Fully 3D Printed Tin Selenide (SnSe) Thermoelectric Generators with Alternating n-Type and p-Type Legs

Tin selenide (SnSe) has attracted much attention in the field of thermoelectrics since the discovery of the record figure of merit (zT) of 2.6 ± 0.3. While there have been many publications on p-type SnSe, to manufacture efficient SnSe thermoelectric generators, ann-type is also required. Publications on n-type SnSe, however, are limited. This paper reports a pseudo-3D-printing technique to fabricate bulk n-type SnSe elements, by utilizing Bi as a dopant. Various Bi doping levels are investigated and characterized over a wide range of temperatures and through multiple thermal cycles. Stable n-type SnSe elements are then combined with printed p-type SnSe elements to fabricate a fully printed alternating n- and p-type thermoelectric generator, which is shown to produce 145 μW at 774 K

Rapid Printing of Pseudo-3D Printed SnSe Thermoelectric Generators Utilizing an Inorganic Binder

There has been much interest in tin selenide (SnSe) in the thermoelectric community since the discovery of the record zT in the material in 2014. Manufacturing techniques used to produce SnSe are largely energy-intensive (e.g., spark plasma sintering); however, recently, in previous work, SnSe has been shown to be produced via a low embodied energy printing technique, resulting in 3D samples with high zT values (up to 1.7). Due to the additive manufacturing technique, the manufacturing time required was substantial. In this work, 3D samples were printed using the inorganic binder sodium metasilicate and reusable molds. This facilitated a single-step printing process that substantially reduced the manufacturing time. The printed samples were thermally stable through multiple thermal cycles, and a peak zT of 0.751 at 823 K was observed with the optimum binder concentration. A proof-of-concept thermoelectric generator produced the highest power output of any reported printed Se-based TEG to date

Photocatalytic degradation of catechol in aqueous solutions: a comparison between UV/Fe2O3 and Fe2O3/sunlight processes

Phenols and phenolic compounds are widely used in everyday life and industry. Environmental stability, solubility in aqueous medium and high toxicity of these compounds are due to their high attention. The purpose of this study is the removal of catechol from wastewater based on the comparative use of two photocatalytic hematite/UV and hematite/sunlight processes. In this experimental laboratory study, the hematite nanoparticles are used with the separate application of UV and sunlight to reduce 10-50 mg L-1 concentration of catechol. The effect of parameters such as hematite concentration, reaction time and pH is studied on the catechol removal efficiency of both processes. The 6-W UV lamp as well as UV-A sunlight is used for radiation on the reactor contents. The remaining catechol concentration in the samples is measured by spectrophotometer within the wavelength of 600 nm. The best catechol removal efficiency by UV/Fe2O3 and Fe2O3/sunlight processes is 92.3% and 88% obtained at pH = 2, contact time of 60 min, hematite concentration of 4.0 g L-1 and catechol concentration of 50 mg L-1. UV/Fe2O3 process with 0.4 g L-1 Fe2O3 obtained COD removal of 71.3%, while sunlight/Fe2O3 process achieved lower COD removal of 50.9%. The results showed that UV/Fe2O3 and Fe2O3/sunlight photocatalytic processes have a good potential in catechol removal from aqueous solutions at pilot scale. However, statistical analysis of results did not show a significant difference between the processes. Therefore, it is proposed to study the performance of these processes as a clean and environmentally friendly practice in full scale with real wastewater

Microstructure and thermal properties of unalloyed tungsten deposited by wire + Arc Additive Manufacturing

