Higher Concentrations Of Sodium Hydroxide Research Articles

Temperature rise and initial shrinkage of alkali-activated fly ash cement pastes

This paper reports on core temperature development and initial shrinkage of fly ash cement pastes activated with sodium hydroxide solution at different concentrations during elevated-temperature curing at 60°C. The results indicate that a high sodium hydroxide concentration might result in a substantial rise in the core temperature of samples, dependent on the mould size and ratio of paste to oven volume. An increase in alkali concentration was also found to increase the initial shrinkage of the pastes during elevated-temperature curing. Excessive initial shrinkage and temperature increase might lead to the appearance of internal stresses in the pastes, which can affect the material performance.

Removal of Oxidation Fragments from Multi-walled Carbon Nanotubes Oxide Using High and Low Concentrations of Sodium Hydroxide

Modification of multi-walled carbon nanotubes surface (MWCNT) using the mixture of $${{{\rm HNO}}_{3}/{{\rm H}}_{2}{{\rm SO}}_{4}}$$ is widely employed for MWCNT surface oxidation, but it also leads to shortening and thinning of the CNT layers causing fragmentation. The carbonaceous fragments had adsorbed on the surface is not removed from the sample in conventional treatments; however, the addition of NaOH successfully cleans the oxidized material. In this article, MWCNT was functionalized using $${{{\rm HNO}}_{3}/{{\rm H}}_{2}{{\rm SO}}_{4}}$$ as oxidizing agent and evaluate the impact of using high and low concentrations of NaOH to purify CNT oxide. The presence of oxidized groups as hydroxyl and carboxyl has been demonstrated by FTIR. The thermal stability of MWCNT and MWCNT-O after and before purification was studied by TGA, and the degree of its crystallinity was examined by XRD. The defect degree occurs during the oxidation process was confirmed by Raman spectroscopy. TEM images showed the presence and the absence of wrinkles and the adsorbed carbonaceous fragments.

Formation of tetragonal and monoclinic-HfO 2 nanoparticles in the oil/water interface

Abstract Pure tetragonal hafnium oxide (t-HfO 2 , ca. 4.5 nm) and monoclinic hafnium oxide (m-HfO 2 , ca. 105 nm × 45 nm) possessing a narrow size-distribution were synthesized with an oil/water interface approach by adjusting various reaction parameters such as aging temperature, reaction time, and concentration of sodium hydroxide. The t-HfO 2 and m-HfO 2 were spherical and spindle-like, respectively. The formation and transformation mechanisms of HfO 2 have been proposed from both of aspects of energy and time. Low temperature, appropriate reaction time and high concentration of sodium hydroxide are kinetically beneficial for the formation of t-HfO 2 . The hafnium oxide transformation from small spherical tetragonal nanoparticles to large spindle-like monoclinic nanoparticles happened due to the decline of their total surface energy with the increases of temperature and reaction time. Moreover, by the use of seeds, formation of HfO 2 nanoparticles was obviously promoted and the size was reduced, suggesting the non-aggregation and surface-deposition growth of nanoparticles.

Chitin and chitosan from Brazilian Atlantic Coast: Isolation, characterization and antibacterial activity

Chitin and chitosan were obtained by chemical treatments of shrimp shells. Different particle sizes (50–1000μm) of the raw material were used to study their effect on size distribution, demineralization, deproteinization and deacetylation of chitin and chitosan isolation process. The particle size in the range of 800–1000μm was selected to isolate chitin, which was achieved by measuring nitrogen, protein, ash, and yield %. Hydrochloric acid (5%, v/v) was optimized in demineralization step to remove the minerals from the starting material. Aqueous solution of sodium hydroxide (5%, w/v) at 90°C for (20h) was used in deproteinization step to remove the protein. Pure chitin was consequently impregnated into high concentration of sodium hydroxide (50%) for 3.5h at 90°C to remove the acetyl groups in order to form high pure chitosan. The degree of deacetylation (DDA) of chitosan was controlled and evaluated by different analytical tools. The chemical structure of chitin and chitosan was confirmed by elemental analysis, ATR-FTIR, H/C NMR, XRD, SEM, UV–Vis spectroscopy, TGA, and acid–base titration. The isolated chitin and chitosan from shrimp shell showed excellent antibacterial activity against Gram (−ve) bacteria (Escherichia coli) comparing with commercial biopolymers.

