Search

This work is devoted to the demonstration of a real multifunctional material – zirconia based nanopowders, which can be used in the manufacture of various types of devices that convert natural energy sources into electricity (electrolyte and anode for SOFC, moisture-to-electricity converter). It was shown that such characteristics of nanopowders as particle size, specific surface area, and type of surface centers, which depend on the temperature of nanopowder synthesis, could play both a positive and a negative role in the formation of the functional properties of a device. It was found that the synthesis of 8YSZ nanopowders at 700 °C is optimal for the manufacture of a dense electrolyte material and a porous SOFC anode material during sintering at 1400–1450 °C. The addition of a small amount of Al 2 O 3 at the synthesis stage accelerates the sintering of the SOFC electrolyte material by 120 °C and leads to increasing the density to 97% of the theoretical value. The strength of the sintered anode material practically does not change after reduction in an atmosphere of N 2 –10% H 2 –5% CO 2 and the value is 100 MPa. The synthesis temperature of 8YSZ nanopowder at 700 °C is also optimal for the manufacture of porous converters of ambient humidity into electricity. The formation of particles with a given size and type of surface centers allows generating an electric potential (100–200 mV) for hundreds of hours, which is 2–3 times higher than that of larger and smaller powders. The result of the work show that there are optimal conditions for the synthesis of powders (synthesis method, additives, synthesis temperature), as a result of which nanopowders are formed with characteristics (particle size, specific surface area, morphology) necessary and sufficient for the manufacture of several types of materials for devices of alternative energy. [Display omitted] • 8YSZ is the universal material for converting ambient energy sources to electricity. • Creating a database powder – technology-characteristics - products – properties. • Testing during the manufacture of SOFC components and MEG converter. • Optimum condition of powder synthesis for the production of SOFC and MEG were found. [ABSTRACT FROM AUTHOR]

Two series of ZrO2 samples—pure ZrO2 and ZrO2 doped by 3% of Y2O3—prepared at 400, 500, and 600 °C were studied. The samples were characterized by powder XRD, TEM, SANS, IR spectroscopy, and nitrogen adsorption at 77 K. Monoclinic ZrO2 was the dominating phase in the samples of pure zirconia, while Y-doped zirconia mainly consisted of tetragonal ZrO2. An increase in the calcination temperature led to the growth of the zirconia nanoparticle (NP) size and a decrease of the specific surface SBET. The size of Y-doped zirconia NPs (9–16 nm by XRD) was smaller compared to pure ZrO2 (12–19 nm), synthesized at the same temperatures. The content of the surface defects in the tetragonal Y-doped ZrO2 was estimated by analysis of IR spectra and other indicators and grew with the increase of the calcination temperature. The strength and content of the acidic surface sites were determined by potentiometric titration. The doping of ZrO2 by Y3+ led to the formation of the sites with lower pKa. The catalytic activity of ZrO2 and Y-doped ZrO2 in the reaction of α-tetralol oxidation by m-chloroperoxobenzoic acid was studied, and it was found that α-tetralone was the main product. The catalytic activity of the Y-doped zirconia samples in α-tetralol oxidation, expressed as conversion or turnover frequency (TOF) per 1 m2 or ZrO2, increased with the increase of the total concentration of the surface acidic centers. [ABSTRACT FROM AUTHOR]

In this work, the influence of additives of rare earth and transition metals on the process of formation of the structure, mechanical and electrical properties of the SOFC electrolyte material based on zirconia was studied in order to identify the key technological and physical parameters affecting this process. A strong influence of the type of doping impurity on the lattice parameter of synthesized particles and sintered ceramics, on the strength and density of ceramics, and on the activation energy of ionic conductivity along grain boundaries was found. The effect of the type of additive on the value of ionic conductivity by grain volume in sintered ceramics was not detected. It was shown that the dopants effects on the ionic conductivity of zirconia electrolyte material in the indirect mode. The ionic radius of the dopants are determines the level of stability of the substitutional solid solution, and the diffusion of the impurity to the grain boundaries during sintering. It has been established that the more the ionic radius of the impurity differs from the equivalent ionic radius of the cation, the greater the activation energy of ionic conductivity along grain boundaries is observed. This depends on the degree of contamination of the grain boundaries with various impurities, which can diffuse to the grain boundaries and segregate there due to a violation of the Hume-Rothery rule. At the same time, the activation energy of ionic conductivity over the grain volume changes insignificantly, which indicates that the conductivity over the grain volume depends strongly on the number of oxygen vacancies, the concentration of which weakly depends on the ionic radius of the impurity. • Additional doping YSZ affects σ gb and does not affect σ g values of SOFC electrolyte • Ionic radius of the dopant does not directly affect the σ gb value • Ionic radius of the dopant determines the stability of the zirconia solid solution • Violation of the Hume-Rothery rule leads to segregation of dopant at grain boundaries • The more R i differs from R 0 the greater E A for ionic conduction at grain boundaries [ABSTRACT FROM AUTHOR]

