Sintering Phenomena Research Articles

Selective lithium recovery from waste lithium-ion batteries by H2SO4 roasting focused on process intensification and conversion mechanism

The purpose of this study is to prove the feasibility, efficiency and selectivity of lithium recovery from waste lithium-ion batteries (LIB) via sulfuric acid roasting-water leaching by thermodynamic analysis and experimental verification. The feasibility was proved by Gibbs free energy calculations and experiments. Then, the effects of H2SO4 concentration, roasting temperature and roasting time were assessed on the leaching rate of valuable metals. The results indicate that the leaching efficiency of lithium increases firstly and then decreases with the increase of H2SO4 concentration, roasting temperature and roasting time, more than 91 % lithium are leached under optimized experimental conditions: 50 wt% H2SO4, roasting temperature of 650°C, and roasting time of 2 h. Meanwhile, the selectivity of lithium is up to 88 % which means overwhelming majority lithium have been separated completely. In addition, the factors which cause sintering phenomenon such as high temperature and longtime roasting will change the microstructure of roasted product extremely, which is inconducive to the subsequent water leaching. The investigations of the phase conversion mechanism by thermodynamic simulation and instrumental characterization indicated that the leaching behaviors of valuable metals might be influenced by the different reaction pathways of the compounds while changing roasting conditions. The recovery process can be divided into two stages: the partial structure of LiNixCoyMnzO2 was destroyed to form metal sulfates at ambient temperature and the solid phase reaction between unreacted LiNixCoyMnzO2 which contained Li+ in the unstable layered structure with transition metal sulfates at high temperature. The fully reduced low-valence states are mainly (NiO)0.75(MnO)0.25 and CoO, and basically all Li within the crystalline LiNixCoyMnzO2 was de-intercalated and transformed to soluble Li2SO4. These results further confirm the advantages of H2SO4 roasting on selective Li recovery, and provide a better understanding of conversion mechanism by combining theory and experiments.

Mechanism and process study of spent lithium iron phosphate batteries by medium-temperature oxidation roasting strategy

In this study, we determined the oxidation roasting characteristics of spent LiFePO4 battery electrode materials and applied the iso-conversion rate method and integral master plot method to analyze the kinetic parameters. The ratio of Fe (II) to Fe (III) was regulated under various oxidation conditions. The results showed that 95.50 % of LiFePO4 was oxidized to Li3Fe2(PO4)3 and Fe2O3 under the most cost-effective roasting conditions (500°C, 1000 mL/min, 30 min, air atmosphere) and only approximately 18 % graphite was involved in the reaction. More than 99 % of the lithium was leached under these roasting conditions, with minimal impurities. Medium-temperature selective oxidation roasting effectively avoided the high-temperature sintering phenomenon that affects the crystal structure of the product. Instead, a fine, uniform oxidized phase was formed, and the polyvinylidene fluoride impurity that typically persists throughout the recycling process was avoided. This study provides a sufficient theoretical basis and experimental prerequisites for selective, time-efficient, and economical lithium leaching or reductive regeneration of the cathode materials.

Study on Water Wash Pretreatment and Al-Si Additives to Relieve the Sintering Behavior of Fungus Bran Combustion Ash

This study focuses on the sintering phenomenon that easily occurs during the direct combustion of molded fuel made from fungus bran (FB). To investigate the key factors influencing sintering, experiments are designed and conducted using a muffle furnace and a high-temperature drop furnace. The experimental results show that the combustion temperature is the primary factor triggering the sintering phenomenon. To effectively mitigate this issue, this study proposes two improvement strategies: water washing pretreatment and the use of additives. The analysis shows that water washing pretreatment effectively removes K and Mg elements, with the removal rates increasing as the washing temperature and time increase. Specifically, the removal rate of K ranges from 37.68% to 55.91%, and that of Mg ranges from 33.16% to 58.52%. Water washing pretreatment also reduces the degree of sintering; at 1400 °C, the TSF (tendency to slag formation) of the fuel increases by 25–40% after pretreatment, with a greater increases observed at higher washing temperatures and longer durations. Kaolin, used as an additive, significantly raises the ash melting point of FB and alleviates sintering, while P2O5 exacerbates it. Increasing the proportion of kaolin does not significantly enhance the TSF of high-temperature ash, but raising the P2O5 content from 5% to 10% lowers the TSF by 10–20% at the corresponding temperature.

