Material Erosion Research Articles

Distribution of potentially toxic elements in soils and sediments in Pearl River Delta, China: Natural versus anthropogenic source discrimination

Although anthropogenic contamination has been regarded as the most important source of potentially toxic elements (PTEs) in soils of large river delta plains, the extent to which human activities affect PTEs in soils is worth exploring. This study used high density geochemical data to distinguish source patterns of PTEs in soils of the Pearl River Delta Economic Zone, a large industrialized and urbanized area in China. Enrichment factor, discriminant analysis, principal components analysis, cumulative distribution function, and positive matrix factorization were used to identify sources of PTEs in soils. The results indicated that parent material was the most significant factor affecting geochemical characteristics of PTEs in soils. Median concentrations of Cd, Cr, Cu, Hg, Pb, and Zn were 0.400, 88.5, 40.5, 0.143, 43.0, and 116.0 mg/kg for stream sediments, 0.333, 75.7, 39.0, 0.121, 42.6, and 98.5 mg/kg for deep soils, and 0.365, 74.0, 45.1, 0.143, 44.6, and 119.5 mg/kg for surface soils, respectively, all of which exceed relevant reference standards. Compared with stream sediments and deep soils, surface soils exhibit substantial concentrations of PTEs. Chemical weathering and erosion of parent materials distributed in the Pearl River Delta were the main sources of PTEs in soils. Diffuse contamination and many small local contamination sources distributed throughout the study area were the most significant anthropogenic sources of PTEs in surface soils. Intensive human activities failed to change the soil geochemical characteristics derived from the parent material at the regional scale. However, it could induce non-point source pollution and local severe PTEs pollution in surface soils.

AN INVESTIGATION ON MEAN ROUGHNESS DEPTH AND MATERIAL EROSION SPEED DURING MANUFACTURING OF STAINLESS-STEEL MINIATURE RATCHET GEARS BY WIRE-EDM

This paper presents the results of an investigation conducted on wire electric discharge machining (wire-EDM) of miniature ratchet gears. Effects of three important process parameters spark duration, ‘Ton’, spark-off-duration ‘Toff’, and wire tension ‘WT’ on surface quality, i.e., mean roughness depth ‘Rz’ and productivity, i.e., material erosion speed ‘MES’, have been investigated by conducting seventeen experimental trials. Both Ton and Toff have been identified as the significant parameters. Further, an optimization of wire-EDM parameters resulted in simultaneously best compromise values of Rz 5.30 µm and MES 6.75 mm/min and is achieved the following cutting regime: Ton 1.5 µs, Toff 42.5 µs, and WT 1500 g. At the end, surface quality study has been conducted to evaluate the tribological fitness of the miniature ratchet gear machined at optimum combination of wire-EDM parameter values. It was investigated that the generation of uniform and shallow craters on the flank surfaces of ratchet gear machined at optimum values of parameters, imparted smoother bearing area curve and lower coefficient of friction. The profile and flank surface of the ratchet gear also found free from cracks, burrs, and dirt.

Parylene-C Coating Protects Resin-3D-Printed Devices from Material Erosion and Prevents Cytotoxicity toward Primary Cells.

Resin 3D printing is attractive for the rapid fabrication of microscale cell culture devices, but common resin materials are unstable and cytotoxic under culture conditions. Strategies such as leaching or overcuring are insufficient to protect sensitive primary cells such as white blood cells. Here, we evaluated the effectiveness of using a parylene C coating of commercially available clear resins to prevent cytotoxic leaching, degradation of microfluidic devices, and absorption of small molecules. We found that parylene C significantly improved both the cytocompatibility with primary murine white blood cells and the material integrity of prints while maintaining the favorable optical qualities held by clear resins.

