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Geopolymer (GP) concrete is a novel construction material that can be used in place of traditional Portland cement (PC) concrete to reduce greenhouse gas emissions and effectively manage industrial waste. Fly ash (FA) has long been utilized as a key constituent in GPs, and GP technology provides an environmentally benign alternative to FA utilization. As a result, a thorough examination of GP concrete manufactured using FA as a precursor (FA-GP concrete) and employed as a replacement for conventional concrete has become crucial. According to the findings of current investigations, FA-GP concrete has equal or superior mechanical and physical characteristics compared to PC concrete. This article reviews the clean production, mix design, compressive strength (CS), and microstructure (Ms) analyses of the FA-GP concrete to collect and publish the most recent information and data on FA-GP concrete. In addition, this paper shall attempt to develop a comprehensive database based on the previous research study that expounds on the impact of substantial aspects such as physio-chemical characteristics of precursors, mixes, curing, additives, and chemical activation on the CS of FA-GP concrete. The purpose of this work is to give viewers a greater knowledge of the consequences and uses of using FA as a precursor to making effective GP concrete. [ABSTRACT FROM AUTHOR]

In the secondary circuit of nuclear Pressurized Water Reactors, corrosion products and impurities lead to the formation of undesirable hard deposits, called hard sludge, on the tube sheet of steam generators. Theses deposits are mainly composed of iron (magnetite), alumina and silica. The formation of hard sludge piles is investigated by reproducing the reaction of precursor oxides in the conditions of the steam generator (275 °C, 58 bar). Mixtures of magnetite, γ-alumina and amorphous silica in binary or ternary systems in an alkaline ethanolamine-ammonia solution at pH25°C = 9.6 are studied. Carbon steel was tested as an alternative source of iron.The analysis of the evolution of the suspensions, completed by the industrial feedback, allows to explain the process of hard sludge formation in the steam generators. The following sequence is proposed: sedimentation of magnetite/confinement of the interstitial fluid/concentration of aqueous species such as aqueous silica and alumina/sorption of Al on magnetite and/or growth of boehmite/reaction with aqueous silica to form kaolinite as a resistant cement. Once formed, the kaolinite cement tends to densify over time while magnetite is passive. The absence of Fe-phyllosilicates predicted by thermodynamics is explained by the low solubility of magnetite making unfavorable the precipitation of Fe-silicate.By contrast, metallic iron is not stable at contact with water and the continual production of divalent iron, whose solubility is much higher than that of magnetite, allows to overpass a threshold concentration what makes possible the precipitation of a berthierine layer at the surface of corroded steel. This layer constitutes the nucleation site for the further precipitation of other aluminosilicates.

In recent years, a great interest has arisen around the integration of naturally occurring clays into a plethora of advanced technological applications, quite far from the typical fabrication of traditional ceramics. This "second (technological) life" of clays into fields of emerging interest is mainly due to clays' peculiar properties, in particular their ability to exchange (capture) ions, their layered structure, surface area and reactivity, and their biocompatibility. Since the maximization of clay performances/exploitations passes through the comprehension of the mechanisms involved, this review aims at providing a useful text that analyzes the main goals reached by clays in different fields coupled with the analysis of the structure-property correlations. After providing an introduction mainly focused on the economic analysis of clays global trading, clays are classified basing on their structural/chemical composition. The main relevant physicochemical properties are discussed (particular attention has been dedicated to the influence of interlayer composition on clay properties). Lastly, a deep analysis of the main relevant nonconventional applications of clays is presented. Several case studies describing the use of clays in biomedicine, environmental remediation, membrane technology, additive manufacturing, and sol-gel processes are presented, and results critically discussed. [ABSTRACT FROM AUTHOR]

