Traditional Sintering Process Research Articles

The synergistic effect of Zn2+ doping and NaF interfacial melting aid increases the ionic conductivity of Na3Zr2Si2.2P0.8O12

All-solid-state sodium batteries, renowned for their leak-proof nature and enhanced safety profile, have become a pivotal focus of research. Their viability hinges on the development of robust solid electrolyte materials. Among these, Na3Zr2Si2PO12 (NZSP) stands out as a particularly promising candidate. However, the practical utility of NZSP has been limited by its relatively modest room temperature conductivity. This paper introduces a novel modification strategy aimed at significantly enhancing room temperature conductivity of NZSP. In the series of experiments, NSZP was synthesized by traditional sintering process with Zn2+ doping and NaF additives. Through the substitution of Zr4+ ions with Zn2+ ions, this innovative approach not only raises the sodium ion concentration but also expands the bottleneck regions within the Na ion transport pathways. This augmentation ultimately translates into heightened grain conductivity. Additionally, the incorporation of NaF during the sintering process induces crystal growth in NZSP, thereby reducing grain boundary concentration and further amplifying grain conductivity's contribution to the overall ionic conductivity. Employing conventional sintering techniques, we successfully synthesized Na3.3Zr1.95Zn0.05Si2.2P0.8O12-0.25NaF (−0.25 NaF indicates that 0.25 mol NaF was added during sintering) electrolyte samples, which demonstrated an impressive high room temperature conductivity of 2.2 × 10−3 S cm−1. This value surpasses the ionic conductivity of undoped NZSP electrolytes by approximately an order of magnitude. Moreover, the Na3.3Zr1.95Zn0.05Si2.2P0.8O12-0.25NaF electrolyte exhibits a remarkable electrochemical window extending up to 4.9 V, accompanied by exceptional cycling stability. These properties render it an ideal candidate for a diverse array of cathode materials.

Infrared Radiation-Assisted Non-Pressure Sintering of Micron-Sized Silver for Power Electronic Packaging

In recent years, silver sintering has gained increasing attention in high-power density electronic packaging due to its characteristics such as a high melting point and excellent thermal and electrical conductivity. Micron-sized silver sintering offers a lower cost, but requires a longer processing time and additional pressure, which constrains its application. This paper presents a low-cost sintering process using infrared radiation (IR) as a heat source. By leveraging the unique properties of IR, the process achieves selective heating. The thermal energy can be mainly absorbed by the specific areas requiring sintering. This innovative approach eliminates the need for external pressure during the sintering process. This feature not only simplifies the overall process but also reduces the processing time required for sintering. The silver joints obtained from IR sintering process for 45 min achieved an average chip shear strength of 38 MPa at a temperature of 225 °C, which is higher than the strength of silver joints obtained from a traditional sintering process for 2 h. Additionally, the IR-sintered silver joints have a resistivity of 9.83 × 10−5 Ω·cm and scanning electron microscope (SEM) images of the joints reveal that the sintered joints obtained through the IR sintering process exhibit less porosity compared to joints obtained through a traditional sintering process. The porosity of the IR silver joints at 225 °C is 6.4% and does not change even after 3000 cycles of thermal shock testing, showing outstanding reliability. A GaN power device using IR silver joint also performed better in thermal and electrical performance testing, showing promising potential for the application of micro-silver paste in power electronic devices.

Co-sintering characteristics of W-Re pre-alloyed powder and Ni, Fe

Tungsten (W) heavy alloys (WHAs) have unique mechanical properties and are widely used in the national defence and military industries. Adding Re to WHAs can produce a good “Re effect” and improve their performance. However, the solid solubility of Re in W particles was limited in traditional sintering processes, which limited its application. This study prepared W-Re solid solution powder by pre-alloying (mechanical ball milling) and W-Re-Ni-Fe alloy with an ultimate tensile strength of 1.05 GPa by co-sintering W-Re solid solution powder with Ni and Fe powders. At the same time, the diffusion path of the Re element in WHAs and its influence on the properties of W particles and matrix phase were determined. The addition of Re can improve the strength and hardness of the alloys but hinder the dissolution and precipitation process of W in the matrix phase, weakening the W-matrix interface, and the ductility of the alloy ultimately decreases. Therefore, it is expected to enhance the interdiffusion reaction between W particles and the matrix phase by regulating the composition of the matrix phase, thereby achieving a synergistic improvement in the strength and toughness of WHAs.

