Sintering Approach Research Articles

Direct Recycling of LiNixMnyCozO2 (NMC) Cathode Materials in Molten Salts

Direct recycling is an emerging technology to retrain the added value of compound structure by healing the compositional and structural defects in spent cathode materials. In our previous work, we developed a successful lithiation via ionothermal synthesis using a cost-effective Li halide as Li source and recyclable ILs as solvents for the direct recycling of LiNi1/3Mn1/3Co1/3O2 (NMC 111) cathodes.[1] Compared to the classic solid-state sintering approach, the flux synthesis in ionic liquids can achieve high-temperature phase products under a lower temperature and ambient pressure. The relithiated NMC 111 exhibited excellent electrochemical performance as a pristine NMC 111 in both half-cell and full-cell tests. For the direct recycling of commercial Ni-rich NMC cathodes, Li containing reciprocal ternary molten salts (RTMS) flux media can serve as both Li sources and solvents to restore Li in spent NMC under relatively low temperatures (below 300 °C).[2] Surpassing the traditional binary or ternary molten salts, the reciprocal ternary molten salts (RTMS) feature two cation species and two anion species, and a lower eutectic temperature. In addition, the highly charged flux media offered by molten salts provide efficient environments for transporting ionic reaction precursors for a successful direct recycling of spent NMC cathodes.Beyond direct recycling, direct upcycling of spent cathodes to the next-generation cathodes can maximize the value of EOL LIBs (Figure 1a). In a typical Li+, Na+||Cl-, NO3 - RTMS system, the reversible reaction: NaNO3 + LiCl ⇌ LiNO3 + NaCl enables a low eutectic melting point for the effective flux process under 300 °C and can provide an oxygen-rich environment, which are critical indexes for a low-temperature upcycling of spent NMC 111 to Ni-rich NMCs (eg. NMC 622).[3] After upcycling, the chemical composition of Up-NMC 622 is Li1.08Ni0.63Co0.19Mn0.18O2, having a restored Li content and higher Ni content compared to spent NMC 111 (Li0.93Ni0.33Co0.33Mn0.33O2), suggesting the successful upcycling in chemical composition. In the half-cell battery tests, the first charge/discharge capacities of Up-NMC 622 are larger than those of spent NMC 111 (charge capacity: 188.6 vs 140.1 mAh/g; discharge capacity: 153.6 vs 119.5 mAh/g at 20 mA/g). Thus, molten salts are promising and effective for the direct recycling/upcycling of spent NMC cathodes.

Near-fully dense nanocrystalline hafnium via pressureless two-step sintering

Grain refinement in hafnium (Hf), a typical refractory metal, encounters significant challenges due to its inherent high sintering temperature requirements and uneven sintered capillary force that lead to rapid grain coarsening and inhomogeneity. Herein, we present a novel approach of the pressureless two-step sintering to prepare near-fully dense nanocrystalline Hf with an average grain size of around 40 nm, which represents the smallest grain and highest density for nanocrystalline pure Hf to the date. Such achievements not only broaden the applicability of pressureless two-step sintering but also offer insights to produce large size of finer-grained refractory metals and their alloys.

Nanoscale sintering of zinc micropowders for high conductivity and sensing applications of transient electronics

Abstract In the face of new social and environmental challenges, there is a need for an alternative approach to the fabrication of electronics. Increasing demand for smart healthcare applications or the growing e-waste problems inspired the work on new adaptations and materials for biodegradable, bioresorbable or even edible electronics. Such a trend is called transient electronics, which is a response to the mentioned problems, yet efficient and affordable fabrication of such elements is challenging. We report a broader approach to the application of zinc inks for printed electronics and a nanochemical sintering approach with several types of organic acids. Selectively spray-printed fine zinc microparticles subjected to acetic, lactic, malonic, ethylmalonic and citric acids were evaluated for obtaining the lowest electrical resistivity and its variations induced by the amount of applied acids. Resulting sintered Zn patterns exhibited sheet resistivity values as low as 15 · 10−2 Ω sq−1. Not all acids are suitable for fabricating stable, conductive paths, as in the case of citric and ethylmalonic acids. On the other hand, with malonic acid, there was a wide range of resistance changes in the function of applied acid doses (from one to fifteen), suggesting application as a chemical sensor for acid concentration. Such results suggest that with a low-cost zinc powder, absorbable by living organisms and disintegrating in the natural environment, using common organic acids, we can efficiently fabricate printed electronic circuits and sensors for transient electronics applications.

