Yttrium silicates are promising materials for improved oxidation and erosion protection for carbon fiber‐reinforced composites. A two‐layer coating system of low‐pressure plasma‐sprayed yttrium silicate on chemical vapor deposition‐SiC‐precoated C/C–SiC was tested under atmospheric re‐entry conditions simulated within a plasma wind tunnel test facility. The thermal expansion behavior of Y2SiO5 and Y2Si2O7 was investigated. The chemical compatibility with and without increasing oxygen partial pressure at the interface of the two‐layer system was calculated by the CALPHAD method. The calculations were compared with experimental results. Furthermore, a thermodynamic explanation is presented to understand and predict the observed coating failure mechanism, identified as blister formation.
Tasks that test conservation of equation and function under transformations of variable illustrate an extension of Piaget's conservation methodology to relational concepts. Less than half of the 30 students interviewed in grades 5-12 gave conserving responses to any one of the four tasks. Mathematical background was a significant factor in performance. Students who did not conserve harbored two misconceptions: (a) that changing a variable symbol implies changing the referent and (b) the linear ordering of the alphabet corresponds to the linear ordering of numbers.
Optical components for space optics -especially coated optical elements which represent the external surfaces of optical space instrumentation -have to work under harsh operation conditions like thermal loads, irradiation by photons, electrons and protons, as well as in atomic oxygen environments at low earth orbits. Additionally they have to withstand other cross contamination coming from the spacecraft. Therefore, the stability against these influences is a decisive factor for the application performance of optical coatings in space-borne devices. Some very recent results, based on the Surface Effects Sample Monitor (SESAM) flight experiment carried out aboard the ORFEUS-Shuttle Pallet Satellite (SPAS), STS-5 1, Discovery, are presented here along with laboratory experiments in an UHV-surface analysis system. The topics include ground simulation of selective and complex particle bombardment of optical coatings analysed by XPS as well as the verification of these results by flight experiments in combination with optical measurements (transmission, scattering).
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