Thermal Physics and Thermal Analysis

Thermal analysis by structural characterization (TASC) is a new thermal technique that is based on image analysis combined with hot-stage microscopy (HSM, also called thermomicroscopy). The image analysis algorithm is sensitive to any change in structure as seen by digital optical microscopy. A key feature of the algorithm is that it accounts for any sample movement. Due to thermal expansion of the sample or the sample chamber, there is, at high magnification, usually some sample displacement and this needs to be removed, so the measurement is purely one of structural change. HSM has a variety of uses but struggles with opaque samples (such as filled samples) and cannot routinely detect glass transitions. TASC, when used with an imposed structure such as an indentation, can routinely measure glass transition temperatures because, when the sample softens, the indentation disappears. This is true even when analyzing opaque samples. TASC can also be used to measure melting temperatures, transitions in small (microgram) samples, dissolution behavior, and heterogeneity.

The historical development of the thermal analysis methods that imply an intelligent control of the reaction temperature by the own sample (SCTA) is outlined. It has been shown that the precise control of the reaction rate involved in SCTA enables a control, either direct or indirect, of both the partial pressure of the gases generated/consumed by the reaction and the heat evolution/adsorption rate associated to the reaction. This control allows to minimize the influences of heat and mass transfer phenomena and to obtain real kinetic parameters of the forward reaction that occur under the conditions far from the equilibrium. Moreover, it is shown that the shape of α–T plots obtained under constant rate of transformation (CRTA) is strongly dependent on the kinetic model, while the α–T plots obtained using the conventional linear nonisothermal method represent a sigmoidal shape irrespective of the kinetic model. Thus, CRTA has a considerably higher resolution power for discriminating the kinetic model obeyed by the reaction. The applications of SCTA methods both for the kinetic analysis of solid-state reactions and for the synthesis of materials with controlled texture and/or structure have been reviewed. The chapter contains 202 references.

Historical maturity of terms temperatura and thermoscope is sketched. Problem of temperature definition and observation (measurement) is studied in detail. Temperature is a typical averaged quantity clear-cut under equilibrium only. A self-measurability condition is implied, and some consequences are outlined. Physical and operational meaning of temperature and its self-measurability during unsteady thermal processes is analysed. Particular case of thermal analysis often idealized under constant temperature changes is thermodynamically examined. For extreme temperature changes as that during quenching, a novel term “tempericity” is proposed. Branched view to the spheres of alternative thermodynamics is shown locating thermal analysis as thermotics and quenching as thermokinetics. Non-equilibrium thermodynamics under a non-constant rate of temperature changes is analysed. Practical aspects of non-equilibrium temperatures due to heat inertia and thermal gradients are specified including cases of modulated experiments. Textbook thermodynamic description under the perceptible impact of second temperature derivatives becomes ambiguous and associated tabular values are unclear. Thermotics, thermokinetics, and the validity of the first and second thermodynamic laws are discussed bringing another dimension of the thermodynamic legacy. The concept of equivalence of work and heat is questioned. The chapter contains 126 references.

Thermodynamics of open systems offers a new concept for description of real material objects including the living systems. The second law of thermodynamics can be interpreted as an evolution law of all material systems, which are in interaction with surroundings. The most important quantity is entropy, which is defined by balance of entropy. The production of entropy gives information about the processes in the systems. The convexity of entropy informs about the stability of the system states. Under the appropriate outer conditions, the fluctuations can force the systems to instability. Consequence is the creation or decay of new dissipative structures. When the new dissipative structure appears, the system is going out of the thermodynamic equilibrium to the new stable state. However, if the dissipative structure disappears, the systems will tend to the thermodynamic equilibrium. From the biological point of view, the thermodynamic equilibrium equals to death.

The innovative sphere of kinetic phase diagrams as a special domain of routine thermodynamic determined diagrams is re-evaluated while accentuating its specificity and practical impact when studying system under rapid changes of temperature (e.g., cooling). Requirement for a certain driving force in order to accomplish transformations is explored. It involves merger of heating–cooling as a nonequilibrium thermodynamic state of a certain sample ‘autonomy.’ The meaning of temperature is discussed when measured during inconstant thermal experiments. Thermodynamic legitimacy when assuming the effect of programmed temperature changes at the constant heating rate is examined and approved. Query about the implication of the term ‘temperature’ under rapid quenching results in a proposal of new tem ‘tempericity.’ Size as another degree of thermodynamic freedom is observed and investigated for the issue of nanomaterials providing the apparent analogy between the temperature-dependent kinetic phase diagrams and those obtained for diminishing particle size. Specific behavior of nanocomposites is explored regarding the particle curvature, temperatures of transformation, dissolution or phase separation, etc. Extension of kinetic phase diagram to the nanostate determinability, involving thermodynamics expanded by ‘one dimension’ as a result of severely contracted particle surface, is dealt with. The chapter contains 92 references.

