Two-step Sintering Process Research Articles

Cu/AlN composite and functionally graded materials with high strength and high electrical- and thermal-conductivity fabricated by spark plasma sintering

In this study, Cu/AlN composites and functionally graded materials (FGMs) were fabricated with the spark plasma sintering method. It was observed that a two-step sintering process, involving sintering under low pressure as the initial stage to remove adsorbed chemicals on the powder, was an effective method for producing sintering objects with high relative density. The hardness of the composites significantly increased with higher volume fraction of aluminum nitride (AlN) particles, while electrical- and thermal-conductivity decreased. Nevertheless, the advanse impact of AlN on thermal-conductivity was found to be minimal. Additionally during compression test, a crack was noted at the interface between Cu and Cu-5 vol%AlN region in two-layered FGMs after, whereas no such crack was observed in the three-layered FGMs. Therefore, it is confirmed that the concept of FGMs is useful in overcoming the shortcomings of mutually exclusiveness among high strength, high electrical- and high thermal-conductively.

Novel insights into the synthesis and tribo-mechanical performance of high-entropy (Hf0.2Zr0.2Ti0.2W0.2Mo0.2)B2 ceramics

High-entropy (Hf0.2Zr0.2Ti0.2W0.2Mo0.2)B2 ceramics were synthesized using a two-step spark plasma sintering process, with densification at 1600 °C followed by sintering at 1850 °C. This method produced dense materials with excellent mechanical and tribological properties. Hardness values ranged from 18.85 GPa to 39.65 GPa, with a maximum Young’s modulus of 319 GPa. Micro-scratch tests showed high resistance to plastic deformation and minimal surface damage, highlighting durability under mechanical stress. Tribological tests at 15 N and 20 N loads demonstrated exceptional wear resistance, attributed to hard primary phases and lubricating soft secondary phases. These findings confirm the material’s robustness and show the effectiveness of the two-step synthesis in optimizing microstructure and enhancing properties, making it suitable for high-stress and wear-intensive applications.

Study on thermoelectric properties and atomic-scale mechanism of B-site molybdenum-modified La0.1Sr0.9TiO3

Extensive studies on strontium titanate thermoelectric materials have shown that their poor conductivity results in a low ZT value. However, elemental doping can effectively improve the thermoelectric properties of these materials. In this study, a two-step sintering process was applied, using physical mixing to introduce 1 % molybdenum powder as a modification to the lanthanum-doped strontium titanate solid powder (La0.1Sr0.9TiO3). The obtained sample exhibited a maximum conductivity of 7830 S/m, with a maximum ZT of 0.12. Furthermore, this study combined experimental data with first-principles simulation calculations to elucidate the mechanism at the atomic scale. The incorporation of Mo6+ in place of Ti4+ at the B-site by molybdenum (Mo) adds two free electrons, leading to an elevated carrier concentration. This change concurrently reduces the Fermi level of the material and improves mobility, collectively resulting in a substantial increase in electrical conductivity. Phonon simulation indicated that Mo doping increased structural defects, thereby reducing lattice thermal conductivity. This significant enhancement in electrical conductivity and decrease in lattice thermal conductivity collectively increased the ZT value of the material.

In-depth approach and establishment from a structural perspective of LiFePO4 cathodes for lithium-ion batteries by a two-step sintering

Most synthesis of olivine LiFePO4 (LFP) studies have emphasized the importance of a two-step sintering process for the formation of a uniform carbon coating. However, in this study, it is found that, as an advantage of the two-step sintering process, stable carbonization not only improves lithium-ion conductivity by forming a coating layer but also increases the uniformity of the internal crystal structure. In addition to basic crystallinity and structure analysis using X-ray diffraction (XRD), in-depth calculations are performed to explain the formation mechanism of crystal structure according to the two-step sintering process and the temperature of the first sintering step. In particular, lattice defects and structural uniformity are closely investigated from the crystal structure perspective by comparing lattice micro-strain and dislocation density. Improvement in lithium-ion conductivity from structural uniformity is also demonstrated through cyclic voltammetry (CV) analysis. As a result, it is confirmed that LFP, which undergoes a high-temperature two-step sintering, has high capacity and excellent cycle retention at high rates. Furthermore, ex-situ XRD analysis demonstrates the performance difference according to lithium-ion mobility by comparing the LiFePO4/FePO4 two-phase transformation reaction of two-step sintered LFP and the plateau stability during charging.