Rational design of enhanced oxygen deficiency-enriched NiFe2O4 embedded in silica matrix as oxygen carriers for high-quality syngas production via biomass chemical looping gasification (BCLG)

Biomass chemical looping gasification has attracted wide attention in syngas production. However, the major obstacle is deactivation of oxygen carriers (OCs) caused by sintering, leading to low gasification efficiency. Developing sintering-resistant oxygen carriers is crucial for enhancing the competitiveness of BCLG. This study proposes an effective strategy of embedding NiFe2O4 in silica matrix (NFSM) to fabricate highly dispersed OCs. The gasification performance and cycling stability of OCs for BCLG are systematically researched in a fixed-bed reactor. Based on the characterization analysis, NiFe2O4 is successfully incorporated into the silica matrix. The well-dispersed active components in OCs create more oxygen vacancies and metal adsorption sites, resulting in higher redox activity. Experimental results verify that the optimal parameters for achieving the highest syngas yield (1254 mL/g) and biomass gasification efficiency (68 %) are 0.6 OCs/B, a temperature of 850 °C, and a water injection rate of 0.3 mL/min. After 10 redox cycles, NFSM demonstrates superior redox activity and excellent cycle stability, maintaining its gasification performance and microstructural integrity throughout all chemical looping gasification processes. The silica matrix-supported NiFe2O4 can be a promising candidate for BCLG. This work provides a novel approach to develop and design future OCs of BCLG for alleviating sintering and deactivation phenomena.

Powder bed fusion with electron beam: The interplay of sintering, porosity, and coordination number in modelling the powder thermal conductivity through a novel tortuosity formulation

For the powder bed fusion with electron beam (PBF-EB) additive manufacturing, properties such as the thermal conductivity of the material surrounding the melting area are critical. Thermal conductivity is influenced by the extremely high temperature reached in a short time and distributed in the building area. This fast temperature growth produces sintering phenomena and the creation of a neck between the particles. Because of this sintering, measuring the thermal conductivity at the process conditions is challenging.This paper proposes an analytical formulation for estimating the effective powder bed thermal conductivity at the PBF-EB conditions, introducing a novel modelling strategy for the tortuosity factor. In a changing net of sintered powder particles, the proposed model for the tortuosity factor considers the neck evolution and the complexity of the heat transfer due to the several heat paths possible through the particle net. To show the effectiveness of the proposed model, the thermal conductivity is evaluated for three 3D structures characterised by an increasing number of powder particles and heat path complexity: a simple cubic, a body centred cubic and a portion of a powder bed. It is shown that thermal conductivity strongly depends on the arrangement of the particles in 3D space, the structure density and the complexity of the heat diffusion path (tortuosity). Also, the numerical results from the proposed model show good agreement when compared with finite element analysis and experimental literature data.

Preparation of Soft Magnetic Composite Using Cold Sintering Technique

Soft magnetic composites are powder metal products under development as an alternative to 2D laminates in electric motor applications. The 3D design of SMCs offers greater energy efficiency but poses a challenge to maintain adequate strength properties required for application. Soft magnetic composites are fabricated through compaction and heat treatment of iron particles coated with insulated coating to form a dense compact. The soft magnetic properties of the compact are affected by the properties of the iron powder, density of compact as well as the efficacy of forming uniform thin insulating coating at the particle boundary. Additionally, the strength of the compact is also affected by the nature of the insulating boundary at the particle interfaces. We report a low temperature process that involves cold sintering phenomenon to densify and strengthen soft magnetic composites. Iron powders have been modified using a co-precipitation method that forms a hydrated copper/iron oxalate coating on individual iron particles. Warm compaction of the modified iron powders at 100°C resulted in a highly dense soft magnetic composite which demonstrated ~ 3x improvement in strength. The compacts can be further heat treated in air at higher temperatures to form high strength oxide coating iron based soft magnetic composites. Results of the AC and DC magnetic measurements of fabricated cold sintered toroid compacts made as a function of heat treatment temperature reveal that DC permeability increased with heat treatment temperature. Analysis of AC core loss data showed that hysteresis power losses dominated the performance at lower heat treatment temperatures (< 300°C) beyond which dynamic core losses significantly increased.

