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Cold Sintering: A New Sintering Technology for Advanced Ceramic Materials

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Chunchun Li, Guobin Zhu, Xiaowei Zhu and Siyu Xiong

Submitted: 21 September 2024 Reviewed: 15 October 2024 Published: 05 March 2025

DOI: 10.5772/intechopen.1007855

Advanced Ceramic Materials IntechOpen
Advanced Ceramic Materials Emerging Technologies Edited by Amparo Borrell Tomás and Rut Benavente Martínez

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Advanced Ceramic Materials - Emerging Technologies

Amparo Borrell Tomás and Rut Benavente Martínez

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Abstract

Ceramic sintering is the process of solidifying ceramic powder into a dense bulk material through the migration of matter, which is the necessary path for the body to transform into a high-strength, dense ceramic body. Low-temperature sintering technology introduces electric fields, solvents, pressure, etc., to change the thermodynamic and kinetic conditions of sintering, which has been widely studied by global scholars since the twentieth century. Currently, there are common sintering processes such as cold sintering, dielectric barrier discharge plasma sintering, hot isostatic pressing sintering, flash sintering, and microwave sintering. Among them, cold sintering has gained widespread attention due to its advantages of simple equipment, convenient operation, and low sintering temperature. Copyright belongs to the author. Commercial reprint requires authorization from the author, non-commercial reprint please indicate the source.

Keywords

  • ceramics
  • sintering
  • cold sintering
  • low-temperature sintering
  • dielectric materials

1. Introduction

Ceramic materials have long played a crucial role in modern technology due to their exceptional physical and chemical properties. From everyday porcelain to electronic components and aerospace parts in high-tech fields, the application of ceramic materials spans a wide range, highlighting their significance. However, conventional sintering processes often necessitate high temperatures, which not only consume significant energy but can also adversely impact the material’s properties.

In recent years, cold sintering technology has gained significant attention within the materials science community as an innovative method for sintering. Compared to traditional processes, this technology enables the densification of ceramic materials at lower temperatures, resulting in a substantial reduction in energy consumption and production costs while maintaining or even enhancing material properties (Figure 1) [1]. The emergence of cold sintering technology not only offers new possibilities for ceramic material production but also paves the way for advancements in materials science.

Figure 1.

The relative density of materials produced by the cold sintering process at low temperatures in comparison with other sintering techniques [1].

In this chapter, we initially examine the early concepts and preliminary experiments of cold sintering technology, followed by a focused exploration of significant technological breakthroughs that have emerged during its development. These advancements have not only propelled the evolution of cold sintering technology but also contributed to a substantial enhancement in its current level of maturity. Through an in-depth analysis of these advancements, we can gain a better understanding of the progressive steps taken in the advancement of cold sintering technology and evaluate its present status within the realm of advanced ceramic materials sintering.

Additionally, this chapter introduces the physical and chemical principles underlying cold sintering technology, compares the mechanisms of traditional sintering and cold sintering, and discusses the procedural steps and operational methods involved in cold sintering. Through these discussions, we aim to elucidate the key parameters and influencing factors in the cold sintering process, providing readers with a comprehensive framework for comprehending this technology.

Finally, this chapter provides a comprehensive overview of the fundamental advantages of cold sintering technology and its application value across diverse fields, underscoring the criticality of ongoing research and development efforts while offering practical recommendations for both industry and academia. Through this chapter, readers will acquire a lucid comprehension of cold sintering technology’s transformative potential as well as a foundational understanding of its pivotal role in advancing the realm of ceramic materials.

