Stoichiometric Concentration Research Articles

Solvent extraction separation of indium and gallium from sulphate solutions using D2EHPA

Abstract Solvent extraction and stripping experiments have been performed to separate indium from gallium in sulfuric acid solutions. In the extraction process, the separation factor between indium and gallium decreased with pH and a maximum value of the separation factor was obtained by extracting metals from the mixed solutions with stoichiometric concentration of di-2-ethyl-hexylphosphoric acid (D2EHPA) to extract both metals. It was found that aliphatic kerosene was superior to benzene as a diluent in respect of loading capacity. In the stripping process, the stripping percentage of indium decreased from 95% to 5% with pH in the pH range of 0.2–1.4, while separation factors increased with the pH of the stripping solutions. From simulation experiments for multistage countercurrent extraction, nearly complete separation of indium and gallium would be accomplished by a two-stage extraction.

Oxidation of cellulose under controlled conditions

Detailed studies on the sodium metaperiodate oxidation of cellulose to yield 2,3-dialdehyde cellulose were carried out to ascertain the effects of concentration of periodate relative to cellulose, temperature of reaction, pH of the medium, effect of morphology of the cellulose, and effect of homogenous versus heterogenous reaction conditions. Microcrystalline cellulose had slightly higher reactivity then cellulose due to its greater purity and lower molecular weight, which gave rise to more reactive end groups. There were no significant changes in the reactivity of cellulose with periodate in buffer solutions of pH 2–5, or of homogenous oxidation of methylcellulose and carboxymethylcellulose as compared to heterogenous oxidation of cellulose powder. It was found that only controlling the concentration of periodate used and the temperature could easily control the rate and extent of oxidation of cellulose. The conclusion is that in order to achieve higher extent of oxidation of cellulose it is preferable to use higher concentration of periodate at 55 °C for short reaction time, instead of stoichiometric periodate concentration for longer reaction times.

Low Corrosive Chemical Decontamination Method Using pH Control, (II). Decomposition of Reducing Agent by Using Catalyst with Hydrogen Peroxide.

In the development of a new chemical decontamination method which provides a high decontamination effect, less corrosion of base metal, and less radioactive waste generation, we developed a decomposition method for oxalic acid coexisting with hydrazine to decrease the amount of radioactive waste. Using a catalyst of 0.5 wt% Ru supported by activated carbon grains, we decomposed oxalic acid and hydrazine, simultaneously and efficiently, with a stoichiometric concentration of H2O22. The decomposition ratios were decreased by the deposition of oxides. But even if the simulated reducing agent solution with high concentrations of coexisting Fe and K ions, which negatively effect decomposition ratio, was decomposed, the decomposition ratios of oxalic acid and hydrazine were kept high during decomposition of the amount of reducing agent used in actual chemical decontamination. Additionally, we examined the deposition ratios of metal ions on the catalyst as metal oxides. These results indicated about 2% of the radioactive species which were removed by the chemical decontamination were deposited on the catalyst column. 59Fe and 51Cr were estimated to be about 90% of the total deposited amount of radioactive species and about 60% of the dose equivalent in the model calculation. But this problem should be easily dealt with by using shielding.

Characterization and activity of Fe-ZSM-5 catalysts for the total oxidation of phenol in aqueous solutions

Fe-ZSM-5 zeolites with of Si/Fe ratios varying from 40 to 200 were synthesized and characterized by IR, XRD, SEM, ESR and ion-exchange techniques. From the obtained results, it is possible to conclude that, these zeolites have a good crystallinity and that the incorporation of Fe3+ ions into the MFI-structure depends on the Si/Fe ratios in the gel: the higher the Si/Fe ratio, the more the percentage of Fe3+ ions is incorporated into the MFI lattice.Catalytic properties of Fe-ZSM-5 were studied in the oxidation of phenol. The reaction was performed in a static system, at the atmospheric pressure, 343K, and with H2O2 concentration, which exceeds stoichiometric concentration for complete oxidation of phenol to carbon dioxide and water. From the catalytic results, it can be concluded that framework Fe can catalyze more completely phenol oxidation than the extra-framework Fe does.

