Variable Heating Rate Research Articles

On the various-heating-rates method for evaluating the activation energies of thermoluminescence peaks

The well-known various-heating-rates (VHR) method for evaluating the activation energy of thermoluminescence (TL) peaks is revisited. The method hinges on the shift of the TL peak with changing heating rate, and is based on the properties of first-order curves. Several works have shown that the same method yields a good approximation of the activation energy when general-order peaks are involved. A recent work by Maghrabi has presented a heuristic explicit expression for the magnitude of the shift between two heating rates within the first-order kinetics framework. In the present work, we address two related points. We show how the expression suggested by Maghrabi can be reached by making a very reasonable approximation of the original equation yielding the maximum condition. We also present an alternative expression which yields the amount of shift of the TL maximum with changing heating rate and with less approximation. The other point dealt with involves the results of a numerical study of the evaluation of the activation energy by the use of various heating rates in the more general one-trap-one-recombination-center (OTOR) situation. The results show that even in this general case, the various heating rates method yields very good results. The same is true for the "mixed-order" kinetics. The numerical results are accompanied by an analytical account which shows that the method yields very accurate activation energies in the rather general OTOR situation.

Aerosol generation from graphite at high temperature: Role of heating rate and air flow rate

Behavior of graphite at high temperature in terms of emission characteristics of aerosols has received notable importance in the recent past. Information on the physico-chemical characteristics of generated particles during air ingress conditions for high temperature reactors (HTRs) is crucial for design and safety considerations. The present study focuses on studying the effects of varying heating rate and air flow rate on the number concentration characteristics of particles and gases (CO and CO2) generated from heated graphite. Overall, the peak of evolution profile of number concentration of particles and volume concentration of CO gas was observed in between 600 and 800 °C. With an increase in heating rate, higher particle number concentration and shifting of peak towards high temperatures was noted. Although this trend remained more or less similar, number concentration reduced with the increase in air flow rate. Experimental observations have also been supplemented with plausible mechanism in this work.

Modeling Coal Swelling during Pyrolysis at Elevated Pressure by Using a Single Bubble Model: Validation and Application

ABSTRACT Pressurized oxy-coal combustion technologies are attracting more attention of researchers because of their advantages of carbon capture. While the ambient pressure could significantly influence the coal pyrolysis behavior. In this study, Yulin coal was used for the pyrolysis experiment in a pressurized drop tube furnace. Pyrolysis temperature of 1273 K, and pressures of 1, 4, 7, 10 atm were considered. The swelling behavior of produced char was analyzed by the scanning electron microscope (SEM). The char evolution process during pyrolysis at elevated pressure was simulated by a revised single bubble model, in which the volatile releasing rate and yield by residence time can be obtained from the CPD (chemical percolation devolatilization) model. Results show that the revised single bubble model is suitable for predicting the char evolution over a wide range of pressure and heating rate. Optimum pressure is present in the range of 7–15 atm, where the swelling ratio and porosity reach the maximum value. This model can predict the two regimes of coal swelling in varied heating rates, which is more obvious at high pressure. The porosity development by time can also be output, and the variation trends are similar to the swelling ratio.

Thermoluminescence characteristics and kinetic analysis of beta irradiated Ca4LaO(BO3)3 phosphor

Thermoluminescence (TL) properties of synthesized Ca4LaO(BO3)3 exposed to beta radiation were analyzed and TL kinetic parameters of activation energy E (eV), the frequency factor s (s-1), and order of kinetics b were determined in this study. TL glow curve recorded in 25–500 °C range presented two TL maxima around 70 and 200 °C and therefore, thermal cleaning was utilized for the further investigations on a single TL maximum. To investigate dosimetric characterizations of Ca4LaO(BO3)3, additive dose and various heating rates, reusability, and storage time measurements were performed. Ca4LaO(BO3)3 has a linear dose range between 10 to 100 Gy with a heating rate of 2 °C/s. An anomalous case of heating rate behavior was attained for the TL measurements carried out using variable heating rates between 0.1 and 10 °C/s which was considered through the semi-localized transition model. Reusability and storage time measurements indicated the results within the 5% standard deviation. The kinetic parameters were estimated by the initial rise (IR) and glow curve deconvolution (GCD) methods. Continuously distributed trapping levels were identified by TM–Tstop with E ranging from 1.25 to 1.45 eV. GCD identified that the glow curve expressed general order kinetics and consist of three overlapping traps.