Geopolymer (GP) concrete is a novel construction material that can be used in place of traditional Portland cement (PC) concrete to reduce greenhouse gas emissions and effectively manage industrial waste. Fly ash (FA) has long been utilized as a key constituent in GPs, and GP technology provides an environmentally benign alternative to FA utilization. As a result, a thorough examination of GP concrete manufactured using FA as a precursor (FA-GP concrete) and employed as a replacement for conventional concrete has become crucial. According to the findings of current investigations, FA-GP concrete has equal or superior mechanical and physical characteristics compared to PC concrete. This article reviews the clean production, mix design, compressive strength (CS), and microstructure (Ms) analyses of the FA-GP concrete to collect and publish the most recent information and data on FA-GP concrete. In addition, this paper shall attempt to develop a comprehensive database based on the previous research study that expounds on the impact of substantial aspects such as physio-chemical characteristics of precursors, mixes, curing, additives, and chemical activation on the CS of FA-GP concrete. The purpose of this work is to give viewers a greater knowledge of the consequences and uses of using FA as a precursor to making effective GP concrete.

In recent years, a great interest has arisen around the integration of naturally occurring clays into a plethora of advanced technological applications, quite far from the typical fabrication of traditional ceramics. This “second (technological) life” of clays into fields of emerging interest is mainly due to clays’ peculiar properties, in particular their ability to exchange (capture) ions, their layered structure, surface area and reactivity, and their biocompatibility. Since the maximization of clay performances/exploitations passes through the comprehension of the mechanisms involved, this review aims at providing a useful text that analyzes the main goals reached by clays in different fields coupled with the analysis of the structure-property correlations. After providing an introduction mainly focused on the economic analysis of clays global trading, clays are classified basing on their structural/chemical composition. The main relevant physicochemical properties are discussed (particular attention has been dedicated to the influence of interlayer composition on clay properties). Lastly, a deep analysis of the main relevant nonconventional applications of clays is presented. Several case studies describing the use of clays in biomedicine, environmental remediation, membrane technology, additive manufacturing, and sol-gel processes are presented, and results critically discussed.

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Geopolymer materials are increasing in scientific interest due to their flexibility in various applications. The geopolymer precursor is a mineral source with reactive Si and Al that is synthesized either mechanically or thermally to improve its cementitious activity. It was found out in previous literature that Nickel-laterite mine waste (NMW) is a prospective geopolymer precursor. However, this potentiality has not been explored in the Philippines, albeit the massive generation of NMW, which is merely dumped as a mining industry downstream process. This paper thus investigates the potential of the NMW as a raw material for geopolymer synthesis. Mechanical activation was performed using a ball mill with the following factors: ball-to-NMW ratio (4:1 and 10:1), mill speed (200 and 500 ​rpm), and grinding duration (30 and 120 minutes). Thermal activation was performed using a furnace treated at temperatures of 600, 700, and 800 ​°C. Response Surface Methodology (RSM) of the mechanical activation shows that a ball-to-NMW ratio of 10:1, mill speed of 443 ​rpm, and grinding duration of 120 minutes achieved optimized leachability of Si and Al. Thermal analysis results showed that NMW could be thermally activated from 600 to 800 ​°C. The results showed that both activation methods enhanced cementitious activity; hence, NMW could be utilized in geopolymer synthesis after thermal and mechanical activations.

Geopolymer cement has been popularly studied nowadays compared to ordinary Portland cement because it demonstrated superior environmental advantages due to its lower carbon emissions and waste material utilization. This paper focuses on the formulation of geopolymer cement from nickel–laterite mine waste (NMW) and coal fly ash (CFA) as geopolymer precursors, and sodium hydroxide (SH), and sodium silicate (SS) as alkali activators. Different mix formulations of raw materials are prepared to produce a geopolymer based on an I-optimal design and obtained different compressive strengths. A mixed formulation of 50% NMW and 50% CFA, SH-to-SS ratio of 0.5, and an activator-to-precursor ratio of 0.429 yielded the highest 28 d unconfined compressive strength (UCS) of 22.10 ± 5.40 MPa. Furthermore, using an optimized formulation of 50.12% NMW, SH-to-SS ratio of 0.516, and an activator-to-precursor ratio of 0.428, a UCS value of 36.30 ± 3.60 MPa was obtained. The result implies that the synthesized geopolymer material can be potentially used for concrete structures and pavers, pedestrian pavers, light traffic pavers, and plain concrete.

