Yttria-stabilized Zirconia Powders Research Articles

Two Component Injection Moulding of Bi-material of Stainless Steel and Yttria Stabilized Zirconia – Green Part

The two component injection molding (2C-PIM) is a promising technique for production of small, complex and high density, metal-ceramic parts in large scales. This method is a viable option for integrating incompatible functions or properties of the materials in a singular part or component. Thus, the production of near net shaped components via 2C-PIM is imperative due to cost effectiveness resulting from high unit volumes. In this study, the feasibility of joining stainless steel (17-4PH) and 3mol% yttria stabilized zirconia (3YSZ) materials in their green states was investigated. Two feedstock of SS17-4PH and 3YSZ powder materials was prepared based on optimum solid loading of 3vol% lower than value of the critical loading. The critical solid loading for the SS17-4PH and 3YSZ powder materials were 71vol% and 53vol% respectively, based on the oil absorption technique ASTM: D-281-12. The binder system utilized comprises of 60wt.% palm stearin (PS) and 40wt.% low density polyethylene (LDPE). The two materials were injected sequentially using the screw type injection molding machine (BOY 22A) to form a bi-material component. The green properties were investigated. The morphology of the individual green parts and composites depicted that the powders were optimally dispersed in the binder matrix indicating good mixture and compaction of the green components. The flexural strength of the single components of the bi-material was above 5 MPa. The strength of the bonding zone which was 1.4 MPa indicates an evidence of bonding.

Low-temperature sintering and microstructure evolution of Bi2O3-doped YSZ

Yttria-stabilized zirconia (YSZ) is one of the most common solid electrolyte materials for solid oxide fuel cells (SOFCs). However, the sintering temperature of commercial YSZ powders is usually above 1500℃. In this work, powders with variable amounts (from 1mol% to 12mol%) of bismuth oxide (Bi2O3) were separately added to commercially available yttria partially stabilized zirconia (3YSZ) powders as sintering additives, in order to lower the sintering temperature of the latter. After the addition, the powder mixtures were dry-pressed and sintered at different temperatures between 850℃ and 1200℃. Then, the relative densities, phases and microstructures of the sintered ceramic specimens were analyzed. The results indicated that the addition of Bi2O3 enhanced the sintering activity of 3YSZ, resulting in a 3YSZ material with an extremely low sintering temperature. When the amount of Bi2O3 exceeded 7mol%, the ceramic specimens were densified up to 96.3% by a pressureless conventional sintering process at 850℃ for only 1.5h. Furthermore, Bi2O3 can affect the degree of crystallinity of different phases, such as the tetragonal phase and monoclinic phase in 3YSZ powder.

Influence of Air Plasma Spraying Process Parameters on Ceramic Layer in Thermal Barrier Coatings<i></i>

The aim of this study was to examine the possibility of application in APS process Yttria Stabilized Zirconia (YSZ) – Metco 6700 ceramic powder normally used in Low Pressure Plasma Spraying (LPPS) method. Powder grain size is around 10 µm. Parameters such as chemical composition of plasma gases and current were changed to obtain the best result. The experiment was divided into two stages. Firstly, temperature, velocity and size of a molten particle of ceramic powder inside plasma plume were measured via DPV eVolution equipment (TECNAR company) during a different set of process parameters. Plasma plume was also scanned to obtain cross-section contour plots of mentioned properties of the molten particle. Secondly, the same processes were repeated to deposit TBC coatings onto sheet metal to examine the structure.The obtained results showed that it is possible to use fine-grain YSZ powder Metco 6700 for APS process. Obtained ceramic coatings had a thickness from 100 to 240 µm. The plasma sprayed coating was characterised by a smooth surface. The measurement of spraying parameters showed the uniform temperature, velocity and particle size of the powder inside plasma plume.

Effect of new zirconia surface coatings on the surface properties and bonding strength of veneering zirconia substrate

