Bimodal Compositional Distribution Research Articles

Intrinsic Kinetic Limitations in Substituted Lithium-Layered Transition-Metal Oxide Electrodes.

Substituted Li-layered transition-metal oxide (LTMO) electrodes such as LixNiyMnzCo1-y-zO2 (NMC) and LixNiyCo1-y-zAlzO2 (NCA) show reduced first cycle Coulombic efficiency (90-87% under standard cycling conditions) in comparison with the archetypal LixCoO2 (LCO; ∼98% efficiency). Focusing on LixNi0.8Co0.15Al0.05O2 as a model compound, we use operando synchrotron X-ray diffraction (XRD) and nuclear magnetic resonance (NMR) spectroscopy to demonstrate that the apparent first-cycle capacity loss is a kinetic effect linked to limited Li mobility at x > 0.88, with near full capacity recovered during a potentiostatic hold following the galvanostatic charge-discharge cycle. This kinetic capacity loss, unlike many capacity losses in LTMOs, is independent of the cutoff voltage during delithiation and it is a reversible process. The kinetic limitation manifests not only as the kinetic capacity loss during discharge but as a subtle bimodal compositional distribution early in charge and, also, a dramatic increase of the charge-discharge voltage hysteresis at x > 0.88. 7Li NMR measurements indicate that the kinetic limitation reflects limited Li transport at x > 0.86. Electrochemical measurements on a wider range of LTMOs including Lix(Ni,Fe)yCo1-yO2 suggest that 5% substitution is sufficient to induce the kinetic limitation and that the effect is not limited to Ni substitution. We outline how, in addition to a reduction in the number of Li vacancies and shrinkage of the Li-layer size, the intrinsic charge storage mechanism (two-phase vs solid-solution) and localization of charge give rise to additional kinetic barriers in NCA and nonmetallic LTMOs in general.

Temporal changes in the subduction of the Paleo-Pacific plate beneath Eurasia during the late Mesozoic: Geochronological and geochemical evidence from Cretaceous volcanic rocks in eastern NE China

Subduction of the Paleo-Pacific Plate played an important role in the evolution of the eastern margin of the Eurasian continent. However, the details of the processes of subduction during the late Mesozoic remain poorly constrained. Here we examine the geochronology and geochemistry of Cretaceous volcanic rocks from eastern NE China, with the aim of understanding the variation of subduction process. Cretaceous volcanism in the region mainly occurs in the Raohe–Mishan-Suifenhe–Wangqing and Jiamusi–Jixi areas in eastern Jilin and Heilongjiang provinces, as well as in the Lesser Xing'an Range where volcanism extends from the continental margin farther inland. The Cretaceous volcanic rocks in the Raohe–Mishan–Suifenhe–Wangqing (RMSW) area are composed of basalts, basaltic andesites, andesites, dacites, and rhyolites with late Early Cretaceous (122–106 Ma) ages and dacites that yield early Late Cretaceous (96–93 Ma) ages. A mixed source of compositionally heterogeneous mantle and crustal rocks is assumed based on the compositional range of volcanic rocks. Adakitic andesites (114–110 Ma) were derived from a mantle source modified by slab-derived melt that infiltrated the mantle wedge. Adakitic dacites (122–106 and 96–93 Ma) were produced by partial melting of thickened lower crust that formed in response to earlier subduction of the Paleo-Pacific Plate beneath Eurasia. The rhyolites and dacites that lack adakitic signatures were derived from partial melting of a depleted lower-crustal block that was accreted during the Neoproterozoic. In particular, the late Early Cretaceous (106 Ma) basalt was derived from a depleted lithospheric mantle that was metasomatized by slab-derived fluids and subsequently by asthenospheric melts at a relatively shallow depths, implying rollrback of the subducted Paleo-Pacific Plate. The Cretaceous volcanism in the Jiamusi–Jixi area formed during the late Early Cretaceous (124–110 Ma) and shows a bimodal distribution of compositions with a prominent ‘Daly Gap’. The mafic members were generated by re-melting of depleted lithospheric mantle that was modified by subduction-related fluids and underwent fractional crystallization. The coeval felsic end-members, with or without A-type characteristics, were generated by partial melting of juvenile crustal material, consistent with an extensional environment related to subduction of the Paleo-Pacific Plate. Cretaceous volcanism in the Lesser Xing'an Range shows a bimodal compositional distribution of volcanic rocks with a ‘Daly Gap’ and a period without volcanism at 108–97 Ma. Andesites with and without adakitic signatures were derived from partial melting of mantle that was hybridized by slab-derived melts and metasomatized by a fluid-rich subduction component. In contrast, the coeval A-type rhyolites were generated by partial melting of juvenile crust, implying the migration of the extensional environment. The formation of, and spatio-temporal relationships between, Cretaceous volcanic rocks in NE China, combined with the regional geological data, suggest a transition from low-angle subduction to slab rollback and subsequent changes in the direction of motion of the Paleo-Pacific Plate during the late Early Cretaceous to the Late Cretaceous.

