Thermoanalytical Measurements Research Articles

Thermoanalytical study of nimesulide and their recrystallization products obtained from solutions of several alcohols

Thermogravimetry, differential scanning calorimetry, and vibrational infrared spectroscopy were used to study nimesulide and its recrystallization products that were obtained from solutions of several alcohols. The thermoanalytical measurements were performed in both air and nitrogen atmospheres and the results suggest that, under the experimental conditions used in this paper, it was possible to obtain neither polymorphic nor pseudopolymorphic forms of this drug. In this investigation, quantum chemical approach methods were used to determine the molecular structures using the Becke three-parameter hybrid method and the Lee–Yang–Parr correlation functional. The performed molecular calculations were done with the Gaussian 09 routine and the theoretical calculation results were correlated with the experimental IR vibrational spectrum.

Kinetics of thermal decomposition of a synthetic K–H3O jarosite analog

The thermal decomposition kinetics of a synthetic K–H3O jarosite analog was determined from thermogravimetric analysis at various heating rates in air. A thermal decomposition mechanism was proposed based on X-ray analysis of partially decomposed material and distinct features observed during thermal decomposition analysis. The decomposition path is complex. The material was treated as a composite of K-jarosite, H3O-jarosite, and a “vacancy component”. The evolution of (OH)− and SO3 from these individual components was modeled. The decomposition is broken into subreactions according to distinct features in the thermoanalytical measurements. The subreactions are arranged sequentially and in parallel according to the evolution of the participating phases. A set of associated apparent activation energies was determined using isoconversion analysis. Kinetic triplets were assigned to each subreaction. A reasonable match with the observed decomposition was achieved by varying pre-exponential factors.

Semi-Solid o/w Emulsions Based on Sucrose Stearates: Influence of Oil and Surfactant Type on Morphology and Rheological Properties

Sucrose stearate blends of intermediate lipophilicity are mild surfactants with thermosensitive gelling behavior. Binary systems and emulsions with sucrose stearate S-970 or S-1170 were developed and investigated by thermoanalytical and rheological measurements. The presence of an oil phase promoted the gelling potential of the esters especially at higher production temperatures. Semi-solid emulsions with viscoelastic properties comparable to weak gels were obtained with different dermatologically acceptable oils. The complex internal structure as visualized by fluorescence microscopy exhibited changes during storage in dependence of oil and surfactant type. A combination of S-970 with cetearyl ethylhexanoate-based oil phases led to superior physical stability.

Kinetics and Mechanism of the Thermal Decomposition of Sodium Percarbonate: Role of the Surface Product Layer

The reaction mechanism and overall kinetics of the thermal decomposition of sodium percarbonate crystals were investigated by thermoanalytical measurements and morphological observations. The reaction proceeds via a surface reaction and subsequent advancement of the as-produced reaction interface toward the center of the crystals, where the seemingly smooth mass-loss behavior can be described by the apparent activation energy Ea of ca. 100 kJ mol(-1). However, considering the rate behavior, as the reaction advances, it is expected that the secondary reaction step characterized by an autocatalytic rate behavior takes part in the overall reaction. The hindrance of the diffusional removal of the evolved gases by the surface product layer, Na2CO3, is the most probable reason for the change in the reaction mechanism. In the deceleration part of the first reaction step, the second reaction step is accelerated due to an increase in the water vapor pressure at the reaction interface inside the reacting particles. We also expect the self-generated reaction condition of the high water vapor pressure and the existence of liquid phase due to the formation of Na2CO3 whiskers as the solid product and the insensitive rate behavior of the second reaction step to a higher atmospheric water vapor pressure. A relevant reaction model for the thermal decomposition of SPC crystals are discussed by focusing on the role of the surface product layer.

