Cold Sintering Research Articles

Room temperature ZnO ageing after Cold Sintering Process: Grain boundaries evolution characterization by in situ electrochemical impedance spectroscopy

The use of in situ characterization techniques is detrimental for the development of low temperature sintering techniques such as the Cold Sintering Process. This is particularly interesting for the investigation of interface regions, thus for grain boundaries. In the present work we focus on the evolution at room temperature, after the cold sintering of two ZnO ceramics sintered at 200 and 250 °C, and show the influence of the presence of remaining acetates on the final properties. Based on in situ impedance measurements at room temperature, the present results highlight the importance of paying attention to the behavior of cold sintered samples and their evolution after sintering, due to the potential presence of even small amounts (<1 wt%) of remaining liquid species that may strongly alter the final properties of the specimen, with almost 2 orders of magnitude resistivity increase.

Si3N4@SiO2/PEEK core-shell structure ceramic matrix composite prepared by cold sintering and its tribological properties

The traditional high-temperature sintering method cannot achieve the combination of ceramics and polymers for the huge sintering temperature difference. The insufficient interfacial bonding strength of the ceramic matrix is the difficulty in the low-temperature preparation of ceramic-polymer composites. To improve the interfacial bonding strength of Si3N4 (Silicon nitride) ceramic matrix composite, an easy-bonding SiO2 (Silica) shell was introduced onto the surface of the hard-bonding Si3N4 core by Stober method, to obtain Si3N4@SiO2 composite. Si3N4@SiO2/PEEK (Polyetheretherketone) composites were prepared by the cold sintering process (500 MPa, 240 °C, and transient liquid phase is NaOH solution). The dry tribological properties of Si3N4@SiO2/PEEK composites with different PEEK percentages were studied by a ball-disc contact form. It is shown that an amorphous SiO2 shell with a thickness of 25 nm is chemically bonded onto the surface of the Si3N4 core. The presence of the SiO2 shell improves the interface bonding strength between Si3N4 ceramic particles. The friction coefficients of Si3N4@SiO2/PEEK composites decrease with the increase of PEEK percentage. Compared with Si3N4@SiO2 composite, the friction coefficient and wear rate of Si3N4@SiO2/50 vol% PEEK composite decrease by about 40% and 26%, respectively. The main wear forms of Si3N4@SiO2/PEEK composites are abrasive wear and adhesive wear. A mixed lubrication layer, mainly including PEEK, Si3N4, and SiO2, exists simultaneously on the surfaces of Si3N4@SiO2/PEEK composite and the counterpart ball, respectively, playing the role of reducing friction and wear.

Cold sintering of perovskite‐based mixed conducting membrane for oxygen separation

AbstractCold sintering has attracted significant attention as its remarkably rapid densification process at low sintering temperatures leads to considerable energy savings. However, the sintering behaviors of cold‐sintered perovskite ceramics remain poorly understood and lack precise control over material microstructure. Here, we fabricated dense SrCo0.8Fe0.2O3−δ (SCF) ceramic oxygen permeation membranes by cold sintering. Adding an appropriate ratio of sub‐micron SCF particles can better bridge the sintering interspaces between micron particles, generate amorphous phase through “dissolution‐precipitation,” and aid in the initial densification. The average relative density of SCF membranes undergoes a significant increase to 95.9% after cold sintering and post‐annealing at 900°C, which is much lower than the temperature required for conventional high‐temperature solid‐state sintering (&gt;1200°C). The oxygen permeation flux of the prepared SCF perovskite membrane reaches 2.8 mL min−1 cm−2, which proves that this method has the potential to be an excellent sintering technique for dense perovskite ceramic membranes.

