Rapid Compaction Research Articles

Rapid Omnidirectional Compaction of Y2O3 Stabilized Tetragonal Zirconia

ABSTRACTThe Rapid Omnidirectional Compaction (ROC) technique has been applied successfully to the densification of TZP (3 mole % yttria) ceramics at 1260°C. The combination of high pressure (830 MPa) and temperature results in the plastic deformation of the ceramic particles. The extent of deformation, and consequently, the ROCing temperature, can be determined by using hot hardness of the ceramic material as an approximation of the ceramic's yield stress. The materials ROCed at 1260°C are characterized by a grain size of 0.15 gim, a flexure strength of 1300 MPa, a hardness of 1340 kg/mm2, and a fracture toughness of 5.0 MPa m1/2.

Controls on peat accumulation in the Permian Vryheid Formation in a part of northern Natal, South Africa

The early Permian Vryheid Formation is a fluviodeltaic tongue of sediment deposited on the passive northern margin of an asymmetric, intracontinental linear trough (Karoo basin). In the study area these strata attain a maximum thickness of about 270 m, comprising three informal lithostratigraphic members (Lower zone, Coal zone and Upper zone). The Coal zone is characterized by arkosic, coarse to very coarse, pebbly sandstones and subordinate fines arranged in upward-fining sequences, many of which are coal-capped. These units are interpreted as distal outwash fan deposits. Sedimentation patterns in the Upper and Lower zones are dominated by superimposed upward-coarsening sequences representing repeated wave/fluvially-dominated fan delta progradation. Peat accumulation in the cool, seasonal climate which prevailed during Vryheid Formation sedimentation was slow. Significant peat thicknesses were deposited only in areas of low basin/compaction subsidence in the Coal zone during a period of general stability. Extensive upper delta plain and alluvial plain peats formed on broad platforms created by abandonment of braided channel systems. The thickest peats accumulated in raised swamps where vegetation-stabilized contemporaneous channels promoted a high water table. Peat erosion by later channel activity was slight since channel widening rather than stream-bed erosion prevailed. Coals thin, split and contain more ash near loci of contemporaneous channel activity. Upper delta plain coals were not marine-influenced. Some lower delta plain coals also formed on broad abandoned deltas and are likewise extensive. Rapid compaction subsidence rates attracted channel activity or marine incursions and the seams are thin. Peats also accumulated in restricted emergent interdistributory bays during delta construction. These coals are thin, discontinuous, marine-influenced and contain numerous clastic partings.

Stages in the compaction of peat; examples from the Stephanian and Permian of the Massif Central, France

Thick coal seams in the intramontane basins of the Massif Central allow a detailed study of peat/coal compaction. Three stages of compaction can be detected. Stage 1—occurred during the deposition of the peat. Coal beds which thicken and dip away from penecontemporaneous sandstones suggest rapid compaction. Stage 2—compaction of peat related to overburden pressure in some cases resulted in the formation of lakes over peat beds. The thickness of the lacustrine deposits may give an indication of the amount of compaction that took place. One possibility is that the early compaction was related to the progradation of siliciclastics over the peat. Stage 3—occurred after the organic sediment achieved some rigidity. Compaction can be calculated from deformed clastic dykes.

Methane-derived authigenic carbonates formed by subduction-induced pore-water expulsion along the Oregon/Washington margin

Authigenic magnesian calcite, dolomite, and aragonite are precipitated in the uppermost terrigenous sediments of the Washington/Oregon accretionary prism by subduction-induced dewatering. These distinctive carbonates are methane-derived and occur at sites of concentrated pore-water expulsion. Unique biologic communities that subsist, at least indirectly, on methane (Suess et al., 1985) are also found at some of these sites. The methane, which is dominantly biogenic, is carried to the uppermost sediments of the prism by fluids and is oxidized by sulfate reducers before being incorporated into a carbonate cement. Carbonate precipitation occurs below the oxic layer, probably no deeper than several centimetres to a few metres below the seabed. Cementation may be induced by three factors: (1) increased carbonate alkalinity resulting from microbial sulfate reduction, (2) decreased σCO 2 solubility resulting from a pressure decrease when the pore water escapes the prism, and/or (3) the addition of Ca 2+ and Mg 2+ ions from sea water near the sediment/water interface. The convergent margin setting engenders precipitation of authigenic carbonates in several ways. Compressive stresses induce anomalously rapid compaction and dewatering rates, and they may cause overpressuring in migrating pore water, thereby delaying precipitation of carbonates until pressure is released near the sediment-water interface. Structural deformation of the accretionary prism creates pathways (such as fault zones), secondary fracture porosity, and dipping permeable layers (often exposed by mass movement) for efficient advection and expulsion of methane-enriched pore water. These characteristic conditions, which lead to the precipitation of methane-derived carbonates, may be found at other convergent margins.

