Papers by Keyword: Zirconium Oxide

Abstract: We have investigated the effect of zirconium oxide on the thermal degradation and flame retardancy of viscose fibers. ZrO₂/cellulose fiber was prepared by wet spinning. Combustion behaviour and flammability were assessed using the limiting oxygen index (LOI) and thermogravimetric analysis from ambient temperature to 800°C and cone calorimetry. LOI results showed that the ZrO₂ increased the LOI of viscose fiber from 20% to 26%, which showed that ZrO₂ particles had a positive effect on cellulose flame-retardancy. Results from thermogravimetric analysis (TG) indicated that the ZrO₂/cellulose fibers produced greater quantities of residues than viscose fibers. The combustion residues were examined using the scanning electron microscopy, indicating that ZrO₂/cellulose fiber produced consistent, thick residues. Cone calorimetry indicated that heat release rate and total heat release values of ZrO₂/cellulose fiber were less than those of viscose fibers.

Abstract: In order to examine if the lead-in threaded devices can replace the traditional threaded devices in practical production, this paper primarily studies the structure and material of the lead-in threaded devices by analyzing its performance, the cleanness, mechanical properties and appearance of raw silk it produces, and by comparing it with traditional threaded devices. The experimental result shows that the lead-in threaded devices performance and the cleanness and mechanical properties and appearance shape of its raw silk are superior to the traditional threaded devices, it can completely replace the traditional threaded devices in process effects in actual production.

Abstract: It is well known that a minor addition of rare earth oxides can provide a beneficial effect towards various catalytic reactions. Use of rare earth oxide in different applications could improve commercial productivity in an affordable way. Among the rare earth oxides, ZrO2, La2O3 and CeO2 are very interesting due to their various characteristics showing a large range of applications in organic reactions. The changes in the molecular properties of materials at the nano scale level greatly enhance their physical properties as well as chemical properties and activity. Due to the extremely small size of the particles, an increased surface area is provided to the reactant enabling more molecules to react at the same time, thereby speeding up the process. In this work, the enhancement in the catalytic activity of these nano structured rare earth oxides has been studied under different reaction conditions. Nano crystalline ZrO2, La2O3 and CeO2 samples were synthesized using precipitation method and optimum reaction conditions have been established; whereas the corresponding bulk samples were synthesized by combustion method. The identification of phase and crystalline size of synthesized oxides have been done by X-ray diffraction, the band gape of these three oxides in both the forms has been analyzed by UV absorbance and surface area has been determined by gas adsorption analysis (BET). Moreover their different properties and the activity of nano crystallite oxides have also been compared with their bulk counterparts. Even the activity of ZrO2 is also compared with the rare earth oxides La2O3 and CeO2.

Abstract: The resistance switching behavior in sputtered Ti/ZrO₂/Pt sandwiched structure was investigated for nonvolatile memory application. Multiple current-voltage measurements reveal highly uniform distribution of the conduction current and switching voltage. This bipolar resistive switching driven by bias of proper magnitude and polarity is interpreted by filament model. The reset threshold increases with the compliance setting imposed on the turn-on transition, while the switching currents in high and low resistance states are not varied for different top-electrode areas. Both characteristics are ascribed to the electro-chemical reactions of field-induced reduction-oxidation processes.

Abstract: We explore the unipolar resistance switching effect in sandwich structures based on Nb, Ta and Zr oxide thin films. The structures were fabricated by pulsed laser deposition and low temperature anodic oxidation methods. After electroforming process memory cells demonstrate reproducible switching between low and high resistance states with a resistance ratio around 10². Nonvolatile resistance storage was traced within 40 days. The low-temperature anodic oxidation of Nb was found to be suitable to fabricate flexible nonvolatile memory elements. The parameters of resistive switching are not degraded after 100000 flexing.