Effect of Al addition on the thermal properties of lead -tin alloy

The effect of aluminium addition on the thermal parameters of Pb–Sn alloy was investigated. The technique of Differential Thermal Analysis (DTA) was selected to determine the phase transformation temperatures and the effect of varying heating rates. Thermal parameters such as melting temperature (Tm), crystallization temperature (Tc), the true melting temperature (Tonset), initial melting peak temperature (Ton), end melting peak temperature (Toff), enthalpy of fusion, activation energy of melting (Em) and activation energy of crystallization (Ec) were calculated. The dependence of activation energies of melting and crystallization with Al content have been discussed in detail.

Characterization of thermoluminescence kinetic parameters of dolomite after exposure to β-radiation dose

Dolomite is a carbonate mineral of calcium and magnesium having the chemical formula CaMg(CO3)2. It is a reservoir for significant petroleum reserves and mainly used as building and ceramic material. Thermoluminescence (TL) emission of this mineral has been examined in the literature, especially collected from Egypt, India, and Brazil. In this study, the aim is to investigate TL properties of dolomite mineral which has a wide reserve in Mersin/Turkey. Structural, morphological, and elemental analyzes were performed by X-ray Diffraction (XRD) Spectroscopy, Scanning Electron Microscope equipped with Energy Dispersive X-ray Spectrometer (SEM-EDS), and Inductively Coupled Plasma Mass Spectrometer (ICP/MS), respectively. TL measurements were carried out using a TL/OSL reader with a90Sr/90Y beta source. The natural TL (NTL) curve of the sample showed two peaks at around 255 and 345 °C by the wideband blue filter whereas an additional peak at 115 °C was observed under the beta irradiation. In addition, at high doses from 50 Gy, a shoulder at around 402 °C occurred. The optimum annealing temperature and duration of the sample were determined as 500 °C and 30 min. In order to remove the low-temperature peak, a preheating process at 200 °C with 23 s duration was applied before each TL readout. TL response to absorbed dose showed good linearity over the 0.1–1200 Gy dose range and the sample was observed to be reusable with only 1.7% change up to 10 cycles under a dose of 100 Gy. The kinetic parameters (activation energy E (eV), frequency factor s (s−1), kinetic order b) of the evident glow peaks were estimated using Peak Shape (PS), Various Heating Rate (VHR), Initial Rise (IR), and Computerized Glow Curve Deconvolution (CGCD) methods. The kinetic analysis indicated that the TL glow curve of the preheated sample consists of four individual peaks having activation energies of ∼1.56, 1.60, 1.78, and 1.73 eV, and these peaks obey second and general-order kinetics.

Thermal kinetic analysis of mustard biomass with equiatomic iron–nickel catalyst and its predictive modeling

Mustard waste briquettes are commercially used as a fuel for power production in boilers, whereas the thermal kinetics of the biomass plays a vital role in deciding the process parameters. The pyrolysis process converts biomass to value-added products such as biochar, bio-oil, and hydrocarbon gases based on the heating rates and temperature. To enhance the pyrolytic activity of mustard biomass, magnetically separable and reusable FeNi alloy catalyst is investigated. The thermo-conversion properties are studied under variable heating rates with 2 and 10% FeNi particles prepared through a facile chemical reduction technique. Thermal kinetics is computed using Flynn-Wall-Ozawa (FOW) and Kissinger-Akahira-Sunose (KAS) methods. The activation energies calculated using FOW and KAS methods increase with FeNi addition in mustard while the calorific value decreases. The FeNi alloy particles with the spike-like morphology provide better metal-biomass binding resulting in higher activation energy and facilitates the easy decomposition of lignin. The 10% FeNi -mustard shows uniform conversion independent of heating rates, suitable for magnetically recoverable catalytic pyrolysis. Response surface methodology analysis predicts optimum conversion for 10% FeNi added mustard and less significance for the heating rates in concurrence with the experiments. Artificial neural network utilized to predict and validate mass loss for mustard biomass exhibits best fit for the three neural hidden layer and one output layered topology.

