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The effects of superalloy composition and Pt content on the high-temperature oxidation behavior of γ–γ’ NiPtAl diffusion coatings were investigated over the temperature range of 1050–1150 °C. Simple NiPtAl diffusion coatings with 7 or 12 µm electroplated Pt thickness were evaluated in 1-h cycles in dry O2 for up to 2500 cycles on four superalloys: directionally solidified (DS) alloy 142, 1st generation single-crystal (SX) alloy 1483, and 2nd generation SX alloys X4 and N5. Coatings on high-Hf alloy 142 experienced severe internal oxidation of Hf at all temperatures. Coatings on ~5 at.% Ti alloy 1483 were protective at 1050 °C, but exhibited severe scale spallation at 1100 °C, with extensive formation of Ti- and Ni-rich oxides at the gas interface. Coatings with 7-µm Pt on X4 were extremely protective at 1100 °C, but failed rapidly at 1150 °C, which also was associated with the formation of Ti-rich oxides. Increasing the coating Pt content on X4 improved the 1150 °C oxidation behavior. Coatings on Ti-free N5 showed the best performance at 1150 °C, especially with 12-µm Pt. Although γ–γ’ coatings can exhibit outstanding cyclic oxidation resistance with minimal Al depletion, they appear to be sensitive to substrate composition, as well as eventual Pt depletion due to interdiffusion.

Primary solidification of ternary compounds Al20Mn2Ce and Al10Mn2Ce were analyzed through the coupling of the thermodynamic modeling and classic nucleation theory. Thermodynamic models of Al20Mn2Ce and Al10Mn2Ce were developed using the CALPHAD approach based on first-principles calculated enthalpy of formation and experimental data obtained from this work and the literature. The analysis suggested that despite the larger thermodynamic driving force for nucleation of Al10Mn2Ce, nucleation is preferred for the Al20Mn2Ce phase in the highly undercooled liquid due to its smaller interfacial energy. Therefore, manufacturing methods with rapid cooling rates will favor primary solidification of Al20Mn2Ce for Al-rich Al–Ce–Mn alloys.

Several factors are being investigated that affect the performance of thermal barrier coatings (TBC) for use in land-based gas turbines where coatings are mainly thermally sprayed. This study examined high velocity oxygen fuel (HVOF), air plasma-sprayed (APS), and vacuum plasma-sprayed (VPS) MCrAlYHfSi bond coatings with APS YSZ top coatings at 900–1100 °C. For superalloy 247 substrates and VPS coatings tested in 1 h cycles at 1100 °C, removing 0.6 wt %Si had no effect on average lifetime in 1 h cycles at 1100 °C, but adding 0.3%Ti had a negative effect. Rod specimens were coated with APS, HVOF, and HVOF with an outer APS layer bond coating and tested in 100 h cycles in air + 10%H2O at 1100 °C. With an HVOF bond coating, initial results indicate that 12.5 mm diameter rod specimens have much shorter 100 h cycle lifetimes than disk specimens. Much longer lifetimes were obtained when the bond coating had an inner HVOF layer and outer APS layer.

Directionally-solidified (DS) superalloy components with advanced thermal barrier coatings (TBC) to lower the metal operating temperature have the potential to replace more expensive single crystal superalloys for large land-based turbines. In order to assess relative TBC performance, furnace cyclic testing was used with superalloys 1483, X4 and Hf-rich DS 247 substrates and high velocity oxygen fuel (HVOF)-NiCoCrAlYHfSi bond coatings at 1100 °C with 1-h cycles in air with 10% H2O. With these coating and test conditions, there was no statistically-significant effect of substrate alloy on the average lifetime of the air plasma sprayed (APS) yttria-stabilized zirconia (YSZ) top coatings on small coupons. Using photo-stimulated luminescence piezospectroscopy maps at regular cycling intervals, the residual compressive stress in the α-Al2O3 scale underneath the YSZ top coating and on a bare bond coating was similar for all three substrates and delaminations occurred at roughly the same rate and frequency. X-ray fluorescence (XRF) measurements collected from the bare bond coating surface revealed higher Ti interdiffusion occurring with the 1483 substrate, which contained the highest Ti content.

We investigated the structural evolution of molybdenum carbides subjected to hot aqueous environments and their catalytic performance in low-temperature hydroprocessing of acetic acid. While bulk structures of Mo carbides were maintained after aging in hot liquid water, a portion of carbidic Mo sites were converted to oxidic sites. Water aging also induced changes to the non-carbidic carbon deposited during carbide synthesis and increased surface roughness, which in turn affected carbide pore volume and surface area. The extent of these structural changes was sensitive to the initial carbide structure and was lower under actual hydroprocessing conditions indicating the possibility of further improving the hydrothermal stability of Mo carbides by optimizing catalyst structure and operating conditions. Mo carbides were active in acetic acid conversion in the presence of liquid water, their activity being comparable to that of Ru/C. The results suggest that effective and inexpensive bio-oil hydroprocessing catalysts could be designed based on Mo carbides, although a more detailed understanding of the structure-performance relationships is needed, especially in upgrading of more complex reaction mixtures or real bio-oils.

Several factors are being investigated that affect the performance of thermal barrier coatings (TBC) for use in land-based gas turbines where coatings are mainly thermally sprayed. This study examined high velocity oxygen fuel (HVOF), air plasma sprayed (APS) and vacuum plasma sprayed (VPS) MCrAlYHfSi bond coatings with APS YSZ top coatings at 900°–1100°C. For superalloy 247 substrates and VPS coatings tested in 1-h cycles at 1100°C, removing 0.6wt.%Si had no effect on average lifetime in 1-h cycles at 1100°C, but adding 0.3%Ti had a negative effect. Rod specimens were coated with APS, HVOF and HVOF with an outer APS layer bond coating and tested in 100-h cycles in air+10%H2O at 1100°C. With an HVOF bond coating, initial results indicate that 12.5 mm diameter rod specimens have much shorter 100-h cycle lifetimes than disk specimens. Longer lifetimes were obtained when the bond coating had an inner HVOF layer and outer APS layer.

