Range Of NaOH Concentrations Research Articles

ОЦЕНКА ЭФФЕКТИВНОСТИ МОДИФИКАЦИИ ГЕОПОЛИМЕРНОЙ СИСТЕМЫ МИНЕРАЛЬНЫМИ НАПОЛНИТЕЛЯМИ С ТОЧКИ ЗРЕНИЯ ФОРМИРОВАНИЯ ПРОЧНОСТНЫХ ХАРАКТЕРИСТИК

Geopolymers, due to their positive features, can fully compete with traditional Portland cement analogues, and often have other valuable properties that can significantly expand the scope of application of mineral binders for construction purposes. This seems possible due to a wide range of raw materials of different origins, as well as a result of the use of modifying additives of different nature, morphology and, as a consequence, functionality. As part of this work, the effect of some formulation factors was studied: the concentration of the alkaline activator, as well as the type and content of the modifying agent on the strength characteristics of a geopolymer binder based on fly ash. The results of the study made it possible to establish that an increase in the concentration of the alkaline component negatively affects the effect of the modifier. Modification of the geopolymer binder with Portland cement in the NaOH concentration range from 9 to 13% leads to strengthening of the geopolymer system with an increase in its content. With a further increase in the concentration of the alkaline activator, it initiates a softening effect from the introduction of Portland cement. In turn, modification with kaolin and metakaolin leads to a decrease in compressive and bending strength characteristics throughout the entire range of alkali concentrations under consideration. Moreover, the higher the alkalinity of the geopolymer matrix, the more pronounced the softening effect takes place.

Exploring the impact of NaOH pre-treatment for H2 and CO2 adsorption on clinoptilolite

The present investigation involved the treatment of natural clinoptilolite with varying concentrations of NaOH solutions followed by calcination. The samples' composition and structure were characterized and their performance was investigated in the context of hydrogen (H2) and carbon dioxide (CO2) adsorption. While a decreasing SiO2/Al2O3 ratio was observed in the NaOH-treated samples, the morphological structure obtained from SEM images and the increase in surface area according to BET results exhibited more pronounced alterations, particularly within the 0.5–1 M NaOH concentration range. The alkali treatment resulted in notable peak sharpening, with the most prominent changes observed in the (020), (100), and (101) lattice planes at the same concentration. However, there were no significant alterations in peak intensities. Although H2 adsorption (4.0192–26.4726 cm3/g) could reach higher values, higher amounts of CO2 adsorption (5.2308–20.2700 cm3/g) occurred as the concentration of NaOH increased. This phenomenon was attributed to structural modifications in clinoptilolites.

Effect of NaOH content on the fluidizing effect of PCEs with different structures in NaOH-activated slag

The effect of NaOH content on the fluidizing effect of PCEs with varied architecture in AAS was investigated. The adsorption behavior of PCEs was measured by TOC, while their molecular stability was investigated via light transmittance and DLS. At high concentrations (>2 M), the fluidizing effect of PCEs with short side chains continuously decreased, while that of PCEs with long side chains first decreased and then increased. The decline in dispersing ability was attributed to the collapse of PCEs molecules rather than competitive adsorption of PCEs and OH−, while the subsequent improvement in the dispersing effect of PCEs with long side chains was attributed to the formation of soluble aggregates assembled by numerous PCE molecules, which resulted in a significant increase in adsorption layer thickness. PCEs with long side chains, an extremely high acid-to-ether ratio, and high molecular weight exhibited excellent dispersing effect over a wide range of NaOH concentrations.

Synthesis and characterization of metakaolin-based crystalline phase sodium aluminum silicon oxide geopolymers using concentrated alkaline medium

Crystalline phase geopolymers that include sodium aluminum silicon oxide were produced with high concentrations of NaOH activator in metakaolin–sodium silicate solution at 80 °C. Low-temperature geopolymerization provided these first-ever reported crystalline geopolymers when high NaOH concentration 12–15 M was used for the aqueous metakaolin medium. By changing the NaOH activator concentration to 10 M, amorphous geopolymers were formed, but crystalline geopolymers of sodium aluminum silicon oxide appeared in the NaOH concentration range. The crystalline phase had dense morphology of the formed bulk ceramics, respectively exhibiting 8.4 ± 0.5 MPa compressive strength at weight ratios of solid/liquid (S/L) and Na2SiO3/NaOH of mixtures for 0.45 and 1.0.

