Thermogravimetry Measurements Research Articles

Controlled oxidation of aluminum nanoparticles

A theoretical and experimental analysis of the oxidation of aluminum nanoparticles is presented. The modeling of the oxidation is based on a modified Mott–Cabrera model. Mass and heat transfer, both at individual particle level are implemented. An investigation of the final oxide layer in the passivation process is carried out for nanometer sized particles. The model predicts the effect of the particle’s radii on the oxide layer growth and on the particle’s temperature. A 2nm particle reaches a passive layer of 8Å in almost 2000s increasing its temperature from 300K to a peak of almost 500K. Parametric analysis on the influence of temperature and partial pressure of oxygen are performed. Thermo-gravimetry measurements are used and compared to the model’s results. Good agreement between the model and the experimental results, especially at low temperatures, makes it possible to estimate and devise a strategy for efficient and safe passivation of aluminum nanopowders.

Metal-organic frameworks-derived mesoporous carbon for high performance lithium–selenium battery

Selenium was confined in mesoporous carbon matrix derived from porous metal-organic frameworks (meso-C@Se) as cathode material for lithium-selenium rechargeable batteries. It was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and thermogravimetry (TG) measurements. It is found that the selenium was dispersed inside the pores of carbon materials. The electrochemical performance of meso-C@Se cathode was tested by cyclic voltammetry (CV), galvanostatic charge-discharge, and electrochemical impedance spectroscopy. It is found that meso-C@Se cathode has great cycling stability, Coulombic efficiency and high rate performance. The meso-C@Se composite with selenium content of 48 wt% displays an initial discharge capacity of 641 mAh g−1 and a reversible capacity of 306.9mAhg−1 after 100 cycles at a current density of 337.5mAg−1 (0.5C). Particularly, the meso-C@Se cathode displays the initial discharge capacity and 100th cycle reversible capacity of 659.9 and 279.5mAhg−1 at 2C, showing great high-rate performance. These favourable performance should attribute to the high conductivity of carbon matrix significantly decreases its charge transfer resistance and effectively suppresses the shuttle effect of polyselenides from the composite cathode.

Low-temperature exothermic reactions in fully-dense Al/MoO3 nanocomposite powders

Low-temperature redox reactions in nano-thermites prepared by arrested reactive milling (ARM) were described by Cabrera–Mott (CM) mechanism, in which the growth of very thin oxide layers is accelerated by an electric field induced across such layers. A reaction mechanism combining the initial CM step with following oxidation steps identified earlier for oxidation of Al and representing growth of and phase transitions in various polymorphs of alumina was proposed and shown to be valid for different Al/CuO nanocomposite powders prepared by ARM. This work explores whether a similar multi-step reaction mechanism can be applied to describe thermal initiation in another ARM-prepared thermite system, Al/MoO3. The powder particles comprise a fully dense Al matrix with nano-sized MoO3 inclusions. The structure, morphology, and compositions of the prepared powder with composition 8Al·MoO3 were characterized using X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy. Differential scanning calorimetry (DSC) and thermogravimetry (TG) data were collected at varied heating rates, in addition to micro-calorimetry data collected both isothermally and at several very low heating rates. The shapes of the recorded DSC and TG traces at low temperatures were substantially different compared to those obtained earlier for Al/CuO. A weight loss representing dehydration of the composite material was observed at low temperature TG measurements. The effect of this endothermic process was quantified to account for it in the micro-calorimetry and DSC experiments. Kinetics of the initial exothermic redox reaction observed in both DSC and micro-calorimetry experiments could be successfully described by the CM mechanism. Reactions at elevated temperatures were also well described by the previously identified sequence of steps associated with phase changes and oxidation of various alumina polymorphs. A modification to the CM kinetics was necessary to describe an intermediate range of temperatures, between approximately 400 and 600K. This modification is suggested to represent a temperature induced change in the structure of a very thin precursor aluminum oxide layer separating Al and MoO3.

