Initial Stage Of Reaction Research Articles

Mechanical and bonding properties of pristine montmorillonite reinforced epoxy asphalt bond coats

AbstractEpoxy asphalt bond coat (EABC) has been widely used as a bonding layer in the construction of orthotropic steel deck bridges. To withstand the vibration of the steel deck, EABC needs to have strong bonding strength. In present article, sodium montmorillonite (Mt) was used to reinforce the neat EABC. The morphology and properties of EABC/Mt nanocomposites were characterized by scanning electron microscopy, X‐ray diffraction, Brookfield rotational viscometer, dynamic mechanical analysis, thermogravimetric analysis, automatic adhesion tester, and universal testing machine. No intercalation structure formed in the EABC/Mt nanocomposites. Mt dispersed uniformly in the EABC matrix. The inclusion of Mt increased the viscosity of the neat EABC in the initial stage of chemical reaction. Whereas, in the later curing stage, the viscosity of the neat EABC was higher than those of EABC/Mt nanocomposites. The presence of Mt slightly reduced the glass transition temperature of the neat EABC. The damping performance of the neat EABC was improved with the inclusion of 1 wt% Mt. Mt had a marginal effect on the thermal stability of the neat EABC. The incorporation of Mt significantly enhanced the mechanical properties of the neat EABC. The tensile strength and toughness of the neat EABC increased by 30% and 26%, respectively, with the inclusion of 3 wt% Mt. The existence of Mt greatly enhanced adhesion strength of the neat EABC. The lap‐shear adhesion strength and pull‐off adhesion strength of the EABC nanocomposite with 5 wt% Mt were 33% and 29% higher than those of the neat EABC.

Electrostatic-field-triggered stress in the lithiation of carbon-coated silicon

The traditional viewpoint “the more the lithiation reaction, the bigger the growth stress” is proved to be improper through the simulation of lithiation reaction of carbon-coated silicon particle in the presence of electrostatic field. In the simulation, a positive correlation between growth stresses and charge density is observed and coincides with the experiment results in Pharr's work. Simulation results also indicate that the growth stresses consist of lithiation-reaction-induced stress (LRIS) and field-triggered stress (FTS). FTS is always neglected but can be comparable to, or even bigger than the LRIS in the initial stage of lithiation reaction. The physical mechanism for the formation of FTS is uncovered based on the standpoint of energy conservation and transformation. The FTS needs to be considered seriously because it can bring much more serious damage to the lattice structure of silicon especially in the development of lithium ion battery featuring rapid charging.

Formation and transition of calcium aluminate and calcium silicate compounds from pre-synthesized mullite in low-calcium system by solid-state reaction

The formation and transition of calcium aluminate and calcium silicate compounds from pre-synthesized mullite in low-calcium system were systematically studied by solid-state reaction at 1350–1500 °C using XRF, XRD, FTIR, SEM and PSD methods. Ca3Al2O6, Ca12Al14O33, CaAl2O4, Ca2SiO4 and Ca2Al2SiO7 can form via direct reaction of mullite with CaO at the beginning of the reactions, then Ca12Al14O33 and Ca3Al2O6 react with mullite to form CaAl2O4 and Ca2SiO4, and finally Ca2Al2SiO7 reacts with CaO to generate Ca2SiO4 and calcium aluminate compounds as the sintering process proceeds. Elevating the sintering temperature is in favor of the formation of Ca12Al14O33, Ca3Al2O6 and Ca2Al2SiO7 at the initial reaction stage, but Ca2Al2SiO7 cannot totally transform to calcium silicate and calcium aluminate compounds in the low-calcium system, which deteriorates the pulverization performance of the final products. Increasing the calcium dosage accelerates the transformation of Ca2Al2SiO7 to Ca12Al14O33, CaAl2O4 and Ca2SiO4, which enhances the pulverization performance. If the CaO/Al2O3 molar ratio exceeds 1.4, Ca3Al2O6 will generate by the reactions of pre-formed CaAl2O4 and Ca12Al14O33 with excessive CaO.

