High-temperature Sintering Process Research Articles

Preparation of water storage ceramsite via dredged silt and biomass waste: Pore formation, water purification and application

Natural water pollution and eutrophication are environmental problems that urgently need to be solved. Porous ceramsite could be applied for both water storage and water purification. This research used biomass and dredged silt to prepare water storage ceramsite (WSC), and investigated the adsorption and removal effects of WSC on phosphorus (P), nitrogen ((NH4+)N) and chemical oxygen demand (COD). The results showed that the biomass was mostly burned and partially carbonized during the high-temperature sintering process to form a rich pore structure inside the material. The rich pore structure effectively improved the water absorption to 105.58 %. The abundant specific surface area could provide many attachment sites, which is conducive to the adsorption of target ions by WSC. Further testing showed that WSC could adsorb ions with different charges in different pH solutions. Therefore, this study provides a sustainable solution for the co-utilization of biomass waste and dredged silt, and the application of WSC could reduce the damage caused by extreme rainfall and water pollution.

Influence of the cold sintering process and post annealing on the microstructure and Li-ion conductivity of LiTa2PO8 solid electrolyte

Recently, LiTa2PO8 (LTPO) has attracted interest as a potential Li-ion solid electrolyte material because of its high bulk ionic conductivity and low grain boundary ionic conductivity. However, most ceramic-based solid electrolytes are fabricated via the high-temperature sintering process (typically above 1000 °C); such temperatures can cause the evaporation of Li from the compound. To replace high-temperature sintering of ceramics, the cold sintering process (CSP) was introduced; this process enables the densification of ceramics and composites at extremely low temperatures (below 300 °C). In this work, we investigate the effect of using the CSP and post annealing on the microstructure and Li-ion conductivity of LTPO pellets. It is found that the CSP pellets have an amorphous phase between particles. This intermediate amorphous phase creates a better contact between particles and is hypothesized to lead to more Li-ion migration paths. The CSP pellet is found to have a high density and high ionic conductivity of (1.19 × 10−5 S/cm). The pellet obtained via the CSP has Li-ion conductivity similar to that of the pellet obtained via dry pressing after it has been annealed. The CSP pellet after post annealing shows good connections between particles and a high Li-ion conductivity of 1.05 × 10−4 S/cm, which is comparable to the conductivity of a pellet obtained via high-temperature sintering. This work provides new evidence that the CSP is a promising alternative to high-temperature sintering for fabricating ceramic solid electrolytes.

Effects of oxygen vacancy concentration and sintering temperature on rechargeable Li-ion storage performance of titanium niobate anode materials

In this study, TiNb2O7 (TNO) was prepared by a simple solvothermal method and subsequently high temperature sintering process as anode materials for Lithium-ion batteries (LIBs). The surface morphology and oxygen vacancies of as-prepared TNO were investigated by using different sintering temperatures from 700oC to 1000 °C, namely TNO-700, TNO-800, TNO-900 and TNO-1000, respectively. The crystal structure, surface morphology as well as pore size distribution and oxygen vacancy content of a series of TNO anodes were characterized by X-ray diffraction (XRD), scanning electronic microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), surface area and pore analyzer (N2 adsorption/desorption isotherms), electron paramagnetic resonance spectrometer (EPR) and X-ray photoelectron spectrometer (XPS), respectively. The condition-optimized TNO-800 electrode exhibited brilliant rate capability and the highest reversible capacity which resulted from the micro-spherical structure and enough oxygen vacancies in terms of 246 mAh/g after 250 cycles and 248 mAh/g at 20C, respectively. The XPS analysis proved that samples in lower sintered temperatures had more oxygen vacancies from Ti/Nb peak shifting and integrated area ratio of the main peak to the shoulder peak in the O 1s spectrum. In addition, they also exhibited a stronger EFP signal than that of other samples at g = 1.99 which means the signal of paramagnetic oxygen vacancies. These results indicated that the porous structure and high specific surface area, as well as the existence of oxygen vacancies, play important roles in the electrochemical performance of TNO anode materials for LIBs. Hence, it is an effective manner to enhance the Li-ion storage applications for anode materials from this research.