Changes in optical properties of polymeric materials due to atomic oxygen in very low Earth orbit

Atomic oxygen (AO) is the dominant constituent of the residual atmosphere in low Earth orbit (LEO). AO collides with spacecraft at a velocity of 8 km/s, causing oxidation and erosion of polymeric materials. Particularly in very low Earth orbit (VLEO) at altitudes below 300 km, the AO density is at least ten times that at 500–700 km, and the concentration of molecular nitrogen (N2) is 10% or more. Such high-flux AO and N2 can cause nonlinear processes and mass losses for polymers. This study aims to clarify the optical property changes for polymeric materials exposed to LEO and VLEO in the Material Degradation Monitor (MDM) mission onboard the Super-Low-Altitude Test Satellite (SLATS). The AO and N2 fluences and the UV irradiances were estimated using the NRLMSISE-00 atmospheric and solar radiation models. The relationships were investigated between the changes in CCD images and the estimated fluences of the samples. For silsesquioxane (SQ)-coated polyimide film, the diffuse reflection of visible light increased noticeably with an AO fluence above 1 × 1021 atoms/cm2. The formation of a silica layer on the coating induces cracks. For silver-coated FEP films, the diffuse reflection increased entirely at AO fluences above 3 × 1021 atoms/cm2. The AO and N2 collisions would erode and roughen the FEP surfaces. Visible transmission through silver-coated FEP films also increased locally with increasing AO fluence, indicating that some AO oxidized the silver layer despite the presence of an Inconel (Ni alloy) layer. The visible reflection from Beta Cloth was decreased by its reaction with UV. Further, the competitive reactions with UV and AO resulted in two-step changes in the visible reflection from the ETFE polymer (cable covering).

A 3D unstructured mesh based particle tracking code for impurity transport simulation in fusion tokamaks

A fully 3D unstructured mesh based global impurity transport code, GITRm is presented in this paper. It is a high-performance Monte Carlo particle (neutral atom and ion) tracking code, based on the trace approximation, to simulate the erosion, ionization, migration, and redistribution of material from plasma-facing components in magnetically confined fusion devices. It is designed to target complex geometries including non-axisymmetric local features such as bumpers, probes, tile gaps etc., and uses strongly graded and anisotropic elements to accurately represent the plasma fields. GITRm is built on the PUMIPic infrastructure [1], executes using distributed meshes and is performant on GPU accelerated computer systems. Three example cases, including a weak scaling study with about 1.5 billion particles on up to 144 GPUs, are used to demonstrate the utility of GITRm.

Modelling the Influence of Erosive Fluidization on the Morphology of Fluid Flow and Escape Structures

Focused fluid flow through sub-seafloor pipes and chimneys, and their seafloor manifestations as pockmarks, are ubiquitous. However, the dynamics of flow localization and evolution of fluid escape structures remain poorly understood. Models based on geomechanical mechanisms like hydro-fracturing and porosity wave propagation offer some useful insights into fluid flow and escape dynamics, but face limitations in capturing features like mobilized granular matter, especially in the upper sediment layers where the link between fracture and pockmark is not always clear. Here, we propose a mathematical model based on the multiphase theory of porous media, where changes in subsurface and seafloor morphology are resolved through seepage-induced erosion, fluidization, transport, and re-deposition of granular material. Through simulation of an idealized scenario of gas escape from overpressured shallow gas reservoir, we demonstrate that our model can capture flow localization and formation of pipes, chimneys, and pockmarks. Our simulations show (1) formation of conical focused-flow conduits with a brecciated core and annular gas channels; (2) pockmarks of W and ring shapes; and (3) pulsed release of gas. Sediment erodibility and flow anisotropy control the morphology of focused fluid flow and escape structures, while permeability shows negligible impact. While the geological setting for this study is theoretical, we show that our results have real-world analogs.

Mathematical Calculation of Material Reliability Using Surface Roughness Feature Based on Plasma Material Interaction Experiment Results

The choice of reactor structural material design must take into account the TOKAMAK fusion reactors' structural reliability. Due to their high levels of heat and energy, fusion reactions have significant deformation effects, which reduce the efficiency of energy production in reactors. Material selection, erosion and damage, heat and stress management, reliability analysis, maintenance, and inspection are crucial elements in determining how reliable fusion reactors are. The focus of this work is on material selection and reliability analysis based on these parameters. The most common wall materials used in fusion reactors are tungsten, beryllium, steel, or graphite. It is advised to utilize aluminum because harmful Beryllium dust limits the study of this element. For this purpose, a target of aluminum samples is established with a plasma of He ions created by glow discharge. The dependability of the samples is determined by calculating the Weibull Distribution and measuring the roughness of the sample surfaces following exposure.