Phase equilibrium modelling of granite magma petrogenesis: B. An evaluation of the magma compositions that result from fractional crystallization

Several fractional crystallization processes (flow segregation, gravitational settling, filter-pressing), as well as batch crystallization, have been investigated in this study using thermodynamic modelling (pseudosections) to test whether they are able to reproduce the compositional trends shown by S-type granites. Three starting compositions comprising a pure melt phase and variable amounts of entrained minerals (0, 20 and 40wt.% of the total magma) have been used to study a wide range of likely S-type magma compositions. The evolution of these magmas was investigated from the segregation from their sources at 0.8GPa until emplacement at 0.3GPa in an adiabatic path, followed by isobaric cooling until the solidus was crossed, in a closed-system scenario. The modelled magmas and the fractionated mineral assemblages are compared to the S-type granites of the Peninsula pluton, Cape Granite Suite, South Africa, which have a composition very similar to most of the S-type granites. The adiabatic ascent of the magmas digests partially the entrained mineral assemblage of the magmas, but unless this entrained assemblage represents less than 1wt.% of the original magma, part of the mineral fraction survives the ascent up to the chosen pressure of emplacement. At the level of emplacement, batch crystallization produces magmas that only plot within the composition of the granites of the Peninsula pluton if the bulk composition of the original magmas already matched that of the granites. Flow segregation of crystals during the ascent and gravitational settling fractional crystallization produce bodies that are generally more mafic than the most mafic granites of the pluton and the residual melts have an almost haplogranitic composition, producing a bimodal compositional distribution not observed in the granites. Consequently, these two processes are ruled out. Filter-pressing fractional crystallization produces bodies in an onion-layer structure that become more felsic with increasing crystallization, culminating in a haplogranitic melt, and is able to reproduce the compositional trends of the granites, but only if the original magmas already had the composition of the granites. Filter-pressing fractionation produces a mineral assemblage that is 1.5 times more mafic than the magma fraction from which it is derived. However, the mineral assemblages produced by crystallization of an originally pure melt phase are still too felsic to account for the bulk of the granites of the Peninsula pluton. For filter-pressing to produce the most mafic granites of the pluton, the original magmas must already contain an entrained mafic mineral assemblage and have the same composition of the granites, otherwise the modelled trends do not match the maficity (FeO+MgO) or the slope against maficity of the granites. Crystallization of the magma in filter-pressing releases a free water phase, whose amount depends on the amount of water of the original magma, and whose behaviour may be controlled by a water-saturation front. In summary, the main control in the composition of S-type granites is the amount and nature of the entrained mineral assemblage, and filter-pressing fractional crystallization can only modify slightly the compositions of the granitic bodies derived from these magmas.

New Insights into Andesite Genesis: the Role of Mantle-derived Calc-alkalic and Crust-derived Tholeiitic Melts in Magma Differentiation beneath Zao Volcano, NE Japan

