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Rare earth element-doped bismuth oxides with the fluorite structure (δ-Bi2O3) exhibit high oxygen ion conductivity at low temperature, which is promising electrolyte materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs). However, traditional co-sintering process is not applicable to the manufacturing of IT-SOFCs using low melting point Bi2O3-based electrolyte, while further high-temperature processing is not required for deposition Bi2O3-based electrolytes. In this study, plasma spraying was used to examine the possibility to deposit high-performance Bi2O3-based electrolytes without the following high-temperature process. (Bi2O3)0.75 (Y2O3)0.25 (YSB) spray powders were prepared by the sinter-crushing method. The YSB electrolytes were fabricated by plasma spraying at different deposition temperatures. The effects of deposition temperature on the coating microstructure, crystalline stability, and ion conductivity were investigated. Results showed that the as-sprayed YSB electrolytes present a dense microstructure with well-bonded lamellar interfaces. The pure δ-phase YSB electrolyte was deposited with 37.5-75 μm powders at a deposition temperature of 350 °C. The deposited YSB electrolyte presented the excellent ionic conductivity of 0.19 S cm−1 at 700 °C in comparison with 0.21 S cm−1 for sintered bulk. [ABSTRACT FROM AUTHOR]

For tubular solid oxide fuel cells (SOFCs), individual cells are connected in series by the interconnector to obtain desired voltage and power output. As the most widely used ceramic interconnector for high-temperature SOFCs, lanthanum chromite-based material is quite difficult to sinter to high density due to the high vapor pressure of the chromium component. In this paper, dense strontium-doped lanthanum chromite (LSC) membranes with enhanced lamellar interface bonding were achieved at an elevated deposition temperature over the critical bonding temperature by atmospheric plasma spraying (APS). The effects of molten droplet particle size on the chemical composition and phase structure of LSC deposits were studied. The preferential vaporization of Cr during plasma spraying was of the greatest interest here. When the particle size of molten droplet was smaller than 30 μm, the vaporization loss of Cr increased remarkably with the decrease in particle size, resulting in impurity phases. When the particle size was larger than 30 μm, the vaporization loss of Cr was greatly reduced. The electrical conductivity of plasma-sprayed LSC deposits reached 8.7 and 2.1 S/cm at 850 °C in oxidizing and reducing atmospheres, respectively. The optimized LSC deposits exhibited good stabilities of phase structure and properties under operation conditions, which is adequate for SOFC interconnector application. [ABSTRACT FROM AUTHOR]

PrBa 0.5 Sr 0.5 Co 2–x Fe x O 5+δ (PBSCF) (X = 0, 0.3, 0.4, and 0.5) is investigated as cathode material for intermediate-temperature solid oxide fuel cells. Suspension plasma spraying is used as a low cost and large-scale manufacturing process to prepare PBSCF cathodes. Fe substitution effects on the crystal structure and electrochemical performance are characterized. All plasma-sprayed PBSCF cathodes exhibit a pure and stable cubic structure. The suspension plasma-sprayed PBSCF deposits show a porous and fine structure, and the microstructures are insensitive to Fe substitution. Subsequent to Fe doping, the polarization resistance of PBSCF cathodes rapidly decreases for increasing Fe substitution concentration from 0 to 0.4. Further increase of the Fe doping concentration increases the cathode polarization instead. At 600 and 700 °C, a 20% Fe-doped (x = 0.4) PBSCF cathode exhibits remarkably low area-specific polarization resistances (R p ) of 0.074 Ω cm 2 and 0.012 Ω cm 2 , respectively. Moreover, the R p of all cathodes remains almost identical after isothermal annealing at 600 °C for 300 h. Furthermore, the thermally-sprayed porous metal-supported cell assembled with the optimal PBSCF cathode shows excellent performance with peak power densities of 0.37, 0.8, and 1.35 W cm −2 at 500, 600, and 700 °C, respectively. [ABSTRACT FROM AUTHOR]

The inhomogeneous composition distribution of atmospheric plasma sprayed La 2 Ce 2 O 7 limits its operation in thermal barrier coatings. Two types of La 2 Ce 2 O 7 powders were used to investigate the effect of the powder size and structure on the preferential evaporation of Ce during plasma spraying. The results indicate that powder particle size is dominant for the Ce evaporation loss. Such effect is significantly intensified with the decrease of particle size. When the particle size is larger than 30 μm, the Ce loss is less or can be neglected. Two mechanisms including the element diffusion mechanism and convection mass transfer mechanism are proposed to well explain the evaporation rule. Moreover, the loss of Ce is higher using the agglomerate-sintered powder due to its higher thermal conductivity than the as-agglomerated powder. Correspondingly, the CeO 2 loss can be neglected in the coatings as the agglomerated powders with a size <30 μm were used. [ABSTRACT FROM AUTHOR]

