Concentrated Alkaline Solution Research Articles

Time-Retrenched Synthesis of BaTaO2N by Localizing an NH3 Delivery System for Visible-Light-Driven Photoelectrochemical Water Oxidation at Neutral pH: Solid-State Reaction or Flux Method?

Among 600 nm class transition-metal oxynitrides, BaTaO2N with a cubic Pm3̅m perovskite-type structure is promising for solar water oxidation due to its absorption of visible light up to 660 nm, narrower band gap (Eg = 1.9 eV), appropriate valence band edge position for oxygen evolution, good stability in concentrated alkaline solutions, and nontoxicity. However, high defect density stemmed from long high-temperature ammonolysis limits the separation and transfer efficiency of photogenerated charge carriers in BaTaO2N. Here, a NH3 delivery system is specifically localized just above the synthesis mixture to reduce the synthesis time and defect density of BaTaO2N by a fresh supply of more active nitriding species and minimizing the generation of N2 and H2. Particularly, the effects of synthesis temperature (700–950 °C), synthesis time (1–8 h), and gas composition are systematically investigated to gain insights into the formation of single-phase BaTaO2N by solid-state reaction and flux method. Time-dependent experiments conducted at 950 °C show that single-phase BaTaO2N can be synthesized ≥6 and ≥4 h by solid-state reaction and flux method, respectively, revealing the advantage of the flux method over solid-state reaction in a localized NH3 delivery system. Subsequently, the separation and transfer efficiency and kinetics of photogenerated charge carriers are studied in BaTaO2N samples. Photoelectrochemical studies made it possible to resolve trends during visible-light-induced water oxidation, evidencing the inverse relationship between recombination and charge transfer phenomena. Transient absorption spectroscopy reveals that the dynamics of the photogenerated charge carriers in both types of BaTaO2N samples are different: (i) BaTaO2N synthesized by flux method has a greater number of holes despite the similar number of deeply trapped charge carriers and (ii) solid-state reaction led to the formation of a higher number of free electrons in BaTaO2N. The findings demonstrate the advantage of reducing the transfer distance of active nitriding species to the surface of the synthesis mixture for enhancing the photoelectrochemical water oxidation of BaTaO2N at neutral pH.

Effect of alkaline and benzoyl chloride treatments on the mechanical and morphological properties of sugar palm fiber-reinforced poly(lactic acid) composites

The present study deals with the effects of alkaline and benzoyl chloride treatments of sugar palm fibers (SPFs) on the mechanical and morphological properties of SPF-reinforced poly(lactic acid) (PLA) composites. Seven different parameters of SPFs were compared, which were untreated, three alkaline solution concentrations of 4%, 5%, and 6% for alkaline treatment, and 50 ml benzoyl chloride-treated SPFs at three different soaking durations of 10, 15, and 20 min. Composites of 30 wt.% SPF–reinforced 70 wt.% PLA were prepared by using a Brabender plastograph mixer and a hot press. The tensile, flexural, and impact properties of the SPF/PLA composites were improved after alkaline and benzoyl chloride treatments on the SPFs. However, the best tensile, flexural, and impact properties of the composites were observed at 6% alkaline treatment of SPF; the morphological analysis also supported this. The 6% alkaline treatment of the SPF/PLA composite demonstrated the highest tensile, flexural, and impact strength values of 17.08 MPa, 32.34 MPa, and 4.39 kJ/m2, respectively. These treated SPF/PLA composites could be appropriate for automobile component applications.

Electrochemically Inert Li2MnO3: The Key to Improving the Cycling Stability of Li-Rich Manganese Oxide Used in Lithium-Ion Batteries.

