8YSZ Samples Research Articles

Enhanced sinterability and conductivity insights of Nb2O5 - Doped 8 mol% yttria-stabilized zirconia: Implications for low-temperature ceramic electrolytes

The study explored the effect of incorporating niobia (Nb2O5) at 1, 3, and 5 wt percent into 8 mol% yttria-stabilized zirconia (8YSZ), made through a mechanochemical process. Niobia-doped 8YSZ samples were synthesized by a mechanochemical process and analyzed with methods including XRD, XPS, UV–Visible spectroscopy, particle size analysis, BET surface area analysis, FESEM-EDX, and EIS. Sintering was achieved at a reduced temperature of 1373 K, and all niobia-doped samples predominantly exhibited a tetragonal phase. Electrochemical impedance spectroscopy indicated that niobia doping inversely affected oxide ion conductivity-higher dopant concentrations resulted in lower conductivity. Nb-doped 8YSZ also displayed lower activation energy for conductivity compared to high-temperature (1473 K) sintered undoped 8YSZ, demonstrating equivalent performance. The combined benefits of lower sintering temperatures and enhanced ionic conductivities highlight crucial progress in developing cost-effective and energy-efficient electrolytes for clean energy applications.

Hot corrosion resistance of oxide‐doped yttria‐stabilized zirconia powder in V2O5 molten salt

AbstractThe hot corrosion resistance of 8 wt.% yttria‐stabilized zirconia (8YSZ) powder, modified with CaO, MgO, Ta2O5, and TiO2 at concentrations of 5, 10, and 15 wt.%, was systematically investigated in a molten vanadium pentoxide (V2O5) environment at 900°C and 1100°C for 48 h. The modified 8YSZ samples, coated with V2O5, underwent thermal cycling totaling 12 cycles. Results revealed susceptibility to hot corrosion for all doped 8YSZ powders, attributed to tetragonal ZrO2 destabilization, forming monoclinic ZrO2. Remarkably, 8YSZ/CaO demonstrated exceptional resistance to hot corrosion when exposed to a temperature of 900°C. The corrosion product found in the 8YSZ/Ta2O5 material was determined to be tetragonal Zr0.66Y0.17Ta0.17O2. Although, 8YSZ/TiO2 undergoes deterioration at 900°C, it exhibits improved resistance at 1100°C, resulting in the formation of TiVO4.

Electric Current‐Assisted Sintering of 8YSZ: A Comparative Study of Ultrafast High‐Temperature Sintering and Flash Sintering

Electric current‐assisted sintering (ECAS) is a promising powder consolidation technique that can achieve short‐term sintering with high heating rates. Currently, main methods of performing ECAS are indirect heating of the powder compact in a conductive tool or direct heating with current flowing through the powder compact. Various influencing factors have been identified to explain the rapid densification during ECAS, such as ultrahigh heating rates, extra‐high temperatures, and electric field. However, the key consolidation‐enhancing factor is still under debate. This study aims at understanding the role of heating rate on the enhanced densification during ECAS of 8 mol% Y2O3‐stabilized ZrO2 (8YSZ) by experimental and numerical methods. Two different heating modes, ultrafast high‐temperature sintering (UHS, indirect heating) and flash sintering (FS, direct heating), are studied. The novel UHS technique is successfully applied to consolidate the 8YSZ samples. Additionally, finite element methods (FEM) combined with a constitutive model is adopted to predict the densification and grain growth. Furthermore, a comparison of UHS and FS is performed to investigate the thermal effect (heating rate) and athermal effect (electric field) individually. The results indicate that the high heating rate is the key factor of the rapid densification during UHS and FS of 8YSZ.

Effect of Two-Step Sintering on the Mechanical and Electrical Properties of 5YSZ and 8YSZ Ceramics.

