A Review of the Erosion of Thermal Barrier Coatings.

The application of thermal barrier coatings (TBCs) to components with internal cooling in the hot gas stream of gas turbine engines has facilitated a steep increase in the turbine entry temperature and the associated increase in performance and efficiency of gas turbine engines. However, TBCs are susceptible to various life limiting issues associated with their operating environment including erosion, corrosion, oxidation, sintering and foreign object damage (FOD). This is a review paper that examines various degradation and erosion mechanisms of TBCs, especially those produced by electron beam physical vapour deposition (EB-PVD). The results from a number of laboratory tests under various impact conditions are discussed before the different erosion and FOD mechanisms are reviewed. The transitions between the various erosion mechanisms are discussed in terms of the D/d ratio (contact area diameter/column diameter), a relatively new concept that relates the impact size to the erosion mechanism. The effects of ageing, dopant additions and calciumâ  magnesiumâ  aluminaâ  silicates on the life of TBCs are examined. It is shown that while ageing increases the erosion rate of EB-PVD TBCs, ageing of plasma sprayed TBCs in fact lowers the erosion rate. Finally modelling of EB-PVD TBCs is briefly intr

Effect of Ambient Temperature and Humidity on Aging of Nanocarbons

We researched effect of ambient temperature and humidity on aging of nanocarbons, including carbon nanotubes and fullerenes. We studied physicochemical properties of these nanocarbons stored in ambient conditions (20oC, 35-55%RH) for 24 months, in 90% relative humidity (RH) environment for 8 months and in 37oC environment for 13 months. We measured surface area and pore volume of samples by using N2 adsorption (77K) technique and characterized surface chemistry by using X-Ray photospectroscopy and FT-IR spectroscopy. We also analyzed structural defects with Raman spectroscopy. All tests were conducted periodically. In ambient condition, we found that nanocarbons exhibited a trend of decreasing surface area and pore volume up to 7 to 15 months but then stabilized. We also observed a trend of decreasing surface oxygen from the beginning with much lower % oxygen observed after 12 to 15 months of aging. There was also evidence that structural-defect concentration was lowered. We conclude that nanocarbons are metastable materials, and that their aging in ambient conditions has an unexpected effect whereby oxygen leaves their surface, the structure repairs itself and they become more thermodynamically stable. Aged nanocarbons (16 months in ambient conditions) were moved to 90% RH environment and 37oC environment. We observed that in 90% RH condition, chemisorption of oxygen and/or water to nanocarbons was enhanced and % oxygen was increased; surface area, pore volume and structural defects were reduced with a trend of approaching to equilibrium. We conclude that humidity could promote chemisorption of oxygen/water in the air to nanocarbons. We found that in 37oC condition, chemical properties of nanocarbons were only slightly decreased, but their surface area and pore volume were deceased in 1 to 3 months, and then increased in 3 to 13 months. Their physical changes may be related to the temperature dependent thermal expansion which softened intertubular interaction and enlarged spaces between tubes. This study demonstrated that ambient temperature and humidity play important roles in aging of nanocarbons and also showed that nanocarbons possess differences from bulk carbons in aging. This study could benefit potential applications of nanocarbons and improve understanding long-term environmental impacts of nanocarbons

Bio-Based Renewable Additives for Anti-Icing Applications (Phase II)

The performance and impacts of several agro-based anti-icers along with a traditional chloride-based anti-icer (salt brine) were evaluated. A statistical design of experiments (central composite design) was employed for developing anti-icing liquids consisting of cost-competitive chemicals such as agro-based compounds (e.g., Concord grape extract and glycerin), sodium chloride, sodium metasilicate, and sodium formate. The following experimentally obtained parameters were examined as a function of the formulation design: ice-melting capacity at 25°F (−3.9°C), splitting strength of Portland cement mortar samples after 10 freeze-thaw/deicer cycles, corrosion rate of C1010 carbon steel after 24-hour immersion, and impact on asphalt binder stiffness and m-value. One viable formula (“best performer”) was tested for thermal properties by measuring its differential scanning calorimetry (DSC) thermograms, the friction coefficient of asphalt pavement treated by this anti-icing formulation (vs. 23 wt.% NaCl and beet juice blend) at 25°F after being applied at 30 gallons per lane mile (1 hour after simulated trafficking and plowing), and other properties (pH, oxygen demand in COD). Laboratory data shed light on the selection and formulation of innovative agro-based snow- and ice-control chemicals that can significantly reduce the costs of winter maintenance operations

Population dynamics, delta vulnerability and environmental change: comparison of the Mekong, Ganges–Brahmaputra and Amazon delta regions

Tropical delta regions are at risk of multiple threats including relative sea level rise and human alterations, making them more and more vulnerable to extreme floods, storms, surges, salinity intrusion, and other hazards which could also increase in magnitude and frequency with a changing climate. Given the environmental vulnerability of tropical deltas, understanding the interlinkages between population dynamics and environmental change in these regions is crucial for ensuring efficient policy planning and progress toward social and ecological sustainability. Here, we provide an overview of population trends and dynamics in the Ganges–Brahmaputra, Mekong and Amazon deltas. Using multiple data sources, including census data and Demographic and Health Surveys, a discussion regarding the components of population change is undertaken in the context of environmental factors affecting the demographic landscape of the three delta regions. We find that the demographic trends in all cases are broadly reflective of national trends, although important differences exist within and across the study areas. Moreover, all three delta regions have been experiencing shifts in population structures resulting in aging populations, the latter being most rapid in the Mekong delta. The environmental impacts on the different components of population change are important, and more extensive research is required to effectively quantify the underlying relationships. The paper concludes by discussing selected policy implications in the context of sustainable development of delta regions and beyond

Predictable hydrodynamic conditions explain temporal variations in the density of benthic foraging seabirds in a tidal stream environment

VC International Council for the Exploration of the Sea 2016. James J. Waggitt was funded by a NERC Case studentship supported by OpenHydro Ltd and Marine Scotland Science (NE/J500148/1). Shore-based surveys were funded by a NERC (NE/J004340/1) and a Scottish National Heritage (SNH) grant. FVCOM was funded by a NERC grant (NE/J004316/1). The bathymetry data used in hydrodynamic models (HI 1122 Sanday Sound to Westray Firth) was collected by the Maritime and Coastguard Agency (MCA) as part of the UK Civil Hydrography Programme. We wish to thank Christina Bristow, Matthew Finn and Jennifer Norris at the European Marine Energy Centre (EMEC); Ian Davies at Marine Scotland Science; Gail Davoren, Shaun Fraser, Pauline Goulet, Alex Robbins and Helen Wade for invaluable discussions; Thomas Cornulier, Alex Douglas, James Grecian and Samantha Patrick for their help with statistical analysis; and Jenny Campbell and the Cockram family for assistance during fieldwork.Peer reviewedPublisher PD