Isothermal Heat Research Articles

Corrosion and isothermal interdiffusion properties of Ni–Al coatings under simulated biomass combustion conditions

The main issue with using biomass fuels in power plants is fireside corrosion. Applying corrosion-resistant coatings is one potential choice. The current study examines how a Ni–Al diffusion coating on austenitic stainless steel reacts to corrosion and interdiffusion (TP347H). Nickel was electrolytically deposited to create Ni–Al coatings, which were then pack aluminized at 650 °C. With an internal layer of Ni and a Ni2Al3 outer layer, a homogenous and dense Ni–Al coating was created. Samples were heated to 560 °C for 168 h in an environment designed to simulate the combustion of biomass. A localized corrosion attack was the result. By using isothermal heat treatment in static air at 650 °C or 700 °C for up to 3000 h, interdiffusion was examined. In the course of the interdiffusion process, the Ni2Al3 eventually changed into NiAl and Ni3Al. At both temperatures, porosity formed at the intersection of the Ni–Al coating and the Ni layer and grew with time.

Efficient searching of processing parameter space to enable inverse microstructural design of materials

Materials design can be accelerated by the use of physics-based forward models that predict the properties of new materials. In cases where the properties of the material depend on its microstructure, the models can be used as part of an optimization scheme to predict the microstructural features that are required to achieve the design objectives. Producing these microstructures, however, requires that we determine the processing parameters necessary to produce the target microstructure. Here we demonstrate the use of Bayesian optimization using simple analytic forward models to enable this inverse process design in the context of optimization of isothermal heat treatment of a commercial aluminum alloy to achieve (i) a target volume fraction of a specific intermetallic phase, (ii) a specified aluminum grain size distribution, and (iii) both objectives simultaneously. We discuss the use, and limitations, of Bayesian optimization with a scalar desirability function for solving multi-objective problems, and demonstrate Bayesian optimization with expected hypervolume improvement to determine the Pareto front describing the trade-off between multiple objectives. We compare Bayesian optimization with a genetic algorithm (NSGA-II) and show that while the two approaches produce similar Pareto fronts, the Bayesian optimization converges on the solution more quickly. We further illustrate the effect of parametric uncertainty in the forward models on the uncertainty of the Pareto front. Finally, we demonstrate experimentally that the optimized process parameters do indeed allow us to make samples with the desired microstructure.

Thermal spreading resistance from an isothermal source into a finite-thickness body

Thermal spreading resistance is encountered during two-dimensional thermal conduction from a hot surface into a body. Thermal spreading and the opposite problem of thermal constriction resistance are of much technological relevance in the design of heat sinks and thermal spreaders for thermal management of microelectronics and other heat-generating devices. Much of the past work in the theoretical analysis of thermal spreading is based on a source with given heat flux. In contrast, the isothermal source problem presents difficulties due to the resulting mixed nature of the boundary condition, due to which, only approximate solutions are available. This work derives the steady-state thermal spreading resistance from an isothermal source into a finite-thickness slab or cylinder. The mixed boundary condition is handled by posing it in the form of a spatially varying convective boundary condition, with a sufficiently large Biot number over the source to represent its isothermal nature. A series solution for the problem is derived, along a sufficient set of linear algebraic equations to determine the series coefficients. Results are shown to agree well with finite-element simulations. Results are compared with previously-reported approximate solutions within the parametric range of validity of the approximate solutions. The impact of key non-dimensional parameters on thermal spreading resistance is quantified. It is shown that thermal spreading resistance increases with decreasing size of the isothermal heat source, as expected. A third-order polynomial correlation with very good accuracy is proposed. This work advances the theoretical understanding of a problem for which only approximate solutions have been reported in the past. Results presented here offer a practical tool for thermal design and optimization of a variety of practical thermal management problems involving spreading or constriction.

