Yttria-stabilized Zirconia Powders Research Articles

Processing of the yttria stabilized zirconia-bioactive glass nano composite produced by electrophoretic deposition method

The yttria-stabilized zirconia (YSZ) is added to a bioactive glass coating through the electrophoretic deposition (EPD) method to significantly improve the mechanical properties, in particular the bonding strength of the coating on the Ti substrate. In this study, suspensions of bioactive glass and YSZ powder (at the same ratio, 20 g/l) are prepared in ethanol solvent; and tri-ethanol-amine is used as the stabilizer. The effects of the EPD parameters such as deposition time and voltage are studied. The optimum coating quality is achieved at a voltage of 60 V for 10 min. After coating, sintering is performed at three different temperatures (800, 850, and 900 °C). The XRD is used to identify the structure and phase of yttria-stabilized zirconia powders and the coated samples. FE-SEM is also employed to assess the microstructure of the specimens. The highest adhesion strength (sim 4.38 MPa) is obtained at the sintering temperature of 850 °C.

Experimental analysis of the combined effect of thermal barrier coating material and the nanoparticle augmented fuel usage on CI engine characteristics

The scope of this work involves the utilization of optimal insulating material and nanoparticles in addition to diesel for enhancing the CI engine performance reduce harmful environmental emissions. The first phase of the research work focused on coating the combustion chamber components, including cylinder-liner as well as a piston with 150 and 100 μm thickness, correspondingly, with equivalent quantities of Yttria Stabilized Zirconia (YSZ) and Alumina (Al2O3) powder using the plasma spraying method. The second phase of experimental work oversees the augmentation of diesel fuel with 30 ppm and 60 ppm of Cerium Oxide (CeO2) nanoparticles independently. Initially, the effectiveness, as well as emissions criteria, were investigated using a thermal barrier coated (TBC) engine & neat diesel. The implications of CeO2 nanoparticles were then compared with the reference engine. Usage of the thermal barrier coated chamber reduced the specific fuel consumption (SFC) by 7.71 % and increased the brake thermal efficiency (BTE) by 1.75 %. Additionally, the SFC was reduced by 8.25 % and 13.19 %, and the BTE was enhanced by 2.43 % and 3.54 % in the TBC engine, which used 30 ppm and 60 ppm CeO2 mixed diesel fuel, respectively, when correlated with the reference engine. Besides, harmful pollutant gases of carbon monoxide (0.0707 % vol), hydrocarbon (37 ppm), and smoke (8.08 %) were minimized extensively by TBC coating material usage and the inclusion of nanoparticles in the fuel.

Material extrusion additive manufacturing of zirconia parts using powder injection molding feedstock compositions

The aim of this study is the evaluation of powder injection molding (PIM) binder compositions for the material extrusion (MEX) additive manufacturing of zirconia parts. Four commercial PIM binder compositions were selected and mixed with 45 vol% of yttria-stabilized zirconia powder. Due to the brittle characteristic of the obtained ceramic feedstocks, a screw based pellet printing head was used for printing dense zirconia structures. To compare 3D printing performance, additionally a commercially available zirconia filament was used in this study. Application of PIM binder compositions was limited either due to phase separation during processing, poor printing performance or delamination during solvent debinding. Only one of the PIM based feedstock compositions could be successfully printed, debound and sintered. A ring-on-ring setup was used to investigate the equibiaxial flexural strength after sintering for both pellet and filament printed disks. For benchmarking, cold isostatic pressed (CIP) ceramic discs were fabricated by commercial, ready-to-press, zirconia powder. The ring-on-ring results showed a low Weibull modulus (3 <m<5) for all samples, regardless of the manufacturing process. Fractography on selected samples demonstrated, that the origins of failures are close to the area of the loading ring which indicates an uneven stress distribution along the contact area between the setup and the sample. The pointwise stress concentration is the reason for the immature failure of the samples and the low Weibull modulus. The characteristic strength and 90% confidence intervals were used to compare the strength of ceramic samples produced via additive manufacturing and CIP. Almost similar mechanical properties were obtained for the CIP pressed (σ0 = 657 MPa) and filament printed (σ0 = 531 MPa) samples. However, a lower strength was obtained by the pellet printed samples based on commercial PIM Binder (σ0 = 203 MPa). Fractography analysis indicated poor fusion of printed layers for the samples produced with PIM binder composition as the main reason for poor mechanical performance.

