Enthalpy Research Articles

Parametric study of a vortex-enhanced supersonic inductive plasma torch

The feed gas injection configuration in radio-frequency (RF) inductively coupled plasma (ICP) torches plays a critical role in discharge stability, gas heating, and device thermal management: particularly if a supersonic nozzle is used to subsequently accelerate the hot gas. A novel injection configuration is the bidirectional vortex, which segments the internal ICP flow field into two counter-propagating vortices that can significantly enhance gas heating and reduce heat losses. The diameter of the interface between the vortices (known as the mantle) is expected to be an important dimensional parameter affecting torch operation, especially relative to the nozzle size. In this work, we investigate the effect of nozzle throat diameter on the behaviour and performance of a vortex-enhanced supersonic ICP torch. The system is operated at RF powers and argon mass flow rates between 200–1000 W and 0–400 mg s−1 respectively, and different nozzle diameters ranging from 1.5 to 4 mm are explored. Because of the high-temperature environment, and to prevent disruption of the vortex flow fields, non-invasive diagnostics are used to measure the gas temperature and plasma density, and to infer the torch thermal efficiency and achievable gas specific enthalpy change. The maximum temperature is between 8500–9500 K with the 1.5 mm nozzle giving the highest temperature for a given power and mass flow rate, while plasma densities vary between 1020–1021 m−3 depending on the operating conditions. The thermal efficiency increases from 29% for the 1.5 mm nozzle to just above 70% for the 4 mm nozzle with a similar maximum specific enthalpy of around 1.5 MJ kg−1. These results demonstrate the important coupling between torch properties, and how system optimization can lead to tailored performance of potential interest to several ground and space-based applications.

DOPO chemically modified mesoporous silica composites: Preparation, flame retardancy, and thermodynamic properties

AbstractOrganic flame retardant 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) was used to decorate the pores of mesoporous silica (m‐SiO2) nanospheres to prepare a new composite flame retardant (DK‐SiO2). The content of DOPO in DK‐SiO2 is about 17 wt%. Due to the chemical bonding, DK‐SiO2 not only enhances the flame retardant performance, but also effectively avoids adverse effects of DOPO on the glass transition temperature and mechanical properties of epoxy resin (EP). At 9 wt% loading, the limiting oxygen index of the EP increased from 25.7 to 31.2, and successfully passed the UL‐94 V‐0 rating. Besides, DK‐SiO2 can significantly reduce the peak heat release rate, total heat release, and total smoke production of EP, with reductions of 26%, 32%, and 20.8%, respectively. Compared with the simple blended sample, DK‐SiO2 not only has better flame retardant performance but also shows significant advantages in thermodynamic properties. The glass transition temperature, impact, and tensile strength, as well as storage and flexural modulus have been improved. This excellent flame retardant performance is mainly attributed to the gas‐condensed synergistic flame retardant mechanism between DOPO and m‐SiO2. The good thermodynamic performance is due to the excellent dispersion of DK‐SiO2 nanospheres in the EP.

A 3D CFD-FEA co-simulation study of low thermal effusivity TBCs applied to the piston and valves of an SI engine

When applied on combustion chamber walls, thermal barrier coatings (TBCs) with low thermal effusivity provide a pathway for reducing heat transfer and improving SI engine efficiency. A 3D CFD-1D FEA co-simulation routine was employed to study the effects of a proprietary TBC on SI engine performance under different permutations of coating the piston, exhaust valves, and intake valves. Marginal reductions (<0.1% points) in total heat transfer and improvements to efficiency were observed when all the three components were coated with the proprietary TBC. Two hypothetical TBC materials with ideally low thermal effusivities were formed by modifying the current material properties and their effect on engine performance was similarly studied at three engine loads at the same engine speed. It was found that coating all the three components with the lowest thermal effusivity TBC offers the largest improvements (∼0.5% points) in net fuel conversion efficiency accompanied by largest reduction (∼1.1% points) in total heat transfer, thus establishing expectations from future TBC materials.