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2. The development of cold sintering

The early concepts of cold sintering technology originated from a reflection and challenge to traditional high-temperature sintering methods, with its earliest traces dating back to the 1980s. As concerns over energy consumption and the preservation of material properties grew, scientists began exploring the possibility of densifying ceramic materials at lower temperatures. Early experiments, through the introduction of specific chemical additives and solvents, successfully densified materials and enhanced their properties at temperatures far below those of conventional sintering. For instance, in 1986, the Yamasaki team from Kochi University in Japan [2] was the first to combine hydrothermal methods with uniaxial pressure, successfully sintering ceramics at 350°C, a process they termed hydrothermal hot pressing (HHP). However, due to complexities in equipment, limitations in product size and shape, and lower densification, this technology did not receive widespread research attention. In 2014, Jantunen et al. [3] successfully prepared well-densified Li2MoO4 ceramics by moistening the powder with deionized water and pressing it at 130 MPa, followed by sintering at 120°C. In 2016, the Randall team [4, 5] from Pennsylvania State University, inspired by natural crystallization phenomena, utilized transient solvents such as aqueous solutions under uniaxial pressures ranging from 100 to 500 MPa and within short durations, successfully sintering various ceramic materials like NaCl, Li2MoO4, V2O5, and BaTiO3 at temperatures ranging from room temperature to 300°C, with densification levels exceeding 90% [6, 7]. This technique, named the Cold Sintering Process (CSP) for the first time, has the potential to shorten sintering times and reduce energy consumption, significantly improving sintering efficiency. Although these preliminary experiments achieved limited success at this time, they laid the foundation for subsequent cold sintering technologies and revealed the feasibility of achieving material densification at lower temperatures.

Subsequently, research teams from Europe and Asia have also successfully implemented low-temperature densification of over 70 ceramic materials [8, 9, 10, 11], including CaCO3, Al2SiO5-NaCl, Al2O3-NaCl, and Na0.5Bi0.5MoO4-Li2MoO4, using this cold sintering method. As research continued, cold sintering technology made significant progress and breakthroughs in various fields. Researchers successfully utilized cold sintering to prepare ceramic-polymer composites, addressing the issue of co-sintering ceramics with polymers at high temperatures, thus opening new avenues for the development of novel composite materials. Additionally, cold sintering achieved breakthroughs in multi-material integration, particularly in the production of solid-state batteries, where it enabled the intimate combination of different materials, paving the way for the production of solid-state batteries with superior performance. Microwave dielectric materials, such as Li2MoO4, prepared using cold sintering, exhibited excellent microwave dielectric properties, maintaining high densification and good microwave dielectric performance even after sintering at low temperatures. Cold sintering technology began to be applied in industrial production, especially in the field of power metallurgy, where its advantages in reducing energy consumption and shortening production cycles made it highly commercially viable. In environmental governance, cold sintering technology was explored for the solidification treatment of heavy metals in fly ash, offering advantages such as volume reduction, weight reduction, and low energy consumption, providing a new solution for fly ash treatment.

In terms of technological breakthroughs, a significant milestone was the development of equipment and methods capable of precisely controlling the sintering atmosphere. By sintering in specific atmospheres, the porosity and grain size of materials could be effectively controlled, resulting in high-performance ceramic materials with specific functions. For example, sintering in a reducing atmosphere could produce solid oxide fuel cell (SOFC) electrolyte layers with excellent electrochemical performance [12]. On the other hand, researchers conducted in-depth studies on the reaction steps and microscopic mechanisms of cold sintering, establishing the fundamental principles and densification mechanisms of cold sintering technology, and providing a theoretical basis for further optimization and application of the technology. Internationally, research institutions such as the University of Oulu in Finland and Pennsylvania State University in the United States have made significant progress in the study of cold sintering technology, bringing new research directions to the field of materials science. These advancements not only propelled the development of cold sintering technology but also demonstrated its broad prospects and commercial potential in theoretical research, material preparation, and industrial applications, indicating that cold sintering technology is expected to play an increasingly important role in future materials science and industrial production.

In summary, cold sintering technology has evolved from a conceptual validation stage to a relatively mature sintering method, showing significant potential in both laboratory settings and future industrial production. Compared to traditional sintering technologies, cold sintering offers clear advantages in energy efficiency, cost, and material performance. Currently, this technology has been applied in various fields such as electronics, energy, and biomedicine. For example, in the production of high-performance ceramic substrates, solid oxide fuel cell electrolyte layers, and biocompatible implant materials. The development trajectory of cold sintering technology reflects its growing maturity and expanding application scope, indicating that it will provide more efficient, economical, and environmentally friendly solutions for the production of advanced ceramic materials. Cold sintering technology offers a broad new approach to the low-temperature sintering of ceramics. The following sections will provide a detailed introduction to the densification principles and process methods of cold sintering technology.