Effect of sintering temperature on the properties of titanium matrix composites reinforced with Al0·5CoCrFeNi high-entropy alloy particles

In this study, the organization and mechanical properties of the composites were analyzed at different sintering temperatures, and it was found that the local high-temperature phenomenon of discharge plasma sintering led to rapid melting and element diffusion at the junction of the high-entropy alloy particles and the Ti matrix, resulting in the formation of the interfacial layer. The increase in sintering temperature promoted close bonding between particles and element diffusion, caused lattice distortion and new phase formation, and increased the thickness of the interface layer and precipitated phase at the grain boundary. Most of the high-entropy alloy particles were dissolved when the sintering temperature reached 1050 °C. The composites were characterized by a high sintering temperature. The comprehensive mechanical properties of the composites first increased and then decreased when the sintering temperature increased, and they were optimized at 850 °C. The nanoindentation results show that the increase in sintering temperature leads to a decrease in the hardness of the high-entropy alloy particles, an increase in the hardness of the titanium matrix, and a higher hardness of the interfacial layer than that of the high-entropy alloy particles and the titanium matrix.

Study on the Catalytic Activity Modification of Pr and Nd Doped Ce0.7Zr0.3O2 Catalysts for Simultaneous Removal of PM and NOX

Cerium-zirconium composite oxides (Ce0.7Zr0.3O2) have a remarkable effect on catalytic removal of carbon particles (PM) and nitrogen oxides (NOX) emitted from diesel engine, in order to further improve the thermal stability, oxygen storage capacity and low temperature catalytic REDOX performance of cerium zirconium composite oxides (Ce0.7Zr0.3O2), a small amount of Pr and Nd rare earth elements are doped to improve the catalytic activity of cerium zirconium composite oxides. In this paper, the composite oxide of Pr6O11–Nd2O3–CeO2–ZrO2 is prepared by unsteady co-precipitation method, and the physicochemical properties of the composite oxide catalyst are analyzed by BET, SEM, XRD and ICP. The gas adsorption capacity and catalytic activity of composite oxide catalysts are measured by temperature programmed reaction technology (TPR). The results show that the composite oxide of Pr0.05Nd0.05Ce0.6Zr0.3O2 prepared by using rare earth elements Pr and Nd inhibits the growth process of grain, refining the grain, and improving the sintering phenomenon at high temperature. The addition of Pr and Nd causes lattice defects, increases the number of oxygen vacancies, and improves the mobility of lattice oxygen, namely promotes oxide oxygen storage property, gas adsorption and catalytic oxidation reduction ability. After modification, Pr0.05Nd0.05Ce0.6Zr0.3O2 has good resistance to high temperature aging performance, prolongs the service life, reduces the PM lowest ignition temperature and minimum catalytic activity temperature of nitrogen oxide, and promotes the NOX reduction rate. For Pr0.05Nd0.05Ce0.6Zr0.3O2, the lowest ignition temperature of PM is about 150 °C, and the lowest catalytic activity temperature of NO is about 130 °C. The maximum CO2 production rate is 68.3%, and the maximum NO reduction rate is 45%.

