Heat Flow Curves Research Articles

Use of isothermal microcalorimetry for prediction of oxidative stability of several amino acids

Isothermal microcalorimetry has been applied as a method for predicting (in)stability of ascorbic acid and several amino acids that undergo oxidative degradation in aqueous media. The fast and simple method involved the addition of different amounts of hydrogen peroxide. The appearance of the heat flow curves gave a clear general indication of how stability was influenced. The accuracy of the microcalorimetric result was investigated by comparing it with an HPLC assay and a good agreement between the results of both methods was demonstrated. It was also established that susceptibility to oxidative degradation decreases in the following order: cysteine, methionine, ascorbic acid, tyrosine and tryptophan.

Isokinetic and isoconversional study of crystallization kinetics of a Zr-based metallic glass

The crystallization kinetics of Zr 69.5Cu 12Ni 11Al 7.5 metallic glass is studied under non-isothermal condition using differential scanning calorimetry (DSC). The kinetic parameters, viz. the activation energy ( E) and the Avrami exponent ( n), for the primary (first) crystallization peak are obtained using the isokinetic and the isoconversional methods. The so-obtained E and n are utilized to derive theoretical normalized heat flow curves through the Kolmogorov–Johnson–Mehl–Avrami (KJMA) equation. The comparison of the experimental and theoretical normalized heat flow curves at different heating rates demonstrates that the completely isokinetic description of the crystallization process is not suitable. On the other hand, the isoconversional methods in combination with the KJMA equation provide better understanding of the kinetics of the crystallization process.

Rheological Study on Polypropylene/Cycloolefin Copolymer Blends

AbstractSummary: Polypropylene, cycloolefin copolymer and their blends were characterized by means of melt flow analysis and capillary rheometry at temperatures between 190 and 230 °C in order to shed more light on COC fiber formation obtained in injection molding process. Melt viscosity and its activation energy as functions of blend composition show negative deviation from the expected additivity (Negative Deviating Blends). The COC/PP viscosity ratio increases with shear rate, but decreases with temperature. High temperature, low viscosity ratio and high shear rate seem to be favorable for fiber formation. Glass transition (from the reversible heat flow curve of modulated DSC) of dumbbell specimens produced by injection molding at 230 °C with COC minor component was 2–4 °C higher than that of grinded pellets obtained from mixing at 190 °C.

Control of Alkali-Silica Expansion by Various Surface Systems

This paper presents the results of long term outdoor exposure of specimens made of reactive aggregate and ASR expansion control by various surface penetrant methods, surface coating methods and injection methods. All methods have been able to control the ASR expansion of specimens. Especially, silane penetrant method can control the ASR expansion even if the surface layer removed. And this paper deals with the basic investigations on the amount of impregnated silane in addition to the impregnation depth by applying differential thermal analysis (TG-DTA) of samples obtained from different depths in concrete. A good linear relation between the exothermic peak area of the heat flow curve and the content of silane was confirmed.

Role of multi-wall carbon nanotube network in composites to crystallization of isotactic polypropylene matrix

The composites (iPP/CNTs) made of isotactic polypropylene (iPP) and multi-wall carbon nanotubes (CNTs) were prepared by solution blending. To improve compatibility between CNTs and iPP and to enhance dispersion of CNTs in iPP matrix, CNTs were chemically modified by grafting alkyl chains. The chemically modified CNTs had about 6wt% grafted alkyl chains. Rheological measurements indicated that CNTs caused gelation in iPP/CNTs due to CNT network formation and the critical gelation CNT concentration was about 7.4wt%, which was considered to be high due to the low CNT aspect ratio in this study. Crystallization behaviors of iPP/CNTs were studied by using optical microscopy (OM) and differential scanning calorimetry (DSC). Radial growth rates of spherulites during isothermal crystallization of iPP/CNTs with CNT concentrations less than 2.0wt% measured by using OM showed decreasing trends with increasing CNT concentration. Avrami analysis of the exothermic heat flow curves during isothermal crystallization of iPP/CNTs measured by DSC indicated that crystallization rates were accelerated when CNT concentrations were lower than the critical gelation concentration, because CNTs mainly functioned as nucleating agents for crystallization, while crystallization rates did not change obviously when CNT concentrations were higher than the critical gelation concentration, because CNT network could form and mainly functioned to provide restriction to mobility and diffusion of iPP chains to crystal growth fronts.

