Yttria-stabilized Zirconia Suspension Research Articles

Controlled synthesis of Bi2O3–YSZ composite powders and their sintering behavior for high‐performance electrolytes

AbstractBismuth oxide (Bi2O3) is a promising additive to decrease the sintering temperature of yttria‐stabilized zirconia (YSZ)‐based electrolyte for solid oxide fuel cell application. However, Bi2O3 tends to grow into large column bars (>50 µm) in a chemical coprecipitation method, which dramatically limits the mixing uniformity of Bi2O3 and YSZ, even much worse than that of mechanical mixing. In this study, the reaction temperature was increased from room temperature to 90°C to increase the number of nucleation during the violate reaction between Bi3+ solution and YSZ suspension in NaOH. On this basis, the violence of the reaction was further moderated by adding half of NaOH first, then YSZ powders and the other half of an NaOH solution. The size of Bi2O3 was further decreased to sub‐micrometer and Bi2O3 was homogeneously mixed with YSZ particles, even when its addition amount was as large as 20 mol%. These composite powders effectively promoted the sintering behavior of YSZ. The sintering temperature of YSZ was decreased to 900 and 1000°C with 10 and 5 mol% Bi2O3 doping, respectively. Increasing the doping ratio induced severe volatilization of Bi2O3 and pore formation. Raising the sintering temperature (no more than 1200°C) enhanced the doping effect of Bi2O3 into the YSZ lattice but induced instability in the YSZ crystal structure.

Development of yttria-stabilized zirconia and graphene coatings obtained by suspension plasma spraying: Thermal stability and influence on mechanical properties

This study investigated the feasibility of depositing graphene nanoplatelet (GNP)-reinforced yttria-stabilized zirconia (YSZ) composite coatings. The coatings were deposited from an ethanol-based mixed YSZ and GNP suspension using suspension plasma spraying (SPS). Raman spectroscopy confirmed the presence of GNPs in the YSZ matrix, and scanning electron microscopy (SEM) analysis revealed a desired columnar microstructure with GNPs distributed predominantly in the inter-columnar spacing of the YSZ matrix. The as-deposited YSZ-GNP coatings were subjected to different isothermal treatments—400, 500, and 600 °C for 8 h—to study the thermal stability of the GNPs in the composite coatings. Raman analysis showed the retention of GNPs in specimens exposed to temperatures up to 500 °C, although the defect concentration in the graphitic structure increased with increasing temperature. Only a marginal effect on the mechanical properties (i.e., hardness and fracture toughness) was observed for the isothermally treated coatings.

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.

Design, preparation, and characterization of Yttria-Stabilized Zirconia (YSZ) coatings obtained by electrophoretic deposition (EPD)

The main objective of this work is the design, preparation, and characterization of YSZ coatings by electrophoretic deposition (EPD) technique. The suspensions used for the preparation of zirconia-derived coatings by EPD have been thoroughly characterized. YSZ suspensions containing particles of different morphology and size have been used to optimize the electrophoretic characteristics of the suspensions. The correlation between the experimental results and the theoretical values predicted by the Hamaker's equation has been analyzed. Coatings have been thoroughly characterized. Surface morphology has been studied by Scanning Electron Microscopy. X-Ray Diffraction and Time of Flight-Secondary Ions Mass Spectrometry have been used to analyze the structure and composition of the samples. Finally, nanoindentation tests have provided information regarding the mechanical properties of the coatings. Optimal coating results were achieved using stainless steel substrates previously treated thermally so that a thin anchoring layer of chromium oxide was generated.

Aging Behavior of Water-Based YSZ Suspensions for Plasma Spraying of Thermal Barrier Coatings.

Suspension stability is a key parameter that should be considered in any coating process utilizing a suspension as the main feedstock. Application of water as the liquid phase for suspension preparation is promising due to its availability, low cost and no toxicity. In the present study, the effects of three surfactants, polyethyleneimine (PEI), 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA) and α-Terpineol, on the functional stability of yttria-stabilized zirconia (YSZ) water-based suspensions were investigated. The changes in the suspensions’ zeta potential, pH, viscosity and Turbiscan Stability Index (TSI) were monitored over their aging time of 1 to 7 days. The results showed that α-Terpineol is the most effective surfactant to produce functionally stable suspensions with low viscosity and surface tension values. Plasma spraying of such stable suspensions results in the formation of thermal barrier coatings (TBCs) with columnar morphology having porosity in the range of 17 to 18 vol.%.