Yttria-stabilized zirconia (YSZ) has been widely used in structural and functional ceramics because of its excellent physicochemical properties. In this paper, the density, average gain size, phase structure, and mechanical and electrical properties of conventionally sintered (CS) and two-step sintered (TSS) 5YSZ and 8YSZ are investigated in detail. As the grain size of YSZ ceramics became smaller, dense YSZ materials with a submicron grain size and low sintering temperature were optimized in terms of their mechanical and electrical properties. 5YSZ and 8YSZ in the TSS process significantly improved the plasticity, toughness, and electrical conductivity of the samples and significantly suppressed the rapid grain growth. The experimental results showed that the hardness of the samples was mainly affected by the volume density, that the maximum fracture toughness of 5YSZ increased from 3.514 MPa·m1/2 to 4.034 MPa·m1/2 in the TSS process, an increase of 14.8%, and that the maximum fracture toughness of 8YSZ increased from 1.491 MPa·m1/2 to 2.126 MPa·m1/2, an increase of 42.58%. The maximum total conductivity of the 5YSZ and 8YSZ samples under 680 °C increased from 3.52 × 10-3 S/cm and 6.09 × 10-3 S/cm to 4.52 × 10-3 S/cm and 7.87 × 10-3 S/cm, an increase of 28.41% and 29.22%, respectively.

Revisiting Fe-doped 8YSZ as the electrolyte of SOFC – From sintering to electrochemical performance

One of the main challenges in preparing a dense and ionic conductive yttria-stabilized zirconia (YSZ) solid electrolyte is its high sintering temperature. Iron has been suggested as an efficient additive for Yttria-stabilized Zirconia (YSZ) to reduce its sintering temperature with the least detrimental effect on ionic conductivity. In this study, a deeper exploration of the iron’s effect on the physical, microstructural, and electrical properties of YSZ was conducted. 8YSZ samples with different contents of Fe2O3 (0, 1, 3, 5, 7 mol%) were prepared by tape casting and sintered at 1200 °C and 1300 °C for 4 h. X-Ray diffraction (XRD) analysis, scanning electron microscopy (SEM), optical dilatometry, and electrochemical impedance spectroscopy (EIS) were performed. The results showed that iron does not affect the stability of the cubic phase structure. Estimating oxygen vacancy concentrations by EIS revealed that increasing Fe2O3 concentration resulted in decreamnet of oxygen vacancy concentrations at the space-charged layer and deteriorates the grain boundary conductivity. On the other hand, adding Fe2O3 led to grain growth and grain boundary length reduction which, as an opposite factor, reduced the destructive effect of grain boundary on conductivity. The maximum total ionic conductivity of 0.044 S/cm was achieved by adding 3 mol% of Fe2O3 to 8YSZ sintered at 1300 °C.

Діоксид цирконію, стабілізований оксидами ітрію та церію (8Ce2YSZ), для анодів керамічних паливних комірок та електролізерів

Solid oxide fuel cells (SOFC) are among the most promising technologies for the electricity generation due to their high efficiency, reliability, flexibility in fuel selection, absence of valuable platinum group metal catalysts, safety and environmental friendliness.Typically, the SOFC is built on the basis of its anode, which is actually also its carrier. This is due to the researchers wish to minimize the ohmic resistance of the electrolyte layer via its thinning that is extremely critical for reducing SOFC operating temperature. In this regard, the anode must be strong enough both to make it easier to handle when making the whole cell and to ensure its stable operation. In addition to the carrier function, the anode shall provide sites for reacting gaseous fuel with oxygen ions, which are delivered through the electrolyte, and supplying the fuel gas components to the reaction sites and removing the fuel oxidation reaction products to the outside.The work deals with the comparative study of ceramic materials based on ZrO2, co-stabilized with CeO2 and Y2O3, and stabilized with Y2O3to be used in producing the SOFC anode, and for further structural optimization for future SOFCs.8Ce2YSZ ceramic samples made by hydrothermal synthesis (with two different modes of drying precipitation) have tetragonal phase and 6—8% residual porosity. The 8Ce2YSZ samples, showed the biaxial bending strength — 542 MPa and 486 MPa, respectively. The 8YSZ and 3YSZ samples have cubic phase with a strength of 181 MPa and tetragonal phase with a strength of 577 MPa, respectively at 1% porosity.The specific electrical conductivity of 8Ce2YSZ and 8YSZ is 1,1•10-3, 4•10-3 S/cm, 1,2•10-2 S/cm and 5,2•10-3, 2,7•10-2 S/cm, 9,3•10-2 S/cm at 600, 700, 800 °C, respectively. Keywords: solid oxide fuel cell, electrolyte, anode, zirconium dioxide, mechanical strength, ionic conductivity.

