Reactant Dosing Research Articles

Using a slit doser to probe gas dynamics during Al2O3 atomic layer deposition and to fabricate laterally graded Al2O3 layers

A special slit doser is used to form near unit steps in the spatial profile of an Al2O3 ALD film thickness. The unit step is formed as the Al2O3 ALD occurs mainly downstream from the slit doser because the trimethylaluminum and H2O reactants are entrained in a viscous flow carrier gas. Spectroscopic ellipsometry measurements yielded thickness profiles of Al2O3 ALD on samples placed at different locations relative to the exit of the slit doser and the ALD growth zone. The effects of carrier gas flow rate, reactor pressure, and reactant dose and purge times on the Al2O3 ALD film profile provided details about the gas dynamics around the slit doser. Experimental indications of gas turbulence were observed at the exit of the slit doser. Lateral gradients in the Al2O3 ALD film thickness were also formed by linear translation of the sample relative to the slit doser during ALD. Lateral gradients of various desired pitches ranging from 119Å/in to 444Å/in were achieved as a result of accurate control of the Al2O3 ALD film thickness and small sample translation steps relative to the slit doser.

Degradation of a xanthene dye by Fe(II)-mediated activation of Oxone process

A powerful oxidation process using sulfate radicals activated by transition metal mediated Oxone process has been evaluated in depth by monitoring the degradation of a xanthene dye Rhodamine B (RhB) in aqueous solution. Ferrous ion was chosen as the transition metal due to its potential catalytic effect and wide availability in dyeing industrial effluent. The effects of parameters including reactant dosing sequence, Fe(II)/Oxone molar ratio and concentration, solution pH, and inorganic salts on the process performance have been investigated. Total RhB removal was obtained within 90min under an optimal Fe(II)/Oxone molar ratio of 1:1. The RhB degradation was found to be a two-stage kinetics, consisting of a rapid initial decay and followed by a retarded stage. Additionally, experimental results indicated that the presence of certain anions had either a positive or negative effect on the process. The inhibitory effect in the presence of SO42− was elucidated by a proposed formula using Nernst equation. Furthermore, dye mineralization in terms of TOC removal indicates that stepwise addition of Fe(II) and Oxone can significantly improve the process performance by about 20%, and the retention time required can be greatly reduced comparing with the conventional one-off dosing method.

Enzymatic treatments of pulp using laccase and hydrophobic compounds

The aim of this work was to develop an innovative method for the internal sizing of paper by use of laccase and hydrophobic compounds. Nine different products containing hydrophobic moieties were tested in combination with laccase derived from Trametes villosa on Eucalyptus globulus kraft pulp in order to assess their internal sizing capability. The strongest internal sizing effect was obtained with lauryl gallate (LG). Heat treatment of the handsheets was found to increase the resistance to water absorption of internally sized samples significantly. Tests were conducted under variable operating conditions, including enzyme and reactant doses and treatment time. In addition to altering the water absorption rate, internal sizing with the laccase-LG treatments was found to affect the mechanical and optical properties of the handsheets. As shown in this work, treatments based on laccase and a hydrophobic compound (particularly lauryl gallate), can provide a new, effective biotechnological method for the internal sizing of paper.

The use of D-optimal design to model the effects of process parameters on mineralization and discoloration kinetics of Fenton-type oxidation

The aim of this experimental investigation was to study kinetics of Fenton and modified Fenton oxidation applied to miscellaneous dye solutions. Several bench scale laboratory tests for the treatment of colored wastewaters containing model pollutant compounds, reactive azo dyes C.I. Reactive Violet 2 (RV2) and C.I. Reactive Yellow 3 (RY3) were performed. In order to examine the effects of initial Fe 2+ concentration, oxidant/catalyst molar ratio and oxidant type on TOC reduction and color removal, the following reactants were used: classic Fenton's reagent (Fe 2+/H 2O 2) and modified Fenton's reagent, where potassium peroxodisulfate, alone and in combination with hydrogen peroxide, was selected as oxidant. Response surface methodology (RSM), particularly D-optimal design, was used for the purpose. This research contributed in several ways: (i) evaluation of more effective Fenton oxidant on pollutant content reduction, in terms of TOC and color removal, (ii) assessment of the optimal reactant doses, (iii) describing the RV2 kinetic behavior in applied systems and (iv) determining the apparent rate constants. Mineralization was described by pseudo-first-order kinetics with observed rate constant k m = 0.0133 min −1. A kinetic model describing discoloration was composed of two first-order in-series reactions with discoloration rates; k 1 = 0.9447 min −1 and k 2 = 0.0236 min −1, at optimal operating conditions and with the highest initial organic load.

