Bottoms Of Pits Research Articles

Rational design patterns for artificial ice cluster construction at bottoms of mined-out kimberlite pits by means of layer-by-layer water filling

Rational design patterns for artificial ice cluster construction at bottoms of mined-out kimberlite pits by means of layer-by-layer water filling

Comparative study of the stress corrosion behavior of a multiuse bainite steel in the simulated tropical marine atmosphere and seawater environments

Stress corrosion cracking (SCC) behavior of a multiuse high-strength low-alloy (HSLA) bainite steel was comparatively studied in the simulated seawater and marine atmosphere environments using electrochemical measurements, static load SCC and slow strain rate tensile (SSRT) tests. The difference in SCC behavior was characterized in detail by morphology observation via scanning electron microscopy (SEM) and corrosion product analysis via X-ray diffraction (XRD) and energy dispersion spectrum (EDS) techniques. The results indicate that the HSLA bainite steel is very sensitive to SCC in the simulated tropical marine atmosphere, mainly due to the thin and uneven electrolyte film, which is characterized by a fast oxygen transportation rate on the steel surface. The rust layer also plays an important role in determining SCC behavior in the simulated marine atmosphere, as it restrains the electrochemically anodic process and promotes the cathodic process, particularly the hydrogen evolution reaction, resulting in the nucleation and transgranular-mode propagation of SCC microcracks at the bottoms of pits. As a result, both localized anodic dissolution (AD) and hydrogen embrittlement (HE) effects are promoted, contributing to the significant increase in the susceptibility of HSLA bainite steel to SCC.

Origin of honeycombs: Testing the hydraulic and case hardening hypotheses

Cavernous weathering (cavernous rock decay) is a global phenomenon, which occurs in porous rocks around the world. Although honeycombs and tafoni are considered to be the most common products of this complex process, their origin and evolution are as yet not fully understood. The two commonly assumed formation hypotheses – hydraulic and case hardening – were tested to elucidate the origin of honeycombs on sandstone outcrops in a humid climate. Mechanical and hydraulic properties of the lips (walls between adjacent pits) and backwalls (bottoms of pits) of the honeycombs were determined via a set of established and novel approaches. While the case hardening hypothesis was not supported by the determinations of either tensile strength, drilling resistance or porosity, the hydraulic hypothesis was clearly supported by field measurements and laboratory tests. Fluorescein dye visualization of capillary zone, vapor zone, and evaporation front upon their contact, demonstrated that the evaporation front reaches the honeycomb backwalls under low water flow rate, while the honeycomb lips remain dry. During occasional excessive water flow events, however, the evaporation front may shift to the lips, while the backwalls become moist as a part of the capillary zone. As the zone of evaporation corresponds to the zone of potential salt weathering, it is the spatial distribution of the capillary and vapor zones which dictates whether honeycombs are created or the rock surface is smoothed. A hierarchical model of factors related to the hydraulic field was introduced to obtain better insights into the process of cavernous weathering.

Field experiment of stress corrosion cracking behavior of high strength pipeline steels in typical soil environments

In this study, the corrosion behaviors of four pipeline steels, i.e., X70, X80, X100, and X120, in acidic soil (Yingtan and Xishuangbanna), alkaline soil (Korla and Dagang), and dry sandy soil (Lhasa) in China were investigated using U-bend samples and notch crevice specimens by exposure testing. The morphologies and compositions of the corrosion products were analyzed by digital photography, scanning electron microscopy, and X-ray diffraction. The results indicated that all the tested pipeline steels exhibited stress corrosion cracking (SCC) susceptibility in the abovementioned three typical soils. The SCC susceptibility increased as the strength of the pipeline steels increased and as the soil pH decreased. In acidic soil, no relationship existed between the locations of SCC crack initiation and pitting occurrences. In alkaline soil, SCC cracks were mainly initiated at the bottoms of pits.

