Adjacent Pits Research Articles

INVESTIGATION ON ELECTROCHEMICAL CORROSION CHARACTERISTIC OF 2A14 ALUMINUM ALLOY IN NITRIC ACID

In order to evaluate the left life of the aircraft tank in the storage stage and enhance the reliability of aircraft, the electrochemical corrosion characteristic of 2A14 aluminum alloy has been investigated by the polarization curve method, electrochemical impedance spectroscopy methods and soaking corrosion test in this paper. The corrosion equivalent relationship of 2A14 aluminum alloy at different conditions was established. Moreover, the corrosion mechanism and law of 2A14 aluminum alloy in the solution of N2O4-HNO3 were obtained. It is shown that the nitric acid with the volume fraction of 30% corrodes 2A14 aluminum alloy had the fastest speed. The corrosion intensity of the specimen increases with the increase of the environment temperature. In the corrosion program, the corrosion is begun with the pit with very small size. As the time passes by, the pits expand and the adjacent pits combines together to be a larger pit. Finally, the thickness of the specimen decreases uniformly as the corrosion product peels off from the surface of the specimen. Therefore, the corrosion evaluation of aluminum alloy structure can be performed by weighting or measuring the thickness in application.

Interacting Effects Induced by Two Neighboring Pits Considering Relative Position Parameters and Pit Depth.

For pre-corroded aluminum alloy 7075-T6, the interacting effects of two neighboring pits on the stress concentration are comprehensively analyzed by considering various relative position parameters (inclination angle θ and dimensionless spacing parameter λ) and pit depth (d) with the finite element method. According to the severity of the stress concentration, the critical corrosion regions, bearing high susceptibility to fatigue damage, are determined for intersecting and adjacent pits, respectively. A straightforward approach is accordingly proposed to conservatively estimate the combined stress concentration factor induced by two neighboring pits, and a concrete application example is presented. It is found that for intersecting pits, the normalized stress concentration factor Ktnor increases with the increase of θ and λ and always reaches its maximum at θ = 90°, yet for adjacent pits, Ktnor decreases with the increase of λ and the maximum value appears at a slight asymmetric location. The simulations reveal that Ktnor follows a linear and an exponential relationship with the dimensionless depth parameter Rd for intersecting and adjacent cases, respectively.

Pluto: Pits and mantles on uplands north and east of Sputnik Planitia

The highlands region north and east of Sputnik Planitia can be subdivided into seven terrain types based on their physiographic expression. The northern rough uplands are characterized by jagged uplands and broad troughs, and it may contain a deeply-eroded ancient mantle. Dissected terrain has been interpreted to have been eroded by paleo-glaciation. The smooth uplands and pits terrain contains broad, rolling uplands surrounding complexes of pits, some of which contain smooth floors. The uplands are mantled by smooth-surfaced deposits possibly derived from adjacent pits through low-power explosive cryovolcanism or through slow vapor condensation. The eroded smooth uplands appear to have originally been smooth uplands and pits terrain modified by small-scale sublimation pitting. The bright pitted uplands features intricate texturing by reticulate ridges that may have originated by sublimation erosion, volatile condensation, or both. The bladed terrain is characterized by parallel ridges oriented north–south and is discussed in a separate paper. The dark uplands are mantled with reddish deposits that may be atmospherically deposited tholins. Their presence has affected long-term landform evolution. Widespread pit complexes occur on most of the terrain units. Most appear to be associated with tectonic lineations. Some pits are floored by broad expanses of ices, whereas most feature deep, conical depressions. A few pit complexes are enclosed by elevated rims of uncertain origin.

Multiaxial fatigue behaviors of 2024-T4 aluminum alloy under different corrosion conditions

In order to study multiaxial fatigue behavior of 2024-T4 aluminum alloy with an aircraft in-service environment, fatigue tests of multiaxial pre-corrosion and alternate corrosion are carried out. With the extension of pre-corrosion time, the multiaxial fatigue life decreases under the same equivalent stress. Pitting caused by corrosion is observed on the surface of specimens. While pre-corrosion time increases, the number and size of pits become larger and connection between adjacent corrosion pits becomes more obvious. For the multiaxial fatigue tests with alternate corrosion, for the same unit corrosion time, the fatigue life decreases with the increase of unit loading cycles. Under the same unit loading cycles, the fatigue life decreases as the unit corrosion time increases. The cyclic hardening appears in both axial and tangential directions at the initial loading stage. Cyclic softening trend becomes obvious as the number of alternation increases. It is shown that cracks initiate at specimen surface and gradually extend to inside. Exfoliation corrosion morphology can be observed on specimen surface. Based on Miner’s rule and data of pre-corroded multiaxial fatigue test, the alternate corrosion-multiaxial fatigue lives are predicted.

