High-resolution Thermogravimetry Research Articles

Effect of the gas mixture composition on high-temperature behavior of magnetron sputtered Si–B–C–N coatings

The effect of the gas mixture composition on the high-temperature behavior of amorphous Si–B–C–N coatings was systematically investigated up to 1700 °C in a flowing air and inert gases (He and Ar). The Si–B–C–N coatings were deposited by reactive dc magnetron co-sputtering using a single B 4C–Si target in two nitrogen–argon gas mixtures (50% N 2 + 50% Ar or 25% N 2 + 75% Ar). A fixed 75% Si fraction in the target erosion area, an rf induced negative substrate bias voltage of − 100 V, a substrate temperature of 350 °C and a total pressure of 0.5 Pa were held constant in depositions. The high-temperature behavior of the coatings, including their oxidation resistance in air and thermal stability in inert gases, was characterized by means of high-resolution thermogravimetry, differential scanning calorimetry, X-ray diffraction, Rutherford backscattering spectrometry and elastic recoil detection analysis. It was found that the Ar fraction in the gas mixture determines an important N / (Si + B + C) concentration ratio in the coatings, and hence their high-temperature behavior. The coating prepared with a 50% Ar fraction exhibits extremely high oxidation resistance (Δ m = 0) up to 1400 °C and very high oxidation resistance (Δ m < 0.02 mg/cm 2) up to 1600 °C in air, and extremely high thermal stability up to 1600 °C in inert gases. The stability of the coating prepared with a 75% Ar fraction is very high up to the onset (at about 1250 °C) of crystallization of its initial amorphous structure.

Thermogravimetric analysis of wheatleyite Na2Cu2+(C2O4)2·2H2O

Evidence for the existence of primitive life forms such as lichens and fungi can be based upon the formation of oxalates. These oxalates form as a film like deposit on rocks and other host matrices. The anhydrous oxalate mineral moolooite CuC2O4 as the natural copper(II) oxalate mineral is a classic example. Another example of a natural oxalate is the mineral wheatleyite Na2Cu2+(C2O4)2·2H2O. High resolution thermogravimetry coupled to evolved gas mass spectrometry shows decomposition of wheatleyite at 255°C. Two higher temperature mass losses are observed at 324 and 349°C. Higher temperature mass losses are observed at 819, 833 and 857°C. These mass losses as confirmed by mass spectrometry are attributed to the decomposition of tennerite CuO. In comparison the thermal decomposition of moolooite takes place at 260°C. Evolved gas mass spectrometry for moolooite shows the gas lost at this temperature is carbon dioxide. No water evolution was observed, thus indicating the moolooite is the anhydrous copper(II) oxalate as compared to the synthetic compound which is the dihydrate.

Purity Evaluation of Carbon Nanotube Materials by Thermogravimetric, TEM, and SEM Methods

Raw and purified samples of carbon nanotubes are considered as multicomponent systems with a distribution of carbonaceous, amorphous, multishell graphitic particles and nanotubes, together with the particles of metal compounds from the catalyst. With respect to the carbon nanotube fractions, a distribution of size, defect concentrations, and functionalities needs to be taken into account. In order to address the problem of quantitative evaluation of purity it is necessary to measure the quality and distribution of the carbon nanotubes. In this research conventional and high resolution thermogravimetry are applied to quantify different fractions of carbonaceous and metallic materials in raw and moderately purified single walled and multiwalled carbon nanotubes. For each oxidized fraction, defined by careful line shape analysis of the derivative thermogravimetric curves (DTG), the temperature of maximum rate of oxidation, the temperature range for this oxidation, related to the degree of homogeneity, and the amount of associated material is specified. The attribution of carbonaceous materials to each fraction in the distribution was based on SEM and TEM measurements and the literature. The MWNT purified sample with 1.6 wt% metal oxide was investigated by high resolution thermogravimetry (HRTG). The quantitative assessment for the carbonaceous fractions was 25 wt% of amorphous and high defect carbonaceous materials including nanotubes, 54 wt% MWNT and 20 wt% multishell graphitic particles. A qualitative evaluation of these fractions was obtained from the SEM and TEM images and supports these results. The accuracy of the values, taking into account other measurements performed on the same batch of material, should be more sensible than +/-4 wt%.

