Journal of the Australian Ceramic Society最新文献

Borides and silicide of tungsten as the refractory intermetallic compounds have high mechanical properties, relatively good thermal shock, and chemical stability. Also, they have less brittleness than ceramic compounds that can lead to its usage in various industrial applications. In this work, for the first time, an alumina-based composite (WB-WB₂-WSi₂-Al₂O₃) was produced by combustion synthesis using aluminothermic reaction of a quaternary mixture (Al-Si-WO₃-B₂O₃) as starting materials. According to standards defined by Merzhanov, Munir, and Anselmi, the combustion synthesis process for the system of Al-Si-WO₃-B₂O₃ is the type of self-propagating high-temperature synthesis (SHS). The milled mixture was formed into cylindrical specimens after cold pressing and was heat-treated using an oxyacetylene flame as the initiator of self-propagating high-temperature synthesis in the air atmosphere. The ignition, the maximum combustion temperature, and the progress speed of the combustion front were measured using several thermocouples and data logger device. The phases formed in the synthesis samples were characterized by X-ray diffraction (XRD) and field emission scanning electron microscope (FE-SEM). The results showed that the combustion front had a temperature above 1800 °C with a speed of about 20 mm·sec⁻¹. Microstructural observations showed the blades of tungsten borides with a hexagonal structure and spheres of tungsten silicates in the matrix of alumina phase. The average of particle size of borides and silicide of tungsten varies in the range of 100 to 200 nm, indicating the formation of sub-micron composite due to the high speed of the combustion synthesis process.

Abstract

The use of lead as a radiation shield is becoming unpopular due to toxicity concern. Glasses are promising alternatives for eliminating this problem. This study is thus aimed at ascertaining the shielding efficacy of a newly developed glass system against gamma-ray, charged particle, fast, and thermal neutrons. The radiation shielding parameters of the novel PPZLC glass system were theoretically calculated and analysed. The chemical structure of the PPZLC glasses is 65P₂O₅–10Pb₃O₄–5ZnO–(20–x)Li₂CO₃–xCuO where x = 0, 0.4, 0.8 and 1.0 mol% represents PPZLC1, PPZLC2, PPZLC3 and PPZLC4 glasses respectively. The gamma-ray mass attenuation coefficient MAC of the glasses for 0.1–10 MeV photons was calculated by FLUKA simulation and XCOM software. Calculated MAC values varied from 2.025 to 0.031, 2.027 to 0.032, 2.029 to 0.032 and 2.027 to 0.032 cm²/g in the order of PPZLC1-4. Analysis of other photon shielding parameters such as half value layer and mean free path showed that the increase in the concentration of CuO improved the shielding ability of the glasses against photons. Similarly, the trend of projected range of electrons, protons, α-particles and carbon ions showed the absorption capacity of charged particles in the glasses increased from PPZLC1-4. Furthermore, the fast neutron removal cross section increased considerably from 0.1006 to 0.1038 cm⁻¹ for CuO molar concentration increase of 0–1.0 mol%. However, the reduction in the molar concentration of Li₂CO₃ led to the decline of absorption and total cross section for thermal neutrons in the glasses. Comparing the photon and neutron absorbing capacity of the PPZLC1-4 glasses with common shielding materials, it was observed that the present glasses have potential to function well in radiation absorbing or collimating applications. They can thus be recommended for use as radiation shields in medical and industrial application of photons coupled with fast neutrons, storage for radioactive materials and other related functions.

The solubility limit of bismuth in orthorhombic structured vanadium pentoxide is determined in V_2-xBi_2xO_5-δ compound systems. Highly polycrystalline single-phased solid solutions of V_2-xBi_2xO_5-δ were synthesized for mole fractions “x” varying from 0.01 to 0.04 and at x = 0.05, the compound contorts into an impure phase. Orthorhombic structured compounds with crystallite sizes varied from 54.80 to 70.23 nm are observed from powder X-ray diffraction analysis and supplementary structural information was obtained by recording micro-Raman spectra. Out of the 21 Raman active phonon modes of the α-polymorphic form of V₂O₅, 10 well-resolved peaks were identified for all “x” values. The dense growths of microstructured constituents were obtained, viz. scanning electron micrographs. The slight increase of optical bandgap from 2.22 to 2.27 eV with the increase in mole fraction is an indication of the replacement of high valency vanadyl cations with Bi³⁺ ions. Intense and broad near-band edge photoluminescent emissions detected are due to the various electronic transitions.

Li₂FeSiO₄ (LFS) has received remarkable attention due to its high thermal stability, environmental benignity, low cost, and low toxicity. However, the electrochemical performance of the material is restricted by achieving its high theoretical capacity (∼330 mA h g⁻¹). Doping is a potentially effective method to enhance the electrical conductivity and performance, and to reduce the operation voltage of the LFS cathode material. In this study, using density functional theory (DFT), fluorine-doped LFS (Li₂FeSiO_3.5F_0.5) and chlorine-doped LFS (Li₂FeSiO_3.5Cl_0.5) are evaluated. The structural properties, structural stability after extraction of the lithium-ions, cycle ability, chemical stability, cell voltage, electrical conductivity, and rate capability are assessed for the considered cathode materials. These theoretical studies predict that F and Cl doping enhances structural stability, chemical stability, electrical conductivity, rate capability, and reducing cell voltages to put the material in the electrolyte voltage tolerance to extract two Li per formula. Accordingly, the results show that the doping increases the performance, rate capability, stability, and capacity of LFS.

