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W.B. Durham

Publications and source records attributed to W.B. Durham.

At least 19 recordsLinked to original sources
USGS2012

Experimental deformation of polycrystalline H2O ice at high pressure and low temperature: Preliminary results

Interest in the mechanical properties of water ice under the conditions in which it exists in the outer solar system has motivated the development and use of a new high‐pressure, low‐temperature triaxial deformation apparatus. Constant displacement rate tests on 70 samples of pure polycrystalline water ice have been performed at temperatures 77≤≤258 K, confining pressures 0.1≤≤350 MPa, and strain rates 3.5×10≤ ≤3.5×10 s. In most cases, the ice polymorph tested was ice . Both brittle and ductile behavior have been observed. Brittle behavior of ice, promoted by lower pressure, lower temperature, and higher strain rate, is analogous to that in rocks, with the important exception that brittle fracture strength becomes independent of confining pressure above 50 MPa pressure and the fracture angle is approximately 45° to the loading direction (i.e., the coefficient of internal friction is approximately zero). Ductile flow, the predominant behavior in our tests at ≥195 K, follows a law of form = σ exp (−*/) (σ is stress; is the gas constant; , * are material constants). Three sets of material constants are required to fit the data, with changes in sets (or mechanisms) occurring near 243 K and 195 K. The value of remains near 4 throughout the measured ductile field, but * drops from 91 to 61 to 31 /mole as temperature decreases. The maximum brittle strength measured was 171 MPa; the maximum ductile strength measured was 91 MPa. At confining pressures near the phase transition pressure of ice → ice II, the ductile strength is observed to drop dramatically. Some overlap with previous work occurs at higher temperatures and lower pressures. Agreement with present work is generally good, both quantitatively in the values of and *, and qualitatively in the mechanism of deformation. Although the ductile strengths measured here are somewhat higher than expected on the basis of extrapolations of previous work, the low value of * at <195 K indicates that the ice layer on icy bodies in the solar system is much weaker than has generally been predicted.

Journal of Geophysical Research B: Solid Earth↗
USGS2012

Friction of ice

The frictional strength of ice seems to be well below that for all other rocks. Triaxial testing of cylinders of pure water ice containing a 45° inclined sawcut, at temperatures of 77 ≤ T ≤ 115 K and confining pressures 0.1 ≤ P ≤ 250 MPa, reveals the frictional laws τ = 0.20 σ n + 8.3 MPa for P ≥ 10 MPa and τ = 0.55 σ n + 1.0 MPa for P ≤ 5 MPa, where τ and σ n are the shear and normal stresses on the sawcut surface. Friction is independent of T and, over the one order of magnitude tested, of average sliding velocity. The sliding behavior is invariably stick slip. Examination of sliding surfaces shows only minor gouge development. A curious arrangement of densely packed short vertical fractures occurs primarily in samples with anomalously low strength. These results apply to models of near‐surface tectonic activity on Jupiter's three large icy moons, Europa, Callisto, and Ganymede. They indicate, for example, that a global expansion on Ganymede of 3 linear percent will cause extensional movement on preexisting faults at depths to 7±3 km.

Journal of Geophysical Research B: Solid Earth↗
USGS2011

Transient and steady state creep response of ice I and magnesium sulfate hydrate eutectic aggregates

Using uniaxial compression creep experiments, we characterized the transient and steady state deformation behaviors of eutectic aggregates of system ice I and MgSO4 11H2O (MS11; meridianiite), which has significance because of its likely presence on moons of the outer solar system. Synthetic samples of eutectic liquid bulk composition, which produce eutectic colonies containing 0.35-0.50 volume fraction MS11, were tested as functions of colony size and lamellar spacing, temperature (230-250 K), and confining pressure (0.1 and 50 MPa) to strains ???0.2. Up to a differential stress of 6 MPa, the ice I-MS11 aggregates display an order of magnitude higher effective viscosity and higher stress sensitivity than do aggregates of pure polycrystalline ice at the same conditions. The creep data and associated microstructural observations demonstrate, however, that the aggregates are additionally more brittle than pure ice, approaching rate-independent plasticity that includes rupture of the hydrate phase at 6-8 MPa, depending on the scale of the microstructure. Microstructures of deformed samples reveal forms of semibrittle flow in which the hydrate phase fractures while the ice phase deforms plastically. Semibrittle flow in the icy shell of a planetary body would truncate the lithospheric strength envelope and thereby decrease the depth to the brittle-ductile transition by 55% and reduce the failure limit for compressional surface features from 10 to ???6 MPa. A constitutive equation that includes eutectic colony boundary sliding and intracolony flow is used to describe the steady state rheology of the eutectic aggregates. Copyright ?? 2011 by the American Geophysical Union.