Fabrication of Flame-Retardant Ammonium Polyphosphate Modified Phytic Acid-Based Rigid Polyurethane Foam with Enhanced Mechanical Properties

Ammonium polyphosphate (APP) and self-made nickel phytate (PANi) were used as modified materials to prepare green biomass rigid polyurethane foam (RPUF). The flame retardancy, thermal stability, smoke toxicity and mechanical properties of the modified RPUF were investigated by limiting oxygen index (LOI), a cone calorimetry (CONE) test, thermogravimetric analysis and a compression test. The results showed that the RPUF with 10 wt% APP (PANi/APP10) had the highest LOI of 26.5%. Its peak heat release rate (PHRR) and total heat release (THR) were reduced by 29.64% and 24.05% compared with PANi/APP0 without APP. And its smoke production rate (SPR) and total smoke release (TSR) decreased by 33.14% and 19.88%, respectively. Compared with pure RPUF, the compressive strength of PANi/APP10 was increased by 50%, mainly because APP itself was an ultra-fine powder, which was better compatible with the matrix and improved the hardness of the material. The results showed that the synergistic effect of the gas phase and the condensed phase mechanism could effectively improve the flame-retardant effect. The current research results provided a new strategy for the preparation of green and low-toxicity RPUF.

Enhanced Fire Safety of Energy-Saving Foam by Self-Cleavage CO2 Pre-Combustion and Phosphorus Release Post-Combustion

Rigid polyurethane foam (RPUF) is widely utilized in construction and rail transportation due to its lightweight properties and low thermal conductivity, contributing to energy conservation and emission reduction. However, the inherent flammability of RPUF presents significant challenges. Delaying the time to ignition and preventing flame spread post-combustion is crucial for ensuring sufficient evacuation time in the event of a fire. Based on this principle, this study explores the efficacy of using potassium salts as a catalyst to promote the self-cleavage of RPUF, generating substantial amounts of CO2, thereby reducing the local oxygen concentration and delaying ignition. Additionally, the inclusion of a reactive flame retardant (DFD) facilitates the release of phosphorus-oxygen free radicals during combustion, disrupting the combustion chain reaction and thus mitigating flame propagation. Moreover, potassium salt-induced catalytic carbonization and phosphorus derivative cross-linking enhance the condensed phase flame retardancy. Consequently, the combined application of potassium salts and DFD increases the limiting oxygen index (LOI) and reduces both peak heat release rate (PHRR) and total heat release (THR). Importantly, the incorporation of these additives does not compromise the compressive strength or thermal insulation performance of RPUF. This integrated approach offers a new and effective strategy for the development of flame retardant RPUF.

Co-Pyrolysis of Mushroom Residue Blended with Pine Sawdust/Wheat Straw for Sustainable Utilization of Biomass Wastes: Thermal Characteristics, Kinetic/Thermodynamic Analysis, and Structure Evolution of Co-Pyrolytic Char

Co-pyrolysis technology is considered to be one of the most promising methods for the sustainable utilization of biomass wastes, as it can realize waste reduction and convert wastes into high-value-added products with little impact on the environment. The evaluation of thermal characteristics and product properties is necessary for understanding this technique. In this paper, thermal characteristics and kinetic and thermodynamic analysis during the co-pyrolysis of mushroom residue (MR) with pine sawdust (PS) or wheat straw (WS) were investigated in a TGA. The carbon structure and surface textures of co-pyrolytic char were explored using Raman spectroscopy and a scanning electron microscope. As the PS or WS mass ratio increased, the devolatilization index increased obviously, indicating that volatile release was promoted and concentrated. Weak interactions were observed between 250 and 400 °C during the co-pyrolysis process, which primarily affected the mass transfer, resulting in a change in the thermal decomposition temperatures and rates. The interactions had no prominent influence on the volatiles’ yields. The non-additive performance of average activation energies for the blends was observed due to the interactions, and the lowest average activation energy was obtained when the PS or WS mass ratio was 50%. The lower average pre-exponential factor of the blends indicated the reduced complicacy of the pyrolysis reaction. The relatively small deviation between the activation energy and enthalpy change (4.94–5.18 kJ·mol−1) signified the energy sensitivity of product formation. PS promoted the formation of small aromatic rings (<6 fused rings) in co-pyrolytic chars, whereas WS favored the production of larger rings (≥6 fused rings). The surface textures of the co-pyrolytic chars became porous, and the greater fractal dimensions of the surface morphology for the co-pyrolytic chars indicated that the char surface became irregular and rough.