Water-enhanced dynamic recrystallization and solution transfer in experimentally deformed carnallite

Cylindrical samples of polycrystalline carnallite (KMgCl 3, 6H 2O) were deformed in a triaxial apparatus at 60°C, at confining pressures between 0.1 and 31 MPa and at strain rates between 10 −4 and 10 −8 s −1. In a number of cases, small amounts of saturated carnallite brine were added. Samples without added brine deform by intracrystalline slip, mechanical twinning, cracking, and by frictional sliding on crack surfaces. Stress-strain curves of these samples are strongly dependent on confining pressure. Addition of brine has a dramatic effect on both microstructural development and mechanical properties. Grain-boundary migration is strongly enhanced. At lower strain rates, additional intracrystalline effects start to appear, together with the onset of solution transfer. Rapid compaction in samples deformed with added brine causes high fluid pressures to develop. At higher strain rates addition of brine results in a decrease of the flow stress by a factor of two. This weakening will increase even further at strain rates below about 10 −9 s −1, when solution transfer becomes rate controlling. It is argued that deformation of carnallite in nature is adequately described by the flow law found for samples deformed with added brine.

Relationships Between Processing, Microstructure, and Tensile Properties of Co–Cr–Mo Alloy

AbstractStellite alloy no. 21 was produced via rapid solidification processing (RSP) in a variety of particulate morphologies (coarse and fine powder, fibres, and ribbons), the various RSP forms showed similar fine microstructures with only slight differences in the scale of the microstructural features. These RSP particulates were consolidated by extrusion, dynamic compaction, and rapid omnidirectional compaction (ROC). Dynamic compaction proved to be unacceptable for this alloy because of non-uniform porosity and the inability to develop a metallurgical bond between particulates. A plot of elongation against yield strength depicted two yield strength-ductility relationships for the Co–Cr–Mo type alloys. As-ROC samples had a low yield strength-ductility relationship. However, after hot forging, the relationship shifted to a level comparable to similar material processed by conventional extruding and forging operations. Atomized powder size also affected the strength-ductility relationships of the extrude...

振動による微粉体充てんの迅速化に関する研究

In general, many factors lead to a decline in the capacity of equipment packing fine powders. These factors are mostly due to the complicated properties of fine powders, such as adhesiveness, poor fluidity and dusting characteristics.This study was undertaken to investigate the rapid compaction of fine powder. The laboratory-size vibration equipment was set up, and the optimum frequency and amplitude were investigated.Three metal soaps were used as a sample. It was found that the vibration during packing was quite effective. Good compaction of fine powder was achieved in a short time period from 1/5 to 1/10 in comparison with no vibration. The optimum frequency varies with the height of the powder bed. When the height of the powder bed is high, the optimum frequency is low and vice versa.A higher amplitude, namely, a higher acceleration of vibration gives a better packing effect within the limits of this experiment.

Side‐scan targets in Lake Superior—evidence for bedforms and sediment transport

ABSTRACTA high‐resolution side‐scan sonar survey of the lake bed off the Keweenaw Peninsula, Lake Superior, demonstrates that bottom currents are affecting lake bed morphology at depths up to 240 m. Numerous lineations which run parallel to the shore appear to be sand ribbons. A field of sedimentary furrows which occurs in one area demonstrates the long‐term directional stability of the near‐bottom flow. Large (100–300 m in diameter, 2–5 m deep), unusual ring‐like or arcuate depressions are common throughout the western half of Lake Superior. These rings themselves do not appear to have been formed by bottom currents, but may have developed as water was released by the rapid compaction of glacial sediments which underlie the lake bed. Off the Keweenaw Peninsula the forms of the rings have been modified by bottom currents. The bottom currents which have modified the lake bed are probably generated when storms cross the lake at times when it is poorly stratified.

Sabkhas, slumping, and compaction at Mufulira, Zambia

Algal structures such as stromatolites have long been recognized as closely associated with the cupriferous dolomitic shales of the Katanga Supergroup of Zaire and Zambia. Discovery of bioherms and biostromes in the predominantly arenaceous deposits of the Mufulira copper mine indicates a similar origin, with the more common copper deposits in dolomitic shale and their barren gaps due to bioherms.Renfro (1974) recognized the worldwide association of sabkhas, algal mats, and stratiform copper deposits. His interpretation of sabkha environments in cyclic depositional sequences at Mufulira is corroborated by detailed features in the mine.Recognition of abundant carbonized debris of algal mat, from 0.5 m down to microscopic size, in the marine sediments of Mufulira indicates an accumulation of decomposing vegetable debris that is more than sufficient to promote anoxic conditions in the bottom waters of the lagoons, with resulting precipitation of copper and iron sulfides contemporaneously with sedimentation.Compaction of algal material explains the 80 percent contraction of sun-cracked mud flakes. Also compaction by roughly two-thirds of the algal-rich graywacke and the C orebody accounts for the rapid sagging of overlying sabkha and terrestrial sediments, which was followed by a second marine invasion allowing deposition of the B orebody and central graywacke. Similar rapid compaction of the latter under its cover of sabkha and red-bed sediment caused further sagging, marine invasion, and deposition of the A orebody and graywacke vertically above the C and B graywackes.Although Renfro's hypothesis of mineralization by ascending groundwaters may account for some initial precipitation of sulfides beneath algal mats, the bulk of the preserved mineralization at Mufulira exhibits features more compatible with syngenetic deposition of sulfides associated with decaying transported algal material in marine lagoons.