Room-temperature fabrication of Pt nanoparticle-dispersed porous WO3 gasochromic switchable films using oxalic acid

Gasochromic switchable films are materials in which light transmittance properties are influenced by gases. In this study, Pt nanoparticle-dispersed tungsten trioxide (Pt-WO 3 ) gasochromic switchable films were fabricated without heat treatment from a precursor solution containing oxalic acid. The fabricated films exhibited a porous structure with uniformly dispersed Pt nanoparticles. X-ray photoelectron spectroscopy profiles confirmed the reduction of Pt ions to metallic Pt. The fabricated Pt-WO 3 films changed from being colorless and transparent to blue and transparent when exposed to 4% H 2 –N 2 gas and transformed back to the colorless transparent state when exposed to air. In particular, the coloration of this film by H 2 gas was faster than decolorization by air, and its durability was confirmed for 400 switching cycles. This fabrication method does not require a high-temperature sintering process, and the films can be fabricated at room temperature, making the method applicable to substrates with low heat resistances. • Pt-WO 3 precursor for gasochromic switchable films was prepared using oxalic acid. • The Pt-WO 3 films were fabricated at room temperature without any heat treatment. • The films were porous and contained uniformly dispersed Pt nanoparticles.

Facile construction of C and TiO2 surface coating to improve the cycling stability of NiMn2O4 composite electrode materials

• The rod-shaped NiMn 2 O 4 electrode materials have been synthesized by the citric acid sol–gel method. • NiMn 2 O 4 @TiO 2 and NiMn 2 O 4 @C composites demonstrate remarkable electrochemical properties. • The mechanism of surface-coating modification can be attributed to the coating layer forming a stabile SEI layer. In this paper, nickel-manganese bimetal oxide is used as the research object. The rod-shaped spinel NiMn 2 O 4 is synthesized by the citric acid sol–gel method and the subsequent high-temperature sintering process, and the surface is modified by carbon coating and titanium dioxide coating, and studied the effect of increasing the sintering temperature on the sample. Electrochemical experiments show that the C coating is beneficial to the improvement of the rate performance, while the TiO 2 -coated electrode material exhibits excellent cycle stability. The reason for the difference is that the TiO 2 coating on the surface can effectively buffer the volume expansion of the material, while the C coating can form a stable SEI layer.

Sintering analysis of garnet-type ceramic as oxide solid electrolytes for rapid Li+ migration

Metallic doping can stabilize cubic phase Li7La3Zr2O12 (LLZO) solid electrolyte for high conductivity, due to the enhanced vacancies and disordered Li-site. However, the understanding of metallic doping in the crystal lattice during the high-temperature sintering process is still not clear. In present study, a gradient series of Fe doped LLZO are formulated via solid-phase reaction, and then investigated through crystal analysis and morphological characterization. Pair distribution function essay implies that doped Fe3+ promotes random distribution of Li+ over the available sites in the located crystal. Additionally, the ceramic morphology confirms that the particles sizes in LLZO pellets suddenly grow above 1000 ℃, and Fe doping can obviously suppress Li loss above 600 ℃. As a result, the LLZF0.15 exhibits the relatively high ionic conductivity of 1.99 × 10–5 S cm–1 at 45 ℃.

Processing and Characterization of β Titanium Alloy Composite Using Power Metallurgy Approach.

The β titanium alloy matrix composite was made from a mixture of elemental metal powders, including boron carbide. During the high-temperature sintering process, in situ synthesis took place as a result of the TiB and TiC reinforcing phases formed. The identification of these phases was confirmed by X-ray diffraction and microstructural analyses. The presence of unreacted B4C particles and the surrounding reaction layers allowed for the evaluation of diffusion kinetics of alloying elements using SEM and EDS analyses. The direction of diffusion of the alloying elements in the multicomponent titanium alloy and their influence on the in situ synthesis reaction taking place were determined. In addition, the relationship between the microstructural components, strengthening phases, and hardness was also determined. It was shown that in situ reinforcement of titanium alloy produced from a mixture of elemental powders with complex chemical composition is possible under the proposed conditions. Thus, it has been demonstrated that sufficiently high temperature and adequate holding time allows one to understand the kinetics of the synthesis of the strengthening phases, which have been shown to be controlled by the concentrations of alloying elements.

