Thermal analysis techniques, common

To obtain the cure kinetic parameters K, m, and n, cure rate and cure state must be measured simultaneously. This is most commonly accomplished by thermal analysis techniques such as DSC. In isothermal DSC testing several different isothermal cures are analyzed to develop the temperature dependence of the kinetic parameters. With the temperature dependence of the kinetic parameters known, the degree of cure can be predicted for any temperature history by integration of Equation 8.5. 

Thermal analysis is an important technique for determining the physical and chemical properties of polymeric materials. It may be defined as a set of methods used to measure the physical or chemical changes of substances as a function of temperature. Some common thermal analysis techniques are given in Table 4.8.1. 

Thermal analysis. Thermal analysis of fibers is very important. The term thermal analysis represents a group of techniques in which the property of a sample is measured while the sample is subjected to a controlled temperature program. The most common thermal analysis techniques are ... 

Although a large number of thermal analysis techniques have been developed, the most commonly applied are those of thermogravimetry (TG, the measure of thermally induced weight loss of a material as a function of applied temperature), differential thermal analysis (DTA, the difference in temperature existing between a sample and a reference as a function of temperature), and differential scanning calorimetry (DSC, the difference in heat capacity between the sample and... 

Table 10.1 Commonly Used Thermal Analysis Techniques ...

Less common thermal analysis techniques encompass those that monitor changes in the less obvious properties of a material as a function of temperature and hence these are specialized techniques, which require specialized and sophisticated equipment. Less common techniques are not synonymous with less used techniques, but relate to a field of thermal analysis that is less well developed as a result of being highly specialized. 

Evolved gas analysis is a coupled thermal analysis technique and essentially characterizes the gases evolved during a thermal analysis investigation and hence augments the information obtained. The most common EGA techniques emerge from the coupling... 

According to the International Confederation of Thermal Analysis (ICTA), the thermal analysis technique of thermoelectromerrv is denned as a technique in which the electrical characteristics of a substance is measured as a function of temperature whilst the substance is subjected to a controlled temperature programme. (49) The most common measurements, according to ICTA. are of resistance, R, conductance. A, and capacitance. C. However, since A = liR I — E/R, and E is usually constant. A = / = k,R thus, many investigations report the use of current. /. plotted as a function of temperature. Indeed. David (97) used the term amperomecric thermal analysis (ATA) to describe the technique that he developed. 

It should be noted that, in many cases, the use of only a single thermal analysis technique may not provide sufficient information about a given system. As with many other analytical methods, complementary or supplementary information, as can be furnished by other thermal analysis techniques, may be required. For example, it is fairly common to complement all DTA or DSC data with thermogravimetry. If one or more gaseous products result, evolved gas analysis may prove useful in solving the problem at hand. Simultaneous thermal techniques are helpful in this respect in that several types of data are obtained from the same sample under identical pyrolysis conditions. 

A detailed account of polymorphism and its relevance in the pharmaceutical industry is given elsewhere in this volume and in the literature [42,46,47]. This section will focus on the use of vibrational spectroscopy as a technique for solid-state analysis. However, it should be noted that these techniques must be used as an integral part of a multidisciplinary approach to solid-state characterisation since various physical analytical techniques offer complimentary information when compared to each other. The most suitable technique will depend on the compound, and the objectives and requirements of the analysis. Techniques commonly used in solid-state analysis include crystallographic methods (single crystal and powder diffraction), thermal methods (e.g. differential scanning calorimetry, thermogravimetry, solution calorimetry) and stmctural methods (IR, Raman and solid-state NMR spectroscopies). Comprehensive reviews on solid-state analysis using a wide variety of techniques are available in the literature [39,42,47-49]. 

The anthracite coal with low ash and sulfur is superior coal resources, although it is a kind of high rank coal, it also occurs spontaneous combustioni 1 Spontaneous combustion of coal is a complicated process of the reaction between coal and oxygen, which includes the oxidation process at low temperature (T < 70°C) and accelerated reaction process (T > 70°C), and the oxidation process at low temperature is the key process of the coal spontaneous combustion prevention and the mechanism researchPi. Because of the weaker oxdability of the anthracite coal at the low-temperature oxidation process than other types of coal, most researches about the character of anthracite coal spontaneous combustion is still on accelerated reaction process, but few in low-temperature oxidation processP i. For the research of reaction mechanism function, thermal analysis technique is widely used because of the advantage on test speed and repeatability. However, the common thermal analysis apparatuses such as DSC and DTA are hard to get accurate changes of heat and mass with the... 

