ABSTRACT The curing kinetics of epoxy resins is commonly described using either model‐fitting or model‐free (isoconversional) approaches. Among model‐fitting methods, the Kamal–Sourour model is widely accepted, but it requires an adjustment to describe the transition to diffusion‐controlled regimes at high conversion. Isoconversional methods, while more flexible, have been traditionally regarded as unable to capture the curing evolution under diffusion control. In this work, we present an extension of isoconversional analysis to diffusion‐controlled regimes and a parallel modification of the Kamal–Sourour model incorporating a diffusion term for consistent comparison. We first demonstrate that isoconversional methods can reproduce all the phenomenology derived from the Kamal–Sourour model. Both approaches are then applied to experimental curing data of the commercial RTM6 epoxy‐based resin, showing that isoconversional analysis provides superior ability to capture the complex experimental phenomenology. Furthermore, the proposed extension of isoconversional analysis yields accurate predictions even when diffusion governs the curing rate. The results demonstrate that isoconversional methods, once extended to account for diffusion control, outperform model‐fitting approaches in reproducing the experimental curing phenomenology. Reliable kinetic models are essential for optimizing cure cycles in industrial manufacturing processes; the proposed methodology provides an accurate and flexible framework to develop such models for epoxy‐based composite structures.

Real curing cycles combine heating ramps and isothermal holds, producing trajectories that conventional charts fail to capture. Isothermal time-temperature-transformation charts (TTT) neglect dynamic heating, while continuous-heating-transformation diagrams (CHT) oversimplify by omitting isothermal stages, leading to significant deviations from experimental observations. In this paper, we develop a comprehensive time-temperature-transformation diagram that considers an initial heating ramp and subsequent isothermal stage (TTT-beta) to assess the processability of the epoxy resins. This chart features the curing, degradation, vitrification, and gelation kinetics evaluated by isoconversional models, thus they allow determining the optimal time and temperature processing. The reliability of these charts has been validated experimentally. Measurements of the curing degree in a typical epoxy-amine resin indicate that, under heating rates, comparable to those used in industrial processes such as autoclave curing, a non-negligible degree of curing is achieved during the heating ramp, before reaching the isothermal stage. Thus, rendering the information from these diagrams unreliable and highlighting the critical importance of the heating phase. We further examined the effects of thermal degradation and vitrification on the interlaminar shear strength (ILSS), compressive strength (sigma c), and the compressive modulus (E c) of the laminate. Our analysis confirms that degradation significantly affects the composite's mechanical properties and that the proposed charts can support the definition of processing conditions for safe curing.

Real curing cycles combine heating ramps and isothermal holds, producing trajectories that conventional charts fail to capture. Isothermal time-temperature-transformation charts (TTT) neglect dynamic heating, while continuous-heating-transformation diagrams (CHT) oversimplify by omitting isothermal stages, leading to significant deviations from experimental observations. In this paper, we develop a comprehensive time-temperature-transformation diagram that considers an initial heating ramp and subsequent isothermal stage (TTT-β) to assess the processability of the epoxy resins. This chart features the curing, degradation, vitrification, and gelation kinetics evaluated by isoconversional models, thus they allow determining the optimal time and temperature processing. The reliability of these charts has been validated experimentally. Measurements of the curing degree in a typical epoxy-amine resin indicate that, under heating rates, comparable to those used in industrial processes such as autoclave curing, a non-negligible degree of curing is achieved during the heating ramp, before reaching the isothermal stage. Thus, rendering the information from these diagrams unreliable and highlighting the critical importance of the heating phase. We further examined the effects of thermal degradation and vitrification on the interlaminar shear strength (ILSS), compressive strength (σc), and the compressive modulus (E c) of the laminate. Our analysis confirms that degradation significantly affects the composite's mechanical properties and that the proposed charts can support the definition of processing conditions for safe curing.

