Densification Technique Research Articles

In-situ twisting of carbon nanotube fiber synthesized by floating catalyst chemical vapour deposition

The carbon nanotube fiber (CNT fiber) represents a remarkable advancement in harnessing nano-level properties akin to those of individual CNTs in macrostructure. The most essential step in achieving this is to densify the CNTs within the fiber. Among various densification techniques, twisting has emerged as one of the prominent methods due to its continuous nature. In this study, we conducted in-situ continuous twisting of CNT fibers synthesized by floating catalyst chemical vapour deposition alongside ex-situ twisting experiments for comparative analysis. Through focused ion beam analysis, we probed the effect of twisting on the densification of CNT fibers, revealing pore elimination and complete fiber densification as outcomes. Intriguingly, in-situ twisting yielded higher density compared to ex-situ twisting despite identical twist levels maintained in both methods. We unraveled the mechanism behind this superior density achieved through in-situ densification. Furthermore, in-situ twisted fibers exhibited superior tensile strength and electrical conductivity when compared to their ex-situ twisted fiber. The in-situ twisting process demonstrated remarkable enhancements, with electrical conductivity increasing by up to 254 % and tensile strength by 125 % compared to untwisted fibers.

Tailoring the lattice thermal conductivity of Al‐incorporated Ag2Se for near room temperature waste heat recovery

Ag2Se is categorized as a typical 'phonon‐liquid‐electron‐crystal (PLEC)'material, exhibiting an extremely low [[EQUATION]] valueTop of FormBottom of Form. In this study, Al substituted Ag2Se samples were synthesized by mechanical alloying process followed by hot press densification technique. The Al substituted sample shows an exceptionally high mobility of 2360 cm2V‐1S‐1 at room temperature and a maximum power factor of 1442 µWm‐1K‐2 at 383 K. The phonon scattering induced by various crystal imperfections due to Al substitution helped to obtain a very low lattice thermal conductivity [[EQUATION]] value of 0.328 W/mK. A high figure of merit (zT) of 0.4 at 383 K was obtained as a result of the simultaneous effect of boosting the electrical transport properties and decreasing the thermal conductivity. This present work summarizes that the Al substitution is highly significant in improving the thermoelectric properties of Ag2Se.

Approaching the low thermal conductivity in layered oxychalcogenide Bi2-xPrxO2Se (0 ≤ x ≤ 0.15) via mass and strain field fluctuatiocn for thermoelectric application

Bi2O2Se, a layered oxychalcogenide has gained much attention among the conventional oxides and chalcogenides based thermoelectric materials because of its high stability and less toxicity. Herein, Bi2-xPrxO2Se (0 ≤ x ≤ 0.15) is synthesized by ball milling followed by hot press densification technique, the x represents the replacement of Bi with Pr in atomic%. The influence of isovalent Pr substitution on the structural and thermal transport properties of Bi2O2Se were studied. The formation of tetragonal crystal structure with space group I4/mmm is confirmed by X ray diffraction (XRD) Pattern. HRTEM micrographs reveals the crystalline nature and lattice defects in the synthesized composition. The influence of 10 at % Pr substitution at Bi site reduces the thermal conductivity to 0.276 Wm−1K−1 at 653 K, originated from short phonon lifetime due to the effect of mass and strain field fluctuation. This result exhibits that the incorporation of Pr substitution in Bi2O2Se can dramatically enhance the thermoelectric performance of Bi2O2Se ceramic by reducing thermal conductivity.

Influence of densification on structural performance and failure mode of cross-laminated timber under bending load

The effect of densification of the laminas was studied relative to the shear performance of cross-laminated timber (CLT) specimens submitted to the bending test. The three-layered CLT panels were fabricated using loblolly pine (Pinus taeda L.). A compression ratio (CR) of 50% was used to densify the lumber using the thermomechanical densification technique. The process included plasticizing the lumbers by soaking them in boiling water for 10 minutes and then hot-pressing to the target thickness at 140 °C. Four groups were made, i.e., a control sample with all three layers non-densified, only mid-layer densified, all layers densified, and all layers planed to the same thickness of densified layers. Specimens were tested in short-span bending with a span-to-depth ratio of eight. For specimens having densified mid-layer, the failure mode changed from rolling shear to tensile failure of the outer layer, and the maximum shear stress was increased by 34%. Densification of the mid-layer at CR of 16% was sufficient to change the failure mode from rolling shear in mid-layer to tensile in outer layer. In the case of all-layer-densified specimens, the maximum rolling shear strength was increased by 129% compared to the control.

Optimization and characterization of hybrid bio-briquettes produced from the mixture of sawdust, sugarcane bagasse, and paddy straw.

