Future long-duration Venusian surface landers will require structural alloys that can withstand the harsh surface conditions; 467 °C temperature and 92.7 bar atmospheric pressure consisting of supercritical CO2. To investigate structural alloy suitability, corrosion and tensile coupons of wrought Ti-6Al-4V (Ti64), laser powder bed fusion printed Ti-6Al-4V (AM Ti64), and wrought 304SS were exposed to a 10-day simulated Venus surface atmospheric condition using the NASA Glenn Extreme Environments Rig (GEER). Corrosion coupons were characterized by gravimetric analysis, X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. Tensile coupons were mechanically interrogated at 460 °C prior to and after GEER exposure. Both Ti-6Al-4V variants formed a thin TiO2 outer scale, a region rich in carbon at the scale-metal interface, and a relatively thick α-case (oxygen-stabilized α-Ti) region. Cu-contamination from fabrication obfuscated SS304 corrosion coupon analysis but not mechanical interrogation. At 460 °C, AM Ti64 was stronger but less ductile than wrought Ti64, and both Ti64 variants were stronger but less ductile than 304SS. No appreciable degradation in mechanical properties (yield strength, ultimate tensile strength, ductility, modulus) was observed for Ti64, AM Ti64, or 304SS after the 10-day Venus exposure, but statistically significant differences in UTS of AM Ti64 (slight decrease after exposure) and wrought Ti64 (slight increase after exposure) were observed and are attributed to microstructural annealing changes rather than corrosion-induced.

Environmental barrier coatings (EBCs) are an enabler for SiC/SiC ceramic matrix composites (CMCs) in gas turbines. One of the most critical EBC failure modes is steam oxidation-induced failure. Long steam oxidation life, therefore, is key to the reliability of CMC components. The chemistry of the EBC and underlying CMC substrate has a significant impact on the steam oxidation resistance of the current state-of-the-art EBC (Gen 2 EBC: Si/ Yb2Si2O7). NASA has developed chemically modified Gen 2 EBCs (Mod Gen 2 EBCs) that reduce the parabolic steam oxidation rate constant of the Gen 2 EBC by more than tenfold. Plasma sprayed Yb2Si2O7 contains a high level of amorphous phases. Post-spray annealing is one way to achieve phase stability in the Gen 2 EBC. This study investigates the effects of three EBC variables (EBC chemistry, substate chemistry, and post-spray annealing) on the steam oxidation kinetics of Mod Gen 2 EBCs at two temperatures (1300 degrees C, 1350 degrees C). Aluminum and boron in the SiO2 oxide scale were the key elements having an overarching influence on EBC oxidation kinetics. Complex interactions among the three EBC variables dictated the concentration of aluminum and boron in the SiO2 oxide scale and thus the EBC oxidation kinetics.

Niobium (Nb) alloy C103 is commonly used in high-temperature aerospace propulsion applications due to its strength at temperatures above 1200 °C and low ductile-to-brittle transition temperature. With the rise of interest in additive manufacturing (AM) for refractory material processing, it is crucial to ensure that the properties of AM-produced C103 match those of conventionally processed materials, particularly concerning ductility and high-temperature performance. This study evaluates C103 produced via laser powder bed fusion (L-PBF) by conducting uniaxial tensile tests from room temperature to 1400 °C in a high-vacuum environment and comparing the results to those of conventionally processed wrought C103 tested under identical conditions. Results from tensile testing indicated that as-built L-PBF C103 has comparable tensile properties to wrought (worked) C103, while hot isostatic pressing (HIP) post-processed L-PBF C103 exhibited similar properties to wrought (recrystallized) C103. In all conditions, whether L-PBF or wrought, C103 exhibited minima in tensile elongation in the 600–800 °C temperature range; however, this was not accompanied by a change in fracture mechanism. HIP post-processing marginally improved material density but significantly reduced low-to-intermediate temperature strength due to recovery of the microstructure and grain growth. These insights into the mechanical behavior of L-PBF C103 enhance confidence in its use for reliable high-temperature aerospace components.