Comprehensive experimental thermal analysis of single bubble nucleation in vertical flow boiling: Whole field temperature and microlayer dynamics

Nucleate boiling, an important heat transfer phenomenon, holds significance in the thermal management of numerous engineering applications. Understanding and predicting its heat transfer characteristics are vital for system optimization. The formation of a microlayer, resulting from rapid bubble growth on a heater substrate, subsequently facilitates further bubble growth through evaporation playing a critical role in overall bubble dynamics. This study examines the intricate relationship between bubble and microlayer dynamics and their impact on heat transfer rates. Experimental work is conducted for varying heat fluxes using rainbow schlieren deflectometry (RSD) and thin-film interferometry (TFI) in tandem for simultaneous mapping of key parameters: bubble dynamics, microlayer dynamics, and two-dimensional temperature field in vertical flow boiling. The analysis of these parameters has provided significant insights into some fundamental aspects of boiling. Firstly, this study emphasizes that the bubble growth rate models need to take into initial microlayer thickness in accurately predicting bubble growth dynamics. The iteratively obtained constant Ceff (describing the initial microlayer thickness) for bubble growth models matches well the value of Ceff obtained experimentally from thin film interferograms. Additionally, this study also validates the applicability of the kinetic theory-based model in predicting the evaporative heat transfer coefficient during the initial stage of flow boiling, while demonstrating that the accommodation coefficient is ∼0.04 for the investigated range of heat fluxes. Subsequently, using the experimentally obtained evaporative heat transfer coefficient, further insights are provided into the dry patch dynamics. Experimental dry patch dynamics were in good agreement with theoretical predictions up to the rewetting phase. The results also indicate a substantial contribution of microlayer evaporation, constituting approximately 34 % of the total heat flux.

Adsorptive removal of anticarcinogen pazopanib from aqueous solutions using activated carbon: isotherm, kinetic and thermodynamic studies

Pazopanib, which is dangerous for aquatic environments due to its toxic and bioaccumulation potential, has been detected at different concentrations in oncology hospital wastewater, sewage, and surface waters. This study aimed to remove pazopanib from wastewater by activated carbon adsorption technique. The effect of the main variables such as initial concentration, pH of pazopanib solution, adsorbent dose, contact time of the phases, and temperature on the adsorption process was evaluated and the optimum adsorption conditions were determined. The experimental data were applied to Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich adsorption isotherm models to describe the adsorption behavior. The experimental data were applied to pseudo-first-order, pseudo-second-order, and intra-particle diffusion kinetic models to describe the adsorption kinetics. Isotherms were established in the 20–50 °C temperature range to study the adsorption equilibrium. According to the results, the highest removal efficiency of pazopanib (95.87%) was obtained at initial concentration (100 mg L−1), adsorbent dose (0.30 g L−1), temperature (20 °C), contact time (120 min) and pH (7.0). The adsorption kinetics was well described by the pseudo-second-order kinetic model (R2 = 0.9998) and the adsorption isotherm by the Langmuir model (R2 = 0.9999). In thermodynamic studies, the negative values of standard enthalpy (ΔH°), standard free enthalpy (ΔG°), and free entropy (ΔS°) indicate that the adsorption process is spontaneous and favorable, i.e. the disorder is reduced. These results indicate that the developed adsorption process can be efficiently and spontaneously applied for the removal of pazopanib from aqueous solutions.

Reduction of the photogenerated electron transport path by modulating the conduction band region to achieve the highest lignin β–O–4 bond photocleavage efficiency under xenon excitation