Local overheating during curing of thermosetting resins is likely to occur for thick laminates or during fast curing. Overheating may lead to heterogeneous mechanical properties along the laminate thickness or even to an uncontrolled reaction. To avoid overheating, most thermoset resin manufacturers recommend a "safe" cure cycle. However, these cure cycles can be improved to shorten cure times in thin laminates and may not be good enough to avoid overheating in thick laminates. In this paper, we propose a new analytical model to determine the critical thickness above which thermal runaway occurs when the laminate is heated at a constant rate up to a constant temperature. The model considers different thermal boundaries between the mould and the laminate, i.e., from a perfect thermal contact to a contact of infinite resistance. The analytical model was corroborated through the numerical integration of the equations governing it and experimental data from the curing process of a thick laminate composed of the commercial VTC401 epoxy resin and M55J carbon fiber system. Model predictions indicate that, under the manufacturer’s recommended cure cycle, which includes an initial heating rate of 2 K/min, thermal runaway occurs in laminates thicker than 12.4 mm, aligning with experimental observations. A 20-mm-thick laminate, exceeding this threshold, was cured using a reduced heating rate of 0.3 K/min based on our criteria, successfully preventing overheating. The maximum temperature gradient recorded experimentally remained below 1°C, confirming the model's prediction of uniform thermalization.

A recurring problem when curing thick specimen carbon-fibre-reinforced polymers is the formation of thermal gradients. Thermal gradients can lead to heterogeneous properties, overcuring and, in some cases, matrix degradation. To address this problem, we have developed a general-purpose analytical solution that allows one to predict the maximum temperature difference within a specimen when the curing reaction takes place under isothermal conditions. The analytical solution is specifically tailored to deal with standard conditions in the manufacture of composites and can be applied to different resins and prepregs. In addition, it allows one to determine the conditions for when a thermal runaway will occur. The analytical solution was validated by comparing the analytical predictions with numerical and experimental results.

In this study, we conducted a comprehensive kinetic analysis of the polymerization and thermal decomposition of an acrylic thermoplastic to establish a time-temperature-transformation (TTT) processability map. The process exhibits an induction period followed by rapid polymerization, indicating a complex mechanism. We introduce a novel methodology to quantify this induction period using differential scanning calorimetry (DSC) under both isothermal and dynamic conditions. The resulting kinetic parameters were used to construct the TTT map, which delineates a broad and practical processing window. This map enables precise control of the polymerization process, minimizes the risk of thermal degradation, and supports the efficient integration of acrylic resins into industrial composite manufacturing.

The unparalleled loss-less electrical current conduction of high-temperature superconducting (HTS) materials encourages research on YBa2Cu3O7-𝛿 (YBCO) to unravel opportunities toward numerous applications. Nonetheless, production costs and throughput of the commercialized HTS Coated Conductors (CCs) are still limiting a worldwide spread. Transient liquid assisted growth (TLAG) is a non-equilibrium process displaying ultrafast growth rate which, when combined with chemical solution deposition (CSD), is emerging as a strong candidate to reduce the cost/performance ratio of YBCO superconductors. This study explores the influence of the (Ba:Cu) molar ratio of the transient liquid composition on the nucleation and growth mechanisms of TLAG. This enables an in-depth analysis of the critical role of the yttrium supersaturation in the transient liquids considering the out-of-equilibrium kinetic character of TLAG. Advanced characterization techniques, including in situ synchrotron X-ray diffraction, coupled to a multi-parameter analysis of the contributions to the physical performance, elucidate the influence of transient liquid supersaturation as driving force toward YBCO nucleation and growth. Understanding the fundamental role played by the initial ink composition allows to disentangle how to reach high superconducting performance. The fabrication of high-performance YBCO films through this novel, high-throughput growth methodology promotes the use of HTS materials in large scale power applications.