Effect of activation temperature of Yttria Stabilized Zirconia (YSZ)/ZnO nanorods thin film on photoelectrochemical cell performance

A photoelectrochemical cell (PEC) is a device that converts solar energy into electrical energy stored in the form of hydrogen and oxygen. The n-type semiconductor that shows promising potential as a PEC cell device is known as ZnO. ZnO in the form of nanorods (NRs) is considered capable of increasing the conversion efficiency of PEC performance due to the large surface area. However, in the energy conversion process, the photoactive layer of the PEC cell corrode easily in the electrolyte solution, reducing the stability of the current produced and shortening the lifetime of the PEC cell. In this study, the stability improvement using solid electrolytes in photoelectrochemical technology was studied. Yttria Stabilized Zirconia is a type of solid electrolyte that has high mechanical properties and ionic conductivity. Activation of YSZ powder at various temperatures is considered very instrumental to the efficiency of the PEC cell device. XRD, SEM-EDX, and UV–Vis characterized the samples. For efficiency measurement through I–V testing, it is equipped with photodetectors such as photoresponse of current and voltage as well as photostability. The higher the YSZ activation temperature, several results were obtained, the larger ZnO NRs/YSZ particle size, the lower the thickness of the film, the higher the absorbance value, and the smaller the band gap. In addition, sample agglomeration occurs at the temperature with the lowest activation and sample response when irradiated enough. Finally, the efficiency of the cell increases, namely at the YSZ activation temperature of 1400 °C, where 1% is produced.

High heat flux burner-rig testing of 8YSZ thermal barrier coatings: Influence of the powder feedstock

Burner-rig thermal cyclic testing of Thermal Barrier Coating (TBC) samples fabricated using different 8YSZ powders was conducted to investigate the influence of the chemical and phase compositions of the powder feedstocks. Four different powder feedstocks were selected. The chemical and phase compositions among the 8YSZ powders were systematically varied while the powder particle size and other physical characteristics were kept nominally the same. The coating process was also selected to achieve similar microstructure among the samples. The testing revealed that (1) higher impurity content (esp. silica) is detrimental to the cyclic life of the TBC; (2) coating porosity has a significant influence on the cyclic life of the TBC, the higher the porosity, the higher the cyclic life, for the range of porosity of the tested samples; (3) a low monoclinic content in the feedstock powder has not been shown to have a positive effect on the cyclic life of the TBC.

Hydrothermally-assisted recovery of Yttria- stabilized zirconia (YSZ) from end-of-life solid oxide cells

Effective and scalable recycling strategies for the recovery of critical raw materials are yet to be validated for solid oxide cells (SOCs) technologies. The current study aimed at filling this gap by developing optimized recycling processes for the recovery of Yttria-stabilized Zirconia (YSZ) from End-of-Life (EoL) SOC components, in view of using the recovered ceramic phase in cell re-manufacturing. A multi-step procedure, including milling, hydrothermal treatment (HT), and acidic-assisted leaching of nickel from composite Ni-YSZ materials, has been implemented to obtain recovered YSZ powders with defined specifications, in terms of particle size distribution, specific surface area, and chemical purity. The overall optimized procedure includes a pre-milling step (6 h) of the EoL composite materials, and a hydrothermal (HT) treatment at 200 °C for 4 h to further disaggregate the sintered composite, followed by selective oxidative leaching of Ni2+ by HNO3 solution at 80 °C for 2 h. In particular, the intermediate HT step was assessed to play an essential role in promoting the disaggregation of the sintered powders, with a related increase of specific surface area (up to 13 m2 g−1) and the overall reduction of the primary particle aggregates. The acid-assisted leaching allowed to fully extract Nickel from the composite Ni-YSZ powders, with retention of YSZ crystallinity and negligible loss of Zr and Y, as revealed by ICP analysis on the recovered supernatants.The developed multi-step pathway offers a promising strategy to recover valuable YSZ materials for the re-manufacturing of SOCs components, with the aim to boost a circular economy approach in the field of fuel-cell and hydrogen (FCH) technologies.

