High-resolution Thermogravimetric Analysis Research Articles

XRD, TEM, and thermal analysis of Arizona Ca-montmorillonites modified with didodecyldimethylammonium bromide

An Arizona SAz-2 calcium montmorillonite was modified by a typical dialkyl cationic surfactant (didodecyldimethylammonium bromide, abbreviated to DDDMA) through direct ion exchange. The obtained organoclays were characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), high-resolution thermogravimetric analysis (HR-TG), and infrared emission spectroscopy (IES). The intercalation of surfactants greatly increased the basal spacing of the interlayers and the conformation arrangement of the loaded surfactant were assessed based on the XRD and TEM measurements. This work shows that the dialkyl surfactant can be directly intercalated into the montmorillonite without first undergoing Na+ exchange. Moreover, the thermal stability of organoclays and the different arrangements of the surfactant molecules intercalated in the SAz-2 Ca-montmorillonite were determined by a combination of TG and IES techniques. The detailed conformational ordering of different intercalated surfactants under different conditions was also studied. The surfactant molecule DDDMA has proved to be thermally stable even at 400°C which indicates that the prepared organoclay is stable to significantly high temperatures. This study offers new insights into the structure and thermal stabilities of SAz-2 Ca-montmorillonite modified with DDDMA. The experimental results also confirm the potential applications of organic SAz-2 Ca-montmorillonites as adsorbents and polymer–clay nanocomposites.

Transport and thermal properties of quaternary phosphonium ionic liquids and IoNanofluids

The transport and thermal properties of phosphonium ionic liquids (ILs) and thermally stable suspensions of phosphonium ILs and multiwalled carbon nanotubes (MWCNT) were determined. The thermal conductivity was measured over the temperature range T=(280 to 360)K, and at atmospheric pressure, using the transient hot-wire method with an accuracy estimated as 5% from (0.2 to 2)W·m−1·K−1 and less than ±0.01W·m−1K−1 from (0.02 to 0.2)W·m−1·K−1. The phosphonium ILs studied were trihexyltetradecylphosphonium phosphinate [(C6)3PC14)][Phosph], tretrabutylmethylphosphonium methylsulfate, [(C4)3PC1)][C1SO4], trihexyltetradecylphosphonium bis(trifluoromethylsulfonyl)imide, [(C6)3PC14][NTf2], and trihexyltetradecylphosphonium trispentafluoroethyltrifluorophosphate [(C6)3PC14][FAP]. For all ILs studied, the thermal conductivities were found to lie within the range (0.12 to 0.16)W·m−1·K−1. Our measurements combined with selected values from the open literature allowed us to determine a linear increase of combined properties (thermal conductivity, density and molar mass) with the increasing of molar mass. The addition of only (0.1 to 0.2)wt.% of MWCNT to ILs (IoNanofluids) revealed a slight increasing of the thermal conductivity from 0.5% to 1%. There was also observed a slight decrease of the thermal conductivity with increasing temperature for the ILs alone and respective IoNanofluids. The rheological behaviour of [(C6)3PC14)][Phosph], and of [(C6)3PC14][NTf2] based IoNanofluids was evaluated at T=(298.15 to 333.15)K and for shear rates in the range γ̇=(3 to 30)s−1. All the samples showed shear thinning behaviour. The thermal stability of the IoNanofluids compared to that of ILs alone was studied by High Resolution Thermogravimetric Analysis. It was found that pure [(C6)3PC14)][Phosph] is a thermally stable IL, whose thermal decomposition under the conditions of this study (2K·min−1) and starts above T=513K. It exhibits a one step thermogravimetric profile ([(C6)3PC14][NTf2] that was already investigated in a previous study). A small shift towards lower temperatures was observed in the thermogravimetric curves of IoNanofluids compared to those of the respective ILs alone indicating comparable thermal stabilities. The heat capacities determined by Modulated Differential Scanning Calorimetry within a temperature interval ranging from ca. (310 to 515)K with an estimated uncertainty of less than ±0.012J·K−1·g−1.

