Differential Scanning Calorimetry Peak Research Articles

Thermal and Crystallographic Properties of Tetra-n-butylammonium Bromide + Tetra-n-butylammonium Chloride Mixed Semiclathrate Hydrates

The thermal and crystallographic properties of tetra-n-butylammonium bromide + tetra-n-butylammonium chloride (TBAB + TBAC) mixed semiclathrate hydrates prepared from mixed aqueous solutions were investigated using phase equilibrium measurements, differential scanning calorimetry (DSC), and powder X-ray diffraction. The equilibrium temperatures gradually vary with both xguest {i.e., the mole fraction of guests to (guests + water)} and xTBAB {i.e., TBAB to (TBAB + TBAC)}. The maximum equilibrium temperatures for each concentration changed from (xTBAB = 0.4 to 0) and were observed at xTBAB = 0 below xguest = 0.012. The dissociation enthalpies of tetragonal mixed hydrates are between those of the pure hydrates. In the tetragonal pure and mixed hydrates, these results indicate that the thermal stabilities are dependent upon the increase of hydration number by the relaxation of crystal distortion with decreasing xguest and xTBAB. In orthorhombic systems, a single endothermic DSC peak is split to a higher tempe...

Early Stages of Cu Precipitation in 15-5 PH Maraging Steel Revisited - Part II: Thermokinetic Simulation

In this part II of the authors' investigation of Cu-precipitation in 15-5 PH steel, the authors complement the experimental analysis of part I with thermokinetic modeling and simulation to aid in the interpretation of processes and mechanisms involved in the two precipitation reactions between around 300 and 500 °C. The kinetic simulations are founded on extended classical nucleation theory, a mean-field model for precipitate growth, a predictive model for interface energy calculation, and CALPHAD-based Gibbs-energy and mobility databases. The authors modeling supports the interpretation that the first peak in the continuous differential scanning calorimetry (DSC) signal is the result of nucleation of Fe-rich Cu clusters, which leads to a partial Cu-depletion of the matrix and produces the first observed DSC signal. The second DSC peak has its origin in the Cu-enrichment of precipitate clusters above approximately 500 °C and the associated enthalpy change. A quantitative reproduction of both exothermic reactions is performed within the framework of the thermokinetic simulation.

The calorimetric analysis as a tool for studying the aging hardening mechanism of a Cu-10wt%Ni-5.5wt%Sn alloy

The transformations of a Cu-10wt%Ni-5.5wt%Sn alloy as a function of the aging time in the range from room temperature up to 600 °C have been followed by Differential Scanning Calorimetry (DSC). The results obtained have shown that this alloy undergone two overlapping exothermic phase transitions with DSC peaks at 208 °C and 305 °C, respectively, followed by an endothermic phase transformation with a DSC peak at 526 °C. The structural analysis by TEM, ED, EDX and XRD of the intermediates phases previously discriminated by DSC suggests that the first exothermic peak is associated to the spinodal decomposition of the sample, while the second one is associated to the segregation of a DO22 (CuxNi1−x)3Sn tetragonal phase coherent with the α-Cu structure of the starting alloy. The endothermic peak has been associated to the precipitation of cubic DO3 nanocrystals from the DO22 phase previously formed. The microhardness measurements carried out in combination with the structural characterization demonstrate that the aging hardening of the alloy under study is exclusively due to the formation of the coherent DO22 phase. The DO22 → DO3 transition leads to a dramatic drop of the hardness of the alloy.

