Thermal analysis of tetraethylammonium and benzyltrimethylammonium montmorillonites

Na-montmorillonite was loaded with tetraethylammonium cations (TEA) or with benzyltrimethylammonium cations (BTMA) by replacing 77 and 81% of the exchangeable Na with TEA or BTMA, labeled TEA-MONT and BTMA-MONT, respectively. TEA- and BTMA-MONT were heated in air up to 900?°C. Thermally treated organoclays are used in our laboratory as sorbents of organic compounds from water. The two organoclays were studied by TG and DTG in air and under nitrogen. Carbon content in each of the heated sample was determined. They were diffracted by X-ray, and fitting calculations of d(001) peaks were performed on each diffractogram. TG and thermo-C analysis showed that at 150 and 250?°C both organoclays lost water but not intercalated ammonium cations. DTG peak of the first oxidation step of the organic cation with the formation of low-temperature stable charcoal (LTSC) appeared at 364 and 313?°C for TEA- and BTMA-MONT, respectively. The charcoal was gradually oxidized by air with further rise in temperature. DTG peak of the second oxidation step with the formation of high-temperature stable charcoal (HTSC) appeared at 397 and 380?°C for TEA- and BTMA-MONT, respectively. DTG peak of the final oxidation step of the organic matter appeared at 694 and 705?°C for TEA- and BTMA-MONT, respectively, after the dehydroxylation of the clay. Thermo-XRD analysis detected TEA-MONT tactoids with spacing 1.40 and 1.46?nm up to 300?°C. At 300 and 360?°C, LTSC-MONT tactoids were detected with spacing of 1.29?nm. At higher temperatures, HTSC-MONT-?? and -?? tactoids were detected with spacings of 1.28 and 1.13?nm, respectively. BTMA-MONT tactoids with spacings 1.46 and 1.53?nm were detected up to 250?°C. At 300 and 360?°C, LTSC-MONT tactoids were detected with a spacing of 1.38?nm. At higher temperatures, HTSC-MONT-?? and -?? tactoids were detected with spacings of 1.28 and 1.17?nm, respectively. At 650?°C, both clays were collapsed. HTSC-??-MONT differs from HTSC-??-MONT by having carbon atoms keying into the ditrigonal holes of the clay-O-planes. At 900?°C, the clay fraction is amorphous. Trace amounts of spinel and cristobalite are obtained from thermal recrystallization of amorphous meta-MONT.     

Thermal characterization of lignocellulosic residue from different sugarcanes

Bagasse samples from four different sugarcane were directly collected as the residues of milling in a processing plant. The samples were dried at 105 °C, compressed to small granules and then their TG/DTA and DSC curves in synthetic air were recorded. Similar thermogravimetric curves were obtained for the different samples and they exhibited four mass loss steps. However, the analysis of the exotherm DSC peaks showed that the oxidation of the organic matter resulted different enthalpy values (ΔH/kJ g⁻¹).     

Monoionic montmorillonites treated with Congo-Red

The adsorption of the anionic dye congo-red (CR) by Na-, Cs-, Mg-, Al- and Fe-montmorillonite was studied by simultaneous DTA-TG. Thermal analysis curves of adsorbed CR were compared with those of neat CR. The oxidation of neat CR is completed below 570°C. Thermal analysis curves of adsorbed CR show three regions representing dehydration of the clay, oxidation of the organic dye and dehydroxylation of the clay together with the oxidation of residual organic matter. The oxidation of the dye begins at about 250°C with the transformation of organic H atoms into water and carbon into charcoal. Two types of charcoal are obtained, low-temperature and high-temperature stable charcoal. The former gives rise to an exothermic peak in the second region of the thermal analysis and the latter in the third region. The exchangeable metallic cation determines the ratio between the low-temperature and high-temperature stable charcoal, which is formed. With increasing acidity of the exchangeable metallic cation higher amounts of high-temperature stable charcoal are obtained. It was suggested that aromatic compounds p bonded to the oxygen plane of the clay framework are converted into charcoal, which is burnt at about 550-700°C. With increasing surface acidity of the clay more species of CR are protonated. Only protonated dye species can form p bonds with oxygen plane and are converted to high-temperature stable charcoal during the thermal analysis. The thermal behavior of the dye complex of Cu-montmorillonite is different probably due to the catalytic effect of Cu. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal characteristics of bitumen pyrolysis