Relationship between Calnexin and BiP in Suppressing Aggregation and Promoting Refolding of Protein and Glycoprotein Substrates

Calnexin (CNX) is a membrane protein of the endoplasmic reticulum that has been defined primarily as a lectin, yet is capable of functioning as a molecular chaperone with non-glycosylated proteins in vitro. Here, we assess the relative contributions of the oligosaccharide- and polypeptide-binding sites of CNX to its in vitro chaperone functions by comparing it with the Hsp70 chaperone of the endoplasmic reticulum, BiP. Both proteins were equally effective in preventing the aggregation of non-glycosylated citrate synthase, indicating that the polypeptide-binding site of CNX is capable of functioning at a level similar to that of Hsp70. However, when confronted with glycoprotein substrates, the lectin site of CNX provided a significant advantage over BiP in suppressing aggregation. CNX also cooperated with BiP and the J domain of Sec63p in the ATP-dependent refolding of glycoprotein and non-glycosylated substrates. The lectin site of CNX was essential for refolding of the glycoprotein. These findings reinforce the function of CNX as a bona fide chaperone and illustrate how its lectin site confers advantages relative to other chaperones when confronted with glycoprotein substrates.

Effect of Laser Wavelength for Surface Morphology of Aluminum Nitride Thin Films by Nitrogen Radical-Assisted Pulsed Laser Deposition

AlN thin films were prepared on Si(100) substrates by the nitrogen radical-assisted pulsed laser deposition method at a low substrate temperature (200°C) as a function of the laser wavelength (1064, 532 and 266 nm). At the laser wavelength of 1064 nm, Al-rich AlN films were deposited and granular crystals with a diameter of 50 nm were observed on the film surface. The surface roughness (Ra) was 15 nm. At the laser wavelength of 266 nm, c-axis-oriented AlN thin films with smooth surfaces (Ra=5 nm) were obtained and the atomic ratio of N/Al was stoichiometric. The full width at half maximum (FWHM) value of the diffraction profile in the 2θ/θ scan mode was 0.55°. It was found that the use of an ultraviolet laser was more effective for preparing the c-axis-oriented AlN films with a stoichiometric concentration and smooth surfaces.

Prediction of flammability of gases by using F-number analysis

A novel method of predicting flammability limits has been proposed. This method utilizes a new flammability index called F-number. For this purpose, an empirical expression of F-number has been derived to account for the flammability characteristics of various organic substances. The analysis has been done by fitting to the observed values of F-number for a wide variety of organic gases and vapors. As a result, it has been found that F-number is an excellent tool to analyze the flammability characteristics of various substances. It has also been shown that the values of upper and lower flammability limits can be derived from F-number together with the stoichiometric concentration corrected for the effect of selective diffusion.

Formation of peroxynitrite at high pH and the generation of S-nitrosothiols from thiols and peroxynitrous acid† in acid solution

The formation of peroxynitrite from hydrogen peroxide and S-nitrosothiols at high pH is shown to involve reaction of the hydroperoxide anion. Kinetic measurements over a pH range 10–13 yield a value close to the literature value for the pKa of hydrogen peroxide and give a quantitative measure of the reactivity of the hydroperoxide ion. S-Nitrosothiols are formed in high yield when peroxynitrous acid reacts with thiols when the thiol is in very large excess, within the pH range 2.7–3.7. Kinetic measurements have shown that reaction occurs by rapid oxidation of the thiol to the disulfide, with release of nitrite ion, which at these pH values is sufficiently protonated to effect nitrosation of the thiol, which is in large excess. Quantitative yields of RSNO can be obtained when there is a very large excess [thiol], when the spontaneous decomposition of peroxynitrous acid cannot compete. The individual kinetic results are fully first order and analysis of the results yields values for the third-order rate constants k (in rate = k [RSH][HNO2][H+]) which are in acceptable agreement with the values in the literature for the direct nitrosation of thiols with nitrous acid. Results were obtained for three thiols [glutathione (GSH), cysteine (Cys) and cysteine ethyl ester], confirming the generality of the reaction. At higher pH values the yield of RSNO drops off sharply as nitrous acid becomes deprotonated. A separate experiment with stoichiometric concentration ratios of thiol and peroxynitrous acid in acid solution gave high yields of nitrous acid. At higher acidities (>0.3 mol dm−3) S-nitrosothiols are still formed, but now there are clearly two sequential first-order processes which can be fitted to a two exponential model. One reaction is believed to be nitrous acid nitrosation, following oxidation of the thiol as before, whilst the other reaction, which is also acid catalysed, is interpreted as nitrosation via a protonated form of peroxynitrous acid as recently reported in the literature, which can compete with the isomerisation of peroxynitrous acid to nitrate anion, when the thiol is at high concentration.