Flash sintering of ZrO2–SnO2–ZrSnO4 composite nanofibers: Fabrication, properties, and biochemical effects in Drosophila melanogaster

ZrO2–SnO2–ZrSnO4 composite nanofibers (CNFs) were fabricated by an electrospinning technique in three different ratios by volume (%v/v). Changing the composition ratio of CNFs affected the temperature and sinter time variation of both the band gap and the flash sintering (FS) phenomenon. FS experiments were used at a current cut-off of 3.77 mA/mm2 under thermal (844–878 °C) and electric field (420 V/mm). Highly dense CNFs were obtained in less than 80 s with a maximum power absorption of 1.58 W/mm3. In addition to the FS process, CNFs were sintered with the conventional sintering (CS) method at 1200 °C for 1 h. As the amount of Sn in the composition (%v/v) increases, the density increases, but the hardness value decreases. The FS process was proven to produce faster, denser, and harder material than CS.Long-term and permanent results are obtained by designing biocompatible nanocomposite materials in health. However, determining the long-term effects of CNFs, which are considered non-toxic, is necessary. Drosophila melanogaster female food was covered with these different v/v% ratios CNFs (ZrSn, Zr2Sn; 2ZrSn) and contact by life span: The effects were evaluated on movement, weight, egg production, longevity, and antioxidant system (Superoxide dismutase-SOD, catalase-CAT, glutathione-GSH, and 2,2-diphenyl-1-picrylhydrazil-DPPH). It can be said that Zr2S CNFs were not toxic by not changing the life span, egg production, climbing, and biochemical parameters of the fly. However, it was determined that CNFs used in ZrSn and 2ZrSn ratios slightly reduced the behavioral (movement and longevity) and antioxidant activities (SOD and CAT) of the individual.

Dealuminated Beta zeolite reverses Ostwald ripening for durable copper nanoparticle catalysts.

Copper nanoparticle-based catalysts have been extensively applied in industry, but the nanoparticles tend to sinter into larger ones in the chemical atmospheres, which is detrimental to catalyst performance. In this work, we used dealuminated Beta zeolite to support copper nanoparticles (Cu/Beta-deAl) and showed that these particles become smaller in methanol vapor at 200°C, decreasing from ~5.6 to ~2.4 nanometers in diameter, which is opposite to the general sintering phenomenon. A reverse ripening process was discovered, whereby migratable copper sites activated by methanol were trapped by silanol nests and the copper species in the nests acted as new nucleation sites for the formation of small nanoparticles. This feature reversed the general sintering channel, resulting in robust catalysts for dimethyl oxalate hydrogenation performed with supported copper nanoparticles for use in industry.

Coalescence of Al2O3/Al, MgO/Mg, and MgO/Al two nanoparticles during combustion

Metal and metal oxide aggregates are easily sintered by migration–diffusion in combustion, and the aggregates hold a complex morphological and structural variability that increases with temperature. The underlying thermomechanical response remains a challenging mystery for active nanoparticles. Here, a computational strategy based on ReaxFF molecular dynamics were performed to shed much light on the coalescence behavior of Al2O3/Al, MgO/Mg, and MgO/Al nanoparticles – a doublet of two spheres. The complex sintering phenomenon was further quantitatively described in terms of coordination number, charge distribution, density distribution, atomic displacement, radius ratio, shrinkage, and sintering time, etc. Results showed that the Al2O3/Al and MgO/Mg two nanoparticles undergo collision and coalescence, and the two were connected through the neck. MgO/Al aggregates are unstable at higher temperatures (T > 1200 K) and segregate at junctions, followed by re-coalescence in the simulation box. A stable neck structure can be formed when enough O atoms are dissolved in MgO nanoparticles or at a lower temperature. The diffusion of Mg, Al, and O atoms in aggregates is driven by concentration gradients and self-generated electromotive forces. The Al2O3 passivation layer forms and hinders the diffusion of O atoms, and the oxygen-rich regions are distributed in the neck (Al2O3/Al) or the contact surface on the side of the Al nanoparticles (MgO1.5/Al) during sintering. In MgO/Al aggregates, Mg atoms tend to wrap Al nanoparticles by surface diffusion.