In this study, suspension plasma spraying (SPS) was applied to deposit double perovskite SrFeMoO (SFM) which can be used as both cathode and anode for solid oxide fuel cells. The effects of SFM concentration on the electrode phase composition, microstructure, and catalytic performance were investigated. The electrodes showed a dense structure when it was deposited at a concentration of 0.05 mol/L. The cathode performance was limited by the limited three-phase boundaries and poor gas diffusion. At 750 °C, cathode polarization ( R ) was 0.19 Ω cm. When the SFM concentration increased to 0.075 mol/L, the deposits revealed a porous microstructure with well-bonded fine particles. As a result, the R decreased significantly to 0.078 Ω cm at 750 °C. However, when the SFM concentration was further increased to 0.1 mol/L, the R increased owing to the limited interface bonding between the non-molten particles. As a result, it was found that the SFM suspension concentration should be optimized to achieve a highly active SFM by SPS process. Moreover, when the optimized deposit was employed as an anode and tested in a hydrogen atmosphere, it showed anode polarization resistance (R) of 1.5 Ω cm at 750 °C. [ABSTRACT FROM AUTHOR]

Active three-phase boundaries (TPBs) significantly influence cathode performance in solid oxide fuel cells, but obtaining long TPBs and understanding the mechanism underlying the improved cathode performance when the electrolyte is prepared with a smooth surface by a high-temperature sintering process remain essential challenges. In this work, we used flame spraying to deposit single-layer semimolten particles on a smooth electrolyte to build a three-dimensional surface with enlarged active surface area and thus increased TPBs. Meanwhile, LaSrMnO (LSM) cathodes with fine microstructure were deposited by solution-precursor plasma spraying (SPPS) on the designed electrolyte to establish a three-dimensional cathode-electrolyte interface. The deposition behavior of the semimolten particles on the smooth electrolyte and LSM cathodes on the three-dimensional electrolyte surface was studied. The effects of the area enlargement factor ( α ) on the polarization resistance of the SPPS LSM cathodes were investigated, using three-dimensional electrolytes with α from 1.29 to 2.48. The results indicated that convex particles with different molten states bonded well with the electrolytes. SPPS LSM cathodes also showed good interfacial bonding with convex particles. Finally, the cathode polarization ( R ) decreased linearly with increase of α . At 800 °C, R decreased from 0.98 to 0.32 Ω cm when α was increased from 1.29 to 2.48. [ABSTRACT FROM AUTHOR]

Abstract: La-doped strontium titanate (LST) is a promising, redox-stable perovskite material for direct hydrocarbon oxidation anodes in intermediate-temperature solid oxide fuel cells (IT-SOFCs). In this study, nano-sized LST and Sm-doped ceria (SDC) powders are produced by the sol–gel and glycine–nitrate processes, respectively. The chemical compatibility between LST and electrolyte materials is studied. A LST–SDC composite anode is prepared by suspension plasma spraying (SPS). The effects of annealing conditions on the phase structure, microstructure, and chemical stability of the LST–SDC composite anode are investigated. The results indicate that the suspension plasma-sprayed LST–SDC anode has the same phase structure as the original powders. LST exhibits a good chemical compatibility with SDC and Mg/Sr-doped lanthanum gallate (LSGM). The anode has a porosity of ∼40% with a finely porous structure that provides high gas permeability and a long three-phase boundary for the anode reaction. Single cells assembled with the LST–SDC anode, La0.8Sr0.2Ga0.8Mg0.2O3 electrolyte, and La0.8Sr0.2CoO3–SDC cathode show a good performance at 650–800 °C. The annealing reduces the impedances due to the enhancement in the bonding between the particles in the anode and interface of anode and LSGM electrolyte, thus improving the output performance of the cell. [Copyright &y& Elsevier]

