DSC Cell Research Articles

Small scale isothermal age technique to determine exothermic onset temperatures

With the increased focus on safety in the chemical industry, there is a greater demand for reliable information as to exothermic onset temperatures before the scale-up of any process. The Small Scale Isothermal Age (SSIA) test is an isothermal DSC technique in which reusable metal crucibles are used to accurately determine exothermic onset temperatures. A typical solid sample, 50–75 mg, is held isothermally at a preset temperature for an extended period of time, usually 12–16h. The aged sample is then run at a standard heat-up ramp to determine any decrease in the size of the original exotherm relative to the unaged sample. The same DSC cell, metal crucible, heat-up rate and sample weight are used to determine the exotherm size in both the unaged and aged sample. The SSIA technique is applicable to both solids and liquids and has the advantages of: i) small sample size, (ii) handling of compounds in which exothermic activity is accompanied by large pressure increases without damaging experimental equipment, (iii) accurate determination of exothermic onset temperature, (iv) ease of experimental set-up, (v) ease of data interpretation, and (vi) rapid experimental turn-around time. The determination of the exothermic onset temperature using the small scale isothermal age technique will be presented and results compared to data obtained using standard and small dewar techniques.

On the plasticization of poly(2,6‐dimethyl phenylene oxide) by CO2

AbstractChange in the glass transition temperature, Tg, of poly(2,6‐dimethyl phenylene oxide), PPO, due to the dissolved CO2 has been measured as a function of the gas pressure, p, using a high‐pressure DSC cell. At 61.2 atm, the highest pressure studied, Tg is depressed by 31.6°C. The depression in Tg is found to be linear with pressure, with dTg/dp of −0.5°C atm−1. The experimental results are in fair agreement with those calculated from a quasilattice solid‐solution model for polymer‐diluent systems. The present results, however, differ markedly from a recent investigation on PPO‐CO2 system which reported a depression in Tg of 226°C at 60 atm and a dTg/dp of −3.8°C atm−. © 1994 John Wiley & Sons, Inc.

Thermokinetic properties of inhibited vegetable oils

Castor, corn and linseed oils with the addition of inhibitors were investigated using a DSC equipped with a pressure DSC cell. The inhibitors used in the experiments were 2,6-di- t-butyl-4-methylphenol and propyl gallate. The measurements were carried out under isothermal conditions in an atmosphere of oxygen. Thermal curves from DSC runs permitted the determination of onset and maximum points of the peak which were then compared to those of the pure oils. The apparent activation energies of oxidation of the oils were calculated using the model of the autocatalytic reaction and the Arrhenius equation.

Hydrogen bonding Part 53. Correlation of differential scanning calorimetric data with IR and dissociation vapor pressure studies of transitions of hexamethonium chloride and bromide dihydrates and hexamethonium bromide monohydrate

Abstract Differential scanning calorimetry of hexamethonium chloride dihydrate shows an endothermic transition of 2.70 kcal mol−1 at 36.81°C. This correlates well with the temperatures observed by IR spectra (36°C) and equilibrium dissociation vapor pressure studies (37°C) for the transition between Type I planar cluster and Type II extended linear HOH⋯Cl− hydrogen bonding, and with the value of 2.77 kcal mol−1 for this transition derived by Hess' law treatment of dissociation vapor pressure data. Differential scanning calorimetry of hexamethonium bromide shows a rapid endothermic transition of 2.38 kcal mol−1 at 35.15°C and a very slow endothermic transition of about 12–13 kcal mol−1 centered near 50°C. This latter endotherm corresponds to the transition between Type I and Type II HOH⋯Br− hydrogen bonding observed by IR and vapor pressure studies at 49°C. The nature of the 35.15°C endotherm is not known. Hexamethonium bromide also shows a third endotherm at 142.91°C, which presumably results from melting of hydrate in the sealed DSC cell. Combined analysis of differential scanning calorimetry and dissociation vapor pressure data predicts a value of about −13 kcal mol−1 for an exothermic disproportionation at 52°C of two hexamethonium bromide monohydrate to Type II dihydrate and anhydrous bromide.

A thermoanalytical study on solid‐state cure of poly(p‐phenylene sulfide)

AbstractDifferential scanning calorimetry (DSC) was used to investigate the solid‐state cure process of poly(phenylene sulfide)(PPS) resin. Virgin PPS resin in an open sample pan was cured in DSC cell. Either air or oxygen was used as a curing atmosphere. Cure temperatures were in the range of 200 and 250 °C, which are below the melting point of PPS resin. Cure temperature as well as atmospheric condition influenced the cure behavior of PPS in the solid state. Both the rate and the amount of cure increased with increasing cure temperature. On the other hand, the time to reach the maximum cure rate was independent of cure temperature. Changing the atmosphere from air to oxygen increased both the cure rate and the amount of cure. The size effect of PPS particles on the cure reaction was also discussed.

