1,720,995 research outputs found
Microstructural analysis of lime paste with the addition of linseed oil, stand oil, and rapeseed oil
No full textThis work aims to study the microstructural evolution of lime paste with the addition of linseed, stand, and rapeseed oils to explore their potential as protective coatings for porous building materials. Paste samples with two dosages of each oil were studied in terms of wettability, porous structure, and composition up to 360 days of curing. The results showed that in the early stage of curing, the carbonation reaction was accelerated with oil addition, but after 28 days, the carbonation was significantly delayed. A striking difference between the porous structure of the pure lime paste and the pastes with oil was observed. Linseed and rapeseed oil were more reactive with lime than stand oil, thus, affecting the microstructure of the paste more significantly. They also altered the carbonation reaction pathways by favouring the formation of amorphous products. The lower reactivity of stand oil is attributed to the considerably lower amount of unsaturated fatty acids as compared with the other oils. Rapeseed oil promoted higher water-repellence and a more homogeneous distribution of bubble-like pores than the other oils
Physical and nanomechanical properties of the synthetic anhydrous crystalline CaCO3 polymorphs: vaterite, aragonite and calcite
No full textThe synthetic anhydrous crystalline CaCO3 polymorphs—vaterite, aragonite and calcite—were tested using dilatometry and nanoindentation. Microstructural changes in the samples before and after measurements were observed under scanning electron microscope and their phase composition quantified with X-ray powder diffraction with the Rietveld method. The thermal expansion coefficients of vaterite and the hardness and elastic modulus of synthetic aragonite are reported for the first time. The physical and nanomechanical properties were measured under similar conditions for each CaCO3 polymorph. Aragonite, calcite and vaterite showed volumetric thermal expansion coefficient at 303 K of 49.2(8), 48.6(2) and 44.1(3) 10−6 K−1, respectively. The elastic modulus increased from 5(4), 16(7) to 31(8) GPa for aragonite, calcite and vaterite, respectively. Average hardness was found lower than values from the literature, ranging from 0.3 to 1.3 GPa. The results are considered of interest for the design of CaCO3-based materials for applications
Assessment of firing conditions in old fired-clay bricks: The contribution of X-ray powder diffraction with the Rietveld method and small angle neutron scattering
No full textFull characterization of fired-clay bricks is crucial for the improvement of process variables in manufacturing and, in case of old bricks, for restoration/replacement purposes. To this aim, five bricks produced in a plant in Czech Republic in the past have been investigated with a combination of analytical techniques in order to derive information on the firing process. An additional old brick from another brickyard was also used to study the influence of different raw materials on sample microstructure. The potential of X-ray diffraction with the Rietveld method and small angle neutron scattering technique has been exploited to describe the phase transformations taking place during firing and characterize the brick microstructure. Unit-cell parameter of spinel and amount of hematite are proposed as indicators of the maximum firing temperature, although for the latter, limited to bricks produced from the same raw material. The fractal quality of the surface area of pores obtained from small angle neutron scattering is also suggested as a method to distinguish between bricks produced from different raw clays
Aqueous polyacrylate latex nanodispersions used as consolidation agents to improve mechanical properties of Prague sandstone
No full textThis investigation aims at assessing the potential of polyacrylate latex nanodispersions as consolidation agents for sandstones. Four different latex types, implementing polymer fluorination and chemical crosslinking, have been synthesized at the scope and fully characterized. The Prague sandstone employed in this study has been selected as an example of highly porous stones used as building materials for many historical monuments. Two different concentration levels of nanodispersions have been adopted. The consolidated stone samples have been tested using a combination of physical-mechanical tests and microscopic observations. Compared to the non-treated samples, significant increments of mechanical properties (e.g. up to 3.3 times higher bending strength) have been detected after the consolidation treatment with concentrated products. Moreover, when 10 times diluted latex nanodispersions have been applied, the improvement of mechanical properties has still been significant, while moisture transport properties, such as water absorption, have been found to be comparable with those of the untreated sample. Fluorinated polymers imparted better hydrophobic properties with a contact angle above 100°. Observations using a scanning electron microscope revealed the good filling and bridging capacity of the applied consolidation agents. As demonstrated, by acting on the polymer structure, that is, by tuning the degree of crosslinking, polymer fluorination and gel content, the properties of these novel polyacrylate latex nanodispersions can be tailored to the specific stone and type of decay in order to improve the effectiveness of the treatments and obtain the desired final properties. The flexibility of their chemistry offers new opportunities for preserving objects of cultural heritage that are also at risk due to the ongoing climate change
