High Heating Rates Research Articles

Efavirenz cocrystals with Ascorbic acid: A Strategy for Polymorphic Modification and improvement of Dissolution properties

The objective of this research was to improve the solubility and dissolution rate of Efavirenz (EFA), a BCS II drug utilized for HIV infection treatment, by cocrystallization with ascorbic acid (AA). An in silico analysis indicated that EFA and AA exhibited physical interaction and compatibility. EFA exists in two polymorphic forms, I and II, with varying crystalline habits, where polymorph II presents better solubility and dissolution rate. Cocrystals were prepared using the solvent evaporation method by varying AA concentration and temperature. FTIR and NMR analysis confirmed the absence of chemical interaction between EFA and AA. Increasing AA concentration and temperature significantly increased the saturation solubility. DSC, XRD and SEM analysis revealed a shift in the endothermic peak of EFA, change in intensity with 2θ values, and modified surface morphology respectively. This also confirmed a polymorphic structure change in the cocrystals due to high heating rates and maximum crystallization rate. The dissolution rate of the cocrystals was enhanced by the optimized batch, which contained an intermediate concentration of AA and was subjected to the highest temperature condition, and the data fitted well with the Higuchi model of kinetics. The stability of the cocrystals was also evaluated by accelerated stability testing to determine the percentage of drug content. Thus, cocrystallization with AA proved to be a suitable approach for enhancing the dissolution characteristics and polymorphic modification of BCS II drugs, such as EFA.

Experimental and numerical study on the tensile ductility of an aluminium alloy with heat-affected zones

In the case of aluminium structures, welding may introduce weak zones, so-called heat-affected zones (HAZ), close to the weld. Such zones should be accounted for when predicting the overall behaviour of structures since the deformation tends to localise within such weak zones leading to the initiation of failure. Whereas the effect of welding on mechanical properties such as yield stress and work hardening is known, the ductility of a HAZ and how to model it in numerical simulations remain uncertain. To address this challenge, this article presents a combined experimental and numerical study on ductile fracture modelling of an aluminium alloy AA6063-T6 exposed to complex heat treatments. The first part includes preparation of specimens and uniaxial tension testing. A Gleeble machine is used to generate well-defined heat treatments involving high peak temperatures and heating rates. Subsequently, uniaxial tension tests at low and high strain rates are conducted. The results show the effect of the complex heat treatments on strength, strain-rate sensitivity, and fracture. The numerical part of this study concerns two widely used damage models, namely the Cockcroft–Latham fracture criterion and the Gurson–Tvergaard model. Calibration of material models and a parameter study are carried out based on analyses of the tension tests. To this end, a case study is conducted elaborating on the importance of the damage parameters within an idealised heat-affected zone and plane-strain tension. The main objective of this study is to obtain a more general understanding of ductile fracture modelling of aluminium alloys exposed to complex heat treatments representative of welding.

Optimization of the power supply and temperature control algorithm for a second-dimension temperature programming system used in comprehensive two-dimensional gas chromatography

This study evaluates the relationship between the power supply output (voltage (V), current (I), power (W)), used for heating a second dimension (²D) column, and the maximum heating rate and temperature offset achievable by custom built ²D temperature programming system (²DTPS). The influence of the gas chromatograph (GC) oven temperature, ²D column flow rate, and ²D column dimensions when heating the ²D column were also explored. This data provided the minimum power needed for heating a ²D column (normalized to its length), based on the heating rate or temperature offset relative to the first dimension (¹D) column. During the study, optimization of the temperature control algorithm was also carried out to expand the dynamic range of the heating rate for a single power supply output (V, I), while maintaining a temperature deviation of < 0.75 °C between the measured temperature and temperature setpoint. This simplified the power supply specification recommendation to voltages which provide 1.5 A for heating rates and maximum temperature offsets below 28 °C/s and 70 °C, respectively, and 1.9 A when higher heating rates or temperature offsets were needed.