Importance of Secondary Porosity in Sandstones to Hydrocarbon Exploration: ABSTRACT

Terrigenous sandstones in many basins owe their reservoir quality to secondary porosity that developed by the dissolution of detrital framework grains (chiefly feldspar) and cement minerals (chiefly calcite and evaporite minerals). This dissolution event is responsible for changing tight sandstones to porous and permeable sandstones slightly prior to the major episode of hydrocarbon migration. Dissolution of most non-evaporite minerals is accomplished by formation water containing carbon dioxide generated during the thermal or bacterial breakdown of hydrocarbons. Dissolution porosity is commonly well developed at 6,000 to 9,000 ft (1,829 to 2,743 m), but gradually is lost during deeper burial stages by recementation (chiefly by ferroan calcite, ferroan dolomite, and kaoli ite). During sandstone burial, variations in the simple scheme of cementation ^rarr decementation ^rarr recementation is complicated in basins with complex plumbing systems and those that experience uplift. For example, dissolution porosity in some uplifted sandstones develops during invasion by meteoric water flowing downdip. Dissolution porosity in sandstones can be suspected from certain log responses and water-saturation characteristics, but is best identified from clues visible in thin sections made of dyed, epoxy-impregnated perm plugs. Clues to secondary porosity in thin section include: (1) oversized pores formed where framework grains have been dissolved; (2) patchy distribution of carbonate or evaporite cement; (3) honeycombed feldspar grains; (4) fossil molds; (5) grains whose margins were etched by previous cement; (6) broken silicate grains that formed when rapid compaction followed removal of cement minerals; and (7) quartz grains that have been reduced to shards when calcite, which invaded quartz along hairline fractures during cementation, was dissolved. Secondary porosity is not likely to d velop good reservoir quality in sandstones whose primary porosity was lost chiefly by compaction. Sandstones with abundant clay clasts, fecal pellets, glauconite, or micaceous rock fragments can lose all effective porosity by ductile grain deformation. A knowledge of sandstone composition is important to predicting reservoir quality. End_of_Article - Last_Page 747------------

Reservoir Quality in Tertiary Sandstones along Texas Gulf Coast: ABSTRACT

Three data bases were developed for a regional survey of reservoir quality in Tertiary sandstones along the Texas Gulf Coast. 1. Core analyses from 252 wells (10,900 datum points) are the basis of plots which indicate that porosity and permeability do not simply decrease with depth but commonly increase at depth by development of secondary leached porosity. 2. Point count analyses of 535 thin sections from 169 wells for mineralogy, diagenetic features, and porosity types indicate, within formations, regional mineralogic trends that affect reservoir quality, especially at depth. The average Tertiary sandstone is a moderately sorted, very fine-grained quartzose lithic arkose. Each Tertiary formation shows a similar general diagenetic history; primary porosity is dominant in the shallow subsurface, and secondary leached porosity is dominant in the moderate and deep subsurface. 3. Plots of interval transit time versus depth for 87 acoustic logs indicate general compaction and consolidation histories of complete stratigraphic sections, and they are useful for comparing compaction and consolidation histories among different areas. Both the Wilcox and Frio trends exhibit a general pattern of more rapid compaction and greater degree of consolidation in the lower Texas Gulf Coast than in the upper Texas Gulf Coast. End_of_Article - Last_Page 488------------

Radiation-Induced Dilatations in Vitreous Silica

It is shown that when vitreous silica is irradiated in a nuclear reactor, three effects cause dimensional changes: a homogenization effect assigned to fast neutrons (period $\ensuremath{\sim}3\ifmmode\times\else\texttimes\fi{}{10}^{20} \mathrm{nvt}$), a compaction (about 3%) assigned mainly to fast neutrons (period \ensuremath{\sim}3\ifmmode\times\else\texttimes\fi{}${10}^{19}$), and a dilatation caused by ionization. The ionization-induced dilatation is negative at the beginning of the irradiation, but becomes positive after a brief irradiation. It probably is responsible for the positive dilatation which occurs after the maximum compaction. Most specimens show internal stresses which give evidence of nonuniform effects. The cause is a radiation gradient due to absorption and/or scattering of the radiation in the specimen. In the period of rapid compaction the strain shows one sign, reaches a maximum, then goes to zero near the maximum in the compaction, and changes sign in the period of expansion. The strain does not seem to saturate when the dilatation saturates. The deformation of the specimens is of the order of magnitude expected from the internal stresses. A thermal effect like a radiation annealing was found in the region between room temperature and 90\ifmmode^\circ\else\textdegree\fi{}C. Results obtained from irradiations by x rays, electrons, as well as by mixed radiation in a nuclear reactor are reported. Because of the concomitant ionization effect it was not found possible to determine the displacement threshold energy by electron bombardment. The ionization effects are taken as evidence of electrostatic effects in the radiation-induced dilatations of silica. However, the electrostatic effects cannot account for all of the volume changes observed in the irradiation of vitreous silica.