Ultrafast Sintering Research Articles

Fabrication of Si3N4 ceramic balls by SPS method with SiC powder bed

AbstractSpark plasma sintering (SPS) is an ultrafast sintering method for the preparation of ceramics and ceramic composites with simple geometrical shapes, with the combined application of uniaxial pressure. This study aims to propose an SPS densification method for Si3N4 ceramic balls without necessitating alterations to tools and equipment. The Si3N4 ceramic balls intended for sintering are positioned within a SiC powder bed inside the conventional die used in SPS. The study systematically investigates the effects of presintering temperature (1400°C, 1500°C, and 1600°C) and SPS temperature (1600°C, 1700°C, and 1800°C) on the sphericity, relative density, phase composition, microstructure, and mechanical properties of Si3N4 ceramic balls. Experimental findings reveal that Si3N4 ceramic balls exhibiting an optimal combination of sphericity (0.94 ± 0.02), relative density (98.4%), and mechanical properties (Vickers hardness: 17.5 ± 0.4 GPa, fracture toughness: 6.4 ± 0.1 MPa·m1/2) were successfully achieved at a pre‐sintering temperature and SPS temperature of 1600°C, coupled with the use of a SiC powder bed and SPS method. Consequently, the SPS method demonstrates its capability to fabricate Si3N4 ceramic balls with excellent performance.

Flash soldering of boron nitride nanosheets for all-ceramic films

The assembly of boron nitride nanosheets (BNNSs) into strong, flexible thin films capable of withstanding extreme conditions, such as high/low working temperatures and corrosive environments, holds promise for numerous applications. However, Assmebling and sintering of BNNS into dense thin film can be challenging. We report the rapid fabrication of dense BNNS all-ceramic films (BACFs) in 30 s by combining the fabrication strategies for 2D and ceramic materials. In this process, densely arranged and highly oriented BNNSs are flash soldered into a monolith achieved by precisely controlled ultrafast sintering. This fusion of BNNS leads to an ultrahigh in-plane thermal conductivity of 134.5 W·m−1·K−1. The as-prepared BACF exhibits the combined advantages of sintered ceramics (durability, stability, acid-alkali resistance) and 2D material films such as flexibility and shock resistance, which is important for practical uses. It also has excellent cooling performance, dielectric properties, and good thermal stability, which is promising for demanding thermal management applications in emerging technologies.

Unraveling the conundrum of electronic leakage in protonic ceramic cells: Operation-specific insights and rational design strategies

Electronic conduction through proton-conducting electrolytes significantly impairs the efficiency of protonic ceramic cells (PCCs). In this study, we explore the electron and ion mixed transport properties of four common protonic ceramics, BaZr0.8Y0.2O3-δ (BZY82), BaZr0.7Ce0.2Y0.1O3-δ (BZCY721), BaZr04Ce0.4Y0.1Yb0.1O3-δ (BZCYYb4411), and BaZr0.1Ce0.7Y0.1Yb0.1O3-δ (BZCYYb1711). It marks the first instance of investigating these properties under operation-specific scenarios: fuel side of electrolysis cell, air side of electrolysis cell, fuel side of fuel cell, and air side of the fuel cell. BZCYYb1711 exhibits the highest ionic conductivity, but two to three times higher electronic leakage when exposed to oxygen-containing environments than the others. BZY82 exhibits approximately two times higher electronic leakage in a hydrogen-containing environment. BZCY721 demonstrates excellent ion transport numbers (∼0.95) across these four operating conditions. BZCYYb4411 behaves quite similarly to BZCY721. The most challenging operating environment for all candidates is the air side of fuel cell mode. This mode leads to a high initial electronic leakage, followed by a significant increase with polarization. The probable cause for this behavior is a H2-free, polarization-induced reduction that leads to the formation of VO•. The electron small polaron associated with VO• is released by the electrical field due to the Poole-Frenkel effect. ZnO and NiO sintering aids are found to be detrimental to the ionic conductivity of the electrolytes. In particular, NiO substantially lowers the ion transport number. The correlation of the operation-specific electronic leakage to full cells is discussed. It is suggested that a rational PCC design should synergistically couple BZCYYb1711 at fuel side with BZCY4411 at air side to deliver a well-balanced performance and faradaic efficiency simultaneously, and the high temperature sintering process with a NiO fuel electrode should be shortened or replaced by ultra-fast sintering techniques or using a fuel electrode scaffold-infiltration fabrication strategy.

Garnet-Based Solid-State Li Batteries with High-Surface-Area Porous LLZO Membranes.