Remediation of PAH-contaminated sediments by chemical oxidation

The aim of this experimental investigation was to assess the feasibility of using chemical oxidation to degrade sorbed polycyclic aromatic hydrocarbons (PAHs) in case of old date sediment contamination. For this purpose several bench scale laboratory tests were performed, with the following liquid reactants: hydrogen peroxide, modified Fenton's reagent, activated sodium persulfate, potassium permanganate, as well as a combination of potassium permanganate and hydrogen peroxide, and a combination of activated sodium persulfate and hydrogen peroxide. The main target of the study was to find out what liquid oxidant was more effective in reducing the pollutant content and to assess the optimal reactant doses. The initial total PAH concentration in sediment samples was about 2800 mg/kg SS (light PAHs about 1600 mg/kg SS, heavy PAHs about 1200 mg/kg SS) and a 95% degradation was required to meet the remediation goals. Based on the results of this study, chemical oxidation proved to be an effective remediation technology, amenably applicable for the ex situ remediation of the sediments of concern. Different reactants resulted however in different removal efficiencies. The best remediation performances were achieved with the use of modified Fenton's reagent, hydrogen peroxide and potassium permanganate, with oxidant dosages about 100 mmols per 30 g sediment sample. In all these cases the residual heavy PAH concentration in the treated samples was below 100 mg/kg SS. The optimal oxidant dosages determined in this study were quite high, as sorbed PAH mineralization requires very vigorous oxidation conditions, especially for soils and sediments with high organic matter content. The results indicated that the optimal oxidant dose must be carefully determined under site-specific conditions. In fact, if the oxidation conditions are not strong enough, the reactants cannot be able to attack the most recalcitrant compounds, while also too high oxidant doses can result in a decrease in the oxidation efficiency, thus failing in meeting the remediation goals.

Evaluation of the intermediates generated during the degradation of Diuron and Linuron herbicides by the photo-Fenton reaction

Freshwater polluted with herbicides is a problem of general concern since these compounds are commonly toxic and non-biodegradable. An innovative technology for the elimination of such compounds is the coupling between an Advanced Oxidation Process (AOP) and a biological treatment. The success of this coupled methodology depends on the biodegradable nature of the by-products originated at the end of the chemical stage. The present paper is based on the analysis of the intermediates generated during the chemical oxidation of Diuron and Linuron herbicides using three different doses of photo-Fenton reactants. Among the three effluents obtained after the chemical pre-treatment, only the most oxidised is completely biodegradable. Several analytical methods: reverse phase ultra pressure liquid chromatography UPLC(RP)/MS, ionic chromatography IC and gas chromatography/MS have been used to elucidate the degradation mechanism. Beyond conventional separation methods, hydrophilic interaction chromatography HILIC coupled with mass spectrometry has been necessary to identify small polar compounds at the end of oxidation process. The first steps of the degradation mechanism have been ascertained. Furthermore, different by-products have been found at the end of the chemical process when different reactant doses were used. These differences have been based on the presence of urea derivates (methylurea, 1,1-dimethylurea) and unidentified chlorinated compounds.