Journal of Geophysical Research E: Planets↗
USGS2006

Preferred crystallographic orientation in the ice I ← II transformation and the flow of ice II

The preferred crystallographic orientation developed during the ice I &larr; II transformation and during the plastic flow of ice II was measured in polycrystalline deuterium oxide (D 2 O) specimens using low-temperature neutron diffraction. Samples partially transformed from ice I to II under a non-hydrostatic stress developed a preferred crystallographic orientation in the ice II. Samples of pure ice II transformed from ice I under a hydrostatic stress and then when compressed axially, developed a strong preferred orientation of compression axes parallel to (10 1 0). A match to the observed preferred orientation using the viscoplastic self-consistent theory was obtained only when (10 1 0) [0001] was taken as the predominant slip system in ice II.

Philosophical Magazine A: Physics of Condensed Mat↗
USGS2006

Laboratory measurements of compressional and shear wave speeds through methane hydrate

Simultaneous measurements of compressional and shear wave speeds through polycrystalline methane hydrate have been made. Methane hydrate, grown directly in a wave speed measurement chamber, was uniaxially compacted to a final porosity below 2%. At 277 K, the compacted material had a compressional wave speed of 3650 ?? 50 m/s. The shear wave speed, measured simultaneously, was 1890 ?? 30 m/s. From these wave speed measurements, we derive V(p)/V(s), Poisson's ratio, bulk, shear, and Young's moduli.

Conference Paper↗
USGS2006

Grain size-sensitive creep in ice II

Rheological experiments on fine-grained water ice II at low strain rates reveal a creep mechanism that dominates at conditions of low stress. Using cryogenic scanning electron microscopy, we observed that a change in stress exponent from 5 to 2.5 correlates strongly with a decrease in grain size from about 40 to 6 micrometers. The grain size-sensitive creep of ice II demonstrated here plausibly dominates plastic strain at the low-stress conditions in the interior of medium- to large-sized icy moons of the outer solar system.

Science↗
USGS2005

Flow strength of highly hydrated Mg- and Na-sulfate hydrate salts, pure and in mixtures with water ice, with application to Europa

We selected two Europan-ice-shell candidate highly hydrated sulfate salts for a laboratory survey of ductile flow properties: MgSO4 ?? 7H2O (epsomite) and Na2SO4 ?? 10H2O (mirabilite), called MS7 and NS10, respectively. Polycrystalline samples in pure form and in mixtures with water ice I were tested using our cryogenic high-pressure creep apparatus at temperatures 232 ??? T ??? 294 K, confining pressures P = 50 and 100 MPa, and strain rates 4 ?? 10-8 ??? ???dot;e ??? 7 ?? 10-5 s-1. Grain size of NS10 samples was > 100 ??m. The flow strength ?? of pure MS7 was over 100 times that of polycrystalline ice I at comparable conditions; that of pure NS10 over 20 times that of ice. In terms of the creep law ???dot;e = A??n e-Q/RT, where R is the gas constant, we determine parameter values of A = 1012.1 MPa-ns-1, n = 5.4, and Q = 128 kJ/mol for pure NS10. Composites of ice I and NS10 of volume fraction ?? NS10 have flow strength ??c = [??NS10??NS10J + (1 - ?? NS10)??iceIJ]1/J where J ??? -0.5, making the effect on the flow of ice with low volume fractions of NS10 much like that of virtually undeformable hard rock inclusions. Being much stronger and denser than ice, massive sulfate inclusions in the warmer, ductile layer of the Europan ice shell are less likely to be entrained in convective ice flow and more likely to be drawn to the base of the ice shell by gravitational forces and eventually expelled. With only smaller, dispersed sulfate inclusions, at probable sulfate ?? < 0.2, the shell may be treated rheologically as pure, polycrystalline ice, with boundary conditions perhaps influenced by the high density and low thermal conductivity of the hydrated salts. Copyright 2005 by the American Geophysical Union.

