Polymeric citrate precursor route to the synthesis of nano-sized barium lead titanates

Monophasic oxides of the formula, Ba_1−xPb_xTiO₃ (0≤x≤1.0) were obtained at temperatures close to 500 °C from polymeric precursors formed using citric acid and ethylene glycol. These oxides were found to be tetragonal for all values of x, the distortion increasing with Pb content. Differential scanning calorimetry (DSC) shows that the decomposition of the precursor to the oxides varies with composition and the decomposition temperature is highest (530 °C) for the x=0.5 composition. X-ray line broadening studies of 900 °C sintered samples show grain size of 50-54 nm in all compositions. TEM studies show agglomerated grains of the size, 40-60 nm. The dielectric constant (ε) decreases with lead-doping having a value 70 for PbTiO₃. The dielectric loss (D) for different compositions varied between 0.005 and 0.01 at 100 kHz. The dielectric constant and loss show excellent frequency stability.     

On the theory of perfectly plastic anti-plane straining

A general formulation of two-dimensional elastic-perfectly-plastic anti-plane straining is presented for materials with arbitrary anisotropic convex yield surfaces. Stress and strain distributions in plastic regions adjoining portions of the boundary are obtained directly in terms of the yield surface geometry. When specialized to the classical torsion problem, results lead directly to a generalization of the well-known plastic roof construction for limit loads. Examples of the determination of fully plastic stress distributions and corresponding limit torques are given for circular and rectangular shafts with various yield conditions. Another specialization is made to the contained plastic deformation created by longitudinal shearing of a body containing a sharp edge notch. Here the determination of the elastic-plastic boundary and strain distribution is reduced to a potential theory problem for a region in the stress plane bounded by straight line segments and a portion of the yield surface, and a membrane analogy is presented which allows effective visualization of the solution. A solution valid for small scale yielding near a crack is given in terms of a conformal transformation of the yield surface to a unit circle, and some specific examples are worked. Particular attention is given to single crystal type yield surfaces made up of straight line segments corresponding to discrete slip planes.     

Immobilization of barium,cadmium and antimony over titania

A simple method of immobilization of barium, cadmium and antimony cations in crystalline titania has been studied. High uptake was observed with¹⁴⁰Ba,¹¹⁵Cd and¹²⁵Sb; weighable quantities of these cations were separately precipitated together with titanium hydroxide and 69.02 wt% Ba, 52.00 wt% Cd and 46.05 wt% Sb were found to be adsorbed. After calcination each of the mixed materials, the leaching of cations by immersing into de-ionized water at room temperature and by a Soxhlet apparatus at 97 °C were found to be of the order of 10^–10 and 10^–7 g cm^–2 day^–1, respectively. X-ray powder diffraction analysis revealed that barium, cadmium and antimony cations were immobilized separately in the titania crystal lattice, which suffered some structural changes with the formation of different mineral phases.     

Large-scale synthesis of nanocrystals of barium titanate and other titanates through solution-phase processes

We reported a large-scale synthesis of nanocrystals of BaTiO₃, SrTiO₃, PbTiO₃, Sr_xBa_1−xTiO₃ through low-temperature and solution-phase processes without any surfactant. The series of samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Samples obtained were of high purity, consisting of nanoparticles with fine crystallinity and uniformity as well as good dispersibility in ethanol. This method might also offer an effectively new way to synthesis other titanate nanocrystals with perovskite structure in the future.     

Effect of alternating-sign plastic straining on the shape memory effects in nickel titanium

The effects of shape memory, martensite transformation plasticity, and two-way shape memory in nickel titanium (TiNi) prestrained in an alternating-sign regime have been studied. The reversible deformation and the temperature-dependent deformation kinetics in the temperature interval of martensite transformation were independent of the degree of prestraining. It is concluded that an increase in the density of dislocations does not significantly influence the mechanical behavior of nickel titanium in the vicinity of the martensite transformation. The results of computer simulation based on the structural analytical theory are in satisfactory agreement with experiment.     

低温水热合成钛酸钡纳米管阵列薄膜及性能研究

以二氧化钛纳米管阵列为模版,用水热法合成了钛酸钡纳米管阵列薄膜.讨论了水热温度、水热时间、碱的浓度对其生长形貌的影响.用X射线衍射仪、扫描电子显微镜表征了其晶体结构及微观形貌;用热重-差示扫描量热仪测定了材料的热学性能;用宽频介电阻抗谱仪测试了样品的介电性能.结果表明,在低至100℃水热温度下反应6h即可制得单一相的钛...     

