Dense Bulk Material Research Articles

Rapid low-temperature densification of Ag2Se bulk material: mass transfer through the dissociative adsorption reaction of Ag protrusions and Se saturated vapor

In materials science, the impact of density on a material’s capabilities is profound. Conventional sintering requires high temperatures and is energy-demanding, propelling the pursuit of less intensive, low-temperature densification methods. Electric field-assisted sintering has recently gained attention for its simplicity and effectiveness, offering a new frontier in low-temperature densification. In this study, dense bulk materials were produced by subjecting monophasic Ag2Se powders to electric field-assisted sintering, where a direct current with an average value of 4 A was applied, achieving a peak temperature of 344 K. The novel low-temperature densification mechanism unfolds thus: nanoscale silver protrusions, stimulated by electrical current, engage in a dissociative adsorption reaction with the ambient saturated selenium vapor. This process swiftly engenders the formation of fresh silver selenide (Ag2Se) compounds, initiating nucleation and subsequent growth. Consecutively, these compounds seamlessly occupy and expand, perpetually bridging the interstices amidst the powders. In a scant 8 s, the density swiftly surpassed 99%, yielding a bulk material that exhibited a ZT value of 1.07 at 390 K. This investigation not only attains an unparalleled density at low temperatures but also charts a pioneering course for material densification in such conditions.

Near-room-temperature water-mediated densification of bulk van der Waals materials from their nanosheets.

The conventional fabrication of bulk van der Waals (vdW) materials requires a temperature above 1,000 °C to sinter from the corresponding particulates. Here we report the near-room-temperature densification (for example, ∼45 °C for 10 min) of two-dimensional nanosheets to form strong bulk materials with a porosity of <0.1%, which are mechanically stronger than the conventionally made ones. The mechanistic study shows that the water-mediated activation of van der Waals interactions accounts for the strong and dense bulk materials. Initially, water adsorbed on two-dimensional nanosheets lubricates and promotes alignment. The subsequent extrusion closes the gaps between the aligned nanosheets and densifies them into strong bulk materials. Water extrusion also generates stresses that increase with moulding temperature, and too high a temperature causes intersheet misalignment; therefore, a near-room-temperature moulding process is favoured. This technique provides an energy-efficient alternative to design a wide range of dense bulk van der Waals materials with tailored compositions and properties.

Synthesis of ultra-high-temperature nitride amorphous bulk by reaction of halide precursors with sodium in liquid ammonia

Amorphous Si-B-N nanoparticles of uniform composition tunable over the entire range spanning pure Si3N4 to pure BN was synthesized through a simple homogeneous chemical reaction of the mixture of SiCl4 and BBr3 with Na in liquid ammonia. With these amorphous nanopowders, dense amorphous bulk material was obtained with SPS sintering at the temperature before the crystallization. The dense amorphous bulk of Si3B3N7 exhibited the highest value of hardness (8.8 GPa), flexural strength s (545 MPa), and fracture toughness KIC (10.6 MPa m1/2). These are significantly higher than those reported for other crystalline ceramics of the same composition and surpass those of the completely dense crystalline ceramics. The fully-dense amorphous bulk material exhibited excellent resistance to oxidation up to 1550 °C.

Scalable Manufacturing of Environmentally Stable All-Solid-State Plant Protein-Based Supercapacitors with Optimal Balance of Capacitive Performance and Mechanically Robust.

The development of advanced biomaterial with mechanically robust and high energy density is critical for flexible electronics, such as batteries and supercapacitors. Plant proteins are ideal candidates for making flexible electronics due to their renewable and eco-friendly natures. However, due to the weak intermolecular interactions and abundant hydrophilic groups of protein chains, the mechanical properties of protein-based materials, especially in bulk materials, are largely constrained, which hinders their performance in practical applications. Here, a green and scalable method is shown for the fabrication of advanced film biomaterials with high mechanical strength (36.3MPa), toughness (21.25MJm-3 ), and extraordinary fatigue-resistance (213000 times) by incorporating tailor-made core-double-shell structured nanoparticles. Subsequently, the film biomaterials combine to construct an ordered, dense bulk material by stacking-up and hot-pressing techniques. Surprisingly, the solid-state supercapacitor based on compacted bulk material shows an ultrahigh energy density of 25.8Whkg-1 , which is much higher than those previously reported advanced materials. Notably, the bulk material also demonstrates long-term cycling stability, which can be maintained under ambient condition or immersed in H2 SO4 electrolyte for more than 120 days. Thus, this research improves the competitiveness of protein-based materials for real-world applications such as flexible electronics and solid-state supercapacitors.