Synthesis of Carbon Nanospheres with Small Diameterby Microwave Pyrolysis of Methane Directly

Carbon nanospheres of uniform diameter around 40 nm have been achieved in the absence of catalyst by microwave pyrolysis chemical vapor deposition. The products have been characterized by field emission scanning electron microscopy, high resolution transmission electron microscopy, X-ray diffraction, Raman spectroscopy and thermogravimetric analysis. The results show that the nanospheres with high purity, which are solid by their cross-sections, consisting of concentric incompletely closed graphitic layers. Their thermal stability in dynamic air atmosphere is also discussed.

Surface modification of layered silicates. I. Factors affecting thermal stability

The resistance of modification molecules bound to montmorillonite platelet surfaces towards structural damage at high temperature is a major parameter guiding the formation of optimal interface between the filler and polymer phases in a nanocomposite material. As nanocomposites are generated by melt-blending of modified mineral and polymer, it is necessary to quantify the thermal resistance of the filler surface modification at the compounding conditions because different modifications differ in chain length, chemical structure, chain density, and thermal performance. A number of different alkyl ammonium modifications were exchanged on the montmorillonites with cation exchange capacities in the range 680–900 µequiv. g−1 and their thermal behaviour was characterised using high resolution thermogravimetric analysis. Quantitative comparisons between different modified minerals were achieved by comparing temperature at 10% weight loss as well peak degradation temperature. Various factors affecting thermal stability, such as length and density (or number) of alkyl chains in the modification, presence of excess modification molecules on the filler surface, the chemical structure of the surface modifications, etc. were studied. The TGA findings were also correlated with X-ray diffraction of the modified platelets.

Surface modification of layered silicates. II. Factors affecting thermal stability

Different aluminosilicates, such as montmorillonite, vermiculite and mica, were surface-treated with a variety of organic modifiers to quantify factors affecting the thermal stability of the modified fillers. Montmorillonites with different cation exchange capacities were also used. Thermal characterisation was carried out via high resolution thermogravimetric analysis and the results were correlated with X-ray diffraction measurements. Modified substrates, such as montmorillonite, vermiculite and mica, differed in their thermal behaviour even when modified with the same surface modifiers. Phosphonium-based modifiers were the most thermally stable, compared to pyridinium and ammonium ions. Mixed brushes from the modifiers also influenced the thermal behaviour of the modified substrates. When further modified using physical adsorption or chemical reactions on the surface, the modified minerals also displayed alterations in the thermal behaviour of the fillers. The results can be used as a guide for the selection of surface modifiers in the nanocomposite synthesis process where compounding of the filler with the polymer at high temperature and shear is required.

Melting and crystallization transitions in organically modified layered silicates studied with differential scanning calorimetry

Melting and crystallization behaviors of the monolayers in the surface modified layered silicates were studied with differential scanning calorimetry. The layered silicates with different layer charge densities were used for the purpose. The ammonium ions forming the monolayer were also varied according to their chemical architecture, chain length and number of chains in the molecular structure. The quality of surface modification of the mineral was quantified using high resolution thermo-gravimetric analysis. At an optimum combination of the cross-sectional area of the ions, chain length as well as chain density, ordered monolayers are formed on the surface which turn to disordered state at a temperature corresponding to the melting of the ordered structure. These transitions are reproducible in nature but may require longer cooling times to regenerate again. The heat flow to the modified mineral (corresponding to melt enthalpy) increased on increasing the chain length as well as chain density, however, the transition temperatures decreased with increasing chain density in the surface modification molecules. The modified minerals were also hygroscopic in nature with first heating cycles showing the evaporation of water, however, with increasing chain length and chain density in the surface modification, the extent of hydrophobicity of the minerals increased. The effect of chemical architecture was not significant as it seemed to be driven by the chain length and capability of the modification molecules to crystallize in general or on the processing conditions used.

Mineralogical evolution of Portland cement blended with silica nanoparticles and its effect on mechanical strength

Mineralogical analysis on pastes of Spanish Portland cement Type I, blended with nanosilica was carried out by conventional and high-resolution thermogravimetric analysis (TG-HRTG) and X-ray diffraction (XRD) in order to determine the quantity of the different mineralogical phases obtained during the hydration process. Simultaneously, mortars with the same materials and replacement ratio were made in order to assess their compressive strength for up to 28days of curing time. In this paper, the rate and quantity of each one of the main constituent phases of the cement during its hydration process (CSH, portlandite, stratlingite, etc.) were determined. A correlation between the quantity of CSH and the development of compressive strength was established. Additionally, the pozzolanic activity of nanosilica was evaluated by quantifying the fixation of calcium hydroxide and its impact on the development of the compressive strength.