Lithium-rich manganese oxide is a promising candidate for the next-generation cathode material of lithium-ion batteries because of its low cost and high specific capacity. Herein, a series of xLi2MnO3·(1 − x)LiMnO2 nanocomposites were designed via an ingenious one-step dynamic hydrothermal route. A high concentration of alkaline solution, intense hydrothermal conditions, and stirring were used to obtain nanoparticles with a large surface area and uniform dispersity. The experimental results demonstrate that 0.072Li2MnO3·0.928LiMnO2 nanoparticles exhibit a desirable electrochemical performance and deliver a high capacity of 196.4 mAh g−1 at 0.1 C. This capacity was maintained at 190.5 mAh g−1 with a retention rate of 97.0% by the 50th cycle, which demonstrates the excellent cycling stability. Furthermore, XRD characterization of the cycled electrode indicates that the Li2MnO3 phase of the composite is inert, even under a high potential (4.8 V), which is in contrast with most previous reports of lithium-rich materials. The inertness of Li2MnO3 is attributed to its high crystallinity and few structural defects, which make it difficult to activate. Hence, the final products demonstrate a favorable electrochemical performance with appropriate proportions of two phases in the composite, as high contents of inert Li2MnO3 lower the capacity, while a sufficient structural stability cannot be achieved with low contents. The findings indicate that controlling the composition through a dynamic hydrothermal route is an effective strategy for developing a Mn-based cathode material for lithium-ion batteries.

Corrosion assessment of ferrocement element with nanogeopolymer for marine application

AbstractCorrosion is the major reason which limits the practical application of ferrocement structures in the marine environment. To protect the thin and strong wire mesh reinforcement, preventive methods are required to be employed. One of such methods implemented in this paper is novel application of geopolymer mortar on the surface of the wire mesh. The microstructural pores present in the highly durable fly ash based geopolymer mortar are further enhanced by using nanomodified fly ash particles to achieve the impermeable surfaces. Effect of alkaline solution concentration on the chloride ion penetration and corrosion has been investigated by using the different concentration of sodium hydroxide solution from 8 to 14 M. From the results, it is noted that for the geopolymer specimens, the chloride ions penetration values of 542.70 Coulombs is observed at 28 days which comes under the category of very low as per ASTM C1202‐10. The chloride ion penetration observed in geopolymer specimen is 17% lesser than ferrocement panel with conventional cement mortar. The time taken for cracking is delayed in the case of ferrocement panel with geopolymer mortar of 10 M concentrated sodium hydroxide solution by thrice the times of specimen with conventional cement mortar. This indicates that the incorporation of nanogeopolymer in ferrocement element not only increased the strength but also its serviceability against cracking and corrosion resulted in the extensive application of ferrocement construction in marine environment.

Efficient soft computing techniques for the prediction of compressive strength of geopolymer concrete

In the recent year, extensive researches have been done on fly ash-based geopolymer concrete for its similar properties like Portland cement as well as its environmental sustainability. However, it is difficult to provide a consistent method for geopolymer mix design because of the complexity and uncertainty of its design parameters, such as the alkaline solution concentration, mole ratio, and liquid to fly ash mass ratio. These mix-design parameters, along with the curing time and temperature ominously affect the most significant properties of the geopolymer concrete, i.e., compressive strength. To overcome these difficulties, the paper aims to provide a simple mix-design tool using artificial intelligence (AI) models. Three well-established and efficient AI techniques namely, genetic programming, relevance vector machine, and Gaussian process regression are used. Based on the performance of the developed models, it is understood that all the models have the capability to deliver higher prediction accuracies in the range of 0.9362 to 0.9905 (based on R2 value). Among the employed models, RVM outperformed the other model with R2=0.9905 and RMSE=0.0218. Theodore, the developed RVM model is very potential to be a new alternative to assist engineers to save time and expenditure on account of the trial-and-error process in finding the correct design mix proportions.