Photocracking of lignin β–O–4 bonds is a green approach for the high-value modification of lignin. Graphitic carbon nitride (g-C3N4) that can photocleave the β–O–4 bond is presently the only stable, metal-free photocatalyst owing to the residual metal ions generated due to photocorrosion of metal sulfides. Herein, g-C3N4 with a N–C3 vacancy structure is prepared by etching site–engineering strategy based on the protection of C–N=C structure by chlorine atom. The N–C3 vacancy structure can reduce the transport path of the photogenerated electrons by tuning the conduction band (CB) region to the edge of the photocatalyst, which impedes the critical complexation of the photogenerated electron–hole pairs and enhances the photoelectric conversion efficiency five-fold. Combined with the unique chemisorption capacity (137.82 kJ/mol) of N–C3 vacancies for oxygen, the g-C3N4 photocatalysts with N–C3 vacancy structure can generate 9.6-fold higher superoxide radicals and 13-fold higher lignin β–O–4 bond photocleavage efficiency lignin compared with untreated g-C3N4. Based on the reaction enthalpy changes and free energies investigated through simulations, a route of lignin Cα–Cβ bonds being oxidized and dehydrogenated twice by photogenerated cavities is proposed for the first time. This work reveals the relation between the properties of g-C3N4 and the photocleavage efficiency of lignin β–O–4 bonds.

Dimensionless thermal performance analysis of a closed isothermal compressed air energy storage system with spray-enhanced heat transfer

The isothermal compressed air energy storage (I-CAES) technology boasts the advantages of high theoretical round-trip efficiency and zero carbon emissions. In order to rapidly and efficiently assess the thermodynamic performance of I-CAES, and addressing the limitations of the overly complex thermodynamic model for spray heat exchanged closed-loop I-CAES (CI-CAES), this paper establishes a dimensionless evaluation model related to container size and initial state , spray water quantity , start or end spraying time , and the ratio of liquid level to droplet velocity . The expressions for evaluation indicators such as round-trip efficiency, indicated efficiency, compression exergy efficiency, and expansion exergy efficiency are summarized, revealing the impact patterns of dimensionless numbers on the thermodynamic performance of CI-CAES. The results show that the relative difference in the percentage of air enthalpy change calculated using the real gas model versus the ideal gas model during the expansion stage is 88.26%. The indicated efficiency and round-trip efficiency of CI-CAES simulated by the real gas model were 88.18% and 60.51%, respectively, for the design parameters, and the variable condition operation of the hydrodynamic machinery was the main reason for the lower round-trip efficiency. The larger the values of and , the closer to the isothermal process, and the greater the effect of on the performance of the CI-CAES system compared to the two. When is 50, the polytropic indices of the compression and expansion stages reach 1.03 and 1.01, respectively. The round-trip, compression exergy efficiency and expansion exergy efficiency all vary parabolically with , suggesting that there is an optimal that optimizes the system performance. The change in pressure ratio has a greater effect on round-trip efficiency and on the percentage change in air enthalpy during compression and expansion, and has a lesser effect on system performance. The results of the research can provide theoretical guidance for the efficient operation of CI-CAES.

Investigation of micellization and thermodynamic properties of cationic gemini surfactant (12-2-O-2-12) in the presence of organic solvents

The micellization behaviour and thermodynamic properties of synthesized cationic gemini surfactant (12-2-O-12-12), N,N′-didodecyl-N,N,N′,N′-tetramethyl-N,N′-(oxybis(ethane-2,1-diyl))-diammonium dibromide were studied in the presence of organic solvents for four different temperatures (25, 30, 35 and 40 °C). Aqueous solutions of 10 % and 20 % methanol (MeOH), ethanol (EtOH), isopropanol (IPOH) and dimethyl sulfoxide (DMSO) were used as solvents. The critical micelle concentration (CMC) of cationic gemini surfactant and the degree of counterion dissociation (α) were determined by the conductometric method. Using the CMC and α values for each of the four temperatures, the values of the standard Gibbs free energy (ΔGmo), Gibbs free energy of transfer (ΔGm,transo), enthalpy (ΔHmo), and entropy (ΔSmo) of micellization were calculated. It was observed that the CMC and α values increased with increasing solvent percentage and temperature. It was found that in all cases, the standard Gibbs free energy and enthalpy values were negative while both the micellization entropy and the standard Gibbs free energy of transfer are positive. Negative Gibbs free energy values indicated that micellization was a spontaneous situation, while positive entropy values indicated the existence of a disordered situation. The positive ΔGm,transo values show that the presence of solvents makes the environment unfavorable for micelle formation.

