1,721,037 research outputs found
Microwave assisted hydrothermal conversion of Ba-exchanged zeolite A into metastable paracelsian
No full textCompositional design of single-phase rare-earth based high-entropy oxides (HEOs) by using the cluster-plus-glue atom model
No full textIn the present study, we discuss a possible extension of our previously proposed empirical predictor for the formation of fluorite-structured High-Entropy Oxides (HEOs) based on equimolar mixtures of Rare-Earth (RE) Oxides. Indeed, by using the so-called cluster-plus-glue atom model, a very recently proposed theoretical model to describe the crystal structure of inorganic compounds, we were able to confirm the results of the standard deviation predictor, i.e. the relation between the formed phase(s) and the standard deviation of cationic radii, justifying them based on the phases' thermodynamic stability and the valency of the involved cations. At the same time, we propose an explanation of the role of Cerium and Zirconium in the formation of fluorite-structured HEOs, designing and predicting the behavior of a completely novel non-equimolar system (based on ZrO2, La2O3 Yb2O3, Sm2O3, Gd2O3), stabilized in a bixbyite-like single phase.
Based on the presented results, we believe that a link between the geometrical aspects of the involved cations and their chemical-thermodynamic properties exists, providing a new tool to predict the behavior of systems in the intricate and intriguing world of High Entropy Oxides
Strategies for the valorization of soil waste by geopolymer production: An overview
No full textThe management of huge amounts of waste deriving from several anthropogenic activities, such as manufacturing, construction, mining and quarrying, dredging, represents a great contemporary environmental challenge for many countries worldwide. Among the different recycling possibilities, the use of the excavated soils, obtained from operations such as tunneling, excavations, mining, dredging etc., which are generally considered as soil waste, in the production of innovative eco-sustainable building materials represents an interesting alternative to their disposal. In fact, considering especially their chemical composition, low cost and easy availability, soil wastes seem to be the ideal candidates to be used as secondary raw materials for the manufacture of geopolymer-based materials. The paper intends to present a review of the recent scientific literature regarding the use of different types of soil waste to produce geopolymeric binders. Particular attention is focused on mining waste (deriving from various types of mining industries) and dredged sediments coming from marine harbors and natural and artificial water reservoirs, in order to understand and critically discuss the limits of their disposal approach and, at the same time, show perspectives and challenges for possible future research activities in this field. The production of geopolymer-based building components, starting from mining waste and reservoir sediments, is widely discussed thanks to the numerous scientific findings, while the recycling of marine dredged sediments through geopolymerization represents a completely new and innovative trend in research activity, in fact only few related papers were found in literature. It can be strongly stated that geopolymerization can significantly contribute to a sustainable improvement of soil waste management systems
New insights in the hydrothermal synthesis of rare-earth carbonates
Full text linkThe rare-earth carbonates represent a class of materials with great research interest owing to their intrinsic properties and because they can be used as template materials for the formation of other rare earth phases, particularly of rare-earth oxides. However, most of the literature is focused on the synthesis and characterization of hydroxycarbonates. Conversely, in the present study we have synthesized both rare-earth carbonates-with the chemical formula RE2(CO3)3.2-3H2O, in which RE represents a generic rare-earth element, and a tengerite-type structure with a peculiar morphology-and rare-earth hydroxycarbonates with the chemical formula RECO3OH, by hydrothermal treatment at low temperature (120 °C), using metal nitrates and ammonium carbonates as raw materials, and without using any additive or template. We found that the nature of the rare-earth used plays a crucial role in relation to the formed phases, as predicted by the contraction law of lanthanides. In particular, the hydrothermal synthesis of rare-earth carbonates with a tengerite-type structure was obtained for the lanthanides from neodymium to erbium. A possible explanation of the different behaviors of lighter and heavier rare-earths is given
Effect of residual Na on the low temperature synthesis of monoclinic celsian from zeolite Ba-A
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Fibre-reinforced geopolymer concretes for sensible heat thermal energy storage: Simulations and environmental impact
Full text linkPower plants based on solar energy are spreading to accomplish the incoming green energy transition. Besides, affordable high-temperature sensible heat thermal energy storage (SHTES) is required. In this work, the temperature distribution and thermal performance of novel solid media for SHTES are investigated by finite element method (FEM) modelling. A geopolymer, with/without fibre reinforcement, is simulated during a transient charging/discharging cycle. A life cycle assessment (LCA) analysis is also carried out to investigate the environmental impact and sustainability of the proposed materials, analysing the embodied energy, the transport, and the production process. A Multi-Criteria Decision Making (MCDM) with the Analytical Hierarchy Process (AHP) approach, taking into account thermal/environmental performance, is used to select the most suitable material. The results show that the localized reinforcement with fibres increases thermal storage performance, depending on the type of fibre, creating curvatures in the temperature profile and accelerating the charge/discharge. High-strength, high-conductivity carbon fibres performed well, and the simulation approach can be applied to any fibre arrangement/material. On the con-trary, the benefit of the fibres is not straightforward according to the three different scenarios developed for the LCA and MCDM analyses, due to the high impact of the fibre production processes. More investigations are needed to balance and optimize the coupling of the fibre material and the solid medium to obtain high thermal performance and low impacts
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