Calorimetric Curves Research Articles

Energetic heterogeneity of Cu+-carbonyl complexes in Y zeolites: Kinetics of CO desorption studied by FTIR combined with CO adsorption microcalorimetry

We analyzed IR spectra of the isothermal (RT) time-dependent CO desorption on Cu+Me+H+–Y zeolites (Me=Li, Na, K) in order to investigate the energetic heterogeneity of Cu+–CO species. After spectrum deconvolution, integral band area is plotted as a function of time and fitted by several kinetic models. The combination of three first-order kinetic processes has to be used for accurate description of CO desorption process for all tested IR bands. Under the band, carbonyl complexes are substantially differing in desorption rate contribution. The energy gap of complexes with similar geometry is ascribed to variable original Cu siting. Cu moves toward faujasite supercage where the adsorption proceeds: the higher the Cu interaction with framework the lower the stability of corresponding carbonyl complex. Stability of carbonyl IR band decreases with wavenumber. Lower frequency bands, due to Cu+ at II sites with 2 (or 3) Al at 6T ring, are characterized by significant population of low-stable carbonyls. IR stabilities are well correlated with CO heats of adsorption and changes on calorimetric curves justifying the kinetic evaluation. The influence of zeolite composition, namely Cu loading and kind of co-cation, on the character of IR spectrum and population of energetic components is discussed.

Use of calorimetry and other methods in the studies of water reducers and set retarders interaction with hydrating cement paste

The calorimetric method was used as a main tool in the studies of the effect of superplasticizing and set retarding admixtures on cement hydration. The experiments were carried out using two types of cements (neat Portland cement CEM I 42.5R and blended Portland cement type CEM II/B-M (S-V) 42.5N), at varying w/c ratio 0.5 and 0.3 respectively. The hampering of cement hydration process at early age in the presence of these admixtures was generally observed. This is in practice equivalent to the set retardation. The dissolution, as well as the precipitation of hydration products were retarded too, as it has been proved by the DTA/TG, conductometric measurements and the evaluation of so-called chemical shrinkage. However in case of superplasticizers, after a prolonged “dormant” period the process is continued; the reactions occur at fairly good rate giving substantial heat effects – it can be concluded from the total heat evolved values after standard 41h. At longer time a significant amounts of products are formed as well, but it seems that the crystallization of calcium oxide is disturbed; simultaneously the amount and composition of calcium silicate hydrates alters towards the “more amorphous” product. This could be observed under SEM. The set retarders give strong delaying effect, particularly at low amount of water and in the pastes produced from Portland cement. This can be due to the formation of insoluble layer of calcium and sugar or calcium and phosphorus containing compounds surrounding the hydrating grains; the formation of this “barrier” can be distinguished as a small peak on the calorimetric curve and it is poorly removable on further hydration. The shrinkage and conductivity measurements seem to prove not only the change of kinetics of heat evolution/hydration but also the modification of the process and resulting products.

Isothermal microcalorimetry as a tool for studying oxidation stability of insulating liquids

The application of an isothermal microcalorimeter for the investigation of the oxidation stability of insulating liquids has been studied. We propose that the total integral heat signal (area below the calorimeter curves) is a good indicator of the degree of oxidation taking place in the sample during the experiment. Known and unknown insulating liquids have been used in this study, and the amount of available oxygen in the samples has been varied. The results show that isothermal microcalorimetry is well suited for characterizing the oxidation stability of insulating liquids.

Hydrogen sorption enhancement by Nb2O5 and Nb catalysts combined with MgH2

Three Nb materials, synthesized oxide (s-Nb2O5), commercial oxide (c-Nb2O5) and metallic Nb, were applied as catalysts to promote the enhancement of hydrogen sorption in MgH2. A high specific surface area, around 100m2g−1, was obtained for both oxides used as catalysts, s-Nb2O5 and c-Nb2O5 after being heat treated at 350°C. X-ray diffraction (XRD) tests, performed prior to milling, revealed the amorphous structure of both oxides. All the catalysts were mixed for only 20min with MgH2 by mechanical milling forming composites. Differential Scanning Calorimetric curves of the s-Nb2O5 and c-Nb2O5 showed the presence of exothermic crystallization peaks. A total capacity of 5.8wt.% was attained when the hydrogen absorption kinetic tests were conducted at 350°C, with the MgH2+5wt.% s-Nb2O5 sample.

