International Scientific Journals
of Scientific Technical Union of Mechanical Engineering "Industry 4.0"

The investigation of influence of modified conditions on formation of complex materials based on tetragonal zirconia doped by d-elements of I group (Cu or Ag) was carried out, in particular the routes of synthesis and type of dopant. The kinetic parameters of separated stage of NPs formation (drying of hydrogel under MW irradiation, dehydration and crystallization of amorphous zirconia NPs) were estimated. It was shown, the dehydration of tetragonal zirconia hydrogel in conditions of MW irradiation occurs due in two stage. In contrast for Cu (or Ag) –modified hydrogels only one stage dehydration is observed. The dehydration and crystallization of unmodified and modified xerogel is studied by DSC method. It was shown that the kinetic parameters of dehydration depend as from nature of zirconium salts that were using for synthesis and type of dopant. For crystallization processes the some parameters (crystallization temperature, enthalpy) are saved features of dependence on route of synthesis for unmodified and modified systems. However, the behaviour of dependence of activation energy on route of synthesis is contrast for unmodified and modified systems.

It is known that the formation of oxide nanopowders takes place in the complex process including as non-isothermal and isothermal stages. In case of powders isothermal heat treatment led to realization of sequential process at transition from amorphous state to crystalline state, in particular, dehydration, crystallization, disintegration of linked nanoparticles in amorphous matrix and ensuing growth of crystals. In this work the questions of forming of particles and ceramic based on these nanoparticles are discussed. The influence of particles characteristics which synthesized at different temperatures on kinetics of isothermal sintering is estimated. It was shown that particles size and surface characteristics influence on kind of diffusion which is realized at ceramic sintering. The possible mechanisms of isothermal stage of nanoparticles and ceramics forming are discussed.

The catalytic activity of material was tested by ESR spectroscopy and investigation of the formation of the super-anion radicals of oxygen on surface zirconia particles in dependence on dopant amount, pressure. UV-visible spectroscopy was used for estimation of optical properties of these materials. It was found the introduction of Y2O3 allows to creation of structure defects in partially stabilized zirconia, and its influence for tetragonal crystals is not monotonic in range 2-4 mol. %. It is connected with boundary of stable tetragonal phase at Y2O3 adding. The pressure is active factor of changing of surface state due to tetragonal – monoclinic transformation and may be used for improvements of catalytic properties of zirconia NPs.

Tetragonal crystals were formed at addition of yttrium oxide on concentration range from 2 to 4 mol. %. It was estimated the thermodynamic functions of these systems, in particular on values of free surface energy (Gs) and elastic energy (Ge) of crystals and their ability to respond on change of external conditions – temperature. It was shown for range of small sizes (size decreases at temperature growth) the concentration of dopants practically doesn’t influence on dynamic of change of Gs then as for range of particles size of 15-35 nm the concentration of dopant more significantly influence on the Gs. Analysis of dynamic of change of Gs and Ge values shows that for systems which have been formed at heat treatment before 700°C the change of these thermodynamics functions is bigger. In this time the dynamic of change of total Gs + Ge value for systems which was synthesized at different temperatures shows the influence on yttria concentration.

A new approach to design of oxide ceramic-ceramic nanocomposites instead of industrial technical ceramics has been proposed. The use of mixing of liquid solutions of reagents instead of powders mixing allows entering in the matrix material the oxide dopants in supersaturated concentrations. The synthesized nanoparticles contain a potential for the formation of various structures. By the controlling of heating regimes during nanopowders sintering processes we can control the diffusion processes on the particles volume and boundaries. The decomposition of initial supersaturated solid solution during heat treatment (especially at fast sintering) can lead to formation of multilevel nanocomposite structure in the ceramic matrix with enhancing mechanical, electrical, optical and magnetic properties. It is established on the example of zirconia that even a slight amount of aluminum oxide, nickel oxide, zinc oxide leads to a significant change of the nanopowders and ceramics properties.