Conventional Sintering Process Research Articles

Mechanical property and heavy metal leaching behavior enhancement of municipal solid waste incineration fly ash during the pressure-assisted sintering treatment

The conventional sintering process of municipal solid waste incineration (MSWI) fly ash is always energy intensive. The process forms a cracked structure because of the difficulty in forming the liquid phase to enhance the mass transfer process. Therefore, exploring a new disposal method to simultaneously decrease the sintering temperature and improve the mechanical and heavy metal leaching properties of sintered samples is necessary. In this study, a pressure-assisted sintering treatment was introduced to dispose fly ash by varying the chemical composition and mechanical pressure at relatively low temperatures (300–500 °C). The results revealed that the compressive strength of treated samples increased with the CaO/SiO2 molar ratio increasing from 0.5 to 1.0, and a maximum value of 238.28 ± 8.50 MPa was obtained. The heavy metal leaching concentration results demonstrated a low risk of contamination in the treated samples. Microstructure analyses suggested that the densification process was enhanced with increased mechanical pressure, and the formed calcium silicates and aluminosilicates positively affected the compressive strength. Moreover, smaller crystal lattices were observed during aggregation formation, suggesting the restraint of anomalous crystal growth, which accelerated the densification process and increased the compressive strength. Moreover, the mass transfer process during the pressure-assisted sintering process was enhanced compared with the conventional thermal process, which was reflected by the transformation of elements from homogeneous to heterogeneous distribution. Therefore, the improved mechanical properties and leaching behavior of heavy metals were attributed to the densified microstructure, formation of new minerals, and enhanced driving force during the pressure-assisted sintering process. These findings suggest that pressure-assisted sintering is a promising method for maximizing the reutilization and minimizing the energy consumption simultaneously to dispose fly ash.

Fabrication and Evaluation of Low-Cost CrSi2 Thermoelectric Legs

CrSi2 is a promising thermoelectric material constituted of non-toxic and earth abundant elements that offer good perspectives for the mass production of inexpensive and reliable thermoelectric modules for waste heat recovery. Realization of robust metallic contacts with low electrical and thermal resistances on thermoelectric materials is crucial to maximize the conversion efficiency of such a device. In this article, the metallization of an undoped CrSi2 with Ti and Nb using a conventional Spark Plasma Sintering process is explored and discussed. These contact metals were selected because they have compatible thermal expansion coefficients with those of CrSi2, which were determined in this study by X-ray Diffraction in the temperature range 299–899 K. Ti was found to be a promising contact metal offering both strong adhesion on CrSi2 and negligible electrical contact resistance (<1 μΩ cm2). However, metallization with Nb resulted in the formation of cracks caused by large internal stress inside the sample during the fabrication process and the diffusion of Si in the metallic layer. A maximum conversion efficiency of 0.3% was measured for a sandwiched Ti/CrSi2/Ti thermoelectric leg placed inside a thermal gradient of 427 K. The preliminary results obtained and discussed in this article on a relatively simple case study aim to initiate the development of more reliable and efficient CrSi2 thermoelectric legs with an optimized design.

Rapid fabrication of lanthanum strontium cobalt ferrite (LSCF) with suppression of LSCF/YSZ chemical side reaction via flash light sintering for SOFCs

The chemical side reaction between a lanthanum strontium cobalt ferrite (LSCF) cathode and an yttria-stabilized zirconia (YSZ) electrolyte is a key problem for solid oxide fuel cell (SOFC) fabrication. Herein, we demonstrate rapid fabrication of an LSCF cathode using a novel flash light sintering (FLS) technique to suppress the chemical side reaction; notably, no Gd-doped ceria interlayer is required. The FLS-fabricated LSCF cathode shows comparable crystalline development and microstructural evolution to a cathode fabricated using the conventional high-temperature sintering process. A clear LSCF/YSZ interface appears, indicating suppression of detrimental chemical side reactions via rapid and surface-dominant sintering kinetics. Detailed interfacial microstructure analysis reveals the absence of Sr segregation and SrZrO3 formation at the FLS-LSCF cathode/YSZ electrolyte interface. Remarkable performance of 0.9 W cm–2 power density at 750 °C is achieved for a cell incorporating the rapidly fabricated LSCF cathode on the interlayer-free YSZ electrolyte owing to suppression of the insulating secondary phases and significantly reduced polarization resistance. Hence, rapid LSCF cathode fabrication via the novel FLS method effectively suppresses secondary phase formation at the LSCF/YSZ interface and greatly simplifies SOFC fabrication by eliminating the doped-ceria-based interlayer. Moreover, this novel method could help overcome interfacial chemical reaction problems in various solid-state devices, while also providing new application opportunities for high-performance electrolyte/electrode materials.