Real-time observation and optimization of tungsten atomic layer deposition process cycle

In the search for a chemical sensing strategy to monitor atomic layer deposition (ALD) processes suitable for real-time application in wafer manufacturing, we have applied downstream mass spectrometry sampling to study process dynamics during ALD cycles for tungsten deposition from WF6 and SiH4. The ALD reactor has UHV cleanliness conditions and incorporated a minireactor chamber to simulate the small reaction volume anticipated for manufacturing tools to achieve adequate throughput. Mass spectrometry revealed essential surface reaction dynamics through real-time signals associated with by-product generation as well as reactant introduction and depletion for each ALD half-cycle. These were then used to optimize process cycle time and to study the effect of process recipe changes on film growth. The reaction by-products were clearly observed as H2 from SiH4 exposure and SiF4 from WF6 exposure. For each of the two half-cycles, rapid increase of by-product leds to steady-state adsorption/reaction conditions, following by by-product decrease and complementary reactant increase as surface saturation was achieved, indicating self-limiting surface reaction. From this direct observation of the surface reactions, exposure times could be minimized without sacrificing ALD growth rate per cycle, as verified experimentally. With gas flow parallel to the wafer surface in the minireactor, deviations from across-wafer uniformity were small when sufficient reactant doses were applied, but uniformity suffered markedly when doses were insufficient for surface saturation. Increasing WF6 concentration accelerated surface saturation as expected. Growth rates per cycle showed a notable temperature dependence, with small but noticeable activation energies (∼3kcal∕mol) consistent with previous reports. The effect of varying gas doses of one reactant while keeping the other constant suggests a complex interdependence between the half-cycles, in which the reactivity in one half-cycle is influenced by the prior dose achieved in the previous half-cycle.

Theoretical Analysis of Non-Catalytic Growth of Nanorods on a Substrate

A theoretical analysis explaining the whole process of the growth of nanorods on a substrate without a catalyst is presented. Prior to the growth of the nanorods, the reaction precursors form nuclei on the substrate. The nuclei undergo cluster migration caused by the surface diffusion of adatoms on the substrate, and this migration continues until the mean free time of the adatoms is larger than surface diffusion time. The most probable mechanism by which cluster migration takes place is the one that leads to the minimization of the cluster free-energy, namely the migration of six adatoms into one fixed adatom. This cluster migration continues during several (typically smaller than 6) consecutive nuclei growth steps. After the process of cluster migration comes to an end, the nuclei grow in an isotropic manner by collection of the adatoms, until the nucleus reaches the thermodynamic size limit. The one-dimensional growth of nanorods on the nuclei, which is associated with the critical radius, begins when the reactant dose is smaller than a certain value, which is determined by the thermodynamic size limit and the mass transport parameter. The mass transport of the reaction precursors leads to the expansion of the radius and elongation of the height of the nanorods, and the growth rate of the height is greater than that of the radius. This difference in the growth rate causes the aspect ratio to increase with increasing growth time. By comparing the experimental data in the literature (ZnO nanorods), the presented analysis explains well the noncatalytic growth of nanorods on a substrate.

Prototype high-throughput system for hydrothermal synthesis and X-ray diffraction of microporous and mesoporous materials

In the hydrothermal synthesis of microporous and mesoporous materials a large number of parameters including chemical composition of the mixture, reagent sources, organic templates, temperature, and time play a role. The high-throughput experimental approach facilitates screening of this multi-parameter space for conditions favoring formation of desired zeolite phases and ordered mesoporous materials. A critical issue in the development of a high-throughput system for hydrothermal synthesis is the avoidance of cross-contamination between the individual synthesis volumes. Further important issues are automation of reactant dosing, product filtration, calcination and identification. In this work, a prototype multi-clave was designed with three 5 mL synthesis vials for operation at temperatures up to 200 °C under autogenous pressure. The multi-clave is equipped with a sample tray for filtration, washing and drying of all of the synthesis products at the same time. This multi-filter also serves as the sample holder for X-ray diffraction characterization. The innovation resides in the multi-clave concept and the integration of the entire process from synthesis over product workup to XRD characterization without necessitating individual sample transfer. The performance of the prototype was evaluated with the synthesis of the mesoporous–microporous hybrid material zeotile-2, and of clathrasils.

