Free Hydroxide Research Articles

Direct growth of Mn(OH)2/Co(OH)2 nanocomposite on carbon cloth for flexible supercapacitor electrodes

The present work reports, direct growth of binary metal hydroxide ((Mn(OH)2)/(Co(OH)2)) nanocomposite on flexible carbon cloth substrate by a simple and affordable chemical bath deposition method. The as-prepared binder free binary metal hydroxide nanocomposite electrode exhibits a specific capacitance as high as 385 F g−1, in the symmetric two-electrode configuration in a stable potential window ranging from 0V to 1V. At a specific power of 1 kW kg −1, the supercapacitor gives a specific energy of 27 W h kg −1. The device exhibits a cycling stability of 96% even after 6000 cycles of charge-discharge at a current density of 2 A g−1. The structural and morphological analyses of the electrodes after the stability measurements, further confirm the superior electrochemical stability of the binary nanocomposite electrode. The results demonstrate the potential of Mn(OH)2/Co(OH)2 nanocomposite for energy storage applications.

MASS TRANSFER PROCESSES DURING CORROSION OF CEMENT CONCRETE OF ROAD PAVEMENT AND AIRFIELD COVERINGS MODELING

Varieties of corrosion processes under the action of various corrosive environments on the cement concretes for pavement and airfield coatings within the classification by V.M. Moskvin are considered and their distinctive features are described. It is noted in the work that the rate of destruction of cement concretes is determined by the processes of mass transfer and chemical reactions. On this basis, we provide the substantiation of a generalized methodological approach to modeling the processes of mass transfer during liquid corrosion of building materials. For corrosion types I and II, analytical solutions are obtained for specific initial and boundary conditions of the problem.
 Development of mathematical models of concrete corrosion processes is based on the physical models of diffusion of components that are imbedded in the porous structure of concrete and the mathematical apparatus of boundary problems of mass transfer using differential equations in partial derivatives of parabolic type. The works, to which the authors refer, provide the results of the development of mathematical models of the processes of corrosion of concrete of the first type, as well as the results of the practical application of these mathematical models. However, the results obtained cannot withstand scrutiny in terms of methods and approaches of classical mathematical physics.
 In this study, these errors, inaccuracies, inconsistencies and incorrectness of the abovementioned works are eliminated. At the same time, models of corrosion of concretes of the first and second types are taken into account. An undoubtedly positive aspect of the dependences obtained in the study is the possibility of solving the inverse problem, when the actual experimental data using this model make it possible to predict the numerical values of free calcium hydroxide, which, as a result, with a minimum error allows to predict the long-term durability of structures and buildings.

The influence of carboxylated styrene butadiene rubber coating on the mechanical performance of vegetable fibers and on their interface with a cement matrix

Carboxylated styrene butadiene rubber (XSBR) coating was applied on several vegetable fibers and its effect on physical–chemical and mechanical performance were evaluated. Curauá, jute and sisal fibers were used in this study. The influence of coating treatment was evaluated by water absorption capacity test, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and thermogravimetry (TGA). Pullout tests were performed in order to evaluate the fiber–matrix bonding. Fiber embedment lengths of 25 mm was used. A free calcium hydroxide cement mortar was used as matrix. Furthermore, direct tensile tests were performed in the treated and virgin natural fibers. The treatment creates a polymer layer surrounding the fiber, reducing the water absorption capability. The results indicate an increase of the tensile strength of all studied fibers. The interaction between the polymer and natural fibers may be ruled by the cellulose amount of fibers and their crystallinity. An increase in maximum load was observed during fiber pullout, as a consequence of the increase of chemical bonding between treated fibers and the cementitious matrix.