Destabilization and Ion Conductivity of Yttria-Stabilized Zirconia for Solid Oxide Electrolyte by Thermal Aging.

The degradation behavior of yttria-stabilized zirconia by thermal aging was investigated in terms of phase transformation, local atomic structure, and electrical conductivity. The average grain size of 8YSZ was increased from 20.83 μm to 25.81 μm with increasing aging temperature. All 8YSZ samples degraded at different temperatures had a predominantly cubic structure. The (400) peak of 8YSZ deteriorated at 1300 and 1400 °C shifted to a high angle, and the peak of tetragonal was not indexed. For 8YSZ degraded at 1500 °C, the (400) peak shifted to a lower angle, and the peak of tetragonal was identified. Analysis of the local microstructure of aged 8YSZ using extended X-ray absorption fine structure showed that the intensity of the Zr-O peak gradually increased and that the intensity of the peak of cationic Zr decreased as the aging temperature increased. The changes in the peaks indicate that the oxygen vacancies were reduced and Y3+ ions escaped from the lattice, leading to the destabilization of 8YSZ. The activation energies of 8YSZ at 1300 °C and 1400 °C were derived to be 0.86 and 0.87 eV, respectively, and the activation energy of 8YSZ at 1500 °C increased significantly to 0.92 eV. With the thermal deterioration of 8YSZ, the cation (Y3+) escaped from the lattice and the number of oxygen vacancies decreased, resulting in the formation of a tetragonal structure and high activation energy at 1500 °C.

Influence of AC fields and electrical conduction mechanisms on the flash-onset temperature: Electronic (BiFeO3) vs. ionic conductors (8YSZ)

This work aims to clarify the influence of AC (up to 50 kHz) vs DC fields on the flash-onset temperature, emphasizing the role of the electrical conduction mechanism. BiFeO3 (BFO) is used as an example of electronic conductor while 8-mol % Yttria-stabilized zirconia (8YSZ) is used as an example of ionic conductor. For 8YSZ, a frequency dependence of the flash-onset temperature and flash-induced heating is observed. This is consistent with the different contributions found in the total electrical response of 8YSZ as characterized by impedance spectroscopy measurements. Estimations based on the blackbody radiation model suggest that 8YSZ samples attain higher temperatures under AC fields due to a more efficient heating. Moreover, a noticeable decrease in the activation energy for the electrical conduction after the flash is triggered is attributed to electronic conduction. Meanwhile, the lack of frequency response and insensitiveness to the type of electrical field found in the case of BFO can be attributed to its mainly electronic bulk conduction.

Microstructural and electrochemical properties of impregnated La0.4Sr0.6Ti0.8Mn0.2O3±d into a partially removed Ni SOFC anode substrate

The microstructural and electrochemical properties of anodes obtained by impregnation of the La0.4Sr0.6Ti0.8Mn0.2O3±d (LSTM) oxide system into two types of anode substrates such as Ni/ 8YSZ substrate (Ni (E)/ 8YSZ) and partially Ni removed Ni/ 8YSZ substrate (Ni(R)/8YSZ) were investigated in order to apply them as anode material for solid oxide fuel cells.All of the samples with LSTM impregnated on Ni (R)/ 8YSZ show higher electrical conductivity values than those of unimpregnated Ni (E)/ 8YSZ under dry H2 condition. The highest electrical conductivity values of 2041.2, 1877.4, and 1764.3 S/cm at 700, 800 and 900 °C can be achieved by samples with 3 wt% impregnated LSTM on Ni (R)/ 8YSZ. From the XPS analysis, the existence of a Ti metal peak on the surface of LSTM was only measured for the LSTM (3 wt%)-Ni (R)/ 8YSZ sample, metallic titanium on the surface can improve the electrical catalytic reaction.LSTM (3 wt%)-Ni (R)/ 8YSZ showed higher electrical conductivity values then those of LSTM (3 wt%)-Ni (E)/ 8YSZ in all the temperature ranges measured in the case of dry CH4 supply. Finally, the electrical conductivity of LSTM (3 wt%)-Ni (R)/ 8YSZ was stably maintained even when exposed to dry CH4 condition at 900 °C for a long time (100 h).