Thermoluminescence dosimetry properties of Tm3+ doped fluoroelpasolite Cs2NaYF6 crystals synthesized under hydrothermal conditions

Detailed research of thermoluminescence (TL) properties of Tm3+ doped fluoroelpasolite Cs2NaYF6 crystals synthesized under hydrothermal conditions has been carried out in order to develop new dosimetric material. The basic dosimetric properties of Cs2NaY0.99Tm0.01F6 crystals (Zeff = 33) exposed to beta radiation, such as a TL glow curve shape, beta-dose response, reproducibility, dark fading, have been investigated by using ordinary TL technique at a typical heating rate of 2 °C/s. At this heating rate the Cs2NaY0.99Tm0.01F6 crystal exhibits three well-separated TL peaks: a rapidly decaying peak at 100 °C (Peak 1), a stable peak at 171 °C (Peak 2), and one more low-intensity peak at 240 °C (Peak 3). The deviation of reproducibility for 10 repeated readings of individual samples after exposure to 5 Gy of beta irradiation is <1%. The TL output as a function of beta irradiation dose exhibits linear dose-response up to 1 kGy. The anomalous fading of the TL signal has been observed for the Cs2NaY0.99Tm0.01F6 crystals. The short time fading characteristics have been studied for different periods of up to one week. Using the various heating rates (VHR), Chen's peak shape, and computerized glow curve deconvolution (CGCD) methods, the kinetic parameters have been calculated specifically for the Peak 2 of the TL glow curve. Spectra of X-ray excited radioluminescence (RL) have been studied in the range of 200–1000 nm. The results of this study show that the simple TL glow curve structure, relatively high sensitivity to ionizing radiation, the wide range of measurable doses from 0.2 Gy up to 1 kGy, and reusability make this novel Cs2NaY0.99Tm0.01F6 dosimetric material a promising candidate for its applications in radiation dosimetry in particular for measurement of high radiation doses.

Use of Terbium Doped Phosphate Glasses for High Dose Radiation Dosimetry—Thermoluminescence Characteristics, Dose Response and Optimization of Readout Method

The phosphate glass samples doped with Tb2O3 oxide (general formula: P2O5-Al2O3-Na2O-Tb2O3) were synthesized and studied for usage in high-dose radiation dosimetry (for example, in high-activity nuclear waste disposals). The influence of terbium concentration on thermoluminescent (TL) signals was analyzed. TL properties of glasses were investigated using various experimental techniques such as direct measurements of TL response vs. radiation dose, Tmax–Tstop and VHR (various heating rate) methods, and glow curve deconvolution analysis. The thermoluminescence dosimetry (TLD) technique was used as the main investigation tool to study detectors’ dose responses. It has been proved that increasing the concentration of terbium oxide in glass matrices significantly increases the thermoluminescence yield of examined material. For the highest dose range (up to 35 kGy), the dependence of the integrated thermoluminescent signals vs. dose can be considered as a saturation-type curve. Additional preheating of samples improves linearity of signal vs. dose dependencies and leads to a decrease of the signal loss over time. All obtained data suggest that investigated material can be used in high-dose radiation dosimetry. Additional advantages of the investigated dosimetric system are its potential ability to re-use the same dosimeters multiple times and the fact that reading dosimeters only requires usage of a basic TL reader without any modifications.

