With the reduction of solid oxide fuel cell (SOFC) operating temperature to the range of 600 °C–800 °C, Cr-containing ferritic alloys have become the preferred interconnect material, which unfortunately are susceptible to continuous scale growth and Cr volatility at the SOFC operating temperatures. The (Mn,Co)3O4 spinel system is widely regarded as the most effective coating for SOFC interconnect protection, due to its high thermal and electrical conductivity, adequate coefficient of thermal expansion, and excellent Cr blocking capability. This article reviews the physical and chemical properties of the (Mn,Co)3O4-based spinels; different types of coating precursors and deposition techniques; and the effects of spinel composition, quality and thickness on the coating performance. It is concluded that the spinel coating composition, quality, and thickness are more critical than the coating process in affecting the overall coating performance.
This study seeks to clarify the effects of off-stoichiometry on the electrical conductivity of spinels in the (Ni,Fe) 3 O 4 and (Mn,Co) 3 O 4 systems. Spinels with the compositions Ni x Fe 3-x O 4 (where x = 0.85, 0.875, 0.9, 1.0, 1.05, and 1.15) and Mn x Co 3-x O 4 (where x = 1.0, 1.2, 1.35, 1.5, 1.75, and 2.0) were prepared using conventional solid-state process. Electrical conductivity measurements were taken between 500 °C and 800 °C using the 4-point DC method. The conductivity in Ni-Fe spinels increased with increasing Fe content. Similarly, the conductivity of Mn-Co spinels increased drastically with increasing Co content. The coefficients of thermal expansion (CTEs) of these samples were also evaluated. All the (Ni,Fe) 3 O 4 spinels were found to exhibit excellent CTE matching with prospective stack components. However, thermal expansion characteristics were highly dependent on the composition in the (Mn,Co) 3 O 4 system, and only a narrow range of compositions was well-matched in CTE with prospective stack components. The significant effect of cation off-stoichiometry and sample preparation on the electrical behavior of spinels was discussed as a possible explanation for the large discrepancies in reported conductivity values for both systems.
The literature shows there is no validated procedure to measure the tensile properties in different regions along the length of human tendons. The slippery surfaces and non-homogeneous properties of tendons reduce the probability of success when using traditional methods. So, there is a need to implement an experimental technique that ensures accurate measurement of the mechanical properties of human tissue. The development of new technologies allows us to face problems with new approaches. Computer vision is a trending topic in the development of new technology, one of its branches is digital image correlation (DIC). DIC is a non-contact technique used for tracking pixels along a group of sequential images and, when combined with tensile testing, can be used to track sample deformation and strain at discrete points in space. This work develops a technique that analyzes bovine tendons using digital image correlation and custom-designed 3D printed clamps. The advantage of DIC is that it analyzes the deformation of the tendon throughout the complete sample, allowing us to quantify the mechanical properties in different regions within the tendon. First, a 3D printed clamp is designed considering the challenges of gripping soft tissue. The clamp prevents damage to the tissue during testing. A random speckle pattern is created on the surface of a roller using open CAD software named OpenSCAD. The bovine tendons are painted with the roller and tested in a uniaxial load frame. These results can be used in the future to repeat this technique with human Achilles tendons to quantify the tensile properties of the tendon and aid in the design and material selection of prosthetic tendons for people suffering from injury or disease.
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