We report high-resolution spectroscopic observations of WD 1145+017-a white dwarf that was recently found to be transitted by multiple asteroid-sized objects within its tidal radius. We discovered ...numerous circumstellar absorption lines with linewidths of ~300 km s super(-1) from Mg, Ca, Ti, Cr, Mn, Fe, and Ni, possibly from several gas streams produced by collisions among the actively disintegrating objects. The atmosphere of WD 1145+017 is polluted with 11 heavy elements, including O, Mg, Al, Si, Ca, Ti, V:, Cr, Mn, Fe, and Ni. Evidently, we are witnessing the active disintegration and subsequent accretion of an extrasolar asteroid.
The surface of Ca(OH)2 powders were pre-treated with alkoxy type aluminium coupling agent (ALC) and phosphate type aluminium phosphorus coupling agent (ALPC), respectively in this work. The shaped ...specimens were calcinated at 1600 °C for 3 h and then the phase compositions and microstructures of CaO specimens were investigated. The results revealed that both ALC and ALPC could conspicuously enhance the hydration resistance of CaO specimens by modifying surface microstructures in different ways. The boundaries of CaO grains in the specimens were covered with C3A glass phase after introducing of ALC, which was replaced by calcium phosphate when the ALC was replaced by ALPC. The hexagonal barrier layer, which was the hydration product of C3A, played a protective role in CaO grains. The obtained results in our work indicated that ALC was more effective in improving hydration resistance of CaO materials.
Hydroalumination of an alkynylphosphine gave an unprecedented P−H functionalized frustrated Lewis pair (FLP). The reactive P−H group does not influence the typical FLP properties, but the activation ...of substrates follows a new reaction pattern involving hydrogen transfer to yield unusual compounds with phosphaurea, iminophosphine, or phosphanyltriazene structural motifs.
Cooperative activation and hydrogen shift is observed as a new reactivity pattern upon treatment of a P−H functionalized Al/P frustrated Lewis pair with various unsaturated substrates. Unusual highly functionalized phosphorus compounds were obtained, such as a phosphinyltriazene or phosphaurea. With benzonitrile, the sequence adduct formation, activation, and H‐shift gives an iminophosphine (see scheme).
Reaction of an Al‐centered anion with toluene proceeded to form C−H cleaved product with a perfect meta‐selectivity and a relatively small kinetic isotope effect (KIE, kH/kD=1.51). DFT calculations ...suggested a two‐step reaction mechanism and electronically controlled meta‐selectivity arising from the electron‐donating methyl group. The reaction with other mono‐substituted arenes was also investigated.
Reaction of an Al‐centered anion with toluene proceeded to form C−H cleaved product with a perfect meta‐selectivity and a relatively small kinetic isotope effect (KIE, kH/kD=1.51). DFT calculations suggested a two‐step reaction mechanism and electronically controlled meta‐selectivity arising from the electron‐donating methyl group. The reaction with other mono‐substituted arenes was also investigated.
A greenhouse study was conducted to determine if concentrations of fluoride (F), which would be added to acid soils via P fertilisers, were detrimental to barley root growth. Increasing rates of F ...additions to soil significantly increased the soil solution concentrations of aluminium (Al) and F irrespective of the initial adjusted soil pH, which ranged from 4.25 to 5.48. High rates of F addition severely restricted root growth; the effect was more pronounced in the strongly acidic soil. Speciation calculations demonstrated that increasing rates of F additions substantially increased the concentrations of Al–F complexes in the soil. Stepwise regression analysis showed that it was the combination of the activities of AlF
2
1+ and AlF
2+ complexes that primarily controlled barley root growth. The results suggested that continuous input of F to soils, and increased soil acidification, may become an F risk issue in the future.
Addition of high rates of fluoride to strongly acidic soils can reduce barley root growth due to the toxicity of aluminium–fluoride complexes formed in soil solution.
To protect their steel structures from corrosion by cathodic protection, many harbours use aluminium sacrificial anodes, which induces aluminium release and potential contamination of the surrounding ...waters and sediments. To study the impact on Al mobility, a natural marine sediment was artificially contaminated with aluminium from different sources: sulphate or chloride salts, or sacrificial anodes. To estimate Al mobility in sediments, single (HCl) and sequential (F6) extractions were performed; they highlighted that aluminium is poorly mobile in natural sediment (HCl-leachable: 2% and F6-leachable: 9%). Contamination by aluminium salts inhibits HCl-leachability (≤2%), whereas the Al F6-leachability is intensified up to 18%, suggesting that the additional aluminium is scavenged in a mobile fraction that HCl is not able to solubilise. In case of aluminium anode contamination, sediments present surging Al HCl-leachable (15%) and F6-leachable (32%) fractions, which are related to aluminium mineralogical speciation. Indeed, contrary to the Al naturally present or introduced by salts, Al released by anodes is partly bound to the acid-soluble fraction, probably because of the integration of the released Al into the calcareous deposit produced at the anodes surfaces that finally comes away and gets mixed up with the sediment. The presence of aluminium in the acid-soluble fraction of sediments could have an important environmental impact as this fraction is easily available. Indeed, Al scavenged in the acid-soluble fraction of sediments participates in enhancing Al lability near the sacrificial anodes and may affect the surrounding ecosystems.