Microstructural evolution and 1500 °C oxidation resistance of Mo(Al,Si)2 fabricated via an innovative two-step SHS-SPS technique

An innovative two-step approach of self-propagating high-temperature synthesis (SHS) and spark plasma sintering (SPS) was developed to rapidly fabricate MoSi2 and Mo(Al,Si)2 ceramics for high-temperature anti-oxidation applications. The SHS process predominantly promoted the synthesis of high-purity and high-yield MoSi2 and Mo(Si,Al)2 phases in the alloyed powders. Subsequently, dense and crack-free MoSi2 and Mo(Al,Si)2 ceramics were produced using SPS. 1500 °C oxidation tests of the ceramics (100 h) revealed the formation of a protective SiO2 oxide layer on the surface of MoSi2 ceramics, while an Al-Si-O composite glassy oxide layer formed on Mo(Si,Al)2 ceramics, which exhibited better thermal stability and lower oxygen permeability compared to the single SiO2 oxide layer. However, an excessive Al content (>0.05 at.%) compromised the oxidation resistance due to the emergence of a Si-depleted Mo5(Si,Al)3 layer with inferior oxidation resistance, which was caused by the high-temperature diffusion of Si. Therefore, via this novel two-step SHS-SPS technique compact and crack-free Mo(Si,Al)2 ceramics can be rapidly synthesized at high temperatures. When trace amount of Al was added (0.05 at.%), Mo(Si0.95Al0.05)2 showed optimum high-temperature oxidation resistance.

Laser Sintering by Spot and Linear Optics for Inkjet-Printed Thin-Film Conductive Silver Patterns with the Focus on Ink-Sets and Process Parameters

The implementation of the laser sintering for inkjet-printed nanoparticles and metal organic decomposition (MOD) inks on a flexible polymeric film has been analyzed in detail. A novel approach by implementing, next to a commonly 3.2 mm diameter spot laser optic, a line laser optic with a laser beam area of 2 mm × 80 mm, demonstrates the high potential of selective laser sintering to proceed towards a fast and efficient sintering methodology in printed electronics. In this work, a multiplicity of laser parameters, primary the laser speed and the laser power, have been altered systematically to identify an optimal process window for each ink and to convert the dried and non-conductive patterns into conductive and functional silver structures. For each ink, as well as for the two laser optics, a suitable laser parameter set has been found, where a conductivity without any damage to the substrate or silver layer could be achieved. In doing so, the margin of the laser speed for both optics is ranging in between 50 mm/s and 100 mm/s, which is compatible with common inkjet printing speeds and facilitates an in-line laser sintering approach. Considering the laser power, the typical parameter range for the spot laser lays in between 10 W and 50 W, whereas for the line optics the full laser power of 200 W had to be applied. One of the nanoparticle silver inks exhibits, especially for the line laser optic, a conductivity of up to 2.22 × 107 S‧m−1, corresponding to 36% of bulk silver within a few seconds of sintering duration. Both laser sintering approaches together present a remarkable facility to use the laser either as a digital tool for sintering of defined areas by means of a spot beam or to efficiently sinter larger areas by means of a line beam. With this, the utilization of a laser sintering methodology was successfully validated as a promising approach for converting a variety of inkjet-printed silver patterns on a flexible polymeric substrate into functionalized conductive silver layers for` applications in the field of printed electronics.