Physical and Mechanical Properties and Damage Mechanism of Sandstone at High Temperatures

The physical and mechanical properties of rocks change significantly after being subjected to high temperatures, which poses safety hazards to underground projects such as coal underground gasification. In order to investigate the effect of temperature on the macroscopic and microscopic properties of rocks, this paper has taken sandstone as the research object and conducted uniaxial compression tests on sandstone specimens at different temperatures (20–1000 °C) and different heating rates (5–30 °C/min). At the same time, the acoustic emission (AE) test system was used to observe the acoustic emission characteristics of the rock damage process, and the microstructural changes after high temperature were analyzed with the help of a scanning electron microscope (SEM). The test results show that the effect of temperature on sandstone is mainly divided into three stages: Stage I (20–500 °C) is the strengthening zone, the evaporation of water and the contraction of primary fissures, and sandstone densification is enhanced. In particular, the compressive strength and elastic modulus increase, the macroscopic damage mode is dominated by shear damage, and the fracture micromorphology is mainly brittle fracture. Stage II (500–600 °C) is the transition zone, 500 °C is the threshold temperature for the compressive strength and modulus of elasticity, and the damage mode changes from shear to cleavage damage, and the sandstone undergoes brittle–ductile transition in this temperature interval. Stage III is the physicochemical deterioration stage. The changes in the physical and chemical properties make the sandstone compressive strength and modulus of elasticity continue to decline, the macroscopic damage mode is mainly dominated by cleavage damage, and the fracture microscopic morphology is of a more toughness fracture. The effect of different heating rates on the mechanical properties of sandstone was further studied, and it was found that the mechanical properties of the rock further deteriorated under higher heating rates.

Heat transfer, crystallization and properties of Bayan Obo tailings-based nanocrystalline glass-ceramics processed with microwave radiation

Using Bayan Obo tailings containing rare earth element as raw material to prepare nanocrystalline glass-ceramics by microwave heating is a feasible scheme for the sustainable development of resources and low-carbon production. In this paper, the effects of conduction, infrared, microwave and plasma heating on nucleation were studied in order to obtain evidence for a thermal and non-thermal microwave effect. The differences in the mechanical properties, high-temperature softening properties and microstructures of the glass-ceramics prepared by conventional and microwave heating were analyzed. The results showed that microwave heating had a higher heating rate than conventional heating. The volumetric heating reduced the dependence of heat conduction within the sample, forming a uniform thermodynamic system for nucleation. The polymeric character of the silicon-oxygen network could be reduced by microwave radiation to promote nucleation, and fine nanocrystals with globular crystals and a uniform microstructure were produced after continuous nucleation-crystallization. In contrast to conventional heat treatment, the flexural strength of the samples increased from 169 MPa to 219.9 MPa under microwave radiation, and the thermal stability improved. The excellent mechanical properties were attributed to the increased Si–O stretching vibration frequency and bond force. In addition, the structure of the diopside cell tended to be dumpy with a decreased β angle, and the crystal orientation was affected. Tailings-based nanocrystalline glass-ceramics with excellent properties can be prepared in a short processing time by microwave heating.

Carbon felt from acrylic dust bags as flexible EMI shielding layer and resistive heater

Carbon felt is widely used due to its lightweight and conductive nature. However, limited research has been conducted regarding the tension applied during its preparation. This study aims to explore the influence of different loading tensions during the carbonization process on the properties of acrylic-based carbon felts. Enhanced flexibility, lower shrinkage and improved mechanical and electrical properties were found for the samples obtained in the edge loading mode. Subsequently, the performance of carbon felts in electromagnetic interference (EMI) shielding and resistive heating was studied. The carbon felts achieved a notable EMI shielding effectiveness of 55 dB. The specific shielding effectiveness values are significantly higher than other reported materials due to their low density and high porosity. Moreover, the carbon felts displayed commendable electrical heating performance through high heating rates and superior heating efficiency. Lastly, the structural stability was assessed via self-designed bending experiments. Good stability of the resistance and heating behavior of the carbon felts across multiple bending cycles was observed. With low manufacturing costs, good stability and air permeability, the flexible carbon felt is expected to be widely used for barrier applications and wearable electronics.