Abstract: One of the methods for the reduction of harmful emissions from diesel engines such as hydrocarbon, soot and NOx is the use of fuel born catalyst Cerium oxide. The oxygen storage capacity of Cerium oxide can be improved by coating it with metal such as Zirconium. Zr – Ce-O nanoparticles were synthesized by Co-precipitation method in the present work. Dynamic Light scattering, XRD pattern and UV-Visible spectroscopy were used for characterization of the prepared samples. Thermo gravimetric studies were conducted to investigate the thermal decomposition of Zr-Ce-O nanoparticles. The oxygen storage capacity of Zr-Ce-O nanoparticles was analyzed using TPR analysis.

Abstract: Chemical looping air separation (CLAS) is a new and energy saving method to separate oxygen from air. In this work, oxygen carrier was prepared by mechanical mixing method using CuO as active phase and ZrO2 as binder. XRD and SEM analysis indicate that ZrO2 cannot react with CuO at high sintering temperature and oxygen carriers prepared by this method are porous. Reactivity tests of oxygen carrier were investigated in STA409PC thermogravimetric analyzer using both temperature-programmed and isothermal thermogravimetry. The results show that the copper-based oxygen carrier has the capability of releasing oxygen when the temperatures higher than 850°C in nitrogen atmosphere. The reaction rates increase greatly as the temperature increases. Moreover, the oxygen carrier can keep high reactivity after several cycles. The copper/zirconium oxides as oxygen carrier were found to be suitable for CLAS process.

Abstract: The zirconia in its cubic phase (C-ZrO2) has gained scientific and technological interest because it has high ionic conductivity and is useful in applications where the transport of oxygen ions prevails, for example, in the oxygen sensors and solid oxide fuel cells [1,. In the pure zirconia, the Zr4+ ion is too small to sustain the fluorite structure at low temperatures, so it has to be partially replaced by a higher atomic radius cation and lower valence number, for example, the Y3 +, Mg2 +, Ca2 + and the rare earth cations TR3 +, [. Currently there are several synthesis methods used to obtain cubic zirconia, the most popular being the mixture of oxides and coprecipitation used industrially in the research labs, but these methods provide powders with different characteristics which will be decisive for a specific application. In this context, the objective of this study was the preparation of homogeneous mixtures of zirconia-rare earth in different concentrations in order to stabilize the C-ZrO2, using the technique of heterogeneous coprecipitation for potential applications in oxygen sensors.

Abstract: In this paper we propose the stabilization of zirconium oxide with controlled additions of a rare earth elements concentrate, in the system ZrO2: ƞ wt% Re2O3 (with ƞ=5.36, 10.47, 13.74, 16.91 e 20) where Re₂O₃ is a rare earth elements concentrate composed mainly of 76.88% of yttrium oxide, 12.1% of Dysprosium oxide, 4.04% of Erbium oxide and 1.94% of Holmium oxide. The synthesis method used was the Pechini method. The results show that additions of 5.36 and 20 wt% of the concentrate are enough to stabilize the tetragonal and cubic zirconia phases respectively, and that zirconium oxide polymorphs can coexist with additions within these limit. In the characterization of the obtained powders are presented and discussed the following results: differential scanning calorimetry, transmission electron microscopy and X-ray diffraction. Also, it was necessary to make analysis by Rietveld refinement because they had severe overlap in the diffraction peaks. One of the most relevant results is obtaining a raw material, cheap to be used in many technological applications.

Abstract: MgO-CaO-ZrO₂ composite materials were prepared in oxidizing atmosphere at 1550 oC with sintered magnesia, calcium oxide and partial stabilized zirconia as raw materials. Sintering performance of the composites was measured by the checking of the bending strength, the apparent porosity, the thermal expansivity and the thermal shock resistance of samples, respectively. The phase compositions and microstructures of the composites were investigated by XRD, SEM and EDS. The results showed that CaZrO₃ phase was formed by high temperture reaction between ZrO₂ and CaO, and phase compositions of the composites consisted of two phases of CaZrO₃ and MgO. The sintering performance of composites were promoted further with increasing the content of ZrO₂ due to the volume expansion caused by the reaction of the added ZrO₂ and CaO to form CaZrO₃ phase in the refractories.