Rechargeable garnet-based solid-state Li batteries hold immense promise as nonflammable, nontoxic, and high energy density energy storage systems, employing Li7La3Zr2O12 (LLZO) with a garnet-type structure as the solid-state electrolyte. Despite substantial progress in this field, the advancement and eventual commercialization of garnet-based solid-state Li batteries are impeded by void formation at the LLZO/Li interface at practical current densities and areal capacities beyond 1 mA cm-2 and 1 mAh cm-2, respectively, resulting in limited cycling stability and the emergence of Li dendrites. Additionally, developing a fabrication approach for thin LLZO electrolytes to achieve high energy density remains paramount. To address these critical challenges, herein, we present a facile methodology for fabricating self-standing, 50 μm thick, porous LLZO membranes with a small pore size of ca. 2.3 μm and an average porosity of 51%, resulting in a specific surface area of 1.3 μm-1, the highest reported to date. The use of such LLZO membranes significantly increases the Li/LLZO contact area, effectively mitigating void formation. This methodology combines two key elements: (i) the use of small pore formers of ca. 1.5 μm and (ii) the use of ultrafast sintering, which circumvents ceramics overdensification using rapid heating/cooling rates of ca. 50 °C per second. The fabricated porous LLZO membranes demonstrate exceptional cycling stability in a symmetrical Li/LLZO/Li cell configuration, exceeding 600 h of continuous operation at a current density of 0.1 mA cm-2.

Ultrafast sintering of boron nitride nanosheet assembled microspheres with strong processability for high-performance thermal management materials

A novel strategy produces BNNS microspheres for isotropic thermal conductivity, utilizing high-temperature ultrafast sintering and surface engineering to enhance processability for producing thermal management materials.

Garnet-type solid-state mixed ionic and electronic conductor

Low ion and electron conductivities of the cathode and poor cathode interface performance severely limit the application of garnet solid-state batteries. While various approaches have been developed to improve the cathode interface contact or enhance ion and electron transport, none of these methods can simultaneously achieve high interfacial electrochemical activity and chemical stability. In this work, we propose to develop a single-phase garnet-type mixed ionic and electronic conductor (MIEC) as the cathode framework, which is expected to achieve the unification of high activity and high stability at the cathode interface. Combining first-principles calculations and ultrafast sintering techniques, we have synthesized and screened a series of garnet-type MIECs by introducing transition metals into garnet SSEs. Among the garnet-type MIECs, Li43Fe3La24Zr12Ta4O96 (3Fe) not only exhibits an excellent electronic conductivity of up to 2.87 × 10−4 S cm−1 but also maintains an ionic conductivity of 4.57 × 10−5 S cm−1. The high electronic conductivity is believed to originate from the high-temperature reduction phase formed during the rapid sintering process under inert conditions. A small polaron hopping mechanism is proposed to explain the electronic conductivity based on electronic structure calculations and activation energy analysis. Since garnet-type MIECs have the same crystal structure as garnet solid-state electrolytes (SSEs) and transition metal elements similar to those of oxide cathode materials, they potentially have good cosintering stability with both electrolytes and cathodes. This work provides a new strategy to solve the cathode interface problem in garnet solid-state batteries.

Ultrafast high-temperature sintering of polymer-derived ceramic nanocomposites for high-temperature thin-film sensors

Polymer-derived ceramic nanocomposites (PDC-NCs) are promising materials for high-temperature thin-film sensor (TFS) applications. However, owing to their inherent high-resistance characteristics and the high-temperature furnace sintering process, it is difficult to integrate PDC-NCs with high-conductive and low high-temperature tolerant alloy/metal components. In this study, an ultrafast high-temperature sintering (UHS) method was employed to prepare PDC-NC TFSs in minutes. The TiB2/SiCNO film sintered by the UHS technique shows high-sensitive microstructure and properties to sintering parameters. The UHS technique allows rapid sintering toward the desired phase, controls the grain size and microstructure, promotes the precipitation of free carbon in the SiCNO matrix within minutes, and suppresses high-temperature oxygen pollution. For example, TiB2/SiCNO films show high conductivity (18.1 S cm−1 at room temperature) and high-temperature stability (up to 800 ℃). In comparison, these properties are orders of magnitude better than those of samples sintered in the furnace. High-quality films sintered using ultrafast heating and cooling rates can also withstand thermal shocks of up to 1000 ℃. With the UHS technique, high-quality and high-conductivity films can be prepared using an ultrafast sintering rate to prevent substrate thermal damage. The TiB2/SiCNO thin-film strain gauge with high sensitivity (GF = 8.6) and low thermal noise was fabricated on alloy substrates, and its high-temperature (25–800 ℃) strain sensing performance was verified. This method offers a new route for co-sintering devices with alloy/metal substrates that suffer from low high-temperature tolerance and regulating the microstructure and electrical performance of these devices.

