Hydroxide System Research Articles

ChemInform Abstract: Selective Hydrolysis of Nitriles to Amides Using NaOH-PEG under Microwave Irradiation.

Abstract We describe here an efficient, rapid and selective method for the conversion of nitriles in to their corresponding amides in the presence of PEG-400, aqueous sodium hydroxide system under microwave irradiation.

Synthesis and magnetic properties of platelet Fe–Co particles

The synthesis scheme for hexagonal shaped Fe–Co platelets with magnetic properties comparable to the bulk is reported for the first time. The hexagonal Fe–Co platelets with the size of about 8 μm and an aspect ratio of about 5.4 were prepared by reducing the platelet shaped intermediate obtained in ethylene glycol-metal salts-sodium hydroxide system. The saturation magnetization and coercivity of the Fe–Co hexagonal platelets obtained by reducing the solid intermediate at 673 K in hydrogen atmosphere were above 220 emu/g and 25 Oe, respectively. Since the use of such particles in high frequency applications demand further reduction in size and increment in aspect ratio, a synthesis scheme for particle morphology control was devised. The proposed synthesis scheme using nucleating agents clearly demonstrated that the shape, size, and aspect ratio of the platelets can be controlled freely. Consequently, platelets with elongated shape and thickness of about few hundred nanometers were produced. Though further reduction in size and aspect ratio is demanded, the proposed synthesis scheme holds promise for the development of Fe–Co platelet particles suitable for high frequency applications.

Desiliconization kinetics of nickeliferous laterite ores in molten sodium hydroxide system

A novel process was proposed for treating nickeliferous laterite ores with molten sodium hydroxide. The effect on silicon extraction caused by the factors, such as stirring speed, reaction temperature, particle size and NaOH-to-ore mass ratio, was investigated. The results show that increasing stirring speed, reaction temperature and NaOH-to-ore mass ratio while decreasing particle size increases silicon extraction rate. The desiliconization kinetics of nickeliferous laterite ores in molten sodium hydroxide system was described successfully by chemical reaction control model. The activation energy of the desiliconization process was found to be 44.01 kJ/mol, and the reaction rate based on a chemical reaction-controlled process can be expressed as: 1–(1–α) 1/3= 27.67exp[−44 010/( RT)] t.

Thin film of coumarin-3-carboxylate and surfactant co-intercalated layered double hydroxide with polarized photoluminescence: a joint experimental and molecular dynamics study

This paper describes a systematic investigation on the photophysical properties, thermal stability, and orientational structure of a coumarin-3-carboxylate (C3C) and dodecylsulfonate (DDS) co-intercalated Mg-Al-layered double hydroxide (C3C-DDS/LDH) system. C3C and DDS with different molar ratios were co-intercalated into the interlayer region of Mg-Al-LDH. The structures of the composites were characterized by X-ray diffraction (XRD), thermogravimetric and differential thermal analysis (TG-DTA). Fluorescence spectra demonstrate that the sample with 1.96% C3C molar percentage (with respect to the total organic components) exhibits the optimal luminous intensity. The fluorescence lifetime of C3C in C3C-DDS/LDH is enhanced significantly compared with that of pristine C3C solution (5.52 ns vs. 2.70 ns), revealing that the co-intercalation method is favorable for the improvement of the luminescence performances of the dye. C3C-DDS/LDH thin film was fabricated by the solvent evaporation method, which exhibits well polarized luminescence with the luminescent anisotropy of 0.10–0.15 at ambient temperature. Furthermore, molecular dynamics (MD) simulation was employed to calculate the basal spacing and molecular arrangement of intercalated C3C and DDS in the LDH matrix. The simulation results show that the intercalated C3C anions exhibit a tendency from tilted to vertical orientation relative to the inorganic layers as the interlayer DDS content increases. Moreover, the increase of the distance between C3C anions can be achieved enough upon the co-intercalation of DDS, presenting the key role of surfactant for preventing dye aggregation. Based on the combination of experimental and simulated studies, the photoluminescence properties of the C3C-DDS/LDH thin film were deeply studied and optimized, and a detailed understanding of the orientation of two individual guest molecules confined within the galleries of host layers was achieved.

