Continental weathering and recovery from ocean nutrient stress during the Early Triassic Biotic Crisis

Following the latest Permian extinction ∼252 million years ago, normal marine and terrestrial ecosystems did not recover for another 5-9 million years. The driver(s) for the Early Triassic biotic crisis, marked by high atmospheric CO2 concentration, extreme ocean warming, and marine anoxia, remains unclear. Here we constrain the timing of authigenic K-bearing mineral formation extracted from supergene weathering profiles of NW-Pangea by Argon geochronology, to demonstrate that an accelerated hydrological cycle causing intense chemical alteration of the continents occurred between ∼254 and 248 Ma, and continued throughout the Triassic period. We show that enhanced ocean nutrient supply from this intense continental weathering did not trigger increased ocean productivity during the Early Triassic biotic crisis, due to strong thermal ocean stratification off NW Pangea. Nitrogen isotope constraints suggest, instead, that full recovery from ocean nutrient stress, despite some brief amelioration ∼1.5 million years after the latest Permian extinction, did not commence until climate cooling revitalized the global upwelling systems and ocean mixing ∼10 million years after the mass extinction

Amorphous Al1-xTix, Al1-xVx, and Al1-xFex phases in the hydrogen cycled TiCl3, VCl3 and FeCl3 enhanced NaAlH4 systems

The twice hydrogen (H) cycled planetary milled (PM) and cryo milled (CM) NaAlH4 + xTMCl3 (transition metal (TM) = Ti, V, Fe) systems (x > 0.1) have been studied by high resolution synchrotron X-ray diffraction, and high resolution transmission electron microscopy (TEM). Intense primary amorphous (a-) Al1−xTMx halos are evident in diffraction data of PM samples for V and Fe, and in CM samples for Ti, V, and Fe. Weaker primary amorphous Al1−xTix halos are evident in PM samples for Ti. The Ti poor a-Al1−xTix phase observed for NaAlH4 + xTiCl3 (x > 0.1) ranges in composition from a-Al86.5Ti13.5 → a-Al92Ti8. High resolution TEM studies of the Al1−xVx phases in the H cycled PM NaAlH4 + 0.1VCl3 system demonstrates that a nanoscopic composite morphology can exist between face centred cubic (fcc) crystalline (c-) Al1−xVx and a-Al1−xVx phases, with the c-Al1−xVx/a-Al1−xVx composite embedded on the NaAlH4 surface. The amorphous Al1−xVx reaches ca. 28 at.% V

Crystalline Al1-xTix phases in the hydrogen cycled NaAlH4+0.02TiCl3 system

The hydrogen (H) cycled planetary milled (PM) NaAlH4 + 0.02TiCl3 system has been studied by high resolution synchrotron X-ray diffraction and transmission electron microscopy during the first 10 H cycles. After the first H absorption, we observe the formation of four nanoscopic crystalline (c-) Ti-containing phases embedded on the NaAlH4 surface, i.e. Al2Ti, Al3Ti, Al82Ti18 and Al89Ti11, with 100% of the originally added Ti atoms accounted for. Al2Ti and Al3Ti are observed morphologically as a mechanical couple on the NaAlH4 surface, with a moderately strained interface. Electron diffraction shows that the Al82Ti18 phase retains some ordering from the L12 structure type, with the observation of forbidden (100) ordering reflections in the fcc Al82Ti18 lattice. After 2 H cycles the NaAlH4 + 0.02TiCl3 system displays only two crystalline Ti-containing phases, Al3Ti and Al89Ti11. After 10 H cycles, the Al89Ti11 is completely converted to Al85Ti15. Al89Ti11, Al85Ti15 and Al3Ti do not display any ordering reflections, and they are modeled in the A1 structure type. Quantitative phase analysis indicates that the Al3Ti proportion continues to increase with further H cycles. The formation of Ti-poor Al1 − x Ti x (x < 0.25) phases in later H cycles is detrimental to hydrogenation kinetics, compared to the starting Ti-richer near-surface Al2Ti/NaAlH4 interface present during the first absorption of hydrogen

A structural review of nanoscopic Al1-xTMx phase formation in the TMCln enhanced NaAlH4 system

