Advanced Sintering Techniques Research Articles

Viability of all-solid-state lithium metal battery coupled with oxide solid-state electrolyte and high-capacity cathode

Owing to the utilization of lithium metal as anode with the ultrahigh theoretical capacity density of 3860 mA h g−1 and oxide-based ceramic solid-state electrolytes (SE), e.g., garnet-type Li7La3Zr2O12 (LLZO), all-state-state lithium metal batteries (ASLMBs) have been widely accepted as the promising alternatives for providing the satisfactory energy density and safety. However, its applications are still challenged by plenty of technical and scientific issues. In this contribution, the co-sintering temperature at 500 °C is proved as a compromise method to fabricate the composite cathode with structural integrity and declined capacity fading of LiNi0.5Co0.2Mn0.3O2 (NCM). On the other hand, it tends to form weaker grain boundary (GB) inside polycrystalline LLZO at inadequate sintering temperature for LLZO, which can induce the intergranular failure of SE during the growth of Li filament inside the unavoidable defect on the interface of SE. Therefore, increasing the strength of GB, refining the grain to 0.4 μm, and precluding the interfacial defect are suggested to postpone the electro-chemo-mechanical failure of SE with weak GB. Moreover, the advanced sintering techniques to lower the co-sintering temperature for both NCM-LLZO composite cathode and LLZO SE can be posted out to realize the viability of state-of-the-art ASLMBs with higher energy density as well as the guaranteed safety.

Microstructure and mechanical properties of SiC-GNPS-SiCW ceramics by oscillatory pressure sintering

The preparation of SiC-based ceramics with high densification, high strength and exceptional toughness is still a severe challenge. In the present work, an advanced sintering technique namely oscillatory pressure sintering (OPS) was applied to prepare SiC ceramics with one-dimensional silicon carbide whiskers (SiCw) and two-dimensional graphene nanoplatelets (GNPs) as reinforcing phases, and the microstructure and mechanical properties were comprehensively investigated. When the contents of GNPs and SiCw were 1 wt% and 5 wt% respectively, the relative density of SiC-based ceramics reached 99.86%, while the Vickers hardness, flexure strength and fracture toughness were 31.55 GPa, 742 MPa and 7.32 MPa m1/2, respectively. The interface was strengthened, meanwhile the grain size was decreased, both of which enhanced the flexural strength of the composites. Results also proved that crack deflection and bridging as well as the bridging of GNPs and SiCw toughened SiC-based ceramics. Furthermore, the coherent interfaces of SiC/GNPS and SiC/SiCw with good match were observed, leading to an enhancement of mechanical properties of such ceramics.

Synergistic toughening effect of SiC whiskers and particles in ZrO2–Al2O3–SiC ceramics

Zirconia ceramics have a good application prospect in the high-tech fields, whereas their potential utilization is highly limited by their mechanical properties. To fabricate zirconia based ceramics with superior mechanical properties, SiC whiskers (SiCw) and SiC particles (SiCp) were selected as the toughening phases for the preparation of ZrO2–Al2O3–SiC ceramics, and an advanced sintering technique called as oscillatory pressure sintering (OPS) was applied in the present work. The mechanical properties of such ceramics with 5 vol% SiCw and 10 vol% SiCp were significantly improved. The Vickers hardness increased to 15.26 GPa while the bending strength reached 917 MPa, and the fracture toughness rose to 6.83 MPa·m1/2. The toughness of the ceramics was improved by synergistic toughening effects including whisker toughening, stress-induced phase transformation toughening and particle dispersion toughening. Furthermore, SiCp and ZrO2, Al2O3 and SiCp, ZrO2 and SiCw as well as Al2O3 and SiCw formed a well-matched coherent phase boundary. The semi-coherent relationship was also generated at the phase boundary of SiCp and SiCw.