Pt and Ni Carbon Nitride Electrocatalysts for the Oxygen Reduction Reaction

A new synthesis route aimed at the preparation of electrocatalysts to be used for fuel cells is described. A precursor material is prepared starting from a platinum chloride and a nickel cyanometalate complex in the presence of sucrose, which acts as an organic binder. The most critical steps for the preparation of the electrocatalysts are the thermal decomposition of the precursor, which was studied in the temperature range, and the procedure for activating the products. The resulting materials were extensively characterized via inductively coupled plasma atomic emission spectroscopy, elemental analysis, high-resolution thermogravimetry, vibrational spectroscopy in the middle and far infrared, X-ray photoelectron spectrosopy, X-ray diffraction, scanning electron microscopy, and cyclic voltammetry. These investigations yielded information regarding the influence of the preparation conditions on the structure of the final materials and their electrocatalytic performance. The electrochemical efficiency in the oxygen reduction reaction of the proposed electrocatalysts proved to be much higher than that shown by standard materials having a similar platinum content. This synthesis route appears very promising due to the ease with which materials having the desired metal composition can be obtained and the promising electrochemical performance of the resulting electrocatalysts.

Adsorption and structural properties of channel-like and cage-like organosilicas

Channel-like and cage-like mesoporous silicas, SBA-15 (P6mm symmetry group) and SBA-16 (Im3m symmetry group), were modified by introducing single ureidopropyl surface groups, mixed ureidopropyl and mercaptopropyl surface groups, and single bis(propyl)disulfide bridging groups. These hexagonal and cubic organosilicas were prepared under acidic conditions via co-condensation of tetraethyl orthosilicate (TEOS) and proper organosilanes using poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) amphiphilic block copolymer templates, P123 (EO20PO70EO20) and F127 (EO106PO70EO106). The modified SBA-15 and SBA-16 materials were synthesized by varying the molar ratio of organosilane to TEOS in the initial synthesis gel. The removal of polymeric templates, P123 and F127, was performed with ethanol/hydrochloric acid solution. In the case of SBA-15 the P123 template was fully extracted, whereas this extraction process was less efficient for the removal of F127 template from the SBA-16-type organosilicas; in the latter case a small residue of F127 was retained. The adsorption and structural properties of the resulting materials were studied by nitrogen adsorption-desorption isotherms at −196∘C (surface area, pore size distribution, pore volumes), powder X-Ray diffraction, CHNS elemental analysis and high-resolution thermogravimetry. The structural ordering, the BET specific surface area, pore volume and pore size decreased for both channel-like and cage-like mesoporous organosilicas with increasing concentration of incorporated organic groups.

Effective method for removal of polymeric template from SBA-16 silica combining extraction and temperature-controlled calcination

An effective method for the removal of polymeric template, which combines extraction and temperature-controlled calcination, is proposed to obtain high pore volume and large pore size ordered mesoporous silicas, SBA-16 (Im3m symmetry group), synthesized in the presence of sodium chloride at low acid concentrations using poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (Pluronic F127) as a structure directing agent and tetraethylorthosilicate as a silica source. The aforementioned materials were characterized by small angle X-ray powder diffraction, nitrogen adsorption, high resolution thermogravimetry and elemental analysis.

Effect of polymer-to-silica ratio on the formation of large three-dimensional cage-like mesostructures

This work shows the influence of polymer-to-silica ratio on the formation of cage-like ordered mesoporous silica, FDU1, having a three-dimensional face-centered cubic symmetry. The FDU1 samples studied were synthesized from tetraethyl orthosilicate (TEOS) under acidic conditions in the presence of poly(ethylene oxide)–poly(butylene oxide)–poly(ethylene oxide) (EO39BO47EO39) triblock copolymer. The molar ratio of triblock copolymer to TEOS in the reaction mixture was varied from 0.0037 to 0.0148. Small angle X-ray scattering, argon adsorption–desorption and high resolution thermogravimetry studies indicate that an optimal EO39BO47EO39/TEOS ratio, which led to a high-quality FDU1 material with uniform cage openings, narrow pore size distribution and high specific surface area, was about 0.0074. The FDU1 silicas obtained for lower and higher ratios than the aforementioned value possessed non-uniform cage entrances, broader pore size distributions, lower BET specific surface areas and smaller mesopore diameters.