Influence of RF Plasma Jet Surface Treatment on Wetting Behavior of Yttria Stabilized Zirconia SPS Coatings

According to the value of water contact angle (WCA), the surfaces can be roughly defined as hydrophilic (with WCA less than 90°) or as hydrophobic (with WCA higher than 90°). Water wetting behavior plays important role and surfaces with special wettability (hydrophobic-superhydrophobic; hydrophilic-superhydrophilic) can be used both in the daily life (solar cells, smartphones, car windows, etc.) and in the industry (corrosion resistance, self-cleaning, anti-icing properties, etc.). Nowadays, the development of hydrophobic surface treatment that may be applied in the industry is very interesting topic. Therefore, it was decided to estimate the influence of radiofrequency (RF) plasma jet in atmosphere on wetting behavior of ceramic plasma sprayed coatings. As the initial material for surface treatment, yttria stabilized zirconia suspension plasma sprayed coatings were used. The influence of RF plasma jet on suspension plasma sprayed coatings was estimated on both hydrophilic and hydrophobic surfaces, and resulted water contact angle and free surface energy of modified samples were measured by sessile droplet method. Microstructure, phase composition and topography investigation were carried out by means of light microscopy, X-ray diffraction techniques and non-contact profilometry.

Improving the rheological and stability characteristics of highly concentrated aqueous yttria stabilized zirconia slurries

Highly concentrated yttria stabilized zirconia (YSZ) aqueous suspensions with improved rheology and stability characteristics are desired in several fields of modern ceramic engineering such as Suspension Plasma Sprayed (SPS) coatings. In this study, water-based suspensions of YSZ with 30 wt% solid loading were selected to investigate the effect of pH, dispersant type and its concentration on the dispersion and rheological properties of the suspensions. Polyethyleneimine solution (PEI), 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA) and alpha-Terpineol (α-Terpineol) were used as dispersant agents. Careful investigations of the suspensions were conducted through viscosity, zeta potential, turbidity, destabilization kinetics, and sedimentation rate measurements. The results showed that dispersant addition, when combined with proper pH adjustment, can significantly decrease the suspensions' viscosity values and improve their stabilities. Optimum viscosity and stability conditions, defined as viscosities lower than 4 cp and Nephelometric turbidity units (NTU) higher than 3000 were obtained with 0.1 wt% PEI addition at pH value of 2.5, 0.05 wt% PBTCA at pH value of 10.5 and 0.1 wt% α-Terpineol at pH value of 2.5.

Microstructures and Thermal Cycling Properties of Thermal Barrier Coatings Deposited by Hybrid Water-Stabilized Plasma Torch

Hybrid water-stabilized plasma (WSP-H) torches provide high-enthalpy plasma which may be utilized for high-throughput and yet economical spraying of coatings from powders, suspensions, and solutions. It was previously demonstrated that microstructures and functional properties of the WSP-H coatings may be tailored to a wide extent for new applications, namely those requiring high coating thickness and/or coating of large components. In this study, applicability potential of WSP-H technology for spraying of novel thermal barrier coatings (TBCs) is demonstrated. WSP-H technology was used for spraying of yttria-stabilized zirconia (YSZ) top-coats from powder, suspension, and solution. Yttria content in the top-coat feedstock was 7-8 wt.%. In addition, gadolinium zirconate (Gd2Zr2O7-GZO) was sprayed from suspension for comparison. NiCrAlY bond-coat was also deposited by WSP-H, and Hastelloy-X alloy was used as substrate material. Microstructure, phase composition, and endurance of the deposited coatings in thermal cycling fatigue (TCF) test and during high-temperature short-term annealing were evaluated. All coatings showed excellent high-temperature stability and TCF resistance withstanding more than 650 cycles, surpassing some of the currently commercially used TBCs. Lifetime of the TBC with columnar top-coat deposited from YSZ suspension exceeded even more than 900 cycles.

In situ coagulation of yttria‐stabilized zirconia ceramic with enhancement of green body via polyvinyl pyrrolidone crosslink

ABSTRACTIn situ coagulation for yttria‐stabilized zirconia (YSZ) suspension via polyvinyl pyrrolidone (PVP) crosslink is reported. PVP is used to prepare sterically stabilized YSZ suspension. Influence of PVP on the dispersion of YSZ suspension was investigated. It indicates that well disperse YSZ suspension with 0.3 wt % PVP can be prepared. Dimethyl sulfate (DMS) was added at 40 °C to coagulate the suspension after degassing. Influence of DMS content and coagulation temperature on coagulation process and properties of green bodies were investigated. It indicates that sufficiently high viscosity to coagulate the suspension is achieved with the addition of 1 vol % DMS at 60~80 °C. The coagulation mechanism is proposed that the YSZ suspension is destabilized by the self‐crosslink of PVP. Coagulated samples with the highest wet compressive strength of 6.34 MPa could be demolded without deformation by treating 50 vol % YSZ suspension at 60 °C. Dense YSZ ceramics with relative density above 99.1% and flexural strength of 920 ± 90 MPa had been prepared by this method sintered at 1450 °C for 3 h. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48889.