Heat and Mass Transfer in Infrared Assisted Heat Pump Drying of Purple Yam

Abstract This study focused on an engineering problem of heat and mass transfer in infrared (IR) assisted heat pump (HP) drying of purple yam including both a drying experiment and theory of heat and mass transfer mathematical equations. The experimental drying of yam by the IR assisted HP drying method was performed to evaluate the effect of IR power on drying rate and heating rate. The input drying parameters included the drying air temperature of 50°C, drying air velocity of 2.5 m·s−1 and IR power of 0, 300 and 350 W, in which, at the IR power of 0 W, the HP-only drying mode was performed. The experimental drying results showed that the IR assisted HP drying method could improve the drying rate and heating rate as compared to HP-only drying. At the IR power of 350 W, the drying time was the shortest (150 minutes), followed by the IR power of 300 W (210 minutes) and HP-only drying (300 minutes). The IR assisted HP drying obtained the high heating rate as the time required for the drying material to reach the drying temperature was about 35 and 25 minutes corresponding to the IR power of 300 and 350 W. While in HP-only drying, it took about 270 minutes for the drying material’s temperature to reach nearly the drying air temperature value. Besides, the comparison between the predicted data by numerically solving the heat and mass transfer equations and experimental drying data was also conducted. The analysis results indicated that the predicted data could be used to predict the experimental data accurately. The theoretical results of heat and mass transfer in the IR assisted HP drying process as well as experimental drying results would be the basis for improving the IR assisted HP drying equipment to achieve the drying efficiency including the drying rate, quality of dried products, and energy consumption.

Cellulose pyrolysis kinetic model: Detailed description of volatile species

Lignocellulosic biomass is typically composed by a major fraction of cellulose. Its decomposition influences on large extent the biomass rate of pyrolysis and product distribution, affecting process behaviour in thermochemical conversion processes. Containing approximately 90 % of volatile matter, volatile products from cellulose pyrolysis are very important in the characteristics of flames and ignition properties. Recent developments in analytical methods allowed a detailed identification of these volatile products, giving valuable information to process development and better understanding of kinetics. Predictions of a previous kinetic model are compared with these new findings, revealing large space for improvements. In this work, we propose a multi-step kinetic model of cellulose pyrolysis, incorporating the most recent experimental findings into the detailed product description. The model consists of four main reactions for the decomposition of cellulose, with formation of gases, volatiles, char and metaplastic species. The release of metaplastic species is described by a set of six reactions. The formation and release of 13 oxygenated hydrocarbons is predicted by the model, including anhydrosugars, furans, aldehydes, alcohols, ketones and carboxylic acids. The model also describes the formation of levoglucosan in metaplastic state before its release, explaining high heating rate mass loss behaviour. The model is compared with a large variety of experiments from literature, and validated for mass loss rates and product distribution, achieving overall good agreement despite experimental uncertainties and the large simplifications characteristic of the model formulation. Besides effectively quantifying the yields of gaseous, condensable and solid products, the model accurately captures the distribution of volatiles in terms of functional groups and C-chain length.

Enhancement effect of Li addition on nitriding reaction and combustion of Al-Li alloy in N2