Fabrication and characterization of Nb2O5‐doped 3Y‐TZP materials sintered by microwave technology

AbstractThe purpose of this research is focused on the manufacture and characterization of a partially stabilized zirconia ceramic with 3 mol% of Yttria and doped with .5 and 1.5 mol% of Nb2O5 to analyze the influence of doping, with the purpose of improving the properties before hydrothermal degradation. In the first instance, the microwave sintering process was used for the consolidation of this material, then the physical and mechanical properties were characterized. Together, the results obtained by the conventional sintering process were compared. A low hydrothermal degradation study (LTD) is presented at low temperatures in which possible changes in the mechanical properties of the ceramic materials are analyzed and its influence on the phase transformation that zirconia may present is observed. The mechanical properties were evaluated through hardness, fracture toughness, and Young's modulus tests. Likewise, their density was analyzed, and microstructure was characterized by FESEM. It was found that the microwave‐sintered samples at 1200°C exhibited superior properties of toughness than even samples sintered by conventional methods at higher temperatures (1400°C). The sample of 3Y‐TZP with 1.5 mol% Nb2O5 sintered by microwave with <.2% of porosity achieved a maximum fracture toughness value around 40% higher than the dense monolithic 3Y‐TZP material.

Efficiently sintering of MSWI fly ash at a low temperature enhanced by in-situ pressure assistant: Process performance and product characterization

Municipal solid waste incineration (MSWI) fly ash disposal is an urgent task with some technical bottlenecks. In this study, a novel pressure-assisted sintering method was employed to treat the MSWI fly ash. A series of pressure-assisted sintering experiments were carried out by varying mechanical pressures and sintering temperatures, and their properties of compressive strength, density and heavy metals leaching behavior were determined to screen out the optimal conditions. Instrumental analysis of XRF, SEM, XRD and TEM-EDX and calculation kinetics were conducted to explore the enhancement mechanism of pressure-assisted sintering. With the help of mechanical pressure, a high-strength ceramic product was produced from MSWI fly ash sintered at a low temperature (400 °C), which never occurred in the conventional low-temperature sintering process. Maximum compressive strength of 218.30 ± 4.08 MPa was obtained at 400 °C and 100 MPa, which was much higher than conventional construction materials of brick and cement. In addition, the leaching concentrations of heavy metals obtained from pressure-assisted sintering process were lower than the standard limitation. The SEM and XRD results revealed that the increased mechanical properties and the decreased heavy metals leaching concentration were mainly attributed to the increased density and crystalline degree. The kinetics calculation results indicated that the sintering activation energy was much lower than the sintering process without pressure, suggesting surface diffusion and grain boundary diffusion were main sintering mechanisms in the pressure-assisted sintering process. These findings proved that pressure-assisted sintering could be a promising method to treat fly ash together with producing high-value building materials.

Large strain and low hysteresis in (0.64-x) Bi0.5Na0.5TiO3- 0.36Sr0.7Bi0.2TiO3- x(K0.5La0.5)(Ti0.9Zr0.1)O3 piezoceramics

In this work, (0.64-x)Bi0.5Na0.5TiO3- 0.36Sr0.7Bi0.2TiO3- x(K0.5La0.5)(Ti0.9Zr0.1)O3 lead-free piezoceramics were designed and fabricated by a conventional solid-phase sintering process. It is found that large strains (0.33 %), low hysteresis coefficients (32 %), and large dynamic d33* (367 p.m./V) were obtained at x = 0.01. The large strain originates from the reversible transition of the relaxor to the long-range ferroelectric order in the electric field. When the ferroelectric and relaxor phases coexist in a proper ratio, they can provide a favorable condition for the easier movement of the domains and improve the strain properties. In addition, after 105 cycles, the bipolar strain loop of x = 0.01 content changed slightly, demonstrating excellent fatigue resistance. This work provides a new way to design piezoelectric ceramics with large strain and low hysteresis.