Ultrastrong, Thermally Stable, and Food-SafeSeaweed-Based Structural Material for Tableware.

Widely used disposable plastic tableware is usually buried or directly discharged into the natural environment after using, which poses potential threats to the natural environment and human health. To solve this problem, nondegradable plastic tableware needs to be replaced by tableware composed of biodegradable structural materials with both food safety and the excellent mechanical and thermal properties. Here, a food-safe sargassum cellulose nanofiber (SCNF) is extracted from common seaweed in an efficient and low energy consuming way under mild reaction conditions. Then, by assembling the SCNF into a dense bulk material, a strong sargassum cellulose nanofiber structural material (SCNSM) with high strength (283MPa) and high thermal stability (>160°C) can be prepared. The SCNSM also possesses good machinability, which can be processed into tableware with different shapes, e.g., knives and forks. The overall performance of the SCNSM-based tableware is better than commercial plastic, wood-based, and poly(lactic acid) tableware, which shows great application potential in the tableware field.

Structured illumination with thermal imaging (SI-TI): A dynamically reconfigurable metrology for parallelized thermal transport characterization

The recent push for the “materials by design” paradigm requires synergistic integration of scalable computation, synthesis, and characterization. Among these, techniques for efficient measurement of thermal transport can be a bottleneck limiting the experimental database size, especially for diverse materials with a range of roughness, porosity, and anisotropy. Traditional contact thermal measurements have challenges with throughput and the lack of spatially resolvable property mapping, while non-contact pump-probe laser methods generally need mirror smooth sample surfaces and also require serial raster scanning to achieve property mapping. Here, we present structured illumination with thermal imaging (SI-TI), a new thermal characterization tool based on parallelized all-optical heating and thermometry. Experiments on representative dense and porous bulk materials as well as a 3D printed thermoelectric thick film (∼50 μm) demonstrate that SI-TI (1) enables paralleled measurement of multiple regions and samples without raster scanning; (2) can dynamically adjust the heating pattern purely in software, to optimize the measurement sensitivity in different directions for anisotropic materials; and (3) can tolerate rough (∼3 μm) and scratched sample surfaces. This work highlights a new avenue in adaptivity and throughput for thermal characterization of diverse materials.

Visualization of Macrophase Separation and Transformation in Immiscible Polymer Blends

Visualization of Macrophase Separation and Transformation in Immiscible Polymer Blends

Numerical Simulation of Resistance Sintering of Titanium by a Porous Continuum Approach

AbstractThis paper presents a numerical model for the simulation of resistance sintering. It involves an electro-thermo-mechanical coupling, where each model is simulated as a continuum with the influence of porosities included through the distribution of relative density, i.e., the ratio of the apparent density to that of the corresponding fully dense bulk material. For the mechanical response, this involves a plasticity model based on a porous formulation. Other material data have to be supplied as a function of relative density and temperature, as, for example, the electrical resistivity. The numerical modeling is compared to experimentally resistance sintered titanium with good agreement in terms of pre-compaction and developed relative density and temperature during the sintering process.

Consolidated Co- and Fe-based Fischer-Tropsch catalysts supported on jellyfish-like graphene nanoflake framework

Different carbon nanomaterials are considered as promising supports for Fischer-Tropsch synthesis (FTS) catalysts of syngas transformation into hydrocarbons. At the same time, consolidation of carbon nanoparticles into a dense bulk material is one of the most important challenges faced by the catalytic industry. In this work consolidated Co and Fe catalysts supported on graphene nanoflakes (GNFs) were for the first time synthesized by spark plasma sintering (SPS). The synthesized catalysts contained reduced carbon-encapsulated metal nanoparticles embedded into the GNF framework, which ensured their activity in FTS without pre-activation. SPS significantly increased both the activity (from 77 to 91 µmolCO×gCo−1 ×s−1) and TOF (from 0.024 to 0.073 s−1) of the Co/GNF catalyst compared to the unsintered sample. In contrast, the activity of the Fe catalysts decreased after SPS, but their C5+ selectivity and olefins to paraffins ratio increased. These enhancements were attributed to the unique core-shell structure of the nanoparticles, highly active surface cobalt atoms, and close contact between carbon support and iron particles. SPS was proved to be a powerful approach to activate carbon-supported FTS catalysts, increase their density and modify their catalytic performance.

