Low Sintering Temperature Research Articles

Low temperature sintering and enhanced piezoelectric properties of BiFeO3–BaTiO3 ceramics by homogeneous calcination

The effect of calcination process on a phase evolution, a microstructure development and the piezoelectric properties were investigated in 0.75BiFeO3-0.25BaTiO3 (0.75BF-0.25BT) ceramics. At the relatively low calcination temperatures of 600 °C–650 °C, a Bi25FeO40 impurity phase was formed in addition to some unreacted raw materials and a perovskite phase. As the calcination temperature increased to the range of 700–900 °C, other intermediate phase BaBi4Ti4O15 was formed concurrently with small amounts of unreacted BaCO3 and perovskite matrix phase. At 950 °C a pure single perovskite phase of 0.75BF-0.25BT solid solution was observed. The sintered samples produced by using the raw powder calcined at a relatively low temperature of 600–900 °C showed a large fraction of pseudo-cubic relaxor phase (0.54–0.71 mass fraction) with the rest of a rhombohedral ferroelectric phase. They showed poor piezoelectric properties at sintering temperature below 1000 °C due to the nonuniform compositional distribution of the calcined powder. The homogeneous calcination at 950 °C for 2 h reduced greatly the optimum sintering temperature and significantly enhanced piezoelectric properties in the BF-BT ceramics. High Curie temperature as well as high piezoelectric properties were obtained at the sintering temperature as low as 920 °C: kp = 0.361, d33 = 123 pC/N and TC = 653 °C in the 0.75BF-0.25BT ceramics and kp = 0.337, d33 = 183 pC/N and TC = 525 °C in the 0.7BF-0.3BT ceramics. This low temperature sintering of the BF-BT ceramics by a homogeneous calcination could be applied to the fabrication of the lead-free multi-layer piezoelectric devices with inexpensive internal electrodes.

Preparation and electrochemical properties of Li6La3Zr0.7Ti0.3Ta0.5Sb0.5O12 high-entropy Li-garnet solid electrolyte

Garnet-type solid electrolytes stand out as promising Li-ion conductors for the next-generation batteries. It has been demonstrated that the inherent properties of garnets can be tailored by introducing various dopants into their crystal structures. Recently, there has been a growing interest in the concept of high entropy stabilization for materials design. In this study, we synthesized high-entropy garnets denoted as Li6La3Zr0.7Ti0.3Ta0.5Sb0.5O12 (LLZTTSO), wherein Ti, Sb, and Ta occupy the Zr site. The formation of the cubic garnet phase in LLZTTSO was confirmed through X-ray diffraction (XRD), and the resulting lattice parameter agreed with predictions made using computational methods. Despite the substantial porosity (relative density 80.6%) attributed to the low sintering temperature, LLZTTSO exhibits a bulk ionic conductivity of 0.099 mS cm−1 at 25°C, and a total ionic conductivity of 0.088 mS cm−1, accompanied by an activation energy of 0.497 eV. Furthermore, LLZTTSO demonstrates a critical current density of 0.275 mA cm−2 at 25°C, showcasing its potential even without any interfacial modification.

Accelerating densification of the terminal electrode with improved adhesion by sodium ions doping for MLCC copper paste

Glass frits effectively facilitate the sintering densification to produce high-density terminal electrodes, crucial for achieving high reliability of MLCC (Multilayer Ceramic Capacitors) devices. However, manufacturing terminal electrodes with high density and strong adhesion under low-temperature sintering condition still has enormous challenges. Herein, Na2O–BaO–ZnO–B2O3–SiO2 glass has been fabricated for low temperature sintering copper paste. We demonstrate that the densification degree and adhesion strength of the terminal electrode can be notably optimized by adjusting the Na2O content in the glass frit. The doping of Na+ in glass effectively improves the wettability of the melt on the copper substrate and the surface tension of the glass melt, enhancing the capillary force in the liquid phase sintering process. The rate of electrode densification is accelerated by the increase in capillary force, thus reducing the sheet resistance of copper film from 4.52 to 4.30 mΩ/□. Furthermore, with the increase in the Na+ content, the work of adhesion between glass and ceramic gradually increases, which effectively enhances the shear strength of the electrode from 19.66 MPa to 29.55 MPa. Our work provides novel insights for the design of glass compositions in the field of terminal paste.