Controllable Constructing Janus Homologous Heterostructures of Transition Metal Alloys/Sulfides for Efficient Oxygen Electrocatalysis

AbstractConstructing novel heterostructures is an effective way for enhancing the oxygen electrocatalytic properties of the catalysts. In this work, a class of Janus homologous heterostructures, compositing transition metal alloys with their corresponding sulfides (TM/TMS), are controllably synthesized through an ultrafast high‐temperature shock (HTS) strategy. The ultrafast sintering rate and carbothermal reduction reaction lead to the formation of sulfides and partial reduction of sulfides to alloys, while the ultrafast cooling rate keeps the homologous heterostructure of TM/TMS stable. The components of TMs in the composites can be well controlled from unary to quaternary. Moreover, benefiting from the synergistic effect of the metallic sites in the interfaces, the adsorption and desorption energy barrier of the active intermediates are significantly optimized and thus leading to the enhanced oxygen catalytic performance. Impressively, the aqueous zinc‐air battery (ZAB) using the binary homologous nanocomposite FeCo/(FeCo)S as air cathodes achieves impressive durability (> 470 cycles) and power density (261.8 mW cm−2). The as‐assembled flexible ZAB can well power the wearable devices and can work for at least 300 cycles without obvious degradation. This work opens a new chemical space for designing homologous heterostructures for their application in energy storage and conversion systems.

Ultrafast Sintering for Ceramic-Based All-Solid-State Lithium-Metal Batteries.

Long processing time and high temperatures are often required in sintering ceramic electrolytes, which lead to volatile element loss and high cost. Here, an ultrafast sintering method of microwave-induced carbothermal shock to fabricate various ceramic electrolytes in seconds is reported. Furthermore, it is also possible to integrate the electrode and electrolyte in one step by simultaneous co-sintering. Based on this ultrafast co-sintering technique, an all-solid-state lithium-metal battery with a high areal capacity is successfully achieved, realizing a promising electrochemical performance at room temperature. This method can extend to other various ceramic multilayer-based solid devices.

High-Performance Protonic Ceramic Electrochemical Cells

Protonic ceramic electrochemical cells (PCECs) have attracted considerable attention owing to their ability to reversibly convert chemical fuels into electricity at low temperatures below 600 °C. However, extreme sintering conditions during conventional convection-based heating induce critical problems for PCECs such as nonstoichiometric electrolytes and microstructural coarsening of the electrodes, leading to performance deterioration. Therefore, we fabricated PCECs via a microwave-assisted sintering process (MW-PCEC). Owing to the ultrafast ramping rate (∼50 °C/min) with bipolar rotation and the resistive heating nature of microwave-assisted sintering, undesirable cation diffusion and grain growth were effectively suppressed, thus producing PCECs with stoichiometric electrolytes and nanostructured fuel electrodes. The MW-PCEC achieved electrochemical performance in both in fuel cell (0.85 W cm–2) and in electrolysis cell (1.88 A cm–2) modes at 600 °C (70% and 254% higher than the conventionally sintered PCEC, respectively) demonstrating the effectiveness of using an ultrafast sintering technique to fabricate high-performance PCECs.

Low-temperature and ultrafast dual-powder spark plasma sintering of (W,Ti)C cermets with the addition of metal core-shell nanopowder

Nickel-coated molybdenum metal core-shell (Mo@Ni) nanopowder was prepared by a heterogeneous nucleation–thermal reduction method and then used as the metal binder phase in (W,Ti)C ceramic materials. (W,Ti)C/Mo@Ni/Co cermet was prepared by dual-power spark plasma sintering. The effects of sintering rate and sintering temperature on the microstructure and mechanical properties of (W,Ti)C/Mo@Ni/Co cermets were investigated. Results showed that when the sintering rate was 400 °C/min and the sintering temperature was 1325 °C, the (W,Ti)C/Mo@Ni/Co tool material had the best comprehensive mechanical properties, with a Vickers hardness of 17.44 ± 0.23 GPa, a fracture toughness of 11.27 ± 0.46 MPa·m1/2, and a flexural strength of 1450.23 ± 23 MPa. The core-shell structure of Mo@Ni made full use of the solid solution characteristics of the MoNi binary alloy and produced a solid solution in situ without liquid phase diffusion, which accelerated the sintering rate. The use of Mo nanopowder took advantage of its small-size effects and high surface energy, which reduced the temperature at which the solid solution effect began and reduced the sintering temperature. The combination of these two aspects was used to prepare a (W,Ti)C cermet with good strength and toughness by low-temperature rapid sintering. Low-temperature and ultrafast sintering are helpful to reduce the energy consumption in the preparation of cermets.

