Increasing Heating Rate Research Articles

Kinetic analysis of slow pyrolysis of oily sludge at medium temperature (350 ℃–650 ℃) and the effects of heating rate on pyrolysis

ABSTRACT Pyrolysis is an effective way for the harmless treatment of oily sludge. The composition, physicochemical properties, and pyrolysis of oily sludge were experimentally studied in the present study. The Starink and Coats-Redfern methods were used to analyze the pyrolysis kinetics of oily sludge. Pyrolysis of oily sludge is divided into four stages: water evaporation stage, light component evaporation stage, heavy component pyrolysis stage, and final pyrolysis stage. The light component evaporation and heavy component pyrolysis stages are the main stages of medium-temperature pyrolysis. The pyrolysis characteristic parameters under heating rates of 10, 20, 30, and 40 K/min were obtained, and the effects of heating rates on the pyrolysis characteristics of oily sludge were discussed. The results show that with the increase in heating rate, the temperature range of each stage expands, and the temperature of the pyrolysis peaks also increases, with an average increase of 14.88%. The activation energies of the main pyrolysis stages obtained by the Starink method and Coats-Redfern method are consistent. In the light component evaporation stage, the activation energies obtained by the two methods are 61.93kJ/mol and 68.6kJ/mol, while the activation energies are 294.88kJ/mol and 367kJ/mol in the heavy component pyrolysis stage. The pyrolysis mechanism functions are obtained, and the pyrolysis kinetic equations under 10, 20, 30, and 40 K/min were constructed and validated by comparison with the results of the calculated properties and experimental measurement. This study can provide a better insight into the heat and mass transfer processes of oily sludge in pyrolysis reactors for further development and optimization.

Reduction of phosphogypsum for SO2 production: Insights into the release characteristics of SO2 following the solid–solid reaction of CaS and CaSO4 under different atmospheres

AbstractPhosphogypsum (PG) severely pollutes the environment and is difficult to recycle. PG is primarily composed of CaSO4 · 2H2O. In this study, the characteristics of SO2 released from the solid–solid reaction between calcium sulphide (CaS) and CaSO4 were thoroughly investigated using thermodynamic calculations. Experiments were performed by tuning the molar ratio of CaS to CaSO4, reaction atmosphere (S, CH4, N2, and air), and the heating rate. As shown by the phase diagram, high reaction temperatures favour CaO stability, and the corresponding maximum SO2 equilibrium partial pressure increases. The total SO2 production significantly increased with increasing molar ratio and slightly increased when the ratio exceeded 1:3. The SO2 productions were ranked from highest to lowest as follows: S, CH4, N2, CO, and air. The total SO2 production decreased with increasing heating rate. For the reaction between CaS and CaSO4, a higher molar ratio of CaS to CaSO4 no less than 1:3, both S and CH4 reductive atmospheres, and a lower heating rate (2°C/min) favour the total SO2 emission.

Residual stress and interface debonding behavior in Si3N4w reinforced SiCN composites prepared by the PIP process: A case study

Polymer infiltration and pyrolysis (PIP), as a preparation route for ceramic matrix composites, employs the polymer-to-ceramic transformation inside the preforms to gradually buildup the matrix. The effects of the structural transformation on the residual stress and on the interface debonding behavior of PIP derived Si3N4 whisker reinforced SiCN (Si3N4w/SiCN) composites are analyzed. Accordingly, the Si3N4w whisker in the composites are under residual compressive stress after the formation of the polymer-derived ceramic matrix. An increase in the pyrolysis heating rate from 1 to 10 ℃/min effectively lowers the residual stress from 195.8 to 91.3 MPa. Interface fracture energies of Si3N4w/SiCN derived from the debonding behavior significantly rise from <11.91 to 21.82 J/m2 with the annealing temperature from 900 to 1400 ℃. The residual stress and interfacial behavior are related to the in-situ densification/shrinkage and structural rearrangement during pyrolysis and annealing.

