Kinetics of nonisothermal dehydration of unirradiated and γ-ray irradiated neodymium (III) acetate hydrate

2019 ◽  
Vol 107 (2) ◽  
pp. 165-178
Author(s):  
Noura Mossaed Saleh ◽  
Ghada Adel Mahmoud ◽  
AbdelRahman AbdelMonem Dahy ◽  
Soliman Abdel-Fadeel Soliman ◽  
Refaat Mohamed Mahfouz
Keyword(s):  
Absorbed Dose ◽  
Isoconversional Methods ◽  
Gas Diffusion ◽  
Conversion Degree ◽  
Monoclinic System ◽  
Air Atmosphere ◽  
Dehydration Reactions ◽  
Γ Ray ◽  
Acetate Hydrate ◽  
Kinetics Of

Abstract Kinetics of dehydration of unirradiated and γ-ray irradiated neodymium (III) acetate hydrate with 103 kGy total γ-ray dose absorbed in air atmosphere were studied by isoconversional nonisothermal method. The dehydration proceeds in two steps with the elimination of 0.8 and 0.4 mol of H2O, respectively. This result indicates that the investigated neodymium (III) acetate hydrate contains 1.2 mol of crystalline water in its structure. The dehydration reactions are best described by nucleation (A2 model) and gas diffusion (D4 model) for unirradiated and γ-ray irradiated samples, respectively. Analysis of the kinetic data using linear and nonlinear isoconversional methods showed that the apparent activation energy, Ea (kJ/mol) is dependent on the conversion degree, α, of the dehydration process. The Ea−α plots for both unirradiated and γ-ray irradiated neodymium (III) acetate hydrate showed that the dehydration is a complex process and contains multistep reactions. The results showed that γ-ray irradiation has a significant effect on the kinetics and thermodynamic parameters of the dehydration reaction. Powder X-ray diffraction showed that neodymium (III) acetate hydrate has a monoclinic system (SG P2/m) and no phase transformation was detected by γ-ray irradiation up to 103 kGy absorbed dose. The system maintains the same crystal structure before and after dehydration.

Thermal decomposition of un-irradiated and γ-ray irradiated holmium acetate tetrahydrate. Part 1: kinetics of nonisothermal dehydration of un-irradiated and γ-ray irradiated Ho(CH3COO)3⋅4H2O

2018 ◽  
Vol 106 (9) ◽  
pp. 775-785 ◽  
Author(s):  
Norhan Farghly Rashwan ◽  
Hossam Wahid ◽  
AbdelRahman AbdelMonem Dahy ◽  
Refaat Mohamed Mahfouz
Keyword(s):  
Thermal Decomposition ◽  
Absorbed Dose ◽  
Isoconversional Methods ◽  
Reaction Model ◽  
Host Lattice ◽  
Isothermal Kinetics ◽  
Conversion Degree ◽  
Acetate Tetrahydrate ◽  
Heating Rates ◽  
Γ Ray

Abstract Nonisothermal dehydration of un-irradiated and γ-ray irradiated holmium acetate tetrahydrate with 103 kGy total γ-ray dose absorbed was studied in air atmosphere. The thermal decomposition experiments were conducted at heating rates of (5, 7.5 and 10°C/min). The results showed that for un-irradiated material, the dehydration process proceeds in two decomposition steps with the elimination of 3.0 and 1.0 moles of H2O, respectively. The apparent activation energy, Ea, as given by both linear and nonlinear isoconversional methods showed dependence upon the conversion degree, α, in the range of 0.2–0.75 for the two dehydration steps. In the first dehydration step, the Ea decreases from 228.0 kJ/mol at the beginning of the decomposition to ≈64.0 kJ/mol at the end of the process. In the second dehydration step, the Ea increases from 42.0 to 72.0 kJ/mol by progressively increasing in α. Compared with solid state reaction models, the two reactions are best described by diffusion (D4) and nucleation (A3) models for the first and second dehydration steps, respectively. The results derived from nonisothermal data present a reliable prediction of isothermal kinetics. Straight lines and reduced time plots methods were applied for the determination of the kinetic triplet [Ea, ln A, and reaction model f(α)] from predicted isothermal data. For γ-ray irradiated samples of Ho(CH3COO)3⋅4H2O with 103 kGy total absorbed dose, the dehydration proceeds in two overlapped steps controlled by D3 model. X-ray data showed phase transformation from monoclinic (SG P2/m) to tetragonal phase (SG P4/mmm) by the elimination of water content from the entire structure of Ho(CH3COO)3⋅4H2O. γ-Ray irradiation effects on the thermal decomposition of Ho(CH3COO)3⋅4H2O were evaluated and discussed based on the formation of trapped electrons, point defects, cation and anion vacancies and cluster imperfections in the host lattice of Ho(CH3COO)3⋅4H2O.

