Effects of nano-sized carborundum particles and amino silane coupling agent on the cure reaction kinetics of DGEBA/EMI-2,4 system

The influence of nano-sized carborundum (nano-SiC) particles and amino silane coupling agent on the curing kinetics of bisphenol-A glycidol ether epoxy resin (DGEBA) initiated with 2-ethyl-4-methylimidazole (EMI-2,4) was studied by means of non-isothermal differential scanning calorimetry (DSC). Besides decreasing the heat of reaction ΔH, the presence of nano-SiC particles results in delayed cure reactions, which is also manifested by the increased values of exothermic peak temperature T_p and cure reaction activation energy E of the filled systems. Meanwhile, the amino silane coupling agent could increase ΔH, and decrease slightly the degree of delayed cure reactions caused by nano-SiC particles, and thereby decreasing T_p of the filled systems. The presence of nano-SiC particles prevents from the occurrence of vitrification, so does the amino silane coupling agent when the nano-SiC particle content is low (?15 wt%). As the nano-SiC particle content is high (?15 wt%), the presence of amino silane coupling agent promotes the occurrence of vitrification. Besides E, the presence of nano-SiC particles could increase the overall order of reaction m+n and the frequency factor A, meanwhile, the amino silane coupling agent decreases these three parameters.     

Comparative cure behavior of DGEBA and DGEBP with 4-nitro-1,2-phenylenediamine

Differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and advanced isoconversional kinetic analysis were used to study the curing reaction of diglycidyl ether of 4,4′-bisphenol A (DGEBA) epoxy monomer with an aromatic amine, 4-nitro-1,2-phenylenediamine (4-NPDA). The first DSC exothermic peak was assigned to the curing process of DGEBA with 4-NPDA. Kinetic analysis suggested that the effective activation energy for the cure process decreases from ≈120 to a practically constant value ≈60 kJ mol⁻¹. This system was compared with diglycidyl ether of 4,4′-bisphenol (DGEBP)/4-NPDA. DGEBA/4-NPDA system shows higher reaction temperature, lower reaction rate and lower glass transition temperature under the same cure condition. This can be explained by stereochemical structure of epoxy monomer and the effect of conjugation.     

Differential scanning calorimetric study of curing of acrylated epoxy resin with benzoyl peroxide

The curing reaction of the acrylated diglycidyl ether of bisphenol-A (DGEBA) with benzoyl peroxide has been investigated by differential scanning calorimetry at three different heating rates. The overall cure kinetics were found to be first-order, with Arrhenius parameters E=83 kJ mol^?1 and In A = 16.5 min^?1, independent of the scan rate, up to at least 90% conversion.     

Influence of multi-walled carbon nanotubes on the cure behavior of epoxy-imidazole system

The effect of multi-walled carbon nanotubes (MWCNTs) on the cure behavior of diglycidyl ether of bisphenol-A glycidol ether epoxy resin/2-ethyl-4-methylimidazole (DGEBA/EMI-2,4) system during the cure process was studied with dynamic differential scanning calorimetry. The results showed that, at the initial curing stage, MWCNTs act as catalyst and facilitate the curing, moreover, this accelerating effect is already noticeable at the lowest content of MWCNTs investigated (1 wt%) with slightly further effect at higher contents, suggesting a saturation of catalyzing action at higher contents investigated (3.5 wt%). Then, at the later curing stage, MWCNTs prevent from the occurrence of vitrification. The cure acceleration effect caused by MWCNTs could bring positive effect on the processing of composite since it needs shorter pre-cure time or lower pre-temperature, however, the hindrance effect to vitrification phenomena would bring negative effect as it needs longer post-cure time or higher post-temperature. Furthermore, it was also found that the addition of MWCNTs does not change the autocatalytic cure reaction mechanism of the DGEBA/EMI-2,4 system, but decreases the overall degree of cure, as evidenced by lower total heat of reaction and lower glass transition temperatures of the cured composites compared to neat epoxy.     