Effects of calcination temperature on grain growth and phase transformation of nano-zirconia with different crystal forms prepared by hydrothermal method

The nano-Zirconia powders doped with different yttrium content (YSZ) were prepared by hydrothermal method, and then calcined in the atmosphere. The grain growth kinetics and mechanism of YSZ powder were analyzed. The addition of Y2O3 can refine the zirconia grains, and the mechanism of its action is discussed, and the grain sizes of the hydrothermal nano-powders (0, 3 and 11 YSZ) prepared with different Y2O3 are 15.4, 13.7 and 8.0 nm, respectively. The phase transformation mechanism of 3 YSZ powder and the influence mechanism of Y2O3 doping in different stages on powder growth are discussed. The growth mechanism of powder in different stages is analyzed and expounded. The first stage grain growth mechanism of 3 YSZ and 11 YSZ powders is dominated by surface diffusion and grain boundary rotational polymerization growth mechanisms, while the second stage grain growth is dominated by lattice diffusion and grain boundary migration polymerization growth mechanisms.

Fabrication, microstructure, and properties of 8 mol% yttria-stabilized zirconia (8YSZ) transparent ceramics

Fine grained 8 mol% yttria-stabilized zirconia (8YSZ) transparent ceramics with high optical and mechanical properties were fabricated by air pre-sintering and hot isostatic pressing (HIP) using commercial 8YSZ powders as the raw material. The pre-sintered ceramics with fine grains and appropriate relative density play a key role to achieve high transparency and suppressed grain size after HIP post-treatment at relatively low temperatures. With the increase of HIP temperature from 1350 to 1550 °C, the in-line transmittance of 8YSZ ceramics at 600 nm increases from 56.9% to 71.5% (2.5 mm in thickness), and the average grain size increases from 2.4 to 16.3 µm. The corresponding bending strength of 8YSZ transparent ceramics decreases from 328±20 to 289±19 MPa, the hardness (H) decreases from 12.9±0.1 to 12.5±0.2 GPa, and the fracture toughness (KIC) decreases from 1.30±0.02 to 1.26±0.03 MPa·m1/2. Systematical investigations were carried out to study the combination of high optical transparency and excellent mechanical properties in 8YSZ ceramics.

Core shell coatings for nuclear thermal propulsion cermets

Magnetron sputtering has been employed to provide conformal tungsten coatings from approximately 70 to 540 nm thicknesses over yttria stabilized zirconia (YSZ) powders. Through a rotating vessel, the powder was continually cascaded exposing its surface enabling the line-of-sight cathode tungsten target to deposit over the entire surface. With increasing coating thickness, a particulate surface morphology developed. These tungsten particulates were plate-like in morphology and faceted in some cases. The formation of these features is contributed to the continual low energy impacts between the hard YSZ powders during deposition as well as the adhesion and de-adhesion of the coatings connecting particle clusters. The results of this work demonstrate the ability of sputter deposition to create refractory coatings for cermet fuels utilized in nuclear thermal propulsion, as well as broader applications where core-shell powder fabrication is needed.

Novel controllable solid/hollow T'-YSZ nanostructured powders for additive manufacturing

Here, we report novel spherical non-transformable yttria-stabilized zirconia (T'-YSZ) nanostructured powders with solid/hollow and controllable microstructure fabricated via a nanoparticle regranulation method for additive manufacturing (AM). The as-obtained T'-YSZ feedstocks are superior to commercial YSZ powders for thermal barrier coatings when thermal spraying is used as the AM method. Furthermore, we confirm for the first time that the state-of-the-art T'-YSZ feedstocks can be successfully used for 3D printing. Therefore, the as-prepared powders are promising for AM, and they will promote the development of AM techniques.