Luminescence of Ce3+ and Li+ co-doped MgO synthesized using solid-state reaction method

MgO:Ce3+,Li+ was synthesized by the solid-state reaction (SSR) method and its luminescence properties were investigated. The X-ray diffraction (XRD) patterns and scanning electron microscopy (SEM) images were used for the structure analysis. The luminescence properties were studied using thermoluminescence (TL), photoluminescence (PL), and radioluminescence (RL) techniques. The step annealing experiment was conducted to find the preheating temperature. The dose–response features as a function of β-ray exposure extended from 0.2 Gy to 2 kGy were investigated. The kinetic parameters such as the activation energy (Ea), frequency factors, and order of kinetics of MgO:Ce3+,Li+ were found using the computerized glow curve deconvolution (CGCD), variable heating rate (VHR) methods, and Tm-Tstop method in combination with the Initial Rise (IR) method. The experimental results of the TL, PL, and RL analyses can serve for a better understanding of the luminescent mechanism in Ce3+ and Li+ activated MgO for the potential use of designing phosphor as a dosimeter and optical ceramic material.

Co-pyrolysis of waste polyvinyl chloride and oil-based drilling cuttings: Pyrolysis process and product characteristics analysis

Oil-based drill cuttings (OBDC) and waste polyvinyl chloride (waste PVC) both are solid wastes. The pyrolysis/co-pyrolysis characterizations of OBDC, waste PVC and OBDC/waste PVC at varying heating rates were investigated using thermogravimetric analysis (TG/TGA). Coats-Redfern and Kissinger integration methods were employed to fit the TG curve. The optimal fitting effect was obtained with reaction order at 2 and Kissinger integration method was better than Coats-Redfern integration method for co-pyrolysis of OBDC/waste PVC. The practical co-pyrolysis condition was optimized using batch experiment and the optimal condition was as following: final temperature for 600 °C, holding time for 60 min, heating rate at 10 °C/min and ratio of PVC as 10% PO. The gas, solid and liquid phase products of pyrolysis/co-pyrolysis were characterized and analyzed using thermogravimetry-mass spectrometry (TG-MS), gas chromatography-mass spectrometry (GC-MS) and X-ray diffraction (XRD). The gas product of pyrolysis/co-pyrolysis indicated the inhibitory effect on HCl emission due to the positive synergic effect of OBDC and PVC. High pyrolysis temperature was beneficial to increase the content of hydrocarbons, which enhanced the quality of oil recovery. This study indicated that the co-pyrolysis of OBDC and waste PVC is a promising method for waste disposal and oil recovery.

Calculation of the Temperature Distribution in Cylindrical Samples of Alumina and Copper Produced by Spark Plasma Sintering

Numerical calculations were carried out to simulate, under conditions of close spark plasma sintering (SPS), the temperature distribution during the passage of current in dense cylindrical samples of two materials: aluminum oxide and copper located in graphite forms and clamped between cylindrical graphite punches. The investigated materials differ greatly in their electrical conductivity and other physicochemical properties. Calculations were carried out for various geometric parameters of the samples, as well as graphite molds and punches at varying heating rates from the passing current.

Lifetime predictions of non-ionic and ionic biopolymers: kinetic studies by non-isothermal thermogravimetric analysis

In this paper, films based on sustainable polymers with variable charge have been investigated by non-isothermal thermogravimetry in order to predict their lifetime, which is a key parameter for their potential use in numerous technological and biomedical applications. Specifically, chitosan has been selected as positively charged biopolymer, while alginate has been chosen as negatively charged biopolymer. Among non-ionic polymers, methylcellulose has been investigated. Thermogravimetric measurements at variable heating rates (5, 10, 15 and 20 °C min−1) have been performed for all the polymers to study their degradation kinetics by using isoconversional procedures combined with ‘Master plot’ analyses. Both integral (KAS and Starink methods) and differential (Friedman method) isoconversional procedures have shown that chitosan possesses the highest energetic barrier to decomposition. Based on the Master plot analysis, the decomposition of ionic polymers can be described by the R2 kinetic model (contracted cylindrical geometry), while the degradation of methylcellulose reflects the D2 mechanism (two-dimensional diffusion). The determination of both the decomposition mechanism and the kinetic parameters (activation energy and pre-exponential factor) has been used to determine the decay time functions of the several biopolymers. The obtained insights can be helpful for the development of durable films based on sustainable polymers with variable electrostatic characteristics.Graphical abstract