Characterization and Acidic Properties of AlMCM-41 Prepared by Conventional and Post-Synthesis Alumination

The catalysts analysed in the current work are variations of MCM-41. The properties of these highly ordered mesoporous aluminosilicates were adjusted by an isomorphous substitution of Si by a trivalent cation, in this case Al3+, generating catalysts of the AlMCM-41 type. The materials were synthesized with a silicon/aluminium ratio of 40, through two methods of impregnation of the metal: conventional and post-synthesis alumination. With the aim of determining the density of the acid sites of the Al40MCM-41 prepared by post-synthesis and conventional alumination, studies of the adsorption of n-butylamine probe molecule were carried out. Further, the studied material was characterized by thermogravimetry measurements, providing the profile of decomposition of the samples, which allowed calculation of the densities of the acid sites. The model-free kinetic algorithms were applied in order to determinate conversion and apparent activation energy. Comparison of energy-dispersive X-ray fluorescence and X-ray photoelectron spectroscopy measurements indicated that the post-synthesis method was more favourable based on the metal positioning, ‘anchored’ in the surface of the catalyst. The textural properties of the calcined Al40MCM-41 prepared by post-synthesis and conventional alumination were characterized by X-ray diffraction, N2 isothermal adsorption measurements (Brunauer–Emmett–Teller and Barrett–Joyner–Halenda), transmission electron microscopy, and X-ray photoelectron spectroscopy.

The optimized preparation and electrochemical properties of LiMn1.95Co0.05O4 and Al2O3-coated LiMn1.95Co0.05O4

Cathode material LiMn1.95Co0.05O4 for lithium ion battery was synthesized via solid state reaction, and calcination temperature and time were investigated, respectively. Thermogravimetry (TG) and differential thermal analysis (DTA) measurements were utilized to determine the calcination temperature of precursor sample. The optimized calcination temperature and time are 850 °C and 15 h. The surface of LiMn1.95Co0.05O4 cathode is coated using Al2O3 coating materials. The phase structures, surface morphologies, and element types of the prepared LiMn1.95Co0.05O4 and Al2O3-coated LiMn1.95 Co0.05O4 were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), and energy spectrum analysis (EDS). The 0.5 wt% Al2O3-coated compound exhibited better specific capacity and capacity retention than bare sample. The initial discharge capacity was 140.9 mAh/g and capacity retention was 96.7 % after 10 cycles at 0.1 C. Such enhancements are attributed to the presence of a stable Al2O3 layer which acts as the interfacial stabilizer on the surface of LiMn1.95Co0.05O4.

“Pesting”-like oxidation phenomenon of p-type filled skutterudite Ce0.9Fe3CoSb12

Oxidation behavior of p-type filled skutterudite Ce0.9Fe3CoSb12 in air was investigated and the oxidation mechanism was discussed in this study. Ce0.9Fe3CoSb12 exhibits interesting “pesting”-like oxidation phenomenon around 800K. The bulk sample completely disintegrates into a crowd of plate-like particles under this temperature range after only 24h exposure in air. However, this abnormal oxidation phenomenon is not observed at temperature below 750K or above 850K. This result is consistent with the thermogravimetry and derivative thermogravimetry measurements which show that the oxidation rate for Ce0.9Fe3CoSb12 around 800K is the highest among 650–900K. Microstructure observations suggest that this “pesting”-like oxidation is related with the severe periodically oxide layer peeling-off behavior around 800K, which makes the Ce0.9Fe3CoSb12 samples are easy to be oxidized because the fresh substrate surface is always exposed to high concentration oxygen atmosphere. X-ray diffraction and X-ray photoelectron spectroscopy measurements indicated that in the oxide scale the direct contact of Fe3+-oxide and CoSb2O4 which possess different formation/growth rate and volume expansion coefficient should be responsible for this peculiar oxide layer peeling-off behavior around 800K. This work can serve as an important reference for the designation of MyFe4−xCoxSb12-based skutterudite thermoelectric device.

