Segregation Of Antimony Research Articles

Free Energy Changes and Boundary Segregation of Tin and Antimony in CrV Steels

Free Energy Changes and Boundary Segregation of Tin and Antimony in CrV Steels

Grain boundary segregation and desegregation of antimony in temper-brittle steel, identified and measured by the elastic scattering of energetic ions

Grain boundary segregation and desegregation of antimony in temper-brittle steel, identified and measured by the elastic scattering of energetic ions

Interfacial free energy of copper-antimony alloys

It was suspected that the brittleness of copper-antimony alloys is partly due to a low surface energy caused by segregation of antimony to interfaces in the Gibbs manner. In these experiments the surface and grain-boundary energies and the surface segregation were measured on pure copper and copper alloys containing 0.26, 0.57 and 0.78 at. % antimony. The surface energies were measured on these alloys in the form of wires in a helium atmosphere at 950 °C and as similar results were obtained in a hydrogen atmosphere it was concluded that no serious unwanted surface contamination occurred. The grainboundary energies were deduced from the surface energies by measuring the dihedral angles in an electron microscope. The surface energies were 1770, 980, 950 and 900 ergs/cm 2 and the grain-boundary energies 600, 290, 280 and 320 ergs/cm 2 in order of ascending antimony content. The creep rates of the wires in the surface energy experiments agreed to within a factor of 3/2 with the rate calculated from Herring’s equation for diffusion creep. The surface segregation was measured on copper and the 0.57 and 0.78 at. % antimony alloys after annealing and irradiating in order to detect antimony radioactively. Surface segregation of antimony was found in the two alloys in an amount equivalent to 0.37 monolayer of pure antimony. The surface composition and surface energies are shown to be consistent. Antimony does therefore drastically reduce the surface and grain boundary energies of copper by segregating in the Gibbs manner.

Measurement of Ternary Distribution Coefficients in Silicon

A method is described for determining the distribution coefficient of an impurity introduced into a semi-conductor by a fused metal contact. Coefficients for the segregation of antimony, arsenic, gallium, and aluminum from a silver contact to silicon at 1250°C are less than at the silicon melting point (1408°C). Gold-doped contacts to silicon yield similar values for the distribution coefficient of these impurities. This value is independent of the concentration of the impurity in the gold or silver alloy for small (less than 1%) percentages of the impurity. At 1250°C, the segregation of aluminum from a dilute solution of aluminum in silver is about the same as from 100% aluminum. The diffusivity of silicon atoms through a liquid zone containing aluminum and saturated with silicon is greater, at any particular temperature, than the diffusivity through a silver-silicon zone at the same temperature. However, these values approach each other at the silicon melting point.

Microsegregation in the Lead‐Antimony Alloys

The freezing process occurring in lead and hypoeutectic lead‐antimony alloys was studied in single crystals and polycrystalline aggregates by examination of the metallographic structure with microscopic, microradiographic, and chemical replica techniques. The formation of dendritic lead crystals was also observed in other systems. The microsegregation occurring in the lead‐antimony alloys was found to be a result of the dendritic mode of growth. Production of a homogenous alloy was found to be impossible even when the amount of antimony was reduced to insignificant amounts. This was true whether the alloy was chill‐cast or very slowly cooled. Segregation is shown to be caused both by the small concentration gradient and the large amounts of lead crystallizing in the first intervals of freezing. Alloys of higher concentration are shown to have a more uniform solid solution of antimony in lead but actual segregation of antimony or an antimony‐rich phase is inevitable. The primary lead dendrites appear to grow by alternate dendritic extension and regular crystal growth, accounting for the structure observed in metallographic sections. The structure in these alloys, commonly referred to as eutectic, is not produced under eutectic conditions and is not representative of true eutectic structure. When chill cast, an alloy with 13 per cent antimony produces a normal eutectic crystallization. Normal eutectic crystallization could not be initiated in any slowly cooled alloy investigated. In general, the segregation that occurs in chillcast alloys is much more uniformly distributed than that in slowly cooled alloys.