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3. The principle of cold sintering technology

Due to the relatively short history of cold sintering technology, research on its densification mechanisms has not yet fully matured. Currently, researchers generally believe that the densification mechanisms of cold sintering mainly include two types: one is the non-equilibrium dissolution-precipitation process caused by the intermediate liquid phase, the other is the plastic deformation process caused by pressure [13, 14]. Based on the theory of liquid phase sintering and microstructure observations on a broad number of systems, a schematic illustrating the three stages of the dissolution-precipitation process is shown in Figure 2 [4]. The first stage is the dissolution-rearrangement process, where the intermediate liquid phase uniformly wets the ceramic powder, forming a liquid film on the surface of the ceramic particles, which increases the slipperiness between the ceramic particles. Under the action of the intermediate liquid phase, the dissolution of the sharp edges of the ceramic particles reduces the interfacial area, facilitating the rearrangement in the subsequent sintering stage. Under appropriate pressure and temperature conditions, the liquid phase redistributes and diffuses into the pores between the particles [4].

Figure 2.

Schematic diagram of the densification mechanism of CSP [4].

The second stage is the dissolution-precipitation process, which triggers a significant chemical driving force, bringing the solid and liquid phases into equilibrium. The intermediate liquid phase evaporates, causing the solution to reach saturation under certain temperature and pressure conditions. Under the action of capillary forces and external pressure, atomic clusters or particles far from high chemical potential contact zones migrate to areas of lower chemical potential and precipitate. This process eliminates pores by reducing the material’s surface-free energy, thereby achieving densification of the ceramic [8, 15].

The third stage is the grain growth stage. The crystalline phase or amorphous phase will be formed in the final sintering process. If the crystal phase is formed, the ceramic particles will grow obviously. If there is an amorphous phase, the amorphous phase will limit the grain boundary diffusion and migration, thereby inhibiting the further growth of ceramic particles. In addition to the dissolution-precipitation mechanism, plastic deformation through viscous flow or dislocation movement is also considered one of the densification mechanisms of cold sintering, which helps to achieve densification under high pressure [16, 17].

3.1 Comparison in the mechanism of traditional sintering and cold sintering

Traditional sintering and cold sintering are two different material densification processes, and they have significant differences in mechanism. Ceramic materials have a high melting point, so the sintering temperature of ceramics is higher in the traditional sintering technology, and the sintering temperature is usually more than 1000°C [18, 19, 20, 21]. At high temperatures, the atoms or molecules inside the material move through a diffusion mechanism, thereby reducing porosity and increasing the compactness of the material. Diffusion can be volume diffusion, grain boundary diffusion, or surface diffusion. In some cases, especially in the sintering with liquid phase participation, the plastic flow of the material can promote particle rearrangement and densification. As the sintering time increases, small particles are gradually absorbed by large particles, increasing particle size and thereby reducing pores [22]. The traditional high-temperature sintering technology has some disadvantages. It not only consumes a lot of energy but also volatilizes unstable additives (such as Bi, Pb, Li, Na, K, and other elements) at high sintering temperature, resulting in the imbalance of stoichiometric ratio, resulting in the change of crystal structure and affecting the performance [23, 24]. It also makes some ceramic materials and metal electrodes co-fire, and other aspects face challenges. When different materials are co-sintered, high temperatures will also cause unexpected chemical reactions, delamination, cracking, and other problems in the product [25, 26].

The cold sintering technology proposed in recent years can reduce the sintering temperature to below 400°C [7]. Using the transient solvent in the form of the liquid phase and uniaxial pressure, the rapid densification of ceramic materials can be achieved through the dissolution-precipitation process of ceramic particles. During the cold sintering process, the applied pressure can activate the interface between the particles, promote the migration of atoms or molecules, and achieve densification even at a lower temperature [6, 27]. Compared with conventional sintering, cold sintering usually does not involve the formation of liquid phases, so it is suitable for materials that decompose or deteriorate at high temperatures. The cold sintering technology has the characteristics of low sintering temperature and short sintering time and has received extensive attention since its development [28].

