Influence of high energy ball milling on structural,microstructural and optical properties of TiO2 nanoparticles

The influence of high-energy ball milling on structural, microstructural, and optical properties of TiO₂ by modifying the nanoparticle size was studied. Five samples were extracted at different milling times (0, 2, 4, 8, and 13 h). The average particle sizes estimated by dynamic light scattering (DLS) were 205, 155.8, 116.8, 82.9, and 82.7 nm at 0, 2, 4, 8, and 13 h, respectively. X-ray diffraction analysis confirmed progressive broadening of the peaks as the milling time elapsed. Besides, a correlation was found between d spacing and the average crystal size. The UV–Vis diffuse reflectance spectra of TiO₂ revealed a decrease in reflectance due to particle size reduction. Similarly, an alteration of the bandgap transition energy was presented, whose values gradually decreased from 2.966 eV to 2.861 eV for the sample without and with the maximum duration milling performed (13 h), respectively. Likewise, the SEM analysis showed a distribution in nanoparticle size that became more homogeneous and smaller average grain size as the milling duration was longer.     

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.     

Influence of Se and Te substitutions at Tl-site of Tl(Ba,Sr)CaCu2O7 superconductor on the AC susceptibility and electrical properties

The Sr and Ba bearing Tl-1212 phase, Tl(Ba,Sr)CaCu₂O₇ is an interesting superconductor. The Sr only bearing TlSr₂CaCu₂O₇ is not easily prepared in the superconducting form. The Ba only bearing TlBa₂CaCu₂O₇ on the other hand does not show improvement in the transition temperature with elemental substitution. In this work the influence of multivalent Se (non-metal) and Te (metalloid) substitutions at the Tl-site of Tl_1-xM_x(Ba,Sr)CaCu₂O₇ (M = Se or Te) superconductors for x = 0–0.6 was studied. The samples were prepared via the conventional solid-state reaction method. XRD patterns showed a single Tl-1212 phase for x = 0 and 0.1 Se substituted samples. The critical current density at the peak temperature, T_p of the imaginary (χ”) part of the AC susceptibility (χ = χ’ +χ”), J_c-inter(T_p) for all samples was between 15 and 21 A cm⁻². The highest superconducting transition temperature was shown by the x = 0.3 Se-substituted sample (T_c-onset = 104 K, T_c-zero = 89 K, T_cχ’ = 104 K and T_p = 80 K). Te suppressed the superconductivity of Tl-1212 phase. The order of highest transition temperatures are as follows: Tl_1-xTe_x(Ba,Sr)CaCu₂O₇<Tl(Ba,Sr)CaCu₂O₇<Tl_1-xSe_x(Ba,Sr)CaCu₂O₇. This work showed that Se was better than Te in improving the transition temperature and flux pinning of the Tl-1212 phase. The roles of ionic radius of Se and Te on the superconductivity of Tl(Ba,Sr)CaCu₂O₇ are discussed in this paper.     

Growth mechanism and gas-sensing characteristics of organic-additive-free zinc oxide of various shapes

Zinc oxide is widely used in gas sensors, solar cells, and photocatalysts because of its wide bandgap and exciton binding energy of 60 meV in various metal oxides. To use ZnO as a gas sensor, it is necessary to synthesize it with surface defects and a large specific surface area. In this study, hydrothermal synthesis without surfactants was employed to obtain organic-additive-free ZnO. For morphology control, we varied the ratio of the hydroxide ion concentration to the zinc ion concentration. To confirm the growth mechanism of ZnO, we performed X-ray diffraction, scanning electron microscopy, and transmission electron microscopy analyses. Raman spectroscopy and photoluminescence measurements were performed to analyze the surface properties. The Brunauer–Emmett–Teller method and probe stations were used to measure the specific surface area and sensitivity of the gas sensor, respectively. The results confirmed that flower-shaped ZnO is the most suitable gas-sensing material.     