Lignin enhances cellulose dissolution in cold alkali

Aqueous sodium hydroxide solutions are extensively used as solvents for lignin in kraft pulping. These are also appealing systems for cellulose dissolution due to their inexpensiveness, ease to recycle and low toxicity. Cellulose dissolution occurs in a narrow concentration region and at low temperatures. Dissolution is often incomplete but additives, such as zinc oxide or urea, have been found to significantly improve cellulose dissolution. In this work, lignin was explored as a possible beneficial additive for cellulose dissolution. Lignin was found to improve cellulose dissolution in cold alkali, extending the NaOH concentration range to lower values. The regenerated cellulose material from the NaOH-lignin solvents was found to have a lower crystallinity and crystallite size than the samples prepared in the neat NaOH and NaOH-urea solvents. Beneficial lignin-cellulose interactions in solution state appear to be preserved under coagulation and regeneration, reducing the tendency of crystallization of cellulose.

Improved understanding of Sodium hydroxide concentration role and kinetic model of cryolite reactive extraction in cathode Spent Pot Linings

Abstract Spent Pot Lining (SPL) cathode pot, waste from the aluminium smelting process needs detoxification from cyanides, washing out water-soluble salts and extraction of the cryolite (Na3AlF6) decomposition products to be recycled. Revealed cryolite decomposition mechanism with NaOH opens possibilities to explore its critical role in the reactive extraction process. Common Na+ ion from NaOH hinders the solubility of the product but also drives mass transfer to the reaction site. Reaction mass balance provides adequate liquid to solid ratio (L/S) and NaOH concentration range. A newly developed kinetic model based on Whitman film theory and NaOH mass flow enables prediction of the reaction time to decompose cryolite to a low enough level. Results show that the internal particle resistance to transport (1/ks) is 19 times larger than the external (1/kl) one and governs the whole process.

Выбор коррозионностойких конструкционных материалов для оборудования получения каустической соды

The article considers the corrosion resistance of domestic and foreign materials, both the base metal and welded joints in the media of concentration of electrolytic alkalis in the range of NaOH concentrations from 12% to 99.5% and temperatures from 115 to 395°С. For testing, specimens of 2080 mm in size with transverse welds with two drilled holes were made from the material under study. polished and assembled into cassettes using nickel alloy rods. For the first time, comparative data on the corrosion state of structural materials during evaporation of electrolytic slits obtained by diaphragm electrolysis and electrolysis using a mercury cathode were obtained. The results of corrosion studies are quite well corrected with the experience of operating nickel pipes at the first stage of alkali concentration. The electrochemical heterogeneity of welded joints of alloys 33 and 201 was evaluated. The conducted studies of the corrosion resistance of alloys 201 and 33 under conditions of evaporation of NaOH obtained by mercury electrolysis confirmed the high corrosion resistance of nickel alloy 201 at the main stages of alkali concentration. The research results can be used as recommendations for the development of structural materials.

Conditions for the Extraction of Polyphenols from Radiata Pine (Pinus radiata) Bark for Bio-Foam Preparation

The use of polyphenol extracts from radiata pine (Pinus radiata) bark as raw materials for bio-foams was investigated along with the optimal NaOH extraction conditions. The targeted yield of alkaline extracts was 60%, and the targeted pH was 11 to 12. The radiata pine bark was composed of 70% of a 1% NaOH extract, which contained mainly polyphenols, such as proanthocyanidin (PA). As the particle size of the bark decreased, the yield of the 1% NaOH extracts increased from 57 to 87%. A range of NaOH concentrations, liquor ratios, and extraction times were explored to establish an economic polyphenol extraction method. More than 60% of the alkaline extract was extracted, and the pH of the extract was approximately 12 when the optimum extraction conditions were employed, i.e., a liquor to bark ratio of 5:1, a NaOH dosage of 17 to 18% based on the bark weight, and a 1 h extraction time. Following neutralization of the alkaline extract, structural analysis indicated severe structural changes in the PA during the alkaline extraction. Because the alkaline extract was barely soluble in the solvent used for the structural analyses, it is assumed that chemical modification is required to increase the solubility of the alkaline extract for the production of bio-foams.