In this study, we extend the application of Time-Temperature-Transformation (TTT) diagrams, typically employed to describe thermoset processing, to address both the processing and reprocessing of vitrimers. To that end, we have used thermal analysis methods to characterize the reactions governing curing and the thermoforming of a disulfide-containing epoxy vitrimer. The resulting diagrams, which account for adverse processing effects such as degradation and vitrification, exclusively rely on predictions derived from isoconversional methods. Notably, we introduce, for the first time, the application of isoconversional methods to the modeling of stress relaxation kinetics. Using these diagrams, we have identified the conditions for safe curing and thermoforming of the vitrimer. Predictions have been experimentally validated, confirming the robustness and versatility of model-free kinetic analyses.

The cost-effective synthesis of a series of metal propionate powders (copper, yttrium, barium, samarium, gadolinium, and ytterbium) is developed through single chemical reactions resulting in five novel crystalline forms. These complexes are valuable precursors for the preparation of epitaxial REBa2Cu3O7-delta (REBCO) superconducting films (here, RE = Y, Sm, Gd, and Yb) through the innovative transient liquid-assisted growth (TLAG) process based on chemical solution deposition (CSD). TLAG-CSD shows impressive results with YBa2Cu3O7-delta (YBCO), obtaining critical current densities of 2.6 MA/cm2 (77 K) on 500 nm films at unprecedented growth rates (50-2000 nm/s), boosting unprecedented high-throughput industrial production. With a cardinal concern on designing the pyrolysis toward optimal nanocrystalline films for TLAG, an analysis of the thermal behavior of the synthesized precursors is essential. Decomposition pathways for each metal propionate are established, and compatibility with TLAG-CSD is corroborated. Metal-organic solutions for these REBCO systems are successfully prepared, and their rheological properties and thermal behavior are analyzed. This work demonstrates homogeneous nanocrystalline films through propionate-based REBCO precursor solutions, including several rare-earth ions, which display exemplary chemical and microstructural characteristics crucial for TLAG, and provides a base for a wide variety of CSD-based functional oxides.

This work provides a comprehensive thermomechanical and rheological characterization of a high-performance epoxy resin synthesized from a vanillin derivative, vanillyl alcohol. The study includes a complete analysis of the curing and decomposition kinetics that enabled a Time-Temperature-Transformation plot accounting for gelation, vitrification, and resin degradation to be developed. These plots allow one to determine the optimal time and temperature processing conditions that will yield the best mechanical properties. Kinetic predictions and experimental results showed that this resin can be cured at room temperature in just a few hours, forming a solid gelled glass. Enhanced mechanical properties are achieved by post-curing the resin at temperatures above Tg infinity = 85.4 degrees C. With a dynamic storage modulus of 2.7 GPa, this bio-based resin proves to be a sustainable alternative to fossil-based resins whose primary source is the ever-prevalent bisphenol A diglycidyl ether. Thermal oxidation is the main cause of the mechanical deterioration at high temperatures, as revealed by FTIR spectroscopy.

Abstract In this work, we review recent progress achieved in the use of chemical solution deposition (CSD) based on fluorinated metalorganic precursors to grow superconducting REBa2Cu3O7 (REBCO) films and coated conductors (CCs). We examine, first of all, the advances in optimizing the steps related to the solutions preparation, deposition and pyrolysis based on novel low-fluorine metalorganic solutions. We show that a new type of multifunctional colloidal solutions including preformed nanoparticles (NPs), can be used to introduce artificial pinning centers (APCs). We analyze how to disentangle the complex physico-chemical transformations occurring during the pyrolysis with the purpose of maximizing the film thicknesses. Understanding the nucleation and growth mechanisms is shown to be critical to achieve a fine tuning of the final microstructure, either using the spontaneous segregation or the colloidal solution approaches, and make industrially scalable this process. Advanced nanostructural studies have deeply modified our understanding of the defect structure and its genealogy. It is remarkable the key role played by the high concentration of randomly distributed and oriented BaMO3 (M = Zr, Hf) NPs which enhance the concentration of APCs, such as stacking faults and the associated partial dislocations. Correlating the defect structure with the critical current density Jc (H,T,θ) allows to reach a tight control of the vortex pinning properties and to devise a general scheme of the vortex pinning landscape in the whole H–T phase diagram. We also refer to the outstanding recent achievements in enhancing the vortex pinning strength by shifting the carrier concentration in REBCO films towards the overdoped state, where the pinning energy is maximum and so, record values of critical current densities are achieved. This confirms the performance competitiveness of nanocomposite CCs prepared through the CSD route. We conclude with a short summary of the progress in scaling the CC manufacturing using fluorinated solutions.