The effect of synthesis conditions on the phase composition and structure of thorium bearing murataite ceramics

Samples of thorium-bearing ceramic with a target composition (wt%) 5 Al₂O₃, 10 CaO, 55 TiO₂, 10 MnO, 5 Fe₂O₃, 5 ZrO₂, 10 ThO₂ were produced by melting in glassy carbon crucibles in a resistive furnace and by cold crucible inductive melting (CCIM) at a vibration power of 10 kW and operation frequency of 5.28 MHz. All the samples contained 85–95 vol% murataite polytypes with 5- (5C), 8- (8C), and 3-fold (3C) elementary fluorite unit cell composing core, intermediate zone and rim of the grains, respectively, and minor crichtonite, perovskite, pyrochlore, rutile, etc. A feature of the ceramics obtained by melting in glassy carbon crucibles is formation of Fe (II) titanate whereas the inductive-melted ceramics contained traces of vitreous phase due to melt contamination with a cold crucible putty material. Melting rate in the cold crucible of up to 350 kg/(m² × h) has been achieved. The ceramics obtained have excellent chemical durability.     

Structural and physicochemical properties of silver-rich Ag–Al alloys

The X-ray diffraction, Scanning Electron Microscopy, Differential Scanning Calorimetry, dilatometric and electrical conductivity measurements were used to study the structural and physicochemical properties of selected silver-rich alloys from Ag–Al system. All the studied alloys, containing from 10 to 37 at. % of Al (Ag₉₀Al₁₀, Ag₈₅Al₁₅, Ag₇₇Al₂₃, Ag₇₅Al₂₅, Ag₇₂Al₂₈, Ag₇₀Al₃₀, Ag₆₃Al₃₇), were prepared from high purity metals by melting in a glove-box filled with a high purity argon atmosphere. The obtained X-ray diffraction patterns and microstructure observation of alloys containing up to 15 at. % of Al suggested that in this range only solid solution of silver exists. The thermal analysis showed heat effects related to phase transitions in Ag–Al system. In addition, the thermal expansion studies revealed an anomalous behavior in expansion for some composition of alloys associated with the phase transition. The electrical conductivity values rapidly changed, which may be associated with the formation of different phase areas in the Ag–Al system.Based on the results obtained in this work and critically reviewed literature data a thermodynamic re-optimization of the binary Ag–Al system using CALPHAD method was proposed. A good agreement between calculation and experiment was found.     

The control of paracetamol particle size and surface morphology through crystallisation in a spray dryer

The parameters governing the crystallisation of paracetamol using various conventional techniques has been extensively studied, however the factors influencing the drug crystallisation using spray drying is not as well understood. The aim of this work was to investigate the crystallisation of an active pharmaceutical ingredient through evaporative crystallisation using a spray dryer to study the physicochemical properties of the drug and to use semi-empirical equations to gain insight into the morphology and particle size of the dried powder. Paracetamol solutions were spray dried at various inlet temperatures ranging from 60 °C to 120 °C and also from a series of inlet feed solvent compositions ranging from 50/50% v/v ethanol/water to 100% ethanol and solid-state characterisation was done. The size and morphology of the dried materials were altered with a change in spray drying parameters, with an increase in inlet temperature leading to an increase in particle Sauter mean diameter (from 3.0 to 4.4 µm) and a decrease in the particle size with an increase in ethanol concentration in the feed (from 4.6 to 4.4 µm) as a result of changes in particle density and atomised droplet size. The morphology of the dried particles consisted of agglomerates of individual crystallites bound together into larger semi-spherical agglomerates with a higher tendency for particles having crystalline ridges to form at higher ethanol concentrations of the feed.     

Sensitivity of a solid Eu(III) complex towards acetonitrile vapor: Structural and spectroscopic characterization

The Eu(III) nitrate complex of the meso- N,N′-bis(2-pyridylmethylene)-1,2-(R,S)-cyclohexanediamine ligand was synthesized and characterized by single crystal and powder X-ray diffraction. The crystal lattice of the complex is capable of absorbing and desorbing selectively acetonitrile molecules, at 293 K upon an acetonitrile vapor pressure of ∼0.1 × 10⁵ Pa. This process, which is partially reversible, can be easily followed by both powder X-ray diffraction (P-XRD) and Eu(III) luminescence spectroscopy. The acetonitrile molecule, located in the outer coordination sphere of the metal ion, does not affect the radiative transition probability of ⁵D₀ level of Eu(III) and also it does not activate further non-radiative channels from this level. On the other hand, this molecule is capable of affecting the energy position and intensities of the crystal field components of the ⁵D₀→⁷F₂ transition. The complex in solid form can be considered a promising material for the optical sensing of acetonitrile vapors.     

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.