Intergranular Matrix Research Articles

Undrained Fragility of Clean Sands, Silty Sands, and Sandy Silts

In this paper, intergranular (\Ie\dc\N) and interfine (\Ie\df\N) void ratios and confining stress are used as indices to characterize the stress-strain response of gap-graded granular mixes. It was found that at the same global void ratio (\ie) and confining stress, the collapse potential (fragility) of silty sand increases with an increase in fines content (FC) due to a reduction in intergranular contact between the coarse grains. Beyond a certain threshold fines content (FC\Dth\N), with further addition of fines, the interfine contact friction becomes significant. The fragility decreases and the soil becomes stronger. The value of FC\Dth\N depends on \ie and the characteristics of fines and coarse grains. At FC FC\Dth\N), fine grain friction plays a primary role and dispersed coarse grains provide a beneficial, secondary reinforcement effect. At the same \Ie\df\N, the collapse potential decreases with an increase in sand content. Beyond a certain limiting fines content, the soil behavior is controlled by \Ie\df\N, the collapse potential decreases with an increase in sand content. Beyond a certain limiting fines content, the soil behavior is controlled by \Ie\df\N only. An intergranular matrix diagram is presented that delineates zones of different behaviors of granular mixes as a guideline to determine the anticipated behavior of gap-graded granular mixes. New equivalent intergranular contact void ratios, (\Ie\dc\N)\Deq\N and (\Ie\df\N)\Deq\N, are introduced to characterize the behavior of such soils at FC FC\Dth\N, respectively.

Authigenic Phyllosilicates in the Middle Triassic Kremikovtsi Sedimentary Exhalative Siderite Iron Formation, Western Balkan, Bulgaria

AbstractTwo distinct assemblages of authigenic phyllosilicates were distinguished in the Kremikovtsi sedimentary exhalative (SEDEX) siderite iron formation (SIF) and noted as important tracers of two styles of mineralization characteristic of this type of ore deposit. Hydrothermal-sedimentary layer silicates are represented by rare occurrences of relict microcrystalline Mg-rich berthierine with a relatively low degree of structural ordering, associated closely with framboidal pyrite as an intergranular matrix cementing sparry siderite grains; the larger silicates are also represented by the diagenetic transformation product of berthierine, chamosite. Berthierine precipitated under anoxic conditions during advanced early diagenesis after chert deposition. Hydrothermal-epigenetic phyllosilicates (berthierine, chamosite, illite-smectite (I-S), and kaolinite) from the barite-sulfide assemblage are characterized by: crystalline and undeformed habits; relatively larger particle size, low-temperature polytypes, low to no mixed layering, and a high degree of crystallinity; absence of impurities and dominant monomineralic aggregates; affiliation to initial open spaces and deposition mainly as vug fillings and linings. They formed under pronounced control by the vuggy porosity of the siderite host caused by the invasion of acid (pH = 3–5), hot (200–230°C) hydrothermal fluids probably at the stage of burial diagenesis of the SIF under relatively stable reducing conditions fluctuating near the sulfide/sulfate stability boundary (logPO2≅−30). The greater Al concentration in hydrothermal solution than in seawater determines the affiliation of phyllosilicates in the Phanerozoic SEDEX SIFs to aluminous species (berthierine, chamosite) unlike low to non aluminous ones (greenalite, stilpnomelane) in the Precambrian IFs. The berthierine compositions, expressed by the Mg/Fe vs. Al/Si ratios, are a sensitive indicator of the geological conditions under which they formed (marine, non-marine, hydrothermal ore and pre-ore), thus allowing the genetic discrimination of this mineral from various localities.

Mechanical properties of a hybrid cemented carbide composite

Microstructural effects on the mechanical properties of a hybrid metal matrix composite, double cemented (DC) carbide, have been investigated. DC carbide contains granules of WC/Co cemented carbide in a matrix of cobalt. Overall composite hardness increases with decreased granule cobalt content as well as with decreased intergranular matrix fraction of cobalt. High-stress abrasive wear resistance also increases with decreased granule cobalt content and matrix fraction. Fracture toughness of the composite increases with increased cobalt matrix fraction and to a lesser extent with increased granule cobalt content. Increased granule size increases both fracture toughness and wear resistance. DC carbide exhibits a superior combination of fracture toughness and high-stress wear resistance than conventional cemented carbide. The combination of toughness and wear resistance in the composite improves with increased granule hardness.