Spectroscopic study of the morphology development of closed-cell polyurethane foam using bio-based malonic acid as chain extender

In this study the advantages of using bio-based multi-functional malonic acid salt as chain extender in preparing closed cell polyurethane foams is demonstrated. We found that the presence of malonic acid salt can alter the reaction kinetics, segmental mobility and hence the relative kinetics of polyurethane and polyurea formation. By analyzing the infrared active vibrations, it is demonstrated that the formation of urethane and urea linkages is accelerated at the initial stage of reaction, resulting in enhanced viscosity build-up attributed to the catalytic activity of the triethylamine complexed with malonic acid. The relative kinetics in formation of different morphological features thus can be used to control the cell opening process. These results, combining information on polymerization kinetics, gas evolution and phase separation, illustrate the capability of using malonic acid salt as the chain extender to manipulate polyurethane foam morphology and its potential application in polyurethane closed cell foam systems.

Solvent Effects on Degradative Condensation Side Reactions of Fructose in Its Initial Conversion to 5‐Hydroxymethylfurfural

Invited for this month's cover is the group of Liangfang Zhu and Changwei Hu at Sichuan University. The image shows a general understanding on the solvent-controlled formation of oligomers (the possible precursors of humins) accompanying with formation of small-molecular carboxylic acids as by-products in the initial reaction stage of fructose dehydration. The Full Paper itself is available at 10.1002/cssc.201902309.

The Promotion Effect of NaCl on the Conversion of Xylose to Furfural†

Summary of main observation and conclusionIn this work, the promotion effect of NaCl on the conversion of xylose to furfural in H2O was studied. It was found that xylose conversion and furfural yield increased with NaCl concentration. NaCl decreased the pH of the solution providing H+ for the acid catalytic dehydration of xylose. The formation of oligomers was determined by GPC and ESI‐MS in the initial stage of reaction, especially at low temperature. Excess NaCl promoted the formation of humins in the late stage of the reaction. NaCl could also change the decomposition route of formic acid. Meanwhile, NaCl had the ability of phase separation. Combining these effects with organic solvent during the reaction could inhibit the formation of humins and increase the yield of furfural. In NaCl‐H2O‐THF biphasic system without other catalyst, the optimal furfural yield of 76.7% and selectivity of 77.6% were achieved at 463 K in 2 h.

Hopeite and scholzite coatings formation on titanium via wet-chemical conversion with controlled temperature

A modified wet-chemical conversion technique with controlled mild temperature has been utilized to prepare zinc phosphate (ZnP) and/or calcium-containing ZnP (Ca-Zn-P) coatings on the surface of pure titanium (Ti). Their X-ray diffractometer (XRD) patterns were indexed to typical hopeite (Zn3(PO4)2·4H2O) and scholzite (CaZn2(PO4)2·2H2O), respectively. The influence of solution temperature on coating composition, microstructure and bonding strength between the coating and substrate was investigated by XRD, field emission scanning electron microscope (FE-SEM) and an acoustic emission scratch tester, respectively. A growth behavior of hopeite and scholzite coating was also explored by morphology evolution within the initial reaction stage. The results indicated that the microstructure and crystal size of the coatings were strongly impacted by solution temperature, while a hopeite or scholzite coating with fine and homogeneous microstructure could be obtained at 55 °C. Moreover, the scholzite crystal represented a radially nucleation-growth pattern through tracking observation of morphology evolution.