Effect of Lycium barbarum L. polysaccharides on the quality of potato chips under low temperature frying and the mechanism of its action

Consumers increasingly desire healthier low-fat snack options. In this study, potato starch served as the substrate, and varying quantities of Lycium barbarum L. polysaccharide (0, 1, 3, and 5 g/100 g) were added to formula potato chips (FPC). The effect of LBPs on the sensory qualities, oil content, microstructure, and starch properties of FPC-LBPs was examined. The results showed that LBPs resulted in enhanced acceptability, reduced oil content, increased RS content, lower straight-chain starch leaching, and a gradual increase in the composite index (CI) of polysaccharides and starch in FPC-LBPs. The FPC-1LBPs exhibited the highest acceptability compared with the control samples. As the quantity of LBPs increased, the pores and cracks in the FPC-LBPs gradually decreased, and a polysaccharide wrapping layer formed on the surface of starch, which was the primary cause of the decrease in the oil content. With an increase in LBPs addition, the long-range and short-range ordered structure of starch progressively increased, and the hydrogen bonding interaction between LBPs and starch gradually strengthened, resulting in thinner FPC-LBPs. The enthalpy change of starch gradually decreased owing to LBPs, which delayed the pasting of starch and increased the RS content.

Construction of biomass-based flame-retardant, antimicrobial and hydrophobic wood coatings with POSS organic–inorganic nanoparticles

The present study utilizes chitosan (CS) and phytic acid (PA) as natural polyelectrolytes, while incorporating Polyhedral Oligomeric Silsesquioxane (POSS), an organic–inorganic hybrid Si-O-Si cage structure, to create a flame retardant, antimicrobial, and hydrophobic coating for wood materials using the layer-by-layer self-assembly method. The POSS flame retardant bisDOPO-NH2-POSS was synthesized by combining 9,10-dihydro-9-oxa-10-phosphaphenathrene (DOPO) with octaminopropyl silsesquioxane (OA-POSS). Subsequently, AgNPs were incorporated into the cage structure of bisDOPO-NH2-POSS through in-situ reduction to fabricate Ag@bisDOPO-NH2-POSS for enhanced antimicrobial efficacy. The CS/PA coating was deposited using the LBL method, which resulted in the formation of a dense char layer during combustion due to both the presence of an inorganic Si-O-Si physical barrier and the synergistic effect of P-N-Si. As a result, self-extinguishing behavior was observed during vertical burning tests, and there was an increase in the limiting oxygen index value to 30.9%. Moreover, by incorporating chitosan, Ag@bisDOPO-NH2-POSS exhibited inhibitory effects against mold such as Aspergillus niger and Lasiodiplodia. The heat release rate (HRR) was reduced by 42.3%, while the total heat release (THR) decreased by 44.4%. The modified wood demonstrates exceptional water repellency, characterized by a static contact angle exceeding 90°. Additionally, the multifunctional coating shows remarkable resilience as it withstands 100 abrasion cycles without compromising its hydrophobic properties. This study presents a sustainable approach to developing a bio-based coating for wood materials that is flame retardant, hydrophobic, and antimicrobial, thereby expanding the potential applications of wood in construction and furniture.

Enhancing flame retardancy and multi-functionalization of environmentally friendly cotton fabrics with a polydimethylsiloxane-based polyurethane

Phosphorus-containing flame retardants are prone to result in the buildup of biotoxins, while halogen flame retardants easily lead to hazardous gases. Therefore, it is crucial to develop a multifunctional flame-retardant cotton fabric without phosphorus and halogen. Herein, single-ended hydroxy-terminated polydimethylsiloxane (PDMS-ID) was synthesized through single-ended hydrosilicone oil and 1,4-butanediol, followed by the preparation of a waterborne polyurethane (RWPU) containing side chain polydimethylsiloxane through the reaction of PDMS-ID with isocyanate prepolymer. Characterization data shows that its particle size distribution is relatively dispersed while maintaining good emulsification performance. Based on this, a halogen-free and phosphorus-free multifunctional flame retardant cotton fabric (COF-BBN@RWPU) was successfully prepared through treatment with boric acid/borax/3-aminopropyltriethoxysilane solution and subsequent RWPU encapsulation. In vertical flammability test (VFT), COF-BBN@RWPU has a char length of 57 mm and a limiting oxygen index (LOI) of 42.3 % with a 11 % weight gain while pure cotton was burned through with a LOI of 18.0 %. In addition, the total heat release and total smoke release of COF-BBN@RWPU decreased by 80.0 % and 47.2 %, compared with pure cotton. Additionally, COF-BBN@RWPU can achieve a maximum contact angle of 140.1° with an oil-water separation rate of 98.4 %. This study presents an eco-friendly approach to achieving the multifunctionality of cellulose fabrics.

