Sintering Activation Energy Research Articles

Sintering activation energy and low-temperature sinterable process of Boron-lanthanide glass/Li2Zn3Ti4O12 ceramic composite systems for LTCC technology

This work investigates the characteristics of wettability, activation energy for sintering, evolution of phase structure, and behavior during the low-temperature sintering process of B2O3-La2O3-MgO-TiO2 (BLMT) glass/Li2Zn3Ti4O12 ceramic composites for low temperature co-fried ceramics technology (LTCC). As the BLMT glass content increases from 0 to 10 wt%, the average sintering activation energy (Ea) of the composite decreases from 450 ± 8 to 356 ± 37 kJ/mol. There are two phases the primary Li2Zn3Ti4O12 phase and the secondary LaBO3 phase, the latter precipitates from the BLMT glass after sintering at 700 °C. This indicates that BLMT glass promotes the sintering of Li2Zn3Ti4O12 ceramic below 900 °C. In composites containing 20 wt% or more glass, sintering is governed by both liquid-phase sintering and reactive viscous sintering. As the BLMT glass content increases, the impact of viscous flow on the densification process becomes more pronounced. Simultaneously, when the glass content is greater than 20 wt%, the glass precipitates LaBO3, TiO2, and MgLaB5O10 phases between 700 and 750 °C. After 850 °C, the glass melts and reacts with Li2Zn3Ti4O12 phase to produce a new TiO2 phase. Accordingly, the activation energy (Ea) of sintering the composite material increases from 393 ± 17 to 667 ± 1 kJ/mol.

Experimental and molecular dynamics multiscale study on sintering and interfacial reaction of Fe2O3/CaO particle system

High-temperature sintering and solid-state reaction within the intricate Fe2O3/CaO system are pivotal factors influencing material characteristics. The current work focused on the sintering and reaction behavior of Fe2O3/CaO particles at high temperatures with a multiscale study of in-situ high-temperature stage microscopy (HTSM) and molecular dynamics (MD). The laws governing atomic migration and the evolution of crystal structure during the sintering process were simulated at the nanoscale. The results elucidated that a heightened heating rate fosters particle shrinkage and concomitant reduction in surface area. The sintering activation energy (Esin) exhibited an increment proportional to the linear shrinkage of the particles. Furthermore, an augmented potential barrier in advanced stages impeded subsequent sintering behavior. Augmented temperature promoted the particle shrinkage and sintering neck formation, culminating in pore closure and a diminution in the free surface. However, this promotional effect attenuated with escalating temperatures. Particle shrinkage and sintering neck formation are contingent upon atomic migration and diffusion, with the growth of sintering necks primarily reliant on atom diffusion along the surface of the sintering necks. The atomic diffusion activation energy was determined to be 49.5 kJ/mol within the temperature range of 1073–1473 K. Within the Fe2O3/CaO system, the preferential generation of Ca2Fe2O5 (C2F) over CaFe2O4 (CF) was found, leading to a decrease in the atomic diffusion barrier and an enhancement of the diffusivity, with the latter dominating in later stages. The highest mobility of O2–, Fe3+, and Ca2+ was discerned in CF, and the sintering shrinkage of the particles predominantly hinges on the generation of CF.

Pressureless sintering kinetics analysis of Ti3SiC2 and Ti2AlC powdered MAX phases

This paper reports the pressureless sintering behavior and the activation energy of the powdered MAX phases Ti3SiC2 and Ti2AlC. A non-isothermal technique was used to determine the sintering kinetic parameter. The Ti3SiC2 and Ti2AlC MAX phases showed the maximum sintering rate at 1723 K, 0.14 and 0.10 µm/s, respectively. The sintering rate of the sample at different temperatures followed a cubic equation which was determined. The sintering activation energy (Ea) for the Ti3SiC2 and Ti2AlC samples was 362.1 kJ/mol and 640.3 kJ/mol, respectively.