Polyvinyl toluene (PVT) scintillator plastic may degrade in the field due to inward water diffusion at elevated temperatures, which exceeds the saturation limit at lower temperatures, and after long periods of time (e.g., many years), leads to the formation of disk-like defects that attenuate scintillation light, leading to detector degradation. Using fractography and high-magnification optical and electron microscopy to characterize the water-induced defects, a model of the fogging process is hypothesized as follows: excess water present at low temperatures diffuses to spheroids to minimize contact with the hydrophobic polymer. Through the hydrophobic effect, the entropy of water increases by forming nanoclusters which minimizes the contact between the water and the PVT. As the water nanoclusters grow, they break and fold the polymer into densely-packed crystalline regions creating more space for water within the spheroids. The polymer outside the spheroid resists the shrinkage which builds up tension within the spheroid. Once the tensile stress exceeds the yield strength of the plastic, the spheroid is torn in half resulting in a defect. Excess water then drains into the cavities along the disk thereby further increasing its entropy. Slower cooling (over 1 day) leads to larger spheroids and hence, larger “permanent” defects. Freezing causes some defects to further grow due to the expansion of water to ice. These findings imply that the remaining lifetime of scintillator plastic in the field could be predicted using temperature and humidity data thereby mitigating security risks of degraded radiation portal monitors.

We have developed a science-based predictive model for fogging of the scintillator plastics deployed in radiation portal monitors. The only input required is the weather conditions [i.e., daily high and low, for temperature and relative humidity (R.H.)]. The code utilizes this information, together with a thermodynamic model of the water content in equilibrium with the plastic surface, a diffusion model of the water transport into the interior of scintillator plastic panel, and a comparison of the resulting paired “water-content/night-temperature” points as a function of position in the panel against an empirical “fog-line” that establishes a water/temperature criterion for the onset of fogging. We have analyzed the behavior of several representative portal monitor sites, and the output of the model analysis is reasonably consistent with observation.

Polyvinyl toluene (PVT) plastic is often used to make gamma ray sensitive scintillators and is used in many important applications. For example, PVT is used to scan recycled steel going into a plant to be processed. It is also used in personnel portals to scan employees, and is used at the borders of many countries to scan cargo and cars passing through. In recent years, it was discovered that PVT can become degraded when it absorbs water and then is subjected to daily temperature swings, as is evidence by a reduction in scintillation light. Water absorption by PVT was notionally associated with temporary fogging (i.e., a rapid decrease in opacity which was reversible over time) and permanent fogging (i.e., permanent crack-like defects) and was for some time suspected to be the leading cause of the fogging due to circumstantial evidence. However, definitive proof was not established and in particular the specific mechanisms by which water entered the plastic and ultimately created temporary and permanent point-like defects was not fully understood. This paper is an overview of an effort initiated to reveal the fundamental root cause and also the dynamics of the fogging and degradation processes. This understanding is important not only to solve degradation problems for PVT in fielded systems, but also (1) to provide direction for future procurements for new equipment, and (2) to provide direction for future R&D efforts into advanced plastics with enhanced spectroscopic capabilities or dual particle gamma/neutron capabilities. Unexpected outcomes of this investigation included (1) the capability to predict the onset of fogging based on models using weather data alone, and (2) new modified formulations of PVT and PS which are fog-resistant. This paper gives an overview of the water uptake and associated mechanisms for various compositions, characterization of resulting temporary and permanent defects, predictive modeling of fogging, and possible solutions including encapsulation, heaters and new formulations. While this paper is an overview of the root cause analysis and solution, five accompanying papers (Lance et al., 2018, Myllenbeck and Feng, 2018, Payne et al., 2018, Zaitseva et al. 2018, Kouzes et al., 2018) from the same conference (SORMA 2018) delve further into the details and also expand upon the scope of what will be reported herein.

To explore the upper temperature limit of a fusion blanket utilizing eutectic Pb-17at.%Li for tritium breeding, a series of three mono-metallic thermal convection loops have been fabricated from alloy APMT (Fe–21Cr–5Al–3Mo) and operated with commercial PbLi and increasing peak temperatures of 550°, 600° and 650 °C, flow rates of 0.4–0.7 cm/s and temperature gradients of 85–115 °C. Chains of APMT specimens including 25 mm long tensile specimens were hung in the hot and cold legs of the loops to evaluate post-exposure room temperature tensile properties after 1000 h exposures in each experiment. For specimens exposed to flowing PbLi above 500 °C, only minor changes in tensile properties were observed after exposure. Most APMT specimens were pre-oxidized to form alumina prior to exposure and exhibited small mass losses as the alumina was partially transformed to α-LiAlO2 that tended to spall after exposure. Specimens without pre-oxidation exhibited higher mass losses and formed γ-LiAlO2 but with less spallation. While promising for increasing blanket temperatures, the small mass losses suggest that the surface oxide is not completely stable. However, even at the highest temperatures, there was no indication of classic dissolution/precipitation behavior suggesting that higher temperature compatibility may be possible.

Furnace cycle testing of superalloy 1483 and X4 substrates with high velocity oxygen fuel (HVOF) NiCoCrAlYHfSi bond coatings and air plasma sprayed (APS) yttria-stabilized zirconia (YSZ) top coatings was conducted at 1100 °C in various environments. Average thermal barrier coating (TBC) lifetimes were 5–6 times longer when 100 h cycles were used to simulate base-load power generation operation, compared to the 1 h aero-engine standard cycle. Longer exposure times for 100 h cycles increased the interdiffusion resulting in no clear effects of H 2 O and CO 2 additions on average TBC lifetime for the 1483 substrates, contrary to the results with 1 h cycles where the addition of H 2 O reduced TBC lifetime. The lower Al content and perhaps the higher Ti content in 1483 compared to X4 resulted in lower TBC lifetimes for 1483. Photo-stimulated luminescence piezospectroscopy (PLPS) and 3D microscopy were used to measure residual stress in the alumina scale and surface roughness, respectively, on specimens with and without a YSZ top coating.

