Investigation of WO{sub 3}-Based H{sub 2}S Sensor Materials for Coal Gasification Systems

The aim of this project was to engineer the materials studied to enhance the so-called 3S criteria: Sensitivity, Selectivity, and Stability, by using the advantage of controlling structure and properties at nanometer dimensions. It targeted sensor materials that are able to detect poisonous gases resulting from coal-gasification processes, especially sulfur containing emissions. Research findings based on this award demonstrate that doping tungsten oxide (WO{sub 3}) with a small amount of Ti (e.g. 5% in our work) results in a new material that has a higher structural symmetry (e.g. tetragonal morphology) as well as narrower crystalline particle size distribution. As high quality materials with excellent ordered structure and narrower particle-size distributions (which can also withstand high-temperature technological environments such as those encountered in furnaces and coal gasification systems without their structure being affected by phase transformations) are needed for developing new, more sensitive sensor materials, W-Ti-O thin films grown by RF sputtering are valuable candidates for such roles. It is well known that pure WO{sub 3} will change its structure at elevated temperatures. Our work indicates that, Ti doping not only increases the stability of the resultant material by promoting structural phase modifications, but also increases its sensitivity by increasing the effective surface area exposed to the poisonous gas (fine microstructure and uniform distribution were observed)

Effects of EB-PVD microstrural features on CMAS infiltration of Yttria-rich zirconia coatings

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Y2O3-ZrO2 ratio studies for CMAS resistant thermal barrier coatings prepared by EB- PVD

Thermal barrier coatings based on the yttria-zirconia system with compositions over 50 mol. % YO1.5 rest ZrO2 have shown potential as CMAS/Volcanic ash (VA) resistant coatings1–4. However, it is still not clear what Y-Zr ratio is the optimal to promote effective CMAS/VA arrest. A previous study has shown that pure Y2O3 coatings are not as effective as their yttria-zirconia counterpart4 making this topic of high relevance for the development of CMAS/VA resistant coatings. Therefore, this study is based on the determination of the optimal Y-Zr ratio for EB-PVD TBCs produced with compositions ranging from 40-70 mol. % YO1.5. Preliminary results for short term infiltration (up to 7 min.) at 1250°C with natural VA from the Eyjafjallajökull volcano show a tendency of increased infiltration resistance with coatings having a higher yttria composition (70 mol. %) seen from Figure 15. The experiments indicate formation of reaction products when a 50 mol. % YO1.5 coating composition is used and no significant reaction with lower yttria compositions. Thus, it appears that the threshold point to saturate the glass promoting formation of reaction products (apatite and garnet) is for compositions with at least 50 mol. % YO1.5. A systematic study will be presented to determine the optimum yttia content in EB-PVD coatings for effective glass crystallization. Please click Additional Files below to see the full abstract

Examination of the Oxidation and Metal–Oxide Layer Interface of a Cr–Nb–Ta–V–W High Entropy Alloy at Elevated Temperatures

The authors report on the evaluation of the oxide scale and the interface microstructure of a Cr–Nb–Ta–V–W refractory high entropy alloy (HEA) at elevated temperatures. The Cr–Nb–Ta–V–W HEA is oxidized at 700 and 800 C in lab air and the substrate/oxide interface is investigated. Combined in situ X-ray diffraction (XRD) coupled with ex situ scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDS) analyses characterize the oxide scale and confirm the phases present in the substrate which have been previously identified in this alloy. The microstructure near the interface is studied for an indication of selective oxidation of this alloy. Cracking and porosity are found along the interface layer which grows directionally outward. Two main oxides are identified: a W-based oxide with a needle-like structure and a Cr oxide containing Ta that has a granular structure, primarily found in clusters. The oxide layers are porous, and no dense protective oxide is identified. It is found that when the temperature is increased to 800 C, the oxide layer exhibits an increase in thickness. In situ XRD indicates that V is the first element to oxidize

High temperature infiltration behavior of three volcanic ashes of YSZ APS-deposited thermal barrier coatings