Because long curing times hinder the mass manufacturing of composite products, there is a constant quest to develop shorter curing cycles that maintain material quality. The authors recently developed a curing prediction methodology for thermoset composites based on an isoconversional model, which is used in this work to shorten the curing time of real practice processes. The investigation presents two optimized cure cycles devised to reduce the curing times recommended by the resin manufacturer while assure a complete degree of cure and restricting the exothermal flow to avoid undesired overheating. The mechanical (compression, in-plane, and interlaminar shear) and physical ( T_g , void content, and outgassing) properties of specimens extracted from panels manufactured according to recommended curing cycles and the two time-reduced cycles (up to 72

To determine the decomposition conditions of carbonates in the form of films, we investigated the dependence of the kinetics on carbon dioxide partial pressure, temperature and film thickness. Three different analyses allow us to determine the functional dependence of the decomposition onset temperature on the CO _2 partial pressure, of the reaction rate on the temperature and of the kinetics on the film thickness. The latter analysis also reveals geometrical aspects of the reaction mechanism. Experiments have been carried out with CaCO _3 and BaCO _3 films. The simple geometry of the films and their relatively fast heat and gas transport allow the reaction kinetics to be easily explored.

A lack of fundamental knowledge about the kinetic mechanisms governing the processing and reprocessing of vitrimers forces a trial-and-error procedure to be adopted when choosing treatment conditions. In this work, we develop diagrams to be used as a straightforward tool to decide the curing and thermoforming parameters of vitrimers. The thermal stability of a disulfide containing epoxy has been evaluated by means of thermal analysis methods. By characterizing the kinetics of the curing and decomposition of the resin through a model-free kinetic method, we have been able to generate an intuitive processability map based on Time-Temperature-Transformation plots. The resulting chart allows for the optimum curing conditions that will avoid degradation to be identified. A similar chart for reprocessability has been obtained by considering the exchange kinetics of the characteristic stress relaxation behavior of vitrimers. Furthermore, we have incorporated into the diagrams criteria to determine the critical thickness below which a tolerable thermal gradient is not exceeded. Our diagrams have been experimentally validated, thus proving to be a useful and valid tool for rapid decision-making situations.

We have developed a new method to measure the viscosity of micrometric films by thermomechanical analysis with a hemispherical probe of millimetric diameter. The loading curve (displacement vs. time) recorded as the probe tip crosses the whole film at constant load until it touches the substrate is fitted to a theoretical curve shape that has been obtained after solving the problem of liquid flow under the probe tip. The method has been validated by measuring the viscosity of rosin films. It has been applied to analyze the thermal evolution of unstable liquid films that appear on Ba propionate, Ce(III) propionate and a low-fluorine precursor film of YBa 2 Cu 3 O 6+x . During pyrolysis of the last two films, viscosity first diminishes due to heating and then it increases as solid oxide particles are formed inside the liquid.

The thermal decomposition of calcium propionate, in inert and oxidative atmospheres, has been investigated by thermogravimetry combined with infrared evolved gas analysis; the main volatiles formed during thermal decomposition have been identified. The intermediate and final products have been characterized by infrared spectroscopy, x-ray diffraction, elemental analysis and scanning electron microscopy. The different mechanisms involved in thermal decomposition are discussed as a function of atmosphere and sample structure. The kinetics of the decomposition and the ability of powders to undergo a thermal runaway are also investigated.