Thermomechanical and thermodynamic analysis of the sintering process of Mn-based oxygen carrier in chemical looping gasification of biomass

The Mn-based oxygen carrier (OC) owns a great oxygen carrying capacity and a high reactivity in the chemical looping gasification of biomass. However, the sintering of the Mn-based OC can cause serious defluidization or even the shut-down of the biomass chemical looping gasifier. In this study, the sintering kinetics and mechanism of Mn-based OC in the gasification of two typical biomass ash were revealed by thermomechanical and thermodynamic analysis. It revealed that the manganese silicate was converted to iwakiite (MnFe2O4) and liquid at high temperatures in the high-Mn OC (OC2), leading to the liquid sintering mechanism and high apparent activation energy of sintering (Es), with a maximum shrinkage rate of 6.14 %/oC. Conversely, the solid sintering mechanism of the low-Mn OC (OC1) was attributed to the FeMn2O4 crystallization, leading to a low shrinkage rate (The maximum shrinkage rate was 0.30 %/oC). The sintering rate of Mn-based OC was closely related to the liquid content, and the biomass ash addition advantaged the liquid formation. Therefore, the Es of OC1 was increased from 44 kJ/mol to 151 kJ/mol at the 15 wt% addition of corn straw ash, and Es of OC2 was increased from 72 kJ/mol to 93–107 kJ/mol at 20 wt% addition of biomass ash. Element distribution analysis supported that Ca in sawdust ash improved the bonding between Mn and Si, improving the Mn-based minerals crystallization and OC expansion. However, the K in corn straw ash facilitated the melting of rhodonite(MnSiO3), and the expansion of Mn-based OC was inhibited. This study provides valuable insights into the sintering mechanism of the Mn-based oxygen carrier and its relationship with liquid evolution behavior in the chemical looping gasification of biomass.

Investigation of sintering properties and behavior of sericite ceramifying powder under low temperature

AbstractPolymer–ceramic composites are widely used in refractory cables. The ceramic fillers provide high temperature and fire resistance, while the polymer matrix provides flexibility and improved electrical insulation. The properties of the polymer–ceramic composites are determined by the ceramization‐forming properties of the corresponding ceramifying powders. Properties such as shrinkage, density, and porosity were characterized to compare the effects of different contents of glass powder. The sintering activation energy was calculated using the logarithmic relationship between shrinkage and holding time. The microstructure, cross‐section, and crystalline phases were investigated by scanning electron microscopy (SEM) and X‐ray diffraction analysis (XRD) to explore the ceramization process of sericite ceramifying powder. The ceramization process of ceramifying powder is proposed. The results show that during low‐temperature sintering, the glass powder and muscovite phases melt and partially transform into α‐quartz and albite low during cooling down.

Effect of LiF addition strategy on the sintering of Li2MgTiO4 microwave dielectric ceramics with cubic rock salt structure

Recently, microwave dielectric ceramics with an oxyfluoride cubic rock salt structure have been widely studied due to their excellent microwave dielectric properties. However, the sintering mechanism of this material, especially the role of F-ions, is not clear. Here, the ceramic samples with two different LiF addition strategies were prepared by a conventional solid-phase reaction method. The sintering mechanisms of both samples were discussed in detail by analyzing the sintering activation energy, F-ions distribution, and concentration of oxygen vacancies by linear shrinkage, SEM-EDS, and XPS. The best microwave dielectric properties were obtained for Li2MgTiO4 +4 wt% LiF (LiF-B) ceramics sintered at 950°C: εr = 18.0, Q×f = 82,100 GHz, and τƒ = −32.7 ppm/°C.

A novel Gd2O3–Al2O3–SiO2 glass-ceramics substrate material with comprehensive performance