Pyrolysates distribution and kinetics of Shenmu long flame coal

China has abundant long flame coal resources, and the effective utilization of long flame coal is important. Using a tubular furnace reactor, the effects of particle size and ultimate temperature on pyrolysates distribution were investigated, and the evolution characteristics of gaseous products were determined. Experimental results showed that increasing the coal particle size leads to increasing char and gas yields and decreasing tar yield. A temperature of 550°C was recommended for low-temperature pyrolysis. The characteristics of pyrolysis and combustion kinetics were determined by thermogravimetry–derivative thermogravimetry measurement. Kinetic parameters were calculated by the Coats–Redfern and Flynn–Wall–Ozawa methods. The activation energy ranges for pyrolysis and combustion were also determined.

Crystal Structures and Spectroscopic Properties of Metal–Organic Frameworks Based on Rigid Ligands with Flexible Functional Groups

Two rigid linear ligands with alkoxy functional groups (L1 = 4,4′-(2,5-dimethoxy-1,4-phenylene) dipyridine; L2 = 4,4′-(2,5-diethoxy-1,4-phenylene) dipyridine) incorporating carboxyl-containing auxiliary ligands (isophthalic acid = H2IPA; terephthalic acid = H2TPA; biphenyl-4,4′-dicarboxylate = H2BPDC) have been adopted to build a series of complexes with M(II) (M = Zn, Co, Cd) under solvothermal conditions. The formula of these complexes are {[Zn(L1)(IPA)]}n (1), {[Zn(L1)(TPA)]·DMF}n (2), {[Co(L1)(TPA)(H2O)2]·2DMF}n (3), {[Cd(L1)(TPA)(H2O)2]·2DMF}n (4), and {[Co(L2)(BPDC)]·0.5H2O}n (5). Five complexes have been characterized by elemental analysis, infrared spectroscopy, powder X-ray diffraction and thermogravimetry measurements. Topological analyses reveal that complex 2 is a 6-connected pcu net with point symbol {412·63}, while complex 5 is a 6-connected rob net with point symbol {48·68·8}, the other complexes 1, 3, and 4 can be simplified as 4-connected sql nets with point symbol {44.62}. Complexes 1, 3...

Cu(II) and Ni(II) complexes of ferrocene-containing unsaturated β-diketones: electrochemical and burning-rate catalytic properties

Ferrocene-containing unsaturated β-diketones and their Cu(II) and Ni(II) complexes have been synthesized and characterized. Cyclic voltammetry investigations revealed that the electron density of the ferrocenyl moieties was influenced by the coordination, making the complexes easier to oxidize than the respective free ligands. Differential thermal analysis (DTA) and thermogravimetry (TG) measurements confirmed the obvious catalytic effect of the Cu(II) and Ni(II) complexes of (1E,6E)-1,7-diferrocenyl-1,6-heptadien-3,5-dione in decreasing the decomposition temperature of ammonium perchlorate (by 68.7 and 41.5 °C, respectively). The results confirm the Cu(II) and Ni(II) complexes of ferrocene-containing unsaturated β-diketones as a kind of potential high-burning-rate catalyst.

Organo‐Gallium/Indium Chalcogenide Complexes of Copper(I): Molecular Structures and Thermal Decomposition to Ternary Semiconductors

Several organo-gallium/indium chalcogenide complexes of copper(I), stabilized by trialkylphosphines, were isolated, structurally characterized by using single-crystal X-ray diffraction, and investigated in thermolysis experiments. The syntheses with [E(Me3Si)2] (E=S, Se) as a starting material and a chalcogen source involve the elimination of volatile silyl acetate, silyl ethers, and methane from copper(I) acetate, and Group 13 metal trimethyl compounds, respectively. Chalcogenide complexes, according to the general formulas [(R3PCu)4(MeM)4E6] (1-6) and [(R3PCu)6(MeM)4M4S13] (7-9; with R=alkyl and M=Ga, In), and mixed chalcogenide-phenylchalcogenolate complexes [(iPr3PCuEPh)3(MeGaE)4] (10, 11) were isolated. The heavy atom cores of 1-6 consist of an octahedron of chalcogen atoms, interpenetrated by a cube of metal atoms. Depending on the steric demand of the phosphine ligands, two constitutions are observed; the metal atoms of the same element either forming tetrahedra, or parallelograms, respectively. This constitutional isomerism is further investigated by quantum chemical calculations. Complexes 7-9 contain a central sulfur atom, surrounded by two interpenetrating tetrahedra of Group 13 metal atoms, an octahedron of copper atoms, and an icosahedron of twelve outer sulfur atoms; the heavy atom framework of 10 and 11 is a "cut-out" of this structure. Thermolysis experiments include thermogravimetry measurements and subsequent Rietveld phase analysis of the residues by using powder X-ray diffraction. The homologous compounds 1, 3, 4, and 6 yield the respective crystalline ternary semiconductor material CuME2 at temperatures below 300 °C. Partial release of Me3 M during the thermolysis process results in excess copper in the residue and therefore in small amounts of additional binary copper chalcogenide phases or metallic CuM alloys. Compound 8 produces nanocrystalline CuGaS2 at about 300 °C.

