Aluminate Ions Research Articles

Parametric Analysis of Aluminum-Air Batteries with Focus on Aluminum Product Layer Management for Enhanced Power Output

Aluminum-air batteries are a promising next-generation technology due to their high energy density coupled with the abundance of aluminum and a well-established supply chain. One field that stands to particularly benefit from these greater capacities is aircraft electrification. Aviation applications pose a unique challenge in that the energy source for flight must provide a considerable upside relative to the weight it adds to the vehicle. Lithium-ion technology has been successfully implemented in drones for short flight times, but aluminum-air batteries have the potential to greatly extend the durations of these flights. While the energy density is where this chemistry has a unique competitive advantage, the power output presents a challenge. Although researchers have investigated lithium-ion battery discharge at high C-rates, most aluminum-air battery research has focused on maximizing utilization and energy density. For viable implementation in electric aircraft, focus must be placed on maximizing the power output of the aluminum-air chemistry with care to maintain the energy density that gives it its competitive advantage. At high power outputs, system performance is largely dictated by ohmic losses on the anode side associated with the aluminum product layer. Turnover of this secondary passivation layer is based on conversion of insoluble aluminum hydroxide to soluble aluminate ions, and this can be strongly influenced by several system parameters including electrolyte concentration, temperature, and flow rate. This investigation conducts a parametric analysis of these parameters with respect to their influence on resistance of the aluminum product film and its dissolution. The effects will primarily be studied using electrochemical impedance spectroscopy and polarization curves in conjunction with insight from Tafel analysis, surface imaging, and extended discharge testing. Both three-electrode and full-cell setups will be used for testing to allow for clear insight to surface-level processes and an idea of how the investigated factors scale up when implemented in a real system. Management of the aluminum product film is critical for achieving high power output, and this investigation will provide further insight to how key cell parameters influence the realization of this goal.

Effect of inorganic anions on precipitation of desilication products based on low-temperature Bayer process

The effect of inorganic anion impurities in sodium aluminate solution on the composition, structure and micro-morphology of desilication products (DSPs) based on the low-temperature Bayer process was systematically investigated via XRD, FT-IR, SEM and PSD methods. The sodalites with chloride-type, carbonate-type and nosean-type precipitate in the presence of chloride, sulfate and carbonate in solution, and the aluminate ions in DSPs are partly replaced by the incorporation of anion impurities. The binding capability of sulfate to the DSPs cage is stronger than aluminate, chloride and carbonate. The particle size, agglomeration degree and thickness of the circular lamellar structure of DSPs are increased by rising the concentration of anion impurities. The anions enhance the dissolution of the zeolite framework and the formation of tetradentate rings in sodalite, which promotes the transformation of zeolite to sodalite.

Synergistic Improvement in Setting and Hardening Performance of OPC-CSA Binary Blended Cement: Combined Effect of Nano Calcium Carbonate and Aluminum Sulfate

The combined effect and corresponding mechanism of nano calcium carbonate (NC) and aluminum sulfate (AS) on the setting and hardening performance of binary blended cement (ordinary Portland cement (OPC) and calcium sulfoaluminate cement (CSA)) were evaluated through multiple experiments, including setting time, calorimetry, compressive strength, X-ray diffraction (XRD), and mercury intrusion porosimetry (MIP). The results showed that, as compared to OPC, OPC-CSA binary blended cement exhibited reduced setting time but decreased early strength, which could be caused by the depressed silicate phase hydration due to the fast supply of aluminate ions during the hydration of aluminate-contained phases contained in CSA. However, through the combined addition of NC and AS, the depressed silicate phase hydration was greatly promoted by NC due to its nucleation effect, and the reduced early strength was significantly improved. Further analysis indicates that the combined addition of NC and AS can promote the formation of C-S-H gel and decrease the porosity of the hardened OPC-CSA binary paste. In this way, one promising repair material with rapid setting and hardening properties was prepared by OPC-CSA binary blended cement with the combined addition of NC and AS.