O experimento foi conduzido para testar a eficiência de dois alumino-silicatos, no controle da aflatoxicose em frangos de corte (machos). Foram efetuadas análises de sangue para verificação da influência da aflatoxina no perfil sanguíneo das aves. Os resultados mostraram efeito negativo (PThis experiment was conducted to evaluate the efficiency of two alumino-silicates against deleterious effects of a toxin on growth performance and blood parameters of male broilers. The products did not counteract the negative effects on growth performance. Total protein and gtotamic-oxalacetic transaminase in blood from birds fed contaminated and non contaminated rations, were negatively affected (P

Abstract: Alumino-silicate coatings and structures formed from alumino-silicate and amorphous chalcogenide submicrometer layers were prepared by pulsed laser deposition. Fabricated thin films were characterized in terms of their structure, morphology, topography, chemical composition, optical properties, and basic anticorrosive functionality. Prepared coatings are amorphous, smooth, without micrometer-sized droplets, with chemical composition close to parent targets. Spectral dependencies of refractive indices and extinction coefficients were derived from variable angle spectroscopic ellipsometry data. Amorphous chalcogenide/alumino-silicate structures present large refractive index differences of individual layers (Δn ~1.2 at 1550nm) which could be useful for optical systems working at infrared telecommunication band wavelengths. Basic anticorrosion data of alumino-silicate layers show promising anticorrosion behavior. [Copyright &y& Elsevier]

Abstract: The HF+HCl leach liquor generated from the dissolution of silica, alumina and silicate gangue minerals in a low-grade molybdenite concentrate contains H2SiF6 and H3AlF6. Studies were conducted to recover the two valuable fluorides as Na2SiF6 and Na3AlF6 (synthetic cryolite) by precipitation with Na2CO3 from the leach liquor. An initial investigation was carried out to determine the precipitation conditions for Na2SiF6 and Na3AlF6 from their individual acid solutions. Subsequently, the conditions were determined for the selective precipitation of the two fluorides from a synthetic mixed acid solution similar to the leach liquor. When the acid solution was neutralized with 3mol/L Na2CO3, Na2SiF6 precipitated first at pH 1.35 whilst Na3AlF6 required an increase in pH above 2.2 before it precipitated. Maximum recovery of the two fluorides was best achieved at about 50°C. A similar trend was observed for the precipitation of Na2SiF6 and Na3AlF6 from the leach liquor of molybdenite upgrading. Phases of precipitated fluorides were identified by XRD and surface morphology by SEM. The purity of the Na2SiF6 precipitate was 99.5% whereas Na3AlF6 was contaminated with Na3FeF6. [ABSTRACT FROM AUTHOR]

Abstract: The synthesis and the physico-chemical characterization of hybrid organic–inorganic crystalline phases referred to as ECS (Eni Carbon Silicate), constituting a new family of organic–inorganic hybrid materials, are described. ECS phases were synthesized in basic medium using 1,4-bis-(triethoxysilyl)-benzene (BTEB), 4,4′-bis-(triethoxysilyl)-biphenyl (BTEBP), 1,4-bis-(2-triethoxysilyl-ethyl)-benzene (BTEEB), 1,3-bis-(trimethoxysilyl)-propane (BTMP) as silica sources, NaAlO2 as source of alumina and an alkali metal hydroxide (NaOH or KOH). Among the bis-silylated organic precursors, BTEB proved to be the most versatile, since three different crystalline phases (ECS-1 to ECS-3) were obtained by changing the synthesis parameters. The presence of Al is in each case critical, since no crystalline products were obtained without NaAlO2. The solid products were deeply characterized by XRD, HRTEM, 29Si, 27Al and 13C MAS NMR, porosimetry, elemental and thermogravimetric analyses. For one of them, ECS-2, the crystal structure was determined and refined starting from the high resolution synchrotron powder diffraction data. It consists of inorganic layers linked by the phenylene groups and built up by [AlO4] and [SiO3C] tetrahedra. [Copyright &y& Elsevier]

Abstract: The hydrostatic and uni-axial pressure dependence of elastic properties of a low-silica calcium alumino-silicate glass (LSCAS) is determined by ultrasonic pulse-echo techniques at room temperature. The experimental results are used to obtain the third-order elastic constants (TOECs) of these glasses. The pressure dependence of fractal bond connectivity of these glasses is discussed. The normal behavior of positive pressure dependence of ultrasonic velocities was observed for the glass. The pressure dependence of both shear modulus and bulk modulus are positive for these glasses. [Copyright &y& Elsevier]

