Applications of low temperature calorimetry in material research

Low temperature calorimetry has been used not only to obtain heat capacity, entropy, enthalpy and Gibbs free energy, but also to investigate and understand lattice vibrations, metals, superconductivity, electronic and nuclear magnetism, dilute magnetic systems and structural transition involved in material research.     

History repeats itself: Progress in a.c. calorimetry

Periodic heating has been applied more than a century ago to study thermophysical properties of materials. The measurement of heat capacity using a.c. calorimetry was first performed by Corbino in 1910. In connection with the technological development and the progress in science and technology, new and sophisticated apparatus have been constructed in an a.c. calorimetric heat capacity measurements. In this measurement, the noise level of a.c. temperature can be reduced markedly as opposed to the other nonperiodic methods and, therefore, high precision determination can be attained. Furthermore, not only the amplitude but also the phase in a.c. temperature is a useful parameter in constructing much advanced apparatus.     

On-line calorimetry as a technique for process monitoring and control in biotechnology

This contribution reviews laboratory-scale investigations carried out on the usefulness of biological heat release measurements, as a means for monitoring and controlling the metabolic state of microbial cultures. Such studies are carried out in high-quality bench-scale calorimeters, but measuring heat generation rates by establishing energy balances ought to be applicable to large-scale bioreactors without resorting to sophisticated instrumentation. The signal received can either be interpreted by more qualitative correlation with the evolution of the culture, or it may be quantitatively exploited - together with other on-line measurements - in order to assess the rates at which various types of metabolisms proceed in the culture. The work described shows how this can be used to keep a culture in a desired metabolic state during fed-batch and transient continuous cultures of the yeast, S. cerevisae, and how a bacterial fed-batch culture can be controlled in order to optimize biosynthesis of an antibiotic.     

Plant calorimetry. Part 2. Modeling the differences between apples and oranges

In a previous review we discussed calorimetric methods for the study of plant metabolism. Since that review, a number of papers describing calorimetric measurements examining plant growth, stress responses and effects of temperature have appeared. This recent work is reviewed here.

In addition to the experimental work, a mechanistic model linking respiration rates to growth has been published. This model is derived from both mass and enthalpy balance equations. It describes specific growth rate and substrate carbon conversion efficiency as functions of the metabolic heat rate, the rate of CO₂ production, the mean oxidation state of the substrate carbon produced by photosynthesis, and enthalpy changes for conversion of photosynthate to biomass and CO₂. Application of this model to understanding the basis for variation in growth rates among individual genotypes in plants is reviewed.

The effects of environment on the plant respiration-growth relation has been an important focus for plant calorimetry studies. Climatic temperature is one of the most important variables determining growth. Extremes of temperature determine limits of growth, and diurnal variation and mean temperature have a major influence on growth rate. Calorimetric measurements of respiratory rates as a function of temperature can be used to relate the temperature influence on respiratory metabolism to the temperature influence on growth rate. These studies have also discovered the existence of an isokinetic point within the range of normal growth temperatures. Studies of temperature dependence are reviewed and the results analyzed in terms of the recently published mechanistic model.     

The advantages and disadvantages of direct and indirect calorimetry

Kleiber's definitions of what constitutes direct and indirect calorimetry are accepted as the beginning of a commentary on the advantages and disadvantages of direct and indirect calorimetry in which calorimetry is divided into a number of categories based on the kind of calorimetric measurement. For non-reaction calorimetry such as entropy determinations and differential scanning calorimetry, the only means of measurement is by direct calorimetry. For reaction calorimetry, a preference of direct over indirect calorimetry depends on the accuracy needed and the ability of the experimenter to define the system. The data necessary to correct the observed heat loss in direct calorimetry are often all that are needed to make an indirect calculation of the true heat loss. In general, because they are convenient and inexpensive to use, indirect calorimetric methods are preferable to direct methods. However, when possible, one method can be used to verify the results of the other.     