Field Measurement of Stresses of Floor Slabs in Excavations

This paper presents field measurement of stresses of floor slabs in excavations. During the study, a typical measurement-section was selected, and concrete strain meters were embedded so as to make stress measurement for floor slabs. Effect of the excavation of adjacent foundation pit for existing structure was discussed deeply. What’s more, the stability of floor slabs was evaluated. Finally, it could be concluded as follows: With the increase of the excavation depth, the excavation of the Transfer Hall Foundation Pit (THFP) had large effect on the internal force of floor slabs beside it, however, such influence tended to be smaller for the foundation pit far from the Transfer Hall (TH);. According to the strain data from field measurement, safety factors of floor slabs were calculated, which turned out to meet national code (JGJ 120-2012). Meanwhile, it can be concluded that floor slabs were in the safe status. In the end, the variation relation of their internal force, which would provide some references for the design and construction of similar projects in future, was obtained.

Application of CFD Simulation to Safety Problems – Challenges and Experience Including a Comparative Analysis of Hot Plume Dispersion from a Ground Flare

Integral or phenomenological consequence models are commonly used for safety related studies at onshore and offshore facilities. These are usually 2D and therefore ignore the influence of the geometry on the ventilation patterns, the dispersion substances and the generation of turbulence that plays a fundamental role in case of explosions. More sophisticated Computational Fluid Dynamics (CFD) models can take into account all these and other relevant phenomena that greatly affect the results. Several design matters can benefit from the use of CFD models in alternative to the simplified consequence models; these include the dispersion of dense gases in low wind conditions, the assessment of explosion risk in congested areas, the dispersion of gases in complex terrains and countercurrent wind, the evaluation of any smoke related impact on plant safety and efficiency. In this paper, the phenomenon of hot plume dispersion from a ground flare is investigated with CFD simulations. The results of a comparative analysis between two CFD codes (Fluent and FLACS), applied to an LNG project, and a phenomenological approach are presented and discussed to identify some peculiar differences between these models. In addition, the study aims at evaluating the effect two adjacent flare pits in simultaneous operation.

Study on nano-pores enlargement during Ag-assisted electroless etching of diamond wire sawn polycrystalline silicon wafers

In this paper, diamond wire sawn (DWS) mc-Si wafers were textured using Ag-assisted electroless etching (AgNO3+HF+H2O2) combined with an auxiliary etching (HF+HNO3). The evolution mechanism of the surface texture structure on the wafers was investigated in detail. It was noted that during the AgNO3+HF+H2O2 etching, there existed the difference in the axial direction and the depth of nano-pores among different grains. This difference made the different grains form different texture structures during the following HF+HNO3 etching. Since the etching of poly-silicon is isotropic in HF+HNO3 solution, it was the AgNO3+HF+H2O2 etching rather than the auxiliary etching (HF+HNO3) that resulted in the different texture structure among different grains. During the HF+HNO3 etching, the diameter of the etched pits on the wafer surface was enlarged quickly through the adjacent pits combination. The depth of the etched pits hardly increased because the top and bottom of pits were etched at the same time. As a result, the ratio of depth to diameter of the pits decreased. The texture difference among the grains and decrease of the ratio of depth to diameter of the pits limited the further enhancement of the PV efficiency of mc-Si solar cell. Therefore, the improving the uniformity of AgNO3+HF+H2O2 etching for the different crystal orientation grains and obtaining a large ratio of depth to diameter of the pits during the HF+HNO3 etching are two critical issues to enhance the PV efficiency of mc-Si solar cell.

GROUPING METHOD OF IMAGE FRAGMENTS OF ADJACENT DISLOCATION ETCH PITS OF THE SEMICONDUCTOR WAFER

An increase in production volumes of gallium arsenide semiconductor devices determines the need for better control of dislocations of semiconductor wafer. The grouping method of image fragments of adjacent dislocation etch pits of the semiconductor wafer is proposed in the article. Adjacent fragments will be allocated in the pre-binarized image of wafer surface, which contains adjacent fragments of etch pits of dislocation loops after treatment by the described method. Improved methods for determining the loop line width determines the edge line width of etch pits of suspected dislocations, given the variability of their display in the binarized image. The current loop line width is compared to the reference line width of the dislocation loop. The grouping method of image fragments of adjacent dislocation etch pits of the semiconductor wafer defines recovery of loop lines branching, takes into account various options of line adjacency and determines the direction of further recovery of loop line of dislocation etch pits. A step by step description of the method is given.

