One-step Sintering Research Articles

Transparent magnesium aluminate spinel ceramics obtained by one-step spark plasma reaction sintering of a sol-gel precursor powder

Transparent magnesium aluminate spinel (MAS) was obtained by one-step spark plasma reaction-sintering (SPRS) of a nanosized sol-gel powder. The sol-gel powder was processed to obtain three powders as precursors materials with different characteristics. The first powder (HT0) was the as-synthesized sol-gel powder, comprising poorly crystallized boehmite and residual magnesium nitrate hexahydrate. The second powder (HT450) was obtained by calcination of the sol-gel powder at 450 °C to produce an incipient formation of MAS. The third powder (HT850) was calcined at 850 °C to produce spinel with low crystallinity. The powders were deagglomerated and then consolidated in one step using a spark plasma sintering (SPS) machine at temperatures ranging from 1260 to 1350 °C to suit their different properties. The one-step SPRS was achieved with relative densities up to 99.98 % and submicron-sized grains. However, transparent ceramics were obtained only with the HT450 and HT850 powders. The ceramic produced from the HT450 powder achieved a light transmittance of 71 % at λ = 1100 nm, Vickers hardness (HV) of 11.98 GPa, grain size of 604 nm, and relative density of 99.98 %. The ceramic produced from the HT850 powder consolidated by one-step SPRS at 1275 °C achieved a light transmittance of 71 %, HV of 12.71 GPa, grain size of 396 nm, and relative density (RD) of 99.90 %. The results showed that the HT450 powder had better sinterability, attributed to the higher reactivity of the partially reacted sol-gel particles used as precursors in this sample.

Preparation of MgO-Nd2Zr2O7 composite ceramics used for inert matrix fuel by one-step sintering method

MgO-Nd2Zr2O7 composite ceramic is a promising candidate as an inert matrix material for the transmutation of Pu and minor actinide. In this work, the MgO-Nd2Zr2O7 composite ceramics (hereafter M-NZO) with 30–70 wt% mass percent of MgO were successfully prepared at 1500 °C for 24 h via direct solid-state reaction one-step method. This method achieved the integration of Nd2Zr2O7 pyrochlore synthesis and M-NZO composites sintering, which shows a significant improvement in the simplification of the preparation process than the traditional two-step method. The structural properties and compactness of the as-prepared composite ceramics were systematically investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM). It was confirmed that the as-prepared M-NZO ceramics are composed of only crystalline MgO and Nd2Zr2O7 phases, and the mass fractions of two phase are almost the same as the designed nominal chemical composition. The composite ceramics showed remarkable densification and the relative density is higher than 98.2%.

Preparation and characterization of foamed glass-ceramics based on waste glass and slow-cooled high-titanium blast furnace slag using borax as a flux agent

Foamed glass-ceramics were prepared at 1000 °C through the one-step sintering process by applying waste glass and slow-cooled high-titanium blast furnace slag as raw materials. This study investigated the effects of borax as the flux agent on the crystalline phases, microstructure, and properties of foamed glass-ceramics, respectively. It was found that the borax would decrease the system's softening temperature and viscosity, thus enhancing the foaming and crystallizing process. Besides, the XRD results showed that the main crystal types of foamed glass-ceramics presented no difference with different contents of borax addition, but their crystallinity and crystal morphology differed. With the increasing borax content, the porosity and water absorption increased, while the volume density, thermal conductivity, and compressive strength all decreased. In particular, the sample added with 6 wt% borax exhibited the optimal comprehensive properties. This study provided a practical guideline for effectively reusing solid industrial wastes to produce foamed glass-ceramics.

Interfacial thermoelectric and mechanical properties of indigenously prepared Ni–Cr–Cu/Co4Sb12 skutterudite thermoelectric joints