Abstract: From a presentation of the various nuclear magnetic resonance (NMR) experiments that allows to characterize the local structure and dynamics of oxide glasses and melts, we show that it becomes possible to evidence not only the details of the coordination state of the constituting atoms but also the nature of polyatomic molecular motifs extending over several chemical bonds. [Copyright &y& Elsevier]

Abstract: The role of some glass network modifiers on the quantum efficiency of the near-infrared fluorescence from the 3H4 level of Tm3+ ion in silica-based doped fibers is studied. Modifications of the core composition affect the spectroscopic properties of Tm3+ ion. Adding 17.4mol% of AlO3/2 to the core glass caused an increase of the 3H4 level lifetime up to 50μs, 3.6 times higher than in pure silica glass. The quantum efficiency was increased from 2% to approximately 8%. On the opposite, 8mol% of PO5/2 in the core glass made the lifetime decrease down to 9μs. These changes of Tm3+ optical properties are assigned to the change of the local phonon energy to which they are submitted by modifiers located in the vicinity of the doping sites. Some qualitative predictions of the maximum achievable quantum efficiency are possible using a simple microscopic model to calculate the non-radiative de-excitation rates. [Copyright &y& Elsevier]

Local environments of oxygen in Al2O3-SiO2 melts have been investigated via Molecular Dynamics (MD) simulation in a model containing about 3000 atoms with the Born–Mayer type pair potentials under periodic boundary conditions. The study has been carried out via determination of temperature and composition dependences of fraction of [n]O at temperatures ranged from 2100 to 7000 K in the system containing 33.33, 50.00 and 66.67 mol% Al2O3. In addition, fraction of [n]O in liquid Al2O3⋅2SiO2 at the density ranged from 2.60 to 4.20 g/cm3 has been estimated in order to observe the pressure dependence. The label [n]O refers to the number of T atoms that are nearest neighbors to a given O (i.e. , T = Al, Si and n= 0,1,2, etc.). The possible relation between local environments of oxygen and dynamics of the system has been discussed. In addition, evolution of triclusters (O atoms surrounded by three cations) and their composition caused by varying temperature, composition and density of liquids has been found and presented. [Copyright &y& Elsevier]

Abstract: A study of the mechanisms responsible for the infra-red to near infra-red up-conversion in Tm3+-doped silica fibers is presented. Up-conversion luminescence was observed from the 3H4 level of Tm3+ under 1586nm pumping into the 3F4 level. The quadratic dependence of the up-conversion luminescence at 800nm on the 1800nm luminescence from the 3F4 level confirms that the 3H4 level is populated by a two photon process. Two possible processes are proposed as mechanisms responsible for the up-conversion: excited state absorption and energy transfer up-conversion. The decay characteristics of the luminescence from the 3H4 level were studied under direct and indirect pumping at 786 and 1586nm, respectively. By comparing the decay waveforms to the solution of a simple set of rate equations, the energy transfer up-conversion process (3F4, 3F4 → 3H4, 3H6) was established at Tm2O3 concentrations greater than 200ppm. [Copyright &y& Elsevier]

Molten system Na 3 AlF 6 − SiO 2 was examined by high temperature NMR. Further characterizations of the samples prepared by Rapid Solidification Processing (RSP) technique and by spontaneous solidification were performed by X–ray diffraction and solid state NMR. The high solubility of SiO 2 in molten cryolite and the immiscibility phenomenon were observed. Using thermogravimetric analysis, weight losses were detected, which could be attributed to the formation of the volatile products. The results of the present study are the evidence that SiO 2 reacts with molten Na 3 AlF 6 under the formation of the volatile SiF 4 , non − volatile NaF, and alumino−silicate AlSi 3 O 8 − species. NMR spectroscopy coupled with diffraction−based methods was proved as a promising approach to obtain information about the structure and chemistry of this rather complex system. Unlabelled Image • First time, high temperature NMR technique was used for the analysis of Na 3 AlF 6 –SiO 2 system. • The silicon anion is incorporated into the melt by the Al–O–Si oxygen bridge and forms NaAlSi 3 O 8. • NMR analysis coupled with the X–ray diffraction, is a powerful tool for the description of glass forming system. [ABSTRACT FROM AUTHOR]

