Article No : b06_001 Thermal Analysis and Calorimetry STEPHEN B. WARRINGTON, Formerly Anasys, IPTME, Loughborough University, Loughborough, United Kingdom Gu€NTHER W. H. Ho€HNE, Formerly Polymer Technology (SKT), Eindhoven University of Technology, Eindhoven, The Netherlands 1. Thermal Analysis.................. 415 2.2. Methods of Calorimetry............. 424 1.1. General Introduction ............... 415 2.2.1. Compensation of the Thermal Effects.... 425 1.1.1. Definitions . ...................... 415 2.2.2. Measurement of a Temperature Difference 425 1.1.2. Sources of Information . ............. 416 2.2.3. Temperature Modulation ............. 426 1.2. Thermogravimetry................. 416 2.3. Calorimeters ..................... 427 1.2.1. Introduction ...................... 416 2.3.1. Static Calorimeters ................. 427 1.2.2. Instrumentation . .................. 416 2.3.1.1. Isothermal Calorimeters . ............. 427 1.2.3. Factors Affecting a TG Curve ......... 417 2.3.1.2. Isoperibolic Calorimeters ............. 428 1.2.4. Applications ...................... 417 2.3.1.3. Adiabatic Calorimeters . ............. 430 1.3. Differential Thermal Analysis and 2.3.2. Scanning Calorimeters . ............. 430 Differential Scanning Calorimetry..... 418 2.3.2.1. Differential-Temperature Scanning 1.3.1. Introduction ...................... 418 Calorimeters ...................... 431 2.3.2.2. Power-Compensated Scanning Calorimeters 432 1.3.2. Instrumentation . .................. 419 2.3.2.3. Temperature-Modulated 1.3.3. Applications ...................... 419 Scanning Calorimeters . ............. 432 1.3.4. Modulated-Temperature DSC (MT-DSC) . 421 2.3.3. Chip-Calorimeters .................. 433 1.4. Simultaneous Techniques............ 421 2.4. Applications of Calorimetry.......... 433 1.4.1. Introduction ...................... 421 2.4.1. Determination of Thermodynamic Functions 433 1.4.2. Applications ...................... 421 2.4.2. Determination of Heats of Mixing . .... 434 1.5. Evolved Gas Analysis............... 422 2.4.3. Combustion Calorimetry ............. 435 1.6. Mechanical Methods ............... 422 2.4.4. Reaction Calorimetry. ............. 436 1.7. Less Common Techniques ........... 423 2.4.5. Safety Studies . .................. 437 2. Calorimetry ...................... 424 References ....................... 438 2.1. Introduction ..................... 424 1. Thermal Analysis within the field of thermal analysis as it is usually understood. The present chapter will 1.1. General Introduction be restricted to major techniques. Since all materials respond to heat in some way, TA 1.1.1. Definitions has been applied to almost every field of science, with a strong emphasis on solving Thermal analysis (TA) has been defined as ‘‘a group problems in materials science and engineering, of techniques in which a physical property of a as well as fundamental chemical investiga- substance and/or its reaction products is measured tions. TA is applicable whenever the primary as a function of temperature while the substance is interest is in determining the effect of heat subjected to a controlled temperature programme’’ upon a material, but the techniques can also be [1]. The formal definition is usually extended to used as a means of probing a system to obtain include isothermal studies, in which the property of other types of information, such as composition. interest is measured as a function of time. The following list summarizes quantities sub- The definition is a broad one, and covers ject to investigation and the corresponding ther- many methods that are not considered to fall mal analysis techniques: Ó 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim DOI: 10.1002/14356007.b06_001.pub3 416 Thermal Analysis and Calorimetry Vol. 36 Mass Thermogravimetry (TG) Temperature difference Differential thermal analysis (DTA) Heat flow rate Differential scanning calorimetry (DSC) Evolved gas Evolved gas analysis (EGA) Dimensions (length, Thermodilatometry (TD) volume) Mechanical deformation Thermomechanical analysis (TMA) Complex modulus Dynamic mechanical analysis (DMA) Optical properties Thermoptometry Electrical properties Thermoelectrometry Magnetic properties Thermomagnetometry Figure 1. Schematic diagram of a thermobalance a) Sam- 1.1.2. Sources of Information ple; b) Sample temperature sensor; c) Furnace temperature sensor; d) Furnace; e) Recorder or computer, logging sample Two journals (the mass, temperature, and time; f) Balance controller; g) Re- Journal of Thermal Analysis cording microbalance; h) Gas; i) Furnace temperature and Calorimetry and Thermochimica Acta) de- programmer vote their contents entirely to TA; the Proceed- The computer may also control the furnace programmer ings of the (now) four-yearly Conferences