The Long-term Stability of Sodium Percarbonate in Presence of Zeolite as Measured by Heat Flow Calorimetry

Abstract Heat flow calorimetry has been evaluated as an alternative technique to conventional stability testing of sodium percarbonate [15630-89-4] (SPC) based on analysis of the hydrogen peroxide content. Stability tests were performed with different SPC samples as well as under various experimental conditions. In general, stable samples exhibiting high concentration of hydrogen peroxide were accompanied by low heat flow values. It was found that the results obtained by heat flow calorimetry and conventional stability testing were in agreement. It was also demonstrated that the long-term stability could be predicted from heat flow data obtained during the initial stage of decomposition. Furthermore, different manufacturing and experimental conditions were manifested as a change of the heat flow curve. The results indicate that the rate of heat production is closely associated with the stability of sodium percarbonate, i. e. the rate of decomposition of sodium percarbonate. In presence of zeolite the stability of sodium percarbonate was reduced, particularly under humid conditions.

A study on the formation of MgAl2O4 and MgO crystals in Al–Mg/quartz composite by differential thermal analysis

The present study has examined the thermodynamics of MgAl2O4 and MgO formations in Al–Mg alloy/quartz (>99% crystalline silica) through differential thermal analysis (DTA). The formation of MgAl2O4 and MgO is detected as exothermic peaks in the heat flow curve and the reaction is confirmed by the Si dissolution peaks observed during the reheating of samples and SEM analysis of the reacted sample. The presence of MgAl2O4 and MgO is confirmed in the XRD analysis of the reacted sample. The study has enabled the production of nano sized MgAl2O4 and MgO crystals at the interface of Al–Mg alloy and quartz. The reaction between them is found to be influenced by the oxidation of Mg, which is reduced by increasing heating rates.

Effects of carbon nanotubes on crystallization and melting behavior of poly(L‐lactide) via DSC and TMDSC studies

AbstractIn this work, multiwalled carbon nanotubes (MWNTs) were surface‐modified and grafted with poly(L‐lactide) to obtain poly(L‐lactide)‐grafted MWNTs (i.e. MWNTs‐g‐PLLA). Films of the PLLA/MWNTs‐g‐PLLA nanocomposites were then prepared by a solution casting method to investigate the effects of the MWNTs‐g‐PLLA on nonisothermal and isothermal melt‐crystallizations of the PLLA matrix using DSC and TMDSC. DSC data found that MWNTs significantly enhanced the nonisothermal melt‐crystallization from the melt and the cold‐crystallization rates of PLLA on the subsequent heating. Temperature‐modulated differential scanning calorimetry (TMDSC) analysis on the quenched PLLA nanocomposites found that, in addition to an exothermic cold‐crystallization peak in the range of 80–120 °C, an exothermic peak in the range of 150–165 °C, attributed to recrystallization, appeared before the main melting peak in the total and nonreversing heat flow curves. The presence of the recrystallization peak signified the ongoing process of crystal perfection and, if any, the formation of secondary crystals during the heating scan. Double melting endotherms appeared for the isothermally melt‐crystallized PLLA samples at 110 °C. TMDSC analysis found that the double lamellar thickness model, other than the melting‐recrystallization model, was responsible for the double melting peaks in PLLA nanocomposites. Polarized optical microscopy images found that the nucleation rate of PLLA was enhanced by MWNTs. TMDSC analysis found that the incorporation of MWNTs caused PLLA to decrease the heat‐capacity increase (namely, ΔCp) and the Cp at glass transition temperature. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1870–1881, 2007

Comparison of TSSD results obtained by differential scanning calorimetry and neutron diffraction

Due to their low absorption cross-section for neutrons, Zr alloys are used for reactor core components. The terminal solid solubility (TSS) for hydrogen in these alloys is very low – in Zr–2.5 wt% Nb, used to fabricate pressure tubes for CANDU (CANDU–CANada Deuterium Uranium is a registered trademark of Atomic Energy of Canada Ltd.) power reactors, the TSS is ∼0.7 at.% H at 300 °C. The mechanical properties of the components may deteriorate when their hydrogen concentration exceeds TSS. Therefore, accurate values of the TSS are needed to assess the operating and end-of-life behaviours of these components. Differential scanning calorimetry (DSC) is used to measure the TSS of hydrogen in Zr alloys. Three distinct features are marked on a typical DSC heat flow curve when the material is being heated and the hydrides are dissolving; ‘peak temperature’, ‘maximum slope temperature’ and ‘completion temperature’. Usually, the maximum slope temperature, being about the average of the three temperatures, is interpreted as the TSS temperature for hydride dissolution ( T TSSD). A set of coordinated DSC and neutron diffraction measurements have been carried out to identify the features of the heat flow signal that closely correspond to the T TSSD. Neutron diffraction was chosen because hydrides generate distinctive diffraction peaks whose intensities approach zero at the transition temperature – an unambiguous indication of dissolution. Neutron diffraction shows that the temperature of hydride dissolution correlates closely with the DSC peak temperature.

