Oxidation protection of Mo-Si-B alloys by magnetron-sputtered coatings

Mo-Si-B alloys with melting temperature above 2000 °C are attractive high temperature materials offering significantly enhanced operating temperatures compared to those of the currently used Ni-based superalloys. However, their oxidation behavior is poor at temperatures below 1000 °C, suffering from evaporation of MoO3. Above 1000 °C oxidation is characterized by a transient state showing considerable mass loss followed by a steady state condition with reduced mass change. To mitigate this degradation by oxidation, application of coatings is an appropriate method ensuring the formation of slowly growing protective scales. The presentation summarizes recent results on overlay coatings that were deposited on coupons of a Mo-9Si-8B (in at.%) alloy using magnetron sputtering. A double layer design was applied: a 2 µm thick intermediate Mo5SiB2 layer to prevent interdiffusion and approximately 5 µm thick protective topcoats with different chemical compositions: Mo-45Si-25B, Mo-55Si-10B, Mo-29Si-15B, Mo-48Si-24Al, Mo-71Si-8Al (all in at.%). The amorphous as-deposited coatings were annealed in a vacuum furnace. In the boron containing Mo-Si topcoats, the MoSi2 and MoB phases formed as well as the Mo5Si3 phase in the Mo-29Si-15B coating. In the annealed Mo-48Si-24Al and Mo-71Si-8Al topcoats, the C40-Mo(Si,Al)2 and C11b-MoSi2 phases were observed, respectively. The oxidation behavior of the coated samples was investigated at 800, 1100 and 1300 °C under cyclic condition in laboratory air. The dwell time at high temperature was 10 or 20 h and the samples were tested for up to 10 cycles. Microstructural examinations of the coated samples were carried out using scanning electron microscopy, energy-dispersive X-ray spectroscopy, glow discharge optical emission spectroscopy and X-ray diffraction measurements. Please click Additional Files below to see the full abstract

Hexagonal microlasers based on organic dyes in nanoporous crystals

Molecular sieves, such as nanoporous AlPO_4-5, can host a wide variety of laser active dyes. We embedded pyridine 2 molecules as a representative of a commercially available dye which fits into the channel pores of the host matrix. Many efficient dye molecules, such as rhodamines, do not fit into the pores. But the amount of encapsulated dyes can be increased by modifying the structure of the dyes such that they match the host templates. The resulting microlasers have properties that depend on size and shape of the microresonators, and we discuss a model for microscopic hexagonal ring resonators. In terms of pump needed to reach lasing threshold molecular sieve microlasers are comparable to VCSELs. For dyes which fit into the pores we observed a partial regeneration of photo-induced damage.Comment: 10 pages, 16 figure

Re-evaluating the taxonomic status of Phaeoisariopsis griseola, the causal agent of angular leaf spot of bean

Angular leaf spot of Phaseolus vulgaris is a serious disease caused by Phaeoisariopsis griseola, in which two major gene pools occur, namely Andean and Middle-American. Sequence analysis of the SSU region of nrDNA revealed the genus Phaeoisariopsis to be indistinguishable from other hyphomycete anamorph genera associated with Mycosphaerella, namely Pseudocercospora and Stigmina. A new combination is therefore proposed in the genus Pseudocercospora, a name to be conserved over Phaeoisariopsis and Stigmina. Further comparisons by means of morphology, cultural characteristics, and DNA sequence analysis of the ITS, calmodulin, and actin gene regions delineated two groups within P. griseola, which are recognised as two formae, namely f. griseola and f. mesoamericana

Analysis of peripheral inflammatory T cell subsets and their effector function in patients with Birdshot Retinochoroiditis

Birdshot Retinochoroiditis (BSRC) is a progressive non-infectious intraocular inflammation that affects choroid and retina. Inflammatory processes have adverse effects on vision by affecting photoreceptor-bearing cells that do not regenerate. This study aimed at characterizing inflammatory CD4(+) and CD8(+) T cell subsets in the peripheral blood of active and inactive BSRCs. Furthermore, we correlated phenotypical and functional immunological analyses with clinical data. We observed a slight increase of terminally differentiated effector memory CD8(+) T cells expressing CD45RA (T-EMRA) in blood of inactive, compared to active BSRCs. Moreover, we identified a trend for a decreased population of T(H)2 cells and increased T(H)1 frequencies in active BSRCs, a typical sign of ongoing autoimmune processes. Functional assays demonstrated severe and overall impairment of effector function of both, CD4(+) and CD8(+) inflammatory T cells, which might reflect T cell exhaustion. Although the eye is the main site of inflammation in BSRC, we observed altered T cell subset compositions in the peripheral blood, dependent on the disease status. Our results indicate that T cells may play a major role in BSRC pathology, although our cohort size is too limited for definitve conclusions. Future studies with larger BSRCs have to be performed

Lifetime of environmental/thermal barrier coatings deposited on an Nb/Nb5Si3- based alloy with FeB-Modified M7Si6-based bond coat

To enhance the performance of aircraft engines, high temperature materials are required being capable to operate at temperatures significantly higher than the temperature limit of about 1150°C approached for Ni-based superalloys currently employed. Nb/Nb5Si3-based composites are promising candidates for turbine engine applications at temperatures up to 1300°C, exhibiting balanced mechanical properties and reduced density compared to Ni-based superalloys [1]. To use these composites in gas turbine combustion atmosphere, environmental/thermal barrier coatings (E/TBCs) are required to protect them against heat, degradation in flowing water vapour and chemical attack of calcium-magnesium-alumino-silicate (CMAS)