Assessment of biochar developed via torrefaction of food waste as feedstock for steam gasification to produce hydrogen rich gas

In this study, the torrefaction of food waste was carried out using a thermogravimetric analyzer (TGA) to produce biochar and assess its suitability as feedstock for steam gasification. Torrefaction was conducted at temperature from 230 to 290 °C and the heating rate from 10 °C/min to 30 °C/min. Subsequently, the detailed characterization was conducted using proximate, elemental, lignocellulosic, nutrient analysis, and TGA analysis. The proximate and elemental analysis showed that biochar had the highest fixed and elemental carbon at the highest temperature (290 °C) and lowest heating rate (10 °C/min). Similarly, TGA indicated that increase in temperature increased the mass loss, however, increase in heating rate did not yield much change in mass loss. Additionally, lignocellulosic and nutrient analysis showed that lignin fraction increased (up to 80%) with increases in severity of the torrefaction due to significant decomposition of hemicellulose, cellulose, starch, proteins, and lipids. Thereafter, the kinetic parameters (activation energy, pre-exponential factor) of torrefaction of food waste were determined using the two-step decomposition model which showed a good fit with experimental data. Finally, the biochar developed was used for energy production using steam gasification which produced syngas with maximum yield of 3.75 m3/Kg and having hydrogen fraction of around 65% at the optimal conditions (temperature: 290 °C, heating rate: 10 °C/min).Graphical

Microstructural refinement by spontaneous recrystallization without prior deformation of a 15-5 PH steel alloy and its mechanism

The recrystallization without previous deformation is reported in literature for a small, selected group of alloys. The present work provides evidence for the first time that the commercial stainless steel 15-5PH also shows this recrystallization phenomenon during austenitization. A set of in-situ and ex-situ high-temperature techniques reveal that, on heating of the martensitic microstructure, recrystallization takes place after phase transformation between 900 and 1000 °C, causing a distinct reduction of the austenite grain size. This work also shows that the recrystallization correlates with the mechanisms involved in the prior martensite to austenite transformation. It is observed that increasing heating rates lead to decreasing grain sizes. This is attributed to increased defect density in the reverted austenite and increased driving pressure for the nucleation of recrystallized grains. It is proposed that, during martensite to austenite reversion, a defect arrangement of highly stable low-angle grain boundaries and, with increased heating rate, an increased density of internal, grown-in dislocations is inherited from martensite laths. This highly defect-loaded microstructure, formed without external plastic deformation, leads to a recrystallization at increased temperatures. The experimental results agree well with thermokinetic calculations based on the proposed defect arrangement, underpinning the mechanism of spontaneous recrystallization in 15-5PH.

Thermal Behavior and Pyrolysis Kinetics of Mushroom Residue with the Introduction of Waste Plastics.

Co-pyrolysis is considered a very promising technology for the treatment of solid wastes as it can rapidly realize the volume reduction of raw materials and obtain high value-added products. To realize the resource utilization of newly emerging solid wastes in relation to edible fungi residue and waste plastics, mushroom residue (MR), a representative of edible fungi residue, was co-pyrolyzed with waste plastic bags (PE), waste plastic lunch boxes (PP), and waste plastic bottles (PET). The thermal behavior and pyrolysis kinetics of the mixtures were investigated. It was found that the softening of the plastics in the mixtures led to an increase in the initial pyrolysis temperature of MR by 2-27 °C, while the pyrolytic intermediates of MR could greatly promote the decomposition of the plastics, resulting in a decrease in the initial pyrolysis temperatures of PE, PP, and PET in the mixtures by 25, 8, and 16 °C, respectively. The mixture of MR and PE (MR/PE) under different mixture ratios showed good synergies, causing the pyrolysis peaks attributed to MR and PE to both move towards the lower temperature region relative to those of individual samples. The increase in heating rate led to enhanced thermal hysteresis of the reaction between MR and PE. The strength of the interaction between plastics and MR based on mass variation was subject to the order PE > PP > PET. The pyrolysis activation energies of MR, PE, PP, and PET calculated from kinetic analysis were 6.18, 119.05, 84.30, and 74.38 kJ/mol, respectively. The activation energies assigned to MR and plastics were both reduced as plastics were introduced to co-pyrolyze with MR, indicating that MR and plastics have a good interaction in the co-pyrolysis process. This study provides theoretical and experimental guidance for the resource utilization of agricultural solid wastes via thermochemical conversion.

