The article presents the issues of replacing leucosapphires in jeweled bearings of the axes of precision instruments with nanostructured crystals of partially stabilized zirconia. The statement is substantiated that doping with rare earth elements provides an improvement in the performance properties of precision instruments by improving the mechanical properties of bearing materials. The efficiency of doping of zirconia crystals with cerium and neodymium oxides is studied. It was found that doped crystals have increased plasticity, which provides an increase in the crack resistance of crystals. Special attention is paid to the issues of increasing the survivability of high-speed rotor bearings by replacing the thrust bearing of leucosapphire with nanostructured crystals of partially stabilized zirconia doped with cerium and neodymium. The efficiency of improving the mechanical properties is confirmed by the X-ray phase analysis of crystals. The phase composition is studied by Raman scattering and the lattice parameters are determined. The increased crack resistance of the thrust bearing is confirmed by tests performed using the kinetic microhardness method.
Magnesia, ceria partially stabilized zirconia (Ce,Mg)-PSZ ceramics with net shape microstructure are prepared using a processing method similar to that of conventional Mg-PSZ ceramics, then heat-treated at 1500°C for different time. Microstructure and phase composition of (Ce, Mg)-PSZ samples with different amount of CeO2 doped were investigated using SEM and X-ray diffraction. The addition of CeO2 could impede the formation of monoclinic phase and inhibit the growth of cubic grains. A microstructure with net-shape cubic grains, in which tetragonal precipitates interweave to a nanoporous structure is obtained by adding 4∼8 mol% CeO2 in 10mol% MgO doped zirconia matrix and then heat treatment at 1500°C for different time. The precipitate morophology might be related with the addition of CeO2 and the heat treatment temperatures.
High temperature plasma nitriding of yttria-partially-stabilized zirconia in atmospheric pressure microwave plasma was investigated. The morphological, mechanical, and physicochemical characteristics of the resulting nitrided layer were characterized by different methods, such as optical and scanning electron microscopy, microindentation, x-ray diffraction, narrow resonant nuclear reaction profiling, secondary neutral mass spectrometry, and x-ray photoelectron spectroscopy, aiming at investigating the applicability of this highly efficient process for nitriding of ceramics. The structure of the plasma nitrided layer was found to be complex, composed of tetragonal and cubic zirconia, as well as zirconium nitride and oxynitride. The growth rate of the nitrided layer, 4 µm/min, is much higher than that obtained by any other previous nitriding process, whereas a typical 50% increase in Vickers hardness over that of yttria-partially-stabilized zirconia was observed.
Al2О3:Dy3+ oxides with different colors luminescence were synthesized using precursor technology. The phase composition and crystal structure of the obtained materials were established by X-ray powder diffraction analysis. The excitation and emission spectra, decay curves, thermal quenching of luminescence were studied. Under UV excitation, the phosphors exhibit blue, purplish blue, white emission depending on the concentration of dysprosium and the temperature of annealing of the Al1-xDyx(OH)(HCOO)2 precursor in air.
This paper presents the results of the studies carried out in the model systems and concerning the tobermorite synthesis with an addition of metahalloysite. Quartz sand and quicklime were the main raw material constituents. The mixtures in the form of slurries underwent hydrothermal treatment with an addition of metahalloysite (5%, 10%, 15%, 20% and 30%) for 4 hours and 12 hours. The resultant composites were analysed for their phase composition using X-ray powder diffraction. The microstructure was examined using the Scanning Electron Microscope. Tobermorite was the principle reaction product. When 30% metahalloysite was added to the mixture containing CaO and SiO2, the formation of katoite was found.
The effect of complex high-energy action, including mechanical milling of Li2CO3-Fe2O3-ZnO initial reagents mixture and its consistent heating by the pulsed electron beam on solid-phase synthesis was studied by X-ray powder diffraction and thermal analyses. The initial mixture Li2CO3-Fe2O3-ZnO corresponds to the ferrite with stoichiometric formula: Li0.5(1–x)ZnxFe2.5–0.5xО4, where х = 0.2. The same studies were carried out with thermal heating in a laboratory furnace for detection the effect of radiation on the formation of phase composition lithium-zinc ferrite. Initial mixture was milled in AGO-2S planetary ball mill with a milling speed of 2220 rpm for 60 min. Radiation-thermal synthesis of the milled mixture was carried out by the pulsed electron accelerator (ILU-6) at 600°C and 750°C. The maximum time of the isothermal stage was 60 minutes. According to the X-ray powder diffraction and thermogravimetric analysis, it was found that the complex high-energy action leads to decrease a temperature and time of obtaining lithium-zinc ferrite homogeneous in phase composition. The proposed high-energy regimes allow to synthesized lithium-zinc ferrites at 600 °C for 60 minutes, which is much lower compared to conventional ceramic technology.
Studies of changes in the flexural strength and phase composition of castable refractories are being carried out in simulated coal gasification reactor environments. This paper describes a pressure vessel in which x-ray powder diffraction measurements can be made by an energy dispersive method while the specimen is being heated to temperatures as high as 1000°C in atmospheres containing H2O, CO2, CO, H2, CH4, NH3 , and H2S at pressures up to 7 MPa (1000 psig).
Improving the mechanical properties of zirconia in instrument bearings