Materials Engineering

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-APU® 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 layer at 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 1000°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.

Carbide Derived Carbon

Prateek Gupta and Chris White, PhD Candidates, Advisor: Dr. Michael J. McNallan

Carbide derived carbon (CDC) is a novel material that has been the subject of a great deal of research within the last decade. CDC forms on the surface of a metal carbide by selectively etching the metal from the carbide, usually with a halogen at high temperature. The remaining material is a carbon mesh that consists of various carbon structures, such as diamond onions, graphite, carbon nanotubes and amorphous carbon. Since CDC has a low friction coefficient in sliding contact, and does not easily delaminate from the surface of the carbide, one set of applications that CDC has advantages over other coatings in tribological applications. Another set of applications where CDC can be useful are those that require materials with high specific surface area. CDC is a viable material for such applications since CDC is known to have a high specific surface area with a tunable porosity.

My research is focused on CDC behavior in different chemical environments. Particularly I am interesting in the adsorption of water onto CDC. CDC is an extremely hygroscopic material, being able to adsorb a significant amount of water from low relative humidity air. Understanding how and why water is adsorbed onto CDC is extremely important for both the synthesis of CDC as well as for its application.

In my work, CDC layers were synthesized on SiC and were exposed to controlled water vapor atmospheres, so that the effects of water vapor pressure on the absorption could be quantified. The isotherms that came from the experiments yielded insights as to the nanostructure when the sample is synthesized. Also the isotherms show that the sample conditions affect the response of the CDC to hydrogen treatment after synthesis. Our data suggests that if the sample is saturated with water before a hydrogen treatment, the CDC will change from having a microporous structure, to a macroporous structure after hydrogen treatment. Also the specific surface area of the CDC will decrease after hydrogen treatment if the CDC is saturated with water before the post treatment occurs.

Fellow PhD candidate, Chris White, has been working on improving the physical and mechanical properties of CDC. While other means of depositing carbon layers currently exist, they often are associated with processing conditions that require relatively expensive overhead costs. CDC synthesis offers a low cost alternative for synthesis of a friction reducing coating. UIC currently holds a patent for the basic CDC formation from metal carbides that is the basis for at least one new start-up company. White’s work focuses on introducing Hydrogen to the CDC matrix either during synthesis of the CDC, as a secondary post treatment or both. This work has shown great improvement in reducing the already good frictional qualities of CDC. Beyond lowering the coefficient of friction of CDC, current research is focused on analyzing how the addition of Hydrogen affects the overall wear of CDC in tribological applications. This work has great promise for commercial uses and is likely to enter into the market as a production enhancement of CDC applications in the near future.

Fracture Mechanics & Material durability Laboratory

Zhenwen Zhou, Senior Research Scientist, PhD in Materials Engineering, Advisor: Dr. Alexander Chudnovsky

Experience in material development & characterization of engineering materials; developing new testing methods & prototypes; researching in fracture mechanics and material durability, stress analysis statistical analysis; consulting with industry companies in material durability, failure analysis & reliability analysis.

Determination of Resistance to Rapid Crack Propagation of Engineering Plastics

An example in current research projects: Determination of Resistance to Rapid Crack Propagation of Engineering Plastics

The destructive potential of rapid crack propagation (RCP) along pressurized plastic pipelines initially required full-scale tests to determine a critical pressure at which a fast-running axial crack could self-arrest. Although the test results are accurate, the scale, difficulty, and expense of full-scale testing limit its use as a quality control test and as a research tool. While the small-scale steady-state test (S4 test) was developed for its comparable ease of execution, it does not provide the material toughness for dynamic crack propagation. Recognizing the value of a small-scale test, we developed an alternative small-scale test that can be safely and easily conducted in most laboratories and establishes a quantitative characterization of material resistance to rapid crack propagation in terms of the energy release rate (ERR) at crack arrest G1AR. In this alternative test, the pressurizing fluid is carried by a rubber tube, which keeps the internal pressure almost unchanged during the rapid crack propagation. Thus the decompression wave speed is effectively zero and the crack propagation driving force, or strain energy, is maintained as a constant during the rapid crack propagation. If the driving force exceeds the material resistance to rapid crack growth, then the crack is able to propagate. On the other hand, if the material resistance exceeds the crack driving force, G 1 < G 1 AR, the crack arrests. Therefore, this test directly establishes a quantitative characterization of material resistance to rapid crack propagation in terms of the energy release rate (ERR) at crack arrest G1 AR.

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