Balance of distribution of some transition metals between theM'M″B and (M' M″)in2B phases

A study has been made of the preferential distribution between the phases (M', M″)2B and (M M″)B present in the two-phase fields of the M'-M″-B systems for the transition metals with atomic numbers between 24 and 28. It has been ascertained that the metal with the smaller atomic number is systematically concentrated in the phase richer in boron. The extreme values of the distribution ratio α°, calculated according to Hägg and Kiessling1 in the temperature range 1073 to 1473 K, diminish progressively in relation to the increase in the difference between the atomic numbers of the metallic atoms. Further, α° increases gradually as the temperature increases. The preferential distribution has been justified considering the different metal-nonmetal affinity, and recalling analogous considerations expressed in relation to nitrides, carbides, and hydrides of transition metals.