Papers by Keyword: Zro₂

Abstract: ZrO₂ fibers and belts have been fabricated by heat-treating the hybrid fibers and belts which were prepared by electrospinning method. Fiber and belt properties, for instance, surface morphology, diameter of fibers, crystallization formation, etc. were investigated by various techniques, scanning electron microscopy (SEM), X-ray diffractometer (XRD), transmission electron microscopy (TEM), energy dispersive spectrum (EDS) included. It was found that more belts and thicker fibers appeared with increasing PVP content. Using N,N,N-trimethyl-1-dodecanaminium bromide (DTAB) can avoid formation of belts and reduce the diameter of fibers from a range of 270 to 750 nm to a range of 90 to 150 nm. It all obtained monoclinic ZrO₂ fibers and belts after heat-treating (respectively at 700, 800, 900 °C) hybrid fibers and belts. The higher temperature heat-treatment leads rougher fibers and belts.

Abstract: The material flow in particle reinforced metal-matrix-composites (MMC) had been investigated. The composite consisted of TRIP steel and magnesium stabilized ZrO₂ particles (Mg‑PSZ) in volume fractions of 0 %, 5 % and 20 %. The basic materials were produced by hot-pressing and showed a very homogeneous particle distribution and a almost full density. Then the samples were cut to wedge shape and hot-rolled with a constant roll gap. Caused by the shape, the true strain increased over the length and reached a maximum of true strain of 0.6. The strain rate was set to be higher than 0.1 and lower than 10/ s. After rolling, it was possible to combine rolling force, true strain and the material flow due to the grid on the surface. With an increase in volume fraction of Mg‑PSZ the rolling force increases as well. Metallographic examinations were performed to determine and document the flow of particles within the composite due to true strain conditions. It was found that the particles flow with the base material and turn parallel to the rolling direction. This effect was measured using the degree of orientation of partially oriented linear structure elements Ω_12, according to ASTM E 1268-01. The index was increasing with increasing true strain value. Further microscopic examination showed debonding of the interface between particles and matrix-material. For MMC’s having a volume fraction of 20 % Mg-PSZ a true strain at fracture of 0.5 to 0.6 was determined.

Abstract: To improve the properties and RH degasser slag corrosion resistance of magnesia-chrome refractory, the effect of the addition of ZrO₂ was investigated. The results showed that the presence ZrO₂ additive can densify the magnesia-chrome samples due to promotion of grain boundary activities and ultimately direct bond formation, which improved the high temperature mechanical properties and corrosion resistance. The results also indicated that in the RH degasser slag system with a high ratio of calcia to silica, the slag resistance behavior of magnesia-chrome composite added ZrO₂ could be described as follows: the ZrO₂ reacts with CaO to form the calcium zirconate compound which is densification lay and simultaneously, could increase corrosion resistance performance by blinding pore and thickening slag viscosity. Therefore, it is expected to be the major reason for the ZrO₂ enhanced corrosion resistance behavior observed for magnesia-chrome refractory.

Abstract: Ceramic materials have become of high industrial importance in some applications as their properties outperform ones of metallic components. However, use of ceramics is limited due to the difficulties in shaping. Electrically conductive ceramics can be machined by Electro-Discharge Machining (EDM) irrespective of its hardness or strength. In this study, yttria stabilized zirconia (YTZP) conductive composite was produced by incorporation of the cost-effective graphene coated alumina nanofibers (ANFC) into the matrix. Almost fully dense YTZP/5 vol.% ANFC nanocomposite was obtained by spark plasma sintering (SPS) at 1250 °C with uniaxial pressure of 40 MPa. Scanning electron microscopy observation of the microstructures showed that ANFCs were homogeneously dispersed in the matrix. Addition of ANFC resulted in slightly decreased mechanical properties, but the electrical resistivity of the composite dropped 9 orders of magnitude compared to monolithic zirconia, exhibiting 1.4 Ω∙m, satisfying the required condition for the EDM.

Abstract: Despite the impressive development in understanding transformation toughening, tailoring the toughness of zirconia toughened alumina (ZTA) ceramics remained a major challenge. In our research, a simple route based on the powders mixing process of ZTA powders with varying CeO₂ additions (0 - 10 wt.%) is developed to investigate this issue. The experimental results clearly reveal that the fracture toughness of ZTA ceramics can be tailored by mixing of ZTA starting powders.

Abstract: Dry sliding wear and friction behavior of cast A356 Al-Si alloy and composite containing 5wt. % ZrO₂ particles were studied by means of a pins-on-disk apparatus over loads of 5N, 20N and a sliding speed of 0.628m/s. The experimental results showed that the composites exhibited a higher wear resistance in comparison to that of the unreinforced A356 alloy. The friction coefficient of tested materials increased with increasing applied load from 5 to 20 N. FESEM investigations revealed that the wear mechanism of the A356 matrix alloy changed from sever abrasive, adhesive wear into mild abrasion and adhesive wear with addition of 5wt. % ZrO₂ reinforcement particles.

Abstract: The design of tribocorrosion resistant composite on Ti6Al4V alloy by laser surface cladding of admixed metal-ceramic powder was successfully achieved using a 2 kW CW ytterbium laser system (YLS). The effects of TiNiZrO₂ addition on the tribocorrosion properties of the synthesized composite coatings were investigated in 1 M H₂SO₄ solution using open circuit potential and potentiodynamic polarization techniques. The experimental results showed that TiNiZrO₂ refined the microstructure to flower-like structure. A strong metallurgical bond was obtained between the coatings and the Ti6Al4V alloy substrate with inter-columnar widmansttaten α΄ grains at the interface. There was a significant increase in surface microindentation hardness values of the clad layers. Also, the presence of zirconia shifted the tribocorrosion potential to more noble values and significantly enhanced the tribocorrosion resistance of the composites.

Abstract: This work aims to synthesize ZrO₂ by the combustion reaction method and its sulfating for future use as a catalyst in esterification of the cottonseed oil. The synthesized sample was produced in batches of 15g, using as precursor the zirconium IV n-propoxide and urea as fuel. The sulfating occurred with an ion content of SO₄^-2 with 30% in relation to the mass of ZrO₂. The samples were characterized by XRD, SEM and particle size distribution. The results revealed the formation of the monoclinic majority phase with traces of the orthorhombic phase referring to the synthesized sample, and a transformation of the orthorhombic phase to the tetragonal phase when sulfated. The morphology have shown the formation of homogeneous and spherical agglomerates, with a mean particle size of 24.34nm. The presence of traces of the tetragonal phase in the XRD of the SO₄^2-/ZrO₂ was a great indicator for future use in the esterification reaction to obtain biodiesel, because this type of phase after sulfating becomes very promising for the ester obtaining.

Abstract: Transparent inorganic-organic film with nanoparticle shows promising application in various technology field. In order to obtain transparent inorganic-organic composite film, the main challenge is to homogeneously disperse inorganic nanoparticle in polymer matrix without coagulation. This study demonstrated that silane-modification can obtain ZrO₂ with chemically bonded silane. The ZrO₂ nanoparticle shows good stability in various organic phase. Thus prepared inorganic-organic composite film has transparence as high as 80%.

Abstract: We report successful synthesis of baddeleyite type monoclinic zirconium oxide nanocrystals formation. The product mixture of zirconium incubated at room temperature for 7 days were thoroughly investigated employing X-ray diffraction, Raman spectroscopy and transmission electron microscopy studies. XRD and Raman studies revealed the formation of baddeleyite type monoclinic zirconium oxide nanocrystals. TEM studies revealed the nanocrystal formation with size ranging from 100 nm to 200 nm.