The high carbon footprint of cement production is dangerous to environmental sustainability, which enforces the current research to discover an alternative of cement in the concrete industry. Geopolymer (GPMR) paste incorporating nanoparticles and micro-fibers is the most suitable replacement for the cement; therefore, it is essential to study the behavior of fiber-reinforced GPMR pastes including nanoparticles. The current study aims to ameliorate the fracture, microstructural, toughness, and mechanical behavior of micro carbon-FR fly ash-based GPMR paste by utilizing different quantities of nano calcium oxide (NCO) along with the combination of micro carbon fiber (CF) (0.5 wt.%). The investigated quantities of NCO in the current study are ranged between 1 and 4%. The control mix is also fabricated for the comparison purpose having only micro-CF without NCO. The results showed that the application of NCO with a content of 3% is the most effective for improving the compressive strength, impact strength, and hardness of micro carbon-FR fly ash-based GPMR paste whereas 3% use of NCO presented the optimum results for the fracture and flexural behavior of GPMR paste. The SEM analysis presented that the CF and GPMR matrix have an effective interlocking that can be attributed to the ability of NCO to refine and give a densified matrix of the GPMR mix.

Hydroxyapatite (HAp) powder was synthesized through a precipitation method using waste cockle shell as a calcium source. HAp powder had a single phase of Ca₅(PO₄)₃OH with a Ca/P ratio of 1.77. The crystals were rod-like, 80–110 nm long, and 20–30 nm wide. HAp ceramics sintered below 1350 °C in air resulted in ceramics with a stable HAp phase. The formation of β-tricalcium phosphate impaired the flexural strength of the specimen. The microhardness increased with sintering temperature due to the modification of density and porosity. The chemical solubility in acetic acid was related to density, porosity, and grain size. HAp ceramic sintered at 1250 °C provided appropriate properties for medical and dental applications. This ceramic had a grain size of 1.44 ± 0.37 µm, a density of 2.85 ± 0.01 g/cm³, a microhardness of 4.17 ± 2.37 GPa, a porosity of 10.3 ± 0.71%, a flexural strength of 46.13 ± 4.53 MPa, and a chemical solubility of 2.64 ± 0.10%.

Abstract

Sodium zirconium phosphate (labeled as NZP)-monazite-type (1-x)Sr_0.5Zr₂(PO₄)₃–xCePO₄ (x = 0–1.0) composite ceramics, which were designed to simultaneously immobilize simulated fission nuclide Sr and variable valence actinide nuclide Ce, were in situ prepared by one-step microwave sintering technique. The feasibility of Sr/Ce co-immobilization was evaluated via an investigation on the phase evolution, microstructure, density, Vickers hardness, and chemical stability of the composite ceramics. The Ce valence state in the composite ceramics was further ascertained by X-ray photoelectron spectroscopy. It was shown that the Sr/Ce co-immobilized composite ceramics only consisted of Sr_0.5Zr₂(PO₄)₃ and CePO₄ crystalline phases that were compatible well to each other. Sr and Ce were independently incorporated into Sr_0.5Zr₂(PO₄)₃ phase and CePO₄ phase, respectively. The valence state of Ce in composite ceramics existed in trivalent state. And the existence of CePO₄ phase caused the grain refinement and facilitated the densification of the composite ceramics. The composite samples all showed a highly uniform and dense microstructure, whose relative density was higher than 95% and Vickers hardness could attain 774 HV1. Importantly, the series of Sr_0.5Zr₂(PO₄)₃–CePO₄ composite ceramics exhibited higher chemical stability than that of the monophase Sr_0.5Zr₂(PO₄)₃ or CePO₄ ceramics, in which the normalized leaching rates of Sr and Ce were below 10⁻⁴ g·m⁻²·day⁻¹ and 10⁻⁷ g·m⁻²·day⁻¹ order of magnitude, respectively. The NZP-monazite-type composite ceramics has the potential to be a host for the disposal of high-level nuclear wastes containing multiple radionuclides.

In this study, the nickel–iron–titanium carbide (Ni–Fe–TiC) nanocomposite was applied on the St14 low-carbon steel via pulse‌ electrodeposition. Electroplating was applied on the substrate with different values ​​of current density, frequency, duty cycle, electroplating time (t) and concentration of TiC nanoparticles, and the properties of the applied coatings were evaluated. To the study the microstructure and morphology of the applied coatings, field emission electron microscope (FESEM) was used. The amount of deposited elements in the coating was determined by energy-dispersive spectroscopy (EDS). To evaluate the corrosion resistance of the coatings, potentiodynamic polarization and electrochemical impedance (EIS) tests were carried out in 3.5% NaCl solution as a corrosive environment. The optimum coating was obtained at the current density (J) of 30 mA/cm², duty cycle ((gamma)) of 60%, frequency (f) of 20 Hz and 2 g/L concentration of TiC nanoparticles. The optimum coating increased the corrosion potential from -0.675 V to -0.332 V and decreased the corrosion current density from 157.200μA/cm² to 0.790μA/cm². The presence of TiC nanoparticles in the coating reduced the corrosion current density from 2.130μA/cm² (Ni–Fe coating) to 0.790μA/cm² (Ni–Fe–TiC nanocomposite coating).