Comparison of GC and DSC monitoring the adulteration of camellia oil with selected vegetable oils

This paper compared the potential application of gas chromatograph (GC) and differential scanning calorimetry (DSC) to verify adulteration of camellia oil (CMO) with sesame oil (SSO), sunflower oil (SFO), peanut oil (PNO), corn oil (CO) and canola oil (CNO) which are cheaper oils mixed as adulterants with CMO. DSC offers unique thermal profiling for each oil. A combination of analysis of FAs and fingerprint were applied for GC to detect the adulteration. According to a similarity calculation (with a standard below 0.9989) of included angle, the detection limit of sesame oil, sunflower oil and corn oil was 10 %, peanut oil 20 %, and rapeseed oil 30 %; for DSC, similarly CMOs had the unique fingerprint according to their DSC peak shape and thermodynamic parameters, and an adulteration contents of 5 % could be detected qualitatively. Satisfactory results were achieved from stepwise multiple linear regression analysis (SMLR) for the data of Ton, Toff, Tpeak, △H and peak height (H) of DSC to quantitatively predict the other five oils adulteration in CMO with R2 to 0.999. The average error obtained from the error analysis corresponding to SMLR was 1.2620 %. The preliminary results presented in this study suggest that DSC analysis is an attractive tool in detecting SSO, SFO, PNO, CO and CNO adulteration in CMO.

Thermal-morphological characterisation of starch from peach-palm (Bactris Gasipaes kunth) fruit (Pejibaye)

ABSTRACTThe objective of this study was to characterize the starch of the peach-palm fruit. The starch was subjected to thermogravimetric analysis, differential scanning calorimetry, Fourier transform infrared spectroscopy, x-ray diffraction, and scanning electron microscopy. The thermogravimetric analysis showed 76.62% of the weight loss in the temperature range from 251.7 to 380.6 ºC. The peak in differential scanning calorimetry was obtained at 70.0 ºC. Fourier transform infrared spectroscopy were obtained with a wavelength band of 528 to 3421 cm−1. The x-ray diffraction corresponded to C-type crystals. The granule sizes ranged from 1.60 to 8.48 μm.

A mathematical model for analysis of sequentially coupled crystallization–melting differential scanning calorimetry peaks and the use of the model for assessing the crystallization resistance of tellurite glasses

Differential scanning calorimetry (DSC) characterization of tellurite glasses doped with lanthanum oxide, which improves their crystallization resistance, has revealed a phase transformation specific to such glasses, in which partial crystallization of a sample is followed by melting of the crystals formed. The experimentally observed dependence of the decrease of crystallization–melting peaks across a series of disperse samples of (TeO2)0.72(WO3)0.24(La2O3)0.04 glass with increasing particle size upon extrapolation to the size of a bulk sample has been used to assess the crystallization resistance of tellurite glasses for optical applications. The assessment technique comprises DSC characterization of particle-size-classified glass samples and the use of a mathematical model for obtaining the degree of crystallization as a function of temperature and time, α(T, t) through analysis of nonisothermal DSC peaks representing a partial glass crystallization process passing into melting. The crystallization resistance of glass is estimated by extrapolating the maximum α values as a function of particle size to a preform size. Tested for (TeO2)0.72(WO3)0.24(La2O3)0.04 glass, the technique offers the possibility of selecting preforms for producing fibers from compositionally new, chemically pure tellurite glasses at a given phase purity level.

DSC and Raman study of DMPC liposomes in presence of Ibuprofen at different pH

Ibuprofen (IbuH), 2-(4-isobutylphenyl) propionic acid, is a well-known nonsteroidal anti-inflammatory drug and is a promising antiatherosclerotic agent. Since IbuH has demonstrated to affect cell membranes structure, the study of the interaction between the membrane components, like phospholipids, and the drug, is of paramount interest. Moreover, liposomes can be used as drug carriers. In this paper, the effect of increasing amounts of Ibuprofen at neutral and acidic pH on the behaviour of dimyristoylphosphatidylcholine (DMPC) liposomes was investigated by means of Raman and differential scanning calorimetry (DSC) techniques. The results showed that pH influenced noticeably the liposome structure. A simple ‘solution-like’ model can explain the system when small or high IbuH or IbuNa (IbuH sodium salt forming at neutral and basic pH) amounts are present (IbuH/DMPC molar ratio ≤1/8.3 or ≥1/2.2 or IbuNa/DMPC molar ratio ≤1/17.5 or ≥1/4), whereas at intermediate amounts, two DSC peaks appeared: these systems could be described as a mixture of ‘phase II’ domains inserted within a structure of smaller and further ramified ‘phase I’ domains. Both DSC and Raman data suggested IbuH can penetrate within the apolar bilayer at pH 3, while at pH 7, the setting up of polar interactions of different strength between the carboxylic groups of IbuNa and the choline head of the DMPC, hamper a further penetration of the drug. Similar results were obtained both inserting directly IbuH molecules into liposomes as well as acidifying IbuNa water solutions, suggesting a possible use of liposomes as drug carriers when polarity is pH dependent.