New Visual Test Method for the Toluene Insolubles in Oil Products

The toluene insolubles (TI) was recognized as coking precursors produced at the initial stage of thermal reaction. The traditional methods can only obtain the overall yield of TI, however, more detailed information, such as the size distribution, and the shape parameters of TI, cannot be provided. In the present work, a new visual test method for the toluene insolubles in petroleum fractions was developed, based on the digital microscopic image processing technology and statistical method. This method can obtain the overall yields of toluene insolubles, provide the particle size distribution and the shape parameters. The optimized test conditions were determined by investigating the influencing factors. The calibration results of this method showed that the relative error of volume concentration is 5%, and the overall error of particle size distribution is less than 5%. Moreover, the detectable concentration of this method is much lower than that of the traditional methods.

Investigation of the Peritectic Phase Transition in a Commercial Peritectic Steel Under Different Cooling Rates Using In Situ Observation

In situ studies of two separate events of the peritectic phase transition during continuous casting, the peritectic reaction and the peritectic transformation, were performed using high-temperature confocal scanning laser microscopy (HTCSLM). The interface migration velocities during the peritectic transformation at different cooling rates were analyzed in situ by measuring the migration distance of the interface vs time. Moreover, the solute distributions near the moving liquid/solid interface during the peritectic reaction and the peritectic transformation were predicted using the commercial software package diffusion-controlled transformation. The results revealed that the images of HTCSLM clearly recorded these two separate events: the peritectic reaction (L + δ → γ) and the peritectic transformation (L → γ and δ → γ). In the initial stage of the peritectic reaction, the austenite (γ) phase was observed to nucleate at the liquid/δ-ferrite (L/δ) interface and then grow along the periphery of primary δ phases. Upon further cooling, these emerging γ phases gradually isolated the liquid and primary δ phases. Subsequently, the laterally growth of the γ phase was regarded as the peritectic transformation. The growth rate of the γ phase was governed by the liquid to γ and δ to γ phase transformations. As the cooling rate increased, the peritectic reaction was observed to occur at lower temperature. Higher cooling rates enhanced the migration rates of the L/γ and γ/δ interfaces during the peritectic transformation. Meanwhile, an interesting massive transformation of δ into γ phase was observed to occur at a cooling rate of 60 °C/min. All primary δ phases were quickly covered by wrinkled γ phases in a short time. Based on the assumption of the solute incomplete diffusion in the liquid phase, the predicted results revealed that the enrichment of carbon near the L/δ, L/γ, and γ/δ interfaces increased as the cooling rate increased. An increase in the cooling rate exacerbated the carbon segregation of the interface during continuous solidification, causing a nucleation suppression of the γ phase. In turn, the increasing carbon enrichment accelerated the interface migration with the diffusion of large amounts of solute across the interface, causing an increase in the driving force for the peritectic transformation.

Gamma-decay from dipole vibrations: Probe for nuclear properties

A review of selected experimental works on the gamma-decay from the Giant and Pygmy Dipole Resonances is presented. The common feature of these experiments is that gamma-decay originates from dipole states populated using reactions induced by heavy ions. The focus is the investigation of dipole modes built on the ground and excited states. The major developments made during the years regarding the detection of high-energy gamma-rays are briefly discussed together with specific results concerning a chosen number of problems among those that were addressed by the theoretical works of P.F. Bortignon. They are: i) the dipole mode in the initial stages of reactions among heavy ions with different $ N/Z$ values for the target and projectile; ii) the problem of isospin symmetry in nuclei at finite temperature; iii) pygmy states far from stability; iv) the nature of the pygmy states.

Factors influencing the morphology and adsorption performance of cellulose nanocrystal/iron oxide nanorod composites for the removal of arsenic during water treatment