In-situ 3D X-ray investigation of ceramic powder sintering at the particle length-scale

We report an in-situ investigation of a high-temperature ceramic powder sintering performed for the first time at the particle length-scale. This was made possible by the phase-contrast X-ray nano-holotomography technique at the ID16B nano-analysis beamline of the European Synchrotron Radiation Facility (ESRF), featuring nanometer resolution (25 nm) capabilities. To perform sintering inside the synchrotron hutch, a compact high-temperature furnace was designed and developed. The sequence of real-time 3D images captured the collective behavior of the particles as well as the local-level specificities. A list of sintering indicators corresponding to the evolution of the particle shape, particle size, inter-particle neck size, pore size and pore curvature were extracted. The effect of these parameters on densification and their influence on the overall microstructural development were analyzed. Our results demonstrate the potential of synchrotron-based X-ray nano-tomography for studying complex sintering phenomena in 3D.

Insights into amine-resin matching strategy for CO2 capture: Adsorption performance tests and Mechanistic investigation

The solid amine adsorbents are potential candidates as materials for post-combustion capture technologies. The type of organic amine and porous material are the key factors influencing the amine-based solid adsorbent performance. Furthermore, there has been relatively little research on the matching mechanism between organic amines and porous materials. This study aims to investigate the effect of the degree of matching between different organic amines and porous materials (X-5 resin) on the performance of CO2 capture. The results indicated that 30 wt% TETA was the highest matching degree with X-5 and had the maximum CO2 adsorption of 205.48 mg/g at 30 ℃. The matching degree between the four amines and the X-5 resin followed TETA > TEPA > PEHA > PEI. Since TETA has the simplest molecular structure, it can be conveniently dispersed in the X-5 pores, which not only significantly improves the utilization of active sites but also prevents the phenomena of agglomeration or sintering. Meanwhile, X-5-30TETA has the highest adsorption energy Eads (−85.22 kJ/mol) and the smallest spatial potential resistance, decreasing the mass transfer resistance effectively, thus further increasing the adsorption capacity. Furthermore, the adsorption kinetics results showed that the Avrami model can relatively accurately predict the experimental results of X-5-TPHI CO2 adsorption. Finally, the in situ DRIFTS indicated that the CO2 adsorption reaction over X-5-30TETA followed predominantly an amphipathic centipede mechanism. This work provides a new idea for the investigation of the matching mechanism between organic amines and porous materials.

Study of a Glass-Ceramic Seal Porosity

Sealing is a major issue in high temperature electrolyzers used for hydrogen production. The specifications that seals must meet are particularly demanding. In addition to sealing, the material must have mechanical, thermomechanical and chemical properties, as well as sufficient electrical resistivity. The geometries are complex and the lengths to be sealed are important. These numerous constraints lead to the use of glass powder suspended in organic solvents. This process allows the installation of the seal by deposition of the suspension on the areas to be sealed. Then, a heat treatment is applied to shape the material and ensure the sealing of the system. The use of a composition that tends to crystallize is implemented to improve, a priori, the thermal and mechanical properties. The reference heat treatment consists in a first temperature rise followed by a crystallization stage. As the temperature rises, the organic solvents evaporate producing CO2 and gas present in the atmosphere of the furnace is trapped during sintering, which causes porosity to appear. Early surface crystallization can compete with the sintering phenomenon and prevent the maximum densification of the glass ceramic by freezing the structure. The objective of the study is to obtain a seal material with maximum density, thus minimum porosity, by controlling the removal of organic solvents, sintering and crystallization. Indeed, a large and interconnected porosity can create preferential leakage paths and decrease the sealing performances of the stack. Moreover, a dense material is known to be mechanically more resistant than a porous one. Indeed, a pore can initiate a crack that will eventually propagate through the seal. This paper will present in particular the study of the material porosity. A quantification by SEM image analysis allows to determine the evolution of the porosity (percentage, size, number) as a function of time and temperature. Swelling, coalescence and rising of the pores are observed at high temperature. Glass powder and slurry are studied. Figure 1