Effect of heating rate on the kinetics of limestone calcination

This paper reports on the effect of heating rates between 0.1 °C/s and 205.0 °C/s on the thermodynamics and kinetics of limestone calcination in air. These heating rates are orders of magnitude higher than those used in the thermogravimetric analysers that have been reported previously (0.1 °C/s to 0.8 °C/s). It was found that the activation energy, E, is reduced by 59%, from 205.0 kJmol−1 to 84.5 kJmol −1, when the heating rate is increased from a low heating rate regime (<1 °C/s) to a moderate heating rate regime (99.2––205.0 °C/s). Additionally, the average reaction rate constant K¯ increases with an increase in the heating rate. As an example, for 205 °C/s, K¯ is 18.7 times higher than that for 0.2 °C/s, when approaching the same asymptotic temperature. It is also found that a higher heating rate increases the specific surface area (SSA), for the same Tas. This is caused by microfractures which are associated with decreased activation energy, and in turn increases the surface-to-volume ratios and speeds up conversion. The results highlight the importance of accounting for both heating rate and calcination time in the modelling of the calcination of limestone.Specific surface area measurements also revealed that the prolongation of calcination under moderate heating rate reduces the SSA, typically by a factor of 1.6 from 15.8 m2/g to 9.6 m2/g when the residence time tr is increased from 120 s to 240 s. Therefore, to maximize the SSA, the residence time should not be longer than that required for complete conversion.

Effects of K2SiF6 on Ignition and Heat Release Characteristic of Nano-Sized Aluminum Powders

ABSTRACT This study investigates the effect of potassium fluosilicate (K2SiF6) on the ignition and heat release characteristics of n-Al50, n-Al100, and n-Al800. It is found that K2SiF6 can effectively improve the ignition and heat release characteristics of nano-aluminum powder (n-Al). This is because K2SiF6 effectively increases the reaction rate. The heat release characteristics of the n-Al/K2SiF6 mixture are improved as the particle size of aluminum powder decreases and the heating rate increases. However, when the particle size reaches a certain level, the enhancement effect will become smaller and smaller. The study revealed that the addition of K2SiF6 influences the ignition delay time, reaction, and combustion products of the n-Al/K2SiF6 mixture. A small amount of K2SiF6 can greatly reduce the ignition delay time of nano-aluminum powder. With the increase of K2SiF6 content, the ignition delay time of n-Al50 decreases first and then increases, while the ignition delay time of n-Al100 and n-Al800 decreases continuously but the extent of this reduction progressively diminishes. The morphology and composition of the combustion products were analyzed. This paper found that K2SiF6 fluorinates the oxidized shell of aluminum, thereby promoting its ignition and combustion. The influence mechanism of K2SiF6 on n-Al ignition in air is discussed.

Combustion, kinetics and thermodynamic characteristics of rice husks and rice husk-biocomposites using thermogravimetric analysis

AbstractPyrolysis of rice husk (RH), alkali-treated cellulose-rich rice husk (RHC), chemically modified RHC (RHCM) and RH-biocomposites by thermogravimetric analysis was carried out to determine combustion and kinetic parameters at three different heating rates of 20, 40 and 50 °C min−1. Combustion performance was analyzed from results of ignition temperature, burnout temperature, combustion rates, flammability index and combustion characteristic index. Increase in heating rate from 20 to 40 and further to 50 °C min−1 increased the onset of degradation, burnout and peak temperatures as observed by curve shifts to the right. Maximum combustion rates were around 0.57–0.59% min−1, 1.03% min−1 and 0.63–0.69% min−1 for RH, RHC and RHCM, respectively. For the RH-biocomposites, the maximum combustion rates were in a 0.76–0.97% min−1 range. Their average pre-exponential factors using KAS method were in the 2.24E-03–8.07E-03 range, respectively, while those for OFW method were in the 7.75E + 04–4.55E + 06 range, respectively. Average activation energies of RH-biocomposites were in the 41.0–58.2 kJ mol−1 and 48.3–67.7 kJ mol−1 ranges for KAS and OFW methods, respectively. The data were well fitting with coefficient of determination (R2) values close to 1. Average ΔG value ranges for RH-biocomposites ranged between 148.2 and 161.7 kJ mol−1. The low-energy barrier (≤ 5.4 kJ mol−1) between activation energy and enthalpy changes indicated that reaction initiation occurs easily.

