Investigating morphological changes in treated vs. untreated stone building materials by x-ray micro-CT

Calcareous stones have been largely used to build historical buildings. Among these, the calcarenites are usually characterized by a high content of calcite and a high open porosity, which make them very sensitive to the weathering caused by physical and chemical agents. In order to prevent their deterioration and to retard their decay, different protective products—mainly polymers—are applied on the stone artefact surfaces. In this work we apply the methodology tested in a preliminary study to investigate the morphological changes of the internal structure of a biocalcarenite (Lecce stone) by micro x-ray computed tomography (μ-CT). The porosity and other morphological parameters of the rock before and after the conservation treatment were calculated on a significant number of samples. The Student’s t test was applied for statistical comparison. The results reveal that the treatment with Paraloid B72 (PB 72) is homogenously distributed and causes small changes to the natural properties of the rock, whereas the application of a fluoroelastomer (NH) causes an appreciable decrease in porosity and variation in terms of wall thickness distribution, probably resulting from its inhomogeneous distribution. Figure Porosity and other morphological parameters of Lecce stone were investigated by μ-CT: the effect of conservation treatment with fluoroelastomer on wall thickness distribution is illustrated     

Subnanometer-scale measurements of the interaction of ultrafast soft x-ray free-electron-laser pulses with matter

At the recently built FLASH x-ray free-electron laser, we studied the reflectivity of Si/C multilayers with fluxes up to 3 x 10(14) W/cm2. Even though the nanostructures were ultimately completely destroyed, we found that they maintained their integrity and reflectance characteristics during the 25-fs-long pulse, with no evidence for any structural changes over lengths greater than 3 A. This experiment demonstrates that with intense ultrafast pulses, structural damage does not occur during the pulse, giving credence to the concept of diffraction imaging of single macromolecules.     

On the influence of ion exchange on the local structure of the titanosilicate ETS-10

The effect of ion exchange with different monovalent cations (NH(4)(+), K(+), Na(+) and Cs(+)) on the local structure of the titanosilicate ETS-10 has been studied by (29)Si MAS NMR and Raman spectroscopy. Although X-ray diffraction shows no significant influence of ion exchange on the long range order, ammonium exchange is found to result in substantial damage to the local structure. Ion exchange experiments with alkali cations under significantly more acidic conditions clearly show that the structural damage brought about by ammonium exchange is not caused by the low pH of the exchange solution. The exchange with potassium and caesium ions also leads to significant changes in the (29)Si NMR and Raman spectra. However, these changes can largely be reversed by sodium back-exchange.     

Scandium as an Element Intermediate between Rare Earth and Transition Metals in Intermetallics: Crystal Structures of Sc2Fe12P7, Sc3.6Fe10.4P7, and Sc2Co4P3. Other New Compounds with Zr2Fe12P7, Hf2Co4P3, Sc5Co19P12, and Yb6Co30P19 Type Structures

Abstract. Twenty five ternary phosphides crystallizing with four different but closely related structure types were prepared using elemental tin as a flux. Their lattice constants are reported. New compounds include Sc₂Fe₁₂P₇, Sc_3.6Fe_10.4P₇, Y₂Co₁₂P₇, and Hf₂T₁₂P₇ with T = Fe, Co, Ni. They crystallize with the hexagonal Zr₂Fe₁₂P₇ type structure, which was refined from single‐crystal X‐ray data of Sc_3.6Fe_10.4P₇: a = 944.1(1) pm, c = 363.4(1) pm, R = 0.041 for 719 unique structure factors and 23 variable parameters. The excess scandium atoms occupy one of the four iron sites of the Zr₂Fe₁₂P₇ type structure which has a higher coordination number than the other three iron sites. The two isotypic phosphides Sc₂Fe₁₂P₇ and Sc_3.6Fe_10.4P₇ do not form a continuous series of solid solutions. The new compounds Sc₂Co₄P₃ and Sc₂Ni₄P₃ are isotypic with Hf₂Co₄P₃. This hexagonal structure was refined for Sc₂Co₄P₃ from single crystal data: a = 1211.5(2) pm, c = 363.7(1) pm, R = 0.025 for 500 F_o and 38 variables. Other new compounds reported are Sc₅Ni₁₉P₁₂, Zr₅Fe₁₉P₁₂, Hf₅Fe₁₉P₁₂, and Hf₅Co₁₉P₁₂ which crystallize with Sc₅Co₁₉P₁₂ type structure, and the Yb₆Co₃₀P₁₉ type phosphides Sc₆Co₃₀P₁₉, Zr₆Co₃₀P₁₉, and Hf₆Co₃₀P₁₉. The structural relationships of these ternary phosphides are discussed with special attention to the environments of the transition metal atoms.     

Synthesis of a GaN Cage Compound with a Hydrazinetetraide Fragment, [N?N]4−, Stabilised by Six Gallium Atoms

Thermolysis of the bicyclic gallium hydrazide [(GaMe₂)₄(NH? NMe)(NH? NHMe)₂] ( 1 ) yielded the unique cage compound [(GaMe)₄(GaMe₂)₄(N₂)(NH? NMe)₄] ( 2 ). Compound 2 contains a remarkable hydrazinetetraide moiety, [N? N]^4?, as the central structural motif which is stabilised by coordination to six gallium atoms.     

A Simple Preparation of Dialkylsulfinyl- and Dialkylsulfonyl-Sulfides

A first general approach to sulfinyl-sulfides R¹-S(O)-(CH₂)_n-S-R² and sulfonyl-sulfides R¹-S(O₂)-(CH₂)_n-S-R² with variable and different alkyl substituents is described.