Effect of Nd-doping on structural,thermal and electrochemical properties of LaFe0.5Cr0.5O3 perovskites

The structural, thermal and electrochemical properties of the perovskite-type compound La_1−xNd_xFe_0.5Cr_0.5O₃ (x=0.10, 0.15, 0.20) are investigated by X-ray diffraction, thermal expansion, thermal diffusion, thermal conductivity and impedance spectroscopy measurements. Rietveld refinement shows that the compounds crystallize with orthorhombic symmetry in the space group Pbnm. The average thermal expansion coefficient decreases as the content of Nd increases. The average coefficient of thermal expansion in the temperature range of 30–850 °C is 10.12×10⁻⁶, 9.48×10⁻⁶ and 7.51×10⁻⁶ °C⁻¹ for samples with x=0.1, 0.15 and 0.2, respectively. Thermogravimetric analyses show small weight gain at high temperatures which correspond to filling up of oxygen vacancies as well as the valence change of the transition metals. The electrical conductivity measured by four-probe method shows that the conductivity increases with the content of Nd; the electrical conductivity at 520 °C is about 4.71×10⁻³, 6.59×10⁻³ and 9.62×10⁻³ S cm⁻¹ for samples with x=0.10, 0.15 and 0.20, respectively. The thermal diffusivity of the samples decreases monotonically as temperature increases. At 600 °C, the thermal diffusivity is 0.00425, 0.00455 and 0.00485 cm² s⁻¹ for samples with x=0.10, 0.15 and 0.20, respectively. Impedance measurements in symmetrical cell arrangement in air reveal that the polarization resistance decreases from 55 Ω cm⁻² to 22.5 Ω cm⁻² for increasing temperature from 800 °C to 900 °C, respectively.     

The Use of Reverse Osmosis in the Removal of PAHs from Municipal Landfill Leachate

Polycyclic aromatic hydrocarbons (PAHs) are relatively well-known organic pollutants and due to their carcinogenic and mutagenic properties their presence in the environment still attracts a lot of attention.

According to literature reports and own research, PAHs presence in wastewaters is common. It was confirmed that PAHs are the components of municipal landfill leachate. Membrane techniques are one of the most interesting ways of removing PAHs from leachate.

The purpose of this article is to monitor PAHs concentration changes during the membrane (reverse osmosis - RO) leachate treatment processes. In the first stage of testing leachates were filtrated on the sand bed (pre-filtration). After the pre-filtration they were directed to the membrane module for the main filtration.

Sixteen PAHs listed by EPA were analyzed. The results with information on PAHs concentration in leachate samples were presented using HPLC with fluorescence detection (FLD). The changes in PAHs concentration were determined in leachate samples before and after pre-filtration as well as after RO. The decrease of PAHs concentration in the samples was observed after these processes. The total concentration of 16 PAHs in raw municipal landfill leachates amounted to 23.64–26.95 μg/L. The research confirmed the high efficiency in removal of PAHs while using a reverse osmosis (59–72%). Including the pre-filtration, the overall level of removed PAHs reached 81–86%. The average PAHs concentration after pre-filtration and RO was in the 4.46–4.99 μg/L range. The municipal landfill leachate with a high concentration of PAHs should be cleaned before it is discharged into the environment.     

Calibration of dynamic tool–workpiece interface temperature measurement during friction stir welding

The objective of this work is to accurately measure the transient temperatures at the tool–workpiece interface during friction stir welding (FSW) using thermocouples that are embedded in the tool. Temperature sensors embedded in the friction stir (FS) tool provide a non-consumable localized temperature measurement capability that is crucial for process research, development, and control. A modification of the ASTM E-1461 standard for measuring thermal diffusivity with pulses of heat flux is proposed for calibrating the transient response of temperature sensors located near the surface of the FS tool. These tests enable the calculation of each sensor’s time constant, which are used in one-dimensional analytical models of the dynamic response to calculate the true interface temperature. Time constants between 21 and 43 ms are measured for 0.25-mm-diameter, sheathed thermocouples located at the FS tool surface.     