For aluminum-based alloy particles, the addition of alloying element lithium (Li) with the properties of a high chemical activity and a low melting/boiling point can significantly improve the thermo-reactive properties of aluminum (Al) particles. To further reveal the combustion mechanism, this paper presents the nitriding reaction and combustion characteristics of Al-Li alloy in nitrogen (N2) through thermogravimetric analysis and differential scanning calorimetry (TG-DSC) analysis at a low heating rate and laser-induced ignition experiments at a high heating rate, considering the influences of two kinds of Li contents (1.0 wt% @ Al-1.0Li and 2.5 wt% @ Al-2.5Li) on these characteristics and making a comparison to the counterpart Al. Al-Li alloy powders as-prepared by gas atomization method showed the texture of the Li-rich eutectic phase compounds on the surface by scanning electron microscope (SEM) characterization. The TG-DSC results demonstrated that the thermal nitriding reaction of Al-Li alloy in N2 was significantly faster than that of pure Al. The nitriding reaction temperature decreased from 853 °C for pure Al to 245 °C for Al-2.5Li alloy with a reduction of 71 %. The final weight gain of Al-2.5Li alloy was almost three times higher than that of pure Al in N2. The SEM photograph of intermediate nitriding products revealed that the cracks and loose “island” structures in the Li-rich zone on the Al-Li surface were the key to preventing the formation of a “passivation effect” into Al and promoting N2 uptake during melting. In addition, Li also acts as a catalytic carrier and “oxygen absorber” to enhance the Al-N reaction. The combustion of single Al-Li alloy microparticles induced by laser showed two stages: preheating and rapid nitriding. Al-Li alloy particles were ignited more rapidly and showed typical gas-phase / surface combustion modes different from pure Al. According to these findings, the combustion mechanism was proposed to help guide the development of Al-based solid propellants containing Li and the synthesis of AlN/Al composites in nitrogen-rich environments.

Karakterisasi Termal Briket Ampas Tebu melalui Uji Termogravimetri

&#x0D; &#x0D; &#x0D; &#x0D; Sugarcane bagasse has potential to be used as one of the renewable energy resources. The present work is dealt with thermal characterization of sugarcane bagasse briquettes through thermogravimetry method. The briquette samples are cylinder of 40 mm in diameter and 20 mm long. Both non-carbonized and carbonized briquettes are considered in this work. The samples comprise two different densities, i.e. 1.3 g/cm3 and 2.3 g/cm3. The samples are heated in an inert and non-isothermal atmosphere with heating rates of 5oC/min and 15oC/min. The TG curves exhibit three phases of thermal decomposition. The decomposition of the samples with higher heating rate and higher density shifts to higher temperature. The decomposition of the carbonized samples also shift to higher temperature, but to a lesser degree. The initial degradation temperature ranges from 186oC to 273oC, while the final degradation temperature ranges from 328oC to 432oC. The temperature at which the rate of decomposition is amximum ranges from 232oC to 303oC. At higher heating rate, the degradation rate shifts to lower temperatures&#x0D; &#x0D; &#x0D; &#x0D;

Optimization of heating profile for superconductor joint performance made by resistive joule heating process

The long-term heating (>60 min) of second generation high temperature superconductor (2G HTS) tape-joints at temperatures above 200 °C leads to the continuous deterioration of their superconducting properties. Previously, we proposed a resistive Joule heating process with a short heating time (∼10 min) that exhibited beneficial critical current (Ic), retention percentages (84–99 %), and joint resistances (74–697 nΩ cm2) in four independent experiments.In this study, we investigated two heating rates and three tape-joint areas. The results show that for the samples with different tape joint areas, the critical current retention percentages (97–100 %) and uniformity of specific joint resistances (82–272 nΩ cm2) were significantly improved at a high heating rate of ∼30 °C/min. The sintering of silver nanoparticles and oxidation characteristics of the copper stabilizers were observed using transmission electron microscopy, scanning electron microscopy, and Raman spectroscopy to elucidate the effect of different heating profiles. This study opens new avenues for improving the quality of 2G HTS tape joint processes for ultrahigh magnetic field applications.

