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 (−∆SM)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.

Enhanced ZT of Ca3Co4O9 by nano-sized precursor

Ca3Co4O9 sample synthesized from nanometer of CaCO3 and Co2O3 sized precursor has been prepared by solid-state reaction and fast sintering by hot press method. The fast-sintering time can maintain the particle size of the nanometer. Their thermoelectric properties at high temperatures have been studied at 300 - 1000 K. When the usage of a nano-sized precursor leads to decrease electrical resistivity, increase power factor, and would lead to huge growth, respectively. The main effect is observed on thermal conductivity that is lower than sample synthesized with micrometer precursors powder from 0.67 W/mK which became 0.36 W/mK at 973 K. The best ZT value of Ca3Co4O9 reaches 0.51 at 973 K.

Microstructure of Ag Nano Paste Joint and Its Influence on Reliability

In this paper, the microstructure of Ag nano paste joint was investigated in pressure-less sintering conditions, and the influence of the microstructure on the joint’s reliability was studied. Firstly, silver nanoparticles (Ag NPs) were synthesized using the redox reaction method. To tightly stack the Ag NPs in nano paste, Ag NPs with sizes of 30~50 nm and submicron-sized Ag particles were mixed. It was found that increasing the sintering temperature or sintering time can reduce the porosity of the bonding layer and the interfacial crack simultaneously, resulting in higher shear strength. When sintering at a temperature of 250 °C, a complete bonding interface was formed, with a 0.68 μm interdiffusion layer. At a higher temperature (300 °C), the bonding interface reached 1.5 μm, providing 35.9 ± 1.7 MPa of shear strength. The reliability of the die attachment was analyzed under thermal shocking from −65 °C to 150 °C for 50 cycles. As the crack could quickly grow through the interfacial defects, the separation ratio was 85% and 67% when sintered at 150 °C and 200 °C, respectively. Because of the reliable bonding interface between the die and the substrate, the Ag nano paste joint formed a slight crack on the edge of the die when sintering at 250 °C. When the joint was sintered at 300 °C, the small voids became large voids, which featured lower resistance to crack growth. Thus, instead of further improved reliability, the separation ratio increased to 37%.

Influence of Sintering Time on Superconducting Properties of Bi, Pb-2223 Compound Doped with Indium

This work was performed to investigate the effect of sintering time on superconducting properties of Bi1.7In0.3Pb0.3Sr2Ca2Cu3O10+d samples prepared by solid state reaction method. The samples properties have been investigated structurally by X-ray diffraction and morphologically by scanning electron microscopy. Structural analysis showed that two superconducting phases coexist in the samples. High temperature Bi-2223 and low-temperature phase 2212 with orthorhombic structure for all samples. Four point probe method used to study the electrical properties of the samples and the results showed that increasing sintering time yields superconductor samples. The sintering time 140 h improves the microstructure of the superconductor and produces greater size platelets as well as leading to the highest TC value of 113 K and highest oxygen content value. Scanning electron microscopy shows increasing sintering time changed morphology of samples. Moreover plate grains of the high Bi-2223 phase appeared in most micrographs of the superconducting samples.

Enhanced electrocatalysts fabricated via quenched ultrafast sintering: physicochemical properties and water oxidation applications

The synthesis of transition metal oxides is typically time- and energy-consuming. Recently, fast sintering methods have demonstrated great potential to reduce ceramic sintering time and energy use, improving the commercial prospects of these materials. In this article, a quenched ultrafast high-temperature sintering (qUHS) technique is developed to sinter metastable brownmillerite SrCoO2.5 (SCO) in less than a minute. Surprisingly, SCO fabricated by qUHS shows higher activity for the oxygen evolution reaction (OER) compared to solid-state-reaction-synthesized SCO. Comparing samples produced by these two techniques, the increased OER performance of SCO qUHS is likely due to the synergistic combination of surface Co chemical state, higher mesoporosity and enhanced hydroxyl ion (OH-) adsorption. This work demonstrates the potential of qUHS for producing high-performance electrocatalysts and provides detailed insights into the impact of ultrafast sintering on the materials' physical properties and electrocatalytic activity.

Preparation and application of water-based nano-silver conductive ink in paper-based 3D printing

Purpose In flexible electronics applications, organic inks are mostly used for inkjet printing. Three-dimensional (3 D) printing technology has the advantages of low cost, high speed and good precision in modern electronic printing. The purpose of this study is to solve the high cost of traditional printing and the pollution emissions of organic ink. It is necessary to develop a water-based conductive ink that is easily degradable and can be 3 D printed. A nano-silver ink printed circuit pattern with high precision, high conductivity and good mechanical properties is a promising strategy. Design/methodology/approach The researched nano-silver conductive ink is mainly composed of silver nanoparticles and resin. The effect of adding methyl cellulose on the ink was also explored. A simple 3 D circuit pattern was printed on photographic paper. The line width, line length, line thickness and conductivity of the printed circuit were tested. The influence of sintering temperature and sintering time on pattern resistivity was studied. The relationship between circuit pattern bending performance and electrical conductivity is analyzed. Findings The experimental results show that the ink has the characteristics of low silver content and good environmental protection effect. The printing feasibility of 3 D printing circuit patterns on paper substrates was confirmed. The best printing temperature is 160°C–180°C, and the best sintering time is 30 min. The circuit pattern can be folded 120°, and the cycle is folded more than 60 times. The minimum resistivity of the circuit pattern is 6.07 µΩ·cm. Methyl cellulose can control the viscosity of the ink. The mechanical properties of the pattern have been improved. The printing method of 3 D printing can significantly reduce the sintering time and temperature of the conductive ink. These findings may provide innovation for the flexible electronics industry and pave the way for alternatives to cost-effective solutions. Originality/value In this study, direct ink writing technology was used to print circuit patterns on paper substrates. This process is simple and convenient and can control the thickness of the ink layer. The ink material is nonpolluting to the environment. Nano-silver ink has suitable viscosity and pH value. It can meet the requirements of pneumatic 3 D printers. The method has the characteristics of simple process, fast forming, low cost and high environmental friendliness.