Journal of Geophysical Research E: Planets↗
USGS2004

Dissolution rates of pure methane hydrate and carbon-dioxide hydrate in undersaturated seawater at 1000-m depth

To help constrain models involving the chemical stability and lifetime of gas clathrate hydrates exposed at the seafloor, dissolution rates of pure methane and carbon-dioxide hydrates were measured directly on the seafloor within the nominal pressure-temperature (P/T) range of the gas hydrate stability zone. Other natural boundary conditions included variable flow velocity and undersaturation of seawater with respect to the hydrate-forming species. Four cylindrical test specimens of pure, polycrystalline CH4 and CO2 hydrate were grown and fully compacted in the laboratory, then transferred by pressure vessel to the seafloor (1028 m depth), exposed to the deep ocean environment, and monitored for 27 hours using time-lapse and HDTV cameras. Video analysis showed diameter reductions at rates between 0.94 and 1.20 ??m/s and between 9.0 and 10.6 ?? 10-2 ??m/s for the CO2 and CH4 hydrates, respectively, corresponding to dissolution rates of 4.15 ?? 0.5 mmol CO2/m2s and 0.37 ?? 0.03 mmol CH4/m2s. The ratio of the dissolution rates fits a diffusive boundary layer model that incorporates relative gas solubilities appropriate to the field site, which implies that the kinetics of the dissolution of both hydrates is diffusion-controlled. The observed dissolution of several mm (CH4) or tens of mm (CO2) of hydrate from the sample surfaces per day has major implications for estimating the longevity of natural gas hydrate outcrops as well as for the possible roles of CO2 hydrates in marine carbon sequestration strategies. ?? 2003 Elsevier Ltd.

Geochimica et Cosmochimica Acta↗
USGS2004

Scanning electron microscopy investigations of laboratory-grown gas clathrate hydrates formed from melting ice, and comparison to natural hydrates

Scanning electron microscopy (SEM) was used to investigate grain texture and pore structure development within various compositions of pure sI and sII gas hydrates synthesized in the laboratory, as well as in natural samples retrieved from marine (Gulf of Mexico) and permafrost (NW Canada) settings. Several samples of methane hydrate were also quenched after various extents of partial reaction for assessment of mid-synthesis textural progression. All laboratory-synthesized hydrates were grown under relatively high-temperature and high-pressure conditions from rounded ice grains with geometrically simple pore shapes, yet all resulting samples displayed extensive recrystallization with complex pore geometry. Growth fronts of mesoporous methane hydrate advancing into dense ice reactant were prevalent in those samples quenched after limited reaction below and at the ice point. As temperatures transgress the ice point, grain surfaces continue to develop a discrete "rind" of hydrate, typically 5 to 30 ??m thick. The cores then commonly melt, with rind microfracturing allowing migration of the melt to adjacent grain boundaries where it also forms hydrate. As the reaction continues under progressively warmer conditions, the hydrate product anneals to form dense and relatively pore-free regions of hydrate grains, in which grain size is typically several tens of micrometers. The prevalence of hollow, spheroidal shells of hydrate, coupled with extensive redistribution of reactant and product phases throughout reaction, implies that a diffusion-controlled shrinking-core model is an inappropriate description of sustained hydrate growth from melting ice. Completion of reaction at peak synthesis conditions then produces exceptional faceting and euhedral crystal growth along exposed pore walls. Further recrystallization or regrowth can then accompany even short-term exposure of synthetic hydrates to natural ocean-floor conditions, such that the final textures may closely mimic those observed in natural samples of marine origin. Of particular note, both the mesoporous and highly faceted textures seen at different stages during synthetic hydrate growth were notably absent from all examined hydrates recovered from a natural marine-environment setting.

American Mineralogist↗
USGS2003

CO2 hydrate: Synthesis, composition, structure, dissociation behavior, and a comparison to structure I CH4 hydrate

Structure I (sI) carbon dioxide (CO 2 ) hydrate exhibits markedly different dissociation behavior from sI methane (CH 4 ) hydrate in experiments in which equilibrated samples at 0.1 MPa are heated isobarically at 13 K/h from 210 K through the H 2 O melting point (273.15 K). The CO 2 hydrate samples release only about 3% of their gas content up to temperatures of 240 K, which is 22 K above the hydrate phase boundary. Up to 20% is released by 270 K, and the remaining CO 2 is released at 271.0 plusmn; 0.5 K, where the sample temperature is buffered until hydrate dissociation ceases. This reproducible buffering temperature for the dissociation reaction CO 2 ·nH 2 O = CO 2 (g) + nH 2 O(1 to s) is measurably distinct from the pure H 2 O melting point at 273.15 K, which is reached as gas evolution ceases. In contrast, when si CH 4 hydrate is heated at the same rate at 0.1 MPa, >95% of the gas is released within 25 K of the equilibrium temperature (193 K at 0.1 MPa). In conjunction with the dissociation study, a method for efficient and reproducible synthesis of pure polycrystalline CO 2 hydrate with suitable characteristics for material properties testing was developed, and the material was characterized. CO 2 hydrate was synthesized from CO 2 liquid and H 2 O solid and liquid reactants at pressures between 5 and 25 MPa and temperatures between 250 and 281 K. Scanning electron microscopy (SEM) examination indicates that the samples consist of dense crystalline hydrate and 50-300 μm diameter pores that are lined with euhedral cubic hydrate crystals. Deuterated hydrate samples made by this same procedure were analyzed by neutron diffraction at temperatures between 4 and 215 K; results confirm that complete conversion of water to hydrate has occurred and that the measured unit cell parameter and thermal expansion are consistent with previously reported values. On the basis of measured weight gain after synthesis and gas yields from the dissociation experiments, approximately all cages in the hydrate structure are filled such that n ≈ 5.75.