Thermal Analysis Kinetics Study of Pulverized Coal Combustion under Oxygen-Rich Atmosphere.

The thermal analysis kinetic behavior of pulverized coal combustion in different oxygen-rich atmospheres is studied with a thermogravimetric (TG) analyzer. The effects of heating rate on combustion characteristic are considered. The results showed that the combustion rate of pulverized coal increased and the burnout time decreased under the conditions of an oxygen-enriched atmosphere and high heating rate. As the heating rate increases, the TG and derivative TG curves of the coal samples generally move toward the high-temperature region, and the thermal hysteresis phenomenon occurs. The changes in oxygen concentration and heating rate mainly affect the combustion stage of coal samples. The decrease in heating rate or the increase in oxygen concentration will cause a decrease in ignition point temperature and burnout temperature. Under the condition of 40% O2, the oxygen concentration and heating rate have the greatest influence on the combustion characteristic parameters. In addition, the combustion reaction of pulverized coal in the warming process was analyzed by FWO and KAS methods, respectively. The results showed that the changes in oxygen concentration and heating rate affected the activation energy, and the activation energy of coal samples increased with the increase in oxygen concentration.

Characterization of Magnetic Susceptor Heating Rate Due to Hysteresis Losses in Thermoplastic Welding

Welding techniques are emerging as a new method to join thermoplastic composite parts. They present a fast and efficient alternative to adhesives and mechanical fasteners. Induction welding is a welding technique that relies on the application of an oscillating magnetic field on the joining interface, where a material called a magnetic susceptor generates heat by interacting with the applied magnetic field. In this work, susceptors relying on magnetic hysteresis losses made of polyetherimide (PEI) and nickel (Ni) particles are investigated with varying Ni concentration. The materials are mixed using an internal mixer and pressed to form films approximately 500μm thick. To characterize the heating rates of the susceptor materials, samples are placed on an induction coil – a water-cooled copper tube in which AC current (frequency 388kHz), generates an alternating magnetic field – and the temperature evolution is measured using a thermal camera. An increasing concentration of Ni particles results in increased heating rate and maximum temperature reached by the samples. The temperature-time experimental curves are compared with theoretical heating curves to verify if the model can be used to predict the temperature evolution at the joining interface during a welding process.

Insights into Pyrolysis Kinetics, Thermodynamics, and the Reaction Mechanism of Wheat Straw for Its Resource Utilization

To realize the energy recovery of wheat straw, the pyrolysis behavior of wheat straw was studied at three heating rates (10, 20, and 30 K/min) based on thermogravimetric analysis (TG–DTG). Kinetics and thermodynamics were analyzed using Flynn–Wall–Ozawa (FWO) and Kissinger–Akahira–Sunose (KAS) model-free methods, and the reaction mechanism was determined using the Coats–Redfern (CR) model-fitting method. The results show that there are three weightlessness stages in the pyrolysis process, of which the second stage was the main weightlessness stage and two distinct peaks of weightlessness were observed in this stage. With increasing heating rate, the main pyrolytic weightlessness peaks of the DTG curve shift to the high-temperature side. The pyrolysis activation energies calculated by the FWO and KAS methods are 165.17–440.02 kJ/mol and 163.72–452.07 kJ/mol, and the pre-exponential factors vary in the range of 2.58 × 1012–7.45 × 1036 s−1 and 1.91 × 1012–8.66 × 1037 s−1, respectively. The thermodynamic parameters indicate that wheat straw has favorable conditions for product formation and it is a promising feedstock. Its pyrolysis reaction was nonspontaneous and the energy output is stable. CR method analysis shows that the A1/3 random nucleation model is the most suitable mechanism to characterize the pyrolysis process and random nucleation may be in charge of the main pyrolysis stage. This study can provide a theoretical basis for the thermochemical conversion and utilization of wheat straw.