Investigation of 15-year-old municipal solid waste deposit profiles by means of FTIR spectroscopy and thermal analysis

Five profiles of a 15-year-old bank containing over three weeks composted municipal solid waste were characterized by means of different parameters habitually applied in waste management (loss on ignition, total organic carbon, total nitrogen, NH(4)-N, pH), and in addition by humic acid determination, FTIR spectroscopy and thermal analysis. Stabilization processes are revealed by humic acid contents. Over the 15 year period organic matter had developed in various ways. Highest humic acid contents were found at 0.5 m below the surface. Below 1.0-1.5 m anaerobic conditions dominated causing a strong decline of humic acid concentrations. Despite similar contents of organic matter at 0.5 m and at 3.0 m organic matter quality differed. These differences were verified by infrared spectroscopic investigations and thermal analyses (differential scanning calorimetry DSC). The spectral pattern of 15-year-old profile samples (municipal solid waste including the biogenic fraction) was compared to current municipal solid waste and abandoned landfill materials. Current municipal solid waste samples comprised different degradation stages from fresh materials to stabilized waste, suitable for landfilling according to Austrian standards. Municipal solid waste originating from abandoned landfills closed in the seventies represented stable material. Principal component analysis was performed to detect similarities and differences. It is evident that the profile samples constitute a particular group in between municipal solid waste and abandoned landfill material. Some differences can be attributed to the divergent composition of municipal solid waste in the eighties when the organic fraction was not separated. Otherwise, landfill materials from the seventies with the same composition regarding the organic fraction were deposited together with construction waste. Heat flow curves (DSC profiles) of municipal solid waste, representing different decomposition stages, illustrate the development of enthalpies and reveal the status of the profile samples. It is evident that mechanical-biological pretreatment leads to a faster stabilization of waste organic matter.

Thermal decomposition kinetic of reactive solids based on isothermal calorimetry measurements

An isothermal method was applied to measure the thermal decomposition of reactive solids in a sensitive heat flux reaction calorimeter, C80. This technique experimentally clarified the decomposition mechanisms of unstable substances based on the shapes of the heat flow curves, from which autocatalysis, first-order reaction or pseudo-autocatalytic reaction could be recognized. Kinetic parameters were derived from the measured data.

Ordering and Steric-Hardening in SBS-Modified Bitumen

Styrene−butadiene−styrene (SBS)-modified bitumen shows good cracking resistance at low temperatures. With the knowledge of the microstructure of SBS-modified bitumen being incomplete, the reasons for the low-temperature performance remain partly unclear. In this work, modulated differential scanning calorimetry (MDSC) was used to study the ordering of crystallizable alkanes and that of alkyl aromatics in SBS-modified bitumen. These compounds are responsible, respectively, for the cold-crystallization (CC) and the steric-hardening (SH) visible on the nonreversing heat-flow (NRHF) curves obtained from MDSC. In blends of bitumen with 3, 6, and 10 wt % SBS, CC and SH enthalpies were measured. SBS was found to reduce both the CC and the SH in bitumen, the reduction being disproportionately higher than expected on the basis of polymer concentration. The loss of CC and SH enthalpies demonstrate the reduced capacity of alkanes and alkyl aromatics to order in the presence of SBS.

Investigation of the Oxidation Behaviour of Pure Hydrocarbon Components and Crude Oils Utilizing PDSC Thermal Technique

