Heating Rate Method Research Articles

Analysis of TL and OSL kinetics in lithium magnesium phosphate crystals

Within this work the samples of the LiMgPO4 compound have been crystallized using a micro pulling down crystal growth method. The measured TL and OSL response was investigated in order to evaluate basic kinetic parameters. Collected data were analyzed using Tm-Tstop, deconvolution and variable heating rate methods. It was found that both the TL and OSL response of the LiMgPO4 samples can be expressed in the form of a linear combination of several first order components. The obtained results suggest that luminescence processes in the studied material may follow a first order kinetics, as the measured TL glow curves do not shift with increasing dose. Increasing the dose of beta radiation up to kGy range, a linear response was measured for all the studied LiMgPO4 samples. The obtained values of kinetic parameters evaluated with Tm-Tstop method remain in agreement with those obtained by deconvolution for low-temperature peaks. In turn, for peaks located at higher temperatures the results obtained by variable heating rate method are close to those of deconvolution. This implies that more detailed analysis is needed to achieve a compatibility between the applied modes of data analysis and to achieve the accurate values of kinetic parameters. By calculating a decrease in the area under the whole LMP glow curve for the two weeks fading time, using the estimated trapping parameters, and comparing the results with previous work one may conclude that Tm-Tstop method combined with the initial rise analysis gives the most reliable values of kinetic parameters.

Thermal degradation kinetics and estimation of lifetime of radiation grafted polypropylene films

In this research work, thermal stability and degradation behavior of acrylic acid grafted polypropylene (PP-g-PAAc) films were investigated by using thermogravimetric (TGA) analysis at four different heating rates 5, 10, 15 and 20°C/min over a temperature range of 40–550°C in nitrogen atmosphere. The kinetic parameters namely activation energy (Ea), reaction order (n) and frequency factor (Z) were calculated by three multiple heating rate methods. The thermal stability of PP-g-PAAc films is found to decrease with increase in degree of grafting. The TGA data and thermal kinetic parameters were also used to predict the lifetime of grafted PP films. The estimated lifetime of neat PP as well as grafted PP decreased with increase in temperature by all the three methods. Studies also indicated that Ea and lifetime of PP-g-PAAc films decreased with increase in degree of grafting, which may also be helpful in biodegradation of grafted PP films.

Iso-conversional kinetic analysis of quaternary glass re-crystallization.

Iso-conversional kinetic analysis is popular in scientific community for analyzing solid-state reactions (e.g., glass/amorphous and amorphous/crystal phase transformations, re-crystallization etc). It is a recognized significant tool to achieve useful outcomes for the solid state reaction under consideration. Present work is devoted to explore some insights of thermally activated crystallization using various heating rates (VHR) method. We have examined the correlation between iso-conversional activation energy and iso-conversional rate of crystal growth. In fact, we have observed the compensation law and iso-kinetic relationship using two different approaches for the study of crystallization phenomenon that drives thermally in an Arrhenian manner.Moreover, we found that the estimated intercepts and gradients (i.e., Meyer-Neldel energy and Meyer-Neldel pre-factor respectively) for both approaches also vary linearly and both sets are remarkably identical. These results approach to an inference for ensuring the equivalence of compensation law and iso-kinetic relationship and provide an understanding of various advanced materials in physical chemistry, materials sciences and solid-state physics.

Characterisation of clay samples from minerals–rich deposits for thermoluminescence applications

Thermoluminescent (TL) characteristics of clay samples from Ijero-Ekiti and Isan-Ekiti, Ekiti State, Nigeria were studied for application in retrospective dosimetry. In order to increase the potentials of the clay material for relevant radiation measurement applications, characteristic glow curves of samples from the clay deposits have been obtained using a Victoreen (2800M) TL reader and the TL properties subsequently examined. The variable heating rate method was used to determine the glow peak shape and intensity by estimating the activation energy or trap depth, E and the frequency factor, S. Most samples demonstrated the dependence of their glow curve on the heating rate, with the peak temperature, Tm increasing with the heating rate. These glow peaks were noted to be a complex trapping system, consisting of several overlapping first order peaks and each with different TL behaviour, except for certain samples, which showed independence of peak temperature with dose. While recommending further heating protocol to isolate each peak for the calculation of other kinetic parameters, we present an approximate 0.29–0.84eV for E and 3.7×101 to 4.0×106s−1 for S. Though the samples with the TL dosimetric property of increased peak intensity with increasing excitation dose could be considered for TL applications, the reduction in TL intensity must be considered for high heating rates applications.

