Factors affecting ceramic abradable coating damage accommodation

High temperature abradable coatings are based on thermal barrier coating compositions and play an integral role in not only providing thermal protection for turbine shrouds, but also in maintaining blade tip clearances for increased turbine efficiencies. As turbine material technologies advance, there is a push for the development of abradable coatings that can withstand more severe operating conditions and retain the optimum balance of abradability and durability. However, as abradable coating technologies are pushed to higher temperatures and greater capabilities, such as compatibility with ceramic matrix composites, there are significant challenges in understanding the underlying mechanisms that aid the design of these inherently brittle materials enabling them to accommodate damage in a controlled manner. This study will first discuss the theories for fracture mechanics and wear mechanisms in ceramics and how they can be related to abradable coatings. The influence of microstructural defects present in current technology ceramic abradable coatings on the preferred wear behavior of these systems will then be investigated. The coatings to be compared are air plasma sprayed dysprosia- or yttria- stabilized zirconia with varying fractions of pore former and secondary phases. The wear of both as-received and aged coatings will be tested, and deformation mechanisms will be reported. Links between different defects, their evolution with aging, and observed wear behavior will be compared with two competing definitions of desired abradable damage accommodation mechanisms, with one being energy dissipation through plastic deformation and the other depending on crack propagation and frictional sliding of the removed material to dissipate energy

Can volatiles emitted by compost during spawn run be used to detect green mould infection early?

In recent years green mould (Trichoderma aggressivum) has presented big problems to the Dutch mushroom industry. T. aggressivum infects compost at a very early stage and in the Dutch situation infection most likely takes place at the compost yard. Even though compost producers in the Netherlands are very keen to prevent green mould problems, occasionally still a number of crops get infected. Therefore there is a need for a reliable method that allows early detection of Trichoderma green mould. Although qPCR methods have been developed for quantitation of T. aggressivum, these cannot be used for detection in compost. In the Netherlands spawn run is performed in bulk at the compost yards and is referred to as phase 3 composting. During this process, spawned compost is incubated in tunnels and ventilated with large volumes of air to control compost temperature. During this process the compost is inaccessible for sampling. Literature data showed that Agaricus bisporus and T. aggressivum use volatiles to affect each other’s growth rate. We tested the possibility to detect Trichoderma green mould using the volatiles that are emitted during spawn run. This eventually could lead to a sophisticated non-invasive detection method of T. aggressivum in the process air of the tunnels, without the need to sample inside the tunnel during spawn run. For this we compared volatiles that are produced in non-infected compost with volatiles that are produced in infected compost. In our experimental model, 300 g of phase 2 compost, is spawned and inserted in aerated glass vessels. Compost is colonised at an air temperature of 24°C. After 7, 10 and 14 days of spawn run, process air is sampled both in infected and non-infected cultures and analysed by coupled gas chromatography mass spectrometry (GC-MS). During this 14-day period white mushroom mycelium develops in the non-infected compost. In the infected compost the compost turns black with occasional tufts of white mycelium and green spores. Volatile blends that are produced during normal compost colonisation (when Agaricus bisporus interacts with Scytalidium thermophilum and other micro flora present in compost) differ from those produced during colonisation of T. aggressivum infected compost. Some of the volatiles appear to be specific for T. aggressivum infected compost. Next to this also consistent differences in the overall pattern of volatile production are seen. Infections with T. harzianum, T. atroviride, an Aspergillus species, or Smokey mould (Penicillium citreonigrum) produce different volatile patterns. Significant differences between the volatile blends of infected and non-infected compost are visible after 7 days of compost colonisation. In commercial practice of phase 3 composting, tunnels are likely to be partially infected. On-going research is directed at studying larger amounts of compost that is only partially infected

On the CMAS Problem in Thermal Barrier Coatings%253A Benchmarking Thermochemical Resistance of Oxides Alternative to YSZ Through a Microscopic Standpoint