3.2 Steps and operation methods of the cold sintering process

A standardized and unique cold sintering process has not been defined yet, especially regarding how the temperature and pressure shall be applied. Here, a description of the approach adopted in previous works is introduced. The solvent is added to the ceramic powder after mixing for a few minutes to promote close contact between the liquid and the solid. The ceramic slurry is then introduced into the mold (usually cylindrical) and pressed by a hydraulic or mechanical press. The device is also equipped with a heating system, usually a heating sleeve wrapped around the mold, or two heating plates placed above and below the mold. Figure 3 resumes schematically the CSP process [14, 29, 30].

Figure 3.

Scheme of the cold sintering route.

3.3 Key parameters and influencing factors in the cold sintering process

The ceramic material system is huge, and the factors affecting the densification of different material systems are different. It is generally affected by factors such as particle size, solubility of particles in the intermediate liquid phase, type of intermediate liquid phase, temperature, and pressure. Figure 4 shows the key sintering parameters for cold sintering to prepare different material systems [29, 31].

Figure 4.

The key parameters that the cold sintering process can take for different materials [29].

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4. Material systems in cold sintering

Among the various ceramic materials prepared using CSP technology, dielectric ceramics have been the most extensively studied, followed by semiconductors, solid-state batteries, and thermoelectric materials. The following sections will provide a comprehensive yet succinct overview of the current significant research progress in these materials.

4.1 Dielectric ceramics

4.1.1 Microwave dielectric ceramics

In recent years, numerous microwave dielectric ceramic material systems have achieved promising preparation outcomes using CSP technology, including molybdates, tungstates, borates, chlorides, and fluorides, among others.

Molybdates and their composites are among the earliest and most extensively studied materials within the realm of cold CSP. In 2014, Kähäri et al. [3] successfully produced Li2MoO4 ceramics with densities ranging from 87 to 93%. Post-heat treatment led to dielectric properties characterized by a relative permittivity (εr) ranging from 4.6 to 5.2 and a quality factor (Q × f) of 10,200–18,500 GHz. In 2016, Guo et al. [4] broadened the scope of research to include Na2Mo2O7 and K2Mo2O7, showcasing the versatility of CSP across various molybdate materials. Moreover, the application of CSP in composite materials has demonstrated effective control over the frequency-temperature coefficient (τf) of the composites [32].

The CSP has made significant strides in the development of tungstate and borate ceramics. In 2019, Hong et al. [33] employed CSP to prepare HBO2-II and H3BO3 ceramics, achieving high densities of 94.5% and 97.7%, respectively, and excellent microwave dielectric properties (HBO2-II: εr ~ 4.21, Q × f ~ 47,500 GHz; H3BO3: εr ~ 2.84, Q × f ~ 146,000 GHz), setting a new record for Q × f values. In 2020, Ding et al. [34] demonstrated an efficient method for dry pressing H3BO3 ceramics at room temperature. That same year, Hao et al. [35] investigated the impact of Na2WO4 grain size on microwave dielectric properties using CSP, resulting in high density (> 92%) and superior dielectric performance (εr ~ 5.8, Q × f ~ 22,000 GHz). Further research indicated that performance could be further enhanced through optimized sintering conditions and heat treatment (εr ~ 5.7, Q × f ~ 70,000 GHz) [36]. In 2021, Chen et al. [37] successfully prepared Na2WO4-xNi0.2Cu0.2Zn0.6Fe2O4 composites with densities of up to 87% and outstanding properties. These achievements underscore the potential of CSP in the fabrication of tungstate and borate materials.