This study is devoted to the development of new oxide materials and devices based on them for direct long-term production of electricity from ambient humidity, which can be used as an auxiliary power supply system for self-sufficient buildings. The simplest device, a tablet pressed from these powders, generates an electrical potential in the presence of a moisture gradient inside the sample. The output voltage level of the converter depends on the type of material and the porous structure of the converter. There is a dependence of the sign of the output voltage on the type of material, which can be related to the type and sign of the surface centers of the converter material particles. The main mechanism of the converter operation is the generation of the streaming potential during the movement of adsorbed moisture (water molecules) in the porous structure of the converter under the influence of the ambient air humidity gradient. An increase in converter thickness increases the generation time of the output voltage by up to several tens of hours, both with an increase and a decrease in the humidity level in the compartment. The results of this study will help to use a huge reservoir of low-potential energy contained in gaseous water molecules to generate "green" electricity. [ABSTRACT FROM AUTHOR]

This study is devoted to creating media for the accumulation of electrical energy based on zirconia nanoparticles. The effect of charge accumulation by compacted zirconia nanoparticles, the manifestation of which depends on the size of the particles and the degree of hydration of their surface, was found. It is shown that for the system of hydrated nanoparticles, the formation of the dielectric constant of the entire structure as a whole is influenced by the dielectric properties of the nanoparticle materials and water on its surface. The difference in the dielectric properties of the filler (water) and the matrix (material of zirconia nanoparticles) leads to a strong increase in the dielectric constant of hydrated compacted nanoparticles due to the Maxwell–Wagner effect, which is a promising application in the development of energy storage media. [ABSTRACT FROM AUTHOR]

XRD, ESR, TRMC and UV–visible spectroscopy are used for the description of characteristics of investigated systems and determination of forming structure mechanism in Al, Zr or Ce doped non-stoichiometric ZnO1−x. It was shown the Al and Zr ions substitute the lattice Zn2+ in the ZnO matrix, and as a result, the donor's levels form in ZnO bandgap and acceptor's level of zinc vacancy. Last level is a trap of phogenerate holes in material and it allows to delay photocatalytic actvity Al- and Zr-doped ZnO. Ce ions incorporate as interstiallite ions or segregate on crystal surface that leads to appearance the f-levels in the bandgap of ZnO, and as a result, the cerium ion will trap for electron. It decreases electron lifetime or increases of hole lifetime and also if cerium ion segregates on the ZnO surface the set of reactions (Ce4+ + e- = Ce3+, Ce3+ + O2 = Ce4+ + O2−) may occur. It leads to form additional reactive oxygen species, in particular, super-anion radicals (O2−, ROS) that improve the activity of the material. As a result, the increasing of phenol degradation by 30% compared to pure ZnO may be achieved at the choice of Ce-doped ZnO catalyst. [ABSTRACT FROM AUTHOR]

In this study we propose a new composite material with an enhanced bactericidal action that utilises the complex interactions with bacteria: mechanical interactions of the bacteria with ZnO tetrapod spikes, a photocatalytic process on ZnO nanoparticles, and disinfection by Ag nanoparticles. ZnO and Ag nanoparticles were immobilised on a single-crystalline ZnO tetrapod by the ultrasonic mixing method. The XRD, TEM, SEM and EDS analyses showed the tetrapod-like crystals covered by ZnO and Ag nanoparticles. This complex photocatalytic material, deposited on a grid support, was tested in the UV purifier air system in the AR Diagnostic company. The active microbial monitoring of the indoor air showed a decrease in the concentration of bacteria in the air of the meeting room, with the door open, at 90% for a duration of 30–40 min. A simple variant of the design of an air purifier system, which can be mounted in different types of air channels and compartments, is proposed. [ABSTRACT FROM AUTHOR]