A Rapid Thermal‐Radiation‐Assisted Sintering Strategy for Nd–Fe–B‐Type Magnets

The green transition has spiked demand for high‐performance sintered Nd–Fe–B permanent magnets, necessitating advanced powder consolidation technologies to enhance production efficiency. This study explores the rapid sintering methodology for an Nd–Fe–B powder using a radiation‐assisted sintering approach. The case study material is an industrially used powder, prepared through strip‐casting, hydrogen decrepitation, and jet milling, with a mean particle size of 5.5 μm. The powder is sintered to full density in a modified spark plasma sintering furnace, achieving pressureless conditions and eliminating electrical currents in the sample to preserve grain alignment and prevent decomposition of the hard‐magnetic phase. Fully dense samples are obtained with heating rates ranging from 10 to 200 °C min−1 and up to 5 min of dwell time at 1100 °C. Rapid heating results in grain size and microstructure comparable to conventionally sintered magnets prepared from the same powder, without compromising magnetic performance after postsinter annealing at 520 °C for 120 min. This sintering method contributes to a novel strategy for optimizing magnet production by utilizing efficient thermal‐radiation heat transfer. The combination of rapid heating and pressureless sintering drastically reduces heat‐up and dwell times, providing a fundamental advantage over slow conventional sintering.

Beam‐Generated Sample Evolution to Emphasize Spatial Inhomogeneities: The Example of HPO42−‐Containing Amorphous Calcium Phosphate

ABSTRACTAmorphous calcium phosphates (ACPs) represent a family of bioactive compounds particularly relevant to bone regeneration. However, due to their intrinsic metastability, their processing into 3D‐shaped materials cannot be undergone by conventional sintering methods and requires cold sintering approaches. Also, their microstructure and local compositional changes still have to be explored in detail. To this aim, spectroscopy techniques are particularly appealing to probe local chemical environments at the microscale. Concerning ACPs, one question regards the distribution of (hydrogenated) phosphate species, as they may lead to various evolutionary trends. In this contribution, we purposely exploited the laser–beam interaction through Raman mapping to trigger the in situ HPO42−‐to‐P2O74− transformation. Analysis by a multivariate approach allowed us to spot P2O74− clusters resulting from HPO42−‐rich initial domains. Moreover, a blue shift of the ν1PO43− band was noticed in the close vicinity of these clusters, thus evidencing a local evolution of the chemical composition of the ACP. These results, corroborated by differential thermal analysis, demonstrate the relevance of using the laser–sample interaction through local heating to probe the spatial evolution induced, in our case, by an ultrafast compaction process. Comparison of outcomes obtained using two different laser/power strategies finally evidenced the need to adapt the Raman analytical conditions to the behavior of the metastable material to analyze.

Microstructure and fracture behaviour of biomimetic Al2O3-ZrO2 composite with 2-levels of structural hierarchy

We report new class of natural nacre-like alumina toughened by zirconia fabricated by the simple two-step approach of unidirectional freeze-casting and spark plasma sintering. The biomimetic alumina-zirconia with a relative density of more than 98 % was achieved by consolidating at temperature of 1300–1425 °C with 50 MPa pressure. The resultant microstructure consists of two levels of structural hierarchy, i.e. level-1: bulk lamellar brick phase (alumina platelets) and level-2: mortar phase (yttria stabilized tetragonal zirconia polycrystals). The increase in volume fraction of zirconia (in tetragonal form) from 0 to 15 vol% was effective in progressively reducing the size of alumina platelets from 12 to 9 μm, and significantly improved the flexural strength of the composite by 60 % (from 172 to 270 MPa). By optimizing the hierarchical architecture from micro to macroscopic level, the structural performance of our synthetic nacre, where strength and toughness of 270 MPa and 13.5 MPa√m respectively are superior to that of natural nacre and many other engineering materials (illustrated in the form of Ashby map). The exceptional damage resistance is rationalized by both intrinsic (stress induced tetragonal to monoclinic phase transformation of zirconia) and extrinsic (crack deflection, crack branching and bridging, multiple cracking, platelets interlocking) toughening mechanisms. For 15 vol% ZrO2 composition, the contribution of intrinsic and extrinsic toughness was quantitatively evaluated as 0.9 ± 0.03 and 4.3 ± 0.07 MPa√m respectively (with experimentally measured toughness at crack initiation as 5.2 ± 0.2 MPa√m).