Analysis of thermal and oxidative stability of biodiesel from Jatropha curcas L. and beef tallow

The oxidation of oils and biodiesels occurs due to several factors: the quantity of double bonds and the presence of allylic and bis-allylic hydrogens. Esters (biodiesel) that have large amounts of unsaturated fatty acids are more susceptible to oxidation than saturated. The aim of this work was to analyze the thermal and oxidative stability of ethyl biodiesel from Jatropha curcas L. and beef tallow by thermogravimetric, pressure differential scanning calorimetry, and PetroOxy methods. The samples of biodiesel from beef tallow present higher oxidation stability compared to biodiesel from J. curcas. In relation to calorimetric curves of biodiesel from J. curcas and beef tallow stored by 60 days without and with antioxidant, there was verified displacement of peak temperature of the transition to higher temperatures, respectively. Just a sample of biodiesel from beef tallow stored for 60 days with 3,000 ppm of antioxidant t-butyl-hydroxyquinone was within the standard established by Brazilian National Agency of Petroleum, Natural Gas, and Biofuels (ANP). The biodiesel from beef tallow was more stable in terms of thermal and oxidative stability than biodiesel from J. curcas. The thermal and oxidative stability of biodiesel depends on its chemical structure; this corroborates the fact that the oils with a predominance of saturated fatty acids are more stable than the unsaturated.

Phosphogypsum Transition to α‐Calcium Sulfate Hemihydrate in the Presence of Omongwaite in NaCl Solutions Under Atmospheric Pressure

Preparation of α‐calcium sulfate hemihydrates (α‐HH) from phosphogypsum (PG) under atmospheric pressure has been a promising way to utilize PG. In this study, the phase transition from PG (the main composition is calcium sulfate dihydrate, DH) to α‐HH is investigated in NaCl solutions with different concentrations and reaction temperatures under atmospheric pressure. The results show that the concentration of NaCl affected the phase transition as well as the crystal morphology. Higher reaction temperature above 85°C is found to accelerate the phase‐transition reaction and the products are stable in 18.8 wt% NaCl solution, which is resulted from decreasing water activity with increasing NaCl concentration. The phase‐transition product of PG is a mixture of α‐HH and omongwaite (Na2Ca5(SO4)6·3H2O). Differential scanning calorimeter and thermogravimetry curves and chemical composition, especially Na2O content variation, suggest a third phase, omongwaite is formed during the transition from PG to α‐HH.

Idebenone Loaded Solid Lipid Nanoparticles Interact with Biomembrane Models: Calorimetric Evidence

The knowledge of the interactions between solid lipid nanoparticles (SLN) and cell membranes is important to develop effective carrier systems for drug delivery applications. Loading idebenone (IDE), an antioxidant drug useful in the treatment of neurodegenerative diseases, into SLN improves IDE antioxidant activity in in vitro biological studies, but the mechanism by which IDE permeation through the blood-brain barrier (BBB) occurs are still unclear. Therefore, in this research, unloaded and IDE loaded SLN interaction with biomembrane models, consisting of dimyristoylphosphatidylcholine multilamellar vesicles (MLV), were studied by differential scanning calorimetry (DSC). In the experiments performed, unloaded and IDE loaded SLN where incubated with the biomembrane models and their interactions were evaluated through the variations in their calorimetric curves. The results of our DSC studies indicated that the SLN under investigation were able to go inside the phospholipid bilayers with a likely localization in the outer bilayers of the MLV from where they moved toward the inner layers by increasing the contact time between SLN and MLV. Furthermore, IDE loaded SLN were able to release IDE into the biomembrane model, thus facilitating IDE penetration into the bilayers while free IDE showed only a low ability to interact with this model of biomembranes. Our results suggest that these SLN could be regarded as a promising drug delivery system to improve IDE bioavailability and antioxidant activity.

