Development of a cathode resistant to vacuum chamber operation conditions

The aim of this work is to develop a thermoemission cathode that would ensure the required operating parameters and remain operable after long, several-day, exposure to the air without any additional ampulization. Cathode thrmoemitter degradation (“poisoning”) processes are overviewed. The problem of degradation of tungsten-barium cathodes is caused by the penetration of chemically active substances (for example, oxygen) into the interior space of a cathode. The “poisoning” process is so complex that it can hardly be simulated by simple theoretical methods. Because of this, the cathode “poisoning” degree under exposure to the atmosphere is usually assessed using experimental data. The analysis of publications on the resistance of cathode emitters to atmospheric exposure showed that one of the most promising solutions to the cathode “poisoning’ problem is the use of an emitter based on barium scandate. A cathode construction diagram was chosen, and a laboratory prototype cathode was made. The current dependence of the discharge voltage at different xenon flow rates and the xenon flow rate dependence of the discharge voltage at different currents were studied experimentally (xenon was the plasma-forming gas). During the trests, the cathode was periodically removed from the vacuuum chamber to inspect it for further use, the maximum duration of continuous exposure to the air was 14 days, and the resets did not reveal any significant change in the performance. The use of barium scandate as an emission-active substance for the thermoemission cathode improved its resistance to atmospheric exposure. The practical use of the cathode developed in experimental studies, for example, in the vacuum chamber of the plasmaelectrodynamic setup of the Institute of Technical Mechanics of the National Academy of Sciences of Ukraine and the State Space Agency of Ukraine, will eliminate frequent cathode replacements, thus significantly speeding up research activities.

Mapping Atmospheric Exposure of the Intertidal Zone with Sentinel-1 CSAR in Northern Norway

The intertidal zone (ITZ) is a highly dynamic and diverse coastal ecosystem under pressure that provides important eco-services. Being periodically under water makes it challenging to monitor, and the only possibility to map it in all tidal stages is by using dense time series of observations. At high latitudes, the Sentinel-1 (S1) constellation of the European Copernicus Program consistently provides radar imagery at fixed times on a near-daily basis, independently of cloud cover and sunlight. As tides have a period of 12 h 25.2 min, 1–2 year long S1 time series are therefore able to sample the whole tidal range and, thus, map the percentage of atmospheric exposure of the ITZ, which is an important environmental parameter. Tidal reference levels of mean high/low water at spring, mean and neap tide correspond each to specific percentiles of tidal heights and inversely correspond to atmospheric exposure. The presented method maps atmospheric exposure on the basis of purely statistical analyses of Sentinel-1 time series without the need for any tidal gauge data, by extracting water lines via simple thresholding of radar backscatter percentiles images. The individual thresholds for the second, fifth, 25th, 50th, 75th, 95th, and 98th percentile image were determined by fitting the threshold contour lines to in situ water line GPS tracks collected at corresponding tidal reference levels at five locations around Tromsø in Northern Norway. They inversely correspond to atmospheric exposures of 98%, 95%, 75%, 50%, 25%, 5%, and 2%, respectively. The method was applied to the whole Tromsø Municipality resulting in an ITZ atmospheric exposure map. The validation shows that the mean low water lines at neap, mid, and spring tide were mapped with accuracies of 93%, 84%, and 64%, respectively. The overall approach should be applicable worldwide.

Rubric Assessment and Spatial Zonal Mapping of Atmospheric Corrosion of Steel in India

Steel is an imperative engineering material due to its endurance accounts for a significant part of the world economy. It has enormous demand all over the world for its extensive use in construction and other industries. These industries are experiencing inevitable atmospheric exposure and are rapidly deteriorating due to induced atmospheric corrosion. The study assessed and interpreted trends in atmospheric corrosion rates in India for the last 39 years, and spatially mapped seasonal decade-by-decade trends. North-east India has been identified as the most corrosive region in the country, with the rainy season being the most corrosive season. Corrosion maps for India are prepared on the basis of 39 years of atmospheric data. A corrosion zone map is prepared to classify the country into five different zones based on the rate of atmospheric corrosion. Long-term atmospheric corrosion rates are projected for the next 50 years in all major cities across the country. Long-term corrosion is estimated to reduce the rate of atmospheric corrosion by 81% after 10 years of exposure and 91% after 50 years of exposure.

Long-Term Atmospheric Aging and Corrosion of Epoxy Primer-Coated Aluminum Alloy in Coastal Environments

Aircraft are subjected to extreme weather conditions in coastal areas. This study reports long-term atmospheric exposure tests carried out on an epoxy primer-coated aluminum alloy in a coastal environment for 7, 12, and 20 years. The micromorphology and characteristics of the section and surface, the products of corrosion, electrochemical impedance, and molecular structure of the coated specimens were examined through a spectrophotometer, scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), electrochemical impedance spectroscopy (EIS), and X-ray photoelectron spectrometer (XPS). The results showed that the angles of contact of the specimens with different numbers of years of atmospheric exposure satisfied the normal distribution. Their fractal dimensions increased with an increase in the duration of exposure. Intergranular corrosion and exfoliation corrosion appeared in the specimens after 20 years, where the product of corrosion was Al(OH)3. The impedances and thermal properties of the epoxy coatings were influenced by the synergistic effects of aging and post-curing. The impedances of the coatings decreased greatly after long-term atmospheric exposure. After 20 years of corrosion, the specimen showed the characteristics of the substrate being corroded. The mechanism of corrosion and the electrochemical equivalent circuit were also analyzed.

Effects of Ru catalyst changes by atmospheric exposure days on the interfacial and impact properties of glass fiber/p-DCPD composites

The ruthenium (Ru) catalyst is the most recently developed poly dicyclopentadiene (p-DCPD) polymer catalyst known to promote stable reactions, even upon contact with oxygen. However, the experimental results showed that exposure times exceeding three days can cause problems during curing due to reaction between oxygen and Ru catalyst. Consequently, 12 days of exposure degraded the mechanical and interfacial properties of p-DCPD or p-DCPD composites reinforced with 40 wt% 50-mm GF by 60%. The structural analysis simulation of the target product also showed noticeable changes in the catalyst that was exposed to air atmosphere for more than six days, which can deteriorate quality. This study demonstrated that when molding structures using p-DCPD, special care should be taken to control atmospheric exposure of the ruthenium catalyst.