Ultrathin Al2O3 Coatings for Improved Cycling Performance and Thermal Stability of LiNi0.5Co0.2Mn0.3O2 Cathode Material

Ultrathin Al2O3 is directly deposited on LiNi0.5Co0.2Mn0.3O2 (NCM523) composite electrodes by atomic layer deposition (ALD). After 4 ALD cycles, the coated cathode exhibits significantly improved cycling performance and thermal stability, especially at high working voltage. The capacity retention of the coated cathode is 76.8% after 30 cycles in the voltage range of 2–4.8V, compared to 58.4% of pristine cathode. The exothermic peak in differential scanning calorimetry (DSC) analysis, corresponding to the reactions between delithiated electrode and electrolyte, is also delayed after cycling. The improvement is attributed to the reduced charge transfer resistance and enhanced Li ion diffusivity, as the Al2O3 coating may suppress the side reactions between electrode and electrolyte, and inhibit the oxygen release under high operating voltage.

A thermoanalytical, X-ray diffraction and petrographic approach to the forensic assessment of fire affected concrete in the United Arab Emirates

For most fires, forensic investigation takes place well after building materials have cooled and knowledge of the structural damage due to heat exposure can reveal the temperature reached during an incident. Recently, there have been significant changes in the types and hence characteristics of cementitious materials used in the United Arab Emirates. Few studies focus on the application of thermo-analytical, X-ray diffraction and petrographic techniques on newly developed structures and this work aims to address this deficiency by utilising a series of parametric laboratory-based tests to assess the effects of heat on hardened concrete. Specimens were made with a design mix typically used for low-rise residential homes and storage facilities. The key constituents were: Portland cement (PC), crushed gabbro stone and dune sand with water/cement ratios of 0.4–0.5. Portland cement substitutes included ground granulated blast-furnace slag (GGBS), and silica fume (SF) at replacement percentages of up to 50% and 4%, respectively. The concrete cubes of 100-mm size were produced and standard cured to 28 days and then exposed to heat inside an electric furnace with pre-determined temperature regimes of 150°C, 300°C, 600°C and 900°C. Petrographic examination was utilised to compare the discolouration of the cooled concrete. Data derived from thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) are reported in order to assess the usefulness of these techniques in fire scene investigation to differentiate between these temperature regimes. The results from the TGA indicate that the majority of the percentage weight loss for all the mixtures occurred in the range 650–700°C, which corresponds to the decarbonation of calcium carbonate, mainly from the aggregates. The endothermic DSC peak at 70–120°C relates to the loss of evaporable water. Since both of these reactions are irreversible, this information can help fire investigators estimate the temperature history of concrete after exposure to fire. On the other hand, the portlandite in the cement matrix dehydroxylates at 450–550°C but then reforms as the concrete cools. The onset temperature for the dehydroxylation of the reformed mineral is always lower than in virgin samples and its enthalpy furthermore depends strongly on the thermal history of the portlandite. Thus, this feature can be used to establish the temperature to which the material was exposed to during a fire incident.