Reusability of a single-walled carbon nanotube-based biosensor for detecting peanut allergens and Y. enterocolitica

Biosensing systems based on electrochemical detection is popular to the industrial community, because the electronic readout from biosensor assays could replace conventional microarray methods. However, the greatest practical barrier to a wider acceptance of biosensors within the industrial field is due to their associated manufacturing and operating costs. In this study, a single-walled carbon nanotube (SWCNT)-based biosensor was tested for reusability after cleaning. The reusability of the existing biosensing system was examined using diverse cleaning reagents. Successful sensor cleaning without affecting their reusable properties was confirmed using sodium hydroxide (NaOH) solution. A range of NaOH concentrations between 70 and 160 mM was tested and the optimum reusable concentration for the biosensor was determined as 100 mM. A 5-time-reuse of the biosensor was achieved using 100 mM NaOH solution for peanut allergen control. Furthermore, re-adding anti-Yersinia antibodies to the biosensor led to the reaction of bacterial cells of Yersinia enterocolitica with the potential biosensor response. Scanning electron microscopy (SEM) results showed that microorganisms (Y. enterocolitica) and peanut allergen (Ara h1) were washed away from the biosensor chip after washing using NaOH (100 mM) for 2 h.

Mechanical properties of coconut trunk particle/polyester composite based on alkali treatment

Coir is a well-known natural fiber extracted from the husk of a coconut tree. In polymer composite materials, the ultimate performance of coir has been shown using surface modification methods. Among them, sodium hydroxide (NaOH) is a comparative and efficient solution used for surface treatment of lignocellulosic fiber. In contrast to coir, coconut timber, a hardwood that dominates the weight of the coconut tree, has not been appropriately considered for use in polymer composites. Therefore, in this article, coconut trunk particle/unsaturated polyester resin composites were experimentally investigated. As a pioneering study, a large range of NaOH concentrations from 2 wt% to 10 wt% (with an interval of 2 wt%) was utilized to treat the surface of the filler. Finally, 4 wt% alkali solution was found as the best content for surface modification based on the mechanical properties of the composite, including those determined by tensile, flexural, and impact test results.

Hydrothermal Synthesis of Sodium Bismuth Titanate Ferroelectrics

We have studied phase formation processes during sodium bismuth titanate, Na0.5Bi0.5TiO3 (NBT), synthesis under hydrothermal conditions at a temperature of 230°C for 24 and 48 h using stoichiometric mixtures of titanium oxide and bismuth hydroxide and NaOH solutions in the concentration range 5–30 M. The results demonstrate that, at sodium hydroxide concentrations in the range ≤10 M, there is almost no reaction between the starting reagents. In the concentration range 10–15 M, two-phase products are formed, containing a perovskite-like phase and the Bi12TiO20 bismuth titanate. Single-phase samples with the perovskite structure are formed at NaOH concentrations from 18 to 20 M, but their composition differs considerably from the stoichiometric one (Na0.61–0.69Bi0.39–0.31TiO2.89–2.81δ0.11–0.19, where δ stands for an oxygen vacancy). In the NaOH concentration range 22–30 M, first partial and then complete Bi3+ dissolution occurs. Increasing the synthesis time helps to stabilize the perovskite phase. The single-phase NBT ceramics have resistivity of 1.3 × 109 Ω cm, dielectric permittivity e/e0 = 360, dielectric loss tangent tan δ = 0.15, longitudinal electromechanical coupling coefficient Kp = 0.068, piezoelectric charge coefficients –d31 = 6.7 pC/N and d33 = 9 pC/N, and piezoelectric voltage coefficients –g31 = 2.07 mV m/N and g33 = 2.84 mV m/N. The relatively low piezoelectric performance of the ceramics is obviously due to the imperfect structure of the synthesized phases.

Bulk etch rate for PADC CR-39 at extended concentration range of NaOH mixed with ethanol and etchant viscosity study

Bulk etch rate of PADC CR-39 detector in a mixture of NaOH and ethanol alcohol aqueous solution of (8 ml of NaOH + X ml of ethanol: X = 0, 1, 2, 3) at 70 °C was determined using fission track diameter method. Wide range of NaOH concentration, never covered before, from 2 to 30 N was studied. Higher NaOH concentrations and ethanol increase the detector etching rate dramatically leading to a reaction rate far from equilibrium. Arrhenius and multi hit equations are no longer hold and therefore a need for new equations is arise. Viscosity of (NaOH + ethanol) in such wide concentration range was also studied at different temperatures to explain the reaction rate. Many efforts and different fitting equations were used to manipulate the data. Some of these equations are statistically as well as chemically rejected and finally three equations seem to read the data quit well are suggested.