Enhanced Electrocatalysts Fabricated via Quenched Ultrafast Sintering: Physicochemical Properties and Water Oxidation Applications

AbstractThe synthesis of transition metal oxides is typically time‐ and energy‐consuming. Recently, fast sintering methods have demonstrated great potential in reducing ceramic sintering time and energy use, improving the commercial prospects of these materials. In this article, a quenched ultrafast high‐temperature sintering (qUHS) technique is developed to sinter metastable brownmillerite SrCoO2.5 (SCO) in less than a minute. Surprisingly, SCO fabricated by qUHS shows higher activity for the oxygen evolution reaction (OER) than solid‐state‐reaction‐synthesized SCO. Comparing samples produced by these two techniques, the increased OER performance of SCO qUHS is likely due to the synergistic combination of surface Co chemical state, higher mesoporosity, and enhanced hydroxyl ion (OH–) adsorption. This work demonstrates the potential of qUHS for producing high‐performance electrocatalysts and provides detailed insights into the impact of ultrafast sintering on the materials’ physical properties and electrocatalytic activity.

Microstructure and mechanical properties of (Ti,W)C cermets prepared by ultrafast spark plasma sintering

To explore the impact of the sintering rate on the microstructure and mechanical properties of cermets, the preparation of (Ti,W)C cermets by ultrafast sintering via spark plasma sintering (SPS) is reported. Compared with a slow heating rate, the electric field produced by an ultrafast heating rate enhances the liquid phase mass transfer of the metal binder phase, thus achieving rapid densification of (Ti,W)C cermets and effectively inhibiting abnormal grain growth. However, an excessive heating rate will lead to an “overflow” phenomenon, which reduces the grain growth difficulty and the bonding strength between grains. The results show that when the heating rate is 500 °C/min, the liquid phase mass transfer is moderate, the densification degree is the highest and the mechanical properties are excellent. The flexural strength, Vickers hardness and fracture toughness are 1340.90 ± 23.55 MPa, 18.42 ± 0.46 GPa and 11.96 ± 0.23 MPa∙m1/2, respectively.

Effect of pressure on the electrical resistance flash sintering of tungsten carbide

The application of external pressure during the Electrical Resistance Flash Sintering of tungsten carbide (WC), a “metallic ceramic” with positive temperature coefficient (PTC) for resistivity, results in a limited densification of the powder. In the present work, the effect of pressure on the ultrafast sintering of WC is analysed in detail. In particular, the application of pressure at different stages of flash sintering is studied by varying independently the processing parameters i.e., voltage, time and pressure. Microstructural characterization performed by FE-SEM and XRD identifies biphasic structures of WC and W2C, which compositions result almost unchanged for different sintering parameters. Increasing the external load from 4 up to 100 MPa leads to microporous materials, limiting the attainable final density. Pressure is demonstrated to control the flash phenomenon directly by affecting the flash duration and intensity, thus controlling the electrical energy dissipated during the power surge with respect to the overall process.

Electrical resistance flash sintering of tungsten carbide

This work explores the possibilities for the ultrafast sintering of binderless tungsten carbide by electric/pressure assisted sintering. A limited voltage (3–4 V) in AC condition was applied to WC powder compact in combination with uniaxial pressure. The thermal insulating ceramic die allows the ultrafast heating (104 °C/min) of the powder compact which undergoes a rapid transition of its electrical properties, from negative to positive dependence of resistivity on temperature, i.e. from NTC to PTC behaviour. Such effect is fundamental for inducing a thermal runaway phenomenon associated with ultrarapid temperature increase and massive electric power dissipation, thus inducing very rapid sintering. The relationship between electrical properties of tungsten carbide and the possibility to achieve “flash sintering” conditions to complete densification in a couple of seconds was investigated. At the optimal conditions of 3.5 V and 4 MPa pressure, pure WC sinters up to 95% in less than 10 s. Longer sintering time after the flash improves only slightly the density, despite a significant energetic consumption. It is also shown that if larger pressure is applied, the flash event duration and final density decrease.