Initial sintering mechanism and additive effect in zirconia ceramics

AbstractY2O3‐stabilized ZrO2 (YSZ) ceramics have been used for various engineering applications because of their excellent mechanical properties or oxide‐ion conductivity applicable to solid‐electrolyte. The performance of YSZ depends on the sintered texture that is directly determined by sinterability of raw powders. A new kinetic analysis method of diffusion mechanism based on an initial sintering theory (grain‐boundary or volume diffusion) is theoretically derived, the initial sintering mechanism of hydrolytic YSZ powder is experimentally determined, and the effects of powder characteristics on sinterability are discussed. Furthermore, the additive‐enhanced sintering is proposed. A small amount of Al2O3 significantly enhances the densification. Using the additive effect, the low‐temperature degradation that is the fault of zirconia ceramics can be improved by decreasing the sintering temperature.

Synthesis of γ‐Bi 2 O 3 /YSZ composite powders using a facile precipitation method

Low melting point and high ionic conductivity of γ-Bi2O3 make it a promising additive to decrease the sintering and operation temperatures of yttria stabilized zirconia (YSZ)-based electrolyte for solid oxide fuel cell application. Herein, γ-Bi2O3/YSZ composite powders with good uniformity and precise control of morphology and phase were successfully synthesized via a low cost chemical precipitation method. Both the concentration of NaOH solution and the reactant adding sequence affect the morphology and synthesis of γ-Bi2O3/YSZ composite powders. When the concentration of NaOH was in the range of 1.25–1.875 M, tetrahedron γ-Bi2O3/YSZ powders were synthesized. While, cubic structural γ-Bi2O3/YSZ powders were obtained when adding Bi3+ and YSZ suspension into 1.5 M NaOH solution. The addition of YSZ facilitates the fabrication of γ-Bi2O3 and widens its process window to a higher NaOH concentration. Thus synthesized γ-Bi2O3/YSZ composite powders effectively decrease the sintering temperature of YSZ to 1050°C due to the uniform distribution of γ-Bi2O3 inside YSZ powders. This work provides a facile method to fabricate γ-Bi2O3/YSZ composite powder with controlled morphology and phase, which will promote the mass production of low cost YSZ-based electrolyte for SOFC applications.

Impact of Preparation Method and Y2O3 Content on the Properties of the YSZ Electrolyte

This study is an effort to cover and interconnect multiple aspects of the fabrication of the yttria-stabilized zirconia (YSZ) from powder preparation to a solid electrolyte suitable for utilization in solid oxide cells. Thus, a series of YSZ electrolytes was prepared, differing in the content of the Y2O3 dopant and in the method of preparation. Combustion synthesis along with the thermal decomposition of precursors was used for YSZ powder synthesis with a dopant content of 8 to 18 mol.%. Post-synthesis treatment of the powder was necessary for achieving satisfactory quality of the subsequent sintering step. The morphology analyses of the YSZ powders and sintered electrolytes produced proved that small particles with a uniform size distribution are essential for obtaining a dense electrolyte. Furthermore, the conductivity of YSZ electrolytes with different Y2O3 contents was examined in the temperature range of 400 to 800 °C. The lowest conductivity was found for the sample with the highest Y2O3 content. The obtained results enable the preparation methods, YSZ powder morphology, and composition to be connected to the mechanical and electrochemical properties of the YSZ electrolyte. Thus, this study links every step of YSZ electrolyte fabrication, which has not been sufficiently clearly described until now.

Effects of Aluminum Oxide Addition on Electrical and Mechanical Properties of 3 mol% Yttria-Stabilized Tetragonal Zirconia Electrolyte for IT-SOFCs.

