Comparing hydrogen absorption kinetics of the samples of intermetallic compound and metal hydride compact on its basis

This work is devoted to an experimental study and comparison of the kinetics of hydrogen absorption by an intermetallic compound LaNi4.4Al0.3Fe0.3 in form of pure intermetallic compound free backfill and a compact based on it obtained by cold pressing with a spiral matrix of nickel-foam. To calculate the kinetic parameters of the hydrogen absorption reaction, the initial rates method is used. The PCT absorption isotherms are measured at temperatures of 313, 333, and 353 K. The experimental data are described with quite high confidence by the chosen model, which assumes that the reaction rate controlling step is the dissociative absorption of hydrogen on the surface of the a-phase. The rate of hydrogen absorption increases with increasing pressure drop and temperature. It is shown that the rate of hydrogen absorption by the sample of pure IMC is significantly less dependent on temperature compared to the compact sample. In addition, the reaction rate at temperatures of 313 and 333 K is higher for the free backfill sample, and at 353 K it is higher for the metal hydride compact. The values of the absorption constant and the activation energy of the hydrogen absorption reaction are determined for both samples.

Processing of Spark Plasma Sintered Fe Alloy and Enhancing Its Surface Properties by AlCrN Monolayer Coating by Cathodic Arc Plasma Physical Vapor Deposition Process

The current investigation observes the outcome of enhancing the surface properties by AlCrN monolayer coating using the cathodic arc plasma method on the Fe–Cu–C–Mo alloys. The compacts were sintered in spark plasma sintering (SPS) with the heat transfer rate of 100 °C/min at 1120 °C for 5 minutes. The Fe–2Cu–0.8C–0.6Mo sample has the highest relative sintered density (97.20%), hardness (96 HRB), and ultimate tensile strength (1000 MPa) compare with the other sintered compacts. AlCrN coating was deposited on Fe, Fe–2Cu, Fe–2Cu–0.8C, Fe–2Cu–0.8C–0.2Mo, Fe–2Cu–0.8C–0.4Mo, and Fe–2Cu–0.8C–0.6Mo samples, using the cathodic arc plasma–physical vapor deposition (CAP-PVD) process. The coated compact samples’ metallography images were examined using a Scanning Electron Microscope (SEM); the Fe–2Cu alloy sintered sample has obtained a uniform structure with high density and a smaller amount of corrosion penetration rate (0.6579 mmpy) as compared to the counterparts. The phase formed in the AlCrN coating was analyzed using the X-ray Diffraction (XRD). The Fe–2Cu–0.8C–0.6Mo coated compact sample exhibited higher hardness (1134.85 HV0.3) than the other coated compact samples. The Fe–2Cu–0.8C–0.2Mo coated compact sample has proven better corrosion resistance compared to the other coated compact sample.

The shock wave compaction of ceramic powders

Joint theoretical and experimental investigations have allowed to realize an approach with use of mathematical and physical modeling of processes of a shock wave compaction of ceramic powders. The aim of this study was to obtain a durable low-porosity compact sample. The explosive compaction technology is used in this problem because ceramic powders such as boron carbide and aluminum oxide is an extremely hard and refractory material. Therefore, its compaction by traditional methods requires special equipment and considerable expenses. In order to better understand the influence of the loading conditions and, in particular, to study the effect of detonation velocity, explosive thickness and explosion pressure on the properties of the final sample, the problem of compaction of the powder in an axisymmetric case using the conditions of the above experiments have been numerically solved. Thus, using the technology of explosive compaction, compact samples of boron carbide and aluminum oxide are obtained. On the basis of experimental and numerical studies of shock waves propagation, the optimum scheme and parameters of dynamic compaction of boron carbide and aluminum oxide are determined in order to maximize the density and the conservation of the samples after dynamic loading.

Preparation of TiAl15Si15 alloy by High Pressure Spark Plasma Sintering

<p class="AMSmaintext"><span lang="EN-GB">This work deals with preparation of intermetallic alloy TiAl15Si15 (wt. %) by powder metallurgy using Spark Plasma Sintering method. Ti-Al-Si alloys are known as materials with low density, relatively good mechanical properties in comparison with their density and good oxidation and corrosion resistance at elevated temperatures. Preparation of intermetallics by melting metallurgy is very problematic. Powder metallurgy using reactive sintering followed by suitable compaction seems to be a promising method. In this work, TiAl15Si15 alloy was prepared by reactive sintering, milling and by unique ultra-high pressure Spark Plasma Sintering within the framework of international cooperation in Krakow. For the comparison it was also prepared by conventional Spark Plasma Sintering. The results show that higher pressure of sintering decreases the porosity of compact sample and increases mechanical properties, especially hardness.</span></p>