Journal of Physical Chemistry B↗
USGS2003

Temperature, pressure, and compositional effects on anomalous or "self" preservation of gas hydrates

We previously reported on a thermal regime where pure, polycrystalline methane hydrate is preserved metastably in bulk at up to 75 K above its nominal temperature stability limit of 193 K at 0.1 MPa, following rapid release of the sample pore pressure. Large fractions (>50 vol.%) of methane hydrate can be preserved for 2-3 weeks by this method, reflecting the greatly suppressed rates of dissociation that characterize this "anomalous preservation" regime. This behavior contrasts that exhibited by methane hydrate at both colder (193-240 K) and warmer (272-290 K) isothermal test conditions, where dissociation rates increase monotonically with increasing temperature. Here, we report on recent experiments that further investigate the effects of temperature, pressure, and composition on anomalous preservation behavior. All tests conducted on sI methane hydrate yielded self-consistent results that confirm the highly temperature-sensitive but reproducible nature of anomalous preservation behavior. Temperature-stepping experiments conducted between 250 and 268 K corroborate the relative rates measured previously in isothermal preservation tests, and elevated pore-pressure tests showed that, as expected, dissociation rates are further reduced with increasing pressure. Surprisingly, sII methane-ethane hydrate was found to exhibit no comparable preservation effect when rapidly depressurized at 268 K, even though it is thermodynamically stable at higher temperatures and lower pressures than sI methane hydrate. These results, coupled with SEM imaging of quenched sample material from a variety of dissociation tests, strongly support our earlier arguments that ice-"shielding" effects provided by partial dissociation along hydrate grain surfaces do not serve as the primary mechanism for anomalous preservation. The underlying physical-chemistry mechanism(s) of anomalous preservation remains elusive, but appears to be based more on textural or morphological changes within the hydrate material itself, rather than on compositional zoning or ice-rind development.

Canadian Journal of Physics↗
USGS2003

Ductile flow of methane hydrate

Compressional creep tests (i.e., constant applied stress) conducted on pure, polycrystalline methane hydrate over the temperature range 260-287 K and confining pressures of 50-100 MPa show this material to be extraordinarily strong compared to other icy compounds. The contrast with hexagonal water ice, sometimes used as a proxy for gas hydrate properties, is impressive: over the thermal range where both are solid, methane hydrate is as much as 40 times stronger than ice at a given strain rate. The specific mechanical response of naturally occurring methane hydrate in sediments to environmental changes is expected to be dependent on the distribution of the hydrate phase within the formation - whether arranged structurally between and (or) cementing sediments grains versus passively in pore space within a sediment framework. If hydrate is in the former mode, the very high strength of methane hydrate implies a significantly greater strain-energy release upon decomposition and subsequent failure of hydrate-cemented formations than previously expected.