Study of the thermal conduction mechanism of nano-SiC/DGEBA/EMI-2,4 composites

This report covers the results of a study on identifying the thermal conduction mechanism of nano-sized SiC/diglycidyl ether of bisphenol-A glycidol ether epoxy resin/2-ethyl-4-methylimidazole (nano-SiC/DGEBA/EMI-2,4) composites. The analysis using FTIR provided an in-depth understanding about how the pretreatment of micro/nano-sized SiC (micro/nano-SiC) particles affects the surface structure of the two different-sized particles, and thereby results in the difference in particles/resin interface structures, which determine different thermal conduction mechanisms. The surface modification approaches included: (1) silane treatment using γ-aminopropyl-triethoxysilane (A1100) and (2) oxidation followed by silane treatment. The results showed that, it is the structure of cross-linked SiC particles/resin three-dimensional network, established by chemical bonding, dominates the thermal conduction mechanism of nano-SiC/DGEBA/EMI-2,4 composites, and leads to the nanocomposites with high thermal conductivity at low filler content. Meanwhile, thermal conduction chains, the prevailing thermal conduction mean in the micro-SiC/DGEBA/EMI-2,4 composites, are the secondary means to conduct thermal diffusion in the nanocomposites.     

Comparative study on the curing kinetics and mechanism of a lignin-based-epoxy/anhydride resin system

Curing kinetics and mechanism of liquid lignin based epoxy resin (LEPL)–maleic anhydride (MA) system accelerated with benzyldimethylamine (BDMA) were studied by Fourier transform infrared (FTIR) spectroscopy and differential scanning calorimetry (DSC). In order to investigate the difference in the curing process, heating FTIR was used to study the change of the functional group. Complete consumption of the epoxides has been observed after the heating temperature was higher than 110 °C. E constant method and E variable method, to study the dynamic DSC curves, were deduced by assuming a constant and a variable activation energy, respectively. With E constant method, the cure reaction activation energy E, the frequency factor A and overall order of reaction n + m are calculated to be 59.68 kJ mol⁻¹, e^20.6 and 1.462, respectively. With E variable method, E is proved to decrease initially, and then increases as the cure reaction proceeds. The value of E spans from 60.16 to 87.80 kJ mol⁻¹. With the E constant method, E variable method and heating FTIR spectra used together, we can have a comprehensive and profound understanding of the cure reactions of the LEPL–MA system.     

Densification and grain growth during solid state sintering of LaPO4

This work is devoted to the kinetic study of densification and grain growth of LaPO₄ ceramics. By sintering at a temperature close to 1500 °C, densification rate can reach up to 98% of the theoretical density and grain growth can be controlled in the range 0.6–4 μm. Isothermal shrinkage measurements carried out by dilatometry revealed that densification occurs by lattice diffusion from the grain boundary to the neck. The activation energy for densification (E_D) is evaluated as 480 ± 4 kJ mol⁻¹. Grain growth is governed by lattice diffusion controlled pore drag and the activation energy (E_G) is found to be 603 ± 2 kJ mol⁻¹. The pore mobility is so low that grain growth only occurs for almost fully dense materials.     

Effects of specific adsorption of copper (II) ion on charge transfer reaction at the thin film LiMn2O4 electrode/aqueous electrolyte interface

This study investigated the effect of a specific adsorption ion, copper (II) ion, on the kinetics of the charge transfer reaction at a LiMn₂O₄ thin film electrode/aqueous solution (1 mol dm⁻³ LiNO₃) interface. The zeta potential of LiMn₂O₄ particles showed a negative value in 1 × 10⁻² mol dm⁻³ LiNO₃ aqueous solution, while it was measured as positive in the presence of 1 × 10⁻² mol dm⁻³ Cu(NO₃)₂ in the solution. The presence of copper (II) ions in the solution increased the charge transfer resistance, and CV measurement revealed that the lithium insertion/extraction reaction was retarded by the presence of small amount of copper (II) ions. The activation energy for the charge transfer reaction in the solution with Cu(NO₃)₂ was estimated to be 35 kJ mol⁻¹, which was ca. 10 kJ mol⁻¹ larger than that observed in the solution without Cu(NO₃)₂. These results suggest that the interaction between the lithium ion and electrode surface is a factor in the kinetics of charge transfer reaction.     