Thermal and biological properties of the Schiff base N,N′-bis(salicylidene)-1,2-phenylenediamine, a potential adjuvant to antibiotic therapy

Schiff base N,N′-bis(salicylidene)-1,2-phenylenediamine, salophen, is a substance that presents synergism when combined with amikacin against Staphylococcus aureus and Escherichia coli. Measurements of temperature dependence of the Raman spectra of salophen combined with thermal analysis investigations are presented. The room temperature crystalline structure seems to be stable up to the temperature where the phase transition from solid to liquid (433–443 K) is observed. The Raman spectra in the temperature range 433–443 K were observed to be characterized by the loss of external vibrational modes, in accordance with thermal analysis curves. According to thermogravimetric analysis, salophen shows a weight loss variation in the temperature range 300–453 K corresponding to 5% loss in weight, which is attributed to dehydration and materials melting temperature. The enthalpy (ΔH) obtained from the integration of the differential scanning calorimetry peak at melting (Tm = 438 K) and decomposition temperature (Td = 484 K) is founded to be – 91 J/g and 239 J/g, respectively. Finally, it was carried out biological assays to evaluate the antibacterial potential of the salophen.

Thermal crystallization of an Al88Ni6Sm6 metallic glass

This work essentially deals with the first stages of crystallization of melt spun Al1−(x+y)NixSmy metallic glasses. Specific emphasis is given to the microstructural and kinetics aspects of primary crystallization because of the high specific strength of this class of materials in the partially crystallized state. The nanometric size of the crystalline particles is measured either by direct transmission electron microscopy or by indirect X-ray diffractometry. The Kissinger model as well as the Friedman model free method is used to estimate the local activation energies and the results obtained with both kinds of approaches are compared. A sustained attention is also paid to the nature of the crystallization phenomenon at the origin of the second exothermic peak in differential scanning calorimetry. This result is indeed the subject of controversy in the literature data concerned by Al–Ni–Sm alloys.

Growth of spherulites: foundation of the DSC analysis of solidification

Solidification is a practically and theoretically important issue, since it allows to design experimental conditions for desired material properties and also to discuss basic relationships between thermodynamics, kinetics and morphology. In this article, an overview on the crystallization theory and on the main traditional techniques to determine the crystallization rates, under constant and variable external temperature, is provided. The differences and similarities of isothermal and non-isothermal crystallization mechanisms are highlighted in the framework of the nucleation and growth theory, also by comparisons of the differential scanning calorimetry (DSC) peaks. The origin, broadness and symmetry of DSC peaks are explained in detail by considering the need for heat removal from the solid front and the coalescence of grains that originated in several points of the liquid phase. Although impingement is responsible for the general slowdown of crystallization, it is shown that the growth rate of a spherulite in the initial stage of coalescence continues to increase up to a maximum even if with a rate of change (i.e., a growth “acceleration”) lower than that before impingement.

Thermal stability and transition temperatures of monovalent salts of high-acyl gellan gels

Summary Thermogravimetry/derivative thermogravimetry (TG/DTG), rheometry and differential scanning calorimetry (DSC) were used to study the thermal stability and determine the transition temperatures of the sodium and potassium salts of high-acyl gellan (HAG) in the presence of 0–100 mm NaCl and KCl, respectively. TG/DTG revealed the potassium gellan (KHAG) gels to be more stable than those of sodium gellan (NaHAG), regardless of external cation concentration. Rheometry and DSC showed the melting (Tm) and gelling (Tg) temperatures to increase with cation concentration. The DSC peak temperatures showed thermal hysteresis contrary to rheometry. In most cases, DSC revealed KHAG to exhibit higher Tm and Tg than NaHAG. Consequently, thermal characteristics of NaHAG and KHAG gels depend on the size of the external cation and its ability to coordinate water molecules. Cation salts of HAG exhibit significantly lower transition temperatures than the commercial preparation from which they were produced.

