Differential Scanning Calorimeter Cell Research Articles

Calculating temperature lag for the correction of D values obtained from differential scanning calorimetry

A heat flux differential scanning calorimeter (DSC) was involved in a new method of determining thermal inactivation kinetic parameters ( D - and z -values) for a bacterial suspension in skim milk. Validating the method against an established method led to the realization that the required sample size caused the sample temperature to appreciably lag that of the DSC cell, leading to consistent but inaccurate D-values. However, only the temperatures of the sample sensor and the DSC cell were available once this was realized. In this report, an analysis is introduced to determine the lag by using only the sensor temperature beneath the sample pan. It relies on equations based on Newton's law of cooling employed elsewhere in the DSC literature. They are used to analyze the sample sensor temperatures at the start of the scan, before a linear temperature rise in the sample is established, along with the constant temperature difference between the DSC cell and that of the sample sensor after the linear temperature rise is established. The analysis was applied to correct the temperatures leading to the D-value, which aligned it with the established value. • A novel approach calculates a mass average temperature lag in a DSC sample using only the sample surface temperatures. • A unique nondimensionalization of the equations for temperature lag halved the number parameters that were required to calculate it. • The approach is shown to give consistently accurate results for the lag.

Comparative Study of Vegetable Oils Oxidative Stability using DSC and Rancimat Methods

A comparative study was carried out to evaluate and compare the oxidative stability of vegetable oils (olive, corn and sunflower) in Egypt, through evaluation of accelerated oxidation at four different isothermal temperatures (110, 120, 130, 140 °C) using two different instruments: a differential scanning calorimeter (DSC) and a Rancimat instrument, taking into account the physicochemical quality characteristics and relationships between oxidative stability and fatty acid composition of oils. The Rancimat instrument was set at the four different isothermal temperatures with an air flow 20 L/h and measures the induction period (IP) of the selected oils. The differential scanning calorimetry (DSC) technique involved accelerated oxidation of oil samples in an air flow of 60 ml/min in DSC cell set at four different isothermal temperatures. A rapid increase in evolved heat was observed with the appearance of a sharp exothermic curve during initiation of the oxidation reaction. From the resulting exothermic curve, the onset of oxidation time (To) was determined graphically by the DSC instrument. There was an excellent correlation (p 0.98) between the two methods with coefficient of determination (R2 >0.89) for DSC independent of the vegetable oil source, imply that DSC can be recommended as an alternative appropriate objective method for assessing the oxidative stability of vegetable oils because of its simplicity, absence of toxic chemicals, small amount of sample and time-saving nature and could be easily used for routine analysis in oils and fats industry.

Isobaric Heat Capacity Measurements of Liquid Methane, Ethane, and Propane by Differential Scanning Calorimetry at High Pressures and Low Temperatures

A commercial differential scanning calorimeter (DSC) was adapted to allow accurate isobaric heat capacity, cp, measurements of cryogenic, high-pressure liquids. At (subcritical) temperatures between (108.15 and 258.15) K and pressures between (1.1 and 6.35) MPa, the standard deviation in the measured cp values was 0.005·cp for methane, 0.01·cp for ethane, and 0.015·cp for propane, which is comparable to both the scatter of cp data for these liquids measured using other techniques and with the scatter of those data sets about the reference equation of state (EOS) values. Three key modifications to the commercial DSC were required to enable these accurate cryogenic, high-pressure liquid cp measurements. First, methods of loading and removing the liquid from the calorimeter without moving the sample cell were developed and tested with high boiling temperature liquids; this modification improved the measurement repeatability. Second, a ballast volume containing a high-pressure vapor phase at constant temperature was connected to the DSC cell so that the liquid sample’s thermal expansion did not cause significant changes in pressure. A third modification was required because the boil-off vapor from the liquid nitrogen used to cool the calorimeter resulted in a temperature inversion, and hence convection, along the tubing connecting the DSC’s sample cell to the ballast volume, that lead to an unstable calorimetric signal at T > 130 K. The modifications to the specialized DSC were tested by measuring cp values for heptane, methylbenzene, and a heptane (1) + methylbenzene (2) mixture with x1 = 0.38 at atmospheric pressure and temperatures of (228.15, 238.15, 303.15, and 313.15) K. The measured values had relative deviations from those measured adiabatically by Holzhauer and Ziegler (J. Phys. Chem. 1975, 79, 590–604) of less than 0.006·cp, indicating that the specialized DSC could be used for liquids and liquid mixtures at conditions relevant to liquefied natural gas production.

