169,775 research outputs found
Structural and spectroscopic characterization of anorthite synthesized from secondary raw materials
No full textRecycling of secondary raw materials is a priority of waste handling in the countries of the
European community. A virtual secondary raw material of great importance is the product of
the thermal transformation of cement – asbestos. This work illustrates the study of calcination
products obtained starting from the product of the thermal transformation of cement-asbestos
at 1200 °C, added to primary raw materials (kaolin, aluminum hydroxide) and boric acid as
mineralizing agent. The calcination has been conducted at 1200 °C for 1 hour. The
crystallization kinetics has been monitored using in situ high temperature X-ray powder
diffraction. The microscopic characterization of the final product of calcination has been
conducted with SEM and TEM imaging supported by X-ray microanalysis. The structure
refinement was conducted on the powder sample using the Rietveld method. The results are
compared with the spectroscopic characterization including Mössbauer and UV-Vis
spectroscopies. The final product of the calcination is essentially anorthite (about 89 wt%)
with minor spinel (11 wt%). All experimental data converge to support the hypothesis that
the anorthite is stoichiometric, and the small amounts of iron detected (1.32 wt%) is Fe3+
hosted in the structure of spinel
One-pot sonocatalyzed synthesis of sol–gel graphite electrodes containing gold nanoparticles for application in amperometric sensing
No full textWe propose here a one-pot synthetic approach to prepare sol–gel graphite electrodes containing gold nanoparticles (AuNPs). At variance with the traditional synthesis, in which AuNPs are prepared in advance with respect to the silica matrix, they were here obtained directly inside the sol–gel, during its formation. Two reduction methods, namely chemical and thermal reduction, were used to achieve AuNPs starting from a suitable gold precursor, either consisting of NaAuCl 4 or HAuCl 4 . Different experimental parameters were tested in order to direct the synthesis of the material to the characteristics sought, namely Si/Au molar ratio, graphite (g): silane precursor (mL) ratio, chemical nature of the gold precursor and of the reductant, duration and temperature of thermal treatment. Sol–gel was prepared by means of sonocatalysis, in order to reduce the amount of solvent and time necessary for the hydrolysis step. Composition of the material, as well as shape, size and distribution of AuNPs inside the silica matrix was evaluated by spectroscopic and microscopic techniques. Furthermore, electrochemical tests allowed us to ascertain the good conductivity of the composite material and the electrocatalytic activity of AuNPs with respect to glucose and ascorbic acid oxidation. These tests demonstrated that the electrodes obtained by thermal reduction show the best performance in terms of sensitivity for the detection of these analytes, suggesting the possible application of this composite in the field of amperometric sensin
Multitechnique approach to V-ZrSiO4 pigment characterization and synthesis optimization
No full textThe synthesis of blue-turquoise V-ZrSiO4 Pigment from an aqueous solution of Na2O center dot 2.5SiO(2)center dot 5H(2)O (soluble glass) and the citrate complexes of zirconium and vanadium was investigated as a function of V2O5 contents, mineralizers (NaF and/or LiNO3) addition and thermal cycle. Blue V-ZrSiO4 was obtained without mineralizers addition for the (ZrO2)(SiO2)(V2O5)(0.09) composition; QPA analysis shows that a thermal cycle 3 h long, T-max = 800 degrees C, can lead to a 78.0 wt.% of ZrSiO4. The addition of mineralizers gave rise to 73.0 wt.% of ZrSiO4 for the (ZrO2)(SiO2)(NaF)(0.16)(V2O5)(0.09)(LiNO3)(0.09) composition and a thermal cycle 2 h long, T-max = 800 degrees C. LiN03 can favour both ZrSiO4 formation and a fairly blue colour, up to LiNO3 = 0.09 moles; NaF seems effective on ZrSiO4 formation only when mixed with LiNO3 through the formation of LiF HT-XRD analysis of this composition agrees with QPA results at the corresponding temperature; ZrSiO4 was present (64.0 wt.%) at 730 degrees C and good colour parameters were obtained. (c) 2006 Elsevier Ltd. All rights reserved
Mineralogical and microstructural study of the phases developed during the hydration process of industrial cement mixtures
