Ambient Melting Research Articles

Improved Parameterizations of Vertical Ice‐Ocean Boundary Layers and Melt Rates

AbstractBuoyancy fluxes and submarine melt rates at vertical ice‐ocean interfaces are commonly parameterized using theories derived for unbounded free plumes. A Large Eddy Simulation is used to analyze the disparate dynamics of free plumes and wall‐bounded plumes; the distinctions between the two are supported by recent theoretical and experimental results. Modifications to parameterizations consistent with these simulations are tested and compared to results from numerical and laboratory experiments of meltwater plumes. These modifications include 50% weaker entrainment and a distinct plume‐driven friction velocity in the shear boundary layer up to 8 times greater than the externally‐driven friction velocity. Using these updated plume parameter modifications leads to 40 times the ambient melt rate predicted by commonly used parameterizations at vertical glacier faces, which is consistent with observed melt rates at LeConte Glacier, Alaska.

Ambient melting behavior of stoichiometric uranium oxides

As UO2 is easily oxidized during the nuclear fuel cycle it is important to have a detailed understanding of the structures and properties of the oxidation products. Experimental work over the years has revealed many stable uranium oxides including UO2, U4O9 (UO2.25), U3O7 (UO2.33), U2O5 (UO2.5), U3O8 (UO2.67), and UO3, all with a number of different polymorphs. These oxides are broadly split into two categories, fluorite-based structures with stoichiometries in the range of UO2 to UO2.5 and less dense layered-type structures with stoichiometries in the range of UO2.5 to UO3. While UO2 is well characterized, both experimentally and computationally, there is a paucity of data concerning higher stoichiometry oxides in the literature. In this work we determine the ambient melting points of all the six stoichiometric uranium oxides listed above and compare them to the available experimental and/or theoretical data. We demonstrate that a family of the six ambient melting points map out a solid-liquid transition boundary consistent with the high-temperature portion of the phase diagram of uranium-oxygen system suggested by Babelot et al.

Constraining the release of Sn to the ambient melting point following shock loading using time-resolved x-ray diffraction

The formation of liquid following release from a shocked state governs the transition from spall to cavitation and the formation of ejecta in metals. In order to build physics-based models of these processes, it is necessary to critically evaluate the relative importance of kinetics and entropy generation during the release along with the accuracy of multiphase equations of state. Tin (Sn) has served as a testbed for a variety of experiments examining strength and ejecta due to its accessible melt boundary and solid–solid phase transitions. This work presents experiments examining the phase evolution of high purity Sn following the shock and release to ambient stress near the melting point. Sn is found to release to states between its ambient solidus and liquidus from approximately 19 to 33 GPa under uniaxial loading, with the two-phase region being characterized by a reduction in the intensity of the (220), (211) β-Sn doublet. Jetting experiments performed at 27–28 GPa exhibit comparable diffraction patterns with what is observed following the uniaxial release. The solid fractions of β-Sn in the ambient mixed phase region are found to decrease linearly with increasing shock stress as increasing liquid Sn is formed. The results provide much needed information for interpreting measurements of dynamic strength at a high strain rate and experiments examining cavitation and shallow bubble collapse in Sn.