Composite tetragonal zirconia (3Y-TZP) sinters with Al2O3 contents of 0, 1, 5, 10 and 15 mol% were obtained from a 3-YSZ powder prepared using the gelatin method, and the influence of alumina addition on the mechanical and electrical properties of the obtained sinters was investigated. Al2O3 was added via two different methods, namely during the preparation of the 3-YSZ powder and via impregnation using an alcohol solution of aluminum nitrate. The obtained green bodies were sintered for 2 h in air at 1773 K. The structure and morphology of the two series of sinters were investigated using XRD and SEM-EDS, their electrical properties were determined using impedance spectroscopy, and their hardness and critical stress intensity factor were measured using the Vickers indentation test. We established that both the amount of alumina and the method used to introduce it into the 3Y-TZP matrix significantly affect the physicochemical properties of the obtained polycrystalline material. The 3-YSZ/10 mol% Al2O3 sinter that had Al2O3 introduced during the preparation of the 3-YSZ powder was found to exhibit the most advantageous mechanical and electrical properties while still having sufficiently low porosity.

Effect of spontaneous polarization of tourmaline on the grain growth behavior of 3YSZ powder

AbstractThis paper introduces a new method for adjusting the particle size of ZrO2 powder through the electric field effect of tourmaline. The 3 mol% yttria‐stabilized ZrO2 (3YSZ) powder was prepared by using ZrOCl2∙8H2O, YCl3∙6H2O, NaOH, and nano‐tourmaline powder as raw materials through direct precipitation. The powder was characterized with thermogravimetric‐differential scanning calorimeter, X‐ray diffraction, Brunauere‐Emmette‐Teller, Fourier transform infrared, scanning electron microscope, and transmission electron microscope, and the mechanism of tourmaline in the process of powder preparation was also discussed. Findings demonstrate that the electric field generated by spontaneous polarization of tourmaline can control the size of ZrO2 crystal grains, improve the dispersibility of the powder, and promote the stability of ZrO2 in the tetragonal phase. When the electric intensity of tourmaline is 9.02 × 106 V/m, and the addition amount is 2.5 vol%, tourmaline/3YSZ powders are mainly tetragonal phase, and the grain size is the smallest, with an average crystallite size of 19 nm. Then the mechanical properties of tourmaline/3YSZ ceramics were tested. Compared with 3YSZ ceramics without tourmaline, the flexural strength and fracture toughness were improved by 39.5% and 35.8%.

Achieving high anti-sintering performance of plasma-sprayed YSZ thermal barrier coatings through pore structure design

Sintering is one of the critical factors leading to thermal and mechanical degradation of plasma-sprayed thermal barrier coatings (TBCs) in service under high temperature. The sintering resistance of the coating is expected to be improved through pore structure design. In this study, through a strategically improved powder feeding process, 8YSZ powders with fine-sized and coarse-sized pores were injected from the tail of plasma flame during plasma spraying to design porous coatings containing two differently flattened particles with different pore structures. The microstructural and property evolutions during sintering of the coatings were systematically studied compared with traditionally structured coatings. The effect of pore morphology on its sintering behavior was analyzed by quasi-in-situ observation of microstructure evolution. Results show that the anti-sintering performance of plasma-sprayed coating can be improved by adjusting the pore structure of coating with porous unmelted particles. In particular, the introduction of unmelted particles with coarse-sized pores can ensure that the coating has excellent thermal and mechanical properties for a long time. The results of this study provide guidance for structural design of anti-sintering plasma-sprayed coatings.

Synthesis of YSZ powders with controlled properties by the CDJP method

In this work, YSZ powders were synthesized by the controlled double-jet precipitation at constant pH values in the range from 3 to 8. It has been shown that weakly bound floccule-like particles with diffuse boundaries, obtained at pH 3, 7 and 8, strongly agglomerate during drying and form large particles of irregular shape. The dense spherical aggregates of zirconium hydroxide are formed only at CDJP at pH 4 and 5 due to the layer-by-layer buildup of primary particles on the surface of the aggregates. These dense aggregates capture less salt, do not undergo additional agglomeration during drying and retain a low size dispersion. YSZ powder obtained at pH 5 has a high bulk density and fluidity, as well as a narrower particle size distribution than conventional thermal spray powders. The use of this powder resulted in the formation of a uniform coating with high adhesion, uniform porosity and reduced roughness.

