Reaction Sintering Process Research Articles

Enhanced Sintering of Refractory Protonic Ceramic Electrolyte by Dual Phase Reaction

Proton conducting oxides, commonly used as electrolytes in ceramic electrochemical cells, boast remarkable proton conductivity, facilitating efficient energy conversion. However, their refractory nature presents challenges in achieving the ideal electrolyte structure and properties. Our novel approach utilizes reaction sintering to effectively lower the electrolyte's sintering temperature, resulting in stable and excellent electrolytic properties. This method transforms a two-phase mixture (comprising fast and slow-sintering phases) into a single-phase compound and densifies the electrolyte in a single-step heating cycle. During the reaction sintering process, rapid growth of the fast-sintering phase grains occurs due to its superior sinterability, aided by Ostwald ripening exhibited by the smaller slow-sintering phase. Lowering the sintering temperature preserves the intended initial stoichiometry of the electrolyte material, leading to a significant enhancement in electrochemical performance.

The synergistic effect of cold sintering and reaction sintering on BST tape casting sheets

In this paper, the tape casting method was used to prepare BST (Barium Strontium Titanate) thin films and the effect of combining cold sintering and reaction sintering processes on the properties of BST sheets was explored. A comparison was made between cold sintering and direct BST sintering combined. The combined process yielded high-density BST sheets with significantly improved dielectric properties (the resulting BST sheets displayed a low dielectric loss of less than 0.02 with a dielectric constant of 720) at a reduced sintering temperature of 950 °C. The underlying mechanisms for this enhanced performance are explored through structural and sintering analysis.

Synthesis and property enhancement of Ti-Si/SiC composites by reactive infiltration for semiconductor applications

Poor machinability and limited electrical conductivity present significant challenges for silicon carbide (SiC) composites used in the semiconductor industry. In this study, Ti-Si/SiC composites were synthesized by liquid infiltration of a Ti-Si eutectic alloy, using SiC and Carbon black as raw materials. The reactive sintering mechanism and properties of Ti-Si/SiC composites were investigated using the reactive infiltration sintering process. The relative density of Ti-Si/SiC composites reached 98.43 % at 1600 °C. The results indicate that continuous infiltration of the Ti-Si eutectic alloy and dissolution-reprecipitation are critical for synthesizing Ti-Si/SiC composites. The coefficient of thermal expansion for the composites is 5.16 × 10−6 °C−1. Remarkably, the exponential increase in electrical conductivity with rising temperature strongly supports the enhanced conductive properties of this composite semiconductor. The Ti-Si/SiC composites exhibit maximum flexural strength, indentation modulus, and hardness values of 310.4 MPa, 434.1 GPa, and 29.4 GPa, respectively. This research aims to advance the application of high-performance Ti-Si/SiC materials in semiconductor technology.

Effect of CeO2@Ni on the Oxidation Resistance of in Situ TiC/Ni Composite Applied for Intermediate Temperature Solid Oxide Fuel Cell Interconnects

The TiC/Ni composites with different CeO2 or CeO2@Ni content are fabricated by pressureless reactive sintering, and the CeO2@Ni particles are prepared by electroless plating technique. The results show that the continuous Ni layer is prepared on CeO2 particles, leading to the decrease of contact angle between CeO2 and Ni from about 116° to 65°. The relative density of composites with 1 wt% CeO2 increases from 85.79% to 96.45% by Ni layer on CeO2 particles. The CeO2 or CeO2@Ni particles exhibit no obvious influence on the microstructure of composites, and Ce atoms of CeO2 diffuse into TiC particles during the reactive sintering process. The mass gain of composite decreases from 7.4709 to 4.9075 mg cm−2 by addition of 1 wt% CeO2@Ni. The Ce‐doped in NiO and TiO2 would restrict the inward diffusion of O atoms and outward diffusion of Ni atoms, resulting in the improvement of oxidation resistance of composite. With the increase of CeO2@Ni content from 0 to 1 wt%, the surface specific resistance of composite decreases from 3.16 to 0.56 Ω cm2 at 800 °C due to the thinner oxide scale and lower bandgap of TiO2 by Ce doping.

