Display omitted
•A core-shell structured Fe2O3/ZrO2@ZrO2 nanomaterial is synthesized by a combination of nanocoating and impregnation methods.•The evolution of iron oxides to metallic iron in ...Fe2O3/ZrO2@ZrO2 is followed by in situ XRD as a function of temperature.•Fe2O3/ZrO2@ZrO2 shows superior redox activity, excellent structural stability and strong capability to resist sintering in CO2 conversion to CO compared to the material without coating.
A novel Fe2O3/ZrO2@ZrO2 nanomaterial with core-shell structure is proposed, where first Fe2O3 nanoparticles are loaded onto a ZrO2 support as a core and afterwards the core is coated with a thin and porous layer of ZrO2. Such combination of nanocoating and impregnation methods has been applied to synthesize core-shell oxygen storage nanomaterials with different iron oxide loading. 2D in-situ XRD patterns recorded during isothermal redox cycles at different temperatures (550–650°C) show the evolution of Fe3O4 to metallic iron in Fe2O3/ZrO2@ZrO2 as a function of temperature. A detailed characterization of fresh and spent samples demonstrates that the Fe2O3/ZrO2@ZrO2 materials exhibit excellent structural stability (stable pore structure, specific surface area and core-shell morphology) and strong capability to resist sintering after 100 redox cycles at 650°C for CO2 conversion to CO compared to the samples prepared by impregnation only. The strong thermal stability of ZrO2 coating materials contributes to keep up the activity of active phase during high-temperature environments.
The 12Cr–3W–0.4Ti–0.25Y2O3 (12YWT) Oxide dispersion strengthened ferritic steel shows a good strength up to 600 °C, while degrades considerably beyond that. In addition, this steel undergoes a week ...ductile to brittle transition temperature. Studies were made to improve of both strength and DBTT. Hence, the mechanically alloyed powders containing different contents of Zr (0.5–1.5%) and Ta (0.05–0.15) were extruded at 850 °C and mechanical properties of these steel nanocomposites were investigated. Mechanical analysis studies indicated that the addition of zirconium element can improve mechanical properties. For example, the presence of 1.5% zirconium in 12YWT resulted in an unprecedented value of 2100 MPa for tensile strength and improved ductile to brittle transition temperature of −27 °C. In contrast of zirconium, increase of tantalum did not change remarkably tensile strength of 12YWT. However, Charpy impact test results presented that tantalum have an important role in improved ductile to brittle transition temperature so that this parameter changed from 13 °C to −44 °C at presence of 0.15% Ta.
•An unprecedented tensile strength of 2100 MPa was obtained by addition of 1.5% Zr.•Zr caused a considerable increase in high temperature strength of ODS steel at 600 °C.•Effect of Ta on tensile strength was not significant.•Effect of Ta to decrease the DBTT of 12YWT was greater compared to Zr.•Addition of 0.15% Ta resulted in a decrease of DBTT from 13 °C down to −44 °C.
This review presents our researches on the preparation and material application of inclusion complexes that comprises an amylose host and polymeric guests through phosphorylase-catalyzed enzymatic ...polymerization. Amylose is a well-known polysaccharide and forms inclusion complexes with various hydrophobic small molecules. Pure amylose is produced by enzymatic polymerization by using α-d-glucose 1-phosphate as a monomer and maltooligosaccharide as a primer catalyzed by phosphorylase. We determined that a propagating chain of amylose during enzymatic polymerization wraps around hydrophobic polymers present in the reaction system to form inclusion complexes. We termed this polymerization "vine-twining polymerization" because it is similar to the way vines of a plant grow around a rod. Hierarchical structured amylosic materials, such as hydrogels and films, were fabricated by inclusion complexation through vine-twining polymerization by using copolymers covalently grafted with hydrophobic guest polymers. The enzymatically produced amyloses induced complexation with the guest polymers in the intermolecular graft copolymers, which acted as cross-linking points to form supramolecular hydrogels. By including a film-formable main-chain in the graft copolymer, a supramolecular film was obtained through hydrogelation. Supramolecular polymeric materials were successfully fabricated through vine-twining polymerization by using primer-guest conjugates. The products of vine-twining polymerization form polymeric continuums of inclusion complexes, where the enzymatically produced amylose chains elongate from the conjugates included in the guest segments of the other conjugates.
Multilayered structure at the macroscale is a prevailing pathway for developing high-performance energy absorbers. Nowadays, most multilayer-structure-based energy absorbers are constructed with ...rigid materials, but research on utilizing soft materials as energy-absorbing devices is still rare. By understanding the function of membranous sheathes in the stimuli responsiveness of fan worms (Polychaeta: Sabellastarte australiensis), in this work, we report a robust biological energy absorber made of multilayer-structured soft material. Our study reveals that structural features govern the mechanical performance and the energy-absorption capacity of this soft energy absorber. Ultimately, through kinematic analysis of fan worms, we elucidate the advantage of soft-material-based energy absorbers in stabilizing assistance compared with rigid counterparts. Our work takes a significant step toward understanding the design principle of soft-material-based energy absorbers and may shed light on flexible protective devices for soft robotics.