Ab Initio Phase Diagram of Chromium to 2.5 TPa

Chromium possesses remarkable physical properties such as hardness and corrosion resistance. Chromium is also a very important geophysical material as it is assumed that lighter Cr isotopes were dissolved in the Earth’s molten core during the planet’s formation, which makes Cr one of the main constituents of the Earth’s core. Unfortunately, Cr has remained one of the least studied 3d transition metals. In a very recent combined experimental and theoretical study (Anzellini et al., Scientific Reports, 2022), the equation of state and melting curve of chromium were studied to 150 GPa, and it was determined that the ambient body-centered cubic (bcc) phase of crystalline Cr remains stable in the whole pressure range considered. However, the importance of the knowledge of the physical properties of Cr, specifically its phase diagram, necessitates further study of Cr to higher pressure. In this work, using a suite of ab initio quantum molecular dynamics (QMD) simulations based on the Z methodology which combines both direct Z method for the simulation of melting curves and inverse Z method for the calculation of solid–solid phase transition boundaries, we obtain the theoretical phase diagram of Cr to 2.5 TPa. We calculate the melting curves of the two solid phases that are present on its phase diagram, namely, the lower-pressure bcc and the higher-pressure hexagonal close-packed (hcp) ones, and obtain the equation for the bcc-hcp solid–solid phase transition boundary. We also obtain the thermal equations of state of both bcc-Cr and hcp-Cr, which are in excellent agreement with both experimental data and QMD simulations. We argue that 2180 K as the value of the ambient melting point of Cr which is offered by several public web resources (“Wikipedia,” “WebElements,” “It’s Elemental,” etc.) is most likely incorrect and should be replaced with 2135 K, found in most experimental studies as well as in the present theoretical work.

Atomic transport properties of liquid iron at conditions of planetary cores.

Atomic transport properties of liquid iron are important for understanding the core dynamics and magnetic field generation of terrestrial planets. Depending on the sizes of planets and their thermal histories, planetary cores may be subject to quite different pressures (P) and temperatures (T). However, previous studies on the topic mainly focus on the P-T range associated with the Earth's outer core; a systematic study covering conditions from small planets to massive exoplanets is lacking. Here, we calculate the self-diffusion coefficient D and viscosity η of liquid iron via ab initio molecular dynamics from 7.0 to 25 g/cm3 and 1800 to 25 000 K. We find that D and η are intimately related and can be fitted together using a generalized free volume model. The resulting expressions are simpler than those from previous studies where D and η were treated separately. Moreover, the new expressions are in accordance with the quasi-universal atomic excess entropy (Sex) scaling law for strongly coupled liquids, with normalized diffusivity D⋆ = 0.621 exp(0.842Sex) and viscosity η⋆ = 0.171 exp(-0.843Sex). We determine D and η along two thermal profiles of great geophysical importance: the iron melting curve and the isentropic line anchored at the ambient melting point. The variations of D and η along these thermal profiles can be explained by the atomic excess entropy scaling law, demonstrating the dynamic invariance of the system under uniform time and space rescaling. Accordingly, scale invariance may serve as an underlying mechanism to unify planetary dynamos of different sizes.

Deciphering magma storage and ascent processes of Taranaki, New Zealand, from the complexity of amphibole breakdown textures

Lava flows that constitute the current edifice of Taranaki volcano, New Zealand, contain a complex crystal cargo including plagioclase, pyroxene, amphibole, oxides, and rarely olivine. Amphibole textures and mineral chemistry indicate that crystals are pargasites entrained at various depths by ascending magmas. The crystals record a complex growth history within a range of temperature and pressure conditions (c. 950–1010 °C at mid- to deep crustal levels). Most amphiboles show the development of distinct reaction rims where the mineral is in contact with the ambient melt. Texturally, the rims are identified as detached, symplectic, granular or coarse. True rim thicknesses vary little (±20%, 1σ, on average) within individual thin sections but show a large variation between samples from different lava flows, from <5 to >50 μm. Reaction rim formation on Taranaki amphiboles is attributed to degassing during magma ascent as well as small increases in temperature. Associated with the formation of rims, the amphiboles also show two types of volumetric decomposition, identified as irregular and aligned. The former is indicative of slow reaction of amphibole with melt entrapped in fractures and cleavages during decompression-induced degassing, while the other is indicative of heating-induced breakdown of amphibole triggered by uptake into hot magmas prior to the onset of eruption. The combined evidence indicates that despite the complex and variable growth history of the remobilized crystal cargo, such crystals may be useful in constraining volcanic pre- and syn-eruptive processes and, when appropriate experimental data become available, their rates, which may be of the order of days to weeks.