Dilational fault slip and pit chain formation on Mars

Pit crater chains that are parallel or collinear with normal faults are common on Mars, but only rarely observed on Earth. We explore the origin of pit crater chains using recent high-resolution imagery from Mars, laboratory simulation of pit chains, investigation of recent pit chains formed in response to seismic fault slip in Iceland, and assessment of rock failure criteria and the Martian crustal stress field to develop a deeper understanding of the relationship between pit chain formation and fault activity. Based on these analyses, we conclude that pit chains form in response to dilational fault slip. Because gravitational acceleration on Earth (9.81 m/s2) is higher than on Mars (3.72 m/s2), stress within Earth is greater than that of Mars for any given depth. Consequently, steep fault segments are likely to extend to about 5 km depth on Mars compared with about 2 km depth on Earth. Dilation of these steep segments associated with fault slip on Mars could result in large volume increase in the uppermost crust, influencing groundwater flow and discharge and mineralization. Based on crosscutting relationships, pristine pit morphologies, and lack of evidence of sediment accumulation in the bottoms of pits, we interpret that some pit craters may be actively forming in response to dilational fault slip. Figure 1. (A) Composite Viking imagery of normal fault scarps defining horsts and grabens in the southeast part of Alba Patera, Mars. Fault segmentation and en echelon arrangement of faults and grabens are common. Scale bar is 50 km. (B) THEMIS visible spectrum image shows detail of normal faults and pit chain (Phlegethon Catena) shown in A. Scale bar is 5 km. (C) Mars Orbital Camera image shows clear association of pit chains with normal fault scarps within graben on the southeast flank of Alba Patera. Scale bar is 1 km.

Repair of impurity-poisoned protein crystal surfaces.

The surface morphology of Bence-Jones protein (BJP) crystals was investigated during growth and dissolution by using in situ atomic force microscopy (AFM). It was shown that over a wide supersaturation range, impurities adsorb on the crystalline surface and ultimately form an impurity adsorption layer that prevents further growth of the crystal. At low undersaturations, this impurity adsorption layer prevents dissolution. At greater undersaturation, dissolution takes place around large particles incorporated into the crystal, leading to etch pits with impurity-free bottoms. On restoration of supersaturation conditions, two-dimensional nucleation takes place on the impurity-free bottoms of these etch pits. After new growth layers fill in the etch pits, they cover the impurity-poisoned top layer of the crystal face. This leads to the resumption of its growth. Formation of an impurity-adsorption layer can explain the termination of growth of macromolecular crystals that has been widely noted. Growth-dissolution-growth cycles could be used to produce larger crystals that otherwise would have stopped growing because of impurity poisoning.

Dissolution of Baryte (001) Observed by Hydrothermal Scanning Force Microscopy

Scanning force microscopy (SFM) provides in situ access to the microtopography of mineral surfaces and its kinematics during dissolution, with monolayer resolution. Informat ion about not only the mechanism of dissolution, but also quantitative data such as the dissolution rate or activation energy can be acquired. However, the lower limit of dissolution rates that can be studied by SFM lies in the range of 10 -9 mol/m2s. Experiments at elevated temperatures (e.g. those requiring elevated pressure) were not possible using commercial microscopes. Therefore, SFM in situ studies were mainly limited to minerals with dissolution rates higher than 10 -9 mol/m2s at near-room temperature. In order to solve this problem, a pressurizable SFM was constructed (Higgins et al., 1998) which allows examination of dissolution kinetics on mineral surfaces beyond the ambient boiling point of water. Here we present kinetic data on the dissolution of baryte (001). Dissolution and growth of baryte is significant in regulating the abundance of solvated Ba in the hydrosphere and has relevance in baryte scale formation in offshore oil wells (Putnis et al., 1995). In deionized water between 90~ and 125~ baryte (001) dissolves by retreat of steps at (001) terraces. The orientation of the steps is parallel to and [010]. The steps occur such that, in alternating half layers (height: c/2), only steps that retreat either in the positive or negative a-direction are stable. In the case that steps retreat in the positive adirection, the [010] steps are only stable retreating in the negative a-direction, and vice versa. Therefore, steps generated by pits form a triangle pointing in alternating half layers in the positive and negative adirections alternately (Fig. la). This alternating pattern can be attributed to the 21 screw axis parallel to [001] (Putnis et al., 1995). Between 90~ and 125~ steps retreat about twice as fast as [010] steps. Due to these different velocities and the alternating step pattern, etch pits, probably generated by linear defects, have a six-sided shape elongated in [0101 (Fig. lb,c). By measuring step velocities between 90~ and 125~ the activation energy for step retreat (Es) can be determined. On baryte (001) we found Es for retreat of steps to be 34 _+ 4 kJ/mol and for [010] steps to be 31 _+ 6 kJ/mol. Due to the error ranges, different activation energies for different steps cannot be resolved. However, judging by the shape of etch pits at room temperature reported by Putnis et al. (1995), a higher activation energy for the retreat of steps seems to be likely. Considering the step velocities and the slopes of the pit walls, the frequency of generating monolayer pits within deep etch pits can be calculated. By this frequency the dissolution rate of a surface consisting exclusively of pit walls can be determined (Jordan and Rammensee, 1998). At 90~ (1250C) this rate is about 7 x 10 7 mol/m2s (1 x 10 .6 mol/m2s). The rates reasonably agree with literature data determined by solution chemistry (1.12 x 10 -7 mol/m2s, 90~ pH 5.7; Dove and Czank, 1995), bearing in mind that due to the fiat bottoms of the etch pits, our rates must be regarded as maximum rates. Figure 1 d shows the baryte (001) surface during dissolution on a large scale. Low dissolution rate areas cover at least 30% of the surface in this scan area. As in the case of the step velocities, it is possible to calculate the activation energy (Ep) by the temperature dependence of the maximum rates (about 10 kJ/mol). However, Ep is primarily the activation energy for monolayer pit formation within etch pits. If step retreat does not contribute to the macroscopic activation energy for dissolution (Em), as observable e.g. in bulk experiments, Ep reflects Era. However, the actual rate and, therefore, the macroscopic activation energy (Em) are determined by the rate of step formation and the step velocities (via the expansion of fast dissolving areas such as pit walls). In comparison to room temperature (Putnis et al.,