The removal of arsenic from reservoirs is a matter of great concern in many parts of the world. Since adsorption is one of the most effective methods for treating arsenic-containing media, iron oxide nanorods were prepared using cellulose nanocrystals (CNs) as a template to remove this harmful metal from aqueous solutions. X-ray diffraction (XRD) analysis showed that Fe(OH)3 was formed in the initial stage of the hydrothermal reaction, and Fe(OH)3 was transformed into Fe2O3 as the hydrothermal reaction proceeded. Transmission electron microscopy (TEM) analysis showed that the length of the iron oxide nanorods was nearly 200 nm, and the width was 10 nm. Moreover, adsorption property studies showed that the maximal amount of As(III) and As(V) adsorption, corresponding to levels of 13.866 mg/g and 15.712 mg/g, occurred at pH levels of 7 and 3, respectively. The adsorption process conformed to the quasi-second-order kinetic and Langmuir adsorption isotherm models, indicating that the adsorption process consists of a chemical adsorption of monolayers. The results indicate that this composite can be used as a potential adsorbent for treatment of water containing harmful substances.

Formation and interdependence of disinfection byproducts during chlorination of natural organic matter in a conventional drinking water treatment plant.

It is crucial to explore the source, formation process and interdependence of disinfection byproducts (DBPs) to reduce their risk on public health. In this investigation, a source water was chlorinated to evaluate the initial formation rates and the maximum yields of trichloromethane (TCM), dichloroacetic acid (DCAA), and trichloroacetic acid (TCAA) based on a hyperbola model. The results showed that TCM achieved the highest initial formation rate and maximum theoretical concentration compared with DCAA and TCAA. The TCM yield can be used to forecast the yields of DCAA and TCAA throughout the whole reaction process, and the yields of chloral hydrate (CH), dichloroacetonitrile (DCAN) and 1,1,1-trichloropropanone (1,1,1-TCP) within the initial reaction stage. Besides, the raw water, settled water and filtered water collected from a drinking water treatment plant were divided into five fractions, respectively, by ultrafiltration membranes to evaluate their DBP formation after chlorination. Compared with the medium molecular weight species, high and low molecular weight organic matters exhibited relatively high specific regulated and unregulated DBP yields (expressed as μg/mg C), respectively. Humic acid-like compositions predominantly contributed to regulated DBP yields, while soluble microbial by-product-like compounds preferentially generated DCAN. The correlation study revealed that the TCM could also serve as an indicator for the measured DBPs from chlorination of sample fractions with different molecular weight. Finally, it was found that the theoretical cytotoxicity was enhanced during chlorination of filtered water compared with chlorination of settled water.

Improvement of Methane Combustion Activity for Pd/ZrO2 Catalyst by Simple Reduction/Reoxidation Treatment

The improvement of methane combustion activity was observed in cyclic temperature-programed and isothermal reactions over Pd/ZrO2 catalysts by simple reduction/reoxidation treatment. The catalytic activity increased during the initial stages of isothermal reaction, and the light-off temperature was lowered as the number of cycles increased in the cyclic temperature-programed reaction. To reveal the origin of activation, variations in the reduction properties after the activation period were carefully investigated through CH4 temperature-programed reduction (TPR) measurements. From the CH4-TPR results, it was confirmed that the reduction temperature decreased significantly after activation. The observation of the CH4-TPR peak at relatively low temperatures is directly proportional to the catalytic activity of CH4 combustion. It was therefore concluded that repeated reduction/reoxidation occurred in the reactant stream, and this phenomenon allowed the combustion reaction to proceed more easily at lower temperatures.

Examining the potential of calcined oyster shell waste as additive in high volume slag cement

The present study investigates the effect of calcined waste oyster shell powder as additive on the fresh, hardened and microstructural properties of high volume slag cement. The results provide that addition of calcined oyster shell powder enhanced the early age compressive strength. The hydration of calcined oyster shell powder resulted in additional portlandite formation during the initial reaction stage. The observations drawn from porosity measurements indicated that calcined oyster shell powder decreased the porosity of binder matrix at early and elongated duration of curing. Furthermore, by 29Si NMR it was observed that the hydration of high volume slag cement was also benefited by calcined oyster shell powder as indicated by increased degree of hydration and chain length. However, excess addition of calcined oyster shell powder caused decreased compressive strength development. Considering the results, calcined oyster shell powder can be used as additive in high volume slag cement.

