Paolo Ballirano

Rietveld refinements on laboratory energy dispersive X-ray diffraction (EDXD) data

Rietveld refinements of corundum, a rutile and anatase nanocrystalline synthetic mixture, and gypsum, on laboratory energy dispersive X-ray diffraction (EDXD) data are reported. Cell parameters, positional and displacement parameters are in reasonable agreement with single-crystal reference data, despite the rather poor resolution of EDXD data. In particular, good results were obtained for gypsum (unrestrained refinement) with counting times as short as 1000 s.

The monoclinic I2 structure of bassanite, calcium sulphate hemihydrate (CaSO4 · 0.5H2O)

A structural analysis of CaSO 4 · 0.5H 2 O, a dehydration product of gypsum, has been carried out through the Rietveld method on X-ray powder diffraction data. A dehydrated powder of synthetic gypsum has been charged inside a non-hermetically sealed capillary in order to allow a slow rehydration. The starting material has been identified as γ-anhydrite, space group P 6 2 22, cell parameters a = 6.9691(2) A, c = 6.3033(2) A. The final product of the rehydration of γ-anhydrite is CaSO 4 · 0.5H 2 O, space group I 2 (unique axis b ), cell parameters a = 12.0350(5) A, b = 6.9294(3) A, c = 12.6705(4) A, β = 90.266(3)°. The structure of the hemihydrate is strongly pseudo-trigonal, space group P 3 1 21. The symmetry lowering arises from water molecules ordering inside the channels.

The thermal behaviour and structural stability of nesquehonite, MgCO3.3H2O, evaluated by in situ laboratory parallel-beam X-ray powder diffraction: new constraints on CO2 sequestration within minerals.

In order to gauge the appropriateness of CO(2) reaction with Mg chloride solutions as a process for storing carbon dioxide, the thermal behaviour and structural stability of its solid product, nesquehonite (MgCO(3).3H(2)O), were investigated in situ using real-time laboratory parallel-beam X-ray powder diffraction. The results suggest that the nesquehonite structure remains substantially unaffected up to 373 K, with the exception of a markedly anisotropic thermal expansion acting mainly along the c axis. In the 371-390 K range, the loss of one water molecule results in the nucleation of a phase of probable composition MgCO(3).2H(2)O, which is characterized by significant structural disorder. At higher temperatures (423-483 K), both magnesite and MgO.2MgCO(3) coexist. Finally, at 603 K, periclase nucleation starts and the disappearance of carbonate phases is completed at 683 K. Consequently, the structural stability of nesquehonite at high temperatures suggests that it will remain stable under the temperature conditions that prevail at the Earths surface. These results will help (a) to set constraints on the temperature conditions under which nesquehonite may be safely stored and (b) to develop CO(2) sequestration via the synthesis of nesquehonite for industrial application.

Characterization of amphibole fibres linked to mesothelioma in the area of Biancavilla, Eastern Sicily, Italy

Abstract An epidemiological and environmental study of the area around Biancavilla (CT, Italy) was prompted by a significant incidence of malignant pleural mesothelioma, which was not related to a specific occupational activity. An environmental dispersion of fibres was found and attributed to local quarry activities, whose extracted volcanic products also contained fibrous amphiboles and had been used extensively in the local building industry, especially in the period 1960-1970. Abundant yellowish and grey-whitish asbestiform amphiboles with strongly asymmetric morphology were identified in this study, intimately associated with albitic feldspar, hematite and very minor orthopyroxene. These minerals fill the pores of the altered volcanic host rock (metasomatized benmoreitic lavas and pyroclastic rocks). The Rietveld method allowed a quantitative mineralogical analysis of the mineral mixture (24% amphiboles-asbestos, 73% feldspar and 3% hematite). The crystal size and morphology of the grey-whitish amphibole fibres do not allow quantitative microprobe analyses; semi-quantitative EDS-SEM analyses of a prismatic mineral known to be fluoroedenite and the unknown fibrous crystals studied here suggest that they are the same mineral, although the fibres are generally depleted in Ca and Mg. The F content is the same in both occurrences. Unitcell parameters of the fibres are: a = 9.815(1), b = 17.992(3), c = 5.2733(6) Å , β = 104.547(9)º, V = 901.4(3) Å3, and the refractive indices are in the range 1.60 -1.63. Optical, chemical and Rietveld analyses of the fibres confirm their similarity with the yellow prismatic fluoro-edenite previously analysed. Biancavilla is the first occurrence of amphibole fibres in a volcanic context (the Etnean volcanic complex). These fibres have a very anomalous composition (high ANa, IVAl and O3F contents) in comparison to other known oncogenic minerals.

Crystal chemistry and IR spectroscopy of Cl- and SO4-bearing cancrinite-like minerals

Abstract Cl- and SO4-bearing cancrinite-like minerals from Italian localities were studied by means of EPMA, X-ray diffraction, and IR spectroscopy to relate their chemical composition, IR data, and structural features. The framework of the cancrinite-like minerals consists of six-membered rings of alumino silicate tetrahedra stacked along c. Six types of subunits resulting from different stacking sequences can be identified: free channel, cancrinite, sodalite, losod, liottite, and giuseppettite cages. The free channel is possible only with an AB sequence; in fact, the insertion of a C layer interrupts the channel forming the various cages. The occurrence of these structural subunits seems to correspond to the different chemistries of the cancrinite-like minerals, especially their anion content. According to this model, the SO4 group seems to playa major role. With the exception of giuseppettite, it tends to fill completely the available voids within the frameworks.

