Yttria-doped zirconia, lead zirconate titanate (PZT) and barium titanate were
successfully obtained using hydrothermal procedures. Based on these results
mathematical models describing the correlation between the nanopowders’
characteristics and the main synthesis parameters are proposed.
Powders from the systems (Y2O3)0.1 (ZrO2)0.9 and (Y2O3)0.04
(ZrO2)0.96
obtained from soluble Zr(IV) peroxide precursors show that cubic/tetragonal
phases have been formed by controlled crystallization from the solution. With
increasing temperature and hydrothermal treatment temperature the mean
crystallite sizes increase from a minimum of 5 nm to a maximum of 22 nm. The
activation energy shows a diffusion-controlled process.
Barium titanate powders with controlled stoichiometry could also be hydrothermally
synthesized in the temperature range 110– 175°C.
Synthesis of PZT powders with controlled stoichiometry and mean crystallite sizes
from 4 to 43 nm is finally presented.
Dense yttria-partial stabilized zirconia with high ionic conductivity and PZT with
a good stability of electric–physical parameters for use in the design of materials
with improved sensorial characteristics was obtained after sintering the
nanopowders.
High entropy alloys are a newly developed class of alloys, which tend to form a single solid solution or a mixture of solid solutions with simple crystal structures. These alloys possess excellent mechanical properties, thermal stability and corrosion resistance. In the present paper, an AlCoCrFeNiTi high entropy alloy was obtained by induction melting, and the influence of the remelting process on the mechanical and corrosion resistance characteristics of the alloy was investigated. Thus, optical and scanning electron microscopy revealed less phase segregation and a fine dendritic structure for the remelted alloy, while corrosion tests indicated that present alloy, in remelted state, has better corrosion resistance than as cast alloy and stainless steel. The Vickers microhardness measurements demonstrated an improvement of the alloy microhardness by remelting process due to the decrease in phase segregation and the increase in dendrite refinement level.
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