Thermal characterization of indinavir sulfate using TG,DSC and DSC-photovisual

The object of the present work is to study the thermal characteristics of indinavir sulfate and to evaluate the quality of the raw materials. Indinavir A, B, C and reference samples were obtained from different suppliers and submitted to TG, DSC and DSC-photovisual analyses. TG/DTG curves indicated a desolvation and dehydration processes and were confirmed by DSC. According to the DSC curves the fusion took place at about 141–142°C for indinavir C and Reference sample B and about 146–149°C for the others. DSC-photovisual showed insoluble raw materials for indinavir C at 160°C. Indinavir sulfate is highly hygroscopic drug which requires attention during storage and manufacture by pharmaceutical industry.     

The highly crosslinked dimethacrylic/divinylbenzene copolymers

The thermal stability of the ionic liquids (ILs) 1-n-butyl-3-methylimidazolium bromide, [BMIM]Br, and 1-n-octyl-3-methylimidazolium bromide, [OMIM]Br, was evaluated through thermogravimetry (TG). Long-term isothermal TG studies revealed that both of these ILs exhibit appreciable decomposition even at temperatures significantly lower than the onset decomposition temperature, previously determined from fast scan TG experiments. The long-term TG studies of both the ILs showed linear mass loss as a function of time at each temperature of 10 °C interval in the range 533–573 K over a period of 10 h. The kinetics of isothermal decomposition of ILs was analyzed using pseudo-zero-order rate expression. The activation energies for the isothermal decomposition of [BMIM]Br and [OMIM]Br under nitrogen atmosphere are 219.86 and 212.50 kJ mol⁻¹, respectively. The moisture absorption kinetics of these ILs at 25 °C and 30% relative humidity (RH) and at 85 °C and 85% RH were also studied. Water uptake of ILs exposed at 25 °C/30%RH follows a simple saturation behavior in agreement with Weibull model while that at 85 °C/85%RH fortuitously fit into the Henderson–Pabis model.     

Thermal behaviour of cephalexin in different mixtures

The thermoanalytical curves (TA), i.e. TG, DTG and DTA for pure cephalexin and its mixtures with talc, magnesium stearate, starch and microcrystalline cellulose, respectively, were drawn up in air and nitrogen at a heating rate of 10 °C min⁻¹. The thermal degradation was discussed on the basis of EGA data obtained for a heating rate of 20 °C min⁻¹. Until 250 °C, the TA curves are similar for all mixtures, up this some peculiarities depending on the additive appears. These certify that between the pure cephalosporin and the excipients do not exists any interaction until 250 °C. A kinetic analysis was performed using the TG/DTG data in air for the first step of cephalexin decomposition at four heating rates: 5, 7, 10 and 12 °C min⁻¹. The data processing strategy was based on a differential method (Friedman), an integral method (Flynn–Wall–Ozawa) and a nonparametric kinetic method (NPK). This last one allowed an intrinsic separation of the temperature, respective conversion dependence on the reaction rate and less speculative discussions on the kinetic model. All there methods had furnished very near values of the activation energy, this being an argument for a single thermooxidative degradation at the beginning (192–200 °C).     

Thermogravimetry as a possible tool for determining modification degree of thermally treated Norway spruce wood

Thermal treatment is one of environmental friendly wood modification processes, developed in order to improve wood’s natural durability and dimensional stability. Beside wood species, mainly isothermal temperature of heat-treatment and process duration affect these properties, which also correlate with the mass losses caused by the treatment. However, there is a lack of suitable external quality control methods. In this work thermogravimetry as a potential method for determining the degree of thermal modification is presented. Several calibration curves, representing the mass losses in a certain temperature range (the values obtained from the TG curves) compared to weight losses caused by previous heat-treatment (known values), were established for spruce wood samples modified at different isothermal temperatures (from 170 to 220 °C). Linear plot and good correlation factors (R ² = 0.95 and 0.96) were obtained for the TG mass losses from 130 to 280 °C and from 130 to 300 °C, both under nitrogen atmosphere. The predominant cause of mass loss in this temperature region was depolymerisation and thermal decomposition of hemicelluloses residues. Lower correlation factors were obtained under the air atmosphere and in the wider temperature range, respectively.     

