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Thermoelectric generation (TEG) is one of the most effective technologies converting heat directly into electric power. In this paper, a nearly kilowatt class TEG system mainly based on radiation h...

How to form a uniform fine-grained structure in n-type polycrystalline Bi2Te3 based alloys to stabilize and improve the thermoelectric properties is the burning issue to be solved. In the present work, equal channel angular extrusion (ECAE) method was used to extrude the cast ingot directly at various temperatures to obtain the BiTeSe polycrystalline bulk alloys with uniform microstructure. The initial lamellae coarse grains (hundreds microns to several millimeters) were efficiently and uniformly refined to a minimum of 4.07 μm at 703 K, which fully demonstrates the feasibility of grain refinement by ECAE for cast n-type BiTeSe ingot. The average grain size of the extruded billets rapidly increased from 5.35 to 29.55 μm with the increase of extrusion temperature from 703 to 823 K. Meanwhile, the behavior of abnormal grain growth became more evident as the extrusion temperature increased because the growth rate increased more rapidly than the rate of nucleation. As the extrusion temperature increased, the Vickers hardness decreased gradually due to grain coarsening. BiTeSe alloys extruded at 703 K achieved the maximum Vickers hardness of 59.8 HV0.05, which was nearly three times higher than that of the initial cast ingot. All extruded BiTeSe billets possessed the much higher dimensionless figure of merit (ZT), compared with the initial cast ingot due to the simultaneously optimization of electrical and thermal transport performances caused by ECAE process. Finally, the specimen extruded at 823 K achieved the maximum ZT of 0.685 at 383 K.

The diffusion of Ni and Sn is undesirable in thermoelectric (TE) device. However, the quantitative effect on TE properties is unknown. In this work, the effect of Ni/Sn doping on the TE properties of p-type Bi2Te3 based alloys and the corresponding mechanism are investigated to provide beneficial reference for device designers and researchers. The results show that nickel doping in Bi0.4Sb1.6Te3 can make the intrinsic excitation temperature shift to lower temperature region due to the formation of the second phase NiTe, which greatly reduces the carrier concentration and increases the electrical resistivity. Ultimately, the thermoelectric figure of merit (ZT value) deteriorates rapidly with the increase of Ni content, and only 7 wt ‰ Ni results in a 32% drop in ZT value. Tin doping moves the intrinsic excitation temperature to higher temperature region due to the promotion of Sn’Bi to the generation of anti-sites (Bi’Te and Sb’Te), which significantly increases the carrier concentration and deteriorates the Seebeck coefficient. At last, the ZT value also declines sharply with the increase of Sn content, and just 7 wt ‰ Sn doping results in a 52% drop in ZT value.

The promotion effect of O2 on the dissociative adsorption of H2O to UO2 surface is studied by first-principles method within generalized gradient approximation formalism corrected by on-site Coulomb interaction. Investigations on all UO2 low index surfaces indicate that U-terminate (001) surface is the highest energy surface. For the adsorption of O2 and H2O on the U-terminate UO2(001) surface, all O2 molecules dissociate spontaneously while H2O molecules only dissociate incompletely in some specific initial configurations. The results of co-adsorption demonstrate the promotion effect of O2 on the dissociative adsorption of H2O, and two different promotion mechanisms are studied detailedly.

Influence of substitutional Fe, Al and Mg atoms on the corrosion of α-U(110) surface was studied by DFT + U method. The calculations results indicate that impurity atoms inhibit the dissociation of H2O molecular. Although the impurity atoms do not impede the dissociation of O2 molecular, they lower the binding energy of the dissociated O atoms with the substitutional surfaces. Through the investigation on the surface diffusion and into-bulk penetration, it could be confirmed that Fe, Al and Mg atoms accelerate the hydrogenation of α-uranium surface, while improve the anti-oxidizing ability of α-uranium.