Evaluation of densification effects on the properties of 8 mol % yttria stabilized zirconia electrolyte synthesized by cost effective coprecipitation route

In the current work, properties of 8YSZ powder synthesized by co-precipitation method and sintered at 1200 °C, 1300 °C and 1400 °C are investigated. XRD analysis shows that all 8YSZ samples exhibit cubic phase and increased crystallite size is observed with increased sintering temperature. The relative density measurements show increased densification due to increased sintering temperature and relative density >96% is obtained for 8YSZ sintered at 1400 °C. SEM micrographs also confirm that structure becomes denser with increase in sintering temperature. EDX analysis confirms the elemental composition of 8YSZ and no impurity is observed while thermal analysis reveals weight losses within different temperature ranges. High ionic conductivity and maximum power density of 0.41 Wcm−2 is obtained for cell having 8YSZ electrolyte sintered at 1400 °C owing to its compact, dense and gas tight microstructure.

Molybdenum Oxide and Nickel Nitrate as Cooperative Sintering Aids for Yttria-Stabilized Zirconia.

The entirely accidental observation of increased sintering performance of nickel-infiltrated yttria-stabilized zirconia (8YSZ) in a molybdenum and oxygen rich atmosphere was explored. Molybdenum and nickel were found to be synergistic sintering aids for 8YSZ. However, sintering had to take place in an atmosphere of flowing oxygen. Samples sintered in air consistently burst. The sintering performance, microstructure, and crystal structure of 8YSZ with additions of both Mo and Ni together are compared to the sintering performance, microstructure, and crystal structure of pure 8YSZ, 8YSZ with only Ni added as a sintering aid, and 8YSZ with only Mo added as a sintering aid. Enhanced densification and grain growth is observed in the Mo–Ni 8YSZ samples when compared to all other sintering samples. Order of magnitude sintering rate increases are observed in the Mo–Ni 8YSZ over that of pure 8YSZ. With a maximum sintering temperature of 1200 °C and a one-hour dwell, sintered densities of 85% theoretical density (5.02 g⁄cm3) are achieved with the Mo–Ni samples: a 57% increase in density over pure 8YSZ sintered with the same sintering profile. EIS results suggest conductivity may not be negatively impacted by the use of these two sintering aids at temperatures above 750 °C. Finally, the spontaneous generation of nickel-molybdenum nano-rods was observed on the 5, and 10 mol.% Mo–Ni infiltrated 8YSZ samples after being left under vacuum in a scanning electron microscope chamber, suggesting evaporation of a possible nickel–molybdenum compound from the sample fracture surfaces.

Phase evolution and enhanced sinterability of cold sintered Fe2O3-doped 8YSZ

Using an Y(NO3)3 solution as a liquid medium, an Fe2O3-doped 8YSZ (8 mol% yttria-stabilized zirconia) electrolyte can be fabricated by a cold sintering process (CSP) and a conventional sintering (CS) at 1100 °C, and a relative density of more than 95% can be achieved. The phase structure, sintering behaviour and electrical properties of the 8YSZ samples were investigated in this study. The results indicate that the sinterability of the 8YSZ electrolyte can be enhanced by the CSP. Moreover, the formation of the monoclinic phase originating from the Fe2O3 dopant was greatly suppressed by introducing the Y(NO3)3 solution into the CSP, which greatly improved the electrical properties (i.e. the ionic conductivity) of the 8YSZ electrolyte. The sintered Fe2O3-doped 8YSZ provides support for the fabrication of high-performance solid oxide fuel cells (SOFCs) in a convenient and energy-saving way.

Relationship between microstructure and fracture toughness in B2O3-doped 8YSZ ceramics

This study aims to increase the fracture toughness of 8 mol.% yttria-stabilised cubic zirconia (8YSZ) at room temperature owing to the addition of boron oxide (B2O3). Therefore, in this study, the effect of B2O3 addition on sinterability and mechanical properties of 8YSZ was investigated using Micro-Vickers hardness tester and scanning electron microscope (SEM). B2O3-doped 8YSZ samples were sintered at different temperatures (1,300-1,500°C). A relative density of approximately 99% was obtained at 1,500°C in the B2O3-doped samples. While the B2O3 addition at 1 wt.% content caused a decrease in the grain size of the 8YSZ, and then when the content was > 1 wt.%, it increased. Furthermore, the mechanical properties results showed that fracture toughness of 8YSZ increased with B2O3 addition, and the hardness decreased with B2O3 addition. Thus, it was found that the fracture toughness of 8YSZ could be improved by B2O3 addition. [Received: 6 December 2019; Accepted: 11 May 2020]