Furnace cycling experiments were performed on free-standing high-velocity oxygen-fuel bond coat samples to investigate the effect of material composition, surface texture, and cycling conditions on the average stresses in the formed oxide scales after cooling. The oxide scale thicknesses were determined by SEM image analyses and information about the stresses were acquired by photo-stimulated luminescence-spectroscopy. Additionally, the scale thickness dependent stress fields were calculated in finite-element analyses including approximation functions for the surface roughness derived on the basis of profilometry data. The evolution of the average residual stress as a function of oxide scale thickness was subject to stochastic fluctuations predominantly caused by local scale spallations. In comparison to the supplemental modeling results, thermal stresses due to mismatch of thermal expansion coefficients are identified as the main contribution to the residual stresses. The theoretical results emphasize that analyses of spectroscopic data acquired for average stress investigations of alumina scales rely on detailed information about microstructural features.

Rare-earth titanates, RE 2 Ti 2 O 7 (where RE = a rare-earth) with the pyrochlore structure continue to be investigated for use as potential stable host materials for nuclear and actinide-rich wastes. Accordingly, the present work is directed towards the elucidation of the fundamental structural, physical, and thermochemical properties of this class of compounds. Single-crystals of the rare earth pyrochlores were synthesized using a high-temperature flux technique and were subsequently characterized using single-crystal X-ray diffraction. The cubic lattice parameters display an approximately linear correlation with the RE -site cation radius. Theoretical calculations of the lattice constants and bond lengths of the subject materials were carried out using density functional theory, and the results are compared to the experimental values. The Sm and Eu titanates exhibit a covalency increase between the RE O 8 and TiO 6 polyhedral resulting in a deviation from the increasing linear lattice parameter through the transition series. Gd 2 Ti 2 O 7 with the 4f 7 half-filled f-orbital Gd 3+ sub-shell exhibits the lowest 48 f oxygen positional parameter. The coefficient of thermal expansion for the rare-earth titanate series is approximately linear, and it has a range of 10.1–11.2 × 10 −6 °C −1 . Raman spectroscopy indicated that the ∼530 cm −1 peak associated with the Ti–O stretching mode follows a general trend of decreasing frequency with increasing RE reduced mass.

Natural graphite powders were subjected to a series of thermal treatments to improve the anode irreversible capacity loss and capacity retention during long-term cycling of lithium-ion batteries. A baseline thermal treatment in inert Ar or N2 atmosphere was compared to cases with a proprietary additive to the furnace gas. This additive substantially altered the surface chemistry of the uncoated natural graphite powders and resulted in significantly improved long-term cycling performance of the lithium ion batteries over the commercial, carbon-coated natural graphite baseline. Different heat-treatment temperatures were investigated ranging from 950 to 2900 °C to achieve the desired long-term cycling performance with a significantly reduced thermal budget. A detailed summary of the characterization data is also presented, which includes X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, and temperature-programmed desorption-mass spectroscopy. Characterization data was correlated to the observed capacity fade improvements over the course of long-term cycling at high charge–discharge rates in full lithium-ion cells. It is believed that the long-term performance improvements are a result of forming a more stable solid electrolyte interface (SEI) layer on the anode graphite surfaces, which is directly related to the surface chemistry modifications imparted by the proprietary gas environment during thermal treatment.

Oxidation of NiAl–9Mo eutectics with three different second-phase Mo dispersion sizes was investigated at 900 °C in dry and wet air. Good oxidation resistance via alumina formation was observed in dry air, with MoO3 volatilization minimized by submicron Mo dispersions. However, although mass change measurements were similar in dry/wet air, extensive volatilization and in-place internal oxidation of prior Mo phase regions was observed in wet air. The ramifications of this phenomenon for the development of multiphase high-temperature alloys are discussed.

Small impurities in the fuel can have a significant impact on the emissions control system performance over the lifetime of the vehicle. Of particular interest in recent studies has been the impact of sodium, potassium, and calcium that can be introduced either through fuel constituents, such as biodiesel, or as lubricant additives. In a collaboration between the National Renewable Energy Laboratory and the Oak Ridge National Laboratory, a series of accelerated aging studies have been performed to understand the potential impact of these metals on the emissions control system. This paper explores the effect of the rate of accelerated aging on the capture of fuel-borne metal impurities in the emission control devices and the subsequent impact on performance. Aging was accelerated by doping the fuel with high levels of the metals of interest. Three separate evaluations were performed, each with a different rate of accelerated aging. The aged emissions control systems were evaluated through vehicle testing and then dissected for a more complete analysis of the devices. Results from these experiments show that increasing the rate of acceleration impacts the amount of fuel-borne metals that are captured by the catalyst, which subsequently impacts the catalyst performance. Beyond a certain threshold, the acceleration rate creates an artificial mechanism for catalyst deactivation. In the range of acceleration rates that were examined in this study, these effects were primarily isolated to the inlet of the catalyst whereas performance further down the length of the catalyst was mostly unaffected.