Phalloidin affects the myosin-dependent sliding velocities of actin filaments in a bound-divalent cation dependent manner.

We examined sliding velocities in vitro of four types of actin filaments, that is, filaments with Ca2+ or Mg2+ bound at the high affinity metal binding site, each with rhodamine phalloidin bound with a high or low stoichiometry. When surfaces coated with a high density of heavy meromyosin (HMM) were used, high stoichiometric concentrations of rhodamine phalloidin reduced sliding velocities of only Ca2+-actin filaments, by 40%. As the HMM density on surfaces was reduced, continuous movement of actin filaments became dependent on the presence of methylcellulose and sliding velocities of all four types became progressively slower. Interestingly, Ca2+-actin filaments with a high stoichiometric concentration of rhodamine phalloidin were the fastest among the four types of filaments on sparse HMM surfaces. In contrast, phalloidin did not affect steady state ATPase activities of HMM in the presence of Ca2+- or Mg2+-actin filaments. We speculate that the reversal of the order of sliding velocities among the four types of actin filaments between high and low densities of HMM relates with different axial elasticity of the actin filaments, so that stiffer filaments move slower on dense HMM surfaces, but faster on sparse surfaces, than elastic ones.

Photocatalytic transformations of CCl3Br, CBr3F, CHCl2Br and CH2BrCl in aerobic and anaerobic conditions

Phototransformations of halomethanes containing chlorine and bromine (CCl3Br, CHCl2Br, CH2ClBr) or bromine and fluorine (CBr3F) have been investigated under aerobic and anaerobic conditions both in homogeneous system and heterogeneous photocatalysis. For all of those compounds, the complete disappearance of the primary compound and the stoichiometric concentration of halides was achieved. Several halogenated intermediates and oxygenated compounds were identified, so that it was possible to predict the degradation pathways followed by such halomethanes. Whereas the reductive steps are predominant in the initial degradation of CCl3Br and CBr3F, the oxidative steps are predominant in the initial CH2ClBr steps. The two pathways have comparable importance for CHCl2Br degradation.Methanol, acting as a hole scavenger, strongly increases the rate of disappearance for CCl3Br and CBr3F.

Aluminum nitride thin films prepared by radical-assisted pulsed laser deposition

A radical-assisted pulsed-laser deposition technique was used to deposit aluminum nitride thin films at low substrate temperature (473 K) with a sintered AlN target and the optical emission spectra were measured during the laser ablation. In a nitrogen gas atmosphere, the optical emission peaks of atomic aluminum and singly ionized Al + were observed from the ablation plume within the limit of detection. In a nitrogen radical atmosphere, that of atomic nitrogen and molecular nitrogen (N 2 and N 2 +) were observed from the ablation plumes. The deposited films prepared in nitrogen gas atmosphere contained aluminum above the stoichiometric concentration. By using nitrogen radicals to assist the pulsed-laser deposition, the concentration of nitrogen in the films increased to 50 at% and stoichiometric AlN films were prepared. It is very effective for the fabrication of high-quality AlN thin films to use the nitrogen radicals to assist the pulsed-laser deposition.

Sulphuric acid pressure leaching of laterites — universal kinetics of nickel dissolution for limonites and limonitic/saprolitic blends

The high-temperature acid pressure leaching of nickeliferous laterites has attracted considerable attention from the nickel industry during the recent years. The process is especially advantageous for low-grade limonitic laterites. It is also applicable to mixtures of limonites and high-grade saprolites, although at higher acid consumption due to magnesium. It is advantageous, therefore, to derive a universal kinetic equation of Ni dissolution that is equally applicable to both types of feed. In the present work, a kinetic equation was derived using the concentration of hydrogen ion “at temperature” calculated from a solution speciation approach, and the assumption that nickel associated with magnesium dissolves instantaneously. This universal kinetic equation was successfully tested against various feeds that contained from 1.2% to 1.9% of Ni and up to 3.85% of Mg at temperatures from 230°C to 270°C, acid/ore ratios from 0.15 to 0.5, and concentrations of solids in the feed (pulp density) of up to 30%. The use of acidity “at temperature” made it possible to explain an apparent dependence of the ultimate Ni extraction on the acid/ore ratio, and on the terminal stoichiometric acid concentration during leaching.