Physical-chemical study of the interactions of aluminum(III) ion with fine decomposed peat of Arroio Silva, Santa Catarina, Brazil

The interactions of the fine decomposed peat (FDP) of Arroio Silva, SC, Brazil, with the Al(III) ion were studied. The infrared (IR) spectrum confirmed the presence of the characteristic functional groups of peat. Kinetic studies revealed that, with a high correlation coefficient, the pseudo-second-order model shows a good agreement between the experimental and calculated qe values. This indicates that in the adsorption of Al(III) ion the determining step is a chemical adsorption, involving chelation. The process is described by the Langmuir adsorption model, which is limited to the formation of a monolayer of metallic ions. According to this model, the maximum adsorption capacities at pH 1.0, 2.5 and 4.0 were, respectively, 5.42, 5.89 and 6.09 ​mg of aluminum per gram of peat. The suggested adsorption mechanism involves the complexation of the Al(III) ion with the oxygenated groups present in the peat. The electron microscopy analysis showed a rough and porous surface and the determination of the point of zero charge (PZC) indicates that the interactions of the Al(III) ion with the peat are much stronger than simple electrostatic interactions. The molar amounts of the most important functional groups present and the equilibrium constants of Al(III) ion interactions with these groups were calculated and the distribution curves were obtained. At pH values up to pH ​= ​4.4, the Al(III) ion is preferably coordinated with the phthalic group. At higher pH values several interactions occur, for instance, between: a monohydroxide and the phthalic group, Al(OH)(Pht); a dihydroxide, a phthalic and a catechol group, which predominates at pH values of 4.5 to 8.2, [Al(OH)2(Pht)(Cat)]3-; and a monohydroxide bisphtalic, [Al(OH)(Pht)2]2-, a dihydroxide, a catechol and a salicylate group, [Al(OH)2(Cat)(Sal)]3-, which competes with the aluminate ion, Al(OH)4- . The linear relationship of Stern-Volmer suppression of the fluorescence of the aromatic groups present in the peat with the Al(III) ion confirms the equilibrium results.

Corrosion Protection Behavior of Aluminate Ion-Loaded Layered Double Hydroxide Coating on AZ31 Magnesium Alloy

Effect of aluminate ion loading on the corrosion behavior of layered double hydroxide (LDH) coating of Mg-3Al-1Zn (AZ31) alloy was investigated. The corrosion inhibition performance of NaAlO2 for AZ31 was examined by immersion and polarization tests. Then, aluminate ion-loaded LDH (LDHAlO2) was synthesized from hydrotalcite (LDHCO3) and co-deposited with magnesium and aluminum double hydroxide on AZ31 by electrophoretic co-deposition. Polarization, electrochemical impedance (EI) and wet-dry cyclic corrosion tests were conducted on the LDHAlO2- and LDHCO3-coated specimens. Adding 10–50 mmol l−1 NaAlO2 to 0.1 mol l−1 NaCl solution induced a clear passive region on the polarization curves of AZ31 and shifted the breakdown potential over −1.0 V (Ag/AgCl), indicating the corrosion inhibition property of NaAlO2. In the polarization and EI tests, the aluminate ion loading did not noticeably enhance the corrosion protection ability of the LDH coating as shown by higher quasi-passive current density and lower R p than without loading. However, in the wet-dry corrosion tests, the LDHAlO2-coated AZ31 demonstrated less weight gain and fewer clusters of shallow micro-pits, while the LDHCO3-coated AZ31 showed numerous deeper pits on the entire surface. It was revealed that loading aluminate ions to the LDH coatings is promising for enhancing their corrosion protection ability in atmospheric environments.

