摘要 :
Pure Fe3O4 and Mn-doped Fe3O4 nanoparticles were synthesized by simple wet chemical reduction technique using nontoxic precursors. Manganese doping of two concentrations, 10 and 15%, were employed. All the three synthesized nanopa...
展开
Pure Fe3O4 and Mn-doped Fe3O4 nanoparticles were synthesized by simple wet chemical reduction technique using nontoxic precursors. Manganese doping of two concentrations, 10 and 15%, were employed. All the three synthesized nanoparticles were characterized by stoichiometry, crystal structure, and surface morphology. Thermal studies on as-synthesized nanoparticles of pure ferrite (Fe3O4) and manganese (Mn) doped ferrites were carried out. The thermal analysis of the three as-synthesized nanoparticles was done by thermogravimetric (TG), differential thermogravimetric, and differential thermal analysis techniques. All the thermal analyses were done in nitrogen atmosphere in the temperature range of 308-1233 K. All the thermocurves were recorded for three heating rates of 10, 15, and 20 K min(-1). The TG curves showed three steps thermal decomposition for Fe3O4 and two steps thermal decompositions for Mn-doped Fe3O4 nanoparticles. The kinetic parameters of the three as-synthesized nanoparticles were evaluated from the thermocurves employing Kissinger-Akahira-Sunose (KAS) method. The thermocurves and evaluated kinetic parameters are discussed in this paper.
收起
摘要 :
The thermal decomposition of lanthanide complexes, with a general formula: [LnL(NO3)2](NO3), where Ln = La, Pr, Nd, Sm, Gd, Tb, Dy, and Er; and L = bis-(salicyladehyde)-1,3-propylenediimine Schiff base ligand, was studied by therm...
展开
The thermal decomposition of lanthanide complexes, with a general formula: [LnL(NO3)2](NO3), where Ln = La, Pr, Nd, Sm, Gd, Tb, Dy, and Er; and L = bis-(salicyladehyde)-1,3-propylenediimine Schiff base ligand, was studied by thermogravimetric (TG) and derivative thermogravimetric (DTG) techniques. The TG and DTG data indicated that all complexes are thermostable up to 398 K. The thermal decomposition of all Ln(III) complexes was a two-stage process and the final residues were Ln _2O_3 (Ln = La, Nd, Sm, Gd, Dy, Er), Tb_4O _7, and Pr_6 O_(11). The activation energies of thermal decomposition of the complexes were calculated from analysis of the TG-DTG curves using the Kissinger, Friedman, and Flynn-Well-Ozawa methods.
收起
摘要 :
Thermal analysis and differential thermal analysis offers a novel means of studying the desorption of acids such as stearic acid from clay surfaces. Both adsorption and chemisorption can be distinguished through the differences in...
展开
Thermal analysis and differential thermal analysis offers a novel means of studying the desorption of acids such as stearic acid from clay surfaces. Both adsorption and chemisorption can be distinguished through the differences in the temperature of mass losses. Increased adsorption is achievable by adsorbing onto a surfactant adsorbed montmorillonite. Stearic acid sublimes at 179 A degrees C but when adsorbed upon montmorillonite sublimes at 207 and 248 A degrees C. These mass loss steps are ascribed to the desorption of the stearic acid on the external surfaces of the organoclays and from the de-chemisorption from the surfactant held in the interlayer of the montmorillonite.
收起
摘要 :
Oxygen concentration and biomass content are key factors of the combustion of a mixed sample of biomass and coal gangue. Herein, we studied the effect of oxygen concentration and biomass content and their corresponding combustion ...
展开
Oxygen concentration and biomass content are key factors of the combustion of a mixed sample of biomass and coal gangue. Herein, we studied the effect of oxygen concentration and biomass content and their corresponding combustion and kinetic characteristics. Experiments were conducted in a thermogravimetric analyzer under an O2/CO2 atmosphere. Results showed that the fixed carbon combustion temperature, ignition temperature, and exothermic peak temperature decreased with oxygen concentration increased. By contrast, the burning rate of volatilization increased with oxygen concentration increased. The total and maximum loss rates of the sample, the burnout temperature, the exothermic peak temperature, and the comprehensive combustion index S gradually increased. As oxygen concentration increased, the activation energy at the initial stage of combustion gradually decreased, whereas the activation energy at the end of the reaction gradually increased when the oxygen concentration increased. Activation energy could be rapidly reduced after a small amount of biomass was added, whereas the biomass content had no significant influence on the activation energy of the samples at the end of combustion.