The sintering behavior of tetragonal zirconia nanopowders modified by the group IV elements at the initial sintering stage was investigated. It was found that different additives SiO2, SnO2, and GeO2 have a significant influence on the densification kinetics of 3Y‐TZP nanopowders obtained by coprecipitation during sintering as it depends on the amount of additives (0‐5 wt%). The shrinkage of zirconia‐based specimens during the nonisothermal sintering was analyzed using the dilatometric data. The constant rate of heating technique was applied in order to determine the dominant mass transfer mechanism at the initial stage of sintering in modified zirconia nanopowders. It was found that there was a change in the mass transfer mechanism and diffusion activation energy in 3Y‐TZP as a result of the additives. The dominant sintering mechanism in 3Y‐TZP changed from the volume diffusion to the grain boundary diffusion due to the addition of SiO2 and SnO2 and the sintering activation energy increased in these cases. However, GeO2 additive activated the viscous flow mechanism in sintering process of 3Y‐TZP nanopowders which led to acceleration of the densification due to the decrease in the diffusion activation energy. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Photocatalytic activity ZnO depends from type of precursor material. • Precursor materials effect on the nature of the structural defects of ZnO. • ZnO with oxygen vacancies is more effective as a photocatalyst for phenol degradation. • Appearance of zinc vacancies in ZnO leads to a decrease in the photocatalytic activity. Abstract The effect of the type of structural defect in zinc oxide on its photocatalytic properties was studied for phenol photodegradation under UV-irradiation. It was shown that the use of different types of precursors (zinc oxalate and zinc hydroxide) for the production of zinc oxide leads to the formation of a material with the same phase composition and equal energy of the forbidden band, but different photocatalytic activities. Simultaneously, the peculiarities of the luminescence and electron spin resonance spectra indicate the formation of different types of defects in the structure of the material, namely, oxygen vacancies (V o) in the anionic and zinc vacancies (V Zn) in the cationic sublattices of zinc oxide synthesised from the zinc oxalate and hydroxide, respectively. Also, the different characteristics of the luminescence decays reveal the different recombination paths for the free charge carriers in the systems synthesised from the different precursors. The different times of the luminescence decay also confirmed the different methods of recombination of free charge carriers in systems synthesised from different precursors. It was shown that the appearance of defects in the cationic sublattice leads to a decrease in the photocatalytic activity of the material relative to phenol degradation. [ABSTRACT FROM AUTHOR]

Ceramics materials based on yttria stabilised tetragonal zirconia nanopowders (3Y-TZP) are widely used in the production fuel cells, oxygen sensors, refractories, etc. and intensively studied due to their outstanding mechanical and electrical properties. To obtain ceramics with specific properties different additives can be used. This allow for control over the features of a nanopowder’ structure and its consolidation during the sintering process. It is important examine in detail the initial sintering stage of tetragonal zirconia based nanopowders modified by third element additives. The present paper shows the impact of SiO2 and SnO2 additives and the influence of different methods of dopant addition (co-precipitation and mechanical mixing) on the kinetics of the initial sintering stage of tetragonal zirconia nanopowders. It demonstrates that sintering mechanism is changed by the addition of a small amount SiO2 and SnO2 by volume to the grain boundary diffusion in 3Y-TZP nanopowders obtained by the co-precipitation method. This change led to increased activation energy. This paper explores the reasons for the acceleration in the sintering process of nanopowders 3Y-TZP with SiO2 and SnO2 additives obtained by the mixing method. It shows that the sintering mechanism is the same as that of the initial 3Y-TZP powder obtained by the co-precipitation technique. The volume diffusion mechanism was the predominant mechanism at the initial sintering stage and was accompanied by a decrease in the activation energy of the sintering process. [ABSTRACT FROM AUTHOR]

The present study is devoted to the problem of structure formation in zirconia ceramic matrix composites. In this paper we have analyzed the general features and distinguish behavior standard mixing and co-precipitation technology to obtain composite zirconia nanopowders. We appreciate the opportunity of co-precipitation technique for its application in the semi industrial production of zirconia powders for ceramic products with wide range of application: structural, wear-resistant, functional etc. It was shown that co-precipitation technique matches for synthesis of zirconia based composite nanopowders with predetermined chemical, phase and granulometric characteristics. It was shown that the mechanical characteristics and durability of zirconia based composites sintered from these nanopowders increase in comparison with materials obtained by standard technology. The formation of unstable solid solutions during synthesis of nanopowders and its controlled decomposition during sintering are the basic distinguish feature of co-precipitation method. These processes lead to the formation of different type of inclusions and changes in phase, chemical and granulometric compositions in matrix material as well as rearrangement of residual stresses fields occurs in composite material. [ABSTRACT FROM AUTHOR]