Phase composition, microstructure, and microwave dielectric properties of Mg1-x(Li0.5Y0.5)xMoxW1-xO4 ceramics with low sintering temperatures

Abstract Generally, doping is an effective method to improve the microwave dielectric properties and regulate the sintering behavior of microwave dielectric ceramics. In this study, the temperature-stable Mg1- x (Li0.5Y0.5) x Mo x W1- x O4 ceramics were prepared by a conventional solid-state reaction method, and the effects of doping on the phase, density, microstructure, and microwave dielectric properties of the samples were investigated. The presence of secondary phase Li0.5Y0.5MoO4 successfully improved the sintering behavior of the sample, achieving densification at low sintering temperatures, while effectively adjusting the temperature coefficient of resonant frequency and improving the temperature stability of the sample. Notably, when sintered at 875°C, Mg1- x (Li0.5Y0.5) x Mo x W1- x O4 ceramics exhibited satisfactory microwave dielectric properties: ε r = 14.83, Q×f = 19, 887 GHz, and τ f = 4.11 ppm/ºC, making the ceramics as candidates for LTCC technology.

Direct Writing Highly Conductive Silver Pattern on Flexible Substrate Based on Particle-Free and Ionic Liquid-Assisted Ink

Abstract Particle-free silver inks have the advantage of low sintering temperature, high stability, and easy synthesis over traditional nanoparticle-based silver inks, which have been widely applied in the printing electronic industry. In this paper, we develop a novel particle-free and ionic liquid-assisted silver ink consisting of silver acetate and formic acid/iso-propanolamine liquid that can be used to print highly conductive silver patterns at low sintering temperatures. A variety of continuous and consistent silver circuits with a resistivity of 7.7 µΩ·cm can be printed by a dispenser machine, which is only 4.8 times bulk silver. Furthermore, the low-resistivity silver patterns can be also printed on the flexible polyimide foil, which maintains the stability of resistivity and mechanical properties after bending multiple times, demonstrating that our ionic liquid-assisted silver ink can be applied in flexible electronic devices. Besides, our particle-free silver ink can be utilized to write electric circuits directly with a ball-point pen.

Preparation of high-performance Bi-YG ferrite based on LTCC technology and theoretical analysis of its sintering mechanism

In the preparation process of Microwave Multi-Chip Module (MMCM), it is necessary to simultaneously sinter both microwave medium (ferrite) and silver electrodes. Hence, this necessitates keeping the sintering temperature below the melting point of silver (961 °C). An excessively low sintering temperature would significantly impair the electromagnetic properties of the ferrite material. To address this concern, this study synthesizes Bi-YIG (Y3-xBixFe5O12, x = 0–1.0) ferrites with optimized characteristics, including low ferromagnetic resonance line-width (ΔH) and high saturation magnetization (Ms), at 945 °C using Low Temperature Co-fired Ceramic (LTCC) technology. The mechanism of low-temperature liquid phase sintering, facilitated by a fluxing agent, was investigated using a theoretical model. The addition of Bi2O3 fluxing agent was found to reduce the reaction activation energy, disrupt the chemical reaction equilibrium, and promote low-temperature liquid phase sintering, thus lowering the critical sintering temperature below the melting point of silver. Furthermore, optimal bismuth content was identified to regulate the dynamic balance between grain growth and boundary diffusion, suppressing abnormal grain growth and enhancing the electromagnetic properties of the ferrite. This exploration, leveraging LTCC technology, may offer valuable insights for enhancing the overall performance of MMCMs.

Low-temperature sintering of ceramic bricks from clay, waste glass and sand

In the present work, bricks were made on a real 1:1 scale for the construction of housing. For the preparation of the mixtures, raw materials such as clay, sand and glass obtained from the recycling of brown beer containers were used, applying the method plastic molding for the preparation of the semi-products. It has been established that the addition of sand containing a small amount of montmorillonite to such clay enabled to realization of plastic molding. The incorporation of glass into the clay provided to substantially reduce the sintering time of the bricks up to 8h and to vary their strength properties. Sintering was carried out at 800°C in an air atmosphere. The results of X-ray diffraction (XRD), X-ray fluorescence (XRF) and field emission scanning electron microscopy (FESEM) and EDS microanalysis have shown that the raw materials and ceramic bricks contains quartz and feldspars. Low-temperature sintering has made it possible to obtain high-quality, high-strength building bricks in accordance with standards.