The pyrolysis behavior of bitumen was investigated using a thermogravimetric analyzer–mass spectrometer system (TG–MS) and a differential scanning calorimeter (DSC) as well as a pyrolysis-gas chromatograph/mass spectrometer system (Py-GC/MS). TG results showed that there were three stages of weight loss during pyrolysis—less than 110, 110–380, and 380–600 °C. Using distributed activation energy model, the average activation energy of the thermal decomposition of bitumen was calculated at 79 kJ mol⁻¹. The evolved gas from the pyrolysis showed that organic species, such as alkane and alkene fragments had a peak maximum temperature of 130 and 480 °C, respectively. Benzene, toluene, and styrene released at 100 and 420 °C. Most of the inorganic compounds, such as H₂, H₂S, COS, and SO₂, released at about 380 °C while the CO₂ had the maximum temperature peaks at 400 and 540 °C, respectively. FTIR spectra were taken of the residues of the different stages, and the results showed that the C–H bond intensity decreased dramatically at 380 °C. Py-GC/MS confirmed the composition of the evolved gas. The DSC revealed the endothermic nature of the bitumen pyrolysis.     

Charcoal produced from cellulosic raw materials by microwave-assisted hydrothermal carbonization

In this work, cellulose-based renewable raw materials were hydrothermally carbonized in a microwave oven at 200 °C during 60, 120, and 240 min. The charcoals obtained were characterized by proximate analysis, gross calorific value, and thermogravimetric analysis on inert and oxidizing atmosphere. The values of fixed carbon were between 38 and 52 %. The mass loss between 300 and 470 °C was assigned to the thermal decomposition of cellulose, followed by the second stage between 470 and 740 °C, attributed to the thermal decomposition of lignin. The gross calorific values were between 22.60 and 27.12 MJ kg^?1, which are comparable to those of charcoals and coals.     

Thermal study of naphthylammonium- and naphthylazonaphthylammonium-montmorillonite

The blue organo-clay color pigment (OCCP) naphthylazonaphthylammonium-montmorillonite was synthesized from the white naphthylammonium-montmorillonite by treating with NaNO₂, the azo colorant being located in the interlayer space. The following effects on the basal spacing of naphthylazonaphthylammonium-and naphthylammonium-clay were investigated: (1) the amount of naphthylammonium loading the clay, (2) the amount of NaNO₂ used for the staining, (3) aging of the preparation suspension and (4) thermal treatment. Samples were heated at 120, 180, 240, 300 and 360°C and diffracted by X-ray. During aging, some of the dye decomposed. Samples, after one day aging, were investigated by DTA. During the dehydration stage both organo-clays gradually decomposed, the naphthylammonium-clay at 120°C and the OCCP at 180°C. That fraction of organic matter, which did not escape, was air-oxidized at above 200°C and charcoal was obtained. The appearance and size of the DTA exothermic peaks depended on the amount of organic matter, which did not escape and this depended on the total amount of organic matter in the DTA cell. DTA proved that naphthylammonium reacted with NaNO₂ to form OCCP.     

A comparative study of the dehydroxylation process in untreated and hydrazine-deintercalated dickite

A dickite from Tarifa (Spain) was used to study the influence of the intercalation and the later deintercalation of hydrazine on the dehydroxylation process. The dehydroxylation of the untreated dickite occurs through three overlapping endothermic stages whose DTA peaks are centred at 586, 657 and 676°C. These endothermic effects correspond, respectively, to the loss of the inner-surface, the inner hydroxyl groups, and the loss of the water molecules, product of dehydroxylation process, which has been trapped in the framework of the dehydroxylated dickite. The intercalation of hydrazine in the interlayer space of dickite and the later deintercalation affect the dehydroxylation process. It occurs through only two endothermic stages which DTA peaks are centred at 575 and 650°C. The first corresponds to the simultaneous loss of both the inner and the inner-surface hydroxyl groups, whereas the second one is analogous to that at 676°C observed in the DTA curve of untreated dickite. These effects appear shifted to lower temperatures compared to those observed in the untreated dickite.     