scholarly journals Gasification Kinetics of Bituminous Coal Char in the Mixture of CO2, H2O, CO, and H2

Energies ◽  
2019 ◽  
Vol 12 (3) ◽  
pp. 496 ◽  
Author(s):  
Junwei Chen ◽  
Weibin Chen ◽  
Yang Jiao ◽  
Xidong Wang
Keyword(s):  
Bituminous Coal ◽  
Gas Diffusion ◽  
Coal Char ◽  
Conversion Degree ◽  
Diffusion Control ◽  
Diffusion Resistance ◽  
Gasification Process ◽  
Control Step ◽  
Kinetics Of ◽  
Gasification Temperature

The gasification kinetics of bituminous coal char was investigated in a mixture of CO2, H2O, CO, H2, and N2 under isothermal conditions. In addition, the impacts of gasification temperature, gasification time, and gas composition on the gasification process were analyzed. As the experimental results suggest, there is a significant increase of the carbon conversion degree of bituminous coal char not just when gasification temperature and time increase, but also when H2 and CO concentration decreases. The kinetics of bituminous coal char in the gasification process was successfully modeled as a shrinking unreacted core. It is concluded that the gasification of bituminous coal char is controlled by an internal chemical reaction in the early stage and diffusion in the later stage. The activation energies of bituminous coal char gasification for different stages were studied. Moreover, it is proposed for the first time, to our knowledge, that the diffusion-control step is significantly shortened with the decrease of the CO2/H2O ratio. As scanning-electron-microscopy results suggest, bituminous coal char gasified in CO2/H2O = 1/3 atmosphere has numerous inner pores (0–5 m). Therefore, in the process of gasification, the inner pores provide a gas channel that reduces the gas diffusion resistance and thus shortens the diffusion-control step. These results can serve as a reference for industrialized application of the technology of coal gasification direct reduced iron.

scholarly journals Determination of the Kinetics and Thermodynamic Parameters of Lignocellulosic Biomass Subjected to the Torrefaction Process

Materials ◽  
2021 ◽  
Vol 14 (24) ◽  
pp. 7877
Author(s):  
Maja Ivanovski ◽  
Aleksandra Petrovic ◽  
Irena Ban ◽  
Darko Goricanec ◽  
Danijela Urbancl
Keyword(s):  
Carbon Content ◽  
Isoconversional Methods ◽  
Conversion Degree ◽  
Heating Rates ◽  
Miscanthus X Giganteus ◽  
Main Method ◽  
Air Atmosphere ◽  
Solid Biofuels ◽  
Lignocellulosic Feedstocks

The torrefaction process upgrades biomass characteristics and produces solid biofuels that are coal-like in their properties. Kinetics analysis is important for the determination of the appropriate torrefaction condition to obtain the best utilization possible. In this study, the kinetics (Friedman (FR) and Kissinger–Akahira–Sunose (KAS) isoconversional methods of two final products of lignocellulosic feedstocks, miscanthus (Miscanthus x giganteus) and hops waste (Humulus Lupulus), were studied under different heating rates (10, 15, and 20 °C/min) using thermogravimetry (TGA) under air atmosphere as the main method to investigate. The results of proximate and ultimate analysis showed an increase in HHV values, carbon content, and fixed carbon content, followed by a decrease in the VM and O/C ratios for both torrefied biomasses, respectively. FTIR spectra confirmed the chemical changes during the torrefaction process, and they corresponded to the TGA results. The average Eα for torrefied miscanthus increased with the conversion degree for both models (25–254 kJ/mol for FR and 47–239 kJ/mol for the KAS model). The same trend was noticed for the torrefied hops waste samples; the values were within the range of 14–224 kJ/mol and 60–221 kJ/mol for the FR and KAS models, respectively. Overall, the Ea values for the torrefied biomass were much higher than for raw biomass, which was due to the different compositions of the torrefied material. Therefore, it can be concluded that both torrefied products can be used as a potential biofuel source.

