Cratering

Hydrocarbons are of a lower density than formation water. Thus, if no mechanism is in place to stop their upward migration they will eventually seep to the surface. On seabed surveys in some offshore areas we can detect crater like features ( pock marks ) which also bear witness to the escape of oil and gas to the surface. It is assumed that throughout the geologic past vast quantities of hydrocarbons have been lost in this manner from sedimentary basins. 

Formation breakdown and subsequent liquefaction of the near surface strata and the initiation of cratering below the rig. This will result in a surface blowout... 

Figure Bl.19.7. A series of time-lapse STM topographic images at room temperature showing a 40 mn x 40 mn area of Au(l 11). The time per frame is 8 mm, and each took about 5 min to scan. The steps shown are one atomic unit in height. The second frame shows craters left after tip-sample contact, which are two and three atoms deep. During a 2 h period the small craters have filled completely with diflhismg atoms, while the large craters continue to fill. (Taken from [29], figure 1.)...

Sulfur is found in meteorites. R.W. Wood suggests that the dark area near the crater Aristarchus is a sulfur deposit. 

Table 19. Cratering Characteristics of ANFO, Slurry Explosives, and TNT ...

Copper wines are used primarily because of thein economy and resistance to sweep, ie, tendency of the wine to move in a plane perpendicular to its length, during plastic encapsulation (11—16). Because copper is harder than gold, more attention is needed during the bonding operation to prevent the chip from cratering. Table 6 fists the various properties for wine materials. 

Pressure—temperature diagrams for the coesite—quart2 equilibrium have been summari2ed (23). Coesite has been found ia nature ia the meteor crater ia Ari2ona. 

Stishovite. Stishovite was first prepared (68) ia the laboratory ia 1961 at 1200—1400°C and pressures >16 GPa (158,000 atm). It was subsequentiy discovered, along with natural coesite, ia the Ari2ona meteor crater. It has been suggested that these minerals are geological iadicators of meteorite impact stmctures. Stishovite (p = 4.35 g/cm ) is the densest known phase of silica. The stmcture, space group P42/nmn is similar to that of... 

Fig. 2. Tool wear mechanisms, (a) Crater wear on a cemented carbide tool produced during machining plain carbon steel, (b) Abrasive wear on the flank face of a cemented carbide tool produced during machining gray cast iron, (c) Built-up edge produced during low speed machining of a nickel-based alloy.

Grater Wear. Crater wear (Fig. 2a) is caused by a chemical interaction between the rake face of a metal-cutting insert and the hot metal chip flowing over the tool. This interaction may involve diffusion or dissolution of the tool material into the chip. 

Built-up Edge. At relatively low speeds in metal-cutting operations, the tool tip does not get hot enough for crater wear to be significant. Under these conditions the metal may, however, become welded to the tool tip as built-up edge (Fig. 2c). 

Straight WC—Co tools are not suitable for machining steels that produce long chips because straight grades undergo crater wear from diffusion of WC into the steel chip surface. However, soHd solutions of WC—TiC, WC—TiC—TaC, etc, resist this type of chemical attack. In addition, tantalum carbide can improve thermal-shock resistance. Steel cutting compositions thus typically contain WC—TiC—(Ta,Nb)C—Co. Tantalum carbide is often added as (Ta,Nb)C because the chemical similarity between TaC and NbC makes their separation expensive. 

Hardness and solubiUty for other carbides make TiC an important component of siatered cemented carbides. Although the addition of TiC or WTiC2 to WC—Co alloys imparts crater wear resistance, it also reduces the transverse mpture strength and fracture toughness of these alloys. Therefore, the amount of TiC or WTiC2 added to WC—Co alloys for steel machining is kept to a minimum, typically no greater than 10 wt %. The TiC-based cermets, on the other hand, may contain 30—85 wt % TiC. 

Low viscosity cellulose propionate butyrate esters containing 3—5% butyryl, 40—50% propionyl, and 2—3% hydroxyl groups have excellent compatibihty with oil-modified alkyd resins (qv) and are used in wood furniture coatings (155). Acetate butyrate esters have been used in such varied apphcations as hot-melt adhesive formulations (156), electrostatically spray-coated powders for fusible, non-cratering coatings on metal surfaces (157—159), contact lenses (qv) with improved oxygen permeabiUty and excellent wear characteristics (160—162), and as reverse-osmosis membranes for desalination of water (163). 

Upon the advent of high performance jet-powered aircraft, the fire bomb became obsolete. When deUvered at speeds approaching Mach one (345 m/s), the design characteristics were often grossly exceeded and many units broke up or functioned while stiU on the aircraft. DeHvery from high altitude created craters and deposited most of the flame agent payload in those craters. 

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