Thermal Barrier Coatings (TBC) have enabled the increase of the operational temperature of aero engines. Raise in the turbine inlet temperatures (TIT) poses a threat to phase stability and safety for the state of the art material 7-8 wt% yttria stabilized zirconia (7YSZ). In addition to the inherent physicochemical restrictions of this material at high temperatures, the interaction of 7YSZ with siliceous airborne particles at temperatures above 1200 °C has been a major concern since the last decades. Sediments of Calcium-Magnesium-Aluminum-Silicates (CMAS) have been found in failed engines and have been correlated to the failure mechanisms of high temperature components. In 2010 the eruption of the Eyjafjallajökull volcano in Iceland heavily disrupted air traffic in Europe. This volcanic event lead to regulations regarding volcanic ash (VA) concentrations in the atmosphere at which aircrafts are allowed to safely fly. Also, it brought to sight the risks associated to VA in the safety of aircrafts with routes close to active volcanos. Nevertheless, reports of the assessment of the high temperature risk using real volcanic ashes is still limited in comparison to analyses carried out with CMAS. Additionally, most reported studies have been focused on the study of electron beam physical vapor deposition (EB-PVD) rather than atmospheric plasma spray (APS) produced TBCs. This contribution addresses the study of the infiltration mechanisms of VA from three sources: Colima and Popocatepetl Mexican volcanoes as well as Eyjafjallajökull Icelandic volcano. Please click Additional Files below to see the full abstract

Smart Sensors to Reduce Pollutant Emissions in Transportation, Phase II

Project DescriptionToday’s automobiles lack flexibility in design and contribute to the major portion of pollution. This project intends to design, develop, evaluate, and demonstrate the feasibility of smart sensors for utilization in advanced transportation to reduce pollution. The project objectives are: (1) Design and performance test oxygen sensors for combustion engines and (2) Demonstrate the temperature independent “smart sensing” features for emission control and fuel efficiency in transportation systems. This is the Phase-II of a multi-year project. The methodologies to be developed are expected to be applicable in a broader context.U.S. Department of Transportation 69A355174711

Smart Sensors to Reduce Pollutant Emissions in Transportation

Project DescriptionToday’s automobiles lack flexibility in design and contribute to the major portion of pollution. This project intends to design, develop, characterize, and demonstrate the feasibility of smart sensors for utilization in advanced transportation and reduce pollution. The project objectives are: (1) To fabricate oxygen sensors for combustion engines, (2) Demonstrate the temperature independent and smart characteristic features of sensors for emission control and fuel efficiency in transportation systems. This is the first year of a multi-year project. The methodologies to be developed are expected to be applicable in a broader context.U.S. Department of Transportation 69A355174711

Smart Sensors to Reduce Pollutant Emissions in Transportation

Project VideoU.S. Department of Transportation 69A35517471191_1rd9mq4

An ab initio study of the elastic behavior of single crystal group (IV) diborides at elevated temperature

We report on an ab initio molecular dynamics study of the lattice parameters, thermal expansion coefficients, and elastic constants of ZrB2 role= presentation style= display: inline; line-height: normal; word-spacing: normal; word-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; padding: 0px 2px 0px 0px; margin: 0px; position: relative; \u3eZrB2ZrB2, TiB2 role= presentation style= display: inline; line-height: normal; word-spacing: normal; word-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; padding: 0px 2px 0px 0px; margin: 0px; position: relative; \u3eTiB2TiB2, and HfB2 role= presentation style= display: inline; line-height: normal; word-spacing: normal; word-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; padding: 0px 2px 0px 0px; margin: 0px; position: relative; \u3eHfB2HfB2 ceramics at ultrahigh temperatures (up to 2200 K). Equilibrium lattice parameters of the ceramics are determined at finite temperatures. A finite strain method is used to extract the stiffness tensor of the ceramics. The results obtained for ZrB2 role= presentation style= display: inline; line-height: normal; word-spacing: normal; word-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; padding: 0px 2px 0px 0px; margin: 0px; position: relative; \u3eZrB2ZrB2 and TiB2 role= presentation style= display: inline; line-height: normal; word-spacing: normal; word-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; padding: 0px 2px 0px 0px; margin: 0px; position: relative; \u3eTiB2TiB2 agree well with experimental results reported in the literature. Our work demonstrate that accurate properties may be obtained from a statistical averaging of the lattice parameters alone neglecting phonon interactions