Investigation of Co-Combustion Characteristics of Waste Biomasses and Anthracite by TG-DTG/DSC and Machine Learning Method

ABSTRACT The co-combustion characteristics and thermodynamics of waste biomasses, namely coconut shell and corncob, with anthracite were investigated using TG-DTG/DSC analysis and artificial neural networks. TG-DTG experiments were conducted at different ratios of CS-AN and CC-AN, and the samples were heated from 293 K to 1273 K at heating rates of 10, 15, 20, 25, and 30 K·min−1. The results indicated three main stages in the combustion process of the mixtures and the combustion profiles shifted to higher temperatures with increasing heating rates. As the mass fraction of biomass in the mixtures increased from 10 wt.% to 90 wt.%, the residual mass of the co-combustion mixture decreased by 19.50 wt.% and 21.78 wt.% for CS-AN and CC-AN, respectively. The comprehensive combustion index of CS-AN increased from 24.645%2·min−2·K−3 to 167.274%2·min−2·K−3, while that of CC-AN increased from 26.262%2·min−2·K−3 to 102.654%2·min−2·K−3. The DSC results showed a peak of heat absorption followed by an exotherm in the co-combustion process. As the mass fraction of anthracite in the mixtures increased, the curve shifted toward the high temperature region and the exothermic time increased. The apparent activation energies (E) for CS, CC, and AN were 75.36, 112.08, and 90.90 kJ·mol−1, respectively. Additionally, 50 wt.% CS and 50 wt.% CC were more conducive to CS-AN and CC-AN co-combustion processes. 63 ANN models were utilized to predict the post-combustion residual weight of CS5-AN5. ANN56 was identified as the best performer, with error results (RSME = 1.482, MBE = 1.120, R 2 = 0.9982) and a topology of (3 × 15 * 5 × 1), which proved to be the most suitable model for the co-combustion characteristics of this mixture. This study provides theoretical and practical guidance for solving engineering problems related to the energy utilization of waste biomasses (coconut shell and corncob) with anthracite.

Pyrolysis characteristics and kinetic parameters assessment of typical agricultural residues using high heating photothermal TGA

Understanding the complexity of thermal degradation characteristics, kinetic behavior, and thermodynamic parameters is pertinent for the efficient design and process optimization of large-scale conversion systems. Comparative assessment of pyrolysis characteristics and thermodynamic parameters of corn cobs (CC), peanut shells (PS) and sugarcane bagasse (SB) are investigated using high heating rates (100–1000 ℃/min) TGA results. Despite the effect of the heating rate increase on the degradation process of individual samples, increasing heating rates affect pyrolysis characteristics due to compositional differences. With increasing heating rates, the comprehensive pyrolysis index increased sporadically for CC (2.54–44.09 ×104%2/min2 ℃3) and PS (1.36–31.13 ×104%2/min2 ℃3), indicating easier release of volatiles at higher pyrolysis heating rates. The pyrolysis stability index (Rw), which relates to thermal degradation stability, presented an increasing trend (CC>PS>SB) with a heating rate increase (≥106%). Kinetic parameters estimated using model-free methods showed that the activation energies of CC and PS were significantly lower than that of SB. Comparative evaluation of fractional conversions and kinetic parameters using traditional and modified parallel models showed that the double random pore model (DRPM) fitted the best for simulating the experimental results at higher heating rates than other models. The change in Gibbs free energy (ΔG) trend for PS and SB showed a deviation, suggesting reaction difficulties due to higher temperature demands.