Fabrication and characterization of nanostructured Ba-doped BiFeO3 porous ceramics

Nanostructured barium doped bismuth ferrite, Bi₀.₈Ba₀.₂FeO₃ porous ceramics with a relatively high magnetic coercivity was fabricated via sacrificial pore former method. X-ray diffraction results showed that 20 wt.% Ba doping induces a structural phase transition from rhombohedral to distorted pseudo-cubic structure in the final porous samples. Moreover, utilizing Bi₀.₈Ba₀.₂FeO₃ as the starting powder reduces the destructive interactions between the matrix phase and pore former, leading to an increase in stability of bismuth ferrite phase in the final porous ceramics. Urea-derived Bi₀.₈Ba₀.₂FeO₃ porous ceramic exhibits density of 4.74 g/cm³ and porosity of 45 % owing the uniform distribution of interconnected pores with a mean pore size of 7.5 μm. Well defined nanostructured cell walls with a mean grain size of 90 nm were observed in the above sample, which is in a good accordance with the grain size obtained from BET measurements. Saturation magnetization decreased from 2.31 in the Bi₀.₈Ba₀.₂FeO₃ compact sample to 1.85 A m²/kg in urea-derived Bi₀.₈Ba₀.₂FeO₃ porous sample; moreover, coercivity increased from 284 to 380 kA/m.

Microwave Absorbency Change of Nitride Powders under Vacuum Heating

We measured the microwave and millimeter-wave behaviors of ceramics and metal powders as a basis for developing microwave and millimeter-wave heating technology. In this study, nitride powders were subjected to microwave absorption measurements at elevated temperature. These measurements were performed using a system comprising a vector network analyzer, a circular wave-guide fixture, and a vacuum furnace. The sample’s microwave absorbency was evaluated by the change in reflection power from the sample in the circular wave-guide fixture under vacuum heating. Measurements were performed at approximately 24 GHz and at temperature up to approximately 1100°C. Boron nitride (BN) exhibited almost no absorption of microwaves up to 1100°C, similar to the results of a low-loss oxide powder such as alumina. Dichromium mononitride (Cr2N) powder exhibited a rather high absorption of microwaves at room temperature. During vacuum heating, absorbency of Cr2N started to decrease at 300°C, and became almost zero at temperature greater than 600°C, similar to the behavior of iron powder. This result indicated that roughly packed Cr2N powder absorbs microwave radiation; however, during vacuum heating, the compact body was sintered and the whole sample body became a reflector of microwaves. This change was irreversible, and the sample maintained its reflection behavior upon the cooling. When a mixed powder of Cr2N (20 mass%) and Al2O3 was heated under vacuum, the compact sample exhibited microwave absorption that increased with increasing temperature. This change was reversible upon cooling. These results indicated that the mixed powder did not become reflector of microwaves; Cr2N particles were not electrically connected each other because the Al2O3 particles kept the Cr2N particles separate during the vacuum heating process.

Novel Honeycomb-Microstructured Asphalt Composite Coatings for Sustainable Photocatalytic Application

The microstructure of asphalt materials on photocatalytic performance was studied in this work. Firstly, asphalt composite coatings with highly ordered honeycomb microstructures were fabricated by a bottom-up approach through adjusting the solution concentration and the content of polystyrene (PS) additive. Further incorporation of titanium dioxide (TiO2) nanoparticles endows the porous coatings with photocatalytic functionality. SEM images demonstrate that TiO2nanoparticles disperse and decorate on the pore walls of coating. In comparison to the compact coatings prepared by traditional method, the obtained honeycomb microstructured asphalt/PS/TiO2coatings possess an enhanced and sustainable efficiency of removing NOx. Specifically, when introducing porous microstructures to the coating, the NOxreduction efficiency is 16% higher than that of traditional compact sample and shows no attenuation in continuous use.

Preliminary Observation on Macro Texture of Nb3Sn Low Temperature Superconductor (LTS)

The macro texture of Nb3Sn superconductor was observed in order to identify the tendency of crystallographic orientation of such A15 compound. The Nb3Sn samples were prepared through the powder metallurgy process with the composition of 24at%Sn-76at%Nb. The well-blended Nb-Sn powder was consolidated by means of the uni-axial compression method, while the subsequent sintering was performed at T = 700°C for t = 96 hr. The macro texture of the sintered samples was measured using D8 Advance XRD Goniometer and the corresponding results were analyzed in the form of pole figures. Preliminary results indicate that the crystallographic orientations of Nb3Sn for both green compact and sintered samples show the strong textures in {112}-pole figures. The intensity of Nb3Sn textures decreases from green compact sample to sintered sample, probably due to the mechanism of recovery recrystallisation following the Nb-Sn inter-diffusion process during sintering.