The heat capacity of Ni40Pd40P20 in the liquid, glass and crystallized states

Abstract

The heat capacities of Ni₄₀Pd₄₀P₂₀ alloy in its liquid, glass and crystallized states were measured by differential scanning calorimetry. Measurements on the undercooled liquid ranged from the glass temperature, T_g ∼ 575–655 K and from 780 K to the liquidus temperature, T₁ ∼ 892 K. The range 655–780 K was inaccessible to measurement because of the rapidity of crystallization, but the two sections of the heat capacity-temperature curve, C_p¹(T) were joined smoothly by interpolation through this range. C_p¹ increases with decreasing T, going through T₁, with no discontinuity, to about 11 cal/deg g atom at T_g. As T decreases from T_g, C_p falls abruptly to a level almost coincident with that of the crystallized alloy. Near T_g. C_p¹(T) exhibits a bump associated with relaxation effects. The heat of melting of the alloy was found to be 1.9 kcal/g atom at T₁,. From this and ΔC_p(T), C_p¹-C_p^s, we calculate that the entropy of melting of the alloy at 610 K, ΔS_m(610) = 0.97 cal/deg g atom = 0.41 ΔS_m(T₁). From measured densities we calculate that, at room temperature, the gram-atomic volume V_a = 7.72 cm³/g atom, of the glassy alloy is 0.28% above that of the crystallized alloy and that V_a agrees closely with the weighted average of the gram-atomic volumes of the pure metal constituents (Ni + Pd) in their crystalline forms.