Ammonium Hydroxide Concentration Research Articles

Oxidative Ammonolysis of Technical Lignins. Part 4. Effects of the Ammonium Hydroxide Concentration and pH

The effects of ammonium hydroxide concentration and pH on the kinetics and reaction mechanism of oxidative ammonolysis of Repap organosolv lignin were studied. The reactions were carried out at 100°C with an oxygen pressure of 8 bar (116 psi) and 0.4–1.6 M [NH4OH] and 9–12.7 pH. The resulting N‐modified lignins were analyzed for elemental composition and methoxyl group content. An increase in ammonium hydroxide concentration increased the rate of nitrogen incorporation, oxygen consumption, CO2 formation, and lignin dissolution. The rate of nitrogen incorporation was 0.5 order with respect to NH4OH concentration. The amount of oxygen consumed, oxygen incorporated into the lignin, CO2 formed, and OMe groups eliminated per mole of nitrogen incorporated decreased with increasing ammonium hydroxide concentration indicating that the increase in [NH4OH] accelerated nitrogen incorporation more than lignin oxidation. The dependence of the rate of nitrogen incorporation on the reaction pH went through a maximum leading to the conclusion that HO− competes with ammonia in reactions with electrophilic lignin centers resulting in interruption of nitrogen incorporation into the lignin.

Optimisation of HSQ e-beam lithography for the patterning of FinFET transistors

FinFET transistors are presented as promising candidates to extend CMOS lifetime. One major challenging technological step in the process fabrication of such devices is the patterning of narrow, sharp, densely packed silicon fins. As an attempt to face this challenge, hydrogen silsesquioxane (HSQ) is used as a negative tone e-beam resist. This paper presents a study on the pre- and post- e-beam exposure process of the HSQ resist to limit the impact of proximity effects. The post application bake (PAB) and the concentration of tetramethyl ammonium hydroxide (TMAH) in the developer solution have been investigated. It is found that contrast can be improved by 7× using a lower pre-bake temperature (80 °C) and a more concentrated TMAH solution (25%). The impact of contrast improvement on the control of the critical dimension (CD) is also studied. Cross-sectional scanning electron microscope (SEM) views show fin networks with a pitch ranging from 40 to 200 nm. The HSQ line profiles are steep with top-angles measured near 90° and an excellent uniformity across the whole network is obtained. The HSQ lines have also been successfully transferred to a silicon layer by dry etching using a SF 6/N 2/O 2 based chemistry. The anisotropy of the etching process is demonstrated by measuring the top-angle of the lines. The process proposed in this paper enables the fabrication of very dense patterns such as silicon fins as thin as 15 nm with 25 nm spaces between lines.

Dispersion and rheological properties of concentrated silicon aqueous suspension

This work focuses on the optimization of the rheological properties of silicon suspensions by changing the concentration of a dispersant and the pH value of the dispersing medium. The zeta potential and rheological properties of silicon suspensions as a function of tetramethyl ammonium hydroxide (TMAH) concentration were carried out. The results show that the isoelectric point of the silicon particles was at pH 1.6. A silicon suspension with 46 vol.% particles displayed a minimum viscosity at pH 9.6. The results also show that TMAH is an efficient dispersant by enhancing the absolute value of the zeta potential of silicon particles. The optimum dosage of the dispersant was 0.4 wt.% of silicon particles.

An optimal high contrast e-beam lithography process for the patterning of dense fin networks

There are many difficulties to overcome towards the integration of 10 nm CMOS technology. One such major challenge is to keep a tight control of the leakage current of devices while increasing the current drive at a reduced supply voltage. In this context, multi-gated structures, which are used to control the transport in ultra-thin channel (e.g. FinFET), are a promising solution. A critical step during the fabrication process of a FinFET is the patterning of dense, high aspect ratio fins. High demand is therefore placed on e-beam lithography techniques to obtain narrow, sharp, densely packed resist lines. This paper presents a detailed study on the optimum e-beam exposure process using a negative tone e-beam resist, namely Hydrogen Silsesquioxane (HSQ). The impact of the pre-exposure bake temperature, of the Tetramethyl Ammonium Hydroxide (TMAH) concentration in development solution and of development time has been investigated. The standard process uses 2.38% TMAH as a developer, samples being pre-baked on a hotplate at a temperature between 150 and 220 °C for 2 min. By using a lower pre-bake temperature of 90 °C and a more concentrated TMAH solution dosed at 25%, a seven-fold improvement of contrast can be obtained in terms of contrast values. Cross sectional SEM views show fin networks with a pitch ranging from 40 nm to 200 nm. The line profiles are steep and an excellent uniformity is obtained across the whole network, even for lines located at the edge. Dense patterns are presented with lines as narrow as 15 nm and with a 25 nm space.

