One-step Sintering Research Articles

From magnesite directly to lightweight closed-pore MgO ceramics: The role of Si and Si/SiC

Partial/full replacement of traditional dense refractory aggregates (for furnace lining) with lightweight aggregates is considered to be an effective and promising strategy for energy saving and emission reduction. In this work, lightweight magnesia refractory ceramics with tailored closed porosity were prepared by one-step sintering at 1600 °C from high-purity magnesite added with silicon kerf waste in different ratios, with the emphasis on the evolution of their phase compositions, micromorphologies, and various properties. With the addition of additives, Mg2–xFexSiO4 solid solution was formed at the grain boundaries of the MgO matrix, and then the volumetric expansion effect (interfacial reaction) and activated sintering effect (vacancy defect) promote the decrease of apparent porosity and the increase of closed porosity, respectively. Consequently, MgO ceramics with apparent/closed porosity of 0.6%/6.5%, bulk density of 3.25 g cm−3, and lightweight index of 7.8% were successfully prepared, suitable for the working lining of metallurgical furnaces.

Manganese-Cobalt Based Spinel Coatings Processed by Electrophoretic Deposition Method: The Influence of Sintering on Degradation Issues of Solid Oxide Cell Oxygen Electrodes at 750 °C.

This paper seeks to examine how the Mn–Co spinel interconnect coating microstructure can influence Cr contamination in an oxygen electrode of intermediate temperature solid oxide cells, at an operating temperature of 750 °C. A Mn–Co spinel coating is processed on Crofer 22 APU substrates by electrophoretic deposition, and subsequently sintered, following both the one-step and two-step sintering, in order to obtain significantly different densification levels. The electrochemical characterization is performed on anode-supported cells with an LSCF cathode. The cells were aged prior to the electrochemical characterization in contact with the spinel-coated Crofer 22 APU at 750 °C for 250 h. Current–voltage and impedance spectra of the cells were measured after the exposure with the interconnect. Post-mortem analysis of the interconnect and the cell was carried out, in order to assess the Cr retention capability of coatings with different microstructures.

One-Step Enameling and Sintering of Low-Carbon Steels

Powder technology allows manufacturing complex components with small tolerances, saving material without subsequent machining. There is a growing trend in using sintered steel components in the automotive industry. Within 2020, about 2544 million US dollars was invested for manufacturing sintered components. Not only does this industry uses steel components, but the gas cooker industry also uses steel in its burners since they are robust and usually demanded by Americans, with forecasts of 1097 million gas cookers in 2020. Steel gas burners have a ceramic coating on their surface, which means that the burner is manufactured in two stages (casting and enameling). This work aims to manufacture the gas burners by powder metallurgy, enameling and sintering processes in a single step. To achieve this aim, the ASC100.29 iron powder has been characterized (flow rate, relative density and morphology); subsequently, the most suitable parameters for its compaction and an adequate sintering temperature were studied. Single-step sintering and enameling was achieved by compacting iron powder at 500 MPa and sintering at 850 °C for 5 min. The necessary porosity for mechanical anchoring of the coating to the substrate is achieved at this sintering temperature. Bending resistance tests, scratching, degradation under high temperature and basic solution and scanning electron microscopy were used to characterize and validate the obtained samples.

Dielectric, mechanical and thermal properties of ZrO2–TiO2 materials obtained by microwave sintering at low temperature

