Structural and electrical properties of grain boundaries in Ce0.85Gd0.15O1.925 solid electrolyte modified by addition of transition metal ions

In this work we present studies on applicability of transition metal additives as sintering and electrical conductivity aids for cerium gadolinium oxide electrolyte. The nanosized Ce_0.85Gd_0.15O_1.925 powder obtained by coprecipitation method was modified with Cr³⁺, Fe³⁺, Ni²⁺ or Cu²⁺ ions. Using high-intensity high-resolution X-ray powder diffraction data we have determined that Cr, Fe and Ni ions do not incorporate into the cerium gadolinium oxide surface or bulk when sintered at 1300 °C, but react with Gd ions to form Cr_0.9Gd_0.1O, GdFeO₃ and GdNiO₃ phases, while Cu incorporates in the material up to 0.7 mol% with a significant fraction of remaining material showing poorly crystalline CuO phase. The nanosized Ce_0.85Gd_0.15O_1.925 material shows already improved sintering properties than previous reports but full sintering is not achieved below 1300 °C, however Cr, Fe and mainly Cu impregnation allows full sintering at 1300 °C. 0.5 mol% Ni impregnated material sintered at 1500 °C shows enhanced grain boundary conductivity that probably indicates that Ni incorporates into Ce_0.84Gd_0.15O_1.925 above 1300 °C. The global results indicate, however, that optimization of ceria microstructure is at least of equal importance for sinterability and grain boundary conductivity than impregnation of the material with transition metal ions.     

Pore formation mechanism and its mitigation in laser welding of AZ31B magnesium alloy in lap joint configuration

Magnesium is one of the lightest structural metals that has been used in different industries such as automobile, aerospace and electronics. However, in fusion joining of magnesium alloys, porosity is one of the main drawbacks to achieve a weld with desirable properties. The oxide layer existing on the surface of magnesium alloy is one of the causes of pore formation in the weld bead. In the current study, a fiber laser with a power of up to 4 kW is used to weld samples in a zero-gap lap joint configuration. Two groups of samples are studied: as-received (AR) surfaces (where an oxide layer remains on the surface) and treated surfaces. The surface treatment includes two techniques: mechanically removed (MR) and the use of a plasma arc (PA) as a preheating source. Also, a separate set of experiments are designed for preheating samples in a furnace for comparison with the PA-treated results. To reveal the chemical compositions of the welds and metal sheet surfaces, an energy dispersive spectroscopy (EDS) is performed. Surface chemical compositions are tested by X-ray photoelectron spectroscopy-reflected electron energy loss spectroscopy (XPS-REELS) to characterize the surface composition on AR and PA-treated samples. The dynamic behavior of the weld pool and laser-induced plasma plume is monitored in real-time using a high speed CCD camera to investigate the stability of the laser welding process. The presence of the oxide layer at the faying surface of two overlapped sheets results in an unstable process. The obtained results reveal that the preheating procedure can effectively mitigate pore formation at the interface of the two overlapped sheets.     

Microstructure and tensile properties of superalloy IN100 fabricated by micro-laser aided additive manufacturing

Layer by layer fabrication using micro-laser aided additive manufacturing (micro-LAAM) was successfully implemented on nickel-base superalloy IN100. It is known that IN100, a type of superalloy having high titanium and aluminum contents, has poor weldability due to weld liquation cracking in the heat-affected zone (HAZ) and strain age cracking. In this study, micro-LAAM process was optimized through a set of designed experiments to eliminate crack formation and reduce porosity. It was found that the crack-free deposition can be achieved owing to the fact that micro-LAAM process used in this study had very low heat input. Three distinct sizes of γ′ precipitates were observed on the post heat-treated samples. The volume fractions of γ to γ′ phases were found to be approximately 60–40%. Microstructure and chemical analysis results showed that γ′ phase was embedded within γ-Ni matrix while various carbides (MC, M₂₃C₆ and M₆C) were observed as precipitates at grain boundaries or within grains. Electron backscatter diffraction (EBSD) was used to compare grain morphologies and size distribution of three distinctly different regions on each layer. The achieved ultimate tensile strength and yield strength are much better than the minimum requirements specified in aerospace material specification 5397 for cast IN100.     

Quickest single-step one pot mechanosynthesis and characterization of ZnTe quantum dots

ZnTe quantum dots (QDs) are synthesized at room temperature in a single step by mechanical alloying the stoichiometric equimolar mixture (1:1 mol) of Zn and Te powders under Ar within 1 h of milling. Both XRD and HRTEM characterizations reveal that these QDs having size ∼5 nm contain stacking faults of different kinds. A distinct blue-shift in absorption spectra with decreasing particle size of QDs confirms the quantum size confinement effect (QSCE). It is observed for first time that the QDs with considerable amount of faults can also show the QSCE. Optical band gaps of these QDs increase with increasing milling time and their band gaps can be fine-tuned easily by varying milling time of QDs.     

Detecting 6 MV X-rays using an organic photovoltaic device

An organic photovoltaic (OPV) device has been used in conjunction with a flexible inorganic phosphor to produce a radiation tolerant, efficient and linear detector for 6 MV X-rays. The OPVs were based on a blend of poly(3-hexylthiophene-2,5-diyl) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM). We show that the devices have a sensitivity an order of magnitude higher than a commercial silicon detector used as a reference. Exposure to 360 Grays of radiation resulted in a small (2%) degradation in performance demonstrating that these detectors have the potential to be used as flexible, real-time, in vivo dosimeters for oncology treatments.     

Martensitic transformation of Ti50Ni30Cu20 alloy prepared by powder metallurgy

Phase transformation behavior of Ti50Ni30Cu20 shape memory alloys prepared by powder metallurgy is analyzed with respect to the duration of mechanical alloying. The processed blends were studied by differential scanning calorimetry and room temperature X-ray diffraction. The martensitic transformations evidenced by thermal scans are discussed in correlation with the relative phase content obtained from the refinement of the X-ray diffraction patterns.     

Solvothermal synthesis of Hg1−xCdxTe nanostructures—Their structural and optical properties

This article describes a facile, low-cost, solution-phase approach to the large-scale preparation of Hg_1−xCd_xTe nanostructures of different shapes such as nanorods, quantum dots, hexagonal cubes of different sizes and different compositions at a growth temperature of 180 °C using an air stable Te source by solvothermal technique. The XRD spectrum shows that the crystals are cubic in their basic structure and reveals the variation in lattice constant as a function of composition. The size and morphology of the products were examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The formation of irregular shaped particles and few nano-rods in the present synthesis is attributed to the cetyl trimethylammonium bromide (CTAB). The room temperature FTIR absorption and PL studies for a compositon of x = 0.8 gives a band gap of 1.1 eV and a broad emission in NIR region (0.5-0.9 eV) with all bands attributed to surface defects.