Relationship between microstructure and fracture toughness in B2O3-doped 8YSZ ceramics

This study aims to increase the fracture toughness of 8 mol.% yttria-stabilised cubic zirconia (8YSZ) at room temperature owing to the addition of boron oxide (B2O3). Therefore, in this study, the effect of B2O3 addition on sinterability and mechanical properties of 8YSZ was investigated using Micro-Vickers hardness tester and scanning electron microscope (SEM). B2O3-doped 8YSZ samples were sintered at different temperatures (1,300-1,500°C). A relative density of approximately 99% was obtained at 1,500°C in the B2O3-doped samples. While the B2O3 addition at 1 wt.% content caused a decrease in the grain size of the 8YSZ, and then when the content was > 1 wt.%, it increased. Furthermore, the mechanical properties results showed that fracture toughness of 8YSZ increased with B2O3 addition, and the hardness decreased with B2O3 addition. Thus, it was found that the fracture toughness of 8YSZ could be improved by B2O3 addition. [Received: 6 December 2019; Accepted: 11 May 2020]

The Thermal Conductivity of 8 Yttria Stabilized Zirconia and Mullite Thermal Barrier Coating on Medium Carbon Steel Substrate

Thermal conductivity is one of the main features of a thermal barrier coating (TBC) that is important in making sure that the TBC gives its best functionality to the system. A good TBC has low thermal conductivity, so that the temperature can drop across the coating which allows the system to operate in extremely high temperatures. There are several factors that can influence the thermal conductivity of the TBC such as the type of ceramic material used, the deposition method and the physical features of the TBC itself. For this research, air plasma spray (APS) is used to deposit 8 wt% yttria stabilized zirconia (8YSZ) and mullite on medium carbon steel substrates to study their respective thermal conductivities. The aim here is to develop a heat shield using TBC to protect the electric motor in an electrical turbocompounding system. The characteristics of the deposited TBC such as microstructure, element composition, phases and thermal conductivity are studied. The thermal conductivity is reduced when medium carbon steel substrate deposited with TBC. The thermal conductivity of 8YSZ, mullite and uncoated sample at minute 60 is 0.868 W/mK, 0.903 W/mK and 1.057 W/mK, respectively. Therefore, the deposition of 8YSZ TBC can lower the thermal conductivity of the medium carbon steel heat shield.

High temperature mechanical properties of zirconia metastable t'-Phase degraded yttria stabilized zirconia

Abstract Air plasma sprayed (APS) 8 wt%-yttria stabilized zirconia (8YSZ) with metastable tetragonal prime phase (t′) has been widely applied as thermal barrier coatings (TBCs) for gas turbine blades because of its outstanding mechanical properties at high temperatures. In the present research, a carefully designed process was used to prepare 8YSZ samples with different phase composition (t′, t and c) simulating the phase degradation of the material during operation conditions. High temperature (1000–1200 °C) bending strength, elastic modulus, and thermal expansion coefficient were measured, which exhibit strong dependence on the phase degradation during heat treatment. Effect of the phase composition on high temperature thermo-mechanical properties and the enhancement of the bending strength have been discussed, providing a new perspective for further improvements.

Properties of 10Sc1CeSZ-3.5YSZ(33-, 40-, 50-wt.%) Composite Ceramics for SOFC Application

There has been studied the effect of addition of 3.5YSZ (3.5-mol. % yttria stabilized zirconia) to 10Sc1CeSZ (10-mol. % scandia and 1 mol. % ceria stabilized zirconia) on the mechanical and electrical properties of the composite ceramics. As a base for comparison with the 10Sc1CeSZ-3.5YSZ properties, 3.5YSZ, 10Sc1CeSZ and 8YSZ (8-mol. % yttria stabilized zirconia) have been used. As result, the 10Sc1CeSZ-3.5YSZ (33-, 40-, 50-wt. %) ceramics have lower electrical conductivity and mechanical strength comparing with 8YSZ samples. The 10Sc1CeSZ-3.5YSZ (50wt. %) samples have predominant tetragonal phase (74 %) due to insufficient amount of the dopants for cubic phase stabilization

