Characterization of superficial modification of ferrous rusted substrates subjected to dechlorination-electrochemical process

Preservation of archaeological artefacts after their removal from saline media is a difficult task due to the chloride content of the oxide layers which are unstable in atmospheric conditions, especially if the relative humidity exceeds 85%. For this reason, removal of chlorides from rust layers is one of the priorities of conservationists or restorers of historical artefacts. However, removal of chloride ions is not an easy procedure because of the many considerations involved in the process. In this research, artificially pre-rusted iron samples and an actual historical cannonball were subject to a dechlorination process in a potassium hydroxide solution to measure constant chloride release in a bulk solution. After the chloride removal process, a commercial protective layer was applied to the rust for stabilization purposes. It was calculated that the kinetics of the dechlorination process is driven by diffusion behaviour following Fick’s second law. When this diffusion process prevails, the dechlorination extraction affects the integrity of rust layers as is demonstrated with scanning electron microscopy and X-ray diffraction analyses. It was proven that the chloride removal procedure causes the studied iron layers to stiffen, provoking superficial modification and, in some cases, fractures of the rust. By means of electrochemical impedance spectroscopy it was calculated that the magnitude of the positive effect of the dechlorinated samples depends on the protective features of the rust. Therefore, this research reveals that an efficient chloride removal procedure depends on the electrochemical properties of the dechlorination process and the initial morphology of the iron rust.     

Thermally-induced phase transformations in KNNS-BNKZ lead-free piezoceramics

Promising piezoelectric properties have been reported in potassium sodium niobate-based ceramics by introducing Bi_0.5(Na_0.82K_0.18)_0.5ZrO₃ (BNKZ) into K_0.48Na_0.52Nb_0.95Sb_0.05O₃ (KNNS) solid solutions in order to control the polymorphic phase transformation temperatures. In the present study, synchrotron x-ray powder diffraction (SXPD) was employed in combination with dielectric and ferroelectric measurements in order to clarify the influence of BNKZ on the phase transition temperatures of (1-x)KNNS-(x)BNKZ ceramics (with x = 0 to 0.05). The results, presented in terms of temperature-dependent SXPD patterns, dielectric permittivity and thermal depolarisation characteristics, confirmed that polymorphic phase transformation temperatures all shifted in a systematic manner with increasing BNKZ content. Broadening of the phase transition regions was also observed with increasing BNKZ content, leading to improvements in thermal stability of the ferroelectric properties. Microstructural examination of the KNNS-BNKZ ceramics revealed the presence of core-shell microstructures; this was correlated with the presence of weak shoulders on the diffraction peaks.     

Experimental phase equilibria study and thermodynamic modelling of the PbO-“FeO”-SiO2-ZnO,PbO-“FeO”-SiO2-Al2O3 and PbO-“FeO”-SiO2-MgO systems in equilibrium with metallic Pb and Fe

Phase equilibria of the PbO-“FeO”-SiO₂-ZnO, PbO-“FeO”-SiO₂-Al₂O₃ and PbO-“FeO”-SiO₂-MgO slags with liquid Pb metal, solid or liquid Fe metal and solid oxides (cristobalite and tridymite SiO₂, willemite (Zn,Fe)₂SiO₄, wustite (Fe,Al)O_1+x, spinel (Fe,Al)₃O₄, olivine Fe₂SiO₄, corundum (Al,Fe)₂O₃, mullite Al₆Si₂O₁₃ and pyroxene (Mg,Fe)SiO₃) were investigated at 1125–1670 °C. These conditions correspond to the minimum solubility of PbO in slag in presence of Pb and Fe metals at reducing conditions and represent the limit of lead smelting and slag cleaning process. High-temperature equilibration on silica, corundum or iron foil substrates, followed by quenching and direct measurement of Pb, Fe, Si, Zn, Al and Mg concentrations in the liquid and solid phases with the electron probe X-ray microanalysis (EPMA) was used. Present data can be used to improve the thermodynamic models for all phases in this system.     

Integrated study of experiment and first‐principles computation for the characterization of a corium type ZrO8 complex in a Zr‐doped fluorite UO2

We, for the first time, observe ZrO₈ complex in Zr‐doped UO₂, which is a corium structure, using experimental characterization integrated with first‐principle computational validation. Atomic level structure of U_1?yZr_yO₂ pellets (y = 0.01, 0.03, 0.05, and 0.1) is identified using Raman spectroscopy measurement and X‐ray diffraction pattern analysis. The lattice constants shrink with increasing Zr doping levels, which consistently represents in the positive shift of T_2g Raman vibration peak around 445 cm^?1. More interestingly, conventionally unknown new Raman peak appears around 598 cm^?1, which has not been observed in neither a pure ZrO₂ nor UO₂ doped with tetravalent elements other than Zr. We unveil that the new peak originates from ZrO₈‐type complex formed on the fluorite UO₂. Our study provides precise understanding on the formation mechanisms and material properties of the corium in the hypervalent oxide.     