Geochemical study on the deposition of silica scale at Olkaria well OW-35: A key to understanding the formation mechanisms of silica scale at the Olkaria Geothermal Field, Kenya

In the Olkaria geothermal field, Kenya, a silica scale formed from geothermal water at the OW-35 production well was geochemically investigated. The geothermal water is highly alkaline, with a pH of 10.13, while the salinity is low, with a total Cl concentration of 432.4 ppm. The silica scale was precipitated from geothermal water with a high temperature (150–190 °C) in the OW-35 separator. For the mineral composition of the scale sample, it is mainly amorphous Opal-A and crystalline quartz. The SiO2 content was 85.47 wt.%, and the Al2O3 and Fe2O3 contents were high at 3.16 and 1.11%, respectively, despite the fact that Al and Fe concentrations in the geothermal water were low. Based on the enrichment factor, Al was extremely concentrated from the geothermal water onto the silica scale during the formation, suggesting that Al may participate in the formation of the silica scale. For Fe, there was no contribution of Fe to the formation of silica scale, which was present as magnetite. This silica scale is a mixture of crystalline quartz and amorphous opal-A. The deposition mechanism was considered as follows. The quartz was formed by continuous and slow adsorption of monosilicic acid on the surface of the solid due to the slight supersaturated condition. On the other hand, opal-A was formed by a reaction between aluminate ion and monosilicic acid or monosilicate ion on the solid surface.

The impact of metakaolin on the hydration of tricalcium silicate: effect of C-A-S-H precipitation

Introduction:Metakaolin (MK) is used as supplementary cementitious material to reduce the CO2footprint of Portland cements. However, the early hydration of Portland cement (OPC) is often retarded due to its use. The present work investigates the mechanisms of this retardation. Focus is laid on the interaction of MK with the main clinker phase C3S (Ca3SiO5, pure form of alite) that is known to govern the kinetics of early hydration of OPC.Methods:Hydration reactions of MK and C3S were analysed by optical emission spectroscopy, electron microscopy, thermal analysis, X-ray diffraction and reaction calorimetry.Results:Results on MK showed that compared to sodium ions the presence of calcium ions reduced the maximum amounts of silicate and aluminate ions released into solution by MK. For MK + C3S mixtures, C-A-S-H was formed at the surfaces of both C3S and MK within minutes with a composition of (CaO)1.3(SiO2)0.8(Al2O3)0.2(H2O)2.7. The solubility constant of (CaO)1.3(SiO2)0.8(Al2O3)0.2(H2O)2.7was determined.Discussion:C-A-S-H appeared to be an unsuitable substrate for C-S-H nucleation. Therefore, its formation during early hydration is expected to play an important role in the retardation of C3S hydration. Indeed, when C-A-S-H seeds are formed, less C-S-H seeds are formed leading to lengthen the duration of the induction period. The presence of sulfate ions reduces the amount of C-A-S-H seeds as most aluminate ions are consumed to form ettringite. Consequently, sulfate ions induce an increase of the hydration kinetics such as observed in MK + C3S mixtures.

Disordered interfaces of alkaline aluminate salt hydrates provide glimpses of Al3+ coordination changes

HypothesisThe precipitation and dissolution of aluminum-bearing mineral phases in aqueous systems often proceed via changes in both aluminum coordination number and connectivity, complicating molecular-scale interpretation of the transformation mechanism. Here, the thermally induced transformation of crystalline sodium aluminum salt hydrate, a phase comprised of monomeric octahedrally coordinated aluminate which is of relevance to industrial aluminum processing, has been studied. Because intermediate aluminum coordination states during melting have not previously been detected, it is hypothesized that the transition to lower coordinated aluminum ions occurs within ahighly disordered quasi-two-dimensional phase at the solid-solution interface. Experiments and simulationsIn situ X-ray diffraction (XRD), Raman and27Al nuclear magnetic resonance (NMR) spectroscopy were used to monitor the melting transition of nonasodium aluminate hydrate (NSA, Na9[Al(OH)6]2·3(OH)·6H2O). A mechanistic interpretation was developed based on complementary classical molecular dynamics (CMD) simulations including enhanced sampling. A reactive forcefield was developed to bridge speciation in the solution and in the solid phase. FindingsIn contrast to classical dissolution, aluminum coordination change proceeds through a dynamically stabilized ensemble of intermediate states in a disordered layer at the solid-solution interface. In both melting and dissolution of NSA, octahedral, monomeric aluminum transition through an intermediate of pentahedral coordination. The intermediate dehydroxylates to form tetrahedral aluminate (Al(OH)4−) in the liquid phase. This coordination change is concomitant with a breaking of the ionic aluminate-sodium ionlinkages. The solution phase Al(OH)4− ions subsequently polymerize into polynuclear aluminate ions. However, there are some differences between bulk melting and interfacial dissolution, with the onset of the surface-controlled process occurring at a lower temperature (∼30 °C) and the coordination change taking place more gradually as a function of temperature. This work to determine the local structure and dynamics of aluminum in the disordered layer provides a new basis to understand mechanisms controlling aluminum phase transformations in highly alkaline solutions.