The aim of this study was to produce yttria-stabilized zirconia nanopowders from zirconium oxychloride and zirconium oxynitrate salts using a co-precipitation technique, and to investigate the influence of hydrostatic pressure on the phase transition in these powders. It is shown that synthesis conditions and calcination temperature have a strong influence on the nanopowder's agglomeration, as well as on the stability of the tetragonal phase to phase transition under pressure conditions. Doped zirconia nanopowders synthesized from oxynitrate salts are more agglomerated and more stable than the oxychloride-based powders. Increasing the role of interfacial energy in agglomerated nanopowders leads to an increase in the stability of the tetragonal phase in doped zirconia nanopowders systems obtained at low and high calcination temperatures. Formation of separated nanoparticles at middle calcination temperature leads to a decrease in the stability of the tetragonal phase to phase transition under hydrostatic pressure conditions. [ABSTRACT FROM AUTHOR]

We have studied the effect of NiO on the sintering of yttria-stabilized zirconia at temperatures ranging from 1300°C to 1500°C in air and argon environments. It was found that the addition of NiO stabilized the cubic phase of ZrO2 independently from the sintering atmosphere. The monoclinic phase of ZrO2 formed only during sintering within the air environment at temperatures higher than 1450°C. The transformation of NiO to Ni by reversible decomposition depends on the sintering atmosphere, and this can lead to variations in the nature of inclusions and in changes of the structure and properties of nanocomposite materials in the system ZrO2–NiO(Ni). NiO and Ni inclusions can increase the indentation fracture toughness of zirconia–nickel oxide composite material more than 50%, which can be compared with zirconia ceramics during sintering in a neutral atmosphere alone. [ABSTRACT FROM AUTHOR]

Abstract: The difference in the magnetic properties between two lanthanum manganite nanopowders with identical phase and chemical composition is discussed in terms of the influence of nanopowder synthesis conditions on their properties. The aim of this investigation was to show the influence of precursor type and structure on the structure and properties of final La0.7Sr0.3MnO3 nanopowders obtained by precipitation technique. The forming of a complex structure of precursor materials during drying and inheritance at firing stage led to the formation of bimodal particle size distribution and magnetic properties typical of coarse powders. The correct choice of precursor material and the technological conditions of the drying and firing stage were allowed for the creation of a uniform powder structure with special magnetic properties. We showed that the magnetic properties of nanopowders were not always determined by chemical or phase composition and mean particle size of synthesized powders. The difference in precipitation process can lead to unpredictable and catastrophic results, and masked the effect of nanoparticles on the magnetic properties of the material. [Copyright &y& Elsevier]

The process of nanoparticles growth has been investigated and discussed in terms of mesoscopic approach on example of ZrO-3 mol%YO system. Growth process of nanoparticles synthesized by co-precipitation has three stages: cooperative-oriented crystallization of ordered areas in xerogel polymer matrix and disintegration of crystallized areas (350-400 °C); oriented attachment of particles into single crystal caused by electrostatic interaction (400-600 °C); attachment of particles to single and poly-crystals by oxygen diffusion through vacancies in surface layers of joining crystals (600-1,000 °C). Proposed conception on mesoscopic processes of nanoparticles formation make the understanding and theoretical description of significant amount of experimental data possible and open the way for purposeful governing by oxide powder system on the stages of obtaining, compaction, and sintering. [ABSTRACT FROM AUTHOR]

In order to evaluate the effect of interparticle contact area on the sintering behavior of 3Y-TZP nanopowder, the shrinkage of powder samples, compacted at different pressures were measured under constant rates of heating. Compaction of zirconia NPs at different pressures allowed to increase the contact area between particles and determined the critical parameters when the volume diffusion mechanism is changing on the grain boundary diffusion. It was found that the volume diffusion mechanism is the dominant densification mechanism at the initial stage of sintering for 3Y-TZP nanopowders at a low relative density of green ceramics, when there are few contacting particles, and the grain boundary diffusion mechanism cannot be realized due to the large diffusion path. The domination of the grain boundary diffusion mechanism during initial stage of sintering of 3Y-TZP nanoparticles was detected in case the contact area between particles increased up to 56%. • The effect of isostatic pressure compaction on the sintering of 3Y-TZP NPs was studied. • The contact area between particles effects on the diffusion mechanism during sintering. • The critical value of the interparticle contact area when GBD realized is ca 56%. • The VD mechanism can be realized in case of low contact area between particles. [ABSTRACT FROM AUTHOR]