Thermo-XRD-analysis of Co-, Ni- and Cu-montmorillonite treated with anionic alizarinate

Co- and Ni-montmorillonites adsorb in aqueous suspensions up to 13 mmol alizarinate per 100 g clay, onto the broken-bonds whereas Cu-clay adsorbs up to 25 mmol dye per 100 g clay into the interlayer space. Unloaded Co-, Ni- and Cu-clays and samples loaded with increasing amounts of alizarinate, were gradually heated in air to 360°C and analyzed by X-ray diffraction. All diffractograms were curve-fitted. Fitted diffractograms of non-heated samples, showed two peak components labeled C and D, at<span lang=EN-US style='font-size:10.0pt;font-family:Symbol;mso-bidi-font-family: Symbol;mso-ansi-language:EN-US'>?1.22 and<span lang=EN-US style='font-size:10.0pt;font-family:Symbol;mso-bidi-font-family: Symbol;mso-ansi-language:EN-US'>?1.32 nm, characterizing tactoids with mono- and non-complete bilayers of water, respectively. After heating at 120°C component D decreased or disappeared and two new components A and B appeared at<span lang=EN-US style='font-size:10.0pt;font-family:Symbol;mso-bidi-font-family:Symbol; mso-ansi-language:EN-US'>?0.99 and<span lang=EN-US style='font-size:10.0pt;font-family:Symbol;mso-bidi-font-family: Symbol;mso-ansi-language:EN-US'>?1.08 nm, representing collapsed tactoids and tactoids with interlamellar oxy-cations, respectively. At 250°C, C and D decreased or disappeared but A and B appeared in all fitted diffractograms. Co- and Ni-clay after heating at 360°C did not show C and D. Components A and B proved that these clays collapsed indicating that initially there was no alizarinate in the interlayers. At 360°C, C and D persisted in the fitted-diffractograms of Cu-clay, representing tactoids with interlamellar charcoal formed from the partial oxidation of adsorbed dye initially located in the interlayers.     

Simultaneous thermal analysis of zirconium(IV) acetylacetonate in a helium atmosphere

TG, DTG, DTA, DDTA and ΔH analyses of zirconium(IV) acetylacetonate, Zr(C₆H₇O₂)₄ (= I), were performed in a helium atmosphere with a Netzsch Thermal Analyser STA 429. The enthalpies of the main steps of transformation were computed to be +42.182 J·g^?1 and ?21.113 J·g^?1. Pure I is thermally stable up to about 199°C in He gas, and melting too occurs at about 199°C. Four well-defined decomposition steps were observed over the range between ambient and 600 °C, accompanied by a weight loss of 61.59%. The final product contained pure ZrO. The unique shapes of the TG and DTA curves could be used for the identification of I.     

Fibers and fiber cocktails to improve fire resistance of concrete

Hybrid organic–inorganic resin matrix, i.e., hexa[3,4-dicyano]-phenyl phosphonitrile trimer (HPPT) has been prepared by the reaction of hexachlorophosphonitrile and 4-hydroxyphthalonitrile in the presence of sodium hydride which on heating at 300 °C yielded a high-temperature-stable highly crosslinked hybrid resin (C-HPPT). The elemental analysis (C, H, and N), FTIR, and ¹H and ¹³C-NMR studies were used to characterize the synthesized hybrid resin. The thermal analysis studies viz. TG and DSC were also carried out to determine the thermal stability and glass transition temperature of the cured resin. The isothermal study of the cured resin after 300 h at 300 °C showed only a mass loss of 4.36%.     

Effect of surface oxygen complexes of sugar charcoal on the half cell potential of carbon-nickel ferrite electrodes

Carbon-nickel ferrite electrodes were prepared by pressing equal amounts of charcoals and nickel ferrite using ABS polymer (in acetone + benzene) as binder on a steel mesh. The half cell potentials reported were measured with reference to saturated calomel electrode. The electrolyte used was 4-N potassium hydroxide and fuel used was methanol. The surface oxygen complexes on the charcoals were varied (i) by heat-treating the sugar charcoal in vacuum at 400, 750 and 1000° C and (ii) by boiling in 4N.HNO₃ for different intervals of time. Half cell potential measured increases with the increase of oxygen content of the charcoals. The oxygen complex which is disposed off as carbon dioxide imparts polarity to the charcoal surface, and is largely responsible for the increase in potential.     

Comportement Thermique du Polypropylene au Cours du Vieillissement

Several samples of polypropylene were studied by thermal analysis. The photo-oxidation and the aging of polypropylene films showed a mass loss more than 7% in heating from 20 to 220°C (5°C min-1), cooling to 20°C and reheating to 220°C. The authors observed also a decrease of the melting and crystallization temperatures. The non aged samples or these ones with preservatives are thermo-oxidised and presented an exothermic peak at about 200°C in DTA heating. The DTA-TG simultaneous apparatus is very useful in the study of polypropylene oxidation by making comparative trials according to a well definite procedure. This revised version was published online in July 2006 with corrections to the Cover Date.     