Biomass briquetting is a viable densification technique that converts waste biomass materials into useful products and alternative energy. This work explores the characteristics and optimization of hybrid bio-briquette production by combining crop residues (paddy straw) and solid biomass materials (sawdust and sugarcane bagasse). A total number of 20 briquettes were fabricated with three input factors: sawdust (SD), sugarcane bagasse (SB), and paddy straw (PS) based on the faced-centered central composite design (FCCCD) approach in the laboratory to investigate the calorific value (CV) and ash content (AC). The bomb calorimeter technique was used to evaluate the briquette's calorific value and ash content. The proposed work focused on optimizing the briquette input parameters (SD, SB, and PS) and output responses (CV and AC) using analysis of variance (ANOVA) and response surface methodology (RSM) and hybrid artificial neural network-integrated with multi-objective genetic algorithms (ANN-MOGA). This study shows that the MOGA-ANN-based model results in the best value of CV (17.07 MJ/kg) and AC (1.95%) with optimal input parameters SD (39.99 g), SB (29.02 g), and PS (69.02 g). The optimal results observed from the MOGA-ANN model have also been validated experimentally. The Fourier transform infrared (FTIR) spectroscopy investigation reveals that biomass briquettes are the sustainable and environment-friendly option of fossil fuels for power generation and indoor cooking. The study suggests a strategy for minimizing agro-waste, which may be converted into future fuel in the form of briquettes.

Perspectives on Li Dendrite Penetration in Li7La3Zr2O12‐Based Solid‐State Electrolytes and Batteries: Materials, Interfaces, and Charge Transfer

AbstractGarnet‐type Li7La3Zr2O12 (LLZO) solid‐state electrolytes have gained significant attention as one of the most promising electrolyte candidates for high‐energy‐density energy storage devices due to their superior stability and high ionic conductivity. However, the problem of lithium (Li) dendrite penetration into LLZO hinders the practical application of LLZO in solid‐state Li metal batteries (SSLMBs). Multidisciplinary evaluations are carried out to understand the mechanism of dendrite penetration. Herein, the formation and evolution of different types of Li dendrites within LLZO are reviewed. The Li dendrite penetration process is addressed from the perspectives of material design, Li/LLZO interfacial adaptability, and the interfacial charge transfer process. On this basis, recent efforts and solutions to inhibiting the penetration of Li dendrites in LLZO, including stabilizing LLZO phase and densification techniques, interfacial modifications, and grain boundary manipulations, are summarized. It is expected that the in‐depth understanding of the Li dendrite penetration and corresponding solutions will provide a systemic guideline toward the development of LLZO‐based solid‐state electrolytes and the commercialization of ultra‐stable SSLMBs.

Recent Advances in W–Cu Composites: A Review on the Fabrication, Application, Property, Densification, and Strengthening Mechanism

Tungsten–copper (W–Cu) composite is a pseudoalloy prepared by powder metallurgy method with tungsten and copper as the main components, which are widely used in electrical contacts, electrical discharge machining electrodes, electronic packaging, aerospace, and military fields due to its good conductivity, thermal conductivity, high melting point, high electrical breakdown strength, low contact resistance, high welding resistance, and high heat resistance. Herein, the recent advances of W–Cu composites are reviewed systematically. First, the preparative techniques of W–Cu composites are introduced in detail, and their advantages and disadvantages are evaluated objectively. Second, an introduction of the main application fields and corresponding characteristics advantages for W–Cu composites are provided. Subsequently, the densification techniques and strengthening mechanisms and their effects on microstructure, mechanical properties, and physical properties of W–Cu composites are mainly discussed. Finally, based on a comprehensive review of W–Cu composites, its future development trends and potential research challenges are summarized and prospected.

A review of the combined torrefaction and densification technology as a source of renewable energy

Densification techniques allow biomass to be used in the energy mix with coal or as a direct replacement for coal as it is a renewable resource. Typically, biomass is bulky, so thermochemical methods, like torrefaction, reduce volatiles and moisture, leaving a higher composition of fixed carbon. After the torrefaction process, the torrefied biomass poses problems during handling, transportation, and storage because it consists of small (<100 μm) disintegrated particles. Densification minimizes these problems through thermal compaction which produces integrated and larger (4 mm – 200 mm diameter) solid particles. This process can be done naturally (without any additives) or by adding binders which improve the torrefied biomass’s physical, chemical, mechanical, and heating properties. This in turn reduces any costs associated with handling/transportation and storage of the biomass before it is used for energy generation. Densification increases the biomass’s energy content per unit volume thereby enabling coal substitution. Recent reviews on densification have mainly focused on the binding of coal fines, raw biomass, and some torrefied biomass. Reviews on the binding theories are also available. This current review focuses solely on the aspect of torrefied biomass densification and the factors associated with the process. Insights and recommendations for the possible application of an integrated biomass torrefaction and densification process were provided herein. In addition, the gaps in literature were identified to enable future research on the application of the process to realize innovative renewable energy production in industry.