A cast Ni50.3Ti29.7Hf20 (at.%) high-temperature shape memory alloy was hot deformed in compression at temperatures from 700 degrees C to 1100 degrees C and strain rates from 0.001 s-1 to 10 s-1. Tests were conducted in vacuum to true strains up to 90% using a Gleeble test system. The flow responses demonstrated a range of behaviors, with most samples exhibiting an initial yield followed by gradual flow softening, ultimately reaching a steady state at a lower flow stress indicative of dynamic recrystallization. In contrast, tests conducted at low temperatures and high strain rates exhibited a nearly flat steady state after yielding, suggesting dynamic recovery. The Prasad Dynamic Material Model was utilized to calculate processing maps from the flow stress data, supported by optical and electron microscopy microstructural observations. The analysis revealed that favorable processing conditions for the cast microstructure lie within a range of 800 degrees C to 1100 degrees C at strain rates between 0.001 s-1 and 0.1 s-1, allowing for optimization of processing parameters for enhanced microstructural control. These results provide valuable insights into the thermo-mechanical processing of NiTiHf high-temperature shape memory alloys, paving the way for future development of wrought processes and products for this alloy.

Boron nitride nanotubes are promising materials for polymeric composites due to their electrical insulation and thermal conductivity properties. In this work, boron nitride nanotubes (BNNTs) are dispersed in a polymer solution that is then spun and drawn to make polymeric fibers with aligned bundles of long BNNTs. These polymer/BNNT fibers are then studied to determine the relationship among processing, structure, and properties. A sonication-centrifuge procedure was conducted to preserve longer BNNTs within the polymer structure and improve the alignment of BNNTs within the fiber. Herein, changes in the internal structure of PAN/BNNT fiber are mapped, highlighting the importance of the dry-jet wet spinning air gap and cold and hot drawing stages to achieve high orientation of BNNTs and a higher draw ratio of 25x. These fibers can be used to produce thermally conductive, electrically insulating composites, which have significant applications in electronics. This approach is scalable and can also be used to produce high-performance neat BNNT fibers.

Thermochemical interactions between Ca2Sm8(SiO4)6O2 (CSmS) apatite and molten calcium-magnesiumaluminosilicate (CMAS) glass having CaO/SiO2 mole ratio 0.37 have been evaluated. CSmS apatite-CMAS diffusion couples were annealed at 1200, 1300, and 1400 degrees C for 1-50 h. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high angle annular dark field imaging, selected area electron diffraction and energy dispersive x-ray spectroscopy were used to characterize the phases formed during the reaction. Formation of a distinct cyclosilicate [Ca3Sm2(Si3O9)2] layer was observed at apatite-CMAS interface in couples heat treated at 1200 degrees C but not at higher temperatures. The cyclosilicate layer nucleated at the apatiteCMAS reaction front, continued to grow into the residual melt and eventually detached from the apatite substrate. Residual CMAS melt became Ca-lean when cyclosilicate was present. Formation of MgCaSi2O6 diopside and dendrites of CaSiO3 wollastonite was also observed within the residual CMAS at 1200 degrees C. At 1300 and 1400 degrees C molten CMAS, due to its much lower viscosity, infiltrated the apatite substrate through open pores and along the grain boundaries. Ca2Sm8(SiO4)6O2 apatite thermal/environmental barrier coating has the potential to provide protection against CMAS attack up to about 1200 degrees C but not at higher temperatures.

Bioremediation using microbes is an eco-friendly approach being explored for reclaiming PAH-contaminated areas. However, isolation and screening of potential bacteria to degrade PAHs are very laborious and cumbersome. To alleviate this issue, we describe a rapid method for screening the bacterial cultures for their ability to degrade PAHs using Folin-Ciocalteu (FC) assay. Six hundred bacterial isolates were tested for their ability to degrade PAH using FC assay. The cultures capable of degrading PAH show blue colouration, resulting from the reaction of FC reagent with phenolic intermediates generated during PAH degradation. Out of the 600 cultures screened, 64 showed an ability to degrade PAH. This study provides a very easy, rapid, less laborious, and sensitive method to screen a large number of bacterial cultures for their ability to degrade PAH.

One of the major environmental concerns today is hydrocarbon contamination resulting from the activities related to the petrochemical industry. Crude oil is a complex mixture of hydrocarbons like alkanes, naphthene and polycyclic aromatic hydrocarbons (PAHs). PAHs are known to be highly toxic to humans and animals due to their carcinogenic and mutagenic effects. PAHs are environmentally recalcitrant due to their hydrophobicity which makes them difficult to degrade, thus making them persistent environmental contaminants. The mechanical and chemical methods in practice currently to remove hydrocarbon contaminants have limited effectiveness and are expensive. Bioremediation is a cost-effective technology for treating hydrocarbon-contaminated sites as it results in the complete mineralisation of the pollutant. This study demonstrates the degradation of crude oil and associated PAHs using ten fungal cultures isolated from the aquatic environment. The current study reported a 98.6% and 92.9% reduction in total PAHs in crude oil by Fusarium species, i.e. isolate NIOSN-T4 and NIOSN-T5, respectively. The fungal isolate, NIOSN-T4, identified as Fusarium equiseti, showed maximum PAH degradation efficiency of LMW PAHs 97.8%. NIOSN-M126, identified as Penicillium citrinum , exhibited a 100% removal of HMW PAHs. Microorganisms possess an untapped potential for various applications in biotechnology, and the current study demonstrated the potential of marine fungi for use in the bioremediation of xenobiotic hydrocarbons in the environment.