Synthesis and reaction mechanism of high injected electron concentration and low work function [Ca24Al28O64]4+:(4e-) by Sol-gel method combined with spark plasma sintering

The high injected electron concentration and low work function C12A7:e- was successfully prepared by the sol-gel method combined with spark plasma sintering(SPS) using calcium nitrate, aluminum nitrate, citric acid, and ethylene glycol as raw materials. By analyzing the morphology of carbon and its role in the reactive synthesis, we reveal the reaction synthesis mechanism of C12A7:e- under the SPS. The analysis shows that C12A7:e- started to be generated at 800 °C. During the SPS reaction sintering process, carbon atoms from citric acid and ethylene glycol were excited by a pulsed current at high temperature, forming the carbon ions C22- and C (gas). Both act as reducing agents and react with the free oxygen ions O2- in the C12A7 cage cavity to form gaseous CO or CO2, enabling electrons to be injected into the cage cavity, thus generating C12A7:e-. Meanwhile, the graphene oxide (GO) formed on the surface of C12A7:e- grain is produced by the precursor of sol-gel synthesis in the high temperature oxidation environment, which will be conducive to improving the stability of C12A7: e- in air and high temperature oxidation resistance.

Dielectric properties of disordered A6B2O17 (A = Zr; B = Nb, Ta) phases

AbstractWe report on the structure and dielectric properties of ternary A6B2O17 (A = Zr; B = Nb, Ta) thin films and ceramics. Thin films are produced via sputter deposition from dense, phase‐homogenous bulk ceramic targets, which are synthesized through a reactive sintering process at 1500°C. Crystal structure, microstructure, chemistry, and dielectric properties are characterized by X‐ray diffraction and reflectivity, atomic force microscopy, X‐ray photoelectron spectroscopy, and capacitance analysis, respectively. We observe relative permittivities approaching 60 and loss tangents <1 × 10−2 across the 103–105 Hz frequency range in the Zr6Nb2O17 and Zr6Ta2O17 phases. These observations create an opportunity space for this novel class of disordered oxide electroceramics.

Porous (Y0.25Ho0.25Yb0.25Lu0.25)2Si2O7: A novel high‐entropy ceramic with high porosity and excellent thermal stability

AbstractWith the rapid development of hypersonic vehicles, the thermal protection systems face great challenges due to the severe aerodynamic heat. As a result, conventional fiber insulation tiles would experience severe shrinkage at high temperatures (>1500°C), endangering the safety of the aircraft. To solve the problem, a high‐entropy effect was introduced to increase the high‐temperature resistance of thermal insulation materials, and highly porous (Y0.25Ho0.25Yb0.25Lu0.25)2Si2O7 was prepared by in situ reaction sintering process in this work. The fabricated porous samples present excellent overall properties, including superhigh porosity (95.09%–93.10%), lightweight (0.29–0.41 g/cm3), and very low thermal conductivity (0.066–0.085 W/(m·K)). More importantly, porous (Y0.25Ho0.25Yb0.25Lu0.25)2Si2O7 has outstanding high‐temperature dimensional stability. Although the porosity of the sample is higher than 90%, its linear shrinkage at 1550°C for 2 h is less than 1%. The results demonstrate that porous high‐entropy (Y0.25Ho0.25Yb0.25Lu0.25)2Si2O7 is a promising thermal insulation material in extreme high‐temperature environments.

Effects of diamond as a main carbon source on the fabrication and mechanical properties of reaction-bonded SiC

RBSC with a low residual Si less than 5 vol% was fabricated using SiC–C preform with diamond as a main carbon source by a conventional reaction sintering process at the temperature range between 1500 °C and 1800 °C. The diamond content in the SiC–C preform varied from 10 wt% to 17 wt%. The diamond as the main carbon source used in SiC–C preform effectively minimized the residual Si in RBSC by increasing the reaction of diamond due to the enhanced Si melt infiltration even in SiC–C preform with high carbon content. The Si melt infiltration should be performed above 1600 °C for the complete reaction of diamond particles with size of 0.5 μm because of the relatively low dissolution rate of diamond in Si melt. The flexural strength of RBSC with residual Si content less than 7 vol% exceeded 400 MPa. The flexural strength of RBSC was increased with decreasing residual Si content, but sharply decreased by the residual carbon accompanying pores in RBSC. RBSC with low residual Si content displayed moderate flexural strengths around 200 MPa even above Si melt temperature because of the formation of continuous SiC structure in RBSC by the enhanced grain growth of SiC. Vickers hardness of RBSC was steadily increased from 17.7 GPa to 24.6 GPa with decreasing residual Si.

