Authors:G. Boskovic, A. Zarubica, M. Kovacevic, and P. Putanov
Properties of two catalysts tailored in the laboratory conditions by sulfation of commercial Zr-hydroxide and Zr-hydroxide
of nitrate origin were compared with those of commercial SO4-Zr-hydroxide. Equally thermally treated samples in the temperature interval 500–700°C, and having the same amount of sulfur,
show different properties indicating memory effect of their solid parent materials. The catalyst obtained by sulfation of
commercial Zr-hydroxide differs in amount of residual sulfates upon calcination from other two catalysts. The instability
of sulfates in the previous case might be connected to the lowest surface area values of catalyst and the highest fraction
of monoclinic phase observed at all applied calcination temperatures.
Authors:Haroune Rachid Ben Zine, Filiz Cinar Sahin, Zsolt E. Horváth, Zsolt Czigány, Ákos Horváth, Katalin Balázsi, and Csaba Balázsi
The effect of the submicrometer-sized Si 3 N 4 addition on the morphological and structuralproperties of the ceramic dispersion strengthened (CDS) 316L stainless steels prepared by powder technology has been studied
Authors:Tea Mihelj, Zoran Štefanić, and Vlasta Tomašić
and structuralproperties of the solid surfactant picrates, some interesting macroscopic observations in bulk aqueous solutions during compounds preparation cannot be omitted. Immediately after mixing components all aqueous systems became multi
Authors:S. Rojas, G. Frigo, M. Bernardi, A. de S. Rastelli, A. Hernandes, and V. Bagnato
We have investigated the thermal and structural properties of different commercial dental resins: FiltekTM Z-350, Grandio®, Tetric Ceram®, and TPH Spectrum®. The purpose of the present study was to evaluate quantitatively the photo-polymerization behavior and the effect of filler
contents on the kinetic cures of the dental resins by using Differential Scanning Calorimetry (DSC) and Fourier Transform
Infrared Spectroscopy (FT-IR) techniques. We have successfully obtained the low and high glass transition Tg values of the dental composite resins from DSC curves. It was also observed a good agreement between the both Tg values, activation energies from thermal degradation, and the degree of conversion obtained for all samples. The results
have shown that Tetric Ceram® dental resin presented the higher Tg values, activation energy of 215 ± 6 KJ mol−1, and the higher degree of conversion (63%) when compared to the other resins studied herein.
Authors:S. Musić, M. Gotić, S. Popović, and B. Gržeta
The effects of iron on the structural properties of Zn-borosilicate glass and Pb-metaphosphate glass were studied using X-ray diffraction,57Fe Mössbauer spectroscopy and IR spectroscopy. Zn-borosilicate glass was prepared with varying amounts of Fe2O3 (up to 30% wt.). It was found that the chemical form of added iron (-FeOOH, -Fe2O3 or Fe3O4) affects the Fe3+/Fe2+ ratio, as well as the distribution of iron ions at different coordination sites. At high concentration of iron the crystallization of zinc ferrite in the glass matrix takes place. X-ray diffraction and57Fe Mössbauer spectroscopy showed that the amount of zinc ferrite in Zn-borosilicate glass decreases with the following order of addition: -FeOOH
Fe3O4. In Pb-metaphosphate glass doped with high concentration of -Fe2O3, the crystallization of Fe3(PO4)2 is pronounced. The assignments of IR band positions and the corresponding interpretation are given. The importance of this study for the technology of vitrification of high-level radioactive wastes is emphasized.
The effects of iron on the structural properties of Zn-borosilicate glasses have been studied using X-ray diffraction, IR spectroscopy and57Fe Mössbauer spectroscopy. Zn-borosilicate glasses were doped with –Fe2O3. In the systems Na2O–ZnO–B2O3–SiO2–Fe2O3 the presence of only one crystalline phase, ZnFe2O4, was detected. X-ray diffraction showed that crystallization is more pronounced in the systems ZnO–B2O3–SiO2–Fe2O3. In these systems the presence of different crystalline phases, such as ZnO, –Fe2O3, Fe3O4, ZnFe2O4 and Fe3BO5, was detected. The crystallization of –Zn2SiO4 in the system ZnO–B2O3–SiO2 was confirmed by X-ray diffraction and IR spectroscopy. The valence state and coordination of iron in Zn-borosilicate glasses were determined by57Fe Mössbauer spectroscopy.