Low-temperature sintering of Li0.33La0.55TiO3 electrolyte for all-solid-state Li batteries

Ceramic solid-state Li batteries have promising electrochemical properties. However, their device integration is hampered by the required high sintering temperature step to obtain good ionic conductivity. The sintering temperature often leads to thermal decomposition of the cathode active material. Advanced sintering techniques, such as field-assisted sintering technology/spark plasma sintering (FAST/SPS), utilizing applied mechanical pressure to achieve a lower sintering temperature and shorter dwell time, are helpful in overcoming thermal stability challenges. While thermal stability issues are overcome by a lower sintering temperature, new challenges in the form of surface impurities arise. Low-temperature sintering does not thermally decompose surface impurities which causes low grain boundary conductivity and thus low total ionic conductivity. In this work, a cleaning method and a low-temperature sintering process is exemplarily developed for Li0.33La0.55TiO3 (LLTO) and the impact of applied mechanical pressure during FAST/SPS on the total ionic conductivity and the phase stability of LLTO is revealed.

Effect of SiC particle size on the strength and stiffness of porous Si3N4–SiC composites fabricated via a low-temperature sintering process

Porous Si3N4–SiC composites are potentially very attractive in various applications such as chemical-gas industries, nuclear power plants, automobile industries, and as heat-absorbing materials for solar thermal power plants and electromagnetic radiation shielding materials for commercial and military applications. The fabrication of these advanced composites generally requires expensive raw materials and very high temperatures necessitating advanced sintering techniques, thereby making these materials very expensive. Within the scope of this work, a novel technique for fabricating these porous composites at a low temperature of 1200 °C using phosphoric acid both as a binder and pore former has been proposed. Two different Si3N4–SiC composites with different SiC particle sizes and varying SiC content, with overall porosities in the range of 33–43 vol%, have been fabricated. A detailed study of the influence of the composites’ composition on their microstructure and mechanical properties has been carried out. The results show that both the SiC particle size and its content strongly influence the strength, stiffness, and elastic anisotropy of the fabricated composites. The most optimum composition resulting in the best combination of stiffness and strength in the porous composites has been identified. This yields a longitudinal elastic constant of 50 GPa, a flexural strength of ∼80 MPa, and compressive strength of ∼200 MPa. These values fare well in comparison to porous Si3N4–SiC composites reported in the literature, albeit fabricated at much higher temperatures in comparison to this work. The strength and stiffness of the porous composite with composition Si3N4-20 vol% fine SiC are considerably higher than monolithic porous Si3N4.

Ta-LLZO Garnet Processed By Spark Plasma Sintering for All Solid State Batteries

All Solid State Lithium based Batteries (ASSLB) using a stable inorganic solid state electrolyte are envisaged as the most promising answer to solve the safety issues of Li-ion batteries using inflammable organic liquid electrolyte. Garnet Li7La3Zr2O7 showing high ionic conductivity and high stability versus metallic lithium is currently the most appealing solid electrolyte to be used in oxide based ASSLB. However, its high reactivity with moisture and sensitivity to all energetic process lead to strong difficulties in obtaining stable fully dense pellets while mandatory to ensure its role as mechanical barrier to avoid the short-circuit caused by Li-dendrites [1-2]. In this work, Spark Plasma Sintering is used as both a characterization and a fast sintering techniques to determine the influence of side products and efficiency of applied processes to remove them in reaching dense pellets with high ionic conductivity.Commercial Ta-doped LLZO powder is fully characterized using conventional techniques to identify chemical and thermal stability. SPS experiments are conducted to determine the influence of the side products on the sintering. The efficiency of powder pretreatment designed to remove side products is determined based on data collected during SPS experiments. SPS parameters (applied pressure, temperature ramping, densification dwell ...) are then optimized allowing reaching in a reproducible way pellets with high density (>97 %) and high mechanical strength. Analysis using XPS, SEM and XRD of obtained pellets shows that decomposition occurs only at the surface while the core of the pellet is made of pure cubic phase Ta-doped LLZO. Impedance spectroscopy is used to evidence the influence of side products on the electrical properties and confirms high ionic conductivity (0.5 mS/cm) and very low electronic conductivity of optimized electrolyte. The sintering temperature and dwell time are then optimized by advanced sintering techniques (high pressure, Flash SPS) allowing to prevent the chemical instability usually observed between LLZO and active materials (LiCoO2 or Li[Ni1-x-yCoxMny]O2 (NCM)) and to obtain a cathodic half-cell (LLZO/positive electrode) in one step. References : [1] H. Yamada, T. Ito, R. Basappa, Electrochimica Acta 222 (2016) 648–656.[2] M. Kotobuki, M.Koishi, Journal of Alloys and Compounds 826 (2020) 15421.