Mechanical Strength of Graphene Reinforced Geopolymer Nanocomposites: A Review

The emergence of high-strength graphene marks a new milestone in the material science field. With only a small percentage inclusion into the matrix system, this organic nanoparticle could tremendously improve the strength in vast arrays of composites. At the same time, there is a growing interest in using the low-cost, lightweight, and high early strength geopolymer as the new binder for concrete. Compared to the traditional Ordinary Portland Cement (OPC), geopolymer emits 80% less CO2 during its production while exerting similar strength. Thus, the geopolymer has the potential to commercialize as new and green concrete. Geopolymer is a mixture of aluminosilicate powders and alkaline solutions. When incorporated with nano-sized graphene, the material forms a composite known as Graphene Reinforced Geopolymer Nanocomposite (GRGN). The addition of graphene enhances the strength of geopolymer, which can further improve its competitiveness. However, this depends on several factors, including the types of graphene, the surface modification of graphene, and the concentration of alkaline solutions. Generally, the presence of graphene alters the porous structure of geopolymer into a substantially filled porous structure, thus increasing compressive strength and flexural strength. On the other hand, Graphene Oxide (GO) undergoes a chemical reduction in the alkaline solution, producing epoxy functional groups. The chemical treatment results in two conditions which are weak interaction between graphene and geopolymer matrix, and better graphene dispersibility in geopolymer matrix. This review also highlights the analytical modelling aspect of GRGN. The dissolution of Si(OH)4 and Al(OH)4- from the aluminosilicate source was consistent with experimental work and analytical modeling, while the dissolution of Si–OH on the surface-modified graphene indicated otherwise. Therefore, this paper will provide an insightful review of the GRGN mechanical properties.

Predicting the geopolymerization process of fly ash-based geopolymer using deep long short-term memory and machine learning

In this study, the geopolymerization process of fly ash-based geopolymer was estimated using the deep long short-term memory (LSTM) and machine learning models. The k-Nearest Neighbors (kNN) and support vector regression (SVR) approaches were used in the machine learning models. The percentages of major chemical components in fly ash, the alkaline solution concentration, the mole ratio, the liquid-to-fly ash mass ratio, and the curing temperature were selected as input variables in the models. The geopolymerization peak time, geopolymerization peak heat, dissolution peak time, and dissolution peak heat obtained from the calorimetric curve of fly ash-based geopolymer were used as the output variables. The deep LSTM, SVR, and kNN models estimated the geopolymerization peak time with 99.55%, 98.83%, and 91.62% accuracy, respectively. The geopolymerization peak heat was estimated by the deep LSTM, SVR, and kNN models with 99.69%, 98.91%, and 88.36% accuracy, respectively. The deep LSTM, SVR, and kNN models predicted the dissolution peak time with 99.49%, 99.43%, and 92.86% accuracy, respectively. The dissolution peak heat was estimated using the deep LSTM, SVR, and kNN models with 99.67%, 99.38%, and 90.60% accuracy, respectively. This study found that the deep LSTM model can be estimated the geopolymerization process of fly ash-based geopolymer with higher accuracy than the SVR and kNN models.

Anticorrosion Performance of PVDF Membranes Modified by Blending PTFE Nanoemulsion and Prepared through Usual Non-Solvent-Induced Phase Inversion Method.

In this study, PVDF/PTFE composite membranes were prepared by adding a PTFE nanoemulsion to a PVDF solution and casting it through the conventional non-solvent-induced phase separation method. The objective was to explore the effectiveness of using a simple and economical method to modify PVDF membranes with PTFE to enhance their anticorrosion performance, especially under highly acidic or alkaline conditions. PTFE nanoparticles (of around 200 nm in size) in nanoemulsion form were blended with PVDF at a mass ratio of PTFE:PVDF in the range of 0–0.3:1. The obtained membranes were examined to determine the effect of the added PTFE nanoparticles on the structure of the modified PVDF membranes as well as on their mechanical strength and surface characteristics. The membranes were then immersed in various concentrations of acidic or alkaline solutions for varied durations ranging from a few days up to as long as 180 days (6 months). The impacts of by the corrosive solutions on the tensile strength, surface roughness, and water flux of the membranes with different exposure times were quantified. The results showed that although a certain extent of change may occur with extended immersion times, greatly enhanced anticorrosion performance was obtained with the prepared PVDF/PTFE membranes compared with the unmodified PVDF membrane. For example, after being immersed in 5 mol-H+··L−1 H2SO4, HCl, and HNO3 solutions for 6 months, the tensile strength at breaking point remained at up to 69.70, 74.07, and 71.38%, respectively, of the initial strength for the PVDF/PTFE (M30) membrane. This was in contrast to values of only 55.77, 70.43, and 61.78% for the unmodified PVDF membrane (M0). Although the water flux and surface roughness showed a change trends to the tensile strength, the PVDF/PTFE (M30) membrane had much higher stability than the PVDF (M0) membrane. In a continuous filtration experiment containing H2SO4 at 0.01 mol-H+·L−1 for 336 h (14 days), the PVDF/PTFE membrane showed a maximum flux change of less than 30%. This was in comparison with a change of up to 50% for the PVDF membrane. However, the PVDF/PTFE membranes did not seem to have a greatly enhanced anticorrosion performance in the alkaline solution environment tested.