Display omitted
•The membrane is solidified by biological mucus combined with substances in seawater•The membrane provides superior mechanical performance•The membrane can simultaneously function as an energy absorber and a stabilizer•An underwater biological anchorage system is proposed
Inspired by a kind of marine worm, Bai et al. demonstrate a multilayer-structured material unique to worms that can simultaneously function as both a robust energy absorber and an efficient stabilizer. This soft material can further extend applications of multilayered materials in limited spaces or unstructured scenarios.
Fine-grained bulk AA2219 material was successfully manufactured by means of milling and hot compression/extrusion of metallic chips. Preliminary milling of the metallic scrap either for 8 or for 30 h ...was found to result in the development of two components of the material structure, i.e. a highly refined matrix and coarse remnants of unmilled chips. The average volume of the highly refined matrix reached 45% and 84% for materials milled for 8 h and 30 h (MA8h and MA30h samples), respectively. Hot compression tests confirmed high strength of preliminarily milled materials attributed to the grain refinement and properly carried out mechanical consolidation methods. An additional solid solution strengthening effect was observed for samples water-quenched after annealing at 808 K/300 min both for preliminarily milled materials and samples made from an industrial material (IM). However, subsequent hot deformation tests did not reveal noticeable hardening of the solution treated MA30h samples due to dynamic precipitation unlike in the case of IM samples. Transmission electron microscopy analyses may lead to the conclusion that the aging of solution treated MA material result in the growth of θ-type stable particles in heavily-refined areas without the preceding precipitation of metastable θ′ particles. Therefore, precipitation hardening of the tested MA-materials becomes inhibited with increased milling time.
•High strength AA2219 material was manufactured from milled metallic chips.•Structure containing highly refined matrix and chip residue was observed.•Dynamic precipitation hardening of the material milled for 30 h was retarded.•Metastable θ′-particles were not detected in heavily-refined material structure.•Direct growth of θ-particles in heavily-refined material inhibits hardening.
A novel nanosheet-structured material, namely graphene oxide anchored with sulfonic acid-functionalized glycerin (GO@Gl-SO
3
H), was prepared and characterized by FTIR, EDS, FESEM, TEM and XRD ...analyses. Afterward, its catalytic performance was examined for the synthesis of
N
,
N
′-alkylidene bisamides through the reaction of benzamide (2 eq.) and arylaldehydes (1 eq.) under solvent-free conditions. GO@Gl-SO
3
H was a highly effective catalyst for the reaction and afforded the products in high yields and short reaction times.
Graphic abstract
•The flow start-up depend on the material time response and compressibility.•Two time scales are important on gel break: shearing and material response time.•The required time for the flow start ...depends on the inlet pressure.•The maximum pressure reached in the restart is a function of the imposed flow rate.
The current work presents a mathematical model to simulate the flow start-up of gelled oils in pipelines. The model comprises the conservation equations of mass and momentum and an elasto-viscoplastic constitutive equation to account for thixotropy of the material. The flow is considered one-dimensional, laminar and compressible and the cross-section shear stress is admitted to vary linearly so that the constitutive equation can be integrated along the pipe radius. The balance equations are solved by the method of characteristics, the constitutive equation by the finite difference method and finally they are altogether integrated iteratively. Two kinds of boundary conditions are investigated: a constant inlet pressure and a constant inlet flow rate. Two time-scales are identified in the current study: the pressure wave propagation time and the material response time. It can be anticipated that the ratio of this two times are quite important on the restart time in case of a constant pressure boundary condition and on the magnitude of the maximum pressure for a constant flow rate boundary condition.
The strength of a rectangular plate with two opening-mode (mode I) edge cracks was studied using the Neuber–Novozhilov approach and a modified Leonov–Panasyuk–Dugdale model with a nonzero prefracture ...zone. A coupled discrete-integral fracture criterion is used since the stress field in the vicinity of the crack tip has a singularity. The ultimate strain fracture criterion is satisfied at the real crack tip, and the normal stress criterion is satisfied at the model crack tip. The constitutive equations of the analytical model are analyzed. Simple formulas for the fracture load are derived for quasi-brittle and quasi-ductile fracture. Plate fracture curves are plotted for a plane stressed state.
Here, we present a 3D printed prism for THz waves made out of an artificial dielectric material in which the dispersion can be tuned by external compression. The artificial material consists of thin ...dielectric layers with variable air spacings which has been produced using a fused deposition molding process. The material properties are carefully characterized and the functionality of the prisms is in a good agreement with the underlying theory. These prisms are durable, lightweight, inexpensive, and easy to produce.
In this paper, a numerical method is proposed to simulate the mechanical behavior of a new polymeric pre-structured material manufactured by fused filament fabrication (FFF), where the filaments are ...oriented along the principal stress directions. The model implements optimized filament orientations, obtained from the G code by assigning materials references in mesh elements. The Gauss points are later configured with the physical behavior while considering a homogeneous solid structure. The objective of this study is to identify the elastoplastic behavior. Therefore, tensile tests were conducted with different filament orientations. The results show that using appropriate material constants is efficient in describing the built anisotropy and incorporating the air gap volume fraction. The suggested method is proved very efficient in implementing multiplex G code orientations. The elastic behavior of the pre-structured material is quasi-isotropic. However, the anisotropy was observed at the yield point and the ultimate stress. Using the Hill criterion coupled with an experimental tabular law of the plastic flow turns out to be suitable for predicting the response of various specimens.
PDF