Experimental investigations on electro erosion milling of Al-SiC metal-matrix composite

ABSTRACT This article demonstrates the electro erosion milling process in Al-SiC metal matrix composites. Material Erosion Rate (MER) and Tool Erosion Rate (TER) are measured which depict the productivity aspect of the process. Depth and width of the slots, surface roughness (Ra) is used to indicate the geometrical accuracy. Maximum MER (0.1097 mm3/min) is obtained at 5A. Maximum TER (0.65 µm/min) is obtained at 2.15A. Minimum Ra (2.13 µm) is obtained at 2.15A. Maximum MER (0.1194 mm3/min) is obtained at 100µs. Lowest TER (0.73µm/min) is obtained at 10µs. Lowest Ra (7.66µm) is obtained at Ton of 100µs. Jaya algorithm is used to optimize and create Pareto front from which the results are extracted and reported. Material removal mechanism has been detailed which includes melting / evaporating of matrix material, electrochemical dislodging of SiC grains. Better surfaces have crater diameters ranging from 40–50µm and the bigger craters are in the range of 100–150µm.

Measurements of material erosion in space by atomic oxygen using the on-orbit material degradation detector

In recent years atomic oxygen (AO) has become a major challenge for the space community. AO is the most dominant species of the residual atmosphere in low Earth orbit (LEO). In addition, AO was found at the top of the Venusian and Martian atmospheres. As a result of exposure to AO, organic space-facing materials erode, leading to changes in their roughness, thermo-optical properties, and mass loss. In the past years, there has been a growing interest in very low Earth orbit missions, below an altitude of 350 km, where AO density and thus, AO flux, are extremely high. At these low altitudes, material degradation by AO erosion poses a great risk to the integrity of any space-facing material, unless well protected. As such, measuring the AO flux and the consequential material erosion by AO, in real-time while under actual space conditions, are of great interest to the space community.Thus, in this work we present real-time AO material erosion measurements that were conducted, for the first-time in LEO, using the on-orbit material degradation detector (ORMADD). The ORMADD is a low-cost and simple to operate detector, comprised of photovoltaic cells coated with semi-transparent AO sensitive coatings. Two ORMADDs were integrated on TAUSAT-1, a 3U CubeSat, deployed into LEO from the international space station. The first ORMADD was coated with a thin amorphous-carbon coating and the second was covered with a thick pyrolytic Kapton film. Using ORMADD, we were able to follow the erosion of the coatings in real-time conditions and calculate the AO flux in TAUSAT-1 orbit. The average in-orbit flux, derived from ORMADD data, was found to be comparable to the theoretical average AO flux calculated by the space environment information system (SPENVIS) software. This work demonstrates the abilities of ORMADD as a space environment detector, as well as a space material degradation research instrument.

Study of the erosion and redeposition of W considering the kinetic energy distribution of incident ions through a semi-analytical model

In today’s nuclear fusion devices, erosion of high-Z metallic plasma-facing materials (PFMs) is mainly caused by physical sputtering. That is, by the exchange of energy between plasma ions and the atoms in the walls. In most of the numerical codes currently in use impinging plasma is approximated as a fluid. By averaging the incident particles’ energy distribution the high-energy population of the eroded material is underestimated. For heavy materials such as W, high-energy eroded particles tend to ionize far from the wall and they are less affected by the sheath electric field hence, not being attracted back to the wall, they have a higher chance to contaminate the core plasma. This could in turn result in an underestimation of the net erosion sources. In this work, a semi-analytical model was developed to include the energy distribution of the incident particles. Then, by Monte Carlo method, the net erosion of tungsten from a smooth PFM was calculated. The results show that the kinetic description in energy is important only for incident particles ionized once. For instance, it is particularly important for plasma ions such as Deuterium. It is seen that Deuterium contribution to the W net sources is not always negligible if compared to light impurities or to tungsten self-sputtering in the range of plasma parameters tested. Finally, results show that the difference between the fluid and kinetic models becomes more pronounced for high-screening plasma conditions.