Zirconia ceramic dental restorations showed a low bond strength to veneering ceramic because of there is no inherent glass content along with a nonpolar covalent bond in its matrix. Two zirconia coatings by airbrush spraying were used as a new surface treatment on zirconia substrate to create surface roughness and improved bond strength to the veneering ceramic. Unsintered yttria stabilized zirconia (YSZ) powder was partially sintered at 1100°C to produce powders with two particle sizes; A=26.0±0.3μm and B=47.0±0.5μm. Unsintered YSZ blocks were sectioned into 50 discs of 25mm in diameter and 2.5mm in thickness. The discs were divided according to the surface treatments into three groups; ten sintered YSZ discs were blasted by airborne particle abrasion (APA) with 50μm aluminium oxide particles as control group; twenty unsintered YSZ discs were coated with a mixture of glaze ceramic and YSZ powders (M1), and twenty unsintered YSZ discs were coated with a mixture of ceramic liner and YSZ powders (M2). Based on the sizes of the YSZ powders, the coated groups subdivided into M1A, M1B, M2A and M2B. The surface area roughness (Sa), surface morphology, elemental composition, phase transition and shear bond strength test (SBS) were assessed. The collected data were analysed with one-way ANOVA and Tukey HSD test at (P<0.05). The Sa results revealed significant differences among all groups (P<0.000). The coated groups showed higher Sa and SBS values with a significant difference than APA. The M1B group exhibited higher values of Sa (10.33μm) and SBS (37.54MPa) with significant differences among the other tested groups. The zirconia specimens treated with new coatings significantly improved the shear bond strength to the veneering ceramic.

Porosity, microstructure and mechanical behavior of NiO–YSZ composite anode for solid oxide fuel cells

Abstract In this study, NiO–yttria stabilized zirconia (YSZ) composite anodes were prepared by using ball-milling followed by a sintering process. For this purpose, two different weight percent ratios of NiO and YSZ powders (50 : 50 and 60 : 40) were mixed by the cost-effective ball-milling method. The morphology and particle size distribution of the mixed powders were investigated using scanning electron microscopy and dynamic light scattering methods, respectively. The powders were then uniaxially pressed to form pellets with a thickness and diameter of around 1 and 22 mm, respectively. Sintering of the pellets was conducted at 1 100 °C and the microstructure and porosity, as well as phase analysis of bulk composites, were then investigated using scanning electron microscopy and X-ray diffraction, respectively. More importantly, the microhardnesses of the prepared pellets were obtained and compared with literature values to evaluate the accuracy of the sintering process. The results showed that the open porosity of the samples varied between 30 to 40 percent, which makes them suitable for anode application in solid oxide fuel cells. The prepared NiO–YSZ composites with a uniform distribution of Ni particles showed a value of microhardness above 0.5 GPa, and these results were discussed in detail.

Effect of Particle Size on the Thermal Shock Resistance of Plasma-Sprayed YSZ Coatings

In this study, yttria-stabilized zirconia (YSZ) coatings were deposited by atmospheric plasma spraying (APS) using feedstocks with two different particle sizes. The effect of particle size on the pore structure and failure mechanism of the coatings was investigated. The evolution of the pore structure of the two kinds of coatings during cyclic thermal shock test was described by quantitative metallography. The influence of pore orientation on the thermal stress of the coating system was analyzed by the finite element method. It was found that the coatings deposited using coarse particles show a high thermal shock life time. The orientation of the pores in the coatings prepared by different particle sizes was different. A structural parameter was proposed to effectively characterize the pore orientation of the coatings. Coatings prepared by coarse YSZ powder tend to form almost the same number of horizontal and vertical pores, while coatings prepared by fine powder tend to form horizontal ones parallel to the direction of the substrate. The simulation results revealed that the vertical pores can reduce the thermal stress in the coating. The results of this investigation are a benefit to the design and integrity of TBCs.

Robocasting of dense yttria-stabilized zirconia structures

Advanced ceramic materials with complex design have become inseparable from the current engineering applications. Due to the limitation of traditional ceramic processing, ceramic additive manufacturing (AM) which allows high degree of fabrication freedom has gained significant research interest. Among these AM techniques, low-cost robocasting technique is often considered to fabricate complex ceramic components. In this work, aqueous ceramic suspension comprising of commercial nano-sized yttria-stabilized zirconia (YSZ) powder has been developed for robocasting purpose. Both fully and partially stabilized YSZ green bodies with complex morphologies were successfully printed in ambient conditions using relatively low-solid-content ceramic suspensions ( 94% of the theoretical density despite its high linear shrinkage (up to 33%). The microstructure analysis indicated that dense fully and partially stabilized YSZ with grain size as small as 1.40 ± 0.53 and 0.38 ± 0.10 μm can be obtained, respectively. The sintered partially stabilized YSZ solid and porous mesh samples (porosity of macro-pores >45%) exhibited hardness up to 13.29 GPa and flexural strengths up to 242.8 ± 11.4 and 57.3 ± 5.2 MPa, respectively. The aqueous-based ceramic suspension was also demonstrated to be suitable for the fabrication of large YSZ parts with good repeatability.