Self-similarity and the orderly crystal (often dendritic) growth are an important parts of nature as well as the source of solid-state thermal chemistry under nonequilibrium (undercooling) conditions providing theoretical roots of chemical swinging clock. Such oscillation processes known in chemistry and biology apply for systems far from equilibrium involving special cases of oscillations extending from the self-organized periodic chemical reactions (such as Liesegang’s or Belousov–Zhabotinsky’s reactions) to ordered solid-state processes, from liquids to atmosphere, from macro to micro, indispensable in biology. The chapter deals with a remarkable problem of thermal physics, unresolved for more than 70 years, concerning class of diffusion-controlled periodic chemical reactions, where macroscopically observed diffusion action attains, with appreciable accuracy, the value of Planck’s quantum. Because the classical and quantum diffusions are processes, which are indistinguishable in the configuration space, a quantum criterion in terms of diffusion constants is valid. This criterion enables one to find out conditions under which the quantum behaviour of self-organized periodic reactions can be observed. Examples are shown for the subcritical and critical oscillatory regimes; a special kind of self-organized Liesegang’s rings—annual growth rings of a trunk of larch tree is discussed. The text even involves a thinkable hypothesis of the light self-organization based on the previously analysed principle on least time (Fermat) and of the least action (Maupertuis). It was already noticed by Galileo who opened this problem aware that the cycloid curve yields the quickest descent leading to the so-called brachistochrone. The chapter contains 130 references.

Following the approach applied by Clapeyron to describe sharp phase transitions in P-T diagrams of unary systems as well as that used by Ehrenfest for so-called second-order phase transitions, we derived a set of analogous equations for partly open binary and higher-order systems. These systems share one or more components with the surroundings (reservoir), and thus, their content in the system is given by their chemical potentials (activities, a _f) in the reservoir. Hence, in addition to P-T diagrams, the phase relations can be represented in T–a _f, P–a _f, and a _f–a _g phase diagrams and three additional Clapeyronian equations describe the corresponding borderlines delimiting the different phase fields. Moreover, it is shown that Ehrenfest equations cannot be applied for λ-transitions; however, their applicability is demonstrated for so-called partial phase transitions such as liquidus curves in closed binary systems. For partly open systems, 28 new Ehrenfestian equations are derived for partial phase transitions which involve, apart from the changes of heat capacity, thermal expansion and compressibility appearing in the original three Ehrenfest equations, the changes of newly defined quantities such as thermal, pressure, proper, and mutual plutabilities. The Clapeyronian and Ehrenfestian equations derived in this chapter can be useful for equilibrium studies and construction of thermodynamic models of nonstoichiometric phases as well as for the construction of simple phase diagrams reflecting the equilibrium phase relations under a given controlled atmosphere.

Nonstoichiometric phases constitute a large family of technologically important materials. Among them, the inorganic materials whose variable stoichiometry of some components originates from their exchange with surrounding atmosphere represent particular thermodynamic systems referred to a partly open system. The phase equilibria in these systems including the homogeneous crystallochemical reactions of the involved crystal defects can be effectively treated using the thermodynamic potential called hyper-free energy derived from the Gibbs free energy by Legendre transformation with respect to the amounts of free components. In this chapter, we focus on general thermodynamic description of systems with variable content of components shared with a dynamical atmosphere, their essential material quantities being influenced by variable stoichiometry, conditions for homogeneous crystallochemical equilibria as well as for phase transitions. The influence of variable stoichiometry on material properties such as isobaric thermal expansion, isothermal compressibility and in particular heat capacity is analyzed and divided into two parts: the direct effect on conventional isoplethal quantities due to deviation from stoichiometry, and so-called saturation contributions determining the difference in material properties measured under isoplethal and isodynamical conditions (constant activities of free components). In the last part, the construction of phase diagrams of partly open systems is demonstrated on several examples of oxide systems, and the relevant phase transitions are classified and discussed.

W. Ostwald predicted with the “rule of stages” formulated by him that phase formation processes in complex condensed matter systems may proceed step by step via different evolution paths involving a discrete series of metastable states, which can be formed in a macroscopic form at the given thermodynamic conditions, until finally, the most stable phase will be reached. Advancing this idea, it was shown in recent years by us that in condensation and boiling, as well as in segregation and crystallization processes in multi-component liquid and solid solutions, critical clusters may be formed and evolve via a continuous sequence of states with properties which may differ from the properties of any of the macroscopic phases present in the respective phase diagram. The kinetics of nucleation proceeds hereby via a scenario similar to spinodal decomposition, i.e., via a continuous amplification of density and/or composition differences accompanied eventually by sequential discrete changes of the structure of the system. The basic ideas and results of this theoretical approach developed by us are described in the present chapter. Recently published experimental results on crystal nucleation are discussed in detail giving additional confirmation of these conclusions. As a second man topic devoted also to the theoretical description of crystal nucleation, the relevance of the concepts of fragility of the liquid for the understanding of crystal nucleation and growth in glass-forming liquids is explored. Finally, a number of directions of research are discussed which may lead to new insights into the complex phenomena of crystal formation and growth processes.