A novel preparation of porous Li2TiO3 pebbles with a distinctive structure

Optimization of the pore structure stands out as an effective approach for bolstering the tritium release performance of lithium-based tritium breeding ceramics, particularly when employing a high open porosity configuration. In this study, Li2TiO3 fibers were synthesized via the hydrothermal method, with the assistance of TiO2-B nanowires acting as templates. Subsequently, porous Li2TiO3 pebbles with varying microstructures were fabricated through a combination of the wet method and a sintering process. Sintering process plays a crucial role in determining the microscopic morphology. An increase in temperature resulted in a suppression of the growth of fibrous grains and the transformation of fibrous grains into quasi-spherical grains. Moreover, a two-step sintering process was proposed as a means of improving the crush load (15.9 N vs. 22.0 N) of Li2TiO3 pebbles while simultaneously preserving their high porosity (24.91%). The Li2TiO3 pebbles, produced by the two-step sintering process, exhibited a distinctive micromorphology characterized by interconnected particles forming short rod-shaped microstructures. This distinctive micromorphology contributes to the maintenance of a high degree of open porosity (10.52%).

High-piezoelectric lead-free BiFeO3–BaTiO3 ceramics with enhanced temperature stability and mechanical properties

BiFeO3–BaTiO3 (BF–BT) ceramics exhibit higher piezoelectric coefficients (d33), Curie temperatures (TC), and temperature stability than other high-temperature lead-free piezoelectric materials. However, despite their crucial role in piezoelectric devices, the mechanical properties of BF–BT ceramics have been underexplored. A thorough evaluation of the mechanical properties of BF–BT is crucial for developing cost-effective and durable lead-free piezoelectric ceramics. Moreover, the specific causes of the high piezoelectric response and excellent temperature stability of BF–BT ceramics remain unclear owing to the instrumental detection threshold, which limits experimental studies to temperatures above 140 °C and below the degradation temperature of d33. To investigate the intrinsic origins of the high piezoelectricity and temperature stability of BF–xBT ceramics and to enhance their mechanical properties, a two-step sintering process is used to fabricate these ceramics (0.25 ≤ x ≤ 0.40). Owing to improvements in grain refinement and reduced Bi3+ volatilization, the BF–0.33BT ceramic exhibits enhanced overall performance, with a modified small punch strength of 155 MPa, Vickers hardness of 5.2 GPa, a d33 of 220 pC/N at room temperature, TC of 466 °C, and d33 values exceeding 400 pC/N at 260 °C. Phase-field simulations, which address the limitations of device detection thresholds, reveal that with increasing temperature, the domain structure relaxes, and polarization intensity decreases. This indicates that changes in the high-temperature piezoelectric properties can be attributed to domain structure relaxation and the increase in dielectric constant. Overall, BF–BT ceramics exhibit superior piezoelectric performance, mechanical properties, and temperature stability, making them highly suitable for use in high-temperature and demanding environments.

Hybrid Cu sinter paste for low temperature bonding of bare semiconductors

A novel hybrid copper paste was developed for low temperature sintering of bare semiconductors. Cu(II) formate (Cu(for)) is complexed in amino-2-propanol (A2P) and added to a paste of etched brass micro flakes. A two-step sintering process is applied: The paste is printed and dried at 120 °C under formic acid (FA) enriched N2 atmosphere (FAN2) for 5 min. Afterwards, bare semiconductors are placed and sintered at 250 °C for 5 min applying a bonding pressure of 20 MPa/10 MPa. By the thermal decomposition of the Cu(for) atomic Cu is released and forms in-situ Cu-nanoparticles. An interconnect is realized with shear strength >100 MPa.

Superior energy storage performance achieved in tungsten bronze SBCN-based ceramics through tape-casting

Simultaneously integrating outstanding energy storage density and good energy storage efficiency in advanced ferroelectrics is crucial to implementing the application of dielectrics in high-power pulse devices. In this work, (Sr0.5Ba0.5)2Ca0.5Nb5-xSbxO15 ceramics were designed and prepared by adopting the B sites substitution engineering together with combining strategies of tape-casting method and two-step sintering process. Benefiting from the refined grain size and high density, the breakdown field of (Sr0.5Ba0.5)2Ca0.5Nb4.8Sb0.2O15 (SBCNS0.2) was promoted to 400 kV/cm. By the substitution of Sb5+ in the B sites, the weaker interaction force of Sb-O bond in BO6 octahedral polar unit induced the occurrence of polar nanoregions (PNRs) at room temperature to strengthen the dielectric relaxation behavior. Then it is noteworthy that SBCNS0.2 ceramics simultaneously obtained excellent recoverable energy density (Wrec, 3.9 J/cm3), energy storage efficiency (η, 90.5 %), power density (PD, 156.0 MW/cm3), and current density (CD, 1356.7 A/cm2). In addition, the SBCNS0.2 ceramics exhibited an ultrafast discharge time (t0.9, 67 ns). These results reveal prospective potential of unfilled tungsten bronze SBCNS0.2 ceramics in power capacitor applications and provide an effective strategy for improving excellent energy storage properties from the perspective of preparation methods.