Production of Monomeric Aromatic Compounds from Oil Palm Empty Fruit Bunch Fiber Lignin by Chemical and Enzymatic Methods.

In this study, oil palm empty fruit bunch (OPEFBF) was pretreated with alkali, and lignin was extracted for further degradation into lower molecular weight phenolic compounds using enzymes and chemical means. Efficiency of monomeric aromatic compounds production from OPEFBF lignin via chemical (nitrobenzene versus oxygen) and enzymatic [cutinase versus manganese peroxidase (MnP)] approaches was investigated. The effects of sodium hydroxide concentration (2, 5, and 10% wt.) and reaction time (30, 90, and 180 minutes) on the yield of aromatic compounds were studied. The results obtained indicated that nitrobenzene oxidation produced the highest yield (333.17 ± 49.44 ppm hydroxybenzoic acid, 5.67 ± 0.25 ppm p-hydroxybenzaldehyde, 25.57 ± 1.64 ppm vanillic acid, 168.68 ± 23.23 ppm vanillin, 75.44 ± 6.71 ppm syringic acid, 815.26 ± 41.77 ppm syringaldehyde, 15.21 ± 2.19 ppm p-coumaric acid, and 44.75 ± 3.40 ppm ferulic acid), among the tested methods. High sodium hydroxide concentration (10% wt.) was needed to promote efficient nitrobenzene oxidation. However, less severe oxidation condition was preferred to preserve the hydroxycinnamic acids (p-coumaric acid and ferulic acid). Cutinase-catalyzed hydrolysis was found to be more efficient than MnP-catalyzed oxidation in the production of aromatic compounds. By hydrolyzed 8% wt. of lignin with 0.625 mL cutinase g−1 lignin at pH 8 and 55°C for 24 hours, about 642.83 ± 14.45 ppm hydroxybenzoic acid, 70.19 ± 3.31 ppm syringaldehyde, 22.80 ± 1.04 ppm vanillin, 27.06 ± 1.20 ppm p-coumaric acid, and 50.19 ± 2.23 ppm ferulic acid were produced.

Preparation and characterization of zinc oxide nanoflakes using anodization method and their photodegradation activity on methylene blue

In this work, we report the formation of leaf-like ZnO nanoflakes by anodization of zinc foil in a mixture of ammonium sulfate and sodium hydroxide electrolytes under various applied voltage and concentration of sodium hydroxide. The morphology and structure of ZnO nanoflakes were investigated by field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy and X-ray diffraction analysis. In addition, the photocatalytic activity of the prepared nanoflakes zinc oxide was evaluated in the photodegradation of organic dye methylene blue (MB) solution under UV irradiation. It was found that zinc oxide prepared under high concentration of sodium hydroxide and high voltage showed better performance in the photodegradation of methylene blue.

Kinetics of Aqueous Extraction of Hemicelluloses from Spruce in an Intensified Reactor System

The aqueous extraction of hemicelluloses has gained increasing interest with new emerging applications for hemicelluloses in the modern forest-based biorefinery concept. The extraction kinetics play a key role in their industrial utilization. The traditional kinetic studies and models for the selective dissolution of softwoods, however, always incorporate high concentrations of sodium hydroxide and sodium sulfide relevant to pulping, and the kinetics in pure water is left outside the scope of these investigations. Aqueous extraction of hemicelluloses from spruce sapwood was investigated with a new cascade reactor setup, which was developed for intensified investigation of solid−liquid dissolution kinetics. The experiments were performed at 150−170 °C with a particle size of 1.25−2 mm and solid loads of about 6.25 g of dry wood/L in the kinetic regime of intrinsic kinetics. The pH of the liquid phase was measured during the reaction. The selectivity of the dissolution and degradation of hemicelluloses was examined qualitatively. The total concentrations of arabinose (Ara), xylose (Xyl), galactose (Gal), glucose (Glc), mannose (Man), rhamnose (Rha), glucuronic acid (GlcA), 4-O-methylglucuronic acid (4-O-MeGlcA), and galacturonic acid (GalA) were analyzed from the liquid and solid phases during the reaction. The dissolution was observed to be highly temperature dependent, and degradation of the compounds was observed. A kinetic model was developed for the overall extraction of the hemicelluloses. The activation energy was determined to be 135 kJ/mol. No significant influence of the pH on the actual extraction kinetics was observed, even though it influences strongly the degradation of the compounds through hydrolysis.