Study of the Crystallization in a Glass-Ceramic Seal

Sealing is a major issue in high temperature electrolyzers used for hydrogen production. The specifications that seals must meet are particularly demanding. In addition to sealing, the material must have mechanical, thermomechanical and chemical properties, as well as sufficient electrical resistivity. The geometries are complex and the lengths to be sealed are important. These numerous constraints lead to the use of glass powder suspended in organic solvents. This process allows for the installation of the seal by simply depositing the suspension on the areas to be sealed. A heat treatment is then applied to shape the material and ensure the sealing of the system. The use of a composition that tends to crystallize allows, a priori, improving the thermal and mechanical properties.The reference heat treatment consists of a first temperature rise followed by a crystallization stage. As the temperature rises, the organic solvents evaporate, producing CO2, which causes porosity to appear. Sintering of the glass powder also takes place during this stage. Early surface crystallization can compete with the sintering phenomenon and prevent the maximum densification of the glass ceramic by freezing the structure. The objective of the study is to obtain a seal material with maximum density, thus minimum porosity, by controlling the removal of organic solvents, sintering and crystallization.This paper will present in particular the study of the material crystallization: phases identification and evolution of crystal morphology as a function of temperature (SEM, XRD) (Figure 1), crystal surface fraction as a function of time and temperature (determined by image analysis). A poikilitic texture phenomenon, particularly important for the crystalline fraction quantification, is also detailed (SEM-EBSD). These data allow to obtain the equilibrium crystalline fraction as a function of temperature, and to further optimize the thermal treatment. Figure 1

Combustion Performance of Agropellets in an Experimental Fixed Bed Reactor versus a Commercial Grate Boiler. Validation of Ash Behavior.

Agrobiomass is presented as a suitable alternative to contribute to the fossil fuel decarbonization strategy at the European level. To achieve the ambitious objectives established in this regard: (i) new biomass resources need to be used and therefore initially tested in order to confirm its potential for different applications, such as energy production, and (ii) biomass supply capacity needs to be enlarged; therefore, agroindustries converted into Integrated Biomass Logistic Center (IBLC) can play a key role. In this research, eight different agropellets (blends of wheat straw and maize stalk with forestry wood) were produced in a IBLC and tested in a commercial boiler, comparing the results with previous ones obtained in a fixed bed reactor test campaign and to a base case (woody pellets). This paper includes both individual results in terms of bottom ash, deposition, and a final comparison of ash behavior in both facilities. All biofuels tested showed an adequate performance in terms of efficiency and emissions, being slightly better for the agropellets produced with wheat straw. Regarding sintering and deposition, the tendencies found in the reactor investigation were also observed in the commercial boiler. Moreover, the assessment of the results from the boiler and reactor's tests proved that reactor experiments are representative and may be used to test new biofuels more efficiently in terms of effort and time allocated and could be used to predict sintering and deposition phenomenon occurrence.

Energy evolution mechanism of a PVDF activated nano-aluminum based metastable intermixed composites

The preparation and energy release mechanism of highly reactive n-Al/F-polymer metastable intermixed composites are both desirable and challenging. In this study, we employed an optimized electrospray sampling strategy to significantly enhance the reaction activity of aluminum-based MICs, as well as their combustion performance. It is evident that the optimization of the sampling strategy yielded remarkable results. Compared to the physical mixture, MICs-1 exhibited a 7.2-fold and 9.9-fold increase in Pmax and Pmax/Δt, respectively. The combustion rate experienced an 8.5-fold improvement, and the energy release efficiency rose from 52.18 % to 68.11 %. An analysis of the energy evolution mechanism reveals a mitigation of the reactive sintering phenomenon observed in MICs-1. The presence of PVDF facilitates the reactivity of aluminum powders by selectively corroding the alumina shell. The reaction kinetics parameters indicate that MICs-1 demonstrates characteristic three-step reaction behavior and exhibits a lower reaction energy barrier. Furthermore, ReaxFF molecular dynamics simulations demonstrate the adsorption and dissociation of PVDF on the surface of aluminum powders, leading to erosion defects in the alumina crystal structure. These defects, in turn, induce the ignition reaction.