Comparative Analysis of Osteointegration in Hydroxyapatite and Hydroxyapatite-Titanium Implants: An In Vivo Rabbit Model Study.

The study evaluates the osteointegration of hydroxyapatite (HAp) and hydroxyapatite-titanium (HApTi) biocomposites implanted in the femurs of rabbits. The biocomposites were fabricated using powder metallurgy and subjected to a two-step sintering process. Scanning electron microscopy (SEM) was employed to analyze the morphology, while mesenchymal stem cells were cultured to assess cytotoxicity and proliferation. In vivo experiments involved the implantation of HAp in the left femur and HApTi in the right femur of twenty New Zealand white rabbits. Computed tomography (CT) scans, histological, immunohistochemical, and histomorphometric analyses were performed to assess bone density and osteoblast activity. Results demonstrated that HApTi implants showed superior osteointegration, with higher peri-implant bone density and increased osteoblast count compared to HAp implants. This study concluded that HApTi biocomposites have potential for enhanced bone healing and stability in orthopedic applications.

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.

Manufacturing of High Purity Cr2AlC MAX Phase Material and Its Characterization

AbstractPresent study discusses about a technique for producing high-purity Cr2AlC MAX phase materials and gaining insight into their thermal behavior for high-temperature applications. The research conducted involved synthesizing a pure layered ternary carbide Cr2AlC MAX phase material by mixing powders of Chromium, Aluminum, and Carbon and then subjecting them to two-step pressureless sintering process in argon atmosphere. First step involves the annealing of ball-milled mixture at 750 °C for 2 h followed by the second step in which the annealed mixture is subjected to heat-treatment at 1350 °C for 2 h. Analysis using XRD and Raman techniques revealed that the synthesized product consists of Cr2AlC phase, without any impurities. SEM studies confirmed that the Cr2AlC had a layered topography, while EPMA analysis indicated that the atomic percentage of Cr, Al, and C was consistent with the XRD phase analysis. XPS investigations confirmed the presence of Cr-C bonds representing Mn+1Xn of the MAX phase material. TG-DSC results showed an approximately 2% increase in weight. The Cr2AlC phase exhibited an endothermic pattern below 725 °C, an exothermic pattern above it, and did not decompose up to 1400 °C in vacuum environment. High-temperature XRD analysis at various temperatures also confirmed no formation of Al2O3 or CrO impurity compounds.

Influence of Ca(OH)2 modification on the pore structure and properties of porous glass-ceramics stepwise sintered from granite sludge

The utilization of granite sludge offers significant economic and environmental advantages. This study focuses on preparing porous glass-ceramics from Ca(OH)2-modified granite sludge through a two-step sintering process comprising dense sintering and high-temperature foaming, with the addition of 1 % SiC powder as a foaming agent. The impact of foaming temperature and Ca(OH)2 addition on the structure, compressive strength, specific strength, and thermal conductivity of the porous glass-ceramics is examined. Incorporating the Ca(OH)2 modifier reduces the glass's viscosity and effectively eliminates micropores on the pore walls. The former promotes foaming and increases porosity, while the latter increases the specific strength of porous glass-ceramics. Increasing both the foaming temperature and the Ca(OH)2 concentration reduces glass viscosity and promotes mineral dissolution, facilitating the foaming process. However, the specific strength of the porous glass-ceramics initially increases before decreasing due to pore coalescence and excessive mineral dissolution. Theoretical evaluations of compressive strength and thermal conductivity indicate that porous glass-ceramics possess a closed-cell pore structure. Porous glass-ceramic made from granite powder containing 3.5 % Ca(OH)2 and foamed at 1240 °C exhibits an apparent density and porosity of 0.73 g/cm3 and 67.1 %, respectively. The compressive strength and thermal conductivity are 14.2 MPa and 0.422 W/(m·K) respectively, with a peak specific strength of 19.4 kN·m/kg. This innovative process enables the scalable recycling of granite sludge into energy-saving building materials.