Properties and composition of the spent electrolyte for premium circulation mediated by Al-air batteries.

Al-air batteries can serve as a bridge for high-quality cyclic utilization of aluminum resources. However, limited insights into the spent electrolyte are challenging to accurately adjust the recovery process to obtain premium Al-containing products. Herein, the properties and composition of the spent electrolyte were explored through experiments and theoretical calculations. The results demonstrate that the viscosity of the spent electrolyte increased with the rise in discharge current density, time and temperature under highly alkaline conditions, while the ionic conductivity and causticity obviously decreased. Al(OH)4- was the prime and balanced aluminate species when the battery was discharged at 25 °C and coexisted with a bit of [Al2O(OH)6]2-, [Al2O2(OH)6]4- and Al(OH)63- ions. Especially, the characteristics of the spent electrolyte were mainly dominated by the discharge time and temperature when the current density was continuously increased. There was only Al(OH)4- in the electrolyte at a higher discharge temperature. The DFT results also reveal that the polynuclear aluminate ions were produced by the interaction between the mononuclear aluminate ion Al(OH)4- and OH-. This work manifests a profound insight into the spent electrolyte from Al-air batteries for the efficient recycling of aluminum resources.

Effects of Methanol on the Seeded Precipitation of Al(OH)3 from Potassium Aluminate Solution

AbstractThe effects of methanol on the seeded precipitation of Al(OH)3 from potassium aluminate solution are investigated. The solubility of Al(OH)3 decreases in the presence of methanol, leading to a faster crystallization and a higher precipitation ratio than the normal seeded precipitation process. Under the optional precipitation conditions of temperature 323.15 K, K2O concentration 170 g L−1, and addition of an equal volume of methanol to potassium aluminate solution, the precipitation ratio can exceed 85% within 7 h. Characterization of the Al(OH)3 products using X‐ray diffraction, scanning electron microscopy, and particle size distribution shows a typical gibbsite crystal phase composed of sheet‐like agglomerates with an average particle size of 74 µm. An interaction model between methanol molecules and Al(OH)3 crystal face is established and calculated by using the molecular dynamics method, which indicates the morphology transition mechanism of the Al(OH)3 crystal. The result indicates that methanol molecules would hinder the growth of the (002) crystal face, so that the (002) crystal face is eventually retained and becomes the main crystal face for the Al(OH)3 product. Infrared radiation and Raman spectra analyses suggest that the added methanol captures water molecules from the aluminate ion hydration sphere and thus catalyzes the crystallization process.

Extraction of alumina from low-grade kaolin in the presence of lime and NaOH via multi-stage hydrothermal process

Kaolinite as an aluminum-rich clay mineral is widely distributed in kaolin, coal gangue and mill tailings, etc. Herein, alumina extraction from the low-grade kaolin was explored via multi-stage hydrothermal process in the presence of NaOH and lime. In single stage, maximum alumina leaching ratio was found to be 33.64% in the presence of 20 g/L NaOH, 180 °C leaching temperature, 2 h leaching time and CaO/SiO2 molar ratio of 0.7. The formation of zeolites due to limited solubility of aluminate ions resulted in the low alumina leaching ratio. Then, a multi-stage hydrothermal process was proposed to improve the alumina leaching, with each stage being carried out at 180 °C for 0.1 h. The cumulative alumina leaching ratio attained 72.09% after three-stage hydrothermal process; after desilication, the lixivium was used for preparing pseudo-boehmite via carbonation. Conclusively, the multi-stage hydrothermal process achieved the efficient extraction of alumina from kaolinite and presented great potential in improving the economic value of low-grade kaolin.