High‐strength TiB2‐B4C composite ceramics sintered by spark plasma sintering

AbstractSpark plasma sintering (SPS) is an advanced sintering technique because of its fast sintering speed and short dwelling time. In this study, TiB2, Y2O3, Al2O3, and different contents of B4C were used as the raw materials to synthesize TiB2‐B4C composites ceramics at 1850°C under a uniaxial loading of 48 MPa for 10 min via SPS in vacuum. The influence of different B4C content on the microstructure and mechanical properties of TiB2‐B4C composites ceramics are explored. The experimental results show that TiB2‐B4C composite ceramic achieves relatively good comprehensive properties and exceptionally excellent flexural strength when the addition amount of B4C reaches 10 wt.%. Its relative density, Vickers hardness, fracture toughness, and flexural strength reach to 99.20%, 24.65 ± .66 GPa, 3.16 MPa·m1/2, 730.65 ± 74.11 MPa, respectively.

Residual stresses in alumina matrix composites reinforced with Ti(C,N)

Ti(C0.5,N0.5)-reinforced alumina matrix composites with an addition of 2 wt% ZrO2 were tested to determine residual stresses of Al2O3 and Ti(C0.5,N0.5) phases. The advanced sintering technique (spark plasma sintering ―SPS) at various temperatures of 1600°C and 1700°C was used. Vickers hardness HV1, Young’s modulus E, apparent density ρ and indentation fracture toughness KIC(HV) were evaluated. An indirectly residual stress measurement by the XRD method using the sin2 ψ technique was applied. Compressive residual stresses in both phases: α-Al2O3 and Ti(C0.5,N0.5) were observed. Residual stresses of α-Al2O3(226) are in the range between −204 ± 20 MPa and −120 ± 20 MPa (for 1600 °C and 1700 °C respectively) are lower compared to Ti(C0.5,N0.5)(420), for which the stresses are in the range of between −292 ± 20 MPa and −256 ± 20 MPa (for 1600 °C and 1700 °C respectively). The results exhibit the influence of the sintering temperature on the residual stresses of the tested phases. The residual stresses revealed at 1700°C are lower by about 40% for α-Al2O3(226) and much less for Ti(C0.5,N0.5)(420), by only about 15%. Microstructure studies using scanning electron microscopy, X-ray and electron diffraction phase analysis were used.

Garnet-Based Composite Cathodes for All Solid-State Li Batteries

All-solid-state Li batteries are regarded as a highly promising system for future electrochemical energy storage. Oxide-ceramic based all-solid-state lithium batteries (ASB) can provide high intrinsic safety, extended operational temperature range and high energy density.As the first two are intrinsic to the materials system, one prerequisite to obtain high energy densities with such ASBs is the manufacturing of thick (approx. 150 µm), dual-conducting free-standing composite cathodes, analogous to that of conventional liquid electrolyte-based lithium batteries. However, the preparation of composite cathodes using oxide-ceramic electrolytes is challenging since high temperature sintering steps are necessary during electrode and cell manufacturing to achieve proper mechanical stability, contact between the individual phases and good ionic and electronic conductivity.[1, 2] For oxide-based ceramic electrolyte materials like Li7La3Zr2O12 (LLZ) or Li1+xAlxTi2-x(PO4)3 (LATP) a sintering temperature around 1000 °C is necessary. However, cathode active materials like spinels (e. g. Li2NiMn3O8) or layered materials (e. g. Li[Ni1-x-yCoxMny]O2 (NCM)) show thermal stability only to around 700 °C and the required sintering temperature for the electrolyte exceeds their thermal stability window.To mitigate these materials interactions, advanced sintering techniques like high-pressure Field Assisted Sintering Technique/ Spark Plasma Sintering (FAST/SPS) is required, as it allows low temperature consolidation.[3]Using high-pressure FAST/SPS we have developed a method to prepare thick mixed-conducting composite cathodes and half-cells at sintering temperatures as low as 700 °C. The analysis of these composite cathodes revealed well sintered pure phases and a homogenous distribution of cubic LLZ and cathode active material. Electrochemical tests showed promising electronic and ionic conductivity (0.4 mS cm-1) values and an increased capacity (4 mA cm-2) compared to cathodes with pure active material.FAST/SPS can, therefore, open new processing windows for ceramic-based ASSLBs to alleviate the problem of interphase formation.