Effects of Pit Excavation on an Existing Subway Station and Preventive Measures

AbstractAs traffic lifelines of modern cities, subways are being rapidly developed in China. With this development, an increasing number of subway interchange stations will be built at deep soft soil areas. Because of the absence of data on the effects of pit construction on existing subway stations, no theory is available to predict deformation of a subway station caused by adjacent pit construction. The proposed Line 10 subway station intersects with the operating Line 4 subway station at Hailun Road, Shanghai, China, where the underlying stratum is composed of several different sandy-silt layers and two confined aquifers. The double-layered confined water meets at the south end well of the proposed subway station. With such complicated hydrogeological conditions, the development of technology that can control the effects of groundwater and guarantee the safe operation of Line 4 during pit construction is essential. In this article, the effects of dewatering and pit excavation on the Line 4 subway stati...

An insight in magnetic field enhanced zero-valent iron/H2O2 Fenton-like systems: Critical role and evolution of the pristine iron oxides layer.

This study demonstrated the synergistic degradation of 4-chlorophenol (4-CP) achieved in a magnetic field (MF) enhanced zero-valent iron (ZVI)/H2O2 Fenton-like (FL) system and revealed an interesting correlative dependence relationship between MF and the pristine iron oxides layer (FexOy) on ZVI particles. First, a comparative investigation between the FL and MF-FL systems was conducted under different experimental conditions. The MF-FL system could suppress the duration of initial lag degradation phase one order of magnitude in addition of the significant enhancement in overall 4-CP degradation. Monitoring of intermediates/products indicated that MF would just accelerate the Fenton reactions to produce hydroxyl radical more rapidly. Evolutions of simultaneously released dissolved iron species suggested that MF would not only improve mass-transfer of the initial heterogeneous reactions, but also modify the pristine ZVI surface. Characterizations of the specific prepared ZVI samples evidenced that MF would induce a special evolution mechanism of the ZVI particles surface depending on the existence of FexOy layer. It comprised of an initial rapid point dissolution of FexOy and a following pitting corrosion of the exposed Fe0 reactive sites, finally leading to appearance of a particular rugged surface topography with numerous adjacent Fe0 pits and FexOy tubercles.

Non-Invasive Imaging of Membrane Dynamics Accompanied with Endocytosis in Living Cells by Atomic Force Microscopy

Macromolecular dynamics around the plasma membrane (membrane proteins, cytoskeleton, lipid bilayer, etc.) play a crucial role in cell signaling, cell motility and cell adhesion. Nano-scale imaging of plasma membrane dynamics has been a difficult task due to a lack of fluorescent labeling method for lipid bilayers in a living cell. Here, we utilized a high-speed atomic force microscope (HS-AFM) to directly visualize the dynamics of the plasma membrane with sub-second time resolution.Imaging of a living COS-7 cell in a serum-free medium exhibited a number of membrane invaginations with a diameter ranging from 90 to 300 nm, which corresponds well to the size of clathrin-mediated endocytosis. Using this method, we identified various unique properties of endocytosis: (i)The duration time of the invagination was 50∼300 sec, and by treating the cell with dynasore (inhibitor for dynamin), the duration time was prolonged to over 1,000 sec, demonstrating that the closing step of the invagination is dependent on dynamin. (ii)Formation of the pit was accompanied with dynamic morphological changes of the invagination; adjacent pits were fused into a larger pit or the pit was split into several smaller pits. (iii)In the final stage of pit closure, different from the canonical model in which dynamin pinches off the membrane vesicle from the flat plasma membrane, the invaginations were capped by a brief swelling of a peripheral region of the membrane.Furthermore, a hybrid HS-AFM with a confocal fluorescence microscope enabled simultaneous imaging of the morphological dynamics of the plasma membrane and the localization of various membrane-associated proteins essential for maturation of endocytic vesicle such as FCHo, Dynamin, etc. This technique will allow for elucidation of the detailed processes of endocytosis with the dynamics of membrane proteins and lipid bilayers.

Congenital Melanocytic Nevus with Distinctive Nevus Cell Proliferation within Multiple Epidermal Cyst-Like Changes.