The effect of volatiles on the measurement of the reaction heat by differential scanning calorimetry

When gases evolve during a chemical reaction, a fraction of the reaction heat is lost with them. We have analyzed, both theoretically and experimentally, the deviations that this effect can produce on the determination of the reaction heat by differential scanning calorimetry (DSC). It is shown that, even in the absence of gas overheating, deviations related to variations in the sample heat capacity can be substantial in experiments involving very intense DSC peaks. However, experiments performed on thermal decomposition of metal organic salts and on evaporation of liquids have shown that deviations usually arise from gas overheating.

Assessment of Post-eutectic Reactions in Multicomponent Al-Si Foundry Alloys Containing Cu, Mg, and Fe

Post-eutectic reactions occurring in Al-Si hypoeutectic alloys containing different proportions of Cu, Mg, and Fe were thoroughly investigated in the current study. As-cast microstructures were initially studied by optical and electron microscopy to investigate the microconstituents of each alloy. Differential scanning calorimetry (DSC) was then used to examine the phase transformations occurring during the heating and cooling processes. Thermodynamic calculations were carried out to assess the phase formation under equilibrium and in nonequilibrium conditions. The Q-Al5Cu2Mg8Si6 phase was predicted to precipitate from the liquid phase, either at the same temperature or earlier than the θ-Al2Cu phase depending on the Cu content of the alloy. The AlCuFe-intermetallic, which was hardly observed in the as-cast microstructure, significantly increased after the solution heat treatment in the alloys containing high Cu and Fe contents following a solid-state transformation of the β-Al5FeSi phase. After the solution heat treatment, the AlCuFe-intermetallics were mostly identified with the stoichiometry of the Al7Cu2Fe phase. Thermodynamic calculations and microstructure analysis helped in determining the DSC peak corresponding to the melting temperature of the N-Al7Cu2Fe phase. The effect of Cu content on the formation temperature of π-Al8Mg3FeSi6 is also discussed.

Effect of Post Spinning Modification Using Potassium Permanganate on the Thermal Specifications of Acrylic Fibres

This study is focused on post spinning treatment of acrylic fibres using 5%wt. potassium permanganate (KMnO4) solution under different impregnation times. The evaluation of initial and modified acrylic fibres by differential scanning calorimetry (DSC) showed that treating acrylic fibres with KMnO4 solution can result in changes of chemical structure and thermal behaviour of fibres. The recorded DSC thermograms of modified samples indicated that with increase of impregnation time, the onset temperature of the cyclization reaction decreased. Also there was a progressive increase in the difference of onset and endset temperature (ΔT) of chemical reactions in the DSC peak.

The crystallization behavior of as-quenched Nd9Fe85Nb0.5B5.5 alloys

The crystallization behavior of as-quenched Nd9Fe85Nb0.5B5.5 alloy was investigated in order to gain further understanding of the structural evolution of the α-Fe and metastable phase, and then verified it by TEM. The result shows that the crystallization can be viewed as a process consisted of the following two steps. Firstly, the TbCu7-type metastable phase and a small amount of α-Fe precipitate from the matrix. Then, the TbCu7-type metastable phase is decomposed into the α-Fe and Nd2Fe14B phase with suitable sizes. The decomposition of metastable phase can promote the crystallization of Nd2Fe14B phase, so it could be considered as an ‘autocatalysis’ process. In addition, the crystallization kinetic parameters of the Nd2Fe14B phase have also been obtained base on the resolved differential scanning calorimetry peaks. The results provide a physical and dynamic insight into the crystallization behavior of as-quenched Nd9Fe85Nb0.5B5.5 alloys.

