Investigation of defect levels in Bi12SiO20 single crystals by thermally stimulated current measurements

2021 ◽  
Author(s):  
Mehmet Isik ◽  
Serdar Delice ◽  
Nizami M Gasanly
Keyword(s):  
Heating Rate ◽  
Czochralski Method ◽  
Intrinsic Defect ◽  
Heating Rates ◽  
Thermally Stimulated Current ◽  
Rate Dependent ◽  
Defect Centers ◽  
Curve Fit ◽  
Maximum Temperatures ◽  
Kinetics Of

Abstract Bi12SiO20 (BSO) single crystal belongs to the sillenite semiconducting family known as defective compounds. The present paper investigates the defect centers in BSO grown by Czochralski method by means of thermally stimulated current (TSC) measurements performed in the 10-260 K range. The TSC glow curve obtained at heating rate of β = 0.1 K/s presented several peaks associated with intrinsic defect centers. The activation energies of defect centers were revealed as 0.09, 0.15, 0.18, 0.22, 0.34, 0.70 and 0.82 eV accomplishing the curve fit analyses method. The peak maximum temperatures and orders of kinetics of each deconvoluted peak were also determined as an outcome of fitting process. TSC experiments were expanded by making the measurements at various heating rates between 0.1 and 0.3 K/s to get information about the heating rate dependent peak parameters.

Thermoluminescence study on TlGaSSe layered single crystals

2014 ◽  
Vol 28 (16) ◽  
pp. 1450133 ◽  
Author(s):  
Serdar Delice ◽  
Nizami M. Gasanly
Keyword(s):  
Single Crystals ◽  
Heating Rate ◽  
Thermal Quenching ◽  
Activation Energies ◽  
Temperature Peak ◽  
Heating Rates ◽  
Quenching Effect ◽  
Defect Centers ◽  
General Order ◽  
Maximum Temperatures

The defect centers in TlGaSSe single crystals have been investigated by performing thermoluminescence (TL) measurements with various heating rates between 0.5 K/s and 1.0 K/s in the temperature range of 10–180 K. The TL spectra, with peak maximum temperatures at 39 K and 131 K, revealed the existences of two defect levels. Curve fitting, initial rise and peak shape methods were used to determine the activation energies of two defect centers. The experimental results also showed that the trapping process was dominated by second-order kinetics for the trap related with low temperature peak while the general order (mixed order) kinetics was dominant for the trap donated to high temperature peak. Furthermore, heating rate dependences and traps distributions were studied for two defect centers separately. Thermal quenching effect dominates the behavior of these defects as the heating rate is increased. Also, quasi-continuous distributions were established with the increase of the activation energies from 16 meV to 27 meV and from 97 meV to 146 meV for the traps associated with the peaks observed at low and high temperatures, respectively.

scholarly journals Synthesis and characterization of a new conjugated polymer containing bithiazole group and its thermal decomposition kinetics

2020 ◽  
Vol 39 (2) ◽  
pp. 227
Author(s):  
Adnan Kurt ◽  
Hacer Andan ◽  
Murat Koca
Keyword(s):  
Thermal Decomposition ◽  
Heating Rate ◽  
Conjugated Polymer ◽  
Three Dimensional ◽  
Heating Rates ◽  
Diffusion Type ◽  
Optimum Heating ◽  
Rate Loss ◽  
Kinetics Of

A new conjugated polymer containing a bithiazole group is prepared by the polycondensation of 2,2'-diamino-4,4'-bithiazole and terephthaldialdehyde in the presence of glacial acetic acid. The kinetics of thermal degradation of the new polymer are investigated by thermogravimetric analysis at different heating rates. The temperature corresponding to the maximum rate loss shifts to higher temperatures with increasing heating rate. The thermal decomposition activation energies of the conjugated polymer in a conversion range of 3–15 % are 288.4 and 281.1 kJ/mol by the Flynn–Wall–Ozawa and Kissinger methods, respectively. The Horowitz–Metzger method shows that the thermodegradation mechanism of the conjugated polymer proceeds over a three-dimensional diffusion type deceleration D3 mechanism. The optimum heating rate is 20 ºC/min.