A commercial lean NOX trap (LNT) catalyst containing Pt, Pd, Rh, BaO, and CeO2 was evaluated in this investigation. The effects of lean/rich cycle timing on the NOX, CO and C3H6 conversions and on the NH3 and N2O selectivities were considered. Two distinct lean/rich cycling regimes were identified. At low temperatures, NOX release and reduction were relatively slow processes. As a result, a longer, lower-concentration rich dose favored increased cycle averaged NOX conversions. For example, extending the rich period from 5 to 15 s at 250 °C, while holding the overall reductant dose constant, resulted in an increase in cycle averaged NOX conversion from 59 to 87%. At high temperatures, the opposite was found to be true. Above 450 °C, NOX release and reduction occurred very rapidly and shorter, higher concentration rich doses yielded significantly higher NOX conversions. For example, extending the rich period from 5 to 15 s at 500 °C, while holding the overall rich dose constant, resulted in a decrease in the cycle averaged NOX conversion from 76 to 54%. The selectivities to NH3 and N2O were found to be primarily a function of temperature, with both being higher at lower temperatures. The effect of cycle timing and reductant concentration were of secondary importance. In contrast, NH3 and N2O yields were significantly affected by the cycle timing since they depend on the NOX conversion. Therefore, any combination of changes in the lean/rich timing protocol or reductant concentrations that resulted in increased NOX conversion also resulted in increased NH3 and N2O yields for a given temperature. Thus, concerted control of NH3 generation by varying the lean/rich cycle timing was demonstrated for this LNT catalyst. At both lower and higher temperatures, variations in the rich cycle duration resulted in NH3/NOX ratios that could extend the region of operation for a close-coupled LNT-SCR system, with the greatest effect observed at temperatures between 250 and 450 °C. However, N2O yield also increased with NH3 yield under the same conditions.

Tri-reforming of methane (TRM) produces syngas by directly utilizing flue gas from a fossil fuel-fired power plant without requiring post-combustion CO2 separation. In this work, different yolk sizes of a NiCe@SiO2 multi–yolk–shell nanotube catalyst were prepared and their catalytic properties were evaluated at different oxidizer (CO2 + H2O + O2) to methane (O/M) feed ratios for TRM. The NiCe@SiO2 multi–yolk–shell nanotube catalyst can exhibit longer stability than the conventional NiCe/SiO2Imp catalyst synthesized by impregnation method due to its controlled morphology and synergetic interactions of Ni–Ce and Ni–Si species. At a low O/M feed ratio of 1.0, NiCe@SiO2 with smaller yolks ( 30 nm) presents stable TRM activity at a high O/M feed ratio of 1.1, whereas NiCe@SiO2 consisting of smaller yolks deactivates. Deactivation of NiCe@SiO2 with smaller yolks can be explained by the re-oxidation of active Ni species, in which carbon formation and oxidation rates, and Ce3+/Ce4+ redox properties play a crucial role. Our results indicate that the NiCe@SiO2 multi–yolk–shell nanotube structures can provide high TRM activity, yet their structure should be tuned for stable performance by considering the yolk sizes and interaction of Ni–Ce species.

The addition of an air plasma sprayed (APS) “flash” bond coating layer on top of a high velocity oxy-fuel (HVOF) bond coating significantly extended the lifetime of APS yttria stabilized zirconia (YSZ) thermal barrier coatings (TBC) on rod specimens of superalloy 247 tested using 100-h cycles in air+10%H2O at 1100 °C. The flash bond coatings of both NiCoCrAlY and NiCoCrAlYHfSi powder were compared to an HVOF-only and a vacuum plasma sprayed (VPS) NiCoCrAlYHfSi bond coating. The flash coatings appear to form a mixed oxide-metal zone, which likely inhibits crack formation and therefore extends lifetime compared to conventional bond coatings. The underlying dense HVOF layer appeared to act as a source of Al for this intermixed zone and prevented the oxide from penetrating deeper into the bond coating. Residual stress in the thermally-grown Al2O3 scale was measured using photo-luminescence piezospectroscopy (PLPS) as a function of time for each coating variation, including a comparison of concave and convex surfaces on a specially designed rod.

Asperities in atmospheric plasma sprayed (APS) CoNiCrAlY bond coatings were observed to rapidly form spinel-type oxides growing into the APS yttria-stabilized zirconia (YSZ) top coating during isothermal exposures. To minimize these transient oxides, bond coatings were either lightly or heavily modified to remove asperities, prior to top coating deposition. After a 100 h isothermal exposure at 1100 °C in dry air, modified regions formed a thin, Al-rich thermally grown oxide (TGO) scale while unmodified regions formed Cr- and Ni-rich transient oxide. However, in 1-h furnace cycle testing (FCT) at 1100 °C, the modified bond coatings showed a reduced average lifetime compared to the specimens with unmodified bond coatings. The benefit of asperities may be to geometrically inhibit crack propagation, but the volume of transient oxide formed may also densify the adjacent YSZ and further inhibit cracking.

Bio-inspired superhydrophobic surfaces were fabricated based on fossilized silica fresh water diatomaceous earth (DE) particles. These nanostructured silicified diatom frustules of cylindrical and circular structures were fluorinated to impart them with superhydrophobic properties. Substrates coated with superhydrophobic DE structures of varying size and shape were found to have water contact angles of approximately 170° and sliding angles of approximately 3°. The substrates were subjected to significant abrasion forces using a standard surface abrader. The ability to retain their superhydrophobic properties was observed to depend on the geometry and average size of the DE particles. The wettability of the abraded coatings was determined by their surface topology, and a transition from a non-wetted state to a partially wetted state was observed to occur and was dependent on the surface roughness. The proposed coatings are scalable, cost-effective, and can be applied on a variety of surfaces on critical infrastructures requiring protection from water saturation, ice formation and water based corrosion.

Photo-stimulated luminescence spectroscopy (PSLS), 3D microscopy and focused ion beam cross-sections were used to study the effect of water vapor on the cyclic (1 h cycle time) oxidation behavior of simple and Pt-modified aluminide bond coatings on several superalloy substrates at 1125° and 1150 °C. By tracking the same region over time, the change in surface roughness with thermal cycling could be attributed to large and small bond coating grains rising and sinking, respectively, with thermal cycling. Oxidation in air with 10% H2O showed a 0–37% increase in surface roughness compared to oxidation in dry air. Reducing the cycle temperature from 1150° to 1125 °C, increased the thermal barrier coating lifetime by > 4X but did not prevent bond coating rumpling. Compared to oxidation in dry air, PSLS identified more θ-Al2O3 formation on the Pt-modified aluminide bond coatings after 1 h at 1125° or 1150 °C in air with 10% H2O but only minor differences in the residual stress after longer cyclic oxidation exposures. Stress histograms produced by PSLS mapping help to elucidate Al2O3 scale damage accumulation in each condition but did not clearly identify a mechanism for the effect of water vapor on coating performance.