Two distinctive differentiation trends, tholeiitic and calc-alkalic, are recognized in Zao volcano, which is located immediately behind the volcanic front of the NE Japan arc. The genetic relationship between these two magma series is critical for a better understanding of andesite genesis, because they often coexist in close spatial and temporal proximity in arc volcanoes. Petrographic features indicative of ‘disequilibrium’ , such as reversely zoned pyroxene phenocrysts, the wide and bimodal compositional distribution in Ca/(CaþNa) of plagioclase phenocrysts, honeycomb textures and dusty zones that these plagioclase phenocrysts often exhibit, and the presence of olivine^pyroxene pairs with different Mg/Fe, are observed exclusively in calc-alkalic rocks. In tholeiitic rocks the Sr isotopic ratios of plagioclase phenocrysts, determined by both micromilling combined with thermal ionization mass spectrometry, and laser-ablation inductively coupled plasma mass spectrometry techniques, are constant at 0 7042^0 7044. On the other hand, those in calc-alkalic rocks (0 7033^0 7042) show more complex characteristics, which can be best understood if at least three end-member components, a calc-alkalic basaltic melt, a tholeiitic basaltic melt and a tholeiitic felsic melt, contribute to the production of mixed calc-alkalic magmas.The Sr/Sr and trace element compositions of the leastdifferentiated basalt magmas, which are inferred from the composition of the calcic plagioclase [Ca/(CaþNa)40 9], suggest that two types of basaltic magma, calc-alkalic and tholeiitic, exist beneath the volcano. The tholeiitic basalt magma has a higher Sr/Sr than the calc-alkalic magma (0 7042 vs 0 7038) and a characteristic trace element signature consistent with the presence of plagioclase and amphibole as melting residues.This suggests that the tholeiitic magmas are produced via anatexis of amphibolitic crust caused by underplating and/or intrusion of mantle-derived calcalkalic basalt magmas into the sub-Zao crust. The mantle-derived calc-alkalic basalt magma mixes with crust-derived tholeiitic melts to form calc-alkalic andesite magmas.The hypothesis proposed here requires revision (or even abandonment) of the general consensus that calc-alkalic magmas have greater contributions of a crustal component than tholeiitic magmas.

Contrast Variation SANS Investigation of Composition Distributions in Mixed Surfactant Micelles

Small angle neutron scattering measurements have been performed on three systems (HFDeP-d5-C (N-1(1,1,2,2-tetrahydroperfluorodecanoyl)pyridinium-d5 chloride)/C16PC in 63 mM NaCl; HFDeP-d5-C/C12PC in 200 mM NaCl, and as an example of an ideally mixed system, SDS/SDS-d25 in 200 mM NaCl) containing micelles formed in a binary mixture of surfactants, in order to investigate the composition distribution of the mixed micelles. The experimental data were collected varying the contrast between the average scattering length density of micelles and aqueous solvent by changing the H2O/D2O ratio. Analysis of data includes a model-independent approach--the indirect Fourier transformation method and direct modeling-simultaneous fit at all contrasts by the scattering from micelles of equal size and shape with composition distribution and an effective interaction. It has earlier been shown (Almgren, M.; Garamus, V. M. J. Phys. Chem. B 2005, 109, 11348) that for micelles of equal size, independent of the composition, and with negligible intermicellar interactions, the scattered intensity at zero angle varies quadratically with the contrast, with the minimum intensity at the nominal match point proportional to sigma2, the variance of the micelle composition distribution. Within the regular solution framework, the composition distribution and its variance are uniquely defined by the value of the interaction parameter and the micelle aggregation number. At 25 degrees C, the first system gave sigma = 0.37, corresponding to a broad, bimodal composition distribution, the second sigma = 0.22, a broad distribution with a shallow minimum at the midpoint. For SDS/SDS-d25, we found sigma = 0.006 +/- 0.030, which is a smaller value than that of the binominal composition distribution expected for an ideally mixed system.

Bimodal polyethylene products from UNIPOLTM single gas phase reactor using engineered catalysts

AbstractAdvanced catalyst engineering from Univation Technologies provides the capability to produce polyethylene with bimodal molecular weight distribution and bimodal composition distribution in a single gas phase reactor. This paper will discuss the structure‐property‐process relationship for these engineered polyethylene products. Examples of High Density Polyethylene (HOPE) polymers with bimodal molecular weight distribution will demonstrate the utility of the engineered catalysts in high molecular weight film production. Examples of Linear Low Density Polyethylene (LLDPE) polymers with broad comonomer composition distribution will demonstrate the utility of the engineered catalysts for high strength film applications. Examples of HOPE polymers with bidmoal molecular distribution and controlled comonomer distribution will demonstrate the capability of Univation's latest engineered catalysts for high performance pipe applications.