Study on the Pyrolysis Kinetics of HCl-Pretreated Soybean Stalk

2014 ◽  
Vol 953-954 ◽  
pp. 261-266
Author(s):  
Dong Yu Chen ◽  
Yan Qing Hu ◽  
Qing Yu Liu
Keyword(s):  
Heating Rate ◽  
Temperature Increase ◽  
Loss Rate ◽  
High Efficiency ◽  
Three Dimensional ◽  
Pyrolysis Kinetics ◽  
Heating Rates ◽  
Acid Washing ◽  
Shoulder Peak ◽  
Kinetics Of

To study the influences of the acid-washing on the characteristics of soybean stalk pyrolysis , and search the high-efficiency catalyst for biomass pyrolysis, pyrolysis experiments of soybean stalk pretreated by 0.1mol/L HCl acid solution were performed by nonisothermal thermogravimetric analysis (TGA) at five different heating rates. The results showed the pyrolysis process of HCl-washed soybean stalk can be separated into four stages (water loss, depolymeri-zation and vitrification, thermal decomposition, and carbonization). At the same heating rate, the maximum pyrolysis rate of HCl-washed is larger than untreated soybean stalk, but the corresponding temperature is higher. All the DTG (differential thermogravimetric) curveas appear a smaller shoulder peak respectively. With the heating rate increasing, the main pyrolysis zone of the TG (thermogravimetric) and DTG curves move to the high-temperature direction, and the maximum pyrolysis rate and its corresponding temperature increase too. HCl-wahsed makes the weight loss rate of the final temperature increase 5% approximately. The value area of activation energy of the main pyrolysis area is 140.19~174.59 kJ/mol calculated by the method of Ozawa. The Šatava method inferred the most possible mechanism function of HCl-wahsed soybean stalk is Zhuralev-Lesakin-Tempelman equation, which is three-dimensional diffusion.

scholarly journals Flash Pyrolysis Kinetics of Extracted Lignocellulosic Biomass Components

2021 ◽  
Vol 9 ◽  
Author(s):  
Stefan Pielsticker ◽  
Benjamin Gövert ◽  
Kentaro Umeki ◽  
Reinhold Kneer
Keyword(s):  
Heating Rate ◽  
Molecular Structures ◽  
Small Scale ◽  
Drop Tube ◽  
Pyrolysis Kinetics ◽  
Heating Rates ◽  
Flash Pyrolysis ◽  
Step Model ◽  
The Individual ◽  
Kinetics Of

Biomass is a complex material mainly composed of the three lignocellulosic components: cellulose, hemicellulose and lignin. The different molecular structures of the individual components result in various decomposition mechanisms during the pyrolysis process. To understand the underlying reactions in more detail, the individual components can be extracted from the biomass and can then be investigated separately. In this work, the pyrolysis kinetics of extracted and purified cellulose, hemicellulose and lignin are examined experimentally in a small-scale fluidized bed reactor (FBR) under N2 pyrolysis conditions. The FBR provides high particle heating rates (approx. 104 K/s) at medium temperatures (573–973 K) with unlimited reaction time and thus complements typically used thermogravimetric analyzers (TGA, low heating rate) and drop tube reactors (high temperature and heating rate). Based on the time-dependent gas concentrations of 22 species, the release rates of these species as well as the overall rate of volatiles released are calculated. A single first-order (SFOR) reaction model and a 2-step model combined with Arrhenius kinetics are calibrated for all three components individually. Considering FBR and additional TGA experiments, different reaction regimes with different activation energies could be identified. By using dimensionless pyrolysis numbers, limits due to reaction kinetics and heat transfer could be determined. The evaluation of the overall model performance revealed model predictions within the ±2σ standard deviation band for cellulose and hemicellulose. For lignin, only the 2-step model gave satisfying results. Modifications to the SFOR model (yield restriction to primary pyrolysis peak or the assumption of distributed reactivity) were found to be promising approaches for the description of flash pyrolysis behavior, which will be further investigated in the future.

scholarly journals A study of isochronal austenitization kinetics in a low carbon steel

2014 ◽  
Vol 67 (1) ◽  
pp. 61-66 ◽  
Author(s):  
Maximiano Maicon Batista Lopes ◽  
André Barros Cota
Keyword(s):  
Carbon Steel ◽  
Heating Rate ◽  
Low Carbon Steel ◽  
Carbon Diffusion ◽  
Austenite Formation ◽  
Low Carbon ◽  
Heating Rates ◽  
Initial Microstructure ◽  
Ferrite Structure ◽  
Kinetics Of