Structure of the Molten Salt Methyl Ammonium Nitrate Explored by Experiments and Theory

We present an analysis of the structure of the monomethylammonium nitrate (MMAN) compound. Vibrational Raman spectroscopy and X-ray powder diffraction have been used to characterize the bulk phases of MMAN, and assignment of the resonant frequencies has been performed by ab initio (DFT) computations on small clusters of the compound. The theoretical spectra are in excellent agreement with the experimental ones and provide a means by which an interpretation of the hydrogen-bonding network that exists in such compound can be analyzed. In particular, we found that the spectrum of one of the solid phases is structurally very similar to that of the liquid. We present experimental evidence for the existence of such phase both from X-ray data and Raman spectra which, in turn, is easily interpreted with a one-to-one correspondence with the ab initio simulation of the small clusters. A geometric structure of the short-range local arrangement in these two bulk phases is therefore proposed.

Crystal structure and iron topochemistry of erionite-K from Rome, Oregon, U.S.A.

Abstract A complete crystal-chemical characterization of erionite-K from Rome, Oregon, was obtained by combining field emission scanning electron microscopy, laboratory parallel-beam transmission powder diffraction, and 57Fe Mössbauer spectroscopy. Rietveld refinement results evidenced that the most striking difference in comparison with the structure of erionite-Ca is significant K at a K2 site (½, 0, 0), which is empty in erionite-Ca. In addition, site Ca1 shows low occupancy and Ca3 is vacant. The oxidation and coordination state of Fe, whose occurrence was revealed by chemical analysis, have been clarified by exploiting room- and low-temperature 57Fe Mössbauer spectroscopy. The majority of Fe (95%) was attributed to Fe3+-bearing, superparamagnetic, oxide-like nanoparticles with dimensions between 1 and 9 nm, and the remaining 5% was attributed to hematite particles with size ≥10 nm, both located on the crystal surface.

Mineralogical characterization of the blue pigment of Michelangelo’s fresco “The Last Judgment”

Abstract The blue pigment and the plaster layer of Michelangelo.s fresco .The Last Judgment. have been characterized by means of powder XRD, FT-IR, and Raman spectroscopy, as well as analytical TEM and SAED. The pigment is composed of a mineralogical assemblage that is consistent with a raw lapis lazuli rock. To try to define the provenance of this pigment, we investigated various lapis lazuli samples from different deposits that are currently considered as possible sources of the material. According to our results, the provenance of the pigment is quite dubious but the Pakistani one seems the most probable.

Effects of the choice of different ionization level for scattering curves and correction for small preferred orientation in Rietveld refinement: the MgAl2O4 test case

The effects of the choice of oxygen scattering curves with different ionization levels and of the number of spherical harmonics terms used to correct for preferred orientation are discussed in the case of the Rietveld refinement of MgAl2O4 spinel. Results indicate that Rietveld refinements, and not only single-crystal analyses, are influenced by the choice of the scattering curves, at least in the case of very simple ionic structures. Improvements are observed both in agreement indices and in displacement parameter modelling by the use of an almost fully ionized model. On the contrary, the choice of the order of spherical harmonics prevalently affects the fractional u coordinate.

In-situ X-ray transmission powder diffraction study of the kinetics of the light induced alteration of realgar (α-As4S4)

An in-situ X-ray transmission powder diffraction study of the kinetics of the light induced alteration of realgar (As 4 S 4 ) has been carried out. Data indicate that the crystalline final products of the process are pararealgar (different As 4 S 4 polymorph) and arsenolite (As 2 O 3 ). Because of the chemical unbalance the evolution of SO x is hypothesized. In fact there are no evidences of the presence of amorphous As-S alloys or amorphous S. The alteration proceeds via the occurrence of an intermediate term along the β-As 4 S 4 -alacranite series joint with an estimated As 4 S 4 .2 composition. This phase reach a maximum wt. fraction of ca. 30 % in the early stages of the process and subsequently disappears. From the fraction X(t) of realgar and pararealgar transformed vs. time was determined the kinetic law of the digestion of realgar and formation of pararealgar according to the JMAK model. The refined n parameters indicate that the behavior of the two transformations is intermediate between that of a diffusion-controlled and a first-order model. The increased expansion of the realgar cell during the alteration could be possibly due to the requirement that structural coherency between at least two of the three sulfide phases is preserved. In particular the coherency between realgar and β-As 4 S 4 is expected to exist along a realgar * sin β and c β-As 4 S 4 , respectively. According to our data we may hypothesize that the light induced alteration of realgar to pararealgar occurs via an intermediate As 4 S 4+x product because it is able to sustain the presence of As 4 S 5 -type cages. Following the model proposed by Kyono et al. , (2005) the As 4 S 5 cage release the extra S atom to form the As 4 S 4 cage of pararealgar-type promoting the development of a new As 4 S 5 cage in a cyclic process.