Effect of Si3N4 Additive on Microstructure and Mechanical Properties of Ti(C,N)-Based Cermet Cutting Tools.

Development of high-performance cutting tool materials is one of the critical parameters enhancing the surface finishing of high-speed machined products. Ti(C,N)-based cermets reinforced with and without different contents of silicon nitride were designed and evaluated to satisfy the requirements. In fact, the effect of silicon nitride addition to Ti(C,N)-based cermet remains unclear. The purpose of this study is to investigate the influence of Si3N4 additive on microstructure, mechanical properties, and thermal stability of Ti(C,N)-based cermet cutting tools. In the present work, α-Si3N4 "grade SN-E10" was utilized with various fractions up to 6 wt.% in the designed cermets. A two-step reactive sintering process under vacuum was carried out for the green compact of Ti(C,N)-based cermet samples. The samples with 4 wt.% Si3N4 have an apparent solid density of about 6.75 g/cm3 (relative density of about 98 %); however, the cermet samples with 2 wt.% Si3N4 exhibit a superior fracture toughness of 10.82 MPa.m1/2 and a traverse rupture strength of 1425.8 MPa. With an increase in the contents of Si3N4, the Vickers hardness and fracture toughness of Ti(C,N)-based cermets have an inverse behavior trend. The influence of Si3N4 addition on thermal stability is clarified to better understand the relationship between thermal stability and mechanical properties of Ti(C,N)-based cermets.

Heterogeneous diamond–TiC composites with high fracture toughness and electrical conductivity

The concurrent enhancement of toughness, electrical conductivity, and thermal stability in polycrystalline diamond composites represents a formidable challenge. Here, a novel diamond-TiC composites (referred to as DTC) with high fracture toughness and conductivity were synthesized through a high-temperature and high-pressure reaction sintering process utilizing two precursors: diamond mixtures containing TiH2 and Ti-coated diamonds. On the one hand, the inherent bonding and encasing of TiC onto the diamond matrix form a heterogeneous structure, providing high strength and excellent fracture toughness up to 11.6 MPa·m1/2. On the other hand, the established oxygen barrier and current pathway offer a thermal stability of 765 °C and high conductivity up to 837 S·m−1. Remarkably, this rare combination of mechanical, electrical, and thermal properties has been realized within a single material under relatively moderate sintering conditions, thus positioning diamond-TiC composites as a promising ceramic for electrical applications in high-stress environments.

In-situ fabrication and characterization of W-ZrC composites via pressureless reaction sintering

This research presents a study on the fabrication and characterization of tungsten‑zirconium carbide (W-ZrC), an ultra-high temperature ceramic, using an in-situ reaction sintering method. Tungsten carbide (WC) and zirconia (ZrO2) powders were used as precursors to synthesize composites with three different ratios. The thermodynamic phase stabilities of the precursor materials were analyzed, and the reaction products were determined based on the total pressure within the system. The fabricated composites were characterized by their microstructures, porosities, hardnesses, and thermal conductivities. The results show that the composites exhibited distinct crystal phases, including those of tungsten, tungsten carbide (W2C), zirconium carbide (ZrC), and tetragonal zirconia (t-ZrO2). The reaction pathways were determined based on the composition ratios and thermodynamic stability. The composites demonstrate good densification and interparticle bonding owing to the in-situ reaction sintering process, which simplifies the fabrication and lowers processing costs. The composites also exhibited desirable properties, such as high hardness and thermal conductivity (maximum 36.4 W·m−1·K−1), making them suitable for high-temperature applications. The findings of this study contribute to the understanding of the synthesis process and properties of W-ZrC composites and provide insights for their potential applications to industries such as aerospace, defense, and nuclear energy.