Electrical resistivity and piezoresistivity of cement mortar containing ground granulated blast furnace slag

Ground granulated blast furnace slag (GGBFS) is a popular used supplementary cementitious material which can increase the resistivity of cement-based composites, contribute to the cement hydration, and dense the composite structure. The piezoresistivity of cement mortar containing GGBFS was studied in this paper. Three GGBFS/cement ratio, 1.2, 1.5, and 1.8, were designed to study the effect of GGBFS content on the piezoresistivity behaviour of cement mortar. Samples were measured before and after drying treatment, and three water/binder ratios were designed to study the influence of water content on the electrical properties. Furthermore, mechanical properties and microscopy analysis were conducted. Results showed that compared to pure cement mortar, samples containing GGBFS showed an improvement in piezoresistivity behaviour. Sample with GGBFS/cement ratio at 1.2 performed the largest fractional change in resistivity of 5.57, 9.23 and 16.73 with water/binder ratio at 0.3, 0.4 and 0.5, respectively, as the concentration of pore solution was higher for samples with GGBFS/cement ratio at 1.2 compared to pure cement mortar. However, with the increasing GGBFS/cement ratio, the piezoresistivity performance was adversely affected due to the reduced pore solution concentration and conductivity caused by the increasing assumption of free calcium hydroxide. Through the investigation, piezoresistivity performance of the cement-based composite was found to be related to the mobile ions transportation with the pore solution.

The effect of added finely dispersed calcite on the corrosion resistance of cement compositions

Many types of the corrosion of Portland cement stone immersed into inorganic liquid media are conditioned by chemical exchange reactions between the substances dissolved in them and cement hydration products. To prevent the corrosion formation in corrosive media it is necessary to form cement clinker hydration products that do not enter into ion exchange reactions in the solutions. The concrete structure defines the penetration rate of corrosive ions and that of the removal of corrosion products, in other words the behavior of corrosive processes. The investigations that were carried out showed that the presence of finely dispersed organogenic calcite (chalk) in the cement stone composition results in a change of the phase composition of the hydrates of new formations, i.e. it results in a decreased content of the free calcium hydroxide and the binding of aluminate phases to form stable hydration products. The use of this additive contributes also to the compaction of the microstructure of cement stone due to the occupation by additive grains of the vacancies in the gaps between the cement grains and due to an increased dispersion of hydration products for which calcite particles serve as crystallization centers. All these factors contribute to an increased corrosion resistance of the cement stone and the concrete exposed to the action of corrosive solutions.

Investigation of Biostability of Concrete Constructions for Special Purpose

Concrete of used sewers is exposed to various aggressive environments. While making concrete pipes for special purposes, special attention is paid to reducing the permeability of the surface layer of concrete. It is possible to increase the operational characteristics of concrete by introducing into the cement system the active components chemically interacting with the cement minerals. When the complex modifier interacts with cement particles, the structure and properties of the modifier undergo qualitative changes. The article presents the results of researching the porosity of the modified cement matrix. It has been established that in the neoplasms of the modified cement matrix of concrete, the quantity of free calcium hydroxide does not exceed 5% that is a necessary condition for getting a corrosion-resistant material. As a result of the analysis of modern technologies, it has been established that physical modification is possible by removing excess mixing water that increases the use of the potential qualities of cement in order to increase the density, impermeability and strength of concrete in the process of compaction of the mixture.

Effect of Carbonate Anions on Quaternary Ammonium-Hydroxide Interaction

Currently, there are two main challenges in state-of-the-art anion-exchange membrane fuel cells (AEMFCs)—first, cation degradation in the presence of hydroxide anions; second, carbonation process during AEMFC operation. Both degradation and carbonation processes lead to a significant decrease in the ionic conductivity of the anion exchange membranes (AEMs), and, in turn, in the AEMFC performance. In this work, we use molecular dynamics simulations to bring first insights into the contributing factors that lead to changes in the degradation of quaternary ammonium cations due to the presence of carbonate anions. Focusing on low hydration levels, we explore the behavior of benzyltrimethylammonium cation (BTMA+) in the presence of a mixture of hydroxide and carbonate anions at different water:cation ratios. Water is shown to have a stronger affinity toward carbonate than hydroxide. Thus, the introduction of carbonate anions effectively lowers the concentration of free hydroxide anions and thereby decreases the conductivity of the AEM. Lower hydration of the hydroxide anion, in turn, leads to higher coordination of hydroxide compared with carbonate around BTMA+, hence increasing the probability of degradation of the cation. Nonetheless, carbonate competes with hydroxide in its interaction with cation, leading to approximately 20% reduction in hydroxide coordination around the BTMA+ when carbonate is present. We examine in detail these two competing factors—steric shielding of BTMA+ by carbonate and effectively lower hydration of the hydroxide—which are critical for understanding the effect of carbonate on the stability of quaternary ammonium cations.