Removal of Zn(II) from aqueous solution with natural Chinese loess: Behaviors and affecting factors

The Chinese loess was proved a promising adsorbent for Zn(II) removal from aqueous solution with adsorption capacities at 70.2-83.2 mg g^− 1 at 15-45 °C. Batch tests were conducted to evaluate the factors affecting the removal efficiency, of which the pH, temperature and initial Zn concentration all found in positive relevance to the increase of Zn(II) removal efficiency except for the slurry concentration. The uptake of Zn(II) on Chinese loess was considered as ion-exchange adsorption based on the calculated adsorption energy at − 12.8 to − 16.18 kJ mol^− 1 by D-R isothermal adsorption model. The adsorption kinetics follows the pseudo-second-order kinetics and the equilibrating duration was found to be > 24 h. Thermodynamic investigation shows that the enthalpy and entropy changes during adsorption are in the range of 18.27-47.83 kJ mol^− 1 and 52.7-129.6 J mol^− 1 K^− 1, respectively. The predicted Gibb's free energies were in the range of − 5.97-3.09 kJ mol^− 1, indicating that the adsorption was in favor of higher temperature and lower initial Zn(II) concentration. The optimal Zn(II) removal efficiency could be obtained under the following conditions: low or intermediate Zn(II) concentration, long reaction time, high temperature and initial pH > 3.0.     

Research into the kinetics of COS elimination from syngas at moderate temperatures

Thermogravimetry at constant temperature and programmed temperatures is used to study reaction kinetics and possible mechanism of COS desulfurization using ferric oxide as the main active component. The apparent reaction activation energy is smaller in hydrogen atmosphere than in nitrogen. The desulfurization reaction of COS takes place easily in a hydrogen atmosphere. At the same time, the influence of the reducing temperature on the desulfurizing reaction was also studied in the TGA apparatus and was shown to play an important part for ferric desulfurization. The optimum temperature for the reducing reaction is under 360 °C. The kinetics of the COS removal reaction are approximately first-order. When the reaction gas contains hydrogen, the apparent reaction activation energy is 12.36 kJ mol⁻¹, in contrast to 21.92 kJ mol⁻¹ in the absence of hydrogen.     

Hydrogenated hydroxy-functionalized polyisoprene (H-HTPI) and isocyanurate of isophorone diisocyanates (I-IPDI): reaction kinetics study using FTIR spectroscopy

The reaction between a hydrogenated hydroxyl-functionalized polyisoprene (H-HTPI) and isophorone diisocyanate isocyanurate (I-IPDI) is followed by using direct FTIR spectroscopy. The reaction kinetics is studied using a simple model taking into consideration the I-IPDI structure. The rates of individual isocyanate groups are described by a second order equation. Influence of dibutyltin dilaurate (DBTL) concentration and temperature on selectivity, defined as the ratio between the rate constant of secondary isocyanate group and the rate constant of the primary isocyanate group, is investigated. It is observed that selectivity decreases when temperature or DBTL concentration increases. Eyring parameters are determined for the catalyzed [ΔH^*=77/35 (kJ mol⁻¹), ΔS^*=12/−100 (J mol⁻¹ K⁻¹)] and uncatalyzed reactions [ΔH^*=48/43 (kJ mol⁻¹), ΔS^*=−179/−167 (J mol⁻¹ K⁻¹)] primary and secondary isocyanate groups being differentiated.     

Non-isothermal curing kinetics of epoxy/mechanochemical devulcanized ground rubber tire (GRT) composites

The curing behavior of diglycidyl ether of bisphenol A (DGEBA) epoxy and specially ground mechanochemical devulcanized ground rubber tire system (GRT) in the presence of polyoxyalkyleneamine curing agent was investigated by non-isothermal differential scanning calorimetry technique at different heating rates. Scanning electron microscopic-energy dispersive X-ray spectroscopy, and attenuated total reflection infrared spectroscopy were used to characterize the GRT particles. The kinetic parameters of curing process were determined by isoconversional method given by Málek. The average activation energy E _a was found to be 52.3–60.7 and 45–59.2 kJ/mol for neat epoxy amine (Epo am 31) and epoxy/amine with GRT (5 Epo am 31) systems, respectively. It was observed that the presence of GRT in epoxy/amine promotes the curing. A two parameter (m, n) autocatalytic model (SB equation) was found to be the most adequate to describe the cure kinetics of the studied epoxy/GRT system. A dominant catalyzing effect of GRT on the curing reaction was observed which is attributed to the complexity of the reaction at later stages of curing, therefore, it was not possible to model the reaction over the whole range of degree of conversion.     

