V. V. Sirota

Structure and properties of nanoporous ceramic Al2O3 obtained by isostatic pressing

Nanoporous ceramic with pore volume of the order of 60% is obtained from nanosize Al2O3 powder by isostatic pressing. The microstructure, porosity and strength of the ceramic obtained are studied. Technological conditions for obtaining nanoporous ceramic which secure the optimal combination of strength and porosity are determined.

Diffuse Phase Transition and Ferroelectric Properties of Ceramic Solid Solutions in New SrTiO3-BiScO3 System

Ceramic solid solutions of (1-x)SrTiO3-(x)BiScO3 system with x=0, 0.05, 0.1, 0.2, 0.3, 0.4 and 0.5 have been for the first time synthesized via solid-state processing techniques. Both of end compounds in this system are not ferroelectric materials. X-ray diffraction analysis revealed that at room temperature the samples under study at x=0.2, 0.3, 0.4 and 0.5 consist of mixture of center-symmetric cubic Pm3m phase and polar tetragonal P4mm phase. Anomalous behaviour of dielectric permittivity and dielectric losses for these samples is found to be specific one for ferroelectrics with diffuse phase transitions. Furthermore, examination of the polarization hysteresis behavior revealed weakly nonlinear hysteresis loops in the ferroelectric phase.

MICROSTRUCTURE AND MECHANICAL PROPERTIES OF ALUMINA POWDER COATINGS BY A NEW MULTI-CHAMBER DETONATION SPRAYER

The dense ceramic coatings based on alumina with hardness of 1100±25 HV0.3 and porosity of less than 1% have been prepared by multi-chamber detonation sprayer (MCDS) with a barrel length of 500mm. The intermetallic compound of type FeAl was revealed in the area of the coating that adjoins the substrate.

Synthesis of Magnesium Oxide Nanopowder by Thermal Plasma Using Magnesium Nitrate Hexahydrate

Magnesium oxide (MgO) nanopowder was synthesized by thermal plasma in a novel thermal DC plasma torch using magnesium nitrate hexahydrate. Magnesium nitrate hexahydrate (Mg(NO3)2·6H2O) was obtained from serpentinite (Mg3Si2O5(OH)4; lizardite) (Halilovskiy array, Orenburg region, Russia). The synthesized samples were characterized by analytical techniques including X-ray diffraction (XRD) and transmission electron microscopy (TEM). XRD and TEM characterization studies confirmed that MgO nanopowder obtained has periclase structure with high purity, and the particle sizes vary within the range of 100 nm to 150 nm. We believe that the present work will promote further experimental studies on the physical properties and the applications of MgO nanopowders in the fields such as high-densed ceramics, additives in bactericide, and refractory products.

Properties and Peculiarities of WCCoCr Coatings Formed by Multi-Chamber Detonation Sprayer

Multi-chamber detonation sprayer (MCDS) was applied for deposition of WC-Co-Cr powder coatings on corrosion-resistant steel. Powder AMPERIT®554.074 WC-Co-Cr was used to deposit of a coatings. The coatings microstructures and phase compositions were characterized using SEM, OM and XRD techniques. Measurement of the microhardness of samples was done with a micro-hardness tester DM – 8B using a Vickers’s indenter with load on of 0.3 N. It was established that MCDS has provided the conditions for formation of a dense layer with porosity of less than 1.5 % and microhardness 750±50 HV0.3.

Properties of Alumina-Titania Coating Formed by a New Multi-Chamber Gas-Dynamic Accelerator

Thermal-sprayed alumina–titania coatings (Al2O3:Ti wt ratio = 60:40) were prepared by a new multi-chamber gas-dynamic accelerator. The coatings were examined by using scanning electron microscopy, X-ray phase analysis and Vickers hardness tester at a test load 0.2 kg. The coating was well-adhered with corrosion-resistant steel substrate. The results show that the microstructure of the alumina–titania coatings consists of areas with different degrees of melting: the lamella built up from the fully melted particles of the powder, and partially melted areas. The developed coating is highly dense (porosity is less than 0.7%). Research results show that hardness of alumina–titania coatings (Al2O3:Ti wt ratio = 60:40) can achieve up to 655 HV0.2 and the specific wear rate of alumina-titania coatings is 52.40∙10-5 mm3 (m∙N)-1.

Microstructure and Microhardness of Alumina-3wt. % Titania Coating Formed by a New Multi-Chamber Gas-Dynamic Accelerator

Alumina-titania coatings are widely used in industry for wear, abrasion or corrosion protection components. This paper presents the results of the investigation of the structure and microhardness of the alumina-titania (Al2O3:Ti wt ratio = 97:3) coating was prepared by a new multi-chamber gas-dynamic accelerator on corrosion-resistant steel substrate. Morphology of the powder particles, microstructure and phase composition of the coating were characterized with the use of scanning electron microscopy, X-ray phase analysis and Vickers hardness tester at a test load 0.2 kg. The results show that the microstructure of the alumina–3wt.% titania coating consists of region with different degrees of melting: the lamella built up from the fully melted particles of the powder, and partially melted regions. The developed coating by this method is highly dense (porosity of less than 0.2%) and tightly adherent.

Structure and Microhardness of Titanium-Based Coatings Formed by Multichamber Detonation Sprayer

A series of titanium-based coatings (50–550 μm thick) on an aluminium substrate was deposited via multichamber detonation sprayer with different barrel lengths (300, 400, and 500, all in mm). The titanium-based coatings obtained in these three experiments were examined by optical microscopy, scanning electron microscopy, and X-ray phase analysis. The hardness tests were carried out by the Vickers method with a test load of 50 g. The multichamber detonation sprayer with a barrel length of 500 mm produced the dense layers of coating with hardness of  HV0.05 and porosity of 0.24%, the best result in the experiments.

Deposition and Characterization of CoCrAlY Coatings by Multi-Chamber Detonation Sprayer

In this study, a multi-chamber detonation sprayer (MCDS) was applied for deposition of Co-Cr-Al-Y powder coatings (200-250 mm thick) on nickel base superalloy JS6U (Russia). Powder Co-25Cr-11Al-1Y (d(0.1): 6.6 μm, d(0.5): 62.7 μm, d(0.9): 123,4 μm) was used to deposit of a coatings. The coatings microstructures and phase compositions were characterized using SEM, OM and XRD techniques. Measurement of the microhardness of samples was done with a micro-hardness tester DM – 8B using a Vickers’s indenter with load on of 0.1 N. It was established that MCDS has provided the conditions for formation of a dense layer with porosity 0.05% and microhardness 600±50 HV0.1.

Particulars of Hydrothermal Synthesis of Nanosize Powder (Zr1–xYx)Oy

Nanocrystalline (Zr1–xYx)Oy powders were synthesized by a method combining co-precipitation and hydrothermal decomposition. The granulometric composition was certified, x-ray phase analysis was performed, and the pycnometric density of the synthesized powder was determined.