Beginning in 2016, CSP has also achieved notable advancements in the preparation of chloride and fluoride microwave dielectric ceramics. In 2016, Guo et al. [4] pioneered the use of CSP to synthesize NaCl ceramics with high density, although the performance metrics were not reported at that time. By 2017, Induja et al. [9] showcased the microwave properties of NaCl ceramics (εr ~ 5.2, Q × f ~ 12,000 GHz) and the performance of Al2SiO5–NaCl composites (εr ~ 4.52, Q × f ~ 22,350 GHz). In 2018, Li et al. [38] explored the impact of varying amounts of deionized water on the microwave properties of NaCl ceramics, finding that cold sintering under specific pressure conditions could yield outstanding performance (εr ~ 5.55, Q × f ~ 49,600 GHz). In 2020 and 2021, Liu et al. [39, 40] significantly enhanced the density and Q × f values of LiF ceramics through CSP and subsequent heat treatment (up to εr ~ 8.45, Q × f ~ 134,050 GHz). Madhuri et al. [41], Zhou et al. [42], and Jin et al. [43] also achieved comparable results with NaCa2Mg2V3O12–xNaCl, LiF–CaTiO3, and BaF2 ceramics, respectively, underscoring the potential of CSP to improve the performance of fluoride ceramics.

4.1.2 Ferroelectric materials

The CSP technology has shown significant potential in the field of ferroelectric materials, successfully preparing a variety of materials including KH2PO4, NaNO2, and BaTiO3 [5]. Studies have found that even under low-temperature and high-pressure conditions, the performance of KH2PO4 and NaNO2 can match that of conventionally sintered materials [44]. After annealing at 900°C, BaTiO3’s performance matches that of materials sintered at high temperatures in Figure 5 [6]. CSP streamlines the fabrication process and improves the properties of the material, thus paving new paths for the application of ferroelectric materials.

Figure 5.

Schematic illustration of the primary stages during cold sintering and post-annealing processes in the case of BaTiO3 nanocrystalline ceramics preparation [6].

Ceramics prepared by Guo et al. [6] and Ma et al. [45] using cold sintering technology exhibit submicron grain sizes, high relative density, high relative permittivity, and low dielectric losses. These ceramics also feature high breakdown strength, energy storage density, and energy storage efficiency. In addition, specific fluxes such as Ba(OH)2/TiO2 aqueous suspensions and NaOH-KOH molten hydroxides make it possible to densify BaTiO3 at even lower temperatures, achieving single-step densification at 150°C [6].

4.1.3 Piezoelectric ceramic materials

In 2019, Huang et al. [27] demonstrated that cold sintering at 180°C followed by heat treatment at 900°C can produce Na0.5Bi0.5TiO3 piezoelectric ceramics with comparable performance to those made by traditional high-temperature sintering methods. Besides, Ma et al. [46] successfully employed a cold sintering-assisted sintering method to fabricate dense K0.5Na0.5NbO3 (KNN) lead-free piezoelectric ceramics with a density exceeding 98%. The cold sintering process, which involved the formation of a potassium-rich second phase at grain boundaries, enhanced the ceramic’s properties and reduced the required post-sintering temperature. Furthermore, doping with 10% LiBiO3 resulted in transparent KNN-0.1LB ceramics with 74% transparency [47], further demonstrating the versatility of cold sintering in producing high-performance lead-free piezoelectric and transparent ceramics.

4.2 Semiconductor materials: ZnO ceramics

The CSP has revolutionized the processing of ZnO-based semiconductor materials, effectively addressing the issues of excessive grain growth and performance degradation caused by traditional high-temperature sintering. By utilizing transient liquid phases such as acetic acid solution, CSP achieves high densification (up to 98%) and excellent electrical conductivity at temperatures below 300°C [48], which is significantly lower than the 1400°C required for conventional sintering. Research has shown that additional methods such as adding deionized water [49], optimizing sintering pressure and temperature, and post-sintering heat treatments can further enhance the performance of ZnO materials. For instance, post-sintering treatments can increase electrical conductivity from 0.0005 to 16.4 S cm−1 [50], while doping with aluminum oxide can optimize the performance of AZO ceramics, achieving a densification of 99.23% and an extremely low resistivity [51]. These advancements indicate that the cold sintering technology holds great potential for enhancing the electrical properties and controlling the microstructure of ZnO materials, opening new avenues for the development and application of semiconductor materials.