Chlorine Heterogeneity in Volcanic Glass as a Faithful Record of Silicic Magma Degassing

AbstractDegassing processes occurring within silicic magma, such as bubble growth, bubble resorption, the welding of magma fragments, and open‐system gas loss are crucial in the control of volcanic eruption and lava emplacement, yet their details are still debated. To examine the possibility that these degassing processes are recorded in volcanic glass as heterogeneous Cl distribution patterns, we experimentally simulated these processes by heating rhyolitic obsidian and analyzed the distribution of Cl content in the recovered sample. The results showed that, for bubble growth, Cl diffused toward the bubble interface, leading to Cl depletion around the bubble. For bubble resorption, Cl was discharged from the bubble to the melt, leading to Cl enrichment in the ambient melt. For welding of magma fragments, Cl was depleted near the welded interface because each fragment had degassed Cl at the surface before the welding took place. For open‐system gas loss, Cl exsolved at the bubble interface while the bubble itself was being collapsed into a chain of small bubbles and a Cl‐depleted tail. These results indicate that Cl distribution is a reliable record of the experienced degassing processes. We then analyzed the Cl distribution in silicic lava from Naruko volcano, Japan, to study the gas flow mechanism. We observed that the glassy matrix was progressively corroded into porous crystalline material. The interface of the glass was highly enriched in Cl. We conclude that a Cl‐rich gas fluxed through hot lava and corroded the glass, developing a porous, gas‐permeable region.

Diffusion Timescales of Magmatic Processes in the Moinui Lava Eruption at Mauna Loa, Hawai`i, as Inferred from Bimodal Olivine Populations

Abstract The 2·1 ka Moinui lava flow field, erupted from the southwest rift zone of Mauna Loa, Hawai`i, exhibits striking textural and geochemical variations, that can be used to interpret magma processes pre-, syn- and post-eruption. From this lava flow, the duration of magma storage and storage conditions, the timescales over which magma is transported to the surface, and flow emplacement mechanisms at Mauna Loa are determined. Electron microprobe analysis (EMPA) and diffusion chronometry of olivine crystals identify two distinct crystal populations: a primitive, polyhedral olivine population with core compositions of Fo90–88 and a more evolved, platy olivine population with core compositions of Fo83–82. Fe–Mg diffusion modelling of these olivine populations gives distinct timescales for each population; platy olivines yield timescales of days up to a few weeks, while polyhedral olivines yield timescales of months to years. Despite the nature of a well-insulated pāhoehoe flow, meaning that post-emplacement diffusion continues for some time, a wealth of time information can be retrieved concerning pre-eruptive magmatic processes as well as the processes associated with the lava extrusion. The short timescales obtained from the platy olivine crystals and the observed equilibrium between its cores and ambient melt suggest late-stage nucleation and crystal growth in the shallow conduit and during lava emplacement. Conversely, the longer timescales and olivine-melt disequilibrium of the polyhedral olivine crystals suggests accumulation from a deeper source and subsequent transportation to shallow magma storage beneath the summit of Mauna Loa months, or even years before eruption. The chemical and textural details of the Moinui lava reflect the mode of flow emplacement and may have implications for the interpretation of the distribution of spinifex and cumulate olivine within komatiites; high-temperature, low-viscosity lavas, common in the Archean.

Meltwater Intrusions Reveal Mechanisms for Rapid Submarine Melt at a Tidewater Glacier

AbstractSubmarine melting has been implicated as a driver of glacier retreat and sea level rise, but to date melting has been difficult to observe and quantify. As a result, melt rates have been estimated from parameterizations that are largely unconstrained by observations, particularly at the near‐vertical termini of tidewater glaciers. With standard coefficients, these melt parameterizations predict that ambient melting (the melt away from subglacial discharge outlets) is negligible compared to discharge‐driven melting for typical tidewater glaciers. Here, we present new data from LeConte Glacier, Alaska, that challenges this paradigm. Using autonomous kayaks, we observe ambient meltwater intrusions that are ubiquitous within 400 m of the terminus, and we provide the first characterization of their properties, structure, and distribution. Our results suggest that ambient melt rates are substantially higher (×100) than standard theory predicts and that ambient melting is a significant part of the total submarine melt flux. We explore modifications to the prevalent melt parameterization to provide a path forward for improved modeling of ocean‐glacier interactions.