The sinterability of 3Y-TZP/TiO2 materials using micrometre-sized ZrO2 and nanometre-sized TiO2 (16 wt%) by one-step fast microwave sintering at low temperature (1200–1300 °C) was investigated. Firstly, in situ detailed analysis of the dielectric properties of the material with temperature was carried out in order to measure the capacity of the material to transform microwave energy into heat. Another related parameter associated to microwave sintering is the penetration depth of the microwave radiation into the material, which showed great homogeneity from 400 °C. Secondly, the effect of sintering conditions on microstructure, density, hardness and coefficient of thermal expansion was evaluated. The X-ray diffraction study and microstructural characterization demonstrate that it is possible to obtain fully dense pieces (>99%) by microwave sintering, a condition yielding to a coarse-grained (~1–2 μm), quite hard (~13.7 GPa) 3Y-TZP/TiO2 material. However, the most important feature is the significant reduction of the thermal expansion coefficient (8·10−6 K−1) as compared to that of 3Y-TZP. In addition, the results from conventional sintering at 1400–1500 °C with 2 and 6 h of dwell time are examined and compared. The materials obtained at 1500 °C showed high density with grain size and hardness similar to those obtained by microwave but with a dramatic difference in the power consumption of the sintering cycle, since the materials obtained by microwave used a maximum absorbed power of 120 W and a heating cycle of only 40 min.

Self-Stabilized LiNi0.8Mn0.1Co0.1O2 in thiophosphate-based all-solid-state batteries through extra LiOH

Nickle-rich LiNi0.8Co0.1Mn0.1O2 (NMC 811) cathode material exhibits engaging properties in high energy density and low cost, making it great potential for the next generation high-energy all-solid-state lithium batteries (ASSLBs). However, NMC 811 suffers from severe surface electrochemical, chemical, and voltage incompatibility towards solid-state electrolytes (SSE), especially thiophosphate-based electrolytes like Li6PS5Cl. Although diverse coating methods have been made to overcome this issue, they are typically cumbersome and expensive. A coating strategy that satisfied all the requirements of cost-efficiency, stability, uniformity, scalability, and easy-achieving is still challenging. In this work, we developed a LiOH-based surface stabilization strategy that provides a ~10 nm stable permeable layer on NMC 811. After one-step sintering of NMC 811 precursor mixed with LiOH, which is commonly used for NMC 811 lithiation process, excessive LiOH simultaneously distributes on NMC 811 particles. Unlike other reported methods, this coating method can be easily controlled and fabricated without additional complicated processes. By simply controlling the thickness of LiOH layer, which protects the Li6PS5Cl solid electrolyte materials from being oxidized, optimized cycling stability can be obtained for 600 cycles with capacity of 130 mAh g − 1 on average at a wide electrochemical window of 2.50−4.20 V (vs. Li-In).

Fabrication of a Full-Scale Pilot Model of a Cost-Effective Sodium Nickel-Iron Chloride Battery Over 40 Ah

To fabricate a full-scale pilot model of the cost-effective Na–(Ni,Fe)Cl2 cell, a Na–beta–alumina solid electrolyte (BASE) was developed by applying a one-step synthesis cum sintering process as an alternative to the conventional solid-state reaction process. Also, Fe metal powder, which is cheaper than Ni, was mixed with Ni metal powder, and was used for cathode material to reduce the cost of raw material. As a result, we then developed a prototype Na–(Ni,Fe)Cl2 cell. Consequently, the Ni content in the Na–(Ni,Fe)Cl2 cell is decreased to approximately (20 to 50) wt.%. The #1 prototype cell (dimensions: 34 mm × 34 mm × 235 mm) showed a cell capacity of 15.9 Ah, and 160.3 mAh g−1 (per the Ni–Fe composite), while the #2 prototype cell (dimensions: 50 mm × 50 mm × 335 mm) showed a cell capacity of 49.4 Ah, and 153.2 mAh g−1 at the 2nd cycle.

Mechanical properties and microstructural evolution of pressureless sintered ceramics obtained from high-energy ball-milled TiB2–TiC powders

A series of TiB2–TiC composites were successfully fabricated through one-step and two-step pressureless sintering using powders obtained by high-energy ball-milling. Effects of ball-milling time on crystal size and morphology of powders as well as microstructural evolution and mechanical properties of TiB2–TiC composites were investigated. The crystal size of TiB2–TiC powders decreases to 14.7 nm after ball milling for 30 h. Two-step pressureless sintering is beneficial to the densification process without obvious grain coarsening. The core-rim structure of carbides in TiB2–TiC composites is formed by nonuniform diffusion of W atoms from the outside to the interior of TiC grains. The phenomenon of selective solution of WC into TiC grains was carried out through experiments and verification of first-principles DFT calculations. An in-situ TiB2 plate toughened microstructure is developed for TiB2-40 wt %TiC composites two-step sintered at 1500 °C for 4 h and 2000 °C for 1 h with excellent comprehensive performances.