Preparation and electrochemical properties of a ceramic solid electrolyte with high ionic conductivity, Li1.3Al0.3Ti1.7(PO4)3

The emergence of lithium-ion solid electrolytes greatly increases the safety risk of liquid electrolytes. Among the many solid electrolytes, aluminum-doped Li1.3Al0.3Ti1.7(PO4)3(LATP) has become a research hotspot due to its high ionic conductivity and good air stability. However, the traditional high-temperature sintering process has the problems of lithium volatilization and secondary phase formation. Therefore, it is very difficult to prepare high-quality LATP solid electrolytes. The X-ray diffraction pattern and analysis showed that the LATP samples prepared in this paper showed rhombohedral structure and could be indexed by the R3c space group, and a new method of excess lithium compensation sintering was proposed, in which lithium compensation (LiNO3) could well reduce the impact of lithium volatilization. It can be used as a sintering additive to promote the sintering densification of LATP. In this paper, the optimal sample for sintering at 900°C was determined by measuring the microstructure and electrochemical properties of the electrolyte, and lithium doping was studied. The LATP solid electrolyte with 10 wt% lithium doped has a conductivity of 7.2× 10−4 S/cm and a low activation energy (0.278 eV). Its mechanical properties (elastic modulus and hardness) are the best, which are 103.024 GPa and 8.053 GPa, respectively, and the value of its elastic modulus is much greater than that of lithium metal shear modulus of 4.25 GPa, which can effectively inhibit the growth of lithium dendrites. And the magnitude of the grain boundary conductivity and particle size of the lithium-doped sample correspond to the dielectric constant results.

Development of Cycloid-Shaped Roll Charging Chute for Sintering Process for Energy Decarbonization and Productivity Improvement in Steel Plants

The global steel industry is rapidly transitioning towards energy decarbonization to address the climate crisis. Sintering is one of the main sources of greenhouse gas emissions from steel mills. Traditional sintering processes use straight inclined chutes to feed raw materials into the sinter machine. However, this design suffers from insufficient horizontal momentum, resulting in poor segregation of the layered materials. This study proposes an improved charging chute design profile that uses a cycloid curve and rolls to enhance segregation, thus reducing coal consumption and increasing productivity. To achieve this, we first modeled a charging chute using the cycloid curve. Secondly, building upon the cycloid concept, we created a roll-type chute by strategically placing rollers along the cycloid trajectory. Finally, the cycloid roll-type charging chute, integrating the cycloid trajectory with the roll-shaped charging chute, was simulated. Pilot tests comparing the cycloid roll-type and straight chute models demonstrated a significant increase in dispersion for the cycloid roll-type design, with a 65% improvement in the Strand-ward segregation (Sw) index compared to the straight chute. Furthermore, actual filed implementation in a sintering process achieved a 2.9% increase in operational productivity and a 6% reduction in fuel consumption. This study is significant not only for proposing an optimal chute design, but also for successfully implementing it in a full-scale steel mill, contributing to a reduction in fuel consumption and carbon reduction in steel mills.

Near-room-temperature fabrication of dense BaZrO3 ceramic via acid–base chemical densification

A novel process to fabricate dense ceramic bulk of BaZrO3 perovskite oxide without firing was established. Although, BaZrO3 conventionally requires a sintering temperature of 1600 °C for densification, a relative density of 90% can be obtained via an acid-base chemical densification (ABCD) at 150 °C. In this process, a dense ceramic bulk body is fabricated through the acid–base reaction between the precursor compact and alkaline solution at temperatures ranging from room temperature to 150 °C. ABCD can reduce the energy consumption and CO2 emission comparing to traditional sintering processes due to its low process temperature. The microstructure of BaZrO3 prepared by this process is unique, consisting of aligned nanocrystals, as indicated by transmission electron microscopy and electron backscattered diffraction analysis. This novel process is a promising technique for fabricating next-generation ceramic devices.