Inflammation and Bone Repair: From Particle Disease to Tissue Regeneration.

When presented with an adverse stimulus, organisms evoke an immediate, pre-programmed, non-specific innate immune response. The purpose of this reaction is to maintain the organism's biological integrity and function, mitigate or eradicate the injurious source, and re-establish tissue homeostasis. The initial stage of this protective reaction is acute inflammation, which normally reduces or terminates the offending stimulus. As the inflammatory reaction recedes, the stage of tissue repair and regeneration follows. If the above sequence of events is perturbed, reconstitution of normal biological form and function will not be achieved. Dysregulation of these activities may result in incomplete healing, fibrosis, or chronic inflammation. Our laboratory has studied the reaction to wear particles from joint replacements as a paradigm for understanding the biological pathways of acute and chronic inflammation, and potential translational treatments to reconstitute lost bone. As inflammation is the cornerstone for healing in all anatomical locations, the concepts developed have relevance to tissue engineering and regenerative medicine in all organ systems. To accomplish our goal, we developed novel in vitro and in vivo models (including the murine femoral continuous intramedullary particle infusion model), translational strategies including modulation of macrophage chemotaxis and polarization, and methods to interfere with key transcription factors NFκB and MyD88. We purposefully modified MSCs to facilitate bone healing in inflammatory scenarios: by preconditioning the MSCs, and by genetically modifying MSCs to first sense NFκB activation and then overexpress the anti-inflammatory pro-regenerative cytokine IL-4. These advancements provide significant translational opportunities to enhance healing in bone and other organs.

Release characteristics of gaseous products during CO2 gasification of char

We investigated the release behaviors and reaction reactivities of gaseous products during CO2 gasification of three chars (Guanghui char, Hongshagang char, and Shenmu char) and graphite using thermogravimetric–mass spectrometry. The three chars with different sulfur contents had similar release behaviors. CO was the primary gaseous product, while SO2 was the main gaseous sulfur product. CO forms through the reaction between carbon and CO2. The temperature ranges at which H2 and COS evolved are similar to that of CO, and both H2S and SO2 were released at around 1100 °C. For the same gas, the differences in release behaviors were mainly due to the reactivity of the evolution reactions. Alkali mineral species had a catalytic effect on char gasification, while the increasing degree of graphitization tended to increase gasification reaction resistance. Larger surface area resulted in decreased reaction resistance at the initial stage of the gasification reaction. The most important factor influencing sulfur release reactivity was gasification activity rather than sulfur species in char. Moreover, acidic minerals may accelerate the release of sulfur.

Mechanisms of mass transfer enhancement by phase-transfer catalysis for permanganate oxidizing dense non-aqueous phase liquid (DNAPL) TCE

Phase transfer catalysts (PTCs) have been shown to be effective in lowering the limitation of mass transfer between aqueous oxidant MnO4− and NAPLs in in-situ chemical oxidation (ISCO) technologies for remediation of NAPLs. This work researched the effects of pentyltriphenylphosphonium bromide (PTPP, used as the representative PTC) for the enhancement of TCE oxidation, the extent of different treatment effects contributions and generalizability of phase transfer. Experimental results revealed that MnO4− exchanged with Br− in PTPP by ion exchange mechanism and then transferred to NAPL phase due to biphasic nature of PTPP-MnO4-. PTPP enhanced TCE dissolution in aqueous phase but had no significant effect on TCE solubilization. Enhanced TCE dissolution gradually weakened after 2.0 h and disappeared after 5.5 h, while the percentage of MnO4− in phase transfer was 14.8% at 7.5 h, which indicated that dissolution acceleration was only effective at initial stage of reaction (0–2.5 h). Therefore, persistent phase transfer process played the leading role in TCE remediation enhancement. Moreover, for different NAPL phase, more effective phase transfer could be achieved in NAPLs with higher solubility and weaker hydrophobicity. The best-fit polynomial relationship (R2 = 0.992) existed between the percentage amount of MnO4− transferred and the solubility of NAPL.