Dear Editor: Congenital melanocytic nevus (CMN) is defined as a lesion present at birth and containing melanocytic nevus cells. It is characterized by the diffuse infiltration of melanocytes in the deepest reticular dermis and subcutis, and by the presence of melanocytes around skin appendages1. Here, we present an interesting case of CMN with distinctive nevus cell proliferation within multiple epidermal cyst-like changes. A 57-year-old man presented for evaluation of a lesion on his face, which he had had since birth. He reported that the lesion had gradually become darker and larger, and complained about foul-smelling cheese-like discharge upon squeezing. Physical examination revealed a solitary 1.2×2.0-cm dark-colored plaque on his right cheek. The lesion had a large dilated pore in the center and multiple adjacent small pits on its surface. The nevus was excised, and a rotational flap was used to cover the defect. Histopathological examination of the excised lesion revealed diffuse infiltration of melanocytes in the reticular dermis, hair follicles, and sebaceous glands, showing typical features of CMN along with multiple cysts filled with keratinous material (Fig. 1A). Unlike other CMN-containing epidermal cysts, melanocytic nevus cells were imbedded along the epithelium of a huge epidermal cyst, resembling buddings from a tree (Fig. 1B). At the 4-month follow-up, the patient had a well-healed scar and no evidence of recurrence. Fig. 1 (A) Solitary dark-colored plaque on the patient's right cheek with foul-smelling discharge on squeezing. (B) Histopathological findings in the excised specimen showed congenital melanocytic nevus with multiple cysts filled with keratinous material (H&E, ... There are multiple cases of nevus with cysts in the literature2,3. Cohen and Rapini4 described several cases of melanocytic nevus overlying or surrounding an epidermal cyst. However, there are currently no reports of nevus cells imbedded in the wall of a cyst as seen in the present case. Thus, here, we report a rare case of CMN with distinctive nevus cell proliferation within multiple epidermal cyst-like changes. We suspect that this happened through migration of nevus cells into the epithelium during the formation of connections between the cyst wall and epidermis, or by direct invasion of the epithelium of the epidermal cyst.

Experimental study on stress corrosion crack propagation rate of FV520B in carbon dioxide and hydrogen sulfide solution

FV520B steel is a kind of precipitation hardening Martensitic stainless steel, it has high-strength, good plasticity and good corrosion resistance. Stress corrosion cracking (SCC) is one of the main corrosion failure mode for FV520B in industrial transportation of natural gas operation. For a better understanding the effect on SCC of FV520B, the improved wedge opening loading (WOL) specimens and constant displacement loading methods were employed in experimental research in carbon dioxide and hydrogen sulfide solution. The test results showed that the crack propagation rate is 1.941×10−7–5.748×10−7mm/s, the stress intensity factor KISCC is not more than 36.83MPa m. The rate increases with the increasing of the crack opening displacement. Under the condition of different initial loading, KISCC generally shows a decreasing tendency with the increase in H2S concentration, and the crack propagation rate showed an increasing trend substantially. For the enrichment of sulfur ion in the crack tip induced the generation of pitting corrosion, promoting the surrounding metal formed the corrosion micro batteries, the pit defects gradually extended and connected with the adjacent pit to form a small crack, leading to further propagation till cracking happened. Fracture microscopic morphology displayed typical brittle fracture phenomena, accompanying with trans-granular cracking, river shape and sector, many second cracks on the fracture surface.

Substantiation of low-capacity equipment sets for open pit coal mining, considering land use efficiency

Under discussion is the equipment for open pit mining of scarce coal reserves. Methods of overburden dumping are systematized. A new dumping method is offered; it allows reducing land withdrawal by means of utilizing adjacent open pit. The author presents relations for area of internal dumping, considering coefficient of dumping in the adjacent open pit and the volume of the adjacent open pit. The feasibility of overburden placement in mined-out pits is analyzed.

Grouting to remove piles from a tunnelling machine cutter-head

This paper provides a summary report on measures taken to remove embedded steel ‘H' pile obstacles from the cutter head of an advancing tunnel-boring machine. The piles were part of the soil-mixing retaining wall built for the cut-and-cover tunnel construction of a Taiwan high-speed rail tunnel and a Taiwan railways administration tunnel, which were directly above the mass rapid transit tunnel that was to be constructed. The collision zone between the boring machine and piles was below groundwater level and was approximately 23 m below the ground surface in a silty sand layer. To remove the piles safely from the cutter head, horizontal grouting from two adjacent work pits was conducted for waterproofing and solidification purposes. By controlling the amount of soil being flushed out during the grout hole drilling first, and also the pressure used for grouting later, the measured tunnel settlement resulting from grouting was negligible. Because of the favourable watertightness of the grouted zone and the dewatering influence of a nearby construction site, pile removal was conducted under particularly dry working conditions. In total, 12 piles were identified in the collision zone and were successfully removed from the cutter head by hand tools.