The twice hydrogen (H) cycled planetary milled (PM) NaAlH4 + xTMCln (transition metal (TM) = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Pd, Pt; 2 &lt; n &lt; 4) and cryo milled (CM) NaAlH4 + xTMCln (TM = Ti, V, Cr, Fe, Ni; 2 &lt; n &lt; 3) systems (x &lt; 0.1) have been studied by high resolution synchrotron X-ray diffraction. Face centred cubic (fcc) A1 crystalline (c-) Al1-xTMx (x &lt; 0.25) solid solutions are evident in PM samples for Sc, Ti, V, Cr, Mn, Zr and Pd while PM samples of Cu, Ni, Pd and Pt display mostly ordered and numerous crystalline Al1-xTMx phases. Very broad reflections in the 2 Å d-spacing region for Cr, Mn, Co, and Pd are identified as partially ordered body centred cubic (bcc) A2 and B2 Al1-xTMx type structures. The amorphous (a-) Al1-xVx phase observed in the H cycled PM NaAlH4 + xVCl3 system ranges in composition from a-Al90V10 (x = 0.02) up to a-Al72V28 (x = 0.1). Across the TM series, the Al1-xTMx particle size ranges as Sc-V 4-25 nm, Cr, Mn, Co &lt;5 nm, Fe 5–15 nm, Ni, Cu &lt;50 nm. A highly ‘compressed’ NaAlH4 phase is observed in the H cycled PM NaAlH4 + 0.1ScCl3 system, with unit cell dimensions of a = 4.9995(2) Å and c = 11.2893(1) Å, compared to the average dimensions of ‘normal’ NaAlH4 across the TM and rare earth (RE) series with a = 5.0228(1) Å and c = 11.3516(1) Å

Highly aligned growth of carbon nanotube forests with in-situ catalyst generation. A route to multifunctional basalt fibres

Hierarchical fabrics are gaining ever-growing practical interest, thanks to the possibility of combining different properties into a single textile, particularly useful for applications such as high-performance composites showing in situ structural health monitoring capabilities. In this study, homogeneously aligned carbon nanotube forests are directly grown on basalt fabrics by a fast (∼15 min) chemical vapour deposition process without any external catalyst addition providing, for the first time, a highly dense coverage of the underlying substrate. It is demonstrated by transmission electron microscopy that the direct growth of nanotubes on basalt fibres is catalysed by the microstructural segregation of ferrous iron and its subsequent reduction in hydrogen atmosphere to nanocrystalline metallic iron. It is shown that in situ growth requires a pre-treatment etching which can be conducted in mild basic or acidic conditions, achieving optimum performance with an alkaline attack, without compromising the tensile strength of the fibres. Post-growth Raman analysis shows characteristic features associated with high graphitic ordering which turn an intrinsically insulating substrate into an electrically conductive (∼260 S/m) fabric, thus suggesting the possibility to employ the newly engineered hierarchical fabric in all those applications where the combination of good mechanical properties and electrical conductivity is a key requirement

Hydrogen absorption kinetics and structural features of NaA1H4 enhanced with transition meal-and Ti-based nanoparticles

The hydrogen cycled (H) planetary milled (PM) NaAlH4 + xM (x TiN > TiC > Ti, with rapid hydrogenation kinetics of ca. 23 wt.% H/hour for TiO2 enhanced NaAlH4, equivalent to TiCl3 enhanced NaAlH4. The TiN and TiC are partially reduced by ca. 7 and 22% respectively, and the TiO2 is completely reduced. The location of the reduced Ti cannot be discerned by X-ray diffraction at these minor proportions

Magnetic domain configuration of (111)-oriented LaFeO 3

In antiferromagnetic spintronics control of the domains and corresponding spin axis orientation is crucial for devices. Here we investigate the antiferromagnetic axis in (111)-oriented LaFeO3/SrTiO3, which is coupled to structural twin domains. The structural domains have either the orthorhombic a- or b-axis along the in-plane ⟨11¯0⟩ cubic directions of the substrate, and the corresponding magnetic domains have the antiferromagnetic axis in the sample plane. Six degenerate antiferromagnetic axes are found corresponding to the ⟨11¯0⟩ and ⟨112¯⟩ in-plane directions. This is in contrast to the biaxial anisotropy in (001)-oriented films and reflects how crystal orientation can be used to control magnetic anisotropy in antiferromagnets