Thermal Study on the Inversion of Cubanite

The orthorhombic and cubic inversion of cubanite from the Omine and Komori mines, Japan has been investigated. By heating at 222℃ for 72 hours and at 227℃ for 28 hours isotropic cubanite appears as a lamellar form in original anisotropic cubanite as shown in Fig.1 C and D. At 228℃ for 72 hours original cubanite mostly becomes to isotropic, but a small amount of anisotropic cubanite locally remains as polysynthetic twin-like form (Fig. 1 E and F), and at 233℃ for 70 hours the cubanite entirely transforms to the isotropic high-temperature form (Table 2). The inversion of cubanite has been also studied by means of X-ray powder diffraction and differential thermal analysis. The powder diffraction data are given in Tables 3 and 4. The thermal change of the powder pattern of X-ray diffraction is shown in Fig.2. From these results, it is found that orthorhombic cubanite from the Komori mine changes to cubic type at 235℃ for 24 hours and the both cubanites coexist at 230℃ for 24 hours. The inversion is also seen as a distinct endothermic peak beginning at 254°±3℃ in the differential thermal curves as shown in Fig.3. The reverse transformation from cubic to orthorhombic form has been very difficult because the reaction of the inversion is sluggish. By annealing at 200℃ for 65 days there was not observed the formation of orthorhombic cubanite from the cubic form.