Orientation Dependence of the Micro-Pillar Compression Strength in an Electron Beam Melted Ti–6Al–4V Alloy

An α/β two-phase Ti-6 Al-4 V alloy was fabricated by electron beam melting to obtain a basketweave structure.The orientation dependence of the mechanical properties of Ti-6 Al-4 V alloy was studied by micro-pillar compression and post-mortem transmission electron microscopy analysis.The results indicate that different grains have different mechanical responses,and the possible attributions were discussed.Besides the orientation effect,due to the limited volumes of micropillars,the size of the a phases,dispersion of the β phases,and the presence of the free dislocation path also affect the mechanical properties of the micropillars to a large extent.Although no direct link was discovered between the mechanical properties and the parent βorientations,this work provided a promising method to further study the anisotropic mechanical behavior in Ti-6 Al-4 V alloy.     

Compressively sampled light field reconstruction using orthogonal frequency selection and refinement

This paper considers the compressive sensing framework as a way of overcoming the spatio-angular trade-off inherent to light field acquisition devices. We present a novel method to reconstruct a full 4D light field from a sparse set of data samples or measurements. The approach relies on the assumption that sparse models in the 4D Fourier domain can efficiently represent light fields. The proposed algorithm reconstructs light fields by selecting the frequencies of the Fourier basis functions that best approximate the available samples in 4D hyper-blocks. The performance of the reconstruction algorithm is further improved by enforcing orthogonality of the approximation residue at each iteration, i.e. for each selected basis function. Since sparsity is better preserved in the continuous Fourier domain, we propose to refine the selected frequencies by searching for neighboring non-integer frequency values. Experiments show that the proposed algorithm yields performance improvements of more than 1 dB compared to state-of-the-art compressive light field reconstruction methods. The frequency refinement step also significantly enhances the visual quality of reconstruction results of our method by a 1.8 dB average.     

Ethylthio-substituted sandwich phthalocyaninato europium (III) semiconductors for sensing NO2 and NH3: Effect of the extended π-conjugate systems on tuning the conductivity and sensing behavior

By using the π-conjugated phthalocyanine macrocycle as the versatile building block, a series of five sandwich-type ethylthio substituted phthalocyaninato europium complexes, namely double-decker Eu[Pc(SC₂H₅)₈]₂ (Pc-1), triple-decker Eu₂[Pc(SC₂H₅)₈]₃ (Pc-2), and their corresponding dimers, [Pc(SC₂H₅)₈]₂Eu₂[BiPc(SC₂H₅)₁₂] (Pc-1@Pc-1), [Pc(SC₂H₅)₈]₃Eu₃[BiPc(SC₂H₅)₁₂] (Pc-1@Pc-2) and [Pc(SC₂H₅)₈]₄Eu₄[BiPc(SC₂H₅)₁₂] (Pc-2@Pc-2), are synthesized and prepared into the solution-processed films by a simple quasi-Langmuir-Shäfer (QLS) method. Combination between the extending π-conjugated system in the longitudinal and transverse directions of Pc macrocycles and/or radical nature of Pc-1 unit among different semiconducting molecules result in unusually small energy gaps (0.345–0.91 eV). Consequently, all of the semiconductors exhibit excellent conductivities. Among these materials, the conductivity for the radical species Pc-1@Pc-1, Pc-1@Pc-2 and Pc-1 is about 3–4 times larger than that for the non-radical compounds Pc-2@Pc-2 and Pc-2. Moreover, the QLS films of five semiconductors take excellent linear responses for both oxidizing NO₂ (100–300 ppb) and reducing NH₃ (4–8.6 ppm). Respectively, the sensitivity (in % ppm⁻¹) gets increased in the order of Pc-1 < Pc-2 < Pc-1@Pc-1 < Pc-1@Pc-2 < Pc-2@Pc-2 for NO₂, and Pc-1@Pc-2 < Pc-1 < Pc-1@Pc-1 < Pc-2@Pc-2 < Pc-2 for NH₃. Depending on the highly extended π-conjugated systems, Pc-2@Pc-2 and Pc-2 films achieve the highest sensitivity of 208.2% ppm⁻¹ and 0.97% ppm⁻¹ to NO₂ and NH₃, respectively. In addition, with a less than 2 min response time within a limit of detection at 10 ppb for NO₂ and 0.48 ppm for NH₃, good reproducibility and selectivity have been revealed for the Pc-2@Pc-2 and Pc-2 films among the best gas sensors obtained so far for all the solution-processed films based on organic semiconductors in dry air at room temperature. More importantly, it is firstly demonstrated that the high NO₂ sensing is resulted from low Oxd₁, and high NH₃ sensing is resulted from high Red₁ among the sandwich Pc-based semiconductors.     