Ignition and combustion of mechanically alloyed Al–Mg powders with customized particle sizes

Adding aluminum to propellants, pyrotechnics, and explosives is common to boost their energy density. A number of approaches have been investigated that could shorten aluminum ignition delay, increase combustion rate, and decrease the tendency of aluminum droplets to agglomerate. Previous work showed that particles of mechanically alloyed Al·Mg powders burn faster than similarly sized particles of pure aluminum. However, preparation of mechanically alloyed powders with particle sizes matching those of fine aluminum used in energetic formulations was not achieved. This work is focused on preparation of mechanically alloyed, composite Al·Mg powders in which both internal structures and particle size distributions are adjusted. Milling protocol is optimized to prepare equiaxial, micron-scale particles suitable for laboratory evaluations of their oxidation, ignition, and combustion characteristics. Oxidation of the prepared powders is studied using thermo-analytical measurements. Ignition is characterized experimentally using an electrically heated filament setup. Combustion is studied using a constant volume explosion setup for the powder cloud combustion, and a laser ignition setup for characterization of combustion rates and temperatures for individual particles. For the prepared materials, ignition and combustion characteristics are compared to those of pure Al. It is observed that the mechanically alloyed powders ignite at much lower temperatures than Al. Once ignited, the particles burn nearly as fast as Al, resulting in an overall improvement of the combustion performance.

Nano-structured Aluminum Powders with Modified Protective Surface Layers

ABSTRACTThe advantage of aluminum powder as a fuel additive in energetic formulation includes its high volumetric combustion enthalpy and relatively low cost. However, the thermodynamically predicted benefits of aluminum combustion are rarely achieved because of extended ignition delays associated with heterogeneous reactions occurring at the alumina surface which surrounds the aluminum particle. In order to fully exploit aluminum’s high reaction energy, this effort focuses on adjusting its combustion dynamics by modifying its surface and structure. The modification is achieved by cryo-milling aluminum with cyclooctane, which is liquid at room temperature, but solid when cooled by liquid nitrogen. The prepared materials consist of micron-sized, equiaxial, mostly Al particles with a small amount of cyclooctane. Aluminum surface in the prepared sample is coated with a cyclooctane-modified layer with properties significantly different from those of regular alumina. Its oxidation kinetics, as observed from thermo-analytical measurements, is different from that of pure aluminum. The powder ignites at substantially reduced temperatures, produces shorter ignition delays, and higher aerosol burn rates compared to a regular spherical Al powder with similar particle sizes.

Kinetic approach to partially overlapped thermal decomposition processes

Practical usefulness of the kinetic deconvolution for partially overlapped thermal decomposition processes of solids was examined by applying to the co-precipitated basic zinc carbonate and zinc carbonate. Comparing with the experimental deconvolutions by thermoanalytical techniques and mathematical deconvolutions using different statistical fitting functions, performance of the kinetic deconvolution based on an accumulative kinetic equation for the independent processes overlapped partially was evaluated in views of the peak deconvolution and kinetic evaluation. Two-independent kinetic processes of thermal decompositions of basic zinc carbonate and zinc carbonate were successfully deconvoluted by means of the thermoanalytical measurements in flowing CO2 and by applying sample controlled thermal analysis (SCTA). The deconvolutions by the mathematical curve fittings using different fitting functions and subsequent formal kinetic analysis provide acceptable values of the mass-loss fractions and apparent activation energies of the respective reaction processes, but the estimated kinetic model function changes depending on the fitting functions employed for the peak deconvolution. The mass-loss fractions and apparent kinetic parameters of the respective reaction processes can be optimized simultaneously by the kinetic deconvolution based on the kinetic equation through nonlinear least square analysis, where all the parameters indicated acceptable correspondences to those estimated through the experimental and mathematical deconvolutions. As long as the reaction processes overlapped are independent kinetically, the simple and rapid procedure of kinetic deconvolution is useful as a tool for characterizing the partially overlapped kinetic processes of the thermal decomposition of solids.