Thermoelectric properties of BiCuSeO were improved combing Y-doping and grain refinement. The samples were prepared by mechanical alloying and resistance pressing sintering. The results indicate Y can reduce the bandgap, increase the carrier concentration and electrical conductivity, increase the lattice vibration amplitude and thermal conductivity. Grain refinement by increasing ball milling strength can increase the concentration and power factor by enhancing Cu vacancies, and enhance the scattering of low- and intermediate-frequency phonons, so as to reduce the thermal conductivity. Finally, the dimensionless figure of merit(ZT) value is increased to 0.93, which is 98% higher than that of the pure sample.

Although the mechanical strength of n-type polycrystalline Bi2Te3 based alloys prepared by conventional powder metallurgy technology is good, its thermoelectric properties have poor repeatability and contamination is introduced. In this work, n-type polycrystalline Bi2Te3 based alloys with uniform microstructure were fabricated by applying equal channel angular extrusion (ECAE) method to extrude the cast ingot directly for four passes at 783 K. The initial lamellae coarse grains with hundreds of microns were broken down efficiently and refined uniformly to only 10–20 μm. And the Vickers hardness was increased by 2.3 times due to the refined grains. On the other hand, it is noteworthy that the ECAE process is also an ideal method to improve the thermoelectric properties of cast ingot by boosting electrical transport properties due to the donor like effect induced by heavy deformation and reducing thermal transport properties due to the enhanced phonon scattering. In order to further optimize the thermoelectric performance, BiCl3 doping was used to precisely tune the carrier concentration to the best range. The intrinsic excitation temperature of Bi2Te3 based alloys gradually shifted from low temperature (below 303 K) to high temperature (463 K) owing to the increased carrier concentration. Finally, the extruded Bi2Te3 based alloy doped with 0.064 wt % BiCl3 obtained the maximum dimensionless figure of merit (ZT) of 0.68 at 423 K, which was far higher than the nearly zero of the initial cast ingot.

Using first-principles calculations, we studied the dissolution and diffusion behaviors of H/He atom in perfect fcc-Fe and vacancy capture multiple H/He atoms meachanism in fcc-Fe. The calculation results show that H/He atom prefers to occupy octahedral site, and they diffused along octahedral site-tetrahedral site-octahedral site in perfect fcc-Fe. Inside vacancy, H atom prefers to occupy octahedral site, while He atom prefers to occupy the vacancy center. The exist of H/He atom would decrease the vacancy formation energy. According to capture energies, a vacancy can trap five H atoms in fcc-Fe, but more He atoms can be accommodated even when the number of He atoms reaches sixteen. Therefore, the result provides an important theoretical basis to research the mechanism of hydrogen and helium embrittlement.

Thermoelectric materials have great application prospects in the fields of micro-refrigeration, waste heat utilization and catalysis, and BiCuSeO is one of the oxide thermoelectric materials with the best comprehensive thermoelectric properties at present. Herein, the dispersion of 20-nm SiC in BiCuSeO matrix has greatly increases the thermoelectric and mechanical properties of the system. SiC nanoparticles dispersed in BiCuSeO matrix can act as energy filters to increase the Seebeck coefficient, on the other hand, as phonon scattering centers to scatter the low- and mid-frequency phonons effectively to reduce the lattice thermal conductivity, combined with point defects such as Pb Bi + scattering the high-frequency phonons, thus achieving the scattering enhancement of full-frequency phonons. In addition, the mechanical strength and machinability of BiCuSeO have been improved significantly due to the dispersion strengthening effect of SiC nanoparticles.

Introduction of porous structure is a feasible and promising method for improving thermoelectric performances for thermoelectric materials. Meanwhile, the uniformity of pores distribution plays a decisive role in the objective evaluation of thermoelectric properties for porous structures. In this work, extremely uniform porous structures in p-type Bi0.4Sb1.6Te3 bulks were obtained by pre-mixing with NH4HCO3 combined with resistance pressing sintering (RPS) process. The thermoelectric performance was obviously affected by the porous structure. The increasing porosity resulted in a significant decrease in electrical and thermal conductivity. It was inspiring that the reduction of thermal conductivity could compensate for the deterioration of electrical conductivity, leading to the enhancement in ZT value. The maximum ZT value of 1.11 was obtained for the sample prepared by pre-mixing with 5 ​wt % NH4HCO3 at 343 ​K, which was 20% higher than that of the fully dense sample. Finally, the advantages on the homogeneity of pores, thermoelectric properties and mechanical properties of the sample prepared by this method are confirmed through comparing with the sample prepared without NH4HCO3, when their relative densities both are 90%.