Effect of two-step heating on transparency of MgAl2O4 ceramics fabricated by pulsed electric current sintering process

In this work, MgAl2O4 transparent ceramics was fabricated from combustion-synthesized nanopowders by pulsed electric current sintering (PECS) combined with two-step sintering. Ceramic powder was densitified using two-step heating, namely the first-step temperature was 1100 oC with holding time of 60 min and the second-step temperatures in range from 1300 oC to 1450 oC with 20 min duration. The results showed that the transparent ceramic samples sintered at 1100 oC/60 min – 1400 oC/20 min had grain size of 177 ± 8 nm, relative density about 99 %, transmittance up to 80 %, and Vickers hardness of 18 GPa. These values were higher than that of samples obtained by one-step sintering at 1400 oC.

Freestanding 3-dimensional macro-porous SnO2 electrodes for efficient electrochemical degradation of antibiotics in wastewater

• A novel freestanding 3-dimensional SnO 2 -Sb anodes with macro-pores were fabricated; • The 3D MP SnO 2 -Sb anode featured a 140-fold increase in the electro-active surface area; • 3D MP SnO 2 -Sb was much more effective than 2D SnO 2 -Sb for the antibiotic removal; • The novel 3D anode exhibited a high stability after more than 200 test cycles; • The 3D MP SnO 2 -Sb anode performed efficiently in actual wastewater effluent. Electrochemical (EC) oxidation is an effective technology for treating wastewaters with emerging and persistent organic pollutants. However, conventional 2-dimensional (2D) film-type anodes have a low efficiency and short service life due to a limited electro-active surface area (EASA) and poor stability. In this study, novel freestanding and highly-stable 3-dimensional SnO 2 -Sb anodes with macro-pores (3D MP SnO 2 -Sb) were fabricated without the Ti base substrate by simply compressing the precursor of SnO 2 -Sb and carbon fibers followed by one-step sintering. Compared with the conventional 2D SnO 2 -Sb/Ti anode, the 3D MP SnO 2 -Sb anode featured a more than 100-fold increase in EASA, which greatly improved the EC efficiency for antibiotic oxidation and mineralization. Nearly 100% of ciprofloxacin (CIP, 20 mg L -1 ) in the synthetic wastewater was degraded by the 3D MP SnO 2 -Sb anode at a very low current density of 5 mA cm −2 within 120 min, which was significantly more effective than that by the 2D SnO 2 -Sb (74%) and a state-of-the-art boron-doped diamond anode (69%). The 3D MP SnO 2 -Sb anode exhibited a high stability (>200 cycles) and performed well in treating actual wastewater. The combined reaction kinetics analysis and porosimetry characterization indicated the importance of macro-pores to the excellent EC oxidation capacity and performance of the anode. The mechanism and pathways of electrocatalytic CIP degradation on the 3D anode were also elucidated from the density functional theory (DFT) calculations, molecular probe-based EC reaction analysis, and intermediate product detection.

Highly selective triethylamine sensing based on SnO/SnO2 nanocomposite synthesized by one-step solvothermal process and sintering

SnO/SnO2 nanocomposites were successfully synthesized by one-step solvothermal process and sintering. Their crystal phase, element composition and morphology were characterized in detail by X-ray powder diffraction (XRD), field emission scanning electron microscope (FESEM) and the transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS). The results of gas sensing measurement on these synthesized materials indicated that the sample annealed at 300 °C showed excellent triethylamine sensing performance at 225 °C. Its response value to 100 ppm triethylamine is 33, 5 times higher than that of pure SnO2. The response time and detection limitation are 2 s and 500 ppb, respectively, which were lower than many other reported sensors. Additionally, it possessed excellent selectivity to triethylamine as well as good stability and repeatability. The rapid response and high sensitivity to trace triethylamine can be attributed to the high levels of chemisorbed oxygen and defective oxygen sites and the p-n junction between SnO and SnO2. The excellent sensing performance of SnO/SnO2 makes it a potential sensing material for triethylamine detection.