Alumina-based ceramic coatings obtained by the SHS process for high temperature corrosion and wear protection of steel tubulars

Ceramic coatings have much potential for steel tubulars' protection against high temperature corrosion of gases and liquids, often containing abrasive solid particles, and to enhance their integrity in severe power generation, mineral and oil & gas production environments. Combining self-propagating high-temperature synthesis (SHS) with high-speed centrifugal process, alumina-based coatings were produced onto the inner surface of tubulars for these applications. According to the developed SHS batch formulation and the designed centrifugal device and process, well-consolidated composite ceramic layers with a thickness of 1.5–3 mm have been obtained. The developed SHS process does not create hazardous gases, and it takes ∼30 s for the ceramic phase formation. A high-level compaction due to centrifugal forces and a liquid phase sintering approach provided a dense gradient ceramic structure formed by oxide grains cemented by a glassy phase and bonded with a steel substrate through a thin iron layer. The coatings were successfully produced onto the inner surface of carbon and stainless steels’ tubes of up to 12 ft-lengths and standard dimensions from 2 to 3/8″ to 7.5” OD. The coatings were tested, for the first time, in wear and high-temperature corrosive environments, e.g., in steam–H2S–CO2 gases and molten salts, with encouraging results due to high contents of Al2O3 and some other oxides and consolidated ceramic structure. They can be recommended for applications in high-temperature (900 °C and greater) corrosive environments and erosive flows.

Field-assisted sintering of barium titanate and 45S5 bioactive glass for biomedical applications

The development of electrically active biomaterials, which create electrical cues on demand to foster cellular stimulation, remains a challenge. Here, we utilized a Field-assisted sintering approach to densify barium titanate and 45S5 bioactive glass to create a piezoelectric and potentially bioactive composite. By using Field-assisted sintering, we aimed to fabricate dense piezoelectric specimens, preserving a low degree of crystallization of the bioactive glass to keep bioactivity as high as possible. Therefore, we have varied the compositions of the materials and processed them at different sintering temperatures. This enabled us to produce dense test specimens in the 94 %–98 % relative density range. The samples were successfully polarized, and piezoelectric charge constants d33 were determined for the composites. The content of bioactive glass and the sintering temperature influence the charge constant d33. It is in the range of 0.8–3.4 pC/N for the composites, approximately in the order of magnitude assigned to natural tissues such as bone. X-ray diffraction was used to analyze the composition of the processed samples and to investigate the influence of an additional thermal post-treatment. Altogether, we established a process window for field-assisted sintering, allowing the fabrication of a piezoelectric and potentially bioactive biomaterial for tissue engineering.

Laser sintering of polyamide 12 with limited thermal degradation

The paper presents, for the first time, the results of PA12 polyamide sintering using the original method of Dual Beam Laser Sintering of polymers (DBLS). The DBLS method, which is a modification of the standard polymer Laser Sintering (pLS) approach, allows to reduce the thermal degradation of the polymer by using selective (in terms of powder volume and process time) heating the material with laser radiation. The paper presents both the properties of sintered parts and the analysis of the degree of thermal degradation of post-process powders. Examination of the sintered parts included X-ray computed tomography (XCT) to visualize and analyze their porosity and a tensile test. Post-process powders were evaluated by Gel Permeation Chromatography (GPC), Melt Flow Rate (MFR), Dry Laser Diffraction Spectroscopy (DLD) and Powder Rheometer (FT4). The analysis of the result of PA12 sintering with the DBLS method was carried out in comparison with the classic pLS approach. As it has been shown, the DBLS approach allows to obtain comparable results for sintered parts compared to the pLS method. What is particularly important, it was shown that the post-process powder in the DBLS method has almost unchanged properties - the change in molecular weight and viscosity is at the level of the measurement error. Reducing thermal degradation is especially important in order to obtain continuous circulation of the powder in the manufacturing process.