Disequilibrium growth of olivine in mafic magmas revealed by phosphorus zoning patterns of olivine from mafic–ultramafic intrusions

Olivine from mafic–ultramafic intrusions rarely displays growth zoning in major and some minor elements, such as Fe, Mg and Ni, due to fast diffusion of these elements at high temperatures. These elements in olivine are thus not useful in deciphering magma chamber processes, such as magma convection, multiple injection and mixing. High-resolution X-ray elemental intensity mapping reveals distinct P zoning patterns of olivine from two mafic–ultramafic intrusions in SW China. Polyhedral olivine grains from lherzolite and dunite of the Abulangdang intrusion show P-rich dendrites similar to those observed in volcanic rocks. Rounded olivine grains from net-textured Fe–Ti oxide ores of the Baima layered intrusion have irregular P-rich patches/bands crosscut and interlocked by P-poor olivine domains. P-rich patches/bands contain 250 to 612 ppm P, much higher than P-poor olivine domains with 123 to 230 ppm P. In electron backscattered diffraction (EBSD) maps, P-rich patches/bands within a single olivine grain have the same crystallographic orientation, indicating that they were remnants of the same crystal. Thus, both P-rich patches/bands and P-poor olivine domains in the same grain show a disequilibrium texture and clearly record two-stage growth. The P-rich patches/bands are likely the remnants of a polyhedral olivine crystal that formed in the first stage, whereas the P-poor olivine domains containing rounded Ti-rich magnetite and Fe-rich melt inclusions may have formed from an Fe-rich ambient melt in the second stage. The complex P zoning of olivine can be attributed to the dissolution of early polyhedral olivine and re-precipitation from the Fe-rich ambient melt. The early polyhedral olivine was in chemical disequilibrium with the ambient melt that may have been developed by silicate liquid immiscibility in a crystal mush. Our study implies that olivine crystals in igneous cumulates with an equilibrium appearance may have experienced disequilibrium growth processes during slow cooling. Therefore, the crystallization sequence of mafic magmas based on textural relationships should be treated with caution.

Universality of the shear viscosity of alkali metals

The universality of the shear viscosity of alkali metals is studied up to high pressure. Equilibrium molecular dynamics simulations are used to calculate the stress autocorrelation function, which allows us to obtain the value of shear viscosity using the Green-Kubo formula. Atomic interactions are computed from Fiolhais pseudopotential and are validated by comparison between pair distribution functions and mean-squared displacements obtained from classical and ab initio molecular dynamics simulations. The description of the interactions is accurate at least up to 12 GPa, 9.4 GPa, 6.6 GPa, and 3 GPa for Na, K, Rb, and Cs, respectively, and to a lesser extent up to 4.8 GPa for Li. A good agreement between simulation and experimental viscosity results along the liquid-gas coexistence curve is found. The viscosity appears to be a universal property over a wide range of the liquid phase of the phase diagram, between 0.85 and 1.5 times the ambient melting density and up to seven times the ambient melting temperature. Scaling laws are proposed following relations formulated in [Meyer, Xu, and Wax, Phys. Rev. B 93, 214203 (2016)] so that it is possible to predict the viscosity value of any alkali metal with an accuracy better than 10% over the corresponding density and temperature range.