Ultrafast Sintering of Solid-State Electrolytes with Volatile Fillers

Ultrafast Sintering of Solid-State Electrolytes with Volatile Fillers

High‐Temperature Ultrafast Sintering: Exploiting a New Kinetic Region to Fabricate Porous Solid‐State Electrolyte Scaffolds

AbstractSolid‐state batteries (SSBs) promise better safety and potentially higher energy density than the conventional liquid‐ or gel‐based ones. In practice, the implementation of SSBs often necessitates 3D porous scaffolds made by ceramic solid‐state electrolytes (SSEs). Herein, a general and facile method to sinter 3D porous scaffolds with a range of ceramic SSEs on various substrates at high temperature in seconds is reported. The high temperature enables rapid reactive sintering toward the desired crystalline phase and expedites the surface diffusion of grains for neck growth; meanwhile, the short sintering duration limits the coarsening, thus accurately controlling the degree of densification to preserve desired porous structures, as well as reducing the loss of volatile elements. As a proof‐of‐concept, a composite SSE with a good ionic conductivity (i.e., ≈1.9 × 10−4 S cm−1 at room temperature) is demonstrated by integrating poly(ethylene oxide) with the 3D porous Li6.5La3Zr1.5Ta0.5O12 scaffold sintered by this method. This method opens a new door toward sintering a variety of ceramic‐SSE‐based 3D scaffolds for all‐solid‐state battery applications.

Microstructure Evolution in a Fast and Ultrafast Sintered Non-Equiatomic Al/Cu HEA

One of the attractive characteristics of high entropy alloys (HEAs) is the ability to tailor their composition to obtain specific microstructures and properties by adjusting the stoichiometry to obtain a body-centered cubic (BCC) or face-centered cubic (FCC) structure. Thus, in this work, the target composition of an alloy of the FeCrCoNi family has been modified by adjusting the Al/Cu ratio in order to obtain a BCC crystalline structure. However, processing conditions always play a key role in the final microstructure and, therefore, in this work, the microstructure evolution of FeCrCoNiAl1.8Cu0.5 HEA sintered by different powder metallurgy (PM) techniques has been investigated. The techniques used range from the conventional PM sintering route, that uses high heating rates and sintering times, going through a fast sintering technique such as spark plasma sintering (SPS) to the novel and promising ultrafast sintering technique electrical resistance sintering (ERS). Results show that the increase in the processing time favours the separation of phases and the segregation of elements, which is reflected in a substantial change in the hardness of the alloy. In conclusion, the ERS technique is presented as a very promising consolidation technique for HEA.

Novel Intense-pulsed-light synthesis of amorphous SnO2 electron-selective layers for efficient planar MAPbI3 perovskite solar cells

Although perovskite solar cells (PSCs) have achieved a high power conversion efficiency (PCE) within a short period of development, the high-temperature sintering of the constituent electron-selective layers (ESLs) impedes the commercialization. In this report, we demonstrate the effectiveness of an intense-pulsed-light (IPL) treatment for the rapid and damage-free sintering of amorphous-SnO2 ESLs for use in PSCs. The IPL treatment of amorphous-SnO2 substantially reduced the amount of surface hydroxyl groups, modified the surface energy, and enabled the growth of a low-stress perovskite layer with large grain sizes, all of which enhanced the photovoltaic properties and led to the proper alignment of band structures for efficient PSCs. Through comprehensive optimization of the IPL conditions, a PCE of 17.68% was achieved from the MAPbI3 planar PSC based on an amorphous-SnO2 IPL treated for a few tens of seconds, which was significantly increased compared with a PCE (7.06%) of nontreated SnO2 based counterpart. In addition, the PCE of the IPL-treated SnO2 based PSC is comparable to the best PCE (18.16%) of PSCs fabricated with SnO2 ESL annealed for three hours at 185 °C. Because of its ultrafast sintering time and tendency to not damage SnO2 ESLs, the new IPL process is expected to open new opportunities for the commercialization of PSCs.

Innovative Densification Process of a Fe-Cr-C Powder Metallurgy Steel

In this study, the efficacy of an innovative ultra-fast sintering technique called electro-sinter-forging (ESF) was evaluated in the densification of Fe-Cr-C steel. Although ESF proved to be effective in densifying several different metallic materials and composites, it has not yet been applied to powder metallurgy Fe-Cr-C steels. Pre-alloyed Astaloy CrM powders have been ad-mixed with either graphite or graphene and then processed by ESF. By properly tuning the process parameters, final densities higher than 99% were obtained. Mechanical properties such as hardness and transverse rupture strength (TRS) were tested on samples produced by employing different process parameters and then submitted to different post-treatments (machining, heat treatment). A final transverse rupture strength up to 1340 ± 147 MPa was achieved after heat treatment, corresponding to a hardness of 852 ± 41 HV. The experimental characterization highlighted that porosity is the main factor affecting the samples’ mechanical resistance, correlating linearly with the transverse rupture strength. Conversely, it is not possible to establish a similar interdependency between hardness and mechanical resistance, since porosity has a higher effect on the final properties.