In situ hot-stage high-resolution transmission electron microscopy (HRTEM) provides unique capabilities for quantifying the dynamics of interfaces at the atomic level. Such information is critical for understanding the theory of interfaces and solid-state phase transformations. This paper provides a brief description of particular requirements for performing in situ hot-stage HRTEM, summarizes different types of in situ HRTEM investigations and illustrates the use of this technique to obtain quantitative data on the atomic mechanisms and kinetics of interface motion in precipitation, crystallization and martensitic reactions. Some limitations of in situ hot-stage HRTEM and future prospects of this technique are also discussed.

Several grades of alumina-forming austenitic (AFA) stainless steel (SS) alloys were probed after exposure to simulated sCO2-based 467 degrees C Venus surface atmospheric conditions using the NASA Glenn Extreme Environ- ments Rig (GEER) for 30 days. AFA samples were characterized by gravimetric analysis, X-ray diffraction (XRD), and electron microscopy. All AFA samples formed multilayered scales in which the outer layer is mainly magnetite (Fe3O4) and nickel sulfides (Ni3S4, Ni4S3), and the inner layer is mainly chromia containing aluminum, (Cr,Al)2O3. The most resistant of the AFA alloys exhibited specific weight gain corrosion resistance similar to SS304, which formed an inner (Fe3_xCrxO4) spinel.

Numerous applications from insulation to catalytic supports and fuel cells can benefit from lightweight, high surface area, mesoporous materials which maintain their mesoporous structure to temperatures of 600 to 1200 °C. Polymeric aerogels are limited to temperatures of nominally 400 °C due to thermal degradation of organic groups. Silica aerogels begin to densify by 700 °C. A number of aerogel systems show stability at higher temperatures, including alumina, alumina silicates, yttrium-doped alumina, and zirconia and yttria-stabilized zirconia aerogels. Within a given chemical composition, the morphology and textural stability of a mesoporous structure is dependent upon the synthesis method used. Other important considerations in choosing an aerogel composition include the time at temperature required for a given application, phase transformations inherent in a given system, and approaches to phase stabilization such as introduction of dopants into the backbone structure. Reinforcement of the aerogel through a composite approach also is addressed.

High temperature corrosion behavior of Ca2Gd8(SiO4)6O2 (CGdS) apatite has been investigated in the presence of molten calcium-magnesium-aluminosilicate (CMAS) glass having the composition 21.9 CaO -4.3 MgO -5.4 Al2O3 -63.0 SiO2 -4.3 Na2O -0.8K2O -0.1 Fe2O3 (weight %). CGdS apatite powder was prepared by solid state synthesis from constituent oxides. Pellets of CGdS apatite + CMAS mixed powder and CGdS-CMAS diffusion couples were annealed at 1200, 1300, 1400, and 1500 degrees C for 1 and 20 h in ambient atmosphere. Development of phases in heat treated specimens was characterized using various analytical techniques as X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high angle annular dark field imaging, selected area electron diffraction and energy dispersive X-ray spectroscopy. In both pellets and diffusion couples, monoclinic cyclosilicate Ca3Gd2(Si3O9)2 formed from reaction of apatite with CaO in the CMAS melt only in samples heat treated at 1200 degrees C for 1 and 20 h or at 1300 degrees C for 1 h. Triclinic CaSiO3 and monoclinic diopside MgCaSi2O6 were also observed in samples annealed at 1200 and 1300 degrees C. At 1400 and 1500 degrees C, because of its low viscosity, CMAS infiltrated along the pores and grain boundaries of the apatite substrates in diffusion couples. Phase compositions predicted from thermochemical computation were in good agreement with those observed experimentally. Ca2Gd8(SiO4)6O2 apatite has the potential for being an effective T/EBC in circum-venting the penetration of molten CMAS up to about 1300 degrees C but not at higher temperatures.