Crosslinked SPEEK membranes: Mechanical, thermal, and hydrothermal properties

Abstract

Polymer-dispersed liquid crystal nanocomposites comprising montmorillonite clay modified by conducting pentamerous oligoaniline

Pentamerous oligoaniline (POA) was protonated with sulfuric acid to form emeraldine salts (ES) and then intercalated in montmorillonite (MMT) CL120 to develop a functional conductive organo-layered material. The characteristics of the modified clay CL120/ES-POA were analyzed by wide-angle X-ray diffraction (WAXD) to find the d-spacing of the MMT layer distance, and by Fourier transform infrared (FTIR) spectroscopy for the oligoaniline functional group in CL120/ES-POA, and high-resolution thermogravimetric analysis (TGA) to determine the theoretical intercalation capacity of the modifying agent in the clay. We successfully intercalated the ES-POA into the MMT by ionic exchange reaction. Polymer-dispersed liquid crystal (PDLC) composites were prepared from the modified clay of 1 wt% loaded in the mixtures of 49 wt% photosensitive monomer and 50 wt% nematic liquid crystal (NLC), in a specific case, so as to generate novel functional nanocomposites. The hybridization of CL120/ES-POA clearly improved the electro-optical properties of the PDLCs. In this work, doping CL120/ES-POA at 1 wt% beneficially lowered the driving voltage by almost 70%, increased the transmission contrast ratio by five times and reduced the response time from 4.6 to 0.7 ms at 25 Vrms at the expense of the viewing-angle properties.

Shape-controlled synthesis of lead zirconate titanate nanocrystallites, microrods, microrolls and 3D complex architectures via the effects of poly-vinylalcohol macromolecular conformation

Shape-controlled synthesis of tetragonal PbZr0.52Ti0.48O3 (PZT) perovskite nanocrystallites, microrolls, microrods and 3D complex architectures composed of microroll-bundles or microrod-bundles were realized via a hydrothermal reaction route by simply adjusting the poly-vinylalcohol (PVA) and KOH concentrations. X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), differential temperature and thermogravimetric analysis (DTA and TG) were used to characterize the phase composition, morphology and thermal behaviors of the synthesized samples. In order to investigate the effect of PVA on the shape-controlled synthesis of the tetragonal PZT perovskite particles, a series of experiments were performed by changing the PVA and KOH concentration. Based on the experimental results, the formation mechanisms of tetragonal PZT perovskite particles with various shapes and the effects of the PVA macromolecular conformation are discussed.

A thermoanalytical assessment of an organoclay

High resolution thermogravimetric analysis (TG) has attracted much attention in the synthesis of organoclays and its applications. In this study, organoclays were synthesised through ion exchange of a single cationic surfactant for sodium ions, and characterised by methods including X-ray diffraction (XRD) and TG. The changes of surface properties in montmorillonite (MMT) and organoclays intercalated with surfactant were determined using XRD through the changes in the basal spacing. The TG was applied in this study to investigate more information of the configuration and structural changes in the organoclays with thermal decomposition. There are four different decompositions steps in differential thermogravimetric curves. The obtained TG steps are relevant to the arrangement of the surfactant molecules intercalated in MMT and the thermal analysis indicates the thermal stability of surfactant modified clays. This investigation provides new insights into the properties of organoclays and is important in the synthesis and processing of organoclays for environmental applications.