Effect of fly ash with or without mechanical activation on early-age cement hydration: A comparative case study by boundary nucleation and growth model

In this study, the modified boundary nucleation and growth (BNG) model is adopted to elucidate the effect of fly ash, with or without mechanical activation, on early-age cement hydration kinetics. Results show that compared with ordinary Portland cement paste, as-received fly ash has impaired the nucleation density. This might be attributed to the aluminate ions in the pore solution, released from the dissolution of cement and fly ash, which have passivated the surface of particles and suppressed nucleation and growth of the main hydration products, i.e., calcium-silicate-hydrate (C-S-H) at the early age. However, mechanical activation towards fly ash has improved its specific surface area, further boosting its reactive area fraction in the nucleation and growth process. The increased boundary area per unit volume for mechanically activated fly ash is less affected by the hindering effect of aluminate ions, and favors the C-S-H nucleation in the paste, which causes the nucleation density for the paste containing mechanically activated fly ash to be higher than the one containing as-received fly ash.

Analysis of the isothermal hydration heat of cement paste containing mechanically activated fly ash

Fly ash is a widely used supplementary cementitious material in the world. Mechanical activation, as a potential approach, can realize maximum bulk utilization of fly ash. In this study, the isothermal hydration heat flows of cement paste containing fly ash with or without mechanical activation are tested and modelled by Avrami equation, reaction order model and three-parameter exponential function at different stages. The results indicate that addition of 20% as-received fly ash retards the cement hydration at the nucleation and growth stage, because the aluminate ions in the pore solution might decrease heterogeneous nucleation sites of C-S-H and suppress its growth. Moreover, as-received fly ash impairs the reaction rate of the whole system at final tail stage owing to its low heat release. However, compared with as-received fly ash, mechanically activated fly ash has promoted cement hydration at the very early age due to the enhanced filler effect. More surface area supplied by mechanically activated fly ash promotes C-S-H growth and partially offsets the retarding effect of aluminate ions. The reaction rate of the whole cementitious system at the deceleration stage is also promoted by the improvement of pozzolanic reactivity after mechanical activation. Furthermore, three different mathematical calculation approaches have been adopted to calculate the ultimate hydration heat Qmax of the cementitious systems. In spite of different values for Qmax, the consensus can be achieved that mechanical activation towards fly ash can promote the reaction degree of the system.

Isotopic Substitution Reveals the Importance of Aluminate Diffusion Dynamics in Gibbsite (Al(OH)3) Crystallization from Alkaline Aqueous Solution

Understanding molecular-scale factors governing the precipitation of aluminum hydroxides, such as gibbsite, under alkaline conditions is important for the formation of laterite deposits, as well as aluminum processing. However, mechanisms enabling tetrahedral aluminate ions to assemble into octahedral sites of the gibbsite lattice remain unclear. Formation of oligomeric complexes has been hypothesized as a critical intermediate step. Here, we report a study of gibbsite solubility in highly alkaline solutions using deuterium substitution to probe equilibrium and kinetic factors that could affect oligomeric intermediate formation, including the reactivity and the diffusivity of aluminate ions. When substituting sodium hydroxide with sodium deuteroxide, solution analysis shows a nearly 40% and 50% increase in gibbsite solubility in 2.4 and 3.3 mol·kg–1 total sodium solutions, respectively. Raman spectroscopy indicated that monomeric aluminate ions are the predominant species in solution irrespective of deuteration. However, both 27Al and 23Na nuclear magnetic resonance (NMR) spectroscopy revealed significant differences in chemical shifts in deuterated solutions, and analysis of 1H, 23Na, and 27Al diffusion coefficients with pulsed-field gradient, stimulated echo NMR spectroscopy shows a decrease in ion diffusivity with increasing total deuterium in solution, consistent with the notion of increasing strength in the hydrogen/deuterium bonding network. Because the relative change in 1H diffusion coefficients are commensurate with the difference in apparent solubility constants, there is evidence for an oligomeric intermediate whose steady-state concentration is maintained by the collision frequency of aluminate ions.