Realizing Superior Luminescence in Oxyfluoride Glass‐Ceramics by Enhancing Nano‐Micro Phase Separation

AbstractIn this work, a novel series of oxyfluoride glasses‐ceramics (GCs) is developed by enhancing the phase separation through the substitution of LaF3 for La2O3. The thus‐derived GCs exhibit a remarkable 2700‐fold increase in up‐conversion (UC) luminescence of Er3+ ions compared to the precursor glass. From the 19F Nuclear Magnetic Resonance analysis, this enhancement is attributed to the structural disorder‐to‐order transition in the fluoride‐rich phase. Upon isothermal heat treatment, the translucent GCs transform into transparent ones, making UC luminescence even stronger. The enhanced UC luminescence leads to strong temperature‐sensing ability of the studied glasses. The nano‐micro phase separation is clarified by atomistic simulations and scanning electron microscopy. This study implies that phase separation engineering is a powerful way to achieve superior photonic performances.

Startup operation of an energetically-intensified single-tube type falling film distillation column: Insights from a pilot-scale study

Technological advancements in the field of energetically intensified falling film distillation columns have not been paralleled by sufficient published research on comparative startup evaluations for the single-tube falling film distillation column under different thermal energy transfer methods. The present study's originality and significance stem from presenting a startup procedure for a single-tube type falling film distillation column that employs a biphasic thermosyphon as a heat source for producing hydrated ethanol at a pilot scale. The concept of three discrete phases, the discontinuous, semi-continuous, and continuous phases, was employed to characterize the startup operation. The time and energy required for each phase of the startup operation were determined. This study also examined the startup operation with respect to two possible thermal energy transfer methods from the steam chamber to the distillation tube: isothermal and non-isothermal. The experiments were conducted in a pilot distillation column consisting of a single vertical tube, which processed a binary mixture of water and ethanol with a flow rate of 33 kg h−1. No relevant variation in startup time was detected for the three distinct stages when comparing the two heating modes, with a total startup duration of 2.2 h being observed irrespective of the heating configuration utilized. The isothermal heating configuration can produce hydrated ethanol at a rate of 3.0 kg h−1, with an ethanol content increase from 12.5 to 62.8 wt%. However, the non-isothermal heating mode yields a higher ethanol content an increase in ethanol content from 12.5 to 64.3 wt.%, albeit with a lower productivity rate of 1.3 kg h−1. Operating the single-tube type falling film distillation column with the steam chamber under the non-isothermal heating mode required only 2.12 kW for the startup, resulting in a 30.30 % reduction in energy demand compared to the isothermal heating configuration. The presented findings provide an empirical foundation for improving the efficiency and effectiveness of energetically intensified falling film distillation columns.

Accurate Measurement of the Isothermal Heat of Capillary Condensation in Nanopores Using Differential Scanning Calorimetry and Adsorption/Desorption Experiments

Accurate Measurement of the Isothermal Heat of Capillary Condensation in Nanopores Using Differential Scanning Calorimetry and Adsorption/Desorption Experiments

Structural, mechanical and thermodynamic stability of the CaIn intermetallic compound for promising hydrogen storage: ab-initio calculations

This study was conducted to investigate the structural, elastic, dynamical, mechanical, and thermodynamic properties of the binary intermetallic compound CaIn in various crystallographic phases, utilizing density functional theory (DFT) calculations. The results reveal that the compound is chemically and mechanically stable, as indicated by the formation energy, stability in the phonon dispersion, and elastic constants calculation. The mechanical and thermodynamic properties of our studied compound are only examined in the most stable calculated phase, which is the orthorhombic phase (Pmma). By calculating Pugh’s ratio it has been determined that this compound possesses a brittle character. The quasi-harmonic Debye (QHD) model was employed to analyze various thermodynamic parameters such as Debye temperature, volume variation, isothermal bulk modulus, heat capacity, and thermal expansion coefficient. These findings are expected to encourage further theoretical and experimental studies on the CaIn intermetallic compound for potential applications as a hydrogen storage material and in various other fields.

