Alkali Hydroxide Research Articles

Radio Brightness Contrasts of Aqueous Solutions of Alkali Metal Hydroxides in the Millimeter Spectral Range

Radio Brightness Contrasts of Aqueous Solutions of Alkali Metal Hydroxides in the Millimeter Spectral Range

Au(111) in [Mppip][Tfsi] in Dependence of Water Content: Revealing the Initial Stages of Cathodic Corrosion Using in-Situ STM

Cathodic corrosion was first observed by Fritz Haber at the end of the 19th century,[1] and was nearly forgotten for a long time, but has recently returned as an important research topic.[2,3] The prospects to form nanoparticles of noble metals and to restructure metal surfaces, in particular, stirred researchers’ interest.[4,5] Moreover, cathodic corrosion may hinder other processes such as metal deposition that occur at highly negative potentials. As ionic liquids have desirable properties of being stable over a relatively wide potential window coupled with low ion mobility, these electrolytes are often used for studies of processes at very low electrode potentials, for example, the deposition of metals with low reduction potentials such as lithium or sodium.[6,7] Unfortunately, if an electrode is cathodically corroded at potentials positive of the onset of metal deposition, this is of little use. Therefore, it is crucial to understand and thus prevent the initial stages of cathodic corrosion in such systems. In-situ scanning tunneling microscopy (STM) was used to study cathodic corrosion of a Au(111) surface in the hydrophobic ionic liquid N-methyl-N-propylpiperidinium bis(trifluoromethanesulfonyl)imide ([MPPip][TFSI]) with various water contents. It has been observed that the onset potential of cathodic corrosion is highly dependent on the presence and the amount of water. This notable role of water has been found already for cathodic corrosion of Au in aqueous methanolic alkali metal hydroxide electrolytes:[8] the higher the water content, the more positive the onset potential. Cathodic corrosion of Au(111) begins at the so-called elbows of the herringbone reconstruction, which can lead to a characteristic pattern of equidistant holes. In hydrophilic ionic liquids, a similar process has already been observed.[9] In contrast, for the hydrophobic ionic liquid [MPPip][TFSI], the pits did not merge with time, instead, the number of pits slowly increased. Furthermore, the number of pits formed during this process was observed to increase with the increase of water content. Further studies are planned to elucidate the dependence of preparation procedure, as well as experimental constituents and contaminants on the cathodic corrosion of Au(111) in the ionic liquid [MPPip][TFSI]. Such studies can help to understand if cathodic corrosion can be induced by the ionic liquid itself or only by contaminants such as water. It is known that adsorbed hydrogen plays a major role in the process[3] and it has been reported that in the absence of water cathodic corrosion is not taking place.[10] On the other hand, other studies proposed that the presence of water is not obligatory if hydrogen can be formed in another way than water reduction, for example by reduction of the IL cation.[11] References [1] F. Haber, Zeitschrift für Anorg. Chemie 1898, 16, 438–449.[2] Y. I. Yanson, A. I. Yanson, Low Temp. Phys. 2013, 39, 304–311.[3] T. J. P. Hersbach, M. T. M. Koper, Curr. Opin. Electrochem. 2021, 26, 100653.[4] T. J. P. Hersbach, V. A. Mints, F. Calle-Vallejo, A. I. Yanson, M. T. M. Koper, Faraday Discuss. 2016, 193, 207–222.[5] M. M. Elnagar, J. M. Hermann, T. Jacob, L. A. Kibler, Electrochim. Acta 2021, 372, 137867.[6] C. A. Berger, M. U. Ceblin, T. Jacob, ChemElectroChem 2017, 4, 261–265.[7] R. Wibowo, L. Aldous, E. I. Rogers, S. E. Ward Jones, R. G. Compton, J. Phys. Chem. C 2010, 114, 3618–3626.[8] M. M. Elnagar, T. Jacob, L. A. Kibler, Electrochem. Sci. Adv. 2021, accepted.[9] A. V. Rudnev, M. R. Ehrenburg, E. B. Molodkina, A. Abdelrahman, M. Arenz, P. Broekmann, T. Jacob, ChemElectroChem 2020, 7, 501–508.[10] M. M. Elnagar, J. M. Hermann, T. Jacob, L. A. Kibler, ECS Meet. Abstr. 2020, MA2020-01, 1011–1011.[11] F. Lu, X. Ji, Y. Yang, W. Deng, C. E. Banks, RSC Adv. 2013, 3, 18791. Figure 1