Surface chemical modification of TEOS based silica aerogels synthesized by two step (acid–base) sol–gel process

Abstract The present paper describes the comparative studies on the hydrophobic and physical properties of the tetraethoxysilane (TEOS) based silica aerogels prepared by two step sol–gel process followed by supercritical drying. Silica alcogels were prepared by keeping the molar ratio of TEOS:methanol (MeOH):H 2 O (acidic):H 2 O (basic) constant at 1:33:3.5:3.5 with oxalic acid and ammonium hydroxide concentrations fixed at 0.001 and 1 M, respectively. In all, nine different co-precursors (CP) of the type R n SiX 4 − n , have been used. The aerogels have been characterized by density, porosity, percentage of volume shrinkage, optical transmission, contact angle and thermal conductivity measurements. The surface chemical modification of silica aerogels was confirmed by the presence of C H and Si C peaks at 2900, 1450 and 840 cm −1 , respectively, from the Fourier transform-infrared spectroscopy (FT-IR). The microstructure of the aerogels was studied using transmission electron microscopy (TEM) and scanning electron microscopy (SEM) techniques. In addition to these studies, the stability of the hydrophobic aerogels against an organic impurity (methanol, in the present studies) in water has also been studied.

Dissolution kinetics of malachite in ammonia/ammonium carbonate leaching

The leaching of oxide copper ore containing malachite, which is the unique copper mineral in the ore, by aqueous ammonia solution has been studied. The effect of leaching time, ammonium hydroxide, and ammonium carbonate concentration, pH, [NH 3]/[NH 4 +] ratio, stirring speed, solid/liquid ratio, particle size, and temperature were investigated. The main important parameters in ammonia leaching of malachite ore are determined as leaching time, ammonia/ammonium concentration ratio, pH, solid/liquid ratio, leaching temperature, and particle size. Optimum leaching conditions from malachite ore by ammonia/ammonium carbonate solution are found as ammonia/ammonium carbonate concentrations: 5 M NH 4OH+0.3 M (NH 4) 2CO 3; solid/liquid ratio: 1:10 g/mL; leaching times: 120 min; stirring speed: 300 rpm; leaching temperature: 25 °C; particle size finer than 450 μm. More than 98% of copper was effectively recovered. During the leaching, copper dissolves as in the form of Cu(NH 3) 4 +2 complex ion, whereas gangue minerals do not react with ammonia. It was determined that interface transfer and diffusion across the product layer control the leaching process. The activation energy for dissolution was found to be 15 kJ mol −1.

Optimization of dye-doped silica nanoparticles prepared using a reverse microemulsion method.

Fluorescent labeling based on silica nanoparticles facilitates unique applications in bioanalysis and bioseparation. Dye-doped silica nanoparticles have significant advantages over single-dye labeling in signal amplification, photostability and surface modification for various biological applications. We have studied the formation of tris(2,2'-bipyridyl)dichlororuthenium(II) (Ru(bpy)) dye-doped silica nanoparticles by ammonia-catalyzed hydrolysis of tetraethyl orthosilicate (TEOS) in water-in-oil microemulsion. The fluorescence spectra, particle size, and size distribution of Ru(bpy) dye-doped silica nanoparticles were examined as a function of reactant concentrations (TEOS and ammonium hydroxide), nature of surfactant molecules, and molar ratios of water to surfactant (R) and cosurfactant to surfactant (p). The particle size and fluorescence spectra were dependent upon the type of microemulsion system chosen. The particle size was found to decrease with an increase in concentration of ammonium hydroxide and increase in water to surfactant molar ratio (R) and cosurfactant to surfactant molar ratio (p). This optimization study of the preparation of dye-doped silica nanoparticles provides a fundamental knowledge of the synthesis and optical properties of Ru(bpy) dye-doped silica nanoparticles. With this information, these nanoparticles can be easily manipulated, with regard to particle size and size distribution, and bioconjugated as needed for bioanalysis and bioseparation applications.