Canadian Journal of Physics↗
USGS2003

The strength and rheology of methane clathrate hydrate

Methane clathrate hydrate (structure I) is found to be very strong, based on laboratory triaxial deformation experiments we have carried out on samples of synthetic, high-purity, polycrystalline material. Samples were deformed in compressional creep tests (i.e., constant applied stress, ??), at conditions of confining pressure P = 50 and 100 MPa, strain rate 4.5 ?? 10-8 ??? ?? ??? 4.3 ?? 10-4 s-1, temperature 260 ??? T ??? 287 K, and internal methane pressure 10 ??? PCH4 ??? 15 MPa. At steady state, typically reached in a few percent strain, methane hydrate exhibited strength that was far higher than expected on the basis of published work. In terms of the standard high-temperature creep law, ?? = A??ne-(E*+PV*)/RT the rheology is described by the constants A = 108.55 MPa-n s-1, n = 2.2, E* = 90,000 J mol-1, and V* = 19 cm3 mol-1. For comparison at temperatures just below the ice point, methane hydrate at a given strain rate is over 20 times stronger than ice, and the contrast increases at lower temperatures. The possible occurrence of syntectonic dissociation of methane hydrate to methane plus free water in these experiments suggests that the high strength measured here may be only a lower bound. On Earth, high strength in hydrate-bearing formations implies higher energy release upon decomposition and subsequent failure. In the outer solar system, if Titan has a 100-km-thick near-surface layer of high-strength, low-thermal conductivity methane hydrate as has been suggested, its interior is likely to be considerably warmer than previously expected.

Journal of Geophysical Research B: Solid Earth↗
USGS2001

Preservation of methane hydrate at 1 atm

A "pressure-release" method that enables reproducible bulk preservation of pure, porous, methane hydrate at conditions 50 to 75 K above its equilibrium T (193 K) at 1 atm is refined. The amount of hydrate preserved by this method appears to be greatly in excess of that reported in the previous citations, and is likely the result of a mechanism different from ice shielding.

Energy and Fuels↗
USGS2000

Methane hydrate dissociation rates at 0.1 MPa and temperatures above 272 K

We performed rapid depressurization experiments on methane hydrate under isothermal conditions above 272 K to determine the amount and rate of methane evolution. Sample temperatures rapidly drop below 273 K and stabilize near 272.5 K during dissociation. This thermal anomaly and the persistence of methane hydrate are consistent with the reported recovery of partially dissociated methane hydrate from ocean drilling cores.

Conference Paper↗
USGS1998

Optical-cell evidence for superheated ice under gas-hydrate-forming conditions

We previously reported indirect but compelling evidence that fine-grained H 2 O ice under elevated CH 4 gas pressure can persist to temperatures well above its ordinary melting point while slowly reacting to form methane clathrate hydrate. This phenomenon has now been visually verified by duplicating these experiments in an optical cell while observing the very slow hydrate-forming process as the reactants were warmed from 250 to 290 K at methane pressures of 23 to 30 MPa. Limited hydrate growth occurred rapidly after initial exposure of the methane gas to the ice grains at temperatures well within the ice subsolidus region. No evidence for continued growth of the hydrate phase was observed until samples were warmed above the equilibrium H 2 O melting curve. With continued heating, no bulk melting of the ice grains or free liquid water was detected anywhere within the optical cell until hydrate dissociation conditions were reached (292 K at 30 MPa), even though full conversion of the ice grains to hydrate requires 6−8 h at temperatures approaching 290 K. In a separate experimental sequence, unreacted portions of H 2 O ice grains that had persisted to temperatures above their ordinary melting point were successfully induced to melt, without dissociating the coexisting hydrate in the sample tube, by reducing the pressure overstep of the equilibrium phase boundary and thereby reducing the rate of hydrate growth at the ice−hydrate interface. Results from similar tests using CO 2 as the hydrate-forming species demonstrated that this superheating effect is not unique to the CH 4 −H 2 O system.

Journal of Physical Chemistry B↗
USGS1997

Creep of water ices at planetary conditions: A compilation

Many constitutive laws for the flow of ice have been published since the advent of the Voyager explorations of the outer solar system. Conflicting data have occasionally come from different laboratories, and refinement of experimental techniques has led to the publication of laws that supersede earlier ones. In addition, there are unpublished data from ongoing research that also amend the constitutive laws. Here we compile the most current laboratory-derived flow laws for water ice phases I, II, III, V, and VI, and ice I mixtures with hard particulates. The rheology of interest is mainly that of steady state, and the conditions reviewed are the pressures and temperatures applicable to the surfaces and interiors of icy moons of the outer solar system. Advances in grain-size-dependent creep in ices I and II as well as in phase transformations and metastability under differential stress are also included in this compilation. At laboratory strain rates the several ice polymorphs are rheologically distinct in terms of their stress, temperature, and pressure dependencies but, with the exception of ice III, have fairly similar strengths. Hard particulates strengthen ice I significantly only at high particulate volume fractions. Ice III has the potential for significantly affecting mantle dynamics because it is much weaker than the other polymorphs and its region of stability, which may extend metastably well into what is nominally the ice II field, is located near likely geotherms of large icy moons.

Journal of Geophysical Research E: Planets↗