Material extrusion of high-density SiCp/7075Al composite via a high nitrogen-flowing assisted sintering

Material extrusion additive manufacturing of particle-reinforced metal matrix composite (MMC) attracts attention due to the features of uniformly sintered microstructure, easy-to-handle and low cost. However, 3D Al-MMC suffers from poor sinterability due to the stable alumina layer on alloy powder, and difficulty in removing of binders at low temperature. Here, we propose a high nitrogen-flow sintering approach for the thermal debinding and sintering of as-printed SiC particle-reinforced 7075Al (SiCp/7075Al) MMC, without using cumbersome high-vacuum system or pressure-assisted densification. Microcrystalline wax-based granular feedstock was developed based on contact angle testing experiment, which shows typical shear-thinning behavior and satisfactory printing performance. Roles of printing parameters and nitrogen flow rate in the microstructure, phases and mechanical properties of SiCp/7075Al MMC are investigated. Nitrogen flow rate of 2–2.5 L/min accelerates the breaking of oxide film, with the precipitation of intergranular MgAl2O4, Mg2Si phases, and intragranular Al2Cu phases. 3D SiCp/7075Al MMC with a high relative density of 97% and tensile strength of 308 MPa after heat treatment (HT) was achieved based on optimized printing parameters. The availability of high dense structure, combined with controlled microstructure, low-energy demand and low cost, provides a facile route for the application of 3D Al-MMC by material extrusion.

Densification of zirconia-based ceramics by non-conventional sintering processes and chemical pathways

The present work reports an overview of the main results we have obtained from non-conventional sintering approaches towards the densification of 3mol.% yttria stabilized zirconia (3YSZ), the lessons learned from these results, and open questions that still need to be addressed. A wide range of techniques have been developed in the field of ceramic sintering, both in high temperature regime with extreme heating rates (>10 000 °C/min), as well as in very low temperatures (<400 °C) regime involving chemical reactivity to activate sintering mechanisms. In this context, we have recently explored several of these methods in order to understand and control the different sintering parameters and their impact on microstructure, crystallinity, grain boundaries and defect chemistry. Due to its complex chemistry, 3YSZ is a playground for the exploration of sintering capabilities and their influence on ceramic properties. Our recent studies in this field are presented in the present work, highlighting the effect of high heating rates through Flash Spark Plasma Sintering ( Flash-SPS) and Ultra High temperature Sintering (UHS) on sintering, but also the combination of low temperature Cold Sintering Process (CSP) and the associated precursors chemistry, with Spark Plasma Sintering (SPS). It also shows the possible densification by reactive hydrothermal sintering, using hydroxide precursors, and the effect of High Pressure SPS (HP-SPS) on 3YSZ nanopowders. All of these results touch upon current trends in the field of sintering, and highlight the possibilities in terms of chemical reactivity of precursors and physical parameter control. In particular, they show the importance of defect chemistry, related to the sintering atmospheres and their impact on both microstructures and properties.

Mechanical and Electrochemical Corrosion Behaviors of Porous Ti-6Al-4V Alloys Prepared by an Electrochemical Sintering Approach

Titanium alloys have been widely used in bone implants, but the mechanical properties, elastic modulus mismatch between bone and metal, and stress shielding effects can occur. However, porous materials can effectively overcome this problem. In recent years, porous structures have attracted enough attention from researchers. Adjustment of the porous structure may make the titanium alloys better able to meet the requirements of the implant. In this study, we have successfully prepared Ti-6Al-4V alloys by combining powder metallurgy with electrolysis in molten salt. At the same time, CaCl2 was used as a sacrificial space holder to adjust the porosity and porous structure. The Ti-6Al-4V alloys prepared by this method contain 29%–60% porosity and elastic modulus has been controlled between 1.8 GPa to 7.8 GPa, which is suitable for cancellous bone, trabecular, and other parts with low elastic modulus. In addition, the higher porosity also showed better corrosion resistance in the Hank’s solution. The potentiodynamic polarization curves show that the corrosion resistance increases significantly with an increase in porosity.