Non-Isothermal Degradation Kinetics of Asphalt in Relation to its Chemical Composition

2016 ◽  
Vol 701 ◽  
pp. 315-319
Author(s):  
Kevinilo P. Marquez ◽  
Rheo B. Lamorena-Lim
Keyword(s):  
Chemical Composition ◽  
Degradation Kinetics ◽  
Isoconversional Methods ◽  
Isoconversional Method ◽  
Conversion Degree ◽  
Gradual Change ◽  
Scanning Calorimetry ◽  
Variable Nature ◽  
Increasing Temperature ◽  
Kinetics Of

Analysis of the complex and variable nature of the chemical composition of asphalt has been a challenge to engineers and scientists, especially as a means to understand its behavior and suggest ways to improve its properties. In this study, the thermal behavior and the non-isothermal degradation kinetics were analyzed using the isoconversional methods, through Thermogravimetric analysis (TGA) and Differential Scanning Calorimetry (DSC). TGA and DSC data show gradual change in the mass of the material at increasing temperature, suggesting behavior typical of a homogenous mixture. Kinetic analysis from the TGA data using the Starink modification of the Kissinger-Akahira-Sunose Isoconversional method show an apparent increase in the magnitude of the activation energies at different conversion degree, which suggests a gradual change in the composition of the material at each successive conversion due to a single heat-promoted transformation of each of the components.

Effect of ionizing radiation on the kinetics of hydrogenation on the Ni-MgO mixed catalyst

1982 ◽  
Vol 47 (7) ◽  
pp. 1780-1786 ◽  
Author(s):  
Rostislav Kudláček ◽  
Jan Lokoč
Keyword(s):  
Experimental Data ◽  
Activation Energy ◽  
Liquid Phase ◽  
Ionizing Radiation ◽  
Oxide Catalyst ◽  
Absorbed Dose ◽  
Hydrogenation Rate ◽  
Solution Composition ◽  
Mixed Catalyst ◽  
Kinetics Of

The effect of gamma pre-irradiation of the mixed nickel-magnesium oxide catalyst on the kinetics of hydrogenation of maleic acid in the liquid phase has been studied. The changes of the hydrogenation rate are compared with the changes of the adsorbed amount of the acid and with the changes of the solution composition, activation energy, and absorbed dose of the ionizing radiation. From this comparison and from the interpretation of the experimental data it can be deduced that two types of centers can be distinguished on the surface of the catalyst under study, namely the sorption centres for the acid and hydrogen and the reaction centres.

scholarly journals Kinetic Analysis of the Thermal Decomposition of Iron(III) Phosphates: Fe(NH3)2PO4 and Fe(ND3)2PO4

2020 ◽  
Vol 21 (3) ◽  
pp. 781
Author(s):  
Isabel Iglesias ◽  
José A. Huidobro ◽  
Belén F. Alfonso ◽  
Camino Trobajo ◽  
Aránzazu Espina ◽  
...  
Keyword(s):  
Thermal Decomposition ◽  
Kinetic Analysis ◽  
Room Temperature ◽  
Isoconversional Methods ◽  
Iron Phosphate ◽  
Dihydrogen Phosphate ◽  
Monoclinic System ◽  
Space Group ◽  
X Ray ◽  
Group A

The hydrothermal synthesis and both the chemical and structural characterization of a diamin iron phosphate are reported. A new synthetic route, by using n-butylammonium dihydrogen phosphate as a precursor, leads to the largest crystals described thus far for this compound. Its crystal structure is determined from single-crystal X-ray diffraction data. It crystallizes in the orthorhombic system (Pnma space group, a = 10.1116(2) Å, b = 6.3652(1) Å, c = 7.5691(1) Å, Z = 4) at room temperature and, below 220 K, changes towards the monoclinic system P21/n, space group. The in situ powder X-ray thermo-diffraction monitoring for the compound, between room temperature and 1100 K, is also included. Thermal analysis shows that the solid is stable up to ca. 440 K. The kinetic analysis of thermal decomposition (hydrogenated and deuterated forms) is performed by using the isoconversional methods of Vyazovkin and a modified version of Friedman. Similar values for the kinetic parameters are achieved by both methods and they are checked by comparing experimental and calculated conversion curves.

scholarly journals The Kinetics Of Ti-1Al-1Mn Alloy Thermal Oxidation And Charcteristic Of Oxide Layer

2015 ◽  
Vol 60 (2) ◽  
pp. 735-738 ◽  
Author(s):  
D. Klimecka-Tatar ◽  
S. Borkowski ◽  
P. Sygut
Keyword(s):  
Titanium Alloy ◽  
Artificial Saliva ◽  
Electrochemical Corrosion ◽  
Mass Gain ◽  
Ti Alloy ◽  
Metallic Materials ◽  
Cyclic Annealing ◽  
Air Atmosphere ◽  
Kinetic Oxidation ◽  
Kinetics Of

Abstract The main goal of the study was to carry out the treatment of cyclic oxidation of Ti alloy (Ti-1Al-1Mn) in air atmosphere. Based on measurements of mass gain of titanium alloy samples (Ti-1Al-1Mn) the kinetic oxidation curves during cyclic annealing were determined. The oxidized surface of the titanium alloy was carefully observed with optical microscopy equipment and the geometrical development, shape and surface morphology were defined. The phase composition of the obtained oxide layers on the Ti-alloy with qualitative analysis of the X-ray were defined. Since titanium alloys are among the most widely used metallic materials in dental prosthetics the corrosion measurements in a solution simulating the environment of the oral cavity were carried out. The results confirmed that the used titanium alloy easily covered with oxides layers, which to some extent inhibit the processes of electrochemical corrosion in artificial saliva solution.