Tungsten is considered as one of the most promising materials for nuclear fusion reactor chamber applications. Wire + Arc Additive Manufacturing has already demonstrated the ability to deposit defect-free large-scale tungsten structures, with considerable deposition rates. In this study, the microstructure of the as-deposited and heat-treated material has been characterised; it featured mainly large elongated grains for both conditions. The heat treatment at 1273 K for 6 h had a negligible effect on microstructure and on thermal diffusivity. Furthermore, the linear coefficient of thermal expansion was in the range of 4.5 × 10−6 μm m−1 K−1 to 6.8 × 10−6 μm m−1 K−1; the density of the deposit was as high as 99.4% of the theoretical tungsten density; the thermal diffusivity and the thermal conductivity were measured and calculated, respectively, and seen to decrease considerably in the temperature range between 300 K and 1300 K, for both testing conditions. These results showed that Wire + Arc Additive Manufacturing can be considered as a suitable technology for the production of tungsten components for the nuclear sector

The ability of Mg2Ge crystals to behave as ‘smart release’ inhibitors of the aqueous corrosion of Zn-Al-Mg alloys

In-situ scanning vibrating electrode technique and time-lapse microscopy are used to investigate the influence of germanium additions (0.19-1.8 wt.%) on the corrosion performance of zinc-aluminium-magnesium model alloys immersed in 0.17 mol.dm-3 NaCl. The addition of Ge results in the formation of Mg2Ge and a decrease in the fractional area of eutectic phase. A 58 % decrease in SVET derived mass loss is achieved at 1.8 wt.% Ge. It is proposed that Mg2Ge crystals are anodically attacked and behave as reservoirs of Mg2+ ions. Mg(OH)2 is precipitated and local electrolyte pH stabilises to values at which the zinc surface is passive

The Effect of Scandium Ternary Intergrain Precipitates in Al-Containing High-Entropy Alloys

We investigate the effect of alloying with scandium on microstructure, high-temperature phase stability, electron transport, and mechanical properties of the Al2CoCrFeNi, Al0.5CoCrCuFeNi, and AlCoCrCu0.5FeNi high-entropy alloys. Out of the three model alloys, Al2CoCrFeNi adopts a disordered CsCl structure type. Both of the six-component alloys contain a mixture of body-centered cubic (bcc) and face centered cubic (fcc) phases. The comparison between in situ high-temperature powder diffraction data and ex situ data from heat-treated samples highlights the presence of a reversible bcc to fcc transition. The precipitation of a MgZn2-type intermetallic phase along grain boundaries following scandium addition affects all systems differently, but especially enhances the properties of Al2CoCrFeNi. It causes grain refinement; hardness and electrical conductivity increases (up to 20% and 14% respectively) and affects the CsCl-type → fcc equilibrium by moving the transformation to sensibly higher temperatures. The maximum dimensionless thermoelectric figure of merit (ZT) of 0.014 is reached for Al2CoCrFeNi alloyed with 0.3 wt.% Sc at 650 °C

Formability prediction of interstitial-free steel via miniaturized tensile specimen for Rapid Alloy Prototyping

This study aims to investigate the feasibility of using non-standard miniaturized tensile specimens (MTS) to characterize the formability features of interstitial-free (IF) steel, specifically DX57 steel. The motivation behind this research is to gain insight into the accuracy of predicted values for the steel's formability using the designed non-standard MTS, which could potentially be used to test materials obtained from rapid alloy prototyping (RAP) routines. Tensile tests were conducted using both standard bars and non-standard MTS with different angles to the rolling directions (0°, 45°, and 90°) and the experiment results were used to determine the material properties for the following numerical simulations, which were based on the cross-die deep drawing concept. The results show that the non-standard MTS over-predicted the strain hardening exponent compared to the values obtained from the standard tensile bars. For the same punch stroke, the non-standard miniatured tensile specimen under-predicted the punch force. However, for the deformed blank, the thickness variation along different paths was compared, and the maximum thickness value difference was found to be less than 5%. In terms of the forming limit diagram (FLD), the MTS's prediction is very close to the standard test-piece's prediction; the overall major-minor strain status of the deformed blank is similar. The results of this research provide confidence in the ability to evaluate formability from small-scale tensile tests for heterogeneous alloys such as synthetic IF steels developed during RAP