Papers by Keyword: YSZ

Abstract: Thermal barrier coatings (TBCs) serve as thermal insulator in the hot region of an aircraft engine. Besides this, it also protects the underlying metal surface from the harsh corrosive and eroding environment. The associated lower thermal conductivity of TBC ceramic materials plays an important role in the improvement of thermal efficiency of the engine in term of increased combustion temperature and power. The thermal conductivity of the conventional yttria stabilized zirconia (YSZ) and three advanced ceramic materials with perovskite (CaZrO₃) and pyrochlore structure (La_0.75Nd_0.25)₂Zr₂O₇ & Nd₂Ce₂O₇) have been determined using differential scanning calorimetry (DSC). With thin metallic disk on the ceramic samples of different heights were heated / scanned using a standard DSC apparatus. The results were evaluated for the thermal conductivity measurement using well established procedure /calculations. The analyzed results were compared with that of other techniques given by other researchers and found to be in good agreement with an error of 10-15%. The result of coefficient of thermal expansion (CTE) that was measured using a dilatometer up to 1273°K has also given.

Abstract: The characterization of CIM feedstock consisting 58, 59, 60vol% of YSZ powder with binder system comprising a palm stearin (PS) and low density polyethylene (LDPE) were studied. The effects of powder loading and temperature (°C) on the rheological behavior of the YSZ were investigated by using Rosand RH2000 Capillary Rheometer. The results showed all the feedstock achieved desirable injection moulding characteristics such as pseudoplastic behavior, flow behavior index (n) less than 1 and low activation energy (E). The rectangular parts were successfully injected moulded at optimum temperature of 170°C with the highest green strength was 12.7 N, obtained from 60 vol% powder loading which correspond to greater density and low porosity of the samples.

Abstract: The Co element was used during the first operation of high temperature reactor (HTR) reactor to distinguish low-enrichment and high-enrichment fuel elements. In this paper the YSZ/CoO ceramic tracer microspheres with YSZ coating were prepared. The design size of the microspheres were about 750μm. The YSZ shell thickness were 100 μm, the mean nuclear roundness were ≤1.03 and the density were ≥5.50g/cm³. Morphology, microstructure and element composition of the core-shell microspheres were characterized by stereo microscope, scanning electron microscopy, x-ray spectrometers etc. The results of both line scan and spot scan of X-ray spectrometer show that dense YSZ shell can efficiently prevent Co element in YSZ/CoO core from diffusing into the YSZ shell at high temperature.

Abstract: Thermally grown oxide (TGO) plays important roles in thermal barrier coating system (TBC) for high temperature application such as in aircraft gas turbine engine blades (GTE). The TGO formed between the bond coat and topcoat interface can increase oxidation resistance to creep of GTE blades by minimizing oxygen diffusion into the metal substrate. In this research a NiCoCrAlYTa metallic bond coat was deposited on Inconel 625 substrate using two methods of deposition namely; high velocity oxy-fuel (HVOF) and atmospheric plasma spray (APS). After coating process, both types of samples underwent pre-oxidation in argon furnace for 12-24 hours at 1000 °C. Results showed that the TGO formation for samples in which the bond coat deposited via HVOF method produced much thinner and continuous TGO formation compared to APS deposition. This TGO characteristic is very useful to lengthen the lifetime of the metals substrate.

Abstract: A simple method to produce graphene-Yytria stabilised zirconia (YSZ) ceramic composite with significant improvement in electrical properties is reported here. The material was consolidated by annealing in presence of Argon gas that allowed densification of the ceramics. A detailed x-ray diffraction (XRD) analysis was used to study the phases and crystallinity of graphene-YSZ ceramic composite. XRD patterns of the sintered composite showed that graphene diffraction peaks were detected at 2θ≈27°. Furthermore, experimental results indicate that electrical conductivity of YSZ composites drastically increased with the addition of graphene platelets, and it reached a value of 2.8 S/cm at 2 wt.%.

