High Temperature Oxidation Behavior of Creep Resistant Steels in Water Vapour Containing Environments

This study describes the water vapour effect on the oxidation resistance of 9Cr creep resistant steels. Boiler P91 and MarBN steels were oxidized for 3000 h in a simulated humid atmosphere with ~10% water vapour. The oxidation kinetics had a stable course for 1000 h and was evaluated by the weight gain curves for both experimental steels and both oxidation temperatures. The oxidation rate was higher at 650 °C versus 600 °C, as reflected by the oxidation rate coefficient. A significant increase occurred after 1000 h of oxidation, which was related to the local breakdown oxide scale and oxide nodules were formed on steel. This oxidation behavior was influenced by the fact that a compact spinel structure of iron oxides and alloying elements were not formed on the steel. Analysis after 3000 h of exposure showed hematite Fe2O3 formed on the outer layer, magnetite Fe3O4 on the middle layer, and the bottom layer consisted of iron-chromium-spinel (Fe,Cr)2O3.

Steering the current flow in twisted bilayer graphene

A nanoelectronic device made of twisted bilayer graphene (TBLG) is proposed to steer the direction of the current flow. The ballistic electron current, injected at one edge of the bottom layer, can be guided predominantly to one of the lateral edges of the top layer. The current is steered to the opposite lateral edge, if either the twist angle is reversed or the electrons are injected in the valence band instead of the conduction band, making it possible to control the current flow by electric gates. When both graphene layers are aligned, the current passes straight through the system without changing its initial direction. The observed steering angle exceeds well the twist angle and emerges for a broad range of experimentally accessible parameters. It is explained by the twist angle and the trigonal shape of the energy bands beyond the van Hove singularity due to the Moiré interference pattern. As the shape of the energy bands depends on the valley degree of freedom, the steered current is valley polarized. Our findings show how to control and manipulate the current flow in TBLG. Technologically, they are of relevance for applications in twistronics and valleytronics.

Prediction of B20 Storage Tank Precipitate Removal Based on Biodiesel Monoglyceride Content

Precipitate in B20 fuel stored in storage tanks can accumulate at the bottom level of the tank and affect the fuel filter, clogging in the fuel distribution and engine system. This study examines the precipitate formation prediction in B20 fuel based on the monoglyceride content in biodiesel. This research used a modified CSFT method of ASTM D7501 for the precipitation test. Monopalmitin was added to biodiesel with a variation of monoglyceride content. Each biodiesel sample was then blended with petroleum diesel fuel to produce two groups of samples. Each sample was separately soaked in the cooling chamber at constant and room temperature for 21 days. The bottom layer of each B20 fuel sample stored in the measuring cylinder was then pipetted and filtered, washed with petro-ether, vacuum-dried, and weighed for a constant amount of precipitate retained on the filter. The simulation results show that the ratios between the amount of collected precipitate at the bottom layer of the 2-liter measuring cylinder and the total amount of collected precipitate for the 2-liter measuring cylinder increased with the monoglyceride content biodiesel. This ratio was used to predict the amount of accumulated sludge for a given volume of B20 fuel loaded into the storage tank. This study shows the effect of monoglyceride content on the precipitation behaviour in the storage tank concerning general tank storage dimension parameters and B20 loading frequency. This approach can be applied to estimate the sludge removal frequency for biodiesel storage.

Development and Evaluation of a Dual-Layer-Offset PET Detector Constructed with Different Reflectors

Dual-layer-offset or multi-layer-offset design of a PET detector can improve spatial resolution while maintaining high sensitivity. In this study, three dual-layer-offset LYSO detectors with three different reflectors (ESR, Toray, and BaSO4) were developed. The top layer consisted of a 17 × 17 array of crystals 1 × 1 × 6.5 mm3 in size and the bottom layer consisted of an 18 × 18 array of crystals 1 × 1 × 9.5 mm3 in size. Neither light guides nor optical glue were used between the two layers of crystals. A custom-designed electronics system, composed of a 6 × 6 SiPM array, two FPC cables, and a custom-designed data processing module, was used to read out signals. An optimized interaction-decoding algorithm using the center of gravity to determine the position and threshold of analog signals for timing methods was applied to generate decoding flood histograms. The detector performances, in terms of peak to valley ratio of the flood histograms and energy resolutions, were calculated and compared. The dual-layer-offset PET detector constructed with BaSO4 reflectors performed much better than the other two reflectors in both crystal identification and energy resolution. The average peak-to-valley ratio and the energy resolution were approximately 7 and 11%, respectively. In addition, the crystals in the bottom layer showed better performance at crystal identification than those in the top layer. This study can act as a reference providing guidance in choosing scintillator reflectors for multi-layer dedicated DOI detectors designed for small-animal PET imaging.

Effect of a Rubidium Chloride Carrier Confinement Layer on the Characteristics of CsPbBr3 Perovskite Light-Emitting Diodes

This work describes the effect of a rubidium chloride (RbCl) interlayer in CsPbBr3 perovskite light-emitting diode (LED) structures. RbCl crystallites exhibited polyhedral structures and lattice parameters similar to those of CsPbBr3 perovskite crystallites. The lattice mismatch between the RbCl interlayer and CsPbBr3 active layer was only approximately 2%. The devices exhibited the best quality and performance when RbCl was used as the nucleation and carrier confinement layer. The crystallite sizes of CsPbBr3 with 0.2-, 0.5-, and 1-nm-thick RbCl bottom layers were 55.1, 65.4, and 55.1 nm, respectively. The full width at half maximum (FWHM) of the photoluminescence (PL) emission peak for CsPbBr3 with the RbCl bottom layer was 0.096 eV.