Synthesis and Characterization of MnIn2S4/Single-Walled Carbon Nanotube Composites as an Anode Material for Lithium-Ion Batteries.

In this study, we synthesized a transition metal sulfide (TMS) with a spinel structure, i.e., MnIn2S4 (MIS), using a two-step hydrothermal and sintering process. In the context of lithium-ion battery (LIB) applications, ternary TMSs are being considered as interesting options for anode materials. This consideration arises from their notable attributes, including high theoretical capacity, excellent cycle stability, and cost-effectiveness. However, dramatic volume changes result in the electrochemical performance being severely limited, so we introduced single-walled carbon nanotubes (SWCNTs) and prepared an MIS/SWCNT composite to enhance the structural stability and electronic conductivity. The synthesized MIS/SWCNT composite exhibits better cycle performance than bare MIS. Undergoing 100 cycles, MIS only yields a reversible capacity of 117 mAh/g at 0.1 A/g. However, the MIS/SWCNT composite exhibits a reversible capacity as high as 536 mAh/g after 100 cycles. Moreover, the MIS/SWCNT composite shows a better rate capability. The current density increases with cycling, and the SWCNT composite exhibits high reversible capacities of 232 and 102 mAh/g at 2 A/g and 5 A/g, respectively. Under the same conditions, pristine MIS can only deliver reversible capacities of 21 and 4 mAh/g. The results indicate that MIS/SWCNT composites are promising anode materials for LIBs.

Effects of three different powder pre-processing and two-step sintering processes on the microstructure and mechanical properties of Cu–Sn–Ti porous matrix materials

It is difficulty to utilize the pore formation function of TiH2 in the copper-based matrices of diamond tools due to the mismatch between dehydrogenation temperature and densification temperature. In this study, Cu–Sn–Ti porous materials were prepared by innovative powder pre-processing and two-step sintering processes. The results showed that Cu–Sn–TiH2 powder with uniform composition, high alloying degree and high TiH2 retention rate were achieved by optimizing pre-processing parameters. During the subsequent sintering process, Sn and Ti elements were precipitated from the copper matrix, leading to the formation of Ti-rich phases at grain boundaries and pore walls. Simultaneously, pores with higher sphericity and uniform distribution were formed due to the thermal decomposition of TiH2. The porosity, average pore size, bending strength, and bending elastic modulus of Cu–Sn–Ti porous material were measured as 30.6%, 2.15 μm, 245 MPa, and 2.23 GPa, respectively. The comprehensive properties were better than the reported results.

Significantly enhanced transmittance and EO property in PMN-PT via optimized two-step pressure-free sintering

It is a great challenge to prepare Pb(Mg1/3Nb2/3)O3–PbTiO3 (PMN-PT) ceramics of very high transparency with only oxygen atmosphere pressureless sintering process. To address this issue, this work proposed an optimal low-cost two-step oxygen atmosphere sintering process with a first step at high temperature (T1) for minutes, followed by a second step at lower temperature (T2) for hours without applied pressure. High transmittance of 70 % in the near-infrared wavelength was achieved by our novel two-step process, which far exceeds the performance of PMN–PT ceramics prepared by only oxygen atmosphere sintering process reported in the past and demonstrates comparable performance compared to the costly hot-pressing sintering process. Meanwhile, it shows a high quadratic electro-optic (EO) coefficient of 42.1 × 10−16 m2 V−2, which is meaningful for applications in EO devices. Furthermore, the effect of the temperature difference between the first and second sintering step on the microstructure, transmittance, domain structure, ferroelectric and dielectric property, and polarization switching were discussed. The enhanced transparency is mainly attributed to the higher relative density, and weaker photoluminescence effect with lesser light absorption loss at optimal T1-T2. The improved EO property is due to greater polarization response originating from the interaction of defect dipoles and nanodomains. Such a process should facilitate the cost-effective preparation of other transparent electro-optic materials for practical applications.