Reactive spark plasma sintering of Si2N2O ceramic: Reaction process, microstructure, mechanical and dielectric properties

Dense Si2N2O ceramic was successfully prepared through the spark plasma sintering method at 1750 °C with nano-sized amorphous Si3N4 powder as raw material. The reaction sintering process, mechanical and dielectric properties of the Si2N2O ceramic were investigated in detail. The results revealed that the amorphous Si3N4 was initially crystallized to β-Si3N4, then oxidized to Si2N2O during the sintering process. With prolonging the dwell time, the grain orientation of Si2N2O gradually developed to the c-axis direction of the orthorhombic crystal. Meanwhile, the density of as-sintered ceramic was improved significantly, which greatly influenced the mechanical and dielectric properties of Si2N2O ceramic. In this work, the optimal dwell time of sintering process was 20 min, which is obviously shorter than the ordinary sintering methods. The Si2N2O ceramic fabricated at the above conditions exhibited the most favorable mechanical and dielectric properties with a bulk density of 2.80 ± 0.01 g cm−3, Vickers hardness of 13.1 ± 0.1 GPa, flexural strength of 214.1 ± 15.8 MPa, fracture toughness of 2.8 ± 0.3 MPa m1/2, and combined with low dielectric constant of around 3.5 to 4.5 at 8.2−12.4 GHz. Thus, the spark plasma sintering method is potentially regarded as a rapid way to prepare Si2N2O ceramic used as the structural and wave-transmitting functional material.

Investigation on Ni-Al Intermetallic Compounds Fabricated through Reactive Sintering Processes

The utilization of nickel aluminide compounds in high-temperature structural applications is advantageous due to their desirable properties. One efficient method for producing nickel aluminide samples with desirable chemical reactions using minimal energy is reactive sintering. In this study, Ni-Al (20 wt.%-80 wt.%) compounds were fabricated by initially cold pressing them, followed by reactive sintering. The reactive sintering process resulted in the formation of NiAl3 and Ni2Al3 phases within the Ni-Al compounds. The microstructure, porosity, and hardness of the samples were thoroughly examined and analyzed. Generally, the compounds produced through reactive sintering exhibited significant porosity attributed to shrinkage and the Kirkendall effect. Microstructural analysis confirmed the presence of porosity, NiAl3, and Ni2Al3 phases. The sintered sample processed at 400 °C demonstrated higher density and hardness. Additionally, the wear test indicated a low wear rate and friction coefficient for the sintered sample processed at 400 °C.

Reactive flash sintering of TiZrN and TiAlN ternary metal nitrides

This study demonstrated the reactive flash sintering (RFS) for two powder mixtures: TiN-ZrN (both conducting) and AlN-TiN (TiN conducting but AlN insulating), targeting ternary metal nitrides (TMN) of Ti0.5Zr0.5N and Ti0.5Al0.5N, respectively. A constant volage and pressure (e.g., 8 V DC, ∼15 MPa) at room temperature triggered the flash (current density up to 27 A/mm2) without pre-heating, and the entire RFS process finished in a few minutes. For TiZrN, the flash was instantaneous whereas for TiAlN, there was a long incubation before the flash followed by a quick and dramatic flash. Both conventional ex situ XRD and in situ synchrotron study had been carried out. They showed a uniform Ti0.57Zr0.43N solution formed in RFS and persisted upon cooling, while (Ti, Al) N solid solution formed at high temperature was not stable and likely went through a very quick phase separation in the cooling process. The final products from RFS had been characterized using SEM/EDS for microstructure. Both TiZrN and TiAlN were dense. Distribution of Ti, Zr, and N was uniform for TiZrN; for TiAlN, Ti and N distribution was uniform, while association of Al with oxygen was observed. TGA-DSC revealed the onset oxidation temperature for TiZrN was comparable to TiN and ZrN, while it was higher by ∼200 °C for TiAlN, likely due to the formation of Al2O3. In terms of mechanical properties such as hardness or fracture toughness, forming a single-phase solid solution (like TiZrN) does not offer obvious benefits. while large grain size from RFS seemed to be unfavorable. Future optimization of RFS condition and in-depth study by both experiments and simulation are needed to fully understand the composition-processing-structure-property relationships for such TMN from the reactive flash sintering process.