Magnesium Oxide Powder Synthesis in Cathodic Arc Discharge Plasma in an Argon Environment at Atmospheric Pressure

Discharges with cathode spots can operate in a wide range of gas pressures. Erosion of the cathode material is an inherent property of such discharges. The erosion products are considered to be ionized atoms and electrically neutral microdroplets. In accordance with this concept, a plasma source based on a pulsed cathodic arc discharge in atmospheric-pressure argon with a current of up to 200 A, a pulse duration of 250 μs, and a pulse repetition rate of 10 Hz was implemented. Using this source, the synthesis of magnesium oxide powder was performed. The chemical composition of the erosion products was determined using the TEM/EDS method and the composition of the gas mixture in which the discharge system operated was evaluated by optical spectrometry. It was shown that particles of the synthesized powder have different morphological features, depending on the nature of the electrical erosion of the cathode material. Micron-sized particles are formed due to the removal of microdroplets from liquid–metal craters on the cathode surface at certain plasma pressures. Submicron particles are produced during the agglomeration of atoms originating from the plasma jets flowing out from cathode spots. These atoms are magnesium ions that are neutralized by collisions with gas particles. The advantages and disadvantages of this synthesis method are discussed in this paper. The reference methods for the powder synthesis of magnesium oxide are compared. The prospects of the studied method from the point of view of its application for obtaining ceramic materials are also evaluated.

SOIL PROPERTIES AND MAPPING OF THE ARALIK-IĞDIR WIND EROSION AREA-I (SURFACE)

In arid and semi-arid regions, one of the biggest problems for soil which is bare and/or has insufficient vegetation is wind erosion caused by strong winds. The second largest wind erosion area of Türkiye is in the province of Aralık-Iğdır. In this study, surface soil analysis of 40 km2 of the wind erosion area (clay,% silt,% sand, carbonate%, OM%, pH and EC), dry sieving analysis (4, 2, 1, 0.84, 0.42, 0.106, 0.020, <0.020 mm), erodible fraction (EF1%, EF2%), stability index (SI) and relative aggregation index (RSI) were determined. In addition, elevation, slope, silt, >0.84 mm, 0.106 mm, >0.020 mm, EF1, EF2, SI and RSI values as percentage were mapped using Geographic Information Systems (GIS). As a result, the texture classes of the wind erosion area of surface soils were determined as S-LS-SL, the carbonate percentages as 0.4-0.8, the organic matter percentages as 0.3-2.4, the pH values as 8.0-9.1, the electrical conductivity measurements as 0.03-0.12. In dry sieving processes; the resistant material (>0.84%) as 0-40, the erosive material (<0.84%) as 43-99; the erodible material percentages calculated with equations EF1 as 50-58, EF2 as 60-100; the stability index SI as 0-1 and the relative aggregation indices were RSI 0-11. It has been determined that the surface soils of all plots in the study area were sensitive to wind erosion, and that some plots were more sensitive.