Potassium Chloride Treatment to Control Alkali Induced Heave in Black Cotton Soil

The results presented in this paper shows that high concentrations of sodium hydroxide causes abnormal changes on the volume change behaviour of illite–smectite (interstratified mineral) soil due to mineralogical changes. The higher swell that occurs is shown in the form of a new second stage of swelling. Increase in negative charges on soil particles and mineralogical changes after interaction with soil, respectively, are responsible for the swelling in these two stages. However, potassium hydroxide does not induce such high swelling in soils. This is mainly due to the fixation of potassium ions. Hence an attempt has been made to control the swelling induced by sodium hydroxide by making used of potassium chloride as an additive. Potassium fixation which is not substantial at neutral pH is favoured at higher pH Addition of potassium chloride salt solution (as 2 and 5% solution) can reduce only the first stage of swelling by linking the unit layers of mineral by reducing development diffuse double layer near clay surface. Potassium chloride is unable to prevent the formation of mineralogical alteration due to soil alkali interaction and hence the swelling associated with mineralogical changes. X-ray diffraction studies have revealed that mineralogical changes leading to formation of zeolite by soil alkali interaction is not inhibited by potassium ions. Morphological changes studied by scanning electron microscope corroborate these observations. Also the compressibility of soil which is increased in alkali solution is reduced in the presence of potassium salts. This reduction is due to reduction in the first stage of swelling.

Investigation of the Physicochemical Changes Preceding Zeolite Nucleation in a Sodium-Rich Aluminosilicate Gel

All industrially available zeolites are obtained from hydrogel systems. Unfortunately the level of understanding of the events preceding zeolite crystallization is far from satisfactory. In this respect, revealing the nature of the processes taking place in the precursor gel is of paramount importance to understanding zeolite nucleation. The investigation of the gel structure, however, is a difficult task due to the complexity of the object in terms of both composition and topology. Therefore, a combination of hyperpolarized (HP) (129)Xe NMR-N(2) adsorption-high-resolution transmission electron microscopy-energy-dispersive spectrometry methods complemented by X-ray diffraction, infrared spectroscopy, scanning electron microscopy, and chemical analyses has been employed to study the changes in composition and structure of sodium hydroxide rich aluminosilicate gel yielding zeolite A. The role of each component in the system and the entire sequence of events during the induction, nucleation, and crystallization stages have been revealed. The high concentration of sodium hydroxide in the studied system has been found to control the size and structure of the gel particles in the beginning stage. During the initial polymerization of aluminosilicate species a significant part of the sodium hydroxide is expelled from the gel into the solution, which restricts extensive polymerization and leads to formation of small aluminosilicate particles with open pore structure. The induction period that follows is marked by incorporation of Na back in the bulk gel. The combined action of the Na ion as a structure-directing agent and the hydroxyl group as a mobilizer results in partial depolymerization of the gel and formation of voids with mesopore sizes. The nucleation maximum coincides temporally with development of pores with sizes in the range of 2-5 nm. The amorphous gel undergoes into crystalline zeolite only after these pores have disappeared and the chemistry of the gel has evolved to reach the stoichiometric zeolite composition. It was established unambiguously by high-resolution transmission electron microscopy and HP (129)Xe NMR that the nucleation of zeolite occurs in the solid part of the system and the succeeding crystallization commences only after the nuclei are released into the liquid, which is consistent with the autocatalytic mechanism. Also this investigation has demonstrated the unrivaled sensitivity of HP (129)Xe NMR that is capable of identifying presence of small amounts of crystalline zeolite material in amorphous medium with detection limit extending below 1 wt %.