Mechanical Properties of Multi-Sized Porous Thermal Barrier Coatings at Micro and Nano Scales after Long-Term Service at High Temperature

Atmospheric plasma-sprayed multi-sized porous structures in thermal barrier coatings (TBCs) were constructed with hollow spherical (HOSP) 8YSZ powders and polypropylene pore formers. The mechanical properties of the multi-sized TBCs were investigated through the nanoindentation method as comparations of the as-sprayed coating and those serving at 1100 °C for a long-term. The results showed that the introduction of the multi-sized pores into TBCs could lead to the decrease of the hardness and modulus as well as the increase of fracture toughness. The hardness and modulus of the coating increased, and the fracture toughness of the coating decreased with the prolongation of the serving times at high temperatures. The mechanical properties of the coating became stable after 60 days’ serving at 1100 °C. The hardness, elastic modulus and fracture toughness of the TBCs increased to 6.51, 7.79, 10.04 GPa and 126.36, 135.13, 145.22 GPa as well as 1.049, 1.157, 1.255 MPa·m0.5, respectively, corresponding to the multi-sized porous TBCs with 0%, 10% and 15% PP powders. The nano-size pores disappeared gradually in the multi-sized TBCs during serving at 1100 °C. The macropores deposited between the ceramic particles penetrated with little diffusion and were not easy to disappear. The introduction of a multi-scale pore structure into the TBCs could improve the stress-strain tolerance of the TBCs.

Tribological property and thermal shock resistance of NiCoCrAlY coated YSZ composite coatings prepared by different laser additive manufacturing scanning speeds

The operating efficiency of aeroengine is significantly affected by the airtightness of its gas path. In this work, the NiCoCrAlY-coated YSZ powder was used and the NiCoCrAlY/Yttria-stabilized zirconia (YSZ) composite coatings were deposited on IN718 substrate with different laser scanning speeds by laser melting deposition to fabricate the seal coating to improve the airtightness. The microstructure, tribological property and thermal shock performance of composite coatings were studied. Due to the extremely high laser energy density, the composite feeding materials are melted thoroughly as well as the IN718 substrate, forming a metallurgical bonding between the composite coating and the substrate. Compared with the pure NiCoCrAlY coating, the reinforced phases γ-NiAl, γ-Ni, ZrO2 and Al2O3 were generated in the composite coating because of the decomposition of YSZ ceramic particles. Due to the uniform nucleation and refined grains, the hardness improves in composite coating hence the wear resistance compared with the pure NiCoCrAlY coating. With increasing laser scanning speeds, the length and width of the microcracks in the composite coating increased correspondingly, thus degrade the thermal shock resistance. The sample prepared by the laser scanning speed of 8 mm/s shows the best wear and thermal shock resistance in this work since its less microcracks while moderate grain size.

Few-layered-graphene/zirconia composites: Single-step powder synthesis, spark plasma sintering, microstructure and properties

The chemical vapor deposition of carbon is performed onto a commercial yttria-stabilized zirconia (3YSZ) powder bed. This produces few-layered-graphene (FLG) film uniformly covering the 3YSZ grains, without the manipulation of any pre-existing nanocarbon in the form of graphene platelets. The powders are then consolidated by spark plasma sintering, producing specimens where FLG is located along the grain boundaries of the 3YSZ matrix, which is below 0.3 μm in grain size. The samples are characterized by Raman spectroscopy, X-ray photoelectron spectroscopy, scanning and transmission electron microscopy. The pure 3YSZ exhibits higher toughness and fracture strength compared to composites, but the trend is that their toughness increases upon the increase in carbon content. Crack-deflection and crack-bridging are observed. The composites are electrically conducting with a percolation threshold between 1.48 and 1.98 vol.% of carbon, reflecting the continuous nature of the FLG film over very long distances.