of the International Confederation for Thermal Analy- techniques from the standpoint of quantitative sis and Calorimetry (ICTAC) constitute an data, and for this reason it is often employed in excellent additional source of research papers. combination with other measurements. Specific information regarding Proceedings vo- lumes for the nine ICTAC Conferences between 1965 and 1991 is available in [1]. The most 1.2.2. Instrumentation complete listing of worldwide TA literature is also found in the ICTAC handbook [1], which in The instrument used is a thermobalance. The addition gives addresses for national TA socie- schematic diagram in Figure 1 presents the main ties and important equipment suppliers. The most components of a typical modern unit. Compo- useful textbooks include [2–5, 40]. nent details vary according to the design, and There is a wealth of information available on choice of a particular instrument is usually dic- the Internet; see, for example, ‘‘Thermal Analy- tated by requirements of the problem under sis’’ in Google or another search engine. [6] investigation (temperature range, sensitivity, etc.). The balance mechanism itself is usually of 1.2. Thermogravimetry the null-deflection type to ensure that the sample’s position in the furnace will not change. 1.2.1. Introduction The balance transmits a continuous measure of the mass of the sample to an appropriate record- Thermogravimetry (TG) is used to measure varia- ing system, which is very often a computer. The tionsinmassasafunctionoftemperature(ortime). resulting plot of mass vs. temperature or time is Processes amenable to study in this way are listed called a TG curve. Balance sensitivity is usually in Table 1. TG is one of the most powerful TA of the order of one microgram, with a total capacity of as much as a few hundred milligrams. Table 1. Processes that can be studied by thermogravimetry Furnaces are available that operate from subam- bient (e.g., À125 C) or room temperature up to Process Weight gain Weight loss as high as 2400 C. A furnace programmer nor- Ad- or absorption * mally supports a wide range of heating and Desorption * cooling rates, often in combination, as well as Dehydration/desolvation * precise isothermal control. The programming Sublimation * Vaporization * functions themselves are increasingly being as- Decomposition * sumed by computers. Most applications involve Solid – solid reactions * heating rates of 5 – 20 K/min, but the ability to Solid – gas reactions * * heat a sample as rapidly as 1000 K/min can be Vol. 36 Thermal Analysis and Calorimetry 417 useful in the simulation of certain industrial cessive mass losses. The particle size of the sam- processes, for example, or in flammability stud- ple, the way in which it is packed, the crucible ies. Special control methods, grouped under the shape, and the gas flow rate also affect the progress term controlled-rate thermal analysis (CRTA), of a thermal reaction. Careful attention to consis- are receiving increasing attention [7], and offer tency in experimental details normally results in advantages in resolving overlapping processes good repeatability. On the other hand, studying the and in kinetic studies. One of these methods is the effect of deliberate alterations in such factors as recently commercially available High-Resolu- heating rate can provide valuable insights into the tion TG, in this case the heating rate is controlled nature of observed reactions. All these considera- by the measured mass change rate. tions are equally applicable to other techniques as The quality of the furnace atmosphere de- well, including DTA (Section 1.3). serves careful attention. Most commercial ther- mobalances operate at atmospheric pressure. Vacuum and high-pressure studies normally re- 1.2.4. Applications quire specialized equipment, either commercial or home-made, as do experiments with corrosive TG has been applied extensively to the study of gases [8]. The ability to establish an inert (oxy- analytical precipitates for gravimetric analysis gen-free) atmosphere is useful, as is the potential [10]. One example is calcium oxalate, as illus- for rapidly changing the nature of the atmosphere. trated in Figure 2. Information such as extent of The mode of assembly of the components hydration, appropriate drying conditions, stabil- varies; for example, the furnace might be above, ity ranges for intermediate products, and reaction below, or in line with the balance. Sample con- mechanisms can all be deduced from appropriate tainers also vary widely in design; cylindrical TG curves. Figure 2 also includes the first deriv- pans are common, typically 5 – 8 mm in diame- ative of the TG curve, termed the DTG curve, ter and 2 – 10 mm high, though flat plates and which is capable of revealing