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  • Author or Editor: M. Gaft x
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Abstract  

The influence of thermal treatments on photoluminescence spectra of several minerals has been investigated. By applying step-wise heating, new luminescence centres were detected which had been not previously recognized in the corresponding minerals. Luminsecence centres appearing as result of valence changing during oxidizing heating include: (i)  (UO2)2+ as a result of nonluminescent U6+ transformation in zircon, barite, francolite and chert; (ii)  Eu2+ as a result of nonluminescent Eu+ transformation in barite. Luminescence centres which were most stable under thermal treatment were Fe3+ in zircon and Mn2+ in barite. Luminescence centres with similar spectral-kinetic properties but with different thermal stability which allowed them to be separated and properly identified were different metaloxygen complexes (MeOn)m− in zircon.

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Abstract  

The photoluminescence (PL) of barite is a noncharacteristic property and cannot be used for the investigation of its structure. After thermal treatment of barite at 600°C several luminescent centers were observed, providing information about different impurities. UO 2 2+ was determined from the vibrational structure and the long decay time of the luminescence band. Two different types of uranyl were detected, thin films of uranyl mineral (most probably, reserfordin) and a solid solution of uranyl ion in barite crystal. Characteristic green luminescence of UO 2 2+ may be used as indicative feature for the prospecting of uranium deposits and for the sorting of barite ores with the aim of cleaning from harmful U impurities. Eu2+ was determined from the spectral position, the half-width and the characteristic decay time of the luminescence band. Mn2+ and Ag+ were determined by comparing luminescence bands spectral parameters to those of synthesized BaSO4−Mn and BaSO4−Ag. Fe3+ or Mn4+ were determined from the spectral-kinetic parameters of the luminescence bands.

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Abstract  

Limestone and monocrystalline calcite tempers (grains) are abundant in ancient pottery. In pottery from the Canaan area the former is common in Iron Age storage and table-ware vessels and the latter is present in cooking pots. Limestone is much more widespread than monocrystalline calcite and the potters used it often as tempers when manufacturing pottery vessels, but usually not for cooking pots. While defects appear frequently around limestone tempers, they do not appear around monocrystalline calcite ones. This study examines the reason for using the latter tempers rather than the former ones. Raw materials of carbonate tempers in a clay matrix were fired and the decarbonation process was followed by quantitative IR thermospectrometry. The results indicate that the monocrystalline calcite tempers prevent formation of defects in the cooking pots during firing or during use. The reasons for this are higher thermostability at elevated temperatures, lower intensity of decarbonation, and retention of grain shape, as compared to limestone tempers.

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