Papers by Keyword: Zirconium Oxide

Abstract: The palygorskite or attapulgite is a mineral clay of fibrous habits, a phyllosilicate 2:1, presented by the formula Mg₅[Si₈O₂₀](OH)₂(OH₂)₄.4H₂O. Taking advantage of this natural resource available in the State of Piauí, this research aims at incorporating the zirconium oxide to the surface of this clay, through the sol-gel method, in order to evaluate the photoactivity of the composite. The material was characterized by the X-ray diffractometry (XRD), indicating the presence of the zirconium oxide, with the emergence of peaks in 30.8° and 60.9°. It was observed the incorporation of zirconium on the clay by transmission electron microscopy (TEM) and verified the fibrous habit and the presence of ZrO₂ on the surface of the clay with 1.35% of incorporated zirconium and 127.4 m² g^-1. The rate of degradation of the Remazol Blue dye was 93.5% when using the composite.

Abstract: Nanocrystalline zirconium oxide (ZrO₂) was synhesized by hydrothermal method in presence of hydrogen peroxide. Surface morphology analysis depicts the formation of the nanorods. The structural analysis confirms that the as-synthesized ZrO2 product is of pure monoclinic phase (m-ZrO₂) with crystallite size of about ~8 nm. The product consists of monodispersed nanoparticles of uniform composition, high purity, and crystallinity. The Raman spectra are quantitatively analyzed and the observed peaks are attributed to various vibration modes of the m-ZrO₂. Photoluminescence (PL) spectrum of ZrO2 nanostructure showed a strong and broad emission peak at around 534 nm, which can be attributed the participation of several energy levels.

Abstract: The morphology ZrO₂-Ti composites depends on used powders substrates, methods of forming and sintering conditions. In this study a composite from the nanosize ZrO₂ powder stabilized by 3 mol% Y₂O₃ and 3 vol. % Ti powder with particle size about 15 μm was prepared. A composite material was formed by uniaxial pressing. Sintering process was conducted in an argon atmosphere at 1300°C with retention time 2h. The selected physical properties of the green body and sintered ZrO₂-Ti composites were determined by Archimedes method. The microstructural characterization was carried out using the x-ray diffraction and the scanning electron microscope (SEM) with EDS analysis. Stereological analysis by using computer programs was supported. The SEM observation and EDS analysis of the cross-section of the samples confirmed that the Ti particles are distributed homogenously in analysed areas. The EDS analysis revealed partial solution of titanium in ZrO₂ matrix. Moreover, the x-ray diffraction exposed the existence of tetragonal zirconium oxide and titanium or a new phase from Ti-Zr-O system. The stereological analysis showed similarity between the starting particles of Ti powder and particles of titanium in the composite matrix.

Abstract: Thin SiO₂ZrO₂ films were prepared, up to 0.2 μm thick, by means of the sol–gel technology and characterized by a Scanning electron microscopy and X-ray diffraction. It is shown the presence of monoclinic, cubic and tetragonal phases of ZrO₂ in the SiO₂ matrix. The crystallites sizes depend on the annealing temperature of the film and amount to 35 and 56 nm for the films annealed at 773 and 973 K, respectively. The films resistance is rather sensitive to the presence of NO₂ and O₃ impurity in air at lower operating temperatures in the range of 30-60°C.

Abstract: To study the fuel debris treatment at Fukushima Daiichi NPP, information on the behaviour of fuel and structural materials in severely damaged reactors, i.e., oxides and metals of uranium and zirconium is essential. Since sea water was introduced to the reactors, situation of fuel debris became different from that for TMI case. In this paper, phase relations of uranium and zirconium oxides were analyzed by powder XRD method at high temperatures. By the heat-treatment of the mixture of UO₂ and ZrO₂ (U:Zr=1:1) under 10 torr air, UO₂ was oxidized to U₃O₈ over 800 ^oC, The UO₂ like phase appeared again at 1350 ^oC which may be caused by the decomposition of U₃O₈. The oxidation behavior of the UO₂-ZrO₂ system was also investigated by using solid solution sample with different U/Zr ratios under different steam and oxygen pressures. The oxidation of the UO₂-ZrO₂ mixture seemed to be suppressed with decreasing U/Zr ratio. The behavior of fuel materials in the presence of seawater was also discussed as well as that for other structural materials.

Abstract: The phase transformation of zirconia from monoclinic to tetragonal polymorph at room temperature under mechanical processing has been a subject of a great interest due to technological importance of this material. Mechanism of this transformation has been widely investigated and plenty of explanation theories of zirconia stabilisation have been developed as well. This article critically reviews the systematic development regarding this transformation under mechanical processing and includes the summarised results of key-publications on this topic.

Abstract: Technology for manufacturing products by magnetic pulse compaction from oxide powders of the (ZrO₂ – Y₂O₃) – Al₂O₃ system is presented in the paper. Diagram of the magnetic-pulse press with its operating principle being based on Ampere's law is given. Physical and mechanical properties of the obtained compacts are determined. The main feature of the designed technology is the reduced sintering temperature (200 °С) and the acquired fine-grained structure of the products. Another significant advantage achieved by applying the technology is the possibility for manufacturing fine-grained structure ceramic products with high mechanical properties.

Abstract: The article is devoted to the investigation of alumina-zirconia ceramics properties depending on its production technology. Analysis of the technological factors that allow acquiring fine-grained structure as well as high physical and mechanical properties of alumina-zirconia ceramics is presented in the paper. It is shown that when using magnetic pulse compaction due to the pulse impact and adiabaticity of the process the most compact structure is formed. It is possible to obtain pressings with the density of up to 68% of the theoretical value. The obtained compact structure secures high physical, mechanical, and operating characteristics of the finished product.

Abstract: The article focuses on the investigation of the properties of alumina-zirconia ceramics possessing high mechanical characteristics and good conductivity at high temperatures. Measurement results of the dielectric dissipation factor, dielectric constant, electric conductivity when using direct and alternating current for the ceramics samples of 80%(ZrO₂-3%Y₂O₃)-20% Al₂O₃ composition are presented in the paper. Measurements were conducted simultaneously in the electrostatic field in vacuum while heating the samples to the temperatures ranging from 300 to 1700K. Investigations showed that alumina-zirconia ceramics at high temperatures obtains ferroelectric properties not typical of these structures.

Abstract: Grinding technology is used in this study to overcome the hard machining of ceramic with hard and brittle characteristics. The grinding machine with diamond grain size 25 and 5 , spindles speed 1720 rpm and 3450 rpm are applied. Combining the unintentional roll clamp and the grinding machine, ceramic rods can be ground to the desired size.In the research, surface profilometer is applied to measure the rod surface roughness of processing results under different conditions. The results show that the grinding wheel with finer particle, the roughness of the ground ceramic rod will be better. While the rotation speed of grinding wheel is increased, the surface roughness will have the same trend.