Low-Temperature Reactive Sintering Coating Technology for Single-Phase Spinel Layer Production

Background

Solid oxide fuel cells (SOFCs) are advanced electrochemical devices that convert fuel directly into electricity at temperatures often exceeding 700°C. To maintain high power density and long-term stability, SOFC stacks require electrically conductive, chemically resistant contact layers at the interface between ceramic electrodes and metallic interconnects. Spinel-type oxide coatings can offer compatible thermal expansion and oxidation protection, addressing fuel cell degradation under harsh, high‐temperature operating conditions. However, fabricating such coatings in a cost‐effective and scalable manner remains a major engineering hurdle.

Current approaches to spinel-layer formation often rely on sintering mixed metal or metal-oxide powders at temperatures of 1000°C or higher, which accelerates oxidation of metallic interconnects and increases electrical resistance. The use of costly cobalt- or lanthanum-containing precursors further drives up material costs while introducing environmental and supply chain concerns. Mixtures of pure metal powders frequently yield multi‐phase layers with residual oxides, stemming from differential oxidation rates and limited interdiffusion. Additionally, balancing porosity for gas transport against layer density for protection demands precise pore-formers or extreme particle-size control—an additional complexity that compromises reproducibility and inflates manufacturing expense.

Technology

This technology enables formation of spinel-type coatings by preparing a paste-like precursor from sub-10 μm pre-alloyed metallic powder—often sub-micron or nano-sized—mixed with an ink vehicle, and applying it to a substrate via painting, spraying, or screen-printing. Subsequent sintering below 1000 °C (preferably 700–950 °C) in an oxidizing atmosphere, with optional pressure (10–5000 psi), converts the alloy into a substantially single-phase spinel layer (≥95%) without liquefaction. By incorporating pore-formers such as carbon or cornstarch, porous structures can be obtained, while finer powder grades promote densification for protective coatings. Primarily employed as cathode-interconnect contact layers in solid oxide fuel cells, these coatings maintain electrical conductivity and minimize substrate oxidation under high-temperature, oxidizing conditions.

Differentiation arises from the use of pre-alloyed powders and reduced-temperature reactive sintering. Traditional approaches rely on mixed pure metal powders and temperatures above 1000 °C, which often produce multi-phase layers, residual oxides, and severe substrate degradation. In contrast, the single-alloy precursor ensures homogeneous inter-diffusion and complete thermal conversion at lower temperatures, preventing oxidation of metallic interconnects, reducing electrical resistance, and enhancing phase purity. The elimination of expensive cobalt- or lanthanum-based precursors and the ability to tune porosity and density further improve commercial viability and performance in demanding SOFC environments.

Benefits

• Lower sintering temperature (700–950 °C) minimizes substrate oxidation and maintains low interconnect resistance
• Pre-alloyed powder precursors yield ≥95% single-phase spinel, ensuring homogeneous microstructure and optimal electrical performance
• Reduced energy consumption and processing costs compared to high-temperature or cobalt/lanthanum-based methods
• Tunable porosity or density via pore formers or powder size control for customized gas diffusion or protective coatings
• Compatibility with standard coating techniques (painting, spraying, screen-printing) for scalable manufacturing
• Enhanced long-term stability of SOFC cathode-interconnect interfaces in oxidizing environments
• Versatility to produce various spinel compositions (e.g., NiFe₂O₄, (Ni,Fe,Co)₃O₄) for tailored conductivity and stability

Applications

• SOFC interconnect contact layers
• SOEC interconnect contact layers
• Turbine blade protective coatings
• Porous catalyst support layers
• Industrial corrosion-resistant coatings

Additional info

Fine pre-alloyed metallic powder (<10 µm) is mixed into a paste, applied to substrates, and sintered in air at 700–950 °C (optionally under 10–5 000 psi). Complete oxidation yields ≥95% single-phase AB₂O₄ spinels (e.g., NiFe₂O₄), with tunable porosity via carbon pore-formers or dense microstructures from nano powders. Ideal for SOFC cathode–interconnect contact layers, this approach prevents substrate over-oxidation and multi-phase formation.