Pyrite, thermal analysis

Figure 3. DSC thermal analysis of pyrite in (A) pyrite mineral (Rico, Colorado), (B) Devonian shale kerogen, and (C) pyrite-reduced kerogen of...

Sintered deposits form at the furnace exit at lower gas temperatures and in zones subject to rapid changes in direction. The deposit is composed of spheroidal particles, <40p, bound together by a molten substance. In those cases where substantial quantities of coarse pyrites are liberated from the pulverized coal, the spheroids are nearly pure FeaOa, as shown in Figure 11. The matrix contained silica, alumina, iron, and potassium, and has an initial deformation temperature of 1832°C, as determined by differential thermal analysis. The heavier pure iron spheroids deposit as a result of inertial impact. The mineral source of the molten phase is most likely illite. 

Slates are related to clays. The DTA technique has been applied to study the weathering quality as well as an aid to the identification of slate of unknown origin. Figure 17 shows the differential thermal analysis of samples of roofing slate of three different qualities.The first curve represents a slate of excellent durability. The peaks at 610 and 850°C may be due to some type of chlorite. The inflection at 575 C is caused by the presence of quartz. In the calcined material (2 curve), the presence of quartz is more clear. The third curve is obtained with a slate that was found in practice to delaminate slowly on roofs under conditions of low atmospheric pollution. The poor durability may be caused by the slow oxidation of pyrite in the slate and subsequent reaction between the oxidation product and calcite to form calcium sulfate. The presence of pyrite and calcite is indicated by the peaks at 450° and 770°C, respectively. The fourth curve of slate of pure quality is dominated by the large calcite peak. The exothermic peaks at 930° and 420°C suggest the presence of chlorite and a small amount of pyrite, respectively. 

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