MFI zeolite synthesis directly from silatrane via sol–gel process and microwave technique

Silatrane was synthesized from the reaction of SiO 2 and triethanolamine using ethylene glycol as solvent under N 2 atmosphere. The obtained silatrane complex was further used as a Si source for MFI zeolite synthesis. The effect of Na +, OH −, and tetrabutyl ammonium hydroxide (organic template) concentration in the reaction mixture was studied. The reaction temperature was varied using the microwave heating technique. The effect of aging the reaction mixture at room temperature for varying times was also investigated. The rate of MFI formation decreases with increasing Na +, decreasing OH −, or lower template concentration. Higher temperatures correlate to shorter aging and heating times. At fixed temperature, longer aging times lead to shorter heating times. It was found that a longer aging time is more important to achieve high crystallinity than the heating time.

Role of kairomones in feeding interactions between seahorses and mysids

Big-bellied seahorses, Hippocampus abdominalis (Chordata: Syngnathidae), feed predominantly on swarming mysids in southern Tasmania. We tested the possibility that kairomones mediate this predator/prey interaction. ‘Fish water’ was prepared by holding one seahorse in 4 l of seawater for 1 h and using this water within 1 h to test for presence of kairomones. One ml of this water pipetted into a tank containing five mysids, Paramesopodopsis rufa (Arthropoda: Mysidacea), induced a significantly increased number of tailflips (mysid escape response) compared with control seawater. The same effect was seen whether seahorses were fed or starved immediately before the experiment. This effect was not seen when realistic concentrations of excretory products, either ammonium hydroxide or urea, were used instead of fish water. When seahorses were kept in visual contact with mysid prey, but unable to capture them, subsequent testing of the ‘fish water’ in the same way as above did not produce a significant increase of tailflipping in mysids. Thus it appears that, when attacking, seahorses can suppress release of kairomones in order to remain chemically inconspicuous to their prey. This is the first demonstration of this phenomenon. When mysids in a cohesive swarm (65 or 100 individuals) were exposed to ‘fish water’, no significant anti-predator response i.e. decrease in swarm volume, could be detected. We interpret these results to indicate the greater vulnerability of mysids when not in social groupings (swarm or school) and the higher likelihood of an energetic response (particularly tailflipping) to a threat.

Fast and efficient separation of cytokinins from auxin and abscisic acid and their purification using mixed-mode solid-phase extraction

A method for separation of cytokinins from auxin and abscisic acid, which allows further separation of cytokinin ribotides from cytokinin bases, ribosides and glucosides and their purification on a single Oasis MCX column was developed. Due to the mixed reversed-phase and cation-exchange mode of the Oasis MCX sorbent the cationic cytokinin bases, ribosides and glucosides as well as the anionic auxin, abscisic acid and cytokinin ribotides are retained and can be sequentially eluted by solvents containing different concentrations of methanol and ammonium hydroxide. Characteristics of the method are high recoveries of analyzed phytohormones and their sufficient purity for quantification by HPLC–ELISA (RIA) or HPLC–MS.

Biological reduction of perchlorate in ion exchange regenerant solutions containing high salinity and ammonium levels.

The most promising technologies to remove perchlorate from water are ion exchange and biological reduction. Although successful, ion exchange only separates perchlorate from water; it does not eliminate it from the environment. The waste streams from these systems contain the caustic or saline regenerant solutions used in the process as well as high levels of perchlorate. Biological reduction could be used to treat the regenerant waste solutions from the ion exchange process. A treatment scheme, combining ion exchange and biodegradation, is proposed to completely remove perchlorate from the environment. Perchlorate-laden resins generate brines containing salt concentrations up to 6% or caustic solutions containing up to 0.5% ammonium. Both, high salt and ammonium hydroxide concentrations are potentially toxic to microorganisms. Therefore, the challenge of the proposed system is to find perchlorate reducing microorganisms that are effective under such stressful conditions. Preliminary results have shown that salt concentrations as low as 0.5% reduced the perchlorate biodegradation rate by 30%; salt concentrations greater than 1% decreased this rate to 40%. Although biodegradation was seen in ammonium levels of 0.4%, 0.6% and 1%, the perchlorate biodegradation rate was 90% of that at 0% ammonium hydroxide. Further research will focus on the isolation and/or acclimation of microorganisms that are able to biodegrade perchlorate under these stressful conditions.

