Density of Liquid Ni-Ti and a New Optical Method for its Determination

Liquid Ni-Ti alloys were processed in a containerless way using the technique of electromagnetic levitation in order to determine their densities. An improved optical method was utilized where, in addition to recording shadowgraph images from the side, a second camera recorded images of the sample from the top. A correction factor for the density was calculated from the top-view images. This method yields measurements insensitive to droplet rotation and static deformation which removes the need to assume axial symmetry. The measured densities are discussed in terms of the molar volume. A negative molar excess volume was obtained, indicating that Ni-Ti is a highly non-ideal system. These measurements were then used to test a recently proposed relationship between the molar excess volume, the excess free energy, and the isothermal compressibility. For the first time, the excess volume of a binary alloy, i.e., Ni-Ti, is adequately predicted by a thermodynamic model.