Papers by Keyword: Partially Stabilized Zirconia

Abstract: Partially stabilized zirconia (PSZ) materials were fabricated using 4 wt% CaO, 3 wt% MgO, and 5.4 wt% Y₂O₃ as stabilizing agents together with monoclinic zirconia powder. The physical properties, phase compositions, and microstructures of the Ca-PSZ, Mg-PSZ, and Y-PSZ samples were investigated by X-ray diffraction, scanning electron microscopy, and energy spectrum analysis. A crucible method was used to explore the relationship between the stabilizing agent and erosion resistance to alkaline steel slag. The results revealed that the zirconia materials stabilized by different stabilizing agents showed obvious differences in their bulk densities, apparent porosities, microstructures, and erosion resistances to alkaline steel slag. The structure of Y-PSZ showed highest density, containing a small number of uniformly distributed pores. In terms of Mg-PSZ, the intergranular bonding in its structure was observed to not be close, and the sample contained some cracks, but no pores. A large number of intragranular pores and a small number of overall pores was observed in Ca-PSZ, resulting in this material having the lowest bulk density. The pores and cracks provide the path to penetrate and diffuse for alkaline steel slag, which weakens the corrosion resistance of PSZ materials. The phase composition of the affected layers in all of the samples after corrosion was almost completely transformed from monoclinic phase to cubic phase, and the phase transition of both the original and transition layers was not obvious due to the formation of a slag film. Y-PSZ did not react with components of the steel slag such as SiO₂ and Al₂O₃, showing the best corrosion resistance to alkaline steel slag.

Abstract: In this study, a magnesium oxide partially stabilized zirconia (Mg-PSZ) sample was prepared by granulation, molding, drying, and calcining. MgO was used as stabilizer, along with chemical-and electrofusion-made zirconium dioxide (ZrO₂) powder, as well as a different mixture of the two as the raw material. The effects of material reactivity on the sintering properties of the Mg-PSZ metering nozzle were studied by analyzing the physical properties and microscopic structure of the sample. The results show that, under the same sample preparation conditions, the electrofusion-made ZrO₂ had lower reactivity, resulting in a lower percentage of stable phase, loose adhesion among particles after sintering, more than 20% porosity, and poor antierosion and antiscouring performance. However, electrofusion-made ZrO₂ only had a shrinking percentage of 6%, leading to a higher sintering yield. However, compared with the electrofusion-made ZrO₂, chemical-made ZrO₂ had a higher reactivity, better sintering properties, more stable phase component, and approximately 75% less porosity. Chemical-made ZrO₂, however, had a shrinking percentage as high as 20%, causing serious sample cracking after sintering. Therefore, both types of ZrO₂ are not ideal as the only raw material for Mg-PSZ metering nozzles. Nonetheless, when a 1:1 mixture of the two types of ZrO₂ was used as the raw material, the calcined sample showed better property parameters in porosity and volume density, as well as compressive strength, satisfying the requirements for Mg–PSZ-based metering nozzles.

Abstract: Materials performance plays a pivotal role to the smooth operation of present and future nuclear energy systems operating in severe irradiation environment in reactors. Therefore selection of structural materials with the desired properties is vital for this field of applications. The present work reports the effect of milling time during mechanical alloying of a novel Oxide Dispersed metal matrix composite consisting of multi-component AlCrFeMnNi high entropy alloy system with minor addition of Partially Stabilized Zirconia (PSZ) (1 wt.%). The main focus of this work is to understand the phase stability behaviour during mechanical alloying. High Entropy Alloy AlCrFeMnNi with Partially Stabilized Zirconia (PSZ) as Dispersoid phase was prepared by mechanical alloying. For study of phases, milled powder was investigated through X-Ray diffraction technique followed by Scanning Electron Microscopy for microstructural morphology. The study reveals that PSZ Dispersed AlCrFeMnNi alloy mainly consists of BCC (Fe Type) and FCC (Ni Type) mixed structure. At the end of 30 h lattice strain and crystallite size were measured to be 0.738 % and 13 nm respectively.

Abstract: The modified calcium oxide partially stabilized zirconia ceramics were fabricated using ZrO₂ powder as raw materials, CaO as stabilizer, and nanometre zirconia as modification agent. The relationship between additive amount of nanometre zirconia and the performance of Ca-PSZ ceramics were researched via testing the physical properties, analyzing mineral phase composition, and observing microstructure of the samples. The results show that the introduction of nanometre zirconia powder has a significant effect on the physical properties of Ca-PSZ, with an addition of 8wt%, bulk density was up to 5.08 g/cm³, and the compressive strength reached 381 MPa. Compared with the unmodified Ca-PSZ sample, the porosity of the modified Ca-PSZ samples decreased by 40%, and the compressive strength increased by 70%. The introduction of nanometre zirconia has an inhibitory effect on the abnormal growth of zirconia grains and improves the densification of the Ca-PSZ ceramics. Through the formation of intragranular structure, nanometre zirconia can induce transgranular fracture and weaken crystalline fracture, thereby increasing the strength of the Ca-PSZ ceramics.