Origin of coercivity in an anisotropic Sm(Fe,Ti,V)12-based sintered magnet

We have demonstrated an anisotropic bulk SmFe12-based sintered magnet with sufficiently large coercivity of μ0Hc=1.0 T and a remanence ratio (Mr/Ms) of 0.84 using conventional liquid sintering process of nitrogen jet-milled powders with the nominal composition of Sm8Fe73.5Ti8V8Ga0.5Al2 (at.%). The moderate saturation magnetization of μ0Ms =0.74 T is due to the dissolution of a large amount of stabilizing elements, Ti, V, and Al, in the 1:12 phase. The anisotropy field of the main 1:12 phase was determined to be µ0HA=10.2 T. Detailed multi-scale microstructure characterizations by scanning electron microscope (SEM) and scanning transmission electron microscope (STEM) showed the magnet consists of Sm(Fe,Ti,V,Al)12 grains with the ThMn12-type crystal structure with a size distribution of ~3 − 15 µm that are enveloped by ~3 nm thick Sm-rich amorphous intergranular phase. Secondary phases including metallic (Sm,Ga)-rich, SmOx, and Fe2(Ti,V) phases coexist with the 1:12 phase. Measured angular dependence of coercivity follows Kondorsky type magnetization reversal, suggesting the coercivity arises due to the pining of magnetic domain walls. Magneto-optical Kerr effect (MOKE) microscopy revealed magnetization reversal starts at the grain boundaries and interphase interfaces and thin amorphous intergranular phases act as the pinning sites against magnetic domain wall propagation. Small micromagnetic parameter α~0.164 estimated by fitting to the Kronmüllar equation suggest that the reduction of the grain size and engineering of the intergranular phase to an Fe-lean composition are necessary to improve the coercivity toward µ0HA/3 = 3.4 T. This work provides guidelines on an optimum microstructure to develop an anisotropic bulk SmFe12-based sintered magnet with a sufficiently large coercivity.

Piezoelectric Properties of (1 – X)BiScO3 – XPbTiO3 System for Actuator Applications

ABSTRACTIn this research, the crystalline and piezoelectric properties of (1 – X )BiScO3–XPbTiO3 (X = 0.60, 0.62, 0.64, 0.66 and 0.68) ceramics were investigated to determine the optimized composition for energy harvester and sensor applications. BS-PT ceramics have strong merits in terms of their high Curie temperature and piezoelectric charge coefficient. Devices of the (1 – X )BS-XPT ceramics were fabricated by a conventional mixed-oxide sintering process with nano-powders. By employing the X-ray diffraction patterns, the morphotropic phase boundary (MPB) region of the monoclinic and tetragonal phases was identified at X = 0.64. Near the MPB region, the piezoelectric and dielectric properties of BS-PT ceramics were improved compared with those of other composition. By optimizing the compositions of the BS-PT ceramics, the maximum values of the dielectric constant (εr), piezoelectric charge coefficient (d33), electromechanical coupling factor (kp) and remanent polarization (Pr) were obtained, with values of 1387, 417 pC/N, 51.4% and 44.8 µC/cm2, respectively. Moreover, a high Curie temperature of 399.2 °C and inverse piezoelectric charge coefficient of 574 pm/V were observed for the 0.36BS–0.64PT composition, which can be a huge merit for actuator applications. These high piezoelectric charge coefficients and inverse piezoelectric charge coefficients can be the strong merits for energy harvester and actuator applications.