HYDRIDE4MOBILITY: An EU HORIZON 2020 project on hydrogen powered fuel cell utility vehicles using metal hydrides in hydrogen storage and refuelling systems

The goal of the EU Horizon 2020 RISE project 778307 “Hydrogen fuelled utility vehicles and their support systems utilising metal hydrides” (HYDRIDE4MOBILITY), is in addressing critical issues towards a commercial implementation of hydrogen powered forklifts using metal hydride (MH) based hydrogen storage and PEM fuel cells, together with the systems for their refuelling at industrial customers facilities. For these applications, high specific weight of the metallic hydrides has an added value, as it allows counterbalancing of a vehicle with no extra cost. Improving the rates of H₂ charge/discharge in MH on the materials and system level, simplification of the design and reducing the system cost, together with improvement of the efficiency of system “MH store-FC”, is in the focus of this work as a joint effort of consortium uniting academic teams and industrial partners from two EU and associated countries Member States (Norway, Germany, Croatia), and two partner countries (South Africa and Indonesia).The work within the project is focused on the validation of various efficient and cost-competitive solutions including (i) advanced MH materials for hydrogen storage and compression, (ii) advanced MH containers characterised by improved charge-discharge dynamic performance and ability to be mass produced, (iii) integrated hydrogen storage and compression/refuelling systems which are developed and tested together with PEM fuel cells during the collaborative efforts of the consortium.This article gives an overview of HYDRIDE4MOBILITY project focused on the results generated during its first phase (2017–2019).     

Application of intensive hydrodynamic cavitation in liquids for synthesis of hydrogen and nanoparticles

In this paper, the results of experimental studies of hydrogen and nanoparticles production using intensive hydrodynamic cavitation in liquids are presented. Physicochemical processes occurring in a cavitation bubble at the last stage of its compression are very similar to processes occurring in the explosion chamber.The values of pressure and temperature achieved in this case ensure the thermodynamic stability of the reaction products and the production of a gaseous hydrogen and nanoclusters as a result of decomposition of molecules of liquid, which is confirmed by theoretical calculations.The controlled addition of hydrogen-containing liquids and the change in the compression conditions of cavitation bubbles make it possible to control the process of hydrogen synthesis, which is an important step in the development of modern high-tech alternative energy methods.The pulsation of a spherical cavity is described by the Kirkwood – Bethe equations, which are one of the most accurate mathematical models of pulsation processes at an arbitrary velocity of the cavity boundary. The model allows to describe the process of pulsations of cavitation cavities, conduct comprehensive parametric studies and evaluate the effect of various process parameters on the collapse of cavities.This work continues with the experiments on cavitation synthesis of carbon nanostructures. With the rapid movement of chemically pure hydrocarbons along the profiled channel in the form of a Venturi nozzle, cavitation bubbles form in the liquid, which are then compressed in the working chamber, in which a sharp pressure surge is created. The pressure in the shock wave, which reaches 80–90 MPa, ensures the collapse of cavitation bubbles close to adiabatic compression. As a result of the number of rapidly occurring physicochemical processes of evaporation, heating, and thermal dissociation of hydrocarbon vapors, a solid carbon phase including graphene oxide nanoparticles and a gaseous hydrogen-containing phase are synthesized in the cavitation, which is then subjected to separation. Synthesized graphene oxide nanoparticles possess activated surface due to the cavitation action and can be subsequently used as substrates for modification with functional nanoparticles, e.g. silver nanoparticles with antibacterial properties.The article is of great help to scientists and design engineers who are engaged in the development of promising hydrogen generating facilities and hydrogen complexes.     

Formation mechanism of maze-like open macropores in Mn3O4 microspheres by heating in water vapor and their single-particle compressive behavior

Thermal decomposition of inorganic salts, such as carbonates, oxalates, and nitrates, is a facile method for synthesizing porous oxides; however, it typically produces either micropores or mesopores with sizes below 50 nm. Macropores larger than 50 nm can capture fine particles from a liquid or gas flow and thus be employed not only for environmental purification but also for the preparation of functional composites. In this study, we investigate the role of water vapor in the formation of macroporous Mn₃O₄ by the thermal decomposition of MnCO₃. It is found that water vapor accelerates the decomposition of MnCO₃ and subsequent particle growth as well as the conversion of manganese oxides at lower temperatures than in air. As a result, maze-like open macropores are formed by the randomly growing primary particle walls. Single-particle compressive tests reveal that small microspheres with sizes of 3 µm are easily deformed to relieve compressive stress. The macropore formation through the thermal decomposition of MnCO₃ in water vapor and microstructural tuning of the pore size, particle size ratio, and degree of curvature of interior walls can potentially expand the application range of porous oxide materials.     