Ｔｉ（ＩＩＩ）イオンを還元剤とする無電解ニッケルめっき浴の開発

A novel electroless Ni Plating bath using Ti (III) ions as reluctant was proposed. In an industrial application of this plating bath, stability of the plating bath and plating rate are particularly important. Effects of plating bath components on Ni deposition rate onto Urethane foam or copper sheet were investigated, elucidating that Ni (II) ions, nitrilotriacetic acid and ammonium hydroxide concentration were important factors to control Ni deposition rate. Purity of Ni film reduced with Ti (III) ions was very high exceeding 99.9%.

Formation of Self-Assembled Monolayers of Alkanethiols on GaAs Surface with in Situ Surface Activation by Ammonium Hydroxide

The formation of self-assembled monolayers (SAMs) of alkanethiols on GaAs was studied using attenuated total reflection Fourier transform infrared spectroscopy. SAMs formed from an ethanol solution containing ammonium hydroxide were more ordered and stable than those obtained by the method previously reported in which surfaces were derivatized from neat molten alkanethiols at elevated temperatures. It is suggested that ammonium hydroxide etches the native surface oxide of GaAs during an initial step followed by the chemisorption of alkanethiols on the chemically reactive surface. The effect of ammonium hydroxide concentrations on the SAM coverage was investigated. Well-ordered layers with close packing were formed when the ammonium hydroxide concentration was 3 vol %. SAMs of alkanethiols with different chain lengths showed that the order increases with increasing chain length (from C12H25SH to C18H37SH).

Atomic structure and magnetic properties of MnFe2O4 nanoparticles produced by reverse micelle synthesis

Using the aqueous cores of reverse micelles as nanoreactors, nanoparticles (d∼10 nm) of the mixed ferrite MnFe2O4 were produced. Seven processing trials were performed where the concentration of ammonium hydroxide, reaction temperature, and the oxidizing agent were varied. All trials result in Mn-ferrite particles with varying chemistry and structure. The Mn concentration in the resulting ferrite is strongly enhanced by both the presence of H2O2 as an oxidizing agent and a surplus of ammonium hydroxide. The increased Mn concentration correlates with a higher fraction of octahedrally coordinated Mn cations. When near-stoic amounts of ammonium hydroxide are used, the resulting ferrites are nearly stoichiometric with a more equitable distribution of Mn cations on the octahedral and tetrahedral sublattices. In all ferrite nanoparticles, the Mn cations have a preference for octahedral site occupancy that is larger than the 20% measured in bulk Mn-ferrite. We attribute the cation filling trends to the stabilization of excess trivalent Mn during processing.

Synthesis of Nanosize Silica in a Nonionic Water-in-Oil Microemulsion: Effects of the Water/Surfactant Molar Ratio and Ammonia Concentration

The effect of ammonia concentration on the region of existence of single-phase water-in-oil microemulsions has been investigated for the system polyoxyethylene (5) nonylphenyl ether (NP-5)/cyclohexane/ammonium hydroxide. The presence of ammonia decreases the size of the microemulsion region. A minimum concentration of surfactant (estimated at about 1.1 wt%) is required for solubilization of the aqueous phase; this value is not significantly affected by ammonia concentration. As indicated by fluorescence spectral data, the transition between bound and free water occurs when the water-to-surfactant molar ratio is about 1 and the presence of ammonium hydroxide does not appear to have a significant effect on this. Ultrafine (30–70 nm diameter), monodisperse silica particles produced by hydrolysis of tetraethoxysilane (TEOS) in the microemulsion show a complex dependence of the particle size on the water-to-surfactant molar ratio (R) and on the concentration of ammonium hydroxide. At relatively low ammonia concentration in the aqueous pseudophase (1.6 wt% NH3) the particle size decreases monotonically with increase in R. However, for higher ammonia concentrations (6.3–29.6 wt% NH3) a minimum in particle size occurs as R is increased. These trends are rationalized in terms of (a) the effects of the concentration, structure, and dynamics of the NP-5 reverse micelles on the hydrolysis and condensation reactions of TEOS, and (b) the effects of ammonia concentration on the stability of the microemulsion phase, the hydrolysis/condensation reactions of TEOS, and the depolymerization of siloxane bonds.