Biochar gasification: Insights from pyrolysis atmospheres and gasification heating rates

Gasification is a promising technology for the synthesis of syngas and hydrogen, with char reactivity being a pivotal factor in the design of industrial gasifiers. Despite extensive studies on the gasification characteristics of biochar, the influence of the pyrolysis atmospheres on the evolution of biochar pore structure and its reactivity in gasification remains poorly understood. This study aims to bridge this gap by comprehensively investigating the effects of char preparation atmospheres (i.e., CO2, H2O, and N2) on ensuring gasification reactivities at varied heating rates. Biochars were synthesized in a horizontal tube furnace at 700 °C with a low heating rate (10 °C min−1) under three different atmospheres: N2, CO2, and H2O. Subsequent gasification reactivities were investigated using i) a thermogravimetric analyzer (TGA) at a low heating rate (10 °C min−1) and ii) a wire mesh reactor (WMR) at a high heating rate (1000 °C s−1), both under CO2 atmosphere at 950 °C. The results showed that the presence of an active atmosphere (CO2 and H2O) during pyrolysis significantly impacts the biochar’s aromaticity, crystalline structure, and surface morphology. The functional group concentration and surface area trends indicated that CO2 and H2O atmospheres during pyrolysis enhance biochar reactivity compared to the N2 atmosphere, with the highest reactivity observed for biochars produced under H2O. Furthermore, biochar gasification reactivity was markedly higher using the WMR compared to TGA, underscoring the pronounced effects of heating rate on gasification behavior. The high heating rate in WMR preserved the biochar’s porous and amorphous structure, whereas the TGA gasification encountered diffusional limitations and thermal annealing effects. These insights underscore the need to consider pyrolysis atmosphere and heating rate in gasification studies, offering a more comprehensive understanding of biochar’s behavior under practical gasification conditions.

The adaptive role of melanin plasticity in thermally variable environments.

Understanding the evolution of adaptive plasticity is fundamental to our knowledge of how organisms interact with their environments and cope with environmental change. Plasticity in melanin pigmentation is common in response to variable environments, especially thermal environments. Yet, the adaptive significance of melanin plasticity in thermally variable environments is often assumed, but rarely explicitly tested. Furthermore, understanding the role of plasticity when a trait is responsive to multiple environmental stimuli and plays many functional roles remains poorly understood. We test the hypothesis that melanin plasticity is an adaptation for thermally variable environments using Hyles lineata, the white-lined sphinx moth, which shows plasticity in melanin pigmentation during the larval stage. Melanin pigmentation influences thermal traits in H. lineata, as melanic individuals had higher heating rates and reached higher body temperatures than non-melanic individuals. Importantly, melanin pigmentation has temperature specific fitness consequences. While melanic individuals had an advantage in cold temperatures, neither phenotype had a clear fitness advantage at warm temperatures. Thus, the costs associated with melanin production may be unrelated to thermal context. Our results highlight the importance of explicitly testing the adaptive role of plasticity and considering all the factors that influence costs and benefits of plastic phenotypes across environments.

Thermal kinetics and flash DSC experimental validation of conventional nitrocellulose and ladder-structured nitrocellulose under non-isothermal condition

To better understand the thermal decomposition mechanism of conventional nitrocellulose (NC) and ladder-structured nitrocellulose (LNC), and effectively improve their safety performance during storage and service, the NC and LNC samples were subjected to non-isothermal DSC experiments to analyze their thermal kinetics. The model-free methods and model-fitting methods were used to analyze the thermal decomposition process of NC and LNC. The reaction autocatalytic behavior is confirmed in the thermal decomposition process of NC and LNC by Friedman analysis. Considering the fitting degree and the degree of freedom of the methods and models, the composite autocatalysis reaction model is the most suitable method to describe the thermal decomposition process of NC and LNC. Furthermore, the prediction accuracy of the composite autocatalysis reaction model is validated by the Flash DSC experimental data. The error between the actual and predicted peak temperatures is only approximately 1.5 %. Based on the composite autocatalysis reaction model of NC and LNC, the process of the thermal decomposition reaction of NC and LNC is obtained with high precision for their Flash DSC experimental data. This study can provide theoretical guidance for the process control of the thermal decomposition of NC and LNC. Novelty and Significance statementThe thermal decomposition mechanism of NC and LNC is studied. The kinetic model for the thermal decomposition of NC and LNC are deduced. The thermal decomposition kinetics equations for NC and LNC is obtained. The accuracy of the thermal decomposition kinetics equations of NC and LNC in predicting thermal decomposition behavior at extremely high heating rates is verified. This study can provide theoretical guidance for the process control of the thermal decomposition of NC and LNC.