Friction and Wear Properties of Plasma Sprayed YSZ/Ni-Cr-Al Coated 6063-T6 Aluminum Alloy

AbstractIn this study T6 heat treated 6063 aluminum alloys were used as substrate material. In order to form a bond between the substrate and the main coating, all samples were coated with Ni-Cr-Al powders. 8 wt% Yttria Stabilized Zirconia powders (YSZ) were coated with plasma spray technique. Thickness of YSZ was 150 μm and bond coating was 36 m. XRD and SEM-EDS analyses were performed to characterize the coating layers. These YSZ coated and uncoated samples were subjected to wear testing under different spindle speed, loading and working distance. Wear test results were compared with the kinetic friction coefficients and weight loss values. Wear marks on YSZ coated and uncoated samples were investigated by SEM analysis. By coating with plasma spray technique, the wear resistance of Al alloys was increased without changing the friction coefficient. It was found that spindle speed had significant effect over the wear properties than the load applied. By YSZ coating, wear properties were increased 10 times.

Effect of Porosity on Strength and Electrical Conductivity of NiO–3.5YSZ Composite and Its Ni–3.5YSZ Cermet

The change in porosity of the Ni–3.5YSZ (ZrO2 stabilized with 3.5 mol.% Y2O3) composite, when produced, and the effect of porosity on the strength and electrical conductivity is studied. The porosity was provided by adding granular starch to the mixture of NiO and 3.5YSZ powders. The content of 18 vol.% pore-forming agent in the Ni–3.5YSZ cermet provides open porosity 47.1%, while its strength and electrical conductivity are 74.3 MPa and 0.93 · 106 S/m, respectively.

Densification and microstructure of spark plasma sintered 7YSZ–Gd2O3 ceramic nano-composites

Spark plasma sintering (SPS) technique was used to densify 7 mol% yttria-stabilized zirconia (7YSZ) powder with Gd2O3-particles, at temperatures ranging between 1000 and 1200 °C. Fine dispersion of Gd2O3-particles into a full-densified matrix was achieved. Shrinkage and microstructure, as well as porosity were investigated. The fine Gd2O3-particles distributed into 7YSZ matrix have influence over the sintering consolidation and final microstructure. An increment in the spark plasma sintering temperature around 70 °C is detected when Gd2O3 particles are present. The thermal characterization was performed using the photothermal infrared radiometry technique. Both thermal diffusivity and thermal conductivity display a similar sigmoidal (Boltzmann type) behavior with the Gd2O3 concentration in the samples.

Regularities of formation of complex oxides with the fluorite structure in the ZrO2–Y2O3 system

The crystal and local structures of the complex oxides (1–x)ZrO2 ∙ xY2O3 (YSZ) (x = 0.08–0.40) prepared by precipitation from solutions of metal salts followed by heat treatment in air were comprehensively studied by X-ray diffraction and Raman spectroscopy. Despite the same crystal structure type of the YSZ powders (cubic system, space group \(Fm\overline 3 m\) (225)), there are differences in the local structure of the samples. Comparison of the Raman spectra recorded at different laser excitation wavelengths provided the conclusion that the peaks observed in the Raman spectra of the YSZ samples with high yttrium content (x = 0.18–0.40) are likely to be due to luminescence of the powders.

Characterization of Yittria Stabilized Zirconia/Titania core-shell powders synthesized via air plasma spray method

In this study, Yittria Stabilized Zirconia/Titania powders synthesized via air plasma spray (APS) method such as morphology changes and phase transformations of core-shell structure characterized. Phase analysis of powders was performed by XRD. The crystallite size and lattice strain of YSZ/TiO2 core-shell structure was calculated by Williamson-Hall method. Morphology was observed with scanning electron microscope. EDS and map analysis were used for core-shell characterization. Results revealed that all TiO2 nano particles were melted around YSZ powders with the thickness between 1 up to 5 μm. After spraying the YSZ/TiO2 mixture in water, strain values increased but crystallite size decreased. Moreover, the monoclinic phase transformed to tetragonal phase but cubic phase remained constant, approximately.