Iron/zinc doped 8 mol% yttria stabilized zirconia electrolytes for the green fuel cell technology: A comparative study of thermal analysis, crystalline structure, microstructure, mechanical and electrochemical properties

Abstract Pristine and Fe/Zn doped 8 mol% yttria stabilized zirconia (8YSZ) were prepared by ball milling technique for potential application in the green fuel cell technology. The series consisted of (8YSZ)0.97(Fe2O3)x(ZnO)3-x, where x indicates 0.5, 1.0, 1.5, 2.0 and 2.5 mol% Fe or Zn alternatively. A number of analytical techniques were used to characterize 8YSZ included X-ray diffraction, scanning electron microscopy, impedance spectroscopy, dilatometer, and hardness test. The analytical results indicated a decrease in the densification in the doped 8YSZ as the activation energy for densification decreased from 1087 kJ/mol in the pristine 8YSZ sample to 264 kJ/mol in the doped 8YSZ. The optimum doped 8YSZ was recognised with 2.0 mol% Fe and 1.0 mol% of Zn exhibit the highest percentage of the cubic phase approaching 62.4 wt%, while the shortest lattice parameter of 0.5132 nm and crystallite size equivalent to 26.34 nm. This composition also indicated pore-free morphology, the highest densification up to ∼94%, the greatest hardness value (above 740 MPa), while improve total conductivity about 7.398 × 10−6 S/cm at 300 °C. The results provide new insights on the effect of mixed dopants as ceramic composite as well as on the fuel cell technology.

Sinterability of 8 mol% Yttria Stabilized Zirconia

The sintering behaviour of low cost 8 mol% yttria stabilized zirconia powders has been studied. The effect of sintering holding time of the sintered granulated and milled 8YSZ were determined using density measurements, scanning electron microscopy (SEM) and X-ray diffraction (XRD). The elemental composition, particle size and morphology of the as-received 8YSZ powder and proceed for milling was investigated. 48 hours of ball milling on granulated 8YSZ resulted rises in specific surface area and sintered at 1550°C with the various period of time (4, 5, 6 and 7 hours). The milled 8YSZ sample with 5h sintering holding period coded as F5, sintering activity improved and the relative density came up to 98.3%. But then, granulated 8YSZ achieved only 62.7% with 5 hours holding time. Crystal structure analysis for milled 8YSZ powder consists of 59.6% of cubic ZrO2 phase, 40.1% of tetragonal ZrO2 and 0.3% of monoclinic ZrO2. Meanwhile, granulated 8YSZ indicated low content in cubic ZrO2 but high amount in monoclinic ZrO2 phase. In brief, low cost 8YSZ reached higher densification of 98% successfully.

Mechanical Properties of Layered La2Zr2O7 Thermal Barrier Coatings

Lanthanum zirconate (La2Zr2O7) has been proposed as a promising thermal barrier coating (TBC) material due to its low thermal conductivity and high stability at high temperatures. In this work, both single and double-ceramic-layer (DCL) TBC systems of La2Zr2O7 and 8 wt.% yttria-stabilized zirconia (8YSZ) were prepared using air plasma spray (APS) technique. The thermomechanical properties and microstructure were investigated. Thermal gradient mechanical fatigue (TGMF) tests were applied to investigate the thermal cycling performance. The results showed that DCL La2Zr2O7 + 8YSZ TBC samples lasted fewer cycles compared with single-layered 8YSZ TBC samples in TGMF tests. This is because DCL La2Zr2O7 TBC samples had higher residual stress during the thermal cycling process, and their fracture toughness was lower than that of 8YSZ. Bond strength test results showed that 8YSZ TBC samples had higher bond strength compared with La2Zr2O7. The erosion rate of La2Zr2O7 TBC samples was higher than that of 8YSZ samples, due to the lower critical erodent velocity and fracture toughness of La2Zr2O7. DCL porous 8YSZ + La2Zr2O7 had a lower erosion rate than other SCL and DCL La2Zr2O7 coatings, suggesting that porous 8YSZ serves as a stress-relief buffer layer.