Simulation of fast-firing densification by the discrete element method

The macroscopic behavior of powder compacts during the sintering process originates at the microscopic level. Despite the marked advance in analytical techniques, the characteristics of microscale densification, including heat transfer phenomena in particulate systems under fast firing, still need to be determined. Here, a numerical approach is used to explore macro and microscale densification gaps aiming to predict the behavior of parts consolidated by non-isothermal sintering. The model was built integrating concepts of heat transfer, transient temperature regime, sintering, and contact forces and implemented within the Discrete Element Method (DEM) framework. The scope of the article includes an alumina-based case study in which simulations were compared with the experimental investigation. The simulation results showed good agreement with the experimental data. Densification microkinetics depicted the evolution of densification gradients inside the sample. The model demonstrated its value for predicting high heating rate sintering features.

Near-Zero Magnetostrictive Nanocrystalline Fe–Si–B–Cu–Nb Alloys Obtained After a High Heating Rate Annealing

A nanocrystalline Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">73.5</sub> Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">15.5</sub> B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7.0</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1.0</sub> Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3.0</sub> alloy has zero-magnetostriction, λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> , a high saturation magnetic flux density, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> , of 1.23 T and a low coercivity, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> , of about 1.5 A/m. This material has been studied with a high heating rate annealing, leading to the finding that Cu-addition does not play an important role for good soft magnetic properties in nanocrystalline ribbons. Near-zero λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> is realised at a Si/Fe ratio of 0.21 which is the same as that of 0.21 for an existing zero-magnetostrictive nanocrystalline Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">73.5</sub> Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">15.5</sub> B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7.0</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1.0</sub> Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3.0</sub> ribbon. A nanocrystalline Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">76.5</sub> Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">16.0</sub> B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6.0</sub> Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1.5</sub> ribbon annealed at 640°C shows near-zero λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> of about 2.3∙10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> and low <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> of 1.1 A/m with a higher magnetic flux density at 8000 A/m, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8000</sub> , of 1.37 T which is higher than that of 1.23 T for the existing nanocrystalline ribbon.

Model-free isoconversional methods to determine the intrinsic kinetics and thermodynamic parameters during pyrolysis of boiled banana peel: influence of inorganic species

Raw banana peel was hydrolyzed to produce boiled banana peel (BBP) that exhibited enhanced volatile matter, calorific value; and lower ash content. BBP was analyzed for proximate, ultimate, TGA, DTG, SEM-EDX and FTIR. TGA and DTG curves exhibited variation in thermal lag at higher heating rates. XPS studies confirmed the dominance of inorganic species in BBP. The activation energy computed using isoconversional models increased with increasing conversion up to 60 %. Beyond that, activation energy suddenly decreased due to the influence of potassium, chlorine, and calcium containing compounds which lowered thermal stability of lignin which decomposed at a faster rate. The average activation energy (Eav) using isoconversional models such as KAS, Starink, FWO, Tang and Friedman are 457.75, 458.16, 468.01, 470.67, and 488.20 kJ/mol, respectively. Enthalpy, entropy, and Gibbs free energy were computed. Reaction mechanism during pyrolysis of BBP at various heating rates was predicted using Criado method (Z-master plots).