The development of various thermal analysis techniques over the past several decades has had a profound effect in accelerating the use of thermodynamic, kinetic and pseudo thermodynamic measurements in the analysis and characterization of materials. All of these methods have in common the use of very small samples and a means of causing the temperature to change linearly with time. 

The term thermal analysis can be applied to any technique which involves the measurement of a physical quantity while the temperature is changed or maintained in a controlled and measured fashion as expressed in Fig. 2.4. Usually the temperature is, for simplicity, kept constant or increased linearly with time. Recently, it was found advantageous to superimpose a small modulation of the temperature to check for the reversibility of the measurement and to separate the calorimeter response from inadvertent gains or losses that do not occur with this modulation frequency (see Sect. 4.4). The professional organizations of thermal analysis are the International Confederation for Thermal Analysis and Calorimetry, ICTAC, and the North American Thermal Analysis Society, NAT AS, described in some detail in Figs. 2.5 and 2.6, respectively. The most common journals dealing with thermal analysis techniques and results are ThermochimicaActa and the Journal of Thermal Analysis and Calorimetry. 

In terms of modulated thermal analysis techniques , TMDSC clearly dominates the group. However, there is limited literature on temperature modulated thermogravimetic analysis (TMTGA) and temperature modulated thermomechanical analysis (TMTMA). Modulation principles have been applied to some less common thermal analysis techniques such as DMA and thermally stimulated current analysis and these developments will be briefly addressed here. It appears that the major development in thermal analysis in the next decade will be in the temperature modulated domain. 

Antioxidants are common additives for polymers. Oven ageing and thermal analysis techniques such as DSC and TGA have been used with varying degrees of success to measure both the concentration and effectiveness of antioxidants. In most cases, the failure of these tests to correlate with actual end-use performance is due to the volatility of the antioxidants and other components at test temperatures. Even at a relatively... 

Thermal analysis techniques are used to study the properties of polymers, blends and composites and to determine the kinetic parameters of their stability and degradation processes.Here the property of a sample is continuously measured as the sample is programmed through a predetermined temperature profile. Among the most common techniques are thermogravimetry (TG) and differential scanning calorimetry (DSC). Dynamic mechanical analysis (DMA) and dielectric spectroscopy are essentially extensions of thermal analysis that can reveal more subtle transitions with temperature as they affect the complex modulus or the dielectric function of the material. 

Besides TMA, two other thermal analysis techniques are also commonly used for measuring Tg and degree of cure differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). 

There are a number of different measurement techniques to determine the Tg. The most commonly used methodologies are thermal analysis techniques. Other techniques are available (such as spectral analysis and electrical characterization), but their use is limited and therefore they will not be discussed here. The three thermal analysis methods that will be discussed in this section are as follows ... 

Sircar and co-workers [8] compared experimental and data from the literature for the Tg of some common elastomers determined by different thermal analysis techniques, including DSC, TMTA, DMTA, dielectric analysis and thermally stimulated current methods. Elastomers examined include natural rubber, styrene-butadiene rubber, polyisoprene, polybutadiene, polychloroprene, nitrile rubber, ethylene-propylene diene terpolymer and butyl rubber. Tg values obtained by DSC, TMA and DMTA were compared. Experimental variables and sample details, which should be included along with Tg data were described, and the use of Tg as an indication of low temperature properties was discussed. 

DPC is a thermal analysis technique that measures the cure rate and degree of DSC to measure the heat of reaction of one or two samples as they are exposed to light. The light source can be of several types, the most common being a high-pressure mercury arc lamp with a maximum intensity in the 200-400 nm (ultraviolet (UV)) range. 

Thermal Analysis (TA) Methods A family of an2ilytical techniques in which various properties of a sample are examined as a function of changing temperature at a particular rate of change. For chemical analysis, the most common thermal analysis techniques include differential thermal... 

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