Goa, a small state in India, is a tourist hotspot known for its coastline and beaches. Anthropogenic activities lead to pollution in the environment. Amongst many other pollutants, polycyclic aromatic hydrocarbons represent a major class of contaminants owing to their widespread distribution and protracted environmental persistence. No information is available about the levels of Polycyclic aromatic hydrocarbon (PAH) contamination in the sediments along the coastline of Goa. The study aimed to establish a baseline for PAH concentrations in the sediments along the shoreline to help comment on the pollution levels caused and thereby understand the risk and their impact on the marine life therein. The total concentration of PAHs along the selected sampling sites of the Goa coastline was 1.00 to 875 μg g −1 . Maximum PAH concentrations were detected in the Divar island mangrove (875 μg g −1 ); the least was observed at Galgibaga beach (365 μg g −1 ). The results revealed that the sediment of the Goa coastline is heavily contaminated with PAH. Source apportionment of PAHs was analysed based on diagnostic ratios, and results exhibited that petroleum products and their combustion were primarily responsible for their generation. The results of risk quotients showed that the values are way above effect range median (ER-M), indicating these could pose a high risk to the ecosystem.

A FIB/STEM interfacial study was performed on a TBC/Ti2AlC MAX phase system, oxidized in an aggressive burner rig test (Mach 0.3 at 1300 °C for 500 h). The 7YSZ TBC, α-Al2O3 TGO, and MAXthal 211TM Ti2AlC base were variously characterized by TEM/STEM, EDS, SADP, and HRTEM. The YSZ was a mix of “clean” featureless and “faulted” high contrast grains. The latter exhibited ferro-elastic domains of high Y content tetragonal t″ variants. No martensite was observed. The TGO was essentially a duplex α-Al2O3 structure of inner columnar plus outer equiaxed grains. It maintained a perfectly intact, clean interface with the Ti2AlC substrate. The Ti2AlC substrate exhibited no interfacial Al-depletion zone but, rather, numerous faults along the basal plane of the hexagonal structure. These are believed to offer a means of depleting Al by forming crystallographic, low-Al planar defects, proposed as Ti2.5AlC1.5. These characterizations support and augment prior optical, SEM, and XRD findings that demonstrated remarkable durability for the YSZ/Ti2AlC MAX phase system in aggressive burner tests.

Polycyclic aromatic hydrocarbons (PAHs) are released into the environment via several natural and anthropogenic sources leading to long-term consequences that severely affect the environment, ecosystem, human and animal health. In this study, the extent of PAH pollution was measured at two estuarine locations of the major rivers of Goa, Zuari and Mandovi. Out of the 16 PAHs marked as carcinogenic, 13 PAHs were detected from the sediment samples collected. Bacterial strains were isolated from these PAH-contaminated sediments using conventional plating method. Six of these selected bacterial isolates were checked for their efficacy to degrade both low (phenanthrene) and high molecular weight (fluoranthene and pyrene) hydrocarbons. Amongst them, two bacterial isolates exhibited over 80% degradation of phenanthrene. Isolate NIOSV7 (Pseudomonas pachastrellae) could degrade 83.33% phenanthrene, 40.22% fluoranthene and 45.28% pyrene, while isolate NIOSV8, identified as Pseudomonas oleovorans, showed 85.09% phenanthrene, 70.61% fluoranthene and 67.18% of pyrene degradation in 120 h, at 100 ppm initial concentration of phenanthrene and 75 ppm of fluoranthane and pyrene. Though many Pseudomonas sp. are documented for PAH degradation, this is the first report showing PAH-degradation by Pseudomonas oleovorans strain. This study also shows that the bacteria isolated from estuarine sediments contaminated with PAH have good potential to degrade low and high molecular weight PAHs. These toxic pollutants can be bio-transformed into nontoxic metabolites with the help of microorganisms isolated from the same habitat.

A thermal barrier coating (TBC) system survived 500 hours in aggressive, 1300 degrees C burner rig testing. The yttria-stabilized zirconia (7YSZ) TBC was plasma sprayed on an oxidation-resistant Ti2AlC-type MAX phase and tested in a jet fuel burner at 100 m/s, using 5 hours cycles. No coating spallation or surface recession was observed; Al2O3-scale growth produced a slight 2.4 mg/cm(2) mass gain. The coating surface exhibited craze-cracked colonies of [111](flourite) textured columns, with no visible moisture attack. The 20 mu m alumina scale remained intact under the YSZ face, about twice that producing failure for TBC/superalloy systems. TiO2 nodules, initially formed on the uncoated backside, were removed, and Al2O3 was etched through volatile hydroxides formed in water vapor (similar to 10%). Overall, the test indicated exceptional stability of the YSZ/Al2O3/Ti2AlC system under turbine conditions due in large part to close thermal expansion matching.