A Comparative Study of YSZ Suspensions and Coatings

The demand for suspensions that are used in thermal spray processes is expanding from research labs using the lab-prepared suspensions toward actual coating production in different industrial sectors. Industrial applications dictate the reduced production time and effort, which may in turn justify the development of the market for ready-to-use commercial suspensions. To this end, some of the powder suppliers have already taken steps forward by introducing, to the market, suspensions of some of the most used materials, such as yttria-stabilized zirconia (YSZ), alumina, and titania. However, there is a need to compare the suspension characteristics over time and the resultant coatings when using these suspensions when compared with the freshly prepared homemade suspensions. In this work, such a comparison is done using YSZ suspensions of the sub-micron to a few micron powders. In addition, some changes in the suspensions’ formula were performed as a tool to vary the coatings’ microstructures in a more predictable way, without any variation of the spray parameters. The coatings were generated while using both radial and axial injection of the suspensions into Oerlikon-Metco 3MB and Mettech Axial III plasma spray torches, respectively. A clear effect of suspension viscosity on the coating microstructure was observed using the 3MB torch with a radial injection of suspension (i.e., cross flow atomization). However, the viscosity role was not dominant when using the Axial III torch with an axial feed injection system (i.e., coaxial flow atomization).

In-situ coagulation of yttria-stabilized zirconia suspension via dispersant hydrolysis using sodium tripolyphosphate

A novel in-situ coagulation method without coagulation agent and adjusting pH value for yttria-stabilized zirconia (YSZ) suspension via dispersant hydrolysis is reported. Sodium tripolyphosphate (STPP) is used as dispersant to prepare electrostatic stabilized YSZ suspension. Influences of STPP contents on the dispersion and pH value of YSZ suspension were investigated. It indicated that there was a well-dispersed YSZ suspension with the addition of 0.3wt% STPP at pH=10. Influence of coagulation temperature on coagulation process and properties of green body was investigated. The sufficiently high viscosity suspension to coagulate was achieved at 60–80°C. The coagulation mechanism was different from traditional direct coagulation casting. The suspension was coagulated by directly shifting the isoelectric point to the original state without increasing the ionic strength and adjusting the pH value. It was proposed that the YSZ suspension could be destabilized via decrease of zeta potential by sodium tripolyphosphate hydrolyzing at elevated temperature. Coagulated samples with wet compressive strength of 3.60MPa could be demolded without deformation by treating 50vol% YSZ suspension with 0.3wt% STPP at 60°C for 30min. Dense YSZ ceramics with flexural strength of 887±110MPa and relative density of 98.9% had been prepared by this method sintered at 1450°C for 3h.

Suspension characterization and electrophoretic deposition of Yttria-stabilized Zirconia nanoparticles on an iron-nickel based superalloy

Yttria-Stabilized Zirconia (YSZ) is the most common material for thermal barrier coatings. Suspensions of 3mol% YSZ nanoparticles in acetone medium have been prepared in presence of different amounts of iodine as dispersant. Size distribution of particles in the suspensions and zeta potential were measured as a function of dispersant concentration. Adding 1.2g/l iodine was found to be effective for the dispersion of YSZ nanoparticles in acetone. The stability of YSZ suspension in acetone increased with iodine content increasing until reached 1.2g/l. Mean diameter of particles and zeta potential of the YSZ suspension in acetone were 912nm and 2.4mV respectively, and with addition of 1.2g/l iodine shifted to 111.6nm and 50.2mV respectively. Electrophoretic deposition (EPD) process has been carried out from this suspension at different applied voltages and deposition times. A uniform green coating was obtained at voltage of 6V and deposition time of 2min the thickness of the green coating is measured about 25µm.