Comprehensive kinetic analysis of thermoluminescence peaks of α-Al2O3:C,Mg

A comprehensive kinetic analysis of the glow peaks in α-Al2O3:C,Mg is reported. A thermoluminescence glow curve measured at 1°C/s after beta irradiation to 1Gy shows a high intensity peak hereafter referred to as the main peak at 161°C and six lower intensity secondary peaks at 42, 72, 193, 279, 330, 370°C respectively. For ease of reference, the secondary peaks are labelled as I, II, IV, V, VI and VII respectively and the main peak denoted peak III. Kinetic analysis of the glow peaks has been carried out using the initial rise, whole glow peak, peak shape, variable heating rate and glow curve deconvolution methods as well as by way of phosphorescence. Using Tm-Tstop, Tm-dose and phosphorescence analyses, the order of kinetics of the peaks has been evaluated as first order. Analysis by the peak shape, whole glow peak and deconvolution methods produce the same conclusion. The activation energy of peaks I through VII are calculated as ~0.83, 0.96, 1.37, 1.20, 1.15, 1.61 and 1.94eV respectively. The frequency factors for all the peaks are of the order of 109 to 1014s−1. The question of thermal quenching affecting the peaks was considered. The peaks III, IV and V, the only ones that could be conveniently studied in this regard, were found to be affected by thermal quenching. The activation energy for thermal quenching was calculated for peak III as 0.96±0.03eV, for peak VI as 0.95±0.07eV and for peak V as 1.26±0.08eV. The thermal quenching phenomenon has been discussed with reference to F+ and F centres. An energy band model has been developed to discuss the luminescence mechanisms in α-Al2O3:C,Mg in light of finding in this work.

Studies on the thermal properties of silicone polymer based thermal protection systems for space applications

Thermal decomposition, thermal conductivity, specific heat and flammability of polydimethyl siloxane (PDMS) resin and three PDMS-based systems with three different types of additives were studied using various thermo-analytical techniques. The additives were found to modify the thermal properties of PDMS to different extents. Among the three systems, highest specific heat and lowest thermal conductivity, desired for thermal protection application, were obtained for System I. The thermal stability of the three systems is in the order System I > System II > System III. Even though System III showed the lowest specific heat and highest thermal conductivity, due to its very high LOI among all other systems, the system finds application as a flame retardant. Thermogravimetric–mass spectroscopic analysis was carried out to find out the decomposition products. The major decomposition product was identified as hexamethylcyclotrisiloxane in all the systems. The decomposition kinetics of these systems was investigated by thermogravimetry using multiple heating rate methods, viz. Kissinger and Flynn–Wall–Ozawa. The kinetic parameters, viz. activation energy and pre-exponential factor, were derived using the two methods for all the systems. From the kinetic study, it is confirmed that the activation energy for the decomposition of the neat PDMS decreased as decomposition progressed, whereas the activation energy increased for the silicone composite systems.

Thermoluminescence measurements of trap depth in alkali feldspars extracted from bedrock samples