Novel Route for Preparing Diamond-Enhanced Cemented Carbides via Reactive Sintering

Hardmetals are cemented carbides consisting of the hard ceramic phase WC and the ductile metallic binder Co. They offer an outstanding combination of hardness and fracture toughness. Hence, they have a widespread use across the manufacturing industry. However, due to the increasing requirements for tool material, the combination of the beneficial properties of hardmetal and diamond is a long sought-after objective. In this work, a new approach was evaluated to reduce the formation of graphite due to the phase transformation of diamond during the sintering of compounds together with hardmetal. Earlier trials could not fully suppress the phase transformation despite using alternative Ni-instead of conventional Co-based binder systems and field-assisted sintering (FAST) to reduce required sintering temperatures and time. To lower the amount of graphite formed during sintering even further, a reactive sintering process was developed. The increased sinter activity due to the in situ synthesis of WC has the potential to decrease the needed temperature to achieve a pore-free compact. For the first time, a WC-Ni hardmetal produced from elemental powders was successfully used as a matrix in a diamond-enhanced cemented carbide (DECC). Different approaches regarding carbon sources and the extent of reactive material were pursued. The introduction of a carbon deficit by adding metallic W to a mixture of WC and Ni, which is essentially partial reactive sintering, leads to an increased relative density compared to the reference of 97.3%.

Enhanced ferroelectric and magnetic properties of the 0–3 type BiFeO3-BaTiO3/BaFe12O19 composite multiferroic material

The 0–3 type (1-x)(0.75BiFeO3-0.25BaTiO3)/xBaFe12O19 (BFO-BTO/BaM) multiferroic composites were successfully prepared by a solid-state reaction sintering process. The coexistence of perovskite BFO-BTO phase and hexagonal BaM phase was confirmed for all BFO-BTO/BaM composites. Due to the large leakage current, the breakdown electric field decreased with increasing BaM content. Nevertheless, the ferroelectric properties of the composite ceramics have also been significantly improved, mainly as the increase of remanent polarization and the decrease of coercive field, where Pr = 19.79 μC/cm2, Ec = 30 kV/cm at x = 0.075. Meanwhile, the magnetic properties of BFO-BTO phase were enhanced, and the remanent magnetization linearly increased with increasing BaM content. The single domain magnetic structure was obtained for all BFO-BTO/BaM composite ceramics, and the magnetic properties changed after electric poling, which indicated the electric field controlled magnetic properties. The electric-controlled magnetic behavior was attributed to the structural phase transition. The magnetoelectric coupling coefficient αME of the composite material has been improved, with a maximum value of 0.61 mV/cm.Oe. Thus, the BFO-BTO/BaM magneto-electric composite system is a promising multiferroic system in information technology and sensing fields.

The formation mechanism of in-situ TaC/Ni0.9Ta0.1 composites prepared by pressureless reactive sintering

The in-situ Tantalum Carbide (TaC)/Ni0.9Ta0.1 composite was fabricated by pressureless reactive sintering method using Nickel (Ni), Tantalum (Ta) and graphite as raw materials. The formation mechanism was investigated through analyzing the phase and morphology evolution process during the reactive sintering process. Results showed that Ni, Ta and graphite completely reacted and dense TaC/Ni0.9Ta0.1 composite was obtained. With the increase of temperature, the solid-phase diffusion of atoms occurs at the interface of Ni, Ta and graphite, leading to the formation of Ni3C, Ni2Ta, Ni3Ta, Ni0.9Ta0.1 and TaC. Meanwhile, the reaction [Ta] (Ta atoms in Ni3Ta) + [C] (C atoms in Ni3Ta)TaC in Ni3Ta takes place, due to the high affinity between Ta and C atoms. The intermediate products Ni3C, Ni2Ta and Ni3Ta vanish, and the composite is consisted of Ni0.9Ta0.1 and TaC before the appearance of liquid phase. The formation of TaC included two ways, namely the diffusion of C into Ta particles and the reaction [Ta]+[C] = TaC in Ni3Ta. Ni0.9Ta0.1 was also generated through two ways, i.e., the diffusion of Ta into Ni and the transformation of Ni3Ta. The liquid phase sintering of composite occurs at about 1320 °C, and the optimum sintering temperature was about 1380 °C.