► The replacement can be taken up to 30% of MSWI fly ash in the raw mix. ► The novelty compositional parameters were defined, their optimum values were determined. ► Expansive property of SAC is ...strongly depended on gypsum content. ► Three leaching test methods are used to assess the environmental impact.
The feasibility of partially substituting raw materials with municipal solid waste incineration (MSWI) fly ash in sulfoaluminate cement (SAC) clinker production was investigated by X-ray diffraction (XRD), compressive strength and free expansion ratio testing. Three different leaching tests were used to assess the environmental impact of the produced material. Experimental results show that the replacement of MSWI fly ash could be taken up to 30% in the raw mixes. The good quality SAC clinkers are obtained by controlling the compositional parameters at alkalinity modulus (
C
m
) around 1.05, alumina–sulfur ratio (
P) around 2.5, alumina–silica ratio (
N) around 2.0∼3.0 and firing the raw mixes at 1250
°C for 2
h. The compressive strengths of SAC are high in early age while that develop slowly in later age. Results also show that the expansive properties of SAC are strongly depended on the gypsum content. Leaching studies of toxic elements in the hydrated SAC-based system reveal that all the investigated elements are well bounded in the clinker minerals or immobilized by the hydration products. Although some limited positive results indicate that the SAC prepared from MSWI fly ash would present no immediate thread to the environment, the long-term toxicity leaching behavior needs to be further studied.
Particulate reinforced aluminium matrix composites (PRAMCs) are extensively substituting the conventional aluminium alloys in several applications and components in aircraft, marine, construction and ...automobile industries. Research is being carried out across the globe to enrich the mechanical, tribological and physical properties of PRAMCs using novel manufacture techniques and reinforcements. In this article, an attempt is made to analyse the influence of the different weight fraction of aluminum nitride (AlN) particle reinforced composites. Aluminium alloy AA7075 was reinforced with several quantities (0, 5, 10 and 15 wt%) of AlN through stir casting route. The microstructures, as well as mechanical properties of the manufactured composites are analysed. The manufactured composites were inspected by using Optical Microscope. Optical micrographs revealed the nearly uniform dissemination of reinforcement particles in the matrix alloy (AA7075). The hardness, as well as the tensile strength of the composite, has increased with the increase in weight fraction of aluminium nitride particulates in the AA7075 matrix.
The effects of Ni on the phases, microstructural evolution, hot tear susceptibility and mechanical properties of Al–6Zn-1.4Mg-1.2Cu alloys fabricated by gravity casting were investigated using X-ray ...diffraction (XRD), scanning electronic microscopy (SEM), optical microscopy, the N-Tec Hot tear and tensile test. The calculation of phase diagrams (CALPHAD) modelling was also conducted to understand the phase formation of the experimental alloys. The results showed that the secondary phases (including η-MgZn2, S–Al2CuMg and Al3Ni) are mainly distributed at grain boundary, while round S–Al2CuMg particles are also found in α-Al matrix. Ni only exists as Al3Ni with different morphologies and its number density ascends with the increase of Ni content in alloys, which also significantly improves the hot tear resistance. As a result, the increased Ni in the alloys remarkably improves the ultimate tensile and yield strength, while the elongation increases when Ni < 0.6 wt% followed by decreases when Ni > 0.6 wt%.
•Ni in Al-Zn-Mg-Cu alloys exists as Al3Ni only and no effect on the phase formation of η-MgZn2 and S–Al2CuMg.•Ni in Al-Zn-Mg-Cu alloys decreases TV and CSC*, thus improving the hot tear resistance.•When Ni < 0.6 wt.% , Ni improves the strength and elongation of Al–Zn–Mg–Cu–Ni alloys.•When Ni > 0.6 wt.%, the strength is increased but the elongation is decreased in Al–Zn–Mg–Cu–Ni alloys.
Uptake of the alkalis K and Na by calcium silicate hydrate (C-S-H) and calcium alumina silicate hydrate (C-A-S-H) of molar Ca/Si ratios=0.6 to 1.6 and molar Al/Si ratio=0 or 0.05 has been studied at ...20°C. Alkalis are thought to be bound in the interlayer space of C-A-S-H and show preferred uptake by lower Ca/Si ratios and by higher alkali concentrations. A consequence of alkali uptake into C-A-S-H is a rearrangement of the C-A-S-H structure. Less calcium is present in the interlayer and shorter silica chains are observed for the same molar Ca/Si ratio.
No significant difference was observed between sodium and potassium uptake. Equilibration times of 91days to 1year or the solid phase being either C-S-H or C-A-S-H had seemingly no effect on alkali uptake.
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