Effect of Self-Assemblies on the Dynamics of the Briggs–Rauscher Reaction

The study involves the dynamic evolution of the Briggs–Rauscher (BR) reaction in the presence of various surfactants—SDS (sodium dodecyl sulphate) as anionic, CTAB (cetyl trimethylammonium bromide) as cationic and TritonX‐100 [4‐(1,1,3,3‐(tetramethylbutyl) phenyl polyethylene glycol] as a neutral one in single as well as mixed mode conditions (SDS + TX‐100 and CTAB + TX‐100). The reaction has been monitored potentiometrically at 30 °C under CSTR conditions. These surfactants affect the reaction dynamics to an extent which depends on the nature and concentration of the surfactant and the formation of their self‐assemblies. The experimental findings indicate that the oscillatory behavior of the BR reaction in the presence of surfactants is due to the efficacy of organized surfactant assemblies to selectively distribute the key species involved in the reaction, and their interaction with the counter ions in cases of ionic micelles. The study reveals that the evolution of oscillatory behavior is a characteristic feature of the surfactant.     

Effect of the processing on the production of cordierite–mullite composite

In this study, effect of process on the production of cordierite–mullite composite was studied. For this reason two different processing methods were used in the production of cordierite–mullite composites. In first process, in situ cordierite–mullite composites were produced from cordierite and mullite layers which were formed by using aqueous tape casting method. In second one, composite was produced by addition of pre-produced mullite powders (in different weight percents, 0–30) into cordierite starting powders. The results show that the addition of pre-sintered mullite powders to the cordierite slip has more effect on densification behavior and mechanical properties of composites than layered production method.     

Investigation of the curing kinetics of alkyd–melamine–epoxy resin system

Properties of coatings based on alkyd resin can be improved via blending with other suitable resins. Recent studies assessed that many properties could be improved by blending with epoxy resins as well as with melamine resins. The aim of this work was to investigate the effect of epoxy resin content on the curing process in alkyd–melamine–epoxy three component blends. The coatings with two mixing ratios of alkyd/melamine (70:30 and 80:20) were formulated. They were made into baking enamels by blending with 3 and 5 wt% of epoxy resin on total resin solid. Curring kinetics was investigated by differential scanning calorimetry (DSC) and application of Ozawa isoconversional method. Fourier transform infrared spectroscopy (FTIR) was used to follow major curing reactions. The absorbance of –OH and –N–CH₂R, showed significant reduction and confirmed that the epoxy resin reacts and inserts in enamel structure. It was found that resin system with alkyd/melamine ratio of 70:30 and 3 wt% of epoxy resin has the lowest apparent activation energy of 141.5 kJ mol⁻¹ and needs the shortest time of 34.2 min to reach final apparent degree of cure. Isothermal DSC experiments have confirmed these findings. The samples with 30 wt% of melamine resin had higher hardness of baked enamels then samples with 20 wt%. They also showed an increase of hardness with the increase of epoxy resin content.     

Coagulation–bubbling–ultrafiltration: Effect of floc properties on the performance of the hybrid process

A novel hybrid process of coagulation–bubbling–ultrafiltration was proposed to study membrane fouling phenomena by surface water. Relationship of bubbles, flocs and the hollow fibers was explored. When applying less than 20 mL/min gas flow rate, membrane fouling was accelerated with air bubbles introduced. When gas flow rate increased further to 40 mL/min and 60 mL/min, TMP showed a two-stage development trend, which was a fast development in the first few hours followed with a relatively slow development after about 4 h. Unified membrane fouling index (UMFI) increased from 0.00216 (without bubbles) to 0.00274 m²/L (40 mL/min gas flow rate) and 0.00219 m²/L (60 mL/min gas flow rate). As gas flow rate increased, bubble size became bigger, and its distribution range became wider, resulting in higher shear rate in the ultrafiltration column, which led to severe floc breakage. Flocs of small size and compact structure accelerated membrane fouling, resulting in highest UMFI value under 40 mL/min gas flow rate. However, under 60 mL/min gas flow rate, with largest bubbles and highest shear rate examined in this study, concentration polarization was effectively limited. As a result, TMP development slowed down when pore blockage reached equilibrium.     

The effect of Si–Bi2O3 on the ignition of the Al–CuO thermite

The ignition temperature of the Al–CuO thermite was measured using DTA at a scan rate of 50 °C min^?1 in a nitrogen atmosphere. Thermite reactions are difficult to start as they require very high temperatures for ignition, e.g. for Al–CuO thermite comprising micron particles it is ca. 940 °C. It was found that the ignition temperature is significantly reduced when the binary Si–Bi₂O₃ system is added as sensitizer. Further improvement is achieved when the reagents are nano-sized powders. For the composition Al + CuO + Si + Bi₂O₃ (65.3:14.7:16:4 wt.%), with all components nano-sized, the observed ignition temperature is ca. 613 °C and a thermal runaway reaction is observed in the DTA.     

