2,287 research outputs found

    Morphogenesis of Cement Hydrate: From Natural C-S-H to Synthetic C-S-H

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    Triggered by the recent advance in materials synthesis and characterization techniques, there has been an increasing interest in manipulating properties of calcium silicate hydrates (C-S-H), which constitute the fundamental, strength-responsible building blocks of concretes. Concretes are the indispensable constituents of today‚Äôs modern infrastructures and simultaneously the most widely used synthetic material on the planet. Despite the widespread impact and high societal values, the production of their major binder component, Portland cement (PC), is the major culprit for global warming since it contributes to 5‚Äď10% carbon dioxide emission worldwide. Consequently, enhancing the ultimate strength and durability of concretes by tuning structural, compositional and mechanical properties of their basic building units and assembling them via bottom-up engineering is one of the key strategies to mitigate the aforesaid concerns. This is simply because the longer the concretes last, the less production of PC would incur. Furthermore, the current role of C-S-H in industry is not only confined to the context of construction materials but to diverse sectors of industry including drug delivery, CO2 sorbent and materials for bone replacement. This wide scope of potential applications can be ascribed to the high versatility regarding tunable structural properties such as porosity, size and morphology, all of which can be fine-tuned during the synthetic procedure. Among the listed properties, understanding and gaining control over morphological factors of C-S-H is particularly important since they are directly associated with their functional roles. C-S-H with various morphologies can be produced by altering key experimental conditions, which encompass types of synthetic procedure, precursor types such as different calcium and silicate sources and types of additives. This chapter discusses a variety of morphologies of C-S-H acquired in multiple environments. The latter include the hydration of PC or PC-blends containing supplementary materials such as slag, synthetic C-S-H produced using silica-lime reactions and crystalline CSH synthesized using hydrothermal treatment. At the end, the chapter will provide a complete review on the current range of morphologies for calcium silicate hydrate

    Morphological changes in biomimetically synthesized hydroxyapatite and silver nanoparticles for medical applications

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    A precise control of morphology, which plays a significant role towards the application of materials, can be achieved by studying the effects of macromolecules as nucleation templates for minerals in a biomineralization process. The present investigation aims to understand such effects on medically important materials. Thus, Silver (Ag) and Calcium hydroxyapatite [Ca10(PO4)6(OH)2] were synthesized in both biopolymer (gelatin) and synthetic polymer (PVA) media, with aqueous medium as the control to portray a collage of how the interface between the macromolecule and the mineral controls the final morphology of the materials. It was also observed that the change of morphology of the products does influence their performances in specific applications like antibacterial property of the nanoparticles of silver was found to the best when synthesized in aqueous media. Thus, we consider that the organic-inorganic interaction to be of vital significance in the synthesis of complex shapes and sizes of nanoparticles for important applications

    Composition, silicate anion structure and morphology of calcium silicate hydrates (C-S-H) synthesized by silica-lime reaction and by the controlled hydration of tricalcium silicate (C3S)

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    The main product of Portland cement hydration is C-S-H. Despite constituting more than half of the volume of hydrated pastes and having an important role in strength development, very little is known about the factors that determine its morphology. To investigate the relationship between the chemical composition, silicate anion structure and morphology of C-S-H, samples were synthesized via silica-lime reactions and by the hydration of C3S under controlled lime concentrations and with/ without accelerators. The silicate anion structure of the samples was studied by 29Si MAS NMR and the morphology and chemical composition by TEM and SEM. All samples prepared via silica-lime reactions with bulk Ca/Si up to 1.5 were foil-like. The hydration of C3S at fixed lime concentration yielded foil-like C-S-H for [CaO]22mmol/L. A relationship between the silicate anion structure and the morphology of C-S-H was found for the samples fabricated with accelerators