Strategy to Elucidate the Reaction Mechanism of Electrodes for Realistic Solid Oxide Electrochemical Cells Using a Dense Bulk Material

Tremendous research has focused on dense thin films to elucidate the reaction mechanism of perovskite-based electrodes in solid oxide electrochemical cells (SOCs). However, thin film studies may not reflect the mechanisms of commercialized electrodes fabricated with bulk materials. Herein, an unprecedented strategy for elucidating the electrode reaction is introduced via a La0.6Sr0.4Co0.2Fe0.8O3−δ dense bulk electrode fabricated by tape casting/lamination. By adjusting the electrolyte composition, the dense bulk electrode was successfully formed onto the electrolyte by co-sintering. The electrochemical properties of the bulk electrode were generally similar to those of the thin films. However, the degradation rate was significantly lower, possibly due to a difference in cation diffusivity, making the bulk electrode suitable for studying the reaction mechanism. Additionally, the bias effect needed for studying electrodes under operating conditions can be easily investigated without lithography. Our experiments provide a new platform for identifying the reaction mechanism of bulk SOC electrodes.

On the reactive sintering of Heusler Fe2VAl-based thermoelectric compounds

Heusler Fe2VAl-based compounds are promising candidates for thermoelectric conversion of waste heat. In comparison to more conventional thermoelectric materials, the constitutive elements of these alloys are indeed abundant, cheap, and non-toxic. Furthermore, the thermoelectric properties of these compounds can be easily enhanced by either doping or controlled deviation from exact stoichiometry while large power factors compatible with energy harvesting applications can be reached.In the present study, Fe2VAl-based compounds were synthesised by powder metallurgy. Almost fully dense bulk materials were obtained either by field-assisted sintering, also referred to as spark plasma sintering (SPS), of pre-alloyed powders or by spark plasma reactive sintering of mixtures of elemental powders. The influence of the processing route and parameters on the resulting microstructure was assessed. In the specific case of the one-step synthesis and rapid densification of the Fe2VAl compound starting from the elemental powders, a detailed insight in the reaction path was obtained by interrupted sintering cycles followed by careful phase analysis of the partially sintered compacts by X-ray diffraction and elemental analysis. Finally, it is worth emphasising that the thermoelectric properties of the compounds processed by reactive sintering are as good as the ones of samples sintered from pre-alloyed powder or processed by melting and casting.

Enhancement in sintering driving force derived from in situ ordered structural collapse of mesoporous powders

AbstractIn this study, the sintering behaviors of a series of mesoporous silica (FDU‐12, SBA‐15, MCM‐41, and mesoporous silica nanoparticles) and microporous zeolite (ZSM‐5) using spark plasma sintering (SPS) technology were investigated. Highly transparent glass was prepared at a low temperature from all the powders. In particular, FDU‐12 type of mesoporous silica could be fully densified at an ultralow sintering temperature (910°C). It is suggested that the collapse of ordered mesostructures during SPS process dependents on the large pore size/pore wall thickness ratio, appropriate pore arrangement and amorphous frameworks of mesoporous silica, which implies that the enhancement in sinterability is possibly derived from the in situ collapse of ordered mesostructures. Such present findings pave a new way toward the construction of functional dense bulk materials from mesoporous powders.