Kinetic analysis and pyrolysis behavior of pine needles by TG-FTIR and Py-GC/MS

The pyrolysis performances and reaction kinetics of pine needles (PN) were investigated by integrating thermogravimetric analysis, Fourier transform infrared spectroscopy, and pyrolysis-gas chromatography/mass spectrometry. The average activation energy of PN was estimated to be 183.2 kJ/mol by Kissinger Akahira Sunose (KAS) and 183.8 kJ/mol by Flynn Wall Ozawa (FWO), respectively at heating rates of 10, 20, and 40 °C/min. The pyrolysis of PN was found to be more efficient at the lower heating rates, while increased heating rates promoted the reaction. Using the King-Kai (K-K) method, the activation energies of hemicellulose, cellulose, and lignin were calculated to be 156, 165, and 172 kJ/mol, respectively. The descending order of evolving gases and functional groups from PN was found to be CO2, C=C, C=O, H2O, CH4, and CO. The main pyrolytic by-products identified were hydrocarbons, phenols, alcohols, ketones, and aldehydes. The determination of kinetic parameters provides fundamental information for predicting the rates at which chemical reactions occur. This study demonstrates the potential of PN as a suitable source for bioenergy.

Laser-induced heating, property changes, and damage modes in carbon fiber reinforced polymer matrix woven composites

Despite numerous efforts to understand mechanical damage in carbon fiber reinforced polymer matrix composites, there are minimal experimental and computational efforts that incorporate temperature effects on mechanical performance of composites. Recent studies have shown temperature changes can be readily monitored and predicted under relatively low heat fluxes. The present study augments such prior work by exploring effects of higher heat fluxes and increased heating rates. Plain-woven composites with T650 carbon fibers in a bismaleimide 5250-4 matrix were heated with a continuous wave laser (3.0 cm diameter flat-top beam profile at 1.0692 μm). Laser powers and durations were designed to reach temperatures near, and exceeding, matrix decomposition temperatures. Three duplicates of specimens were irradiated with four powers and two durations, yielding an irradiance range of 4.2 – 12.7 W/cm2. Resulting spatial and temporal temperature changes were measured with calibrated infrared cameras for both composite surfaces. Post-test surface photography and X‐ray CT scans were used to assess morphology changes and damage characteristics. Two key findings are reported herein: (i) delamination events dramatically impacted thermal transport, and (ii) TGA data and appropriate kinetic models can be used to account for temperature- / rate- dependent thermal responses and damage behaviors in the composites.

Fast co-pyrolysis behaviors and synergistic effects of corn stover and polyethylene via rapid infrared heating

Rapid infrared heating with fast heating rates and the capacity to load materials on the gram scale help investigate the co-pyrolysis behaviors, minimizing the gap of materials’ pyrolysis temperature and volatile release during the co-pyrolysis. This work explored the effects of temperature and heating rate on the co-pyrolysis product s behaviors and synergistic interactions of corn stove and polyethylene. Initial increases in oil yield were followed by decreases when the heating rate rose, and when the temperature increased from 500 °C to 600 °C, the oil yield rose from 17.91 wt% to 20.58 wt% before falling to 14.75 wt% at 800 °C. High heating rate promoted the oil generation, and the maximum oil yield was at 25 °C/s with varying heating rates from 15 °C/s to 35 °C/s. The pyrolysis gas produced at 25 °C/s exhibited the highest LHV (Low heating value) and lowest CO2 yield, which were 17.23 MJ/nm3 and 39.29 vol%, respectively. The suitability of heating rate and temperature may improve the interaction between H-radicals of PE and oxygenated groups of CS to generate stable macromolecular compound and enhance oil production. GC–MS studies of the oil products demonstrated that oxygenated compounds such as furans, phenols and acids from lignocellulosic depolymerization had been converted to high molecular weight long chain alcohols (mostly C26, C20 and C14 alcohols) via stronger interactions during fast infrared-heated co-pyrolysis. The alcohols increased from 32.29 % to 65.06 % as temperatures rose from 500 °C to 800 °C. Few furan heterocycles, acids and phenols were detected, suggesting that the oil presented higher quality and stronger synergistic effects. Rapid infrared heating accelerated the synergistic effects between volatile-volatile interactions during co-pyrolysis of corn stover and polyethylene, and the increases in temperature and heating rates further enhanced the release of many volatile substances and the formation of fine pores. Raman results showed char of 600 °C deposited more pure aromatic structures, the influence of temperature on aromatization was stronger than that of heating rate.