Experimental study on heat transfer performance of high temperature heat pipe under axial non-uniform heat flux

Non-uniform high-temperature large heat flux is commonly encountered in engineering applications, posing challenges to heat transfer processes and affecting system performance. High temperature heat pipes offer an effective solution to mitigate the adverse effects of non-uniform heat flux by leveraging the unique characteristics of their inner alkali metal (or alloy) working fluid, such as high latent heat of vaporization, strong heat flux density, and ability to operate at elevated temperatures. These features enable high temperature heat pipes to achieve excellent isothermal and uniform heat transfer performance, thereby improving overall thermal management in heat transfer systems. Building upon the investigation of the original high temperature heat pipe, this study designed and fabricated a specially shaped high temperature heat pipe with a spherical crown surface as the evaporator. Experimental research was conducted to assess its frozen start-up performance and heat transfer characteristics under the influence of axial non-uniform heat flux. The results were also analyzed theoretically, providing valuable insights into the frozen start-up performance and heat transfer performance of the high temperature heat pipe in the presence of non-uniform heat flux conditions. The analysis results reveal several important findings: (1)The high temperature heat pipe demonstrates its capability to convert axial non-uniform high-temperature large heat flux into a uniform heat flux, thus achieving excellent uniform heat transfer performance. (2)The theoretical solution obtained through the lumped heat capacity analysis method shows satisfactory agreement with the actual frozen start-up process of the high temperature heat pipe. This theoretical reference can aid in the transient analysis of the frozen start-up process under the influence of axial non-uniform high-temperature large heat flux. (3)The experiment investigated the influence of heating power on heat transfer performance and temperature uniformity. The results indicate that the temperature uniformity of the high temperature heat pipe exhibits a trend of initially increasing and then decreasing. Specifically, the best temperature uniformity is achieved when the heating power is 1084.7 W. Moreover, when the heating power is 1197.9 W, the high temperature heat pipe exhibits the lowest equivalent thermal resistance of 0.0265 K/W, indicating the best heat transfer performance. (4) The variable power heating approach demonstrates that increasing the heating power leads to an extension of the effective length of the heat pipe. The most favorable heat transfer performance and temperature uniformity are observed when the heating power is set to 1133.7 W, allowing the full length of the condenser of the high temperature heat pipe to participate actively in the heat transfer process. These results can provide quantitative experimental data and theoretical references for improving the thermal shock of non-uniform high-temperature large heat flux.

Desolvation Processes in Channel Solvates of Niclosamide.

The antiparasitic drug niclosamide (NCL) is notable for its ability to crystallize in multiple 1:1 channel solvate forms, none of which are isostructural. Here, using a combination of time-resolved synchrotron powder X-ray diffraction and thermogravimetry, the process-induced desolvation mechanisms of methanol and acetonitrile solvates are investigated. Structural changes in both solvates follow a complicated molecular-level trajectory characterized by a sudden shift in lattice parameters several degrees below the temperature where the desolvated phase first appears. Model fitting of kinetic data obtained under isothermal heating conditions suggests that the desolvation is rate-limited by the nucleation of the solvent-free product. The desolvation pathways identified in these systems stand in contrast to previous investigations of the NCL channel hydrate, where water loss by diffusion initially yields an anhydrous isomorph that converts to the thermodynamic polymorph at significantly higher temperatures. Taking the view that each solvate lattice is a unique "pre-organized" precursor, a comparison of the pathways from different starting topologies to the same final product provides the opportunity to reevaluate assumptions of how various factors (e.g., solvent binding strength, density) influence solid-state desolvation processes.

Practical Approach for Determining Material Parameters When Predicting Austenite Grain Growth under Isothermal Heat Treatment.