收起
摘要 :
In the present study, we synthesize nanoneedle structures of MnO_2/graphene nanocomposites (N-RGO/ MnO_2) and birnessite-type MnO_2/graphene nanocomposites (B-RGO/MnO_2). The morphologies and microstructures of as-prepared composi...
展开
In the present study, we synthesize nanoneedle structures of MnO_2/graphene nanocomposites (N-RGO/ MnO_2) and birnessite-type MnO_2/graphene nanocomposites (B-RGO/MnO_2). The morphologies and microstructures of as-prepared composites are characterized by X-ray diffractometry, field-emission scanning electron microscopy, X-ray photoelectron spectroscopy, and thermogravimetric analysis. Our characterizations indicate that nanoneedle structures of MnO_2 and birnessite-type MnO_2 are successfully formed on graphene surfaces. Capacitive properties of the N-RGO/MnO_2 and B-RGO/MnO_2 electrodes are measured using cyclic voltammetry, galvanostatic charge/discharge tests, and electrochemical impedance spectroscopy in a three-electrode experimental setup using a 1 M Na_2SO_4 aqueous solution as the electrolyte. The N-RGO/MnO_2 electrode displays a specific capacitance as high as 327.5 F g~(-1) at 10 mV s~(-1), which is higher than that of a B-RGO/MnO_2 electrode (248.5 F g~(-1)). It is believed that the nanoneedle structure of MnO_2 shows excellent electrochemical properties than birnessite-type MnO_2 for the electrode materials for supercapacitors.
收起
摘要 :
In the present study three thermoanalytical methods: differential thermal analysis (DTA), thermogravimetric analysis (TGA), and derivative thermogravimetric analysis (DTG) were used to investigate the thermal behavior of medicinal...
展开
In the present study three thermoanalytical methods: differential thermal analysis (DTA), thermogravimetric analysis (TGA), and derivative thermogravimetric analysis (DTG) were used to investigate the thermal behavior of medicinal plant raw materials. In order to describe DTA curve, designation of the onset Ti, and peak Tp, temperatures was required. In TGA the mass losses Δm, and in DTG the temperature range of peak ΔT, peak temperature Tp, and peak height h, were recorded. All parameters were read for three stages of the thermal decomposition of plant samples which resulted in obtaining eighteen thermal variables for each sample. Some similarities in the course of thermal decomposition of the same plant organs were recognized, but complexity of the obtained data made it very difficult to determine if they could differentiate between medicinal plant materials and which of them encode the most valuable information about the studied herbals. In order to confirm the existence of any relations between the chemical composition of medicinal plants and their thermal decomposition and to find out which thermoanalytical variables or decomposition stages can be considered as the most significant in terms of their evaluation, it was decided to apply fully connected feedforward artificial neural networks (ANN). Two different training algorithms were used to address the problem: back-propagation of error and conjugate gradient descent. To verify the results two-dimensional (2-D) Kohonen self-organizing feature maps (SOFMs) were employed. Two alternative datasets of thirteen key variables discriminating plant samples have been proposed.
收起
摘要 :
Carbothermic reduction of chromite is an important industrial process for extracting chromium from the chromite. To have a better understanding of the effect of iron on the carbothermic reduction of chromite, the reduction of synt...
展开
Carbothermic reduction of chromite is an important industrial process for extracting chromium from the chromite. To have a better understanding of the effect of iron on the carbothermic reduction of chromite, the reduction of synthetic chromite (FeCr_(2)O_(4)) by graphite with/without the addition of iron powder was investigated in this paper by Thermogravimetric Analysis (TGA) in argon atmosphere. The fractional reduced samples were examined by SEM/EDS and XRD analysis, and the reduction process was thermodynamically and kinetically evaluated. The experimental results show that the iron powder addition enhances the reduction of FeCr_(2)O_(4) and this effect increases when increased amounts of iron powder are added. This phenomenon is attributed to the in situ dissolution of chromium into the iron and mixed carbide (Cr,Fe)_(7)C_(3), which can decrease the activity of the nascent chromium formed by the reduction of the FeCr_(2)O_(4). The experimental results indicate that the reduction of FeCr_(2)O_(4) with up to 80 wt.% iron powder addition is likely to be a single-step process and the kinetic analysis suggests that the reduction reaction is likely to be either (a) chemical reaction at the surface of FeCr_(2)O_(4) or (b) diffusional dissolution of the product (FeCr_(2)) into the iron/alloy particles or the mixed control of (a) and (b).