Structural morphology and surface recrystallization properties of GaN nanoparticles with different sizes during sintering

GaN is a promising third-generation semiconductor material for fabricating nanodevices with nanoscale dimensions. In particular, thick-film sensors fabricated with GaN nanoparticles (NPs) have good gas-sensing characteristics. This study used molecular dynamics simulation to investigate the effect of temperature and size on the structural morphology and surface recrystallization of GaN NPs during sintering. The diffusion behavior and changes in the structural morphology of atoms were analyzed based on the shrinkage ratio, mean square displacement, potential energy, and other methods. The results show that during sintering, the surface of two GaN NPs experienced recrystallization, which expanded with increasing temperature; however, the obvious sintering phenomenon occurred at 3000 K. Interestingly, the surface recrystallization of NPs exhibited a lamellar structure formed through a specific stacking method of the crystal structure. However, when the size of one of the two NPs was reduced, the small NP rapidly melted and was induced to crystallize into a complete NP (having the same crystal orientation as the large NP) by the large NP. Moreover, NPs underwent rigid-body rotation and relative rotation during sintering; however, plastic deformation and dislocations resulting from rotation were only found in the neck of NPs of the same size. The study results provide valuable insights at the atomic scale regarding the sintering of GaN NPs and a useful reference for preparing and processing nanodevices.

Differential Sintering and Self‐Stress Effects on YSZ Ionic Conductivity

Thermomechanical stress simulations are combined with experimental tests to assess the effects of rigid inclusions on the sintering of 8 mol% yttria‐stabilized zirconia (8YSZ) green compacts and the phenomena of restricted and differential sintering on microstructure development and electrical properties are investigated. Rigid inclusions of sintered ceramic particles with different shapes (spherical and jagged) and compositions (alumina, 3YSZ, and 8YSZ) are added in different volume fractions (1, 5, and 15 vol%) to 8YSZ commercial powders, which are formed by isostatic pressing and sintered by conventional method. Restricted and differential sintering effects are observed in the development of the microstructure varying in function of volume fraction, shape, structural composition, and thermomechanical properties of the inclusions, resulting in different combinations of tensile and compressive strain states in the matrix, and varying electrical behaviors. The addition of 1 vol% of 8YSZ irregular rigid inclusions leads to an increase of 36% in total electrical conductivity and a 33% increase in power density under solid oxide fuel cells operation conditions compared to samples without inclusions.

Thermochemical heat storage utilization of MSWI fly ash after carbonation enhancement with ammonia water regulation: Carbon sequestration efficiency, heavy metal immobilization, and heat storage characteristics analysis

Accelerated carbonation is an effective method of treating municipal solid waste incineration fly ash (FA). However, the efficiency of CO2 sequestration is limited and the usage of products is uncertain. This study proposed a method for enhancing carbonation by ammonia water (NH4OH) regulation and thermochemical heat storage of its products. The influences of NH4OH on CO2 sequestration and heavy metals immobilization were investigated. The results demonstrated that the carbon sequestration efficiency improved from 65.2% to 98.3%, with the NH4OH addition increasing (0–20%). NH4OH promoted the conversion of calcium chloride (CaCl2) and calcium sulfate (CaSO4), which were not originally involved in the carbonation reaction, to calcium carbonate (CaCO3). Excess NH4OH increased the release of heavy metals into the liquid phase due to the chelation of heavy metals by ammonia ions (NH4+) and the effect of high pH. The appropriate amount of NH4OH (8%) offered a high-efficient immobilization of heavy metals. The energy density of FA samples increased from 226.6 kJ/kg to 1207.8 kJ/kg with the NH4OH addition increasing, positively correlating with the content of CaCO3. After the thermal cycle treatment, the non-ammonia carbonated FA had a serious sintering phenomenon with chlorellestadite (Ca5(P,Si,S)3O12(Cl,OH,F)), which was produced from the reaction between CaSO4 and other compounds; while the carbonated FA with NH4OH addition (8%) showed good thermal cycle stability with fine particles and single component (calcium oxide). Therefore, the carbonation treatment in this study is a novel and highly-efficient method, with the final products providing an alternative material for thermochemical heat storage.