The results of theoretical analysis of the electronic and crystal structural properties and bonding in relation to thermal
decomposition process in anhydrous calcium oxalate are presented. The methods used in this analysis—topological analysis of
electron density (Bader’s Quantum Theory of Atoms in Molecules approach) obtained from DFT calculations performed by Wien2k
package (Full Potential Linearized Augmented Plane Wave Method); bond order model (Cioslowski&Mixon), applied to topological
properties of the electron density; as well as Brown’s Bond Valence Model (bonds valences and strength’, and bond and crystal
strains, calculated from crystal structure and bonds lengths data) are described. The analysis of the obtained results shows
that these methods allow us to explain the way of thermal decomposition process of anhydrous calcium oxalate to calcium carbonate
as a decomposition product, and to describe the structural transition taking place during such process (from monoclinic anhydrous
CaC2O4 to rhombohedral calcite structure). In the light of the results of our similar calculations performed previously for other
anhydrous oxalates (zinc, cadmium silver, cobalt, and mercury) the proposed theoretical approach can be considered as promising
and reliable tool, which allow analyzing the properties of the structure and bonding and hence predicting the most probable
way of thermal decomposition process for given crystal structure.
Authors:Anne Garrido Pedrosa, M. Souza, A. Silva, Dulce Melo, and A. Araujo
The study of the incorporation
of rare earth elements as additives in Y zeolites is a very interesting field
of research, mainly by its potential application as additives in catalytic
cracking process. In this work was studied the thermal and structural properties
of cerium, holmium and samarium supported on HZSM-12 zeolite. The obtained
materials were characterized by X-ray diffraction (XRD), infrared spectroscopy
(FTIR), nitrogen adsorption, thermogravimetry (TG/DTG), differential scanning
calorimetry (DSC) and differential thermal analysis (DTA). TG/DSC/DTA analyses
showed that the dehydration temperatures of RE/HZSM-12 zeolites (RE=Ce, Ho, Sm) increase in relation to pure HZSM-12.
The acid properties were investigated by pyridine thermo desorption via TG.
The results showed two events of mass loss attributed to elimination of pyridine
adsorbed on the weak+medium acid sites and on the strong acid sites.
Authors:H. Aoki, S. Kosakabe, M. Inumaru, A. Kuboki, S. Ohira, and M. Kodama
D-erythro sphingomyelines (SM) having a defined acyl chain were synthesized with sphingosylphosphorylcholine as a starting material,
and both a structural property and its relating phase transition phenomenon were compared between a symmetric chain length
SM (palmitoyl-SM: C16-SM) and asymmetric chain length SMs (behenoyl-SM: C22-SM, lignoceryl-SM: C24-SM). Furthermore, effect
of increasing a content of asymmetric chain SMs in the mixture systems of C22-SM/C16-SM, and C24-SM/C16-SM was investigated.
The present calorimetric and electron microscopic studies revealed that (1) The main transition enthalpy is smaller for the
asymmetric chain SMs than for the symmetric chain SM by about 3 kJ mol−1, although the acyl chain length is longer for the former than for latter; (2) Relatively small size vesicles (100∼200 nm
diameters) surrounded by one or more lamellae are observed for the asymmetric chain SMs, in contrast to large multilamellar
vesicles (1500∼2500 nm diameters) having at least fifteen stained lamellae for the symmetric chain SM and (3) The coexisting
asymmetric chain SMs cause the decrease in size and multiplicity for the MLV of the symmetric chain SM, simultaneously with
a decrease in the main transition enthalpy.
Authors:M. Caira, A. Foppoli, M. Sangalli, L. Zema, and F. Giordano
The thermal and structural characteristics of two crystal forms of ambroxol, (trans-((amino-2-dibromo-3,5-benzyl)amino)-4-cyclohexanol), a drug with remarkable mucolytic and expectorant properties marketed
in several drug products, were investigated. Form II (m.p. 92.4C) is obtained by spontaneous cooling from a hot water/ethanol solution while Form I (m.p. 99.5C) slowly separates from the mother liquor. The two forms can be identified by PXRD and DSC analyses. On the basis
of both thermal and structural data the thermodynamic relationship of enantiotropy was deduced. No metastable (Form I)?stable
(Form II) conversion was observed upon storage at ambient conditions. Form I crystallizes in the space group P21/n (alternative setting of P21/c) with Z=8. Form II crystallizes in the space group P21/c with Z=4 and a significantly different crystal packing arrangement from that in Form I. A third crystalline modification, Form III
(space group P21/c with Z=16) was detected on cooling a single crystal of Form I down to -70C. On warming to ambient temperature Form III was found
to revert to Form I. This reversible single crystal to single crystal transition was structurally characterised and found
to involve subtle changes in the types and extent of molecular disorder as well as the hydrogen bonding arrangement.