Fabrication of nanocrystalline SiO2–ZrO2 glass-ceramic via a high-pressure cold sintering process

The nanocrystalline 0.35SiO2-0.65ZrO2 (65 mol% monoclinic ZrO2) glass-ceramic was successfully fabricated via a high-pressure cold sintering process (CSP), displaying remarkable nano hardness and elastic modulus of 12.5 and 154.8 GPa, respectively. We conducted a thorough investigation of the influence of NaOH solution concentration, liquid-to-solid mass ratio, sintering temperature, and pressure on the phase compositions, microstructural evolution, and densification. Notably, excessive NaOH concentration (>0.7 M) results in the transformation of SiO2 from an amorphous phase to α-quartz, hindering densification. However, below 0.7 M, increasing NaOH concentration enhances the densification processes. Furthermore, higher temperature and pressure contribute to improved densification. It is worth mentioning that there is no grain growth for the ZrO2 phases during the CSP, indicating that the densification of the nanocrystalline 0.35SiO2-0.65ZrO2 glass-ceramic is primarily governed by the glass phase.

Thermoelectric properties of aliovalent Zn doped Cu1.8S polycrystalline materials

Cu1.8S-based materials are regarded as promising thermoelectric materials due to their super ionic nature. The Cu1.8-xZnxS (x = 0, 0.01, 0.03, and 0.09) samples were synthesized by the hydrothermal method followed by cold pressing and sintering. The powder X-ray diffraction pattern has confirmed the phase purity and rhombohedral crystal structure of Cu1.8S. Additionally, FE-SEM micrographs along with the EDX elemental mapping detected the existence of CuS as the secondary phase in the Cu1.8S matrix and uniform distribution of the constituent elements. Upon doping the Zn atom, the Seebeck coefficient subsequently increases owing to the decrement in the carrier concentration, whereas the electrical conductivity gradually reduces. Essentially, the presence of CuS secondary phase and the defects induced by the Zn atom effectively scattered low-mid wavelength phonons, where a very low thermal conductivity of 3.65 W/mK was achieved for Cu1.71Zn0.09S at room temperature. Ultimately, an overall maximum zT of 0.07 at 573 K was observed for Cu1.77Zn0.03S, which is about 3.5 times greater than that of the pristine sample.

The effect of SiC amount on microstructure and wear properties in SiC-reinforced Mo5SiB2

This study aimed to investigate how silicon carbide (SiC) reinforcement affected the microstructure and wear properties of Mo5SiB2-based alloy fabricated by powder metallurgy. The main reasons for using SiC in this study are that it is affordable and improves the wear resistance of the Mo5SiB2-based alloy. SiC at 2 %, 4 %, and 6 % by volume was added to Mo5SiB2-based alloy. After cold pressing and sintering, the samples' microstructure, density, hardness, and wear properties were analyzed in detail. Scanning electron microscope (SEM) images indicated that a porous and skeletal structure formed as a microstructure. This structure became more pronounced with an increased SiC rate. X-ray diffraction (XRD) results showed that Mo5SiB2 (T2 phase), Mo3Si (A15 phase), α-Mo, SiO2, and SiC phases formed in the microstructure. With increasing SiC rate, the peaks of binary and ternary phases increased. The experimental densities dropped upon the reinforcement of SiC. The hardness of the samples reached the maximum value (1639HV2) in the Mo-Si-B alloy at 6 % SiC rate. The results of the pin-on-disk wear tests run to assess the wear performance of the samples indicated that the best wear performance was achieved in the 6 % SiC-reinforced sample with a coefficient of friction (COF) of 0.49 and a wear rate of 0.43 × 10−5 mm3 (N.m)−1.

Cold Sintering Mediated Engineering of Polycrystalline SnSe with High Thermoelectric Efficiency.

Despite the attractive thermoelectric properties in single crystals, the fabrication of high-performance polycrystalline SnSe by a cost-effective strategy remains challenging. In this study, we prepare the undoped SnSe ceramic with remarkable thermoelectric efficiency by the combination of a cold sintering process (CSP) and thermal annealing. The high sintering pressure during CSP induces not only highly oriented grains but also a high concentration of lattice dislocations and stacking faults, which leads to large lattice strain that can shorten the phonon relaxation time. Meanwhile, the thermal annealing breaks the highly resistive SnOx layers at grain boundaries, which improves the electrical conductivity and power factor. In addition, the grain growth during annealing further turns the broken SnOx layers into nanoparticles, which further lowers the thermal conductivity by enhanced scattering. As a result, a peak ZT of 1.3 at 890 K and a high average ZT of 0.69 are achieved in the polycrystalline SnSe, suggesting great potential in mid-temperature power generation. This work may pave the way for the mass production of SnSe-based ceramics for thermoelectric devices.