Garnet-Based Composite Cathodes for Polymer-Ceramic Solid-State Li Batteries

Ceramic solid-state Li batteries (SSLBs) with high capacity composite cathodes have a huge potential to outperform conventional Li-ion batteries [1]. Among the most promising ceramic electrolytes is garnet-based Li7La3Zr2O12 (LLZ), which has a wide electrochemical window, stability vs metallic Li, and good Li-ion conductivity at room temperature [1]. However, so far, the electrochemical cycling stability of all ceramic solid-state SSLBs is low [1]. The volume changes in the cathode active materials (CAMs) during cycling can cause cracks at the rigid CAM/ceramic electrolyte interface if the density of the mixed cathode is low. To mitigate the detrimental effects of crack formation, polymer electrolyte can be added to fill the cracks could and ensure a good contact between CAM and ceramic electrolyte. Such a concept is called polymer-ceramic SSLB [2].LLZ-based polymer ceramic SSLBs have already shown good electrochemical properties. Commonly the cells are constructed based on a LLZ separator with a dense and porous side that are manufactured by tape-casting [2, 3]. The tape-casting process is not straight forward as it requires the preparation of a slurry with organic solvents. Furthermore, the grain morphology has a major impact on the final LLZ microstructure. Afterwards, the tape-casted LLZ separator is conventionally sintered and grain growth and loss of volatile elements, such as Li, occurs. The sintered LLZ separator is then infiltrated by CAM solution [3]. After drying the CAM solution the polymer electrolyte is added.In a powder-based process, co-sintering the LLZ and CAM simplifies the manufacturing. Another advantage is that the porous LLZ framework is stabilized by the CAM and allows to reduce the LLZ amount in the porous framework in order to achieve higher CAM loadings. However, the high sintering temperature and long dwell time for the sintering of garnet-based LLZ electrolyte lead to reactions with cathode active materials (CAMs) and hamper the manufacturing of composite cathodesA reduction in sintering temperature and dwell time can be achieved by advanced sintering techniques, such as Field-Assisted-Sintering-Technique/Spark Plasma Sintering (FAST/SPS). FAST/SPS applies rapid Joule heating and mechanical pressure. This shortens the required processing times due to faster heating and an increased sintering rate and reduces the sintering temperatures. By that less grain growth is observed, and the loss of volatile elements is reduced.Recently, we showed, that FAST/SPS can co-sinter LLZ and LiCoO2 (LCO) and allows the preparation of an LLZ/LCO composite cathode in one step. The LLZ/LCO phases are clean and provide a low interface impedance [4]. Another advantage is that the thickness of the composite cathode is easily scalable. However, the obtained density was around 95 % and only closed porosity was observed, that prevents the polymer infiltration.In this work, the FAST/SPS process is adjusted to manufacture phase pure porous LLZ/LCO-composite cathodes in one sintering step. The porosity is easily controllable, without the requirement of pore former by the applied pressure during FAST/SPS. Infiltration of polymer electrolyte into the pores within the composite cathode leads to significantly lowered interfacial impedances. The porous composite cathode can be assembled into a polymer ceramic SSLB by attaching it to an anodic half-cell (separator and anode) to demonstrate the functionality of the presented concept.

Advances in Sintering Techniques for Calcium Phosphates Ceramics

Calcium phosphate (CaP) biomaterials are extensively used to reconstruct bone defects. They resemble a chemical similarity to the inorganic mineral present in bones. Thus, they are termed as the key players in bone regeneration. Sintering is a heat treatment process applied to CaP powder compact or fabricated porous material to impart strength and integrity. Conventional sintering is the simplest sintering technique, but the processing of CaPs at a high temperature for a long time usually leads to the formation of secondary phases due to their thermal instability. Furthermore, it results in excessive grain growth that obstructs the densification process, limiting the application of CaP’s ceramics in bone regeneration. This review focuses on advanced sintering techniques used for the densification of CaPs. These techniques utilize the synergy of temperature with one or more parameters such as external pressure, electromagnetic radiation, electric current, or the incorporation of transient liquid that boosts the mass transfer while lowering the sintering temperature and time.