Abstract: Al₂O₃ composite ceramics materials used for heat transmission pipeline were prepared by pressureless sintering in air. Calcined bauxite, talc and commercial alumina powder were used as the main raw materials, partially stabilized zirconia was also added to improve the thermal shock resistance of the samples. The effects of composition and sintering temperature on density, phase composition, microstructure and thermal shock behavior of samples were evaluated. It shows that the B2 sample which was sintered at 1400 °C for 2 h has optimal properties with porosity 0.4%, bulk density 3.2 g•cm^-3.The bending strength increases 19.46 MPa after 30 times thermal shock cycles from 1100 °C to room temperature. The main phases of B2 are corundum and spinel, meanwhile, a small amount of monoclinic zirconia and α-quartz are also detected according to XRD pattern. Microstructure analysis reveals that spinel crystals are interlocked by prismatic corundum crystals, bright white beaded monoclinic zirconia particles are distributed uniformly, and it is beneficial to improve the thermal shock resistance of sample.

Abstract: In this paper the wear performance between Partially Stabilized Zirconia (PSZ) plate and silicon nitride ball under dry conditions was investigaed. The wear durability of PSZ with shot peening was higher than that of PSZ without shot peening in the sliding wear test under low Hertzian contact pressure. By shot peening, the transformation from tetragonal to monocryclinic phase with compressive residual stress occurred locally on the PSZ surface. Due to this transformation, the wear durability on the surface of the PSZ plate was improved.

Abstract: This paper mainly discusses the influences of heating temperatures and CeO₂ additive contents on the phase transformations of zirconia from zircon ore by carbothermal reduction. The phase transformations of zirconia from zircon ore by carbothermal reduction were monitored by X-ray diffraction. The microstructure of the product was characterized by scanning electron microscopy. The results show that without adding CeO₂, the optimized heating temperature of zircon carbothermal reduction was 1600 °C and the main phases of the product were m-ZrO₂, ZrC and β-SiC, t-ZrO₂; After adding CeO₂, the main phase of the products consists of t-ZrO₂, m-ZrO₂, ZrC and β-SiC when the heating temperature is 1600 °C. CeO₂ additive can be introduced into zirconia lattice and can cause it to form cerium stabilized zirconia. Zirconia in the product would be turned into partially stabilized zirconia with cerium addition from 5 wt% to 20 wt%. However, the form of zirconia in the product is not changed greatly with the amount of CeO₂ additive increase.

Abstract: 3 mol% yttria-stabilized zirconia (YSZ) powders were sintered into pellets. The YSZ ceramics were electrically polarized by applying dc voltage at an elevated temperature. After cooling the samples to room temperature, the polarized YSZ ceramics were heated at a constant heating rate. The formed polarizations were relaxed with increase of the increase temperature. The depolarization current was measured as thermally stimulated depolarization current (TSDC). Each of the TSDC spectra had two peaks located at lower and higher temperatures. The lower and higher peaks are attributed to dipole polarization and space charge polarization, respectively.

Abstract: Alumina (Al2O3) is one of the most successful advanced ceramics due to its high hardness, chemical resistance as well as thermal stability under various severe operating conditions. Therefore, the Al2O3 and Al2O3 matrix composites were generally employed as cutting tool materials. The present work investigates an improvement in fracture toughness of the Al2O3-based composites reinforced by tungsten carbide (WC) particles. A change in toughness of the Al2O3/WC composites according to the additions of cobalt (Co) or partially stabilized zirconia (PSZ) is also of interest. The 90 wt% of Al2O3 and 10 wt% of WC powders, containing various amounts of Co or MgO-doped PSZ (Mg-PSZ), were formed by a conventional uniaxial pressing. The percentages of Co and Mg-PSZ were varied up to 3 and 4.5 wt%, respectively. The specimens were sintered in argon atmosphere at 1600 °C for 2 hours. The sintered specimens were subjected to testing and characterisation. The density was measured by water immersion method. Microstructure and phase analysis were investigated by scanning electron microscopy (SEM) and X-ray diffractometry (XRD), respectively. Vickers indentation technique was used to determine hardness and fracture toughness. Density of higher than 95% of the theoretical values could be achieved in all cases. The hardness values of the WC reinforced Al2O3 composites were higher than those of the monolithic Al2O3. The hardness of the composites did not change significantly with the Co addition but it gradually decreased with PSZ additions. However, the presence of both Co and PSZ led to slightly higher fracture toughness. The hardness and fracture toughness of the fabricated composites were in the range of 16-18 GPa and 5-8 MPa.m1/2, respectively, which were in the same ranges as commercial cutting tools currently used in the market.

Abstract: Effect of surface charges induced by polarization treatment on Low Temperature Degradation (LTD) in 3mol%Y-doped ZrO₂ was studied. Samples were polarized by applying voltage (7kV/cm) at 200°C for various time (1~30min). LTD acceleration test was conducted using polarized samples. LTD was inhibited on negatively charged surface in all the polarized samples, which is independent on polarization time. We carried out thermally stimulated depolarization current (TSDC) analysis for investigate polarization mechanism. Two polarization elements were confirmed: orientation polarization and space charge polarization. A comparison of the result of LTD acceleration test and TSDC analysis indicates that orientation polarization is considered superior element in inhibition of LTD.