Effect of cell sintering temperature on the performance of non-noble metal loaded cerium oxide SOEC anodes

Abstract Introducing methane oxidation reaction into the anode of the high-temperature solid oxide electrolysis cell (SOEC) can reduce the power consumption for water electrolysis. Compared to the traditional conditions of methane oxidation, the methane oxidation catalyst sintered at the SOEC anode, which is closely related to the cell sintering process. This study uses non-noble metals as active sites for methane oxidation, zirconia, and samarium oxides doped ceria as catalyst support and oxygen ion conductors. The effects of anode sintering temperature on the electrochemical performance of SOEC assisted by methane oxidation were investigated. The results indicate that the high-temperature sintering process promotes the performance of the SOEC anode with Ni as the active site, while high temperature harms the performance of the Co-loaded anode. The sintering temperature exhibits a poor effect on the Fe-loaded anode. The Ni exhibits good enhancement of methane oxidation on reducing the electrolysis voltage of SOEC, while Co only exhibits methane oxidation assistance at low-temperature sintering. Differently, Fe has almost no obvious methane oxidation assistance for SOEC, which mainly represents good oxygen evolution performance.

Obtaining ultra-high hardness in spark plasma sintered Ge40As40Se20 bulk glass

In order to overcome the narrow glass-forming compositional range with traditional melt-quenching method, we here performed the mechanical milling and Spark Plasma Sintering technology to fabricate a high Ge content chalcogenide glass, the Ge40As40Se20 glass, which locates edge of the Ge-As-Se glass-forming domain. By using the optimal ball milling time of 50 h and sintering stress of 37.5 MPa, the large size Ge40As40Se20 bulk glasses were obtained, which possesses both a large Vickers hardness of 369 kgf/mm2 and a relative high infrared optical transmission of 43 % (@5 and 9 μm). Moreover, it was found there are pores in the sintered glasses more or less, and the pore size and number significantly affect the transmission, i.e., the optimal Ge40As40Se20 bulk glasses were demonstrated has the smallest and least pores via scanning electron microscope. The combination of mechanical milling and low-temperature sintering methods has been confirmed can be used to improve the glass formability and then obtain the high Ge content component with a potential high hardness glass to break through the limited mechanical property of chalcogenides.

Optimization of sintering process to fabricate high-density ultrafine-grained (HfNbTaTiZrW)C ceramic: A comparative study

The fabrication of senary carbide (HfNbTaTiZrW)C was achieved by carbothermal reduction process combined with three different kinds of sintering paths, including conventional single-step sintering (CS) and two kinds of two-step sintering (TSS-1 and TSS-2). It is revealed that the synthesized nanosized powders (∼102 nm) through carbothermal reduction exhibited excellent sintering capability to obtain a high density single-phase solid solution with homogeneous metal cation distributions at macro- and sub-micrometer scales, while atomic-level heterogeneity existed with Zr segregation. Compared to CS samples with bimodal microstructure, the application of two-step sintering significantly reduced the amounts of intergranular pores and (ZrHf)O2, accompanied with grain refinement. In particular, a well-designed TSS-2 route comprising short-term high-temperature followed by low-temperature sintering achieved ultrafine-grained bulk with grain size of 1.44±0.22 μm and excellent mechanical properties of elastic modulus of 480 MPa, microhardness of 23.4 GPa, and fracture toughness of 3.8 MPa·m1/2.

