Technological quality determination of pharmaceutical disintegrant by DSC cooling and DSC photovisual

A number of disintegrants are available on the market. They improve tablets’ disintegration. The objective of this work is the comparison of the technological quality parameters of disintegrants using different analytical techniques. Three batches of disintegrants and their binary mixtures (water:disintegrants) were investigated. Cooling experiments were used from –30 up to 200°C. The data obtained showed calorimetric differences between the samples. In the binary mixtures water showed different crystallization behaviour from the one found in the literature. According to the results DSC technique helped the quality control of different disintegrants.     

Thermal stability and crystallization kinetics of Se–Te–Sn alloys using differential scanning calorimetry

The present article deals with the differential scanning calorimetric (DSC) study of Se?CTe glasses containing Sn. DSC runs are taken at four different heating rates (10, 15, 20 and 25?K?min^?1). The crystallization data are examined in terms of modified Kissinger, Matusita equations, Mahadevan method and Augis and Bennett approximation for the non-isothermal crystallization. The activation energy for crystallization (E _c) is evaluated from the data obtained at different heating rates. Activation energy of glass transition is calculated by Kissinger??s relation and Moynihan theory. The glass forming tendency is also calculated for each composition. The glass transition temperature and peak crystallization temperature increases with the increase in Sn % as well as with the heating rate.     

Use of differential scanning calorimetry to study polymer crystallization kinetics with longer half times

A method has been developed to determine polymer crystallization parameters with longer half times using differential scanning calorimetry. This method can be used irrespective of the crystallization temperature, sample weight, nature of the polymer and the sensitivity of the instrument. The results obtained from this method for polyethylene samples are compared with those obtained from dilatometry. Similar values for the kinetic parameters are obtained using both techniques. The calorimetric method has been used for other polymers such as polypropylene and poly(4-methyl-1-pentene).     

Comparison of different chemical modifiers for the direct determination of arsenic in sea water by electrothermal atomic absorption spectrometry

A comparative study of different chemical modifiers for the direct determination of arsenic in real and in synthetic sea water samples of high (72.8 per thousand ) and low (34.2 per thousand ) salinity was carried out. The use of lanthanum chloride and magnesium nitrate (LOD=3.0 microg l(-1)) offers good recoveries for low salinities, while for high salinities an enhancement higher than 200% was obtained, rendering this method unsuitable for sea water samples. The use of silver nitrate (LOD=2.0 microg l(-1)) produces unfavourable analytical recoveries, around 150 and 300% for synthetic sea water of low and high salinity. Zirconium oxychloride (LOD=1.8 microg l(-1)) and palladium nitrate alone or combined with magnesium nitrate and reducing agents (LOD=1.1-1.3 microg l(-1)) produce analytical recoveries close to 100% for all arsenic concentration tried over all salinities; thus, a single calibration curve using aqueous standard solutions may be applied to the analysis of sea water samples over all salinities. Finally, the addition of reducing agents and magnesium nitrate to palladium does not improve the sensitivity.     

Comparative study of magnesium nitrate,palladium nitrate and reduced palladium for the direct determination of mercury in sea water by electrothermal atomization atomic absorption spectrometry

A comparative study of different chemical modifiers in graphite furnace atomic absorption spectrometry for the direct determination of mercury in sea water samples, in synthetic sea water sample of high (72.8%) and low 34.2%) salinity and in aqueous solutions, was carried out. The use of reduced palladium produces better results. The mixture of palladium nitrate and ascorbic acid, gives the best limit of detection (1.9 gl^–1). The use of reduced palladium and magnesium nitrate produced excellent recoveries (close to 100%) in the whole salinity range for all mercury concentration tested. The use of palladium nitrate alone or combined with magnesium nitrate gave good recoveries with respect to a real sea water sample for low salinities. The interference from the major components of sea water were completely removed by using reduced palladium and magnesium nitrate modifiers. Thus, a single calibration curve with synthetic sea water may be applied to the analysis of sea water samples of widely differing salinities.     

On the stability of extremely diluted solutions to temperature

Conductometric and calorimetric titrations of extremely diluted solutions (EDS) were performed by adding HCl or NaOH solutions. The aim of this work was to confirm the hypothesised presence of molecular aggregates of water molecules in EDS stored for 15 months at 5 different temperatures. Conductometric and calorimetric measurements on the EDS samples revealed significant differences compared to the solvent. The experimental data can be interpreted as indicating a favourable interaction between the H₃O⁺ and OH^? ions and the dissipative structures, leading to the formation of complexes between the two ions deriving from probes and the molecular aggregates of water molecules. These results suggest that storing EDS at different temperatures does not alter the non-equilibrium changes in the supramolecular structure of water in the studied solutions.     