Development of a novel proton conducting fuel cell based on a Ni‐YSZ support

AbstractA new proton conducting fuel cell design based on the BZCYYb electrolyte is studied in this research. In high‐performance YSZ‐based SOFCs, the Ni‐YSZ support plays a key role in providing required electrical properties and robust mechanical behavior. In this study, this well‐established Ni‐YSZ support is used to maintain the proton conducting fuel cell integrity. The cell is in a Ni‐YSZ (375 μm support)/Ni‐BZCYYb (20 μm anode functional layer)/BZCYYb (10 μm electrolyte)/LSCF‐BZCYYb (25 μm cathode) configuration. Maximum power density values of 166, 218, and 285 mW/cm2 have been obtained at 600°C, 650°C, and 700°C, respectively. AC impedance spectroscopy results show values of 2.17, 1.23, and 0.76 Ω·cm2 at these temperatures where the main resistance contributor above 600°C is ohmic resistance. Very fine NiO and YSZ powders were used to achieve a suitable sintering shrinkage which can enhance the electrolyte sintering. During cosintering of the support and BZCYYb electrolyte layers, the higher shrinkage of the support layer led to compressive stress in the electrolyte, thereby enhancing its densification. The promising results of the current study show that a new generation of proton conducting fuel cells based on the chemically and mechanically robust Ni‐YSZ support can be developed which can improve long‐term performance and reduce fabrication costs of proton conducting fuel cells.

Preparation of Ni–YSZ Cermet through Reduction of NiO–YSZ Ceramic for SOFC Anode

Research on the synthesis of Nickel–Yttria Stabilized Zirconia (Ni–YSZ) cermet for Solid Oxide Fuel Cell (SOFC) anode has been performed. The preparation was carried out through the reduction process of the Nickel Oxide–Yttria stabilized Zirconia (NiO–YSZ) ceramic. NiO and YSZ were prepared separately, the NiO powder was prepared by calcination of CH4Ni3O7.xH2O at 500°C for 3 hours, while YSZ powder was prepared by calcination of 7mol% Y2O3 and 93mol% ZrO2 mixture at 1350°C for an hour. The NiO–YSZ ceramic preparation was carried outby mixing of YSZ and NiO powder with natural white starch by weight ratio NiO: YSZ: natural white starch = 4:6:1 followed by sintering at 1200°C for 4 hours. The completion of reduction process of NiO–YSZ ceramic was performed at 1000°C in flowing Argon (Ar) containing 10% Hydrogen (H2) up to 4 hours. The characterisations include thermogravimetric analysis (TGA), XRD, SEM–EDX and Impedance Analyzer meter. The synthesised Ni–YSZ cermet at composition 33wt% Ni and 67wt% YSZ, shows relative density 70% and electrical conductivity 10-2 S/cm at 700°C, it qualifies as anode for SOFC.

A Comparative Study on the Densification Behavior of Yttria-Stabilized Zirconia Electrolyte Powders

Solid oxide fuel cell (SOFC) electrolytes are usually co-sintered with one of the electrodes (support component) at temperatures ≥1400 °C to get a fully densified microstructure. Lowering this temperature to 1200–1300 °C offers several advantages such as prevention of microstructure coarsening of the electrode and undesirable reactions between the electrolyte and electrode materials, lower sintering cost, and shorter production cycle time. To lower the electrolyte sintering temperature, a thorough understanding of the densification behavior of the electrolyte materials is important. In the current work, we compared the densification behavior of three different types of 8 mol% yttria-stabilized zirconia (YSZ) electrolyte powders: (i) TZ-8Y from Tosoh (Japan), (ii) MELox 8Y from MEL Chemicals (UK), and (iii) YSZ-HT from Huatsing Power (China). The YSZ powders were pressed to form disc-shaped pellets that were sintered at different temperatures ranging 1200–1400 °C. The density and linear shrinkage of the sintered pellets were measured. Among the three YSZ powders, MELox 8Y showed the best densification behavior at lower sintering temperatures with 93 and 96% of the theoretical density at 1250 and 1300 °C, respectively. Although YSZ-HT showed higher sintering rate than TZ-8Y, a sintering temperature of 1350 °C was required for both the powders to reach a theoretical density ≥95%. Our results indicate that different factors besides the particle size play a significant role in determining the sintering rate and densification behavior of the YSZ electrolyte. These factors possibly include the powder synthesis method, post-processing of the powder (such as spray drying), and so on. Figure 1

Synthesis of YSZ/TiO 2 core–shell feedstock powders via the air plasma spray method

The core–shell structures can improve material properties and easier material selections for applications in new purposes. In this study, yttria-stabilised zirconia (YSZ)/TiO2 feedstock powders were synthesised via the air plasma spray method to investigate morphology changes, phase transformations and formation of core–shell structure. X-ray powder diffraction, scanning electron microscope (SEM) and EDS were used for phase analysis, morphology and core-shell characterisation, respectively. Results revealed that YSZ/TiO2 core–shell powders can be employed using the plasma spray method. SEM images showed that entire TiO2 nanoparticles had melted around YSZ powder. The shell thickness was estimated between 1 and 5 μm. In the plasma process the YSZ monoclinic phases transformed to the tetragonal phases, but no changes were observed in the cubic phases.