STUDYING THE THERMOCHEMICAL CHARACTERISTICS OF SINTERING WITH ALKALI CONCENTRATE FROM WASTE COPPER TAILINGS

A long period of deposit development leads to a reduction in the volume of balance reserves of ores, while the volume of accumulation of waste (tailings) from mining and processing production increases. In connection with this, an urgent problem is the processing of waste tailings, which can serve as an additional source of commercial products of non-ferrous metals. The set objectives can be achieved by implementing comprehensive extraction of valuable components, reducing fuel, and energy costs at the stage of low-temperature sintering to produce white soot (grade BS-100). In order to determine the amount of heat of chemical reactions during sintering of rough copper concentrate with sodium hydroxide, thermochemical calculations were carried out. For the research, we used rough copper concentrate with a copper content of 4.40% and silver of 77.03 g/t. An equation has been obtained for calculating the heat of chemical reactions of rough concentrate sintering. According to this equation, the greatest contribution to the heat release is provided by the iron content (60%), three times less and equally (19%) - copper and silicon and about 0.2% is absorbed by aluminum. The thermal effect of sintering will be -920.45 kW·h/t of concentrate. From the heat balance of sintering it follows that with an alkali consumption of up to 200% of the mass of the concentrate. The heat of chemical reactions will be sufficient for the autogeneity of the process. Research has been carried out on sintering the concentrate with alkali in the temperature range of 250-500 °C and obtaining white soot from a productive leaching solution with the extraction of 60% silicon. White soot (mSiO2·nH2O) was isolated by two-stage carbonization of a silicate solution with carbon dioxide in a recirculation system with further washing of the precipitate with a solution of sulfuric acid. For citation: Karimova L.M., Kairalapov Ye.T., Makascheva G.K., Kharchenko Ye.M. Studying the thermochemical characteristics of sintering with alkali concentrate from waste copper tailings. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2024. V. 67. N 7. P. 72-79. DOI: 10.6060/ivkkt.20246707.7004.

Quantifying Microstructure Features for High-Performance Solid Oxide Cells.

The drive for sustainable energy solutions has spurred interest in solid oxide fuel cells (SOFCs). This study investigates the impact of sintering temperature on SOFC anode microstructures using advanced 3D focused ion beam-scanning electron microscopy (FIB-SEM). The anode's ceramic-metal composition significantly influences electrochemical performance, making optimization crucial. Comparing cells sintered at different temperatures reveals that a lower sintering temperature enhances yttria-stabilized zirconia (YSZ) and nickel distribution, volume, and particle size, along with the triple-phase boundary (TPB) interface. Three-dimensional reconstructions illustrate that the cell sintered at a lower temperature exhibits a well-defined pore network, leading to increased TPB density. Hydrogen flow simulations demonstrate comparable permeability for both cells. Electrochemical characterization confirms the superior performance of the cell sintered at the lower temperature, displaying higher power density and lower total cell resistance. This FIB-SEM methodology provides precise insights into the microstructure-performance relationship, eliminating the need for hypothetical structures and enhancing our understanding of SOFC behavior under different fabrication conditions.

Synthesis of High-Performance YAG:Ce Phosphor Powder with Low Sintering Temperature and YAG:Ce-Doped Bi-B Glass by a One-Step Method

Synthesis of High-Performance YAG:Ce Phosphor Powder with Low Sintering Temperature and YAG:Ce-Doped Bi-B Glass by a One-Step Method

Microstructure and mechanical properties of TiB2-TiNw ceramic composite fabricated by SPS

A TiN whisker toughening TiB2 based ceramic composite was fabricated by spark plasma sintering (SPS). The influence of sintering temperature and holding time on the microstructure and mechanical properties of the composite was investigated. The results indicate that, at a sintering temperature of 1500 °C and a holding time of 9 min, the composite exhibits a relative density of 99.24 %, flexural strength of 906 MPa, fracture toughness of 8.6 MPa m1/2, and Vickers hardness of 22.3 GPa. The sintering aid composed of Ni and Mo within the composite significantly enhanced atomic diffusivity in TiB2 grains, promoting a balanced grain growth rate. SPS technology promoted the rapid formation of numerous necks between TiB2 grains in a very short duration. Concurrently, the pinning effect exerted by TiN whiskers effectively inhibited excessively rapid migration of grain boundaries. These factors ensured that the composite could achieve optimized microstructures and good mechanical properties at a low sintering temperature.