RheoDSC: design and validation of a new hybrid measurement technique

A newly developed hyphenated technique is presented that combines an existing rheometer and differential scanning calorimeter (DSC) into a single experimental setup. Through the development of a fixation accessory inside the cell of the calorimeter and the introduction of an add-on unit for the rheometer, the simultaneous calorimetric and rheological measurement inside the well-controlled thermal environment of a Tzero™ DSC cell opens new experimental possibilities. The evolution of thermal and flow properties of a material can be simultaneously monitored during steady or oscillatory shear flow and regular or modulated temperature DSC measurements. The technique offers interesting opportunities for the investigation of flow-induced transitions, such as crystallization or phase separation, and provides a possibility for high-throughput screening of materials. The signal quality of the novel technique in comparison to the stand-alone techniques is demonstrated by the evaluation of the calibration factors and by measurements on standard materials. Finally, combined rheological and calorimetric melting and crystallization experiments on polycaprolacton are performed.

MEMS Scanning Calorimeter With Serpentine-Shaped Platinum Resistors for Characterizations of Microsamples

We report a new design and operation of a microelectromechanical systems (MEMS) differential scanning calorimeter (DSC) for heat-capacity measurements. The sensor consists of a 500-nm silicon nitride membrane supported by four bridges on a silicon wafer. On one side of the membrane, a serpentine-shaped platinum layer is deposited and used as both a resistive heater and a thermometer during the DSC measurement. This MEMS design can provide a self-alignment between the DSC cell and the material to be analyzed in order to prevent its deposition on the sloping side walls of the silicon frame. According to FEM calculations, the system exhibits good thermal isolation and high uniformities in the temperature field in the sensing area of the device. To evaluate the use of this calorimetric device for liquid samples, we measure the heat of vaporization of nanoliter-scale water droplets with high preciseness using the calorimeter in both scanning and heat conduction modes.

Measurements of methane hydrate heat of dissociation using high pressure differential scanning calorimetry

The methane hydrate heat of decomposition was directly measured up to 20 MPa and 292 K using a high pressure differential scanning calorimeter (DSC). The methane hydrate sample was formed ex-situ using granular ice particles and subsequently transferred into the DSC cell under liquid nitrogen. The ice and water impurities in the hydrate sample were reduced by converting any dissociated hydrate into methane hydrate inside the DSC cell before performing the thermal properties measurements. The methane hydrate sample was dissociated by raising the temperature (0.5–1.0 K/min) above the hydrate equilibrium temperature at a constant pressure. The measured methane hydrate heat of dissociation (H→W+G), Δ H d , remained constant at 54.44±1.45 kJ/mol gas (504.07±13.48 J/gm water or 438.54± 13.78 J/gm hydrate) for pressures up to 20 MPa. The measured Δ H d is in agreement with the Clapeyron equation predictions at high pressures; however, the Clausius–Clapeyron equation predictions do not agree with the heat of dissociation data at high pressures. In conclusion, it is recommended that the Clapeyron equation should be used for hydrate heat of dissociation estimations at high pressures.

Differential approach for dynamic analysis to initial onset in heat flow rate spectroscopy of differential scanning calorimeter

A differential approach is proposed for the determination of initial onset in differential scanning calorimeter (DSC) diagram of phase change material (PCM). By dissecting the spacing between extrapolated onset determined with traditional method and origin attributes to various delay mechanisms. A position-dependent term added into the traditional energy change equation accounts for thermal delay from any moving interfaces between separated phases of PCM inside a DSC cell pan. With the aid of Euler's equation in calculus of variations, the heat flow rate equation in relation to three major delay functions and temperature is formulated using chain rule of variables. The second-order differential operation with regard to heat flow rate in DSC diagram helps shortening the distance from extrapolated onset to origin, so as to initial onset can accurately located. The rampant fluctuation in the second-order derivative of heat flow rate in DSC diagram vindicates inadequate compensation of control unit in DSC, a result of serious feedback delay due to poor thermal conductivity and large latent heat in PCM.

