Composite materials based on nanostructured zinc oxide

Composites formed from ZnO nanorods in combination with CuO or Ag nanoparticles are produced by the deposition of CuO or Ag nanoparticles onto ZnO nanorod arrays grown by the hydrothermal technique. The CuO nanoparticles are synthesized by the vacuum thermal deposition of a Cu layer followed by vacuum annealing at a temperature of 350°C for 1 h. CuO particles covered with a layer of nanoneedles are obtained. The current-voltage characteristics of the ZnO/CuO layers are indicative of the formation of a p-n junction. The ZnO/Ag composites are produced by the electrical deposition of Ag nanoparticles synthesized in an aqueous solution of silver nitrate and sodium citrate. The surface morphology and the optical and electrical properties of the samples are studied.     

Feasibility of uranium spallation target in accelerator-driven system

A feasibility study on natural uranium spallation target in accelerator-driven system (ADS) for minor actinide (MA) transmutation was performed. As a result of comparative study of uranium and lead-bismuth (PbBi) targets in the bare case without blanket surrounding, it was found that uranium target had better neutron generation performance, but limited by the geometrical size due to high neutron absorption in ²³⁸U. In ADS for MA transmutation, uranium used as target instead of PbBi also absorbs neutrons passing the target area.More realistic concept of pin type uranium spallation target cooled by liquid PbBi was considered aiming at enhancing spallation target performance in terms of neutron generation efficiency and operation temperature. The uranium pin target design had nothing better effects on neutron balance of such system than a conventional PbBi target in ADS and it was concluded that uranium target was not suitable for the full-scale ADS.     

Transmutation by adiabatic resonance crossing experiment (TARC) benchmarking

In present study the benchmarking of TARC experiment was done. MCNPX code with JENDL-HE, JENDL-4, JENDL-3.3 and LA-150 nuclear data libraries were used for simulations. The calculated neutron fluences, energy-time correlations of resonance reactions and transmutation rates of ⁹⁹Tc and ^127,129I were compared with experimental measurements. On the base of comparative analysis of simulations the validation of nuclear data libraries was performed and recommendations were given, as follows:

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the JENDL-4 library contains better neutron elastic cross-section data for natural lead in energy range from ∼0.01 eV to ∼100 eV comparing to other considered data libraries;     

Performance improving of small-dimension IR photodetectors

The design and operation principles of a new IR photodetector with a conducting layer cross-sectional size much smaller than the effective collection length of minority carriers photogenerated in peripheral regions with the opposite type of conductivity are considered. The possibility of achieving very high photosensitivity levels limited by thermal generation at a significant decrease in power consumption is demonstrated.     

Mining tailings as raw materials for reaction-sintered aluminosilicate ceramics: Effect of mineralogical composition on microstructure and properties

This paper presents studies on the utilization of aluminosilicate-based mining tailings as raw materials for mullite-based ceramics. Based on the 3:2 stoichiometric composition, mullite was synthesised by reactive sintering with a series of powder mixtures with alumina additions. X-ray diffractometry and scanning electron microscopy analyses revealed that, at the specific mineralogical composition, mullite structure formed surrounded by an amorphous glass phase in reaction-sintered powder mixtures. Results demonstrated that the chemical and mineralogical composition of mining tailings do have an effect on mullite formation possibilities and, only with the particular mineralogical composition, the mullite formation is possible regardless of the correct Al:Si ratio in tailings. Physical and mechanical properties of the formed ceramics were defined, showing comparable values to 3:2 mullite reference. Mullite structure formation enables a better thermal resistance up to above 1450?°C of the formed tailings-based ceramics compared to other aluminosilicates, reflecting their utilization potential for refractory ceramic applications.     

Stereolithography as a manufacturing method for a hierarchically porous ZSM-5 zeolite structure with adsorption capabilities

Hierarchically porous structures are important in adsorption applications and can be used in gas treatment. Hierarchy in adsorbents offers flow channels on different scales, resulting in fast gas flow into a structure. Additive manufacturing, a technology capable of forming intricate geometries, was seen as a potential method to form porous adsorption structures. Stereolithography was chosen as the fabrication method for hierarchically porous zeolite structures because of its high resolution and superior forming capability. The focus of this study was on tailoring the properties of light-cured resin to maximize stability during shaping and shape retention in the debinding stage. Successful slurry preparation was required for demonstrating that monoliths with channel geometry and retained adsorption properties can be manufactured with stereolithography. The final printed structures exhibited hierarchical porosity consisting of flow channels, macropores between the primary particles and the characteristic microporosity of zeolite framework. The structure was manufactured by using blue light to cure layers of resin containing ZSM-5 zeolite. An appropriate debinding heat-treatment cycle was generated based on the TGA and DSC thermal analysis results. The properties of the porous structure were analysed by comparing the BET surface area, XRD patterns and SEM images of as-received powder and a debound piece. The measured BET adsorption properties of the final monoliths remained comparable to the as-received ZSM-5 powder. Based on this study, stereolithography can be utilized to manufacture porous zeolite structures.     

Cd x Hg1 − x Te-based photodetector with the spectral characteristic controlled by the voltage

A photodetector with a spectral characteristic of the photoresponse controlled by the bias voltage is realized on the basis of the Al-n-Cd _x Hg_{1 ? x} Te heterostructure with a narrow insulator gap. The features of the spectral characteristic of the photocurrent are accounted for by the variation in the ratio between the surface and bulk components of the photocurrent upon varying the bias voltage. The possibility of simultaneous detection and control over the spectral characteristic of photosensitivity at the fundamental adsorption edge and in the short-wavelength spectral region is shown.

     

Heat conductivity of TlxGa1−xX (0⩽x⩽1; X = S,Se, Te) monocrystals

The present paper gives the results of experimental heat conductivity studies carried out on a series of complex semiconductive AX and ABX₂-type compounds. Measurements were performed over a wide temperature range at different crystallographic directions of the materials studied. In doing so, reguliarities have been revealed in the variation of the heat conductivity coefficient, depending on crystal orientation and temperature as well as on the substitutions in respective sublattices. Experimental data are presented for mixed crystals of Tl_xGa_1?xSe and Tl_xIn_1?xSe (0?x?1) representing solid solutions of isovalent substitution. The experimental data are correlated with estimated results on the basis of phonon scattering from local distortions of crystal lattices.