Study on the compressive behavior of Ti–53.22 at%Ni alloy sheets after pre-compression and aging treatments

Three factors and three levels of orthogonal experiments were conducted to study the effects of pre-compression, aging temperature and aging time on the compressive behavior of Ti–53.22at%Ni alloy sheets. Phase transformation temperatures and compressive behavior at room temperature were investigated. Range analysis of differential scanning calorimeter (DSC) curves shows that R-phase transformations are dependent on aging temperature, and there is no R-phase transformation after aging at 523K, the R-phase transformation reliably occurs after aging at 673K. A saw tooth shape on the stress–strain curves is observed and indicates the occurrence of martensitic transformation. Two kinds of martensitic transformation exist under the compression conditions. Higher compressibility can be achieved by pre-compression of 0.2%, and aging at 523K results in better recovery.

Microcalorimetric study of the annealing hardening mechanism of a Cu–2.8Ni–1.4Si (at%) alloy

The precipitation processes in a Cu–2.8at% Ni–1.4at% Si alloy were studied using differential scanning calorimetry (DSC), transmission electron microscopy (TEM) and microhardeness measurements. The analysis of the calorimetric curves from room temperature to 900K shows the presence of one exothermic reaction attributed to the formation of δ-Ni2Si particles in the copper matrix that was confirmed by Transmission Electron Microscopy (TEM) and EDS microanalysis. The activation energies calculated for the precipitation of δ-Ni2Si was lower than the ones corresponding to diffusion of nickel and silicon in copper. A correlation between of microhardness of the alloy and the formation of δ-Ni2Si particles has been found.

Improvement of acid resistance of Portland cement pastes using rice husk ash and cement kiln dust as additives

This paper represents a laboratory study on the acid resistance of hardened ordinary Portland cement (OPC) and blended OPC pastes at two different curing temperatures. The blended materials used are rice husk ash (RHA) and cement kiln dust (CKD). The blended cement pastes were prepared using a water/solid (W/S) ratio of 0.3. The effects of immersion in deionized water (pH 7) and sulfuric acid solutions (pH 1, 2 and 3) at two temperatures (20 and 50 °C) on the compressive strength and phase composition of the various hardened blended cement pastes were studied. The results of compressive strength revealed that the increase of curing temperature from 20 to 50 °C resulted in increase the reduction of compressive strength due to acid attack up 2 months, but the resistance to sulfuric acid attack increases after that time due to the formation of crystalline calcium silicate hydrates (CSH) which have higher resistance to acid attack than the amorphous CSH formed at the early ages of hydration. The presence of RHA and CKD improves the resistance to sulfuric acid attack at both curing conditions. From the results of X-ray diffraction analysis and differential scanning calorimetric technique curves, the main hydration products identified are CSH, portlandite, and calcium sulfoaluminate hydrates.

Hydration of C3A–gypsum systems

Hydration of C3A–gypsum systems with different gypsum additions was investigated in terms of the phase assemblage, kinetics and microstructural development. The second stage of the reaction, which begins after the depletion of gypsum, was of particular interest. From in-situ X-ray diffraction results, it was seen that the dissolution of ettringite and C3A to form monosulfoaluminate and/or hydroxy-AFm phases is a rapid reaction that occurs right after the depletion of gypsum. The observation of the calorimetric curves obtained for the different gypsum additions leads us to the conclusion that the mechanism controlling the hydration rate during this period is the nucleation and growth of the AFm phases. The microstructural study showed that the formation of AFm phases occurs in the space between the C3A grains but also within the boundaries of the original C3A grains. Hydrogarnet was observed growing as a shell around the C3A grains.

Calorimetric effects during the α → γ transformation in Fe-Ni-Ti metastable alloys

A calorimetric study of the reverse α → γ transformation has been carried out in five metastable Fe-Ni-Ti alloys. The amount of the α phase in the initial samples is more than 50%. The exothermic processes of the decomposition of the α and γ phases exceed the endothermic reactions of formation of the reverted austenite upon heating to the midpoint of the temperature interval of the reverse α → γ transformation. In the middle part of the interval in which the maximum rate of the transformation is recorded by the magnetometric method, the calorimetric curve does not exhibit thermal effects. This disagreement indicates the complex character of the transformation. At the finishing stage of the α → γ transformation, there is clearly detected an endothermic reaction.