Synthesis and regeneration of mesoporous Ni–Cu/Al2O4 catalyst in sub-kilogram-scale for methanol steam reforming reaction

A green template-free method is proposed for the synthesis of mesoporous Ni–Cu/Al2O4 catalyst in sub-kilogram scale. In the convenient synthetic method, an intermediate is formed via electrostatic forces and hydrogen bonding interactions between the aluminate ions and the metal ions and/or metal hydroxides under suitable pH conditions. The desired Ni–Cu/Al2O4 composites, with Ni/Cu molar ratios of 10%, 20% and 30% of Cu at Cu/Al molar ratio of 10.0%, respectively, are then obtained from calcination. The nitrogen adsorption-desorption isotherms show that the Ni–Cu/Al2O4 composites have specific surface areas of 136–170 m2g-1. The Ni–Cu/Al2O4 products are used as catalyst materials in the methanol steam reforming (MSR) of hydrogen and are shown to have a high conversion efficiency (>99%), a low methane concentration, good stability, and a high hydrogen yield (H2/methanol molar ratio ≈ 3.0) at low reaction temperatures in the range of 200–300 °C. In addition, the coke formation on the catalyst surface is less than 1.0 wt% even after a reaction time of 30 h. Notably, the Ni–Cu/Al2O4 catalyst can be regenerated by calcination at 800 °C and retains a high methanol conversion efficiency of close to >99% when reused in MSR.

Theory-Guided Inelastic Neutron Scattering of Crystalline Alkaline Aluminate Salts Bearing Principal Motifs of Solution-State Species.

Aluminate salts precipitated from caustic alkaline solutions exhibit a correlation between the anionic speciation and the identity of the alkali cation in the precipitate, with the aluminate ions occurring either in monomeric (Al(OH)4-) or dimeric (Al2O(OH)62-) forms. The origin of this correlation is poorly understood as are the roles that oligomeric aluminate species play in determining the solution structure, prenucleation clusters, and precipitation pathways. Characterization of aluminate solution speciation with vibrational spectroscopy results in spectra that are difficult to interpret because the ions access a diverse and dynamic configurational space. To investigate the Al(OH)4- and Al2O(OH)62- anions within a well-defined crystal lattice, inelastic neutron scattering (INS) and Raman spectroscopic data were collected and simulated by density functional theory for K2[Al2O(OH)6], Rb2[Al2O(OH)6], and Cs[Al(OH) 4]·2H2O. These structures capture archetypal solution aluminate species: the first two salts contain dimeric Al2O(OH)62- anions, while the third contains the monomeric Al(OH)4- anion. Comparisons were made to the INS and Raman spectra of sodium aluminate solutions frozen in a glassy state. In contrast to solution systems, the crystal lattice of the salts results in well-defined vibrations and associated resolved bands in the INS spectra. The use of a theory-guided analysis of the INS of this solid alkaline aluminate series revealed that differences were related to the nature of the hydrogen-bonding network and showed that INS is a sensitive probe of the degree of completeness and strength of the bond network in hydrogen-bonded materials. Results suggest that the ionic size may explain cation-specific differences in crystallization pathways in alkaline aluminate salts.