Quantitative Analysis of Strengthening Effect Contributed by Microstructure Characteristics in Pure Titanium Consolidated by Severe Plastic Deformation

Chips of commercial pure titanium (ASTM Grade 2) were consolidated into fully dense bulk material by severe plastic deformation (in the form of multi-pass equal channel angular pressing). The strengthening effect (as contributed by microstructure characteristics) was quantitatively analyzed by electron backscatter diffraction and mechanical tests. The effects of grain parameters (e.g., grain size and grain orientation) on yield strength and the Vickers micro-hardness were analyzed by the Hall–Petch relationship. The tensile curve of the consolidated sample was modeled by the Ludwik–Hollomon equation. The strain-hardening of the consolidated titanium was analyzed by the Taylor formula and the Kocks–Mecking equation. The theoretical analysis is consistent with the experimental results obtained from microstructure characterization and mechanical testing.

Mechanical properties of REBaCuO single-grain bulk fabricated by the infiltration growth technique

In order to investigate the mechanical properties and fracture mechanisms of (Gd,Dy)BaCuO dense bulk material fabricated by the infiltration growth technique, tensile tests were carried out for specimens cut from the as-grown bulk material. The average tensile strength value of the (Gd,Dy)BaCuO dense bulk material fabricated by the infiltration growth technique was 44 MPa, which is superior to that of a porous bulk material fabricated through melt-processing in a 50% O2 atmosphere (37 MPa), and comparable to that of a dense bulk material fabricated through melt-processing in 100% O2 (45 MPa) that have been reported elsewhere. Through the observations of the flow-like patterns formed by the crack propagations on the fracture surfaces, the fatal crack initiation site was identified. One extraordinarily large pore, segregated secondary phase particles and some inclusion that mainly consists of Pt were observed around the crack initiation site on the fracture surfaces of the (Gd,Dy)BaCuO dense bulk material.

Back Pressure Equal Channel Angular Pressing of Consolidate Pure Al Particles

In this study, pure aluminum particles were successfully consolidated to fully dense bulk material by back pressure equal channel angular pressing (BE-ECAP) at room temperature, the evolutions of microstructure and densification mechanism were systematically investigated using an FEI-TECNAI G20 transmission electron microscope (TEM) operating at 200kV, FEI field-emission scanning electron microscope (FE-SEM) and hardness testing. The results indicated that the strong bulk materials from particles were successfully produced. After 4 BE-ECAP passes, the present samples show finer grains with the average grain size of ~10μm, the density of the sample was considerably higher compared to those of the materials that had undergone ECAP without back pressure, and was approach to the theoretical density of pure Al. This was related to the combination of hydrostatic pressure, shear deformation and strain accumulation. The mechanisms of grain refinement was the dislocation generated inside grains moves towards the grain boundary continuously, and accumulates, tangles annihilates at the grain boundaries, which resulting in the grains continuously fragmented and refined.

Oxidation resistance of Ti3AlC2 and Ti3Al0.8Sn0.2C2 MAX phases: A comparison

AbstractTi3AlC2 and Ti3Al0.8Sn0.2C2 MAX phase powders are densified using Spark Plasma Sintering (SPS) technique to obtain dense bulk materials. Oxidation tests are then performed over the temperature range 800°C‐1000°C under synthetic air on the two different materials in order to compare their oxidation resistance. It is demonstrated that, in the case of the Ti3Al0.8Sn0.2C2 solid solution, the oxide layers consist in TiO2, Al2O3, and SnO2. The presence of Sn atoms in the A planes of the solid solution leads to an easy diffusion of Sn out of the MAX phase which promote the formation of the nonprotective and fast growing SnO2 oxide. Moreover, the small Al/Ti atom's ratio promotes the growth of a nonprotective rutile‐TiO2 scale as well. In the case of the Ti3AlC2 MAX phase, the oxide layer consists in a protective alumina scale; a few TiO2 grains being observed on the top of the Al2O3 layer. The parabolic oxidation rate constants are about 3 orders of magnitude smaller for Ti3AlC2 compared to Ti3Al0.8Sn0.2C2.

A New Approach for Consolidation of Pure Magnesium Powder Using an Integrated Severe Plastic Deformation Route

In this paper, a new approach using a novel severe plastic deformation route is presented for consolidation and processing of a high-density and ultrafine-grained pure magnesium. Pure magnesium particles were successfully consolidated at 400 °C into a sufficiently dense bulk material using a new combined method including cyclic extrusion compression, equal channel angular pressing (ECAP) and conventional extrusion. The grain refinement, consolidation behavior and mechanical properties were deeply investigated. Results showed that the as-consolidated material had a fine grain structure with excellent tensile strength and ductility compared to as-cast and as-ECAPed specimens. Vickers microhardness increased from 38.75 to 52.58 during the process. Porosity also reduced considerably from 12.55 to 1.2% during the process which led to a dense bulk material. Results indicate that the introduced method is a promising and effective process for producing strong bulk materials from metal powders.