Hybrid composite membranes based on SPEEK and functionalized PPSU for PEM fuel cells

Composite membranes formed by sulfonated poly-ether-ether-ketone (SPEEK) and sulfonated and/or silylated poly-phenyl-sulfone ((Si,S)PPSU) were prepared. (Si,S)PPSU was used as anchor phase to reinforce membranes based on SPEEK with high degree of sulfonation, which is proton conducting but morphologically unstable. The ionomer membranes were characterized by several techniques, including high resolution thermogravimetric analysis, static and dynamic mechanical measurements, water uptake by immersion and in vapour phase. Properties of hybrid blends with 93 wt% SPEEK and 7 wt% of (Si,S)PPSU were compared to those of pure SPEEK. Thermal properties are discussed in view of ionomer composition. The presence of bulky phenyl-silanol groups leads to an evident reduction of water uptake and greatly enhanced mechanical strength.

Study on growth of hollow nanoparticles of alumina

This article addresses the growth of hollow nanocrystalline particles of γ-alumina by the post-oxidation of nano-aluminium particles in air. The nanoparticles of aluminium were synthesized in a DC-transferred arc thermal plasma reactor. The as-synthesized nano-aluminium particles were oxidized, in air, at different temperatures. The as-synthesized parent nano aluminium and their daughter nanoparticles of aluminium oxide were thoroughly characterized with the help of X-ray diffraction analysis, high resolution transmission electron microscopy and thermogravimetric analysis. Two-step oxidation behaviours, unique in nanoparticles, are found to be the main driving force behind the formation of hollow spherical structures. The entire phenomenon is compared with the oxidation behaviour of coarse grain aluminium. The content of γ-alumina, identified by X-ray diffraction, relative to that of unreacted aluminium, has increased almost exponentially with the oxidation temperature in the case of nano aluminium. Similar behaviour is not observed in the case of coarse grain aluminium. The crystalline features of alumina, forming the walls of the hollow sphere, were confirmed by high resolution transmission electron microscopy.

Hydrothermal Synthesis of Layered Sodium Manganese Oxide Nanowires and Their Electrochemical Performance

A new method for preparing black birnessite nanowires is introduced. Layer-structured manganese oxide nanowires were synthesized by a facile hydrothermal method, and using both NaMnO4 and CH3CH2OH as the precursors in a concentrated NaOH solution. The structure, composition, appearance and electrochemical performance of the product were characterized by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), energy diffraction (ED), high-resolution transmission electron microscopy (HRTEM), thermogravimetric analysis (TGA) and constant current charge/discharge. The XRD patterns showed a single phase corresponding to a crystalline birnessite-based manganese oxide. TEM studies suggested their wire-like structures. The TGA measurement demonstrated that they possessed an excellent thermal stability up to 400 degrees C. In the potential window of 2.0-4.3 V, the product exhibited excellent cyclic stability and rapid charge-discharge performance.

Quantification of thin graphene sheets contained in spherical aggregates of single-walled carbon nanohorns

Spherical aggregates of single-walled carbon nanohorns (SWNHs) produced by CO 2 laser ablation of graphite contain thin graphene sheets (TGSs), and their quantities depend on formation conditions. To adjust laser ablation condition to increase TGS quantities, TGS quantification in products is necessary; however, its method has not been established. We have found that high resolution thermogravimetric analysis (HRTGA) showed SWNHs and TGSs combusting at 554 and 581 °C, respectively. Transmission electron microscopy observations of HRTGA-residues obtained by stopping HRTGA on the way supported these assignments. Thus TGS was able to be quantified by analyzing derivative curves of weight vs. temperature curves.

Preparation and Analysis of Kaolinite Intercalated by Potassium Acetate

The kaolinite-potassium acetate composite was prepared by the immersion method. The intercalation composites were characterized by means of Scanning Electron Microscope (SEM), X-ray diffraction (XRD), Fourier transformation infrared (FT-IR) and High-resolution thermogravimetric analysis (HRTG). The results of XRD show that the intercalation of kaolinite by potassium acetate causes an increase of the basal spacing from 0.718 to 1.42nm. Thermal analysis shows the dehydroxylation of kaolinite decreased from 464 °C to 459.5 °C after intercalation of potassium acetate and three endotherms at 280, 323 and 459.5 °C attributed to the loss of water in the composite, potassium acetate and hydroxyl in the composite.