High-performance thermoelectric properties of Cu2Se fabricated via cold sintering process

The concept of a ‘phonon-liquid electron-crystal’ has received significant interest in recent years, with copper selenide (Cu2Se) emerging as one of the high-performance thermoelectric materials within this framework. This study focuses on the fabrication of Cu2Se bulk pellets through a low-temperature sintering method known as cold sintering process (CSP). The introduction of a liquid phase (thiol-amine solution) in this process facilitates the dissolution and precipitation of ion/atom clusters, resulting in sample densification. Remarkably, a sample density of nearly 90 % is achieved at a low sintering temperature of only 473 K. Furthermore, this CSP approach preserves the morphology of the Cu2Se precursor powders and effectively inhibits grain growth. Consequently, the lattice thermal conductivity of the CSP samples is significantly reduced, attributed to enhanced grain boundary phonon scattering. This leads to a substantial improvement in the figure-of-merit (ZT), increasing from 0.65 at 800 K in the hot-pressed sample to 2.13 at 800 K in the CSP sample. The advantages of CSP can be extended beyond Cu2Se, as it holds promise for enhancing the performance of various high-performance thermoelectric materials.

Porous Lithium Disilicate Glass-Ceramics Prepared by Cold Sintering Process Associated with Post-Annealing Technique.

Using melt-derived LD glass powders and 5-20 M NaOH solutions, porous lithium disilicate (Li2Si2O5, LD) glass-ceramics were prepared by the cold sintering process (CSP) associated with the post-annealing technique. In this novel technique, H2O vapor originating from condensation reactions between residual Si-OH groups in cold-sintered LD glasses played the role of a foaming agent. With the increasing concentration of NaOH solutions, many more residual Si-OH groups appeared, and then rising trends in number as well as size were found for spherical pores formed in the resultant porous LD glass-ceramics. Correspondingly, the total porosities and average pore sizes varied from 25.6 ± 1.3% to 48.6 ± 1.9% and from 1.89 ± 0.68 μm to 13.40 ± 10.27 μm, respectively. Meanwhile, both the volume fractions and average aspect ratios of precipitated LD crystals within their pore walls presented progressively increasing tendencies, ranging from 55.75% to 76.85% and from 4.18 to 6.53, respectively. Young's modulus and the hardness of pore walls for resultant porous LD glass-ceramics presented remarkable enhancement from 56.9 ± 2.5 GPa to 79.1 ± 2.1 GPa and from 4.6 ± 0.9 GPa to 8.1 ± 0.8 GPa, whereas their biaxial flexural strengths dropped from 152.0 ± 6.8 MPa to 77.4 ± 5.4 MPa. Using H2O vapor as a foaming agent, this work reveals that CSP associated with the post-annealing technique is a feasible and eco-friendly methodology by which to prepare porous glass-ceramics.

Consolidation of Spray-Dried Amorphous Calcium Phosphate by Ultrafast Compression: Chemical and Structural Overview.

A large amount of research in orthopedic and maxillofacial domains is dedicated to the development of bioactive 3D scaffolds. This includes the search for highly resorbable compounds, capable of triggering cell activity and favoring bone regeneration. Considering the phosphocalcic nature of bone mineral, these aims can be achieved by the choice of amorphous calcium phosphates (ACPs). Because of their metastable property, these compounds are however to-date seldom used in bulk form. In this work, we used a non-conventional "cold sintering" approach based on ultrafast low-pressure RT compaction to successfully consolidate ACP pellets while preserving their amorphous nature (XRD). Complementary spectroscopic analyses (FTIR, Raman, solid-state NMR) and thermal analyses showed that the starting powder underwent slight physicochemical modifications, with a partial loss of water and local change in the HPO42- ion environment. The creation of an open porous structure, which is especially adapted for non-load bearing bone defects, was also observed. Moreover, the pellets obtained exhibited sufficient mechanical resistance allowing for manipulation, surgical placement and eventual cutting/reshaping in the operation room. Three-dimensional porous scaffolds of cold-sintered reactive ACP, fabricated through this low-energy, ultrafast consolidation process, show promise toward the development of highly bioactive and tailorable biomaterials for bone regeneration, also permitting combinations with various thermosensitive drugs.

