Search Results

You are looking at 11 - 20 of 2,452 items for :

  • "calorimetry" x
  • All content x
Clear All

Abstract  

Materials with high surface areas and small particle size (nanophases), metastable polymorphs, and hydrated oxides are increasingly important in both materials and environmental science. Using modifications of oxide melt solution calorimetry, we have developed techniques to study the energetics of such oxides and oxyhydroxides, and to separate the effects of polymorphism, chemical variation, high surface area, and hydration. Several generalizations begin to emerge from these studies. The energy differences among different polymorphs (e.g., various zeolite frameworks, the - and -alumina polymorphs, manganese and iron oxides and oxyhydroxides) tend to be small, often barely more than thermal energy under conditions of synthesis. Much larger contributions to the energetics come from oxidation-reduction reactions and charge-coupled substitutions involving the ions of basic oxides (e.g., K and Ba). The thermodynamics of hydration involve closely balanced negative enthalpies and negative entropies and are very dependent on the particular framework and cage or tunnel geometry.

Restricted access
Journal of Thermal Analysis and Calorimetry
Authors: M. Angiuli, C. Ferrari, L. Lepori, E. Matteoli, G. Salvetti, E. Tombari, A. Banti, and N. Minnaja

Abstract  

Extra Virgin olive oils (7 samples) originating from different areas of Tuscany, defective olive oils (5 samples), commercial edible seed oils (4 samples) and two commercial samples of olive oil (one declared ‘extra virgin olive oil’ and one ‘olive oil’) were studied by different calorimetric techniques: high sensitivity isothermal, differential scanning, and modulated scanning calorimetry. The temperature interval (–60) – (+30)C was explored for monitoring: i) the main features of the liquid↔solid phase transitions, ii) the nucleation and growth rate of the polymorphous crystalline phases of the triacylglicerols, and iii) the melting process. This investigation was planned for verifying the utility and effectiveness of calorimetry for screening quality and origin of olive oil. To this end, the main calorimetric operation modes have been applied, the experimental results reported and their utility for developing an effective and reliable screening protocol discussed.

Restricted access

Abstract  

This paper shows an application of bomb calorimetry used in the procedure of regeneration of waste industrial mineral oils. Using the treatment here reported a recovery of nearly 50% of the used oils was achieved. Furthermore, the oils so recovered contain concentrations of potentially contaminant elements far below the requirements of the European Union (EU). Generally speaking, it can be said that the used oil treatment is based on the proper combination of two main procedures, namely the addition and mixture of certain chemicals-precipitant, flocculant and demulsifying agents- in a permanently stirred reactor, at high temperature, and the centrifugation of the mixture. This oil, recovered through the technique of oil regenerating, cleaning, and fitness, can be used either as a raw material for the elaboration of new oils or as a fuel to be used for cogeneration of thermal or electric energy. The treatment described is highly remunerative, both as regards to cost -used oil is subject to a low-cost process, especially if compared to its elaboration from raw materials- and as regards to ecology, since it is recycled, thus saving a great amount of raw materials.

Restricted access

Abstract  

A procedure is described for dealing with the error sources inherently present in any real calorimeter: work of powerP s input from stirrer and possibly temperature sensor, and heat exchange at a rate −G(T−T e) whereT andT c are the temperatures of calorimeter and surroundings respectively. The constantsP s andG are calculated from a period of thermal decay, and afterwards are used to correct the entire run. A calorimeter was designed with high thermal homogeneity and used in a test. The curve of calculated temperature exactly traces the heater energy, even after 5 h, with a standard deviation of about 1 mK. The relative error inC p is less than 1/1000.

Restricted access

Abstract  

Classical adiabatic methods for measuring specific heat in a wide temperature range are very suitable for homogeneous, well defined materials. However, measurements on inhomogeneous materials require large samples, which makes using of adiabatic treatments extremely expensive. In this paper, a nonadiabatic method for determining the specific heat of inhomogeneous building materials within the wide temperature range of −30 to 1200°C is presented. The method is relatively simple, very cheap, and sufficiently accurate for use with building materials. Tests of the new developed method on two typical building materials, concrete and basalt fibreboards, demonstrate the method's applicability to practical measurements.

Restricted access

Modulated differential scanning calorimetry in the glass transition region

II. The mathematical treatment of the kinetics of the glass transition

Journal of Thermal Analysis and Calorimetry
Authors: B. Wunderlich, A. Boller, I. Okazaki, and S. Kreitmeier

Temperature-modulated differential scanning calorimetry (TMDSC) is based on heat flow and represents a linear system for the measurement of heat capacity. As long as the measurements are carried out close to steady state and only a negligible temperature gradient exists within the sample, quantitative data can be gathered as a function of modulation frequency. Applied to the glass transition, such measurements permit the determination the kinetic parameters of the material. Based on either the hole theory of liquids or irreversible thermodynamics, the necessary equations are derived to describe the apparent heat capacity as a function of frequency.

Restricted access

Abstract  

In this work two aluminic pozzolans (metakaolins) and a non-pozzolan were added to two Portland cements with very different mineral composition, to determine the effect on the rate of heat release and the mechanisms involved. The main analytical techniques deployed were: conduction calorimetry, pozzolanicity and XRD. The results showed that the two metakaolins induced stimulation of the hydration reactions due to the generation of pozzolanic activity at very early stage, because of their reactive alumina, Al2O3 r− contents, mainly. Such stimulation was found to be more specific than generic for more intense C3A hydration than C3S, at least at very early on into the reaction, and more so when 7.0% SO3 was added, and for this reason, such stimulation is described as ‘indirect’ to differentiate it from the ‘direct’ variety. As a result of both stimulations, the heat of hydration released is easy to assimilate to a Synergistic Calorific Effect.

Restricted access

Modulated differential scanning calorimetry (MDSC) uses an abbreviated Fourier transformation ≼r the data analysis and separation of the reversing component of the heat flow and temperature signals. In this paper a simple spread-sheet analysis will be presented that can be used to better understand and explore the effects observed in MDSC and their link to actual changes in the instrument and sample. The analysis assumes that instrument lags and other kinetic effects are either avoided or corrected for.

Restricted access
Journal of Thermal Analysis and Calorimetry
Authors: L. Núñez-Regueira, J. A. Rodríguez-Añón, J. Proupín, B. Mouriño, and R. Artiaga-Diaz

Summary The European policy on energy focus on the search for alternative and renewable sources of energy where forest biomass plays a significant role. In this article, calorific values of different kinds of forest residues (leaves, thin branches, barks, etc.) are reported. These values were measured by combustion bomb calorimetry with the objective of understanding, through different risk indices, the behaviour of forest waste in the case of wildfires, and also to study the use of forest residues as raw materials to be used as energy sources. The study was complemented with determination of elemental analysis, flammability using a standard epiradiator, thermodegradation analysis, and different mechanical tests trying to get relationships between thermal behaviour and some physical properties. The study was carried out on Eucalyptus globulus Labill and Pinus pinaster Aiton, because these forest formations have both high economical and ecological interest in Galicia (NW Spain).

Restricted access