Influence of additions of synthetic anhydrous calcium carbonate polymorphs on nanolime carbonation
No full textThe influence of synthetic anhydrous calcium carbonate polymorphs, calcite, vaterite and aragonite, on carbonation of nanolime suspension, has been investigated. The higher rates of carbonation observed after 7 days in mixtures containing vaterite and aragonite particles, found explanation in the control exerted by heterogeneous nucleation on the water-mediated reaction mechanism and in the enhanced carbon dioxide diffusivity in the sample volume, both facilitated by the higher specific surface of the powders and the microporous sample fabric. Introduction of synthetic calcium carbonate allowed for exerting control on formed polymorphs, subverting the order of their (meta-)stability. The peculiar microstructure obtained by adding aragonite rod-like particles, mitigates the propagation of desiccation cracks (which impair continuity of the carbonated nanolime film). The mechanism, although still not completely understood, likely involves the regulation of evaporation of liquid fraction and redistribution of the tensional stresses during drying and nanolime crystallization. The obtained results provide new insights into the crystallization of carbonates from nanolime particles and may help in the design of innovative compatible products for consolidation of lime-based materials and carbon dioxide sequestration
Evolution of fine microstructure during firing of extruded clays: A small angle neutron scattering study
No full textThe microstructure of extruded fired-clay bodies in the interval 800–1100 °C has been investigated with small angle neutron scattering. The evolution of the retrieved pore size distribution is compatible with the coarsening of the pore network with increasing temperature. The analysis of the scattering curves in combination with results of electron microscopy, indicated a multiscale nature for the pore-matrix microstructure. A structural parameter obtained from the analysis of the scattering curves, is proposed as indicator of maximum firing temperature through the implementation of a linear calibration curve. Such method has been successfully tested on a material of industrial production and can be considered of interest for the production of custom made replacement materials in the conservation of cultural heritage or for the characterization of the manufacturing process of archaeological fired-clay objects. Textural features originated by the forming process of extrusion have been detected as anisotropy of the pore network. They are still present above 1000 °C and, because of the use of screw extrusion, they are observed in both sections cut parallel and perpendicular to the direction of extrusion
Influence of linseed oil on the microstructure and composition of lime and lime-metakaolin pastes after a long curing time
Full text linkThis study investigates the effect of linseed oil on the microstructure of lime and lime-metakaolin pastes after 68 months of curing under controlled conditions. The hydrophobicity imparted by linseed oil to the pastes’ bulk was confirmed by measuring water drops’ contact angle. The results of thermal analysis, X-ray powder diffraction, and Fourier transform infrared spectroscopy showed that linseed oil significantly hindered the carbonation reaction in both lime and lime-metakaolin pastes and promoted the development of amorphous phases. The obtained results also indicated that linseed oil could foster the pozzolanic reaction in the lime-metakaolin system by stabilizing and/or promoting the development of hydration products resulting in reduced shrinkage in comparison with the reference
CLAYS WITH NO CARBONATES IN BRICK MANUFACTURING: LINK MICROSTRUCTURAL AND MINERALOGICAL EVOLUTION TO FIRING CONDITIONS
Full text linkMechanism of magnesium phosphate cement retardation by citric acid
No full textCitric acid modulates the release of heat and the rates of reaction in magnesium phosphate cements, chemically-bonded ceramics employed in biomaterials, for the encapsulation of nuclear wastes and in civil engineering. To gain knowledge on the mechanism of action of citric acid and, therefore, help in the effective material design, the reaction was studied in-situ to address molecular issues. The results indicated that citric acid enhances dissolution of MgO by promoting surface ligand-exchange reaction which leads to a net acceleration of the first reaction step. The Mg2+ ions released in solution are complexed by citrates. The degree of supersaturation is therefore reduced, delaying the nucleation of phosphates. The growth of stable nuclei, the crystal growth, and the amorphous-to-crystalline transformation are hindered due to citrate adsorption. The formed surface complexes are prevalently inner-sphere complexes exhibiting the combined coordination of hydroxyl and carboxylate groups. The mutating chemical environment dictates the coordination modes of citrate, the competition with phosphates, and the stable forms of phosphate products
Investigation of the crystallization reaction of calcium carbonate from amorphous precursor with quasielastic neutron scattering
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