Fabrication of aramid-coated asymmetric PVDF membranes towards acidic and alkaline solutions concentration via direct contact membrane distillation

An asymmetric membrane for direct contact membrane distillation (DCMD) was first prepared with the ability to concentrate strongly acidic and alkaline solutions. The membrane was fabricated by a simple coating and non-solvent phase separation process. The successful preparation of the aramid-coated polyvinylidene fluoride (PVDF) asymmetric membrane was demonstrated by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR), and X-ray photoelectron spectroscopy (XPS) characterization. Furthermore, it was verified via contact angle measurements that this modified membrane had better acid and alkali resistance than the pristine PVDF membrane at an elevated temperature. During the DCMD process, the pH of the permeate side did not fluctuate significantly when solutions with different pH values were used as the feed solutions, thus also demonstrating the excellent separation efficiency of the modified PVDF membrane. Moreover, the modified PVDF membrane exhibited a higher concentration factor for acidic and alkaline solutions than the pristine membrane. Therefore, it is believed that the modified membrane has great potential for application in DCMD process with the concentration of acidic and alkaline solutions.

Investigation of Various Influencing Factors of Hydrothermal Synthesis of Analcime Zeolite

This study presents an investigation of the use of the natural mineral of Nakhchivan Autonomous Republic to produce analcime zeolite of potential practical importance. The influence of temperature and crystallization time, the concentration of alkaline solution and mineralizer on the process of synthesis of analcime has been evaluated. The optimal conditions established for the synthesis of pure analcime with a 100% degree of crystallinity are as follows: temperature of 180°C, alkaline and mineralizer solution of 10-15% KOH and 5-10% KCl and processing time of 50 hours. It has been shown that the presence of the KCl mineralizer promotes the production of pure analcime with a 100% crystallinity, and the natural mineral of Nakhchivan represents a good source for the synthesis process.

Effect of synthesis parameters on the development of unconfined compressive strength of recycled waste concrete powder-based geopolymers

The main object of this study is to investigate the geopolymerization potential of recycled waste concrete powder (RWCP) as well as the effects of synthesis parameters, including the molarity of NaOH solution, the mass ratio of water glass to NaOH solution (WG/NH), the mass ratio of liquid alkali activator to solid powder (L/S), and the curing conditions (curing temperature, curing time and curing method), on the development of unconfined compressive strength (UCS) of recycled waste concrete powder-based geopolymers. The recycled waste concrete powder (RWCP) (size < 0.075 mm) was utilized as source material, and water glass and sodium hydroxide (NaOH) were used as alkaline activators to synthesize geopolymer specimens. The dissolution of alumino-silicate from the RWCP under different concentrations of alkaline solutions was studied. The UCS of the resulting geopolymers synthesized under different conditions was tested. Further, the microstructure and mineral composition of the final products were characterized by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) technology. The results indicate that the dissolution of Si4+ and Al3+ in raw materials (RWCP) was highly affected by the alkali content and dissolution time. Increasing the alkali content, water glass content and L/S ratio was all conducive to enhancing the UCS of geopolymers. The optimum NaOH concentration corresponpded to 14 mol/L, WG/NH ratio of 1.5 and L/S mass ratio of 0.4. A maximum 7-day UCS of 14.32 MPa was achieved by wet curing at 70 ℃ for 24 hours. Microscopic analysis showed that the final products were mainly composed of amorphous hydrated calcium silicate and hydrated sodium aluminosilicate gels. However, due to the low activity and high calcium content of RWCP, most of crystalline phases and some unreacted substances still existed in the end products as inactive fillers, resulting in a relatively low UCS of the synthesized geopolymers. Baded on the research, it can be concluded that RWCP can be recycled as the precursor to synthesize geopolymer binder.