Intergranular state variables and stress–strain behaviour of silty sands

Relative contributions by the coarser and finer grains in a silty sand to its stress–strain response are affected by the intergranular matrix structure. The nature of this contribution is illustrated using an intergranular matrix phase diagram in terms of void ratio (e), fines content (FC), and intergranular and interfine void ratios (es and ef). New intergranular state parameters (ψs, ψf) and (es, ef) are introduced as state variables to characterize silty sands; es and ef dictate the steady-state characteristics of silty sand at low and high fines contents, respectively; ψs and ψf reflect the plastic compressibility characteristics at low and high fines contents, respectively. Using these state variables, the anticipated stress–strain–strength behaviour of silty sand in comparison to that of the host sand is presented. Similar stress-strain behaviour is expected at the same es and initial confining stress σ′c, with a few exceptions. At a constant void ratio e, es increases while ef decreases with addition of fines; a silty sand passes through different states. First, at low fines content, es (< emax,HS, the maximum void ratio of the host sand, case 1), and high ef the stress–strain behaviour is primarily governed by intergranular friction between the coarser grains. The steady-state line (SSL) is primarily dependent on es and is fairly independent of σ′c; When compared at the same es and at the same σ′c(or at the same ψ or ψs), the silty sand and the host sand show similar (not identical) stress–strain behaviour; with addition of fines, as es increases, the collapse potential increases and the stress–strain response becomes weaker. Second, with further addition of fines, when es approaches or exceeds emax,HS, the SSL is influenced by es and σ′c. When es is near emax,HS (case 2), the stress–strain curves for silty sands are similar at the same es and the same σ′c (or at the same ψ or ψs), but different from and stronger than that of the host sand. At very loose states (es > emax,HS; case 3), the stress–strain curves, normalized with respect to σ′c, are similar at the same es (or at the same ψ or ψs). Third, with further addition of fines beyond a threshold value, ef becomes sufficiently low (case 4); the fines impart a significant influence, while the role of intergranular (coarser-grain) friction diminishes; the silty sand is expected to behave similarly (not identical) to the host fines at the same ef and ψf ; at this stage, with further addition of fines, the collapse potential decreases.

Interface magnetism in Fe-based nanocrystalline alloys

Nanoscale materials exhibit properties that can not be find in larger scale system due to the crystal size effects as well as structural variations between the interfacial regions and the crystalline interior. In this paper the consideration of the finite-size effects are limited to a special class of nonconventional granular materials produced by the devitrification of Fe-based amorphous ribbons. The complementary microstructural and magnetic studies show that in such mesoscopic systems the interfaces exhibit identifiable properties. The data presented do not provide the detailed picture of the internal structure of the boundary regions but bring information about their basic structural and magnetic properties. In particular the influence of the magnetic state of the intergranular amorphous matrix (ferro-or paramagnetic) on the local magnetic behavior of the interfaces is considered. The effect of the symmetry restriction at grain boundaries on the structurally sensitive parameter such as a magnetostriction is also presented and discussed.

Magnetic flux penetration and creep in BSSCO-2223 composite ceramics

We have experimentally investigated the magnetic flux penetration through a Bi-2223 polycrystalline superconductor synthesized by a classical solid-state reaction method. Electrical resistance, AC susceptibility, the Campbell method and magnetic flux waveform recordings have been analysed and compared in order to separate clearly intergrain and intragrain contributions. The AC susceptibility frequency dependence has been also examined at T = 77 K in a broad field range (0.01 G < BAC < 100 G). The activation energy as a function of AC applied magnetic field is found to present a pronounced minimum for an induction (8 G) corresponding to full magnetic flux penetration through the intergranular matrix.

Magnetoresistance of granular ferromagnets

We report a comparative study of the magnetic and magnetoresistance phenomena in two types of granular ferromagnets: ferromagnet-normal-metal mixtures Ni-Ag, Co-Ag, and ferromagnet-insulator mixtures Ni-${\mathrm{SiO}}_{2}$ , Co-${\mathrm{SiO}}_{2}$ . Anisotropic magnetoresistance and giant magnetoresistance (GMR) are identified in both types of systems above and below the magnetic component percolation threshold respectively. The GMR effect in granular ferromagnets is shown to be essentially independent of the nature and resistance of the nonmagnetic intergranular matrix.