The potential application of plasma spraying in the preparation of ceramic electrolyte for porous metal-supported solid oxide fuel cells (SOFCs) is highlighted by its ability to eliminate the need for a high-temperature sintering process. However, the challenge of achieving highly dense electrolytes through plasma spraying remains to be addressed. In this study, a novel electrolyte for porous metal-supported SOFCs (PMS-SOFCs) is developed. This involved the preparation of a highly dense structure of gadolinium-doped ceria (GDC)-lanthanum strontium gallium magnesium oxide (LSGM) composite coating using plasma spraying under atmospheric conditions. The composite electrolyte is prepared using atmospheric plasma spraying (APS). The addition of the low-melting-point LSGM phase enhanced the microstructural densification of the GDC-based composite coating and diminished electron loss in a reducing atmosphere, thereby improving the cell's open-circuit voltage. At 36 kW plasma arc power, the single cell with composite electrolyte exhibited a maximum power density of 371 mw/cm2 at 750 °C and achieved the highest open-circuit voltage (1.03 V) at 600 °C. Moreover, the open-circuit voltage remained stable over a 100-h test. These findings suggest that using APS to deposit a composite electrolyte with added low-melting-point secondary phases presents a promising approach for achieving relatively high OCV in PMS-SOFCs based on cerium oxide electrolytes. [Display omitted] • Bulk-like composite electrolyte directly fabricated by atmospheric plasma spray. • OCV can reach 1.03V at 600 °C for ceria-based composite electrolyte. • LSGM splats effectively blocked the electron conducting in GDC deposits. • Low melting point LSGM could enhance the interface bonding of plasma-sprayed GDC electrolyte. [ABSTRACT FROM AUTHOR]

The effect of chamber pressure on the microstructure and ablation behavior of ZrB2 coatings deposited by low-pressure plasma spraying was investigated. The results showed that as the spray chamber pressure further was reduced to less than 50 kPa, the porosity of the coating deposited at the same distance decreased with the chamber pressure, and the coating prepared under 100 Pa presented the lowest porosity of about 0.89%. The ablation performance test subjected to high-temperature plasma jet revealed that the linear ablation rate of ZrB2 coating increased with the porosity of the coating. As a result, among the ZrB2 coatings deposited at chamber pressures of 100 Pa, 5 kPa, 10 kPa and 50 kPa, the dense coating deposited at 100 Pa showed the lowest ablation rate of 0.33 µm/s. The dense ZrB2 coating with a thickness of about 100 μm was able to withstand 300 s ablation by a plasma flame with a net power of 25 kW resulting in an ablating coating surface temperature of about 2000 °C. The ablation mechanism of the coating was also examined. [ABSTRACT FROM AUTHOR]

It was known for long that Ni-Al composite powders can be used to deposit self-bonding coating as a bond coat for common ceramic coatings due to the exothermic reaction between Ni and Al. However, it was found that with commercial Ni-Al composite powders with a large particle size, it is difficult to ignite the self-propagating reaction between Ni and Al to form Ni-Al intermetallics by plasma spraying. In this study, Ni-Al composite powder particles of different sizes were used to prepare Ni-Al intermetallics-based coatings by plasma spraying. The dependencies of the exothermic reaction between Ni and Al and the coating microstructure on powder particle size and spray parameters were investigated. The phase composition, microstructure, porosity and oxide content of the coatings were characterized by x-ray diffraction, scanning electron microscope and image analyzing. The results show that particle size of Ni-Al composite powders is the dominant factor controlling the exothermic reaction for the formation of Ni-Al intermetallics during plasma spraying. When the powders larger than about 50 μm are used, the reaction forming aluminide cannot complete even by heating of plasma flame generated at high plasma arc power. However, when smaller powders less than 50 μm are used, the exothermic reaction can completely occur rapidly in plasma spraying, contributing to heating of Ni-Al droplets to the highest temperature for development of the self-bonding effect. The positive relationship between molten droplet temperature and tensile adhesive strength of the resultant coatings is recognized to confirm the contribution of high droplet temperature to the adhesive or cohesive strength. [ABSTRACT FROM AUTHOR]