Feasibility study: Resin-based functionally graded material incorporated with carbonized waste rice husk

Feasibility study was conducted in exploring the fabrication and characterization of resin-based functionally graded material (FGM) incorporated with carbonized waste rice husk. The waste rice husks were converted into carbon materials through heat treatment under the presence of inert gas at 500°C for 2 hours. Then, they were incorporated into resin to form FGM by centrifugal method to achieve desired gradation. Sample B3 with 5 wt.% of carbonized rice husk (CRH) incorporated into polyester resin (including hardener and ethanol) was centrifugated at 4000 rpm for 30 minutes to form FGM. The fabricated samples were cut into three parts, namely upper, middle, and bottom layer to further characterize the properties at various gradation levels. The density of sample B3 increased gradually, 4.10%, 6.54%, and 6.93% when compared to bulk resin, from upper to bottom layer, respectively. The hardness of sample B3 increased gradually, 27.38%, 42.57%, and 47.08% in contrast to bulk resin, from upper to bottom layer, respectively. FGM proposed in this study can be further manipulated based on the centrifugal force and time, ratio of solvents/hardener, and weight percentage of CRH that indicate they can be exploited for specific of numerous appropriate applications.

Thin Concrete Overlays with Carbon Reinforcement

In many countries like Germany, concrete pavements are normally built as Jointed Plain Concrete Pavements (JPCP). Due to a lack of alternatives, maintenance of concrete pavements usually requires a replacement of the whole pavement structure, which is labour- and resource-intensive. Therefore, new techniques like the application of thin concrete overlays as a partial repair of deteriorated concrete pavements have been developed. As a major disadvantage of such overlays, the existing joints in the retained concrete bottom-layer have to be transferred in the overlay in order to avoid reflection cracking. When using non-corrosive carbon-textile reinforcement in such concrete overlays, cracks might be distributed more finely, enabling jointless repairs while keeping a thin repair layer. In addition, the bond behaviour between the retained concrete and the applied concrete overlay as well as between the concrete overlay and the textile reinforcement is crucial for a successful repair. In this paper, the basic principles and feasibility of such a repair method are examined. On the one hand, the decisive influencing variables and parameters such as bond behaviour between the concrete layers and the cracking behaviour of the overlay are pointed out and discussed. On the other hand, the evaluated laboratory tests carried out are presented. These include large-scale beams built with an overlay on top of a retained concrete layer, which were subjected to cyclic flexural stress and to a subsequent detailed investigation of the bond behaviour and durability. Furthermore, the crack formation in the overlay was determined by means of tensile and flexural tensile strength tests.

Asymmetric Interfaces in Epitaxial Off-Stoichiometric Fe3+xSi1−x/Ge/Fe3+xSi1−x Hybrid Structures: Effect on Magnetic and Electric Transport Properties

Three-layer iron-rich Fe3+xSi1−x/Ge/Fe3+xSi1−x (0.2 < x < 0.64) heterostructures on a Si(111) surface with Ge thicknesses of 4 nm and 7 nm were grown by molecular beam epitaxy. Systematic studies of the structural and morphological properties of the synthesized samples have shown that an increase in the Ge thickness causes a prolonged atomic diffusion through the interfaces, which significantly increases the lattice misfits in the Ge/Fe3+xSi1−x heterosystem due to the incorporation of Ge atoms into the Fe3+xSi1−x bottom layer. The resultant lowering of the total free energy caused by the development of the surface roughness results in a transition from an epitaxial to a polycrystalline growth of the upper Fe3+xSi1−x. The average lattice distortion and residual stress of the upper Fe3+xSi1−x were determined by electron diffraction and theoretical calculations to be equivalent to 0.2 GPa for the upper epitaxial layer with a volume misfit of −0.63% compared with a undistorted counterpart. The volume misfit follows the resultant interatomic misfit of |0.42|% with the bottom Ge layer, independently determined by atomic force microscopy. The variation in structural order and morphology significantly changes the magnetic properties of the upper Fe3+xSi1−x layer and leads to a subtle effect on the transport properties of the Ge layer. Both hysteresis loops and FMR spectra differ for the structures with 4 nm and 7 nm Ge layers. The FMR spectra exhibit two distinct absorption lines corresponding to two layers of ferromagnetic Fe3+xSi1−x films. At the same time, a third FMR line appears in the sample with the thicker Ge. The angular dependences of the resonance field of the FMR spectra measured in the plane of the film have a pronounced easy-axis type anisotropy, as well as an anisotropy corresponding to the cubic crystal symmetry of Fe3+xSi1−x, which implies the epitaxial orientation relationship of Fe3+xSi1−x (111)[0−11] || Ge(111)[1−10] || Fe3+xSi1−x (111)[0−11] || Si(111)[1−10]. Calculated from ferromagnetic resonance (FMR) data saturation magnetization exceeds 1000 kA/m. The temperature dependence of the electrical resistivity of a Ge layer with thicknesses of 4 nm and 7 nm is of semiconducting type, which is, however, determined by different transport mechanisms.

Morphology and Performance Characterizations of 316 Stainless Steel Additively Fabricated by Laser Thermal-Joule Heating Composite Process

The Laser Thermal-Joule Heating Composite Process was studied by orthogonal tests based on an analysis of fabrication parameters such as the laser power, wire feeding speed, and electric current. Temperature profiles and the geometric morphology of deposited layers under different process parameters were analyzed, and the overlaps between the layers and the substrate were observed. Results show that when the temperature at the bottom layer of the additive manufacturing is higher than the melting point of the substrate, and the highest temperature at the top layer does not exceed the over-firing temperature, good morphology and close bonding with the substrate can be obtained. Finally, appropriate process parameters were identified and verified to print multiple layers continuously.