Quantitative aspects of differential scanning calorimetry

The quantitative performance of differential scanning calorimeters is reviewed. Temperature calibration is discussed in terms of an isothermal correction plus a contribution from thermal lag, this can be derived from individual curves and is valid in both, heating and cooling. It is emphasised that baselines that are drawn to thermal events, such as melting and transition phenomena, must have thermodynamic significance and a general procedure is suggested. When this is used, a power compensation calorimeter calibrated for heat-capacity work can reproduce heats of fusion and transition for a diverse range of materials to better than 1%.     

Applications of micro-scale combustion calorimetry to the studies of cotton and nylon fabrics treated with organophosphorus flame retardants

Effective testing methods are critical for developing new flame retardant textiles by the industry. However, the current testing methods all have limitations. In this research, we applied micro-scale combustion calorimetry (MCC) for evaluating the flammability of the cotton woven fabric treated with a traditional reactive organophosphorus flame retardant in combination with a synergistic nitrogen-containing additive and the nylon-6,6 woven fabric treated with a hydroxyl-functional organophosphorus oligomer and crosslinkers. We found that MCC is capable of differentiating small differences among the treated fabric samples with similar flammability. MCC is able to make quantitative measurement of the peak heat release rate, the most important parameter related to fire hazard of materials, of textile whereas such analysis is more difficult using cone calorimetry due to textile fabrics’ low thickness. By using the thermal combustion parameters measured by MCC, we were able to calculate the limiting oxygen index (LOI) of various treated cotton fabric samples with near-perfect agreement between the experimentally measured and the predicted LOI values of treated cotton fabrics. We also compared the capability of MCC and differential scanning calorimetry for analyzing flame retardant cotton textiles.     

Temperature modulated differential scanning calorimetry (TMDSC) in the region of phase transitions. Part 1: theoretical considerations

For temperature modulated differential scanning calorimetry (TMDSC) a simple model, the low pass filter, is presented which allows to see and calculate the influence of heat transfer into the sample on magnitude and phase shift of the modulated part of the measured heat flow rate and the heat capacity determined from it. A formula is given which enables to correct the measured magnitude of the periodic heat flow rate function and the calculated heat capacity in dependence on the thermal resistance and heat capacity of the sample. The correction becomes very important in regions where the heat capacity changes considerably as in the melting region. The approach is successfully tested with model substances with well-known excess heat capacity in the transition region.     

Determination of the heats of gasification of polymers using differential scanning calorimetry

The amount of heat that is required to gasify unit mass of material is one of the key properties that define its ignition resistance and fire response. Knowledge of this property is necessary to assess a material's fire hazard in a particular fire scenario. Nevertheless, even for the most common polymers the values of this property are not well established. Here we present a method for determining the heat of gasification using differential scanning calorimetry and apply this method to a set of ten common plastics and engineering polymers.     

Combined use of adiabatic calorimetry and heat conduction calorimetry for quantifying propellant cook-off hazards

Recent work performed at DERA (now QinetiQ) has shown how accelerating rate calorimetry (ARC) can be used to obtain time to maximum rate curves using larger samples of energetic materials. The use of larger samples reduces the influence of thermal inertia, permitting experimental data to be gathered at temperatures closer to those likely to be encountered during manufacture, transportation or storage of an explosive device. However, in many cases, extrapolation of the time to maximum rate curve will still be necessary. Because of its low detection limit compared to the ARC, heat conduction calorimetry can be used to obtain data points at, or below, the region where an explosive system might exceed its temperature of no return and undergo a thermal explosion.Paired ARC and heat conduction calorimetry experiments have been conducted on some energetic material samples to explore this possibility further. Examples of where both agreement and disagreement are found between the two techniques are reported and the significance of these discussed. Ways in which combining ARC and heat conduction calorimetry experiments can enhance, complement and validate the results obtained from each technique are examined.     

The heat capacity of polymers

The long path to an understanding of heat capacity is traced from isothermal and adiabatic calorimetries to the most recent three methods of isoperibol, scanning, and temperature-modulated calorimetry (TMDSC). These latter three methods are: the traditional method of scanning thermal analysis; the quasi-isothermal method of finding the maximum amplitude of the periodic heat flow in response to a temperature modulation at a constant base temperature; and the pseudo-isothermal analysis of a temperature-modulated scanning experiment by subtracting the effect due to the underlying constant heating rate. In parallel, the development of the knowledge about phases and molecules is traced from its beginning to present-day nanophases and macromolecules.     

