Visible damage on the surface of historic glass, iridescence, is developed by the influence of environmental factors during time. Iridescence is usually considered as an age indicator in historic glass. Samples from the ancient Sasanian historic site called "Tomb-e Pargan" in the Boushehr Province of Iran were subjected to microscopic analyzing with ESEM, ICP-OES, and polarization microscopy to characterize structural damages and its impact on the surface deposition. Chemical-mineralogical studies were also performed. The current investigation suggests that the iridescent layer is developed as the result of alkali ion depletion on the glass surface following the formation of a shelly layer. Due to the porosity of ancient glass surface, ions migrate and deposit continuously on the surface in the form of crust. The phenomenon causes fine lamellar structure on the surface. Samples from Tomb-e Pargan characteristically contain potassium and magnesium.
In this study, the effect of Al on the high temperature oxidation of Al-containing refractory high entropy alloys (RHEAs) Ta-Mo-Cr-Ti-xAl (x = 5; 10; 15; 20 at%) was examined. Oxidation experiments were performed in air for 24 h at 1200 °C. The oxidation kinetics of the alloy with 5 at% Al is notably affected by the formation of gaseous MoO3 and CrO3, while continuous mass gain was detected for alloys with the higher Al concentrations. The alloys with 15 and 20 at% Al form relatively thin oxide scales and a zone of internal corrosion due to the formation of dense CrTaO4 scales at the interface oxide/substrate. The alloys with 5 and 10 at% Al exhibit, on the contrary, thick and porous oxide scales because of fast growing Ta2O5. The positive influence of Al on the formation of Cr2O3 followed by the growth of CrTaO4 to yield a compact scale is explained by getter and nucleation effects.
High-resolution microscopy investigations on ancient ceramics recommend the complex progression of crystalline phases in an antique object via the sintering process. Based on materials-science point of view, sintering is not a routinely reaction in all crystalline phases with the same crystallographic pattern, but also is a transition pathway. Sintering depends on the processing of raw materials via the manufacturing process. Five samples are chosen for this analytical approach from two different periods from Tappeh Zaghe, Iran (5100 millennium BC). A multimicroscopical approach was carried out by means of polarized light microscopy, environmental scanning electron microscopy, and atomic force microscopy. Crystalline phases were determined by X-ray diffraction and refined after Rietveld method. The observation of the behavior of phase–interphase boundaries of a crystalline part in the nano area suggests that the partial sintering is the point at which the mineral began to be decomposed, and the conditions of the occurrences of this phenomenon depend on crystallographic properties.
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