Synthesis and characterization of morphology-controllable BiFeO3 particles with efficient photocatalytic activity

The single phase BiFeO3 (BFO) particles were synthetised by a facile hydrothermal method under the special sodium hydroxide (NaOH) concentration. The particles have been systematically characterized by X-ray diffraction technique, field emission scanning electron microscopy, energy dispersive spectrometer, fourier transform infrared spectroscopy and UV–vis spectra. It is found that a wide range of NaOH concentration of 1–3 M could induce a high crystalline quality of BFO. Interestingly, it is noted that different NaOH concentrations have a significant effect on the morphology of BFO particles. With the increase of NaOH concentration, the morphology changes from alveolate BFO to cubic BFO particles. Moreover, the light absorption characteristics and the band gap of BFO particles are strongly dependent on their morphology. This result in the difference of photocatalytic degradation ability of alveolate BFO particles compared to that of cubic BFO particles.

Feasibility analysis of SO2 absorption using a hydrophilic ceramic membrane contactor

Abstract Hydrophilic ceramic membranes would be potential candidates for membrane gas absorption if they could be applied to appropriate separation processes. This study highlights a novel concept for the practical implementation of SO2 absorption in hydrophilic ceramic membrane that exhibits outstanding thermal and mechanical stabilities. With this aim, we investigated experimentally the performance of SO2 absorption into aqueous sodium hydroxide (NaOH) solution in a hydrophilic alumina (Al2O3) membrane contactor in terms of SO2 removal efficiency and SO2 mass transfer flux, and compared the performance with that in a hydrophobic one. A series of experiments were performed at various conditions over a NaOH concentration range of 0–1.0 mol·L− 1, a liquid flow rate range of 30–180 ml·min− 1, a gas flow rate range of 120–1000 ml·min− 1, an inlet SO2 concentration range of 400–2000 μl·L− 1, and a temperature range of 10 –35 °C. It was found that the hydrophilic membrane was more competitive when using a NaOH concentration higher than 0.2 mol·L− 1. Furthermore, it can be inferred that the hydrophilic α-Al2O3 membrane exhibited exceptional long-term stability under 480 h continuous operation.

Electrochemical synthesis of bismuth molybdates with controllable composition and their photocatalytic performance

AbstractBismuth molybdate photocatalysts were controllably prepared via an electrochemical approach at room temperature. The composition and optical property of each product were determined according to the NaOH and Na2MoO4 quantities in the electrolyte. Pure Bi3.64Mo0.36O6.55 was prepared at a NaOH concentration range of 0.2‐0.8 mol L−1, whereas the Bi3.64Mo0.36O6.55/Bi14MoO24 composite was obtained in an electrolyte containing 0.4 mol L−1 NaOH and 0.5 mol L−1 Na2MoO4. The results of rhodamine B degradation under visible light indicated that Bi3.64Mo0.36O6.55 nanoparticles with a size of 10‐50 nm displayed the best photocatalytic efficiency, which was considerably higher than that of composite one and bulk Bi3.64Mo0.36O6.55.

Hydroxide Ion Oxidation in Aqueous Solutions Using Boron-Doped Diamond Electrodes.

The electrochemical oxidation behavior of hydroxide ions at the surface of boron-doped diamond (BDD) electrodes is presented. The hydroxide ion oxidation behavior was found to be affected by the surface conditions of the BDD electrode. Over the NaOH concentration range of 0.5-10 mM, a well-defined voltammetric wave attributed to hydroxide ion oxidation was observed at ∼1.25 V versus a Ag/AgCl reference electrode when using an anodically oxidized BDD (AO-BDD) electrode, while it was observed at around ∼1.15 V when a cathodically reduced BDD (CR-BDD) electrode was used. Although the hydroxide ion oxidation profiles were slightly different for the AO-BDD and CR-BDD electrodes, the peak currents was each found to have linear relationships with the NaOH concentration over the same range.