Decomposition of acid dissolved titanium slag from Australia by sodium hydroxide

The kinetics of the decomposition of acid dissolved titanium slag with a sodium hydroxide system under atmospheric pressure was studied. The effect of reaction temperature, particle size and NaOH-to-slag mass ratio on titanium extraction was investigated. The results show that temperature and particle size have significant influence on titanium extraction. The experimental data of titanium extraction show that the shrinking core model with chemical reaction controlled process is most applicable for the decomposition of slag, with an apparent activation energy of 62.4 kJ.mol(-1). Approximately 85 wt.%-90 wt.% of the titanium can be extracted from the slag under the optimal conditions. In addition, the purity of titanium dioxide obtained in the product is up to 98.5 wt.%.

Heat Transfer under Buoyancy-Induced Flow at the Chemical Reaction Front Using Thermochromic Liquid Crystal Sheet

Heat transfer and hydrodynamics at the chemical reaction front have been investigated experimentally using a thermochromic liquid crystal sheet. If the chemical reaction occurs, a band region where the temperature, due to the heat of reaction, is higher than the initial temperature appears at the reaction front. Natural convection due to the temperature difference at the reaction front plays an important role in conveying the higher temperature fluid. For the hydrochloric acid (HCl)–sodium hydroxide (NaOH) system, as the frequency of contact between HCl and NaOH due to convection increases with the concentration of ethanol, the temperature beyond the stagnation point becomes higher than that in other areas. On the other hand, for the acetic acid (CH3COOH)–NaOH system, the heat transfer depends mainly on the heat of reaction, because the rate of CH3COOH dissolution is smaller than that of HCl.

Characterization of self-assembled films of NiGa layered double hydroxide nanosheets and their electrochemical properties

In this study, we have demonstrated the synthesis and delamination of a rarely studied NiGa layered double hydroxide (LDH) system. Hydrothermal treatment under agitation conditions at 200 °C for 4 h resulted in the formation of highly crystalline NiGa LDHs in a shorter time than those synthesized without agitation. The LDH was delaminated into the individual nanosheets in formamide. The most significant finding in this study is the electrochemical behavior of interlayer ferricyanide anions intercalated with the layer-by-layer (LBL) assembly method. The morphology of LBL film with one layer is also monitored with atomic force microscopy. The cyclic voltammogram is similar to potassium metal hexacyanoferrate systems with its unique two-peak wave. Raman spectrum of the film revealed that the metal center of the interlayer cyano complex is in interaction with the Ni 2+ of the host layer. It was concluded that the two-peak cyclic voltammogram of the film is a result of two different forms of the hexacyanoferrate in the interlayer.

Decomposition kinetics of titanium slag in sodium hydroxide system

A novel process was proposed for preparing titanium dioxide by the decomposition of titanium slag in sodium hydroxide system under atmospheric pressure. The kinetics on the decomposition of titanium slag was mainly investigated. The results on effect of reaction temperature, particle size and NaOH-to-slag mass ratio on titanium extraction show that the temperature and particle size have significant influence on the titanium extraction. The experimental data of titanium extraction indicate that the shrinking core model with chemical reaction controlled process is most applicable for the decomposition of titanium slag, with the apparent activation energy of 40.8 kJ mol − 1 . Approximately 95–98% of titanium in the titanium slag could be extracted under the optimal reaction conditions. In addition, the content of TiO 2 obtained in the product is up to 99.3%.