A reusable metal crucible for use in differential scanning calorimetry analysis of closed reaction system samples

A specially designed sample crucible has been developed and evaluated for use with differential scanning calorimetry to determine whether if an exotherm is present in a closed system without the use of a high pressure DSC cell. The problems associated with the use of a crimped aluminum sample pan, with its low pressure containment and chemical reactivity, are overcome with the use of these crucibles. This crucible eliminates the need to purchase a high pressure DSC cell, in which the chemically reactive aluminum pan is often used, and overcomes the high pressure DSC problems of duplication of results and noisy baselines. The crucibles are useful with samples containing volatile components or those which release gaseous by-products during decomposition. The crucibles are constructed of either 316L or Hastelloy B, have a volume of ≈ 60 μ 1, and have a removable glass liner for use with highly corrosive systems. The crucibles are reusable, with a screw-on cap containing a replaceable 400 psi “rupture disk” seal, and have an operating temperature range from < 0 to = 300°C. Many of the commercially available high pressure cells are not reusable, do not have chemically resistant liners and are difficult to seal properly. The determination of the calibration coefficient of a DSC cell using this sample crucible, both with and without the glass liner, will be presented and the value compared with the calibration coefficient determined using a typically sealed aluminum pan.

New pressure DSC cell and some applications

Physical properties and chemical reactions can be investigated by pressure DSC. There are 3 possibilities of sample preparation with respect to the contact with the furnace atmosphere which are illustrated by typical applications: 1. Free access of furnace atmosphere 2. Sealed crucible (constant volume) 3. Limited access of furnace atmosphere (self generated atmosphere)

Design, specifications and application of a high pressure DSC cell

The construction of a high pressure DSC measuring head for the Perkin-Elmer DSC-7 is presented. The DSC cell is developed to work in a range of temperature from 290 to 570 K at a maximum pressure of 500 MPa using different silicon oils as pressure medium. This calorimeter works with the common heating rates from 0,1 K min to 30 K min . The noise of the base line is about 50–100 μW depending on the pressure in question. The repeatability of the base line amounts to 2–3 mW. The new high pressure cell is especially useful for DSC measurements in polymer science preliminary results are presented.

Thermal conductivity of polymer melts

The Du Pont 910 DSC cell and base have been modified for the measurement of steady-state heat flux and temperature gradients through molten polymeric specimens. This is a comparative method for thermal conductivity determination. The calculation for polymer melts is based on the measured thermal quantities and a calibration factor obtained from reference materials. The measurements at several steady-state temperatures can be carried out consecutively. Furthermore, the thermal diffusivity k can be obtained from the relationshipκ = λ/ρ C p , where λ is the thermal conductivity, ϱ is density, and C p is specific heat. Construction of sample holders and modifications of the DSC cell and base are described.

Tracing the spontaneous mixing and mobility of miscible polymer blends using differential scanning calorimetry [Cellulose acetate‐poly(styrenephosphonate ester)

AbstractA method in which the dissolution of a miscible polymer pair is traced in a differential scanning calorimetry cell is described. The polymer blend is initially prepared as an heterogeneous system with microdomains of one component embedded in the continuous matrix of the second polymer. Annealing the system in the DSC cell above the glass‐transition temperature causes a spontaneous mixing of the polymer pair which can be observed by the progressive shift of the Tgs of both components until they merge. The time scale for dissolution and aspects of mass‐transport phenomenon are thus determined for the specific blend, cellulose acetate‐poly(styronephosphonate ester). Rather sharp progressive shifts of the Tgs are shown to prevail without significant broadening of the transition curve (ΔTg). Mass‐transport analyses supported by electron microscopy observation of the blend, before and after annealing, suggest that the domain sizes remain nearly unchanged and the physicochemical makeup of the phase boundary interfaces determines the time scale of dissolution in the system. A model from which mean‐value diffusion coefficients are calculated for both components at different annealing temperatures is reported.

The effect on heat flux DSC measurements of physico-chemical properties of the sample

In order to account for the dependence of the calibration constant of a heat flux DSC cell on experimental variables and standard related properties, a study has been undertaken of the entire DSC trace. Part of this study has already been published. The present report completes the general picture of the cell behaviour by defining the linkage between the measured signal and the relevant sample and experimental parameters. The proposed model is verified on the basis of the results of several calibration runs performed using different metal standards (In, Pb, Zn).

Simultaneous measurement of light transmission and heat flow in a modified differential scanning calorimeter

A commercial DSC cell has been modified to allow simultaneous measurement of heat flow and light transmission. A special fiber optic probe capable of transmitting and receiving light is located immediately above the sample. The sample is held in a reflective aluminum pan during the measurement. Maximum optical signal intensity is recorded when the sample becomes completely transparent. The light from the probe will pass through the sample, reflect off the bottom of the pan, and then pass up through the sample again and back into the probe. The method was developed to augment the normal DSC heat-flow measurement. We find that the additional optical information is useful in elucidating the nature of thermal transitions in polymeric materials. Any transition, physical or chemical, that is accompanied by an appreciable change in optical transmission can be studied by this technique. The probe is useful even in investigations where only the optical signal is desired, because one can make use of the temperature programming and data aquisition capabilities of the DSC instrument. The presence of the probe tip near the sample does not seriously degrade the heat-flow signal. Good calorimetric accuracy is maintained, albeit some baseline curvature is introduced. Several applications of the technique are described. These include melting and crystallization of polymers, solubility behavior of polymer–polymer and polymer–additive blends, and sintering of polymer particles during oxidative degradation.

