Sorption performance of light rare earth elements using zirconium titanate and polyacrylonitrile zirconium titanate ion exchangers

Lanthanum, cerium, neodymium, and samarium were sorption from aqueous solutions using zirconium titanate (ZrTi) and polyacrylonitrile zirconium titanate (PANZrTi) ion exchangers. The characterizations of prepared materials were performed using XRD, SEM, FTIR, TGA, and DTA techniques. The sorption behavior of various ions toward synthesized resin has been studied depending on reaction temperatures, pH values, and initial concentrations. The selectivity order found is Sm³⁺?>?Nd³⁺?>?Ce³⁺?>?La³⁺ on ZrTi-100, Ce³⁺?>?Sm³⁺?≈?Nd³⁺?>?La³⁺ on ZrTi-150, and Sm³⁺?≈?Ce³⁺?>?Nd³⁺?>?La³⁺ on PANZrTi depending on the condition of prepared ZrTi samples. The K_d for lanthanide ions was slightly decreased with temperature increased, which indicated the exothermic nature. The sorption data obtained for equilibrium conditions have been analyzed using the different isotherm models, and the applicability of these isotherm equations was compared by the correlation coefficients, R². It was established that the equilibrium isotherm models’ applicability follows the order: Langmuir?>?Dubinin– Radushkevich?>?Freundlich. It is found the Ce³⁺ has high adsorption capacity on each of ZrTi-100 and ZrTi-150, while Nd³⁺ has high adsorption capacity on PANZrTi.     

Ordered arrays of lead zirconium titanate nanorings

Periodic arrays of nanorings of morphotropic phase boundary lead zirconium titanate (PZT) have been successfully fabricated using a novel self-assembly technique: close-packed monolayers of latex nanospheres were deposited onto Pt-coated silicon substrates, and then plasma cleaned to form ordered arrays of isolated nanospheres, not in contact with each other. Subsequent pulsed laser deposition of PZT, high angle argon ion etching and thermal annealing created the arrays of isolated nanorings, with diameters of ～100?nm and wall thicknesses of ～10?nm. Energy dispersive x-ray analysis confirms that the rings are compositionally morphotropic phase boundary PZT, and high resolution transmission electron microscopy imaging of lattice fringes demonstrates some periodicities consistent with perovskite rather than pyrochlore material. The dimensions of these nanorings, and the expected 'soft' behaviour of the ferroelectric material from which they are made, means that they offer the most likely opportunity to date for observing whether or not vortex arrangements of electrical dipoles, analogous to those seen in ferromagnetic nanostructures, actually exist.     

Inorganic sol gel synthesis of zirconium titanate fibres

This note describes the preparation of zirconium titanate gel fibres from an aqueous mixed zirconia titania sol. The fibres are well formed and free of shot. Heat treatment to 750 °C produces a crystalline porous zirconium titanate fibre which shows a good (1%) strain to break. Further firing to 1100 °C causes a deterioration in properties, with retention of some porosity and a reduced strain to break. Recommendations for improving the material are suggested.     

Microwave assisted synthesis of barium zirconium titanate nanopowders

The paper reports the synthesis, structural and high frequency dielectric properties of Ba(Zr _x Ti_1−x )O_3,BZT, nanopowders where x = 0, 0.1, 0.2, 0.3. These powders were synthesized using both microwave assisted and conventional heating, with the former requiring lower temperature and shorter times compared to the latter, viz., 700 °C for 30 min versus 900 °C for 5 h. The synthesized nanopowders were characterized using X-ray diffraction, micro-Raman spectroscopy, transmission electron microscopy, BET surface area analysis, differential scanning calorimetry and high frequency dielectric measurements. All the microwave synthesized BZT compositions were found to have well crystallized, finer nanoparticles with less agglomeration and higher dielectric permittivity compared to the conventionally prepared powders. The rapidity and less demanding processing conditions associated with the microwave assisted method augers well for the general applicability of the technique for the production of nanocrystalline powders.     

On the viscoelastic behaviour of fluid-saturated porous materials

It is well known that fluid-saturated porous materials undergo time-depending deformation processes under external loads, as occur, e.g., during the so-called consolidation process. The reason for this behaviour lies in the flow-dependent viscous properties of the pore-fluid, which, in case of viscoelastic skeleton materials is overlayed by flow-independent dissipative effects. In the present contribution, we intend to describe the flow-dependent as well as the flow-independent viscoelastic behaviour. Therefore, a linear viscoelastic two-phase model based on the macroscopic Theory of Porous Media is developed. The applied linear viscoelasticity law to describe the intrinsic energy absorbing behaviour of the solid skeleton is given in differential form deduced from rheological considerations. The governing model equations are treated within the finite element method for spatial discretization. This leads to a system of differential-algebraic equations in the time domain. To show the capability of this approach, the model is applied to cartilage tissues, where some representative initial boundary value problems are computed. On this occasion, the influence of the viscoelasticity of the solid skeleton alone is studied. In addition, the problem of separating the flow-independent dissipative behaviour from the flow-dependent consolidation process is discussed. Received: 16 June 1999     