Durability properties of alkali pozzolan cement (APC)

This paper compares the durability properties of alkali pozzolan cement (APC) with high volume fly ash (HVFA) cement and ordinary Portland cement (OPC). The susceptibility to durability issues was investigated through the water absorption test using 28-day-old samples. Durability against chemical attacks was investigated through sulphuric acid attack, chloride ion penetration and carbonation tests on 1-year-old samples. The results indicated that APC occupies a median position in relation to OPC and HVFA, having greater resistance than HVFA for water absorption and carbonation, and greater resistance than OPC for sulphuric acid attack and chloride ion penetration. Chemical and microstructural reasons for the above behaviours are presented. A key index of durability performance is the free calcium hydroxide available and/or generated during cement hydration and durability exposure.

Effect of Water-Binder Ratio and Complex Organic-Mineral Additive on Properties of Concrete for Marine Hydrotechnical Constructions

Large-scale construction of marine structures in the coastal and offshore areas of Vietnam requires the development of new compositions of hydrotechnical concrete and innovative technologies for the preparation of concrete mixes, as well as their transportation to the place of placement. A preliminary composition of heavy concrete was determined and its properties were studied. The effect of the water-binder ratio (W/B) and the effect of using the developed complex organo-mineral modifying additive consisting of fly ash (FA) of Vung Ang TPP, microsilica SF-90 (SF90) and polycarboxylate superplasticizer SR 5000F (SP) on the concrete properties. To process the obtained results, the method of mathematical planning of the experiment with the construction of a four-factor plan was used. As a result of the studies conducted, first-order regression equations were obtained depending on the objective functions - the mobility of the concrete mixture on the cone sediment, the compressive strength of concrete and the deformations of concrete on input factors - x1 (W/B), x2 (amount of SP), x3 (amount of FA) and x4 (amount of SF90). From the obtained regression equations, it follows that the water-binder ratio, as well as the content of superplasticizer, fly ash and microsilica in the composition of the additive have a significant impact on the mobility of concrete mixtures. When reducing W/B and the amount of FA, as well as the increase in the amount of SF90 (x4) concrete compressive strength in 28 days also increases. The result of this study showed the relative deformation of concrete also increases with an increase in the content of FA and reducing W/B and the amount of SF90. At the same time, the effect of the water-binder relationship is most pronounced. It can be assumed that, in the composition of the developed modifying additive, the particles FA and SF90 played the role of a kind of “sliding bearings” between the grains of cement, with which you can control the dispersion of cement and finely dispersed mineral grains in the concrete mixture, and hence its mobility and persistence construction sites in the coastal areas of Vietnam. In addition, SF90, containing 91.65% of amorphous silica, binds free calcium hydroxide to less soluble low-basic calcium silicate silicates, compresses the structure of concrete and increases its compressive strength.

Structure of road soil cement compositions modified by complex additive based on organosilicon compounds and electrolytes