On the quantitative reliability of heat flux DSC

In an attempt to explain how the calibration factor of a heat flux DSC cell depends both on the standard utilized and on the experimental variables, a study has been undertaken of the entire DSC trace. This report deals with the second half of the peak and shows that, other experimental conditons being fixed, the peak area increases with increasing heating rate. This accounts for the observed decrease in the calibration factors with increasing heating rate.

A calibration study of the dupont DSC 910 module

In this paper a calibration study of the Dupont 910 DSC module is presented. According to our view of the cell construction, this type of calorimeter combines the advantages and disadvantages of a DTA and DSC cell. It was found that the calibration constant E is independent of temperature (as it should be for any DSC cell) but is dependent on the heating rate and the mass or the total absolute heat exchange by the sample.

Water Vapor Transmission Rates Through Textile Materials as Measured by Differential Scanning Calorimetry

The permeability of small textile samples to water vapor has been evaluated using a conventional DSC cell. The technique enables evaporative rate data to be determined and comparisons made of materials having different characteristics. The data are useful in predicting evaporative sweat loss rates, thereby helping to evaluate metabolic heat loss problems associated with protective clothing for firefighters.

Enthalpic study of structural relaxation and crystallization in some metallic glasses

Structural relaxation and crystallization have been studied in the metallic glasses Fe39Ni36Cr5P14B6, Fe81B19, Fe76Co4B20 and Fe75V4B21 by DSC.Different coefficients of calibration of the DSC cell were determined for the two phenomena.The enthalpy of relaxation increases with increasing quenching rate for Fe39Ni36Cr5P14B6 and with increasing number of alloy components for Fe-B-based glasses. In the latter systems. relaxation is never completed before the start of crystallization.The enthalpy of crystallization does not depend on the quenching rate for Fe39Ni36Cr5P14B6, and does not change during annealing within the relaxation field before crystallization.

An analysis of the factors affecting the peak shape and the quantitative reliability of a heat flux DSC cell

In a previous work it was shown that unexpected problems may arise in the calibration of a heat flux DSC cell. To understand the origin of these problems an analysis has been undertaken of what happens in the cell before, during and after the peak. Here the first part of this analysis is reported dealing with the baseline and with the dependence of the recorded signal on time. Analytical expressions are obtained connecting the measured signal with experimental variables and instrument constants. Completely independent on sample related properties, a maximum measurable ΔT is introduced as limiting factor for quantitative reliability.

Performances of a heat flux DSC cell

Five different metals have been used to determine the calibration constant of a heat flux DSC cell and measurements have been performed under a variety of experimental conditions. Different results have been obtained by different standard meaning that some physical property of the sample may affect the instrument response. An analysis of the details of the instrument response showed that sample density and latent heat of fusion per unit mass can both affect the final result. In addition the heating rate too has been shown to exert an influence on the calibration constant value.

DSC investigation of the thermal behaviour of (NH 4) 2SO 4, NH 4HSO 4 and NH 4NH 2SO 3

Gaseous products evolved from (NH 4) 2SO 4, NH 4HSO 4 and NH 4NH 2SO 3 during successive heating and cooling cycles were flushed with inert gas into analyzer Dräger tubes hooked tightly to the terminal port of the DSC cell base. This simple procedure allowed the starting temperature of the decomposition to be determined and the amount of the individual gases in the mixture to be identified and even estimated. NH 4NH 2SO 3 at 523 K in humid air produced HNH 2SO 3 initially and, on further cycling, (NH 4) 2SO 4 and NH 4HSO 4 also appeared. The Δ H f values for NH 4HSO 4 were (kJ mole −1): in an airtight sample holder 12.67, in a dry argon atmosphere 11.93, and in a static air atmosphere 10.92. Endothermic peaks for (NH 4) 2SO 4 and 498 and 411 K represented the incongruent melting point and the polymorphic transition of (NH 4) 2SO 4·NH 4HSO 4. After the first heating in air to 530 K, (NH 4) 2SO 4 and NH 4HSO 4 exhibited closely similar cyclic DSC curves. The endothermic peaks at about 393–420 K may be assigned to different combinations of (NH 4) 2SO 4 and NH 4HSO 4.

Electrothermal analysis of carbon black loaded polymers

A Du Pont DSC cell has been modified, without any permanent alteration, to measure absolute values of resistivity of polymer compounds. Carbon filled polymer compounds show transitions not observed by other thermal methods. Electrothermal analysis (ETA) can predict thermal stability of amorphous polymers. This approach has advantages over other existing methods in the case of PVC. For semi-crystalline polymers, ETA can be used as a scanning tool for temperature sensitivity of resistivity of compounds for uses such as cable or PTC materials.