Theoretical Analysis of Non-Catalytic Growth of Nanorods on a Substrate

ABSTRACTA theoretical analysis explaining non-catalytic growth of one-dimensional (1D) nanorods on a substrate is presented. The nuclei undergo cluster migration which continues until the mean free time of the adatoms is larger than surface diffusion time during several consecutive nuclei growth steps. The most probable mechanism is the migration of six adatoms into one fixed adatom. After the cluster migration, the nuclei grow in an isotropic manner, until the nucleus reaches the size limit. The 1D growth of nanorods on the nuclei begins when the reactant dose is smaller than a certain value. The growth rate of the height is greater than that of the radius. This difference in the growth rate causes the aspect ratio to increase with growth time. The presented analysis explains well the experimental results of the non-catalytic growth of nanorods.

Theoretical analysis of reactant dosing concepts to perform parallel-series reactions

The possibility of enhancing selectivities and yields in networks of parallel and series reactions is investigated theoretically. Isothermal tubular reactors are considered where reactants can be introduced at the entrance and also over the wall. The latter way of dosing could be realised, e.g., in a membrane reactor where one or several reactants can be dosed through a porous reactor wall. Besides numerical solutions of the underlying mass balance equations of simplified reactor models, instructive analytical solutions were derived which are valid under certain constraints. Using these solutions an optimisation of the reactor performance could be performed. As objective function the molar fraction of a desired intermediate product at the reactor outlet was maximised. The impact of influencing via the dosing strategy applied the local composition (and thus the local reaction rates) and the component residence time distributions is elucidated.

Temperature-Induced Apparent Mass Changes Observed during Quartz Crystal Microbalance Measurements of Atomic Layer Deposition

The quartz crystal microbalance (QCM) is a valuable in situ probe of surface chemistry and film growth during atomic layer deposition (ALD). Unfortunately, the QCM is sensitive to both mass and temperature effects that complicate the interpretation of QCM measurements. To characterize the temperature effects, QCM measurements are performed at 170 °C in a hot-wall, ALD flow reactor using pulses of inert and other unreactive probe gases that simulate reactant dosing during ALD. The difference between the probe gas temperature and the QCM sensor temperature is shown to cause instantaneous positive or negative apparent mass transients during the gas pulse. In addition, there is a net apparent mass drift after the gas pulse. The apparent mass transients and apparent mass drifting can lead to misinterpretation of ALD surface chemistry and produce error in measured ALD growth rates. Temperature-induced apparent mass changes are shown to be affected by the temperature profile in the ALD flow reactor before the QCM sensor. Changes in the gas flux during the ALD dosing sequence, changes in the type of dosing gas, and adiabatic cooling of the dosing gas can also produce temperature-induced apparent mass changes. The temperature effects on the QCM sensor are also demonstrated during Al2O3 ALD growth using Al(CH3)3 and H2O. Experimental methods using unreactive probe gases, such as SF6, are developed to tune the temperature profile of the ALD flow reactor to minimize the temperature-induced apparent mass changes.

Applications and limitations of the colloid titration method for measuring activated sludge surface charges

Surface charge quantification of polymer solutions and sludge suspensions were investigated by the colloid titration technique and compared to charge densities obtained by pH-titration. The colloid titration technique worked well for polymer samples. The charge quantity of humic acid and activated sludge extracellular polymers (EPS) was estimated to be −1.51 and −0.42 meq/g, respectively. These values are reasonable when compared to pH-titration results. The surface charge of activated sludge particles appears to be below the limit of detection. However, surface charge estimates are obtained, when the reactant doses and sample concentration are increased. It is suggested that such estimates are not correct, but artefacts of the non-stoichiometric precipitation of the polymeric reactants at high doses. It appears that the colloid titration method is limited to conditions of low reactant doses and valid for charge determination of extracted sludge polymers, whereas the method is not valid for charge determination of whole sludge.

Realization of atomic layer etching of silicon

An experimental system and methodology were developed to realize dry etching of single crystal silicon with monolayer accuracy. Atomic layer etching of silicon is a cyclic process composed of four consecutive steps: reactant adsorption, excess reactant evacuation, ion irradiation, and product evacuation. When successful, completion of one cycle results in removal of one monolayer of silicon. The process was self-limiting with respect to both reactant and ion dose. Control of the ion energy was the most important factor in realizing etching of one monolayer per cycle.