An investigation of austenite grain growth (AGG) during the isothermal heat treatment of low-alloy steel is conducted. The goal is to uncover the effect of time, temperature, and initial grain size on SA508-III steel grain growth. Understanding this relationship enables the optimization of the time and temperature of the heat treatment to achieve the desired grain size in the studied steel. A modified Arrhenius model is used to model austenite grain size (AGS) growth distributions. With this model, it is possible to predict how grain size will change depending on heat treatment conditions. Then, the generalized reduced gradient (GRG) optimization method is employed under adiabatic conditions to characterize the model's parameters, providing a more precise solution than traditional methods. With optimal model parameters, predicted AGS agree well with measured values. The model shows that AGS increases faster as temperature and time increase. Similarly, grain size grows directly in proportion to the initial grain size. The optimized parameters are then applied to a practical case study with a similar specimen size and material properties, demonstrating that our approach can efficiently and accurately predict AGS growth via GRG optimization.

Towards a heat‐ and mass‐balanced kinetic model of TATB decomposition

AbstractTATB (1,3,5‐triamino‐2,4,6‐trinitrobenzene) was thermally degraded by two small‐scale analytical methods – simultaneous differential scanning calorimetry and thermogravimetric analysis (SDT) and a hot‐stage microscope with Fourier Transform Infrared (FTIR) analysis capabilities. SDT used ramped heating, isothermal soaking, and thermal pretreatment at various conditions. The heat flow and mass loss were monitored during various treatment conditions to derive chemical decomposition kinetics and Arrhenius parameters. FTIR experiments used isothermal heating, and changes were monitored spectroscopically. Solid samples generated at specific conditions were collected from both methods and were analyzed by DMSO extraction followed by chemical speciation by optical and mass spectrometric methods. Characterization provided the following reaction insights:1. TATB decreases in a sigmoidal pattern in isothermally heated samples. Other soluble products gradually increase in concentration and then abruptly decline in concentration during the second exotherm, such as diamino‐dinitro‐benzofurazan and amino‐nitro‐benzodifurazan.2. FTIR showed gradual changes in the amino and nitro functionality, shifting positions and decreasing intensity for the first 40 min. Then the solid gradually appeared more like an amorphous C with N incorporated, similar to previous studies on thermally degraded TATB‐type materials.3. Extracted residues (DMSO‐soluble components removed) examined by FTIR showed an abrupt change in chemical composition between 40‐ and 45‐min isothermal treatment, indicating early forming solids are different than later forming residues.4. A reliable mass‐ and energy‐balanced global reaction network must include at least two autocatalytic reactions, either in parallel or series, and at least one must have an explicit initiation reaction having a low activation energy.

Thermal stability of microstructure and corresponding hardness variations in two high-carbon nanostructured bainitic steels

The autotempering phenomenon and carbon partitioning from bainitic subunits during the bainite transformation suggest that the tempering behavior of the nanostructured bainite may be different compared to that of martensite. This article aims to investigate the thermal stability of the microstructure in two low alloy nanostructured bainitic steels containing 0.89 wt% carbon content. Nanostructured bainite was obtained after austempering at 250 °C for optimum heat treatment time. Nanostructured bainitic steels were tempered at the temperature range of 300–700 °C for 30 min. Additionally, the effect of prolonged austempering beyond the optimum heat treatment condition at austempering temperature was studied. Microstructural characteristics were evaluated using optical and field emission gun scanning electron microscopes and X-ray diffraction methods. Hardness variations during tempering of nanostructured bainite compared with that of martensite microstructure obtained in the same primary steels after austenitizing and quenching. Results indicated that microstructural characteristics of nanostructure bainite didn’t change significantly at heat treatment times longer than that needed for bainite transformation completion at isothermal bainite heat treatment temperature. Moreover, results approved the higher tempering resistance of nanostructured bainite compared to that of martensite in the same steel. It has been shown that tempering the nanostructured bainite up to 400 °C didn’t change the microstructure and hardness, while the changes were pronounced at higher tempering temperatures. It has been suggested that cementite precipitation was more significant when a higher number of dislocations were present in nanostructured bainite before starting the tempering process.