Moisture influence on the resilient deformation behaviour of unbound granular materials

The influence of moisture on the resilient deformation properties of unbound granular materials was investigated based on repeated load triaxial tests. Results showed that the resilient modulus (M_R) decreased with increasing moisture for a relatively low number of load cycles (N) where the deformation behaviour was mostly resilient with a negligible amount of associated accumulated permanent deformation (PD). Modelling attempts on this behaviour were quite satisfactory. Furthermore, the M_R showed an increasing trend with increasing moisture, up to the optimum, when the N was relatively large with a significant amount of accumulated PD. Above the optimum, the M_R generally decreased. Further investigation suggested that moisture aided the post-compaction (PC) and possible particle rearrangement that resulted in the increased PD and increased M_R. The existing model did not work in this case indicating that the effect of PC on M_R should be considered in modelling.     

On the modelling of interfacial transition behaviour in composite materials

Here, the development of two types of models for describing the transition behaviours of interfacial regions such as interlayers in laminated composites has been presented. The first model is defined based on physical considerations, using a spatial function continuously varying/describing the graded properties of the interlayer, for example, in the case of epoxy laminates, it depends on resin enrichment and fibre specific distribution. The second kind of model is proposed using interface laws defined on material surfaces (with no thickness). These laws, obtained by asymptotic analysis, are equivalent to the evolutive behaviour model primarily developed for the interlayer. Depending on the flexible or rigid nature of the interlayer, two types of interface laws have been suggested. Finally, these models are employed in a numerical analysis for studying the stress concentration due to free-edge effects in a multilayered symmetric cross-ply (0°/90°)s laminate having different kinds of interlayers. The present results are compared with those of classical/ideal perfect interface model to show the significance of the proposed models, incorporating the influence of the interlayer transition behaviour on the free-edge effect evaluation.     

Anomalous crystallization behavior of strontium titanate aluminosilicate glass-ceramics

The crystallization of glasses with a nominal composition consisting of 65 wt% SrTiO₃, 29 wt% SiO₂, and 6 wt% Al₂O₃, were investigated. Two glass batches of this composition, prepared from different chemicals and similar processing conditions, resulted in glass-ceramics with very different crystalline phases. One glass batch resulted in glass-ceramics with perovskite SrTiO₃ as the primary crystalline phase, while the second glass batch resulted in glass-ceramics with fresnoite Sr₂TiSi₂O₈ as the primary crystalline phase. The different crystallization sequences of glass-ceramics of the two glass batches were traced to differences between the first phases to crystalline from each glass. The crystallization behavior of these glass-ceramics was further complicated by the presence of several unidentified phases.     

Variation of the structure of amorphous lead titanate in the course of crystallization

The laws of formation of an equilibrium crystalline structure of lead titanate during crystallization from an amorphous state were studied. The initial thermal treatment leads to structural relaxation of the amorphous state. Subsequently, an intermediate state is formed whereby cubic phases with perovskite and pyrochlore structures coexist in the amorphous matrix. Finally, an equilibrium tetragonal phase is established at room temperature.     

Crystal structure and photocatalytic properties of titanate nanotubes prepared by chemical processing and subsequent annealing

Anatase TiO₂ nanoparticles were synthesized from sol–gel processing, and they were used as a precursor for titanate nanotubes (TNT) formation. TNT were synthesized under reflux heating of anatase TiO₂ in concentrated NaOH solution followed by repeated washing with distilled water and 0.1 M HCl. The nanotubular structure was preserved till 450 °C, above which nanorod formation started. The as-synthesized nanotubes were found to have mixed crystal structure of anatase and Na _x H_2?x Ti₃O₇·nH₂O (where 0 < x <  2), contrary to what has been reported before. The XRD peaks of titanate were slightly shifted to higher angles upon calcination along with prominent anatase peaks. Complete transformation to nanorods occurred at 600 °C and crystal structure was transformed to Na₂Ti₆O₁₃ and anatase. Sodium presence in TNT was confirmed by EDX, and Na–O and H–O–H along with Ti–OH vibrations were found by FTIR. Ti–OH/H–O–H vibrations were less prominent for samples calcined at 500 °C and above, which confirms structural water loss is associated with morphological change. The as-synthesized TNTs had a specific surface area of 157 m² g^?1, and it decreased by increasing calcination temperature. TNTs were applied to methylene blue aqueous solution to observe their decolorization capability under UV irradiation. The as-synthesized TNTs showed enhanced photocatalytic decolorization as compared to anatase titania nanoparticles due to presence of Ti–OH groups and higher specific surface area. The photocatalytic activity reduced when TNTs were annealed at high temperatures. The changes in the photocatalytic activity are related to the existence of hydroxyl groups in the structure, decrease in specific surface area of annealed nanotubes, change in morphology from nanotubes to nanorods, and bandgap shift to visible light when TNTs were calcined at higher temperatures.     