Comparison of Conventional and New-generation Nickel-Titanium Files in Regard to Their Physical Properties

IntroductionThis study investigated the surface, fractured structure, and physicochemical properties related to cyclic fatigue in various nickel-titanium (NiTi) files. MethodsAmong a total of 10 groups of NiTi files, conventional NiTi files (ProFile [Dentsply Maillefer, Ballaigues, Switzerland] and K3 [SybronEndo, Orange, CA]) and new-generation NiTi files (ProFile Vortex [PV; Tulsa Dental Specialties, Tulsa, OK], Vortex Blue [VB; Tulsa Dental Specialties], and K3 XF [XF; SybronEndo, Orange, CA]) with the same tip diameter (ISO size 25) and 2 types of taper (0.04 and 0.06) were used in this study. Scanning electron microscopy of the file surface structure, differential scanning calorimetry, and cyclic fatigue resistance tests were conducted. ResultsMany mechanical grooves were recognized on the file surface. The surface in the ProFile group was extremely smooth compared with that observed for the other files. Many shallow hollows besides mechanical grooves were noted on the surface in the XF group. A smooth curve was observed in the ProFile, K3, and PV groups. Defined peaks in differential scanning calorimetry were observed in the VB and XF groups. The 0.04 taper files exhibited a statistically higher number of cycles to fracture than the 0.06 taper files in all groups (P < .05). Cracks along the mechanical grooves were observed in the NiTi files, with the exception of the XF group. The start of cracking was detected at U-shape sites in the ProFile group, the cutting edge in the PV and VB groups, and radial islands in the K3 and XF groups. ConclusionsThe present findings suggest that new-generation NiTi files are not necessarily improved compared with conventional files.

Thermoanalytical study of linkage isomerism in coordination compounds. Part 5: A DSC and DFT study on the linkage isomerization of the dinitrito and dinitro isomers of cis-tetraamminecobalt(III) complexes

The solid-state linkage isomerization of cis-[Co(NH3)4(NO2)2]X (dinitro) and cis-[Co(NH3)4(ONO)2]X (dinitrito) (X=Cl−, NO3−, ClO4−) was investigated by differential scanning calorimetry (DSC). All three salts of the dinitrito isomer show an exothermic peak associated with linkage isomerization, while only the chloride salt of the dinitro isomer exhibits an endothermic DSC peak. The results imply that the chloride salts of both isomers are metastable at ambient temperature and can convert to a stable equilibrium mixture of both isomers at elevated temperatures, but the NO3− and ClO4− salts of the dinitro isomer are in stable state even at high temperatures. The DSC peak temperature and the enthalpy changes of the dinitrito to dinitro isomerization depend upon the nature of counterion as follows: NO3−<Cl−<ClO4−. The stepwise enthalpy changes of the linkage isomerization of the dinitro (only for the Cl− salt) and dinitrito complexes were obtained through mathematical resolution of the observed peak into two peaks, assuming a two-stage reversible isomerization for the Cl− salt and a similar irreversible process for the NO3− and ClO4− salts. The nature of the counterion has little effect on the kinetics of the linkage isomerization. The electronic structures and transition states of the linkage isomers were optimized by DFT and their electronic spectra calculated by TDDFT/PCM methods.

A Differential Scanning Calorimetry and Theoretical Study on the Isomerization of trans‐[Co(cyclam)(ONO)2]X (X = PF6–, ClO4–)

AbstractThe solid‐state interconversion of trans‐[Co(cyclam)(ONO)2]X (X = PF6–, ClO4–; cyclam = 1,4,8,11‐tetraazacyclotetradecane, [14]aneN4; dinitrito isomer) and trans‐[Co(cyclam)(NO2)2]X (dinitro isomer) was investigated by differential scanning calorimetry (DSC). The conversion of the dinitrito isomer to the dinitro isomer was accompanied by the appearance of exothermic peaks. However, no isomerization DSC peak was observed for the dinitro isomers. The observed DSC peak for the dinitrito isomer was resolved into two peaks that correspond to two isomerization stages. The low‐temperature peak was ascribed to the conversion of the metastable dinitrito isomer to an unstable nitro–nitrito one, whereas the high‐temperature peak was attributed to the subsequent conversion of the nitro–nitrito isomer to the dinitro isomer. The kinetic parameters of the isomerization were determined by the Kissinger method. The electronic structures and thermodynamic stabilities of the linkage isomers, as well as the nature of the transition states, were investigated by DFT.