Nitrogen-doped porous carbon nanofiber webs/sulfur composites as cathode materials for lithium-sulfur batteries

Nitrogen-doped porous carbon nanofiber webs-sulfur composites (N-CNFWs/S) were synthesized for the first time with sulfur (S) encapsulated into nitrogen-doped porous carbon nanofiber webs (N-CNFWs) via a modified oxidative template route, carbonization-activation and thermal treatment. The composites were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET), X-ray powder diffraction (XRD), and thermogravimetry (TG) measurements. The results show that sulfur is well dispersed and immobilized homogeneously in the micropores of nitrogen-doped porous carbon nanofiber webs (N-CNFWs) with high electrical conductivity, surface area and large pore volume. The electrochemical tests show that the N-CNFWs/S composites with 60wt. % of S have a high initial discharge capacity of 1564mA h g−1, a good cycling stability at the current density of 175mAg−1, and excellent rate capability (reversible discharging capacity of above 400mA h g−1 at 1600mAg−1).

Kinetics of High Temperature Oxidation and Chromia Volatilization for HfC-Containing Nickel-Based Alloys

Many cast chromia-scale forming nickel-based superalloys are reinforced by carbides. In such alloys the primary chromium carbides or tantalum carbides rapidly lose their strengthening effect in service at high temperature. This is due to decrease of the volume fraction of the these carbides and to their morphology evolution. Other carbides, notably HfC, are more stable at high temperature and they can be candidates for the reinforcement of this type of superalloys. In this work, three nickel-based alloys containing 25 wt%Cr, 0.25 or 0.50 wt%C, and Hf with contents high enough (3.7 and 5.6 wt%) to promote the formation of numerous primary HfC carbides, were prepared in a foundry. They were tested by oxidation in air for 46 h at 1,200 °C with thermogravimetry measurement and subsequent metallographic characterization. All the mass-gain curves obtained are parabolic and the oxidation rates of the studied alloys are only slightly faster than for the corresponding Hf-free ternary nickel alloys containing the same chromium and carbon contents. The obtained values of the parabolic constant kp and of the chromia volatilization constant kv, deduced by applying the {m × dm/dt = kp–kv × m} method, are typical of a chromia-scale forming system. However, small quantities of HfO2 and NiCrTaO4 oxides are observed in addition to the chromia scale. In the bulk, the volume fraction and morphology of the HfC carbides only changed a little. These alloys appeared thus resistant enough against hot oxidation, this allowing first high temperature mechanical characterization in oxidizing atmosphere, before possibly considering these alloys for real applications.