Soft magnetic wood composites with chain-aligned Fe3O4 nanoparticles for magnetically driven actuators

Intelligently responsive wood-derived materials have long been sought due to their sustainability, earth abundance, and low carbon footprint, with promising applications in sensors, flexible electronics, and soft robotics. However, insensitive responsiveness and unsatisfactory mechanical properties have hindered the development of intelligent drive systems. This work reports on soft magnetic wood composite (SMWC) with a sandwich structure consisting of densified wood and polydimethylsiloxane (PDMS) mixed with Fe3O4. We treat natural wood chemically to improve flexibility, especially the lignin partial removal while keeping the wood structure intact. Benefiting from densification and magnetic-assisted techniques, multilayer SMWC with chain-arranged Fe3O4 can be prepared, which exhibits 183.5 MPa mechanical strength along the longitudinal direction, flexible bending capacity, a water contact angle of 100.9° and a saturation magnetization strength of 9.81 emu g−1 for 40 wt% Fe3O4. Importantly, the chain arrangement of Fe3O4 facilitates the sensitive control of SMWC compared to non-chain arranged structures. We have designed a star-shaped actuator that demonstrates controlled magnetic response, which can perform transporting cargo through linear and rotational movements on the water. SMWC with chain-aligned Fe3O4 exhibits good flexibility, excellent mechanical properties, and superior magnetic responsiveness, which is essential for exploring the responsiveness of wireless sensors and soft robots.

Interface scattering induced low thermal conductivity in Ag2Se/MWCNT for enhanced thermoelectric application

Ag2Se is a narrow bandgap semiconductor with an orthorhombic crystal structure at room temperature, resulting in an intrinsically low lattice thermal conductivity and large power factor, which is favourable for thermoelectric. In this work, we reported the improved thermoelectric properties of Ag2Se/MWCNTs nanocomposites synthesized by ultrasonication-assisted hydrothermal method followed by hot press densification technique. Here, MWCNTs act as scattering channels in the Ag2Se matrix to provide extra heat-carrying phonon scattering centres and reduced lattice thermal conductivity (κL) of 0.15 Wm−1 K−1 at 393 K. As a result, the maximum figure of merit (zT) of 0.73 at 393 K is achieved with better thermal stability. Our work provides a new concept to enhance thermoelectric properties through interface regulation.

Recent Case Histories of Carbon-Neutral Activity Using Ground Improvement Technology in Japan

Global warming due to greenhouse gas emissions has led to record-breaking heat waves, torrential rains and droughts on a global scale in recent years. For this reason, people around the world are more keenly aware of the need to reduce greenhouse gas emissions. The construction industry is one of these sources of greenhouse gas emissions. A lot of ground improvement techniques have been developed and applied to improve the physical and mechanical properties of soil in order to achieve stability improvement, ground settlement control, reinforcement, liquefaction prevention, etc. These techniques use a lot of natural materials such as sand and crushed stone and industrial products such as cement. In order to reduce their environmental impact and to economize these techniques, many kinds of industrial waste and by-products have been beneficially used in many types of ground improvement techniques. In response to the growing awareness of carbon neutrality in recent years, it is necessary to further promote initiatives such as the beneficial use of the industrial materials that have been used so far and the development of new materials and construction methods to reduce carbon dioxide emissions. It is expected that various biomass materials will be applied in ground improvement techniques to enhance “negative emission technology”. In this paper, recent developments and applications of certain sorts of environmentally friendly ground improvement techniques, soil densification techniques and soil stabilization techniques are briefly introduced. It is to be expected that these will be further developed and applied to contribute to the reduction in carbon dioxide emissions.