Effect of alkali and sulfate on early hydration of Portland cements at high water to cement ratio

In this work, the hydration kinetics and the development of concentrations in the pore solution of cement clinker, neat and composite cements pastes were investigated.Early alite hydration is mainly limited by the nucleation and growth of the hydrates (C-S-H, CH, ettringite). Only after 4 to 10 h, when the main alite reaction starts, the dissolution rate of the alite becomes the limiting factor. The kinetics of the reaction of C3A with anhydrite is initially limited by the slow nucleation and formation of ettringite and only later by the dissolution rate of calcium aluminate phase. The change of the mechanisms corresponds to the initiation of the portlandite precipitation. The slower reaction of clinker sample cannot be explained by the high Al concentration alone but rather by the effect of available sulfate; high sulfate concentrations accelerate the hydration. Higher alkali hydroxide concentration does not show an accelerating effect on PC hydration.

Waste-derived glass as a precursor for inorganic polymers: From foams to photocatalytic destructors for dye removal

Synthetic alumino-silicate glasses may yield inorganic polymers, through activation with alkali hydroxide solutions. In this framework, we formulated a glass prepared by the melting of red mud from bauxite refinement, combined with coal combustion fly ash, discarded pharmaceutical glass and a minor addition of sodium carbonate. The activation with 6 M NaOH aqueous solution allowed for the manufacturing of highly porous foams, by gas generation at the early stages of gelation. These foams featured an extensive formation of zeolite at cell walls which, combined with the presence of magnetite formed upon cooling of the melt, favoured the application of the foams as sorbents for dye removal from contaminated water. The powders prepared by crushing the highly porous foams showed an excellent water purification ability documented by efficient removal of methylene blue used as a model contaminant. The specific iron oxide polymorph facilitated both magnetic recovery of dispersed powders and photocatalytic destruction of the dye under UV irradiation.

Enhanced removal of COS from blast furnace gas via catalytic hydrolysis over Al2O3-based catalysts: Insight into the role of alkali metal hydroxide

As blast furnace gas (BFG) can cause air pollution, it is an effective route to convert BFG into a kind of energy. However, it is important to remove carbonyl sulfide (COS) from BFG before burning it. This can be done with catalytic hydrolysis which is considered as a high-efficient technology. In this work, a series of catalysts are prepared via impregnation method to remove COS, in which aluminum oxide (Al2O3) and alkali metal hydroxide (MOH, M = Li, Na and K) are used as base and active component, respectively. Compared with other prepared catalysts, Al2O3 modified with 10% KOH has better catalytic performance in removing COS. The characterization results imply that alkali metal plays a significant role in the enhancement of COS removal efficiency. The capacity of catalysts to adsorb COS is significantly improved with the modification of alkali metal. Moreover, few carbonate or bicarbonate species can be found on the surface of the catalyst during COS hydrolysis. Furthermore, the catalytic mechanism and degradation route of COS hydrolysis on Al2O3 modified with 10% KOH are explored.

Effect of different alkali metal cations on the oxygen evolution activity and battery capacity of nickel electrodes in concentrated hydroxide electrolytes

The effect of different alkali metal cations on the oxygen evolution activity and battery capacity of nickel electrodes has recently been studied in low concentration alkali hydroxide electrolytes. As high concentration hydroxide electrolytes are favored in applications due to their high conductivity, we investigate if the cation effects observed in low concentration electrolytes translate to more industrially relevant conditions for both alkaline water electrolysis and nickel iron batteries. We investigate the alkali metal cation effect on the electrochemical properties of nickel electrodes in highly concentrated hydroxide electrolytes by adding Li+, Na+, Cs+ and Rb+ cations to a 6.5 M KOH electrolyte, while keeping the hydroxide concentration constant. For OER we find a trend in activity similar to that at low concentrations Rb+>Cs+>K+>Na+>Li+, where especially larger additions of Rb+ and Cs+ (1 M or 0.5 M) cause a significant decrease in OER potential. Smaller cations interact with the layered hydroxide structures in NiOOH to stabilize the α/γ phases and increase the potential for OER. The intercalation of small cations also causes an increase in battery electrode capacity because of the higher average valence of the Ni(OH)2/NiOOH α/γ pair. Small concentrations of Li+ added to a concentrated KOH electrolyte can therefore be beneficial for the nickel electrode battery functionality and for an integrated battery and electrolyser system, where it increases the battery capacity without a significant increase in OER onset potential.