Electrical properties of (1-x)BiFe0.94Zn0.03Ti0.03O3-xBaTiO3 lead-free ceramics obtained via sol-gel route and two-step sintering process

(1-x)BiFe0·94Zn0·03Ti0·03O3-xBaTiO3 (BFZN-BT) ceramics are prepared via sol-gel method, followed by conventional solid-state sintering or two-step sintering processes. Then, systematic experimental characterization and performance evaluation are carried out to investigate this technique and its effects on eight different ceramic samples. Owing to morphotropic phase boundary and optimal sintering conditions, 0.7BiFe0·94Zn0·03Ti0·03O3-0.3BaTiO3 ceramic sintered at T1 = 1025 °C and T2 = 900 °C shows the largest rhombohedral distortion (90°−αR = 0.14°) and tetragonal distortion (cT/αT = 1.021), as well as low leakage (1.19 × 10−5 A/cm2), excellent d33 = 149 pC/N, 2Pr = 85.1 μC/cm2 and Curie temperature of 461 °C. Moreover, large unipolar strain of 0.307% and d33∗ value of 516 p.m./V are also obtained for this ceramic. Overall, the proposed strategy exhibits promise in the advancement of eco-friendly lead-free piezoceramics.

Numerical investigation of the thermal conductivity of UO2 – Mo microplate fuel pellets to realize enhanced heat transfer in the fuel radial direction

• Thermal conductivity of radially arranged UO 2 –3 vol% Mo microplate pellets increased. • Effective thermal conductivity increased by 53% at 1000 °C. • Central pellet temperature decreased by 149 °C under LHGR of 200 W/cm. • Recommend arranging Mo microplates parallel to the main heat transfer flow. The thermal performance of composite UO 2 fuel pellets, as a potential candidate for accident-tolerant fuels, is being attempted to be actively enhanced by employing high conductivity materials as additives. Herein, we numerically investigated the thermal performance of UO 2 – 3 vol% Mo microplate fuel pellets with microsized Mo plates to enhance the corresponding thermal conductivity in the fuel radial direction. UO 2 – 3 vol% Mo microplate fuel pellets were successfully fabricated through the conventional sintering process, and the characteristics of the thermal conductivities were investigated in terms of the shape factor of the Mo microplate, amount of Mo content, and arrangement (such as the spacing and angle) of the Mo microplates in the UO 2 fuel pellets. The results demonstrated that the arrangement of the Mo microplates parallel to the main heat transfer flow direction could further enhance the thermal conductivity. The numerical results pertaining to the calculation based on the microplate arrangement exhibited a reasonable agreement with the measured values, and the thermal conductivity was noted to be enhanced by 47% at 1000 °C compared to that of UO 2 . Moreover, the UO 2 – 3 vol% Mo microplate fuel pellets with enhanced thermal conductivities could reduce the maximum pellet temperature by 149 °C compared to that of the UO 2 pellet under a linear heat generation rate of 200 W/cm.

A Novel Preparation of Ag Agglomerates Paste with Unique Sintering Behavior at Low Temperature.

A novel bonding process using Ag agglomerates paste prepared by Ag2O reduction has been proposed, which solved the problem of Cu substrate oxidation in the conventional Ag2O sintering process for Cu–Cu bonding. By applying the Ag agglomerate paste to Ag–Ag bonding, a shear strength of 28.3 MPa at 150 °C was obtained. Further studies showed that the optimum sintering temperature was at 225 °C, and a shear strength of 46.4 MPa was obtained. In addition, a shear strength of 20 MPa was obtained at 225 °C for Cu–Cu bonding. Compared to common Ag pastes, the results in this paper revealed that the sintering behavior of Ag agglomerates was unique, and the sintering mechanisms for Ag–Ag and Cu–Cu bonding were also discussed.

Doping effects of Pd2+ on physicochemical and biomechanical properties of calcium silicate in nano-regime towards treating osteoporotic bone

Fully dense biphasic calcium silicates with improved biomechanical behavior were fabricated via mechanothermal method followed by the conventional sintering process. The effects of dopant concentration on the phase composition, structural evolution, and mechanical properties of palladium-doped calcium silicates (PCSs) were investigated. The results showed that the coalescence of nanoparticles, coarsening of particles, and the formation of large agglomerates occurred during the mechanothermal reactions. Attenuated total reflection (ATR) spectroscopy spectra of the PCSs represented the characteristic bands of the calcium silicates, including the bending mode of Si–O–Si and O–Si–O, the stretching vibration of O–Si–O group, the stretching mode of Si–O–Ca, as well as the symmetrical stretching mode of Si–O–Si group. The results of the Rietveld refinement indicated that the phase compositions and structural features noticeably affected by the dopant concentration so that the phase fraction (PF) of Wollastonite-1A and Pseudowollastonite was 0.318 ± 0.035 and 0.526 ± 0.025 in the case of undoped calcium silicate (PCS0), which respectively reached 0.411 ± 0.021 and 0.589 ± 0.021 for the Pd-doped calcium silicate (PCS20). Comparing with the PCS0, the Vickers hardness of the consolidated PCS20 increased by ~79%. From the biomineralization analysis, the surface of the consolidated sample was covered by the bone-like apatite after soaking in a simulated body fluid (SBF) for 2 weeks.

