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Alkali activation is a novel method of soil stabilisation, which could be used for the production of compressed blocks as walling materials. Given that much of the fundamental research into the chemical behaviour of this process has been done for small specimens, there is a knowledge gap over the potential effects of increasing specimen size. In this study, blocks were made from a mix of soil, sand and sodium hydroxide solution using a manual block press. Their phase composition and microstructure were investigated using powder X-ray diffraction and scanning electron microscopy; drying behaviour and compressive strength were also measured. No major microstructural or phase differences were found between the central and edge regions of the blocks. Longer curing time had little effect on phase formation and microstructure, but resulted in increased compressive strength. There are no fundamental chemical issues obstructing the scale-up of this stabilisation method, but further research should focus on the measurement of properties in line with building standards and eliminating hazards in the manufacturing process.

Here, we report a study of white-ochre powders with targeted composition MnWO4 prepared via a coprecipitation method. Through X-ray total scattering combined with pair distribution function analysi...

To future-proof alkali-activation technology, there is a need to look beyond well-established precursors such as fly ash and blast furnace slag, due to resource competition, geographical distribution and technical limitations. Clay minerals are abundant and diverse aluminosilicate resources available around the world. However, due to the mineralogical complexity amongst the most common 1:1 (kaolinite, halloysite) and 2:1 (montmorillonite, illite) clay minerals, and practical issues such as workability, their use has been more limited. Recent advances have improved understanding both of pre-activation treatments (thermal, mechanical, chemical), and of the factors influencing clay reactivity, phase assemblages and properties of final products. This opens new opportunities for the exploitation of these resources to produce sustainable cements. A one-size-fits-all approach for processing and activating clay minerals is not viable. Instead, activation routes need to be tailored according to the clay mineralogy to achieve the binder properties required for key applications. Published with golden open access ispartof: Cement And Concrete Research vol:132 status: published

Alkali-activated soils have potential as low carbon, low cost construction materials. There is a lack of fundamental understanding around how soil composition influences alkali activation behaviour, especially for uncalcined soils. The types and relative amounts of clay minerals can vary greatly throughout soils across the world. Since clays are typically the dominant reactive aluminosilicate constituent in soils, it is desirable to understand how the types and relative amounts of clay minerals influence reaction products in alkali activation. In this study, mixtures of kaolinite, montmorillonite and illite precursors were activated with sodium hydroxide solutions. By comparing with extrapolations of cross-characterisation from the behaviour of individual clays, it was shown that phase formation behaviour deviated from an ideal rule of mixtures model. Instead, there was a hierarchy between the clays in determining the reaction products: kaolinite and montmorillonite dominated illite in this regard. This study demonstrates that the viability of a given soil for alkali activation depends not only on the total amount of clay, but the types and relative amounts of clay minerals present. In order to unlock the potential of alkali-activated soils, more understanding is needed of the role of the different components in soil.

Here, we report a study of white-ochre powders with targeted composition MnWO

Visible light promoted photocatalytic water oxidations for potential solar fuel production have been studied widely, with many reports on optimization of reagent components. Here we report an exploration on the effects upon ongoing reactions of daylight equivalent light intensity illumination with regulated short dark periods of a few seconds duration as compared to standard continuous illumination. Comparison was made with systems employing synthesized low cost earth abundant iron oxide, calciumoxomanganite and cobalt oxide nanoparticulate catalysts together with a [Ru(bpy)3]2+ light harvesting dye and an electron acceptor. Yields of gaseous O2 and proton production were measured in situ and in real time. The study found that low cost catalysts could give very significantly increased O2 yields, turn over frequency and improved reaction profiles by use of simple on/off illumination. A range of timings with identical overall photon flux were tested and an optimum determined. Analysis of effects upon the light sensitizer under the range of lighting conditions (through mass spectrometry and UV-vis measurements), together with implementation of a continuous flow system as comparison to the batch reactions, were all employed to help elucidate the mechanisms for the clear improvements in reaction yields observed. These are believed to stem from reduction in self-decomposition of excess oxidized sensitizer and better synchronization of cyclic sensitizer oxidation/reductions with water oxidation at the metal oxide surface at specific light on : off timing.

Alkali activation of clay minerals in soil can be used to form a stabilising phase, such as a geopolymer. Because this requires low-temperature curing, typically

We show that the type-II multiferroic properties of bulk MnWO4 are kept in nanostructured ceramics of 50 nm grain size prepared via spark plasma sintering (SPS). This means that ferroelectric polarization is robust against downsizing, which is at variance with standard ferroelectrics like BaTiO3. We ascribe this stability to the spin-driven nature of the ferroe-lectric correlations in type-II multiferroics while it is resulting from lattice distortion in other cases. This may open the way for persistent type-II multiferroicity with no need for external stabilization like substrate-generated strain.

Visible light promoted photocatalytic water oxidations were conducted with a synthesized iron oxide nanoparticulate catalyst together with a [Ru(bpy)3]2+ light harvesting dye and electron acceptor. With highest intensity set at daylight equivalent levels, the effects of fluctuating illumination upon ongoing reactions were studied and gaseous O2 and proton production measured. A light oscillation cycle was identified that significantly increased reaction TOF and quantum yields, which is suggested to arise from improvements in synchronization of the cyclic reaction steps and minimization of light sensitizer self-decomposition.

International audience; Polycrystalline samples of Mn1-xCuxWO4 (x ≤ 0.5) have been prepared by a solid-state synthesis as well as from a citrate synthesis at moderate temperature (850 °C). The goal is to study changes in the structural, magnetic, and dielectric properties of magnetoelectric type-II multiferroic MnWO4 caused by replacing Jahn-Teller-inactive Mn(2+) (d(5), S = 5/2) ions with Jahn-Teller-active Cu(2+) (d(9), S = 1/2) ions. Combination of techniques including scanning electron microscopy, powder X-ray and neutron diffraction, and Raman spectroscopy demonstrates that the polycrystalline samples with low copper content 0 ≤ x ≤ 0.25 are solid solution that forms in the monoclinic P2/c space group. Rietveld analyses indicate that Cu atoms substitutes for Mn atoms at the Mn crystallographic site of the MnWO4 structure and suggest random distributions of Jahn-Teller-distorted CuO6 octahedra in the solid solution. Magnetic susceptibility reveals that only 5% of Cu substitution suppresses the nonpolar collinear AF1 antiferromagnetic structure observed in pure MnWO4. Type-II multiferroicity survives a weak Cu substitution rate (x < 0.15). Multiferroic transition temperature and Néel temperature increase as the amount of Cu increases. New trends in some of the magnetic properties and in dielectric behaviors are observed for x = 0.20 and 0.25. Careful analysis of the magnetic susceptibility reveals that the incorporation of Cu into MnWO4 strengthens the overall antiferromagnetic interaction and reduces the magnetic frustration.