Reduction of lead in the lead sulfide-molten sodium hydroxide system

Based on thermodynamic investigations of the reduction of lead from its sulfide compounds using the electron-donating properties of sulfur of its sulfide, we studied the effect of various factors on the reduction of lead (“metallization”) in molten sodium hydroxide. In the range of temperatures of smelting PbS with the alkali (470–510°C), there occurs a “burst” metallization reaching 95% at T = 550°C; at T = 650°C, the process is completed in 15 min; at 650–500°C, the reduction of the metal occurs in the diffusion region. The NaOH: PbS weight ratio (α) exerts a direct effect on the yield of the compact metal (‘lens’). At α = 1.8−0.8, the yield of the compact metal is 96–98%. It has been confirmed experimentally that the chemism of the utilization of elementary sulfur is related to a disproportionation of the latter with the accumulation of S2− and SO42− ions and the possible formation of polysulfide sulfur Sn2−.

Hydrothermal synthesis of CeO2 nano-particles

Nano-crystalline particles of CeO2 have been synthesized via a low temperature hydrothermal synthesis process. Two types of precursors were studied—cerium hydroxide and ceria acetate. The precursors were adjusted to a basic (pH 10) and acidic (pH 4) medium before hydrothermal treatment at various durations of 6, 12, 18, and 24 h at 250 °C using a Teflon-lined hydrothermal bomb. The synthesized samples were characterized using DTA/TGA, XRD and TEM. Based on the characterization results, both precursor systems produced crystalline ceria nano-particles after 6 h of hydrothermal synthesis at 250 °C. The average crystallite sizes were 6 and 15 nm for the hydroxide and acetate system, respectively. The acetate precursor system appeared to produce better particles in terms of crystallinity and morphology. Based on the DTA/TGA analysis, hydrothermal synthesis had been effective in reducing the amount of intermediate products. With increasing hydrothermal treatment duration of up to 24 h, the samples did not exhibit a remarkable improvement in properties. The synthesized nano-particles were subsequently heat treated at 500 and 1000 °C for 2 h. After the heat treatment, enhanced crystallinity and growth in crystallite size was observed, but particles appeared more agglomerated.

Removal of Methyl Mercaptide by Iron/Cerium Oxide−Hydroxide in Anoxic and Oxic Alkaline Media

The oxidation of methyl mercaptide by Fe/Ce oxide−hydroxide was studied as a potential approach to deal with the methyl mercaptan contamination from total reduced sulfur (TRS) emissions in the pulp and paper industry. The reaction was studied in aqueous solutions at 22 °C and different alkaline pH values (10.5−12) both in anoxic and oxic conditions. Mercaptide reactivity was strongly dependent on pH in anoxia, whereas in oxic conditions it was noticeably higher but tributary of dissolved oxygen (DO2). Interference with bisulfide comixed with mercaptide caused an inhibition in the conversion for both pollutants. Such inhibition was due to the incipient polysulfides formed via bisulfide oxidation. On the contrary, the mercaptide conversion was found to improve at the expense of bisulfide when large quantities of exogenous polysulfides were present initially in the reaction medium. The conversion of mercaptide was unaffected with the comixing of dimethyl sulfide. The oxidation of methyl mercaptide by the O2/Fe/Ce oxide−hydroxide system did not affect the reoxidative regeneration of surface Fe(III) by DO2. This feature pinpoints the sine qua none condition for a redox process based on the O2/Fe/Ce oxide−hydroxide system to remove methyl mercaptan in pulp and paper emissions.

Solid-state NMR investigations of the pyrolysis and thermo-oxidative decomposition products of a polystyrene/red phosphorus/magnesium hydroxide system