Electrochemical behaviour of titanium in H2SO4-MnSO4 electrolytes

The corrosion of titanium in H₂SO₄ electrolytes (0.001-1.0 M) at temperatures from ambient to 98 °C has been investigated using steady-state polarization measurements. Four distinct regions of behaviour were identified, namely active corrosion, the active-passive transition, passive region and the dielectric breakdown region. The active corrosion and active-passive transition were characterized by anodic peak current (i_m) and voltage (E_m), which in turn were found to vary with the experimental conditions, i.e., d(log?(im))/dpH=−0.8±0.1 and dE_m/dpH which was −71 mV at 98 °C, −58 mV at 80 °C and −28 mV at 60 °C. The activation energy for titanium corrosion, determined from temperature studies, was found to be 67.7 kJ mol⁻¹ in 0.1 M H₂SO₄ and 56.7 kJ mol⁻¹ in 1.0 M H₂SO₄. The dielectric breakdown voltage (E_d) of the passive TiO₂ film was found to vary depending on how much TiO₂ was present. The inclusion of Mn²⁺ into the H₂SO₄ electrolyte, as is done during the commercial electrodeposition of manganese dioxide, resulted in a decrease in titanium corrosion current, possibly due to Mn²⁺ adsorption limiting electrolyte access to the substrate.     

Thermodynamics,kinetics, and isotherms studies for gold(III) adsorption using silica functionalized by diethylenetriaminemethylenephosphonic acid

A novel hybrid material silica gel chemically modified by diethylenetriaminemethylenephosphonic acid GH-D-P has been developed and characterized. The results of the adsorption thermodynamics and kinetics of the as-synthesized GH-D-P for Au(III) showed that this high efficient inorganic–organic hybrid adsorbent had good adsorption capacity for Au(III), and the best interpretation for the experimental data was given by the Langmuir isotherm equation, the maximum adsorption capacity for Au(III) is 357.14 mg/g at 35 °C. Moreover, the study indicated the adsorption kinetics of GH-D-P could be modeled by the pseudo-second-order rate equation wonderfully, and the adsorption thermodynamic parameters ΔG, ΔH and ΔS were −20.43 kJ mol⁻¹, 9.17 kJ mol⁻¹, and 96.24 J K⁻¹ mol⁻¹, respectively. Therefore, the high adsorption capacity make this hybrid material have significant potential for Au(III) uptake from aqueous solutions using adsorption method.     

The non-isothermal kinetics analysis of the thermal decomposition of kaolinite by Effluent Gas Analysis technique

The thermal decomposition of kaolin with high-content of the medium ordered kaolinite was studied by Effluent Gas Analysis (EGA) under non-isothermal conditions. This technique enables to distinguish two overlaying processes during the thermal decomposition of kaolin: oxidation of organic compounds and dehydroxylation. The kinetic of non-isothermal dehydroxylation of kaolinite is controlled by the rate of the third-order reaction. For the given reaction mechanism, the overall activation energy (E_A) and pre-exponential (frequency) factor (A) values are 242 kJ mol⁻¹ and 2.21 × 10⁸ s⁻¹, respectively.     

Kinetics and thermodynamics of isothermal curing reaction of epoxy‐4, 4′‐diaminoazobenzene reinforced with nanosilica and nanoclay particles

The kinetics of the cure reaction for a system of bisphenol‐A epoxy resin (DGEBA), with 4, 4′‐diaminoazobenzene (DAAB), reinforced with nanosilica (NS), and nanoclay (NC) by means of isothermal technique of differential scanning calorimetry were studied. The Kamal autocatalytic‐like kinetic model was used to estimate the reaction orders (m, n), rate constants (k₁, k₂), and also active energies (E_a) and pre‐exponential factors (A) of the curing reaction. However, the existence of NS and NC with hydroxyl groups in the structure improves the cure reaction and influence the rate of reaction and therefore kinetics parameters. The E_a of cure reaction of DGEBA/DAAB system showed a decrease when nanoparticles were present and therefore the rate of the reaction was increased. Using the rate constants from the kinetic analysis and transition state theory, thermodynamic parameters such as enthalpy (ΔH^#), entropy (ΔS^#), and Gibbs free energy (ΔG^#) changes were also calculated. The thermodynamic functions were shown to be very sensitive parameters for evaluation of the cure reaction. POLYM. COMPOS., 31:1442–1448, 2010. © 2009 Society of Plastics Engineers     

Ethanol electrooxidation on novel carbon supported Pt/SnOx/C catalysts with varied Pt:Sn ratio