Extraction and value-added utilization of alumina from coal fly ash via one-step hydrothermal process followed by carbonation

Coal fly ash (CFA), containing 25–50 wt% of Al2O3, is a typical and massive secondary aluminum resource. However, alumina recovery from the CFA by traditional processes is very difficult due to 40–60 wt% SiO2 content and low Al2O3/SiO2 mass ratio. In this study, a “one-step” hydrothermal process was proposed to extract Al2O3 from CFA; a mixture of lime and NaOH was used to enhance the dissolution and separation of Al/Si components. The results showed that 60.14% Al2O3 leaching could be obtained for treatment at 210 °C temperature for 3 h in the presence of 30 g/L NaOH and CaO/SiO2 molar ratio of 1.0. During the hydrothermal process, the Si- and Al-bearing components of CFA were sufficiently decomposed in lime and NaOH mixture; the dissolved silicate ions were then combined with calcium ions to form tobermorite, while the aluminate ions were concentrated in the liquor, thereby achieving selective leaching of alumina from CFA. Owing to the limited solubility, part of the aluminate ions was also converted into aluminiferous zeolite, hence lowering the alumina leaching ratio. The lixivium was of low caustic ratio that was favorable for the preparation of high-value pseudo-boehmite via carbonation process at 80–90 °C with the ultimate pH of 9.5–10.0.

Hydrothermal formation mechanism of the efficient desilication product hydroandradite (3CaO·Fe2O3·xSiO2·(6-2x)H2O)

As a theoretically ideal and efficient desilication product without Na2O and Al2O3, the formation behavior of hydroandradite under different hydrothermal conditions by adding synthetic sodium ferrite was systematically investigated by adding synthetic sodium ferrite. Thermodynamic calculations indicate that increasing the reaction temperature is advantageous to promote the formation of hydroandradite, and hydroandradite with a high iron substitution coefficient is more difficult to precipitate than that with a low iron substitution coefficient. The existence of aluminate ions in solution significantly accelerates the formation of hydroandradite and shifts the characteristic peaks of the XRD spectra to the left by 0.4–0.5°/2θ. The hydroandradite in sodium aluminate solution is formed mostly by a substitution reaction from the preformed hydrogrossular and partly by spontaneous nucleation. Increasing the reaction temperature and prolonging the holding time can increase the mass fraction, silicon saturation coefficient and iron substitution coefficient of hydroandradite, while decreasing the contents of the hydrogrossular and zeolite phases

Microstructural evolution of condensed aggregates during the crystallization of ZSM-5 from a heterogeneous system

The microstructural evolution of precursors of ZSM-5 zeolite crystallized from a heterogeneous system using fumed silica, sodium aluminate and tetrapropylammonium ions as reagents is investigated. Entities previously described by Ren et al. (Chem. Mater. 2012, 24, 10, 1726-1737) as condensed aggregates, were extensively studied using scanning electron microscopy, and energy dispersive spectroscopy. It was observed that the condensed aggregates first comprise a core of nanocrystals that is enveloped by a shell of amorphous gel phase. During crystallization, the amorphous shell surrounding the core is converted into ZSM-5 crystals that grow to a film surrounding the core. The crystals in the film grow competitively with nutrients provided by the liquid phase from the surroundings, while the nanocrystals in the core show little or no signs of growth.

A comparative study of the effects of two alkanolamines on cement hydration

The effects of two alkanolamines, triethanolamine (TEA) and diethanol-isopropanolamine (DEIPA), on cement hydration were comparatively investigated by several techniques including calorimetry, in situ X-ray diffraction analysis and pore solution analysis. Results show that the cement hydration regime is greatly altered by the alkanolamines, depending on their types and dosages. At the dosage of 0.5%, the aluminate reactions, including the formation of AFt and the reaction of C4AF, are greatly accelerated, and consequently the silicate hydration is retarded. Compared to DEIPA, TEA increases the [Al] in pore solution, probably due to the stronger complexation with aluminate ions (Al(OH)4−), while DEIPA notably enhances the dissolution of C4AF after depletion of gypsum, suggesting a stronger complexation with iron ions (Fe3+). Through a comparison of the hydration of pure alite and cement systems, it is found that the effects of the two alkanolamines on cement hydration are primarily influenced by their impacts on the aluminate reaction.