Detection of Animal Fat Contaminations in Sunflower Oil By Differential Scanning Calorimetry

In this study, the use of differential scanning calorimetric heating thermograms was investigated to detect the presence of lard, beef tallow, and chicken fat as contaminants in sunflower oil. Sunflower oil samples spiked separately with lard, beef tallow, and chicken fat in levels ranging from 1 to 20% (w/w) were analyzed using high performance liquid chromatography to get triacyl-glycerol profiles and differential scanning calorimetric to obtain their heating profiles. The results showed that below 20% (w/w) level of contamination, both lard and beef tallow in sunflower oil can be detected using characteristic contaminant peaks appearing in the higher temperature region (0–50°C) of differential scanning calorimetric curve. However, chicken fat contamination in sunflower oil did not show any characteristic peaks in this region, but caused changes only in the exiting thermal transitions in the low temperature region of the differential scanning calorimetric curve. Based on the characteristic differences in the peak size, shape, and position, it was also possible to make a distinction between lard and beef tallow contaminations in sunflower oil.

Calorimetry and other methods in the studies of expansive cement hydrating mixtures

In this study, the calorimeter was applied to follow the hydration of special cement mixtures exhibiting expansion or shrinkage compensation. The shrinkage-less and expansive binders were produced by mixing of Portland cement with an expansive additive produced by sintering and composed of calcium sulfoaluminate (yeelimite), calcium sulfate (anhydrite) and lime. The studies were focused on the synthesis of this aluminate—sulfate—lime additive (temperature of burning process as a parameter controlling the relative activity of components) from the materials being the by products and subsequently on the mixture proportions to ensure the hydration process resulting in non-shrinkage or expansion effect. In the experiments the proportions of expansive mixture and cementitious materials were variable. The investigations with aim to find the relationship between the volume changes and composition of initial mixtures in cement pastes and mortars (with sand) were also carried out. The phase composition and microstructure of products were characterized. The expansive additive in the environment of hydrating cement transforms into ettringite and gives an increase of volume when the plastic material transforms to the more rigid matter but before the ultimate hardening takes place. Proper, moderate setting and hardening in strongly modified mixtures is achieved when the calorimetric curve corresponding to the heat evolution on hydration is analogous to that for the basic Portland cement. The rate of heat evolution data are well compatible with the other results related to the other methods of hydration kinetics assessment (e.g. chemical shrinkage) and discussed in terms of the phase composition of hydration products.

Quantitative kinetic and structural analysis of geopolymers. Part 1. The activation of metakaolin with sodium hydroxide

Isothermal conduction calorimetry (ICC) is used here to measure the kinetics of geopolymerisation of metakaolin by reaction with NaOH solution under a variety of conditions. Three exothermic peaks are observed in the calorimetric curve, and are assigned to the dissolution of metakaolin, the formation of geopolymer with disordered or locally ordered structure, and finally the reorganization and partial crystallization of this inorganic polymer gels. For the purpose of further quantifying the ICC data, the geopolymeric reaction products are assumed to have an analcime-like local structure, and their standard formation enthalpies are estimated from the available data for this structure. This assumption enables ICC to be used for the first time in a quantitative manner to determine the real reaction kinetics of geopolymerization. Increasing the NaOH concentration up to a molar overall Na/Al ratio of 1.1 is seen to enhance the reaction extent observed at 3 days, up to a maximum of around 40% in the high liquid/solid ratio systems studied here, and accelerates the crystallization process. However, further addition of NaOH does not give any additional reaction within this period, or any further acceleration. Raising the reaction temperature from 25°C to 40°C increases the initial reaction rate but has little effect on the final reaction extent, particularly when Na/Al>1.

Study of the Thermal Stability in Air of LaNi5 by DSC, EDX, TEM and XRD Combined Techniques

In this work, the thermal stability in air of LaNi5 and its reaction products were analyzed. The structural and microstructural parameters were determined by X-ray diffraction and TEM techniques. According to the results of XRD/TEM, the starting material is monophasic with hexagonal structure (P6/mmm, a = 5.019 (0) Å, c = 3.982 (7) Å). Thermal measurements were made by differential scanning calorimetry, using heating rates between 1 and 25°C.min-1. The calorimetric curve corresponding to a heating rate of 1°C.min-1 shows stability of the intermetallic up to (140 ± 1) °C. The thermal decomposition evolves as three successive exothermic global events. According to the measured curve, the maximum peaks are produced at (205 ± 1) °C, (258 ± 1) °C and (391 ± 1) °C, respectively. Thermal evolution lead to the formation at 600°C of the final products La2O3 (P-3m1, a = 3.945(0) Å; c = 6.151(0) Å), NiO (Fm3m, a = 4.178(0) Å) and LaNiO3 (R-3c, a = 5.457(3) Å; and c = 13.146(2) Å). The elemental composition was analyzed by EDS.