INFLUENCE OF SINTERING TEMPERATURE ON TRANSLUCENCY OF YTTRIA-STABILIZED ZIRCONIA FOR DENTAL CROWN APPLICATIONS

This study aims to investigate the effect of sintering temperature on the translucency of yttria-stabilized zirconia (YSZ) for dental crown applications. YSZ suspension was treated by colloidal processing and 24 h of sedimentation to eliminate agglomerates and aggregates. The green bodies of YSZ were then shaped into pellets through slip casting. These bodies were sintered into a final shape at 1450 °C–1650 °C. The densities of the specimens were measured using Archimedes method. Light transmission of the YSZ specimen was also evaluated using a spectrophotometer with an integrating sphere. Morphological analysis was conducted with field-emission scanning electron microscopy. Results showed that sintering temperature significantly influenced the density, light transmission, and microstructure of YSZ. High sintering temperatures produced YSZ with a compact and homogeneous microstructure and a high density. Furthermore, the low light scattering effect on the porosity-free microstructure yielded light transmission as high as 37% in YSZ sintered at 1650 °C. The optimal sintering temperature was found to be 1600 °C, at which 34% light transmission was generated. In conclusion, high sintering temperatures improved the translucency of YSZ. This effect was attributed to effective densification of grains and elimination of pores at high temperatures, thereby alleviating the light scattering effect of the pores. At the optimal temperature, YSZ with high density and translucency and a compact microstructure was formed

Direct coagulation casting of yttria-stabilized zirconia using magnesium citrate and glycerol diacetate

Direct coagulation casting via controlled release of high valance counter ions (DCC-HVCI) has been reported in recent years. In this paper, concentrated yttria-stabilized zirconia (YSZ) suspensions were coagulated using DCC-HVCI method with magnesium citrate as coagulating agent assisted by pH shift in the presence of glycerol diacetate. The effect of ammonium polyacrylate (PAA-NH4) on the dispersibility of YSZ powder was investigated. The influence of concentrations of glycerol diacetate and magnesium citrate on pH and viscosities of YSZ suspensions was studied. The results indicate that concentrated YSZ suspensions can be coagulated by adding 2vol% glycerol diacetate and magnesium citrate above 0.5wt% at room temperature for 2–5h. The compressive strength of coagulated wet samples is above 2.0MPa. YSZ ceramics sintered at 1450°C show homogeneous microstructures with relative densities of 98.9–99.2%. Flexural strength of YSZ ceramics is 869±84MPa.

Rheology, structure, and sintering of zirconia suspensions with pyrogallol-poly(ethylene glycol) as polymeric surfactant

Abstract Yttria-stabilized zirconia (YSZ) nanoparticles have been dispersed in water with pyrogallol-poly(ethylene glycol) polymer (i.e., Gallol-PEG) as surfactant. Fluid YSZ suspensions with an apparent viscosity 99% theoretical) upon subjected to sintering.

Desenvolvimento e testes de células a combustível suportadas pelo anodo com eletrólitos depositados por spin-coating

No presente estudo são apresentados os desenvolvimentos de células suportadas pelo anodo usando os materiais convencionais, à base de zircônia estabilizada com ítria (ZEI) e NiO, e técnicas químicas de síntese e de deposição de camadas dos demais componentes: camada funcional, eletrólito e catodo. Os eletrodos foram sintetizados no Instituto de Pesquisas Energéticas e Nucleares (IPEN) por técnicas químicas que garantem homogeneidade de fases e controle de distribuição de tamanho de partículas. Suspensões de ZEI foram desenvolvidas para a deposição por spin-coating (SC) com características que permitam a deposição de camadas do eletrólito com cerca de 10 µm de espessura em poucas etapas. Após as deposições, as meias células são co-sinterizadas em temperaturas na faixa de 1300-1500°C. A deposição de catodos à base de manganita de lantânio dopada com estrôncio (LSM) foi feita pela técnica de wet powder spray de suspensões à base de etanol. As propriedades eletroquímicas das Células a Combustível de Óxidos Sólidos (CCOSs) unitárias foram medidas na faixa de temperatura entre 600 e 800°C, usando hidrogênio umidificado (3 vol.%H2O) como combustível e ar como oxidante. Os principais resultados mostram que as camadas do eletrólito são homogêneas e estanques. As células exibiram voltagem de circuito aberto ~1 V e bom desempenho em temperaturas intermediárias, confirmando a boa qualidade dos eletrólitos produzidos por SC.