Geopolymer cement has been popularly studied nowadays compared to ordinary Portland cement because it demonstrated superior environmental advantages due to its lower carbon emissions and waste material utilization. This paper focuses on the formulation of geopolymer cement from nickel–laterite mine waste (NMW) and coal fly ash (CFA) as geopolymer precursors, and sodium hydroxide (SH), and sodium silicate (SS) as alkali activators. Different mix formulations of raw materials are prepared to produce a geopolymer based on an I-optimal design and obtained different compressive strengths. A mixed formulation of 50% NMW and 50% CFA, SH-to-SS ratio of 0.5, and an activator-to-precursor ratio of 0.429 yielded the highest 28 d unconfined compressive strength (UCS) of 22.10 ± 5.40 MPa. Furthermore, using an optimized formulation of 50.12% NMW, SH-to-SS ratio of 0.516, and an activator-to-precursor ratio of 0.428, a UCS value of 36.30 ± 3.60 MPa was obtained. The result implies that the synthesized geopolymer material can be potentially used for concrete structures and pavers, pedestrian pavers, light traffic pavers, and plain concrete. [ABSTRACT FROM AUTHOR]

Engineering the permanent storage of CO 2 in earth-abundant Ca- and Mg-bearing silicate and alumino-silicate rocks and minerals as carbonates requires a fundamental understanding of the extents of carbonate conversion that can be achieved at conditions relevant to geologic formations. While many studies have reported the reaction rates and the carbonation extents of specific minerals, the data is limited in terms of reaction conditions and the mineral samples were relatively pure to start with. Thus, understanding of the effect of the chemical and mineralogical heterogeneity on the carbon mineralization behaviors of various minerals and rocks in geologic conditions is lacking. Therefore, this study investigated the reactivities of a selection of minerals and rocks such as (a) Mg-rich olivine (Mg 1.74 Fe 0.26 SiO 4) as previously reported by Gadikota and co-workers (2014), [1] labradorite (plagioclase feldspar with Ca 0.53 Na 0.47 Al 1.53 Si O 8), (b) anorthosite (a mixture of plagioclase (Ca 0.98 Na 0.02 Al 1.98 Si 2.02 O 8), olivine (Mg 1.32 Fe 0.68 SiO 4) and magnetite (Fe 3 O 4)), and (c) basalt (a fine-grained volcanic rock containing a mixture of plagioclase (Ca 0.6 Na 0.4 Al 1.6 Si 2.4 O 8), calcic pyroxene (~Mg 0.48 , Fe 0.52 CaSi 2 O 6) and low Ca pyroxene (~Mg 0.48 Fe 0.52 SiO 3)), that are relevant to CO 2 storage. The reaction conditions were also selected to mimic the conditions relevant to geologic CO 2 storage sites (T max = 185 °C, P max = 164 bar, 0–1 M NaHCO 3 , 0–1 M NaCl, 1.0 M NaCl + 0.64 M NaHCO 3). Our studies show that the extents of carbonation of olivine, labradorite, anorthosite, and basalt are 85, 35, 19 and 9%, respectively, when reacted for three hours at 185 °C, P CO2 of 139 atm in 1.0 M NaCl + 0.64 M NaHCO 3 with 15 wt% solid reactant and a stirring rate of 800 rpm. Further, our results indicate that increasing the reaction temperature over the range of 90 to 185 °C, and increasing the concentration of NaHCO 3 over the range of 0 to 1 M, both enhance the extent of carbon mineralization. On the other hand, increasing the partial pressure of CO 2 from 64 atm to 169 atm and raising the concentration of NaCl to 1.0 M have no significant effects within the time-scale of these experimental studies. Comparison of our results with previous studies suggests that the reactivity of Ca- and Mg-bearing alumino-silicates is lower compared to Ca- and Mg-bearing silicates. [ABSTRACT FROM AUTHOR]