The Pu-He pair potential fitted by ab initio data, and the Pu-Pu and He-He modified embedded atom method (MEAM) potentials have been implemented to perform multi-scale simulations for the interactions of fracture with the self-interstitial atom (SIA), He interstitial atom and He-vacancy clusters. The simulation results indicate that Pu atoms around the fracture agglomerate into an elliptic self-interstitial loop. Interstitial He atoms evolve into separate interstitial atoms, small He atom clusters and some substitutional He atoms. The He-vacancy cluster forms a spheric structure with a 1:1 He-to-vacancy ratio. Finally, the existence of self-interstitial atoms will lead to the local change of Pu lattice and an increasing disorder, and the whole simulation cell shows a melting state at about 10.0 ps.

A rapid and effective polymerase chain reaction (PCR) test, specific for the detection of Mycobacterium bovis and Mycobacterium avium subsp. paratuberculosis in invasive flies, was developed. This duplex PCR technique was specifically designed to amplify the sequences of IS6110 of M. bovis and IS900 of M. avium subsp. paratuberculosis. The results of the interference test, simulated contamination test, and several other experiments indicated that this technique had high stability, specificity, and sensitivity with detection limits at 92.98 pg of M. bovis and 110.27 pg of M. avium subsp. paratuberculosis. Therefore, this duplex PCR test is a rapid and effective technique to simultaneously detect M. bovis and M. avium subsp. paratuberculosis.

We design the structural dimensions of the reactor for the supersonic-based disposing radioactive waste water in this paper. The disposing efficiencies have been simulated under several conditions, and obtained the total α radioactive concentration for the waste water as a function of disposing time, the impact of the supersonic frequency and the time-mean sound energy density on the disposing effectiveness, and the decontamination factor vs. disposing time. The results show that the total α radioactive concentration diminishes as the disposing time increases. The total α radioactive concentration will below the national emission standard, and the disposing time for reaching the emission standard diminishes as the supersonic frequency increases. When the supersonic frequencies are same, the total α radioactive concentration of the disposed radioactive waste water diminishes as the time-mean sound energy density increases under same disposing time, and the decontamination frequency increase as the time-mean sound energy density increases. The total α radioactive concentration of the disposed radioactive waste water diminishes as the time-mean sound energy density increases under other conditions being same. Under the same supersonic conditions, the supersonic decontamination factors for 10Bq/L and 20Bq/L radioactive waste water are same, namely the decontamination factors are independent of the initial radioactive concentration. Moreover, the supersonic decontamination factor for the suspended particles that obey the normal distribution with expectation value of 0.7μm and variance of 0.21 in the waste water is higher than that of the suspended particles that belong to the monodispersity particles. The designed supersonic reactor can satisfy the requirement of the disposing efficiency.Copyright © 2013 by ASME

Pu material can generate surface corrosion and self-radiation effect during storage, leading to the creation and recoil of uranium and helium ions, which produce defects through displacement cascades, these self-irradiation defects tend to change plutonium properties. To study these aging behavior, calculations at the spin unrestricted generalized gradient approximation (GGA) level of density functional theory (DFT) have been performed using the DMol3 programs. Relativistic effects, such as mass-velocity, Darwin term, are considered in this code. Some conclusions are draw as follows: 1) Band structure of the (100) surface of γ-Pu is very narrow around the Fermi level, showing that the eigenstate of this level is mainly composed of local atomic orbital, the local property of electrons in this band is very strong, while the band around the Fermi level is mainly constituted by 5f narrow band; 2) DOS of the (100) surface of γ-Pu are mainly composed of the density of states in −48–41eV, −23–16eV, −3–2eV; 3) Contribution of s shell to the total DOS is mainly distributed in the first interval, and p shell is mainly in the second interval, while d and f shells are mainly in the third interval.Copyright © 2010 by ASME