The performance of thermal barrier coating (TBC) specimens with superalloy 1483 and X4 substrates and high velocity oxy fuel (HVOF)-NiCoCrAlYHfSi bond coatings was evaluated in dry and wet air in 1 h furnace cycles at 1100 °C. Compared to a prior study of NiCoCrAlYHfSi bond coatings, the HVOF bond coatings were rougher Ra = 8 μm, closer to commercial HVOF coatings. For TBC coatings on the X4 substrates cycled in air with 10% water vapor, increasing the roughness from Ra = 5 to 8 μm had little effect on the average TBC lifetime. The presence of 10% water vapor reduced the average TBC lifetime for 1483 by 13%, however, in both wet and dry conditions, the lifetimes for this substrate were 30–50% below those observed for X4 substrates. This may be attributed to the lower Al content and higher Ti content in 1483. Roughness and residual stress in the alumina scale were measured on specimens without a ceramic top coating, but no effects were observed due to the change in substrate or the addition of water vapor.

A monometallic V–4Cr–4Ti thermal convection loop was run for 2355 h with a peak temperature of 700 °C (973 K) and Li flow rate of 2–3 cm/s. Specimens of V–4Cr–4Ti exposed in the hot and cold legs of the loop and tensile tested in vacuum at 500 °C (773 K) showed an increase in the 0.2% yield and ultimate tensile strengths and a decrease in the serration amplitude with decreasing exposure temperature in the loop. However, only minor changes in ductility were measured. With the higher temperature exposures, a decrease in Vickers hardness was measured, but little change in the grain size was observed. Characterization of the microstructure after exposure at 627 °C (900 K) in the loop showed an increase in the density of Ti- and N-rich grain boundary and matrix precipitates near the specimen surface after exposure corresponding to an increase in the hardness in the near-surface region. Two-layer V/Y2O3 coatings on V–4Cr–4Ti substrates also were exposed in the loop, and initial room temperature characterization was conducted.

This article reports on the results of experimental efforts aimed at improving the understanding of the mechanisms and conditions at play in the fouling of exhaust gas recirculation coolers. An experimental apparatus was constructed to utilize simplified surrogate heat exchanger tubes in lieu of full-size heat exchangers. The use of these surrogate tubes allowed removal of the tubes after exposure to engine exhaust for study of the deposit layer and its properties. The exhaust used for fouling the surrogate tubes was produced using a modern medium-duty diesel engine fueled with both ultra-low-sulfur diesel and biodiesel blends. At long exposure times, no significant difference in the fouling rate was observed between fuel types and hydrocarbons levels. Surface coatings for the tubes were also evaluated to determine their impact on deposit growth. No surface treatment or coating produced a reduction in the fouling rate or any evidence of deposit removal. In addition, microstructural analysis of the fouling...

In this study, we developed two frameworks to investigate the thermophoretic particulate deposition in non-isothermal tube flows conveying particles ranging from 10 to 300 nm; a one dimensional model where the variables are assumed to be uniform in each cross section perpendicular to the tube axis and an axi-symmetric model where the aforementioned assumption is relaxed. In the one dimensional model, the rate of mass deposition along the inner surface of the tube is computed based on the local thermophoretic velocity of the particulate phase at the wall. This velocity is proportional to the radial gradient of the temperature at the wall and is calculated via some empirical correlations for heat transfer in tube flows. In the axi-symmetric model, the rate of deposition is computed through the Fick’s law after solving the species transport equation for the solid phase. We included the formation of the soot layer through moving the gas–solid interface in both models. The tube effectiveness (the ratio of actual heat transfer to the maximum possible heat transfer) decreases due to the formation of the layer. Model outputs including deposited mass along the tube wall and the tube effectiveness drop have been compared against experiments. While the computed results through both models agree with the trend of experimental data, the axi-symmetric results are closer to the experiments in most cases. The calculated deposited mass is smaller (and closer to experiments) for the axi-symmetric model compared to the one dimensional model in all cases. This indicates that the axi-symmetric model estimates the deposited mass more accurately.

Biodiesel is a renewable fuel with the potential to displace a portion of petroleum use. However, as with any alternative fuel, in order to be a viable choice it must be compatible with the emissions control devices. The finished biodiesel product can contain up to 5 ppm Na+K and 5 ppm Ca+Mg, and these metal impurities can lead to durability issues with the devices used to control emissions in diesel vehicles. Significant work has been performed to understand how the presence of these metals impacts each individual component of diesel emissions control systems, and this chapter summarizes the findings of these research efforts.

International audience; The safety assessment of Sodium-cooled Fast Reactors (SFR) requires to account for hypothetical severe accidents involving the melting down of the core materials. This paper deals with the modeling of a fuel vaporization transient that might occur in a SFR in case of severe accident. After a nuclear power excursion, some fuel might be molten and vaporized. In this case, the expansion of fuel vapor might generate a mechanical stress on the reactor vessel and structures. Assessing the vessel integrity is of major importance for the reactor design. A fuel vaporization and expansion modeling, which has been simplified using a Dimensional Analysis, is presented. The modeling is implemented in a tool, called DETONa, able to perform fast calculations, of the order of one minute. The vaporized fuel’s thermal exchange with the reactor liquid coolant leading to a possible coolant vaporization is simulated by DETONa. The coolant is assumed to be entrained into the fuel vapor. A droplet entrainment model based on Rayleigh-Taylor instabilities associated to their diameter’s limitation using Weber stability criterion is proposed. The modeling is validated on experimental results and on code-to-code comparisons. Parametric calculations are conducted on a reactor case. The impact of the initial molten fuel mass, its initial temperature, critical Weber number and radiative heat transfer are investigated. The non-adiabatic modeling and the adiabatic modeling yield results different by 40 percent in certain cases. DETONa is shown to be sensitive to the fuel initial temperature, the heat transfer coefficient and the Rayleigh-Taylor wavelength, involving variations that can range to 18 percent.

