•High performance of p-type BiSbTe based bimodal structures are fabricated.•bulk fracture displayed a dense & inhomogeneous diversification of mixed.grains.•high scattering rate of carriers/phonons ...increases α values & reduced κ values.•The ZTmax of 1.202, and ZTAvg of 1.14 are obtained for the composite.structures.
In this work, we fabricated bimodal structured high performance p-type BiSbTe alloys by combining coarse and sub-micron scale water atomized powder, followed by spark plasma sintering. The bulk fracture analysis revealed a dense and inhomogeneous distribution of mixed grains on the surface, while the texture analysis using EBSD revealed that the bulk specimens had a bimodal microstructure with random grain alignment due to the distribution of initial powder sizes. The coarse grain specimen exhibited high electrical conductivity of 1257 Ω−1cm−1 because of its high carrier mobility and carrier concentration. A high Seebeck coefficient (214 μV/K) and low thermal conductivity (0.95 W/mK) were observed for the bimodal structured specimens because scattering of carriers and phonons was higher compared with the coarse specimen. The maximum thermoelectric figure of merit, ZT of 1.2, and ZTAvg of 1.14 was achieved in the bimodal structure specimen, due to its high-power factor, and low thermal conductivity.
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Manufacturing an economically viable, efficient commercial thermoelectric (TE) module is essential for power generation and refrigeration. However, mediocre TE properties, lack of good mechanical ...stability of the material, and significant difficulties involved in the manufacturing of large-scale powder as well as bulk samples hinder the potential applications of the modules. Herein, an economically feasible single-step water atomization (WA) is employed to synthesize BST powder (2 kg) by Cu doping within a short time and consolidated into large-scale bulk samples (500 g) for the first time with a diameter of 50 mm and a thickness of about 40 mm using spark plasma sintering (SPS). The incorporation of Cu into BST greatly boosts the carrier concentration, leading to a significant increase in electrical conductivity, and inhibits the bipolar thermal conductivity by 73%. Synchronously, the lattice contribution (κL) is greatly reduced by the effective scattering of phonons by comprising fine-grain boundaries and point defects. Therefore, the peak ZT is shifted to the mid-temperature range and obtained a maximum of ∼1.31 at 425 K and a ZT ave of 1.24 from 300 to 500 K for the BSTCu0.05 sample, which are considerably greater than those of the bare BST sample. Moreover, the maximum compressive mechanical strength of large-size samples manufactured by the WA-SPS process is measured as 102 MPa, which is significantly higher than commercial zone melting samples. The thermoelectric module assembled with WA-SPS-synthesized BSTCu0.05 and commercial n-type BTS material manifests an outstanding cooling performance (−19.4 °C), and a maximum output power of 6.91 W is generated at ΔT ∼ 200 K. These results prove that the BSTCu x samples are eminently suitable for the fabrication of industrial thermoelectric modules.
It is difficult to synthesize ceramics with ultra-fine nanostructures because of inevitable grain growth during the sintering process. In this work, a novel technique, i.e. combustion synthesis ...assisted water atomization (CSAWA) method, was invented to synthesize supersaturated Al2O3/ZrO2 solid solution powders. The huge cooling rate supplied by CSAWA greatly improved the solubility of Al3+ in ZrO2 lattice. Subsequently, the synthesized powders underwent a solid solution precipitation process. The ultra-fine ZrO2 nanoparticles and Al2O3 matrix are precipitated from metastable phase, and the ZrO2 nanoparticles are uniformly dispersed in Al2O3 matrix. Simultaneously, the powders were densified and formed compact ZTA ceramics. Together with detailed microstructure, phase composition, interface characteristic, mechanical properties, as well as the toughening mechanisms were collaboratively outlined. CSAWA-SSPP not only produces impressive comprehensive properties, but also much lower costs and simpler process than currently methods, which opens up a new route to industrially produce nano-ZTA ceramics with high performance.
Water atomization of low alloyed steels is a very cost-effective way to produce metal powders for laser powder bed fusion. In this study, water atomized C35 steel powder is used to 3D-print samples ...with different powder bed fusion machines. The porosity of the samples was analyzed. Chemical analysis of printed samples and the powder feedstock was carried out. The gas atmosphere during laser powder bed fusion process was measured to investigate changes in carbon and oxygen content of the samples.
With optimal processing parameters, samples with a porosity of only 0.1% can be achieved. Gas atmosphere measurements have shown, that a reaction between carbon and oxygen in the melt pool occurs, leading to the formation of volatile carbon monoxide. By in-situ reduction of the oxygen and carbon level, negative effects caused by oxygen like balling of single melt tracks can be prevented to produce nearly dense parts.