Ferroelastic domain switching toughening in spark plasma sintered t’-yttria stabilized zirconia/La2Zr2O7 composite ceramics

Abstract The poor fracture toughness of La 2 Zr 2 O 7 hinders its practical application as a thermal barrier coating topcoat material. To toughen La 2 Zr 2 O 7 , metastable tetragonal 8 wt% yttria-stabilized zirconia ( t ’-8YSZ), has been introduced into the La 2 Zr 2 O 7 matrix by plasma spray quenching of 8YSZ powders and spark plasma sintering. An evident fracture toughness improvement has been achieved due to ferroelastic domains switching. The resulting toughness increase has a quadratic relationship with t ’ phase volume fraction below a critical value (30 vol%), beyond which it is far smaller to what expected owing to the residual stress being smaller than the ferroelastic coercive stress.

A Comparative Study on the Densification Behavior of Yttria-Stabilized Zirconia Electrolyte Powders

We compared the densification behavior of three different types of 8 mol% yttria-stabilized zirconia (YSZ) powders used as the electrolyte for solid oxide fuel cells (SOFCs): (i) TZ-8Y from Tosoh (Japan), (ii) MELox 8Y from MEL Chemicals (UK), and (iii) YSZ-HT from Huatsing Power (China). The YSZ powders were pressed to form disc-shaped pellets that were sintered at different temperatures ranging 1200–1400 °C. Among the three YSZ powders, MELox 8Y showed the best densification behavior at lower sintering temperatures with 93 and 96% of the theoretical density at 1250 and 1300 °C, respectively. Although YSZ-HT showed higher sintering rate than TZ-8Y, a sintering temperature of 1350 °C was required for both the powders to reach a theoretical density ≥95%. Our results indicate that different factors besides the particle size play a significant role in determining the sintering rate and densification behavior of the YSZ electrolyte.

Hot corrosion behaviour of nanostructured zirconia in molten NaVO3 salt

Plasma sprayed coatings were fabricated from nanostructured yttria-stabilized zirconia powders (n-YSZ) with different crystalline grain sizes, prepared via sintering of nano ZrO2-4 mol% Y2O3 powders at different temperatures. The hot corrosion behaviour of both n-YSZ powders and their corresponding coatings with sodium metavanadate (NaVO3) were investigated at 700 °C. During hot corrosion, NaVO3 reacts with Y2O3 in YSZ to form YVO4, leading to a tetragonal to monoclinic destructive phase transformation of YSZ. The crystalline grain size of n-YSZ powders did not affect the hot corrosion mechanisms of both the n-YSZ powders and their corresponding coatings. However, compared with n-YSZ powders, the coatings were more easily corroded, and the coatings formed from starting powders with crystalline grain sizes <30 nm featured better degradation resistance to hot corrosion.

Hot corrosion studies on plasma sprayed bi-layered YSZ/La 2 Ce 2 O 7 thermal barrier coating fabricated from synthesized powders

Abstract La 2 Ce 2 O 7 (LCO) with a pyrochlore structure has been considered as a propitious thermal barrier coating (TBC) system possessing high temperature (>1200 °C) phase stability. In the present study, double ceramic layer of yttria stabilized zirconia (YSZ) and lanthanum cerium oxide (La 2 Ce 2 O 7 , LCO) TBCs are fabricated by atmospheric plasma spraying (APS). Individual LCO and 8YSZ and bilayered LCO/YSZ coatings are developed using flowable YSZ and LCO powders synthesized by co-precipitation and combustion routes respectively and are characterized for phase and microstructure. The coatings subjected to hot corrosion (Na 2 SO 4 +V 2 O 5 salt at 910 °C for 30 h) are characterized by X-ray Diffractometry and Scanning Electron Microscopy and Energy Dispersive X-Ray Spectroscopy. XRD shows the phase transformation of YSZ from tetragonal to monoclinic zirconia accompanied by the formation of LaVO 4 and YVO 4 as hot corrosion products. Considerable decrease in volume fraction of monoclinic zirconia phase has been observed for bilayered LCO/YSZ coating compared to 8YSZ single layer.