アルミニウムの交流エッチングにおけるポーラス層の生成におよぼす諸因子の影響

The effect of such variables as etchant concentration, bath temperature, current density and current sweep rate on the cubic pit propagation and porous etch structure formation is discussed by means of electron microscopy and galvanovoltammetry. Maximum values of electrostatic capacitance were obtained under conditions for the formation of a deep porous etched layer. The formation of such a layer was found to be due to the formation and breakdown of a thin anodic film covering the inner surface of the cubic pits during etching. As indicated by the shape of cyclic polarization curves, the breakdown of the anodic film was facilitated by increases in the concentration and temperature of the etching solution, and suppressed by increases in the current sweep rate. This is explained by the rate at which Cl- ions are supplied to the bottoms of cubic etch pits.

Supernova rates and galaxy inclinations

The supernova frequency in Shapley-Ames galaxies of types Sc-Sd shows a sharp peak in objects with inclinations of about 25 deg or less. This suggests that many supernovae occur at the bottoms of deep steep-walled pits in the equatorial layer of gas and dust in late-type galaxies. Such pits might have been excavated by previous supernovae in rich clusters or associations. 14 refs.

The Influence of Environment Purity on Gaseous Iodine Embrittlement of Zircaloy-2 and High Purity Zirconium

Abstract The influences of environment purity on gaseous iodine embrittlement of high purity zirconium were investigated and compared to data obtained for Zircaloy-2. Iodide zirconium was embrittled at 350 C by constant extension rate tensile loading in highly purified and low constant partial pressure (40 Pa) iodine gas. Cracking was preceded by significant plastic deformation. Crack initiation probably involved sample pitting and subsequent cracking at the bottoms of pits. Brittle crack propagation proceeded by mixed intergranular separation and transgranular cleavage processes, compared to microvoid nucleation, growth, and coalescence typical of ductile fracture in argon. Purified and oxygenated (6 kPa) iodine gas also embrittled zirconium; however, the mechanism for crack initiation was influenced by oxygen additions. Sample pitting was eliminated, and crack initiation required local plastic strain concentrated at microstructural discontinuities such as grain boundaries. Similar findings were obtained...

Optical and interferometric studies on ferroelectric guanidinium aluminum sulphate hexahydrate cleavages and their etch patterns

GASH single crystals have been cleaved along (0001) planes and the cleavage faces have been studied by multiple-beam interferometry. The cleavage faces have also been chemically etched and the etch patterns studied optically. By etching a cleavage successively for three different periods it was found that the bottoms of the point-bottomed pits follow a linear etch path. Correspondence both in the etch patterns on matched pairs and in the etch patterns on the opposite sides of thin plates has been established. From the displacement in the etch patterns on the two sides of thin plates, the angle of inclination of dislocation lines has been determined to be about 10°. Intersecting rows of pits forming nodes at which three or four rows meet have been observed. The implications are discussed.

Dislocations in calcium fluoride

The cleavage faces of transparent calcium fluoride crystals collected from Amba Dungar of Chhota-Udepur, Gujarat State, have been etched and the etch pattern has been optically studied. It is observed that the point-bottomed pits are eccentric. By etching matched pairs of cleavage faces for successively different periods, it has been shown that point bottoms of the point-bottomed pits follow linear path. It is also observed that the eccentricity in the case of matched pits on matched faces is in the same sense. The eccentricities of the pits have been explained by postulating the existence of inclined linear dislocation lines in the body of the crystal. The inclinations of the dislocation lines have been computed from the measurements made on the pits, and it is observed that they are the same in case of matched pits on matched pairs. Thus it is conjectured that the pits nucleate at the site of inclined dislocation lines. This is also confirmed by etching the matched faces, one by one etchant and the other with a different etchant. It is shown that dislocation lines have different inclinations, but large majority of them are inclined at angles between 16° to 20° with the normal to the cleavage face.