Universal behavior of susceptibility in the 110 K phase of the Bi-Pb-Sr-Ca-Cu-O system.

We demonstrate here the universal behavior of the fundamental intergranular matrix susceptibility (${\mathrm{\ensuremath{\chi}}}_{\mathit{m}}$) in terms of a single parameter (\ensuremath{\delta}) in the 110 K phase of the Bi-Sr-Ca-Cu-O system, in the regime where flux profile is linear in the sample. Following the observation of universality of the third harmonic susceptibility ${\mathrm{\ensuremath{\chi}}}_{3}$(T,${\mathit{H}}_{\mathrm{dc}}$${)}_{\mathit{H}\mathrm{ac}}$ by Shatz et al. in Y-Ba-Cu-O, we have examined the field and temperature dependences of \ensuremath{\chi}(${\mathit{H}}_{\mathrm{dc}}$,${\mathit{H}}_{\mathrm{ac}}$${)}_{\mathit{T}}$ and \ensuremath{\chi}(T,${\mathit{H}}_{\mathrm{dc}}$${)}_{\mathit{H}\mathrm{ac}}$, respectively, measured in ${\mathrm{Bi}}_{1.2}$${\mathrm{Pb}}_{0.3}$${\mathrm{Sr}}_{1.5}$${\mathrm{Ca}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{\mathit{y}}$ superconductor. Our analysis shows that the field dependence of ${\mathit{J}}_{\mathit{c}}$ is better described, for the present sample, by the power-law model and also demonstrates the universality of ${\mathrm{\ensuremath{\chi}}}_{\mathit{m}}$ in terms of \ensuremath{\delta}.

Magnetic interactions in Fe-Zr-B-Cu nanocrystalline materials at elevated temperatures.

Nanocrystalline samples were obtained by subsequent annealing of the Fe93-x-yZr7BxCuy metallic glass ribbons either in a conventional furnace or by electric current flowing through the ribbon. The coercive field of the slightly crystallized material shows a drastic increase at temperatures about the Curie point of the amorphous matrix, whereas for samples with high content of the crystalline phase the coercivity increases slowly in the temperature range well above TC. Temperature dependencies of the coercive field show that at elevated temperatures the magnetic interactions between ferromagnetic particles, most probably of exchange origin, take place through the paramagnetic intergranular matrix. © 1994 The American Physical Society.

Ac-susceptibility study of the 110-K superconducting phase of Bi-Sr-Ca-Cu-O.

ac-susceptibility (\ensuremath{\chi}',\ensuremath{\chi}'') measurements as a function of temperature and ac field amplitude have been carried out on cylindrical samples of the 110-K phase of the Bi-Sr-Ca-Cu-O system. The two single-phase samples used for studies were prepared under different experimental conditions with an aim to understand the regimes of validity of Bean's and Kim's critical-state models. Material-dependent parameters such as critical current density as a function of temperature and effective volume fraction of grains, were estimated using these models. Improvements in the critical-current density and intergrain coupling strength were found when a sample was subjected to intermediate cold pressing between sintering. Field variation of intergranular matrix susceptibility of the sintered sample could be fitted well to Kim's model whereas the data on the press sintered sample were in agreement with Bean's model.

Low field ultrasonic studies on melt-textured YBa2Cu3O7−δ

Ultrasonic attenuation and velocity measurements have proved to be a useful probe for the study of conventional superconductors, where the electron–phonon coupling is the dominant pairing mechanism. Since the discovery of high Tc superconductors, ultrasonic measurements have been performed on these systems with moderate success. In the absence of large single crystals, measurements have been performed on isotropic sintered pellets and partially oriented sintered pellets of these high Tc compounds. Low field ultrasonic measurements in the melt textured YBa2Cu3O7 have proved to be interesting. With shear waves one can see a coupling of the sound waves to the flux lattice. As the field is increased, there is an abrupt jump in both the sound velocity (ΔV) and the attenuation (Δα) at a field Hc1’, which is close to Hc1. The temperature dependence of Hc1’ is the same as that of Hc1. ΔV is found to be proportional to the square root of Hcl’, that is inversely to the average distance between the flux lines. Δα goes to zero at Tc and at T=0, going through a maximum at ∼55 K. Measurements have been done for various orientations of the magnetic field. As no anisotropy is seen in the value of Hc1’, it is surmised that Hc1’ is the lower critical field for the intergranular matrix. [Work supported by ONR.]