Novel high entropy alloy/NiAl2O4 photocatalysts for the degradation of tetracycline hydrochloride: Heterojunction construction, performance evaluation and mechanistic insights

Novel NiAl2O4 (NAO)/high entropy alloy (HEA) (Ti), NAO/HEA (Mn) and NAO/HEA (Mo) heterojunction photocatalysts with high photocatalytic activity for the degradation of tetracycline hydrochloride (TC) under simulated sunlight irradiation were synthesized by the polyacrylamide gel method combined with a low temperature sintering technique. The effects of environmental parameters, including drug concentration, catalyst content and pH value, on the photocatalytic activity of NAO/HEA photocatalysts were investigated in detail on the basis of the response surface methodology (RSM) and experimental results. The optimal initial TC concentration, catalyst content, and pH were 100 mg/L, 1 g/L, and 5, respectively. The photocatalytic activity of NAO/HEA photocatalyst (84.6 %) was significantly improved compared to the degradation percentage of HEA (Ti) photocatalyst (36.5 %). The roles of active free radicals including h+, •O2−, •OH and oxygen vacancy in photocatalysis were verified using multiple characterization methods. In-depth analysis was conducted on the degradation pathway of TC, the safety of degradation intermediates, and the photocatalytic mechanism of NAO/HEA (Ti) photocatalyst. The Z - scheme heterojunction can significantly improve the transport efficiency of photogenerated carriers and inhibit the recombination rate of electron hole pairs in the system, which provides a new idea for exploring the application of new HEA - based heterojunction photocatalysts in the field of photocatalysis.

Structural and dielectric properties of Eu3+,B3+ co-doped CoNb2O6 ceramic

The boron co-doped CoNb2O6:xEu3+, yB3+ (x=1, 3, 6, 9, 12 mol%, y=10 mol%) ceramics were obtained by the molten salt method, which has advantageous properties such as short reaction time, low sintering temperature, improved homogeneity, and crystallinity. The ceramic samples were examined by structural and dielectric analyses. In X-ray diffractions, the orthorhombic columbite type CoNb2O6 structure was obtained, and also a minor EuNbO4 phase was detected with increasing Eu3+ doping concentrations. Additionally, increasing Eu3+ concentration led to a slight increase in crystallite size, and two theta peak shifts occurred towards higher angles associated with shrinkage in the lattice or reduction in the lattice constant. In SEM examinations, a slight increase was observed in grain sizes from 1 to 9 mol% Eu3+ in the range of 1-30 m, while some decrease occurred in grain sizes at 12 mol%, and there was an evident increase in plate-shaped and elongated grains. The dielectric constant (ε') of the ceramic samples increased with increasing Eu3+ concentration and reached approximately 35 and 0.24 at 20 Hz for 9 mol% Eu3+, respectively. The increase in dielectric loss with increasing Eu3+ was associated with an increase in ionic conductivity, in which Eu3+ substitution does not suppress oxygen vacancies or make them more ordered.

The Effect of Sintering Temperature on the Densification and Magnetic Performance of NiCuZn-Ferrites (CuO: 0-6 wt.%).

This article reported on the effect of Cu-content and sintering temperature on the magnetic permeability and power losses of monolithic iron-deficient NiCuZn-ferrite components with low Cu-contents aimed to be used for power applications at frequencies up to 1 MHz. In particular NiαZnb1-xCuxFe1.9O4 ferrite compositions are investigated with a constant Ni/Zn atomic ratio a/b = 0.9 and 0 < x < 0.017. As found, the addition of Cu enables the achievement of good magnetic performance at lower sintering temperatures and, therefore, lower production cost. At all Cu-contents, the initial permeability as a function of the sintering temperature passes through a maximum above which structural deterioration due to asymmetric grain growth occurs. The temperature at which this maximum permeability occurs depends on the Cu content and coincides with the achievement of the maximum density of 5.1-5.2 g cm-3 (relative density ~97%). At Cu-contents x = 0.006-0.012 and sintering temperatures 1200-1100 °C power losses (tan(δ)/μ at 1 MHz, 25 °C) οf 50 × 10-6 could be achieved and initial permeabilities (10 kHz, 0.1 mT, 25 °C) of around 400 with very good frequency and temperature stability. At CuO content higher than 4 wt.% (i.e., x > 0.012) and sintering temperatures higher than 1150 °C, pronounced microstructural disturbances due to asymmetric grain growth result in low permeabilities and high losses. It is suggested that at low CuO contents and low sintering temperatures, the densification enhancement may not proceed through Cu-rich phase segregation but through the creation of oxygen vacancies.