Abstract: Different contents of bismuth oxide doped in 3YSZ material and the mixed powder formed. After press forming,the samples were sintered at 850°C, 900°C, 1000°C and 1100°C respectively. The electrical properties,the thermal shock resistance,the phase components and the microstructure morphology were analyzed to study the solid solution mechanism of Bi₂O₃-Y₂O₃-ZrO₂ three-phase system. It was found that the Bi₂O₃ can effectively reduce sintering temperature as a flux. Sintered at 1000°C, t-ZrO₂ can be induced into m-ZrO₂ by Bi₂O₃ doped. With the increasing of Bi₂O₃ content, system shock resistance decreases. The thermal shock resistance of the 2-3mol% Bi₂O₃-YSZ is the best. In the different content of Bi₂O₃ system, 3mol% doped materials has the highest conductivity.

Abstract: In this paper, La_0.65Sr_0.35MnO₃ (LSM) oxide powder with ultrafine structure has been synthesized by self-propagating combustion method. The powders were characterized by X-ray diffraction, scanning electron microscopy and laser size analysis. Compared to the powders prepared by traditional solid-phase method, the grain size of powders prepared by self-propagating combustion method is relatively small and uniform. Starting from ultrafine LSM powders, sensing electrode (SE) for NO₂ mixed-potential sensors based on yttria-stablized zirconia (YSZ) was fabricated. As-obtained NO₂ sensor displays fast response and high sensitivity (25.4mV/decade). The response values of the sensor have good linear relationship with the logarithm of NO₂ concentration varying from 30ppm to 500ppm.Keywords:Self-propagating combustion method; La_0.65Sr_0.35MnO₃; NOx sensor; YSZ

Abstract: In this study, Yttria-stabilized zirconia (YSZ) electrochemical sensors attached with the WS₂ sensing electrode (SE) were fabricated and examined for NO₂ sensing properties. Due to its internal stratiform structure, surface and edge of the lamella have high chemical activity, WS₂ was used as a kind of highly efficient catalyst. WS₂ was partial oxidated to WO₃ at 400°C, and with the increment of temperature, oxidation will accelerate. The ΔEMF to 500 ppm NO₂ was as high as 125mv at 400°C, while the value of WO₃-based sensor was as small as 10 mv in the same condition. These WS₂-attached devices gave a linear correlation between EMF and the logarithm of NO₂ concentration from 30 to 500 ppm in the temperature range 350–500°C. The response time of the device is about 1 min at 400°C.

Abstract: Thermal barrier coatings (TBCs) are used in the cooled parts of gas turbines to reduce the temperature of blades and hot engine components, allowing higher operating temperatures and yielding increased efficiency. The corrosive gases which come from combustion of low grade fuels can penetrate into the TBCs and reach the metallic components and bond coat and cause hot corrosion and erosion damage. Mullite thin films have been applied onto the top layer of yttria-stabilized zirconia (YSZ) coatings by sol-gel dipping process in order to decrease the porosity as well as improve thermal stability of the coatings. Glazing the top layer by laser beam is an advanced approach to seal TBCs surface. The laser beam has the advantage of forming a dense thin layer composed of micrograins. CO₂ laser beam assisted in the densification of the surface by remelting a thin layer of the exposed surface. The laser glazing converted the rough surface of TBCs into smooth micron-sized grains with size of 1-4 microns. Mullite compounds have remained on the surface after laser treatment since alumina and silica are still present, as indicated in EDX spectra. The results revealed that the roughness increases as the grain size decreases.

Abstract: Formation of thin and continuous layer of thermally grown oxide (TGO) in thermal barrier coating (TBC) are essential in order to avoid coating failure for high temperature applications. As-sprayed high velocity oxy-fuel (HVOF) bond coat can provide more uniform TGO layer in TBC system and much less oxide compare to air plasma spray (APS). In this paper, both APS and HVOF method are used to deposit NiCoCrAlYTa bond coat on Inconel 625 substrate followed by topcoat, YSZ deposition. Pre-oxidation process was done in normal oxygen furnace at 1000°C for 12 to 24 hours to study the characteristic of TGO formation via these two different methods. From the result obtained, it shows that HVOF method provide better TGO formation as compared to APS.