收起
摘要 :
Understanding and controlling the performance of ceria nanoparticle (CNP) catalysts requires knowledge of the detailed structure and property of CNP surfaces and any attached functional groups. Here we report thermogravimetric ana...
展开
Understanding and controlling the performance of ceria nanoparticle (CNP) catalysts requires knowledge of the detailed structure and property of CNP surfaces and any attached functional groups. Here we report thermogravimetric analysis results showing that hydrothermally synthesized~30 nm CNPs are decorated with 12.9 hydroxyl groups per nm~2 of CNP surface. Quantum mechanical calculations of the density and distribution of bound surface groups imply a scaling relationship for surface group density that balances formal charges in the functionalized CNP system. Computational results for CNPs with only hydroxyl surface groups yield a predicted density of bound hydroxyl groups for ~30 nm CNPs that is ~33% higher than measured densities. Quantitative agreement between predicted and measured hydroxyl surface densities is achieved when calculations consider CNPs with both -OH and -O_x surface groups. For this more general treatment of CNP surface functionalizations, quantum mechanical calculations predict a range of stable surface group configurations that depend on the chemical potentials of O and H, and demonstrate the potential to tune CNP surface functionalizations by varying temperature and/or partial pressures of O_2 and H_2O.
收起
摘要 :
The surface functionalization of silica by alkoxysilane can improve its dispersion into polymers by beneficially modifying interparticle and particle–polymer interactions. Thermogravimetric analysis (TGA) has been used to study t...
展开
The surface functionalization of silica by alkoxysilane can improve its dispersion into polymers by beneficially modifying interparticle and particle–polymer interactions. Thermogravimetric analysis (TGA) has been used to study the kinetics of binding a bifunctional alkoxysilane onto silica over the temperature range of 50 to 110 °C. DerivativeTGAcurves of the reacted silica show distinct peaks, which correspond to the alkoxysilane bound to one or two surface silanol sites. Binding at two silanol sites is postulated to occur in a two-step series reaction model. An Arrhenius analysis for the alkoxysilane binding reactions shows that the activation energies of the two reaction steps are similar, which is expected because the alkoxysilane contains two identical binding groups. This work demonstrates the suitability of theTGAtechnique to investigate the reaction kinetics for modifying the surface of silica.
收起
摘要 :
The use of magnetic nanoparticles (MNPs) in real-world applications is often limited by the lack of stable solutions of monodisperse NPs in appropriate solvents. We report a facile one-pot ligand exchange reaction that is fast, ef...
展开
The use of magnetic nanoparticles (MNPs) in real-world applications is often limited by the lack of stable solutions of monodisperse NPs in appropriate solvents. We report a facile one-pot ligand exchange reaction that is fast, efficient, and thorough for the synthesis of hydrophilic MNPs that are readily dispersed in polar organic and protic solvents (polarity index = 3.9?7.2) including alcohols, THF, DMF, and DMSO for years without precipitation. We emphasize the rational selection of small-molecule ligands such as 4- hydroxybenzoic acid (HBA), 3-(4-hydroxyphenyl)propionic acid (HPP), and gallic acid (GAL) that provide strong bonding with the MNP (FePt and FeO_x) surfaces, hydrophilic termini to match the polarity of target solvents, and offer the potential for hydrogen-bonding interactions to facilitate incorporation into polymers and other media. Areal ligand densities (Σ) calculated based on the NP core size from transmission electron microscopy (TEM) images, and the inorganic fractions of NPs derived from thermogravimetric analysis (TGA) indicated a significant (2?4 times) increase in the ligand coverage after the exchange reactions. Fourier transform infrared spectrometry (FTIR) and ~1H nuclear magnetic resonance (NMR) studies also confirmed anchoring of carboxyl groups on NP surfaces. In addition, we demonstrate a facile one-step in situ synthesis of FePt NPs with aromatic ligands for better dispersibility in solvents of intermediate polarity (polarity index = 1.0?3.5) such as toluene, chlorobenzene, and dichloromethane. The creation of stable dispersions of NPs in solvents across the polarity spectrum opens up new applications and new processing widows for creating NP composites in a variety of host materials.
收起
原文获取