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•Water-atomized C35 medium carbon steel powder was used for laser powder bed fusion•Samples with porosity of only 0.1% can be built using appropriate parameters•During LPBF, oxygen reacts with carbon inside of the melt pool•Volatile CO forms during LPBF to reduce carbon and oxygen content of samples•Excessive pore formation is prevented due to deoxidation during the process
Soft magnetic Fe81.3Si4B10P4Cu0.7 powders have been fabricated by using spinning-water atomization process (SWAP) under the water pressure of 17.5 MPa and gas pressure of 2 MPa. To clarify the ...amorphous forming ability, thermal stability, and the corresponding soft magnetism, the as-SWAPed powders have been sieved into 6 groups with different powder sizes from 0 – 150 μm. After the analysis of the amorphous and crystalline characteristics, the morphology, and soft magnetic properties of these 6 groups of as-SWAPed powders, it is concluded that the SWAPs with a high cooling rate of 105 K/s can improve the amorphous forming abilities of Fe81.3Si4B10P4Cu0.7 powders up to 53 μm, the saturated magnetic flux density as high as 170 – 173 emu/g and the thermal stabilities higher than 112.8 K. The characteristic parameters of as-SWAPed powders above mentioned are close to those of the counterpart rapid solidified ribbons. The surface oxide layers on as-SWAPed powders mainly consist of Fe2O3, and are 10 nm thick, much thicker than these counterpart ribbons, which might help to weaken the eddy effects accompanying with the slight decrease of the saturated magnetic flux density. Due to the higher cooling rates of SWAPs than gas atomization processes and the better spheroidization of powders for SWAPs than water atomization processes, it is key for NANOMET® family alloys to increase their amorphous forming abilities and better the soft magnetic performances.
In daycare centers, infants come in close contact with each other, and contact, droplet, and mouth-to-mouth infections may occur owing to sharing of toys. Additional effective disinfection methods ...should be considered aside from wiping with disinfectants—including alcohol or sodium hypochlorite solution—for environmental disinfection of daycare centers. We aimed to examine the usefulness of hypochlorous acid water atomization in the effective disinfection of the classroom environment and toys at a nursery school.
Environmental cultures of the nursery and toys were prepared to evaluate the species and bacterial load and to assess the contaminated areas. Staphylococcus aureus petri dishes were placed at high-frequency contact sites, and hypochlorous acid water was atomized to achieve a 0.03-ppm atmospheric chlorine concentration. After the atomization, the amount of S. aureus bacteria on the Petri dish and the changes in bacterial count isolated from the environment and toys were evaluated.
Hypochlorous acid water atomization was performed for 5 h to avoid condensation. After a 3-h atomization, ≥99.99% of S. aureus was eliminated on petri dishes; furthermore, a significant disinfection effect was observed on environmental bacteria at least 1 h after atomization. For rubber and textile toys, the significant disinfection effect was observed 1 h after atomization, and for plastic toys, the effect was observed 3 h after atomization.
Hypochlorous acid water atomization is a useful strategy to disinfect nursery school classrooms.
Silver powder was prepared through water atomization at 1280℃ under the nitrogen atmosphere. As-prepared silver powder consisted of various particles with morphologies such as spherical, irregular ...and coarse and had high crystallinity. Relationship between the volume average particle size (D50) of silver powder and production factors was investigated. In this work, the production factors such as atomization pressure, angle, nozzle diameter, suction amount of air and water temperature were selected to verify the influence on D50. It was found that D50 decreased with decreasing atomization pressure, angle, nozzle diameter and water temperature. When the atomization pressure was 100 MPa, the uniform water stream was disturbed and then D50 became higher. On the other hand, it was confirmed that D50 decreased with increasing suction amount under reduced pressure. Crystallite size and crystallinity of silver powder increased with decreasing water temperature.
Binder jet is one of the metal additive manufacturing methods. In this method, metal powder is used as a raw material, and a metal part is obtained by sintering a green body produced by jetting a ...binder on a metal powder bed leveled with a roller. Powders produced by the gas atomization method with an average particle size of around 10 μm is mainly used in the binder jetting method for metal additive manufacturing. The water atomization method used in this study has a higher production yield, so the cost of powder is lower than that of gas atomized powder. It is also possible to produce ultra-fine powders. However, there are few studies on the use of water-atomized powder in the binder jetting method. This paper aims to evaluate the basic characterization using water atomized powder for practical use in the binder jetting method. Three different water atomized powders with average particle sizes ranging from 4 μm to 10 μm and the gas atomized powder with an average particle size of 10 μm for comparison were used in the evaluation. The results confirmed that the flowability of water atomized powder decreased as the average particle size became smaller, and the flowability was lower than that of gas atomized powder due to differences in powder shape even at the same average particle size. The apparent density of the green body was found that tapped density of powder had a significant effect. The sintering process confirmed that the green body with smaller average particle size powder had higher sintering performance. This result is in line with the existing theory in the sintering technology using metal powders. It is clear that tap density and powder flowability are important for the practical use of water atomized powder in the binder jetting method.
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•We succeeded in the time-resolved high-speed visualization of water atomization process for molten metal particles.•Metal particles are produced by collision with fast water spray ...and vapor explosion.•The molten metal fragmentation proceeds with solidification.
Liquid metal fragmentation by impinging fast water spray, so called water atomization, is widely used to produce metal powders efficiently. In the present paper, we conduct the high-speed visualization experiments and theoretical modeling for elucidating the mechanism of fragmentation and solidification processes, which are essentially important to control the metal powder characters. We successfully visualize the detailed sequential events from the water spray ejection, freely dropped molten metal of 42Sn-58Bi, followed by their collision, metal fragmentation in liquid phase, and solidification, leading to revealing the fragmentation processes as the impact of water spray and the vapor explosion. Quantified metal particle size convinces that the water atomization simultaneously proceeds fragmentation of metal in liquid phase with solidification. The experimental results of size distribution and mean diameter well validate the proposed physically-consistent theoretical modeling for the prediction of particle size.
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