Estudo da mistura do éter diglicidílico do bisfenol-A com poli(etileno-co-acetato de vinila)-g-poli(metacrilato de metila) por espectroscopia dielétrica e calorimetria exploratória diferencial

As curvas calorimétricas e os espectros de relaxação dielétrica correspondentes às misturas do éter diglicidílico do bisfenol-A com diferentes concentrações do copolímero poli(etileno-co-acetato de vinila)-g-poli(metacrilato de metila) (EVA-g-PMMA) foram obtidos utilizando a calorimetria exploratória diferencial (DSC), e a espectroscopia de relaxação dielétrica (DSR), respectivamente. A temperatura de transição vítrea (Tg) do segmento de PMMA aumenta com o conteúdo de copolímero na mistura. O comportamento da Tg foi descrito pela equação de Gordon-Taylor, utilizando a fração mássica de PMMA. Nos espectros dielétricos, aparecem as relaxações do tipo α características dos dois segmentos moleculares. Neste caso, o aumento da concentração de copolímero provocou o aumento da temperatura de relaxação α correspondente ao segmento de PMMA, e não foi observada mudança na relaxação α para a fração de EVA. Estes comportamentos revelam que os segmentos estruturais do copolímero apresentam interações bem diferenciadas com o monômetro epoxídico. O segmento de PMMA é miscível, portanto, provocou fortes interações com a resina quando comparado à fração de EVA, que não manifestou interação aparente e originou a heterogeneidade do sistema.

Compatibility of paroxetine hydrochloride and GW597599B

In this study, we present a full thermal characterization of antidepressant paroxetine and summarize the results for another drug which treats depression: GW597599B. The main aim is to analyze how the thermodynamic and structural properties of these compounds are modified when the two drugs are mixed in the solid state. We begin by putting into evidence how dehydration and melting concur in shaping the calorimetric curves of paroxetine under different experimental conditions. Equipped with this knowledge, we are able to interpret the thermal response of the physical mixtures paroxetine:GW597599B, in terms of partial eutectic formation and simple superposition of contribution from the two compounds.

Effects of the Cooling Rate on the Plasticity of Pd40.5Ni40.5P19 Bulk Metallic Glasses

We prepare Pd40.5Ni40.5P19 glassy samples with purified ingots by copper mold casting at a high cooling rate and by water quenching at a low cooling rate. Both of them exhibit different supercooled liquid regions and multiple glass transition characteristics in their differential scanning calorimetric curves. The plasticity of the glassy sample prepared by copper mold casting is about 5% while that prepared by water quenching is almost zero (0.2%), indicating that cooling rate has influenced the plasticity of glassy alloys. By using high resolution TEM image analysis, it is revealed that there exist characteristic regions with different contrasts in the full glassy samples. The characteristic size is about 20–40 nm for the glassy sample prepared by water quenching and 2–4 nm for the one prepared by copper mold casting. The large difference in the plasticity of the glassy samples prepared by different cooling rates is believed to be related to the difference in the size of the characteristic nanoscale structures. The results indicate that adjusting cooling rate in preparation of glassy samples could modify the thermal and mechanical properties of the glassy alloys.

Simultaneous thermogravimetry–calorimetry study on the combustion of coal samples: Effect of heating rate

Combustion characteristics of two different coal samples were investigated using power compensating type differential scanning calorimeter (DSC) and thermogravimetry (TG–DTG) at different heating rates (5, 10 and 15 °C/min). Differential scanning calorimeter (DSC) and thermogravimetry (TG–DTG) curves revealed two main reaction regions at each heating rate studied. Reaction regions, peak and burn-out temperatures, weight loss and heat of reactions of the samples were determined. Kinetic parameters of the coal samples were also determined by different methods and it was observed that the activation energy values of the coal samples were in the range of 27.2–76.2 kJ/mol for different reaction regions studied.