Coastal landforms and fetch influence shoreline restoration effectiveness

Coastal shorelines are a key interface between terrestrial and aquatic ecosystems and are vital for human livelihood. As a result, shorelines have experienced substantial human modifications worldwide. Shoreline “hardening” – the construction of armor including seawalls, bulkheads, or rip-rap – is a common modification that has substantial negative ecological effects. Currently, restoration involving the removal of armor and replacement with “living” shorelines is becoming an established practice. Still, the ecological response to armor removal is oftentimes unpredictable and site-specific. We hypothesized that the confluence of larger-scale geophysical features might strongly influence ecological restoration outcomes at particular locations. To measure the effectiveness of armor removal in the context of broad-scale geophysical features across the Salish Sea, WA, USA, we studied 26 paired restored and natural reference beaches of the same shoretype (feeder bluff, accretion shoreform, or pocket beach), as well as corresponding fetch, sub-basin, and percent of shoreline sediment drift cell armored. Sites were restored for an average of six years. We gauged restoration effectiveness based on levels of five ecological response variables: beach wrack (percent, depth), logs (count, width), sediments (percent sand), vegetation (percent overhanging, count of fallen trees), and insects (density, taxa richness). We found that armor removal often restored these variables to natural levels, but that restoration response was dependent on geophysical features such as shoretype and fetch. Natural beaches did have higher measurements of overhanging vegetation, fallen trees, and insect taxa richness, as these features likely take time to mature at restored beaches. Feeder bluffs had a higher proportion of surface sand and number of fallen trees than other shoretypes, coinciding with the erosion of bluff material, whereas natural pocket beaches within bordering rocky headlands had higher insect densities. Sites with a large fetch had higher input of deposited wrack and logs, whereas sites with a small fetch had higher input from localized terrestrial sources – fallen trees and eroding sand. By incorporating the effectiveness of restoration with landscape features such as shoretype and fetch, we can more effectively plan for future restoration actions and better predict their outcomes.

Geomorphological hazards on transportation roads in Sarkapkan township

Sarkapkan sub-district, in terms of administration, belongs to Ranya district in Slemani province. Astronomically, it is located between the located in latitude (northern Longitude °36: ¯28:꓿27-°36: ¯15: ꓿21.) (°45: ¯51: ꓿35- east °45: ¯46: ꓿39)eastern longitudes. It is located in the northwest of Slemani Province. The study area includes a strategically important economic and military road that borders with Warte sub-district in Erbil province, as well as a number of secondary roads that connect human settlements to the urban center, and in physiography is located in a hard mountainous area. The main objective of this study is to identify the environmental characteristics of the study area and draw a specific map for each of them in order to analyze the risks faced by the roads in the study area. The study begins with an analysis of the natural environment in Sarkapkan sub-district and its impact on roads, such as (geology, topography, climate, soil, and vegetation cover). In the second part, we discussed the introduction of road networks in terms of (main, secondary, and village roads) and then the role of humans in destroying the balance of the earth and as a factor in the creation of danger on roads, this is an analysis of each of these natural features and their direct and indirect impact on traffic networks. In the third part, each of the processes (water erosion and movement of materials) is discussed and their impact on the creation of hazards on the roads is examined, and then a morphodynamics map is created to determine the level of morphodynamics risk in the study area. The results of the study show that natural characteristics and human activities play a major role in the creation of geomorphological hazards on traffic networks and their destruction.

Mapping Abandoned Uranium Mine Features Using Worldview-3 Imagery in Portions of Karnes, Atascosa and Live Oak Counties, Texas

Worldview-3 (WV3) 16-band multispectral data were used to map exposed bedrock and mine waste piles associated with legacy open-pit mining of sandstone-hosted roll-front uranium deposits along the South Texas Coastal Plain. We used the “spectral hourglass” approach to extract spectral endmembers representative of these features from the image. This approach first requires calibrating the imagery to reflectance, then masking for vegetation, followed by spatial and spectral data reduction using a principal component analysis-based procedure that reduces noise and identifies homogeneous targets which are “pure” enough to be considered spectral endmembers. In this case, we used a single WV3 image which covered an ~11.5 km by ~19.5 km area of Karnes, Atascosa and Live Oak Counties, underlain by mined rocks from the Jackson Group and Catahoula Formation. Up to 58 spectral endmembers were identified using a further multi-dimensional class segregation method and were used as inputs for spectral angle mapper (SAM) classification. SAM classification resulted in the identification of at least 117 mine- and mine waste-related features, most of which were previously unknown. Class similarity was further evaluated, and the dominant minerals in each class were identified by comparison to spectral libraries and measured samples of actual Jackson Group uranium host rocks. Redundant classes were eliminated, and SAM was run a second time using a reduced set of 23 endmembers, which were found to map these same features as effectively as using the full 58 set of endmembers, but with significantly reduced noise and spectral outliers. Our classification results were validated by evaluating detailed scale mapping of three known mine sites (Esse-Spoonamore, Wright-McCrady and Garbysch-Thane) with published ground truth information about the vegetation cover, extent of erosion and exposure of waste pile materials and/or geologic information about host lithology and mineralization. Despite successful demonstration of the utility of WV3 data for inventorying mine features, additional landscape features such as bare agricultural fields and oil and gas drill pads were also identified. The elimination of such features will require combining the spectral classification maps presented in this study with high-quality topographic data. Also, the spectral endmembers identified during the course of this study could be useful for larger-scale mapping efforts using additional well-calibrated WV3 images beyond the coverage of our initial study area.