Complexes Containing N-(2-hydroxyethyl)-ethylenediamine with Tetracyanometallate (II): Synthesis, IR Spectra, Thermal Behavior, Crystal Structure, Magnetic Properties and Catalysis

Two novel cyano-bridged Ni2+ and Cu2+ compounds, {[M2+(hydeten)2(μ-CN)2Ni(CN)2] n , M2+ = Ni2+ (c1) and Cu2+ (c2), N-(2-hydroxyethyl)-ethylenediamine (hydeten), were prepared and characterized by elemental analysis, IR spectroscopy and thermoanalytical measurements. The one-dimensional polymeric structure of c2, which was determined by X-ray diffraction techniques, was formed with a 2,2-TT-type chain, –Cu(hydeten)2-NC-Ni(CN)2-CN-Cu(hydeten)2-, linkages. Also, while the EPR spectra and magnetic properties of complexes c1 and c2 with [Ni(hydeten)2Pd(CN)4] (c3) and [Cu(hydeten)2Pd(CN)4] (c4) [Karadag, Z Kristallogr 222:39, 2007] were investigated, the catalytic activity of c3 and c4 was studied. The EPR spectra of c2 and c4 showed that Cu2+ was located in tetragonal distorted octahedral sites (D 4h ) and the ground state of the paramagnetic electron was \( d_{{ x^{2} - y^{2} }} \). The magnetic behavior exhibited weak antiferromagnetic interactions in all the complexes. Also, the catalytic properties of c3 and c4, which were assigned with Suzuki and Heck coupling reactions, showed that they did not have catalytic effects.

Thermodynamic modeling of the LiF–YF3 phase diagram

A thermodynamic optimization of the LiF–YF3 binary phase diagram was performed by fitting the Gibbs energy functions to experimental data that were taken from the literature, as well as from own thermoanalytic measurements (DTA and DSC) on HF-treated samples. The Gibbs energy functions for the end member compounds were taken from the literature. Excess energy terms, which describe the effect of interaction between the two fluoride compounds in the liquid phase, were expressed by the Redlich–Kister polynomial function. The calculated phase diagram and thermodynamic properties for the unique formed compound, LiYF4, are in reasonable agreement with the experimental data.

Sintering study of injection molded W–8%Ni–2%Cu compacts from mixed powders by thermoanalytical techniques

Heavy alloy parts from W–8%Ni–2%Cu powder mix were fabricated by MIM using a feedstock with 50 vol.% binder. The binder was removed by solvent de-binding followed by thermal de-binding. Sintering of the heavy alloy brown parts was investigated by employing various thermoanalytical techniques such as DIL, TGA and DTA up to 1460 °C. During sintering, the evolved gases were analyzed in a mass spectrometer which was coupled to the dilatometer. Thermal analysis helps to understand the sintering process regarding phase transformation, melting of alloy matrix and chemical reactions. From these thermoanalytical measurements, a kinetic analysis was made. High sintered density (> 99%) and fine-grained homogeneous microstructures were achieved by rate controlled sintering as confirmed by metallographic analysis.

ChemInform Abstract: Characterization of AlPO4-14 by Magic-Angle-Spinning Nuclear Magnetic Resonance Spectroscopy and Thermoanalytical and Adsorption Measurements.

AlPO4-14 has been prepared using piperidine as templating agent. Uniform crystals of tabular habit were obtained. By thermoanalytical measurements of the as-synthesized sample the content of occluded piperidine was determined and its degradation was followed. From the 31P MAS NMR spectra it follows that there should exist at least three non-equivalent sites in the framework of calcined AlPO4-14. Completely reversible changes in the 27Al and 31P MAS NMR spectra were found in dehydration/hydration cycles. The relative small pore diameter of AlPO4-14 (ca. 0.4 nm) prohibits the adsorption of n-alkanes. From the adsorption isotherms of methanol and water the saturation capacities were determined to be 0.17 and 0.27 cm3 g–1, respectively.