Difference in high-temperature oxidation resistance of amorphous Zr–Si–N and W–Si–N films with a high Si content

The high-temperature oxidation resistance of amorphous Zr–Si–N and W–Si–N films with a high Si content (≥20 at.%) deposited by reactive dc magnetron sputtering at different partial pressures of nitrogen was systematically investigated by means of a symmetrical high-resolution thermogravimetry in a flowing air up to an annealing temperature of 1300 °C (a temperature limit for Si(1 0 0) substrate). Additional analyses including X-ray diffraction (XRD), light optical microscopy (LOM), scanning electron microscopy (SEM), atomic force microscopy (AFM), and microhardness measurement were carried out as well. The obtained results showed (i) an excellent high-temperature oxidation resistance of the Zr–Si–N films up to 1300 °C, (ii) a considerably lower oxidation resistance of the W–Si–N films. The W–Si–N films are completely oxidized at 800 °C with a subsequent volatilization of unstable WO x oxides. On the other hand, the Zr–Si–N films are oxidized only very slightly on the surface, where a stable oxide barrier layer preventing further inward oxygen diffusion is formed. The thickness of the oxide layer is only about of 3% of the total film thickness. The phase composition, thermal stability of individual phases and amorphous structure were found to be key factors to achieve a high oxidation resistance.

Application of high resolution thermogravimetry to the study of thermal stability of poly(vinyl chloride) resins

The influence of microstructure on thermal degradation behaviour was studied in five samples of pure poly(vinyl chloride) (PVC) obtained at different polymerisation temperatures. Tacticity of the samples was characterized by Fourier transform infrared spectroscopy (FTIR), and their thermogravimetric behaviour was measured by high resolution (Hi-Res™) TGA. This technique is able to detect two independent weight loss steps in the dehydrochlorination. The relative contribution of these two steps responds to different syndiotacticity tendency of PVC samples, in accordance with FTIR results.

Comparative thermogravimetric and adsorption study of highly ordered mesoporous materials

A comparative study was carried out for highly ordered mesoporous materials using high resolution thermogravimetry (HR-TG) and adsorption techniques. These materials were synthesized with mixed surfactants of various alkyl chain lengths. For thermogravimetry measurements n-butanol was used to probe the adsorbent surface and high-resolution TG curves as well as their 1st and 2nd derivatives were obtained for this probe molecule. It is shown that the values of the mesopore volume and specific surface area evaluated from TG data are in a good agreement with those evaluated from low-temperature nitrogen adsorption isotherms. This comparative study was performed to confirm the usefulness of the HR-TG technique as an alternative method for evaluation of the mesopore volume and specific surface area of ordered mesoporous materials.

High-temperature oxidation resistance of Ta–Si–N films with a high Si content

The high-temperature oxidation resistance of ternary Ta–Si–N films with a high (≥ 20 at.%) Si content deposited by reactive dc magnetron sputtering on silicon substrates was systematically investigated by means of a symmetrical high-resolution thermogravimetry in a flowing air up to an annealing temperature of 1300 °C. Additional analyses including optical microscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD) and the microhardness measurement were carried out as well. The obtained results showed an excellent high-temperature oxidation resistance Ta 12Si 26N 62 films up to 1300 °C. A slight oxidation starts just above 800 °C and stops approximately at 1080 °C due to the formation of a thin barrier oxide layer composed dominantly of orthorhombic Ta 2O 5 phase. The thickness of the oxide layer is almost constant with the annealing from 1080–1300 °C ( h oxide / h film ≈ 18%), however, the crystallinity is much improved. The microhardness decreases from 25 to 16 GPa with increasing annealing temperature due to the formation of the oxide layer of a lower microhardness. The microhardness and the oxide layer thickness almost do not change with increasing annealing time up to 1 h at a constant annealing temperature of 1300 °C.