Chemical Energy‐Driven Lithiation Preparation of Defect‐Rich Transition Metal Nanostructures for Electrocatalytic Hydrogen Evolution

Transition metal nanostructures are widely regarded as important catalysts to replace the precious metal Pt for hydrogen evolution reaction (HER) in water splitting. However, it is difficult to obtain uniform-sized and ultrafine metal nanograins through general high-temperature reduction and sintering processes. Herein, a novel method of chemical energy-driven lithiation is introduced to synthesize transition metal nanostructures. By taking advantage of the slow crystallization kinetics at room temperature, more surface and boundary defects can be generated and remained, which reduce the atomic coordination number and tune the electronic structure and adsorption free energy of the metals. The obtained Ni nanostructures therein exhibit excellent HER performance. In addition, the bimetal of Co and Ni shows better electrocatalytic kinetics than individual Ni and Co nanostructures, reaching 100mAcm-2 at a low overpotential of 127mV. The high HER performance originates from well-formed synergistic effect between Ni and Co by tuning the electronic structures. Density functional theory simulations confirm that the bimetallic NiCo possesses a low Gibbs free energy of hydrogen adsorption, which are conducive to enhance its intrinsic activity. This work provides a general strategy that enables simultaneous defect engineering and electronic modulation of transition metal catalysts to achieve an enhancement in HER performance.

Inorganic–Organic Hybrid Electrolytes Based on Al-Doped Li7La3Zr2O12 and Ionic Liquids

Organic–inorganic hybrid electrolytes based on Al-doped Li7La3Zr2O12 (LLZO) and two different ionic liquids (ILs), namely N-ethoxyethyl-N-methylpiperidinium bis(fluorosulfonyl)imide (FSI IL) and N-ethoxyethyl-N-methylpiperidinium difluoro(oxalato)borate (DFOB IL), were prepared with the aim of improvement of inherent flexibilities of inorganic solid electrolytes. The composites were evaluated in terms of thermal, spectroscopical, and electrochemical properties. In the impedance spectra of LLZO composites with 15 wt% ILs, a semi-circle due to grain boundary resistances was not observed. With the sample merely pressed with 1 ton, without any high-temperature sintering process, the ionic conductivity of 10−3 S cm−1 was achieved at room temperature. Employing a ternary composite of LLZO, FSI IL, and LiFSI as an electrolyte, all-solid-state lithium metal batteries having LiFePO4 as a cathode were assembled. The cell exhibited a capacity above 100 mAh g−1 throughout the course of charge–discharge cycle at C/20. This confirms that FSI IL is an effective additive for inorganic solid electrolytes, which can guarantee the ion conduction.

Effect of precursor structure transformation on synthesis and performance of LiNi0.5Co0.2Mn0.3O2 cathode material

The precursor has great influences on electrochemical performance of LiNi1-x-yCoxMnyO2 cathode materials. However, the effect of precursor structure transformation on the synthesis and electrochemical performance of LiNi1-x-yCoxMnyO2 is rarely mentioned. In this paper, Ni0.5Co0.2Mn0.3(OH)2 and different-temperature-preheated Ni0.5Co0.2Mn0.3(OH)2 were synthesized to prepare LiNi0.5Co0.2Mn0.3O2. The results show that Ni0.5Co0.2Mn0.3(OH)2 precursor transform into spinel-type solid solution (Ni0.5Co0.2Mn0.3)3O4 after preheating, and the contents of Ni3+, Co3+ and Mn4+ increase significantly. Comparative analyses reveal that the precursor structure change has no obvious effects on the crystal structure and surface morphology of the prepared LiNi0.5Co0.2Mn0.3O2. But the preheated precursors can reduce the undesirable lithium loss due to lithium volatilization in the high-temperature sintering process, leading to excess lithium ions enter into transition metal ions layer. Lithium excess can affect the amount of Ni3+, lattice parameters and residual lithium compounds on the particle surface, which in turn lead to different electrochemical behaviors of the prepared LiNi0.5Co0.2Mn0.3O2.