Alkali-Free Hydrothermally Reconstructed NiAl Layered Double Hydroxides for Catalytic Transesterification

NiAl layered double hydroxides (LDHs) are promising bifunctional catalysts comprising tunable redox and Lewis acidic sites. However, most studies of NiAl LDH employ alkali hydroxide carbonate precipitants which may contaminate the final LDH catalyst and leach into reaction media. Here, we report an alkali-free route to prepare NixAl LDHs with a composition range x = 1.7 to 4.1 using (NH4)2CO3 and NH4OH as precipitants. Activation of LDHs by calcination–rehydration protocols reveal NixAl LDHs can be reconstructed under mild hydrothermal treatment (110 °C for 12 h), with the degree of reconstruction increasing with Ni content. Catalyst activity for tributyrin transesterification with methanol was found to increase with Ni content and corresponding base site loadings; TOFs also increased, suggesting that base sites in the reconstructed LDH are more effective for transesterification. Hydrothermally reconstructed Ni4.1Al LDH was active for the transesterification of C4–C12 triglycerides with methanol and was stable towards leaching during transesterification.

Assessment of alkali-induced heave in soil and its stabilisation using slag

Soil–alkali-interaction results in unexpected heaving and other negative effects of soil properties, which can lead to complete failure of structures. An investigation was carried out on the impact of highly concentrated sodium hydroxide alkali on the heaving behaviour of low-plasticity clay. The effect of ground-granulated blast-furnace slag as a stabiliser for alkali-interacted soil was also investigated. The interaction of alkali with the soil showed heaving up to 5.25% after 30 days, while a slag content of 20% showed maximum suppression of heave. The alkali-interacted soil stabilised with slag was also compared with un-interacted soil mixed with slag. There was a marginal increase in friction angle with an increase in curing period, and a significant increase in cohesion for both. A substantial improvement in unconfined compressive strength was also evident with increased slag content and curing period. The results were supported by microstructural examinations. The application of slag as a liquid-based stabiliser for alkali-interacted soil was also conducted using electrokinetics. Statistical analysis indicated that the curing period was a dominant parameter in affecting the compressive strength of un-interacted soil while, for alkali-interacted soil, slag content was more dominant.

Residual properties of alkali-activated slag concrete exposed to elevated temperatures

PurposeThis paper attempted to study the alkali-activated (AA) binder consisting of 94% of ground granulated blast furnace slag (GGBFS) and 6% of blended powder of alkali metal hydroxide and metal sulfate, which acted as an activator.Design/methodology/approachSeveral concrete specimens (cubes, cylinders and prisms), which were casted using AA binders, were further tested for mechanical properties after exposure to elevated temperatures of 200 °C, 400 °C, 600 °C and 800 °C. Additionally, to understand the structural behavior in uniaxial compressive load, reinforced concrete short columns were cast, cured and tested at ambient temperature as well as after exposure to 300 °C, 600 °C and 900 °C, to know the residual strength after exposure to elevated temperature.FindingsThe findings for the residual strength of alkali-activated slag binder concrete (AASBC) indicated a substantial agreement with the results obtained for the residual strength of Portland slag cement (PSC) concrete, thereby showing the effectiveness of binder when used as a replacement of cement.Originality/valueThe study clearly indicates that the binder developed is an effective approach for the 100% replacement of cement in the concrete.

Role of Noncovalent Interactions on the Electrocatalytic Oxidation of Ethanol in Alkali Metal Hydroxide Solutions

Ethanol is considered to be one of the most promising fuels for fuel cells. However, ethanol fuel cells have a sluggish Faraday efficiency due to complex interactions between the electrolyte, electrode, and ethanol. Recent studies have further suggested that noncovalent interactions originated from the hydrated alkali metal cations and the adsorbed OHad at the Pt electrode surface also played an important role in the electron transfer. In this regard, the noncovalent interactions in different alkali metal hydroxide (AMH) solutions have been systematically investigated in this study, and it was observed that the noncovalent interactions could result in the occupation of the Pt electrode surface active sites and sluggish migration of ethanol molecules in the electrical double layer, significantly affecting the electro-oxidation efficiency. Further, it was concluded that the electro-oxidation efficiency in different AMH solutions followed the order of K+ > Na+ > Rb+ > Cs+ > Li+ due to the noncovalent interactions.