Thermogravimetric studies of benzoylthiourea-modified MCM-41 after adsorption of mercury ions from aqueous solutions

High-resolution thermogravimetry (HR TG) was used to study the adsorption of mercury(II) ions by modified MCM-41 material and regeneration of the loaded adsorbent with mercury ions by using different eluents. The weight change curves were measured for MCM-41 samples modified with 1-benzoyl-3-propylthiourea ligand loaded with mercury ions. The differential thermogravimetric (DTG) curves were analyzed to investigate the adsorption of mercury ions by the aforementioned multifunctional ligand and to monitor the decomposition of the metal-ligand complexes. A series of experiments performed for different Hg(2+):ligand ratios allowed us to correlate the adsorption data for mercury ions measured by means of UV spectrophotometry with those obtained by HR TG analysis. The DTG results provided additional information about mercury-ligand interactions as well as the thermal stability of mercury-ligand complexes. This study shows that HR TG is a very attractive technique for studying the adsorption of mercury ions on modified nanoporous silicas and monitoring their regeneration. Since the samples used are small, this method seems to be promising for studying adsorption systems of environmental significance.

Vibrational and thermal characterization of Nafion ® membranes substituted by alkaline earth cations

The vibrational spectra of Nafion ® membranes with alkaline earth cations as counterions have been obtained by photoacoustic infrared spectroscopy (PAS–IR) and Fourier transform Raman spectroscopy (FT-Raman). The symmetrical stretching band of the sulfonate group (∼1060 cm −1) decreases with increasing atomic mass of the countercation, excepting for Mg 2+, in both techniques. The thermal behavior of Nafion membranes by means of differential scanning calorimetry (DSC) curves showed a dependence on the water content and a similar profile between Nafion-Mg 2+ and -Ca 2+, and between Nafion-Sr 2+ and -Ba 2+, for the first scanning curve. An ageing effect was also observed on Nafion by DSC curves. High-resolution thermogravimetry (TG) curves under nitrogen atmosphere showed similar decomposition profiles. It was determined from TG curves that there is a decreasing water content with increasing ionic radius of cation, and the thermal stability increasing from Nafion-Mg 2+ to -Ba 2+.

Thermal decomposition of peisleyite: a thermogravimetry and hot stage Raman spectroscopic study

High resolution thermogravimetric analysis (HRTG) coupled with a gas evolution mass spectrometer was used to study the decomposition of peisleyite Na 3Al 16(SO 4)(PO 4) 10(OH) 17·20H 2O. Peisleyite, a hydrated hydroxylated multianion mineral, shows thermal decomposition in five stages, indicative of a loss of water, hydroxyl units and sulphate. Thermal analysis shows the loss of water and hydroxyl units occurs in three distinct stages; at 36, 105 and 162 °C. The high resolution thermogravimetry was complimented with hot stage Raman spectroscopy, which follows the dehydration of peisleyite. This dehydration can be followed by the decrease in intensity of the OH stretching vibrations which occur between 4000 and 2500 cm −1 and by the shift in the sulphate and phosphate peaks which occur due to changes in the mineral structure.

The 'cave' mineral oxammite - a high resolution thermogravimetry and Raman spectroscopic study

The thermal decomposition of natural ammonium oxalate known as oxammite has been studied using a combination of high resolution thermogravimetry coupled to an evolved gas mass spectrometer and Raman spectroscopy coupled to a thermal stage. Three mass loss steps were found at 57, 175 and 188 °C attributed to dehydration, ammonia evolution and carbon dioxide evolution respectively. Raman spectroscopy shows two bands at 3235 and 3030 cm - 1 attributed to the OH stretching vibrations and three bands at 2995, 2900 and 2879 cm - 1 , attributed to the NH vibrational modes. The thermal degradation of oxammite may be followed by the loss of intensity of these bands. No intensity remains in the OH stretching bands at 100 °C and the NH stretching bands show no intensity at 200 °C. Multiple CO symmetric stretching bands are observed at 1473, 1454, 1447 and 1431 cm - 1 , suggesting that the mineral oxammite is composed of a mixture of chemicals including ammonium oxalate dihydrate, ammonium oxalate monohydrate and anhydrous ammonium oxalate.