Ba13Si6Sn8As22: A Quaternary Zintl Phase Containing Adamantane-Like [Si4As10] Clusters

A new quaternary arsenide Zintl phase, Ba13Si6Sn8As22, has been synthesized from the Sn-flux reactions, and the structure was determined by the single-crystal X-ray diffraction methods. The compound crystallizes in the tetragonal non-centrosymmetric space group I42m (No. 121) with unit cell parameters of a = b = 14.4857(3) Å, c = 13.5506(7) Å, V = 2843.40(17) Å(3). Its polyanion structure can be viewed as composed of [Si4As10] adamantane-like clusters and SiAs4 tetrahedra, which are linked via the [Sn2As4] groups built through two edge-sharing SnAs3 triangular pyramids. Differential thermal analysis and thermogravimetry measurements indicate that Ba13Si6Sn8As22 has good thermal stability, and does not melt or decompose below 1045 K under Ar atmosphere. Density functional calculations were performed on Ba13Si6Sn8As22 and the results suggest a band gap of around 1.0 eV for Ba13Si6Sn8As22, confirmed by the diffuse reflectance spectrum measurement. In addition, the extensively existing lone pairs of electrons on the p-orbitals of As and Sn may also hint interesting nonlinear optical properties considering the noncentrosymmetric structure.

Application of random pore model for synthesis gas production by nickel oxide reduction with methane

Recently, there is a great interest in the noncatalytic gas–solid reactions between methane, as an environmentally friendly reducing agent, and metal oxides to yield synthesis gas and the related metal at low temperatures. In the present work, reduction of nickel oxide with methane was investigated. It has been proven that it is possible to produce metallic nickel and synthesis gas, simultaneously. The thermogravimetry measurements and instantaneous mass spectrometry analysis of the gaseous products have been performed for the NiO+CH4 reaction. In addition, the complete mathematical model was developed by applying the random pore model to predict the conversion–time profiles at the temperature range of 600–750°C. Some important parameters such as concentration dependency, external mass transfer resistance, solid structural changes, product layer resistance, and pore size distribution have been considered in this sophisticated mathematical model. In addition, the random pore model has been modified for consideration of the bulk flow effect. Results obtained from this kinetic study indicate that the model performs well in predicting the experimental data. However by neglecting the bulk flow effect, there are lower predicted rate constants for this reaction. The analysis of the gaseous products showed that the synthesis gas could be produced with a H2/CO ratio near two.

Thermal, physical and mechanical properties of hydrogenated dimer acid-based Nylon 636/Nylon 66 copolymers

Hydrogenated dimer acid-based Nylon 636/Nylon 66 copolymers were synthesized by in situ polymerization. The effects of Nylon 66 contents on the copolymers were characterized by intrinsic viscosity measurements, attenuated total reflection-Fourier transform infrared spectroscopy, X-ray diffraction, differential scanning calorimetry, thermogravimetric analysis and mechanical tests. The results showed that incorporation of Nylon 66 into hydrogenated dimer acid-based Nylon had no significant effect on the glass transition or melting temperatures. However, the crystallization temperature, crystallinity degree and the maximum rate of decomposition temperature from derivative thermogravimetry measurements vary. Mechanical testing data revealed that with increasing Nylon 66 concentrations, the tensile strength of copolymers increased, while the elongation at break point and notched izod impact strength decreased. The physical and mechanical properties of HN-40, HN-50 and HN-60 are similar to those of the current PA11, PA1212, and PA1111 Nylon products.

Additive effects of tripalmitin on morphologies and tensile properties of polybutene-1 and its composite with micro fibrous cellulose

Morphologies and tensile properties of polybutene-1 (PB)/tripalmitin (TP) blend and PB/micro fibrous cellulose (MFC)/TP composite were studied. The scanning electron microscope observation showed that the PB(70 %)/TP(30 %) had a microphase-separated structure. The DSC measurement showed that the crystallization of the PB part was affected by the TP existence. A new crystal structure was observed in the X-ray diffraction pattern of the PB(70 %)/TP(30 %). Quicker saturation of the PB crystal phase transformation from the metastable tetragonal (II) to the stable hexagonal (I) phase was observed in the PB(70 %)/TP(30 %) under the aging at r.t. The saturation controlled the Young’s modulus increment of the PB(70 %)/TP(30 %) in the aging process. The elongation at break value of the PB/TP increased by the loading of the TP, suggesting that the TP worked as the plasticizer. The thermogravimetry measurement of the PB(70 %)/TP(30 %) suggested that there existed an interaction between them. The TP addition provided a good dispersibility and ductility enhancement for PB/MFC composite. It was found that the TP worked as a good compatibilizer for the composite.