Quantitative Effects of Mixture Parameters on Alkali-Activated Binder-Based Ultra-High Strength Concrete at Ambient and Elevated Temperatures

This work investigates the effects of mixture parameters on the slump flow and compressive strength of a new type of alkali-activated binder-based ultra-high strength concrete (AAB-UHSC) before and after exposure to high temperatures. The innovative UHSC adopts a combination of sodium silicate (SS) and potassium carbonate (PC) as the activator. Compared with the alkali hydroxide that is currently used in existing AAB-UHSC, alkali carbonate salts are environmental- and user-friendly and cost-effective. Four mixture proportioning parameters, including water/precursor ratio, activator/precursor ratio, silica fume (SF) replacement percentage, and SS/PC ratio, are evaluated regarding their quantitative effects on fresh and hardened properties of AAB-UHSC using Taguchi method. The analysis of variance (ANOVA) reveals that the activator/precursor ratio is the decisive parameter controlling the slump flow diameter of fresh AAB-UHSC, whereas all four parameters have considerable influence on compressive strength of AAB-UHSC at room temperature. Although increasing the activator/precursor ratio increases compressive strength of AAB-UHSC at room temperature, it is adverse for residual strength of AAB-UHSC after exposure to high temperatures. Based on the test results and ANOVA, a mixture proportioning method of AAB-UHSC, which is lacking in existing literatures, is proposed and experimentally validated.

ALKALI-SILICA REACTIVITY OF SOME GRANITIC ROCKS IN KUMASI, GHANA: IMPLICATIONS FOR USE OF ROCK AGGREGATES FOR CONSTRUCTION

This paper seeks to assess the potential of Alkali-Silica Reaction on some granitic rocks in Kumasi in Ghana. Alkali-Silica reactions occur over time between alkaline cement paste and silica contained in rock aggregates as a result of the swelling due to the reaction of certain constituents in the rock aggregates with alkali hydroxides. Alkali-Silica reactions become potentially harmful when they cause significant expansion. Aggregates used for this research were sought from three different quarries, namely, Consar Stone Quarry in Barekese, Nnagot Quarry in Kona and Modern Granite Quarry in Buoho. To achieve the objectives of this project, two test methods were employed such as Accelerated Mortar Bar test (ASTM C1260) and Petrographic analysis. Presence of strained quartz is an indicator for the occurrence of Alkali-Silica Reaction. Samples from Kona contained quite an appreciable amount of strained quartz and exhibited an expansion above the ASTM C 1260 specification, implying that it is potentially reactive and thus not useful for construction works, whilst samples from Barekese, and Buoho were innocuous and may be used for construction works. Supplementary cementing materials such as pozzolans (which are readily available) can be added to concrete mixtures with aggregates from Kona to reduce the harsh effects of ASR.

Hetero-bimetallic alkali titanosilicates [MOTi{OSi(OtBu)3}3]2 (M = Li-Cs) with terminal Ti-O- groups.

The molecular titanosilicate [(tBuO3)3SiO]3TiNEt2 (1) was obtained from the reaction between silanol (tBuO3)3SiOH and titanium amide Ti(NEt2)4. The reaction of 1 with alkali metal hydroxides MOH (M = Li, Na, K, Rb, Cs) offers a straightforward route to the alkaline salts of titanosilicates [MOTi{OSi(OtBu)3}3]2 with a terminal Ti-O- moiety. All compounds were characterised by single-crystal X-ray diffraction studies. Hirshfeld atom refinement and QTAIM analysis of the electron density in 1 and in the Rb salt 5 revealed the D-A nature of the Ti-O and Ti-N bonds and the presence of agostic C-H⋯Rb interactions.