This study focuses on experimental modelling of the failure of Thermal Barrier Coatings (TBCs) due to attack of CMAS (Calcia-Magnesia-Alumina-Silicate), which is often found in harsh environments, via glassy phase infiltration. Volcanic ash and dust, sand particles, and fly ash, which contain CMAS, are imminent threats impeding predictable lifetimes of TBCs. Such incurrence directly affects the geometry and clinging to bond coat, and intrinsic material properties such as thermal conductivity and crystal structure of TBC are modified after exposure to CMAS, which ultimately results in delamination, spallation and failure of the coating material. The scope of this work is to survey the reactivity of CMAS with various oxide systems, and evaluate possible oxide systems that can be replaced and%252For used with Yttria-stabilized Zirconia (YSZ) by investigating the penetration depth and reactivity after sintering with CMAS. A cost-effective method to observe the reaction of candidate oxides with CMAS is suggested and administired%253B understanding the main mechanism that causes the failure of top coat in the wake of CMAS infiltration, and seeking solutions for the problem is performed by taking advantage of Scanning Electron Microscopy (SEM). Recently suggested ceramic oxide systems that form in pyrochlore structure, some perovskite structures in various compositions, monazite, mullite and YSZ are studied. The possible outcome consequent upon CMAS infiltration are concluded and course for designing novel material systems that are expected to withstand the CMAS attacks better than the state-of-the-art 4mole%25 YSZ is defined. 5%25 mole Yb-doped SrZrO3(5Yb-SZ) and favored pyrochlores such as Gd2r2O7 and GdYbZr2O7 are found to be better mitigating CMAS attacks

Microstructural evaluation with type i hot corrosion degradation of gas turbine alloys during burner-rig testing

The hot corrosion resistance of selected gas turbine alloys was evaluated, as a baseline for assessing candidate new hot-section materials. The alloys were tested under burner rig exposures, using ASTM standard seawater for the salt contaminant and combustion conditions that provide representative materials evolution and degradation behavior relative to what is observed with marine gas turbines under service environments. Modern characterization techniques were utilized to evaluate the hot corrosion behavior and resistance of the evaluated material systems, to observe the degradation of the alloys and to study the underlying degradation mechanisms active during hot corrosion attack. Please click Additional Files below to see the full abstract

Measurement of Interfacial Shear Mechanical Properties in Thermal Barrier Coating Systems by a Barb Pullout Method

A test technique has been developed to facilitate evaluation of the fracture characteristics of coatings and interfaces in thermal barrier coating (TBC) systems. The methodology has particular application in analyzing delamination crack growth, where crack propagation occurs under predominantly mode II loading. The technique has been demonstrated by quantitatively measuring the effective delamination fracture resistance of an electron-beam physical vapor deposition TBC

Effect of Calcium Source, Dietary Calcium Concentration, and Gestation Phase on Various Bone Characteristics in Gestating Gilts

Sixty gravid crossbred gilts were allotted to a 2 x 3 x 2 factorial arrangement of treatments: two Ca sources (sun-cured alfalfa meal and CaC03), three dietary concentrations of Ca (50, 75, and 100% of NRC requirements), and two phases of gestation (55 and 105 d). The objectives were to determine the effect of Ca source, dietary Ca concentration, and gestation phase on bone characteristics (bone breaking strength, bone ash percentage, bone density, and bone ash density in the rib, thoracic, and coccygeal bones), to correlate bone responses to determine relative bone activity, and to determine reliability of the coccygeal bones as indicators of Ca status in the body. At 55 d, rib strength and coccygeal ash content were lower (P \u3c .01) than at 105 d of gestation. A gestation phase x Ca concentration (P \u3c .05) interaction occurred. As Ca concentration increased, thoracic strength and rib ash responded quadratically during each gestation phase, for which at 55 d a minima and at 105 d a maxima was produced at 75% of NRC. A Ca source x Ca concentration ( P \u3c .05) interaction occurred. Gilts fed alfalfa had the lowest rib bone and ash density when fed 75% of NRC for Ca, whereas gilts fed CaC03 were highest at this level of Ca compared with the other concentrations. Generally, all bones were positively correlated with respect to their response to dietary Ca concentration. Few negative correlations were observed. At this level of physiological maturity, there was no effect of Ca source and little effect of gestation phase on the bone variables measured at the dietary Ca concentrations used in this experiment. The rib and thoracic bones seem to be the most responsive to dietary Ca concentration