Effect of microwave sintering on the microstructure and mechanical properties of AA7075/B4C/ZrC hybrid nano composite fabricated by powder metallurgy techniques

AA7075 + 6%B4C+3%ZrC nano hybrid composite was successfully fabricated, with nano reinforcements composition in AA7075 alloy selected based on previous investigation, to achieve better mechanical performance. Two different sintering techniques, namely conventional and microwave, were implemented to determine the effect on microstructural and mechanical properties. Microstructural investigation was performed with the help of W-SEM. Tensile, compression, and hardness were measured with the help of UTM and Vickers microhardness machine. Porosity was calculated by using Archimedes principle. It was observed that the added nano ZrC particles formed agglomerates and the B4C particles were distributed homogenously. Composites processed by microwave sintering showed excellent mechanical properties compared to the conventionally sintered composites. No intermetallic compounds were detected in microwave sintered composites through XRD analysis, indicating strong and clean interface bonds between matrix and reinforcement particles. High strain to fracture value of 12.24% was noted in microwave sintered nano hybrid composite, while it was 6.12% for conventional sintered one. Fractography revealed no peeling action of reinforcements from the matrix material, and the mode of failure was brittle. It was concluded that, while fabricating nano range hybrid composites, the implementation of advanced sintering technique (microwave sintering) with low sintering temperatures and low sintering times with internal heat generations, helps in eliminating defects that may develop because of high surface energies of nano range reinforcements.

Li7La3Zr2O12 solid electrolyte sintered by the ultrafast high-temperature method

All-solid-state Li batteries (ASSLBs) are regarded as the systems of choice for future electrochemical energy storage. Particularly, the garnet Li7La3Zr2O12 (LLZO) is one of the most promising solid electrolytes due to its stability against Li metal. However, its integration into ASSLBs is challenging due to high temperature and long dwell time required for sintering. Advanced sintering techniques, such as Ultrafast High-temperature Sintering, have shown to significantly increase the sintering rate. Direct contact to graphite heaters allows sintering of LLZO within 10 s due to extremely high heating rates (up to 104 K min−1) and temperatures up to 1500 °C to a density around 80 %. The LLZO sintered in vacuum and Ar atmosphere has good mechanical stability and high phase purity, but kinetic de-mixing at the grain boundaries was observed. Nevertheless, the Li-ion conductivity of 1 mS cm−1 at 80 °C was comparable to conventional sintering, but lower than for Field-Assisted Sintering Technique/Spark Plasma Sintering.

A review on spark plasma sintering of duplex stainless steels

Duplex stainless steels contain ferrite and austenite phases in balanced proportions. They exhibit good corrosion resistance in numerous environments and are resistant to pitting corrosion and stress corrosion cracking. DSS are employed in the process industries due to their ability to withstand erosive and aggressive environments and high pressure. Characteristic strength of DSS is twice that of the austenitic stainless steel. They are difficult to machine due to high toughness and low thermal conductivity. Conventional methods deteriorate machined surface and irregular wear that creates a negative impact on the efficacy of the material and productivity. The powder metallurgy is a prominent solution to produce DSS and is possible to control the chemical and phase composition, by eliminating number of difficulties present during the production of DSS by conventional methods. SPS is an advanced sintering technique used to fabricate poorly sinterable materials. SPS has a major advantage in the processing of high temperature materials with poor deformability. The ultra-fine grain structure obtained by SPS allows increase of strength and hardness in various stainless steel grades. In this review, nano structured DSS powders of composition Fe-25Cr-7Ni (wt. %) were prepared by dual drive planetary ball mill. The nano structured DSS powders consolidated by SPS technique were studied and characterized by X-Ray diffraction while morphology of DSS powders were studied by Scanning Electron Microscope.

A spark plasma sintering densification modeling approach: from polymer, metals to ceramics

The powder compaction modeling of advanced sintering techniques such as spark plasma sintering is a crucial step in the conception of complex shape objects and the understanding of the process. The complete identification of common powder compaction models requires lengthy experimental investigations based on creep and compaction tests. In order to circumvent this problem, a semi-theoretical approach can be employed whereby the mechanical behavior of the powder material is determined theoretically and the temperature-dependent equivalent creep behavior of the material is determined experimentally. Extending the use of this approach to polymers, metals and ceramics is discussed and compared to other independent methods.