Abstract High Pressure Air Injection (HPAI) is an Improved Oil Recovery (IOR) technique in which compressed air is injected into light oil, high-pressure reservoirs. The objective of this process is the oxygen from the injected air reacts with a small fraction of the reservoir oil at an elevated temperature to produce a mixture of carbon dioxide and nitrogen. The produced gas flowing from the reaction region mobilizes the oil downstream of the reaction zone towards the production wells. Knowledge of the oil's oxidation behaviour is a key to the successful implementation of this process. However, information on oxidation behaviour of oils based on their compositions is limited, especially for light oils. An experimental study was designed to examine the oxidation behaviour of three crude oils (a light oil, a medium oil, and an Athabasca bitumen) by using the Pressurized Differential Scanning Calorimeter (PDSC) at pressures from 110 to 6,894 kPa. Pure hydrocarbon aromatics and paraffin samples were also selected for the current study. The study shows an increase of pressure results in an increase in the rate of oxidation reactions and heat released from the oxidation reactions. The PDSC heat flow curves also clearly demonstrate the effect of chemical structure of the samples on their oxidation behaviour. The extent of oxidation of hydrocarbon samples is strongly dependent on the nature of the hydrocarbon. Introduction Air injection continues to be an important oil recovery process, used to increase both the amount and the rate of oil recovered from a petroleum reservoir(1,2). When air is injected into a light oil reservoir, exothermic chemical reactions occur between the reservoir oil and the oxygen contained in the injected air. The reactions are mainly oxidation reactions resulting in heat generation and the production of carbon dioxide, carbon monoxide, and water corresponding to the consumption of oxygen. The heat of reactions results in a temperature elevation leading to vapourization of some lighter components and a decrease of viscosity of the oil, even though the heat effect is not very important for light or medium oil compared to heavy oil. Therefore, the driving gas, which can sweep the oil to production wells, is not the injected air but an in situ-generated flue gas, composed of CO, CO2, N2, and vapourized light hydrocarbon components. Air injection is a complex process involving simultaneous heat and mass transfer in a multiphase environment coupled with oxidation chemical reactions. Oxidation reactions play an important role in this process. In order to improve the efficiency of the air injection process, it is necessary to have additional knowledge of the factors influencing the process and how they affect the oxidation of oil. In recent years, the application of thermal analysis techniques, thermogravimetry (TG/DTG), and differential scanning calorimetry (DSC) have obtained wide acceptance in the study of combustion behaviour of oil. Attempts to use thermal analysis techniques to study crude oil combustion began with Tadema(3).

Temperature memory effect of Ti 50Ni 30Cu 20 (at.%) alloy

After the reverse thermal induced martensitic transformation process of shape memory alloy is arrested at a temperature between the reverse transformation start and finish temperatures ( A s and A f), and then cooled to a temperature below M f, a kinetic stop will occur in the next heat flow curve during the heating process. The kinetic stop is closely related to the arrested temperature. This phenomenon is called temperature memory effect (TME). TME of Ti 50Ni 30Cu 20 (at.%) shape memory alloy with phase transformation between B2 austenite and B19 martensite has been investigated by differential scanning calorimeter in this paper. The results indicate that TME of Ti 50Ni 30Cu 20 alloy only exists in the heating process.

Thermal properties of polypropylene post-consumer waste (PP PCW)

Differential scanning calorimetry has been used to study the heat flow during melting and crystallisation of a range of polypropylene post-consumer waste (PP PCW) grades and blends. The heat flow curves and the heat capacity curves indicated that the PP PCW grades and blends contained contaminants even after manual sorting and a cleaning process. The enthalpies of the PP PCW grades were lower than that for the virgin grades, as a result of degradation. Small amounts of polymeric contaminants (up to 10%) did not affect the enthalpies of PP PCW although other contaminants may have had some effect. The enthalpies of the PCW blends could in general be predicted by a linear additive rule, which is of importance for recycling a variety of PP PCW products.

Extended rigidity percolation and chemical thresholds in Ge–Te–Pb glasses as revealed by MDSC

Thermal analysis of Ge 20Te 80− x Pb x (2≤ x≤8) glasses has been undertaken using modulated differential scanning calorimetry (MDSC). The compositional dependence of thermal parameters is investigated. The crystallization temperatures ( T c) estimated from the total heat flow show detectable changes at compositions x=4, 6.5 and 7.5. Further, the heat capacity change at the glass transition temperature, measured from the reversible heat flow curve (Δ C p R), is found to exhibit a maximum and an inflexion at compositions x=4 and 6.5 and minimum at x=7.5, respectively. Also, the relaxation enthalpy, estimated from the area under the non-reversing heat flow curve (Δ H NR), exhibits similar features at the said compositions. From the observed MDSC results, it has been proposed that the compositions x=4 and x=6.5 denote to the onset and completion of rigidity percolation and x=7.5 corresponds to the chemical threshold of the system.