Using E. coli NfsA as a model to improve our understanding of enzyme engineering

There is a substantial gap between the levels of enzyme activity that nature can achieve and those that scientists can evolve in the lab. This suggests that conventional directed evolution techniques involving incremental improvements in enzyme activity may frequently fail to ascend even local fitness maxima. This is most likely due to the difficulty for step-wise evolutionary approaches in effectively retaining mutations that are beneficial in combination with one another, but on an individual basis are neutral or deleterious (i.e., exhibit positive epistasis). We sought to determine whether a superior enzyme identified using a simultaneous mass site directed mutagenesis approach could have been identified using a step-wise approach. We conducted simultaneous mass randomisation of eight key active site residues in Escherichia coli NfsA, a nitroreductase enzyme that has diverse applications in biotechnology. Using degenerate codons, we generated a diverse library containing 394 million unique variants. We then applied a powerful positive selection using chloramphenicol which is toxic to E. coli but can be detoxified via nitro-reduction. This has enabled us to recover a diverse range of highly active nitroreductase variants. For two of the most active variants, we have created all possible combinations of single mutations. This allowed us to examine whether a step-wise mutagenesis pathway could have also yielded these enzymes. As anticipated, we identified complex epistatic interactions between residues in these enzyme variants. We have also investigated the “black-box” effect of enzyme engineering, examining the consequences that evolving NfsA towards one specialist activity had on the other promiscuous activities of NfsA. Variants generated in this study have also had practical applications, in particular for targeted cell ablation in zebrafish. We have identified NfsA variants that are highly active with nil-bystander prodrugs that can selectively ablate nitroreductase expressing cells without harm to adjacent cells. In ongoing work, our lead variants are being evaluated for their utility in transgenic zebrafish models of degenerative disease

Courtship pheromones in parasitic wasps: comparison of bioactive and inactive hydrocarbon profiles by multivariate statistical methods

Cuticular hydrocarbons play a significant role in the regulation of cuticular permeability and also in the chemical communication of insects. In the parasitoid Lariophagus distinguendus (Hymenoptera: Pteromalidae), male courtship behavior is mediated by a female-produced sex pheromone. Previous studies have shown that the chemicals involved are already present in the pupal stage of both males and females. However, pheromonal activity in males decreases shortly after emergence. This pheromonal deactivation occurs only in living males, suggesting an active process rather than simple evaporation of bioactive compounds. Here, we present evidence that the sex pheromone of L. distinguendus is composed of a series of cuticular hydrocarbons. Filter paper disks treated with nonpolar fractions of cuticular extracts of freshly emerged males and females, 72-hr-old females, and yellowish pupae caused arrestment and stimulated key elements of courtship behavior in males, whereas fractions of 72-hr-old males did not. Sixty-four hydrocarbons with chain length between C25 and C37 were identified in the fractions by gas chromatography-mass spectrometry (GC-MS). Methyl-branched alkanes with one to four methyl groups were major components, along with traces of n-alkanes and monoalkenes. Principal component analysis, based on the relative amounts of the compounds, revealed that cuticular hydrocarbon composition differed among all five groups. By using partial least squares-discriminant analysis, we determined a series of components that differentiate bioactive and bioinactive hydrocarbon profiles, and may be responsible for pheromonal activity of hydrocarbon fractions in L. distinguendus