Photoelectrochemical properties of titanates with the hollandite structure

The photoelectrochemical properties and the diffuse reflection spectra of the titanates K_1.8M²⁺_0.9Ti_7.1O₁₆ (M²⁺ = Mg²⁺, Ni²⁺) and K_1.8M³⁺_1.8Ti_6.2O₁₆ (M³⁺ = Al³⁺, Cr³⁺) with the hollandite structure are reported. The white titanates K_1.8Mg_0.9Ti_7.1O₁₆ and K_1.8Al_1.8Ti_6.2O₁₆ show an optical absorption edge near 3.7 eV. These compositions can be coloured by transition-metal ions due to the occurrence of Meⁿ⁺ → Ti⁴⁺ charge-transfer transitions. When these coloured titanates were used as photo-anodes in a photoelectrochemical cell for water electrolysis, no photoresponse was observed with visible light irradiation. Possible reasons are discussed.     

Preparation and dielectric properties of ceramics based on mixed potassium titanates with the hollandite structure

We have studied the crystallization of potassium polytitanates (PPTs) modified in aqueous solutions of salts of various transition metals. The results demonstrate that the modified materials crystallize in the form of solid solutions with the hollandite structure. Ceramic materials obtained using the PPT/Fe, PPT/Ni, and PPT/Co systems have high dielectric permittivity in the low-frequency region (ε ~ 10⁵), whereas PPT/Cu ceramics have lower ε (~10³), retaining it to a frequency of 1 MHz, and very low dielectric losses (tanδ ~ 10^–2).     

Effect of mechanical activation on the formation of lead titanates from PbCO3 – TiO2 mixtures

PbTiO₃ powders have been prepared by mild annealing (2h at 600°C) of PbCO₃:TiO₂ mixtures previously subjected to mechanical activation, while a thermal treatment of about 12h at T > 850°C is needed to obtain PbTiO₃ from a physical mixture. Although the temperature and enthalpy of the DSC peak corresponding to PbCO₃ decomposition are not affected by mechanical energy, in the case of the mechanically activated mixtures an exothermic event due to the reaction PbO + TiO₂ → PbTiO₃ shows up. Furthermore, SEM micrographs and the XRD line broadening allow to conclude that PbTiO₃ powders obtained from activated mixtures are of nanometer size. PbTi₃O₇ has been prepared starting from mechanically activated PbCO₃:3TiO₂ mixtures by 1h annealing at 850°C while 100h at 800°C were required to yield this compound from unmilled mixtures.     

Effects of barium dissolution on dispersing aqueous barium titanate suspensions

Dissolution of barium ion and its effect on dispersion behavior of aqueous barium titanate suspensions at various pH values have been investigated. The amount of leached barium ion decreases with increasing pH value. The dissolution of barium ion also causes an increase in pH value of suspension, but the change decreases with increasing initial pH value. The iso-electric point (IEP) of leached barium titanate powder increases with increasing leaching pH value and solid loading as well. The dissolution of barium ion enhances the colloidal stability of aqueous barium titanate suspension, in agreement with zeta potential measurement.     

Simultaneous polarographic chemometric determination of lead,copper, vanadium,cadmium and nickel

Chemometric approaches, such as classical least squares (CLS), principal component regression (PCR), partial least squares (PLS) and iterative target transformation factor analysis (ITTFA), were applied to the simultaneous determination of mixtures of lead, copper, vanadium, cadmium and nickel by differential pulse polarography (DPP). The conventional and first-derivative polarograms of the mixtures were used to perform the optimization of the calibration procedure by chemometric models. The proposed method was applied satisfactorily to the determination of a set of synthetic mixtures of metal in Britton–Robinson buffer (pH 2.87) and potassium thiocyanate and acceptable results were obtained. The results obtained by the application of the different chemometric approaches are discussed and compared. It was found that factor analysis methods generally give better results than CLS and no significant advantages were found with the application of derivative technique, except for ITTFA in this polarographic work.     