A study of sulphonated and oxidized coals by thermal analysis

Earthy and xylytic brown coals from Poland have been sulphonated with 98% sulfuric acid at temperatures of 60°, 90° and 140°C. The main exothemic peak shifts to higher temperatures with increase in sulphonation reaction temperature whereas overall weight loss to 1000°C decreases. DTA curves of earthy and xylytic coals sulphonated at higher temperatures are similar, even though DTA curves of the unmodified coals differ appreciably. Thermal decomposition of earthy coal oxidized by nitric acid follows a different pattern. Nitric acid causes oxidation and depolymerization of the organic components and this is reflected in the shapes of DTA and TG curves of oxidized coals. As the nitric acid concentration and reaction temperature increase, the main exothermic peak shifts to lower temperatures (from 330°C for basic coal to 270°C for coal oxidized with 30 and 50% nitric acid). The weight loss is higher for oxidized coal than for coal unmodified by nitric acid.     

Thermal behavior of a bentonite

The mineralogical composition of the Kütahya calcium bentonite (CaB) from Turkey was obtained as mass% of 60% calcium rich smectite (CaS), 30% opal-CT (OCT), trace amount illite (I), and some non-clay impurities by using chemical analysis (CA), X-ray diffraction (XRD), and thermal analysis (TG-DTA) data. The crystallinity, porosity, and surface area of the samples heated between 25–1300°C for 2 h were examined by using XRD, TG, DTA and N₂-adsorption-desorption data. The position of the 001 reflection which is the most characteristic for CaS does not affect from heating between 25–600°C and then disappeared. The decrease in relative intensity (I/I ₀) from 1.0 to zero and the increase in full width at half-maximum peak height (FWHM) from 0.25 to 1.0° of the 001 reflection show that the crystallinity of the CaS decreased continuously by rising the heating temperature from 25 to 900°C and then collapsed. The most characteristic 101 reflection for opals intensifies greatly between 900 and 1100°C with the opal becoming more crystalline. The total water content of the natural bentonite after dried at 25, 105 and 150°C for 48 h were determined as 8.8, 5.0 and 2.5%, respectively. The mass loss occurs between 25 and 400°C over two steps with the maximum rate at 80 and 150°C, respectively. The exact distinction of the dehydration temperatures for the adsorbed water and interlayer water is seen almost impossible. The temperature interval, maximum rate temperature, and mass loss during dehydroxylation are 400–800°C, 670°C and 4.6–5.0%, respectively. The maximum rate temperatures for decrystallization and recrystallization are 980 and 1030°C, respectively. The changes in specific micropore volume (V _mi), specific mesopore volume (V _me), specific surface area (S) were discussed according to the dehydration and dehydroxylation of the CaS. The V _mi, V _me and S reach to their maxima at around 400°C with the values of 0.045, 0.115 cm³ g⁻¹ and 90 m² g⁻¹, respectively. The radii of mesopores for the bentonite heated at 400°C are distributed between 1–10 nm and intensified approximately at 1.5 nm.     

Thermal behaviour of sericite clays as precursors of mullite materials

Thermal analysis of some sericite clays, from several deposits in Spain, which are not exploited at this time, has been studied. The samples have been previously characterized by mineralogical and chemical analysis. Sericite clays have interesting properties, with implications in ceramics and advanced materials, in particular concerning the formation of mullite by heating. According to this investigation by differential thermal and thermogravimetric analysis (DTA-TG), the sericite clay samples can be classified as: Group (I), sericite–kaolinite clays, with high or medium sericite content, characterized by an endothermic DTA peak of dehydroxylation of kaolinite with mass loss, which overlapped with dehydroxylation of sericite, and Group (II), sericite–kaolinite–pyrophyllite clays, with broader endothermic DTA peaks, in which kaolinite is dehydroxylated first and later sericite and pyrophyllite with the main mass loss, appearing the peaks overlapped. X-ray diffraction analysis of the heated sericite clay samples evidenced the decomposition of dehydroxylated sericite and its disappearance at 1050 °C, with formation of mullite, the progressive disappearance of quartz and the formation of amorphous glassy phase. The vitrification temperature is ~ 1250 °C in all these samples, with slight variations in the temperatures of maximum apparent density (2.41–2.52 g mL^?1) in the range 1200–1300 °C. The fine-grained sericite content and the presence of some mineralogical components contribute to the formation of mullite and the increase in the glassy phase by heating. Mullite is the only crystalline phase detected at 1400 °C with good crystallinity. SEM revealed the dense network of rod-shaped and elongated needle-like mullite crystals in the thermally treated samples. These characteristics are advantageous when sericite clays are applied as ceramic raw materials.     