In Situ Activation of a Manganese Perovskite Oxygen Reduction Catalyst in Concentrated Alkaline Media.

The reaction pathway of the oxygen reduction reaction (ORR) is strongly affected by the electrolytic environment. Meanwhile, the ORR mechanism on transition-metal oxide catalysts has not been studied intensely in very concentrated alkaline solutions that are used in practical metal-air batteries. Herein, we report the in situ activation of ORR catalysis on manganese perovskite in a concentrated alkaline solution, mediated by the spontaneous formation of oxygen vacancy sites. Electrochemical analyses of the (100) epitaxial film electrodes reveal that the exchange current and electron number of the ORR on La0.7Sr0.3Mn0.9Ni0.1O3 significantly increase with the duration of the ORR when the KOH concentration is greater than 4 M. However, these values remain unchanged with time at less than 1 M KOH concentration. Operando synchrotron X-ray spectroscopy of the (100) epitaxial film confirmed that La0.7Sr0.3Mn0.9Ni0.1O3 involves the oxygen vacancy sites with the reduction of Mn atoms in concentrated KOH solution via the hydroxylation decomposition of perhydroxyl intermediates. Hence, the O2 adsorption switched from an end-on to a bidentate mode because the cooperative active sites of the oxygen vacancy and neighboring Mn allow bidentate adsorption of the dissolved O2. Due to the simultaneous interaction with the oxygen vacancy and Mn sites, the O-O bonds are activated and the potential barrier for the electron transfer to adsorbed O2 is lowered, resulting in a shift in the reaction mechanism from that involving an indirect "2 + 2" transfer pathway to a direct 4-electron pathway.

Synthesis and Characterization of Zeolites Produced from Low-Quality Coal Fly Ash and Wet Flue Gas Desulphurization Wastewater.

This study investigated a low-energy-consuming procedure for the synthesis of zeolite materials from coal fly ash (CFA). Materials containing zeolite phases, namely Na–X, Na–P1, and zeolite A, were produced from F–class fly ash, using NaOH dissolved in distilled water or in wastewater obtained from the wet flue gas desulphurization process, under atmospheric pressure at a temperature below 70 °C. The influence of temperature, exposure time, and alkaline solution concentration on the synthesized materials was tested. In addition, chemical, mineralogical, and textural properties of the obtained materials were determined by X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM), and cation exchange capacity (CEC). Cd(II), Ni(II), NH4+ cation, and Se(VI) anion sorption experiments were conducted to compare the sorption properties of the produced synthetic zeolites with those of the commercially available ones. Zeolitization resulted in an increase of CEC (up to 30 meq/100 g) compared to raw CFA and enhanced the ability of the material to adsorb the chosen ions. The obtained synthetic zeolites showed comparable or greater sorption properties than natural clinoptilolite and synthetic Na–P1. They were also capable of simultaneously removing cationic and anionic compounds. The structural, morphological, and textural properties of the final product indicated that it could potentially be used as an adsorbent for various types of environmental pollutants.

The effect of stone waste on the properties of cemented paste backfill using alkali-activated slag as binder

The decorative stone processing generates a large amount of stone waste, which is associated with several environmental problems. This paper investigated the potential utilization of the stone waste (mainly containing calcite and dolomite) in the alkali-activated slag based paste backfill (APB). The effects of stone waste fineness, solid mix proportion and sodium hydroxide to sodium silicate ratio (SH/SS) on the fresh and hardened APB were experimentally studied at 7- and 28-day curing time. Results showed that ultra-fine portion (<20 μm) of 30%–40% had a more positive effect on the fluidity and mechanical strength of APB. Active calcium from the dissolution of stone waste in high concentration of alkaline solution accelerated the hydration reaction. Besides, increasing of both slag and alkaline solution content enhanced the mechanical strength of APB samples. It was also found that APB with SH/SS of 1 achieved better mechanical performance. These findings will be conducive to the potential application of building stone waste and alkali-activated slag in paste backfill.