Regimes of the Combustion of Organic Coal–Water Fuels

The results of an analysis of the combustion behavior of the drops of organic coal–water fuels (OCWFs) prepared based on the flotation products (cakes) of the enrichment the coal of five grades (longflame, gas, coking, low-caking, and lean coals) and two petroleum products (petroleum residue and spent turbine oil) are presented. The experiments were performed under the conditions of the stationary fastening of an OCWF drop on the junction of a quick-response thermocouple in a flow of heated (from 500 to 1000°C) air. The following three combustion regimes were revealed for all of the test OCWF compositions: stepwise regime with slow heating (smoldering), intense gas generation regime with the boiling of liquid fuel components (boiling), and regime with a distinct tear-off zone of gas flow (torch). It was shown that the occurrence of the above combustion behaviors substantially depends on the characteristics of the OCWF components: the ash content and the yield of volatile substances of coal cakes and the boiling points and the ignition and combustion temperatures of the petroleum products used. Based on the results of the experiments, the ranges of air temperature changes characteristic of each of the three combustion regimes of fuel suspensions were established.     

Prediction of solid–gas equilibria with the Peng–Robinson equation of state

In many applications related to Supercritical-Fluid (SCF) technology, solids are dissolved in SC fluids. Experimental data are now available for many systems but cannot cover all cases of potential practical interest. The prediction of solid solubilities in SC fluids, often in the presence of co-solvents, is useful for rational design of SCF extraction and related processes. Recently, thermodynamics has made considerable steps towards describing complex systems (gases with polar compounds) at high pressures using the so-called Equation of State/Excess Gibbs Free Energy (EoS/G^E) models. The success of these models is so far restricted to Vapor–Liquid Equilibria (VLE) for which they have been primarily developed and tested. In this work we evaluate such a predictive model, the LCVM EoS, for solid–gas equilibria (SGE) including systems with co-solvents. LCVM is chosen due to its success for VLE of asymmetric systems such as CO₂ with heavy alkanes and alcohols. Successful predictions are obtained for several solids as well as for some systems with co-solvents, but the results are less satisfactory for complex, multifunctional solids. A discussion of several factors, which affect modeling of SGE with cubic EoS, is included.     

The effect of the heat treatment of spruce wood on the curing of melamine–urea–formaldehyde and polyurethane adhesives

The effect of the heat treatment of spruce wood on the curing of melamine–urea–formaldehyde (MUF) and polyurethane (PUR) adhesives was monitored by measuring their rheological properties by means of a rheometer. Instead of the standard aluminium discs, wooden discs, made from heat-treated wood with different degrees of thermal modification and conditioned in different climates, were used. The wooden discs provided more realistic curing of the adhesives compared to the real-life bonding of wood, because of solvent absorption. The results of the rheological measurements suggested that the modified wood inhibited the curing of MUF and PUR adhesives. The curing of the MUF adhesive was slower because of the reduced absorption of water from the adhesive. The curing of the one-component PUR adhesive was affected by the lower moisture content (MC) of the modified wood.     

Effect of pH on the Catalytic Properties of Mo–V–Te–P–O Catalysts for Selective Oxidation of Isobutane

Mo–V–Te–P mixed oxide catalysts, prepared by a dry-up method at various pHs (in the range of about 1.0–9.0), have been tested in the partial oxidation of isobutane. The best catalytic performance was achieved over a catalyst prepared at a pH about 7.0. In this case, high selectivity to methacrolein (37.0%) at an isobutane conversion of 12.7% has been obtained at 380 °C. The surface V⁴⁺/V⁵⁺ ratios of the calcined samples were strongly influenced by the pH in the synthesized solution, which is one of the key factors in the catalytic performance for selective oxidation of isobutane.     

Electrochemistry of the SUCOPLATE® Electroplating Bath for the Deposition of Cu–Zn–Sn Alloy; Part II: Influence of the concentration of bath components

The chemistry of a commercial alkaline cyanide electroplating bath used for the deposition of a Cu–Zn–Sn alloy has been investigated. The voltammetry, the deposit composition and the morphology have been investigated as a function of the concentrations of the three metal ions, Cu(i), Zn(ii) and Sn(iv) as well as the concentrations of cyanide, hydroxide, carbonate and `Copper Glo' additive. It is shown that all components combine to control the bath performance although the trends in alloy composition and quality can be predicted from the known chemistry of the bath. It is also concluded that the deposition of tin has an important role in initiating the growth of alloy layers.     