Thermal treatment of moolooite

Evidence for the existence of primitive life forms such as lichens and fungi can be based upon the formation of oxalates. These oxalates form as a film like deposit on rocks and other host matrices. Moolooite as the natural copper(II) oxalate mineral is a classic example. High resolution thermogravimetry coupled to evolved gas mass spectrometry shows decomposition takes place at 260°C. Evolved gas mass spectrometry shows the gas lost at this temperature is carbon dioxide. No water evolution was observed, thus indicating the moolooite is the anhydrous copper(II) oxalate as compared to the synthetic compound which is the dihydrate. The high resolution thermogravimetry was complimented with hot stage Raman spectroscopy. The temperature at which no intensity remains in the bands assigned to the oxalate vibrations is the upper limit of the stability of the moolooite.

Dehydration and crystallization process in sol-gel zirconia

Sol-gel zirconia was characterized using high-resolution thermogravimetry (Hi-Res TG) and differential scanning calorimetry (DSC) and compared with X-ray diffraction, Raman scattering, and UV-Vis spectroscopy. ZrO2-x(OH)2x·yH2O annealed below 400°C show typical behavior of amorphous material. As the annealing temperature is increased, the tetragonal and monoclinic phases crystallize. Typical Hi-Res TG curve shows that the samples are continuously dehydrated in a long temperature range, between room temperature and 600°C. The total mass loss relative to the initial mass is of about 29%. The DSC analysis coupled with TG and structural information, indicate that the exothermic processes about 355 and 447°C can be related to the nucleation process of the formation of tetragonal zirconia, with bulk crystallization at 447°C.

Thermal treatment of whewellite—a thermal analysis and Raman spectroscopic study

Thermal transformations of natural calcium oxalate monohydrate known in mineralogy as whewellite have been undertaken using a combination of thermal analysis and Raman microscopy with the use of a thermal stage. High resolution thermogravimetry shows that three mass loss steps occur at 162, 479 and 684 °C. Evolved gas mass spectrometry shows that water is evolved in the first step and carbon dioxide in the second and third mass loss steps. The changes in the molecular structure of whewellite can be followed by the use of the in situ Raman spectroscopy of whewellite at the elevated temperatures. The whewellite is stable up to around 161 °C, above which temperature the anhydrous calcium oxalate is formed. At 479 °C, the oxalate transforms to calcium carbonate with loss of carbon dioxide. Above 684 °C, calcium oxide is formed.

Thermal treatment of mechanochemically activated kaolinite

The mechanochemical activation of a high defect kaolinite has been studied using a combination of high-resolution thermogravimetry and DRIFT spectroscopy. The effect of grinding causes a decrease in the dehydroxylation temperature and an increase in the amount of adsorbed/coordinated water. The temperature of dehydration also increases with grinding time. It is proposed that this dehydroxylation occurs through a homogenous process involving proton transfer through point heating. The amount of adsorbed water decreases with the increase in temperature of the thermal treatment.

Thermodesorption studies of ammonium nitrate prills by high-resolution thermogravimetry

High-resolution thermogravimetry was used to study the thermodesorption of octane from ammonium nitrate (AN) prills with different porosities. The samples were wetted by immersion in octane. Multiple steps were obtained from the measured mass-loss curves, which reflect the evaporation of the excess liquid, as well as the thermodesorption of octane from the pores and the surface of the AN prills. The quantity of octane desorbed in these steps was correlated with the volume in the pores and the amount adsorbed on the surface, and used to estimate the adsorption capacity, porosity and surface area of AN prills. The results were also compared to observations from scanning electron microscopy.