Research on historical bricks from a Baroque Church

Baroque bricks were investigated by DTA, TG, EGA, TDA, and XRD. The analyses showed that the brick consisted of dehydroxylated illite, quartz, and calcite. Dehydroxylation as a consequence of the former rehydroxylation was not found probably because of protection of the bricks by plaster. Between the temperatures 600 and 800 °C, (a) intensive mass loss in TG, (b) endothermic minimum in DTA, (c) intensive escape of CO₂ in EGA, and (d) contraction of the sample in TDA were observed. All these events belong to decomposition of calcite. As follows from these results, the maximum firing temperature was about 700 °C. The bricks have relatively high porosity ~43 % and specific surface area ~18.6 m² g^?1.     

Thermal behaviour and slow molecular mobility in two isomers of biphenylmethanol

This research was aimed to investigate the role of clay on the combustion and kinetic behavior of crude oils in limestone matrix. For this purpose, simultaneous TG (thermogravimetry) and DTA (differential thermal analysis) experiments were performed at three different heating rates as 10–15 and 20°C min^–1, respectively. A uniform trend of decreasing activation energies was observed with the addition of clay. It was concluded that clays surface area affects the values of Arrhenius constant, while it is the catalytic properties of clay, which lower the activation energies of all the reactions, involved in the combustion process.     

Thermal analyis of hexadecyltrimethylammonium–montmorillonites

Na-montmorillonite (Na-MONT) was loaded with hexadecyltrimethylammonium cations (HDTMA) by replacing 41 and 90% of the exchangeable Na with HDTMA, labeled OC-41 and OC-90, respectively. Na-MONT, OC-41, and OC-90 were heated in air up to 900 °C. Unheated and thermally treated organoclays heated at 150, 250, 360, and 420 °C are used in our laboratory as sorbents of different hazardous organic compounds from waste water. In order to get a better knowledge about the composition and nature of the thermally treated organoclays Na-MONT and the two organo-clays were studied by thermogravimetry (TG) in air and under nitrogen. Carbon and hydrogen contents in each of the thermal treated sample were determined and their infrared spectra were recorded. The present results showed that at 150 °C both organoclays lost water but not intercalated HDTMA cations. At 250 °C, many HDTMA cations persisted in OC-41, but in OC-90 significant part of the cations were air-oxidized into H₂O and CO₂ and the residual carbon formed charcoal. After heating both samples at 360 °C charcoal was present in both organo clays. This charcoal persisted at 420 °C but was gradually oxidized by air with further rise in temperature. TG runs under nitrogen showed stepwise degradation corresponding to interlayer water desorption followed by decomposition of the organic compound, volatilization of small fragments and condensation of non-volatile fragments into quasi-charcoal. After dehydroxylation of the clay the last stages of organic matter pyrolysis and volatilization occurred.     

Thermal decomposition kinetics of diethyl dithiocarbamate complexes of copper(II) and nickel(II)

Thermogravimetric (TG), derivative thermogravimetric (DTG) and differential thermal analysis (DTA) curves of CuL₂ and NiL₂ (L^?=diethyl dithiocarbamate anion) in air are studied. The main decomposition temperature ranges are: For CuL₂, DTG 250–350°, DTA 300–320° and for NiL₂, DTG 290–390°, DTA 360–400°. Mass loss considerations at the main decomposition stages indicate conversion of the complex to sulphides. Mathematical analysis of TG data shows that first order kinetics are applicable in both cases. Kinetic parameters (energy and entropy of activation and preexponential factor) are reported.

     

Non-isothermal kinetic study on the decomposition of Zn acetate-based Sol-gel precursor

The isoconversional methods (Friedman (FR), Flynn-Wall-Ozawa (FWO) and Kissinger-Akahira-Sunose (KAS)) were applied for evaluating the dependencies of the activation energy (E) on the mass loss (Δm) corresponding to the non-isothermal decomposition of two Zn acetate-based gel precursors for ZnO thin films whose preparation differs by the drying temperature of the liquid sol-precursor (125°C for sample A, and 150°C for sample B). Although both investigated samples exhibit similar decomposition steps, strong differences between E vs. Δm curves as well as among the characteristic parameters of the decomposition steps, directly evaluated from TG, DTG and DTA curves, were put in evidence.