Characterization of a promising luminescence-based graphite radiation dosimeter

Characterization has been undertaken of the thermoluminescence (TL) properties of 0.3 mm polymer pencil lead graphite (PPLG). For 60Co gamma irradiation doses from 0.5 Gy up to 20 Gy readout data have been taken at different heating rates, from 2 to 15 °C s−1, linear TL responses with radiation dose being found, also with a greater degree of sensitivity at the lowest dose. Estimation has been made of the principal trap parameters of the PPLG, use being made of the variable heating rate method via the Hoogenstraaten, Booth - Bohun – Parfianovitch and Two Point Two Heating Rate techniques. Among the trap parameters are included the order of kinetics, activation energy, the frequency factor, and the initial concentration of trapped electrons. Also determined are relations that allow estimation of the temperature lag between the heating element and that of the sample. The stability of TL signal has been examined at peak temperatures with the lifetime of the TL glow peak calculated. Structural alterations of the irradiated PPLGs have been observed via Raman and Photoluminescence (PL) spectroscopy, also via X-ray diffraction (XRD), providing information on physical parameters relating to the defects participating in the luminescence process. The results indicate 0.3 mm PPLG to offer promising potential as a new generation of radiation dosimeter, including for medical radiation applications.

A comparative study on the effect of Zr, Sn, and Ti on the crystallization behavior of nepheline glass

In alkali aluminosilicate glasses, additions of 4+ cations like Zr and Ti are often added to promote crystallization. In this study, Zr, Ti, or Sn are progressively substituted for Si in nepheline (NaAlSiO4) glass to determine their impact on the crystallization behavior. For glasses homogeneous on quenching, up to NaAlZr0.075Si0.925O4, NaAlSn0.100Si0.900O4, and NaAlTi0.300Si0.700O4, respectively, crystallization temperatures were investigated by thermal analysis. A subset of compositions was subjected to additional thermal analysis, varying heating rate and particle size, to investigate the subtleties of crystallization behavior. Subsequent heat treatment of glass powders was performed to maximize crystallization, and glass-ceramic microstructure was assessed by optical microscopy and electron microprobe, while crystalline phases were determined by X-ray diffraction. In all cases the major crystalline phase was orthorhombic carnegieite, which accommodated Ti in its structure but not Zr or Sn, and excess 4+ cations formed MO2, i.e., brookite, baddeleyite, and cassiterite, respectively.

Thermoluminescence study and trapping parameters of beta irradiated NaBaBO3:Gd3+ phosphor

A series of Gd3+ doped NaBaBO3 phosphors were synthesized via a combustion approach. The TL data collected by means of a combination of a commercial SCHOTT BG39 and HC414/46 filters was studied to evaluate basic kinetic parameters. Tm-Tstop and, various heating rate (VHR) and computerized glow-curve deconvolution analyses were utilized to analyze collected data. Our findings indicate that luminescence process in scrutinized material may obey first-order kinetics because no shift in the experimental TL glow curves with increased dose was observed. The TL dose response of the TL glow peaks exhibited a linear characteristic up to 20 Gy. The Tm-Tstop method revealed that the number of the component TL glow peaks in the complex glow curve with and without preheating process consisted of six well-isolated and three overlapping glow peaks, respectively. The number of peaks obtained by deconvolution was perfectly matched with those obtained by Tm-Tstop and the figure of merit (FOM) values with and without preheating were 0.84% and 1.48%, respectively. The activation energy value found for the peak at 312 °C using the various heating rate (VHR) method was very close to those of deconvolution method. The total loss of response of TL glow curve sensitivity was much less (only ± 2%) after 10 cycles of reuse.