The effects of densification on rolling shear performance of southern yellow pine cross-laminated timber

This study evaluated the improvement in the shear performance of cross-laminated timber (CLT) through the densification of the transverse layers. Loblolly pine (Pinus taeda L., one of ten species known as Southern Yellow Pine (SYP)) lumber was used to fabricate CLT rolling shear specimens. Considering the compression ratio, thickness reduction to the initial thickness, lumber with an average density of 641.23 kg/m3 was compressed to three different levels: 16.67%, 33.33%, and 50.00%. For this compression, a thermomechanical densification technique was employed, in which lumber was softened by soaking in boiling water for 10 min and then hot-pressed at 140 °C to the target thicknesses. To differentiate the improvement in the shear performance due to the increased density from that of the aspect ratio, non-densified lumbers with the same aspect ratio as densified specimens were also used to fabricate CLT rolling shear specimens. The rolling shear performance of CLT specimens was evaluated using modified planar shear testing. The rolling shear strength increased by about 108% when the transverse layer was compressed for 50%. Likewise, it was found that there is a linear relationship between the percentage of increase in rolling shear strength and the compression ratio. Although the increased aspect ratio improves the rolling shear strength, results revealed that specimens with densified transverse layers outperformed those with non-densified specimens at the same aspect ratio.

Optimization of elephant dung green fuel briquette production using a low-pressure densification technique and its characterizations, and emissions

Elephant dung is densely packed with undigested fiber, complicating disposal. To manage this waste more efficiently, the dung was converted into biofuel briquettes. Four variables in the briquette production were investigated using three levels of optimization techniques, including a response surface and a central composite design with 95 % confidence. The results show that when compressing a 7:3:1 weight ratio of elephant dung, binder, and water at 40 bars, a briquette density of 613 kg/m3 or 9.09 GJ/m3 could be achieved. Although its dimensional stability was consistent and its shatter resistance was acceptable, its water resistance was poor. The briquettes had atomic ratios of 0.15 and 1.17 for H/C and O/C, respectively. It had a high heating value of 17 MJ/kg and could enhance the stove's overall thermal efficiency by 22 %. The emission study demonstrated that the combustion of the briquettes released mainly CO2 (5.49 × 104 ppm), whereas other gases were negligible.

Adaptation and Evaluation of Pellet Press Briquette Machine

A good substitute for coal, lignite, and firewood is briquetted fuel made from agricultural leftovers. Compared to loose agro-residues, which have a specific density of 60 to 180 kg/m3 , briquettes have a high (1200–1450 kg/m3 ). Briquettes are formed right where they are made, thus reducing air pollution. In this work, a sawdust and coffee husk briquetting machine is redesigned and built. In this work, briquettes (solid fuels) were made using a screw-type briquetting to compress sawdust and coffee husk at different ratios. An effective densification technique that is suitable for small-scale applications is being adapted by screw press briquetting. The equipment has been modified to generate briquettes at a rate of 187.62 kg per hour. Briquette density, power consumption per kilogram of briquette produced, and calorific value per kilogram of briquette have all been examined in relation to the effect of moisture content in agro-residues and binders utilized. Paper was used as the binding agent, and different biomass binder ratios of 100:10, 100:12.5, and 100:15 were tested to assess the briquette's physical characteristics. The binder level has a big impact on the briquette's physical characteristics. level.

On the Temperature‐Induced Equilibration of Phase Distribution and Microstructure in a Gas‐Atomized Titanium Aluminide Powder

Powder production by gas atomization of γ‐TiAl based alloys typically yields a highly nonequilibrium material regarding the occurring phases and their microstructural appearance. In particular, the equilibration of the powder and the associated phase transformations during heating are of great importance for the subsequently applied densification techniques. The present work employs in situ high‐energy X‐ray diffraction to investigate how this thermodynamic equilibration manifests itself in the resulting phase distribution, the ordering behavior of the disordered α and β phase, both evidenced in the powder, and the change of the γ lattice parameters during heating of a Ti–46.3Al–2.2W–0.2B (at%) powder up to 850 °C. Complementary microstructural characterization of the gas‐atomized powder and the heat‐treated material condition reveals that the temperature exposure predominately affects the dendritic parts of the microstructure, especially when the α phase is transformed into γ phase with small embedded grains of α2 and βo.

Fabrication of highly transparent thulium-doped Al2O3 nanocrystalline ceramics with broadband emission at 1.8 μm

Rare earth (RE) doped polycrystalline Al2O3 ceramics have attracted increasing research interest in the past decade for lasing and lighting applications because of their outstanding thermal conductivity and fracture strength enabling power scaling. However, the optically anisotropic nature of Al2O3 causes birefringent scattering in polycrystals, limiting the in-line transparency across visible and NIR wavelength range. To improve the transparency of Al2O3 ceramics, great control over powder processing and densification techniques are required to optimize its nanostructure. In this work, we present the first report of thulium incorporated nanocrystalline Al2O3 ceramic. The Tm:Al2O3 ceramic presented has the highest transparency among RE:Al2O3 reported to date, with a total loss coefficient of 0.6 cm−1 at the major emission wavelength 1.78 μm.