As alternative lubricant anti‐wear additives are sought to reduce friction and improve overall fuel economy, it is important that these additives are also compatible with current emissions control catalysts. In the present work, an oil‐miscible phosphorous‐containing ionic liquid (IL), trihexyltetradecylphosphonium bis(2‐ethylhexyl) phosphate ([P66614][DEHP]), is evaluated for its impact on three‐way catalysts (TWC) and benchmarked against the industry standard zinc‐dialkyl‐dithio‐phosphate (ZDDP). The TWCs are aged in different scenarios: neat gasoline (no‐additive, or NA), gasoline+ZDDP, and gasoline+IL. The aged samples, along with the as‐received TWC, are characterized through various analytical techniques including catalyst reactivity evaluation in a bench‐flow reactor. The temperatures of 50% conversion (T50) for the ZDDP‐aged TWCs increased by 30, 24, and 25 °C for NO, CO, and C3H6, respectively, compared to the no‐additive case. Although the IL‐aged TWC also increased in T50 for CO and C3H6, it was notably less than ZDDP, 7 and 9 °C, respectively. Additionally, the IL‐aged samples had higher water‐gas‐shift reactivity and oxygen storage capacity than the ZDDP‐aged TWC. Characterization of the aged samples indicated the predominant presence of CePO4 in the ZDDP‐aged TWC aged by ZDDP, while its formation was retarded in the case of IL where higher levels of AlPO4 is observed. Thus, results in this work indicate that the phosphonium‐phosphate IL potentially has less adverse impact on TWC than ZDDP.

a b s t r a c t Carbon fibers made of textile and aerospace grade polyacrylonitrile precursor fibers were surface treated by a continuous gas phase thermochemical treatment. The surface chemistry generated by the surface treatment was characterized by X-ray photoelectron spectroscopy. The surface and the average entire microstructure of the fibers were characterized by Raman spectroscopy and X-ray diffraction, respec- tively. Depending on the grade of the precursor, the final surface concentration of oxygen was comprised between 14% and 24%, whereas the typical commercial electrochemical surface treatments led to concen- trations of around 8% with the same fibers. The final concentration of oxygen was directly correlated to the size of the crystallites which was a function of the grade of the polyacrylonitrile precursor and to the corresponding surface microstructure. The thermochemical surface treatment enabled a better control of the nature of the oxygen-containing functionalities as well. Whatever the grade of the precursor, desired hydroxyl groups and carboxylic acid functionalities were preferably generated, which is observed to be difficult with electrochemical surface treatments. Published by Elsevier B.V.

Silicon nanowires (NWs) have been reported as a promising anode that demonstrated high capacity without pulverization during cycling, however, they present some technical issues that remain to be solved. The high aspect ratio of the NWs and their small contact areas with the current collector cause high electrical resistance, which results in inefficient electron transport. The nano-size interface between a NW and the substrate experiences high shear stress during lithiation, causing the wire to separate from the current collector. In addition, most reported methods for producing silicon NWs involve high-temperature processing and require catalysts that later become contaminants. This study developed a new self-aligned Cu–Si core–shell NW array using a low-temperature, catalyst-free process to address the issues described. The silicon shell is amorphous as synthesized and accommodates Li-ions without phase transformation. The copper core functions as a built-in current collector to provide very short (nm) electron transport pathways as well as backbone to improve mechanical strength. Initial electrochemical evaluation has demonstrated good capacity retention and high Coulombic efficiency for this new anode material in a half-cell configuration. No wire fracture or core–shell separation was observed after cycling. However, electrolyte decomposition products largely covered the top surface of the NW array, restricting electrolyte access and causing capacity reduction at high charging rates.

Mountain whitefish (Prosopium williamsoni) are among the most abundant native fishes in western North America, yet their role in ecosystems is largely unknown. We investigated their ecology in Big Creek, a 7th-order wilderness watershed in central Idaho. Based on underwater visual counts and hook and line surveys conducted during summer months, as well as tissue analysis, we estimated mountain whitefish distribution and abundance, total biomass, production, and energy and nutrient contributions along a 60 km segment of Big Creek. We observed that abundance decreased with distance upstream, and 93% of mountain whitefish surveyed in Big Creek were greater than 200 mm (≥ 3 years); few juveniles were observed, suggesting that rearing occurs in habitats downstream. Mountain whitefish were the dominant fish in Big Creek, in terms of both abundance (33% of fish observed) and biomass (57% of salmonid biomass). We estimated their production averaged across the study segment as 0.51 g m-2 yr-1, though it r...

The silicon oxynitride glasses take advantage of nitrogen-bonding to attain high elastic modulus, increased softening temperatures and viscosities, greater slow crack growth resistance and modest gains in fracture resistance. Of the oxynitride glasses, the Si-Y-Al based oxynitride glasses have been most extensively studied and a degree of success has been achieved in understanding how changes in glass composition affect structural parameters and their relationship to properties. More recent studies have focused on the Si-RE-Me oxynitride glasses where Me is primarily Al or Mg and RE includes most of the lanthanide series elements. These glasses possess a range of elastic, thermal, mechanical and optical properties, which can be correlated with the strength of the RE bond in terms of the cationic field strength. However, such correlation require knowledge of not only the RE valence state but also its coordination with the anions. Herein, the current state of the art understanding of the properties and structural parameters of oxynitride glasses and their interrelationships are reviewed.