Analysis of mixed cattle manure: Kinetics and thermodynamic comparison of pyrolysis and combustion processes

The study investigates the non-isothermal thermogravimetric analysis of cattle manure at varied heating rates to compare the kinetic and thermodynamic behaviors of cattle manure in N2 and air atmospheres. The Thermogravimetric (TG) curves indicated that the decomposition of the manure can be divided into three different regions. Exclusive of stage I (dehydration), the activation energy (Ea) values of stage II (devolatilization) for all model-free methods varied between 144 - 270 and 32–227 kJ/mol in pyrolysis and combustion respectively. While in stage III, Ea values varied in ranges of 49–336 kJ/mol and 71–136 kJ/mol for pyrolysis (carbonation) and combustion (char burning), respectively. The overall average Ea for the pyrolysis (≈146 kJ/mol) is higher than the combustion process (≈127 kJ/mol). The variation in the values of frequency factor “A” also indicated the complexity of both processes. Pyrolysis followed overall 2-Diffusion (D2) reaction models, while combustion followed 3-Power law (P3) and reaction Order-1 (O1) in stage II and III respectively. The thermodynamic study was also conducted to evaluate the important parameters, change in Enthalpy change (ΔH), Gibbs free energy (ΔG), and Entropy (ΔS).

Finite-amplitude RF heating rates for magnetized electrons in neutral plasma

A theoretical model is developed and evaluated using a Vlasov–Poisson treatment to calculate radio frequency (RF) electric field heating rates for magnetized electrons in neutral plasma when the magnetic and electric field directions are colinear and when the RF is of sufficiently high frequency. This calculation reduces to the theory for magnetized longitudinal AC conductivity introduced by Oberman and Shure [Phys. Fluids 6, 834–838 (1963)] in the low-amplitude limit when the electron oscillation velocity is much less than the thermal velocity. For electron coupling strengths Γ = 0.15–0.015 and RF fields accessible to ultracold neutral plasma experiments, the model predicts mild variations in heating rate of order unity across magnetization strengths spanning orders of magnitude. The predicted effect of including a Bhatnagar-Gross-Krook-type collisional relaxation term in the Vlasov equation reduces the heating rate by 5% or less across magnetizations.

Pyrolysis of soybean residue: Understanding characteristics of the products

Soybean residue (SR) is a main solid waste produced during the extraction of soybean oil with bulk volume. In addition to the use as vegetable protein feed, SR could also be used as feedstock for producing biofuels and carbon materials via pyrolysis. In this study, the pyrolysis behaviors of SR at varied temperatures and heating rates were investigated. The results show that the pyrolysis of the organic components in SR could reach completion even at 500 °C, due to the lower thermal stability of the organic component than that in the typical biomass. This also leads to the bio-oil with little heavy organics and also low carbon content of the resulting biochar, as the organic components decomposed to a significant extent while the charring reactions were insignificant. This leads to the biochar with low heating value and low energy yield when compared with that in the pyrolysis of typical biomass. In addition, the high content of proteins, amino acids and other nitrogen-containing nutrients make the SR derived bio-oil nitrogen-rich and a significant portion of nitrogen could also be retained in the biochar. These specialties have to be considered during their applications as either biofuels or functional carbon materials.

Characterization of thermoluminescence kinetic parameters of beta irradiated B doped Ca5(PO4)3OH powder obtained from eggshell

In this study, we have synthesized B doped Ca5(PO4)3OH (HAP) by a sonication chemical method. The thermoluminescence (TL) properties of the family of synthesized samples (B doped Ca5(PO4)3OH (HAP) were investigated using an IRSL-TL 565 nm filter. This gave the highest TL intensity of each phosphor after 2 Gy β-irradiation. Three TL glow peaks of B doped Ca5(PO4)3OH (HAP) are centered at around 84, 208 and 324 °C (with a heating rate of 2 °Cs-1). The trapping parameters such as activation energy (E), order of kinetics (b), frequency factor (s) were calculated by using initial rise (IR), various heating rates (VHR) and computerized glow curve deconvolution (CGCD) method. The response of TL glow curves remained constant within ±5% deviation from the initial value after 9 cycles of reuse; but only at tenth cycle the deviation goes up to 6%.