Unsymmetrically substituted N-heterocyclic phosphenium ions

Abstract Reduction of an unsymmetrically substituted α-diimine followed by condensation with PCl3 yielded a P-chloro-N-aryl-N′-alkyl diazaphospholene which was further converted into an unsymmetrical diazaphospholium triflate by reaction with trimethylsilyl triflate. Reaction of tetramers of N-H- or N-alkyl-benzo-1,3,2-diazaphospholes with methyl triflate or triflic acid led in one step to triflate salts of unsymmetrically substituted benzo-1,3,2-diazaphospholium cations. Determination of the crystal structures of two of these derivatives by single-crystal X-ray diffraction studies revealed that individual cations and anions in the crystal lattice interact via specific electrostatic, π-stacking, or van-der-Waals type interactions to form supramolecular assemblies. Thermoanalytical measurements disclosed that benzo-diazaphospholium triflates with medium length alkyl chains melt below 100 °C and exhibit a strong tendency to form supercooled liquids.

Thermoanalytical investigation of different hip joint arthropathies

The main purpose of this study was to compare the altered metabolism in rheumatoid arthritis to normal hyaline cartilage by thermoanalytical methods. Further aim of this investigation was to elucidate the importance of water content and kinetic character of water loss. A limited number of papers have been published earlier on the subject of thermal analysis of degenerative and healthy human hyaline cartilage. Rheumatoid arthritis has not been studied previously by thermogravimetry. The only use of thermoanalytical techniques was the measurement of the enthalpy change during denaturation of the rheumatoid and normal cartilage. All samples for this investigation were obtained during live surgeries. According to the presented data, the water content of the hyaline cartilage is lower in patients with rheumatoid arthritis, than in the healthy donors. The reaction order turned out to be approximately 1 in all the cases, and the standard deviation was low. The TG curve's slope of the linear region showed, that the rate of water loss depends on the water amount remaining in the tissue. It can be concluded that the lower water content in the RA samples bound stronger to the matrix. The newly established compositional thermoanalytical measurement was sufficient for the study and differentiation of normal and rheumatoid human hyaline cartilage.

Amorphization of a crystalline active pharmaceutical ingredient and thermoanalytical measurements on this glassy form

Amorphization is nowadays a method that is frequently applied in the pharmaceutical industry. The primary aim of this study is to achieve the amorphization of clopidogrel hydrogen sulphate as an active pharmaceutical ingredient (API) with various solvents and to choose the most suitable one. A secondary aim was to determine the glass-transition temperature (Tg) of this API and to classify it as a good or poor glass former. To investigate the amorphous form, differential scanning calorimetry, X-ray powder diffraction, and FT-IR analysis were applied. The melting point (Tm) was 177.4 C (450.6 K), and Tg was determined to be 88.9 C (362.1 K). The quotient Tg/Tm was 0.80, and this API was therefore classified as a good glass former.

Tribological properties of PTFE‐filled thermoplastic polyimide at high load, velocity, and temperature

AbstractThe effect of 20 wt% polytetrafluoroethylene (PTFE) fillers on the friction and wear properties of thermoplastic polyimides (TP) are investigated, under dry sliding in line contact against steel under 50 to 200 N, 0.3 to 1.2 m/s, and 60 to 260°C. Besides the lubricating mechanisms of PTFE based on mechanical shear, the thermal and tribophysical interactions in the sliding interface are considered in this research by using thermoanalytical measurements, Raman spectroscopy, and calculating the maximum polymer sliding temperature T*. The effect of hydrolysis of the TP bulk material, causing high friction at 100 to 140°C, is covered by PTFE. A transition at pv‐values 2.2 MPa m/s (T* = 120°C) is due to thermally controlled sliding of PTFE, while a transition at pv‐values 3.2 MPa m/s (T* = 180°C) remains controlled by degradation of the TP bulk material into monomer fractions. The reduced coefficient of friction in the presence of PTFE leads to smaller degradation and orientation of the molecular back‐bone and side‐chains within the TP structure. The formation of a homogeneously mixed transfer film is only observed at 180 to 260°C. The PTFE forms a fibrillar structure during wear at high sliding velocities, while they wear as separate particles at high normal loads. POLYM. COMPOS., 2009. © 2009 Society of Plastics Engineers

