Chemical characterisation of metakaolin and fly ash based geopolymers during exposure to solvents used in carbon capture

This paper presents an investigation into the chemical resistance of blended alkali activated aluminosilicate materials, specifically under exposure to two solvents used in post-combustion carbon capture, monoethanolamine (MEA) and potassium carbonate, as well as during immersion in distilled water. Geopolymers are formulated based on metakaolin and aon fly ash as aluminosilicate precursors, with the addition of ground granulated blast furnace slag (GGBFS) as a source of Ca. The samples are subjected to mineralogical and chemical characterisation in this paper, with data obtained through leaching analysis and X-ray diffraction, supported by compressive strength data. Exposure to solvents generally results in significant alteration of the geopolymer microstructure. The zeolitic phases formed in undamaged metakaolin-based binders are reduced to undetectable levels after 28 days of solvent exposure, although the hydrosodalite formed in the fly ash binders does persist. Leaching analysis indicates that resistance to structural damage in MEA is quite high, due to the low solubility of Na and hydroxides upon immersion. KCO solutions are aggressive towards geopolymers via alteration of the binder structure and dissolution of network-forming species (Si and Al), leading to the loss of binder strength. This is most marked in the fly ash/GGBFS formulations. Despite the low to intermediate level of Ca present in these geopolymer binders, significant formation of Ca-containing carbonate phases occurs upon exposure to KCO. The limited curing duration of the specimens tested here is certainly contributing to the degradation taking place under KCO exposure, whereas the low water activity in the MEA solutions used means that bond hydrolysis in the aluminosilicate geopolymer framework is restricted, and the materials perform much better than in a more water-rich environment. © 2014 Elsevier Ltd

Random data Cauchy theory for supercritical wave equations II : A global existence result

We prove that the subquartic wave equation on the three dimensional ball $\Theta$, with Dirichlet boundary conditions admits global strong solutions for a large set of random supercritical initial data in $\cap_{s<1/2} H^s(\Theta)$. We obtain this result as a consequence of a general random data Cauchy theory for supercritical wave equations developed in our previous work \cite{BT2} and invariant measure considerations which allow us to obtain also precise large time dynamical informations on our solutions

Water content modifies the structural development of sodium metasilicate-activated slag binders

The effect of modifying the water content of an alkali - activated slag binder was assessed, in terms of the kinetics of reaction and the structural development of the material. There is not a s ystematic correlation between the water content of the mix and the rate of reaction, indicating that there is an optimal value that favours dissolution of the slag and precipitation of reaction products. A h igher water content reduce d the crystallinity and density of the reaction products, especially at advanced age. Small changes in the water content can have a significant impact on the compressive strength development of alkali - silicate activated slag mortars, suggesting that when producing materials base d on alkali - activated binders , it is essential to carefully control the water content

Role of carbonates in the chemical evolution of sodium carbonate-activated slag binders

Multi-technique characterisation of sodium carbonate-activated blast furnace slag binders was conducted in order to determine the influence of the carbonate groups on the structural and chemical evolution of these materials. At early age (<4 days) there is a preferential reaction of Ca2+ with the CO3 2− from the activator, forming calcium carbonates and gaylussite, while the aluminosilicate component of the slag reacts separately with the sodium from the activator to form zeolite NaA. These phases do not give the high degree of cohesion necessary for development of high early mechanical strength, and the reaction is relatively gradual due to the slow dissolution of the slag under the moderate pH conditions introduced by the Na2CO3 as activator. Once the CO3 2− is exhausted, the activation reaction proceeds in similar way to an NaOH-activated slag binder, forming the typical binder phases calcium aluminium silicate hydrate and hydrotalcite, along with Ca-heulandite as a further (Ca,Al)-rich product. This is consistent with the significant gain in compressive strength and reduced porosity observed after 3 days of curing. The high mechanical strength and reduced permeability developed in these materials beyond 4 days of curing elucidate that Na2CO3-activated slag can develop desirable properties for use as a building material, although the slow early strength development is likely to be an issue in some applications. These results suggest that the inclusion of additions which could control the preferential consumption of Ca2+ by the CO3 2− might accelerate the reaction kinetics of Na2CO3-activated slag at early times of curing, enhancing the use of these materials in engineering applications

Phase evolution of Na2O–Al2O3–SiO2–H2O gels in synthetic aluminosilicate binders

This study demonstrates the production of stoichiometrically controlled alkali-aluminosilicate gels (‘geopolymers’) via alkali-activation of high-purity synthetic amorphous aluminosilicate powders. This method provides for the first time a process by which the chemistry of aluminosilicate-based cementitious materials may be accurately simulated by pure synthetic systems, allowing elucidation of physicochemical phenomena controlling alkali-aluminosilicate gel formation which has until now been impeded by the inability to isolate and control key variables. Phase evolution and nanostructural development of these materials are examined using advanced characterisation techniques, including solid state MAS NMR spectroscopy probing 29Si, 27Al and 23Na nuclei. Gel stoichiometry and the reaction kinetics which control phase evolution are shown to be strongly dependent on the chemical composition of the reaction mix, while the main reaction product is a Na2O–Al2O3–SiO2–H2O type gel comprised of aluminium and silicon tetrahedra linked via oxygen bridges, with sodium taking on a charge balancing function. The alkali-aluminosilicate gels produced in this study constitute a chemically simplified model system which provides a novel research tool for the study of phase evolution and microstructural development in these systems. Novel insight of physicochemical phenomena governing geopolymer gel formation suggests that intricate control over time-dependent geopolymer physical properties can be attained through a careful precursor mix design. Chemical composition of the main N–A–S–H type gel reaction product as well as the reaction kinetics governing its formation are closely related to the Si/Al ratio of the precursor, with increased Al content leading to an increased rate of reaction and a decreased Si/Al ratio in the N–A–S–H type gel. This has significant implications for geopolymer mix design for industrial applications