Supercooled Sugar Alcohols Stabilized by Alkali Hydroxides for Long-Term Room-Temperature Phase Change Solar-Thermal Energy Storage

Supercooled Sugar Alcohols Stabilized by Alkali Hydroxides for Long-Term Room-Temperature Phase Change Solar-Thermal Energy Storage

Cathodic corrosion of Au in aqueous methanolic alkali metal hydroxide electrolytes: Notable role of water

AbstractCathodic corrosion is an electrochemical process that induces restructuring, roughening, and etching of metal surfaces at a highly negative surface charge density, yet, details of the reaction mechanism are not fully resolved. An in‐depth fundamental understanding of the processes and parameters underlying cathodic corrosion is crucial for tailoring the surface structure of the metal electrodes and for synthesizing shape‐ and size‐controlled nanoparticles. Here, we investigate the relevance of water and hydrogen evolution in the cathodic corrosion process. To achieve this aim, Au electrodes were polarized at ‐1.6 V versus RHE in KOH and NaOH electrolytes prepared using different water + methanol mixtures. Structural changes of the Au surfaces were studied by cyclic voltammetry and monitored by scanning electron microscopy (SEM). Most importantly, cathodic corrosion does not take place in the absence of water. There is no detectable bubble formation due to the hydrogen evolution reaction on Au in purely methanolic alkali. Furthermore, the electrochemically active surface area, facet distribution, and surface morphology of Au electrodes are significantly altered upon cathodic polarization as a function of the water concentration. Cathodic corrosion features become more and more pronounced with a further increase in water content. In addition, substantial differences in the surface structure of Au are observed as a function of the nature and concentration of alkali metal cations. Overall, this study provides a more detailed understanding of the role of water and the hydrogen evolution reaction in dominating cathodic corrosion, which might advance the understanding of this phenomenon.

Gelatin-Tannin-Based Greener Binder Technology for Stone Shot and Stone Wool Materials: A Detailed Study.

The detailed study presented herein of gelatins modified with tannins as greener binder systems for stone wool and related materials has unveiled a versatile technology that offers a wide range of possibilities for tailor-making properties toward various application areas. Thus, high unaged and aged mechanical strengths in combination with low water solubilities may generally be obtained from the use of gelatins with higher gel strength (and hence, generally, higher molecular weights), low-to-mid range tannin addition levels (3–20%), alkali metal hydroxides for pH adjustment, and final pH in the range 8–9. Comparatively low water uptake properties may be obtained using higher gel strength type A gelatins, lower tannin addition levels, alkali metal hydroxides for pH adjustment, and lower final pH. Even lower water uptake properties may then be obtained using Ca(OH)2 in place of alkali metal hydroxides. If desired, higher water uptakes may be obtained using type B gelatins (or lower gel strength gelatins in general), higher tannin addition levels, and higher final pH. Mechanistic studies indicated that the optimal modification of gelatin with the tannin component occurs via several pathways.

Reactions of Neptunium(V) in Alkali-Metal Hydroxides.

The preparation of two new neptunium hydroxide compounds synthesized in concentrated potassium and rubidium hydroxide is reported. The phases K4[(NpO2)2(OH)6]·4H2O and Rb4[(NpO2)4(OH)8]·2H2O were prepared and their chemical structures determined using single-crystal X-ray diffraction. Raman spectra of the compounds are also presented. The newly synthesized phases are structurally related to Np2O5 and Na[NpO2(OH)2]. The potassium-containing phase reported here consists of infinite chains of edge-sharing neptunium hydroxide polyhedra but lacking the cation-cation interactions (CCIs) observed in Np2O5 and Na[NpO2(OH)2]. Rb4[(NpO2)4(OH)8]·2H2O is a an expanded three-dimensional framework based on NpO2+ CCIs like those observed in Np2O5 and Na[NpO2(OH)2]. Together these complexes begin to develop a structural series of neptunium(V) oxides and hydroxides of varying dimensionalities within the alkali-metal series. The potential roles of the alkali-metal cations and neptunyl(V) CCIs in directing the resulting structures are discussed.

Novel and Polynuclear K- and Na-Based Superalkali Hydroxides as Superbases Better Than Li-Related Species and Their Enhanced Properties: An Ab Initio Exploration.