Direct cold sintering of translucent gamma-Al2O3 ceramics

Gamma-Al2O3 ceramics can hardly be densified by conventional sintering methods because of the low surface energy of gamma-Al2O3 powder and phase transformation at elevated temperature. Here, we report the preparation of translucent gamma-Al2O3 ceramics by cold sintering process at merely 350 °C via using the gamma-Al2O3 as starting powder. Due to the enhanced solubility and reaction of gamma-Al2O3 in alkaline solution, the nanocrystalline particles can be densified to ∼92% of full density via adding 10 M NaOH solution as the transient liquid. It is proved that the high concentration of alkaline solution can greatly accelerate the dissolution-precipitation process, leading to the activation energy as low as 16.9 kJ/mol. Consequently, a translucent ceramic with in-line transmittance reaching 16% around 800 nm can be obtained, despite the residual porosity. Considering the stable hardness and translucency after water leaching or heating to 1000 °C, the cold sintered gamma-Al2O3 ceramic may have the potential application as optical windows under extreme environments.

Improving the stability of ceramic-type lithium tantalum phosphate (LiTa2PO8) solid electrolytes in all-solid-state batteries

Solid-state battery (SSB) systems are among the most promising next-generation batteries for electronics and electric vehicles because of their high volumetric energy density, safety, nonflammability, and chemical stability, compared to lithium-ion batteries using conventional liquid electrolytes. However, SSBs have several limitations, including the reactivity of the electrode materials. Herein, we address these issues by synthesizing lithium tantalum phosphate (LTPO) solid-electrolyte disks through a cold sintering process and assembling them with a lithium manganese iron phosphate (LMFP) electrode into an all-solid-state battery. The SSB fabricated with LTPO/LMFP exhibited a high initial discharge capacity (~130 mAh/g) and capacity retention (70 % after 100 cycles) at room temperature (RT). The LTPO with an amorphous lithium-based composite in the grain boundaries has high ionic conductivity and stability at the interface of the LMFP electrodes. In addition, the LMFP cathodes with an adhesive layer infiltrating the pores of the electrode significantly improved the cyclic performance of the SSB system with an initial capacity of 125 mAh/g and capacity retention of approximately 98 % after 100 cycles at RT. The analysis and future experimental results proved that this novel material and approach can improve the electrochemical performance of rechargeable SSBs and contribute to the development of high-performance energy storage devices for various applications.

Cold sintering process for densification of Fe3O4 ceramic magnets with improved properties

Iron oxide-based ferrite ceramics, widely applied in high-frequency applications, are conventionally produced through high-temperature sintering processes, often resulting in grain growth and phase transformation. In this study, we used a cold sintering process (CSP) with oxalic acid (OA) as a solvent to consolidate iron oxide (Fe3O4) ceramics at a low temperature of 160 °C. The OA-assisted CSP technique has demonstrated a remarkable capacity to facilitate the dissolution and redeposition of iron oxide ions, leading to the interconnection of Fe3O4 particles, forming densely packed ceramics even at low-temperature sintering. Importantly, CSP maintained particle sizes and hindered phase transitions of Fe3O4. The OA concentrations in CSP had a minimal impact on crystal structure and magnetic properties, but it significantly enhanced microstructural features, density, hardness, and electrical resistance. Compared to reference samples prepared without an aqueous solution or with water alone, the CSP-prepared Fe3O4 ceramics with OA exhibited substantially improved density (a relative density of ∼80 %), mechanical properties (Vickers hardness of 3.5–4.0 GPa), magnetic properties (saturation magnetization >70 emu/g), and electrical resistance (electrical conductivity ∼10−3 S/cm at 102–106 Hz). These findings demonstrate a novel approach to fabricating Fe3O4 ceramics at significantly lower temperatures while still achieving properties comparable to those sintered at high temperatures.