Various measurements of thermal trap depth are evaluated for K-feldspar grains extracted from a bedrock sample. The initial rise method and the various heating rates method yield consistent results for both the natural signal (E = 1.23 and 1.16 eV, respectively) and for a regenerative dose of 64 Gy (0.83 and 0.78 eV). For the fractional glow curve, apparent E-values range from 0.39 eV to a plateau around 1.50 eV. The highest values for the natural and regenerative signals are obtained using the newly-developed post-isothermal TL (pI-TL) method wherein the isothermal loss curves (gotten by subtracting TL curves obtained after different preheat durations) are fitted in the initial rise region on an Arrhenius plot. For a dose of 12.8 Gy, this method measures apparent E-values ranging from 0.73 eV to a plateau near 1.84 ± 0.06 eV. We repeat this analysis on three additional feldspar samples (two perthites and a high albite) to get a mean value of E = 1.86 ± 0.03 eV. The same analysis of natural aliquots of the K-feldspar sample yields similar results, with the two highest E-values at 1.81 and 1.86 eV. The kinetic order does not systematically vary with isothermal holding temperature or duration but remains relatively constant at 1.6 ± 0.3 (regenerative dose) and 1.5 ± 0.5 (natural dose). The apparent frequency factor, measured assuming a single E-value of 1.86 eV, decreases systematically (∼1023−1012s−1) with hold temperature and duration, a result which is consistent with a thermally-activated, distance-dependent tunneling model for feldspar thermoluminescence (i.e., a single trap depth and a continuum of apparent frequency factors). Frequency factor values measured following identical isothermal treatments are comparable between the natural and regenerative post-isothermal TL curves. By contrast, if different E-values are assumed, the apparent frequency factor values appear stochastic. Finally, it is speculated that the plateau of pI-TL E-values may be interpreted as the thermal depth of the main dosimetric trap measured with IRSL protocols.

Thermoluminescence of α-Al2O3:C,Mg: Kinetic analysis of the main glow peak

The kinetic analysis of the thermoluminescence of aluminium oxide doped with carbon and co-doped with magnesium (α-Al2O3:C,Mg) is reported. Measurements were made at 1°C/s following beta irradiation to 1Gy. The glow curve consists of a dominant peak at a peak-maximum Tm of 161°C and six secondary peaks of weaker intensity at 42, 72, 193, 279, 330 and 370°C. Kinetic analysis of the main peak, the subject of this report, was carried out using initial rise, whole glow peak, peak shape, curve fitting and variable heating rate methods. The order of kinetics of the main peak was determined as first order using various methods including the Tm–Tstop technique and the dependence of Tm on irradiation dose. The activation energy of the peak is about ~1.36eV and the frequency factor of the order of 1014s−1. The peak area changes with heating rate in a manner that shows that the peak is affected by thermal quenching. The activation energy of thermal quenching was evaluated as 0.99±0.08eV. A comparison of analytical results from the main peak before and after correction for thermal quenching show that the kinetic parameters of the main peak are not that affected by thermal quenching.

Thermal decomposition kinetics and mechanism of low-temperature hydrogenated acrylonitrile butadiene rubber composites with sodium methacrylate

Thermal decomposition processes and mechanism of low-temperature grade hydrogenated acrylonitrile butadiene rubber(LTG-HNBR) composites with sodium methacrylate(NaMAA) were investigated by thermogravimetric analysis(TGA) and Fourier transform infrared spectroscopy(FTIR) coupling technology in this article. The results of TGA demonstrate that the addition of NaMAA can enhance the thermal decomposition temperature of the rubber. Moreover, it was found that the composites spent more activation energies to decompose than pure rubber by the calculations of multiply heating rate method. Time-resolved FTIR spectra show that NaMAA affects the initial decomposition of the composites. But in the following process, the composites maintained a similar behavior to the matrix. During the decomposition, PNaMAA nanostructures, in-situ generated by NaMAA, helped reduce the diffusion speed of decomposition products and thus improved the thermal stability of the composites. We believe that these findings can provide some guides to direct the applications of LTG-HNBR composites with unsaturated metal methacrylates.

Photoluminescence, thermoluminescence and evaluation of some parameters of Dy3+ activated Sr5(PO4)3F phosphor synthesized by sol-gel method