Thermal analysis of vitamin PP Niacin and niacinamide

Vitamin PP includes two vitamers, niacin and niacinamide which are essential for energy production. Vitamins are sensitive and losses can occur during shelf life and heating processes. Thermal analysis can provide information about thermal behavior of each vitamer relating them with time and/or temperature exposure. The vitamers thermal behavior were studied by TG/DTG and DSC under air and nitrogen atmosphere and the results showed that niacin is more stable than the niacinamide and the decomposition happens by volatilization at 238 °C while niacinamide melts at 129 °C and volatilize at 254 °C when there is the total mass loss in the TG/DTG curves.     

Thermal behavior of verapamil in pure and in solid dosage forms

Verapamil is a phenyl-alchil-amine type pharmaceutical largely used as a specific calcium antagonist. Knowledge of drug-excipient compatibility represents an important phase in development of different dosage forms. Hyphenated techniques are versatile for obtaining such necessary information’s. The TG/DTG/DTA curves were obtained in air at different heating rates and in nitrogen. The IR spectra of pure compound and its char at 400 °C (by U-ATR technique) and the IR identification of Evolved Gasses allowed some discussions on the thermally induced events. In the solid dosage forms verapamil was mixed with talc, magnesium stearate, starch, and cellulose, and the corresponding thermoanalytical curves were compared with that one of pure I. No physical or chemical interactions were observed till 250 °C. A kinetic analysis was performed for TG step of verapamil between 250 and 350 °C. The data at four heating rates (7, 10, 12, 15 °C min⁻¹) were processed on a strategy using at last three different kinetic methods. For these, the NPK method seems to be less speculative, allowing an objective determination of the kinetic parameters.     

Nonisothermal decomposition kinetics of [CoC<Subscript>2</Subscript>O<Subscript>4</Subscript>·2.5H<Subscript>2</Subscript>O]<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript>

The authors present their results concerning the decomposition in air of the homopolynuclear coordination compound [CoC₂O₄·2.5H₂O] _n . In the temperature range 20–300 °C, the heating curves TG, DTG and DTA allowed to evidence three decomposition steps. The kinetic analysis was performed on the second step which proved to be the only workable one. The application of nonlinear regression procedure shows that this is a complex process consisting in three successive steps. The checking of the mechanism and corresponding kinetic parameters for quasi-isothermal data (T = 150 °C) shows that the obtained results could be used for prediction of the thermal behaviour of the investigated compound in both isothermal and non-isothermal conditions.     

Thermal behavior of drugs

Data on the thermal stability of drugs was required to obtain information for handling, storage, shelf life and usage. In this study, the thermal stability of two nonsteroidal anti-inflammatory drugs (NSAIDs) was determined by differential scanning calorimetry (DSC) and simultaneous thermogravimetery/differential thermal analysis (TG/DTA) techniques. The results of TG analysis revealed that the main thermal degradation for the naproxen and celecoxib occurs in the temperature ranges of 196–300 and 245–359 °C, respectively. The TG/DTA analysis of compounds indicates that naproxen melts (at about 158.1 °C) before it decomposes. However, the thermal decomposition of the celecoxib started about 185 °C after its melting. The influence of the heating rate (5, 10, 15, and 20 °C min⁻¹) on the DSC behavior of the both drug samples was verified. The results showed that, as the heating rate was increased, decomposition temperatures of the compounds were increased. Also, the kinetic parameters such as activation energy and frequency factor for the compounds were obtained from the DSC data by non-isothermal methods proposed by ASTM E696 and Ozawa. Based on the values of activation energy obtained by various methods, the following order for the thermal stability was noticed: naproxen > celecoxib. Finally, the values of ΔS ^#, ΔH ^#, and ΔG ^# of their decomposition reaction were calculated.     

Elastic properties and mechanical relaxation behaviors of PVDF (poly (vinylidene fluoride)) at temperatures between −20 and 100 °C and at 2 MHz ultrasonic frequency

The elastic properties of PVDF have been investigated as a function of temperature. The propagation velocity and absorption of longitudinal and transverse ultrasonic waves have been measured at a constant frequency of 2 MHz and temperatures between –20 and 100 °C. Hence, the temperature dependences of storage and loss elastic constants have been obtained for temperatures between –20 and 100 °C. It has been seen that the relaxation behavior is affected from the form of mechanical disturbance. For the longitudinal mode, only one relaxation peak at 42 °C, but for transverse mode three relaxation peaks at 28 °C, 60 °C, and 94 °C have been observed. The results have been compared with the literature values obtained previously for PVDF. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2862–2873, 2005     

AgNbO<Subscript>3</Subscript> ceramics synthesized by aqueous solution-gel method

AgNbO₃ powders and ceramics were prepared by aqueous solution-gel method. The phase evolution of the powders was investigated by TG/DSC and XRD. The results showed that the pure AgNbO₃ phase was obtained at 600 °C without special treatment. The sintering behavior and dielectric properties of the AgNbO₃ ceramics were also investigated. It showed the dense ceramics were obtained as lower as 925 °C, which had the excellent dielectric properties with the permittivity of 291 and dielectric loss of about 1.7% at 1 MHz. The coarse grains were observed for the sample sintered over 975 °C, and then they decreased with the sintering temperature further increasing to 1,050 °C.     