Micron-sized aluminum particle combustion under elevated gas condition: Equivalence ratio effect

Micron-sized aluminum (Al) particle combustion under elevated gas condition is critical for improving energetic material performance, impacting propulsion and explosives technology. This study utilizes Eulerian-Lagrangian method to investigate Al particle combustion dynamics, encompassing both heterogeneous reaction (HTR) and homogeneous reaction (HMR). It focuses on the critical role of the equivalence ratio in single Al particle combustion, highlighting the interplay between HTR and HMR, aiming to optimize energy release and emission control. Our study identifies four stages in the combustion of a single Al particle, where the highest heat release is attributed to HTR, succeeded by HMR, and the minimal from unburned Al vapor. We observe a decline in the total heat release rate with an increasing equivalence ratio, primarily due to the differential impacts of heterogeneous and homogeneous reactions. The thermal-runaway stage in HTR is governed by the particle temperature, while the subsequent decaying stage is influenced by either the diminishing effective Al droplet diameter or the availability of oxygen, contingent upon the fuel conditions. Utilizing Cantera software to analyze HMR allows us to elucidate the thermal effects of elementary reactions and the key reaction pathways. These findings underscore the complex interactions between Al particles and the surrounding gas, providing insights into optimizing the conditions for Al-containing reaction systems.

Thermal and electrical performance evaluation of single and double pass photovoltaic-thermal solar collector with cross-flow baffles and varying transparency: A computational analysis

The present work deals with the development of a semi-transparent photovoltaic thermal (PV-T) solar collector (STPVT) through computational fluid dynamics (CFD) modelling using COMSOL Multiphysics. The study was carried out in three stages; firstly, the CFD model was developed for STPVT and validated with experimental data. Secondly, three different configurations of semi-transparent PV-T collector were investigated, i.e., single pass with PV module on top (SPC), double pass with PV module on top followed by glass cover and absorber plate (DPT), and double pass with PV module in between the glass cover and absorber plate (DPS). The absorber plate was incorporated with cross-flow baffles for improved thermal performance due to increased surface area and turbulence. The study found a thermal efficiency of 76.94% for DPS configuration and a total heat utilisation of 289.63 W at 50% transparency level, i.e., 2-4 times higher than other configurations. Furthermore, the DPS model was investigated for thermal and electrical performance with different PV module transparency levels (52,42,27,13%). The DPS with 18 solar cells having 13% transparency exhibited peak power density (8%) at 717 W/m2 and 101.89°C panel temperature, achieving superior thermal efficiency (84%) and total heat utilization (315.09 W), surpassing configurations with higher transparency.

Laser powder bed fusion sintering mechanism of phenolic resin investigated by ReaxFF molecular dynamics simulations

ABSTRACT This study presents an innovative approach utilising molecular dynamics simulations to elucidate the polymerisation and neck formation mechanisms of phenolic resin during laser powder bed fusion (L-PBF). By developing system and dual-particle models and employing infrared thermal imaging, we established a heat source model for phenolic resin under varying parameters. Our molecular dynamics simulations, using the ReaxFF reactive force field, indicate that high-power lasers significantly enhance cross-linking, achieving a peak polymerisation degree of 78.9% at 30W and 35W power levels. Conversely, increased scanning speed slows product degradation, reducing the polymerisation degree. The interplay of laser power and scanning speed influences polymerisation, with total input energy and heating rate impacting polymerisation and molecular size. Additionally, we investigated neck formation, revealing that small vortices evolve into larger ones during sintering, promoting neck formation. Optical microscopy confirmed diverse neck shapes under different conditions. Quantitative data showed that at a scanning speed of 1000 mm/s, the polymerisation degree reached 93%, with only 2 molecules remaining post-simulation. At 30W power, the largest individual molecule observed was C849H703O117. This research offers crucial insights for selective laser sintering processes, emphasising the importance of high energy input and optimal heating rates for well-formed necks.