A Method for Subsurface-Banding Poultry Litter in Plots Not Accessible with Conventional Field Equipment

<abstract> <b><sc>Abstract. </sc></b>Subsurface band application of poultry litter has been shown to be effective in reducing nutrients in runoff and leachate, relative to surface broadcast application of litter. Some field plot arrangements, such as plots having adjacent pits in the soil, prevent the use of conventional field equipment because the equipment cannot traverse the pits. A small trencher and a method using a forklift were developed for making trenches in soil for subsurface band application of poultry litter in plots where conventional field equipment such as a tractor and trailing implement cannot be used. A cantilever beam was mounted to the forklift and the trencher was attached to the end of the beam. The forklift was upslope or downslope from the plots and the forklift traveled parallel to the lengths of the trenches that were formed, so it was not necessary for a vehicle to traverse the pits. The method was used for subsurface band application of broiler litter in rainfall simulation plots which had a pit on each side of each plot. The pits enabled installation of wick and zero-tension pan lysimeters beneath the plots. The method worked well for making trenches in plots in this field experiment. Broiler litter was applied in the trenches and the experiment investigated phosphorus and nitrogen in runoff and leachate during rainfall simulation.

Effect of surface Si redistribution on the alignment of Ge dots grown on pit-patterned Si(001) substrates

Thermally activated redistribution of Si surface atoms is found to be a crucial factor for the growth of aligned Ge dots on pit-patterned Si(001) substrates. A phenomenon of Si accumulation around the edge of pits significantly alters the substrate surface morphology. As the pit spacing is reduced to below 100 nm, a convex morphology developed between adjacent pits causes a chemical potential distribution that drives the Ge dots into the pits. In addition, the pits of an etching depth greater than 60 nm will evolve into truncated inverted pyramids with sharp base corners that provide deep potential wells for the confinement of Ge dots. Perfectly aligned Ge dots are obtained on pit-patterned Si substrates with this range of pit spacing and etching depth. We also find that the initial geometric shape of the pits does not affect the spatial arrangement of Ge dots.

Study on Sheltering Effect of Underground Building to Horizontal Displacement of Retaining Wall of Foundation Pit

Due to the existence of underground building, the distribution of displacement field of adjacent foundation pit is obviously different from that of general foundation pit, and it is of great significance to correctly understand the sheltering effect of underground building to displacement field for determining the protection class of foundation pit while supporting design of foundation pit, and protecting the safety of metro station built near and surrounding buildings during the construction. Relying on the foundation pit project of metro station and combining the sensitivity theory through mechanism analysis, this article discovers that the sheltering effect is most obvious when the spacing between the underground building and retaining wall of foundation pit is 0.5H, and the sheltering effect can be ignored when the distance is more than 2H.

Time evolution of off-state degradation of AlGaN/GaN high electron mobility transistors

The evolution of AlGaN/GaN high electron mobility transistors under off-state stress conditions is studied by gate leakage current (Ig) monitoring, electroluminescence (EL), and atomic force microscope (AFM) imaging at room temperature. It is found that the number of off-state failure sites as identified by EL increases over time during stress until it reaches a saturation value. Ig increases accordingly during stress until this saturation number of failure sites is reached. AFM scanning of the device surface stripped of metal contacts and passivation reveals surface pits corresponding to the location of the EL spots. These pits have an elongated shape oriented towards the drain contact whose length is correlated with the distance to the adjacent pits and with the time since their appearance during the stress experiment. A model for the generation and evolution of the off-state stress-related failure sites is proposed consistent with the experimental results, bringing together surface migration of electrochemical species with trap-based leakage mechanisms and resulting in the formation of an exclusion zone around each failure site.

Statistical Analysis of Pit Dimensions for Pre-Corroded AA 7075-T6

Aluminum alloy 7075-T6 specimens were corroded in 3.5% NaCl solution for 120 hours and 240 hours, respectively. Morphology and dimensions of corrosion pits on specimen surface were inspected with white light confocal profiler. Statistical analysis shows that pit dimensions can be fitted well with log-normal and Gumbel distribution. After surface inspections, we performed high-cycle fatigue tests for the specimens. Fracture analysis shows that fatigue cracks initiate from single pit or two adjacent pits, and the crack-initiation pit shape and dimensions were examined with SEM. It is found that initiation pit dimensions can be well described with the log-normal distribution. Additionally, initiation pit dimensions are significantly larger than those measured on specimen surface before fatigue tests.