Flexible Energy-Storage Ceramic Thick-Film Structures with High Flexural Fatigue Endurance

When developing flexible electronic devices, trade-offs between desired functional properties and sufficient mechanical flexibility must often be considered. The integration of functional ceramics on flexible materials is a major challenge. However, aerosol deposition (AD), a room-temperature deposition method, has gained a reputation for its ability to combine ceramics with polymers previously considered incompatible with the conventional high-temperature sintering process. In this work, 0.9Pb(Mg1/3Nb2/3)O3–0.1PbTiO3 (PMN–10PT) thick films were deposited directly on a polyimide substrate using the AD method. As a result, dense and flexible relaxor-ferroelectric thick films were produced by a one-step direct-integration, suitable for large-scale production. After annealing of as-deposited PMN–10PT films at 400 °C, stress-relaxation occurs, which is responsible for the development of a relaxor-ferroelectric character. Achieved high polarization (38 μC·cm–2), high dielectric breakdown strength (∼1000 kV·cm–1), and low hysteresis losses lead to improved recoverable energy density and energy-storage efficiency of the annealed thick films, reaching 10 J·cm–3 and 73% (at 1000 kV·cm–1), respectively. The thick films were subjected to flexural bending tests, which showed high flexibility (1.1% bending strain) and high durability (105 bending cycles). This stable energy-storage operation makes ceramic-polymer layered structures promising for integration into a wide range of flexible electronic devices.

Self-powered flexible piezoelectric sensors based on self-assembled 10 nm BaTiO₃ nanocubes on glass fiber fabric

Hardness or brittleness limits the broad applications of currently available high-performance piezoelectric sensors in emerging fields like human-machine interface and wearable electronics, while existing technologies for fabricating flexible piezoelectric sensors often require high-temperature sintering or complex processes. Here, we reported flexible piezoelectric sensors based on 10 nm BaTiO3 nanocubes self-assembled on glass fiber fabric (GFF). The simple self-assembly process avoids high temperature sintering process which can well maintain the mechanical performance of GFF. Owing to the superior piezoelectric performance of BaTiO3 nanocubes and robust mechanical properties of GFF, the integrally fabricated flexible piezoelectric sensors achieved high sensitivity (101.09 nA kPa−1 and 3.31 V kPa−1 in the low pressure range of 0–10 N) and short response time (19 ms). The sensors can intelligently identify handwriting or recognize the user of keyboard, and the initially collected electrical signals are essentially the same as those after 3000 bending cycles. This work provides a novel self-assembly process to develop fabric-based flexible electronics, which promotes the development of self-powered piezoelectric sensors and creates advancements in human-machine interfaces.

Micro-fracture behavior of a single-aggregated cBN grain and its relation to material removal in high-speed grinding of Ti–6Al–4V alloys

Aggregated cubic boron nitride (cBN) abrasive grains were developed using high-temperature liquid phase sintering processes and then the single-grain scratching trial was conducted to study the grain wear behavior and material removal characteristics. Characterizations of grain wear evolutions and related surface scratches grinded by aggregated and monocrystalline cBN grains are performed, respectively. The evaluations of wear-resistance and self-sharpening abilities of both abrasive grains are carried out based on the proposed indicators of volumetric pile-up ratio, volumetric groove removal rate, and grain grinding ratio. Compared to the monocrystalline cBN grain, the as-developed aggregated cBN grain exhibits the more stable grinding process, excellent self-sharpening ability as well as a higher material removal volume provided by the dynamic balance between microfracture and partial macrofracture of multi-layer micro cBN particles.

A Review of Binderless Polycrystalline Diamonds: Focus on the High-Pressure-High-Temperature Sintering Process.

