs. Later V. M. GoldSchmidt and his collaborators, however, could add to this list quite a number of other substances, which were all found to have this so-called nickel-arsenide structure (5)+ All of them are good conductors and have metal lustre so that they may be counted amongst the alloys even though they may contain up to 50 atomic per cent. As, S or Se.
The structure type of nickel arsenide is shown in Fig. 2.
The two kinds of atoms are here not structurally equivalent ; atoms of the one kind are arranged in a simple hexagonal lattice, while those of the other define a hexagonal close-packed lattice, inserted into the former.
V. M. Goldschmidt has pointed out the following fact in his important papers on the connection between crystal structure and atomic properties (5, 6). All substances which we know for certain to possess the atomic arrangement of nickel-arsenide consist partly of atoms which belong to a transition element, and partly of large, easily polarized atoms, such as those of the elements Sn, As, Sb, Bi, S, Se and Te, the numerical proportion of the two kinds being about equal. The atoms of the first kind always take the position of the points of a simple hexagonal lattice, as seen in Fig. 2.
........
From the data already available Goldschmidt has, however, been able to infer that the condition mentioned above is not sufficient for the formation of a nickel-arsenide phase, It is also necessary that the ratio of the radius of the large atoms to that of the small ones should exceed a certain minimum value. Thus, iron, cobalt, and nickel form phases of the nickel-arsenide type with sulphur and selenium as well as with tellurium. Manganese, however, whose atoms are slightly larger than those of iron, cobalt and nickel, appears to form a nickel-arsenide phase only together with tellurium, and not with sulphur and selenium.
No comments