An aqueous solution-gel method for low temperature synthesis of nanocrystalline NaNbO<Subscript>3</Subscript> and their ceramics

Nano-sized NaNbO₃ powder has been successfully prepared by aqueous solution-gel method. The phase evolution of NaNbO₃ powder is investigated by TG/DSC, X-rays spectra, FT-IR, and Raman spectra. The results show that the pure NaNbO₃ phase has been obtained at about 375 °C, which is lowered by about 100 °C comparing to others’ work. In TEM studied, it shows the average particle size of ~ 70 nm for the powders heat-treated at 750 °C for 4 h. The powders heat-treated below 650 °C for 4 h shows a Pmnm symmetry, then change from O₃ orthorhombic to O₁ orthorhombic with the heat-treatment temperature above 650 °C.     

Thermal decomposition of metal methanesulfonates in air

The thermal decompositions of dehydrated or anhydrous bivalent transition metal (Mn, Fe, Co, Ni, Cu, Zn, Cd) and alkali rare metal (Mg, Ca, Sr, Ba) methanesulfonates were studied by TG/DTG, IR and XRD techniques in dynamic Air at 250–850 °C. The initial decomposition temperatures were calculated from TG curves for each compound, which show the onsets of mass loss of methanesulfonates were above 400 °C. For transition metal methanesulfonates, the pyrolysis products at 850 °C were metal oxides. For alkali rare metal methanesulfonates, the pyrolysis products at 850 °C of Sr and Ba methanesulfonates were sulphates, while those of Mg and Ca methanesulfonate were mixtures of sulphate and oxide.     

Study by DTA/TG of the formation of calcium aluminate obtained from an aluminium hazardous waste

A Spanish hazardous waste from tertiary aluminium industry was used as a raw material for the synthesis of calcium aluminate. An amorphous precursor was obtained by a hydrothermal method at different values of pH. The transformation of the precursor in a crystalline aluminate was followed by TG/DTA up to 1300 °C. At temperatures between 719 and 744 °C, the precursors evolve towards the formation of C₁₂A₇ which becomes CA at circa 1016 °C. Mass spectrometry coupled to thermal analyser allowed the identification of the decomposition products.     

SrSnO<Subscript>3</Subscript>:Nd obtained by the polymeric precursor method

In this work, the synthesis of Nd-doped SrSnO₃ by the polymeric precursor method, with calcination between 250 and 700 °C is reported. The powder precursors were characterized by TG/DTA and high temperature X-ray diffraction (HTXRD). After heat treatment, the material was characterized by XRD and infrared spectroscopy. Ester and carbonate amounts were strictly related to Nd-doping. According to XRD patterns, the orthorhombic perovskite was obtained at 700 °C for SrSnO₃ and SrSn_0.99Nd_0.01O₃. For Sr_0.99Nd_0.01SnO₃, the kinetics displayed an important hole in the crystallization process, as no peak was observed in HTXRD up to 700 °C, while a XRD patterns showed a crystalline material after calcination at 250 °C.     

Thermal degradation of poly(lactic acid) measured by thermogravimetry coupled to Fourier transform infrared spectroscopy

Thermogravimetric (TG), differential thermal analysis (DTA) and thermal degradation kinetics, FTIR and X-ray diffraction (XRD) analysis of synthesized glycine–montmorillonite (Gly–MMT) and montmorillonite bound dipeptide (Gly–Gly–MMT) along with pure Na–MMT samples have been performed. TG analysis at the temperature range 25–250 °C showed a mass loss for pure Na–MMT, Gly–MMT and Gly–Gly–MMT of about 8.0%, 4.0% and 2.0%, respectively. DTA curves show the endothermic reaction at 136, 211 and 678 °C in pure Na–MMT whereas Gly–MMT shows the exothermic reaction at 322 and 404 °C and that of Gly–Gly–MMT at 371 °C. The activation energies of the first order thermal degradation reaction were found to be 1.64 and 9.78 kJ mol⁻¹ for Gly–MMT and Gly–Gly–MMT, respectively. FTIR analyses indicate that the intercalated compounds decomposed at the temperature more than 250 °C in Gly–MMT and at 250 °C in Gly–Gly–MMT.     