The mechanism of NOx removal in the sintering process based on source reduction of carbon emissions.

This study systematically investigates the mechanism of NOx emissions during the sintering process, with a focus on the utilization of biochar as an auxiliary fuel to replace a portion of the coke traditionally used in iron ore sintering. The research involved the simulation of sintering raw material ratios using iron ore, biochar, and coke powder. Substitution levels of biochar for coke were set at 0%, 20%, 40%, 50%, 60%, 80%, and 100%. NOx emissions during the sintering process were monitored using a sintering flue gas detection system. Simultaneously, a comprehensive analysis of the sintered ore was conducted with the aim of producing samples that meet sintered ore requirements while reducing NOx emissions. Experimental results revealed that when biomass charcoal substitution for coke reached 50%, the lowest NO emissions were observed during the sintering process, with a reduction of over 90% in accumulated NO emissions in the exhaust gas. In this process, due to the participation of biochar, CO2 emissions were reduced by approximately 50% compared to traditional sintering processes. The study also analyzed the physicochemical properties of the sintered ore using methods such as XRD, Raman, FTIR, and Vickers hardness testing. The results indicated that the hardness fluctuated within the range of 610 to 710N for sintered products with different levels of biochar substitution, and there were minimal changes in Fe element content and crystal phase transformations.

Bone-inspired hydroxyapatite nanowire-based bioceramics with superior mechanical performance

The fabrication of hydroxyapatite (HAP)-based bioceramics with similar mechanical performance to bone by traditional sintering process is still challenge. In bone tissues, HAP mineralized collagen fibrils and fiber-oriented microstructure play key roles in superior mechanical performance of bone. Inspired by the fiber-oriented microstructure and biomineralization process of bone, the mineralized HAP-based bioceramics (M-HAP) are successfully fabricated via directional assembly and biomimetic mineralization strategies based on ultralong HAP nanowires. The M-HAP bioceramics show comparable mechanical performance to human cortical bone in terms of flexural strength, tensile strength, Young's modulus and hardness, which could overcome the issue of mismatched mechanical properties between traditional HAP implants and host bone. In addition, the M-HAP bioceramics also exhibit good cytocompatibility in vitro and no obvious inflammatory response after implantation in vivo. Such bone-inspired bioceramics with both high mechanical property and good biocompatibility have great potential in the field of bone regeneration.

Flash sintering improves magnetic properties of spinel zinc ferrite

We report on a simple protocol for one step synthesis and sintering of single-phase magnetic spinel ZnFe2O4 zinc ferrite (ZFO) using an electric field assisted sintering. The resultant materials show improved saturation magnetization and higher coercivity compared to conventionally sintered ferrite. The changes in properties have been attributed to generation of non-thermal lattice defects when processed under electric field. Instead of using the high temperatures (>1000 °C) and extended dwell periods (> 4 h) required by the traditional sintering processes, this method permits sintering of ZFO at a furnace temperature of only 950 °C in just a minute by applying a minimal field of 25 Vcm−1. This magnetic material with decreased coercivity and increased saturation magnetization will improve the efficiency of solenoids, transformer/inductor cores, microwave devices and magnetic shields.

Luminescence properties of Ca2GdNbO6: Sm3+, Eu3+ red phosphors with high quantum yield and excellent thermal stability for WLEDs