Performance optimization of Si/SiC ceramic triply periodic minimal surface structures via laser powder bed fusion

AbstractSiC ceramic lattice structures (CLSs) via additive manufacturing (AM) have been recognized as potential candidates in engineering fields owing to their various merits. Compared with traditional SiC CLSs, SiC triply periodic minimal surface (TPMS) CLSs could possess more outstanding properties, making them more promising for wider applications. Since SiC CLSs are hard to be fabricated through stereolithography techniques because of inferior light performance, the laser powder bed fusion (LPBF) process via selective sintering is an effective method to prepare near‐net‐shaped SiC TPMS lattices. As the mechanical performances of lattice structures are the foundation for future practical applications, it is of great significance to optimize the preparation process, thus improving the mechanical properties of SiC TPMS structures. In this work, the optimal printing parameters of the LPBF and liquid silicon infiltration process for SiC ceramic TPMS CLSs with three different volume fractions were systematically illustrated and analyzed. The effects of the printing parameters and carbon densities on the fabrication accuracy, microstructure, and mechanical performance of SiC TPMS CLSs were defined. The mechanism of the reactive sintering process for the SiC TPMS lattice structure was revealed. The results reveal that Si/SiC TPMS CLSs with optimum preparation have superior manufacturing accuracy (most less than 6%), relatively high bulk densities (about 2.75 g/cm3), low residual Si content (6.01%), and excellent mechanical properties (5.67, 15.4, and 44.0 MPa for Si/SiC TPMS CLSs with 25%, 40%, and 55% volume fractions, respectively).

Impact of Sintering Temperature Variation on Porous Structure of Mo2TiAlC2 Ceramics.

Mo, TiH2, Al and graphite elemental powders were used as starting materials for the activation reaction sintering process, which was employed to fabricate porous Mo2TiAlC2. The alteration of phase constitution, volume expansion, porosity, pore size and surface morphology of porous Mo2TiAlC2 with sintering temperatures ranging from 700 °C to 1500 °C were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and pore size tester. Both the pore formation mechanism and activation reaction process at each temperature stage were investigated. The experimental results illustrate that the sintered discs of porous Mo2TiAlC2 exhibit obvious volume expansion and pore structure change during the sintering process. Before 1300 °C, the volume expansion rate and porosity increase with the increment of temperature. However, with the sintering temperature above 1300 °C, the volume expansion rate and porosity decrease. At the final sintering temperature of 1500 °C, porous Mo2TiAlC2 with a volume expansion rate of 35.74%, overall porosity of 47.1%, and uniform pore structure was synthesized. The pore-forming mechanism of porous Mo2TiAlC2 is discussed, and the evolution of pressed pores, the removal of molding agents, the decomposition of TiH2, and the Kirkendall effect caused by different diffusion rates of elements in the diffusion reaction are all accountable for the formation of pores.

Effects of TiO2 addition on phase, mechanical properties, and microstructure of Cr2O3–Al2O3 ceramic composite

TiO2 is a sintering additive that can significantly improve the sintering and mechanical properties of Cr2O3–Al2O3 refractory materials with high Cr2O3 contents. In this study, TiO2-reinforced Cr2O3–Al2O3 composite refractories were prepared using a reaction-sintering process. The microstructure, phase composition, mechanical properties, and strengthening mechanism of the TiO2-reinforced Cr2O3–Al2O3 composite refractories were investigated. The results indicated that the Al2O3–Cr2O3–TiO2 composite refractory with a TiO2 content of 3.0–4.5 wt% had good compactness (porosity of 5.89%), hardness (17.21 GPa), wear resistance (wear rate of 0.4 mm3/Nm), flexural strength (101.10 MPa), and compressive strength (420.90 MPa). This is mainly because when the added amount of TiO2 was <3.0 wt%, TiO2 was solidly soluble in the matrix, forming a Ti3+-doped (Cr, Al)2O3 solid solution, inhibiting abnormal grain growth, rapidly increasing the sintering shrinkage of the sample, rapidly increasing the bulk density, rapidly decreasing the apparent porosity, and improving the sintering and mechanical properties of the composite resistant material. When the TiO2 addition exceeded 4.5 wt%, a large amount of (Cr, Al)2TiO5 phase was distributed between the grain boundaries of the solid solution, and its bulk density started to decrease. The sintering shrinkage and apparent porosity did not change significantly, and the bonding between the solid solution was not improved. Thus, the sintering and mechanical properties of the composite resistant material deteriorated. Taking into account the slag resistance and mechanical properties of the material, Al2O3–Cr2O3–TiO2 with a TiO2 content of 3.0–4.5 wt% can meet the service requirements for mechanical properties of the lining of smelting reduction ironmaking furnaces.