Nowadays, synthetic diamonds are easy to fabricate industrially, and a wide range of methods were developed during the last century. Among them, the high-pressure–high-temperature (HP–HT) process is the most used to prepare diamond compacts for cutting or drilling applications. However, these diamond compacts contain binder, limiting their mechanical and optical properties and their substantial uses. Binderless diamond compacts were synthesized more recently, and important developments were made to optimize the P–T conditions of sintering. Resulting sintered compacts had mechanical and optical properties at least equivalent to that of natural single crystal and higher than that of binder-containing sintered compacts, offering a huge potential market. However, pressure–temperature (P–T) conditions to sinter such bodies remain too high for an industrial transfer, making this the next challenge to be accomplished. This review gives an overview of natural diamond formation and the main experimental techniques that are used to synthesize and/or sinter diamond powders and compact objects. The focus of this review is the HP–HT process, especially for the synthesis and sintering of binderless diamonds. P–T conditions of the formation and exceptional properties of such objects are discussed and compared with classic binder-diamonds objects and with natural single-crystal diamonds. Finally, the question of an industrial transfer is asked and outlooks related to this are proposed.

Three electrodes analysis of a 3 V-class all-solid-state lithium-ion battery based on garnet-type solid electrolyte Li6.4La3Zr1.4Ta0.6O12

At present, fabrication of all-solid-state lithium-ion batteries using garnet-type electrolytes is still challenging due to issues with interfacial stability and interfacial impedance caused by the high-temperature sintering process. In this work, we employ Li2CO3 as additive to mitigate high-temperature side reactions and prepare an all-solid-state battery LNM|LLZT|LTO using spinel-structured LiNi0.5Mn1.5O4 (LNM) and Li4Ti5O12 (LTO) as electrodes and garnet-type Li6.4La3Zr1.4Ta0.6O12 (LLZT) as the electrolyte. The battery voltage reaches beyond 3 V and can be charged and discharged for 5 cycles at a rate of C/10. The three-electrode setup of the battery allows the separation of positive and negative electrodes in their voltage profiles and impedance responses during cycling. Our results suggest that the high-voltage electrode LNM can work with LLZT in a solid-state-battery configuration and the negative electrode is the performance-limiting component.

Enhanced quantum efficiency of a self-organized silica mixed red phosphor CaAlSiN3:Eu

This study develops self-organized silica mixed CaAlSiN3:Eu (CASN) powder which improves light extraction efficiency (LEE) of the phosphor particles by enhanced scattering. A simple powder process conducted at room temperature, which is free from high temperature sintering process often applied for glass coated phosphors. Red phosphor CASN particles with a size of a few microns are mixed with nano-sized silica which was prepared in a tetraethyl orthosilicate (TEOS) solution of an alkali hydrolysis bath. The pair distribution function (PDF) profile obtained by an X-ray total scattering experiment indicates that the obtained nano-sized silica powders were amorphous. Compared to pure CASN powders, the composite CASN has an increased diffuse reflection, a reduced amount of absorption light, and an improved quantum efficiency (QE) of about 15%. QE is the product of internal quantum efficiency (IQE) and light extraction efficiency (LEE). The light emission lifetime measurement does not show a noticeable change between the pure and composite samples, indicating that the mixing process does not affect the electronic state of the Eu2+ luminescence center of CASN powder. That is, IQE of composite CASN is the same with that of pure CASN particles. Therefore, the improvement of QE of the composite CASN powders is due to the improvement of LEE.

High-temperature solid-phase synthesis of lithium iron phosphate using polyethylene glycol grafted carbon nanotubes as the carbon source for rate-type lithium-ion batteries