A series of Ca2GdNbO6: xSm3+ (0.01 ≤ x ≤ 0.15) and Ca2GdNbO6: 0.03Sm3+, yEu3+ (0.05 ≤ y ≤ 0.3) phosphors were synthesized by the traditional solid-state sintering process. XRD and the corresponding refinement results indicate that both Sm3+ and Eu3+ ions are doped successfully into the lattice of Ca2GdNbO6. The micro-morphology shows that the elements of Ca2GdNbO6: 0.03Sm3+, 0.2Eu3+ phosphor are evenly distributed in the sample, and the particle size is about 2 μm. The optical properties and fluorescence lifetime of Ca2GdNbO6: 0.03Sm3+, Eu3+ phosphors were detailedly studied. The emission peak at 5D0→7F2 (614 nm) is the strongest and emits red light under 406 nm excitation. The increase of Eu3+ concentration causes the energy transfers from Sm3+ to Eu3+ ions, and the transfer efficiency reaches 28.6%. Ca2GdNbO6: 0.03Sm3+, 0.2Eu3+ phosphor has a quantum yield of about 82.7%, and thermal quenching activation energy is of 0.312 eV. The color coordinate (0.646, 0.352) of Ca2GdNbO6: 0.03Sm3+, 0.2Eu3+ phosphors is located in the red area. The LED device fabricated based on the above phosphor emit bright white light, and CCT = 5400 K, Ra = 92.8. The results present that Ca2GdNbO6: 0.03Sm3+, Eu3+ phosphors potentially find use in the future.

A review on the preparation and application of BN composite coatings

Hexagonal boron nitride (h-BN) is a kind of functional ceramic material with excellent physical and chemical properties. This paper analyzes it from the aspects of mechanical, thermal, electrical and wetting properties. However, the high melting point of hexagonal boron nitride makes it difficult to prepare coating materials by traditional sintering process. This paper summarizes several processes for preparing h-BN composite coatings. Then, several application forms of h-BN composite coatings are reviewed according to the characteristics of h-BN composite coatings, and the future application prospects of h-BN coatings are forecasted in view of the existing problems.

Study on the Structure and Properties of SrTiO3 Modified K0.5Na0.5NbO3 lead-Free Ceramics with a Sintering Aid of NiO

In this experiment, a new piezoelectric ceramic system (1-x)K0.5Na0.5NbO3-xSrTiO3−0.4%molNiO (abbreviated as KNNST) with high properties and density was obtained by using K0.5Na0.5NbO3 (abbreviated as KNN) as matrix, adding new component SrTiO3 and sintering aid NiO, and adopting traditional solid-state sintering process at lower sintering temperature. XRD, SEM and other modern test analysis show that when a small amount of sintering aid NiO is added, KNNST ceramic samples with SrTiO3 doping in the range of 0 ≤ x ≤ 0.08 can form a single perovskite structure without any impurity phase. When 0.02 < x < 0.06, KNNST ceramics exist a polymorphic phase boundary (PPB) between orthorhombic and tetragonal phases, and thus excellent properties were obtained when x = 0.04, they are respectively d 33 = 287pC/N, k p = 48%, ε r = 1216, tanδ = 2.2%, T C = 373°C, P r = 26.5 μC cm−2, E C = 2.06 kV mm−1. This shows that by introducing new component and adding sintering aid, a new phase boundary can be constructed, a new solid solution ceramic can be formed, and the compactness and electrical properties of the KNNST ceramics can be improved. This provides an effective way to improve the properties of KNN based piezoelectric ceramics, and also provides hope for practical applications.

A phase-field study of neck growth in electron beam powder bed fusion (EB-PBF) process of Ti6Al4V powders under different processing conditions

Traditional sintering processes are carried out to achieve complete material densification. In an electron beam powder bed fusion (EB-PBF) process, the same sintering mechanisms occur but only with the aim to form small connections between the particles (necks). A proper neck formation is central for the EB-PBF process because, among other effects, ensures the thermal stability of the process and helps to avoid smoke phenomena. This work presents a numerical study of neck formation under the EB-PBF processing conditions. A new type of modelling is introduced for the temperature sintering load and included in a phase-field model, which simulates the neck growth during the EB-PBF process of Ti6Al4V powders. The model was validated with an ad-hoc experiment, which provided a deviation with respect to the estimated neck diameter of about 9%. The deviation was investigated by reasonably varying the processing conditions. The results showed that the thermal history, the process time scale (including also the cooling phase), and the geometrical characteristics of the particles significantly affected the sintering rate and neck radius.

