The Differential Thermal Analysis of Ore Minerals (I) : The Automatic Recording Apparatus of DTA and Its Analytical Data

To make a automatic recording DTA apparatus, PID program controller, DC amplifier, recorder, etc. were assembled. The schematic arrangement of the appartus is shown in Fig. 7. The accuracy of the apparatus is within ±5℃ in comparison with melting points of standard metals, such as zinc, antimony and aluminium. The DTA of the apparatus was tentatively carried out on behavior of transition, decomposition, and congruent, eutectic and solid solution melting on such sulfide minerals as cubanite, chalcocite, monoclinic pyrrhotite, stibnite, cuprobismuthite CuBiS_2 and horobetsuite BiSbS_3. The specimen and inert material (alumina) are severally sealed in evacuated silica glass tubes which are able to insert chromel-alumel thermo-couples into their bottoms. The DTA curve (Fig. 12) of chalcocite shows large and small endothermic reactions at 105℃ and 485℃ which are transitions from orthorhombic to hexagonal form and from hexagonal to cubic form respectively. Cubanite (Figs. 11 and 12) is also found to transform from low temperature form to high temperature form by the DTA curve showing a distinct endothermic peak beginning at 258℃. The DTA curve (Fig. 12) of monoclinic pyrrhotite also represents a transition from monoclinic form to hexagonal form at 325℃. Both stibnite and bismuth (Fig. 13) are shown to melt congruently at temperatures of 545℃ and 273℃ respectively. The DTA curve (Fig. 12) of cuprobismuthite shows three endothermic reactions at 487℃, 528℃ and 615℃. The first reaction represents its decomposition into wittichenite and Cu_3Bi_5S_9,and the second and third suggest eutectic melting of the mixture of wittichenite and Cu_3Bi_5S_9,corresponding to composition of cuprobismuthite. Horobetsuite is found to be a solid solution of Bi_2S_3 and Sb_2S_3 from its DTA curve (Fig. 13). The temperature of its solidus and liquidus are 670℃ and 703℃ respectively.