The engineering of doped zirconia nanoparticles (NPs) for energy application is realized in concept Research Smart Laboratory. To improve nanomaterials' engineering, correlations of "salt concentration—powder dispersity" and "calcined temperature—particle's sizes" were built. The correlation of "materials structure—materials functionality" is made. The technology forming ceramics with varying grain sizes and densities under the same thermodynamic conditions (1350 °C) from NPs with different sizes is developed. The impedance spectroscopy with the distribution of relaxation time analysis is used for ionic conductivity ceramic investigation in range 240–900 °C. The activation energies of the grain and grain boundary oxygen diffusion are calculated. It was shown that the energy activation of bulk oxygen diffusion does not depend on ceramic grain size (Ea = 0.9 eV). The energies activation of grain boundary oxygen diffusion estimated in the framework of the bricklayer model show a weak growth with the rising of ceramic grains sizes. The values of the volume activation energy are close to the grain-boundary activation energy for ceramics obtained from nanoparticles smaller than 18 nm. It was found that the grain boundary space contains two types of elements with different geometries. The size of NPs used for ceramic determines the size of grain boundaries elements. It was shown that the density of sintered ceramic has a more substantial effect on its electrophysical properties than grain size. The NPs sizes of 18–24 nm are optimal for forming pressed powder compacts and sintered ceramics with high density. [ABSTRACT FROM AUTHOR]

It was shown the forming of Ag-contained ZnO-CeO 2 composites occurs due to the complex decomposition and structure transformation of oxide materials and Ag-complexes. It allows us to realise one synthesised approach for obtaining photosensitive materials with different particle sizes, defects and kinds of architecture. The possible mechanisms of photosensitivity of these materials are determined. For composite nanoparticles (NP) with sizes up to 30 nm, the photosensitivity is connected with an abnormal decrease of bandgap energies at reducing NP sizes and an effective charge separation due to electron stocks on [Се3+...O 2 ] centres and surface [Ce4+...O 2 -] oxidative centres formation. The appearance of the hyperfine structure pattern of six lines centred at g =2.002 and split by 93–94 G in the ESR spectra of the composite structure confirms the realization of this mechanism. For more big NP sizes of this composite, the surface plasmon resonance plays a more significant role in the material's photosensitive properties. The position of surface plasmon resonance depends on the kind of realised structure. The phase composition, temperature and reduction determine the type of structure (NPs/AgNPs ore core/Ag shell) that will be recognised in the Ag-contained CeO 2 -ZnO system. • Design of Ag- ZnO-CeO 2 system determined by temperature calcination, ZnO amount. • HFS lines of ESR spectra marks on produce of O 2 - for NP with size in 3 time bigger than in ceria. • SPR position depends on calcination temperature and system structural features. • Mi theory predicate the creation of CeO 2 /Ag Nps and CeO 2 (AgCl) core/Ag shell structure. • The difference mechanism photoactivity vs NP sizes are described. [ABSTRACT FROM AUTHOR]

Positron lifetime ( LT) and coincidence Doppler broadening ( CDB) measurements on nanopowders and ceramics of ceria- and magnesia-stabilized zirconia ( CeSZ and MgSZ, respectively) are presented. The nanopowders were prepared by the coprecipitation technique. Effects of nanopowder calcination and sintering at various temperatures were investigated. In the nanopowders, the two kinds of open-volume defects associated with grain boundaries ( GBs) could be identified via positron trapping: (i) vacancy-like misfit defects situated along GBs and (ii) larger defects at the intersections of at least three GBs (triple points). CDB measurements on CeSZ compacted nanopowders indicated a segregation of Ce ions along GBs. A few percent fractions of positrons were found to form positronium localized in pores of ≈1.8 nm diameter in compacted nanopowders. Sintering of nanopowders at 1500°C appeared to be sufficient for disappearance of pores and triple point defects. In sintered ceramics, contrary to compacted nanopowders, positrons were trapped in zirconium vacancies in grain interiors. [ABSTRACT FROM AUTHOR]