Toward high stability single crystal material by structural regulation with high and low temperature mixing sinter

Single-crystal cathode materials are a potential research focus for high-nickel ternary cathode materials owing to their high compaction density and good electrochemical stability. However, in the traditional sintering process, lithium is lost because of the long-time and higher-temperature sintering, which reduces the migration energy barrier of Ni2+ and increases the degree of mixing of Li+ and Ni2+. Herein, for the first time, a method for short-time high-temperature sintering combined with low-temperature heat preservation is proposed to prepare LiNi0.6Co0.6Mn0.2O2 (NCM622) single crystal materials in a mixed molten salt system of LiOH and Li2CO3. In analyses of morphology, structure and electrochemical properties, the prepared NCM622 exhibits excellent cycling stability owing to an ordered layered structure and low cation mixing degree. The single-crystal material shows an excellent capacity retention of 93.19% (150.49–140.24mAh·g−1) after 100 cycles at 1 C in the voltage range of 2.8–4.3 V. The single crystal particles exhibit reliable stability after long cycling without microcracks in the cycled particles. Furthermore, the preparation cost could be significantly reduced with a closed loop of the flux salt. The short-time high-temperature combined with the low-temperature holding sintering method may provide an effective strategy for the synthesis of other single-crystal materials with excellent electrochemical properties.

Manufacture aluminum alloy tube from powder with a single-step extrusion via ShAPE

The mechanical performance of aluminum (Al) in terms of strength, wear, and corrosion resistance, especially high-temperature strength, has been shown to improve with the addition of transition metal (TM) elements of Fe, Cr, and Ti. However, the feedstock of Al-TM alloy occurs as powders. Making extrudate from powders requires multiple procedures and consumes considerable energy. This study developed Shear Assisted Processing and Extrusion (ShAPE) as a single-step process that manufactures tubes directly from Al-TM powders obtained via gas atomization. Meter-long Al-TM alloy tubes are extruded from powders with different processing conditions. The average density of ShAPE tubes is 2.94 kg/cm3, equal to or higher than parts fabricated by hot extrusion and sintering. The powder-to-tube fabrication process was revealed and discussed by examining the microstructural evolution. The Vickers hardness of ShAPE tubes ranges from 110 to 140 HV through the wall thickness and at different extrusion speeds. The variation in hardness was correlated with the extent of refinement of intermetallics and attributed to the shear deformation per unit extrusion length. Energy cost analysis shows that ShAPE saves about 60 % energy compared to the traditional sintering and extrusion processes. Results indicate ShAPE is a low-cost, high-efficiency manufacturing process for producing tubes from metallic powders.

Densification and strengthening mechanism in spark plasma sintering of B4C–VB2 ceramics via carbide boronizing

To reduce the negative effects of the long-time and B2O3 phase on the traditional sintering process for B4C-based composite ceramics, nearly fully dense B4C–VB2 composite ceramics were prepared by reactive spark plasma sintering (SPS) technology at 2000 °C with B and V8C7 powders as raw materials in this paper. The effects of the degassing time during SPS on the microstructure and the mechanical properties of the final products were investigated in detail. The results revealed that the proper degassing time was beneficial for the vent of B2O3 during the sintering process, which refined the grain size, promoted densification and improved the mechanical properties of the composite ceramic. However, the redundant degassing time increased the holding time at high temperature, resulting in abnormal grain growth and mechanical performance deterioration. In the present work, the optimal degassing time was 6 min, and the final product prepared under the above conditions exhibited excellent comprehensive performance with a relative density of 99.2%, Vickers hardness of 31.2 GPa, bending strength of 654 MPa and fracture toughness of 5.7 MPa m1/2. In addition, the strengthening and toughening mechanisms of the products were mainly attributed to the residual thermal stresses and bridging structure caused by the fine B4C and VB2 grains distributed uniformly.