Gastric mucosal barrier: intergranular matrix of gastric surfactant in the mucous lining.

Transmission electron microscopy of rat gastric mucosa fixed by a novel procedure designed for barriers to water-soluble solutes has shown that the intergranular matrix material of gastric mucus is oligolamellar surface-active phospholipid. It is a gastric surfactant similar to that seen on deeper mucus-free surfaces also exposed to acid.

A common physical basis for the gastric mucosal barrier and the action of sucralfate

A novel explanation for the action of sucralfate in gastric ulcers has been proposed based on a new theory for gastric mucosal protection derived, in effect, from the very common industrial practice of adsorbing surfactants to surfaces needing protection against acid. Standard physical tests have been employed to show that sucralfate is highly surface-active at both liquid and solid interfaces, with the capability to be adsorbed—but not as active as the indigenous surface-active phospholipid (SAPL). This finding can explain the ability of sucralfate to “bind” to an ulcer site. Unlike SAPL or surfactants in general, adsorbed sucralfate does not render hydrophilic surfaces hydrophobic, suggesting a dual role in substituting for both SAPL and the mucus needed to stabilize it. Electron microscopy, using a novel fixation procedure specifically designed to allow for the known properties of any gastric mucosal barrier, revealed essentially the same oligolamellar lining of SAPL as previously reported in rats. Prolonged (16-day) exposure to sucralfate did not appear to change the situation, whereas there were as many, if not more, lamellar bodies (freshly secreted SAPL) adjacent to the stomach wall. Mucus-free oxyntic ducts showed the same oligolamellar lining as controls. An interesting new finding was the presence of oligolamellar SAPL as the intergranular matrix of gastric mucus—as though preparing to protect the next layer in anticipation of the surface mucin granules being eroded.

Intergranular Volume (IGV) Decline Curves for Evaluating and Predicting Compaction and Porosity Loss in Sandstones

In contrast to conventional empirical porosity prediction schemes based on porosity decline with depth or thermal maturity, development of a conceptually sound porosity prediction algorithm requires quantitative assessment with depth (or thermal maturity) of two independent processes: compaction (as monitored by intergranular volume or IGV) and cementation. IGV is the sum of intergranular porosity, matrix, and cement as measured in thin section. For this study, in order to evaluate the effects on porosity of compaction alone, a plot of IGV versus depth was constructed using data from greater than 350 relatively uncemented ({lt}5% cement) sandstones from a wide variety of depths, ages, and geographic locations. Because texture and composition affect the initial IGV, the following additional restrictions were applied to the data set: {ge}0.1 mm grain size, well to moderately well sorted, {lt}5% matrix, {lt}15% feldspar grains, and {lt}5% ductile grains. The resulting IGV decline curve reveals that sands compact mechanically and IGV declines rapidly from 40 to 42% at the surface to about 28% at 5000 ft. Between 5000 and 8000 ft, decline continues slowly until the framework stabilizes at around 26%. No further significant IGV decrease is observed to the depth limits of the data set at 22,000more » ft. The most significant implications of this curve for porosity prediction in sandstones are that (1) primary porosity can be preserved to great depths in the absence of cement, suggesting that reported volumes of secondary porosity in sandstones are exaggerated, (2) intergranular pressure solution plays a minor role in localized quartz cementation, and (3) cement prediction is a major key to porosity prediction.« less

High‐Temperature Mechanical Properties of a Uniaxially Reinforced Zircon‐Silicon Carbide Composite

Mechanical properties of a monolithic zircon ceramic and zircon‐matrix composites uniaxially reinforced with either uncoated or BN‐coated silicon carbide monofilaments were measured in flexure between 25° and 1477°C. Monolithic zircon ceramics were weak and exhibited a brittle failure up to about 1300°C. An increasing amount of the plastic deformation was observed before failure above about 1300°C. In contrast, composites reinforced with either uncoated or BN‐coated SiC filaments were stronger and tougher than the monolithic zircon at all test temperatures between 25° and 1477°C. The ultimate strength and work‐of‐fracture of composite samples decreased with increasing temperature. A transgranular matrix fracture was shown by the monolithic and composite samples tested up to about 1200°C, whereas an increasing amount of the intergranular matrix fracture was displayed above 1200°C.