Defect control and ionic conductivity of oxynitride perovskite Sr0.83Li0.17Ta0.83O1.88N0.74

Perovskite lattice was tailored by introducing site vacancies and mixed anion composition, to produce Sr_0.83Li_0.17Ta_0.83O_1.88N_0.74 (Li02N). Further, Li02N was converted to a defect oxide Sr_0.83Li_0.17Ta_0.83O₃ (Li02O) by applying an optimized treatment: heating in air at 1173 K for 2 h. According to the neutron Rietveld refinement, Li02N and Li02O are tetragonal and orthorhombic, respectively, where the lattice volume of Li02O is significantly smaller than that of Li02N. The ionic conductivity (σ_ion) of Li02N and Li02O was evaluated by the ac impedance spectroscopy and the equivalent circuit analysis. Both Li02N (σ_ion = 10^?5.5 S/cm at 671 K) and Li02O (σ_ion = 10^?6.2 S/cm at 667 K) exhibited an Arrhenius behavior of ionic conductivity with activation energies of 0.87 eV and 0.75 eV, respectively. It is interpreted that the nitride component enhances the ionic conduction of Li02N, while the vacancy of the anion lattice makes an opposite effect.     

Spark plasma sintering of B4C and B4C-TiB2 composites: Deformation and failure mechanisms under quasistatic and dynamic loading

Spark plasma sintering (SPS) was employed to consolidate powder specimens consisting of B₄C and various B₄C-TiB₂ compositions. SPS allowed for consolidation of pure B₄C, B₄C-13 vol.%TiB₂, and B₄C-23 vol.%TiB₂ composites achieving ≥99 % theoretical density without sintering additives, residual phases (e.g., graphite), and excessive grain growth due to long sintering times. Electron and x-ray microscopies determined homogeneous microstructures along with excellent distribution of TiB₂ phase in both small and larger-scaled composites. An optimized B₄C-23 vol.%TiB₂ composite with a targeted low density of ～3.0 g/cm³ exhibited 30–35 % increased hardness, fracture toughness, and flexural bend strength compared to several commercial armor-grade ceramics, with the flexural strength being strain rate insensitive under quasistatic and dynamic loading. Mechanistic studies determined that the improvements are a result of a) no residual graphitic carbon in the composites, b) interfacial microcrack toughening due to thermal expansion coefficient differences placing the B₄C matrix in compression and TiB₂ phase in tension, and c) TiB₂ phase aids in crack deflection thereby increasing the amount of intergranular fracture. Collectively, the addition of TiB₂ serves as a toughening and strengthening phase, and scaling of SPS samples show promise for the manufacture of ceramic composites for body armor.     

Effect of the microstructure of graphitic boron nitride on the kinetics of the formation of boron nitride high-pressure phases

Three types of hexagonal boron nitride (h-BN) with graphitic crystal structure having different microstructures were subjected to high pressures (HP) and high temperatures (HT), and the kinetics of the phase transitions to the sp³-hybridized phases (w-BN, c-BN) was studied using in situ synchrotron diffraction. The analysis of the phase transformation kinetics revealed the transformation paths and activation energies E_a of the transformation of h-BN to the high-pressure forms of BN for different microstructures of h-BN. Defect-poor h-BN transforms to metastable wurtzitic BN (w-BN) with E_a ≈ 0.3 eV/at. Defect-rich forms of h-BN transform directly to c-BN, but with a higher activation energy. It was observed that the turbostratic disorder in h-BN retards the phase transition as compared to h-BN containing corrugated basal planes and a low degree of turbostracity. The experimental results are discussed in view of the microstructure changes during the HP/HT treatment and compared to available theoretical phase transition models.     

Analysis of Damage on the Streptococcus mutans Immersed in Ozonated Water: Preliminary Study for Application as Mouth Rinse

Ozonated water has been demonstrated to induce significant results in terms of the elimination of microorganisms. The present study assessed the damage to Streptococcus mutans after exposure to ozonated water; the ozone generator was adjusted to provide an outlet concentration of 60 mg/L, the samples were submitted to different ozonation times 1, 2, 4, 6, and 10 mi. Scanning electron microscopy and atomic force images were obtained to identify damage to the bacteria, followed by reactive oxygen species (ROS) evaluation and microbial viability. The results showed a significant reduction in viability and the images evidenced the generation of gaps on the microbial wall and surface layer alterations. Ozone can induce significant damage to S. mutans, thus suggesting that the use of ozonated water to prevent carious lesion formation is extremely promising.     

Validating the efficiency of γ-Al2O3/La0.6Sr0.4Co0.2Fe0.8O3-δ double-layer electrolyte for low temperature solid oxide fuel cell

Perovskite La_0.6Sr_0.4Co_0.2Fe_0.8O_3+δ (LSCF) as a promising cathode material possessed overwhelming electronic conduction along with certain ionic conductivity. Its strong electron conduction capability hinder the application of pure-phase LSCF as electrolyte in semiconductor membrane fuel cell (SMFC). In order to constrain the electron transport and take advantage of the decent ion conduction of LSCF, a thin layer of γ-Al₂O₃ with insulating property was added as an electron barrier layer and combine with LSCF to form a two-layer structure electrolyte. Through adjusting the weight ratio of LSCF/γ-Al₂O₃ to optimize the thickness of double layers, an open circuit voltage of 0.98 V and a maximum power density of 690 mW/cm² was received at 550 °C. At the same time, SEM, EIS and other characterization technology had proven that the LSCF/γ-Al₂O₃ bi-layer electrolyte can work efficiently at low temperature. The advantage of this work is the application of double-layer (γ-Al₂O₃/LSCF) structure electrolyte to instead of mixed material electrolyte in low-temperature solid oxide fuel cells. Structural innovation and the using of insulating materials provided clues for the further development of SMFC.