Influence of laser process parameters on the densification, microstructure, and mechanical properties of a selective laser melted AZ61 magnesium alloy

We present a detailed, systematic study of how laser process parameters affect the formation characteristics, densification, microstructure, and mechanical properties of AZ61 magnesium alloy specimens prepared by selective laser melting (SLM). The results allow us to develop a method to control defects and optimize the SLM parameters for the fabrication of a dense, bulk AZ61 magnesium alloy. A bulk AZ61 magnesium alloy prepared by SLM is used to investigate how hatch spacing, large-scale scanning speed, and energy input affect the macrosurface morphology (before and after polishing) and how the surface roughness and the relative density of the specimens affect the microstructure and mechanical properties of the dense bulk material. The results show that process parameters strongly influence the macrosurface topography, which we divide into four stages: a strong surface balling pore region, weak surface balling pore region, rough scan track region, and flat smooth region. In addition, the surface roughness changes from 18.95 to 7.49 μm. Two types of pore shapes (meniscus and circular) are governed by the scan speed, and pore size is a function of hatch spacing. We also obtain unusual X-ray diffraction results that depend on input energy in the range of 138.89–208.33 J/mm3. The α-Mg diffraction peak shifts to the right and reaches a maximum at 156.25 J/mm3 (scanning speed of 400 mm/s and hatch spacing of 0.06 mm), and the relative density reaches a maximum of 99.4% because the amount of Al in solid solution is maximized. The microstructure results show that the microstructure evolution involves dispersed α-Mg grains (refined equiaxed α-Mg grains) and coarsened equiaxed α-Mg grains with an average grain size ranging from 1.61 to 2.46 μm. The tensile properties of the as-built AZ61 Mg alloy at room temperature are superior to those of an as-cast AZ61 Mg alloy. The ultimate tensile strength of the as-built AZ61 is 93% greater than that of the as-cast AZ61 alloy, and the yield strength is increased by 136%.

High-Temperature Wear Behaviour of Spark Plasma Sintered AlCoCrFeNiTi0.5 High-Entropy Alloy.

In this study, the wear behaviour of a powder metallurgically produced AlCoCrFeNiTi0.5 high-entropy alloy (HEAs) is investigated at elevated temperatures. Spark plasma sintering (SPS) of inert gas atomised feedstock enables the production of dense bulk material. The microstructure evolution and phase formation are analysed. The high cooling rate in the atomisation process results in spherical powder with a microstructure comprising two finely distributed body-centred cubic phases. An additional phase with a complex crystal structure precipitates during SPS processing, while no coarsening of microstructural features occurs. The wear resistance under reciprocating wear conditions increases at elevated temperatures due to the formation of a protective oxide layer under atmospherical conditions. Additionally, the coefficient of friction (COF) slightly decreases with increasing temperature. SPS processing is suitable for the production of HEA bulk material. An increase in the wear resistance at elevated temperature enables high temperature applications of the HEA system AlCoCrFeNiTi0.5.

Corrosion behavior of Sc2O3–Y2O3 co-stabilized ZrO2 thermal barrier coatings with CMAS attack

Abstract Traditional viewpoints state that defects, such as pores or cracks, that generally exist in plasma sprayed thermal barrier coatings (TBCs) can provide fast infiltration channels for molten calcia-magnesia-alumino-silicate (CMAS). In contrast with this viewpoint, results from this study suggest that the effect of defects on the CMAS infiltration of the yttria stabilized zirconia (YSZ) coating is limited, even though the dense YSZ bulk material still cannot inhibit the infiltration of CMAS. However, a few additions of Sc2O3 can significantly improve the CMAS resistance of the YSZ coating owing to the lower solubility of Sc3+ in the CMAS. Our findings provide key insights for the development of CMAS-resistant TBCs.