Aerosol Jet® Printing of functionally graded SOFC anode interlayer and microstructural investigation by low voltage scanning electron microscopy

Yttria-stabilized zirconia (YSZ) electrolyte and functionally graded anode interlayers with compositional variation were deposited by Aerosol Jet® Printing (AJP) using ink suspensions of NiO and YSZ. The AJP system's dual atomizer configuration that allows on-demand material mixing was used to deposit the graded composite anode interlayer. These layers together with an LSM (strontium doped lanthanum manganite) based pasted cathode layer were integrated in an anode supported SOFC button cell. Cells with graded anode interlayers performed better than cells with a non-graded anode interlayer. The enhancement in electrochemical performance can be attributed to the compositional gradation. The current printing method of fabricating SOFC layers shows clear advantages of high reproducibility. In routine SEM (scanning electron microscopy) evaluation of microstructures, acceleration voltages typically used are 10–20 kV. Due to the similar backscattering coefficients of YSZ and Ni, it is difficult to clearly distinguish between the two phases in the image. In this work, low accelerating voltages (<5 kV) were used to introduce a divergence of the YSZ and Ni backscatter coefficients to investigate the composite layers printed. The backscattering mechanism for image contrast was confirmed and clarified by specially designed SEM experiments that isolated BSE (back scattered electrons) from SE (secondary electrons).

Manufacture of YSZ-LSM Semi-Cell by Colloidal Processing

Yttria stabilized zirconia (YSZ) is the most common electrolyte in solid oxide fuel cells (SOFC). The planar configuration is widely used for designing single cells, in which a thick cathode layer can be used as the supporting electrolyte film. The manufacture of the semi-cell formed by anode and electrolyte has been widely studied and there are many works dealing with its colloidal processing. However, the semi-cell formed by cathode and electrolyte has received much lower attention. This work deals with the manufacture of a semi-cell consisting of YSZ as electrolyte and strontium-doped lanthanum manganite (LSM) as a cathode through a colloidal processing route. The colloidal behavior of diluted suspensions of YSZ and the rheology of their concentrated suspensions were studied as a function of deflocculant content, mixing time by using ultrasounds probe and ageing time. The colloidal stability of aqueous suspensions of LSM was studied by measuring the zeta potential as a function of pH and deflocculant content. These concentrated suspensions were used to obtain thick self-sustained substrates by casting methods. The YSZ electrolyte and LSM cathode were prepared by tape casting in water medium.

Aqueous Tape Casting Using Organic Binder: A Case Study with YSZ

Aqueous tape casting of yttria stabilized zirconia (YSZ) having very wide particle size range was investigated using bio‐polymer, gelatin as binder and glycerol as plasticizer. Best dispersion of YSZ powder was obtained by using an anionic polyelectrolyte DARVAN 821A at pH 7.5. Gelling properties of gelatin, plasticized with water and glycerol have been studied by dynamic shear measurements. Decreasing concentration of gelatin significantly decreases the gelling temperature of it. With the addition of optimum amount of binder and plasticizer, it has been possible to prepare stable YSZ suspension of 45–50 wt% solid loading that exhibited the desired shear‐thinning behavior. Green tapes with good flexibility (strain to failure: 12%–24%) and strength (2–3 MPa) with total organics content of 10–14 wt% were obtained. After removal of organics, the tapes were sintered at 1550°C for 3 h. The sintered density of the tapes thus obtained was about 99% of the theoretical density. The grain size of the sintered tape was fairly large (10–20 μm); but the surface of the sintered tape (thickness: 100 μm) did not show any visible porosity.

Electrophoretic deposition of YSZ thin-film electrolyte for SOFCs utilizing electrostatic-steric stabilized suspensions obtained via high energy ball milling

This manuscript describes a facile alternative route to make thin-film yttria-stabilized zirconia (YSZ) electrolyte by liquid-phase assisted electrophoretic deposition utilizing electrostatic-steric stabilized YSZ suspension followed by sintering. Very fine YSZ particles in ball-milled suspension facilitate their sustained dispersion through electrostatic mechanism as evidenced by their higher zeta potentials. Binder addition into the ball-milled suspension is also demonstrated to contribute complementary steric hindrance effects on suspension stability. As the consequence, the film quality and sinterability improve in the sequence of film made from non ball-milled suspension, film made from ball-milled suspension and film made from ball-milled suspension with binder addition. The specific deposition mechanisms pertaining to each suspension are also postulated and discussed below. A very thin dense electrolyte layer of ∼10 μm can be achieved via electrophoretic deposition route utilizing ball-milled suspension and binder addition. This in turn, makes the electrolyte resistance a more negligible part of the overall cell resistance. Further on, we also tested the performance of SOFC utilizing as-formed 10 μm YSZ electrolyte i.e. YSZ-NiO|YSZ|LSM (La0.8Sr0.2MnO3-δ), whereby a maximum power density of ∼850 mW cm−2 at 850 °C was demonstrated.