4.3 Solid-state battery materials

Solid-state batteries, utilizing solid electrolytes and electrodes, provide improved safety and energy density but necessitate high-temperature sintering above 1000°C to minimize grain boundary resistance and enhance conductivity. Excessive sintering temperatures may result in the evaporation of volatile elements and the formation of secondary phases, which can impair the ion transport properties of the solid electrolyte [12]. Additionally, prolonged sintering durations can limit the advancement of sodium-ion solid electrolyte materials.

4.3.1 Solid electrolyte

The Seth [1] team was the first to use CSP to prepare the Li1.5Al0.5Ge1.5(PO4)3 solid electrolyte, achieving 80–88% densification by holding at 120°C for 20 min. However, the amorphous phase resulting from cold sintering lowered the room-temperature ionic conductivity. Post-heat treatment at 650°C led to recrystallization of the amorphous phase, increasing the ionic conductivity to 5.4 × 10−5 S cm−1. By incorporating PVDF-HFP polymer, the room-temperature ionic conductivity was further improved to 1.0 × 10−4 S cm−1 in Figure 6 [1], demonstrating the potential of cold sintering technology in the preparation of solid electrolytes [52].

Figure 6.

Summarizes the processing conditions for achieving the conductivity at 25°C and the proposed lithium-ion conduction mechanisms [1].

Wang et al. [53] utilized cold sintering technology to prepare the garnet-type Li6.1Al0.3La3Zr2O12 solid electrolyte, achieving 87.7% densification of LLZO electrolyte at 350°C through the “dissolution-precipitation” mechanism of CSP. However, the precipitated β-Li5AlO4 impurity significantly affected its conductivity to only 3.38 × 10−9 S cm−1. Subsequently, Seo et al. [54] prepared an LLZO-SM composite electrolyte with conductivity up to 4 × 10−4 S cm−1 by doping Mg and Sr. elements, under a sintering temperature of 120°C and a pressure of 400 MPa.

Leng et al. [11] prepared a dense Mg-doped Na3.256Mg0.128Zr1.872Si2PO12 electrolyte material with 83% densification using 30 wt% deionized water as a transient liquid phase in cold sintering at 140°C. After post-heat treatment at 800–1100°C, the conductivity increased to 1.36 mS cm−1, significantly higher than that of the 1000°C sintered sample without liquid phase (0.1 mS cm−1). Subsequently, Leng [55] further increased the conductivity to 1.5 mS cm−1 by adding 1.1 wt% Bi2O3 to the Mg-doped NASICON. Silva used different liquid phases such as water, acetic acid, nitric acid, and strong base to prepare NASICON solid electrolytes via cold sintering. Studies showed that using a strong base as the liquid phase achieved the highest densification (95%), but the conductivity of the cold sintered samples was two orders of magnitude lower than that of conventionally sintered samples. This was attributed to the smaller grain size in cold sintered samples, which increased the total grain boundary resistance and thus reduced the conductivity [56]. In addition, Nakaya et al. [57] successfully prepared CsH2PO4 proton electrolyte material with 98% densification using cold sintering technology at 200°C, achieving an ionic conductivity of 2.30 × 10−4 S cm−1. Thabet et al. [58] prepared BaCe0.8Zr0.1Y0.1O3 proton electrolyte material with 83% densification at 180°C, which was improved to 94% densification after post-treatment at 700°C, reaching a total conductivity of 4 × 10−2 S cm−1.

4.3.2 Electrode material

Seo et al. [59] successfully addressed the challenge of low capacity in LiFePO4 cathodes by creating a composite material with improved density and performance. By mixing 80% LiFePO4 with 10% conductive carbon and 10 wt% PVDF and using cold sintering at 240°C with LiOH solution as an intermediate liquid phase, they achieved a relative density of 89% for the LiFePO4-PTFE cathode composite material. This material exhibited a volume capacity of 340 mAh/cm3 at a charge-discharge rate of 0.03–0.1C, surpassing the performance of other high-performance LiFePO4 cathodes [60]. Furthermore, the composite material retained 87% of its initial capacity after 40 cycles at 0.2C, indicating excellent capacity retention. V2O5, a semiconductor, acts as a cathode in lithium-ion batteries when combined with Li+ ions [61]. To enhance its conductivity and stability, it is mixed with conductive polymers. Cold sintering technology produced a V2O5/poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) composite material with a densification of 90.2% and a sheet conductivity of 4.8 × 10−4 S cm−1 [61, 62].