A family of alumina-forming austenitic (AFA) stainless steels is under development for use in aggressive oxidizing conditions from ~600–900 °C. These alloys exhibit promising mechanical properties but oxidation resistance in air with water vapor environments is currently limited to ~800 °C due to a transition from external protective alumina scale formation to internal oxidation of aluminum with increasing temperature. The oxidation behavior of a series of AFA alloys was systematically studied as a function of Cr, Si, Al, C, and B additions in an effort to provide a basis to increase the upper-temperature oxidation limit. Oxidation exposures were conducted in air with 10% water vapor environments from 800–1000 °C, with post oxidation characterization of the 900 °C exposed samples by electron probe microanalysis (EPMA), scanning and transmission electron microscopy, and photo-stimulated luminescence spectroscopy (PSLS). Increased levels of Al, C, and B additions were found to increase the upper-temperature oxidation limit in air with water vapor to between 950 and 1000 °C. These findings are discussed in terms of alloy microstructure and possible gettering of hydrogen from water vapor at second phase carbide and boride precipitates.

10B isotope doped p-type diamond epilayer grown by chemical vapor deposition on (110) oriented type IIa diamond single crystal substrate was subjected to neutron transmutation at a fluence of 2.4 × 1020 thermal and 2.4 × 1020 fast neutrons. After neutron irradiation, the epilayer and the diamond substrate were laser annealed using Nd–YAG laser irradiation with wave length, 266 nm and energy, 150 mJ per pulse. The neutron irradiated diamond epilayer and the substrate were characterized before and after laser annealing using different techniques. The characterization techniques include optical microscopy, secondary ion mass spectrometry, X-ray diffraction, Raman, photoluminescence and Fourier Transform Infrared spectroscopy, and electrical sheet conductance measurement. The results indicate that the structure of the irradiation induced amorphous epilayer changes to disordered graphite upon laser annealing. The irradiated substrate retains the (110) crystalline structure with neutron irradiation induced defects.

We report observations of the nature and spatial distribution of sulfur species on a sulfated Ba-based commercial lean NOx trap (LNT) catalyst. The monolithic catalyst was sulfated in a bench flow reactor during 60/5-s NOx-storage/reduction cycling to achieve a total sulfur loading of 3.4 g L−1 of catalyst. Washcoat composition, structure and sulfur distribution were analyzed with electron probe microanalysis, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and temperature-programmed reduction. The most significant washcoat elements of catalytic relevance were Pt, Pd, Rh, Ba, Ce, Zr, Mg, Al, and these were present mainly in four distinct domains: (i) Mg/Al mixed oxide with Pt, Ce; (ii) Al oxide with Rh, Pd; (iii) Ce/Zr mixed oxide with Pt, Pd, Ba (high Ba content); (iv) Ce/Zr mixed oxide with Pt, Pd, Ba (low Ba content). Sulfur was present in the form of sulfates that decreased in concentration along the LNT axis from front to back. Barium showed the highest sulfur affinity leading to a plug-like axial progression of its sulfation. The sulfation of Al, Mg/Al, and Ce/Zr oxides was less vigorous with a more axially dispersed and less penetrating front.

System integration and miniaturization demands are driving integrated thin film capacitor technologies towards ultrahigh capacitance densities for noise-free power supply, power conversion and efficient power management. Hydrothermal route can deposit crystalline ferroelectric films at low temperatures of less than 150 C. It is hence an attractive route for integrating high permittivity thin film capacitors on organic, silicon or flex substrates. However, hydrothermal films are not commercialized so far because of their inferior insulation characteristics. Embedded hydroxyl groups are attributed to be the cause for high leakage currents, temperature dependent properties and lower Breakdown Voltages (BDVs). This paper discusses the dielectric characteristics such as capacitance density, leakage currents and Temperature Coefficient of Capacitance (TCC) of hydrothermal barium titanate films and correlates them to the embedded water and OH groups, film morphology, stoichiometry and crystallinity. With thermal treatment, majority of the OH groups can be removed leading to improved insulation characteristics. The room temperature I-V characteristics agreed with ionic conduction models for films baked at 160 C while higher baking temperatures of above 300 C resulted in Poole-Frenkel type conduction. A brief perspective is provided on the suitability of hydrothermal thin film capacitors for power supply applications.

Laser physical vapor deposition was used to deposit thin films of boron carbide on Si (100) and WC–Co substrates at 550 °C under different pressures of methane atmosphere. Grazing incidence X-ray diffraction was used to identify a boron carbide phase, which exhibited weak peaks. The presence of particulates in the size range of 50 nm–3 µm embedded in an amorphous matrix was observed by scanning electron microscopy. Raman spectroscopy indicated that as methane partial pressure was increased during deposition, the amount of disorder with the boron carbide structure also increased. Also, the nanoindentation hardness decreased, while the coefficient of friction and scratch adhesion strength increased. These effects are attributed to an increase in amorphous phase/disorder in the films. Wear tests conducted by machining particleboard using boron carbide coated WC–Co tools in the absence of methane showed the same wear rate as tools coated under higher methane pressures.

The impact of different types of diesel particulate matter (PM) and different sampling conditions on the wall deposition and early soot cake build-up within diesel particulate filters has been investigated. The measurements were made possible by a newly developed diesel exhaust filtration analysis system in which in-situ diesel exhaust filtration can be reproduced within small cordierite wafer disks, which are essentially thin sections of a diesel particulate filter wall. The different types of PM were generated from selected engine operating conditions of a single-cylinder heavy-duty diesel engine. Two filtration velocities 4 and 8 cm/s were used to investigate PM deep-bed filtration processes. The loaded wafers were then analysed in a thermal mass analyser that measures the soluble organic fraction as well as soot and sulphate fractions of the PM. In addition, the soot residing in the wall of the wafer was examined under an optical microscope illuminated with ultraviolet light and a variable pressure scanning electron microscope to determine the bulk soot penetration depth for each loading condition. It was found that a higher filtration velocity results in a higher wall loading with approximately the same penetration depth into the wall. PM characteristics impacted both wall loading and soot cake layer characteristics. Results from imaging analysis indicate that the soot penetration depth into the wall was affected more by PM characteristics (which changes with engine operating conditions) than by filtration velocity.