Nanostructural effects beyond Hall-Petch: Towards superhard tungsten carbide

Industrial application of superhard materials (Vickers hardness, HV > 40 GPa) such as diamond and cubic boron nitride is limited by high costs and complex routes of synthesis. Tungsten carbide (WC) is a common industrial material valued for its hardness, but falls well short of qualification as a superhard material even in its less common but harder binderless form (HV ∼ 26 GPa). Importantly, recent efforts have demonstrated the potential for alternative materials, such as WC, to achieve similar hardness to diamond and cubic boron nitride via microstructural refinement. However, despite recent advances in sintering technology, even the smallest grained binderless WC (< 100 nm) has failed to achieve HV values above 33 GPa. In this work, multiple hardening mechanisms are exploited through a unique sintering approach proving WC as a candidate superhard material. Environmentally Controlled – Pressure Assisted Sintering (EC-PAS) is utilized to produce > 99 % dense, binderless nanocrystalline WC ceramics with hardness as high as 39 GPa. The unprecedented WC hardness is attributed to the combined effects of small average crystallite size and, importantly, deformation-induced nanoscale intragranular defects including stacking faults. The demonstration of the superposition of multiple hardening mechanisms provides a new avenue to improve hardness of ceramics beyond traditional Hall-Petch hardening, yielding new classes of superhard materials.

Stabilization of metastable γ-co: Combustion synthesis and rapid processing

This study reports a novel method for stabilizing the metastable γ-Co phase, which has a face-centered cubic structure. This phase is known for its challenging synthesis due to its tendency to transform into the stable hexagonal-closed packed (ε-Co) allotrope. Combustion synthesis and a rapid pressure-less sintering approach overcome the traditional barriers to γ-Co preparation. The combustion process involves exothermic reactions in a solution of cobalt nitrate hexahydrate and hexamethylenetetramine, generating enough heat to increase the synthesis temperature above the γ↔ε phase transition temperature (∼690 K). Rapid cooling of the solid product by gases is critical to preventing the reverse transition to ε-Co, thus stabilizing the γ-Co phase with a minimal amount of the stable phase. Thermal analysis has demonstrated that the decomposition of cobalt nitrates hexahydrate leads to the formation of cobalt oxides. These oxides are then reduced to Co by methane (CH4) and hydrazine (N2H4), released during hexamethylenetetramine decomposition. Kinetic data analysis shows that the rate-limiting step in forming Co is the CH4 (or N2H4)-mediated reduction of CoO. When subjected to rapid pressure-less sintering at 1275 K, the combustion synthesized materials consolidate into compact samples with a relative density of ∼90 % and micrometer-size grains. High-resolution electron microscopy investigation shows increased lattice dislocation due to the ε→γ transition at high-temperature processing. Prepared γ-Co exhibits a higher nanohardness and Young's modulus than ε-Co prepared by slow melt solidification and rolling methods.

Realizing BiCuSeO-based thermoelectric device for ultrahigh carrier mobility through texturation

The thermoelectric conversion technology, as a promising renewable energy technology, enables direct and efficient conversion between electricity and heat. In the past ten years, there has been an increasing curiosity towards oxide thermoelectric materials due to their environmentally friendly nature, low cost, and excellent thermal and chemical stability. However, the intrinsic low carrier mobility of BiCuSeO limits its potential to be a high-performance thermoelectric material. Herein, we propose a dynamic sintering approach to enhance carrier mobility of BiCuSeO. As a result, carrier mobility at room temperature of three-step textured Bi0.94Pb0.06Cu0.97Se1.05O0.95 reaches an ultrahigh value of 13.1 cm2 V−1 s−1, which is the highest reported in the conventional doping of BiCuSeO system. Based on the ultrahigh carrier mobility, the power factor of three-step textured Bi0.94Pb0.06Cu0.97Se1.05O0.95 sample could reached 20 μV cm−1 K−2 near room temperature, and the average power factor of 300–923 K could reach 18.0 μV cm−1 K−2, effectively optimizing the electrical performance throughout the entire test temperature span. As a result, we successfully attain a ZT of ∼ 1.5 at 923 K and a ZTave of 0.89 within the temperature span of 300–923 K for three-step textured Bi0.94Pb0.06Cu0.97Se1.05O0.95 sample. Based on the outstanding performance, we have successfully built a 7-pair thermoelectric device based on three-step textured Bi0.94Pb0.06Cu0.97Se1.05O0.95 paired with the N-type two-step textured Bi2Te2.7Se0.3Cu0.01, which is the first BiCuSeO-based thermoelectric device. The thermoelectric device, exhibits a maximum conversion efficiency of 2.8 % at the temperature difference 215 K and simultaneously achieves a cooling temperature difference of 23.5 K with the hot end at 286 K. This work indicates that texturation is an effective approach for enhancing the carrier mobility of oxide TE materials. Besides, BiCuSeO oxyselenide is promising for pollution-free and cost-effective thermoelectric devices of power generation and cooling, thereby offering potential implications for sustainable energy solutions.