Thermoelectric and mechanical properties of indigenously prepared Ni–Cr–Cu/Co4Sb12 skutterudite thermoelectric joints are reported. Co4Sb12 based skutterudite compounds are highly enticing mid-temperature thermoelectric materials for waste-heat harvesting. Ni–Cr–Cu electrode powder is prepared by ball milling, and a one-step sintering route is adopted to fabricate the Ni–Cr–Cu electrode/n-type Dy0.4Co3.2Ni0.8Sb12 thermoelectric joints. The processed Ni–Cr–Cu/skutterudite joint interface is continuous without having any crack and has low contact resistance (<12 μΩ cm2). The contact resistance at the interface of the joints decreases to 7 μΩ cm2 under thermal ageing at 823 K for 15 days in a vacuum. The mechanical properties of the joints are not degraded even after ageing at 823 K for 15 days. The theoretical lifetime of the skutterudite device using the Ni–Cr–Cu/Dy0.4Co3.2 Ni0.8Sb12 joints is calculated to be 11 years while maintaining the hot side temperature of the device at 773 K. Our results demonstrate that indigenously prepared Ni–Cr–Cu/Co4Sb12 thermoelectric joints can be effectively used for skutterudite module fabrication.

Carbothermal reduction synthesis of high porosity and low thermal conductivity ZrC-SiC ceramics via an one-step sintering technique

In this work, porous ZrC-SiC ceramics with high porosity and low thermal conductivity were successfully prepared using zircon (ZrSiO4) and carbon black as material precursors via a facile one-step sintering approach combining in-situ carbothermal reduction reaction (at 1600 °C for 2 h) and partial hot-pressing sintering technique (at 1900 °C for 1 h). Carbon black not only served as a reducing agent, but also performed as a pore-foaming agent for synthesizing porous ZrC-SiC ceramics. The prepared porous ZrC-SiC ceramics with homogeneous microstructure (with grain size in the 50–1000 nm range and pore size in the 0.2–4 µm range) possessed high porosity of 61.37–70.78%, relatively high compressive strength of 1.31–7.48 MPa, and low room temperature thermal conductivity of 1.48–4.90 W·m−1K−1. The fabricated porous ZrC-SiC ceramics with higher strength and lower thermal conductivity can be used as a promising light-weight thermal insulation material.

One-step sintering of porous TiAl3 intermetallics using TiH2 as raw material in thermal explosion reaction

Porous TiAl3 intermetallics with high porosity of 56.0% were synthesized by thermal explosion (TE) reaction using TiH2 as raw material, from TiH2-75 at.%Al elemental powders. Results shown that an obvious thermal explosion reaction occurs (1225 ℃) when one-step sintering is carried out without the pre-heat treatment. After TE, TiAl3 was the dominate phase in the sintered products. Porous TiAl3 intermetallics exhibited an open pore structures and uniform pore size distribution, which ensures the application of porous TiAl3 materials in the fields of solid–liquid filtration and separation.

Insights into the electrooxidation of florfenicol by a highly active La-doped Ti4O7 anode

In this study, a novel active La-doped Ti4O7 (La-Ti4O7) electrode was fabricated through a simple one-step spark plasma sintering method. Characterization results revealed that La was successfully incorporated into the crystal lattice of Ti4O7, leading to an increase in the surface oxygen vacancy content (from 26% to 31%), oxygen evolution potential (from 2.24 to 2.75 V vs SCE), hydroxyl radical yield [•OH, from 0.123 to 0.205 μmol/(min·cm2)] and interfacial charge-transfer rate compared to pristine Ti4O7. La-Ti4O7 electrodes achieved efficient anodic oxidation of florfenicol (FLO, one of the most widely used antibiotics), which mainly due to the indirect oxidation mediated by electro-generated •OH. The degradation of FLO by La-Ti4O7 electrodes fitted well with the pseudo-first-order kinetic model, and the optimal degradation rate constant (kFLO, 0.021 min−1) was achieved by 1.60% La-Ti4O7 electrode. In addition, the degradation efficiency of FLO increased with the increasing current density, decreasing pH and co-existing Cl-, while an opposite pattern was observed with co-existing NO3–. Seven degradation products of FLO were identified by UPLC-MS/MS. The main degradation pathways included hydrolysis, hydroxylation, dechlorination and C-N bonds cleavage. The energy consumption (EC) for FLO degradation ranged from 1.91 to 29.53 Wh/L, and the optimal practical conditions were obtained by the analysis of the calculated ratios of kFLO and EC. Moreover, La-Ti4O7 electrode maintained excellent removal efficiency of FLO (>93.5%) within 20 degradation cycles. This study suggested that La-Ti4O7 is a promising anodic material for the efficient treatment of FLO-polluted water.