Accumulation Effect of Bombarding N2+ Ions in Al for Crystal Growth of AlN Film

Dynamic observations of crystallographic structure by reflection high energy electron diffraction (RHEED) and measurement of sputtering yield with a quartz oscillator were performed simultaneously for an Al surface under 12 keV N2+ ion bombardment, in order to elucidate the optimum conditions for crystal growth of AlN. A simple theoretical model of sputtering was used to evaluate the accumulation of N-atoms, and a surface concentration of implanted N-atoms of ∼44 at.% was estimated, close to the stoichiometric concentration of AlN. Thus, AlN crystal growth under 12 keV N2+ ion bombardment was achieved with considerable success.

Reactive processing of poly(ethylene terephthalate) modified with multifunctional epoxy-based additives

The use of multifunctional epoxy-based modifiers to increase the melt strength of poly(ethylene terephthalate) (PET) has been investigated, with the aim of producing PET foams by an extrusion process. The reaction conversion has been studied as a function of time by the measurement of torque in an internal mixer. A tetraglycidyl diamino diphenyl methane (TGDDM) resin was selected for the investigation of the modifier concentration effect on the reaction conversion. Using a stoichiometric concentration of TGDDM, the molecular weight distribution of modified PET, as determined by gel permeation chromatography (GPC), showed an eight-fold increase of the z-average molecular weight ( M z ) and the presence of branched molecules of very large mass. The resulting intrinsic viscosity of the modified PET was 1.13 dl/g.

Reversible Hydriding of LaNi5 − x Al x ― Pd Composites in the Presence of Carbon Monoxide

Carbon monoxide is one of the most dangerous impurities in gas mixtures involved in the hydriding of intermetallic compounds, and up to the present time the concentration limit 0.03 vol.% CO has not been surmounted. The objective of the present work was to investigate the possibility of reversibly hydriding LaNi5 − xAlx ― Pd composites in gas mixtures containing up to 5 vol.% CO. The experimental specimens were mixtures of palladium black and LaNi5, LaNi4.7Al0.3, LaNi4.5Al0.5, LaNi4.2Al0.8, and LaNi4Al powders cold pressed at 300 MPa. The intermetallics were preliminarily dispersed by hydriding and mechanical grinding. The concentration of palladium black in the powder mixtures was varied from 0 to 1.5 mass%. It was shown that it is possible to reversibly hydride LaNi5 − xAlx ― Pd composites in mixtures of hydrogen and carbon monoxide containing up to 5 vol.% CO at the temperatures 423 and 473 K. It was established that alloying LaNi5 with aluminum in amounts which raised the stoichiometric concentration above 0.5 stabilized the absorption properties of LaNi5 − xAlx ― Pd in the presence of CO. The composition LaNi4Al was optimal. Palladium additions to LaNi5 − xAlx ― Pd composites also increased the stability of hydrogen absorption by the intermetallic. It is noted that the effect of palladium was more positive than that of aluminum.

Effects of non-uniform solvation on thermal response in poly(N-isopropylacrylamide) gels

The quantitative analyses on the dehydration of poly(N-isopropylacrylamide) (NIPA) hydrogels were conducted by means of differential scanning calorimetry (DSC) as a function of polymer volume fraction, φ. It was found that the thermal properties of NIPA gels were strongly dependent on the history of the gel treatment before DSC measurements. In particular, a disagreement in the hydrophobic dissociation temperature at which an endothermic peak appears, Thd, and in the enthalpy of dehydration, ΔH, was clearly detected between gels having different histories: one prepared by adding a given amount of water to a dried gel (non-equilibrated gels) and the other made by gradual shrinking along the isobar line by heating (equilibrated gels). The phase diagram, i.e. the plot of Thd vs. φ, for the equilibrated gels has a convex function of φ, whereas that of the non-equilibrated gel shows an anomalous dip for φ>φst≈0.4 (i.e. above the stoichiometric concentration of NIPA-water hydration). The values of ΔH for the non-equilibrated gels are less than those for the equilibrated gels in the concentration regime of φ>φst. This implies that the non-equilibrated gels have a higher degree of non-uniform solvation than the equilibrated gels.