Effect of Alkali Seepage Erosion on Physical and Mechanical Properties of Laterite

Using a modified permeameter, laterite samples that were corroded and permeated by alkaline solutions at different concentrations for varying amounts of time were subjected to triaxial compression tests, chemical composition analysis, particle composition tests, and microstructure analysis. The results showed that the strength parameters c, φ, and K of the laterite samples that were corroded by alkaline‐solution permeation were reduced with increasing corrosion time and alkaline‐solution concentration. The alkaline‐solution corrosion had a minor effect on the strength parameters n and Rf. The contents of Al2O3 and Fe2O3 in the laterite fluctuated and decreased with increasing alkaline‐solution concentration and corrosion time. There were no distinct patterns in the relationships between the SiO2 content and the increases in the alkaline‐solution concentration and corrosion time. Due to the corrosion during the alkaline‐solution permeation, the content of clay particles increased with increasing time and concentration of the alkaline solution. After the permeation with the alkaline solution, the soil particles became smaller and were arranged in an ordered state. The analysis suggested that the permeation effect of the alkaline solution changed the chemical composition of the laterite and the connecting strength of the soil particles, resulting in changes in its physical and mechanical properties.

Effects of alkali stress on dry matter accumulation, root morphology, ion balance, free polyamines, and organic acids of sugar beet

Sugar beet is strongly resistant to salt-alkalinity. Understanding the physiological alkali stress resistance mechanism of sugar beet is important for fully utilizing saline–alkaline soil. Sugar beet seedlings from cultivars KWS0143 (alkali-tolerant) and Beta464 (alkali-sensitive) were treated with five concentrations of mixed alkaline solutions (NaHCO3: Na2CO3, 2:1), namely, 0 (control), 25, 50, 75, and 100 mM (mole concentration was calculated in Na+). A sharper decrease in dry weight per plant (87.1%) and total root length (91.7%) of Beta464 were observed compared to the 61.5% and 85.0% decrease in those of KWS0143 under 100 mM alkali treatment. With increasing alkaline stress, Na+ accumulation hindered K+ and Ca2+ absorption by roots. Free polyamines contents and phosphoenolpyruvate carboxylase (PEPC) activity in roots of both cultivars were all significantly enhanced by 50 and 75 mM alkali treatments. KWS0143 exhibited higher dissociated putrescine (Put), spermine (Spm), as well as spermidine (Spd) levels within the roots compared to Beta464 under alkali conditions. Root free Spd contents of KWS0143 and Beta464 increased by 154.2 and 64.5% treated with 50 mM alkali in comparison with the control. After treated with the dose of 25 mM, root succinic acid (SA) contents of KWS0143 and Beta464 increased by 90.4 and 14.3%, respectively, compared to the plants subjected to the control. Our results imply that polyamines and PEPC contribute to the tolerance of sugar beet to alkali stress. Those results could be useful for enriching the theory of plant stress response.

Feasibility study of commercially viable sustainable aerated geopolymeric foam based block

Production of geopolymer material, light-weight materials like Aerated Autoclaved Concrete block, chemically aerated geopolymer material, foamed concrete were developed at high alkaline solution concentration, high temperature and duration for heat curing and pressure which pose a challenge for commercial production. Present study focused on manufacturing sustainable and commercially viable geopolymer aerated block using alkaline foam being need of industry. Present study aims to produce cost effective aerated geopolymer foamed blocks by altering Granulated Blast Furnace Slag and cement content (i.e. 10% to 30% each) with reduced concentration of the Na-based alkaline solution (1–4 M). These Geopolymer Foam blocks were heat cured at 100 °C for 3-hour duration and tested to determine various mechanical properties such as compressive strength, water absorption, shrinkage analysis and durability properties followed by cost analysis of optimized sample. The experiments revealed optimum result (i.e. 4.8 MPa compressive strength) for 60% fly ash, 30% Granulated Blast Furnace Slag, 10% cement with 2 M alkaline solution providing cost efficiency. Analysis of developed Geopolymer Foam block proved that these blocks are cost effective solution compared to conventional clay brock and Aerated Autoclaved Concrete block. Maximum use of generated industrial waste with lower alkaline solution makes it commercially viable and environment friendly product.

