Characterizations of Tb:Zn2SiO4 films on silicon wafer prepared by sol-gel dip-coating and solid-phase reaction

Terbium-doped Zn_2SiO_4 films were successfully prepared on Si wafers by a simple sol-gel dip-coating and solid-phase reaction method of ZnO and SiO_2. X-ray diffraction (XRD) and UV－Vis absorption results revealed that films processed below 850℃ were ZnO in wurzite structure, and films processed above 850℃ were Zn_2SiO_4 in wellimite structure. Photoluminescence measurements of the Tb-doped Zn_2SiO_4 films showed two strong emission bands at 490 and 545nm. The photoluminescence lifetime was 4.6ms.     

Spectrofluorimetric Method for the Determination of Aluminum with Alizarin Red PS

 A simple and direct spectrofluorimetric method has been developed for the determination of aluminum using alizarin red PS (1,2,4-trihydroxy 9,10-anthraquinone-3-sulfonic acid). The method is based on the strong fluorescence (480/564 nm) of Al³⁺ and alizarin red. Experimental parameters such as pH, concentration of the ligand, ionic strength of the solution, reaction time and temperature were optimized in order to maximize the analytical signal. Interferences of several ions (anions and cations) were studied and evaluated. The linear range of the method extends from 3 to 100 μg L⁻¹. Limit of detection (3s_b) was 0.9 μg L⁻¹. The method was tested with a silicate certified reference material. Interferences were eliminated by a liquid extraction with cupferron. Author for correspondence. E-mail: aucelior@rdc.puc-rio.br Received September 10, 2002; accepted January 15, 2003 Published online May 5, 2003     

New poly(butylene succinate)/layered silicate nanocomposites. II. Effect of organically modified layered silicates on structure,properties, melt rheology,and biodegradability

A series of new poly(butylene succinate) (PBS)/layered silicate nanocomposites were prepared successfully by simple melt extrusion of PBS and organically modified layered silicates (OMLS). Three different types of OMLS were used for the preparation of nanocomposites: two functionalized ammonium salts modified montmorillonite and a phosphonium salt modified saponite. The structure of the nanocomposites in the nanometer scale was characterized with wide-angle X-ray diffraction and transmission electron microscopic observations. With three different types of layered silicates modified with three different types of surfactants, the effect of OMLS in nanocomposites was investigated by focusing on four major aspects: structural analysis, materials properties, melt rheological behavior, and biodegradability. Interestingly, all these nanocomposites exhibited concurrent improvements of material properties when compared with pure PBS. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 3160–3172, 2003     

4-Benzoylbenzoate intercalated in layered double hydroxides: a new catalyst for photo-oxidation of sulfides in solution and in the gas phase

A new mixed organic-inorganic photosensitizer, based on 4-benzoylbenzoate intercalated into a layered double hydroxide has been prepared, characterized and successfully tested for the photo-oxidation of dialkylsulfides, both in acetonitrile and in the gas phase.     

The 2D Rancieite-type manganic acid and its alkali-exchanged derivatives: Part I — Chemical characterization and thermal behavior

The 2D Rancieite type manganic acid was prepared by reduction of KMnO₄ in acidic medium. Its ion exchange behavior allows to prepare alkali derivatives. All compounds were characterized with use of a combination of X-ray diffraction, chemical analyses, TGA, magnetic measurements and spectroscopic techniques. The evolution of their chemical composition versus temperature was studied between 180 and 400 °C. It shows that the dehydration process is partly reversible in these compounds whereas the weak reduction is irreversible. The 2D Rancieite-type manganic acid is readily different from a Birnessite-type phyllomanganate, as shown by several features: the interlayer distance, the ion exchange capacity, the thermal behavior, the interlayer cation content, the manganese average oxidation state, the magnetic behavior and the IR spectrum.     