The famous Kissinger’s kinetic evaluation method (see Anal. Chem. 1957) is examined with respect to both the relation between the DTA signal θ(t) and the reaction rate r(t) ≡ dα/dt, the requirements on reaction mechanism model f(α), and the relation of starting kinetic equation to the equilibrium behavior of sample under study. Distorting effect of heat inertia and difference between the temperature T _p of extreme DTA deviation and the temperature T _m at which the reaction rate is maximal are revealed. DTA equation of Borchard and Daniels is criticized regarding the neglection of heat inertia correction. The kinetic equations respecting the influence of equilibrium temperature T _eq , especially fusion/melting temperature T _f , are tested as bases for a modified Kissinger-like evaluation of kinetics. Crystallization kinetics on melt solidification is examined under integration of undercooling and needed Gibbs approximations are explored. This chapter provides a new insight into the routine practice of nonisothermal kinetics showing forward-looking outlook and encompasses hundreds of references.

In the present chapter, the macroscopic (recorded by methods of thermal analysis) manifestation of the structural relaxation and cold crystallization phenomena occurring in the glassy matrices will be discussed. Present formalism and methodological background are reviewed. Equilibrium viscous flow is introduced as an interconnecting element between the two phenomena. The consequent part then deals with the rheological and viscosity-related aspects of the glassy state itself. Viscosity behavior in view of so-called fragility is renovated in terms of thermal sensitivity. The chapter contains 98 references.

Shakhmatkin and Vedishcheva proposed the associated solutions’ thermodynamic model (SVTDM) of glasses and glass-forming melts. This model considers glasses and melts as an ideal solution formed from saltlike products of chemical reactions between the oxide components and the original (unreacted) oxides. The model does not use adjustable parameters; only the standard Gibbs energies of the formation of crystalline compounds and the analytical composition of the system considered are used as input parameters. A nonlinear regression treatment with the help of a genetic algorithm is used for the optimization of molar Gibbs energies by minimizing the sum of squares of deviations between experimental and calculated structure units’ distributions. In such a manner, the non-ideality of glass systems is reflected. The proposed method of using the optimized effective parameters (i.e., reaction Gibbs energies) within the SVTDM copes with most frequently met weak points of this method, i.e., missing of thermodynamic data for some components of SVTDM; missing of some components in the SVTDM because of insufficient knowledge of particular phase diagram or because of taking into account only the stable crystalline phases (and ignoring, e.g., the metastable ones); the assumption of zero mixing enthalpy connected with the supposed ideality of the studied glass system; the assumption of regular mixing entropy connected with the supposed ideality of the studied glass system; and the uncertainty in the mixing entropy originating in the uncertainty of molecular weight of individual components.

It is shown that the kinetic data can be equivalently described in the temperature range of measurement by the Arrhenius, Harcourt–Esson and Berthelot–Hood temperature functions. The reason is that, in a narrow temperature range, 1/T, ln T and T are linearly related to each other. Therefore, the kinetic parameters obtained from one function can be recalculated to the parameters from another one. This equivalence holds for the incremental and differential isoconversional methods only; due to their mathematical incorrectness, the equivalence does not take place for the integral isoconversional methods. It is reasoned that the temperature functions are equivalent not only in the case of the isoconversional methods, but also for the model-fitting methods. An incremental isoconversional method without any approximations or transformations of the experimental data and with a statistically well-grounded and physically justified objective function based on the maximum likelihood approach is mentioned.

Modeling tradition is reviewed within its historical maturity from Greek Plato to modern Penrose. Metaphors in non-isothermal kinetics achieved a wide application mostly employing models derived by means of undemanding isothermal descriptions. Geometrical basis of such modeling is revised and discussed in terms of symmetrical and asymmetrical (pentagonal) schemes. The properties of interface (reaction separating line) are found decisive in all cases of heterogeneous kinetics and can be acquainted with defects. The use of yet atypical fractal geometry is accredited, and associated formal kinetic models based on non-integral power exponents are acknowledged. Mathematical commencement and impact of logistic models are used highlighting the Sesták–Berggren (SB) equation and the impact of logistic approach as a generalized exploit. Typical erroneous beliefs are dealt with showing common kinetic misinterpretation of measured data and associated mathematical manipulability of kinetic equations. The correction of a measured DTA peak is mentioned assuming the effects of heat inertia and temperature gradients. The chapter contains 117 references.