A novel transparent material based on KNN ferroelectric ceramics

Highly transparent lead-free ceramics of La-doped KNN based were synthesized by conventional solid state reaction method and ordinary sintering process for the first time. The optical and electrical properties of the KNN based lead-free transparent ferroelectric ceramics were investigated in this work. The transparent ceramics exhibited a transparency as high as 60% for the infrared wavelength. Meanwhile, the electrical properties of the ceramics still maintained relatively high levels (d 33 = 55 pC/N, T c = 402 °C), suggesting that it should be a novel and promising lead-free material that used in a large variety of electro-optical devices.

Increase of the mechanical response of pure aluminum by grain refinement retained with an alternative rapid sintering route

High-frequency induction heating is frequently used to consolidate solid pieces of refractory ceramics. However, this valuable technique has not been deeply evaluated for sample preparation in light metal-based systems as an economical and feasible alternative for rapid sintering routes such as spark plasma sintering. This work deals with the potential use of induction heating to produce highly densified samples with refined microstructure, enhanced mechanical properties, and lower oxygen contamination. Here we demonstrate that induction-sintering can increase the hardness and yield strength in 70 and 80% respectively, compared to a commercial hardened alloy (AA-1350-H19). Theoretical calculations demonstrate that this behavior can be attributed to two main reinforcement mechanisms: dislocations obstruction and grain refinement. The increased mechanical response can be imputed to the effective sub-micron microstructure retention due to its shorter processing time and lower temperature compared to the conventional sintering process.

Experimental Investigation and Comparative Study of Sintering of Microcrystalline Nickel Using Microwave and Conventional Method

The present work has been conducted to investigate and compare the mass transport mechanism of Ni-powder particles in conventional and microwave sintering process. The linear shrinkage method was used to investigate the mass transport mechanism on the basis of estimated sintering exponent (n) at different temperatures. Both types of sintering were carried out at various temperatures, and the results revealed that microwave sintering provides better results of densification and shrinkage as compared to conventional sintering. Field emission scanning electron microscopy (FESEM) and energy-dispersive X-ray spectroscopy (EDX) analysis were carried out for the characterization of Ni-powder for microstructural and elemental analysis. The value of sintering exponent found through linear shrinkage method for conventional was 9.4791, 8.1836, 6.9013, 7.3286, 5.2006 and 4.9531 at 500 °C–1000 °C, respectively, and microwave sintering was 7.0972, 5.2957,5.2942 and 6.0934 at 500 °C—800 °C, respectively.

Ultra‐low temperature preparation of mullite glass‐ceramics with high transparency sintered from EMT‐type zeolite

AbstractNanocrystalline mullite glass‐ceramics have been regarded as an ideal optical window material due to its excellent thermal shock resistance, low dielectric constant, and perfect high‐temperature strength. However, the fabrication of high‐purity mullite glass‐ceramics at a low temperature still faces great challenges. Herein, highly transparent mullite glass‐ceramics have been prepared at an ultra‐low temperature (~800°C) via the spark plasma sintering (SPS) of EMT‐type zeolite. Unlike the mullite glass‐ceramics made by the conventional sintering process, the one obtained in this study present high transparency both in the visible and infrared regions. The sintering activity and linear thermal shrinkage behavior of sample during the SPS process has been thoroughly investigated. Benefitted from the existence of ultra‐small mullite nanocrystals, the derived glass‐ceramics g‐950 possess a high Vickers hardness (7.0 GPa), Young's modulus (86.6 GPa), and MSP strength (123.2 MPa), which show more excellent mechanical properties than conventional aluminasilicate or silica glass.