Boosting the cycling performance of spinel LiMn2O4 by in situ MnBO3 coating

Spinel LiMn2O4 (LMO) is a promising cathode material for lithium-ion batteries (LIBs) due to its low cost, high safety, and high energy density. However, surface dissolution of manganese and irreversible phase transitions reduce its long-term cycling performance. Although surface coating is a promising strategy for improving the structural stability of LMO, the commonly used coating process is tedious and complicated. In this work, a one-step sintering process is developed to prepare LMO materials coated in situ with MnBO3. It is found that the MnBO3 layer formed in this way is uniformly coated on the surface of LMO, and effectively suppresses Mn dissolution and undesirable phase transition during repeated charge/discharge cycles. Furthermore, the MnBO3-coated LMO has improved electrode kinetics, demonstrating significantly improved rate performance compared to the pristine LMO. As a result, the optimized LMO sample exhibits 85.2% capacity retention after 1000 cycles at 1 C and still can deliver 96 mAh g−1, even at 5 C. This work proposes a facile and efficient coating strategy for improving the electrochemical performance of LMO as a cathode material for LIBs.

One-step fabrication of double-layer nanocomposite coating by plasma electrolytic oxidation with particle addition

A novel double-layer structural nanocomposite coating was prepared via one-step plasma electrolytic oxidation-synchronous deposition & sintering of nanoparticles (PEO-SDSN) technique under unique threshold conditions of concentration of added nanoparticles, electrolyte temperature, and applied voltage. The special discharges at the coating/electrolyte interface lead to the directional migration, deposition and sintering of organic (eg. PTFE) or inorganic (eg. SiC) nanoparticles, combined with the dynamic growth equilibrium of bottom oxide layer and outer nanoparticle deposition & sintering layer. Different from traditional PEO, the addition of nanoparticles creates interesting rising and falling changes in current and corresponding discharging characteristics. The underlined formation mechanism of the double-layer coating was detected by OES combined with discharging phenomena and coating structure evolution. Moreover, compared with the single PEO coating, the double-layer structural nanocomposite coating has better comprehensive performances, such as corrosion protection, and low and stable friction coefficient. The PEO-SDSN technique is energy saving, more importantly, it provides a brand-new fabrication strategy for a series of double-layer multifunctional coatings by tailoring the nanoparticles species. Eventually, the potential applications and guiding strategies of double-layer nanocomposite coating are presented.

Orthorhombic to tetragonal polymorphic transformation of YTa3O9 and its inhibition through the design of high-entropy (Y0.2La0.2Ce0.2Nd0.2Gd0.2)Ta3O9

To explore the mechanism of phase transformation, YTa3O9 was prepared by an integrated one-step synthesis and sintering method at 1500 °C using Y2O3 and Ta2O5 powders as starting materials. High-temperature XRD patterns and Raman spectra showed that a phase transformation from orthorhombic to tetragonal took place in YTa3O9 through the bond length and angle changes at 300–400 °C, which caused a thermal conductivity rise. To inhibit the phase transformation, a high-entropy (Y0.2La0.2Ce0.2Nd0.2Gd0.2)Ta3O9 (HE RETa3O9) was designed and synthesized at 1550 °C using the integrated solid-state synthesis and sintering method. In tetragonal structured HE RETa3O9, phase transformation was inhibited by the high-entropy effect. Furthermore, HE RETa3O9 exhibited low thermal conductivity, and its tendency to increase with temperature was alleviated (1.69 W/m·K, 1073 K). Good phase stability, low thermal conductivity and comparable fracture toughness to YSZ make HE RETa3O9 promising as a new thermal barrier coating material.

Rational design of interfacial energy level matching for CuGaS2 based photocatalysts over hydrogen evolution reaction

CuGaS2(CGS) is effectively synthesized by a one-step solid-phase sintering method. The conduction band maximum, valence band maximum and flat band potential of the obtained CGS are −1.14, 1.21 and 0.33 V vs RHE, respectively. When the Cu to Ga atom ratio is 1: 1.4 in the raw material, the prepared CuGaS2 exhibits the highest visible-light (λ˃420 nm) H2 production activity. The hydrogen production rate of CuGaS2 reaches 1.12 mmol g−1 h−1 under visible-light radiation. When Ruthenium is loaded as cocatalyst, the H2 production rate of CuGaS2@Ru is promoted to 3.38 mmol g−1 h−1. At the same, the interior component of photo-induced carries transfer among photoharvestor and cocatalyst has been revealed. This research provides a facile strategy to fabricate CuGaS2 with excellent photocatalytic performance for H2 production.