Pore morphology design and grinding performance evaluation of porous grinding wheel made by additive manufacturing

Open porous structure is of great importance for metal-bonded grinding wheel but hard to realize with traditional hot pressing and sintering process. In this article, a novel design and fabrication method of porous metal-bonded grinding wheel is proposed based on triply periodic minimal surfaces and additive manufacturing. The control method of pore morphology is specifically studied in terms of pore connectivity constraint condition and parametric control equation. With control equation, the porosity, equivalent aperture, relative density, specific surface area and pore connectivity of porous structure can be accurately controlled and predicted under given design parameters. With additive manufacturing, porous metal-bonded grinding wheel with well-formed pores and firmly-embedded abrasives can be realized. The grinding test results indicate that the novel porous metal-bonded grinding wheel behaves better than electroplated wheel in terms of grinding force and specific grinding energy. The proposed method can realize the design and fabrication of metal-bonded grinding wheel with large porosity and open porous structure, so as to effectively improve the problems such as surface blockage and grinding burn.

A simple preparation process of lithium titanium aluminum phosphate solid electrolyte with ultra-high ionic conductivity

Lithium Aluminum Titanium Phosphate (LATP) solid electrolyte has many advantages such as high ionic conductivity, good air stability, and low raw material cost, which has great potential for industrial development. However, the existing preparation process still can not meet the needs of industrialization well. We propose a novel simple solid-liquid mixing process to prepare LATP. By optimizing the reactants and adopting the "vacuum self-mixing" process, in the case of removing the mixing step, a high-performance LATP solid electrolyte with high purity is also obtained, the total ionic conductivity of the which at room temperature is as high as 1.7 ​mS/cm, the bulk conductivity is as high as 7.2 ​mS/cm, both reaching the highest value in published literature, the obtained sheet density is also as high as 99.4%. The process also avoids the problems of material sticking to the pot and low sintering yield in the traditional sintering process, which will provide a more convenient technological route for the industrialization of LATP solid electrolyte.

Efficient double-layer sintering of titanomagnetite concentrate

The traditional titanomagnetite sintering process consumes high fuel and produces weak-strength sinter. In this study, double-layer sintering was used to solve above problems. The theoretical analysis and sintering pot test results showed that sintering of feed bed constituted by two different-basicity layers could improve mineralization and permeability. By using the double layer structure of sintering bed and controlling the basicities of lower and upper layer (2.5 and 1.5, respectively), the yield, productivity, and reduction disintegration index (RDI+3.15) were 67.32%, 1.65 t m2 h−1, 49.68% respectively, which were improved 33.12%, 1.74%, and 9.27%, respectively than those obtained by the traditional sintering process. Meanwhile, 1.69 kg t−1 of solid fuel consumption and nearly 10% of electricity and gas consumption for sintering were saved. It was demonstrated that using different basicities for upper and lower layer of sintering bed would promote formation of silica-ferrite of calcium and aluminum (SFCA) with simultaneous reduction of perovskite, improving the sinter quality.

Effect of compressive stress on power loss of Mn–Zn ferrite for high-frequency applications

In this work, the low-power-loss Mn–Zn ferrite was prepared by the traditional ceramic sintering process. This sample shows the good wide-temperature stability of power loss (Pcv). In the whole measurement temperature range of 25 - 120 °C, Pcvs maintain less than 100, 682, and 1455 kW/m3 at 100 kHz/100 mT, 500 kHz/100 mT and 800 kHz/100 mT, respectively. The effect of uniaxial compressive stress on power loss at 100, 500 and 800 kHz was investigated. Stress has greater impact on Pcv at high frequencies and Pcv increases remarkably. To clarify the mechanism of stress on power loss, Pcv was divided into three parts including hysteresis loss (Phv), eddy current loss (Pev) and residual loss (Prv), and the effect of stress on each part of loss was discussed. At the low frequency of 100 kHz, Pcv is mainly contributed by Phv. The applied stress leads the local anisotropic stress and makes domain wall displacement more difficult, which is the reason of the increase of Phv. When frequency increases to 500 and 800 kHz, Pev and Prv become more important. The compressive stress is in favour of electron transfer between Fe3+ and Fe2+ in grains and electron tunnelling effect at grain boundaries, which leads to the decrease of resistivity. This is the origin of enhanced Pev under the compressive stress. The enhanced Prv is related to the enhanced electronic diffusion under the compressive stress. The clarification of the mechanism of stress on power loss is beneficial to develop new soft ferrite materials with low stress sensitivity for high-frequency applications.