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The kinetics of thermal degradation of ß-chitin extracted from Dosidicus gigas squid pen, was studied at normal conditions as well as after being subjected to the action of high-pressure impact of 9.7 GPa. The integral iso-conversional procedure of Kissinger-Akahira-Sunose (KAS) recommended by the ICTAC kinetics committee was applied to the non-isothermal data obtained from thermogravimetry (TGA). Lifetimes were predicted without assumption of any reaction model. Heating rates of ß = 10, 15, 20 and 25 °C/min under nitrogen atmosphere were used from room temperature to 1300 °C. A comparative study with α-chitin was performed. All the samples were structurally and chemically characterized by several techniques. The extracted ß-chitin was found to be in the monohydrate form; while with the action of high-pressure impact, it was transformed into ß-chitin dehydrate showing slightly higher stability. Reliable prediction for lifetimes considering working temperatures over 425 K was found for α and ß-chitin.

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Symmetry reduction in the basic structure of thortveitite-type compound FeInGe2O7-mC22 (C12/m1, No. 12) promoted by the incorporation of yttrium in the formula FeIn1-xYxGe2O7 gives rise to a derivative structure called thortveitite-like AA'Ge2O7-mP44, with symmetry described by the space group P121/m1 (No. 11) for x = 0.50, 0.75 and 0.90. The structure remains unchanged within the structural type of thortveitite when x = 0.25. In order to establish structural models for performing a Rietveld refinement to the derivative structure, symmetry relations between space groups connecting the basic and derivative structures were used. The higher contrast to X-rays of Fe3+, In3+ and Y3+ as well as by the behaviour during the refinements of the isotropic thermal displacements, the values of interatomic distances and calculated bond-valence sums for each atom in the asymmetric unit, were helpful for elucidating the relocation of cations in the different available crystallographic sites generated by the symmetry reduction.

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Research and development of lead-free piezoelectric materials are still the hottest topics in the field of piezoelectricity. One of the most promising lead-free family of compounds to replace lead zirconate-titanate for actuators is that of Bi0.50Na0.50TiO3 (BNT) based solid solutions. The pseudo-binary (1 - x)Bi0.50Na0.50TiO3-xBa1 - yCayTiO3 system has been proposed for high temperature capacitors and not yet fully explored as piezoelectric material. In this work, the solid solution with x = 0.06 and y = 0.10 was obtained by two different synthesis routes: solid state and Pechini, aiming at using reduced temperatures, both in synthesis (<800 °C) and sintering (<1150 °C), while maintaining appropriated piezoelectric performance. Crystal structure, ceramic grain size, and morphology depend on the synthesis route and were analyzed by X-ray diffraction, together with scanning and transmission electron microscopy. The effects of processing and ceramic microstructure on the structural, dielectric, ferroelectric, and piezoelectric properties were discussed in terms of a shift of the Morphotropic Phase Boundary, chemically induced by the synthesis route.

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The extraction of calcareous chitin from shrimp cephalothorax was successfully achieved using a subcritical water treatment to attain a deproteinization up to 96%. The treatments also increased the crystalline domain size in the α-chitin fibers. An experimental design of Taguchi allowed the optimization of experiments. The macroelements identified in all samples were Ca, P, S, K, Cl and Al, whereas Cr, Mn, Fe, Ni, Cu, Zn, Br and Sr were also detected as microelements. The assigned crystalline phases by XRD were α-chitin, calcite, HAP and traces of quartz. The presence of these phases was corroborated by ATR-FTIR and SEM-EDS analyses. The highest content of α-chitin (82.2wt%) was obtained for the 0.17 chitin:dH2O (wt/wt) ratio for 30min treatment at 260°C. Noteworthy, this treatment promotes the crystallization of both minerals as microcrystals of calcite and nanocrystals of hydroxyapatite with needle and flake shapes as well as intermediate morphologies.

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INTRODUCTION: Composition and crystalline phases of the endodontic material mineral trioxide aggregate (MTA) is of fundamental importance for understanding its physical and chemical properties. This research was done to determine the composition of crystalline phases for ProRoot MTA. METHODS: For phase identification, powder of ProRoot MTA was analyzed by x-ray diffraction (XRD), comparing the MTA peaks with the data contained in the Powder Diffraction File of the International Centre for Diffraction Data (ICDD). To help the task of identifying a phase, chemical analysis by energy-dispersive spectrometry (EDS) and particle-induced x-ray emission (PIXE) were applied. Quantitative phase analysis was performed by applying Rietveld refinement to the XRD data. RESULTS: ProRoot MTA is composed of bismuth oxide (19.8%), tricalcium silicate (51.9%), dicalcium silicate (23.2%), calcium dialuminate (3.8%), and calcium sulfate dehydrated (1.3%). The trace elements detected were Fe, Ni, Cu, and Sr. CONCLUSIONS: Rietveld refinement was able to analyze the composition of ProRoot MTA, which is based basically on a mixture of Portland cement (with smaller quantities of calcium dialuminate and calcium sulfate dehydrated) and bismuth oxide for radiopacity.

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A new indium holmium digermanate, In(1.06)Ho(0.94)Ge(2)O(7), with a thortveitite-type structure, has been prepared as a polycrystalline powder material by high-temperature solid-state reaction. This new compound crystallizes in the monoclinic system (space group C2/c, No. 15). The structure was characterized by Rietveld refinement of powder laboratory X-ray diffraction data. The In(3+) and Ho(3+) cations occupy the same octahedral site, forming a hexagonal arrangement on the ab plane. In their turn, the hexagonal arrangements of (In/Ho)O(6) octahedral layers are held together by sheets of isolated diortho groups comprised of double tetrahedra sharing a common vertex. In this compound, the Ge(2)O(7) diortho groups lose the ideal D(3d) point symmetry and also the C(2h) point symmetry present in the thortveitite diortho groups. The Ge-O-Ge angle bridging the diortho groups is 160.2 (3) degrees, compared with 180.0 degrees for Si-O-Si in thortveitite (Sc(2)Si(2)O(7)). The characteristic mirror plane in the thortveitite space group (C2/m, No. 12) is not present in this new thortveitite-type compound and the diortho groups lose the C(2h) point symmetry, reducing to C(2).

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Indium gadolinium digermanium heptaoxide, In(1.08)Gd(0.92)Ge(2)O(7), with a thortveitite-type structure, has been prepared as a polycrystalline powder material by a high-temperature solid-state reaction. As in the mineral thortveitite, the crystal structure belongs to the monoclinic system, with space group C2/m (No. 12). The precise structural parameters were obtained by applying the Rietveld method of refinement to the X-ray powder diffraction data. This layered structure presents, on one side, a honeycomb-like arrangement of the unique octahedral site, which is occupied randomly by In and Gd atoms, and, on the other side, sheets of isolated Ge(2)O(7) diortho-groups made up of double tetrahedra sharing a common vertex and displaying C(2h) point symmetry. This compound showed a remarkable photoluminescence effect when it was irradiated with the X-ray beam during the X-ray diffraction measurements, and with the alpha beam during the Rutherford back-scattering spectrometry experiments employed to analyze the chemical stoichiometry.

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Tetrahedrally coordinated oxides usually present polymorphism, but for NaGaO(2), only the beta polymorph has been reported. In this work, the synthesis and structural characterization of gamma-sodium gallate, gamma-NaGaO(2), are presented. The crystal structure belongs to the orthorhombic system, space group Pbca (No. 61), and has been characterized by a Rietveld refinement of the X-ray powder diffraction pattern. The structure is similar to those exhibited by the gamma phases of many tetrahedral oxides.