In this study, we have synthesized Dy3+ activated Sr5(PO4)3F (S-FAP) phosphors by sol-gel synthesis method. The synthesized phosphors were characterized by X-ray diffraction pattern (XRD), scanning electron microscopic (SEM), photoluminescence (PL) and thermoluminescence (TL) for structural, morphological and luminescent properties. Dy3+ activated Sr5(PO4)3F phosphor shows its characteristic PL emission at 481 nm and 574 nm due to 4F9/2 → 6H15/2 and 4F9/2 → 6H13/2 transitions, respectively. TL characteristics of Dy3+ doped Sr5(PO4)3F phosphors were taken after irradiation by 60Co gamma exposure. Two separate TL peaks at 126 °C and 279 °C were observed in case of Dy3+ doped phosphor. Sr5(PO4)3F:Dy3+ phosphor was irradiated within a wide range of exposure of 50 Gy to 7 kGy doses. Linearity was found up to 2 kGy and thereafter TL response saturates. Fading study was also carried out over the duration of six weeks for Sr5(PO4)3F phosphor. Trapping parameters were calculated using Chen's peak shape method, initial rise method and various heating rate method. Glow curve is deconvoluted using computerized glow curve deconvolution program. TL sensitivity of Sr5(PO4)3F:Dy3+ phosphor is found to be less by a factor of 2.08 than commercially used CaSO4:Dy phosphor. In order to identify the defect centers formed upon γ-ray irradiation in Sr5(PO4)3F:Dy3+ phosphor, EPR measurements were carried out on un-irradiated and irradiated phosphors.

Defect characterization in neodymium doped thallium indium disulfide crystals by thermoluminescence measurements

Characteristics of defect centers in neodymium doped TlInS2 single crystals have been investigated in virtue of thermoluminescence measurements carried out at low temperatures (10–300K) with various heating rates between 0.4 and 1.2Ks−1. One glow peak was detected with peak maximum temperature of 26K at a rate of 0.4Ks−1. The observed glow peak was analyzed using three points and heating rate methods. The analysis results revealed the presence of one trap level with activation energy of 14meV. Three points method showed that mixed order of kinetic dominates the trapping level. Shift of peak maximum temperature to higher values and decrease in TL intensity were observed as the heating rate was increased progressively. Distribution of traps was demonstrated using an experimental method based on illumination temperature varying between 10 and 14K.

Thermally Stimulated Luminescence of $$\hbox {Y}_{2}{\mathrm {Si}}{\mathrm {O}}_{5}{:}~{\mathrm {Ce}}^{3+}$$ Y 2 Si O 5 : Ce 3 + Commercial Phosphor Powder and Thin Films

We report on the thermoluminescence (TL) properties of $$\hbox {Y}_{2}{\mathrm {Si}}{\mathrm {O}}_{5}{:}\,{\mathrm {Ce}}^{3+}$$ phosphor powder and thin films. For the phosphor powder, the TL intensity increases with an increase in UV dose for up to 20 min and then decreases. The TL intensity peak shifts slightly to higher-temperature region at relatively high heating rates, but with reduced peak intensity. Important TL kinetic parameters, such as the activation energy (E) and the frequency factor (s), were calculated from the glow curves using a variable heating rate method, and it was found that the glow peaks obey first-order kinetics. For the films, broad TL emissions over a wide temperature range with reduced intensity relative to that of the powder were observed. The maxima of the TL glow peaks of the films deposited in oxygen ambient and vacuum shift toward higher temperature relative to the TL peak position of the film deposited in an argon environment. Vacuum environment resulted in the formation of a deep trap relative to oxygen and argon environments. Furthermore, the structure of $$\hbox {Y}_{2}{\mathrm {Si}}{\mathrm {O}}_{5}{:}\,{\mathrm {Ce}}^{3+}$$ phosphor powder transformed from $${x}_{2}$$ -monoclinic polycrystalline phase to $${x}_{1}$$ -monoclinic polycrystalline phase, for deposition at low substrate temperature.

Absorbed dose estimation using LET dependence in glow curve of thermoluminescent phosphor Li3B7O12:Cu in therapeutic carbon beams

ABSTRACTA high temperature ratio (HTR) method has been proposed to correct the linear energy transfer (LET) dependence of thermoluminescent (TL) efficiency. To realize the use of the slab-type thermoluminescence detector (TLD) that based on the phosphor Li3B7O12:Cu for heavy charged particle beam, the HTR method has been considered. To improve the reproducibility of HTR, the slow heating rate method is introduced in this report and the coefficient variations of HTR decreased from 10%–20% to 8%. The relation between TL-efficiency, HTR, and LET for Li3B7O12:Cu was manifested and the TL-efficiency as a function of HTR was derived in an attempt to measure the absorbed dose without LET information. The feasibility of the HTR method in therapeutic carbon beams was evaluated by comparing the dose estimated by Li3B7O12:Cu and by an ionization chamber. The accuracy of dose estimation in carbon beams was improved by using the HTR method, but there is room for further improvement. The use of Li3B7O12:Cu in heavy charged particle beams can be materialized with further improvement of HTR sensitivity.