Complex rare-earth oxide ceramics with pyrochlore structure (A2B2O7) are considered as promising candidate materials for next generation thermal barrier coatings (TBCs) due to low thermal conductivity and high phase stability. During plasma spraying, the component with a higher vapor pressure would experience preferential vaporization. In this study, Gd2Zr2O7 (GZO) powders with a hollow spherical structure in a wide range of particle size distribution were used to examine the preferential vaporization behavior of Gd2O3 during plasma spraying. Individual GZO splats were deposited to study the effect of particle size on Gd vaporization loss. The results show that almost all particles experienced Gd preferential vaporization loss that increased remarkably with the decrease in particle size. The Gd vaporization loss was significantly suppressed only when the particle size of molten droplet was larger than about 35 μm. The relationship between the Gd/Zr ratio and the droplet size reveals the significant effects of particle size and powder structure on Gd vaporization loss. It is clear that the vaporization behavior of in-flight GZO particles is dominated by molten droplet size rather than the size of feedstock powders with a porous hollow structure. The particle size effect on Gd vaporization resulted in wide distributions of Gd/Zr ratio in plasma-sprayed GZO coatings. Furthermore, it is found that after annealing at 1300 °C, the vaporization loss of Gd led to the formation of monoclinic ZrO2 from metastable pyrochlore phase in GZO coatings with inhomogeneous chemical composition. [ABSTRACT FROM AUTHOR]

Self-fluxing alloy coatings are usually utilized by spray fusing two-step process for fully dense microstructure and metallurgical bonding to the substrate. The fusing process brings out limitations for coating applications due to the need of high-temperature fusing. In this study, it is found for the first time that metallurgical bonding between NiCrBSi splats can be achieved by deposition of super-hot droplets created by plasma spraying. Thus, a sufficiently dense NiCrBSi coating can be prepared by one-step plasma spraying. NiCrBSi powders with a size range of 30-50 μm were used as typical material for plasma spraying. The particle temperatures were measured by a DPV-2000 thermal spray in-flight particle diagnostic system. The microstructure of coatings was characterized using scanning electron microscopy. Results show that particles can be heated to a significantly high temperature over 2400 °C by the optimal design of the nozzle internal structure, and the plasma-sprayed NiCrBSi coatings are almost fully dense with effective metallurgical interparticle bonding. Based on the numerical simulation result of the interfacial temperature evolution between spreading splat and NiCrBSi substrate, a self-fusing mechanism is proposed for plasma spraying of NiCrBSi. Furthermore, the coating prepared by one-step plasma spraying reveals superior abrasive wear resistance and corrosion resistance as compared with the flame spray and fusing counterpart. It is clearly demonstrated that the new approach to deposit highly dense coatings directly by plasma spraying with self-fusing effect could greatly expand the applications of fluxing alloy coating materials. [ABSTRACT FROM AUTHOR]

In-flight particle temperature is a vital factor controlling the formation of the interface bonding and therefore the overall properties of thermally sprayed coatings. In our previous study, a novel shell-core-structured powder approach was proposed which was designed by cladding low melting point alloy NiCr powders with refractory Mo shell to significantly raise the in-flight particle temperature during plasma spraying to improve the interface bonding within the plasma-sprayed coating. Previous results revealed that the significantly improved interface bonding was obtained for the plasma sprayed NiCr-Mo coating. Therefore, in this study, in order to clarify the effect of Mo-cladding on the temperature evolution of the Ni-based alloy particle, the heating history of the Mo-clad-NiCr particle injected into plasma jet during in-flight process are numerically simulated and further experimentally measured. Effect of particle surface vaporization on the heating characteristic of particle was examined. As a result, both the numerical and experimental results show that through such novel particle design, the elemental vaporization of NiCr core is effectively suppressed and the Ni-based alloy particle is definitely heated up to an ultra-high temperature, 2920 K, which is comparable to that of molten Mo particles and is about 500 K higher than that of conventional NiCr particle. Consequently, an almost fully-dense NiCrMo coating with excellent interface bonding can be obtained by plasma spraying of this ultra-high temperature Mo-clad-NiCr particle. [ABSTRACT FROM AUTHOR]

Very low pressure plasma spraying (VLPPS) is an attractive method for metal-supported solid oxide fuel cells, wherein it can significantly avoid the oxidation of metal substrate. In this study, scandia-stabilized zirconia electrolyte was fabricated by VLPPS. To investigate the microstructure of coatings, the spraying distances were set to 150, 250 and 350 mm. The fractured morphology suggests that, at a relatively low deposition temperature (< 350 °C), typical lamellar structure was replaced by trans-granular structure. The apparent porosity of coatings ranges from 4.75 to 6.83%, as per the image analysis method. The ionic conductivity of coating at 250 mm was 0.068 S cm−1, which was ~ 68% of bulk. The ratio of surface area to projected area of coatings surface could reach 6.53-8.30 measured by a 3D confocal laser microscope. Finally, testing cells showed a maximum output power density of 1112 mW cm−2 and an OCV of 1.07 V at 750 °C. The ohmic resistance of whole cell was 0.1 Ω cm2, and the total resistance was 0.15 Ω cm2. The results suggest that very low pressure plasma spraying is a promising approach for the manufacturing of high-performance MS-SOFCs. [ABSTRACT FROM AUTHOR]