Studies on α to β phase transformations in mechanically deformed PVDF films

AbstractPVDF cast films were drawn at different temperatures to different draw ratios at constant draw rate to understand the mechanism of α to β phase transformation during mechanical deformation. WAXD and FTIR studies were carried out to determine the formation and content of β phase in the drawn films. Lower stretch temperatures gave higher fractions of β phase. The cast PVDF films were also drawn at suitable temperatures below the PVDF ambient melting point to the draw ratio of 6.4. The highest fraction of β phase obtained in these ultra drawn films was 0.98. SALS studies carried out for films at different stretch ratios show the change in spherulitic structure with the stretching parameters and give information for the understanding of phase transformation during stretching of PVDF films. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Basalt magma genesis and fractionation in collision- and extension-related provinces: A comparison between eastern, central and western Anatolia

Experimental studies of synthetic and natural basalt systems suggest that conditions of magma genesis and fractionation depend fundamentally on mantle temperatures and lithospheric stress fields. In general, compressional settings are more conducive to polybaric fractionation than extensional settings and in this regard, the Anatolian magmatic province offers a natural laboratory for comparing near-coeval basalt eruptions as a function of regional tectonics — compressional (collision-related) régimes dominating in eastern Anatolia and extensional tectonics characterizing a western province related to Aegean Sea opening. Projection of Plio-Quaternary basalt normative compositions from the Western Anatolia Extensional Province (WAEP), the Central Anatolian ‘Ova’ Province (CAOP), and Eastern Anatolia Compressional Province (EACP) are projected onto Ol–Ne–Cpx and Pl–Cpx–Ol planes in the simplified basalt system (Ne–Cpx–Ol–Qz), each showing distinctive liquid lines of descent. WAEP basalts are mostly constrained by low-pressure (< 0.5 GPa) cotectics while CAOP and EACP compositions conform to moderate and/or high-pressure (0.8–3.0 GPa) cotectics. Overall, a quasi-linear shift from moderate and/or high-pressure to low-pressure equilibria matches the westward transgression from compressional east Anatolia to the extensional west Anatolian–Aegean region. Comparison of their respective primary (mantle-equilibrated) magmas–simulated by normalizing their compositions to MgO = 15 wt.% (Mg-15)–with parameterized anhydrous and H 2O-undersaturated experimental melts suggests they segregated from spinel- to garnet-lherzolite mantle facies at pressures between c. 2 and 3 GPa (c. 70–100 km depth) under H 2O-undersaturated conditions. Interpolated potential temperatures ( T p) and lithospheric stretching factors ( β) range as follows: (1) eastern Anatolian basalts associated with the Arabian foreland show T p varying between 1250 and 1400 °C (except for the Karacalidag alkali basalts, south of the Bitlis–Zagros fracture zone, for which T p ranges up to 1450 °C), for β values of 1.2–1.8. T p values for central Anatolia (e.g. Sivas) range between 1300 and 1375 °C (except for Karapinar, Egrikuyu and Hasandag, which show < 1150 °C), and β values of 1.3–1.4. For western Anatolian basalts, T p range mostly between 1250 and 1330 °C, except for a single value for Canakkale of 1400 °C and Kula sample showing T p < 1200 °C, and β values of 1.3–2.0. Variation of these conditions is as great or greater than that between provinces, although there are clearly significant constraints on the inferred polybaric to low-pressure isobaric fractionation régimes. Covariation of total FeO, TiO 2, La/Yb, Ce/Sm, Zr/Y and Zr/Nb reflects small but significant differences in bulk composition and ambient melt fraction while the covariance of Ce/Sm and Sm/Yb is consistent with the segregation of primitive melts at the spinel- to garnet-lherzolite transition.

Superdrawing of polytetrafluoroethylene nascent powder by solid-state coextrusion