179 Batch time optimization using both reactant dosing and external cooling for tight temperature control: P. Djavdan, pp 297–302

179 Batch time optimization using both reactant dosing and external cooling for tight temperature control: P. Djavdan, pp 297–302

Batch Time Optimization Using both Reactant Dosing and External Cooling for Tight Temperature Control

Abstract The reaction heat of exothermic reactions is often removed by using external cooling. The reactor temperature is then controlled by adjusting the cooling liquid flow in the jacket directly or the cooling liquid temperature, using a Master-Slave control structure. The ability to remove the reaction heat depends, amongst other things, on the heat exchange coefficient in the reactor. In the case of a (semi-)batch reactor the heat exchange coefficient varies during the reaction. In some cases it can become too small, leading to temperature runaways. In this paper a new control structure is discussed which controls the temperature of a semi-batch reactor by using both external cooling and reactant inlet flow adjustment. The controller maximizes the reaction rate by using the cooling capacity of the external heat exchanger always close to its maximum, leaving only some control margin for disturbance rejection. Simulation results show that this control structure significantly increases the production rate compared with more conventional control structures. In the case that, due to a buyer’s market, a higher production rate is not desired, this control structure can be used to decrease catalyst consumption.

Mass spectrometry study of ZnS atomic layer epitaxy process

Surface reactions in ALE were studied with quadrupole mass spectrometer when growing polycrystalline ZnS from ZnCl2 and H2S. The desorption of ZnCl2 was found to affect the growth most. On the other hand, the growth is relatively insensitive to reactant dose. Real time mass spectrometry is shown to be a powerful measurement technique for studying surface dynamics, because the step by step growth in ALE separates the reaction phases from each other.

Thermokinetic studies in adsorption and heterogeneous catalysis

Thermokinetic studies in adsorption and heterogeneous catalysis

Pathology of reversed passive Arthus reaction in the chicken

Sequential study of gross and microscopic changes in the chicken skin revealed that it was possible to induce a reversed passive Arthus reaction in 14- to 20-week-old chickens, using bovine serum albumin and anti-bovine serum albumin. However, high doses of immune reactants were required to elicit lesions of optimal intensity. The lesions were characterised by erythema, oedema, and the formation of thrombi in the vessels of the superficial dermis. Thrombosis, caused by the adherence of thrombocytes to vascular endothelium, induced widespread necrosis and haemorrhage. The inflammatory changes, which were confined to the deep dermis, included a necrotising vasculitis with infiltration of heterophils, monocytes and basophils. Phagocytosis of carbon particles by heterophils and basophils appeared to be sensitisation-dependent. The reaction was also characterised by the development of perivascular lymphoid foci. The findings indicate that in chickens the thrombocyte appears to be the principal cell involved in the induction of tissue damage.

Factors which influence late cutaneous allergic responses

Increased doses of ragweed antigen E, grass pollen extract, and the IgG of sheep antiserum to human IgE (anti-IgE) were injected in intracutaneous tests in humans. With increasing doses of reactants, in individual subjects, there were the expected increases in the sizes of early wheal-and-flare responses; moreover, there was an associated increase in the magnitude and the frequency of late cutaneous allergic responses (LCAR). LCAR were shown to be a usual sequel to allergic reactions of sufficient intensity. In persons with allergic bronchopulmonary aspergillosis, cutaneous responses to Aspergillus fumigatus allergen were compared with responses to other allergens and to anti-IgE; in relation to early wheal-and-flare responses, the corresponding LCAR induced by A. fumigatus were approximately the same size as those induced by the other reactants. Skin reactions induced by the prick test method and by intracutaneous injection were compared; for early responses of given sizes, there were apparently equal tendencies to proceed to LCAR in reactions to allergen in the two types of administration. In one subject, anti-IgE-induced responses in the skin of a forearm with sensory denervation were compared with responses in the other normally innervated forearm. At the denervated site was the expected absence of the early flare but no apparent reduction in LCAR. Similarly, local anesthesia immediately prior to anti-IgE eliminated the flare of the early response but did not prevent the occurrence of a LCAR.