Structural characterization of arsenate ion exchanged MgAl-layered double hydroxide

This paper describes a study on the adsorption and exchange of toxic and carcinogenic arsenate (AsO 4 3−) ions on positively charged surface of MgAl layered double hydroxides (LDH). The basal spacing of arsenate-free LDH containing nitrate and carbonate ions were d 003 = 0.863 and d 006 = 0.435 nm, which decreased to d 003 = 0.778 and d 006 = 0.387 nm, after ion-exchange adsorption of arsenate, an ion that is smaller than nitrate. After heating up to 350 °C the basal spacing d 003 of arsenic-containing LDH is reduced due to the dehydration of arsenate ions, and the 006 reflection disappears. The X-ray reflections of arsenic-free LDH remain nearly unchanged, because the adsorption of interlamellar water is reversible. Thermo-analytical measurements on LDH samples with identical initial nitrate and carbonate ion ratios but diverse arsenic contents reveal that the extent of mass loss decreases with increasing arsenic content up to 1000 °C. Thermally unstable arsenic oxides are stabilized between the lamellae and are converted to form mixed oxides with the ions constituting the layers of the LDH. TG and DSC measurements reveal that dehydration of LDH samples is shifted to lower temperatures, and water elimination increases proportionally with arsenic content up to 300 °C. This increase is also confirmed by the calculated values of specific enthalpy changes. The values obtained were 2504 J/g for arsenic-free LDH and 2589, 2736 and 3367 J/g for LDH samples containing 9.8, 26.8 and 54.9 mg As(V)/g, respectively. This excess originates from the conversion of arsenate ions to oxides. The peak near 830 cm − 1 appearing in the Raman spectra of LDH samples with relatively high arsenic contents is due to the symmetric vibration of the coordinative bond between arsenate and Mg 2+ and/or Al 3+ ions (As–OMe, where Me = Mg 2+, Al 3+). When the relative area of peak characteristic of the As–OMe bond increases, that of the peaks associated with nitrate and carbonate ions (1045–1070 cm − 1 and ~ 714 cm − 1 ) decrease, which means that, in addition to ionic interactions, single coordinative bonds were also formed.

Low Temperature Precursor Route for Highly Efficient Spherically Shaped LED-Phosphors M2Si5N8:Eu2+ (M = Eu, Sr, Ba)

The highly efficient nitridosilicate phosphors M2Si5N8 (M = Sr, Ba, Eu) for phosphor-converted pc-LEDs were synthesized at low temperatures using a novel precursor route involving metal amides M(NH2)2. These precursors have been synthesized by dissolution of the respective metals in supercritical ammonia at 150 °C and 300 bar. The thermal behavior and decomposition process of the amides were investigated with temperature programmed powder X-ray diffractometry and thermoanalytical measurements (DTA/TG). These investigations rendered the amides as suitable intermediates for reaction with silicon diimide (Si(NH)2). Thus, the desired nitridosilicate phosphors were obtained at relatively low temperatures around 1150−1400 °C which is approximately 300 °C lower compared to common synthetic approaches starting from metals or oxides. The influence of the thermal treatment on the phosphor morphology has been studied extensively. The accessibility of spherical phosphor particles represents another striking feature of this route since it improves light extraction from the crystallites due to decreasing light guiding and decreasing re-absorption inside the phosphor particle. The synthesized luminescent materials M2Si5N8:Eu2+ (M = Sr, Ba) exhibit quantum efficiencies and emission band widths (FWHM 70−90 nm) comparable to standard phosphor powders. Employment of Eu(NH2)2 as dopant reagent for synthesis of Ba2Si5N8:Eu2+ proved favorable for the formation of spherical crystallites compared to doping with Eu metal, halides, or oxide.