Electronic spectra of cationic forms of meso-tetrapropylporphin in a nanoporous silicate gel matrix

We have studied the fluorescence and fluorescence excitation spectra at 300 K, 77 K, and 4.2 K for silicate gel matrices colored with meso-tetrapropylporphin by impregnation of the matrix with a solution of the pigment. Comparison of the data obtained with the absorption spectra in acidified solutions and analysis of the low-temperature fine-structure vibronic spectra, and also taking into account data obtained earlier for octaethylporphin in a xerogel showed formation of two cationic forms of meso-tetrapropylporphin in the gel matrix: the short-wavelength form has a dicationic structure, while the long-wavelength form has a monocationic structure. We have traced out the correlations of the vibrational structure in the spectra of the dicationic form with data for the porphin dication, and we have drawn a number of conclusions concerning the normal vibrational modes that are active in the vibronic fluorescence and absorption spectra of the studied cationic forms. Using the AM1 semiempirical quantum chemical method, we optimized the geometry of the mesotetrapropylporphin dication: the most stable of the possible conformers is the dication structure with saddleshaped macrocycle nonplanarity. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 4, pp. 453–461, July–August, 2006.     

Transition between layered and filamentary types of anisotropy in layered superconducting structures

A model of layered superconducting structure consisting of alternating anisotropic superconducting layers S₁ and S₂ with different transition temperatures is considered. It is shown that due to competition between two origins of anisotropy - effective-mass anisotropy of individual layers and proximity-induced anisotropy the effective anisotropy of the whole system signficiantly varies temperature. The components of the effective-mass tensor m_c (along the anisotropy axis) and m_a (perpendicular to the anisotropy axis) strongly depend upon temperature. This may lead to transition between layered (m_c > m_a) and quasi one-dimensional (m_c < m_a) types of anisotropy as well as to biaxial-type anisotropy which is also temperature dependent. The field distribution in a tilted vortex in a biaxial superconductor is calculated. The change in the properties of the vortex lattice with temperature in such systems is also investigated. The properties of YBa₂Cu₃O_x/PrBa₂Cu₃O_y multilayers are discussed in this connection.     

Indentation responses of piezoelectric films

Frictionless indentation responses of transversely isotropic piezoelectric film/rigid substrate systems under circular cylindrical indenter (i.e., punch), conical indenter (i.e., cone), and spherical indenter (i.e., sphere) are investigated. Both insulating and conducting indenters are considered. The technique of Hankel transformation is employed to derive the corresponding dual integral equations for the mixed boundary value indentation problems. For the two limiting cases of infinitely thick and infinitely thin piezoelectric films, closed-form solutions are obtained. For piezoelectric films of finite thickness, a numerical method is constructed to solve the dual integral equations and semi-empirical models having only two unknown parameters are proposed for the responses of indentation force, electric charge and electric potential, and contact radius. With the two parameters inferred from the numerical results, the semi-empirical formulae are found to provide good estimates of the indentation responses for the two limiting cases of infinitely thick and thin piezoelectric films, as well as those in between. The inferred parameters in the proposed semi-empirical formulae for normalized indentation force and electric charge are checked against four different piezoelectric materials and are found to be insensitive to the selection of piezoelectric materials. It is believed that the proposed semi-empirical indentation formulae are useful in developing experimental indentation techniques to extract the material properties of piezoelectric films.     

Chemical component exchange and transport phenomena accompanying phase transformations in minerals and materials

Chemical component exchange and transport phenomena accompanying the multistage phase transformations of several silicate and aluminosilicate-phosphate glasses and borates as model systems are considered. It is demonstrated that the component transport limitations modify the role of chemical affinity influence and determine the sequence of new compound formation.The work was supported by grant P040703406 from the National Committee of Scientific Research of Poland.     

氯离子柱撑水滑石共沉淀法合成反应动力学

根据氯离子型层状复合氢氧化物(LDH-Cl)制备过程中溶液浓度变化的监测结果和不同反应进程时产物的EDS、IR、XRD、TEM、TG-DTA表征结果,研究了合成LDH-Cl的共沉淀反应动力学特征及机理.实验结果表明, LDH-Cl的生成符合多核层表面反应动力学模型;反应过程中LDH的晶胞参数c从2.421 nm变为2.399 nm,通道高度h由0.3321 nm减小为0.3228 nm,粒子直径Da由6.40 nm增大为15.16 nm, Dc由7.43 nm增大到10.93 nm,纵横比由0.86增大为1.39; IR和TG-DTA特征变化表明了层板对阴离子作用的强度和层板的结构稳定性随反应进程而提高.