Papers by Author: Tadeusz Chudoba

Abstract: Mechanically alloyed Al65Cu20Ti15 amorphous alloy powder with 10 wt.% nano-TiO2 dispersion was consolidated by high pressure sintering (HPS) at room temperature and/or 300- 450oC for about 1 min using a uniaxial pressure of 8GPa. The sintered material was examined by XRD and TEM. Excellent hardness and strength were obtained in selected sintered samples of 8.34 GPa and 1600 MPa respectively, although ductility was very low (< 1%).

Abstract: Time-resolved luminescence characteristics have been studied for cerium doped YAG nanopowders (NP) and nanostructured ceramics (NC). The results obtained have been compared to the luminescence characteristics for the well studied YAG:Ce3+ single crystal (SC). It was detected that the luminescence decay kinetics of Ce3+ related emission in nanocrystals can be closely approximated by two exponents, whereas a single exponential decay was observed in the single crystal. It was also found that the luminescence decay time and light yield of Ce3+ emission are strongly dependent on the cerium concentration and an unusual concentration quenching of Ce3+ emission was observed in YAG nanocrystals. The origin of the differences of luminescence characteristics for cerium doped nanocrystals and SC are discussed. It is suggested that there are special Ce3+ sites which are closely related to the surface states and that they have a strong influence on the luminescence properties of cerium doped YAG nanocrystals.

Abstract: The agglomeration of YAG (Yttrium-Aluminum Garnet Y3Al5O12) nanopowders doped with various rare earth ions obtained by the coprecipitation and calcination route is a major problem if it is wished to exploit the nano-size properties such as the transparency of dispersions of the powders or low temperature sintering. Investigations to optimize the preparation process of powders for High Pressure-Low temperature Sintering (HPLS) of semi-translucent pellets was undertaken. The appropriate milling time to decrease the agglomeration was evaluated with the help of ZETA- potential measurement. The dependence of the agglomerate size against the time of hand milling was used to optimize the process.