Influence of the thermal treatment in the crystallization of NiWO4 and ZnWO4

NiWO₄ and ZnWO₄ were synthesized by the polymeric precursor method at low temperatures with zinc or nickel carbonate as secondary phase. The materials were characterized by thermal analysis (TG/DTA), infrared spectroscopy, UV–Vis spectroscopy and X-ray diffraction. NiWO₄ was crystalline after calcination at 350 °C/12 h while ZnWO₄ only crystallized after calcination at 400 °C for 2 h. Thermal decomposition of the powder precursor of NiWO₄ heat treated for 12 h had one exothermic transition, while the precursor heat treated for 24 h had one more step between 600 and 800 °C with a small mass gain. Powder precursor of ZnWO₄ presented three exothermic transitions, with peak temperatures and mass losses higher than NiWO₄ has indicating that nickel made carbon elimination easier.     

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 analysis applied in the crystallization study of SrSnO3

SrSnO₃ was synthesized by the polymeric precursor method with elimination of carbon in oxygen atmosphere at 250 °C for 24 h. The powder precursors were characterized by TG/DTA and high temperature X-ray diffraction (HTXRD). After calcination at 500, 600 and 700 °C for 2 h, samples were evaluated by X-ray diffraction (XRD), infrared spectroscopy (IR) and Rietveld refinement of the XRD patterns for samples calcined at 900, 1,000 and 1,100 °C. During thermal treatment of the powder precursor ester combustion was followed by carbonate decomposition and perovskite crystallization. No phase transition was observed as usually presented in literature for SrSnO₃ that had only a rearrangement of SnO₆ polyhedra.     

The flash points and thermal behaviors of diesel blends with biodiesels, α-pinene,d-limonene and caffeic acid as antioxidants

The present study assessed the effects of antioxidants on the flash point and thermal behavior of diesel fuel blended with 3–10 vol% biodiesel made from spent coffee grounds oil (SCGO) or Jatropha seed oil (JSO) extracted using with n-hexane or acetone, with or without α-pinene and d-limonene (as volatile antioxidants) or caffeic acid (as a non-volatile antioxidant). Effects were evaluated by assessing flash points and by thermogravimetry/differential thermogravimetry and differential thermal analysis (DTA). The flash points of the JSO and SCGO biodiesels obtained from oils extracted using n-hexane were higher than those extracted using acetone, and the addition of 10 vol% JSO or SCGO biodiesel made using acetone extraction increased the flash point by up to 2 °C. The DTA results for JSO and SCGO biodiesels also changed according to the extraction solvent. The flash points of diesel/α-pinene/d-limonene mixtures decreased as the amount of α-pinene was increased up to 10 vol%. TG peaks obtained from 10% α-pinene/d-limonene (50 vol%/50 vol%) in diesel were lowered by approximately 20 °C. The addition of 100–1000 mg kg^?1 caffeic acid to diesel lowered the flash point by 2 °C and shifted the TG peak to approximately 75 °C from the value of 66 °C for pure diesel. This effect was constant regardless of the caffeic acid content, while DTA results were largely unaffected by this additive. The results of this work confirm that both flash point and thermal behavior are dependent on the particular type of antioxidant employed.

     

Carbon dioxide adsorption over DIPA functionalized MCM-41 and SBA-15 molecular sieves

The capture of carbon dioxide was carried out using MCM-41 and SBA-15 as adsorbents. These mesoporous materials were synthesized by the hydrothermal method, and subsequently functionalized with the di-iso-propylamine (DIPA). Then, they were characterized by XRD, BET, and TG/DTG. The X-ray diffraction patterns of the synthesized samples showed the characteristic peaks of MCM-41 and SBA-15, indicating that the structures of these materials were obtained. The functionalized samples presented a decrease of the intensities of these peaks, suggesting a decreasing in the structural organization of the material; however, the mesoporous structure was preserved. For the adsorption capacity measurements, the materials were previously saturated with carbon dioxide at 75 °C, and then desorbed in a thermobalance in the temperature range of 25–900 °C, under helium atmosphere. Desorption tests showed that the functionalized MCM-41 presented a weight loss of 7.5 wt%, against 5.9 wt% for SBA-15. The obtained values indicate that these nanostructured materials can be used as adsorbent for carbon dioxide capture.