Dimensional effect in forming the niobium alloy with cadmium ultradispersed particles with low temperature

Abstract

Previous studies have established a significant – a few hundred degrees lowering the melting point of metals with a decrease in particle size. Such a phenomenon is explained by the effect of thermofluctuation melting, in which the ultradisperse particle is in a quasi-liquid state, with an increase in the size of which up to some critical crystallization occurs. With the co-existence and contact of two unlike metal particles in a quasi-liquid state, they can coalesce to form a solution at a low temperature. Similar studies for the niobium-cadmium system are currently lacking. For the formation of alloys at low temperature (50-100 oC), it is necessary to determine the critical dimensions of niobium and cadmium capable of forming an alloy under these conditions. The method of formation of samples of alloy coatings consisted in ion-plasma sputtering of niobium and cadmium and their co-precipitation on non-heated substrates moving relative to the plasma streams in the form of sublayers of a certain thickness of each of the metals at low pressure and successively decreasing the sizes of the sublayer particles, in the preparation of an alloy-solid cadmium solution in niobium, the critical size of niobium clusters is 2.12-2.15 nm, cadmium is 3.12-3.19 nm. The coefficients in the hyperbolic dependence of the melting point decrease on the crystallite size, equal to 5.02 • 10-6 for niobium, and 6.89 • 10-7 K • m for cadmium are determined. Dependences of the decrease in the melting temperature ( ) are as follows: for niobium , for cadmium  , where r – is the radius of a small particle, m. The estimated value of the surface tension at the crystal-melt boundary for temperatures 50-100 оС was for niobium – 2.33-2.38 J / m2, for cadmium 0.28-0.34 J / m2.