Fractionation and magma mixing within intruding dike swarm: evidence from the Miocene Shitara-Otoge igneous complex, central Japan

The analysis of intrusion pattern and petrological character of the central dike swarm in the Miocene igneous complex of the Shitara district, central Japan clarified that magma mixing between a strongly differentiated magma and a less-differentiated magma occurred within a dike swarm. The dike rocks have a wide compositional variation ranging from 5.5 to 0.7wt.% MgO. They are divided into P1- and P2-types. The P2-type rocks provide many lines of evidence for magma mixing such as reversely zoned phenocrysts, bimodal composition distribution, and dissolution texture, whereas P1-type rocks do not. Phenocryst compositions of P2-type suggest that the magma mixing occurred between a less-fractionated phenocryst-poor magma and a strongly fractionated crystal-rich magma. Concentration ratios among incompatible elements show that the mixing end components were derived from a similar parental magma common to P1-type by fractional crystallization in a near closed system. The dikes with evidence for the magma mixing (P2-type) are distributed only in the southern marginal part of the dike swarm, whereas P1-type dikes do not show any such localization. The distribution and the intrusion direction of the dikes indicate a nearly horizontal outward flow of magmas in the southern part of the dike swarm and accompanied magma mixing in the dike during intrusion. The fractionated end component is inferred to be a product of crystal fractionation within small and ephemeral magma pockets in the dike swarm. Magma mixing is thought to have occurred when a newly intruded dike ruptured the magma reservoir. The frequency of magma mixing was controlled mainly by competition between the lifetime of ephemeral magma reservoir and frequency of dike intrusions. The condition of magma mixing was satisfied only in the southern part of the dike swarm affected by the preceding volcanic activities.

The effect of aluminium compounds in the copolymerization of ethylene / α‐olefins

AbstractTwo types of copolymerizations were found with the catalyst system Cp2ZrCl2/MAO. One was a less exothermic reaction, and another was a more exothermic one. The former provided a polymer with a single composition distribution because of a single cationic active site. The latter provided a polymer with a bimodal composition distribution, indicating the existence of two active sites. The two active sites were investigated through the comparison of MAO systems and alkylaluminium / borate systems. We speculated that the two active sites were the normal cationic site and the active site where the interaction between a cationic metallocene and an aluminium compound was strong.

Carbonate magmas

Abstract For 40 years, the case for the existence of carbonate magmas rested on field observations of carbonatite intrusions, in which the lack of thermal effects raised an apparent conflict with the high melting temperatures of pure carbonates. Since 1960, the position has changed, with the growth of experimental studies and increasing observations of effusive carbonate rocks. A nephelinite/phonolite volcano in Tanzania is currently erupting Na-Ca-K carbonate magma (around 600 °C). This is unlike all other intrusive and effusive carbonatites (350 examples worldwide) which are dominantly composed of Ca, Mg, Fe carbonates, and have negligible alkali contents. Although a number of effusive calcio-carbonatites are considered to be degraded alkali carbonatites, there are several examples (including one magnesio-carbonatite) which are close to their erupted composition, and substantiate the existence of high T carbonate magmas lacking essential alkalis at the time of eruption. In these associations silicate magmas are absent (or minor), and in most the effusive carbonatites have been erupted directly from the mantle (with entrained peridotite debris and minerals). They provide a link with the ultramafic association (peridotite and pyroxenite), seen in some carbonatite intrusions, with the commonly associated ultramafic lamprophyres (which may also carry mantle xenoliths), and with carbonate-rich kimberlites. Many carbonatite intrusions also have little or no associated silicate magmas, putting in question a popular view that carbonatites normally form only minor parts of alkaline igneous complexes of nephelinite/phonolite type. The corollary, that the carbonatites are normally differentiates is even less sound, because in alkaline complexes the carbonatite is always last in the eruption sequence. Here the carbonatite may represent the final residua expelled from the source region. Most large carbonatite intrusions seem to have been emplaced at lower T than effusives, probably as a near-solidus mush, with the interstitialfluid metasomatizing the country rocks. A wider perspective of carbonate magma genesis is called for, to encompass various kinds of differentiation from alkaline silicate magmas, and primary carbonate magmas from various depths in the mantle (with or without silicate melts). The strongly bimodal composition distribution of calcic and dolomitic carbonatites is a further factor awaiting explanation. Half of the known carbonatites are in Africa, and their timing and distribution indicate that the activity is a response to lateral forces acting across the plate. Carbonate magmatism is waiting to be unleashed. This activity demands attention because it is now clear that carbonate magmatism is a crucial surface expression of deep mantle processes.