Degradation of tetrabromobisphenol a by ozonation: Performance, products, mechanism and toxicity

This study systematically investigated the performance of ozonation on tetrabromobisphenol A (TBBPA) degradation under different ozone dosages (5.21–83.33 μmoL/L), initial solution pH (3.0–11.0) and temperatures (10–50 °C). At the same time, the generations of inorganic products (bromide ion and bromate) under different experimental conditions were evaluated and the organic products were also identified. Then, the possible mechanism was proposed and verified by the quantum chemical calculation. In addition, variations and controlling of the toxicity were also analyzed, including acute toxicity, chronic toxicity and genotoxicity. Ozonation was proved to be an efficient and promising technology for removing TBBPA from water. TBBPA of 1.84 μmoL/L could be completely degraded within 5 min under the ozone dosage of 41.67 μmoL/L in wide ranges of pH (3.0–11.0) and temperature (10–40 °C). During the degradation of TBBPA, over 65% of the average bromine ion was detected and nine products were identified. The proposed degradation pathways verified that TBBPA might undergo addition and stepwise oxidative debromination, the hydrogen extraction, and the deprotonation. The results of toxicity testing showed that ozonation could effectively control the acute and chronic toxicity of the water samples, although the toxicity increased in the initial reaction stage due to the accumulation of more toxic intermediates.

Etching of gold nanorods: The effects of diameter on analytical performances

Gold nanorods (GNRs) have been well employed for sensing/bio-sensing based on analytes modulated morphology or self-assembly states. Herein, we employed H2O2 based etching system (H2O2 molecules themselves and H2O2-Fe2+ Fenton reagents) as an example to study the diameters of GNRs on the analytical performances, for the colorimetric platforms using GNRs as reporters. We have found that the thinner GNRs possess a higher sensitivity; while the thicker ones bring more abound color presentation during the etching processes, which is especially for naked eye detection. In addition, a red shift of the plasmonic bands is observed for three kinds of thinner GNRs at the initial stage of the etching reaction, and the mechanism is also discussed.

Effect of particle gradation of aluminum on the explosion field pressure and temperature of RDX-based explosives in vacuum and air atmosphere

Abstract To optimize the energy output and improve the energy utilization efficiency of an aluminized explosive, an explosion device was developed and used to investigate the detonation pressure and temperature of R1 (Al6) aluminum powder and the aluminum powder particle gradation of R2 (Al6+Al13), R3 (Al6+Al24) and R4 (Al6+Al flake) in a confined space. By using gas chromatography, quantitative analysis and calculations were carried out to analyze the gaseous detonation products. Finally, the reaction ratios of the aluminum powder and the explosion reaction equations were calculated. The results show that in a confined space, the quasi-static pressures and equilibrium temperature of the aluminum powder in air are higher than in vacuum. In vacuum, the quasi-static pressures and equilibrium temperatures of the samples in descending order are R1>R3>R4>R2 and R3>R4>R1>R2, respectively. In air, the quasi-static pressures and equilibrium temperatures of the samples in descending order are R1>R2>R4>R3 and R1>R4>R2>R3, respectively. R4 (Al6+Al flake) and R3 (Al6+Al24) have relatively higher temperatures after detonation, which shows that the particle gradation method can enhance the reaction energy output of aluminum during the initial reaction stage of the explosion and increase the reaction ratio by 10.6% and 8.0%, respectively. In air, the reaction ratio of Al6 aluminum powder can reach as high as 78.16%, and the reaction ratio is slightly reduced after particle gradation. Finally, the reaction equations of the explosives in vacuum and in air were calculated by quantitative analysis of the explosion products, which provides a powerful basis for the study of RDX-based explosive reactions.