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Combined use of thermal and surface analyses

Study of the smelting process of iron ores from Monte Ferru (Sardinia)

Journal of Thermal Analysis and Calorimetry
Authors: G. M. Ingo, G. Padeletti, G. Chiozzini, and G. Bultrini

In order to attempt the location of the iron ore sources exploited at Tharros (Sardinia) during the Phoenician-Punic period and to elucidate some chemical aspects of the iron ore smelting process, the iron ore outcrops of Monte Ferru located near to this archaeological site, have been first sampled and then, differential thermal analysis (DTA) and thermogravimetry (TG) have been used for simulating and studying the iron ore smelting process under a carbon monoxide atmosphere. Furthermore, in order to obtain a qualitative identification of minerals present in the iron bearing rocks and for obtaining some thermochemical data, the smelting process has been carried out also under air and Ar-5% H2 atmospheres. The microchemical aspects involved during the smelting process of the iron ore to crude iron, the formation and the chemistry of new no metallic phases that results from the smelting, i.e. the slags, and the final product of the pyrometallurgical process have been identifiedvia small area X-ray photoelectron spectroscopy (SA-XPS), X-ray induced Auger electron spectroscopy (XAES) and scanning electron microscopy + energy dispersive spectroscopy (SEM + EDS). These results are compared with those obtained from the characterisation of the smelting slags found during the excavation of the archaeological site of Tharros and a relationship is found.

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Abstract  

Amorphous SiO2, TiO2 and xSiO2–(1–x)TiO2 ceramic materials with selected values of x 0.5, 0.7 and 0.9, have been prepared via sol-gel process using silicon tetraethoxysilane (TEOS) and titanium tetraisopropoxide Ti(OPri)4. By means of the combined use of differential thermal analysis (DTA),thermogravimetry (TG), X-ray diffraction (XRD), scanning electron microscopy (SEM),X-ray photoelectron spectroscopy (XPS) and X-ray induced Auger electron spectroscopy(XAES), the surface microchemical structure and morphology of the sol-gel materials have been studied as a function of thermal treatments carried out in air up to 1200C. In the range of temperature from 50 to 450C, DTA-TG results evidence a remarkable mass loss due to the evaporation of organic solvents entrapped in the sol-gel materials and of the remnant organic components of the precursor metal alkoxides. In the range of temperature from 400 to about 1000C, by means of the combined use of DTA, XRD, XPS and XAES techniques as a function of temperature and of chemical composition, it is possible to evidence the formation of crystalline phases such as quartz, anatase and rutile. Furthermore, line shape analysis of O1s XPS peak allows to distinguish between single O–Ti and O–Si bonds and also to disclose the presence of cross linking Si–O–Ti bonds, that act as bridges between SiO2and TiO2 moieties. As a function of temperature, Si–O–Ti bonds are broken and the formation of new Ti–O and Si–O bonds as in TiO2 and SiO2takes place as well as a silica segregation phenomenon.

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Abstract  

By means of the combined use of scanning electron microscopy+energy dispersive spectrometry(SEM+EDS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), differential thermal analysis (DTA) and thermogravimetry (TG), the thermal decomposition of gypsum and gypsum bonded investment used for casting jewellery products has been studied in order to gain a further insight into the origin of the gas porosity in gold-based alloys produced via lost wax casting. The occurrence of the defect is related to the thermal decomposition of CaSO4 that constitutes with silica the investment material and the decomposition of which takes place at a temperature very close to the casting temperature of some typical gold alloys. The decrease of the thermal decomposition temperature of gypsum is induced by the presence of silica and is related to the surface acid-base interaction between SiO2 and CaSO4. On the base of these results, the solid state thermal decomposition of calcium sulphate in the presence of other metal oxides characterised by different acid-base nature has been investigated and a correlation between the surface acid-base properties measured as isoelectric point of the solid surface (IEPS) and via XPS analysis and the temperature of CaSO4 thermal decomposition is observed.

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The thermal behaviour of hydroxide mixtures aimed at Mg-Al spinel preparation is reported. The mixtures of hydroxides were prepared by precipitation reaction from Mg and Al nitrate solutions, stoichiometric to the spinel formation. Hydroxide mixtures with different phase distributions were investigated, prepared by varying the precipitation procedure. The results were related to the thermal behaviour of mechanical mixtures of separately precipitated hydroxides. The spinel formation was identified performing XRD analysis on powder samples heated at different temperatures. The coprecipitated mixtures are completely decomposed to spinel at 400‡C. The presence of the Mg-Al mixed hydroxide phase in the mixture is of primary concern to get spinel at low temperatures.

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The thermal behaviour of hydroxide mixtures, precursors to the synthesis of MgFe2O4 spinel powders, was investigated.

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The thermal behaviour of the square-planar dithiocarbazate derivative complexes Pt[NRNC(S)SR']2 (R=n-hexyl, R′ = methyl or benzyl) has been investigated.

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