Upcycling plastic waste into fully recyclable composites through cold sintering.

Plastics have substantial societal benefits, but their widespread use has led to a critical waste management challenge. While mechanical recycling dominates the reuse of post-consumer plastics, it is limited in efficacy, especially for composites. To address this, we propose a direct reprocessing approach that enables the creation of hybrid, long-lasting, and durable composites from difficult-to-recycle plastics. This approach utilizes cold sintering, a process that consolidates inorganic powders through fractional dissolution and precipitation at temperatures far below conventional sintering; these temperatures are compatible with plastic processing. We show that this process can create inorganic-matrix composites with significant enhancements in tensile strength and toughness over pure gypsum, which is commonly found in construction waste. These composites can be recycled multiple times through direct reprocessing with the addition of only water as a processing promoter. This approach to recycling leads to composites with orders of magnitude lower energy demand, global warming potential, and water demand, when compared against common construction products. Altogether, we demonstrate the potential for cold sintering to integrate waste into high-performance recyclable composites.

Consolidation and characterization of Cu, Mg substituted hydroxyapatite by cold sintering

Cold sintering method is an effective route to consolidate powders at temperatures below 300?C. In this study, pure and (Cu, Mg) substituted hydroxyapatite were sintered at 250?C. Ultrapure and substituted hydroxyapatite powders were synthesized by wet precipitation method. Sintering pressure of 250 MPa was used to compact the powders while they were heated simultaneously. 10% (H3PO4) solution was used as a transsolvent for the ionic-substituted hydroxyapatite while distillated water was supplied to the pure one. The yield geometries were characterized for density, thermal stability, microstructure, and the biodegradation in Tris-HCl buffer. The findings indicate that the pure hydroxyapatite compacts has a density of 2.876 g/cm3 (86% TD). Owing to the low sintering temperature the resulting hydroxyapatites have not experienced thermal decomposition, besides no additional phases have appeared. Biologically, the sintered sample (Cu0.25Mg0.75Ca9(PO4)6(OH)2) showed larger degradability (0.0001 g/mm2) than to others after one day of immersion.

Achieving high ionic conductivity of LATP solid electrolyte via a LiTFSI-assisted cold sintering process

A LATP solid electrolyte with an island structure and amorphous layer was synthesized via a LiTFSI-assisted cold sintering process, which is conducive to the rapid Li+ migration and excellent cycling stability in Li/LiFePO4 full batteries.

Cold Sintering of Nickel Manganese Oxide for Thermistors Fabrication

In this paper we successfully densified NiMn2O4 (NMO) ceramics using the cold sintering process (CSP) with various molten salt fluxes as a transient liquid phase, achieving relative densities exceeding 95%....

Cold sintering process of hydroxyapatite derived from natural bone and co-precipitation method: a comparative study

Cold sintering process of hydroxyapatite derived from natural bone and co-precipitation method: a comparative study

Two-step cold sintering of Li1.3Al0.3Ti1.7(PO4)3 composite solid electrolyte with non-equilibrium microstructures for enhanced electrochemical performance

High densification and high electrochemical performance were obtained in solid-state electrolytes with non-equilibrium microstructures by two-step cold sintering.

Hydroflux-assisted cold sintering: eutectic mixtures for boosting ionic conductivity in LATP solid-state electrolytes

Superior electrical properties have been achieved for a Li1.3Al0.3Ti1.7(PO4)3 (LATP) solid-state electrolyte (SSE) by using the novel hydroflux-assisted cold sintering process (HACSP) at 400 MPa, 200 °C and 90 minutes of sintering time.