Features of strontium tetraborate synthesis by means of borate rearrangement

The results of thermoanalytical and x-ray diffraction measurements show that strontium tetraborate (SrB4O7) is formed as the result of crystallization of an amorphous substance at 750°C. The amorphous substance was obtained by dehydration of a mixture of strontium borate crystal hydrates synthesized at 95 ± 5°C via solid-state interaction of orthoboric acid with strontium carbonate. Conditions for reproducible synthesis of single-phase SrB4O7 by means of borate rearrangement have been established.

Thermal Decomposition of Indium(III) Hydroxide Prepared by the Microwave‐Assisted Hydrothermal Method

Cubic‐shaped In(OH)3 particles with average size of 0.348 μm were precipitated from a mixed aqueous solution of InCl3 and urea by a microwave‐assisted hydrothermal method. The kinetics and mechanisms of the thermal decomposition of the sample were investigated by means of thermoanalytical measurements under three different modes of temperature program, complemented by several physicochemical techniques. No intermediate compound was found during the course of thermal decomposition from cubic‐In(OH)3 to cubic‐In2O3. Distinguished induction period for the thermal decomposition was identified as one of the most characteristic kinetic phenomena of the present reaction, together with the crack formation on the surface product layer during the second half of the reaction. The kinetic rate behavior of the reaction was characterized physicogeometrically as the surface nucleation and subsequent advancement of the established reaction interface inward toward the center of the reactant particle, where the apparent activation energies for the surface nucleation and advancement of the reaction interface were estimated as 257 and 140 kJ/mol, respectively.

Investigation of the structure and swelling of poly(N-isopropyl-acrylamide-acrylamide) and poly(N-isopropyl-acrylamide-acrylic acid) based copolymer and composite hydrogels

We synthesized, thermo- and pH-sensitive gels and tested them as skin extenders. Our aim is the development of copolymer and composite hydrogels that, when implanted under the human skin, swell osmotically and thereby induce skin growth. In the course of the polymerization reaction, we produced copolymers with variable compositions, starting from different acrylic compounds [N-isopropyl-acrylamide (NIPAAm), acrylamide (AAm), and acrylic acid (AAc)]. The mechanical strength and the swelling stability of the gels are enhanced by the addition of fillers [Na-montmorillonite and Na-montmorillonites organophilized with alkylammonium ions (Cn-m.), n = 4, 12, 18]. With this method we synthesized composite hydrogels. We observed that in the case of composites synthesized with the addition of fillers, relatively low filler contents (1–5 wt.%) resulted in more extensive swelling and stronger gel structure. During the experiments, the monomer composition (0/100–100/0 mol% NIPAAm/AAm or AAc) and the cross-link density (50–1500 mol%) of the gels (M/C ratio) and, in the case of composites, the quality and quantity of fillers are varied. The filler content of composites varies between 1 and 25 wt.%. The extent of swelling and the viscoelastic properties can be manipulated through the ratios of these parameters. In the case of certain copolymer and composite gels, values of desorption enthalpy (ΔHm) corresponding to the actual water contents were also determined by thermoanalytical measurements (differential scanning calorimetry, DSC). Swelling values determined by gravimetry and enthalpies calculated from DSC measurements were found to be in good correlation. Even in the case of the relatively hydrophobic poly(NIPAAm)-based gels, an enthalpy value of 98.41 kJ/mol was obtained, which is twice the value measured in pure water (41.74 kJ/mol). Evaluation and comparison of the rheological and DSC results also allowed conclusions to be drawn concerning the types of interaction operating among the three components of the system, i.e., the polymer skeleton and the filler and water molecules.