Synergistic effect of well/over-tempered hierarchical martensitic structure and carbides (M23C6 and MX) on austenite growth in 9Cr steel

To clarify the synergistic effect of well/over-tempered hierarchical martensitic structure and carbides (M23C6 and MX) on austenite growth, the austenite growth during step-heat austenitization for a selected 9Cr steel was investigated by dilatometry, multi-scale characterization and cellular automaton simulation. The austenite grain inherits the geometrical characteristics of the hierarchical martensite substructure to a significant extent through covariant and free growth. In particular, the initially heterogeneous grains with non-uniform martensitic substructure can easily produce mixed and heterogeneous grains. Step isothermal heating under AC1 can promote the evolution of martensitic structure to recrystallized ferrite and recovered equiaxed substructure, associated with coarsening of M23C6 and precipitation of MC. Apart from the recrystallized ferrite promoting the growth of equiaxed austenite grains, the recovered approximate equiaxed substructure decorated with coarse M23C6 and a large amount of MX can promote the subsequent development of fine spherical austenite grains by reducing the abnormal austenite growth and increasing the resistance to interfacial migration. The synergistic effect of the well/over tempered martensitic hierarchical structure and the carbides (M23C6, MX) is critical to the final austenite grain distribution. A window of critical temperature values for step heating austenitization to generate homogeneous austenite grain growth was established by exploiting the inheritance of the equiaxed substructure and reasonably reducing abnormal growth.

Reinvestigating the concurring reactions in early-stage cellulose pyrolysis by solution state NMR spectroscopy

Low temperature pre-treatments increase the char yield during cellulose carbonization. Although this effect is mostly understood on a kinetic basis, the formed chemical structures leave room for scrutiny. In ongoing ambitions to enhance the char yield of bioderived precursors, the thereby occurring chemistry was reinvestigated. A set of isothermal heating protocols ranging from 150° to 250°C was applied to man-made Ioncell® cellulose fibers and to Avicel® PH-101 microcrystalline cellulose. The prepared cellulosic samples were examined by solution state NMR using a tetra-n-butyl phosphonium acetate ([P4444][OAc]): DMSO-d6 (1:4 wt%) electrolyte as dissolving medium. Complementary, IR spectroscopy, size-exclusion chromatography (SEC) and thermogravimetric analysis coupled with mass spectroscopy (TGA-MS) measurements were performed. The NMR spectra evidenced the formation of levoglucosan end capped moieties as being the first and major occurring reaction during low temperature pre-treatments. In contrast to other mechanistic proposals, no signs for carbonyl or alkene functionalities were discernible in the cellulosic material soluble in the NMR electrolyte, even after treatment at 250 °C for several hours. Thermal cross-linking was observed in SEC already at temperatures not known to significantly influence the overall char yield. In the solution state analytics only partial solubility was observed, owing to the formation of a reluctant fraction previously described as “thermostable condensed phase”. This resulted in analytical blind spots and led to discrepancies between NMR results and FTIR spectra in which carbonyl and alkene vibrations were clearly discernible. Those discrepancies might also imply the co-existence of different fractions in the early stages of cellulose pyrolysis.

Coarsening of needle-shaped precipitates in CoNiCrAl alloys during isothermal heat treatment: Kinetics in length and thickness

This paper investigated the coarsening kinetics of needle-shaped γ precipitates in CoNiCrAl alloys after isothermal heat treatments at 900 °C and 1100 °C. The CoNiCrAl alloys were prepared by vacuum induction melting and casting process. They were characterised to exhibit a two-phase γ + β structure and some needle-shaped secondary γ precipitates were formed within the primary β phase during isothermal heat treatments. The coarsening of the needle-shaped secondary γ precipitates occurred with heat treatment time and became more rapid at elevated temperatures. In particular, the coarsening kinetics of needle-shaped γ precipitates in length and thickness were specifically studied. It was found that the coarsening kinetics in length and thickness was a volume diffusion governed process and generally followed the classic Lifshitz-Slyozov-Wagner (LSW) theory. An analytical model was proposed to estimate the lengthening and thickening of the precipitates, which considered the aspect ratio and volume fraction of the precipitates. The calculated coarsening rate in thickness agreed well with the experimentally determined value. But some discrepancies were found between the predicted and measured coarsening rate in length. This might be due to the termination migration effects of the needle-shaped precipitates which restricted the coarsening rate in length.