    Processing of titanium production sludge with the extraction of titanium dioxide

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    An urgent task at the present time is the disposal and processing of large-tonnage waste of titanium production of Ust-Kamenogorsk titanium-magnesium plant of the Republic of Kazakhstan. This work shows research on the development of sludge technology with the extraction of titanium dioxide and calcium nitrate, which will eliminate the formation and discharge of technological waste into the environment. Ammonium fluoride processing of cakes from sludge leaching made it possible to first isolate silicon fluorides in the form of fumes, and then sublimate titanium fluorides. Silicon and titanium fluorides were converted to silicon and titanium dioxides by alkaline hydrolysis

    Microstructural characterization of laser sintered synthetic calcium phosphate-natural dentine interface for the restoration of enamel surface

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    Tooth sensitivity is a common occurrence and it is caused by acid induced erosion of enamel surface. In this investigation we report the results of calcium phosphate based minerals which are irradiated with lasers ex vivo for the analysis of photo activated densification of minerals. The photo-activation in these minerals may primarily arise from the absorption centres, namely OH- and rare-earth (RE)3+ ion dopants (e.g. Er3 ions) incorporated during synthesis. The loss of hydroxyl group from mineral is characterized using the thermogravimetric technique. The microstructural changes under the conditions of continuous wave (CW) and pulsed laser irradiation are reported together with the measured temperature rise. The preliminary data on surface hardness of occluded dentine with photo-activated calcium phosphate minerals are also reported, for aiming an eventual hardness value of 3300 MPa which is known for natural enamels

    Processing of titanium production sludge with the extraction of titanium dioxide

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    An urgent task at the present time is the disposal and processing of large-tonnage waste of titanium production of Ust-Kamenogorsk titanium-magnesium plant of the Republic of Kazakhstan. This work shows research on the development of sludge technology with the extraction of titanium dioxide and calcium nitrate, which will eliminate the formation and discharge of technological waste into the environment. Ammonium fluoride processing of cakes from sludge leaching made it possible to first isolate silicon fluorides in the form of fumes, and then sublimate titanium fluorides. Silicon and titanium fluorides were converted to silicon and titanium dioxides by alkaline hydrolysis

    Contents and Index Vol. 35

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    Contents and Index Vol. 35

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    The discrimination of 72 nitrate, chlorate and perchlorate salts using IR and Raman spectroscopy

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    Inorganic oxidizing energetic salts including nitrates, chloratesand perchlorates are widely used in the manufacture of not only licit pyrotechnic compositions, but also illicit homemade explosive mixtures. Their identification in forensic laboratories is usually accomplished by either capillary electrophoresis or ion chromatography, with the disadvantage of dissociating the salt into its ions. On the contrary, vibrational spectroscopy, including IR and Raman, enables the non-invasive identification of the salt, i.e. avoiding its dissociation. This study focuses on the discrimination of all nitrate, chlorate and perchlorate salts that are commercially available, using both Raman and IR spectroscopy, with the aim of testing whether every salt can be unequivocally identified. Besides the visual spectra comparison by assigning every band with the corresponding molecular vibrational mode, a statistical analysis based on Pearson correlation was performed to ensure an objective identification, either using Raman, IR or both. Positively, 25 salts (out of 72) were unequivocally identified using Raman, 30 salts when using IR and 44 when combining both techniques. Negatively, some salts were undistinguishable even using both techniques demonstrating there are some salts that provide very similar Raman and IR spectra

    Development of a flow method for the determination of phosphate in estuarine and freshwaters - Comparison of flow cells in spectrophotometric sequential injection analysis

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    A sequential injection system with dual analytical line was developed and applied in the comparison of two different detection systems viz; a conventional spectrophotometer with a commercial flow cell, and a multi-reflective flow cell coupled with a photometric detector under the same experimental conditions. The study was based on the spectrophotometric determination of phosphate using the molybdenum-blue chemistry. The two alternative flow cells were compared in terms of their response to variation of sample salinity, susceptibility to interferences and to refractive index changes. The developed method was applied to the determination of phosphate in natural waters (estuarine, river, well and ground waters). The achieved detection limit (0.007 mu M PO43-) is consistent with the requirement of the target water samples, and a wide quantification range (0.024-9.5 mu M) was achieved using both detection systems.info:eu-repo/semantics/submittedVersioninfo:eu-repo/semantics/acceptedVersio
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