One-Step Sintering Process for the Production of Magnetocaloric La(Fe,Si)13-Based Composites

A one-step sintering process was developed to produce magnetocaloric La(Fe,Si)13/Ce-Co composites. The effects of Ce2Co7 content and sintering time on the relevant phase transformations were determined. Following sintering at 1373 K/30 MPa for 1–6 h, the NaZn13-type (La,Ce)(Fe,Co,Si)13 phase formed, the mass fraction of α-Fe phase reduced and the CeFe7-type (La,Ce)(Fe,Co,Si)7 phase appeared. The mass fraction of the (La,Ce)(Fe,Co,Si)7 phase increased, and the α-Fe phase content decreased with increasing Ce2Co7 content. However, the mass fraction of the (La,Ce)(Fe,Co,Si)7 phase reduced with increasing sintering time. The EDS results showed a difference in concentration between Co and Ce at the interphase boundary between the 1:13 phase and the 1:7 phase, indicating that the diffusion mode of Ce is reaction diffusion, while that of Co is the usual vacancy mechanism. Interestingly, almost 100 % single phase (La,Ce)(Fe,Co,Si)13 was obtained by appropriate Ce2Co7 addition. After 6 h sintering at 1373 K, the Ce and Co content in the (La,Ce)(Fe,Co,Si)13 phase increased for larger Ce2Co7 content. Therefore, the Curie temperature increased from 212 K (binder-free sample) to 331 K (15 wt.% Ce2Co7 sample). The maximum magnetic entropy change (−ΔSM)max decreased from 8.8 (binder-free sample) to 6.0 J/kg·K (15 wt.% Ce2Co7 sample) under 5 T field. High values of compressive strength (σbc)max of up to 450 MPa and high thermal conductivity (λ) of up to 7.5 W/m·K were obtained. A feasible route to produce high quality La(Fe,Si)13 based magnetocaloric composites with large MCE, good mechanical properties, attractive thermal conductivity and tunable TC by a one-step sintering process has been demonstrated.

Laser-sintering fabrication of integrated Al/Ni anodes for lithium-ion batteries.

Integrated Al/Ni electrodes of lithium-ion batteries (LIBs) with variant atomic ratios were successfully fabricated by a one-step laser-sintering process. The microstructure, phase composition, and pore structure were controlled by the raw material composition and laser parameters. The electrodes showed working merits without any conductive agent and binder, or even the collector used in a traditional battery. It was shown that the electrode consisted of multi-phases, i.e., Al, Al3Ni2, Al3Ni, and Ni, when the Al/Ni atomic ratio was higher than 5 : 5. A lower Al/Ni atomic ratio less than 5 : 5 favored the formation of a dual-phase electrode consisting of Al3Ni2 and Ni. As the Al content increased, the specific surface area of the as-sintered electrodes increased in the initial stage and then decreased. The formation of pores was closely related to the content of the residual Al phase after the laser sintering. The residual Al phase filled the pores when the Al content was high, leading to a lower pore size. In contrast, the liquid Al phase completely reacted with the Ni component, leaving a large number of pores at its original sites. The linked pores can serve as transport channels for Li+ ions, provide mass sites for electrochemical reactions, and also buffer huge volume changes of the active material. Among the electrodes, the one with an Al/Ni ratio of 3 : 7 showed the best cycling/rate performance, i.e., a capacity of 522.8 mA h g−1 by a current of 0.1 A g−1 after 200 cycles, even holding to 338.4 mA h g−1 by a big current impact at 2 A g−1. It formed a metallurgical combination between the conductive network and the active material with multiple porous structures, which is helpful for the electrodes to provide high capacity and maintain structural stability during cycling. In addition, the average laser-sintering time of a single electrode was within 10 s, which is suitable for industrial mass production.