Effect of centrifugation on the crystal structure of barium nitrate

The structure of barium nitrate crystals grown from supersaturated aqueous solutions under normal conditions and during centrifugation at 11.8×10³ g is studied for the first time by a high-precision powder neutron diffraction method. It is established for the first time that centrifuging leads to displacement of the nitrate oxygen atoms in the xy plane (resulting in rotation of the NO₃ trigonal prism about the third-order axis) and to variation of the bond lengths and angles in the coordination polyhedron of Ba atoms. The latter changes result in the appearance of a torsional mode in the phonon spectrum of barium nitrate and in increasing stiffness of the crystal lattice, as evidenced by a significant increase in microhardness of the samples grown in the centrifuge.     

Effects of processing method and fiber size on the structure and properties of wood–plastic composites

The aim of this study was to understand the roles of processing method and fiber size on the properties of wood–plastic composites (WPC). Composites were manufactured using extrusion or injection molding (IM) and fibers of different fiber length-to-diameter (L/D) ratio. IM resulted in better mechanical properties and lower water absorption and swelling than extrusion. These differences can be explained by the structure and surface quality of the composites. Fiber L/D ratio had a beneficial effect on mechanical properties but resulted in decreased water absorption characteristics. These results allow identifying a suitable forming process and/or fiber size according to application needs. This study provides a better understanding of the relationships between processing method, fiber characteristics, and composite behavior.     

Characterization of the biosorption of cadmium, lead and copper with the brown alga Fucus vesiculosus

The recovery of cadmium, lead and copper with the brown alga Fucus vesiculosus was characterized and quantified. The biosorption data fitted the pseudo-second order and Langmuir isotherm models, but did not adjust to the intraparticle diffusion model. The metal uptakes deduced from the pseudo-second order kinetic model and the Langmuir isotherm model followed a similar sequence: Cu>Cd approximately Pb. The Langmuir maximum metal uptakes were: 0.9626mmol/g, Pb 1.02mmol/g, and Cu 1.66mmol/g. According to the equilibrium constants of this isotherm model, the affinity of metals for the biomass followed this order: Pb>Cu>Cd. Biosorption was accomplished by ion exchange between metals in solution and algal protons, calcium and other light metals, and by complexation of the adsorbed metals with algal carboxyl groups. FTIR spectra showed a shift in the bands of carboxyl, hydroxyl and sulfonate groups.     

Betel quid chewing elevates human exposure to arsenic, cadmium and lead

Several studies have reported increased skin lesions in betel quid (a mixture of Piper betel leaves, areca nut, tobacco/flavoured tobacco, lime) chewers compared to non-chewers, exposed to arsenic (As) contaminated drinking water in Bangladesh and India. The current study has determined As, cadmium (Cd) and lead (Pb) levels of betel quids and its components using inductively coupled plasma mass spectrometry (ICP-MS). The highest concentrations of As were found in slaked lime (4.56 mg kg(-1)) followed by Piper betel leaves (0.406 mg kg(-1)) and flavoured tobacco (zarda) (0.285 mg kg(-1)), with a mean concentrations of As in betel quids of 0.035 mg kg(-1) (SD 0.02 mg kg(-1)). Mean concentrations of Cd and Pb in ordinary quids were 0.028 (SD 0.07 mg kg(-1)) and 0.423 (SD 1.4 mg kg(-1)), respectively. We estimated that a daily intake of 6 betel quids could contribute 1.2, 1.9 and 8.5% of the provisional maximum tolerable daily intake (PMDTI) for As, Cd and Pb, respectively. Since betel quid chewing is most prevalent among women, our finding raises concern that women chewers - especially pregnant chewers - may be harming their health and that of their unborn babies through increased exposure to a mixture of toxic elements (As, Cd and Pb).     

Photoelectrochemical properties of MgTiO3 and other titanates with the ilmenite structure

The photoelectrochemical properties and the diffuse reflection spectrum of MgTiO₃ are reported. MgTiO₃ shows an optical absorption edge' near 3.7 eV. This makes the material unsuitable for solar energy applications. The diffuse reflection spectra of CoTiO₃ and MnTiO₃ are presented. The optical absorption edge shifts to lower energy due to the occurrence of Me²⁺ → Ti⁴⁺ charge-transfer transitions. For various reasons discussed no photocurrents were observed for CoTiO₃ and MnTiO₃.