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Southern Africa is characterised by unusually elevated topography and abnormal heat flow. This can be explained by thermal perturbation of the mantle, but the origin of this is unclear. Geophysics has not detected a thermal anomaly in the upper mantle and there is no geochemical evidence of an asthenosphere mantle contribution to the Cenozoic volcanic record of the region. Here we show that natural CO2 seeps along the Ntlakwe-Bongwan fault within KwaZulu-Natal, South Africa, have C-He isotope systematics that support an origin from degassing mantle melts. Neon isotopes indicate that the melts originate from a deep mantle source that is similar to the mantle plume beneath Réunion, rather than the convecting upper mantle or sub-continental lithosphere. This confirms the existence of the Quathlamba mantle plume and importantly provides the first evidence in support of upwelling deep mantle beneath Southern Africa, helping to explain the regions elevation and abnormal heat flow. The elevation and high heat flow of Southern South Africa has controversially been attributed to a mantle plume. Here, the authors link degassed CO2 to a non-degassed mantle source rather than the convecting upper mantle, confirming plume-related mantle melting. [ABSTRACT FROM AUTHOR]

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The composition of Earth’s atmosphere depends on the redox state of the mantle, which became more oxidizing at some stage after Earth’s core started to form. Through high-pressure experiments, we found that Fe2+ in a deep magma ocean would disproportionate to Fe3+ plus metallic iron at high pressures. The separation of this metallic iron to the core raised the oxidation state of the upper mantle, changing the chemistry of degassing volatiles that formed the atmosphere to more oxidized species. Additionally, the resulting gradient in redox state of the magma ocean allowed dissolved CO2 from the atmosphere to precipitate as diamond at depth. This explains Earth’s carbon-rich interior and suggests that redox evolution during accretion was an important variable in determining the composition of the terrestrial atmosphere. [ABSTRACT FROM AUTHOR]

Highlights • A simple and fast degassing method using a PDMS membrane and a microsupport array. • Disposable degassing microfluidic device using a micrometer-thick PDMS membrane. • Quantitative analysis of degassing rate with assembly disposable degassing (ADD)-method. • Development of an active bubble-trap structure based on the ADD-method. • Applications of the ADD-method to complex structured and functional microfluidic devices. Abstract We introduce an assembly disposable degassing (ADD)-method as a simple and fast active degassing method. The ADD-method is achieved with a microstructured disposable superstrate and a reusable microsupport substrate, which can be assembled and disassembled simply by vacuum pressure. The reusable substrate can be equipped with functionalities to create an elaborately patterned energy field for active manipulation of substances in the microchannel. Degassing performance was evaluated for varying thicknesses of the polydimethylsiloxane (PDMS) membrane and heights of the microsupport array. Based on the ADD-method, an active bubble-trap structure was developed to prevent bubble injection into the microchannels. Deterministic lateral displacement and microvortex devices, as complex structured microfluidic devices that are easily suffered by bubble formation, were used to demonstrate the usefulness of the ADD-method. As a test vehicle of active functional microfluidic devices, an assembly-disposable degassing lateral magnetophoretic microseparator (CTC-addChip) was developed. For the CTC-addChip, a ferromagnetic wire array was inlaid on the reusable substrate to create a high-gradient magnetic field, which can transfer through the PDMS membrane and isolate circulating tumor cells with magnetic nanobeads in the microchannel without bubble interference. [ABSTRACT FROM AUTHOR]

An experimental study of the gas‐liquid dynamics in a water model of an aluminum ladle was conducted. The rotor degassing performance was evaluated for two commercial rotor‐injector devices compared to a new rotor design. In this work, the influence of the turbulent properties of the flow fields on the bubble size distribution is analyzed for a better understanding of its impact on the degassing efficiency in aluminum refinement operations. The degassing process was analyzed by two different methods: (a) a high‐speed camera was used to obtain the bubble size distribution into the container; and (b) the particle image velocimetry technique (PIV) was employed to obtain the liquid flow properties. It was found that the rotor geometry plays an important role on the average size and distribution of the bubbles. The energy dissipation rate contours show significant differences for the distinct rotors tested. These hydrodynamic states and bubbles distribution dominate the kinetic and efficiency of the degassing processes. It was shown that the new rotor configuration enhances the degassing kinetics, due to a more suitable bubble dispersion compared to the commercial rotors tested. [ABSTRACT FROM AUTHOR]

The present study aims to estimate the variability in the tensile properties of the A5052 aluminium alloy processed through ultra-high-density sonication. An in-depth look at the quality index of the tensile properties to microporosity variations through a quantitative description based on a modified constitutive model for tensile instability. The test specimens were prepared as billets of 4 inches in diameter via gravity casting using a pilot-scale melt amount (30 kg) under the ultrasonic frequency of 20 kHz (4.4 kW). The ultimate tensile strength and yield strength of the as-cast A5052 alloy were increased by approximately 40 MPa and 10 MPa due to effective grain refinement through sonication compared to those of specimens without sonication. In addition, the nominal value of fracture elongation also exhibited a remarkable improvement of more than 5% by reducing the microporosity through degassing of the melt during sonication. The ultra-high-density sonication treatment using a Ti-horn to aluminium melt clearly maximised the effect of grain refinement by heterogeneous nucleation of foreign nuclei and fragmentation of dendrites, simultaneously with the degassing action accompanying the melt convection provided by ultrasonic excitation. The dependence of the tensile properties on the microporosity variation can be expressed in terms of a quality index chart, which considers the porosity level, the distribution of micro-voids, and the strain hardening exponent through the modified constitutive model. [ABSTRACT FROM AUTHOR]