A New Perspective on Hydrogen Chloride Scavenging at High Temperatures for Reducing the Smoke Acidity of PVC Cables in Fires V: Comparison between EN 60754-1 and EN 60754-2

Regulation (EU) No 305/2011 lays down harmonized conditions for marketing construction products in the European Union. One of its consequences has been the introduction of the product standard EN 50575 and standard EN 130501-6, concerning power, control, and communication cables permanently installed in buildings to prevent the risk of a fire and its consequences. EN 13501-6 provides the reaction to fire classifications for cables, the test methods to be performed, the requirements to meet a specific reaction to fire, and additional classifications for smoke production, flaming droplets, and acidity. It requires EN 60754-2 as the technical standard to assess acidity, and it defines three classes: a1, a2, and a3 (the less performant). Due to the release of hydrogen chloride during the combustion, acidity is the weak point of PVC cables, which are not yet capable of achieving the a1 or a2 classes required for specific locations according to fire risk assessments. EN 13501-6 does not include EN 60754-1, used in harmonized standards outside the scope of Regulation (EU) No 305/2011. EN 60754-1 and EN 60754-2 are common standards for determining halogen gas content, and acidity/conductivity, respectively. While they involve the same type of test apparatus, they differ in heating regimes, final temperatures, and detection methods. In particular, EN 60754-2 requires testing at temperatures between 935–965 °C in the tube furnace, where the sample burns, the smoke is collected in bubblers, and pH and conductivity are measured as an indirect assessment of acidity. On the other hand, the temperature regime of EN 60754-1 is a gradual heating run, followed by isothermal heating at 800 °C. The paper shows that when potent acid scavengers are used in PVC compounds, performing EN 60754-2 with the thermal profile of EN 60754-1 or at 500 °C in isothermal conditions, the evolution of hydrogen chloride changes significantly up to 10 times less than the test performed in isothermal at 950 °C. The reason lies behind the kinetic of hydrogen chloride release during the combustion of PVC compounds: the higher the temperature or faster the heat release, the quicker hydrogen chloride evolution and the lower the probability for the acid scavenger to trap it. Thus, these findings emphasize the “fragility” of EN 60754-2 as a tool for assessing risks associated with the release of hydrogen chloride during fires.

Modeling the thermal and mechanical properties of early age concrete containing ground granulated blast furnace slag

In this study, a multi-component hydration model of cementitious material was applied to estimate the heat of hydration, adiabatic temperature rise (ATR), and compressive strength of concrete containing ground-granulated blast furnace slag (GGBFS). Different types of GGBFS were hydrated in limewater solution to measure their heat generations. The reference heat of slag in the multi-component hydration model (DuCOM) was revised using the heat measured from each type of GGBFS. Hence, the revised model is sensitive to the chemical compositions of slag. Isothermal and adiabatic heat measurements, as well as compressive strength experiments, were conducted using concrete with four different types of GGBFS. Results show that the proposed model is able to estimate the heat of hydration, adiabatic temperature rise, and compressive strength of concrete mix using different types of GGBFS with various w/cm ratios and air contents. The model predictions versus experimental results show reasonable agreement with the maximum average error percentage of 6.8% and 11% for the heat of hydration and compressive strength, respectively. The proposed method can be a useful technique to obtain the thermal and mechanical properties of GGBFS blended concrete with different cement and GGBFS sources.