Strategy for tailoring thermoplastic forming process incorporating the influence of process variables in bulk metallic glasses

The technical interest in bulk metallic glasses (BMGs) has grown over the past few decades due to their potential for new areas of applications based on thermoplastic forming (TPF), which was previously unattainable in conventional crystalline alloys. However, the difficulty in controlling the TPF process due to the metastability of the amorphous phase has posed a barrier to widespread commercial use. This study provides practical guidelines for tailoring the TPF process incorporating the influence of process variables in BMGs. Specifically, we constructed a continuous heating transformation (CHT) diagram with iso-viscosity contours for LM1b (Zr44Ti11Cu10Ni10Be25) using Flash-DSC measurement. As an example of a TPF process utilizing the obtained CHT diagram, we demonstrated three TPF procedures from bulk to nano scales, namely BMG pressing, BMG joining, and hologram nanopatterning. Interestingly, with increasing heating rate, the TPFA is enhanced, although the incubation time for crystallization decreases. Furthermore, we proposed a new TPFA parameter, P, which considers both the supercooled liquid viscosity and crystallization kinetics to compare the TPFA of various BMGs. Especially, we constructed a plot depicting the correlation between P and calculated maximum elongation, and heating rate to investigate quantitatively the relationship between TPFA and heating rate. These results will enable us to select the most suitable BMG for the targeted applications and precisely optimize the TPF processes, which could lead to further improvements in their performance and expanded applications in various industries.

Poroviscoelastic Gravitational Dynamics

AbstractGlobal‐scale periodic deformation has been studied using the (visco)elastic gravitational theory, which assumes a planetary body consists of solid or liquid layers. Recent planetary exploration missions, however, suggest that a global layer of a mixture of solid and liquid exists in several planetary bodies. This study provides a theory of periodic deformation of such a layer unifying the viscoelastic gravitational theory with the theory of poroelasticity without introducing additional constraints. The governing equation system and a formulation suitable for numerical calculation are given. Equations used to calculate the energy dissipation rate are also given. The analytical solutions for a homogeneous sphere are obtained using an eigenvalue approach. Simple numerical calculations assuming a homogeneous sphere reveal that a numerical instability occurs if a thick porous layer, a low permeability, or a high frequency is assumed. This instability can be avoided by choosing an appropriate interior structure model that is numerically equivalent. Different simple numerical calculations adopting a multilayered, radially varying interior profile reveal that the radial profile of the tidal heating rate for a fluid‐saturated porous layer and that for a low‐viscosity solid layer are completely different. In addition, the radial variation in porosity can lead to a factor of ∼100 increase in the local heating rate. These results indicate that future studies should consider a wider variety of detailed interior structure models.

Investigation of Thermal Quenching Effect for Lithium Fluoride (LiF) Type Dosimeters

Thermal quenching is described as a decrease in luminescence efficiency with increasing measurement temperature. Luminescence intensity decreases with increasing heating rates in the presence of thermal quenching. In such a case, the heating rate to be used in the measurements becomes important. Lithium fluoride (LiF) type dosimeters have been widely used in radiation dosimetry for many years. In this study, thermal quenching effect was investigated for LiF:Mg,Ti (TLD-100) and LiF:Mg,Cu,P (TLD-100H), 6LiF:Mg,Ti(TLD-600) and 7LiF:Mg,Ti (TLD-700) at two different doses (10, 1000mGy) using 90Sr/90Y beta source. TLD-100, TLD-600 and TLD-700 showed different thermal quenching behaviors according to dose values, while TLD-100H had the same characteristics at both doses. On the other hand, other dosimeters showed thermal quenching based on the total area at 10mGy, while they did not show thermal quenching when ROI was used. Again, thermal quenching was not observed at 1000mGy for all dosimeters. In conclusion, it is recommended to use ROI or low heating rate during measurements at a low dose (in the order of mGy) for TLD-100, TLD-600 and TLD-700, while desired heating rate can be used at a high dose (Gy) for all dosimeters.