Changing the polar order using different sintering methods

In this study, solid solution ceramics (1–x)Bi0.5K0.5TiO3–xBi0.2Sr0.7TiO3 (x = 0.1, 0.15 and 0.2, abbreviated as BKST1 for a one-step sintering method and as BKST2 for a two-step sintering method) were prepared using two different sintering methods. The BKST1 ceramics exhibited an average cubic structure, while the BKST2 ceramics had tetragonal distortions. As the Bi0.2Sr0.7TiO3 content increased, spontaneous relaxor-ferroelectric transition disappeared in the BKST1 ceramics owing to the formation of the polar nanoregions (PNRs). The compositions developed using the two-step sintering method exhibited a noticeable dielectric anomaly with respect to spontaneous relaxor-ferroelectric transitions. Double ferroelectric hysteresis loops appeared near the ergodic relaxor-ferroelectric (or non-ergodic relaxor) transition points. The relationship between the piezoelectric coefficient (d33) and compositions suggested that 0.15BKST1 exhibited the optimum piezoelectric properties (d33, 128 pC/N). The 0.15BKST ceramic developed using the one-step sintering method had a low depolarisation temperature (~176 °C in 0.15BKST1 compared to ~227 °C in 0.15BKST2). The improved piezoelectric properties were attributed to the electrical field-induced transformation from PNRs to the long-range ferroelectric ordering as evidenced by the poling effects on the XRD patterns and dielectric behaviours.

Mg-Ti composites fabricated by a novel one-step high-pressure sintering: The correlation between microstructures and mechanical properties

Simultaneous sintering of low-melting-point Mg and high-melting-point Ti was achieved by a novel one-step high-pressure solid-state sintering technique. The correlation between the microstructures and the mechanical properties of the high-pressure-sintered Mg-Ti composites is elucidated. The Young's modulus of the sintered Mg-Ti composites is in good agreement with the theoretical value, indicative of a sufficient sintering which is difficult to obtain via conventional sintering techniques. The compressive yield strength of the Mg-Ti composites increases with the contents of Ti. However, the plasticity shows a parabolic trend, where the composites with a bicontinuous microstructure show the lowest plasticity. The low plasticity can be mainly attributed to: i) the inherent deformation incompatibility between soft Mg and hard Ti phases, and ii) the Mg/Ti interfaces which are not sufficiently strong to resist cracks initiation and propagation.

Phosphor-in-glass with full-visible-spectrum emission based on ultra-low melting Sn-F-P-O glass pumped by NUV LED chips

Herein, the phosphor-in-glass (PiG) with full-visible-spectrum emission has been successfully fabricated by incorporating SrSi2O2N2: Eu2+ (SSON:Eu) and CaAlSiN3: Eu2+ (CASN:Eu) phosphors in ultra-low melting Sn-F-P-O glass using one-step sintering method. The Sn2+ ions show intense blue-green emission characteristics under the excitation of NUV chips, which are highly dependent on its coordination environment in Sn-F-P-O glass. Then, it was investigated in detail for the first time that fluoride from Sn-F-P-O glass substrate migrates and gathers around the embedded phosphors, which is closely related to the emission performance of Sn2+ activators in the PiG. Furthermore, the mechanism of enhancing the PL intensity of Sn2+ ions by embedded phosphors is proposed. As a result, the PiG with full-visible-spectrum emission can be achieved under 370 nm excitation. Importantly, the PiG pumped by NUV LED chips shows excellent-quality white-light with high CRI (Ra = 91) and lower CCT (4993 K). The WLED based on this PiG has been demonstrated as a promising candidate for solid warm light source in the future because of the excellent optoelectronic performance and easy-preparation process.