Thermal Analysis on Dehydroxylation of Sol-Gel Derived Zinc Doped Calcium Phosphate Powders

2015 ◽  
Vol 1115 ◽  
pp. 353-356
Author(s):  
Gunawan ◽  
I. Sopyan
Keyword(s):  
Phase Stability ◽  
Room Temperature ◽  
Sol Gel ◽  
Conversion Degree ◽  
Zn Concentration ◽  
Calculated Activation Energy ◽  
Controlling Processes ◽  
Kinetics Of ◽  
Calculated Activation ◽  
Wall Method

The dehydroxylation of Zn free and 4 mol% Zn CaP powder was investigated using thermogravimetric analysis over the range of room temperature to 1200 °C. The kinetic result of dehydroxylation of Zn free and 4 mol% Zn CaP was calculated by means of the Ozawa–Flynn–Wall method. The XRD result indicated that the amount of Zn incorporated in HA lattice influences the phase stability of HA as it decreases with an increase in Zn concentration. According to calculated activation energy and conversion degree, the kinetics of HA dehydroxylation was identified, which included four successive conversion stages kinetically controlled by different rate-controlling processes. The dehydroxylation analysis of TG/DTG data show that Zn incorporation in HA lattice influences the phase stability of HA.

scholarly journals A Comparative Study on Cure Kinetics of Layered Double Hydroxide (LDH)/Epoxy Nanocomposites

2020 ◽  
Vol 4 (3) ◽  
pp. 111
Author(s):  
Zohre Karami ◽  
Seyed Mohammad Reza Paran ◽  
Poornima Vijayan P. ◽  
Mohammad Reza Ganjali ◽  
Maryam Jouyandeh ◽  
...  
Keyword(s):  
Layered Double Hydroxide ◽  
Cure Kinetics ◽  
Frequency Factor ◽  
Isoconversional Methods ◽  
Epoxide Ring ◽  
Epoxy Nanocomposites ◽  
Scanning Calorimetry ◽  
Noncatalytic Reaction ◽  
Double Hydroxide ◽  
Kinetics Of

Layered double hydroxide (LDH) minerals are promising candidates for developing polymer nanocomposites and the exchange of intercalating anions and metal ions in the LDH structure considerably affects their ultimate properties. Despite the fact that the synthesis of various kinds of LDHs has been the subject of numerous studies, the cure kinetics of LDH-based thermoset polymer composites has rarely been investigated. Herein, binary and ternary structures, including [Mg0.75 Al0.25 (OH)2]0.25+ [(CO32−)0.25/2∙m H2O]0.25−, [Mg0.75 Al0.25 (OH)2]0.25+ [(NO3−)0.25∙m H2O]0.25− and [Mg0.64 Zn0.11 Al0.25 (OH)2]0.25+ [(CO32−)0.25/2∙m H2O]0.25−, have been incorporated into epoxy to study the cure kinetics of the resulting nanocomposites by differential scanning calorimetry (DSC). Both integral and differential isoconversional methods serve to study the non-isothermal curing reactions of epoxy nanocomposites. The effects of carbonate and nitrate ions as intercalating agents on the cure kinetics are also discussed. The activation energy of cure (Eα) was calculated based on the Friedman and Kissinger–Akahira–Sunose (KAS) methods for epoxy/LDH nanocomposites. The order of autocatalytic reaction (m) for the epoxy/Mg-Al-NO3 (0.30 and 0.254 calculated by the Friedman and KAS methods, respectively) was smaller than that of the neat epoxy, which suggested a shift of the curing mechanism from an autocatalytic to noncatalytic reaction. Moreover, a higher frequency factor for the aforementioned nanocomposite suggests that the incorporation of Mg-Al-NO3 in the epoxy composite improved the curability of the epoxy. The results elucidate that the intercalating anions and the metal constituent of LDH significantly govern the cure kinetics of epoxy by the participation of nitrate anions in the epoxide ring-opening reaction.

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