Structural and defect chemistry guidelines for Sr(V,Nb)O3-based SOFC anode materials.
Structural and defect chemistry guidelines were used for Nb-substituted SrVO3-δ materials, designed to meet SOFC anode requirements, with emphasis on redox tolerance, thermochemical compatibility with other SOFC materials, electrical conductivity and adjustable changes in oxygen stoichiometry for their prospective impact on electrocatalytic performance. SrV1-xNbxO3-δ (x = 0-0.30) ceramics were prepared by solid-state synthesis and sintered at 1773 K in a reducing atmosphere. XRD and SEM/EDS showed that under these conditions a single-phase cubic perovskite structure appears up to x ≈ 0.25. Electrical conductivity is metallic-like and nearly p(O2)-independent. Although substitution by niobium decreases the conductivity, which still exceeds 100 S cm(-1) for x ≤ 0.20 at temperatures below 1273 K, it also expands the stability domain of the cubic perovskite phase and suppresses partly high thermochemical expansion characteristic of parent SrVO3-δ. The upper p(O2) limit of phase stability was found to shift from ∼2 × 10(-15) atm for the undoped material to ∼2 × 10(-12) atm for x = 0.30, whereas the average thermal expansion coefficient at 773-1223 K decreased from 22.7 × 10(-6) to 13.3 × 10(-6) K(-1). SrV1-xNbxO3-δ perovskites undergo oxidative decomposition in air, which causes dimensional and microstructural changes. However, sluggish kinetics of oxidation under inert gas conditions results in nearly reversible behavior in relatively short-term redox cycles between reducing and inert atmospheres. Subtle structural changes and a close correlation with point defect chemistry clarify these sluggish changes and provide guidelines to retain the metastability.
Thermo-chemical lattice expansion in La0.6Sr0.4Co1 − yFeyO3 − δ
Abstract La0.6Sr0.4Co1 − yFeyO3 − δ (LSCF) mixed-conducting perovskite oxides, a SOFC cathode candidate material, exhibit oxygen nonstoichiometry under reducing atmosphere and elevated temperatures. Reduction of the B-site transition metals and formation of oxygen vacancies result in chemical expansion of the LSCF lattice. Knowledge of both thermal and chemical lattice expansion as a function of composition is an essential tool to tailor mismatches between different materials exposed to reducing and high temperature environments and avoid mechanical failure of the device. In this paper, thermal and chemical expansion coefficients were determined by measurement of the lattice parameters by HT-XRD as a function of pO2 (in the range of 10− 4 to 1 bar), temperature (773–1173 K) and B-site composition. The lattice parameters were correlated with the previously investigated oxygen nonstoichiometry of the LSCF series. While the thermal expansion coefficient increases almost linearly with increasing Co content, the chemical expansion coefficient appears to be independent of B-site composition.
Fault Diagnosis and CAN Bus/Ethernet Redundancy Design of a Monitoring and Control System
The ship monitoring system is used to monitor and control the working status of various equipment on the ship. The navigational safety of the ship is affected directly by the stable working of the monitoring system. In this paper, a ship monitoring system with fault-type judgment function and bus redundancy is designed to improve system reliability and reduce fault checking cost. A redundant Ethernet/CAN bus communication network is constructed in the system, which connects multiple simulation nodes. The simulation node can simulate the faults that may occur during the communication process and feeds back the fault information to the host computer. The host computer will analyze and display the corresponding fault type on the user interface with the feedback information is received. The system reconfigures the network route autonomously when the simulation node has a communication fault. Routing of fault nodes can be switched to redundant routing, and the load balancing of the communication network can be maintained. Through experimental tests, the system can accurately locate faults and achieve fast switching of redundant routes between buses. Hence, the reliability of data transmission is improved.