Minerals thermal analysis

Differential thermal analysis curves of iUite show three endothermic peaks in the ranges 100—150, 500—650, and at about 900°C, and an exothermic peak at about 940°C, or immediately following the highest endothermic peak. Minerals formed from iUite at high temperature vary somewhat with the... 

The hydrated alumina minerals usually occur in ooUtic stmctures (small spherical to eUipsoidal bodies the size of BB shot, about 2 mm in diameter) and also in larger and smaller stmctures. They impart harshness and resist fusion or fuse with difficulty in sodium carbonate, and may be suspected if the raw clay analyzes at more than 40% AI2O2. Optical properties are radically different from those of common clay minerals, and x-ray diffraction patterns and differential thermal analysis curves are distinctive. 

A variety of instmmental techniques may be used to determine mineral content. Typically the coal sample is prepared by low temperature ashing to remove the organic material. Then one or more of the techniques of x-ray diffraction, infrared spectroscopy, differential thermal analysis, electron microscopy, and petrographic analysis may be employed (7). 

The quadrupole mass spectrometer has been found to be particularly suitable for EGA in thermal analysis. Published reports include descriptions of the various systems used [153—155] and applications in studies of the pyrolysis of polymers [155], minerals [156] and many inorganic solids [157—159]. 

XPD [18]. Similarly, mineral impurities in talc were analyzed by polarizing light microscopy, differential thermal analysis, and XPD [19]. It must be recognized, however, that small amounts of crystalline impurities (usually <0.5% w/w) may not be detected by XPD. In case of noncrystalline impurities, mrch higher concentrations may be nondetectable. 

Although a number of secondary minerals have been predicted to form in weathered CCB materials, few have been positively identified by physical characterization methods. Secondary phases in CCB materials may be difficult or impossible to characterize due to their low abundance and small particle size. Conventional mineral identification methods such as X-ray diffraction (XRD) analysis fail to identify secondary phases that are less than 1-5% by weight of the CCB or are X-ray amorphous. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM), coupled with energy dispersive spectroscopy (EDS), can often identify phases not seen by XRD. Additional analytical methods used to characterize trace secondary phases include infrared (IR) spectroscopy, electron microprobe (EMP) analysis, differential thermal analysis (DTA), and various synchrotron radiation techniques (e.g., micro-XRD, X-ray absorption near-eidge spectroscopy [XANES], X-ray absorption fine-structure [XAFSJ). 

Thermal analysis of humic-mineral complexes has shown there is an overall reduction in the decomposition temperatures of humic acid that has been com-plexed to a mineral surface. Changes in the exothermic peak temperatures of humic substances in the free and complexed state are well-documented for synthetic mineral complexes with humic and fulvic acid (Schnitzer and Kodama, 1972 Tan, 1977 Schnitzer and Ghosh, 1982) as well as for authentic soil complexes. 

Fau t, G.T., 1951. Thermal analysis and X-ray studies of sauconite and of some zinc minerals of the same paragenetic association. Am Mineralogist, 36 795-822. 

The compression of starch in the presence of some mineral salts (CoCl2 and FeCl3) and of elemental iodine leads to the formation of starch-additive inclusion complexes. Among many salts tested, some form only physical mixtures, as proved by thermal analysis.63,64 (See Appendix for additional text.)... 

D. N. Todor, Thermal Analysis of Minerals, Abacus Press, Kent, England, p. 170 (1976). 

T. Smyth, Temperature Distribution during Mineral Inversion and its Significance in Differential Thermal Analysis , J. Am. Ceram. Soc. 34 221-224 (1951). 

C. M. Earnest, Thermal Analysis of Clays, Minerals, and Coal, Perkin-Elmer Corporation, Norwalk, CT (1984). 

Mitchell, B. D., and R. C. Mackenzie An Apparatus for Differential-Thermal Analysis under controlled-atmosph. conditions. Clay Minerals Bull. 4, 31/43 (1959). 

Thermal analysis is suitable for the study of the changes under heat, including the changes in mass and enthalpy (Smykatz-Kloss and Warne 1991 Liptay 1973). In addition, when the minerals are qualitatively or semiquantitatively known from x-ray diffraction studies, their quantity can be determined more precisely on the basis of characteristic thermal changes of the minerals. Thermal analytical methods give very useful information on the types of water in clay minerals and on the valency of the interlayer cation (Chapter 2, Section 2.1.2 Foldvari 1991 Foldvari et al. 1998). 

Foldvari, M. 1991. Measurement of different water species in minerals by means of thermal derivatography. In Thermal analysis in the geosciences. Ed. W. Smykatz-Kloss, and S. St. J. Wame. 84—100. Berlin Springer. 

The literature on MKP mineral is scarce. Sivaprasad et al. [33] and Wagh et al. [34] consider this material as an analog of struvite, in which NH4 is replaced by K, and have determined its crystalline structure. Differential thermal analysis (DTA) and thermo-gravimetric analysis (TGA) indicated that the 6 mol of water in the crystal are loosely bound and escape upon heating at 120°C (Fig. 9.9), after which anhydrous MKP is formed. 

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

Gleadow A. J. W., Duddy 1. R., Green P. F., and Lovering J. F. (1986) Confired track lengths in apatite—a diagnostic tool for thermal analysis. Contrib. Mineral. Petrol. 94,405-415. 

MgCOj decomposes at substantially lower temperatures the dissociation pressure reaches atmospheric pressure at 400—480 C. The reaction enthalpy is 121 kJ (28.9 kcal) per mole at 25 °C. MgC03 bound in dolomite decomposes at a temperature somewhat higher than pure MgC03. The dissociation pressures are plotted in Fig. 27. The decomposition of dolomite proceeds in two stages as illustrated by differential thermal analysis curves, showing two distinctly separate endothermal peaks for MgCOa and CaCOj respectively. The DTA curves for various minerals are shown in Fig. 28 (Ivanova et al., 1974). 

FIG. 28. Differential thermal analysis curves of various minerals. 

Ivanova V. P. et al.. Thermal Analysis of Minerals and Rocks (in Russian), Leningrad 1974 (HBanoBa B. 11. h koh., TepMHHecKHtt aHa.TO3 MHHCpanoB h ropHWX nopofl, JlemiHrpafl). 

Differential thermal analysis (DTA) data for talc exhibit an endotherm at approximately 950-975°C. This thermal event has been attributed to decomposition of the talc to MgSi03, Si02, and water [25, 26]. DTA has also been used to determine mineral impurities in talc batches [27]. 

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