Seo et al. [63] fabricated a binder-free Li4Ti5O12 (LTO) based anode using the cold sintering process. Initially, a composite anode was formed by tape casting with a binder, followed by heat treatment to remove the binder. The binder-free composite was then humidified to provide a transient liquid phase and subsequently cold sintered at 120°C under a uniaxial pressure of 500 MPa, directly deposited on a current collector. The resulting LTO/CNF composite anode had a density of 2.82 g/cm3 (87% relative density), and its volumetric capacity density was found to be approximately 380 mAh/cm3.

4.4 Thermoelectric materials

Santos [64] conducted a comparative study on the performance differences of thermoelectric ceramic materials Ca3Co4O9 prepared by conventional sintering and cold sintering. Compared to the 58% density of conventionally sintered samples, the cold sintered samples exhibited a significant increase in density to 78.2%, along with an electrical conductivity of 6459 S/m.

4.5 Other materials

4.5.1 Ceramic-polymer composites

The introduction of CSP has enabled the one-step sintering of ceramic-polymer composites, providing a straightforward and effective method for the preparation of traditionally incompatible materials [65, 66]. Notable advancements include Guo’s successful creation of Li2MoO4-PTEE microwave dielectric material and Li1.5Al0.5Ge1.5(PO4)3/(PVDF-HFP) composite electrolyte, demonstrating significant improvements in material densification and properties [52].

4.5.2 Metastable ceramic materials

The CSP technology has shown potential in processing metastable ceramic materials, which are prone to decomposition at high temperatures [67]. Research by Bang et al. [68] and Yang et al. [69] has demonstrated the successful preparation of SnO and ZrW2O8 materials with high relative densities and good thermoelectric properties, highlighting the technology’s ability to control microstructure and enhance performance [70].

4.5.3 Nuclear and spent waste treatment

The CSP technology has been applied to the treatment of radioactive elements in nuclear and spent waste, offering a new environmental treatment method. Hassan and colleagues have immobilized radioactive iodine in apatite and sodalite, achieving high densification and retention rates, and low leaching rates, indicating the technology’s effectiveness in immobilizing radioactive materials [71, 72, 73, 74].

In addition to these materials, cold sintering technology has also been successfully applied in the preparation of various ceramic materials, including nano-TiO2 [75, 76], CaSO4 [77], CeO2 [78], Y2O3 [79], ZrO2 [80, 81], and InGaZnO4 [82] targets.

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5. Application fields of cold sintering

Cold sintering technology has demonstrated significant potential and adaptability in the field of ceramics. By utilizing lower temperatures and higher pressures, this technique effectively enhances the densification process of materials, significantly improving the efficiency of material densification and the precision of microstructural design. This method notably reduces processing time, energy consumption, and production costs, making it particularly suitable for applications requiring precise control over the microstructure and properties of materials [29].

To date, nearly 100 different materials have successfully been densified through cold sintering technology, with the majority being dielectric ceramics. Consequently, the primary application areas of cold sintering include piezoelectric media, microwave dielectrics, semiconductors, capacitors, patch antennas, and solid-state batteries. This technology not only provides a new method for material preparation but also exhibits significant potential and broad application prospects in practical applications [83, 84, 85].