Hydroxides of superalkalis (particularly, K- and Na-related species) are shown for the first time to function as superbases. A new small series of hydroxides (XMn+1OH) is designed based on superalkali species (XMn+1) where M (K and Na) is alkali metal atoms, n is the maximal formal valence of the central atom X (F, O, and N), and n ≥ 1. To probe whether such fascinating polynuclear superalkali hydroxides (SAHs), especially the K- and Na-associated moieties are as basic as the representative alkali metal hydroxides (KOH, NaOH, and LiOH) as well as similar Li-based SAHs, a comprehensive computational exploration (in the gas phase) has been reported using the framework of an ab initio method. The ab initio calculations reveal that both the K- and Na-related SAHs consisting of larger gas-phase proton affinity (PA) and gas-phase basicity (GB) values demonstrate stronger basic character compared to the LiOH and Li-based SAHs. However, the available SAHs act as strong bases as well as superbases; among the proposed K- and Na-based SAHs, remarkably, the OK3OH moiety having the highest PA (1168.4 kJ/mol) and GB (1146.9 kJ/mol) values shows the evidence of the strongest basicity (i.e., superbase/hyperbase), which exceed enough (ΔPA: 142.1 kJ/mol and ΔGB: 146.9 kJ/mol) the IUPAC-defined superbasicity threshold values (PA: 1026.3 kJ/mol and GB: 1000 kJ/mol) of 1,8-bis(dimethylamino)naphthalene (DMAN). Furthermore, theoretical signatures have been predicted via the electronic structure calculation approach in probing the dissociation energy, ionization potential, electron affinity, HOMO–LUMO gap, and chemical hardness as well as the NCI plot and QTAIM tools are used for the bonding feature analysis and such parameters are well linked with the basicity analyzing parameters. In this study, the ab initio-based computational experiments provide some new insights into the basicity features and understanding of the structural and electronic features of a small series of designed K- and Na-related SAHs. Design and synthesis of such theoretically examined SAHs may pave alternative routes for the experimentally rewarding applications.

Alkali Metal Dithiocarbamato Carboxylates (DTCCs) – Synthesis, Properties, and Crystal Structures

AbstractA series of alkali metal salts of dithiocarbamate‐substituted carboxylate (DTCC) anions were prepared by reaction of the parent amino acids with carbon disulfide and an alkali metal hydroxide. The target compounds, which were isolated in anhydrous form or as hydrates, were extensively characterized by elemental analyses, IR and NMR spectroscopy, thermal analyses, cyclic voltammetry, and single‐crystal X‐ray diffraction. The isolated compounds are more or less hygroscopic and display a varying dehydratization and decomposition behavior upon heating. The assumed degradation of the DTCC scaffold was found to depend on the substitution pattern as well as on the alkali metal counterion, and covers a range between 200 and 340 °C. In aqueous solution, the DTCC anions show irreversible electrochemical oxidations, where the corresponding redox potentials are governed by the substitution pattern of the nitrogen atom. Single‐crystal structural analyses of sodium and potassium derivatives revealed that these compounds exist as two‐ or three‐dimensional coordination polymers in the solid state, with the alkali‐metal ions adopting typical irregular coordination environments with coordination numbers of six or higher.

Pyrolysis of water buffalo manure: Influence of temperature and alkali hydroxide additives on the quality of bio-oil

In this study, the influence of catalytic and non-catalytic pyrolysis of the water buffalo manure on the physical-chemical characterizations, pyrolysis product yield and chemical composition of bio-oil was studied. The first part of the experiments was performed in a reactor with a diameter of 24 mm and height of 36 cm, running with varying temperature from 350 °C to 550 °C. The highest yield of bio-oil was found 27.6 wt% at 450 °C. After optimum temperature was determined, effects of alkali hydroxides catalysts were investigated. Under the influence of NaOH and KOH used as alkali hydroxide, a reduction in liquid product yield was recorded, while an increase was observed on char and gas yield. The obtained results from elemental analysis depicted that the H/C ratios increased while O/C ratios decreased under the influence of alkali hydroxides catalysts. 1H NMR analysis results showed that aliphatic OH groups constitute the majority of pyrolysis bio-oil. The chemical characterization of bio-oil was conducted by gas chromatography-mass spectrometry (GC-MS). Alkali hydroxides catalysts had important effect on the chemical content, especially hydrocarbons and carboxylic acids. When the catalysts applied, the percent of hydrocarbons increased, on the other hand the percent of carboxylic acids decreased. This research study revealed the potential of bio-oil obtained from water buffalo pyrolysis can be used as a renewable energy source.