The complex introduction of organosilicon compound (octyltriethoxysilane) and electrolyte (sodium hydroxide) maximizes the frost resistance and strength of soil cement. However, the effect of complex additive based on octyltriethoxysilane and sodium hydroxide on the soil cement structure has not been sufficiently studied. Therefore, the aim of this work was to study the phase composition of hydrated newgrowths and soil minerals in soil cement with optimal content of complex additives. The study was conducted by methods of complex thermal analysis, X-ray powder diffraction and electron microscopy. On the XRD pattern of the sample with and without complex additive, we marked identical peaks of soil minerals, unhydrated cement clinker minerals and hydrated newgrowths. In the result of differential thermal analysis, we determined that soil cement with complex additive is characterized by the smaller amount of free calcium hydroxide formed, as well as saturation of the soil complex with sodium ions. In the soil cement sample with complex additive, we observe a smaller amount of coagulated soil aggregates in comparison with the sample without an additive. Complex additive contributes to the formation of a more dense and uniform structure of soil cement, reduces the amount of adsorption water associated with clay minerals, reduces the formation of free calcium hydroxide, which increases the physicomechanical properties of the resulting material.

СОДЕРЖАНИЕ РЕДКОЗЕМЕЛЬНЫХ ЭЛЕМЕНТОВ В ПОДЗЕМНЫХ ВОДАХ ВЕРХНЕЮРСКИХ ОТЛОЖЕНИЙ ВЕРХ-ТАРСКОГО НЕФТЯНОГО МЕСТОРОЖДЕНИЯ (ЗАПАДНАЯ СИБИРЬ)

The results of the analysis of rare earth elements distribution in groundwater of J1 reservoir of the Verkh-Tarka oil field are reported for the first time. It was established that groundwater with Cl Na composition are predominate, with a value of total mineralization from 24.7 up to 48.9 g/dm3. The content of REE ranges from 3.72 to 30.49 µg/dm3 with an average of 13.61 µg/dm3. The highest concentrations are observed (µg/dm3) in La (up to 20.8), Eu (up to 7.9), Gd (up to 1.8) and Dy (up to 0.65). The level of dissolved REE is determined by their distribution in the water-bearing sandstones. Migration of rare-earth elements is carried out in the form of free ions and hydroxide complexes.

Superionic conduction along ordered hydroxyl networks in molecular-thin nanosheets

Single-layer LDH nanosheets serve as a free hydroxide ion donor and 2D hopping lane for superionic conduction.

Physical and mathematical modelling of the mass transfer process in heterogeneous systems under corrosion destruction of reinforced concrete structures

The article presents the equations of "free calcium hydroxide" mass transfer describing the liquid corrosion of cement concretes. The boundary value problem of "free calcium hydroxide" mass conductivity in dimensionless variables is obtained. Also, in order to obtain a solution to the boundary value problem of mass conductivity, it is proposed to use a combined approach, which consists in the fact that at the beginning of each microprocess an analytical solution is obtained, and then the whole process is gradually calculated on a computer. It should be noted that the method gives good results if it is carried out in conjunction with the Laplace integral transformation method. In addition, the Laplace transform often makes it possible to obtain a solution in two forms: at Fom ˃0,1 and Fom ˂˂ 0,1, this is the advantage of using this transformation. The solution of the boundary value problem of mass conductivity is obtained, which allows to find not only the profiles of dimensionless and dimensional concentrations of “free calcium hydroxide” in concrete thickness, but also makes it possible to determine the value of this value gradient at the phases interface. The obtained solution allows further determining the time of reaching the critical concentration of “free calcium hydroxide” at the phases interface, corresponding to the beginning of high-basic components decomposition, and hence moving on to the further stages of study and corrosion processes modeling, which is confirmed by the graphical dependencies presented in the paper.