Effects of TaCx on the microstructure and properties of WC composites

WC-5vol%TaCx (where x = 0.5, 0.7, 0.8 and 0.9) binderless cemented carbides with different carbon vacancy contents were prepared by spark plasma sintering (SPS) at a lower sintering temperature of 1800 °C. The phase evolution, microstructure and mechanical properties of these materials were investigated. The results show that the presence of WC, W2C and (Ta1-x, Wx)Cn phases in the sintered body. The formation of (Ta1-x, Wx)Cn solid solution is attributed to the dissolution of WC into TaCx, and the existence of vacancies promotes the atomic diffusion. (Ta1-x, Wx)Cn solid solution was uniformly distributed around the WC matrix, which inhibited the WC grain growth. In terms of fracture mode, the WC-5vol%TaCx composites exhibit a combination of intergranular and transgranular fracture, with crack deflection and bridging contributing to enhanced fracture toughness. Compared to other WC-TaCx composites with varying carbon vacancy content, the WC-5vol%TaC0.8 composite possesses the smallest average particle size and highest intrinsic hardness. Additionally, a semi-coherent interface is formed between (Ta1-x, Wx)Cn and WC, leading to improved mechanical properties such as highest hardness (24.4 GPa) and fracture toughness (8.5 MPa·m1/2). The WC-5vol%TaC0.8 composite, however, exhibits the lowest oxidation onset temperature attributed to its relatively smaller grain size. The introduction of carbon vacancies serves to facilitate atom diffusion and lower the densification temperature, while also functioning as a toughening agent.

Near-zero thermal expansion ZrW2O8/SiO2f wave-transparent composites: Interfacial anti-debonding structures based on polymeric films

The thermal stability of fiber-optic gyroscopes (FOGs) limits their application in harsh environments. This work utilized the unique water-retention properties of hyaluronic acid and the low-temperature cold sintering process combined to fabricate near-zero thermal expansion ZrW2O8/SiO2f composites with thermal resistance. Based on this novel process, the interface debonding of the composites is effectively suppressed and the mechanical and thermal properties of the composites are significantly improved (flexural strength increased by 69.47 %). Moreover, the interface anti-debonding structure reduces the interfacial polarization and reflection loss of the composites, and enhances the wave-transparent properties in the 2–18 GHz frequency range, with a minimum reflection loss of −0.21 dB. Furthermore, the interface anti-debonding structure of the composite provides creep resistance with enhanced sintering densities (increased by 13.61 %). Simultaneously, the composites achieve a controllable coefficient of thermal expansion (CTE) by regulating the liquid phase content and reach near-zero CTE (−0.246 × 10−6 °C−1 [30–300 °C]). Finally, finite element analysis and thermal shock experiments show that the anti-debonding interfacial structure has excellent thermal resistance, and the densest ZrW2O8/SiO2f composites exhibit the best thermal resistance due to minimal thermal strain during thermal shock, which is expected to meet the requirements of FOGs applications.

Advanced Hierarchical Biomorphous Silicon Carbide Monoliths

Porous silicon carbide (SiC) has attracted considerable attention in the field of cellular ceramics for a variety of applications such as catalyst supports, filters, or in the biomedical field due to its excellent structural properties, mechanical strength, and chemical stability. However, SiC has certain limitations due to high‐temperature profiles and costly manufacturing methods. Therefore, it is investigated that porous biomorphic silicon carbide monoliths using a powder blend of paper‐derived carbon fibers, phenolic resin, and silicon, resulting in comparatively low sintering temperatures (T = 1300 to 1550 °C) and good mechanical strength. This near‐net‐shape process uses low‐cost raw materials and enables the production of silicon carbides with high open porosity (P = 51.48% to 68.28%) and low shrinkage. The influence of different amounts of carbon sources (Cfibers and Cresin) on the mechanical (4‐point bending) and thermal properties (laser flash method) is investigated. In addition, to improve the pressure gradients, macrochannels with multiple layers of sacrificial polymer lattices are incorporated, resulting in hierarchical structures with high permeability. Thus, this advanced biomimetic approach offers great potential for structured cellular ceramics with tailored properties for biomedical, catalyst support, or nuclear fuel cladding materials.