Examination of the growth of probiotic culture combinations by the isoperibolic batch calorimetry

Probiotic (“intestinal friend”) foods, and probiotic dairy products in particular, have substantially increased in number recently. In the production of some of these products a problem is caused by the fact that the thermotolerant microbes that produce the probiotic effect do not generate an aroma; the taste of the product is given by aroma-producing mesophilic microbes. The growth optima of the two microbe groups do not coincide. Given that heat is released in the course of microbe reproduction, the isoperibolic calorimetry method appears the best and fastest for monitoring the process. During the experiments the thermotolerant Prebiolact, owned by the Hungarian Dairy Research Institute (HDRI) and clinically verified to be probiotic, and Hansen Company’s CHN-22 mesophilic butter culture were examined bred separately and together. The cultures were incubated at 30 °C, at which temperature prior studies had shown both lactic acid bacteria cultures were capable of growing. The cultures were injected into milk, then the microbe growth heat flow-time curve over 18 h was taken on the Setaram Micro DSC-II calorimeter at 30 °C under isothermic conditions. Analysis of the heat flow curves led to the following conclusions. Both lactic acid bacteria cultures grow well at the non-optimal temperature of 30 °C, thermotolerant Prebiolact somewhat faster and mesophilic CHN-22 slower. The two cultures do not impede each other in mixed cultures; the growth peaks of the two cultures were easily isolated on the power–time curve by a deconvolution program. In sum it can be stated that mixed cultures of the two cultures examined can be used to produce dairy products which are probiotic, but their taste character (e.g. aroma) is determined by the butter culture. To date we have elaborated production procedures for probiotic butter cream and heat-resistant sour cream using the two cultures in a mixed one.

The calorimetric investigation of the graphite–HNO 3–R system (R=CH 3COOH, H 2SO 4)

The interactions of highly oriented pyrolytic graphite with HNO 3–R (R=CH 3COOH, H 2SO 4) solution were investigated by Calvet type calorimeter at 305.5 K and X-ray diffraction. It was shown that in the graphite–98% HNO 3–100% CH 3COOH system the enthalpy of the formation and the stage number of graphite nitrate depends on HNO 3 percentage in the solution. Calorimetric investigation of the graphite–98% HNO 3–96% H 2SO 4 system demonstrated that the shape of the heat flow curves corroborates the co-intercalation of HNO 3 and H 2SO 4 into graphite. It was established that the formation of the first stage of ternary compounds of variable composition takes place.

Temperature-modulated DSC provides new insight about nickel-titanium wire transformations

Differential scanning calorimetry (DSC) is a well-known method for investigating phase transformations in nickel-titanium orthodontic wires; the microstructural phases and phase transformations in these wires have central importance for their clinical performance. The purpose of this study was to use the more recently developed technique of temperature-modulated DSC (TMDSC) to gain insight into transformations in 3 nickel-titanium orthodontic wires: Neo Sentalloy (GAC International, Islandia, NY), 35°C Copper Ni-Ti (Ormco, Glendora, Calif) and Nitinol SE (3M Unitek, Monrovia, Calif). In the oral environment, the first 2 superelastic wires have shape memory, and the third wire has superelastic behavior but not shape memory. All wires had cross-section dimensions of 0.016 × 0.022 in. Archwires in the as-received condition and after bending 135° were cut into 5 or 6 segments for test specimens. TMDSC analyses (Model 2910 DSC, TA Instruments, Wilmington, Del) were conducted between −125°C and 100°C, using a linear heating and cooling rate of 2°C per min, an oscillation amplitude of 0.318°C with a period of 60 seconds, and helium as the purge gas. For all 3 wire alloys, strong low-temperature martensitic transformations, resolved on the nonreversing heat-flow curves, were not present on the reversing heat-flow curves, and bending appeared to increase the enthalpy change for these peaks in some cases. For Neo Sentalloy, TMDSC showed that transformation between martensitic and austenitic nickel-titanium, suggested as occurring directly in the forward and reverse directions by conventional DSC, was instead a 2-step process involving the R-phase. Two-step transformations in the forward and reverse directions were also found for 35°C Copper Ni-Ti and Nitinol SE. The TMDSC results show that structural transformations in these wires are complex. Some possible clinical implications of these observations are discussed.

Determination of Solubility of Polymorphs Using Differential Scanning Calorimetry

In this paper, we present a technique for determining the solubility of both stable and metastable polymorphs. The technique was developed during a study of the thermodynamic relationships, between the polymorphic forms of carbamazepine (forms I and III), glycine (α and γ forms), and mefenamic acid (forms I and II), using a Mettler Toledo 822e differential scanning calorimeter (DSC). The three systems under investigation were found to be enantiotropic with transition points at 78 °C (carbamazepine), 177 °C (glycine), and 86.6 °C (mefenamic acid). Solubility determination of the metastable polymorphic form of the systems was carried out by slow heating (0.08 K/min) of the sample, and using heat flow derivative curves, where the saturation point and hence the solubility at a known weight percentage are given by the peak of a heat flow curve.