A novel Gd2O3–Al2O3–SiO2 glass-ceramics (GAS GCS) for substrate application was prepared using the melt-quenching method. The present study pay attention to investigate the crystallization and sintering behaviors, phase compositions, micromorphology, dielectric and mechanical properties of GAS glass-ceramics. An appropriate amount of Gd2O3 diminished the glass viscosity while enhancing structural stability, thereby reducing the activation energy for crystallization and sintering. This contributed to the GAS GCS achieve dense microstructure and high crystallinity. X-ray diffraction (XRD) and Raman spectroscopy analyses confirmed the presence of high-density crystal phases, namely Gd2SiO5 and Gd2Si2O7, which significantly contribute to the enhanced density of the samples. Moreover, a positive correlation was observed between the dielectric constant and crystallinity. Notably, the GAS GCS composition of 41 wt% Gd2O3-21.3 wt% Al2O3-37.7 wt% SiO2 exhibited optimal properties, including a flexural strength of 243.4 MPa, Vickers hardness of 7.77 GPa, elastic modulus of 154.02 GPa, coefficient of thermal expansion of 5.9 × 10−6/°C, dielectric constant of 7.43, and dielectric loss of 4.05 × 10−3. These outstanding characteristics position it as a promising candidate for substrate materials.

Microstructure, mechanical, and thermal properties of (MoTaTiVW)CX high entropy ceramics with different carbon stoichiometries

In present work, high entropy (MoTaTiVW)CX ceramics with different carbon stoichiometries (X = 3–6) were produced using spark plasma sintering. The microstructure, mechanical properties, and thermal properties of (MoTaTiVW)CX with different carbon stoichiometries were studied. At X = 3, the carbon deficiency resulted in a multiphase structure of the sample, (MoTaTiVW)C3 with a Mo-rich carbide phase. At X = 3.5, the single-phase rock salt structure was formed despite carbon vacancies of up to 30 %. The relative density of (MoTaTiVW)CX gradually decreases as the carbon stoichiometry increases from X = 3 to X = 6. The concentration of carbon vacancies affects the sintering activation energy, which can enhance mass transfer and promote the densification process. The Vickers hardness of (MoTaTiVW)CX shows an overall decreasing trend as the carbon stoichiometry increases from X = 3.5 to X = 6, peaking at 20.4 ± 0.4 GPa at X = 3.5. The fracture toughness increases and then decreases, peaking at 4.4 ± 0.2 MPa m1/2 at X = 4. The thermal conductivity of (MoTaTiVW)CX gradually increases, then decreases and finally increases with the increase of carbon stoichiometry. At room temperature, the maximum value of thermal conductivity is 6.35 ± 0.29 W/m·K of (MoTaTiVW)C5 and the minimum value is 5.32 ± 0.35 W/m·K of (MoTaTiVW)C5.5. At 1000 °C, the thermal conductivity of (MoTaTiVW)CX ranges from 15.94 ± 0.37 W/m·K to 19.56 ± 0.45 W/m·K. As the concentration of carbon vacancies decreases, the decrease in point defect concentration will reduce the degree of lattice distortion, thereby reducing phonon scattering and affecting thermal conductivity. The study suggests that carbon stoichiometry can be used to adjust the microstructure, mechanical properties, and thermal properties of high entropy carbide ceramics.

Sintering activation energies of anisotropic layered and particle alumina/zirconia-based composites and their mechanical response

Information on the sintering activation energy is currently focused on evaluation of single-phase ceramic systems. This work shows the results of high-temperature dilatometry measurements of layered and particle composites based on alumina and zirconia. Layered composites with different layer thickness ratios and particle composites with variable composition in the entire concentration range were prepared by electrophoretic deposition allowing manufacturing composites with precious design and strongly bonded interfaces. The phenomena observed during the high-temperature dilatometry measurements are discussed, and the data were used to calculate the sintering activation energies of composites using the modified Master Sintering Curve concept. By covering a wide range of composite designs, it was possible to determine differences in activation energies and to show their dependence on the direction in the case of laminate composites given by the directionally dependent sintering behaviour. Sintering activation energies of layered composites were always higher than for monoliths due to constrained sintering showing maximum sintering activation energies at lower volumes of zirconia in the layers for longitudinal and transversal orientation of the samples. A similar trend was identified in particle composites due to slowed down alumina densification by the pinning effect. Additionally, mechanical properties represented by Vickers hardness and indentation elastic modulus were related to the microstructure developed during sintering. The effects of interconnectivity of phases present in the composites together with other parameters of the microstructure were described.