Receptor-mediated endocytosis of the intrinsic factor—cobalamin complex in HT 29, a human colon carcinoma cell line

AbstractA HT 29 cell line derived from human colonic carcinoma was shown to express the intrinsic factor receptor, with about 5000 binding sites per cell and an association constant of 20 × 109 1/mol at pH 7.4 and 4°C. The number of binding sites increased dramatically between 7 and 10 days of culture time. Endocytosis of the intrinsic factor-cobalamin-receptor complex was inhibited by two ways: at 4°C and at 37°C by incubating the cells with vinblastine, monensin and chloroquine. The plasma membrane receptor was cross-linked to [57Co]cobalamin-intrinsic factor and solubilized with Triton X-100. The cross-linked complex had a relative molecular mass of 330 kDa in native PAGE

Structural evolution of synthetic alkali-activated CaO-MgO-Na2O-Al2O3-SiO2 materials is influenced by Mg content

Stoichiometrically controlled alkali-activated materials within the system CaO-MgO-Na2O-Al2O3-SiO2 are produced by alkali-activation of high-purity synthetic powders chemically comparable to the glass in ground granulated blast furnace slag, but without additional minor constituents. Mg content controls the formation of hydrotalcite-group and AFm-type phases, which in turn strongly affects C-(N)-A-S-H gel chemistry and nanostructure. Bulk Mg content and the Mg/Al ratio of hydrotalcite-group phases are strongly correlated. With sufficient Ca, increased bulk Mg promotes formation of low-Al C-(A)-S-H and portlandite, due to formation of hydrotalcite-group phases and a reduction in available Al. Hydrotalcite-group phase formation is linked to increased C-(N)-A-S-H gel polymerisation, decreased gel Al uptake and increased formation of the ‘third aluminate hydrate’. These findings highlight the importance of considering available chemical constituents rather than simply bulk composition, so that the desired binder structure for a particular application can be achieved

An in situ intercomparison exercise on passive samplers for the monitoring of metals, polycyclic aromatic hydrocarbons and pesticides in surface water

An intercomparison exercise on passive samplers (PSs) was organized in summer 2010 for the measurement of selected metals, polycyclic aromatic hydrocarbons (PAHs) and pesticides in surface waters. Various PSs were used and compared at 2 rivers sites and one marine lagoon. A total of 24 laboratories participated. We present selected significant outputs from this exercise, including discussion on quality assurance and quality control for PSs, the interlaboratory variability of field blanks, time weighted average water concentrations and its uncertainties, the representativity of DGT samples, the ability of PSs to lower limits of detection, PAH fingerprints in various PSs compared with spot samples, and the relevance of the permeability reference compounds (PRC) approach for POCIS with pesticides. These in situ intercomparison exercises should enable to progress on the harmonization of practices for the use of passive sampling, especially for priority chemical monitoring and regulatory programs in compliance with the Water Framework Directive (WFD) and Marine Strategy Framework Directive (MSFD)

Obtaining cloud top height from WRF model vertical profiles: application to the EUSO program

The objective of the Extreme Universe Space Observatory (EUSO) program is detection and measurement of high-energy particles that reach earth?s atmosphere from space. Clouds at mid and upper levels of the troposphere can interfere with such detection. Therefore, determining cloud top height with high accuracy is crucial to estimating the effect of clouds on these measurements.With this aim, we developed a method to extract that height using cloud temperature via vertical profiles predicted by the WRF model

Investigation of crack propagation resistance of 304L, 316L and 316L(N) austenitic steels in liquid sodium

In order to assess the susceptibility of candidate structural materials to Liquid Metal Embrittlement (LME), the fracture behavior of three grades of austenitic steels was investigated in oxygenated (200 wppm) liquid sodium in the temperature range [473–673 K] on notched axisymmetric tensile specimens. The tests were carried out in an inert glove box at very low concentrations of dioxygen and humidity (<1 ppm) to prevent further contamination after pre-exposure in oxygenated liquid sodium. A decrease in crack propagation resistance of the three austenitic steels (304 L, 316 L(N), 316 L) is observed in oxygenated liquid sodium (200 wppm) from 573, 623 and 673 K respectively after pre-wetting in oxygenated sodium. This reduction is correlated with a ductile to brittle change of the fracture surface. This effect observed with the three austenitic steels is attributed to the onset of LME after significant plastic deformation