Thermoluminescence and photoluminescence study of KY3F10:Ho3+ commercial phosphor powder

Thermoluminescence (TL) and photoluminescence (PL) properties of KY3F10:Ho3+ phosphor powder is reported. The TL measurements were carried out for different heating rates and for various durations of UV exposure. The TL intensity increases with the duration of UV exposure up to 20 min and then decreases. A decrease of the glow peak height was observed for the glow curves with an increasing heating rate. The area under the TL-time plot is calculated for each heating rate at a constant UV dose and it is found to be constant and independent of the heating rate. It is found that the observed decrement in intensity of each glow curve following an increment in the heating rate is not attributed to the thermal quenching effect. Important TL kinetic parameters namely, the activation energy (E) and the frequency factor (s) were calculated using a variable heating rate (VHR) method. The glow peaks obey first order kinetics. PL emission spectra were also investigated at four main excitation wavelengths; namely, 362, 416, 454 and 486 nm. Green emission at 540 nm and faint red emission at 750 nm were observed for all the excitations. The green emission at 540 nm is ascribed to the 5F4–5I8 and 5S2–5I8 transitions and the faint red emission at 750 nm is due to the 5F4–5I7 and 5S2–5I7 transitions. In addition to the sharp green emission at 540 nm, a broad emission centered at 600 nm was observed for excitation wavelength of 362 nm.

Thermoluminescence kinetic analysis and dosimetry features of MgSO 4 :Dy and MgSO 4 :Cu nano-rods

Abstract MgSO 4 :Dy and MgSO 4 :Cu nano-rods (NRs) were synthesized for the first time by semi co- precipitation method. X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS) were utilized for sample characterization. The optimum amount of dysprosium and copper concentrations were obtained both at 0.1 mol% in MgSO 4 :Dy and MgSO 4 :Cu NRs. T m -T stop and computerized glow curve deconvolution (CGCD) methods were used for identifying the number of component glow peaks and kinetic parameters of the synthesized NRs. Initial rise and variable heating rate methods were also used to ensure the reliability of obtained kinetic parameters. Results show that the TL sensitivity of MgSO 4 :Dy is about 7 times more than that of magnesium sulfate doped with Cu. The TL dose response of MgSO 4 :Dy and MgSO 4 :Cu NRs are linear up to absorbed dose of 10 KGy. Other TL dosimetry characteristics of the produced NRs are also presented and discussed.

Evaluation of trapping parameters of annealed natural quartz

The thermoluminescence (TL) trapping parameters of annealed quartz have been investigated. The apparent TL peaks observed at temperatures of 133°C, 211°C, 266°C and 405°C, respectively, were named Peak I, Peak II, Peak III and Peak IV. The Tm − Tstop method is applied to investigate the number of peaks and their positions, and to obtain the trap distributions in the quartz. Peak shape (PS), Hoogenstraaten method (Various Heating Rates Method, VHR), and Computerized Glow Curve Deconvolution (CGCD) are used to evaluate the trapping parameters of the annealed quartz. The glow curve can be considered as a superposition of at least nine overlapping peaks. These peaks show up at 133°C, 211°C, 266°C, 308°C, 333°C, 384°C, 441°C, 466°C and 484°C. The PS method can be only used in evaluating the parameters for Peaks I. The VHR method can be used in evaluating the trapping parameters for the first three peaks. CGCD method is complementary to obtaining parameters for the sub-peaks, and the thermal quenching correction with the Urbach’s method is necessary. The Urbach’s coefficient for the quartz is 30.03kTm.