Improving the stability of La0.6Sr0.4Co0.2Fe0.8O3-δ electrode for solid oxide fuel cells by introducing sintering inhibitors

In this study, nano-sized Al2O3 and Gd0.1Ce0.9O1.95 (GDC) particles are added to La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) cathode material as sintering inhibitors for solid oxide fuel cells (SOFC) to improve the stability of the cell performance. Studies reveal that as the amount of the inhibitors increases, the sintering activation energy of the composite LSCF sample increases, resulting in retarded sintering kinetics indicated by the suppressed grain size of the sintered composite LSCF cathode. Long-term durability tests show that due to the enhanced stability of the microstructure of the composite LSCF cathode, the composite cathode exhibits improved performance stability. Furthermore, both the Al2O3 and GDC additions can improve the hardness and elastic modulus of the cathode, while the electrical conductivity of both cathodes exceed 100 S/cm and can still meet the requirements for the SOFC in the operation temperature range of 600–800 °C. In light of the boosted electrochemical durability of the Al2O3-added LSCF cathode and much lower cost of Al2O3 compared to the rare-earth element based GDC materials, LSCF cathode with a proper amount of the nano-sized Al2O3 inhibitors is a good solution to enhance the mechanical property, electrochemical durability of LSCF cathode for the SOFCs at low cost.

Additive manufacturing-assisted sintering: Low pressure, low temperature spark plasma sintering of tungsten carbide complex shapes

Tungsten carbide (WC), renowned for its exceptional hardness and wear resistance, plays an essential role in various industrial applications (cutting tools, abrasives, and wear-resistant components). While traditional methods involve hot pressing, Spark Plasma Sintering (SPS) combined with Additive Manufacturing (AM) offers a cutting-edge approach, utilizing high-voltage electric current and mechanical pressure for rapid densification, particularly advantageous for fabrication of complex shape components made from challenging materials like nanosized binderless tungsten carbide. The study encompasses the entire spectrum of the powder's characterization, extending to the development of an intricate finite element simulation tailored for SPS sintering. Sintering cycles underscore the exceptional quality of the powder, demonstrating full density microstructures even under low-temperature (1550 °C) and low-pressure (50 MPa) conditions. The nanosized powder exhibits minimal microstructural coarsening, reflecting the high quality of the initial pure tungsten carbide nano powder. The core of this study revolves around the methodology employed for deriving constitutive parameters, following the Skorohod-Olevsky theory of continuum sintering. The derivation methods include variations in temperature, heating regimes, and stepwise pressure application during SPS. Additionally, a grain growth model is formulated based on microstructural analysis. Critical parameters, including the apparent sintering activation energy (800 kJ/mol) and the creep law stress exponent (n = 4.0), are discussed. The article concludes with the integration of the mechanical sintering model into finite element method (FEM) software, considering thermal and electrical aspects for a comprehensive SPS-AM modeling approach and its application to complex shape production. The research aims to enhance the understanding of SPS for tungsten carbide, providing insights for its application in manufacturing cutting-edge components in challenging environments.

Influence of particle size and aggregates on translucent alumina ceramics fabricated by gelcasting

Three types of alumina powders and a polymer electrolyte Isobam system were used to fabricate translucent alumina ceramics via gelcasting, and each powder had the highest attainable solid loading. The effects of alumina particle size on slurry dispersion, microstructures and properties of green bodies and ceramics were investigated. All of the high-solid loading slurries contained strong aggregates, which could bridge with each other to form weak agglomerates. The smaller the initial particle size was, the more the contained particle number per aggregate. In addition, the smaller the aggregate size was, the lower the sintering activation energy of the ceramic and, finally, the higher the relative density. The initial particle size of the powder may not be the critical factor determining ceramic sintering, but the aggregate size and effective volume fraction of the aggregates may be the critical factors. Finally, the in-line transmittance of the ceramic with a higher density reached 22% at a wavelength of 650 nm and a thickness of 0.8 mm.

