Palygorskite-TiO2 nanocomposites were prepared by deposition of the anatase form of TiO2 on the clay surfaces using a sol-gel method with titanium isopropoxide as a precursor under hydrothermal ...treatment at 180 C. The same procedure was followed in the formation of halloysite-TiO2 nanocomposites using a halloysite sample. Phase composition, particle morphology and physical properties were characterised using XRD, SEM and microanalysis by EDS, TEM, attenuated total reflection using FTIR and N2 surface area analysis by BET. The photocatalytic activities of clay-titania nanocomposites in decomposing NOx gas were measured. After treatment with TiO2, the halloysite and palygorskite samples had mesopores of about 5.6 and 6.5 nm, respectively, while the macropores of halloysite disappeared. This is attributed to the covering of the central hole in halloysite tubes by TiO2 nanoparticles making the pore size of the TiO2-treated halloysite was significantly smaller. The clay-titania samples showed significantly higher activity in decomposing NOx gas under visible-light irradiation (wavelength > 510 nm) and UV light irradiation (wavelength > 290 nm) compared to that of the standard commercial titania, P25.
Two widely different kaolin deposits of Greece were studied in order to compare the impact of the alteration mechanism to the presence of thorium and rare earth elements (REE) in the deposits and to ...find a measure for their migration during the alteration processes. Halloysite and kaolinite coexist in gneissic weathering profiles, developed under a temperate climate in the Leucogia area, NE Greece. The kaolin occurrences of Kos island, Aegean sea, Greece, are products of hydrothermal alteration of rocks of rhyolitic composition. Monazite is found as an accessory mineral in both areas and it is the only mineral that contains lanthanum, cerium and neodymium and in addition thorium, in the kaolins of Leucogia area. To resolve the genetic relationship between monazite and its alteration products, the mineralogy of the primary rocks and kaolins and their microtextures were examined, and bulk rock chemical analyses were performed in order to correlate major and trace elements behaviour with the alteration mechanisms.
In the gneissic weathering profiles of the Leucogia area, monazite (Ce) is partially altered to a ThSiO
4 or Th–OH silicate microcrystalline phase with very low concentrations of light rare earth element (LREE). The relict monazite crystals are depleted in thorium. The depletion and/or the enrichment of the various elements in the bulk sample appear to be related to mineral breakdown rather than to mild leaching of primary minerals by meteoric water. The only element that is apparently immobile is thorium and this element can be used as a measure for the depletion in this environment. Monazite (Ce), in the hydrothermally altered rhyolitic rocks of Kos island, is altered to P-bearing crandallite–goyazite. During this alteration process, LREE are depleted with respect to the fresh monazite crystals. Phosphorus, which was found to be the only element with an immobile behaviour, can be used as a reference to evaluate the amount of REE leached during monazite alteration in this hydrothermal environment.
Roman ceramic red-painted and unpainted lamps from two workshops excavated in the area of Patras, NW Peloponnese, Greece were examined in order to determine the mineralogical characteristics of the ...raw materials used for their production and to elucidate the ceramic manufacturing technologies employed. Optical microscopy, X-ray diffraction analysis (XRD), inductively coupled plasma-emission spectroscopy (ICP-OES) and scanning electron microscopy (SEM-EDS) were the analytical techniques used.
The preliminary results presented here indicate that calcareous clays were used in the manufacture of the pottery by the two workshops. Based on a number of mineral assemblages observed, the chemical composition of prograde mineral phases developed in the sherds, the variability of colours of the body of the sherds, the chemical composition of the sherds and the textural and vitrification structures, it is shown that the two workshops used oxidizing conditions in the kilns and firing temperatures ranging from about 850 to 1050 °C. Only small differences in the production technology, which has been used by the two workshops have been recognized, especially in the body preparation and in the clay to temper ratios.
Palygorskite-TiO
2 nanocomposites were prepared by deposition of the anatase form of TiO
2 on the clay surfaces using a sol-gel method with titanium isopropoxide as a precursor under hydrothermal ...treatment at 180
°C. The same procedure was followed in the formation of halloysite-TiO
2 nanocomposites using a halloysite sample. Phase composition, particle morphology and physical properties of these samples were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and microanalysis by energy dispersive spectrometry (EDS), transmission electron microscopy (TEM), attenuated total reflection using Fourier transform infrared spectroscopy (ATR-FTIR) and N
2 surface area analysis by BET. The photocatalytic activities of clay-titania nanocomposites in decomposing NO
x
gas were measured. After treating with TiO
2, the halloysite and palygorskite samples showed mesopores of about 5.6 and 6.5
nm, respectively, while the macropores of halloysite (central hole in halloysite tubes) disappeared. The latter is attributed to the covering of the central hole in halloysite tubes by TiO
2 nanoparticles and for that reason the pore size of the TiO
2-treated halloysite was significantly smaller. The clay-titania samples showed significantly higher activity in decomposing NO
x
gas under visible-light irradiation (λ
>
510
nm) and UV light irradiation (λ
>
290
nm) compared to that of the standard commercial titania, P25.