The development of more efficient engines and power plants for future supersonic transports depend on the advancement of new high-temperature materials with temperature capabilities exceeding those of Ni-based superalloys. Having theoretical modelling techniques to aid in the design of these alloys would greatly facilitate this development. The present paper discusses a successful attempt to correlate theoretical predictions of alloy properties with experimental confirmation for ternary NiAl-Ti alloys. The B.F.S. (Bozzolo- Ferrante-Smith) method for alloys is used to predict the solubility limit and site preference energies for Ti additions of 1 to 25 at. % to NiAl. The results show the solubility limit to be around 5 % Ti, above which the formation of Heusler precipitates is favored. These results were confirmed by transmission electron microscopy performed on a series of NiAl-Ti alloys.

Thermochemical interactions between a calcium-magnesium aluminosilicate (CMAS) glass and ytterbium disilicate (Yb2Si2O7), a candidate environmental barrier coating (EBC) material, have been investigated. Pellets of Yb2Si2O7 and CMAS glass powder were heat treated at 1200, 1300, 1400 and 1500 degrees C for 1, 10 and 50 h in air. Powder X-ray diffraction was employed to identify the resulting phases. In a second series of experiments, Yb2Si2O7 substrates were prepared by hot pressing, and cylindrical wells were drilled into the material surface. CMAS glass powder was added to the wells to achieve a loading of similar to 35 mg/cm(2) and subsequently heat treated at 1200, 1300, 1400 and 1500 degrees C for durations of 1, 10 and 50 h in air. Sample cross-sections were characterized using scanning electron microscopy, X-ray energy-dispersive spectroscopy, X-ray diffraction, electron microprobe analysis and transmission electron microscopy to evaluate the resulting microstructure, phases and compositions at the CMAS/Yb2Si2O7 interface. Dissolution of ytterbium silicate into molten CMAS followed by precipitation of Yb2Si2O7 coupled with CMAS grain boundary penetration at elevated temperatures were the dominant mechanisms by which CMAS effectively infiltrated and altered the Yb2Si2O7 substrate microstructure.

A slurry process was employed to develop advanced environmental barrier coatings (EBCs) for SiC based composites. Yb2Si2O7 and mullite (3 Al2O3.2 SiO2) were chosen as the base materials for the bond coat to enable temperatures beyond the melting point of the current silicon bond coat (1414 degrees C). Various sintering aids, such as mullite, Yb2Si2O7, Al2O3, and silicon enabled sintering at 1500 degrees C - 1550 degrees C. Yb2Si2O7 was used as the top coat to provide water vapor recession resistance. A HfSiO4 intermediate layer prevented the 1500 degrees C eutectic reaction at the mullite/Yb2Si2O7 interface. Parabolic oxidation behavior and good adhesion as well as chemical and microstructural stability were observed after 500 h / 500 cycle steam oxidation at 1427 degrees C in 90 % H2O-10 % O-2 steam. Kinetic analyses on Yb2Si2O7-coated SiC showed the independence of TGO growth rates on EBC thickness indicating that the oxidant permeation through the silica scale is the rate controlling factor.

The mechanical grinding of prealloyed NiAl powder in liquid nitrogen (cryomilling) results in an intermetallic matrix composite where micron sized particle free aluminide cores (grains) are surrounded by thin mantles comprised of nanometer sized A1N particles and NiAl grains. Under high temperature, slow strain rate conditions both compressive and tensile creep testing have shown that the mechanical strength of hot extruded cryomilled NiAl approaches the levels exhibited by advanced NiAl-based single crystals and simple Ni-based superalloys. Transmission electron microscopy of cryomilled materials tested between 1100 and 1300 K revealed little, if any, dislocation structure within the mantle regions, while the NiAl cores contained subgrains and dislocation networks after testing at all strain rates between 10-4 and 10-8 s-1. These and other microstructural observations suggest that creep strength is the result of a fine NiAl grain/subgrain size, the inability of dislocations to move through the mantle and stabilization of the microstracture by the A1N particles.