Abstract A super long and stable laminar plasma jet was used in the atmospheric plasma spray process in this work. Microstructures evolution and properties of alumina coatings that were obtained using a long spraying distance ranging from 200 mm to 350 mm in an atmospheric environment were studied in this work. These processes were carried out by using a total gas flow rate of 14 slpm with 70% nitrogen and 30% argon in volume and output power of 25.4 kW (current of 160 A). A long particle residence time was obtained in this study, which compared with other current atmospheric plasma spray methods. The microstructures of coatings showed the multi-island protrusions on the top surfaces and overlapped lamellar splats at the fracture surfaces. The microstructural evolution was significantly affected by the heating and motion behaviors of alumina particles when these were flowing in the long laminar plasma jet at different spraying distances. Highlights • A long and stable laminar plasma jet in air is used in this work. • A super long spraying distance of 350 mm is used in this article. • Long particle residence time when flowing in the laminar plasma plume • Multi-island protrusions at the top surface of coatings [ABSTRACT FROM AUTHOR]

A novel structure of yttria stabilized zirconia coatings was developed in this study by a newly laminar plasma spraying technology in atmospheric environment. The unique microstructures of coatings showed the multi-island protrusions feature at the top surface, quasi-columnar structures along the cross-section distributed as a certain interval and hybrid droplet/vapor deposited structures at the fracture surface. The distributions of particle velocity and surface temperature along the axial direction of long laminar plasma jet were investigated and compared with other plasma spraying methods. The effects of different microstructures to thermal conductivities comparing with other current plasma spray methods were also demonstrated. [ABSTRACT FROM AUTHOR]

The behavior of low-velocity NiCrBSi particles with a high surface temperature of 1800 °C during the long laminar plasma spraying process was studied. During the experiment, the maximum length of the laminar plasma jet exceeded 600 mm, and coatings were obtained using a laminar plasma spray at a wide spray distance ranging from 250 to 500 mm. Interestingly, the coatings obtained at a short spray distance of 250 mm showed special alternate porous and compact lamellar structure with island-like bulges that were evenly distributed on the coating surface. This type of structure was possibly formed by a low-velocity splashes deposition process intensified by the furry-like structure, which can be attributed to vapor phase deposition. The coatings obtained at an extremely long spray distance of 500 mm showed massive cracks. Moreover, the medium-distance sprayed coatings of 350–450 mm showed similar lamellar-like microstructure and mechanical performance because of the similarity in the particle states in the low-energy-gradient laminar plasma jet. Thus, a laminar plasma spray shows great reproducibility and potential for improving the spraying efficiency on an uneven plane. Unlabelled Image • Stable laminar plasma jet longer than 600 mm was adopted. • NiCrBSi coatings show similar properties regardless of spray distance within 500 mm. • Island-like bulges were found in atmospheric laminar plasma sprayed metal coatings. • A splashes gathering model was proposed and deposition mechanism was established. [ABSTRACT FROM AUTHOR]

La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ (LSCF) is a promising cathode material for solid oxide fuel cells (SOFCs). Hence, structured LSCF coatings were deposited in this study by atmospheric laminar plasma spraying (ALPS) at the spraying distances from 150 mm to 250 mm. Particles with high temperature were obtained at low plasma arc power of only 15 kW. The microstructural characterization of the coatings showed cluster-like morphologies on the top surfaces and columnar features with large-scale vertical cracks at the cross section. An evolution mechanism of the coatings was proposed based on particle size. The movement of particles during laminar plasma jet depended on particle size, which was studied experimentally and by simulation to explain the selective deposition. The coatings showed lower polarization resistance when compared to LSCF coatings deposited by atmospheric plasma spraying (APS) due to large vertical crack densities. The high output performance of the SOFCs with the LSCF cathode also proved this phenomenon. The results suggest that ALPS provides extensive options for SOFCs manufacturing. • LSCF coatings were deposited at the long spraying distances, although at low plasma arc power of only 15 kW. • The selective deposition depended on particle size was proposed to explain various structures of coatings. • Structured coatings with large-scale vertical cracks revealed lower polarization resistances compared to APS coatings. [ABSTRACT FROM AUTHOR]