Optimization of surface charge transfer processes on rutile TiO2 nanorods photoanodes for water splitting

Electrochemical impedance spectroscopy (EIS) has been performed to investigate the photocatalytic properties of titanium dioxide nanorods in a photoelectrochemical water splitting system. A two-channel transmission line model has been proposed to interpret the frequency response of the main charge transfer processes that occur at nanorod/electrolyte and platinum/electrolyte interfaces. EIS was then employed to determine that the dramatic effect of the annealing treatment on the photocurrent density had its origin on a poor charge transfer at the titania/electrolyte interface. X-ray photoelectron spectroscopy and thermogravimetry measurements have been used to prove the relevance of the presence of chlorine coming from the synthesis process of TiO2 nanorods.

Rapid synthesis of CuO nanoribbons and nanoflowers from the same reaction system, and a comparison of their supercapacitor performance

One-dimensional CuO nanoribbons and three-dimensional CuO nanoflowers were synthesized via a facile, rapid, low-temperature, one-pot water bath method, in which the synthesis was performed in Cu(CH3COO)2/NaOH and aqueous/ethanol systems at 70 °C for 15 min. Control over the shape and dimensionality of the well-defined CuO single crystals was achieved simply by varying the order of addition of the reactive materials. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and selected area electron diffraction were used to characterize the products. The formation mechanism in the in situ, rapid reaction was investigated. In Brunauer-Emmett-Teller and thermogravimetry measurements, the nanoribbons exhibited a higher specific surface area and higher adsorption capabilities than the nanoflowers. Using cyclic voltammetry, chronopotentiometry and EIS measurement for supercapacitance, it was shown that the nanoflower electrodes had better performance than the nanoribbon electrodes, however, the nanoribbon/C electrodes had better performance than the nanoflower/C electrodes at lower current density, but were worse at higher current density.

A simple SDS-assisted self-assembly method for the synthesis of hollow carbon nanospheres to encapsulate sulfur for advanced lithium–sulfur batteries

The hollow carbon nanospheres (HCNSs) were prepared using a simple SDS-assisted self-assembly method, and a sulfur–carbon composite based on HCNSs was synthesized for lithium–sulfur batteries by a vapor phase infusion method. The sulfur–HCNS composite was characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (SEM), transmission electron microscopy (TEM), and thermogravimetry (TG) measurements. It is found that the elemental sulfur was dispersed inside the pores of carbon spheres. It is demonstrated from the galvanostatic discharge–charge process and cyclic voltammetry (CV) that the sulfur–HCNS composite has a large reversible capacity and an excellent cycling performance as cathode materials. The sulfur–HCNS composite with a sulfur content of 47.6 wt% displays an initial discharge capacity of 1031 mA h g−1 and a reversible discharge capacity of 477 mA h g−1 after 100 cycles at 0.5 C charge–discharge rate.

Carboxylate and Amino Group Coated Silver Nanoparticles as Joining Materials for Copper-to-Copper Silver Joints

Organic silver complexes are introduced where silver is linked either with a carboxyl group or with an amino group. Upon heating, nanoparticles are generated if the respective ligands are long enough to act as stabilizing agents in the nanoparticulate regime. With decomposition and volatilization of the organic material, the sintering of silver occurs. The thermal characteristics of the carboxylates silver-n-octanoate, silver-n-decanoate, and AgOOC(CH2OCH2)2CH2OCH3 are compared with silver-n-alkylamines (n = 8, 9, and 12), and their thermal behavior is discussed based on thermogravimetry (TG) measurements. The consecutive stages of a metallization process are addressed based on the properties of AgOOC(CH2OCH2)2CH2OCH3, and the usable effects of the individual phases of this metal organic compound are analyzed by cross-sectional scanning electron microscope (SEM) images of silver joints. Selection criteria are addressed based on the thermal behavior. A mechanism for the joining process is proposed, considering formation and sintering of the nanoparticles. It was found that the bulk material can be used for low-temperature joining processes. Strong adherence to copper as a basic material can be achieved.