Effect of Carbon on the Melting Behavior of a Mold Powder under High Heating Rates

Mold powders used for the continuous casting of steels contain different carbon carriers controlling the melting behavior. During melting, carbon particles may accumulate at the liquid slag pool surface resulting in steel recarburization, which significantly changes the product quality. Thus, to reduce or prevent this reaction, mold powders with considerably reduced carbon content, or even without free carbon, are required. To replace carbon with another melting-controlling component, the effect on the melting behavior of mold powders under near-process conditions, such as high heating rates, should be investigated. Consequently, a different procedure was developed to evaluate the effect of various carbon contents on the melting behavior. In this contribution, a granulated ultra-low carbon (ULC) mold powder was selected, and different graphite contents (0, 1, 2, and 5%) were added. Furthermore, a sample obtained by granule disintegration and 5% graphite addition was produced and compared with a powdery sample. Subsequently, the steel crucibles were covered to reduce oxygen supply, filled with the samples, inserted into a preheated furnace (700–1300 °C), held at the selected temperatures for 10 min, and quenched to room temperature. The samples were mineralogically investigated, and the experimental method was applicable for characterizing the melting behavior of mold powders. At lower temperatures, carbon reduces the reactions between raw material components owing to reduced particle contact and prevents the formation of new solid (for example, cuspidine) and liquid phases. With increasing carbon content, the reactions shifted to higher temperatures, further delaying liquid phase formation. This effect was more evident for the powdery mold powder than for the granulated mold powders. At elevated temperatures, the powdery sample contained a coherent liquid phase, whereas the granules melted independently. This contribution provides a foundation for alternative melting-controlled additives for mold powders. It demonstrates that carbon substitutes should delay the reaction between raw material components and be stable until high temperatures.

Microstructural evolution investigation of irradiated oxide fuels by means of electron backscattered diffraction

In this paper, both irradiated UO2, together with a fresh UO2.001 sample from the same batch as a reference, and irradiated FR-MOX U0.55Pu0.45O1.99 (TRABANT 2/3) fuel were studied using Electron Back Scattered Diffraction (EBSD). Irradiation of both oxide fuels was carried out at the High Flux Reactor (HFR) Petten, the UO2 at a moderate maximum Linear Heat Rate (LHR) of 200 W/cm to a burn-up of 5.4 % FIMA (fission per initial metal atom) or 50 MWd/kgUO2, and the MOX at a high maximum Linear Heat Rate (LHR) of 374 W/cm to a burn-up of 1.7% FIMA. In the irradiated UO2, the grain growth was observed in the fuel centre. The irradiated MOX (U, Pu)O2 showed the typical FBR fuel microstructure zones, i.e. as-fabricated (at the fuel edge), equi-axed and columnar grains as observed from the fuel-clad region towards fuel central hole.The LAGB (Low Angle Grain Boundary), 3° < θ < 15°, as an initial state for the HBS structure was observed on both UO2 and MOX. This restructuring mechanism for both oxide fuels is proposed to follow the well-known polygonization mechanism in which an arrangement of dislocations at the grain boundaries occurs.

Phase transformation kinetics of high-carbon steel during continuous heating

Effects of heating temperature, heating rate, and holding time on the austenitization process of near-eutectoid high-carbon steel have been investigated. The dilatometric tests were carried out at different heating rates of 1–100 °C/Sec. The Ac1 and Ac3 critical temperatures, the volume fractions of the parent and produced austenite phases, and consequently, the coefficient of the Johnson–Mehl–Avrami–Kolmogorov (JMAK) equation were obtained from dilatometric diagrams. The activation energy for the transformation was estimated using the Kissinger equation. The optical microscope was used for the microstructural characterization of samples austenitized at different temperatures and durations. The grain growth kinetics of austenite during processing was also characterized. Cellular Automata simulation was used to investigate the nucleation and growth of austenite from the initial full pearlitic structure. Based on the results, the activation energy of 242.6 kJ/mol at low heating rates (1 °C/Sec to 12 °C/Sec) and 436.94 kJ/mol at high heating rates (25 °C/Sec to 100 °C/Sec) were obtained, which indicated the different phase transformation mechanisms. This was attributed to the presence of boron, which postpones nucleation at grain boundaries and helps to activate the shear mechanism at high heating rates. Finally, a continuous heating transformation (CHT) diagram was drawn, which is an indispensable tool to consider the effect of heating rate on the austenitization process and austenite grain size.