Thermal, thermo-oxidative and fire residues of high impact polystyrene/magnesium hydroxide/red phosphorus (HIPS/Mg(OH) 2/P r) are investigated by solid-state NMR and compared with the results for the binary subsystem Mg(OH) 2/P r. The influences of oxygen, nitrogen and temperature are discussed. For a thermal decomposition and pyrolysis during combustion, the main pyrolysis of HIPS takes place while the remaining residue is a rather intact polymer, with a major share of the embedded P r still present. Subsequently, mainly amorphous phosphates and a slight amount of crystalline Mg 3(PO 4) 2 and Mg 2P 2O 7 are formed at the highest temperatures. Only with increasing mass loss does the remaining polystyrene structure decompose and graphitic structures occur. The influence of oxygen on the decomposition mechanism is most obvious for the binary system Mg(OH) 2/P r. P r vanishes more rapidly and crystalline, oxygen-rich magnesium phosphates are formed. In HIPS/Mg(OH) 2/P r systems the polymer acts as a barrier to reaction by the embedded particles, so that major characteristics of an anaerobic decomposition are found. Significant amounts of phosphorus are retained in the condensed phase through a reaction of P r with Mg(OH) 2 to mostly amorphous phosphates. This formation of amorphous inorganic magnesium phosphates can act as an additional physical barrier. This study outlines some advanced approaches for controlling the condensed-phase mechanisms of phosphorus and underlines that solid-state NMR is a most powerful tool for investigating the organic and inorganic residues.

Study of hydromagnesite and magnesium hydroxide based fire retardant systems for ethylene–vinyl acetate containing organo-modified montmorillonite

A new flame retardant (FR) system for ethylene–vinyl acetate, mainly based on the combination of hydromagnesite (HM, obtained from an industrial by-product) and organo-modified montmorillonite (oMMT) has been compared with a magnesium hydroxide (MDH) and oMMT flame retardant system. The presence of oMMT in association with both hydrated minerals gave a strong decrease of heat release rate in cone calorimeter tests. Moreover, the HM/oMMT combination leads to a better improvement of resistance to ignition and self-extinguishability in comparison with the MDH/oMMT one. The study of residues formed during thermal decomposition revealed the formation of forsterite (Mg 2SiO 4) when either MDH or HM was used in combination with oMMT. SEM observations of residues showed sintering of the mineral particles at high temperature particularly in the case of HM/oMMT composition.

Friberg Correlations in Oil Recovery

The current status of “Friberg correlations” is reviewed and illustrated in model and industrial systems relevant to the oil industry. For a model naphthenic acids/sodium hydroxide two‐phase system, a third, liquid crystal (LC), phase is formed at the o/w interface from sodium naphthenates, which is produced in situ by a chemical reaction. This LC layer spreads spontaneously on the o/w interface, thus it is a “surface‐active phase” in the sense defined by R. G. Laughlin. When this additional phase covers the oil/water interface it modifies the transport processes throughout the interface. The LC layers on water droplets may be one of the reasons for the high water‐in‐oil emulsion stability observed in industrial systems. This suggestion is supported by the increased stability of water‐in‐bitumen emulsions doped with sodium naphthenates at concentrations higher than 50 ppm. The stability of the emulsion droplets can be further enhanced by capturing solid particles or precipitated asphaltenes at the LC‐coated interfaces. At equilibrium, optically anisotropic structures are detected in the bitumen/water/sodium hydroxide system, indicating the presence of a liquid crystal (LC) phase in industrial systems. The possible source of errors and proper use of polarization microscopy are discussed for LC phase containing emulsions.

Rapid Coprecipitation Technique with Hybrid Hydroxide System Using Ytterbium(III), Gallium(III), and Magnesium(II) for Simultaneous Concentration of 13 Elements in Concentrated Salt Solution Prior to Their Inductively Coupled Plasma Atomic Emission Spectrometric Determination