Binary V–Mo sulfides grown on CNTs with morphological and electronic modulation for enhanced hydrogen evolution

Binary V–Mo sulfides on carbon nanotubes with superior electrocatalytic water splitting performance in acid media are successfully synthesized by a facile one-step sintering method.

Simultaneous sintering of low-melting-point Mg with high-melting-point Ti via a novel one-step high-pressure solid-phase sintering strategy

Ti-Mg composites have been successfully fabricated by a novel high-pressure solid-state sintering technique, by which simultaneous solid-state sintering of the low-melting-point Mg with the high-melting-point Ti is achieved at a high temperature of upto 1000 °C under a high pressure of 4 GPa. The well-sintered composites with a fully dense microstructure exhibit a continuous Ti matrix and a strong interfacial bonding, which are difficult to achieve by other sintering methods. Meanwhile, both Ti-Mg composites and the derived porous Ti exhibit superior mechanical properties, demonstrating promising prospect for load-bearing implant applications.

Ablation resistance of HfC(Si, O)-HfB2(Si, O) composites fabricated by one-step reactive spark plasma sintering

A dense HfC(Si, O)-HfB2(Si, O) composite was fabricated by reactive spark plasma sintering using HfC and SiB6 as starting reactants. The best ablation resistance was obtained with the composite fabricated with the addition of 15 vol.% SiB6. After ablation under an oxyacetylene flame for 60 s, the mass and linear ablation rates of this composite were −0.007 mg cm−2 s−1 and −0.233 μm s−1, respectively. The negative ablation rates are the result of a slight mass gain/thickness increase, which indicate that the oxidation process was stable and mechanical scouring was limited during ablation. This enhanced ablation resistance was attributed to a unique double-layered oxide formation, which possessed lower oxygen permeability and better mechanical strength. The solid solution nature of the composite and its appropriate phase composition were responsible for the stable oxide structure formation.

Fabrication and performance of graded ultrafine WC–Co cemented carbide tool by one/two-step spark plasma sintering

Ultrafine WC–Co cemented carbides with Co gradient were prepared by one-step (1300 °C/5 min) and two-step (1300 °C/3 min→1200 °C/5 min) spark plasma sintering. Effects of Co gradient and sintering process on the microstructure and mechanical properties were studied. The higher Co content of core layer provides the good fracture toughness and transverse rupture strength for graded cemented carbides, while the grain growth of surface caused by the migration of Co from the interior to the surface results in a slight decrease of surface hardness. Two-step sintering inhibits the grain growth and improves comprehensive mechanical properties of graded WC–4Co/WC–12Co/WC–4Co cemented carbide. Its surface grain size, hardness, fracture toughness and transverse rupture strength are 231 nm, 2080 kg/mm2, 8.93 MPa⋅m1/2 and 1829 MPa, respectively. In addition, the cutting performance of graded cemented carbides prepared by two-step sintering was investigated. The graded WC–4Co/WC–12Co/WC–4Co cemented carbide tool has a high wear resistance due to the high surface hardness, and its cutting edge has a good resistant capacity against breakage due to the high internal strength. It presents the longer tool life and higher machined surface quality than commercial YG8 tool.

LiNi0.5Mn1.5O4-based hybrid capacitive deionization for highly selective adsorption of lithium from brine