OPTIMIZATION OF PRESERVATIVE FOR PROTECTION OF CONCRETE PAVEMENT OF HIGHWAYS

Disadvantages of road concrete pavement quite well known professionals-standards. They were mainly low elasticity modulus asphaltic concrete, as well as a fairly rapid aging of asphalt concrete core component-bitumen. And, as a consequence, is relatively low durability of the coating, the need for frequent repair. To some extent, cement concrete cover signifi cantly outperform this index of asphalt, convinces experience roads of Germany, the United States and other countries. The correct structure of concrete, overall compliance technology laying concrete, comprehensive quality control production work, sufficient technical personnel qualifications provide long defect-free work road re-coated. However, violations by manufacture of works or in the process of exploitation, particularly in the harsh conditions of freezing and thawing, saturation-drying, especially under the influence of salts-defrosting, cause defects, reduce its durability. There are two directions of increase of durability of the coating. Firstly, it is the primary protection is the creation of concrete with minimal possible on data components mixture water cement ratio that provides reception of concrete with minimum porosity and consequently with maximum durability. Secondly, the secondary protection, providing increased resistance already ready-mixed concrete cover external aggressive actions. In this case against the background of other ways quite promising looks impregnation of the surface concrete integrated structure. Composition must contain multiple components, primarily water repellents, preventing penetration of fluid into the body of the concrete, and finely dispersed silica sol in particular silica, providing reduction of the porosity of the surface layers of concrete by interacting with the free calcium hydroxide. The problem of optimization of impregnation structure and is dedicated to this work.

Use of glass powder residue for the elaboration of eco-efficient cementitious materials

Abstract The glass powder is a waste resulting of the manufacturing process of flat glass (regular glass). This study evaluates the eco-efficiency of cement production using glass powder residue as partial replacement of cement. The glass powder residue (GPR) was used as partial replacement up to 50% by weight in cement pastes to evaluate the potential use of this matrix for application in fiber cement composites. For mortar specimens, the percentage of substitution of cement (up to 20% by weight) was used to evaluate the applicability of the glass powder in masonry construction. Primarily, several experiments such as thermogravimetric analysis, compressive strength tests, pozzolanic activity and durability tests were carried out to evaluate the potential use of GPR in cement industry. Secondly, to evaluate the eco-efficiency of the material elaborated, the energy demand of cement partially replaced by glass powder residue and the energy performance of mortars were calculated using mathematical equations. The results showed that GPR presents a pozzolanic activity and a free calcium hydroxide cement matrix is obtained when the ordinary Portland cement is partially replaced by 50% by weight of GPR in cement pastes. Moreover, the partial replacement of cement by 10% by weight of GPR leads to an increase of physico-mechanical properties of mortars. Finally, the energy consumption per MPa of mortars partially replaced by GPR (10 and 20% by weight) is lower than the one of original Portland cement suggesting the eco-efficiency of GPR for applications in cement production and the elaboration of cementitious materials. According to the results of the study, the residue from polishing process of flat glass can be used for the elaboration of green cement and eco-efficient cementitious materials.

Modifying admixtures to cement compositions produced from local raw materials

Durability of hardened cement paste depends on chemical and mineralogical composition of Portland cement. The main factor for hardened cement paste is higher content of calcium aluminate and free calcium hydroxide, binding of which into water-insoluble compounds causes increase in resistance to water, frost and corrosion. The purpose of this research is to develop modifying admixtures to cement compositions based on local raw material - rock sand. Chemical and mineralogical properties of the source materials were studied using X-ray spectroscopy and X-ray diffraction analysis. Standard methods were used for defining physico-mechanical properties of sand and binder. Influence of the degree of mechanochemical activation of modifying admixture on the properties of binder and hardened cement paste made on its basis was studied. Research methods of scanning electron microscopy and spectral measurements were applied. The possibility of using admixture based on rock sand as a modifier was determined, its usage providing increase of strength, sulphate and frost resistance, which causes higher durability of cement concrete.

Microstructure and mixture proportioning of non-structural foamed concrete with silica fume

This paper presents the results of an experimental study conducted to investigate the microstructure and mixture proportioning of non-structural foamed concrete with silica fume (SF). For the purposes of this study, 20 mix designs were made, including four different proportions of SF to cementitious materials (SF/CM) (0%, 5%, 10% and 15%) and five different densities (450, 500, 600, 700 and 750 kg/m3). All the mix designs were prepared with a water-to-cementitious materials ratio (W/CM) of 0·6. Compressive strength was measured at curing ages of 7, 14, and 28 d. It was found that replacement of cement with SF resulted in higher compressive strengths for the given densities examined. Scanning electron microscopy and X-ray diffraction tests showed that SF in foamed concrete reacts with the free calcium hydroxide of hydrated cement and produces calcium–silicate–hydrate, which is stiffer and more durable than calcium hydroxide. In addition, ettringite content reduces when the SF/CM ratio increases. Therefore, SF decreases the risk of sulfate attack in foamed concrete. Finally, it is shown that the method proposed in this study can be successfully exploited to develop foamed concrete mix designs for any given density.