Removal of sodium dodecyl benzene sulfonate using bagasse fly ash and surface functionalized modified fly ash from aqueous solutions

AbstractThis study explores the efficacy of a cost‐effective, functionalized adsorbent derived from bagasse fly ash (FA) for the removal of the surfactant sodium dodecylbenzene sulfonate (SDBS) from aqueous solutions. The raw bagasse FA underwent a modification process involving reflux with TiO2 in NaOH at 100°C for 24 h, resulting in a modified fly ash (MFA). Comparative analyses of the sorbents were conducted using scanning electron microscopy (SEM), transmission electron microscopy (TEM), powder X‐ray diffraction (pXRD), Brunauer–Emmett–Teller (BET) surface analysis, and Fourier‐transform infrared spectroscopy (FT‐IR). The surface area of the original FA was found to be 10.795 m2 g−1, which increased to 30.597 m2 g−1 postmodification. Similarly, the crystallinity of FA was initially 49.36% and enhanced to 79.70% after the modification process. The adsorption process of SDBS onto both FA and MFA were found to follow pseudo‐second‐order kinetics. Moreover, the Langmuir adsorption isotherm was the most fitting model, as evidenced by the R2 values at 298 K for SDBS‐FA (0.99) and SDBS‐MFA (0.99), both of which are remarkably close to unity. The dimensionless separation factor (RL) was determined to be less than one, indicating favorable adsorption. The maximum adsorption capacities predicted by the Langmuir model are 156.00 mg/g for FA and a notably higher 231.48 mg/g for MFA. Thermodynamic analysis revealed a positive change in enthalpy (ΔHo) for SDBS‐FA and SDBS‐MFA of 54.50 and 124.48 KJ mol−1, respectively, suggesting endothermic adsorption. Additionally, the Gibbs free energy (ΔGo) was negative for both SDBS‐FA and SDBS‐MFA, suggesting that the adsorption of SDBS is spontaneous.

Electrophile-Arene Affinity: An Energy Scale for Evaluating the Thermodynamics of Electrophilic Dearomatization Reactions.

Rational design and development of organic reactions are lofty goals in synthetic chemistry. Quantitative description of the properties of molecules and reactions by physical organic parameters plays an important role in this regard. In this Article, we report an energy scale, namely, electrophile-arene affinity (EAA), for evaluating the thermodynamics of electrophilic dearomatization reactions, a class of important transformations that can rapidly build up molecular complexity and structural diversity by converting planar aromatic compounds into three-dimensional cyclic molecules. The acquisition of EAA data can be readily achieved by theoretically calculating the enthalpy changes (ΔH) of the hypothetical reactions of various (cationic) electrophiles with aromatic systems (taking the 1-methylnaphthalen-2-olate ion as an example in this study). Linear correlations are found between the calculated ΔH values and established physical organic parameters such as the percentage of buried volume %VBur (steric effect), Hammett's σ or Brown's σ+ (electronic effect), and Mayr's E (reaction kinetics). Careful analysis of the ΔH values leads to the rational design of a dearomative alkynylation reaction using alkynyl hypervalent iodonium reagents as the electrophiles.

The effect of veneer-surface modification with fumed nanosilica on the selected properties of water-resistant plywood

ABSTRACT The aim of the presented research was to investigate the effect of veneer modification with both 2% aqueous dispersion of fumed nanosilica and dispersion of fumed nanosilica containing additional 5% of wood fire retardant, on bonding quality and the flammability parameters of water-resistant plywood. The veneer modification was evaluated using SEM images. The bonding quality was determined through shear strength tests conducted post-aging procedures. Flammability tests were conducted using a mass loss calorimeter and the French method. Parameters such as heat release rate, average rate of heat release, mass loss, time to ignition, time of flameout, total heat release, burned surface area were determined to assess the fire resistance. The results showed that the modification of veneers with nano-SiO2 did not affect the bonding quality, however, the application of a dispersion containing a small amount of fire retardant resulted in a significant reduction in the shear strength. Significantly shorter ignition time was recorded for both modification methods, but at the same time, a reduction in a mass loss and an amount of heat released was also observed. The obtained results indicate the potential of veneer’s surface modification with fumed silica to increase fire resistance of plywood with high bonding quality.