This chapter describes a dynamical scenario in which an autonomous system can incorporate many oscillation modes of different frequencies, and where the oscillations can intermittently combine with each other to produce extremely complex self-sustained behaviors with multiple time scales. The complex oscillations are illustrated by means of the experimental devices with which they were discovered, which are simple enough to offer a comprehensive view of what is happening at the physical level. At the same time, we consider what remains to be understood in order to explain the observed behavior and how the qualitative methods of nonlinear dynamics can be used to provide such an understanding. Although a proper mathematical theory for the oscillatory mixing mechanism has yet to be developed, its features suggest significant possibilities for scalability, making it potentially relevant for the study of systems exhibiting rich oscillatory dynamics.

The mass manufacturing of composite products is hindered by long curing times, and composite manufacturers demand shorter curing cycles while keeping material properties. This requires reliable methods to predict the curing kinetics of each resin formulation. Isoconversional methods are easy to implement and able to deal with complex processes. However, scientists still limit their isoconversional predictions of curing degree to isothermal or constant heating programs. In this study, we perform combined dynamic and isothermal DSC measurements for two different commercial epoxies for aerospace applications (M18 and VTC401). Based on the isoconversional kinetic analysis, we show the feasibility of predicting the evolution of an epoxy resin cure for an arbitrary and complex temperature program using two different unexplored methods for this purpose. Because of the versatility of both prediction methods, they are especially suited to deal with actual conditions in industrial processes. The proposed approach is validated experimentally by comparing predictions against the curing degree of these epoxies during a temperature program that comprises isothermal and dynamic stages. These reliable and straightforward predictions open the door to optimize curing times and increase productivity in composites.

Transient liquid assisted growth (TLAG) is an ultrafast non-equilibrium growth process mainly governed by kinetic parameters, which are only accessible through fast in situ characterizations. In situ synchrotron X-ray diffraction (XRD) analysis and in situ electrical resistivity measurements are used to derive kinetic diagrams of YBa2 Cu3 O7-x (YBCO) superconducting films prepared via TLAG and to reveal the unique peculiarities of the process. In particular, diagrams for the phase evolution and the YBCO growth rates have been built for the two TLAG routes. It is shown that TLAG transient liquids can be obtained upon the melting of two barium cuprate phases (and not just one), differentiated by their copper oxidation state. This knowledge serves as a guide to determine the processing conditions to reach high performance films at high growth rates. With proper control of these kinetic parameters, films with critical current densities of 2-2.6 MA cm-2 at 77 K and growth rates between 100-2000 nm s-1 are reached. These growth rates are 1.5-3 orders of magnitude higher than those of conventional methods.

Research involved in developing alternative energy sources has become a necessity to face global warming. In this context, superconductivity is an appealing solution to enhance clean electrical energy provided that lower production costs can be attained. By implementation of chemical solution deposition techniques and high-throughput growth methods, low-cost nanostructured epitaxial cuprate superconductors are timely candidates. Here, we present a versatile and tunable solution method suitable for the preparation of high-performance epitaxial cuprate superconducting films. Disregarding the renowned trifluoroacetate route, we center our focus on the transient liquid-assisted growth (TLAG) that meets the requirement of being a greener chemical process together with ultrafast growth rates beyond 100 nm/s. We developed a facile, fast, and cost-effective method, starting from the synthesis of metal-propionate powders of Y, Ba, and Cu of high purity and high yields, being the precursors of the fluorine-free solutions, which enable the chemical and microstructural nanoscale homogeneity of YBa2Cu3O7-x (YBCO) precursor films. These solutions present endured stability and enable precise tunability of the composition, concentration, porosity, and film thickness. Homogeneous precursor films up to thicknesses of 2.7 mu m through eight layer multidepositions are demonstrated, thus establishing the correct basis for epitaxial growth using the fast kinetics of the TLAG process. YBCO films of 500 nm thickness with a critical current density of 2.6 MA/cm(2) at 77 K were obtained, showing the correlation of precursor film homogeneity to the final YBCO physical properties.