No full textThe phases identified in two industrial cement mixtureswere qualitatively and quantitatively characterizedbefore and during their hydration process. The studywas carried out as a function of time, water/cement ratioand temperature; the characterization was performedusing XRPD (with the Rietveld method to obtainquantitative phase analysis, hereafter QPA), SEM/EDSand ESEM techniques. QPA revealed that the drymixtures have similar composition and that differ for thesource of calcium sulphates. The use of differentcalcium sulphates need different w/c ratios and givesrise to a different amounts of C6AS3H32, amorphousphase and to a different reaction rate. Results fromESEM technique agree with XRPD results and confirmthe different behaviour of the mixtures. Hightemperature reduces the difference in the reaction rat
Evaluation of the behaviour of hydrogels containing mesoporous glasses doped with cerium and loaded with polyphenols
No full textFluoride-containing bioactive glasses: surface reactivity in simulated body fluids
No full textThe issue of the contribution of the addition of F to glass bioactivity is not well resolved. This work reports on the surface reactivity in different solutions (DMEM and Tris) for some potentially bioactive glasses based on the composition of 45S5 glass, in which CaF2 is substituted alternately for (part of) CaO and Na2O. The reactivity of F-containing glasses has been compared with that of the reference 45S5 system. The aim of this study is to explain in detail the mechanism of formation of an apatitic crystalline phase at the interface between the inorganic material and simulated biological media. A multi-technique investigation approach proposes a set of reactions involving Ca-carbonate formation, which are somewhat different from that formerly proposed by Hench for 45S5 bioactive glass, and which occur when a F-containing glass surface is in contact with a SBF. The usefulness of IR spectroscopy in recognizing the starting step of apatite (and/or FA) formation with respect to XRD technique is well established here
Substituent effect on the coordination ability of the amide group of N-protected amino acids
No full textThe binary system Cu(II)-hydantoic acid (hydaH) and the corresponding ternary systems with 2,2'-bipyridine(bpy) and 1,10-phenanthroline (ophen) were investigated both in the solid state and solution. The crystal and molecular structure of the complex [Cu(ophen)(hyda)2].H2O was also determined. The crystal of the compound C18H20CuN6O7 is monoclinic, space group P2(1)/c, a = 7.601(5), b = 14.647(2), c = 19.714(3) angstrom, beta = 96.57(3), Z = 4, R = 0.049, R(w) = 0.053. The structure consists of discrete [Cu(ophen)(hyda)2] units and lattice water molecules. The Cu(II) atom is coordinated in the equatorial plane by two nitrogens from the ophen molecule and two oxygens from two hydantoate anions; the nitrogen atom of the neutral NH group of a hydantoate anion occupies the more distant fifth position (Cu-N(l) = 2.541(5) angstrom) giving rise to elongated square-pyramidal geometry. In solution the carboxylate species [CuL2] is formed in the binary system and the species [CuAL2], [CuAL(OH)] in the ternary systems with bpy and ophen. Spectroscopic data indicate that any possibility of the NH group being coordinated in solution can be excluded
Reactivity of biological and synthetic hydroxyapatite towards Zn(II) ion, solid-liquid investigations
No full textThe reaction of biological and synthetic hydroxyapatite Ca-5(PO4)(3)OH (HAP) with Zn2+ ions is investigated as a function of Zn2+/Ca2+ molar ratio, time, temperature and electrolyte type (NaCl, NaHCO3, Na2HPO4) by means of pH, pZn, pCa measurements, in aqueous solution. Biological powdered HAP invariably affords an almost quantitative reaction, while Zn2+ precipitated only partially by reaction with cubelets of biological HAP. Using powdered biological HAP and synthetic HAP (dried at 100 degreesC), the reaction with Zn2+ ion is fast and takes place without addition of precipitating anion; synthetic HAP (dried at 1000 degreesC) reacts if free phosphate ions are present. The solid phases separated after different reaction times are investigated by means of X-ray diffraction (XRD), IR, SEM techniques and elemental analysis (C,H,N). The solid phases contain Zn-3(PO4)(2) . 4H(2)O (Hopeite) at the beginning of reaction and CaZn2(PO4)(2) . 2H(2)O (Scholzite) at the equilibrium
Cadmium(II) N-(p-toluenesulphonyl)-L-glutaminate
No full textCrystals of [Cd(C12H15N2O5S)(2)] contain dimensional polymeric network in which Cd2+ ions are octahedrally coordinated by O atoms
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