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.
Materials Science. Non-Equilibrium Phase Transformations.
Vol. 2 (2016), Issue 1
Table of Contents
In the present study authors examined the sintering behavior on the initial sintering stage of fine tetragonal zirconia nanopowders (containing 3 mol % Y2O3) with and without mechanical activation in a ball mill. The initial sintering behavior was examined by constant rate of heating method (CRH) at different heating rates. We defined a role of the particles surface mechanical activation and its influence on the sintering mechanisms during the sintering of yttrium-stabilized zirconia nanopowders. We found that even a small mechanical action causes change initial characteristics of nanopowdres which can accelerate sintering processes. Increases of milling time causes change of sintering mechanism from volume (VD) to the grain-boundary (GBD).
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.
INVESTIGATION OF NANOPOWDER DISPERSED SYSTEM BASED ON ZIRCONIA BY TRANSMISSION ELECTRON MICROSCOPY, ELECTROCHEMICAL IMPEDANCE SPECTROSCOPY AND SPIN-ECHOpg(s) 22-25
A comprehensive study of the structure and electrical properties of nanopowder system based ZrO2 + Y2O3 3mol% was conducted. The presence of electrically continuous ion atmosphere, which consist from hydrogen-containing functional groups with different spin-spin relaxation times of hydrogen nuclei 1H was revealed. An original method of investigation of electrical properties of nanoparticles and surrounding ionic atmosphere based on electrochemical impedance spectroscopy was suggested.
INFLUENCE OF CHEMICAL COMPOSITION OF TOOL STEEL ON PERMANENT PLASTICITY DURING HEAT TREATMENT TRANSFORMATIONSpg(s) 26-29
The work presents the research of permanent strain occurred when metallurgical transformations take place even under small stress applied externally lower than the yield stress of weaker phase. Four tool steel grades were tested: THG2000 (Uddeholm, Sweden), 20X13, 40X13 and 95X18 (GOST). All steel grades differ in carbon content and amount of alloying elements and behave differently when transformation plasticity occurs. This phenomenon was observed during bending test when bending stress was 100MPa and was less than 10 % of yield strength of the steel. The steel specimens were heated to 950-1050 °C temperature and then bent during air quenching. Plastic deflections were observed though all cooling process that involved martensitic transformation as well. Different effect of compression and tensile stresses on microstructure evolution during martensitic transformation was determined as both type of stresses formed in bent specimens.
SYNTHESIS OF MULTICOMPONENT ADVANCED COMPOSITE OXIDE NANOMATERIALS – NEW APPROACHES TO OLD INDUSTRIAL METHODSpg(s) 3-6
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.
RESEARCH AND DEVELOPMENT OF AN SPD TECHNIQUE FOR THE PRODUCTION OF NANOSTRUCTURED ALUMINUM WIRE FOR APPLICATION IN ELECTRICAL ENGINEERINGpg(s) 30-32
This paper presents the results of the computer and experimental study of a promising technique of severe plastic deformation (SPD) – Multi-ECAP-Conform (M-ECAP-C) for the fabrication of long-length nanostructured billets (wire rods) with an enhanced strength and electrical conductivity from the aluminum alloy EN-AW 6101 in a single processing cycle. On the basis of the obtained results, a new rational geometry of the pressing channel for the M-ECAP-C technique has been developed. The stress-strained state, structure and mechanical properties of pilot samples of wire rods have been studied. It has been established that processing by the new technique leads produces enhanced mechanical and physical properties.
DETERMINE THE FATIGUE LIFETIME FOR ALUMINIUM ALLOY EN AW 2007.T3 DURING CYCLIC BENDING – TORSION LOADING UNDER IN-AND-OUT OF PHASE SHIFT Φ = 0° AND Φ = 90° USING SELECTED FATIGUE CRITERIApg(s) 33-36
The article deals with determining of fatigue lifetime of aluminium alloy EN AW 2007.T3 during by multiaxial cyclic loading. The theoretical part deals with the fatigue and with the criteria for evaluation of multiaxial fatigue lifetime, in region low-cycle and high-cycle fatigue. The experimental part deals with modeling of combined bending – torsion loading and determining the number of cycles to fracture in region low-cycle and high-cycle fatigue and also during of loading with the sinusoidal wave form under in phase φ = 0° and out phase φ = 90°.