Trap characteristics of UV-activated Y3(Al,Ga)5O12:Ce3+ phosphors

This paper reports on the trap characteristics of commercially obtained Y3(Al,Ga)5O12:Ce3+ phosphor powder. The effects of UV irradiation time and different heating rates have been discussed using different thermoluminescence (TL) techniques. In the TL glow curves of the Y3(Al,Ga)5O12:Ce3+ phosphor measured in the temperature range between room temperature (RT) and 250°C, two TL peaks were observed, a maximum centered around 74°C and a shoulder at around 163°C when excited with UV radiation. Varying the UV irradiation (exposure) time or hence absorbed dose and heating rate significantly affected the peak intensity (Im) and peak temperature (Tm) of the glow curve. The UV exposure time was varied from 3min to 20min and we noted that the TL intensity increased with UV exposure time in the range 3–15min. This may be explained on the basis of second order recombination kinetics taking place due to a re-trapping process of the excitation. The intensity of the two TL peaks moved to the higher temperature side with an increase in the heating rate. The kinetic parameters at various heating rates namely activation energy (E), order of kinetics (b) and frequency factor (s) of the Y3(Al,Ga)5O12:Ce3+ sample were determined by the variable heating rate method, peak shape method and TL Anal Glow Curve Deconvolution (GCD) techniques.

Near white light emitting ZnAl2O4:Dy3+ nanocrystals: Sol–gel synthesis and luminescence studies

ZnAl2O4:Dy3+ nanoparticles were synthesized using citrate sol–gel method and characterized systematically using X-ray diffraction, scanning electron microscopy and photoluminescence spectroscopy. Emission spectrum of pure ZnAl2O4 shows intense violet blue emission under ultra violet irradiation. Based on electron paramagnetic resonance (EPR) results; it was attributed to presence of singly ionized oxygen vacancy centres in ZnAl2O4. On doping Dy3+ in ZnAl2O4, complete host–dopant energy transfer does not take place. Local structural investigation and lifetime measurements reveal that dysprosium ion is distributed between both Zn2+ and Al3+ sites. Near white light from ZnAl2O4:Dy3+ is attributed to combined host and dopant luminescence. The trap parameters such as activation energy (E) and frequency factor (s) for TSL glow peak 165°C were determined using different heating rate method. Thermally stimulated emission showed the presence of oxygen related defect centre.

Non-isothermal coal char gasification with CO2 in a micro fluidized bed reaction analyzer and a thermogravimetric analyzer

The so-called micro fluidized bed reaction analyzer (MFBRA) and a thermogravimetric analyzer (TGA) were adopted to comparatively investigate the non-isothermal gasification of coal char with CO2. Experimental results demonstrated that heating rate obviously affected the coal char gasification reaction. Raising heating rate evidently increased the temperatures at the initiating reaction (Ti), the maximal reaction rate (Tm) and the finishing reaction (Tf). Nonetheless, it decreased the char conversion at a given reaction temperature and also the activation energy estimated by the single heating rate method. Comparing the data tested by TGA and MFBRA under the same heating rate clarified that the temperatures of Ti, Tm, and Tf were all relatively lower for MFBRA. The difference for such characteristic reaction temperatures between TGA and MFBRA increased with raising the heating rate. The measurement in MFBRA also led to the higher activation energy estimated according to both the single heating rate and the combination heating rate methods. Perhaps all these results are attributed to the lower limitation from heat and transfer including gas diffusion in MFBRA than in TGA.

A thermogravimetric analysis of the combustion kinetics of karanja (Pongamia pinnata) fruit hulls char

The combustion characteristics of Karanj fruit hulls char (KFH-char) was investigated with thermogravimetry analysis (TGA). The TGA outlined the char combustion thermographs at a different heating rate and isoconversional methods expressed the combustion kinetics. The Kissinger–Akahira–Sunose (KAS) and Flynn–Wall–Ozawa (FWO) methods authenticated the char average activation energy at 62.13 and 68.53kJ/mol respectively, enough to derive the char to burnout. However, the Coats–Redfern method verified the char combustion via complex multi-step mechanism; the second stage mechanism has 135kJ/mol average activation energy. The TGA thermographs and kinetic parameters revealed the adequacy of the KFH-char as fuel substrate than its precursor, Karanj fruit hulls (KFH).