On the fracture toughness of cemented carbides

A model for the fracture toughness of cobalt reinforced tungsten carbide hardmetals is presented. The fracture energy of the composite is obtained from the sum of the energies dissipated during fracture along the four crack paths that are available in this composite (i.e. dimple rupture across the binder or in the binder near a binder/carbide interface, brittle trans- and intergranular matrix fracture). While specific energies for matrix cracking are known from previous work, the plastic work spent during formation of unit area of binder rupture has been calculated on the basis of a recent stereometric evaluation of the dimple morphology in the binder. The specific work of fracture in the reinforcing binder phase scales with its mean flow stress and the depth that suffers plastic deformation. Estimates for the mean flow stress of submicrometer binder layers, as present in WC-Co, and for the mean size of the plastic zone are obtained subsequently by combination with the yield stress and the work hardening parameters of the binder and the microstructure of the composite respectively. Combining these results with recent experimental data for the distribution of the four crack paths on the fracture surface renders eventually the fracture energy of the composite. It is recognized that the effects of the depth of plastic deformation and the distribution of fracture paths combine to yield the well known effects of microstructural geometry (i.e. volume fraction and mean linear intercept of the metal phase) on composite toughness in accordance with experimental observations of crack propagation in WC-Co. It is emphasized that beside geometric effects both the matrix toughness and the plastic properties of the binder play a dominant role for the fracture resistance of metal reinforced brittle matrices.

Reservoir Properties of Submarine-Fan Facies: Great Valley Sequence, California

Submarine-fan sandstones of the Great Valley sequence west of the Sacramento Valley, California, have low porosities and permeabilities (64 samples averaged 10.1% porosity and 0.87 millidarcies permeability). However, petrography and scanning electron microscope studies indicate that most sands in almost all submarine fan environments are originally porous and permeable. Thin turbidite sandstones deposited in areas dominated by shale in outer-fan, basin-plain, and overbank environments are cemented mainly by calcite; shale dewatering is inferred to contribute to rapid cementation early in the burial process. Sands deposited in inner- and middle-fan channels within interchannel and fan-fringe environments that contain only thin shale beds have small percentages of intergranular matrix or cement. The original porosity is substantially reduced mechanically at shallow depths and by pressure solution at deeper levels. Permeability decreases systematically with increasing age of the rocks, presumably as a result of increasing burial depths. Computer-run stepwise regression analyses show that the porosity is inversely related to the percentage of calcite cement. Such parameters as the contents of quartz, feldspar, and unstable rock fragments have no correlative effect on either porosity or permeability. The results reported here indicate original porosity and permeability can be high in deep-water submarine fans and that fan environments dominated by sand (with high sand/shale ratios) are more likely to retain higher porosity and permeability to greater depths than sand interbedded with thick shale sequences.

Microscopic Distribution of Uranium in Oakville Sandstone, South Texas: ABSTRACT

End_Page 475------------------------------When uranium ore is mined and processed in the conventional crushing plant there is little urgency to know what mineral contains the uranium and how that mineral is distributed within the ore. However, solution mining techniques depend for their success on bringing the dissolving solutions into contact with the uranium-bearing mineral and dissolving it. With that requirement in mind, a study was undertaken to help understand the character and location of the uranium-bearing mineral in the Oakville Sandstone of south Texas where solution mining is being carried out. Thin-section and electron-microprobe analyses were conducted on a sample of high concentration ore to confirm that uranium was located in the space between framework sand grains. Moreover, uranium was not uniformly distributed throughout the silt and clay intergranular matrix material. The disaggregated and fractionated sandstone showed the highest concentration of uranium to be in the silt-size fraction. Further separation of the ore was carried out by heavy liquids and magnetic fractionations. The uranium-bearing mineral was concentrated along with dense and magnetic minerals. Openwork intergrowths of pyrite crystals made up most of this fraction. In spite of having concentrated uranium in excess of 43,000 ppm U3O8, it was still not possible to identify any ura ium-bearing mineral by X-ray diffraction. This suggests that uranium may be held in the sandstone as an amorphous oxide. End_of_Article - Last_Page 476------------