Review of zirconia-based bioceramic: Surface modification and cellular response

Zirconia is gaining interest as a ceramic biomaterial for implant applications due to its biocompatibility and desirable mechanical properties. At present, zirconia-based ceramic is often seen in the applications of hip replacement and dental implants. This paper briefly reviews different surface modification techniques that have been applied to zirconia such as polishing, sandblasting, etching, biofunctionalization, coating, laser treatment, and ultraviolet light treatment. The cellular response of osteoblast-like cell, osteoblast cell, fibroblast, and epithelial cell to the modified surface is discussed in terms of their adhesion, proliferation, and metabolic activity. The potential of surface modification to make zirconia a successful implant material in the future is highly dependent on the establishment of successful in vitro and in vivo studies. Hence, further effort should be made in order to deepen the understanding of tissue response to the implant and the tissue regeneration process. The review concludes with future prospect of research and further challenges in developing better zirconia bioceramics.     

New precursors to SiCO ceramics derived from linear poly(vinylsiloxanes) of regular chain composition

Two linear polysiloxanes with vinyl groups regularly distributed in their chains (D₂V polymer with a vinyl group at every third and V₃ polymer with a vinyl group at each Si atom) were cross-linked with different hydrogensiloxanes (linear difunctional ^HMM^H, linear branched tetrafunctional Q(M^H)₄, cyclic tetrafunctional D₄^H) and studied as new precursors to SiCO ceramics. It was found that thermal properties of the cross-linked D₂V and V₃ polymers are governed mainly by functionality of the initial macromolecule as well as functionality and molecular structure of hydrogensiloxane. Transformation of the systems into ceramics was examined by recording FTIR spectra of the samples obtained after heat treatment of the cross-linked polymers under Ar at several temperatures. Analysis of the products formed at 1 000 °C, allowed establishing that they are a mixture of silicon oxycarbides and a free carbon phase. Lack of pores is a characteristic feature of these materials.     

Low variation in relative permittivity over the temperature range 25–450 °C for ceramics in the system (1 − x)[Ba0.8Ca0.2TiO3]–x[Bi(Zn0.5Ti0.5)O3]

The dielectric and ferroelectric properties of the ceramic system, (1 − x)Ba_0.8Ca_0.2TiO₃–xBi(Zn_0.5Ti_0.5)O₃, were investigated for compositions 0 ≤ x ≤ 0.4. X-ray powder diffraction patterns indicated tetragonal symmetry at x ≤ 0.05, switching to pseudocubic at x ≥ 0.1, with a single-phase solid solution limit at 0.2 < x < 0.3. The x = 0 and 0.05 samples were ferroelectric; a change to relaxor behaviour occurred at x ≥ 0.1, with broad frequency dependent peaks in plots of relative permittivity versus temperature. A significant reduction in the temperature dependence of relative permittivity occurred at x = 0.3, with ɛ_r = 1030 ± 15% over the temperature range ∼25–425 °C, and loss tangent, tan δ ≤ 0.01 from 110 °C to 420 °C. The dc resistivity values for x = 0.3 were ∼10⁹ Ω m at 300 °C and ∼10⁶ Ω m at 450 °C.     

Free energy formulation of fatigue crack initiation along persistent slip bands: calculation of SN curves and crack depths

A theory of fatigue crack initiation along PSBs based on free energy considerations has been developed. The PSB is modelled as an accumulation of vacancy dipoles. The total free energy of the system increases with fatigue cycle number due to the increase in elastic strain energy. It is shown that there exists a critical fatigue cycle number above which the initial state of dislocation accumulation along the slip band becomes energetically unstable, leading to the initiation of a microcrack within the PSB. SN curves for initiation can be calculated and the resulting crack depths determined. The theory correctly predicts several observed phenomena of fatigue crack initiation: (i) crack initiation is easier in air than in vacuum; (ii) crack initiation is easier at room temperature than at cryogenic temperatures; (iii) just-initiated cracks are shallow.     

Theoretical study of hydrogen transport during plastic deformation in iron

In order to model hydrogen transport during plastic deformation, it is essential to take into account the combined effect of several interactions: the interaction of hydrogen with newly generated dislocations, the interactions between hydrogen in lattice sites and moving dislocations, and the effect of both of these on the diffusion process. Both atomistic and macroscopic diffusion models, which take into account all of the above interactions, have been developed. The results show that the hydrogen flux due to moving dislocations strongly depends upon the kinetics between hydrogen in moving dislocations and that in lattice. It was also found that the dynamic trapping effect, i.e. trapping associated with an increase in the population of dislocations, should be taken into account to properly model hydrogen transport during plastic deformation.