Mechanical properties of Al2O3 and Al2O3/Al with Gyroid structure obtained by stereolithographic additive manufacturing and melt infiltration

To obtain both plasticity and toughness of the material at the same time, various manufacturing techniques of ceramic-metal composites and structures have been studied. In this work, a bio-inspired Al₂O₃ ceramic scaffold with Gyroid structure was designed and prepared by stereolithographic (SL) additive manufacturing, then the Al₂O₃/Al ceramic-metal hybrid structure was prepared by infiltrating molten Al into the Al₂O₃ ceramic structure. The performances of the Al₂O₃ ceramic scaffold and the Al₂O₃/Al ceramic-metal hybrid structure were compared and analyzed by a quasi-static compression experiment. The quasi-static compressive strength of the pristine Al₂O₃ scaffold was 14.36 MPa, while that of the Al₂O₃/Al ceramic-metal hybrid structure was up to 89.06 MPa. Moreover, the plasticity of the Al₂O₃/Al ceramic-metal hybrid structure was much higher than that of the Al₂O₃ scaffold. During compression, the Al₂O₃/Al ceramic-metal hybrid structure had excellent energy absorption, reaching up to 2569.16 KJ/m³, 15 times that of the Al₂O₃ scaffold. Therefore, this method can obtain materials with excellent ductility and toughness.     

Additive manufacturing,quasi-static and dynamic compressive behaviours of ceramic lattice structures

Ceramic lattice structures (CLSs) are used for construction in common and extreme environments because of the extraordinary properties of ceramics. In this study, we designed and additively manufactured CLSs with distinct structural parameters to explore their quasi-static and dynamic compressive behaviours in detail. It was demonstrated that both the relative density (?ρ) and inclination angle (ω) had a significant impact on the quasi-static and dynamic mechanical properties of the CLSs. Furthermore, the mathematical relationships between the quasi-static compressive properties, including quasi-static compressive strength (QS), quasi-static Young’s modulus (QY), and quasi-static energy absorption (QE), versus ?ρ and ω obeyed the Gibson–Ashby and Deshpande and Fleck models, respectively. It was revealed by experiment and simulation that as the stiffness increased, the quasi-static failure mode of the CLSs changed from a parallel-vertical-inclined mixed mode to a parallel-vertical mode. In addition, the relationship between the dynamic mechanical properties of the CLSs versus ?ρ and ω also followed the Gibson–Ashby and Deshpande and Fleck models. The exceptional dynamic increase factor indicated that CLSs are highly suitable for extreme environments. These findings will aid in the research and development of customised additively manufactured CLSs.     

Surface and interface properties of monolayer graphene on hydrophobic and hydrophilic ultrananocrystalline diamond structures for hydrogen sensing applications

Here, for the first time, we synthesize hybrid hydrophilic and hydrophobic nanocarbon materials with reliable and stable gas sensing performance. The hybrid monolayer graphene (Gr)–nitrogen and argon (N₂ and Ar) gas incorporated ultra-nanocrystalline diamond (Gr/N₂@UNCD and Gr/Ar@UNCD) structures were synthesized using a microwave plasma enhanced chemical vapor deposition (MPECVD) method. The presented nanohybrid combinations have a unique morphology with diamond defects (sp³) covered by a graphene sheet (sp²). Sample sensors with metal electrodes were fabricated to study the H₂ gas sensing properties of the material. Thus, the as-fabricated Gr/N₂@UNCD exhibited higher sensor response (14.6%) than those of the as-fabricated Gr, N-UNCD and Gr/Ar@UNCD (3.6, 1.07 and 11.2%) based devices. The Gr/N₂@UNCD nanohybrid based sensor showed outstanding repeatability, selectivity and stability over ～56 days. The substantial improvement in the H₂ sensing performance of the as-fabricated Gr/N₂@UNCD nanohybrid based sensor was attributed to the modifications in surface morphology and resistance. The partial-hydrophobic surface of Gr/N₂@UNCD alters the beneficial resistivity and improved absorption, which assists in the efficient transport of electrons and H₂ gas molecules. The hybrid nanostructure of Gr-N₂@UNCD exhibits several unique properties that paves the way to future opportunities for advanced gas sensor fabrication.