Fabrication and comprehensive structural and spectroscopic properties of Er:Y2O3 transparent ceramics

Transparent Er:Y2O3 ceramics with sub-micron grain size (<1 μm) were fabricated by using one-step vacuum sintering followed by hot isostatic pressing (HIPing) technique. The transmission of the undoped Y2O3 reaches 83%. The structural characteristics including the phonon energy were investigated through X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) analysis and scanning electron microscopy (SEM) measurement. The overall spectroscopic properties of transmission, fluorescence emission up to 3000 nm, lifetime, up-conversion luminescence, and refractive index were systematically studied for both 0.25 at% and 7.0 at% Er:Y2O3 ceramics with different thicknesses. The comparison of the spectra of the fluorescence emission and up-conversion luminescence under both 976 and 808 nm laser excitation was performed. The multiple high-energy-state transitional processes after the excited state absorption (ESA) processes involved in the up-conversion are discriminated between the multi-phonon non-radiative transitions and the radiative transitions according to the measured maximum phonon vibrational energy. The calculation was performed based on the Judd–Ofelt theory.

Fabrication of a permeable SnO2-Sb reactive anodic filter for high-efficiency electrochemical oxidation of antibiotics in wastewater.

Electrochemical oxidation (ECO) is an appealing technology for treating emerging organic pollutants in wastewater. However, the conventional flow-by ECO process is expensive with a low energy efficiency owing to the limitations of mass transport of contaminants to the limited surface area of the anode. In this study, a novel freestanding porous and permeable SnO2-Sb anode was fabricated by one-step sintering using micrometer-sized (NH4)2CO3 grains as the pore-forming agents. This permeable SnO2-Sb anode without Ti substrate functioned as a reactive anodic filter (RAF) in an ECO cell to treat wastewater containing ciprofloxacin (CIP). Forcing the wastewater through the porous RAF depth-wise improved the mass transport and vastly enlarged the electroactive surface area. Compared with the conventional flow-by configuration, the flow-through RAF exhibited a 12-fold increase in the mass transfer rate constant (60.7×10-6 m s-1) and a 5-fold increase in the CIP degradation rate constant (0.077min-1). At a cell potential of 4.0V, more than 92% of the CIP was degraded in a single-pass operation at a filtration flux of 54 L m-2 h-1 and a short retention time of 1.7min through the RAF. The robustness and stability of the RAF were demonstrated by its remarkable CIP degradation efficacy of 99% during 200h of operation. The mechanism of CIP degradation was examined using probe molecules and density functional theory calculations and found to be a combined effect of direct electron transfer and oxidation by generated radicals (OH and SO4-). The great potential of RAF in flow-through ECO was further validated by its effective removal (>92%) of various organic pollutants in actual municipal wastewater at a low energy consumption of 0.33 kWh m-3. The RAF-based ECO process thus provides an advanced environmental technology for the oxidation of toxic and recalcitrant organic pollutants in wastewater treatment.

Low-cost preparation and characterization of MgAl2O4 ceramics

Low-cost magnesium aluminate spinel ceramics were successfully synthesized from the minerals of magnesite(M) and bauxite(B) via the one-step sintering method. The effect of the ratio of bauxite to magnesite on the phase evolution, microstructure, as well as the mechanical properties was thoroughly investigated. The phase structural analysis indicated that Mg2+ or Al3+ ions were dissolved in the spinel lattice and formed Mg-rich/Al-rich spinel MgAl2O4 (MA). The microstructure analysis revealed that the liquid phase gradually appeared with the increment of bauxite content. Appropriate but not saturated cation solution had the effects of structural densification, homogenization of crystal grains, and the enhancement of strength. Ceramics with 1.31 bauxite to magnesite stoichimetric ratio exhibited the highest density of 3.43 g/cm3 and flexural strength of 93.5 MPa.

Binder-jetting additive manufacturing of Mg alloy densified by two-step sintering process

Difficult to effectively densify in a short time is an important issue that limits the application of magnesium (Mg) alloy fabricated by binder jetting additive manufacturing (AM) process. In this study, two-step sintering (TSS) process was utilized to improve the density of printed Mg alloy samples. Results show that the relative density, mechanical properties and corrosion resistance of the samples after different TSS process were dramatically improved in a short time. A suitable sintering temperature of first sintering step can rapidly increase the density of the samples in a short time. During the second step sintering process, little exceeding the liquidus temperature can further increase the density of the sample, but little lower than the liquidus temperature will lead to a sharp increase in grain size. The sample after sintering at 680 °C for 30 min then sintering at 610 °C for 6 h shows the highest relative density (0.995), the highest strength (394 MPa), the lowest corrosion rate (101 mm/year) and the smallest corrosion current density (60.4 μA/cm2). Compared with one-step sintering process, TTS process has higher sintering efficiency.