The Effect of Zincate Ions in Alkaline Solution on the Electrochemical Behavior and Crystal Structure of Nickel Cathode

IntroductionZn is known as one of the most promising anode candidates for aqueous rechargeable batteries because it is a low cost and an abundance, and shows a comparatively higher hydrogen overpotential. When Zn is used with nickel cathode to construct a rechargeable alkaline Zn/ Zn/NiOOH battery, it shows high specific energy of 55-85 Whkg-1 and excellent specific power of more than 200 Wkg-1 1). However, a rechargeable alkaline Zn/NiOOH battery has not been commercialized yet because dendrite formation and shape change of Zn during charge-discharge cycles shorten the lifetime of a Zn anode, and the ZnO dissolved in a concentrated alkaline solution might affect the charging and discharging behaviors of the NiOOH cathode. Though numerous works have been done to prevent the dendritic formation and shape change of Zn anode during charging and discharging cycles,2) the works on the effect of dissolved Zn on NiOOH electrode of the cathode of Zn/NiOOH battery are relatively small, and the effect is unclear. For example, migration of dissolved Zn to the NiOOH electrode might cause the capacity loss of the cathode and, zinc-additive on Ni(OH)2 increases the cathode potential3,4). In this study, we have investigated the effect of Zn dissolved in a concentrated alkaline solution on redox reaction and crystal structures of NiOOH cathode to obtain an indication for designing the cathode.ExperimentalNi(OH)2 is electrochemically precipitated on a Pt sheet with the constant current density of -1.6 mA cm-2 for 10 min from 0.02 M Ni(NO3)2 aqueous solution at room temperature. Cyclic voltammetry was adopted to study the redox behaviors of the Ni(OH)2/Pt in ZnO saturated or ZnO free 6 M KOH at the scan rate of 1 mV s-1 using a pair of Pt sheets counter electrodes and a 1 M Hg/HgO reference electrode. XRD and ICP and SEM/EDX were used to characterize the nickel oxides sample on a Pt sheet at the charged and the discharged states.Results and DiscussionIn the cyclic voltammograms of Ni(OH)2/Pt in ZnO free 6 M KOH, two oxidation peaks at around 350 mV and 400 mV, which are ascribed to oxidation of Ni(OH)2, were observed during anode sweep and a reduction peak at around 210 mV, which is ascribed to the reduction of NiOOH, was observed during cathode sweep. While the oxidation peak currents at 350 mV gradually decreased with increasing the cycle number and those at 400 mV increased with the cycle numbers, the reduction peaks gradually shifted towards an anodic direction about 40 mV after 20 cycles. In ZnO sat. 6M KOH, on the other hand, only one oxidizing peak and one reduction peak were observed at around 420 mV and 280 mV, respectively. Though the anodic potential sifted 20 mV towards anodic direction after 20 cycles, no significant changes in both potentials and shapes were observed. Degradation in the discharge capacities of NiOOH/Pt during the CV cycles in ZnO sat. KOH was smaller than that in ZnO free KOH. The results indicated that the charge and discharge stability Ni(OH)2/NiOOH was improved by the presence of zincate ions in the electrolyte. The redox peak potentials in ZnO sat. KOH is similar to those of Zn doped Ni(OH)2 4) Regardless of cycle number, the XRD patterns of the nickel oxides on a Pt sheet after CV cycles in ZnO sat. 6M KOH indicated that the peaks for the reduced and the oxidation states are in good agreement with those of Zn substituted α-Ni(OH)2 and γ- NiOOH, respectively 5,6). The distance corresponds to (003) of Zn substituted α-Ni(OH)2 is approximately 8.4 Å. When as prepared Ni(OH)2/Pt was immersing in ZnO sat. 6M KOH for 4 hours at room temperature, the XRD patterns coincide with those of Zn substituted α-Ni(OH)2, while α-Ni(OH)2 is assumed to be preferentially formed.In addition to the above results ICP and EDX measurement indicated that Zn might be incorporated into Ni(OH)2 when it is immersing in ZnO sat. 6 M KOH. Therefore, the formation of Zn substituted α-Ni(OH)2 in ZnO sat. 6 M KOH has a possible advantage on the stabilization of the redox reaction of Ni(OH)2/NiOOH.References(1) W. Taucher et al, Journal of Power Sources, 58, 93 (1996)(2) T. Ishida and K. Katakura, Electrochemistry, 83(10), 864 (2015)(3) W.H. Zhu, Journal of Power Sources, 56,75,(1995)(4) D. A. Corrigan et.al, J. Electrochem. Soc., 136, 723 (1989)(5) C. Tessier et al, Solid State Ionics, 133, 11 (2000)(6) C. Tessier et al, J. Mater. Chem, 10, 1185 (2000)