A film of nascent powder of polytetrafluoroethylene (PTFE), compacted below the ambient melting temperature (Tm, 335 °C), was drawn by two-stage draw techniques consisting of a first-stage solid-state coextrusion followed by a second-stage solid-state coextrusion or tensile draw. Although the ductility of extrudates was lost for the second-stage tensile draw at temperatures above 150 °C due to the rapid decrease in strength, as previously reported, the ductility of extrudates increased with temperature even above 150 °C when the second-stage draw was made by solid-state coextrusion, reflecting the different deformation flow fields in a free space for the former and in an extrusion die for the latter. Thus, a powder film initially coextruded to a low extrusion draw ratio (EDR) of 6–20 at 325 °C was further drawn by coextrusion to EDRs up to ∼︁400 at 325–340 °C, near the Tm. Extremely high chain orientation (fc = 0.998 ± 0.001), crystallinity (96.5 ± 0.5)%, and tensile modulus (115 ± 5 GPa at 24 °C, corresponding to 73% of the X-ray crystal modulus) were achieved at high EDRs. Despite such a morphological perfection and a high modulus, the tensile strength of a superdrawn tape, 0.48 ± 0.03 GPa, was significantly low when compared with those (1.4–2.3 GPa) previously reported by tensile drawing above the Tm. Such a low strength of a superdrawn, high-modulus PTFE tape was ascribed to the low intermolecular interaction of PTFE and the lack of intercrystalline links along the fiber axis, reflecting the initial chain-extended morphology of the nascent powder combined with the fairly high chain mobility associated with the crystal/crystal transitions at around room temperature. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3369–3377, 2006

Understanding solid/solid organic reactions.

The concept of an organic reaction between two macroscopic solid particles is investigated. Thus, we study several reactions that have been recently reported to proceed "in the solid phase" and clearly show that, in most cases, grinding the two solid reactants together results in the formation of a liquid phase. This is true both for catalytic transformations (e.g., aldol condensations and oligomerization of benzylic compounds) and for noncatalytic reactions (Baeyer-Villiger oxidations, oxidative coupling of naphthols using iron chloride, condensation of amines and aldehydes to form azomethines, homo-etherification of benzylic alcohols using p-toluenesulfonic acid, and nuclear aromatic bromination with NBS). This liquefaction implies the existence of a eutectic mixture with T(fusion) below ambient temperature (although both reagents have higher than ambient melting points). In cases where heating is required, it is again clear that a phase change (from solid to liquid) occurs, explaining the observed reaction kinetics. On the basis of 19 experimental examples, we discuss the possibility of solid-phase organic reactions and the implications of these findings to the reaction between two solid reagents. A general description of such reactive systems is proposed, based on a consideration of the potential for eutectic (or peritectic) formation between the constituents of the liquid phases that arise during the process of mechanical mixing of the solid reagents and products.

Dike ascent in partially molten rock

Field observations indicate that dikes form and grow in magma source regions, but the mechanics of this process are poorly understood. I derive time‐dependent and self‐similar solutions for the growth of buoyant dikes fed by porous flow in partially molten rock. The host rock is treated as poroelastic; for basaltic (but not rhyolitic) dikes, large‐scale viscous deformation of the rock is insignificant for dikes large enough to meet the classical Griffith fracture criterion. Observed wetting angles in partially molten peridotite suggest that subcritical crack growth may be important in crack initiation and render viscous deformation insignificant for dikes that are shorter still. Melt is driven into the dike by the difference between the ambient pore pressure and the least compressive stress and driven up the dike by magma buoyancy. The volume increase of the melting reaction, driven by the local drop in pore pressure, may be more important than elastic compressibility of the pore volume and pore fluid in driving melt into the dike. Because channel flow is very efficient relative to porous flow, the dikes are thin, about 6 mm wide when they are a few kilometers tall, for an ambient melt pressure that exceeds the least compressive stress by 1 MPa. This thickness is relatively insensitive to all relevant parameters (including the dike height) because the channel flux increases as the cube of the channel thickness. One implication appears to be that dikes that traverse the lithosphere must drain large segregations of magma, rather than partially molten rock. If dikes feed compliant sills at a depth where the source region is conductively cooled, crystallization onto the dike walls could increase the observable thickness while mass balance maintains a narrow aperture for flow.