Alkali Silica Reaction In The Presence Of Metakaolin - The Significant Role of Calcium Hydroxide

Reducing the internal corrosion, which is the result of reactions between alkalis and reactive aggregates is especially important in ensuring durability properties of concrete. One of the methods of inhibiting the reaction is using some mineral additives which have pozzolanic properties. This paper presents the efficacy of high-reactivity metakaolin in reducing expansion due to alkali-silica reaction. It was demonstrated that metakaolin in the amount from 5% to 20% by mass of Portland cement reduce linear expansion of mortar bars with opal aggregate. Nevertheless, the safe expansion level in the specimens, classified as non-destructive to concrete, was recorded for the mortars prepared with 20% addition of metakaolin. Depletion of free calcium hydroxide content was considered as one of the most beneficial effects of metakaolin in controlling alkali silica reaction. Based on thermogravimetric analysis (TGA) performed on mortar bars with and without metakaolin the differences in portlandite content were determined. Microstructural observation of the specimens containing metakaolin indicated the presence of a reaction products but fewer in number than those forming in the mortars without mineral additives.

Rationally tuning host–guest interactions to free hydroxide ions within intertrimerically cuprophilic metal–organic frameworks for high OH− conductivity

Rationally tuning host–guest interactions to free hydroxide ions within intertrimerically cuprophilic MOF for high OH− conductivity.

Effect of concentration-dependent disjoining pressure on drainage process of vertical liquid film

For the drainage under the gravity of a vertical foam film containing insoluble surfactant, an improved concentration-dependent disjoining pressure model is formulated based on the published experimental results. The lubrication theory is used to establish the evolution equations of the film thickness, the surface concentration of insoluble surfactant, and the surface velocity, and the evolution characteristics of the film under different disjoining pressures are simulated numerically. The results show that the drainage process of a vertical liquid film generally undergoes two stages:the first stage is the thick film stage and the gravity plays a leading role in the drainage process; the subsequent stage is the thin film stage, the effects of capillary pressure and disjoining pressure increase gradually, and the disjoining pressure dominates the evolution of the film. The disjoining pressure effect is closely related to surfactant type and the correlation strength between the surfactant concentration and electrostatic repulsion force of disjoining pressure. For the ionic surfactant, electrostatic repulsion force increases with the increase of the surfactant concentration, but it is opposite for the nonionic surfactant. It is likely that the free hydroxide ions, which are considered to render the surface negatively charged, are partly adsorbed by the nonionic surfactant. So the surface charge of the foam film decreases as the concentration of the nonionic surfactant increases, resulting in a decrease in electrostatic repulsion. Therefore, some ionic surfactants can improve the stability of liquid film drainage and slow down the drainage process, while the effects of some nonionic surfactants are opposite. When the disjoining pressure is positively correlated with surfactant concentration, with the increase of correlation strength coefficient α, the thinning and drainaging processes of the film tend to slow down, hence the stability of the film is enhanced. When the disjoining pressure is negatively correlated with surfactant concentration, with the increase of the absolute value of α, the drainage process of the film is accelerated and the risk of film rupture is augmented. The results obtained in this paper are consistent with some of the experimental results, indicating that the concentration-dependent disjoining pressure is indeed an important factor in maintaining the stability of foam film containing some certain anionic or nonionic surfactants. The improved concentration-dependent disjoining pressure model established in this paper could not explain the phenomena of parts of cationic nor non-ionic surfactant film in drainage experiments. It can be inferred that the structure of surfactant molecule, the more detailed disjoining pressure model and the coupling of the disjoining pressure and surface elasticity should be considered in the future work.