The simultaneous detection of heat flow and chemiluminescence intensity during oxidation of unstabilised polypropylene particles

A new experimental technique combining highly sensitive heat flow measurements (microcalorimetry) with the simultaneous detection of chemiluminescence intensity was developed. A perfusion ampoule was connected by fibre optics to an external photo-multiplier and photon counter device. The perfusion ampoule was placed in a 201 calorimetric unit used with a 2277 TAM thermostat. The simultaneous approach offers the advantage of using the same sample and experimental conditions, which reduces the risk for experimental artefacts. Results from the combined equipment confirmed the existence of a time shift between the oxidation profiles of unstabilised polypropylene (PP) previously reported using non-simultaneous MC and CL techniques. The results demonstrate that microcalorimetry is a highly sensitive and versatile tool in studying oxidation of polymers. The success of implementing fibre optics into a perfusion ampoule implies further the possibilities of introducing other probes for the simultaneous detection of oxygen uptake, formation of oxidation products and for studying the effects of UV irradiation among others.     

精密溶解量热装置的建立与标定

本文报道了自行建立的用热敏电阻作为测温元件的精密溶解量热装置,并用量热标准物质光谱纯氯化钾和美国国家标准局提供的三羟甲基氨基甲烷(TRIS)对仪器进行了标定,在25℃所得实验结果:KCI溶解焓为17518±15 J·mol~(-1);TRIS与0.1 mol/L HCI的反应焓为-29729±31J·mol~(-1),与文献值吻合,检验了该装置的可靠性.     

Heat capacity and thermodynamic functions of LuPO4 in the range 0-320 K

The heat capacity of LuPO₄ was measured in the temperature range 6.51-318.03 K. Smoothed experimental values of the heat capacity were used to calculate the entropy, enthalpy and Gibbs free energy from 0 to 320 K. Under standard conditions these thermodynamic values are: (298.15 K) = 100.0 ± 0.1 J K⁻¹ mol⁻¹, S⁰(298.15 K) = 99.74 ± 0.32 J K⁻¹ mol⁻¹, H⁰(298.15 K) − H⁰(0) = 16.43 ± 0.02 kJ mol⁻¹, −[G⁰(298.15 K) − H⁰(0)]/T = 44.62 ± 0.33 J K⁻¹ mol⁻¹. The standard Gibbs free energy of formation of LuPO₄ from elements Δ_fG⁰(298.15 K) = −1835.4 ± 4.2 kJ mol⁻¹ was calculated based on obtained and literature data.     

Isobaric specific heat capacity of typical lithium chloride liquid desiccants using scanning calorimetry

Three kinds of lithium chloride desiccants were selected, which are considered to be potential and interesting working fluids for a desiccant/dehumidification or absorption refrigeration system, and their isobaric specific heat capacities were determined in this context. Experiments were conducted at a high accuracy twin-cell scanning calorimeter. The temperature accuracy and heat flux resolution of the calorimeter are ±0.05 K and 0.1 μW respectively. The data of lithium chloride + water and lithium chloride + triethylene glycol (TEG)/propylene glycol (PG) + water systems were achieved at temperatures from 308.15 K to 343.15 K and atmospheric pressure. The mass fraction of LiCl ranged from 15% to 45% in the LiCl + H₂O system, and the mass fraction of LiCl and glycol ranged from 10% to 23.3% and 20% to 46.7% in the ternary systems respectively. Based on the experimental heat capacity data, a universal empirical formula was correlated as a function of temperature and solute mass fraction. In the experimental mass fractions and temperatures range, the average absolute deviation (AAD) between experiment results and calculated values is no more than 0.15%, and maximum absolute deviation (MAD) is within 0.38%. These thermodynamic data of lithium chloride solutions can be effectively used for analysis and design of desiccant/dehumidification systems and absorption refrigeration systems in both refrigeration and chemical industry.