Advanced Sensor Development for Life Assessment of Power Plants
Alberto Polar-Rosas, PhD Candidate, Advisor: Dr. Indacochea
In power plants, boilers and turbines are exposed to stresses and high temperatures which are key factors in creep damage. Although new steels are designed for creep resistance, there is always need to monitor and asses the remaining life of structures and equipment. The conventional technique is to use metallographic replica to evaluate creep, however it requires a plant shutdown and the inspection is mainly superficial. Among some NDT utilized to evaluate creep damage are acoustic resonance, Barkhausen magnetoacoustic inspection, magnetoelastic inspection, etc. Magnetic inspection appears to have great potential in the detection of creep, because of the microstructural changes associated with the different stages of creep; in turn these changes affect the magnetic response of ferromagnetic materials. A correlation between magnetic hysteresis and the microstructural state of the material can be established. In the present study a number of martensitic steel rods were systematically submitted to different levels of creep; the magnetic responses of each sample to an applied magnetic field were measured generating a number of magnetic hysteresis curves. In parallel the corresponding microstructural changes were assessed by optical and electron microscopy produced during the degradation of the material. This information is being used to assess the creep damage of the material and estimate the remaining life of the structural materials and equipment.
Joining Yttria Stabilized Zirconia (YSZ) to Crofer22-APUÂ® for Applications in Solid Oxide Fuel Cells
Oscar Quintana, PhD Candidate, Advisor: Dr. Indacochea
The objective of this study is to develop a filler material and brazing procedure that provides a high quality hermetic seal to enhance the performance of Solid Oxide Fuel Cells (SOFCs). Reactive brazing has proved to be the most effective and efficient method for joining ceramics–to-metals. The addition of reactive elements to filler metals improve wetting in ceramics by the formation of a reaction layer that insures bonding. The thickness of the reaction layer must be optimized because it impacts directly on the soundness and strength of the joint.
YSZ was brazed to itself and to Crofer22-APU using Ag-Cu-Ti alloys. Light microscopy, electron microscopy, dispersive energy spectroscopy (SEM-EDS), and X-ray diffraction (XRD) were used to study the interface YSZ/Ag-Cu-Ti. YSZ reacted with the active filler metals (Ag-Cu-Ti) to form a reaction layerat the interface. This reaction layer was rich in Ti and the presence of d – TiO was confirmed using XRD analysis and SEM-EDS.
Our goal is to develop a sound interconnect-electrolyte seal that can operate at temperatures up to 1000Â°C, using novel materials.
Development of Ultrafast AAO Nanowell/Pd Nanoparticle Structures for Hydrogen Detection at Low Temperature
Francisco Rumiche, PhD Candidate, Advisor: Dr. Indacochea
Hydrogen has been envisioned as a futuristic energy system. Gas detectors will be key components to ensure safety and reliability in a hydrogen based infrastructure. There are limitations of current hydrogen sensing devices such as long response time, low sensitivity, and poor performance at room temperature. Our approach is to use nanomaterial technology since very large active surface and nanoscale dimensions make nanostructures a promising alternative to overcome current limitations in hydrogen detectors. An anodic aluminum oxide (AAO) nanowell array has been selected as a substrate because it provides a robust, insulating, and ordered structure for catalyst deposition. Palladium nanoparticles have been selected as catalyst due to their high sensitivity and selectivity to react with hydrogen and have been deposited on the substrate. This nanostructure is then being characterized and tested for hydrogen detection. Dimensions and configuration are being systematically studied to attain a best performance. The electrical resistance is being determined as function of the level of hydrogen. The electrical resistance of the nanostructure increases with hydrogen concentration due to the formation of a non conductive Pd hydride phase. In addition the response time is greatly faster compared to that for other nanostructured and micro sensing devices.
Francisco Rumiche obtained his BS in Mechanical Engineering degree from the Pontificia Universidad Catolica del Peru in 2001. He received his MS in Materials Engineering degree from UIC in 2005. Currently he is working to obtain a PhD in Materials Engineering under the supervision of professor Ernesto Indacochea. He holds a TA position in the CME department and a guest graduate appointment in the Materials Science Division at Argonne National Laboratory