The austenite formation under isochronal conditions in Nb microalloyed low carbon steel was studied by means of dilatometric analysis and the data was adjusted to the Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation, for different heating rates and for three initial microstructures. It was shown that the kinetics of austenitization of a pearlite+ferrite structure is faster than that of martensite (tempered martensite) at a heating rate of 0.1ºC/s. For heating rates higher than 0.1ºC/s, the kinetics of austenitization of a martensite structure is faster than of pearlite+ferrite one. The K parameter of the JMAK equation increases with the heating rate for the three previous microstructures and it is greater for the initial microstructure composed of ferrite+pearlite. At lower heating rates, the formation of austenite in this steel is controlled by carbon diffusion, independently of the initial microstructure. At higher heating rates, the formation of austenite from an initial microstructure composed of pearlite and ferrite is controlled by interface-controlled transformation.

scholarly journals Thermal behavior and kinetics of sulfide concentrates

2019 ◽  
Vol 23 (5 Part A) ◽  
pp. 2801-2811 ◽  
Author(s):  
Hui Liu ◽  
Chenglang Xiang ◽  
Rui Hong ◽  
Yimeng Song ◽  
Kan Jin ◽  
...  
Keyword(s):  
Thermal Behavior ◽  
Heating Rate ◽  
Spontaneous Combustion ◽  
Mass Loss Rate ◽  
Heating Rates ◽  
Sulfide Concentrates ◽  
Maximum Mass Loss ◽  
Kinetics Of ◽  
Sulfide Concentrate ◽  
Representative Samples

Thermal behavior of sulfide concentrates can give rise to many serious problems in its storage and transportation. In order to uncover the thermal behavior of sulfide concentrates, as well as obtain the kinetic parameters, four representative samples were tested using TG-DTG-DSC techniques in the presence of oxygen from 20? to 1000? and with three different heating rates of 5, 10, and 15? per minute. Meanwhile, corresponding activation energies of sulfide concentrates were also determined by the Coats-Redfern method (199.4-234.9 kJmol?1 for Sample 1, 203.6-235.9 kJmol?1 for Sample 2, 234.7-255.6 kJmol?1 for Sample 3, and 199.7-254.9 kJmol?1 for Sample 4). Results indicate that the heating rate is an important factor affecting the thermal behavior of sulfide concentrates. The peak temperature corresponding to the maximum mass loss rate of the ore sample at different heating rates is different and the sulfide concentrates at heating rate of 5? per minute is more prone to spontaneous combustion. Furthermore, this thermodynamic method was demonstrated to be effective for investigating and predicting the thermal behavior of sulfide concentrate and the activation energy index was reasonable for determining its spontaneous combustion tendency.

scholarly journals The kinetics of austenite formation at high heating rates

2011 ◽  
Vol 64 (2) ◽  
pp. 163-167 ◽  
Author(s):  
Marciano Quites Macedo ◽  
André Barros Cota ◽  
Fernando Gabriel da Silva Araújo
Keyword(s):  
Heating Rate ◽  
Correlation Coefficients ◽  
Austenite Formation ◽  
Empirical Equations ◽  
Heating Rates ◽  
Critical Temperatures ◽  
High Heating ◽  
Kinetics Of

The variation in critical temperatures for the formation of austenite when increasing the heating rate was studied by dilatometry. The analysis was performed at heating rates between 10 and 90ºC/s. Empirical equations are herein proposed for calculating Ac3 with respect to the heating rate. The results showed that an increase in the heating rate had no influence on Ac1, but Ac3 increased 115ºC. The equations proved to be of a more general use, as they also predicted the results of works on other steels with high values of correlation coefficients.

scholarly journals Melting Kinetics of Nascent Poly(tetrafluoroethylene) Powder

Polymers ◽  
2020 ◽  
Vol 12 (4) ◽  
pp. 791
Author(s):  
Fotis Christakopoulos ◽  
Enrico Troisi ◽  
Theo A. Tervoort
Keyword(s):  
Kinetic Model ◽  
Heating Rate ◽  
Melting Temperature ◽  
Melting Behavior ◽  
Slow Heating ◽  
Heating Rates ◽  
Scanning Calorimetry ◽  
Exponential Factor ◽  
Melting Kinetics ◽  
Kinetics Of