Tuning mechanical and electrical performances of B 4C–TiB 2 ceramics in a two-step spark plasma sintering process

Tuning mechanical and electrical performances of B ₄C–TiB ₂ ceramics in a two-step spark plasma sintering process

Effect of sintering mechanism on dielectric properties of Ba0.5Sr0.5TiO3-ZnAl2O4 composite ceramics synthesized by two-step sintering with low energy consumption

The application of Ba1-xSrxTiO3-based composites in microwave field has become a popular research topic. Ba0.5Sr0.5TiO3-ZnAl2O4 (BST-ZA) composite ceramics were successfully fabricated by both conventional sintering and two-step sintering process. The microstructure and dielectric properties of Ba0.5Sr0.5TiO3-ZnAl2O4 composite ceramics prepared by two sintering methods were compared. The samples prepared by the two-step sintering method have lower ion diffusion degree, shorter holding time and lower energy consumption, and it is easier to obtain samples with higher density and uniform grain size distribution, compared with those fabricated by the conventional sintering method. The dielectric permittivity and Curie temperature of two-step sintered samples are lower than those obtained by conventional sintering, while the dielectric tunability is almost unchanged (two-step sintering: 17.7 %, conventional sintering: 18.6 %). These results indicate that two-step sintering method is an efficient and energy-saving method in preparing BST-ZA composites.

Improvement of mid-temperature ZT in a Bi-Se-Te via a two two-step sintering process

A wide range of thermoelectric materials are available for selection. The standard classification is based on the temperature range of the application. This study fabricated mid-temperature Bi-Se-Te using spark plasma sintering (SPS). This analysis focused on the impact of sintering conditions on thermoelectric properties. The structural analysis indicated that initial and secondary sintering processes effectively produced the low-temperature thermoelectric material Bi2Se0.45Te2.55. The sintering duration and temperature changes mainly influenced the grain boundary density, with elevated temperatures inducing defects that impacted the performance. Secondary sintering resulted in layered structures with elongated grains, which enhanced the phonon scattering effect. This configuration markedly decreased the thermal conductivity, increasing the ZT value by 60%.

Design of TiC intergranular-dispersed Al2O3 composites via in situ and two-step sintering with enhanced mechanical and electrical properties

To further enhance the mechanical properties of the Al2O3/TiC composites and reduce the percolation threshold induced by the controlling microstructures, composites containing 0–20 % TiC were fabricated in this work using the two-step sintering (TSS) method, in which TiC was in situ synthesized from carbon nanotubes and TiH2. From the acquired results, it was indicated that the TiC particles were completely dispersed at the grain boundaries. As the first-step temperature (T1) increased, the Al2O3 grains grew up, while the second-step temperature (T2) mainly affected the densification of the whole structure. The composites could be listed as follows, 1550/1400 > 1600/1400 > 1600/1300 > 1550/1300, which corresponds to a descending order of the balanced Young’s modulus, Vickers hardness, flexural strength, fracture toughness, and electrical conductivity. Moreover, the largest fracture toughness exhibited by 1600/1400-20 was 5.83 MPa m1/2, which increased by 69 % compared with monolithic Al2O3. The similarity of the Al2O3 grain size and the TiC particles size, as well as the complete grain-boundary dispersion of the relatively large TiC particles significantly contributed to the lower percolation value (10.5 %) of the Al2O3/TiC composites produced via the two-step sintering process compared with the composites fabricated by utilizing the conventional single-step sintering (percolation value: 11.2 %) method. The lower percolation value facilitates the fabrication of conductive Al2O3/TiC composites with excellent mechanical properties.

Cold sintering of BaZr0.8Y0.2O3-ẟ ceramics: Phase formation and grain boundary properties

Electrochemical devices based on the proton conducting ceramic BaZrO3 have shown their immense potential for efficient energy conversion and gas separation processes at intermediate temperatures. A major drawback of this material class is the inevitably high sintering temperature, which is necessary to reach sufficient densities for gas tightness. Recently, cold sintering has been applied to densify BaZrO3 – BaCeO3 solid solutions at low temperatures using a partial dissolution of the Ce-rich phase. Here, we apply the method to BaZr0.8Y0.2O3-ẟ (BZY20), which is a Ce-free proton conducting ceramic. We show that densification by cold sintering is viable at temperatures between 150 °C and 250 °C under uniaxial pressures of 400 MPa and deionized water as a sintering aid. The dissolution of yttrium from BZY20 during cold sintering acts as the trigger for densification at low temperatures but forms Y(OH)3 as an instable side product. Therefore, we developed a two-step cold sintering process that adds an additional thermal treatment between 900 and 1100 °C directly after the cold sintering process to enable electrochemical characterization and transmission electron microscopy investigations.