Evaluation of the susceptibility to erosion of materials used as a base of rigid pavements using a vertical shaking table

ABSTRACT Erosion of the base layers in rigid pavements is a complex hydro-mechanical process that rapidly reduces the structural integrity of these structures. This research revisits a vertical shaking table testing method to characterise the erosion susceptibility of the materials used on base layers in rigid pavements. The procedure consists of applying a vertical vibration to a cylindrical sample of the material under evaluation, which is partially immersed in water in a cylindrical metallic container with a high-strength concrete base. The vertical movement of the sample causes a radial flow of water on its base, which induces high shear forces that eventually erode the bottom of the sample. The volumetric loss of material from the testing sample under different water velocities and pressure conditions is used to quantify its susceptibility to erosion. After presenting the theoretical principles and the numerical formulation of the hydro-mechanical erosion processes occurring in this test, the experimental method was applied to characterise the erosion susceptibility of five different materials. The results suggest that the vertical shaking experimental technique is more versatile and accurate in quantifying the erosion susceptibility of base materials than available standardised tests.

Neural computing and Taguchi’s methodbased study on erosion of advanced Mo2C–WC10Co4Cr coating for the centrifugal pump

ABSTRACT Nowadays, computational and computing tools are widely used in prediction applications. Neural computing is a modern and emerging technique to predict data efficiently and precisely. In this context, erosion investigation of Mo2C–WC10Co4Cr high-velocity oxy-fuel (HVOF) deposited on AISI 316L was carried out in the present work by implementing a neural computing and Taguchi’s method. This research paper focuses on neural network (NN) technique for the prediction of erosion in Mo2C–WC10Co4Cr HVOF coating. The WC10Co4Cr powder was composed of 3% (by weight) of molybdenum carbide, each with a concentration of 3 wt.%. The input parameters used for designing the NN model were erodent properties (bulk density, circularity factor, average particle size, and slurry concentration), material properties (hardness and porosity of bare/coated), and process parameters (speed and time). A set of experiments was optimised by using Taguchi’s method (L16 2 × 5 array). Results indicated that the overall accuracy of Pearson coefficient (R) was found as 0.99582 with experimental data. However, R = 1 was found for testing results.

Quantitative impact assessment of the 2019 tropical cyclone Kammuri lahars: Mayon volcano, Philippines

Lahars (volcanic mudflows) are frequent occurrences in communities near active Philippine volcanoes due to intense and prolonged rainfall. Mayon Volcano is the most active volcano in the Philippines, ejecting pyroclastic deposits that serve as erodible materials for lahars. Damaging lahars have occurred in the past, with the more recent ones in 2006, 2015, 2019 and 2020 posing impacts such as erosion, burial, and flash flooding in low-lying areas. This paper presents the results of an interdisciplinary case study on lahar impact assessment for a selected pilot community at Mayon Volcano. Lahar hazard modeling, an exposure database, and a Filipinized lahar damage state table were combined to estimate potential lahar impacts to buildings for the study area using a lahar impact assessment software tool called REDAS Quick Lahar Impact Simulation Tool (REDAS-QLIST). The tool can estimate lahar losses such as physical damage, economic loss, and total population affected including age-sex distribution. Being able to accurately quantify impact and damage is one of the added values provided by REDAS-QLIST. The damage and loss estimates produced for our case study area were tested using an actual lahar event scenario from Tropical Cyclone (TC) Kammuri in 2019. Stakeholders, especially from local government units, can utilize the methods and results presented to plan and apply adaptable and sustainable disaster risk reduction programs in their communities. Importantly, the methodology can be used with additional lahar modeling results and exposure data through the REDAS QLIST to assess hazard and loss for other volcanic regions in the Philippines.