"High frequency silicon alloy transistor"

The silicon alloy transistor is a high-frequency, p-n-p-type transistor capable of operation at high temperatures. Its temperature characteristic, derived principally from the use of silicon as the semiconductor, permits operation from-70° to 150°. It achieves its high-frequency characteristic through accurate control of the base geometry. The n-type base of silicon is accurately machined by jet electrochemical techniques. Alloy contacts of aluminum are fused into the bottoms of the etch pits without producing appreciable change in base geometry. The depth of alloy is limited by the thickness of the aluminum, by the temperature and by the length of time for alloying. Lead wires are soldered to the aluminum contacts and the transistor hermetically sealed in glass-metal containers.

High-frequency silicon alloy transistor

The silicon alloy transistor is a high-frequency, p-n-p type transistor capable of operation at high temperatures. Its temperature characteristic, derived principally from the use of silicon as the semiconductor, permits operation from - 70°C to 150°C. It achieves its high-frequency characteristic through accurate control of the base geometry. The n-type base of silicon is accurately machined by jet electrochemical techniques. Alloy contacts of aluminum are fused into the bottoms of the etch pits without producing appreciable change in base geometry. The depth of alloy is limited by the thickness of the aluminum, by the temperature, and by the length of time for alloying. Lead wires are soldered to the aluminum contacts and the transistor hermetically sealed in glass-metal containers. The electrical characteristics of typical silicon alloy transistors include an I <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">co</inf> of 0.005 µa, a common emitter forward current gain of 12, and an alpha-cutoff frequency of 12 mc.

Notes on Micronesian Pteridophyta

CERATOPTERIS THALICTROIDES (L.) Brongn. Bull Soc. Philom. Paris (1821): 186. 1821. This widely distributed species, usually found growing rooted in the muddy bottoms of rice and taro pits, has been known from Micronesia since Volkens reported it from Yap in 1901. Both Kanehira and Hosokawa added reports from Palau in 1935, with Hosokawa mentioning also Guam, probably basing this record on Safford's report in 1905. Hosokawa's specimen, no. 6858 (Fo), from Palau represents a very slender plant, with fertile fronds only, but is in all probability correctly referred to this species. Guam specimens from either Safford or Hosokawa have not been seen, but probably belong with the plants discussed as C. gaudichaudii below. To the records of true C. thalictroides may be added Fosberg & Wong 25488 (US, BISH, Fo)2 and Lessa 97 (BISH), both from Mogmog Islet, Ulithi Atoll, Caroline Islands. This is a large robust plant, with fronds up to 45 cm. tall, which was growing in the water of a taro pit. The vernacular name recorded by Lessa is walbwong.

THE OLFACTORY SENSE OF COLEOPTERA

In making a comparative study of the olfactory pores in beetles, 50 species belonging to 47 genera and representing 34 families were used. A group of pores is always present on the peduncle of each elytron. It lies on the dorsal side of the well-exposed radial plate. The number of pores on a pair of elytra varies from 12 to 310. As a rule, the more pores in the group the smaller they are and the closer they are together.Of the 47 winged species examined, 11 have only one group of pores on each wing, 21 have two groups on each wing, 12 have three groups on each wing, and 3 have four groups on each wing. These groups are always located on the dorsal surface. Only occasionally are a few scattered pores found on the ventral side of a wing. When one or two groups are present, they lie on the radius. When three groups are present, all three may lie on the radius, or two may lie on the radius and the third on the media. When four groups are present, one lies on the subcosta, two on the radius and one on the medi...

On the Geology of the Gold-fields of Nova Scotia

The observations which are the subject of this memoir were made at the request of the Provincial Government Commission for the International Exhibition. While engaged in their service, procuring a representation of the geology and mineral resources of the Province, I was specially directed, about the end of November last, to give some attention to the illustration of the geology of the gold-fields. The field of observation being very extensive, and the time fit for the work short, I deemed it most expedient to select, from the many, that locality which might appear to be the most interesting and instructive, and to examine it as thoroughly as time ad circumstances would permit. The gold-fields known as “Allen's” and “Laidlaw's” appeared best to meet the above conditions. They are interesting beyond a doubt, and are contiguous to excellent sections of rocks on two lines of railway, and are therefore somewhat favourably situated for the purpose of observation. In describing these gold-fields, we shall begin with the position that is lowest, gcolo~cally and otherwise ; this is Allen's field. The rock in situ is dark-coloured clay-slate; it is often talcose. This contains abundance of crystals of mispickle. It is pervaded by a number of vertical veins of auriferous quartz. These are exposed on the sides and bottoms of pits and trenches. It is only from report that I can say that they are auriferous; I could not get any information on the spot. The top of the slate-rock was glacierscratched; and in