Effect of Ti and Zr on high temperature mechanical and thermal properties of MoCu composites

Based on the design concept of diversified alloys, the reinforcement of TZM alloys was combined in the fabrication of MoCu composites. The MoCu composites were prepared by vacuum hot press sintering under the effect of Ti, Zr elements added separately or simultaneously, and the microstructure adjustment was realized by mechanical ball milling on the pretreatment of the original alloy powder. The results show that Ti and Zr elements form metal-based solid solutions and intermetallic compounds by diffusion with Mo and Cu matrix during the sintering process. It can not only reduce the sintering activation energy of MoCu composites to improve the densification, but also improve the mechanical properties of the composites through certain solid solution strengthening and second phase strengthening. When Ti, Zr elements are added at the same time, Zr elements can enhance the β-stabilizing effect of Mo on Ti elements and improve the solid solution effect between Ti and Mo, Cu matrix, which further improves the interfacial bonding. Therefore, the 60Mo35Cu2.5Ti2.5Zr composites have the best overall performance, and their thermal properties and mechanical properties at room and high temperatures are greatly improved compared with the original 60Mo40Cu composites.

Sintering behavior and activation energy calculation of nanoparticulate Fe3O4: a molecular dynamics simulation

This study employs molecular dynamic simulations to investigate the sintering mechanisms of Fe3O4 nanoparticles and determine the sintering activation energy. The melting temperature has been calculated using atomic volume to verify the accuracy of this EAM function and its parameters. Neck width has been defined to demonstrate the sintering degree under different temperatures, from 1373 K to 1773 K. Following sections divide the whole evolution into three mechanisms: surface diffusion, grain boundary diffusion and viscous flow according to the atomic migration vector. Finally, the sintering activation energy has been figured out based on the neck diameter ratio which later has been employed to predict the neck growth curve at 1523 K. Therefore, this investigation reveals the sintering mechanisms and introduces a method to predict the growth rate using activation energy.

Powder sintering kinetics during electron beam based additive manufacturing

Electron Beam Powder Bed Fusion (PBF-EB) allows not only for the additive manufacturing of fully dense metallic components via melting but also parts with defined local pore structures and tailored functional properties through selective sintering. The hybrid PBF-EB technology based on the combination of selective sintering and melting is, e.g., of great interest for the fabrication of porous electrodes composed of titanium-based alloys with high specific surface area, which are widely used for electrochemical processes (e.g., as anode for water electrolysis cells). This study aims to provide a comprehensive understanding of the sintering kinetics of Ti6Al4V (especially in the first and second sintering stages) during PBF-EB. The sintering degrees of the PBF-EB-processed Ti6Al4V samples are characterized by determining the thermal diffusivity measured by laser flash analysis. At the same time, the thermal history during PBF-EB is analyzed using a pyrometer. The correlation between the sintering degrees and the process parameters utilized in the PBF-EB procedure is discussed by calculating the activation energy of sintering and described using a master sintering curve. Based on the findings of this study, it is possible to control the sintering process of Ti6Al4V powder in a targeted manner by utilizing various PBF-EB parameters.

Sintering kinetics of cerium-stabilised tetragonal zirconia

Zirconia ceramics stabilised by CeO2 (Ce-ZrO2) exhibit low strength owing to their coarse grain sizes, which are typically larger than 1–2 μm. A promising approach to enhance the mechanical properties of Ce-ZrO2 is refining of the grain size. This study focuses on achieving fully dense Ce-ZrO2 ceramics with sub-micron grain sizes by identifying a sintering kinetic window that facilitates active sintering while suppressing grain growth. Both non-isothermal and isothermal sintering techniques were systematically employed to investigate the sintering and grain growth behaviour of the Ce-ZrO2 ceramics. The activation energies for sintering and grain growth were also determined. The existence of a sintering kinetic window for the Ce-ZrO2 ceramics was confirmed by a comparative analysis of the calculated activation energies. Accordingly, we successfully prepared fully dense sub-micron Ce-ZrO2 ceramics (with relative density >98%) by sintering within this kinetic window, leading to an average grain size of 0.55 μm. This is a significant step towards tailoring the microstructure of Ce-ZrO2 ceramics to improve their mechanical performance.