RheoDSC: A hyphenated technique for the simultaneous measurement of calorimetric and rheological evolutions

A newly developed hyphenated technique is presented combining an existing rheometer and differential scanning calorimeter into a single experimental setup. Through the development of a fixation accessory for differential scanning calorimeter (DSC) crucibles and a novel rotor, the simultaneous measurement is performed inside the well-controlled thermal environment of a Tzero DSC cell. Hence, the evolution of thermal and flow properties of a material can be simultaneously measured using steady or oscillatory shear measurements and regular or modulated temperature DSC measurements. Along with the construction of a prototype, a validation of the design was performed. The technique offers interesting opportunities for the investigation of flow-induced transitions, for instance, crystallization or phase separation, and provides an asset for high-throughput screening of materials. The potential of the novel technique is demonstrated by two case studies: the chemorheology during the cure of a thermosetting epoxy-amine system and the flow-induced crystallization of syndiotactic polypropylene.

Application of arrhenius kinetics to evaluate oxidative stability in vegetable oils by isothermal differential scanning calorimetry

AbstractIn this study, 10 different vegetable oils were oxidized at four different isothermal temperatures (383, 393, 403, and 413 K) in a differential scanning calorimeter (DSC). The protocol involved oxidizing vegetable oils in a DSC cell with oxygen flow. A rapid increase in evolved heat was observed with an exothermic heat flow appearing during initiation of the oxidation reaction. From this resulting exotherm, the onset of oxidation time (To) was determined graphically by the DSC instrument. In our experimental data, linear relationships were determined by extrapolation of the log (To) against isothermal temperature. The rates of lipid oxidation were highly correlated with temperature. In addition, based on the Arrhenius equation and activated complex theory, reaction rate constants (k), activation energies (Ea), activation enthalpies (ΔH‡), and activation entropies (ΔS‡) for oxidative stability of vegetable oils were calculated. The Ea′, ΔH‡, and ΔS‡ for all vegetable oils ranged from 79 to −104 kJ mol−1, from 76 to −101 kJ mol−1, and from −99 to −20 J K−1 mol−1, respectively. Based on the results obtained, differential scanning calorimetry appears to be a useful new instrumental method for kinetic analysis of lipid oxidation in vegetable oil.

Studies on glass transition temperature during staling of bread containing different monomeric and polymeric additives

Glass transition temperature (Tg) of bread containing different antistaling agents and also of bread superquenched and annealed in a DSC cell and outside, was determined using differential scanning calorimeter (DSC). Increase in Tg during the staling of bread correlated with firming as measured by Instron. Singlet Tg was an indication of miscibility or compatibility of bread components with each other. The lowest increase in Tg was found in bread containing propylene glycol (singlet) followed by glycerol (doublet), maltodextrin (broad), gelatin (singlet), antistaling enzyme (singlet), and polypropylene glycol (doublet) in the order of increase in Tg. Superquenching produced a maximum increase in Tg of bread. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1147–1152, 1999

Studies on glass transition temperature during staling of bread containing different monomeric and polymeric additives

Glass transition temperature (Tg) of bread containing different antistaling agents and also of bread superquenched and annealed in a DSC cell and outside, was determined using differential scanning calorimeter (DSC). Increase in Tg during the staling of bread correlated with firming as measured by Instron. Singlet Tg was an indication of miscibility or compatibility of bread components with each other. The lowest increase in Tg was found in bread containing propylene glycol (singlet) followed by glycerol (doublet), maltodextrin (broad), gelatin (singlet), antistaling enzyme (singlet), and polypropylene glycol (doublet) in the order of increase in Tg. Superquenching produced a maximum increase in Tg of bread. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1147–1152, 1999