Iso-conversional kinetic study of non-isothermal crystallization in glassy Se98Ag2 alloy

The crystallization kinetics of glassy Se₉₈Ag₂ alloy is studied at different heating rates (5, 10, 15, and 20?K?min^?1) using differential scanning calorimetric technique. Endothermic and exothermic peaks are obtained at glass transition (T _g) and crystallization temperature (T _c). Four iso-conversional methods (Kissinger?CAkahira?CSunose (KAS), Flynn?CWall?COzawa (FWO), Tang and Straink) were used to determine the various kinetic parameters (crystallization temperature T _?? , activation energy of crystallization E _??, order parameter n) in non-isothermal mode.     

Melt-crystallization, glass transition and morphology of a (R)-3-hydroxybutyrate pentamer

The melt-crystallization of an oligo[(R)-3-hydroxybutyrate] with five repeating units has been analyzed using standard and temperature-modulated calorimetry, optical microscopy, and atomic force microscopy. Specimens of different crystallinity and supermolecular structure were generated by variation of the rate of cooling of a quiescent melt, or by variation of the temperature of isothermal crystallization. Completely amorphous samples can be obtained by cooling of the melt at a rate of 40 K min⁻¹, or faster, to a temperature lower than the glass transition. The crystallinity depends on the crystallization temperature. The maximum enthalpy-based crystallinity of about 40-45% is obtained by crystallization at temperatures lower than the temperature of the maximum crystallization rate, which is between 310 and 320 K. Analysis of the apparent heat capacity in metastable structural equilibrium reveals reversible melting at temperatures between 320 and 370 K by observation of an excess heat capacity above the level of the vibrational heat capacity, i.e., in the temperature range of irreversible reorganization and melting. The reversible melting is discussed in the context of coupling of the crystalline and amorphous phases, and compared to earlier studies on oligoethylene and oligo(oxyethylene). The presence of crystals causes formation of a rigid amorphous fraction of about 30% at a crystallinity of 40%. Optical and atomic force microscopy reveal spherulitic crystallization. At relatively high crystallization temperature, and in the early stage of the crystallization process, dendrites are observed which finally yield spherulites of decreased perfection. Larger spherulites of higher perfection grow at relatively low crystallization temperature, as deduced from the appearance of the Maltese cross, and the regularity of banding. The band spacing is less than 5 μm, as is accurately determined by atomic force microscopy. The temperature dependence of the spherulitic growth rate is in accord with the calorimetric analysis of the crystallization rate.     

Kinetics of polymer crystallization from the melt (calorimetric approach)

Crystallization kinetics for 12 polymers including polyolefins, polyesters, polyurethanes, polysiloxanes was measured by the evolution of heat in a modified Calvet-type calorimeter over wide temperature ranges. The results are analyzed in terms of the Avrami equation and a comparison between calorimetric and dilatometric results is carried out. It is concluded that, although in the majority of cases experimental results do not obey the Avrami equation, for some polymers the agreement is rather good. The Avrami parameter obtained, however, depends on the experimental technique. Possible reasons for this disagreement are discussed. Analysis of the calorimetric crystallization rate in the vicinity of the melting point by using the kinetic theory of crystallization shows that the growth is controlled by surface (two-dimentional) nucleation. Energy parameters for the crystallites were determined and it is shown that the surface energy of the crystallites depends on the molecular structure of the polymer. Temperature dependence of the calorimetric crystallization rate of the polymers for which crystallization rates could be determined above and below the maximum rate are analyzed using a kinetic equation with common approximations for the transport term. The influence of melting conditions on the crystallization rate was studied. The results indicate heterogeneous nucleation in the polymer melt. It is concluded that this may be due both to impurities and to high regularity of macromolecules in the polymer melt.     

Comparison of different chemical modifiers for the direct determination of arsenic in sea water by electrothermal atomic absorption spectrometry

A comparative study of different chemical modifiers for the direct determination of arsenic in real and in synthetic sea water samples of high (72.8) and low (34.2) salinity was carried out. The use of lanthanum chloride and magnesium nitrate (LOD=3.0 gl^-1) offers good recoveries for low salinities, while for high salinities an enhancement higher than 200% was obtained, rendering this method unsuitable for sea water samples. The use of silver nitrate (LOD=2.0 gl^-1) produces unfavourable analytical recoveries, around 150 and 300% for synthetic sea water of low and high salinity. Zirconium oxychloride (LOD=1.8 gl^-1) and palladium nitrate alone or combined with magnesium nitrate and reducing agents (LOD=1.1–1.3 gl^-1) produce analytical recoveries close to 100% for all arsenic concentration tried over all salinities; thus, a single calibration curve using aqueous standard solutions may be applied to the analysis of sea water samples over all salinities. Finally, the addition of reducing agents and magnesium nitrate to palladium does not improve the sensitivity.     