Low-temperature sintering and electrical properties of Ba0.68Sr0.32TiO3 thick films

Ba0.68Sr0.32TiO3 (BST) thick films were prepared by screen printing on a flexible fluorophlogopite substrate. In order to realise the co-firing of the BST film with a silver electrode at a lower temperature, the BST precursor was used as a solvent for the screen-printing slurry and the cold sintering technique was used to pretreat the film. The sintering temperature of BST thick films prepared by conventional sintering process was higher than 1200 °C. When sintered at 950 °C, the thick films exhibited a high porosity. The density of the thick films was significantly improved after pretreatment with the cold sintering process (CSP). After the cold-sintered thick films were sintered at 950 °C for 30 min and then fired with a silver electrode, the samples exhibited a relative dielectric constant of 773 (at 25 °C and 10 kHz), a dielectric loss of 0.025, a remanent polarization of 5.3 μC/cm2, and a coercive field strength of 38.1 kV/cm. Therefore, the low-temperature co-firing of BST thick films with a silver electrode was successfully realised.

Effects of mechanical milling time on densification, microstructural characteristics and hardness of Cu–SiC nanocomposites prepared by conventional sintering process

In this study, effects of the milling time on densification, microstructural characteristics and mechanical properties of Cu–SiC nanocomposite produced by high energy mechanical milling and conventional sintering process are investigated. Cu–SiC powder was milled for different durations and then cold compacted under 800 MPa pressure followed by conventional sintering at 900 °C under argon atmosphere for 1h. The microstructural characterization was conducted by x-ray diffraction (XRD), scanning electron microscope (SEM), and scanning transmission electron microscope (STEM). The highest densification for the composite powder was obtained at a short milling time, where the powder showed flake morphology and lower strain-hardening. By increasing the milling time, the size of the Cu matrix grains refined and the level of microstrain and microhardness of the nanocomposite improved. The incorporation of the nanoparticles in the Cu matrix increased the microhardness of the copper. This effect was more evident in lower milling durations.

Flash light sintered SDC cathodic interlayer for enhanced oxygen reduction reaction in LT-SOFCs

To commercialize solid oxide fuel cells, many methods for reducing the production time of manufacturing a fuel cell membrane-electrode-assembly (MEA) using a non-vacuum process have been studied and still the post-heat treatment process is an issue. This paper discusses an alternative sintering method to replace the conventional thermal sintering step for ceramic thin film fabrication, which is time consuming and costly. We fabricated samarium-doped ceria (SDC) thin films, which has high ionic conductivity and high surface exchange coefficient for oxygen reactions at the cathode side. The films were deposited by chemical solution deposition (CSD) method utilizing electrostatic spray deposition (ESD) technique. Thermal decomposition and crystallization steps are required as a post-heat treatment process to obtain desired material properties. For this purpose, the flash light sintering method is adopted and compared with the conventional thermal sintering process using halogen furnace. With this flash light sintering method, the conventional post-heat treatment process time can be significantly reduced from tens of hours to a few seconds. Scanning electron microscopy, X-ray diffraction, and transmission electron microscopy analyses were carried out for material characterizations. Additionally, electrochemical impedance analysis and current-voltage behavior measurements were conducted. By successful fabrication of SDC cathodic functional layer utilizing flash light irradiation process, the 2-folds of fuel cell performance enhancement was obtained in terms of the peak power density at the measurement temperature of 450 °C.

Processing of MMC through conventional sintering and spark plasma sintering process: A review

Spark plasma sintering (SPS) is one of the advanced methods to produce MMC with the desired quality. The high amount of heat was achieved through direct pulse heating to enhance the diffusion mechanism and it’s involved in the grain growth. Many of the researchers are doing the development of the sintering process for attaining better substance properties with lesser time. SPS was used to fabricate all kinds of materials including ceramics, glass, etc., Direct heat was applied to the graphite die and compact unit. The rate of heat was an essential role in this process to control the densification of powder particles. In the present situation, aluminium MMC plays an essential role in every field such as automobile, aerospace, manufacturing, and electrical sectors. It has superior substance properties such as specific strength, creep, toughness, and corrosion resistance. These properties are enhanced through the addition of reinforcements to the base metal.