Revisit on energy flow: accurate predictions and analysis of heatlines for thermal convection within enclosures of various configurations

PurposeA few earlier studies presented infeasible heatline trajectories for natural convection within annular domains involving an inner circular cylinder and outer square/circular enclosure. The purpose of this paper is to revisit and illustrate the correct heatline trajectories for various test cases.Design/methodology/approachGalerkin finite element based methodology and space adaptive grid have been used to simulate natural convective flows within the annular domains. The prediction of heatlines involves derivatives at the nodes, which are evaluated based on finite element basis functions and contributions from neighboring elements.FindingsThe heatlines in the earlier work indicate infeasible heat flow paths such as heat flow from one portion to the other of isothermal hot walls and heat flow across the adiabatic walls. Current results illustrate physically consistent heat flow paths involving perpendicularly emerging heatlines from hot to cold walls for conductive transport, long heat flow paths around the closed-loop heatline cells for convective transport and parallel layout of heatlines to the adiabatic walls. Results also demonstrate complex heatlines involving multiple flow vortices and complex flow structures.Originality/valueCurrent work translates heatfunctions from energy flux vectors, which are determined by using basis sets. This work demonstrates the expected heatline trajectories for various scenarios involving conductive and convective heat transport within enclosures with an inner hot object as a first attempt, and the results are precursors for the understanding of energy flow estimates.

Study of structure evolution of ultra-rapidly annealed Fe75.3Ni10B14Cu0.7 alloys

The article concerns modern soft magnetic materials made by rapid solidification and subsequent ultra-rapid annealing. Due to the lower amount of non-magnetic elements, higher magnetisation is possible. Unfortunately, the lack of those elements causes difficulty during isothermal nanocrystallisation operation, being crucial from the final product properties point of view. Instead of isothermal heat treatment, ultra-rapid annealing (URA) is implemented. The seconds-long annealing at a higher temperature than the temperature of conventional nanocrystallisation enables material with a higher amount of ferromagnetic elements and optimal structure. It reflects in materials with good magnetic softness and higher possible magnetisation values. The amorphous alloy with Fe75.3Ni10B14Cu0.7 chemical composition in the shape of a ribbon was heat treated between cooper blocks at 773 K (500 °C) for different times in the 1–60 s range. To study structure evolution, we brought XRD, DSC, Flash DSC, Mössbauer spectroscopy, TEM, and HRTEM techniques to play. Based on the DSC results, we estimated the minimum heating speed to obtain optimal structure at 6000 K/min. The Mössbauer results allowed us to study annealing time-dependent local atomic ordering in the amorphous state. A comparison of X-Ray and synchrotron diffraction results drove us to the conclusion that X-Ray measurements are sufficient to determine the material structure. TEM shows the formation of α-Fe crystallites even after an annealing time of 0.5 s. The increase in annealing time leads to an increase in the crystalline phase volume fraction and growth of α-Fe crystallite size.

Physics of Starch System: Rheological and Mechanical Properties of Hydrothermally Modified Elephant Foot Yam Starch

Heat moisture treatment (HMT) was used to improve the functionalities of elephant foot yam starch (EFYS) by using selected heating techniques such as hot air oven (HAO), autoclave (AL), and microwave (MW). The swelling power and solubility were reduced significantly after HMT modification, whereas an increase in amylose content was detectable after HMT modification, and the maximum changes were identified in HAO-modified EFYS (28.48%) as compared to its native counterpart (18.01%). The study demonstrates that the maximum drop in peak viscosity (1045 cP) was perceived in HAO-modified EFYS, which confirms its thermostability as compared to native (1114 cP) and other treated starches (1059 to 1098 cP). All the starch pastes exhibited shear-thinning behavior, however, isothermal heating of starch paste at 95 °C revealed a rise in apparent viscosity with increasing shear rate in all HMT-modified EFYS. Large amplitude oscillatory shear (LAOS) measurements of modified starch samples showed the predominating solid-like behavior in modified EFYS. The HAO-treated EFYS had the highest elasticity of the others, which represents the enhanced structural rigidity due to the formation of transient network structures. Furthermore, Lissajous-Bowditch plots confirmed the early deviation of the structural integrity from elastic to viscous behavior in HAO-treated EFYS. Overall, the HAO-modified EFYS showed significant improvement in functionalities and structural integrities under high shear and high oscillation strain, which infers its potential industrial applications. Based on our results, we propose specific physical models suggesting the effect of molecular structural arrangements of amylose and amylopectin expressing the essential rheological differences between native and HMT EFYS.