Responses of the murine esophageal microcirculation to acute exposure to alkali, acid, or hypochlorite

Background/Purpose Although ingestion of alkali-based and/or hypochlorite-based household cleaners as well as strong acids remains a major cause of esophageal wall injury, little is known about the mechanisms that underlie the injury response to these toxic agents. This study examined the roles of vascular dysfunction and inflammation to the esophageal injury response to different caustic substances in mice. Methods The esophageal responses to sodium hydroxide (10%, 5%, and 2.5%), potassium hydroxide (10%, 5%, and 2.5%), sodium hypochlorite (5.25%), and hydrochloric acid (10%, pH 2) were evaluated by intravital videomicroscopy and histopathology. Intravital microscopy was used to monitor changes in the diameter of arterioles and venules, the adhesion and movement of leukocytes in venules, and the time of cessation of arteriolar blood flow in mouse esophagus. The esophageal mucosa was exposed to caustic substances for 0 to 60 minutes before evaluation. Results The higher concentrations of sodium hydroxide and potassium hydroxide elicited rapid stasis in both arterioles and venules, which was accompanied by arteriolar constriction and thrombosis. An accumulation of adherent leukocytes in venules was not observed with any agent. Histopathological evaluation revealed marked cellular and interstitial edema in the mucosa with alkali, whereas hydrochloric acid and sodium hypochlorite decreased the thickness epithelial layer. Conclusion These findings suggest that ischemia and thrombosis are dominant processes, whereas inflammation is less important in the pathogenesis of acute corrosive injury to the esophageal mucosa.

Synthesis of methylated chitosan containing aromatic moieties: Chemoselectivity and effect on molecular weight

N-Arylated chitosans were synthesized via Schiff bases formed by the reaction between the primary amino group of chitosan with aromatic aldehydes followed by reduction of the Schiff base intermediates with sodium cyanoborohydride. Treatment of chitosan containing N,N-dimethylaminobenzyl and N-pyridylmethyl substituents with iodomethane under basic conditions led to quaternized N-(4- N,N-dimethylaminobenzyl) chitosan and quaternized N-(4-pyridylmethyl) chitosan. Methylation occurred at either N,N-dimethylaminobenzyl and N-pyridylmethyl groups before the residual primary amino groups of chitosan GlcN units were substituted. The total degree of quaternization of each chitosan varied depending on the extent of N-substitution (ES) and the sodium hydroxide concentration used in methylation. Increasing ES increased the total degree of quaternization but reduced attack at the GlcN units. N,N-dimethylation and N-methylation at the primary amino group of chitosan decreased at higher ES’s. Higher total degrees of quaternization and degrees of O-methylation resulted when higher concentrations of sodium hydroxide were used. The molecular weight of chitosan before and after methylation was determined by gel permeation chromatography under mild acidic condition. The methylation of the N,N-dimethylaminobenzyl derivative with iodomethane was accompanied by numerous backbone cleavages and a concomitant reduction in the molecular weight of the methylated product was observed. The antibacterial activity of water-soluble methylated chitosan derivatives was determined using Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive) bacteria; minimum inhibitory concentrations (MIC) of these derivatives ranged from 32 to 128 μg/mL. The presence of the N,N-dimethylaminobenzyl and N-pyridylmethyl substituents on chitosan backbone after methylation did not enhance the antibacterial activity against S. aureus. However, N-(4- N,N-dimethylaminobenzyl) chitosan with degree of quaternization at the aromatic substituent and the primary amino group of chitosan of 17% and 16–30%, respectively, exhibited a slightly increased antibacterial activity against E. coli.

Dissolution of porcine incisor pulps in sodium hypochlorite solutions of varying compositions and concentrations

The solubility of dental pulp tissue in sodium hypochlorite has been extensively investigated but results have been inconsistent; due most likely to variations in experimental design, the volume and/or rate of replenishment of the solutions used and the nature of the tissues assessed. Traditionally, the sodium hypochlorite solutions used for endodontic irrigation in Australia have been either Milton or commercial bleach, with Milton being the most common. Recently, a range of Therapeutic Goods Administration (TGA) approved proprietary sodium hypochlorite solutions, which contain surfactant, has become available. Some domestic chlorine bleaches now also contain surfactants. The purpose of this study was to perform new solubility assessments, comparing Milton with new TGA approved products, Hypochlor 1% and Hypochlor 4% forte, and with a domestic bleach containing surfactant (White King). Ten randomly assigned pulp samples of porcine dental pulp of approximately equal dimensions were immersed in the above solutions, as well as representative concentrations of sodium hydroxide. Time to complete dissolution was measured and assessed statistically. White King 4% showed the shortest dissolution time, closely followed by Hypochlor 4% forte. White King 1% and Hypochlor 1% each took around three times as long to completely dissolve the samples of pulp as their respective 4% concentrations, while Milton took nearly 10 times as long. The sodium hydroxide solutions showed no noticeable dissolution of the pulp samples. The composition and content of sodium hypochlorite solutions had a profound effect on the ability of these solutions to dissolve pulp tissue in vitro. Greater concentrations provided more rapid dissolution of tissue. One per cent solutions with added surfactant and which contained higher concentrations of sodium hydroxide were significantly more effective in dissolution of pulp tissue than Milton.