• The presence of PEG effectively solves the problem of agglomeration of CNTs. • LiFePO 4 cathode material synthesized by high-temperature solid-phase method using PEG/CNTs as carbon source, forming uniform tube- net -like 3D conductive network on the surface. • In the synthesis of LiFePO 4 cathode material, PEG plays the role of dispersant, binder and conductive agent. Lithium iron phosphate (LiFePO 4 )/polyethylene glycol (PEG)/carbon nanotubes (CNTs) are successfully synthesized by the high-temperature solid-phase. PEG grafted onto CNTs surface by covalent functionalization. During the high-temperature sintering process, PEG/CNTs form the uniform tube- net -like 3D conductive network, significantly improving electron mobility. Beneficial effects of PEG include: (1). The addition of PEG improves the dispersion of CNTs by increasing the number of surface defects and groups. (2). The cracking PEG forms porous carbon layer uniformly coated around LiFePO 4 to improve its electrical conductivity. (3). As a thermoplastic polymer, PEG becomes a binder at sintering temperatures up to around 70 °C, making the CNTs and LiFePO 4 contact more closely. Compared to LiFePO 4 /CNTs, LiFePO 4 /PEG/CNTs has superior electrochemical performance, as evidenced by improving rate performance (LiFePO 4 /PEG/CNTs discharges 113.5 mAh g −1 at 15C, LiFePO 4 /CNTs discharges 71.6 mAh g −1 at 15C) and high rate cycling retention (capacity retention of 96.6% at 5 C after 300 cycles for LiFePO 4 /PEG/CNTs, capacity retention of 90.6% at 5 C after 300 cycles for LiFePO 4 /CNTs). The architecture of the composite conducting network effectively solves the issue of the poor electron migration of LiFePO 4 .

ESB 소결 조제를 이용한 고체산화물 연료전지용 YSZ 전해질의 초고속 광소결 공정에 관한 연구

A high temperature sintering process for solid electrolyte is the main cause of the increase in manufacturing costs of SOFCs. In this study, we developed a novel flash light sintering technique as an alternative sintering process of the conventional thermal sintering process. The YSZ electrolyte films were fabricated by conventional screen-printing method and the flash light sintering process and ESB sintering aid were applied to improve the flash light sinterability of the YSZ electrolyte. In the flash light sintering process, the effect of various pulse conditions such as energy density, and pulse interval were investigated and the microstructure, crystallinity, and sintering behavior of the sintered films were analyzed to demonstrate the effectiveness of the flash light sintering process. The flash light sintered YSZ electrolyte layer was used to fabricate the anode-supported SOFCs and its functionality is successfully demonstrated with the high open circuit voltage. The significance of this study includes minimization of the process time from tens of hours to just a few seconds, thus facilitating the commercialization of SOFCs.

Development of intertwined nanostructured multi-phase air electrodes for efficient and durable reversible solid oxide cells

The development of nanostructured electrodes of solid oxide cells is largely hindered by the high temperature sintering process and limited in the loading and choices of catalytic phases. Here, a nanostructured multi-phase air electrode is fabricated via facile combination of Gd0.2Ce0.8O1.9 (GDC) decorated PrBa0.8Ca0.2Co2O5+δ (PBCC) and direct assembly approach. The highly flexible decoration process and the in situ formation of multi-phases lead to the formation of intertwined core-shell type nanostructures with intimate electrode/electrolyte interface. A cell with a 40 wt% GDC decorated PBCC electrode achieves a peak power density of 1.74 W cm−2 at 750 °C and an electrolysis current density of 1.77 A cm−2 at 1.3 V with excellent durability for 200 h. The combined decoration and direct assembly approach provides a unique and general pathway to develop a new class of nanostructured air electrodes for efficient and durable solid oxide cells.

Influence of incongruent dissolution-precipitation on 8YSZ ceramics during cold sintering process

The incongruent dissolution-precipitation behaviors of 8YSZ (8 mol% yttria-stabilized zirconia) ceramics during cold sintering process is studied in this paper by changing the pH of liquid media. The different solubility of Y3+ and Zr4+ at the same lattice position causes the disparate dissolution behaviors, and results in incongruent precipitation. Compared with acidic or alkaline solution, neutral solution is more conducive to the incongruent dissolution-precipitation process, and the concentration ratio of dissolved Y3+ and Zr4+ can reach ∼6385. The incongruent dissolution-precipitation process facilitates the formation of neck structure and promotes the ionic migration and diffusion at the subsequent high-temperature sintering process, which improves the mechanical properties and electrochemical properties of 8YSZ ceramics. This work reveals the principle of incongruent dissolution-precipitation process of zirconia-based ceramics, and it is of significance for selecting suitable liquid media to control the incongruent dissolution-precipitation behaviors in cold sintering process to prepare high-performance zirconia-based ceramics.