Recovery of Silicon Dioxide from Waste Foundry Sand and Alkaline Activation of Desilicated Foundry Sand

This study was conducted to recover silica (desilication) as a valuable metalloid from waste foundry sand (WFS) by a leaching process and to find application for desilicated foundry sand (DFS). The leaching time applied was 5 h; 3 M of potassium hydroxide (KOH) was used as a leaching reagent. The agitation speed of 200 rpm and the liquid/solid ratio of 25 were found to be the best conditions for optimum leaching results. A geopolymer from DFS was developed by using NaOH as an alkaline activator. The results obtained showed that the optimum conditions for the synthesis of a geopolymer were 15 M NaOH, 150 µm DFS particle size, and a curing temperature of 80 ℃ for 72 h. The geopolymer strength development was due to the formation of Phillipsite and Kalsilite as new hydration products. At the optimum alkaline solution concentration, the highest unconfined compressive strength (UCS) of 4.8 MPa was achieved. The developed geopolymer met the minimum strength requirements for load bearing material. This study provides an innovative and novel solution for the beneficiation of spent foundry sand and the recovery of a valuable metalloid, resulting to zero waste generation.Graphical

Recycle of Zincates and Aluminum to Fed Zn-Air Fuel Cells

It is well known that the Zn-air battery dept of discharge is mainly governed by the electrochemistry of zinc anode in concentrated alkaline solutions leading to undesired precipitation of insulating zinc oxide at the electrode surface due to progressive increase in zincate concentration. Among the different approaches adopted to overcome this problem, mechanically and electrically rechargeable as well as refuelable systems have been deeply studied for automotive and stationary applications. In a refuelable Zn-air battery, the alkaline aqueous electrolyte is pumped into the cell, either carrying Zn electroactive fuel or flowing through a packed bed of Zn particles. In a previous paper, we adopted a mechanically refuelable tapered-end flow Zn-air fuel cell with Zn micro-spheres, and we studied the effect of electrolyte aging on the behavior of the Zn anode during battery discharge. The results have shown that the cell potential decrease in the battery discharge curve is mainly due to the anodic overpotential increase, as evidenced by means of EIS (Electrochemical Impedance Spectroscopy) measurements. Given that this effect can be attributed to the physicochemical modifications induced by the Zn passivation occurring at higher zincates concentration, the performance of the battery system can be notably improved by a relevant regeneration of spent alkaline zincate bath. Here, we propose a novel method to recover zinc from alkaline zincate baths by using aluminum electrodes. Aluminum metal and zincate ions give place to a single-displacement reaction producing a layer of zinc on the Al surface. The deposits of zinc metal on aluminum foils have been studied by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), and the electrochemical process has been followed by open circuit measurements in order to put the basis of future developments.