ANALISIS PENGARUH VARIASI WAKTU SINTERING DAN KOMPOSISI TERHADAP SIFAT MEKANIK DAN MORFOLOGI KOMPOSIT ECENG GONDOK-PVC-LDPE

“Pemanfaatan material komposit pada saat ini semakin berkembang, seiring dengan meningkatnya penggunaan bahan tersebut yang semakin meluas mulai dari yang sederhana sampai sektor industri. Hal ini dikarenakan karakteristik material komposit mempunyai banyak kelebihan dibandingkan dengan jenis bahan lain yaitu ringan, kuat, tidak terpengaruh korosi dan mampu bersaing dengan logam, dengan tidak kehilangan karakteristik dan kekuatan mekanisnya. Penelitian ini bertujuan untuk mengetahui pengaruh variasi waktu sintering dan komposisi terhadap ketangguhan impak dan kekerasan komposit Eceng Gondok-PVC-LDPE. Bahan yang digunakan merupakan tanaman gulma dan limbah plastik. Proses pembuatan spesimen dilakukan dengan metode pressured sintering, yaitu dengan cara pembuatan serbuk, dan di screening 60 mesh. Selanjutnya serbuk di mixing dengan variasi komposisi perbandingan K1: EG 50%, PVC 10%, LDPE 40%; K2: EG 55%, PVC 10%, LDPE 35%; K3: EG 60%, PVC 10%, LDPE 30%; K4: EG 65%, PVC 10%, LDPE 25% dan K5: EG 70%, PVC 10%, LDPE 20% dan dikompaksi dengan tekanan 1,013 bar. Selanjutnya di sintering dengan temperatur 1800C. Pada penilitian ini variasi waktu sintering yaitu; 5 menit, 8 menit, 10 menit, 13 menit dan 15 menit. Sifat mekanik dilihat dari nilai kekerasan dan impak dengan menggunakan standar ISO 2039-1:2001, ISO 179-1:2010. Selain itu menganalisis morfologi dengan Scanning Electron Microscope (SEM). Pengujian untuk sifat kimia dilihat dengan analisis morfologi SEM. Berdasarkan hasil pengujian sifat mekanik didapatkan nilai kekerasan tertinggi dimiliki oleh komposit K2 sebesar 22.30 MPa dan 2.1 kJ/m2 untuk nilai impak.” Kata kunci: eceng gondok, komposit, LDPE, pressured sintering, PVC. Abstract“The utilization of composite materials nowadays is currently growing, along with the increasing use of these materials, which are expanding ranging from the small scale to the industrial sector. This is because the characteristics of composite materials have many advantages compared to other types of materials i.e. light, strong, not affected by corrosion and able to compete with metals without losing their mechanical characteristics and strength. This research aims to determine the effect of variations in sintering time and it’s composition against impact toughness and hardness of the Water Hyacinth-PVC-LDPE composite. The materials used are weeds and plastic waste. The process of specimen fabrication was performed by using pressured sintering method, i.e. by making it into powder and were screening by using screen 60 mesh. Furthermore, the powder were mixed with the variation of the composition K1: EG 50%, PVC 10%, LDPE 40%; K2: EG 55%, PVC 10%, LDPE 35%; K3: EG 60%, PVC 10%, LDPE 30%; K4: EG 65%, PVC 10%, LDPE 25% dan K5: EG 70%, PVC 10%, LDPE 20% and compacted with a pressure of 1,1013 bar. After that is sintering with temperature 180oC. In this research the sintering time variations is 5 minute, 8 minute, 10 minute, 13 minute and 15 minute. Mechanical properties if were seen from the hardness and impact values by using a standard ISO 2039-1:2001, ISO 179-1:2010. In additions to analyze the morphology by using a Scanning Electron Microscope (SEM). Tests for chemical properties can be seen with the morphological analysis of SEM. Based on the testing results, the mechanical properties obtained the highest hardness value owned by a composite K2 by 22.30 MPa and 2.1 kJ/m2 for the value of the impact.” Kata kunci:water hyacinth, composite, LDPE, pressured sintering, PVC.

Analysis of the Electroconsolidation Process of Fine-Dispersed Structures Out of Hot Pressed Al2O3–WC Nanopowders

Fabrication of alumina–tungsten carbide nanocomposite was investigated. Characteristics of the densification and sintering were analyzed considering both the nano-size particle starting powders and the processing stages. Different heating rates were generated during densification and consolidation with a maximal load was applied only after a temperature of 1000 °C was reached. Due to the varying dominance of different physical processes affecting the grains, appropriate heating rates and pressure at different stages ensured that a structure with submicron grains was obtained. With directly applied alternating current, it was found that the proportion Al2O3 (50 wt.%)–WC provided the highest fracture toughness, and a sintering temperature above 1600 °C was found to be disadvantageous. High heating rates and a short sintering time enabled the process to be completed in 12 min, saving energy and time.