Metallurgical, erosion, and sensitization performance of TiAlN monolayer and TiAlN/TiN multilayer ceramic coatings on AISI 304 boiler steel

In the present work, TiAlN monolayer and TiAlN/TiN multilayer ceramic coatings were deposited on AISI 304 austenitic stainless steel by plasma arc physical vapor deposition (PAPVD) process. The metallurgical, erosion, and sensitization performance of these coatings were compared with uncoated 304 boiler steel. Metallurgical studies depicted formation of Al and Ti nitrides on monolayer and multilayer coated steel surfaces, which resulted into higher nitriding at the surface and dense coating formation on boiler steel substrate. Multilayer film exhibited comparatively lesser porosity, lower surface roughness, and higher hardness than monolayer coated and uncoated steel. The erosion performance was evaluated at 30° and 90° besides 2 g/min and 3 g/min flow rates of Al2O3 erodent material for coated and uncoated steel substrate. Multilayer coated 304 steel possessed lower erosion wear rate as evaluated through lesser weight loss before and after erosive wear, smaller crater formation, and minimal adherence of erodent material along with lesser Fe content on eroded surface relative to monolayer coated and uncoated steel. Multilayer coated steel thermally aged at 750° for 24 h had least degree of sensitization (DOS) compared to monolayer coated and uncoated aged boiler steel. Although monolayer coated steel performed better than uncoated one in erosion and sensitization performance but multilayer coating performance was best among all coated and uncoated steel used for present study. Thus, it was established that TiAlN/TiN multilayer coating on AISI 304 boiler steel has improved its metallurgical, erosion, and sensitization performance.

Decay of ignimbrite fairy chimneys of Arizona's Basin and Range Province, USA

AbstractFairy chimneys of ignimbrite are well studied in Cappadocia in central Anatolia, Turkey. The ignimbrite landforms of Arizona's Basin and Range, USA, in contrast, remain relatively unexplored in geomorphic scholarship, despite decades of geological research on the characteristics of the ignimbrites themselves. This research focuses on the rock‐decay processes that modify Arizona's Basin and Range fair chimneys. Dissolution of glass and groundmass, measured along joints using digital image processing of back‐scattered electron microscope imagery, reveal a 3× higher porosity than inside the rock interior. This method also measured a 3‐4× increase in dissolution near the base of the chimney compared with the rock interior, leading to notch development that promotes chimney mass wasting and subsequent ballistic impacts. Epilithic organisms studied with electron microscopy both enhance rock decay and promote case hardening. These observations are consistent with prior understanding of how fairy chimneys evolve over time: columnar joints exposed on cliff faces experience enough decay to allow erosion of joint material, this erosion separates the chimney from the rock face and notch development near the chimney base promotes mass wasting. The rock‐decay processes studied here likely operate on very different timescales. Mass wasting events leading to ballistic impacts occur at observable timescales. Varnish microlamination dating, using ultrathin sections of rock varnish formed on fairy chimneys, indicates that the case hardening of the top of fairy chimneys are much more stable than the sides; the tops last experienced surface detachment during the early Holocene, as opposed to the sides that experienced flaking throughout the late Holocene. The timescale of basal notch development is not known, with the exception that the very surface of notches erode at rates too fast to accumulate rock varnish. The timescales of epilithic organisms enhancing rock decay and dissolution of columnar joints are not known.