International audienceThe structural recovery upon heat treatment of a highly metamict, actinide-rich zircon (U~6000 ppm) has been studied in detail using a range of techniques including X-ray powder diffraction, Raman spectroscopy, SHRIMP ion probe, electron microprobe, transmission electron microscopy and cathodoluminescence analysis. The structural regeneration of the amorphous starting material depends on random nucleation. It starts between 800 and 950°C when amorphous ZrSiO4 decomposes to form crystalline ZrO2 and amorphous SiO2. At around 1100°C, well-crystallised ZrSiO4 grows at the expense of the oxides. U has been retained in the newly grown zircon whereas Pb was evaporated during the heat treatment. This process is in marked opposition to the reconstitution of moderately metamict minerals, which experience a gradual recovery controlled by the epitaxial growth at the crystalline–amorphous boundaries. Both of these recovery processes are not the direct inverse of metamictisation. The structural regeneration was found to be connected with a significant increase in the emission of CL. In all cases (annealing heavily damaged zircon and moderately damaged zircon and monazite), we observe that the final, wellcrystallised annealing products emit more intense CL than their radiation-damaged starting minerals, although having almost identical elemental composition. Our observations are taken as evidence that the CL is not only determined by the chemical composition of the sample but is also strongly controlled by structural parameters such as crystallinity or the presence of defect centres

The phase equilibria and reaction temperatures in the system Al–Cu were re-investigated by a combination of optical microscopy, powder X-ray diffraction (XRD) at ambient and elevated temperature, differential thermal analysis (DTA) and scanning electron microscopy (SEM). A full description of the phase diagram is given. The phase equilibria and invariant reactions in the Cu-poor part of the phase diagram could be confirmed. The Cu-rich part shows some differences in phase equilibria and invariant reactions compared to the known phase diagram. A two phase field was found between the high temperature phase η1 and the low temperature phase η2 thus indicating a first order transition. In the ζ1/ζ2 region of the phase diagram recent findings on the thermal stability could be widely confirmed. Contrary to previous results, the two phase field between δ and γ1 is very narrow. The results of the current work indicate the absence of the high temperature β0 phase as well as the absence of a two phase field between γ1 and γ0 suggesting a higher order transition between γ1 and γ0. The structure of γ0 (I-43m, Cu5Zn8-type) was confirmed by means of high-temperature XRD. Powder XRD was also used to determine the structure of the high temperature phase η1-Al1−δCu. The phase is orthorhombic (space group Cmmm) and the lattice parameters are a = 4.1450(1) Å, b = 12.3004(4) Å and c = 8.720(1) Å; atomic coordinates are given.

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A series of substituted triarylmethylium cations, including malachite green, tris(4-methoxyphenyl)methylium, and bis(4-methoxyphenyl)phenylmethylium cations, has been prepared adsorbed on tridirectional large pore zeolites Y and β in their H+ or La3+ form, as well as within the novel mesoporous aluminosilicate MCM-41, by ship-in-a-bottle synthesis from the corresponding benzaldehyde and N,N-dimethylaniline or anisole. The resulting composites exhibit diffuse reflectance and IR spectra characteristic of these trityl dyes. The cation content was determined by thermogravimetry−differential scanning calorimetry. Preparation of these triarylmethylium cations exclusively on the external surface of ZSM-5, a medium pore zeolite whose internal voids are too small to accommodate these cations, is also possible. Therefore, the methodology based in the diffusion of smaller precursors does not guarantee itself the intrazeolite location of the synthesized guests. In this work, we have experimentally determined that the dyes are blocked in the interior of the faujasite pores. Thus, direct evidence showing the location of the organic material inside the zeolite supercages was obtained using X-ray diffraction and X-ray photoelectron spectroscopy. These dyes incorporated within microporous solids can act as heterogeneous photosensitizers to promote the sensitized dimerization of 1,3-cyclohexadiene.