The melting behavior of nascent poly(tetrafluoroethylene) (PTFE) was investigated by way of differential scanning calorimetry (DSC). It is well known that the melting temperature of nascent PTFE is about 344 ∘ C, but reduces to 327 ∘ C for once molten material. In this study, the melting temperature of nascent PTFE crystals was found to strongly depend on heating rate, decreasing considerably for slow heating rates. In addition, during isothermal experiments in the temperature range of 327 ∘ C < T < 344 ∘ C, delayed melting of PTFE was observed, with complete melting only occurring after up to several hours. The melting kinetics of nascent PTFE were analyzed by means of the isoconversional methodology, and an apparent activation energy of melting, dependent on the conversion, was determined. The compensation effect was utilized in order to derive the pre-exponential factor of the kinetic model. The numerical reconstruction of the kinetic model was compared with literature models and an Avrami-Erofeev model was identified as best fit of the experimental data. The predictions of the kinetic model were in good agreement with the observed time-dependent melting of nascent PTFE during isothermal and constant heating-rate experiments.

Effect of Heating Rate on Chemical Kinetics of Chicken Manure With Different Gas Agents

2020 ◽  
Vol 142 (10) ◽  
Author(s):  
Osama M. Selim ◽  
Mohamed S. Hussein ◽  
Ryoichi S. Amano
Keyword(s):  
Carbon Dioxide ◽  
Heating Rate ◽  
Measurement Errors ◽  
Chemical Kinetic ◽  
Chicken Manure ◽  
Slow Heating ◽  
Quasi Equilibrium ◽  
Heating Rates ◽  
Gasification Process ◽  
Kinetics Of

Abstract This paper presents the study on the effect of different heating rates on the pyrolysis and gasification process of the chicken manure. The obtained results are shown by the extent of reaction, the kinetics of the reaction, and differential thermal analysis. In total, 24 cases were carried out; eight heating rates with three different gas agents each. The results show that when using nitrogen or carbon dioxide as gas agents, the reactions were endothermic. Consequently, the energy must be supplied in terms of heating to sustain the reaction. Furthermore, the air gasification was exothermic, which means that the reaction can be sustained without external heating, where the self-ignition was observed between 450 °C–600 °C. The thermal degradation of the three main components of the chicken manure was obtained. The pyrolysis process was divided into two regions at 360 °C and the order of reaction of five for both regions. For the gasification process, it was observed that carbon dioxide had the most complicated mechanism with four stages. Finally, it is recommended to use the lowest heating rate to allow a quasi-equilibrium state through slow heating. Consequently, the delay in response or any transient error can be avoided as they are the main reason for measurement errors. These chemical kinetic parameters can be used in the future for the chicken manure simulation using the order of reaction mechanism for solid-state gasification.

scholarly journals Pyrolysis Reactive Behaviors and Kinetic Characteristics of HSW Vitrinite Coal based on Coats-Redfern and DAEM Models

2021 ◽  
Author(s):  
Ruihan Wang ◽  
Qiang Wang ◽  
Zhuangmei Li ◽  
Zhe Liu ◽  
Yong Wu ◽  
...  
Keyword(s):  
Activation Energy ◽  
Weight Loss ◽  
Heating Rate ◽  
Loss Rate ◽  
Coal Tar ◽  
Coal Pyrolysis ◽  
Heating Rates ◽  
Weight Loss Rate ◽  
Weight Loss Behavior ◽  
Kinetics Of

Abstract In this work, the weight loss behavior of vitrinite in hongshiwan coal at different heating rates was investigated by thermogravimetric mass spectrometry (TG-MS). Then Coats-Redfern and DAEM models were established to analyze the kinetics of coal pyrolysis. The results show that the weight loss rate of pyrolysis decreased with the increase of heating rate. When the pyrolysis temperature reaches 400–500°C, the weight loss rate reaches the maximum, which is 0.1593, 0.1539, 0.1478 and 0.1414%/°C respectively at the heating rates of 5, 10, 15 and 20°C/min, With the increase of heating rate, the corresponding temperature peaks of the five pyrolysis gases are shifted to the high temperature direction, and the amount of gas escaping is increasing. The trend of higher heating rate delayed the release of volatile compounds was consistent with TG-DTG results. Two kinetic models both prove that the activation energy of coal pyrolysis increases with the increase of temperature. The maximum activation energy occurs between 600 ℃ and 900 ℃, because the multi condensation of coal tar and the re solidification of semi coke will occur in this temperature range.

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