Search results for "Sintering"

Peculiarities of luminescent properties of cerium doped YAG transparent nanoceramics

2010

Abstract Optical and luminescence properties of transparent nanosized cerium doped Y 3 Al 5 O 12 (YAG:Ce) ceramics have been studied. YAG:Ce nanoceramics were obtained by means of low temperature and high pressure (LTHP) sintering method. Nanoceramic samples were sintered in the 2–8 GPa pressure range, whereas Ce 3+ concentration was varied in the 0.5–5 at. % range. It is shown that, in contrast to the single crystal, a strong rise of absorption coefficient was detected already at wavelength shorter than 400 nm in all nanoceramic samples studied. Furthermore, in nanoceramic samples unusual UV emission band near 3.1 eV was observed, which is not observed in the YAG:Ce single crystal. High pr…

The luminescence of ZnO ceramics

2010

Abstract The luminescence properties of ZnO ceramics with grains 100–5000 nm sintered by different techniques from nanopowders were studied. The luminescence decay times were compared with that obtained for ZnO single crystal. The temperature dependence of non-exponential decay of defect luminescence (2.0–2.6 eV) was measured in wide time, intensity and temperature range. The luminescence decay kinetic at T ≤ 20 K shows the decay close to I(t) ∼ t−1 dependence. At temperature region 50–250 K the decay kinetics is more complicate since the TSL was observed in this temperature region. It is shown that the luminescence properties of NP and ceramics strongly depend on defect distribution on gra…

Luminescence of ZnO nanopowders

2004

Abstract The luminescence of ZnO nanocrystals prepared by different methods was studied under pulsed electron beam excitation. It is shown that the luminescence intensity depends on the nanocrystal sintering conditions and does not depend on the nanocrystal size within the range 10–50 nm. The relative luminescence intensities for the 3.32 eV (free exciton) and ∼3.20 eV (bound exciton) bands showed a dependence on nanocrystal size. The role of the nanocrystal surface in excitonic luminescence is discussed.

Radioluminescence, thermoluminescence and dosimetric properties of ZnO ceramics

2017

The authors gratefully acknowledge the financial support for this work from research grant ERA.NET RUS Plus Nr.609556 and from the SFERA II project Transnational Access activities (EU 7th Framework Programme Grant Agreement no 312643) for supporting ZnO nanopowders preparation.

Numerical modeling of the solid-state sintering at the microstructural level: Multiphysics approach and application to metal additive manufacturing

2023

Numerical modeling of the solid-state sintering at the microstructural level: Multiphysics approach and application to metal additive manufacturing

Polymer-matrix route to (Bi, Pb)2Sr2Ca2Cu3O10+δ: The role of Ca2CuO3☆

1993

Abstract The use of polyethylenimine as active matrix agent has provided a fast synthesis method for (Bi, Pb)2Sr2Ca2Cu3O10+δ, starting from aqueous acetic solutions combined with careful control of the procedural variables. The 110 K phase is obtained as the only superconducting phase after sintering in air during 42 h at 860°C. This technique yields homogeneously sized, large (ca. 20 μm) platelets of the superconducting material. The presence of an excess of calcium and copper over the stoichiometric requirements accelerates the formation of the superconducting phase. This excess, which appears in the resulting material as Ca2CuO3, influences the superconducting properties, other than Tc, …

Microscopic Studies of YBCO-Based Polycrystalline Materials

1997

Improvement of the critical current density of spark plasma sintered MgB2by C60addition

2010

We investigated the influence of fullerene (C60) addition on the superconducting parameters of MgB2 bulk samples obtained by spark plasma sintering (SPS). It was found that 1.5?wt% C60 addition leads to the reduction of the critical temperature by a few K, whereas the magnetically determined critical current density increases by approximately one order of magnitude in an applied magnetic field H = 70?kOe at temperature T = 10?K. This indicates substitution of B by C in C60 added MgB2 processed by SPS, contrary to some data reported in the literature obtained using conventional methods. For our relatively large specimens, the occurrence of macroscale flux jumps was observed over a wide (H, T…

Fast synthesis of single-phased 110 K bismuth superconductor by freeze-drying of acetic precursors. Kinetic role of calcium and copper oxides

1993

Abstract Although the usefulness of solution procedures to improve the synthesis of bismuth HTSC has been argued, an adequate control of the procedural variables has allowed us to isolate the 110 K phase as the only superconducting phase after such a short sintering time as 22 h. The precursors used have been freeze-dried powders resulting from acetic solutions containing excess Ca and Cu. TGA-DTA and XRD experiments have been performed to follow the subsequent solid-state reaction processes. The initial formation of a mixed bismuth-lead oxoacetate, as intermediate to (Bi 1− y Pb y ) 2 CuO 4 , and the presence of an excess of Ca 2 CuO 3 in the last reaction step are two of the main factors …

Polymer solution processing of (Bi, Pb)SrCaCuO

1991

Abstract A simple polymer processing route to the 110 K phase (Bi, Pb) 2 Sr 2 Ca 2 Cu 3 O 10+δ superconductor has been developed. The influence of the polymer to metal starting ratio, as well as the sintering temperature and time on the quality of the resulting superconducting powders has been studied by XRD, a.c. susceptibility and resistivity measurements. Microstructure of ceramic compacts has been studied by SEM, and qualitatively analysed by EDS for compositional homogeneity. The results indicate that the polymer synthesis route described here may offer a good alternative to the conventional solid state preparation methods towards attaining homogeneous 110 K superconductor powder withi…