INCREASE OF WEAR RESISTANCE OF METASTABLE AUSTENITE Cr-Mn-N STEEL DIFFUSION BORIDE COATINGS IN CONDITIONS OF ACTION THE EXTERNAL MAGNETIC FIELDpg(s) 37-40
In this paper it was investigated the formation of complex boriding diffusion layers on metastable austenite Cr-Mn-N steel powder method. Defined phase and chemical composition, thickness, microhardness and wear resistance obtained by layers of metastable austenite Cr-Mn-N steel. It is established that the application of an external magnetic field (EMF) leads to a redistribution of the proportion boride phases in the surface layers of the crystal lattice period changes. EMF allows in 1.5 – 2 times to reduce the period of saturation details, microhardness diffusion boride coatings increase to 20,5 – 21 GPa and increase their wear resistance in 2.4 – 3 times compared to steel without protective coating. Boriding a magnetic field will increase the microhardness boride coatings 6 – 7 GPa compared to the boriding without application of a magnetic field.
EFFECT OF AL2O3 NANOMATERIALS ON CONVECTION HEAT TRANSFER ENHANCEMENT IN A PLATE HEAT EXCHANGER CHANNELpg(s) 41-45
Intensive studies are being carried out in order to produce high-efficiency compact heat-exchanger devices to use energy more efficiently and to look for new working fluids for the purpose of enhancing heat transfer. Channels with corrugated surfaces and traditional fluids (water, oil ethylene glycol, etc.) ensuring heat transfer by convection are widely used in the industry. In this study, convection heat transfer by using nanofluids (distilled water + nanomaterial) was investigated experimentally in order to investigate the effect on Al2O3 nanomaterials on heat transfer enhancement in a corrugated channel with a chevron geometry extensively used in plate heat exchanger.
Ti and its alloys are mostly used for implant production. Their biocompatibility depends on the formation of thin TiO2 layer on the surface. It can be improved by modification of oxide structure in tubular. For biomedical applications, the adhesion of the coating layers is essential. The aim of the present paper is to investigate the adhesion of TiO2 nanocoatings on titanium surface.
Commercially pure Ti (CP Ti) and Ti-6Al-4V alloy samples were grinded, etched and anodized. The anodization was done in 0.5 wt.% HF electrolyte with duration of 7 hours for the CP Ti samples and 6 hours for Ti-6Al-4V alloy samples. The adhesion was investigated by tape and scratch tests. The critical loads that generate the first failures during the scratch test are used for characterization of the adhesion of the TiO2 nano-tubular coating. The critical loads were measured by CSEM-Revetest macroscratch tester under progressive scratching mode. The samples were characterized by SEM and EDX analysis. The areas around the critical load were further observed by optical and scanning electron microscopy for detail inspection of failure mechanism.
It was established that the higher micro-roughness of the surface of CP Ti sample after anodization is responsible for the detachment only of small areas of the nano-tubular coating situated mainly on the top surface. The lower micro-roughness of the sample made of titanium alloy and the presence of large flat areas lead to detachment of large coating’s portions. The scratch test reveals that the TiO2 nano-tubular coating on the CP Ti fails at an early stage (Lc1 ~ 8 N; Lc2 ~ 26 N), while that on the Ti-6Al-4V sample undergoes cohesive failure and completely fails at higher load values (Lc1 ~ 13 N and Lc2 ~ 40 N respectively). As titanium alloy is ductile material with higher strength than the CP Ti, it provides better support for the coating and produces higher critical loads.
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.