Ultra-low thermal conductivity through the reduced phonon lifetime by microstructural and Umklapp scattering in Sn1−xMnxSe nanostructures

Tin selenide (SnSe), a layered material with low thermal conductivity high thermoelectric properties, has recently attracted a lot of attention in the field of thermoelectrics. Herein, Sn 1−x Mn x Se is prepared by single-step hydrothermal route and the effect of Mn on the TE properties of SnSe compound were investigated. The formation of orthorhombic crystal structure is confirmed by X-ray diffraction (XRD) pattern. High crystalline nature of the sample and nanoparticles formation is observed in high resolution transmission electron microscopy (HRTEM). Thermal conductivity is obtained in the temperature range from 303 K to 653 K. The effect of Mn substitution leads to low thermal conductivity of 0.204 W/mK at 653 K, due to the shortened phonon lifetime through the various scattering mechanisms. This result demonstrates that the introduction of Mn substitution in SnSe can effectively lift the thermoelectric performance of polycrystalline SnSe via reduced thermal conductivity. ● Mn substituted SnSe samples were synthesized by hydrothermal method followed by cold pressing densification technique. ● Formation of grain boundaries, dislocations and mass fluctuation scattering synergistically reduced the phonon life time. ● Reduced phonon life time resulting in ultra-low thermal conductivity of 0.204 W/mK at 653 K.

Enhanced critical current density in K-doped Ba122 polycrystalline bulk superconductors via fast densification

SummaryIron-based superconductors are expected to be used in strong magnet applications owing to their excellent superconducting properties. The process of sintering a mechanically alloyed precursor powder is effective in achieving a high upper critical field and critical current density in BaFe2As2 (Ba122) polycrystalline bulk materials. However, when this process is applied to K-doped Ba122, which shows the highest critical temperature in the Ba122 family, suppressing the vaporization of potassium is challenging. In this study, spark plasma sintering (SPS) method was applied to K-doped Ba122 to achieve fast densification. In contrast to the conventional synthesis method, which requires several tens of hours, optimally K-doped bulks with near theoretical density were obtained after only 5 min of SPS, and the magnetic critical current density reached 105 A/cm2 at 5 K. The demonstrated superconducting properties suggest that this fast densification technique is a useful tool for applying K-doped Ba122 to bulk trapped field magnets.

Controlled grain boundary interfaces of reduced graphene oxide in Ag2Se matrix for low lattice thermal conductivity and enhanced power factor for thermoelectric applications

Silver Selenide (Ag2Se), a promising thermoelectric (TE) material due to its high proficient performance in (300–400) K. In this report, Ag2Se and its composites with reduced graphene oxide (rGO) were synthesized by sonochemical assisted hydrothermal method followed by hotpress densification technique. The structural analysis confirmed the orthorhombic phase of Ag2Se and the composition of Ag–Se–Ag with rGO is confirmed from binding energy shift in X-ray photoelectron spectroscopy (XPS) analysis. The phase transition from orthorhombic to cubic phase is identified around (390–450) K from TG-DTA analysis. For 30 wt % of rGO in Ag2Se, the very low thermal conductivity (κ) of ∼0.492 Wm−1K−1 is obtained at 333 K. The maximum zT of ∼0.39 is achieved at 363 K for Ag2Se with 30 wt % rGO. The facile synthesis with modification by rGO shows the untapped potential of very low thermal conductivity in Ag2Se that is yet to be uncovered for TE generators.

Fracture in self-lubricating inserts: A case study

A case study is carried out to reveal the fracture mechanism of self-lubricating inserts. The insert is made up of 98.5 wt% Zirconia Toughened Alumina (ZTA) reinforced with 1.5 wt% CuO. The insert is fabricated through the powder metallurgy route, followed by the hot isostatic pressing (HIP) technique (for densification). After densification, the insert is shaped and sized according to ISO SNUN 120408. The workpiece material used for machining is AISI 4340 steel. A conventional NH-26 lathe is used for machining as well as for creating facture inside the insert. In this investigation, the machining operations are carried out till the failure of inserts does not take place. The fracture analysis suggested a synonymous fracture mechanism that occurs for brittle facture (facture without any deformation). The fracture analysis seen through FESEM images observed that the initiation of crack that happened without any dislocation movement results in chipping, cracking, and flaking on the surface. The crack is initialized due to the generation of high localized stresses. The stresses were developed due to the continuous movement of chips concentrated slightly away from the cutting edges. The developed stresses are relieved by creating small cracks beneath the surface. These cracks are propagated in the radial direction without any dislocation-induced plasticity. The mechanism is well confirmed through the FESEM images of fracture specimens.