Ordering and Clathrate Hydrate Formation in Co‐deposits of Xenon and Water at Low Temperatures

Local ordering in co‐deposits of water and xenon atoms produced at low temperatures can be followed uniquely by ¹²⁹Xe NMR spectroscopy. In water‐rich samples deposited at 10 K and observed at 77 K, xenon NMR results show that there is a wide distribution of arrangements of water molecules around xenon atoms. This starts to order into the definite coordination for the structure I, large and small cages, when samples are annealed at ～140 K, although the process is not complete until a temperature of 180 K is reached, as shown by powder Xray diffraction. There is evidence that Xe ? 20 H₂O clusters are prominent in the early stages of crystallization. In xenon‐rich deposits at 77 K there is evidence of xenon atoms trapped in Xe ? 20 H₂O clusters, which are similar to the small hydration shells or cages observed in hydrate structures, but not in the larger water clusters consisting of 24 or 28 water molecules. These observations are in agreement with results obtained on the formation of Xe hydrate on the surface of ice surfaces by using hyperpolarized Xe NMR spectroscopy. The results indicate that for the various different modes of hydrate formation, both from Xe reacting with amorphous water and with crystalline ice surfaces, versions of the small cage are important structures in the early stages of crystallization.     

Isoconversional Analysis of the Nonisothermal Crystallization of a Polymer Melt

The advanced isoconversional method can be used to determine effective activation energies of the nonisothermal crystallization of polymer melts. The application of this method to differential scanning calorimetric data on the crystallization of poly(ethylene terephthalate) yields an activation energy that increases with the extent of crystallization from –270 to 20 kJ·mol^–1. The variation is interpreted in terms of accepted crystallization models.     

Application of Periwinkle Shell Coagulant (PSC) for the Remediation of Petroleum Produced Water (PPW) by Coag-Flocculation

Jar test was used to investigate the coag-flocculation treatment of petroleum produced water (PPW) using Periwinkle shell coagulant (PSC). Instrumental characterization of samples was performed using Fourier transform infra-red, x-ray diffraction, scanning electron microscopic, and differential scanning calorimetric/thermogravimetric analyses. The process efficiency, statistics, and kinetics were investigated for time, pH, and dosage variations. 83.57% optimal efficiency was obtained at 100 mg/l dosage and pH 4 for periods/rate constant of 24.797 seconds/4.8E-05 m^?3kg^?1s^?1, respectively. At the conditions of the experiment, it could be concluded that PSC was effectively applied for the treatment of PPW.     

Crystallization Kinetics of Polypropylene-polyethylene-based Copolymers

A crystallization kinetics analysis of several polypropylene-polyethylene (PP-PE), PP-rich copolymers was made by means of differential scanning calorimetry. The crystallization was studied via calorimetric measurements at different cooling rates. Several additives were added to the base material. Some test samples were subjected to artificial ageing processes. A modified isoconversional method was used to describe the crystallization process under non-isothermal conditions. The value of the Avrami parameter was determined for primary and secondary crystallization. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermal Stability Study of Fe-Ni-Based Alloys Determination of T-HR-T and T-T-T diagrams

The low-temperature parts of the temperature-heating rate-transformation (T-HR-T) and temperature-time transformation (T-T-T) diagrams were obtained for crystallization processes. A knowledge of the kinetic model governing crystallization is not needed because both transformation curves can be obtained from non-isothermal calorimetric experiments. The calorimetric study was performed by means of differential scanning calorimetry. The method was applied to analyse crystallization processes of Fe-Ni-based amorphous alloys prepared by melt spinning. The compositions studied were Fe₄₀Ni₄₀P₁₄Si₆, Fe₄₀Ni₄₀P₁₀Si₁₀ and Fe₄₀Ni₄₀P₆Si₁₄. A good concordance was observed between the experimental T-HR-T curves obtained by calculation and the experimental data, which verifies the reliability of the method. In the T-T-T diagrams, the agreement was good in process B1, while in processes A1 and C1 there are small differences that could be related to different crystallization products obtained in isothermal/non-isothermal experiments. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of molecular weight and temperature on the isothermal crystallization of poly(oxetane)