Potentiometric and Coulometric Determination of 5-Phenyl-1,3,4-Oxadiazole-2-Thiol

A method for the determination of 5-phenyl-1,3,4-oxadiazole-2-thiol involving its reaction with iodine in an alkaline medium has been presented. In volumetric titration with potentiometric endpoint detection, the determination range is 25–500 µmol. In coulometric titration using biamperometric endpoint detection, 0.5–5 µmol of 5-phenyl-1,3,4-oxadiazole-2-thiol were successfully determined. The errors and the relative standard deviations were below 1%. The shapes of the obtained potentiometric titration curves of the tested compound are unusual at higher concentrations of sodium hydroxide and depend on the material of the indicator electrode (platinum and gold). Addition of iodine resulted in a significant potential drop. The studied system did not exhibit Nernstian behavior.

VS-1 zeolite synthesized directly from silatrane

VS-1 zeolite was successfully synthesized using silatrane as the precursor via sol–gel processing and microwave heating methods. Various factors, which influence the product properties, were investigated, viz. water content, reaction temperature, sodium hydroxide concentration, and amount of vanadium loading. XRD, SEM, UV–visible and ESR were applied to characterize synthesized VS-1. Lower water content and higher temperature promote incorporation of vanadium in the zeolite structure, and lower sodium hydroxide concentration gives more highly condensed vanadium species. Higher sodium hydroxide concentration can lead to extrinsic formation of vanadium and does not promote vanadium into the framework structure but rather weakens the crystal structure. Samples prepared with high sodium hydroxide concentration are susceptible to destruction during calcinations. Using the novel silatrane precursor, VS-1 zeolites with high vanadium loading can be prepared via hydrothermal synthesis.

Study of the possible use of intermediate flax as raw material for production of cellulose

In treating intermediate flax with concentrated solutions (greater than 5 M) of sodium hydroxide, crystalline regions of cellulose totally pass from modification CI to modification CII, despite the presence of contaminants (lignin, hemicellulose, etc.). The presence of hydrogen peroxide in basic solutions shifts the beginning of the CI → CII phase transition toward higher concentrations of sodium hydroxide. A sufficiently high degree of purification of intermediate flax (~93% cellulose content) can be attained in two-step treatment including acid-peroxide cooking in the first stage and alkaline cooking in the second stage and in alkaline-peroxide cooking.

Potentiometric Titration of Triazolethiols and Tetrazolethiols with Iodine in Alkaline Medium

The iodimetric determination of triazolethiols and tetrazolethiols in alkaline medium is presented. The volumetric titration with potentiometric end-point detection was applied. The range of determination, in which the error is lower than 1%, is 20-2 000 μmol for 1H-1,2,4-triazole-3-thiol (1), 25-1 000 μmol for 3-phenyl-1H-1,2,4-triazole-5-thiol (2), 25-500 μmol for 4-methyl-5-(trifluoromethyl)-4H-1,2,4-triazole-3-thiol (3), 50-500 μmol for 3-amino-1H-1,2,4-triazole-5-thiol (4), 10-1 000 μmol for sodium (5-mercapto-1H-tetrazol-1-yl)acetate (5), 125-500 μmol for 1-phenyl-1H-tetrazole-5-thiol (6) and 50-1 000 μmol for 1-(4-hydroxyphenyl)-1H-tetrazole-5-thiol (7). The relative standard deviation for all determinations was below 1%. The shape of potentiometric titration curve of 6 and 7 is noteworthy at higher concentrations of sodium hydroxide and depends on the type of the indicator electrode (platinum, gold). An introduction of iodine results in a strong potential drop. Some systems do not follow the Nernst equation.