Effects of low–frequency ultrasound on heterogenous deacetylation of chitin

The effects of low frequency ultrasound to the heterogeneous deacetylation of chitin from the shell of white shrimp (Penaeus vannamei) were examined. The deacetylation process was carried out in the range of NaOH concentrations from 35% to 65% (w/w) with and without the ultrasound in the frequency of 37kHz, RMS=300W. The chitosan obtained was characterized in the degree of deacetylation, solubility, FT-IR and X-ray diffraction. The results showed that the behaviors of the deacetylation in two cases, with and without ultrasound, were similar but the ultrasound enhanced the deacetylation rate and therefore reduced the time of the reaction to get the same degree of deacetylation. The role of ultrasound in the process showed more clearly in the low concentration of sodium hydroxide, below 45% (w/w). At the higher concentration of sodium hydroxide, the influence of ultrasound on facilitating deacetylation decreased significantly, however, ultrasound was still keeping on its improving effect on the solubility of the chitosan obtained. The data from FT-IR and X-ray diffraction did not show any considerable change in structure of both kinds of chitosan. This study showed the potential of using low frequency ultrasound in enhancing the deacetylation of chitin for reducing the chemical consumption.

Synthesis and surface enhanced raman scattering properties of gold nanoworms

We have devised a simple seedless, high-yield protocol for the synthesis of gold nanoworms (NWs). NWs were grown simply by reducing HAuCl4 with ascorbic acid (AA) in the presence of cetyltrimethylammonium bromide (CTAB) and NaOH. The nucleation was induced by the addition of AgNO3 in the reaction medium. We have observed that an optimum range of NaOH concentration is essential for NW formation. Furthermore, we have seen that the synthesis of gold NWs is very sensitive to the supplier of the CTAB used for the synthesis. With the same recipe, CTAB from different suppliers gave different yield and lengths of NWs. The NWs show excellent potential for surface enhanced Raman spectroscopy (SERS).

An RDE Investigation of NaOH Effect on Electrosynthesis of Lead Dioxide in Alkaline Solution

An electrochemical investigation of NaOH concentration on electrosynthesis of lead dioxide in alkaline solutions was performed using rotating disk electrodes (RDE). The results show that Pb(II) does not modify the evolution of oxygen in alkaline solutions, and the reaction taking place at 0.84 VSHE is under the mixed control of ionic transport and charge transfer. The Koutechy-Levich equation was used to calculate the value of diffusion coefficient D and apparent heterogeneous rate constant k of the PbO2 electrodeposition process at 0.84 VSHE. The results indicate that NaOH has a negative influence on the diffusion of Pb(II) within a NaOH concentration range of 2.5 ∼ 4.5 M. In addition, NaOH has a positive influence on the apparent heterogeneous rate constant of Pb(II) oxidation reactions within a NaOH concentration range of 2.5 ∼ 3 M, but a negative influence within a NaOH concentration range of 3 ∼ 4.5 M. XRD and SEM were employed to investigate the effects of NaOH concentration on phase composition and surface microstructures of deposits. The results show that PbO2 synthesized in an alkaline solution consists of pure α phase. The deposits are all composed of rounded nanocrystallites, except for the deposit synthesized in a solution of 3 M NaOH, which exhibited rod-like crystallite.

English

The aims of this study were to determine the good conditions for fibers extraction from Retama monosperma young stems and their mechanical, physical and chemical characteristics. The fibers were extracted using a range of NaOH concentration from 1 to 16% in a period of treatment of 1 to 24 h, coupled with a physical treatment. For the evaluation of physico-mechanical characteristics, 200 samples were performed in the tensile test. The biochemical composition of the fibers was determined after separation of the parietal compounds. The results show that the best fiber yield was 11.51% obtained by a treatment of 14% NaOH for 8 h, followed by a physical treatment. The fibers biocomposition was 87.3% of cellulose, 7.5% of hemicelluloses and 1% of lignin. The Young's modulus was 13.3 GPa, tensile strength was 110 MPa and a density was 1.3 g/cm3. The average fiber length was 155.7 mm. The fibers yield and characteristics showed that R. monosperma plant may in future be suitable source for natural fibers. Key words: Retama monosperma young stems, fibers, extraction, characterization.