In recent years, the demands for lithium are increasing sharply with the fast development of electrical vehicles, new green energy and portable electronic devices. To meet the demands, selective recovery of lithium from brine/seawater has attracted extensive attention. LiMn2O4 (LMO) is a good redox material for lithium recovery. However, the dissolution of Mn is inevitable during the redox process which can lead to severe capacity decay and poor cycle performance. In this paper, LiNi0.5Mn1.5O4 (LNMO) nanoparticles were prepared through one-step solid-state sintering and applied as a positive electrode in the hybrid capacitive deionization cell for lithium recovery. Cyclic voltammetry (CV) scan of the LNMO electrode in LiCl aqueous solution presented clear redox peaks, illustrating the reversible intercalation/de-intercalation of Li+ into/from LNMO; while the Na+, K+, Mg2+ and Ca2+ cations had negligible intercalation. Combined with an activated carbon (AC) negative electrode, the hybrid capacitive deionization cell (LNMO||AC) was assembled to selectively adsorb lithium, arriving at the adsorption amount of ~260 µmol/g, almost three times higher than that of the symmetric AC cell (AC||AC). Even in the Mg2+ and Li+ mixed binary salt solution at a high CMg2+/CLi+ ratio of 30, LNMO remained high selectivity to Li+ with the separation factor of ~104 achieved. In the synthetic brine water containing various salts, the LNMO||AC cell kept excellent selectivity to Li+ with the adsorption amount still remaining ~230 µmol/g. And the cell can preserve a retention of ~86% after 100 cycles, much higher than the LMO||AC cell (~50%). Meanwhile, neither Mn2+ nor Ni2+ were found in the cycling solution of LNMO||AC cell. Nevertheless, the LMO||AC cell deteriorated gradually with the dissolution loss ratio of Mn in LMO close to 40%. Such excellent selectivity and high stability of LNMO enable it applicable for practical lithium recovery application, superior to LMO.

Highly thermal stable phosphor LiSrPO4:Eu2+ with a new crystal structure

ABPO4-type structures are attractive host candidates for phosphors owing to their versatile crystal structures, which makes the great possibility for tuning of luminescent properties. Up till now, there are still some related compounds lack detailed crystal structure informations. And there are also upcoming ABPO4-type structures and related phosphors are under discovering. In this work, Eu2+-activated LiSrPO4 phosphor with a new crystal structure is discovered. Rietveld refinement suggests that it belongs to a monoclinic (m-) system, which exhibits a higher symmetry than the already reported monoclinic one (PDF#53–1238). The Eu2+-activated phosphor exhibits a narrow emission band at 420 nm with a full width at half maximum of 28 nm, which is different from Eu2+ in the old monoclinic or hexagonal (h-) LiSrPO4 with an emission band at around 450 nm. The difference is discussed by comparing the crystal structures especially the coordination environments between the newly found m- and h-LiSrPO4. Eu3+ ion was also used to probe the difference in crystal structure. An additional thermal treatment at 900 °C for the as-prepared samples greatly enhances their emission and quantum efficiency, which is due to the increase of Eu2+/Eu3+ ratio. Integrated emission intensity at 150 °C remains ~94% of the room-temperature value for either one-step or two-step sintering process. Results suggest that the as-prepared phosphor can be a good candidate for phosphor-converted white light-emitting diodes.

Nanosponge-like Solid Solution of NiMo with a High Hydrogen Evolution Reaction Performance over a Wide Range of Current Densities

Owing to unstable electrical energy generation from intermittent solar and wind energy sources, the development of efficient and durable nonnoble electrocatalysts is extremely desirable, in particular, those that can be used over a wide range of current densities for the hydrogen evolution reaction (HER), especially >1 A cm–2, which is extremely desirable for energy transformation in power systems. Here, a nanosponge-like NiMo solid solution based on a nanoscale Kirkendall effect is fabricated via a one-step high-temperature sintering method. A polycrystalline layer of NiMo oxyhydroxide is formed on the surface of the as-prepared electrode after aging, thus achieving a low overpotential and Tafel slope of 37 mV at 10 mA cm–2 and 39.2 mV dec–1, respectively. The electrode displays superior electrochemical stability over a wide range of current densities without compromising its electrocatalytic activity; in particular, it is durable for over 300 h at 2 A cm–2. This is attributed to the combination of the 3D-interconnected nanosponge structure, synergistic effect between the Ni and Mo species, lattice distortion of the solid solution, and its high conductivity. This work provides a possible commercialization for the fabrication of nonprecious electrocatalysts with high performance in large-scale energy conversion.