Oxygen reduction on silver catalysts in solutions containing various concentrations of sodium hydroxide – comparison with platinum

In air cathodes for chlorine–sodium hydroxide production, silver is a suitable catalyst for the oxygen reduction reaction (ORR), as is platinum. The ORR mechanism, studied with both rotating disc and ring-disc electrodes and impedance spectroscopy, is first order towards O2. However, the reaction can involve a direct four-electron or two-electron pathway. Although the latter involves different chemistry, including decomposition of hydrogen peroxide, the two pathways are difficult to distinguish, probably because they have the same rate-determining step. Considering kinetics/solubility ratios, temperature increase favours the ORR kinetics on both metals, whereas an increase in sodium hydroxide concentration is only positive for silver: for high sodium hydroxide concentration, platinum properties are hindered by greater adsorbed oxygenated species coverage. Thus, silver becomes competitive to platinum in high concentration alkaline media.

Process Development Aspects of Production of Dibenzyl Ether

To develop an economically viable process for the synthesis of dibenzyl ether, the reaction of benzyl chloride with aqueous sodium hydroxide in the presence of phase-transfer catalysts has been investigated. The effects of agitation speed, catalyst type and concentration, reaction temperature, mole ratio of reactants, concentration of aqueous sodium hydroxide on the conversion of benzyl chloride, and yield of dibenzyl ether have been evaluated. Tributylamine is found to be a suitable catalyst. The reaction is favored by high molar ratio of sodium hydroxide to benzyl chloride. Conversion of benzyl chloride to benzyl alcohol is found to be the rate-controlling step at high sodium hydroxide concentration. Deprotonation of benzyl alcohol at the interphase by aqueous sodium hydroxide is a key step in the formation of dibenzyl ether. The yield of dibenzyl ether is dependent on the concentration of sodium hydroxide in the aqueous phase, the yield being almost 100% at high concentrations of sodium hydroxide. The successful recycle of excess NaOH in the aqueous phase in subsequent batches, without affecting the progress of the reaction, has been demonstrated.

The kinetics of aluminium (III) extraction from sodium hydroxide solutions by an alkylated hydroxyquinoline (Kelex 100)

The rate of the extraction of aluminium (III) from sodium hydroxide solutions by 7-(5,5,7,7-tetramethyl-1-octen-3-yl)-8-hydroxyquinoline (Kelex 100, hereafter called HQ) in kerosene has been investigated under non-equilibrium conditions. In the extraction expressed as Al(OH) 4 − (aq) + 3HQ (org)⇌AlQ 3 (org)+OH − (aq)+3H 2O (aq), it was found that the rate of the forward reaction is first order with respect to aluminium concentration in the aqueous phase; and zero and first order at low and higher concentrations of sodium hydroxide, respectively, with respect to the sodium concentration in the aqueous phase and to the Kelex 100 concentration. As a result, it is inferred that aluminium(III) is taken up through the formation of activated species such as [Al(OH) 3] · OH − and Na + [Al(OH) 3] · OH −.

Studies on the Functional Polysaccharides. (Part 2). Cyanoethylation of pullulan and some physical properties of products.

A water soluble polysaccharide, pullulan was cyanoethylated using acrylonitrile in the presence of sodium hydroxide. The reaction conditions which gave the highest DS of 2.7 were the following: sodium hydroxide concentration, 6%; reaction temperature, 60°C and reaction time, 120min. If the reaction conditions were severer than the above conditions, i.e., higher sodium hydroxide concentration, higher reaction temperature and/or longer reaction time, either the elmination of cyanoethyl group or the formation of acrylonitrile homopolymer was observed. The relatively low DS of 2.7 may be interpreted based on the fact that in pullulan molecules the reactive primary hydroxyl groups at C-6 take part in the backbone linkages. Another possible reason would be the influence of their higher ordered structure and also conceivable steric hindrance. The cyanoethylated pullulan dissolved completely in DMSO, and dissolved almost in DMF and dichloromethane, but the solution in the latter solvent was significantly colored. Thermal decomposition temperatures were remarkably affected by the DS: 227.0°C for DS 1.99 and 262.8°C for DS 2.72. The higher DS resulted in the higher thermal decomposition temperature.