Poly(oxetane) fractions ranging in number-average molecular weights from 7800 to 157000 have been isothermally crystallized in the temperature range from –50 to 19 C, using dilatometric and calorimetric techniques. In both cases, reproducible isotherms were obtained with an Avrami exponent equal to three. The crystallization rate against crystallization temperature presents a maximum at –30 C. The level of crystallinity changes with molecular weight and the influence of this parameter on the rate of crystallization is pronounced. The crystallization temperature coefficient was studied using nucleation theory and it was found an slight increase in the basal interfacial free energy for the lowest molecular weight fraction. For the analysis of the temperature coefficient at the higher undercoolings, different approximations for the free energy of fusion and the transport term have been considered. The conclusion of this analysis is that, independently of these approximations, the obtained temperature coefficients are the same.     

Constant transformation rate thermal analysis of HGdP<Subscript>2</Subscript>O<Subscript>7</Subscript>·3H<Subscript>2</Subscript>O

Summary The aim of this work is the optimization of the preparation of anhydrous gadolinium hydrogen phosphate with good fluorescence properties. The products obtained by dehydration of gadolinium hydrogen phosphate trihydrate depend on the conditions chosen for the thermal treatment. For this reason, the dehydration was followed by Constant Rate Thermal Analysis whilst strictly controlling the water vapour pressure above the sample. Intermediate samples, obtained during dehydration were characterised by IR spectroscopy and X-ray diffraction. It has thus been shown that the thermal pathway taken for the dehydration depends on the water vapour pressure above the sample in the region from 10^-2to 5 mbar. Under the lowest water vapour pressure (5·10^-3mbar), the elimination of the crystallization water is carried out in a continuous way and produces a quasi-amorphous intermediate. Under higher water vapour pressure (5 mbar), well crystallized intermediate products are obtained. The results obtained suggest that the trihydrate contains zeolitic water which confirms a prior structural study.     

Effect of in impurity on crystallization kinetics of (Se.7Te.3)100−xInx system

The effect of In impurity on the crystallization kinetics and the changes taking place in the structure of (Se₇Te₃) have been studied by DTA measurements at different heating rates (α=5 deg·min^?1, 10 deg·min^?1, 15 deg·min^?1 and 20 deg·min^?1). From the heating rate dependence of the values ofT _g,T _c andT _p, the glass transition activation energy (E _t) and the crystallization activation energy (E _c) have been obtained for different compositions of (Se₇Te₃)_100?xIn_x (0≤×≤20). The variation of viscosity as a function of temperature has been evaluated using Vogel-Tamman-Fulcher equation. The crystallization data are analysed using Kissinger's and Matusita's approach for nonisothermic crystallization. It has been found that for samples containing In=0, 10, 15, 20 at%, three dimensional nucleation is predominant whereas for samples containing In=5 at%, two dimensional nucleation is the dominant mechanism. The compositional dependence ofT _g and crystallization kinetics are discussed in terms of the modification of the structure of the Se?Te system.     

Microcalorimetric Study of the Interaction between Water and Cation-Substituted Clinoptilolites

Heats of ion exchange and adsorption of water vapors on cation-substituted clinoptilolites are studied by microcalorimetry. Based on the results obtained, the composition of hydrates of Na⁺, Cs⁺, Co²⁺, and Ba²⁺ ions on various ion-exchange sites of clinoptilolite is determined. Their structure is identified using the combined analysis of calorimetric and X-ray diffraction data. The usefulness of energy–stoichiometry approach to the discussion of the results of adsorption calorimetry study of the interaction between water and cation-substituted clinoptilolites is demonstrated.     

Analysis of stress-induced crystallization in high-cis-1,4-polybutadiene

Stress-induced crystallization of a crosslinked polybutadiene with a high 1,4-cis content is investigated, at room temperature. The change in the fraction of crystallinity with deformation is evaluated by two different methods. The first is based on simultaneous measurement of birefringence and stress. The second is based on calorimetric analysis. The data on crystallinity obtained by these two methods are in good agreement in the range of low deformations, while, in the range of higher deformation (λ > 5), the degree of crystallinity obtained by calorimetry is higher than that obtained by the optical method. Qualitative information on the crystallization was also obtained by optical analysis of the hysteresis behavior. The hysteresis data show the presence of ordering phenomena at deformations at which there seems to be no crystallinity according to both quantitative methods.