Pressureless sintering behaviour of Al2O3/ZrO2 amorphous/solid solution powder with ultra-fine ZrO2 nanoparticle precipitation

In this paper, we present a novel Al2O3/ZrO2 amorphous/solid solution powder that exhibits a low pressureless sintering temperature and can precipitate numerous ultra-fine ZrO2 nanoparticles. The powder was prepared by combustion synthesis and bead milling. A series of characterizations were conducted to investigate the sintering behaviour and sintering activation energy of the as-synthesized powder. Commercial Al2O3 and ZrO2 powders with similar sizes were mixed and served as the referential sample. The experimental results and analysis indicated that the sintering activation energy and temperature of the Al2O3/ZrO2 amorphous/solid solution powder were much lower than that of the commercial powder due to its metastable state and lattice defects, its sintering activation energy and temperature were much lower than that of the commercial powder. As a result, its sintering temperature decreased to only 1400 °C, more than 100 °C lower than the commercial powder. Furthermore, we observed that the solid solution could decompose during sintering, forming a significant number of ultra-fine ZrO2 nanoparticles measuring 5 nm. These nanoparticles effectively enhanced the mechanical performance of the ceramic by shifting the fracture mode from intergranular to transgranular. Consequently, the fracture toughness and bending strength of the ceramic could reach up to 6.03 MPa m0.5 and 525 MPa, respectively, which is much higher than that of the ceramic sintered with commercial powder. The insights gained from this study may be of assistance to the synthesis of high sintering activity ceramic powders and nanocomposite ceramics.

Studies towards activation of cobalt in W-Mo-Cu alloy sintered via large current electric field

W-Mo-Cu alloy is a novel, potential pseudo-alloy but demand efficient and reliable manufacturing approaches. In this study, W-Mo-Cu alloys with (1–5 wt%) Co additives were fabricated using large current electric field sintering at a pressure of 25 MPa and a low temperature of 950 °C. The effects of Co on the microstructure and properties of the W-Mo-Cu alloys were investigated. The results revealed an activation effect of Co on W-Mo-Cu alloys. Increasing the Co content from 0 to 5 wt%, resulted in a substantial reduction of the calculated sintering activation energy by 69.6%, thereby enhancing the sinterability of W-Mo-Cu mixed powder and increasing the sintering densification degree of W-Mo-Cu alloy. During the sintering process, a large quantity of Co was enriched around the matrix particles and partially dissolved in the W, Cu, whereas a small number of matrix atoms dissolved into Co, which followed the classical activated sintering model. Moreover, an appropriate increase in the Co content was conducive to an optimal microstructure with increased sintering densification accompanied by increased hardness. However, the addition of Co adversely affected the electrical conductivity of W-Mo-Cu alloys.

Densification process of a 95% alumina ceramic during the intermediate stage of sintering in air, and O2

Sintering in pure O2 can enhance the densification of oxide ceramics during the final stage of sintering, but little attention has been paid on its effect on the densification process during the intermediate stage of sintering. This paper measures the shrinkage processes of a 95% alumina ceramic during the intermediate stage of sintering in air and O2 at different heating rates, and analyzes them by the master sintering curve (MSC) theory. It is found that the densification of the alumina ceramic sintered in air is obviously rapider than that in O2 at the heating rate of 15 K/min, while it is slower than that in O2 at the heating rate of 2.5 K/min. MSC analysis reveals that the apparent activation energy of sintering in O2 is lower than that in air, and this might be attributed to it that O2 restrains the diffusion of aluminum vacancies together with oxygen vacancies stoichiometrically, but favors the diffusion of aluminum vacancies and the transformation between O2 and aluminum vacancies on the surface.

Microwave dielectric properties of NaMgF3 ceramic

Microwave dielectric properties of NaMgF3 ceramics prepared by reactive sintering (RS) and conventional sintering (CS) processes have been reported in this paper. Phase pure NaMgF3 ceramics with relative densities of ∼95% could be obtained at 800–950 °C/2h by both sintering processes. The RS sample demonstrates lower sintering activation energy and a much large grain size compared with the CS sample. Both densified samples exhibit similar microwave dielectric properties: εr ∼ 6.9, Q × f value ∼63000 GHz, and τf ∼ −114 ppm/°C. However, the large negative τf value needs to be further improved for practical applications.