New insights into phosphate based materials for the immobilisation of actinides

Abstract This paper focuses on major phosphate-based ceramic materials relevant for the immobilisation of Pu, minor actinides, fission and activation products. Key points addressed include the recent progress regarding synthesis methods, the formation of solid solutions by structural incorporation of actinides or their non-radioactive surrogates and waste form fabrication by advanced sintering techniques. Particular attention is paid to the properties that govern the long-term stability of the waste forms under conditions relevant to geological disposal. The paper highlights the benefits gained from synergies of state-of-the-art experimental approaches and advanced atomistic modeling tools for addressing properties and stability of f-element-bearing phosphate materials. In conclusion, this article provides a perspective on the recent advancements in the understanding of phosphate based ceramics and their properties with respect to their application as nuclear waste forms.

Development of ZrB<sub>2</sub>–SiC–Ti by multi stage spark plasma sintering at 1600°C

Zirconium diboride based ceramics, owing to their superior high temperature properties are potential materials for use as leading edge components in hypersonic space vehicles. However, the difficulty in sintering these ultra high temperature ceramics limit their applications to some extent. Sintering of such materials is usually accomplished by resorting to advanced sintering techniques such as Spark Plasma Sintering (SPS) accompanied by sinter aids to improve the sinterability. In this backdrop, the current work investigates the effect of Ti addition on the mechanical properties and sinterability of ZrB2-based ceramic composites. Tailored addition of Ti to ZrB2-18 wt. % SiC baseline composites not only improves the densification but also increases hardness and indentation toughness, when sintered using Multi Stage Spark Plasma Sintering technique. Microstructure and X-ray diffraction analysis reveals the presence of ultrafine grains of ZrB2 and SiC, which is found to be effective in obtaining a good hardness (up to 29 GPa) and reliable indentation toughness (up to 9 MPa center dot m(1/2)). (C) 2016 The Ceramic Society of Japan. All rights reserved.

Reactive Spark Plasma Sintering: Successes and Challenges of Nanomaterial Synthesis

Spark plasma sintering (SPS), initially developed as an advanced sintering technique for consolidating nanopowders into nanostructured bulk materials, has been recently looked at in much broader perspective and gained a strong reputation of a versatile method of solid state processing of metals, ceramics, and composites. The powders in the SPS‐dies experience the action of pulsed electric current and uniaxial pressure; they are heated at very high rates unachievable in furnace heating and sintered within shorter times and at lower temperatures than in conventional methods. The principle of SPS and convenient design of the facilities make it attractive for conducting solid state synthesis. In this paper, based on our own results and the literature data, we analyze the microstructure formation of the products of chemical reactions occurring in the SPS in an attempt to formulate the requirements to the microstructure parameters of reactant mixtures and SPS conditions that should be fulfilled in order to produce a nanostructured material. We present successful syntheses of nanostructured ceramics and metal matrix composite with nanosized reinforcements in terms of microstructure stability and attractive properties of the materials and discuss the challenges of making a dense nanostructured material when reaction and densification do not coincide during the SPS. In the final part of the paper, we provide an outlook on the further uses of reactive SPS in the synthesis of nanostructured materials.

Performance of carbide composites for cyclic loading applications

The present study attempts to give deeper insight into the surface damage process of carbide composites such as WC hardmetals and TiC-based cermets in the blanking of sheet metals (in cyclic loading conditions). In addition, it focuses on the relationships between the blanking performance of composites on the one hand and the structure-composition and properties wear resistance, plasticity, fatigue strength on the other hand. The influence of advanced sintering techniques on the performance of carbide composites is estimated. A set of laboratory (abrasive wear, adhesive wear, strength, fatigue) and functional tests (blanking of sheet metals) were performed and the effect of advanced sintering techniques (sinter/HIP) on the properties and microstructure developments during testing was analysed by SEM and XRD.

Reducing costs of MIM feedstocks by coarse iron powder and advanced sintering techniques : M.Wright et al. (Remington Arms Co, USA.)

The development of improved metal powders has been a significant factor in the growth of the powder metallurgy structural parts industry in the last few years. After five years R&D, leading Swedish ferrous powder producer Höganäs AB has released a material, Astaloy CrM®, that it believes will allow further gains. Magnus Johansson outlines the characteristics of the chrome alloy ferrous powder.