Determination of the optimum parameters in the high resolution thermogravimetric analysis (HRTG) for cementitious materials

In this article, the methodology to implementation of high resolution thermogravimetric analysis (HRTG) for construction materials like Portland cement pastes is presented. The aim of this technique is to make easier the identification of the decomposition reactions that frequently are overlapping on conventional thermogravimetric analysis (TG) like is the case of some mineral phases in the cement pastes. The optimum parameters related to sample mass and purge flow gas were established. It is necessary carried out the analysis with high quantity of sample (60 mg in this case) and without purge gas in order to get better results and excellent reproducibility. The tests have average heating rate higher than 3 °C min−1 in the temperature range studied (35–300 °C), showing that the HRTG is not time-expensive technique.

Porous polymer structures obtained via the TIPS process from EVOH/PMMA/DMF solutions

The thermally induced phase separation (TIPS) process was used to study the phase behavior of ternary solutions containing poly(ethylene- co-vinyl alcohol) (EVOH) with 38 and 32 wt.% of ethylene content, poly(methyl methacrylate) (PMMA) and N, N-dimethylformamide (DMF) and to prepare microporous membranes. EVOH/PMMA/DMF solutions, with 0.92 and 0.83 DMF volume fraction and variable volume polymer ratios, were submitted to experiments to determine the cloud temperature ( T cloud ) by optical microscopy and the dynamic crystallization temperature ( Tc d ) by differential scanning calorimetry (DSC), related to liquid–liquid (L–L) and solid–liquid (S–L) phase separation, respectively. L–L phase separation takes place as the temperature decreases, an UCST behavior, followed by S–L phase separation due to EVOH crystallization. At room temperature the ternary solutions show two macroscopic phases, F1 and F2, whose compositions were determined by high resolution thermogravimetric analysis in order to determine the tie lines. The ternary solutions (phases F1 and F2) were slowly dried and the morphology of the resulting membranes were analyzed by scanning electronic microscopy (SEM). The membranes show a bi-layer structure, one dense layer richer in PMMA and another porous layer richer in EVOH. The connected porous structure probably derives from the phase separation through a nucleation and growth mechanism.

Analysis of Biomass Composition Using High-Resolution Thermogravimetric Analysis and Percent Bark Content for the Selection of Shrub Willow Bioenergy Crop Varieties

Rapid determination of biomass composition is critical for the selection of shrub willow varieties with optimized biomass properties for conversion into fuels or chemicals. In order to improve the process for identifying and selecting shrub willow clones with distinct biomass composition, high-resolution thermogravimetric analysis (HR-TGA) was developed as a rapid, low-cost method for analyzing large numbers of willow biomass samples. In order to validate the HR-TGA method, bulk biomass collected from 2-year-old stems of a selected set of 25 shrub willow clones was analyzed using traditional wet chemistry techniques in addition to HR-TGA. The results of the wet chemistry and the HR-TGA method were compared using regression analysis resulting in R-squared values above 0.7 for the three main wood components, cellulose, hemicellulose, and lignin. Bark was removed from duplicate stem samples of the same clones, the proportion of bark was determined, and the debarked wood was used for HR-TGA analysis of composition. While there were significant differences in the proportions of lignin and cellulose in debarked wood compared to bulk biomass, as well as significant differences in bark percentage among clones, there was no correlation between bark percentage and bulk biomass component analysis. This work validates the effectiveness, precision, and accuracy of HR-TGA as a reasonably high-throughput method for biomass composition analysis and selection of shrub willow bioenergy crop varieties.

Synthesis of Single-Walled Carbon Nanotube Films with Large Area and High Purity by Arc-Discharge

A novel method to synthesize single-walled carbon nanotube(SWCNT) films with large area and high purity was introduced.An arc-discharge facility was improved by adding two graphite plates to the electrodes to form a spherical cap capacitor in the vacuum cavity so that an additional electric field of appropriate intensity could be generated.Using this new facility,single-walled carbon nanotube films of different thicknesses ranging from a few microns to a millimeter(controlled by the discharge time) were synthesized on a spherical cathode graphite plate.The film structures were characterized by field emission scanning electron microscopy(FESEM),high resolution transmission electron microscopy(HRTEM),Raman spectroscopy,and thermogravimetric analysis(TGA).Results show that this is an efficient way to produce single-walled carbon nanotube films of high purity.