Origin of podiform chromite deposits by magma mingling

I have oversaturated the immiscible system SiO 2 Al 2O 3 FeO K 2O with FeCr 2O 4 to study the fractionation of chromite between conjugate siliceous and fayalitic melts. Although both melts are oversaturated with chromite, chromite only nucleates in the fayalite-rich melt where the crystal/melt interfacial energy ( γ SL ) is lowest. In less than three days at 1150°C, all excess chromium in the bulk composition is concentrated as cumulus chromite in the fayalitic melt pools, producing nodular cumulate textures as observed in podiform chromite ore. When these results are applied to the lithospheric mantle, podiform chromite deposits may form when droplets of olivine-normative high-pressure, low-viscosity melt mingle with siliceous low-pressure, more viscous melt in shallow magma conduits. It is inferred from the experimental analogue that chromite only nucleates in the melt where γ SL is lowest, which in the mantle would be the high-pressure melt. The low-pressure melt only serves as the diffusive chromium reservoir. The richest chromite ores form when the volume ratio of the melt nucleating chromite is small relative to the ambient melt.

The effect of mixed modifiers on nuclear waste glass processing, leaching, and Raman spectra

Borosilicate glasses with different waste loadings were prepared by ambient melting, quenching, and annealing. Some melt compositions partially crystallize to durable phases of zircon and forsterite. The coexisting liquid quenches to glass and endures the leach tests. The waste loading dependent leach rate trends of these glasses are reminiscent of the mixed alkali effect. Raman spectra suggest initial increase in durability with increases in the depolymerization of silicate species. Fluorine and hydroxyl ions also contribute to depolymerization. Tetraborate and metaborate rings are identified in the Raman spectra. The durability is enhanced when tetraborate bands are more intense than the metaborate bands.

Solid-state deformation of polytetrafluoroethylene powder

Polytetrafluoroethylene (PTFE) powder of a high molecular weight (~ 107) was drawn by solid-state extrusion in the temperature range 100–340°C, which covers the glass transition temperature (125°C) and the ambient melting point (334°C). Draw was attainable only above 100°C. The maximum achievable extrusion draw ratio (EDRmax) was almost constant, ~ 10, from 100–280°C, yet increased rapidly with further increasing temperature, reaching a maximum of 60 at 330–340°C. At yet higher temperatures, the drawability was lost due to melting. The structure and properties of drawn products were found to be complexely affected by extrusion temperature and EDR. For extrusion at 330–340°C, near the melting point, an effective and high draw was achieved. The crystalline chain orientation function, crystallite sizes, both along and perpendicular to the chain axis, differential scanning calorimetry heat of fusion, and flexural modulus increased with EDR and approached a maximum at EDR of 30–40, depending on the extrusion temperatures. Above a specific EDR, the efficiency of draw decreased due to the formation of flaws. The highly oriented PTFE consisted of microfibrils of a significantly large lateral dimension (~ 45 nm) compared to those (6–20 nm) generally found in oriented polymers. The modulus of a drawn PTFE was sensitive to the test temperatures, reflecting the reversible crystal/crystal transitions at ~ 19 and 30°C. The optimization of the extrusion conditions resulted in the maximum achieved flexural modulus at 24°C of 20 GPa at an EDR 40 for extrusion at 340°C.

Two-stage drawing of ultra-high molecular weight polyethylene reactor powder

A two-stage drawing technique has been successfully applied for drawing of ultra-high molecular weight polyethylene reactor powder. Compacted powder films prepared below the ambient melting point of the initial powder was solid-state coextruded to a low extrusion draw ratio of 6 followed by tensile drawing at elevated temperatures of 120–135°C. The drawability for the second-stage tensile drawing and the uniformity of the resultant ultradrawn films were significantly affected by the drawing temperature and rate. The initial powder and drawn films were characterized by the tensile measurements, differential scanning calorimetry (d.s.c.) and X-ray diffraction. The results show the characteristic morphology of the reactor powder. Thus, the compacted powder films were effectively drawn up to a draw ratio of 77. Such highly drawn films exhibited tensile moduli up to 107 GPa. As the samples fractured by a repetitive partial rupture at the edge of cramp, the observed tensile strength at break were fairly low and in the range 1.0–1.4 GPa at a draw ratio range of 35 to 77.