Production of Permanent Magnets from Recycled NdFeB Powder with Powder Extrusion Moulding

In the last fifteen years, several groups have investigated metal injection moulding (MIM) of NdFeB powder to produce isotropic or anisotropic rare earth magnets of greater geometric complexity than that achieved by the conventional pressing and sintering approach. However, due to the powder’s high affinity for oxygen and carbon uptake, sufficient remanence and coercivity remains difficult. This article presents a novel approach to producing NdFeB magnets from recycled material using Powder Extrusion Moulding (PEM) in a continuous process. The process route uses powder obtained from recycling rare earth magnets through Hydrogen Processing of Magnetic Scrap (HPMS). This article presents the results of tailored powder processing, the production of mouldable feedstock based on a special binder system, and moulding with PEM to produce green and sintered parts. The magnetic properties and microstructures of debinded and sintered samples are presented and discussed, focusing on the influence of filling ratio and challenging processing conditions on interstitial content as well as density and magnetic properties.

Preparation and interfacial microstructure of high thermal conductivity diamond/SiC composites

Diamond/SiC composites offer valuable applications in thermal management because of their exceptional thermal properties. Currently, the predominant method employed for crafting diamond/SiC composites is the reaction sintering approach. However, it encounters the challenge of a high residual silicon content. In this study, we introduced techniques such as bimodal diamond particles and high-density carbon sources (submicron diamond powder) to enhance the diamond content and reduce the residual silicon, optimizing the phase composition. The results indicated the diamond/SiC composite demonstrated a thermal conductivity of 666 W/m·K, a thermal expansion coefficient of 2.73 × 10−6 K−1, and an elastic modulus of 753 GPa. Furthermore, the meticulous assessment of the interface microstructure of diamonds in the diamond/SiC composite was conducted using transmission electron microscopy. The formation of nanocrystal-SiC and interface defects were elucidated by the mechanism of carbon dissolution saturation.

Development and investigation of salt based composite phase change material containing diatomite as skeleton substance by cold sintering technology for medium and high temperature thermal energy storage

This work concerns the development of a nitrate salt based form-stable composite phase change material by cold sintering technology with the employment of diatomite as skeleton substance. Such fabrication strategy has never before been reported in the literature and we demonstrate for the first time the feasibility of salt-diatomite composite production through a cold sintering process by means of sodium hydroxide solution as sintering additive. The microstructural characteristics and development mechanism, chemical and physical compatibility, mechanical strength, phase change behaviour, thermal and shape stability of the composite are investigated to reveal the structure formation and densification mechanism of salt and diatomite. The results show that the composite could be sintered at a temperature of 180 °C, far lower than that required in the traditional hot sintering approach. Due to the congruent solubility of the salt and diatomite in aqueous alkali, a rigid and dense structure induced by a so-called dissolution-precipitation process could be generated in the composite, which provides solution to accommodate the salt, endowing the composite with splendid capacity to maintain the structure stability and restrain the liquid leakage over the phase change process. An excellent chemical and physical compatibility has been achieved between the salt and other components, and over 60 wt% salt could be encapsulated in the composite by which a melting temperature around 278 °C and an energy storage density over 650 kJ/kg at a temperature range of 50–600 °C are attained. The results also reveal that the composite exhibits preeminent mechanical strength and excellent thermal cycling performance. For a given cycling temperature range of 50–500 °C, a stable macroscopic shape with a compressive strength over 210 MPa could be achieved in the composite even after 100 times of thermal cycles.