Abstract Beryllium(II), chromium(III), manganese(II), iron(III), cobalt(II), nickel(II), copper(II), zinc(II), arsenic(V), selenium(IV), cadmium(II), antimony(III), and lead(II) ions in concentrated salt solutions, such as seawater or sodium chloride and sulfate solutions, were collected quantitatively by coprecipitation with hydroxides of ytterbium(III), gallium(III), and magnesium(II). In this method, a rapid coprecipitation technique combined with internal standardization was applied to simplify the operation; yttrium was used as an internal standard. The 13 elements collected were readily determined by inductively coupled plasma atomic emission spectrometry using internal standardization. The detection limits (3σ, n = 10) were in the range of 0.003 μg (for beryllium(II)) to 0.13 μg (for zinc(II)) in the initial sample solution (up to 150 mL). The proposed method was applied to the analyses of some commercially available salts and an effluent as well as the certified reference materials; the elements ranging from 0.03–0.14 μg g−1 in the salts, 0.004–0.041 mg L−1 in the effluent, or 0.006–0.30 mg L−1 in the certified reference materials could be determined with the relative standard deviation of 7–33, 0.3–3, or 2–17%, respectively. The time required for the preconcentration was approximately 20 min.

Voltammetry of Dissolved Iron(III)–Nitrilotriacetate–Hydroxide System in Water Solution

AbstractThe investigation of the dissolved iron(III)–nitrilotriacetate–hydroxide system in the water solution (I=0.1 mol L−1 in NaClO4; pH 8.0±0.1) using differential pulse cathodic voltammetry, cyclic voltammetry, and sampled direct current (DC) polarography, was carried out on a static mercury drop electrode (SMDE). The dissolved iron(III) ion concentrations varied from 2.68×10−6 to 6×10−4 mol L−1 and nitrilotriacetate concentrations were 1×10−4 and 5×10−4 mol L−1. By deconvoluting of the overlapped reduction voltammetric peaks using Fourier transformation, four relatively stable, dissolved iron(III) complex species were characterized, as follows: [Fe(NTA)2]3−, mixed ligand complexes [FeOHNTA]− and [Fe(OH)2NTA]2−, showing a one‐electron quasireversible reduction, and binuclear diiron(III) complex [NTAFeOFeNTA]2−, detected above 4×10−4 mol L−1 of the added iron(III) ions, showing a one‐electron irreversible reduction character. The calculations with the constants from the literature were done and compared with the potential shifts of the voltammetric peaks. Fitting was obtained by changing the following literature constants: log β2([Fe(NTA)2]3−) from 24 to 27.2, log β1([FeNTA]−) from 8.9 to 9.2, log β2([Fe(NTA)2]4−) from 11.89 to 15.7 and log β2([Fe(OH)2NTA]3−) from 15.63 to 19. The determination of the electrochemical parameters of the mixed ligand complex [FeOHNTA]−, such as: transfer coefficient (α), rate constant (ks) and formal potential (E°') was done using a sampled DC polarography, and found to be 0.46±0.05, 1.0±0.3×10−3 cm s−1, and −0.154±0.010 V, respectively. Although known previously in the literature, these four species have now for the first time been recorded simultaneously, i.e. proved to exist simultaneously under the given conditions.

Density, viscosity, refractive index and electrical conductivity of saturated solutions of the lithium hydroxide + ethanol + water system at 298.15 K, and thermodynamic description of the solid–liquid equilibrium

The water + ethanol + lithium hydroxide system has a great potential for implementing drowning-out crystallization processes in industrial lithium hydroxide production. For this reason, a knowledge of both the most relevant physical properties as well as the thermodynamic description of the solid–liquid equilibrium of this system is of great interest for designing industrial applications. In this paper, the density, viscosity, refractive index and electrical conductivity of the saturated solutions of water + ethanol + lithium hydroxide at 298.15 K were measured for different mass fractions of ethanol/solution in a range from 0 to 0.6. Equations are given for the values of the measured properties as a function of the mass fraction of ethanol. The phase diagram at 298.15 K was determined and its regions were illustrated. Under our experimental conditions, the precipitated salt was, in all cases, LiOH·H 2O. Finally, a thermodynamic description of the solid–liquid equilibrium of the ternary system is provided based on the Chen model for calculating the mean ionic activity coefficients. This approach requires nine binary interaction parameters for a ternary system. Here, only the three binary interaction parameters corresponding to the LiOH + ethanol system were fitted, while the six remaining parameters (those corresponding to the water + ethanol and LiOH + water systems, respectively) were taken from previous published values.