Carbonate magmas

For 40 years, the case for the existence of carbonate magmas rested on field observations of carbonatite intrusions, in which the lack of thermal effects raised an apparent conflict with the high melting temperatures of pure carbonates. Since 1960, the position has changed, with the growth of experimental studies and increasing observations of effusive carbonate rocks. A nephelinite/phonolite volcano in Tanzania is currently erupting Na-Ca-K carbonate magma (around 600°C). This is unlike all other intrusive and effusive carbonatites (350 examples worldwide) which are dominantly composed of Ca, Mg, Fe carbonates, and have negligible alkali contents. Although a number of effusive calcio–carbonatites are considered to be degraded alkali carbonatites, there are several examples (including one magnesio-carbonatite) which are close to their erupted composition, and substantiate the existence of high T carbonate magmas lacking essential alkalis at the time of eruption. In these associations silicate magmas are absent (or minor), and in most the effusive carbonatites have been erupted directly from the mantle (with entrained peridotite debris and minerals). They provide a link with the ultramafic association (peridotite and pyroxenite), seen in some carbonatite intrusions, with the commonly associated ultramafic lamprophyres (which may also carry mantle xenoliths), and with carbonate-rich kimberlites. Many carbonatite intrusions also have little or no associated silicate magmas, putting in question a popular view that carbonatites normally form only minor parts of alkaline igneous complexes of nephelinite/phonolite type. The corollary, that the carbonatites are normally differentiates is even less sound, because in alkaline complexes the carbonatite is always last in the eruption sequence. Here the carbonatite may represent the final residua expelled from the source region. Most large carbonatite intrusions seem to have been emplaced at lower T than effusives, probably as a near-solidus mush, with the interstitial fluid metasomatizing the country rocks. A wider perspective of carbonate magma genesis is called for, to encompass various kinds of differentiation from alkaline silicate magmas, and primary carbonate magmas from various depths in the mantle (with or without silicate melts). The strongly bimodal composition distribution of calcic and dolomitic carbonatites is a further factor awaiting explanation. Half of the known carbonatites are in Africa, and their timing and distribution indicate that the activity is a response to lateral forces acting across the plate. Carbonate magmatism is waiting to be unleashed. This activity demands attention because it is now clear that carbonate magmatism is a crucial surface expression of deep mantle processes.

Petrochemical evidence for coupled magma chambers beneath the Sakurajima volcano, Kyushu, Japan.

We report systematic petrochemical changes of historical lava flows from the Sakurajima volcano. The lavas are all calc-alkalic in composition. They change in composition from dacitic to andesitic at an increasing rate with time, and show a straight-linear correlation in chemical composition. Plagioclase phenocrysts show a bimodal compositional distribution with peaks at about An58 and An85, regardless of variation in bulk rock composition. The intensity of An85 peak increases, while that of the An58 peak decreases with eruption stage. Orthopyroxene phenocrysts also show a bimodal compositional distribution. K2O content of the lavas progressively drops at almost the same rate with every gigantic eruption. These chemical and petrological aspects with other lines of evidence support binary mixing of dacitic and basaltic magmas, and a progressive increase in proportion of basaltic magma in the mixed magmas. The mixing has progressively proceeded for 475 years at least. The magma chamber model proposed in this paper consists of upper and lower chambers and a set of a huge cylinder and a mobile plug between the chambers. Both the cylinder and the plug have same frustum form. The plug subsiding into the lower chamber drives the basaltic magma upward through an opening between the cylinder-wall and the plug, and mixes it with dacitic magma in the upper chamber. Continuous influx of volatile-rich basaltic magma into the upper chamber may result in repetitive volcanic eruptions, and causes a continuous change in magma composition in the upper chamber, which erupts as lavas with discrete compositions.