Novel carbon supported Pt/SnO_x/C catalysts with Pt:Sn atomic ratios of 5:5, 6:4, 7:3 and 8:2 were prepared by a modified polyol method and characterized with respect to their structural properties (X-ray diffraction (XRD) and transmission electron microscopy (TEM)), chemical composition (XPS), their electrochemical properties (base voltammetry, CO_ad stripping) and their electrocatalytic activity and selectivity for ethanol oxidation (ethanol oxidation reaction (EOR)). The data show that the Pt/SnO_x/C catalysts are composed of Pt and tin oxide nanoparticles with an average Pt particle diameter of about 2 nm. The steady-state activity of the Pt/SnO_x/C catalysts towards the EOR decreases with tin content at room temperature, but increases at 80 °C. On all Pt/SnO_x/C catalysts, acetic acid and acetaldehyde represent dominant products, CO₂ formation contributes 1-3% for both potentiostatic and potentiodynamic reaction conditions. With increasing potential, the acetaldehyde yield decreases and the acetic acid yield increases. The apparent activation energies of the EOR increase with tin content (19-29 kJ mol⁻¹), but are lower than on Pt/C (32 kJ mol⁻¹). The somewhat better performance of the Pt/SnO_x/C catalysts compared to alloyed PtSn_x/C catalysts is attributed to the presence of both sufficiently large Pt ensembles for ethanol dehydrogenation and C-C bond splitting and of tin oxide for OH generation. Fuel cell measurements performed for comparison largely confirm the results obtained in model studies.     

Adsorption of Cu from water using raw and modified coal fly ashes

In this study, we found that both raw and modified coal fly ashes effectively adsorb Cu²⁺ from wastewater. The adsorption capacities followed the order CFA> CFA-600> CFA-NaOH. The adsorption isotherms for Cu²⁺ on the raw and modified coal fly ashes fit the Langmuir, Freundlich, and DKR isotherms quite well. These adsorptions were endothermic in nature; the values of E (between 1.3 and 9.6 kJ mol⁻¹) were consistent with an ion-exchange adsorption mechanism. The adsorptions of Cu²⁺ onto CFA, CFA-600, and CFA-NaOH followed pseudo-second-order kinetics.     

The nucleation, crystallization and dispersion behavior of PET-monodisperse SiO2 composites

To more accurately investigate the nucleation, crystallization and dispersion behaviors of silica particles in polymers, the composites of PET with monodisperse SiO₂-PS core-shell structured particles were prepared with SiO₂ size from 380 nm to 35 nm.For these SNPET samples, DSC results showed that the nucleation rate of silica particles increased as their size decreased, in which 35 nm SiO₂ particles produced the most obvious nucleation effect. At 2.0 wt.% load of 35 nm silica, Avrami equation proved that the isothermal crystallization rate G of SNPET was ca. 30% higher than that of pure PET and the crystallization activation energy for SNPET was −218.7 kJ mol⁻¹ lower than −196.1 kJ mol⁻¹ for PET. While, the non-isothermal crystallization ΔE for SNPET was −199.8 kJ mol⁻¹ lower than −185.5 for PET.On non-isothermal crystallization, Jeziorny equation presented the primary and secondary crystallization stages in PET and SNPET, in which nano SiO₂ accelerated the crystallization rate. Their Ozawa number m was from 2.1 to 2.7, which was smaller than that of Avrami number n.The nucleation and dispersion behaviors of SiO₂ particles were directly observed. POM results demonstrated that SNPET samples crystallized more quickly from melt and their crystallization rate increased as silica load increases but accelerated at 2-3 wt.%. The spherulites grew well in PET but their size was smaller in SNPET due to the silica barrier on their growth. SEM and TEM observed the homogeneous silica dispersion morphology and the vivid ordered patterns formed in SNPET. The monodisperse particles are highly expected to give more accurate and valuable references than multi-scale ones in obtaining novel advanced PET composites.     

Hydrogen evolution on conducting polymer electrodes in acidic media

Hydrogen evolution reaction (HER) was studied on polyaniline (PAn), polypyrrole (PPy) and on aniline/pyrrole (PAn–PPy) copolymer in acidic solutions. The cathodic Tafel slopes (b_c) and exchange current densities (j₀) were calculated from Tafel curves obtained in solutions of X M H₂SO₄ (X = 0.1, 0.2, 0.3, 0.4 and 0.5 M). Activation energies (E_a) were determined. The E_a-values were found to be ca. 26 for PAn, 36.5 for PPy, 40.6 for PAn–PPy and 20.6 kJ mol⁻¹for Pt.