Role of lanthanide elements on the catalytic behavior of supported Pd catalysts in the reduction of NO with methane

In this study, the role of lanthanide elements (Ce, Gd, La, and Yb) on Pd/TiO 2 catalysts in the catalytic reduction of NO with methane was investigated. Steady-state reaction experiments in the presence of oxygen showed that the addition of lanthanide elements increases the oxygen resistance of the catalyst. The post-reaction XPS characterization results revealed that majority of the Pd sites remained in the zero oxidation state in the presence of Ce or Gd. The effect of SO 2 (145 ppm) and H 2O (0–6.6%) in NO–CH 4–O 2 reaction over supported Pd and Gd–Pd catalysts was also investigated. Over the Gd–Pd catalyst with the presence of SO 2, more than 70% NO conversion was obtained for over 6 h while the Pd only catalyst showed a sharper drop in NO conversion. Over the Gd–Pd catalyst, the presence of H 2O showed no effect on NO conversion activity (>99% conversion) during the 18 h the catalyst was kept on stream. Among the lanthanide elements tested, Gd is the most effective, allowing the use of above stoichiometric oxygen concentration.

Thermoreversible Gelation with Two-Component Networks

This paper studies thermoreversible gelation in two-component polymer mixtures (A/B) in which both polymers carry associative groups capable of forming reversible pairwise bonds. The type of association is classified into the following three main categories: (i) association of polymers within the same species (AA and BB); (ii) association only between the different species (AB); (iii) all associations allowed (AA, BB and AB). On the basis of a recent theory of associating polymers, we derive possible phase diagrams for interpenetrating networks, alternating networks, and randomly mixed networks corresponding to each category, with special attention to the interference between gelation and macroscopic phase separation. For all types, homogeneously mixed networks are most easily stabilized near the stoichiometric concentration where the total number of A associative groups in the mixture agrees with that of B associative groups.

Nitride layers formed by nitrogen implantation with an energy scanning mode

We reported that a very smooth surface was obtained by room temperature nitrogen implantation into Zr with the energy increasing mode from 35 to 65 keV even with a high dose of 7×10 17 ions cm −2 in contrast to the implantation with the energy decreasing mode and 50 keV mono-energy implantation by which many blisters were observed on the surface. In order to understand the mechanism that causes radiation damage, a dynamic Monte Carlo simulation with the dynamic-SASAMAL code was performed for such an energy scanning mode. The movement of the nitrogen at the stage where the excess nitrogen over stoichiometric concentration just starts to migrate towards the surface was carefully analyzed and the results for the energy increasing mode from 15 to 85 keV with a uniform distribution were compared with that of the energy decreasing mode and 50 keV mono-energy implantation. It was found that, when nitrogen concentration exceeds the stoichiometry, the nitrogen that is enforced to migrate towards the surface is not the newly implanted nitrogen but is the previously implanted one which is moved by the newly implanted nitrogen through binary collisions. The moment given through the collision is towards the surface in the energy increasing mode and it will enhance the migration. In contrast to this, the moment is towards the deeper side in the energy decreasing mode and the mono-energetic implantation, so it will disturb the migration and cause nitrogen gas bubble formation which induces the surface radiation damage with many blisters. Finally, it is proposed that a thick nitride layer without surface damage can be obtained by the energy increasing mode implantation with an adequate energy distribution.

Copper removal from molybdenite concentrate by sodium dichromate leaching

Molybdenite flotation concentrate was leached with sodium dichromate–sulfuric acid solutions in order to remove the copper sulfide impurities. The experimental results indicated that the temperature has a large influence on the copper dissolution. The concentration of dichromate has also a pronounced effect for concentrations under 0.10 M, while sulfuric acid concentration over the stoichiometric value has a deleterious effect on the copper dissolution. The purification of molybdenite concentrates by this method is feasible, and the best results were obtained by leaching the concentrate with the stoichiometric concentration of H 2SO 4 and 0.12 M Na 2Cr 2O 7 solution for 90 min at 100°C. Under these conditions, about 95% of the copper was dissolved with little dissolution of molybdenum. The kinetic study showed that the dissolution of copper from the concentrate is well represented by a shrinking core model controlled by diffusion through a porous layer, 1/3 ln(1− α)−[1−(1− α) −1/3]= k t. The apparent activation energy obtained was 40 kJ/mol for the temperature range 50 to 100°C.