Structural Changes of Cellulose Crystallites Induced by Mercerisation in Different Solvent Systems; Determined by Powder X-ray Diffraction Method

The completeness of mercerisation can be evaluated by investigating the changes in the crystalline regions of cellulose from cellulose I (C-I) to cellulose II (C-II) by the X-ray powder diffraction method. Mercerisation experiments in four different solution systems: ethanol/water, acetone, DMSO and xylene, are reported. Also the effect of some additives, external pressure, treatment time and alkalisation temperature were studied. In two-phase solvent systems, structural changes of cellulose crystallites depended primarily on the distribution and solubility of sodium hydroxide in the solvent phases. The sodium hydroxide concentration in the hydrophilic phase must exceed 7–8 w/w-% before complete crystal change from C-I to C-II can occur. The precipitation of sodium hydroxide due to high concentration prevents the successful use of one-phase ethanol/water system in slurry process. On the contrary, the 2-propanol/water/sodium hydroxide system separates into two layers; to the water-rich lower layer and the 2-propanol-rich upper layer, where the sodium hydroxide remains mainly in the water-rich lower layer. This prevents the precipitation of sodium hydroxide and promotes the alkalisation of cellulose. Ammonium chloride and ammonium hydroxide clearly had a positive effect by promoting the crystal changes, however, the urea concentration used in this study was obviously too small. In the advantageous two-phase 2-propanol/water systems, the alkalisation time was only 15 min when the treatment temperature was kept between 0 and 10 °C. Reduced external pressure was found to have a small but still detectable positive effect on cellulose alkalisation while over-pressure prevented crystal changes.

Catalytic role of ammonia in the anodic oxidation of gold in copper-free thiosulfate solutions

Literature data is re-interpreted to show that the anodic oxidation of gold in ammoniacal thiosulfate solutions is dependent upon the concentration product [M 2S 2O 3][NH 3] to the order 0.8 (M=Na or NH 4). Analysis of chemical speciation in solution shows that the concentration of NH 4S 2O 3 − ion-pair is equal or larger than that of the unassociated S 2O 3 2− ion. A species distribution diagram for the gold(I)–ammonia–thiosulfate–hydroxide system in solutions of 1 M ammonium thiosulfate solutions containing 0.5–2 M ammonia at pH 10–11 shows that although Au(S 2O 3) 2 3− is the predominant complex (>99%), a small fraction of Au(S 2O 3)(NH 3) − is present. It is proposed that ammonia facilitates gold dissolution via oxidation of the surface adsorbed species Au(S 2O 3)(NH 3) 2− (ads). This oxidation corresponds to a rate constant of k Au=2.8×10 −4 mol m −2 s −1 to produce Au(S 2O 3)(NH 3) − (ads/aq) followed by desorption and re-equilibration in solution to Au(S 2O 3) 2 3−.

Self-Alignment of Inorganic Biomimetic Liquid Crystals: Magnetic Field Effects

The Al-Fe hydroxide system is one of a limited number of inorganic liquid crystals systems. It is a biomimetic analoque to collagen, and has the advantage that it can be prepared with a specific size, so its self-alignment can be studied as a function of size. It responds to surface forces as well as magnetic fields. For a grated surface, we find that the smaller (<300 nm) and intermediate (2–3 μm ellipsoidal plates) particles align following the contour of the surface, whereas the large particles (>2 μm equiaxed plates) tend to agglomerate and sit on the surface with no order at all. When we apply a magnetic field to the particles on the surface, we find that, for the smaller particles, there is a competition between the magnetic field and the surface. The top particles will align with the magnetic field. The intermediate particles act as though they are large particles, and tend to agglometrate in the magnetic field, even in the presence of a grated surface. The large particles behave the same as in contact with the surface. The smaller particles behave like an organic liquid crystal.