A pressure-induced phase transformation in the lithium aluminum silicate β-eucryptite was studied with in situ Raman spectroscopy. Dense β-eucryptite composites were made via powder synthesis followed by sintering. The specimens were then subjected to diamond indentation up to applied contact stresses of about 8 GPa, while collecting Raman spectra. The appearance of a Raman peak (∼520 cm−1) at a contact stress of about 3 GPa likely corresponds to the reversible phase transformation of β-eucryptite to the orthorhombic phase ɛ-eucryptite. Loading and unloading in situ Raman indentation experiments are discussed with regards to this transformation.

The efforts for designing a meaningful and acceptable standard test method for characterization of kinetic parameters of air oxidation of graphite helped identify several practical issues that must be considered for the development of such a test. Using standard size (and shape) specimens, large enough in size to accommodate the inherent local microstructure differences between graphite samples, resulted in non-uniform oxidation profiles and preferential binder oxidation; this was not expected based on the linearity of Arrhenius plots and the (large) values of activation energy. It was found that the transition between the regimes 1 and 2 of graphite oxidation occurs gradually, depending both on the oxidation temperature and rate of oxygen supply. Nevertheless, measuring oxidation rates obtained on standard size samples provides a basis for a meaningful comparison among materials, which may serve as much needed information for predictive models.

The surface morphology, and chemical/structural modifications induced during chemical sputtering of ATJ graphite by low-energy (

Formation of a sinking carbon dioxide (CO 2 ) hydrate composite has been investigated as an alternative to direct liquid CO 2 injection and pure CO 2 hydrate formation for ocean carbon sequestration. Raman spectroscopy of the CO 2 hydrate composite was also performed to determine the presence of various components in the composite produced by the co-injection of liquid CO 2 and water. This work is focused on the formation and spectroscopy of a semi-solid sinking CO 2 hydrate composite formed using a co-flow injector in 72-liter and 0.45-liter pressurized vessels at pressure and temperature conditions equivalent to approximately 1.3-km depth in the ocean. The Raman wavenumber shifts (Δcm − 1 ) corresponding to CO 2 and water molecules as well as shifts in Raman peak positions due to different CO 2 phases were obtained. The Raman spectra of the composite showed that both liquid and hydrate phases of CO 2 are present. The dissolution rate of CO 2 hydrate composite in water was also studied. An attempt was made to calculate the hydration number for the CO 2 hydrate composite and also the percentage of liquid CO 2 and water loss during formation.

Free standing {sup 10}B isotope doped diamond films deposited by chemical vapor deposition in a microwave chamber were irradiated to thermal neutron fluence values of 0.32 x 10{sup 19}, 0.65 x 10{sup 19}, 1.3 x 10{sup 19}, and 2.6 x 10{sup 19} n/cm{sup 2}. Cooling of the diamond films was maintained during irradiation. In a separate experiment, neutron irradiation to a total fluence of 2.4 x 10{sup 20} n/cm{sup 2} with equal fast and thermal neutrons was also performed on a diamond epilayer without cooling during irradiation. The formation of defects in the diamond films was characterized using Raman, FTIR, photoluminescence, electron paramagnetic resonance spectroscopy, and X-ray diffraction. It was found that defect configurations in diamond responsible for an increase in continuum background in the one-phonon region of Raman spectrum were absent in the films that have been cooled. The FTIR peak at 1530 cm{sup -1} annealed in the sample irradiated to a fluence of 2.6 x 10{sup 19} n/cm{sup 2} indicating that the sample reached a temperature of 300 C during irradiation. Absence of characteristic infrared absorption peaks that were observed only upon annealing neutron irradiated diamond is used to conclude that the temperature of the sample during neutronmore » irradiation to a fluence of 2.6 x 10{sup 19} n/cm{sup 2} was well below 650 C needed for mobility of defects and accumulation of stable unrecoverable damage. On the other hand, results from diamond epilayer subjected to equal thermal and fast neutron fluence of 2.4 x 10{sup 20} n/cm{sup 2} and without cooling showed that defects formed from displaced carbon atoms became mobile and formed complex configurations of irrecoverable damage. Electrical conductance of the unirradiated and irradiated diamond samples was measured as a function of temperature to determine the compensation of the p-type by the n-type charge carriers.« less

A high-purity CVD β-SiC showed a relatively low corrosion rate in deoxygenated supercritical water at 500°C. The corrosion rate was lower than that previously reported for CVD SiC in 360°C water and much lower than that reported for sintered and reaction-bonded SiC. The present study confirmed that CVD SiC was preferentially attacked at the grain boundaries. Analytical examinations did not reveal the presence of a measurable oxide scale. As a result, it is believed that corrosion of the high-purity SiC occurred via hydrolysis to hydrated silica species at the surface that were rapidly dissolved into the supercritical water.

Diamond films were deposited via microwave plasma chemical vapor deposition on lithium niobate (LN) substrates. Characterization of the interfacial regions formed between diamond films and LN substrates was carried out by several techniques. Secondary ion mass spectroscopy (SIMS) was used to determine the depth profiles of carbon, lithium, niobium, and oxygen in the LN substrate covered with diamond nuclei and in the substrate without nucleation. Results indicate that the diamond nuclei promoted growth of diamond, and in addition, a reduced depth of the lithium deficient zone formed in the LN substrate was observed. Grazing incidence x-ray diffraction and transmission electron microscopy observations corroborated the results obtained by SIMS. Residual stresses determined experimentally by an x-ray method or by the shift in the characteristic diamond peak in Raman spectroscopy were much smaller than the calculated thermal residual stresses. The results further emphasize that the interfacial phases are resp...