5.1 Advancing research fields

As an innovative method for preparing ceramics and ceramic matrix composites, cold sintering technology has shown its vast potential and application prospects. The technique enables the rapid production of dense materials by applying external pressure, under limited temperature conditions, and adding a liquid phase. Compared to traditional sintering methods, this process significantly lowers the processing temperature, shortens production time, simplifies chemical treatment steps, and greatly reduces production costs. The unique aspect of cold sintering is its ability to fabricate hybrid composites in a single step, such as embedding polymer fillers within ceramic matrices. The primary densification mechanism is pressure-solution creep, and the addition of a liquid phase facilitates a smoother path for powder consolidation and atomic diffusion [28, 44]. Therefore, cold sintering technology not only enhances material performance but also offers new solutions for the fields of materials science and engineering.

5.2 Future application potential and challenges

In the future, cold sintering technology holds great potential, especially in the automotive and biomedical fields. It is expected to be used for producing ceramic composite brake pads and ceramic-polymer composites for orthopedic implants and drug delivery systems. By reducing energy consumption and production costs, cold sintering technology is anticipated to play a key role in promoting the development of a green economy and providing high-performance materials for the development of new electronic devices [29].

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6. Current challenges and future outlook

6.1 The main challenges facing

However, the promotion and application of cold sintering technology face several challenges. First, the acquisition and maintenance costs of high-pressure equipment are high, increasing the initial investment burden. Additionally, to ensure the high quality and performance of the materials produced, strict control over process conditions, including temperature, pressure, and time, is necessary. Moreover, the long-term stability and material compatibility of cold sintering technology are also issues that need to be addressed. Overcoming these challenges will help cold sintering technology to be applied in a wider range of fields and provide innovative solutions to the fields of materials science and engineering [86, 87, 88].

To overcome these challenges, future research should focus on the following aspects.

6.1.1 Optimizing process parameters to enhance material performance

This involves precise control over key process parameters such as temperature, pressure, and time to further refine the cold sintering process, thereby improving the performance and quality of materials. A thorough understanding of the relationship between processing parameters, microstructure, and material properties is essential.

6.1.2 Exploring new applications in emerging fields

Cold sintering technology holds great potential in new areas such as the automotive industry and biomedicine. For instance, the development of ceramic composite brake pads and ceramic-polymer composites can reduce energy consumption and production costs while providing high-performance material solutions for these sectors.

6.1.3 Contributing to the green economy

Cold sintering technology is poised to become a pivotal force in promoting the development of a green economy. It can provide high-performance materials for the manufacture of new electronic devices, thereby facilitating the sustainable development of the electronics industry.

6.2 Exploring future research directions and technological advancements

The further development of cold sintering technology requires close collaboration among multiple disciplines, including materials science, chemical engineering, and mechanical engineering, to drive technological innovation and application breakthroughs. Future research directions should focus on the following four core themes [14, 89, 90, 91].

6.2.1 Optimizing process parameters and expanding application areas

By fine-tuning process parameters such as temperature, pressure, and time, the efficiency and material performance of cold sintering technology can be further enhanced. At the same time, the potential for applying cold sintering technology in more fields, such as aerospace and automotive manufacturing, should be explored.

6.2.2 Deepening the understanding of the cold sintering mechanism

In-depth research into the physical and chemical mechanisms of the cold sintering process, including the mechanism of liquid-phase-assisted sintering and the impact of pressure on material densification, is necessary to achieve more precise control and prediction of the cold sintering process.

6.2.3 Interdisciplinary research collaboration

Encouraging interdisciplinary collaboration, combining knowledge and technology from materials science, chemical engineering, mechanical engineering, and other fields, to jointly address current challenges faced by cold sintering technology, such as material compatibility and process stability.

6.2.4 Cross-disciplinary integration of experimental research and applications

Combining experimental research with applications in different fields, such as electronic ceramics, energy materials, and bioceramics, to explore the cross-application of cold sintering technology. This can lead to the development of new composite materials with specific functions, meeting the demand for high-performance materials across various industries.

Through the in-depth exploration of these research directions, cold sintering technology is expected to achieve broader applications in the fields of materials science and engineering, providing innovative solutions to related industries.

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Written By

Chunchun Li, Guobin Zhu, Xiaowei Zhu and Siyu Xiong

Submitted: 21 September 2024 Reviewed: 15 October 2024 Published: 05 March 2025

© The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution 4.0 International License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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