Effect of the fractional composition of the solid components of coal–water fuel on the characteristics of ignition and combustion

The experimental results of studies of the ignition and subsequent combustion processes of the single drops of organic coal–water fuels (OCWFs) arranged on the junction of a quick-response thermocouple (thermal inertia, <1 s) in an atmosphere of heated (600–1000 K) air are presented. The particles of 2B brown coal and D coal, water, and oils of different types (turbine, motor, and transformer oils) were used as the main OCWF components. The effect of the degree of grinding (fineness) of the solid fuel components of OCWFs on the following integral characteristics of the ignition and combustion of prepared fuel compositions was established: the delay times of ignition and complete combustion. A decrease in the delay times of ignition and complete combustion with decreasing the degree of grinding was detected (in a range of 40–200 μm used as an example). The reasons and special features of the influence of this factor on the integral characteristics of the test processes were recognized.     

Influence of the temperature dependence of the thermophysical properties of coal–water fuel on the conditions and characteristics of ignition

The results of an experimental study and mathematical simulation of the ignition of coal–water fuel (CWF) particles, the main thermophysical characteristics of which (thermal conductivity (λ), heat capacity (C), and density (ρ)) depend on temperature, are reported. Based on the results of the numerical study, the influence of changes in the thermophysical properties upon the heating of the main bed of fuel on the conditions and characteristics of its ignition was analyzed. The ignition delay times (t _i) of CWF particles were determined under the typical furnace conditions of boiler aggregates. As a result of the mathematical simulation of the process of CWF ignition, it was established that the temperature dependence of thermophysical characteristics can exert a considerable effect on the characteristics and conditions of ignition. In this case, it was found that the ignition of coal–water drops is possible under the conditions of their incomplete dehydration. A good agreement of the theoretical ignition delay times of the CWF particles and the experimental values of t _i was established.     

Comparison of the effects of different retention appliances on the oxidant–antioxidant system

The aim was to compare oxidative stress (OS) levels with different types of retention appliance. Thirty orthodontic patients were divided into three groups: Group 1 (Essix retainer), Group 2 (lingual retainer with stainless steel retainer wire), and Group 3 (lingual retainer with fiber-reinforced material). OS was assessed in the subjects’ saliva. Saliva samples were taken from the patients at T₀ (before using the retention appliance), T₁ (first month of retention), and T₂ (third month of retention). The specimens were investigated to detect changes in total antioxidant status (TAS), total oxidant status (TOS), and oxidative stress index (OSI). TAS values in Group 2 were significantly higher than in Group 3. TOS values in Group 3 were significantly lower than in the other groups. TOS values in Group 2 were lower than in Group 1. OSI values of Group 1 were higher than those in Group 2 or 3. There was no statistically significant difference among the time periods. The type of retention appliance affected OS values. A fiber-reinforced material may have a lower OSI. OS or products can affect some systemic disease; therefore, the selection of the retainer will be important on these patients.     

Influence of novel shrinkage-reducing polycarboxylate superplasticizer on the nature of calcium–silicate–hydrates

Currently, a novel shrinkage-reducing polycarboxylate superplasticizer (SR-PCA) is used to control cementitious shrinkage. To clarify its mechanism when applied in cementitious materials, the influence of SR-PCA on the composition, morphology, and structure of synthetic calcium–silicate–hydrate (C–S–H), together with the interaction between SR-PCA and C–S–H at the atomic level, is investigated. For comparison, a commercial polycarboxylate superplasticizer (PCA) is also employed. The results show PCA and SR-PCA can adsorb on the C–S–H surface rather than intercalate into the layers. Compared with PCA, SR-PCA has a milder impact on C–S–H crystallinity. SR-PCA refines the pore structure of C–S–H drastically, whereas PCA loosens the structure by increasing the mesopore volume. In addition, the adsorption effect of SR-PCA on the C–S–H surface is less significant than that of PCA. At the atomic level, this less adsorption of SR-PCA is attributed to the lower adhesion energy of the C–S–H/SR-PCA interface due to the weaker Ca–O bond strength.     

A study of the NOx storage catalyst of Ba–Fe–O complex oxide

The complex oxide Ba–Fe–O catalysts were prepared by sol–gel method. The XRD, DTA, NO-TPD, XPS and NSC measurements were used to characterize the structures, NO_x storage property and sulfur resistance ability. It is concluded that when coadsorption of NO and O₂ at 400 °C, the sample calcined at 750 °C possesses high NO_x storage capacity and sulfur resistance. The perovskite type BaFeO₃ and BaFeO_3−x phases are the active centers in the catalyst for NO_x storage.