Constructing multi-type defects in In0.1Sb1.9Te3-(MgB2)x composites: Simultaneously enhancing the thermoelectric and mechanical properties

Nanostructure technologies promote Sb2Te3 based alloys as powerful candidates for mid-temperature thermoelectric materials, but their actual application needs further breakthrough on both zT value and mechanical properties. Here, we prepare nanostructured In0.1Sb1.9Te3 with MgB2 addition, obtaining a high zT value of 1.01 at 673 K with significantly enhanced mechanical strength. It is found that the magnesium dissolves into the matrix lattice, while the boron (B) mainly precipitates out or enters into the van der Waal gaps. Combining with the occurrence of twin and domain boundaries, multi-type defects are constructed to simultaneously adjust the carrier and phonon transport, leading to enhanced power factor and reduced lattice/bipolar thermal conductivity. Meanwhile, the B interstitials and B-rich nanoprecipitates could effectively strengthen the materials. Especially at 673 K, the compressive strength is increased over 600% from < 1 MPa for In0.1Sb1.9Te3 to 7.5 MPa for In0.1Sb1.9Te3-(MgB2)0.015, overcoming the high-temperature softening problem and guaranteeing the service stability. Ultimately, a segmented leg composing of this material and low-temperature ternary alloy (Bi, Sb)2Te3 is fabricated through simple one-step sintering with a high conversion of 7% under a temperature difference of 375 K.

Investigation on thermal conductivity and mechanical properties of Si3N4 ceramics via one-step sintering

High thermal conductivity Si3N4 ceramics were fabricated using a one-step method consisting of reaction-bonded Si3N4 (RBSN) and post-sintering. The influence of Si content on nitridation rate, β/(α+β) phase rate, thermal conductivity and mechanical properties was investigated in this work. It is of special interest to note that the thermal conductivity showed a tendency to increase first and then decrease with increasing Si content. This experimental result shows that the optimal thermal conductivity and fracture toughness were obtained to be 66 W (m K)-1 and 12.0 MPa m1/2, respectively. As a comparison, the nitridation rate and β/(α+β) phase rate in a static pressure nitriding system, i.e., 97% (MS10), 97% (MS15), 97% (MS20) and 8.3% (MS10), 8.3% (MS15), 8.9% (MS20), respectively, have obvious advantages over those in a flowing nitriding system, i.e., 91% (MS10), 91% (MS15), 93% (MS20) and 3.1% (MS10), 3.3% (MS15), 3.3% (MS20), respectively. Moreover, high lattice integrity of the β-Si3N4 phase was observed, which can effectively confine O atoms into the β-Si3N4 lattice using MgO as a sintering additive. This result indicates that one-step sintering can provide a new route to prepare Si3N4 ceramics with a good combination of thermal conductivity and mechanical properties.

Analysis of process parameters affecting the crystal orientation of Na+-β″-Al2O3 solid electrolyte in one-step synthesis cum sintering process

Na+-ion conducting Na+-β"-Al2O3 solid electrolyte has been prepared by a one-step synthesis cum sintering process as an alternative to the conventional solid-state reaction process, and the degree of crystal orientation was evaluated by the Lotgering factor with XRD Cu-Kα radiation source. In order to analyze the process parameters which affect the value of Lotgering factor, two experiments were carried out separately, i.e. on dwelling at various temperatures before sintering and different granule sizes selected in the press-forming. The Na+-β"-Al2O3 fabricated by one-step synthesis cum sintering process fully crystalized without any secondary phase. As a result, lower values of Lotgering factor indicated a higher ionic conductivity of Na+-β"-Al2O3. Among the processes including the heat treatment step, the smallest Lotgering factor was observed in the dwelling temperature of 1000 °C for 2 h. In terms of granule size, the smaller grain size showed the lower Lotgering factor.