Chemical processing of modified lead titanate

A modified lead titanate composition has been synthesized by two different chemical techniques. The influence of the powder processing methods and the calcination temperatures on the physical characteristics, e.g. surface area and phase compositions of the powders, has been investigated. Powders of the same composition have also been prepared by attrition milling the raw materials. Results of the preliminary investigations indicate that the above physical characteristics are strongly dependent on the powder processing methods and calcination temperatures.     

Study of the kinetics in crystallization of neodymium-iron-boron alloy containing zirconium additives

The possibility of applying the Kolmogorov-Avrami equation to describe the kinetics of crystallization of Nd₂Fe₁₄B-based alloys is discussed; for the estimation of the fraction of the transformed volume, the results of magnetic measurements are used. A significant influence of zirconium additives on the kinetics of crystallization is revealed.     

Effect of electric field on the crystallization of lead titanate in a glass

An electric field was applied to a PbO-TiO₂-Al₂O₃-SiO₂ glass during the crystal nucleation treatment at 570°C in order to produce oriented glass-ceramics. After the crystallization treatment at 620°C of the nucleated glass, an enhanced a-axis preferred orientation of the lead titanate cubic perovskite, which is not ferroelectric, was developed in the surface-layer region. However, the a-axis orientation was difficult to develop in the interior region of the sample, possibly due to ion migration during the nucleation treatment. The degree of a-axis orientation on the as-heated surface showed a maximum at an optimum nucleating time t _max and the t _max-value decreased with an increase in the applied electric field strength.     

The relationship between the microstructure and microwave dielectric properties of zirconium titanate ceramics

Zirconium titanate (ZrTiO₄) ceramics have been prepared by the mixed oxide route using small additions of ZnO, Y₂O₃ or CuO. Specimens were sintered mainly at 1400 °C and cooled at various rates: water-quench, air-quench, 300 °C h^–1, 120 °C h^–1, 6 °C h^–1 and 1 °C h^–1. Products prepared with additives exhibited densities of at least 93% of the theoretical value. As the cooling rate after sintering was decreased, the length of the lattice parameter in the b direction was reduced and transmission electron diffraction revealed superlattice reflections associated with cation ordering. For specimens cooled at 1 °C h^–1, electron diffraction patterns exhibited features consistent with an incommensurate superstructure in the a direction. The dielectricQ value of rapidly cooled (air-quenched) ceramics was 2000 at 5 GHz. With an increase in the degree of cation ordering theQ value increased to a maximum of 4400 for specimens cooled at 6 °C h^–1. For specimens cooled at the slowest rate (1 °C h^–1) theQ value fell to 2000 due in part to the presence of microcracks and exsolved ZrO₂. Diffusion of trivalent impurities (yttria) into the host ZrTiO₄ grains also led to a lowering of theQ values.The microwave dielectric properties of zirconium titanate ceramics are sensitive to processing conditions and mircrostructural features. The highestQ values (lowest loss) should be achieved in homogeneous specimens, free of trivalent impurities and lattice defects, in which lowQ-value second phases, microcracks and pores are eliminated.     

Electrical characterization of zirconium substituted barium titanate using complex impedance spectroscopy

This paper reports complex impedance analysis of polycrystalline complex perovskite structured BaZr _0·025Ti _0·975O₃ prepared by solid state reaction method. XRD analysis reveals the formation of single phase perovskite structure. SEM has been used to investigate grain morphology of the material. Impedance plots have been used as a tool to analyse electrical properties of the sample as a function of frequency and temperature. Bulk resistance is observed to decrease with an increase in temperature showing a typical negative temperature coefficient of resistance (NTCR) type behaviour. Nyquist (Cole–Cole) plots show both inter and intra grain boundary effects. Relaxation time is found to decrease with increasing temperature and it obeys the Arrhenius relationship. The variation of d.c. and a.c. conductivity as a function of temperature is also reported.     

Lamination of magnesium oxide spacers to barium strontium zirconium titanate ceramics

We propose an innovative idea to bond the dielectric barium strontium zirconium titanate (BSTZO) plates with magnesium oxide (MgO) as the spacers to achieve a hermetic module without any air gaps between the dielectric and the spacer. The gold metallization can be applied across the whole assembly to create an integrated electrode. The gold metallization also eliminates pressure contact by external copper plates assemblies, which are required to achieve good contacts between the copper plates and the metallized surfaces of the BSTZO. The MgO spacers are processed using a dry-pressing and pressureless-sintering method. The thermal expansion coefficient (CTE) of BSTZO and MgO spacer was measured. In addition to matching the CTE between BSTZO dielectric and the MgO spacer, it is also critical to develop a good bonding material with CTE matching to BSTZO and MgO spacer. The effect of CTE for various bonding compositions on the dielectric properties was thoroughly studied and reported. The mechanism explaining the high and low dielectric constants for the laminates is proposed and discussed based on the CTE results and their effect on microstructural development.