Investigation of problems associated with the determination of iodine in glacial acetic acid samples using flow injection analysis-inductively coupled plasma-mass spectrometry†

Determination of iodine in glacial acetic acid is a major concern of acetic acid manufacturers and consumers. The use of ICP-MS for iodine determinations in acetic acid is hindered by memory effects that produce an elevated background signal necessitating long rinse times between samples. In this work, different analysis methods are employed in an attempt to minimize memory and matrix effects allowing for the accurate determination of iodine in glacial acetic acid using ICP-MS. Ammonium hydroxide solutions (3.7 and 7.4 M) were better at reducing the elevated iodine signal present after the introduction of an acetic acid sample than water or 0.3 M nitric acid. Memory effects were decreased when the sample was introduced by flow injection rather than constant sample aspiration. Peak areas generated by flow injection decreased significantly with increasing ammonium hydroxide concentration in the carrier solution. Iodine determinations made with 1.7 M ammonium hydroxide as the carrier solution were higher than determinations made with 3.7 M ammonium hydroxide as the carrier solution for the same samples, however, the percentage difference between the two determinations varied widely from sample to sample. All samples were analyzed by the method of standard additions in an attempt to compensate for matrix effects. This work illustrates the importance of the carrier solution in the determination of iodine in glacial acetic acid samples.Introduction

Fabrication Process of Color Filters Using Pigmented Photoresists

The fabrication process of color filters produced with a series of new pigmented photoresists (CX513RGB) and their performance are described. The novel resist materials offer excellent contrast, good film uniformity and a stable shelf life exceeding 6 months, which was achieved by optimization of the amount and the molecular weight of a proprietary pigment dispersant. The development conditions of the pigmented resists were found to be influenced by their adhesion to the substrate materials (glass, chromium oxide and pixels). Dissolution type development was observed for prebake temperatures below 135°C or when developers with higher tetramethyl ammonium hydroxide (TMAH) concentrations were used. The desired overcut pattern profiles were obtained when development times ranged from 60–180 s. CX513RGB resists obey the “reciprocity law” over 3 mW/cm2 and thus the resist sensitivity is not affected by the irradiation power generated by conventional mask aligners (15–20 mW/cm2).

The cementation of lead from ammoniacal ammonium sulphate solution

Due to increasingly stringent SO 2 emissions legislation, there have been numerous research efforts to find a hydrometallurgical replacement for lead-acid battery smelter recycling operations. One promising possibility is the use of ammoniacal ammonium sulphate (AAS) solution to dissolve the lead sulphate found in used battery pastes. This paper examines the possibility of recovering metallic Pb from AAS solution via cementation, using Ni powder as the reductant. The highest recovery rates were achieved with high (17 mol/1) ammonium hydroxide and moderate (2 mol/l) ammonium sulphate concentrations. Below 135°C, reaction kinetics are rate-controlling and above 135°C, diffusion is rate-controlling.

Experimental optimization of fed-batch culture for poly-β-hydroxybutyric acid production

The optimal feed rate profiles of glucose and ammonium hydroxide were calculated using a proposed model, and implemented for the production of poly-beta-hydroxybutyric acid (PHB) by Alcaligenes eutrophus. By implementing these optimal feed rates with a high glucose feed concentration of 700 g/L and an ammonium hydroxide concentration of 7%(w/w), it was possible to achieve a high final cell concentration of 141 g/L and a high PHB concentration of 105 g/L in 40 h of fed-batch operation. The PHB productivity was as high as 2.63 g/(L hr). (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 697-705, 1997.

Development of ammoniacal lixiviants for the in-situ leaching of chalcopyrite

Researchers at the U.S. Bureau of Mines are investigating the ammonia-oxygen leaching of chalcopyrite at conditions anticipated in an in-situ environment. Two major problems were identified in a review of the literature: (1) providing sufficient oxidant to drive the leaching reaction, and (2) decreased leaching kinetics due to the build-up of a ferric oxide reaction product layer at the mineral surface. Preliminary characterization studies were performed in a 2-1, well-mixed autoclave system incorporating automated sampling and data acquisition. A statistical experimental design was utilized to determine which parameters were most influential in the dissolution of copper from relatively pure chalcopyrite specimens. The most significant leaching parameters for the ammoniacal leaching of copper from chalcopyrite were determined to be temperature, oxidant concentration, ammonium hydroxide concentration, and an interaction between temperature and the ammonium hydroxide concentration. Preliminary leaching studies indicate that further research must be undertaken to evaluate oxidant delivery to an in-situ orebody and that the addition of organic compounds, such as simple sugars or polyvinyl alcohols, stabilize at least some of the reacted iron in solution, which could result in decreased passivation due to the formation of an iron oxide coating. In order to determine the practicality and effectiveness of this approach, researchers have been investigating several types of organic additives, the extent to which iron is sequestered, and methods to control the sequestered iron.