The basic interrelations and consequences of heat transfer (1701 Newton cooling law) are analyzed showing its unambiguous importance and historical origin already known since 1933 in the form of basic caloric equation by Tian. It results in the heat inertia due to the sample heat capacity changes and undertakes two forms, integral and differential, the latter specific in providing s-shape background of DTA peaks. Its impact in the DTA measurements is examined showing misinterpretation by the origin work of Borchard and Daniels leading to further abandonment. The heat inertia correction was already suggested by authors in 1978 and verified on the basis of externally inserted rectangular heat pulses. Further corrections to heat inertia waited until 2009 (Netzsch commercial software). Relations following from general kinetic equation for the first-order reactions are substantiated, and the kinetic compensation effect explained as a correlation of pair activation energy pre-exponential factor and maximum rate temperature-heating rate. Kissinger erroneous assumption on temperature of maximum reaction rate is examined, and a correct solution is then suggested while determining the correct temperature of maximum reaction/transition rate and its correlation to the apex of a DTA peak. Both the kinetic equation and Kissinger equation are shown crucial when including the heat inertia term. Often forgotten influence of thermodynamic equilibrium as to kinetic equation is analyzed giving away its significance. New concept of a more sophisticated nonisothermal kinetics is suggested happy to be first when introducing the concept of equilibrium background which stays an important part of advanced kinetics anticipating that our innovative notions of temperature inertia, gradients, and even the operational meaning of temperature itself may facilitate modern kinetic understanding. We believe that kinetic progress means practice-verified improvements while including detailed thermal phenomena of real thermoanalytical measurements, nor just making changes at any case. We neither should be afraid of changes while complicating our pervious practice nor should we feel troubled examining examples presented in this chapter. The chapter contains 72 references.

The concept of “sample temperature” in non-isothermal thermal analysis experiments is analyzed. From the analysis of the heat balance inside the sample, it is shown that the existence of such sample temperature is restricted to experimental conditions, where the thermal gradients are negligible. Two different sources of thermal gradients are studied: the sample thermal inertia and the heat of reaction that is not quickly removed. The conditions to prevent the formation of thermal gradients as well as the condition for a thermal runaway to occur are deduced. Finally, it is shown that the aspect ratio is a crucial parameter for the formation of thermal gradients within the sample.

A new theoretical basis, fitting thermal analysis of solids more adequately than the Arrhenius equation developed for reacting gas molecules, is proposed for gas-evolving reversible decompositions. Such complex processes are theoretically dissected into elementary steps, showing distinctions between micro-kinetics and macro-kinetics; only the slowest step being recordable thermoanalytically. Practical procedures of determination whether a thermoanalytical process is controlled by chemical kinetics on micro-level, or by physical macro-processes of heat- and gas-transport in the bulk, based on exposing the samples to changing degrees of heat transfer, and (separately) to the changing degree of exposure to the gaseous decomposition product, are postulated as a prerequisite before choosing the calculation model. It is shown that many typical processes of gas-evolving reversible decomposition are controlled not by chemical micro-kinetics, but by the physical processes of escaping of the gases and of the heat transfer. Even in smallest samples, the overlapping gradients of the temperature and of the gas concentration, plus two or three interwoven reaction fronts, invalidate micro-kinetic calculations and indicate that thermoanalytical data reflect globally the behavior of the sample as a whole, not of its individual grains or molecules—those two classes being completely different. The meaning of decomposition temperature is revisited. A family of TG curves obtained at the specified conditions enables distinguishing between the true decomposition temperature and the procedural one; only the latter being normally recorded. A pitfall of determination of decomposition temperature by CRTA is discussed. Implication for industrial processes are suggested.

Thermodynamic description of systems with nanoparticles in the frame of the Gibbs theory of interfaces is presented. Although much attention has been paid to thermodynamic modelling of nanosystems, the calculation of phase diagrams of nanoalloys as well as the assessment of effects of surface-related phenomena on the solubility of nanoparticles and gas–solid reactions, some discrepancy still remains dealing with the expression of the surface contribution to molar Gibbs energy and chemical potential of components. It is shown that due to the non-extensive nature of the surface area, these contributions are different for molar and partial molar quantities. The consistent expressions for molar Gibbs energy and chemical potentials of components of spherical nanoparticles are put forward along with the correct forms of equilibrium conditions. Moreover, the applicability of the shape factor α = A _{non-spherical}/A _spherical (V _{non-spherical} = V _spherical) which is used in the expressions involving surface-to-volume ratio of non-spherical particles is addressed. A new parameter, the differential shape factor α′ = dA _{non-spherical}/dA _spherical (V _{non-spherical} = V _spherical, dV _{non-spherical} = dV _spherical), is proposed which should be used in equilibrium conditions based on the equality of chemical potentials. The enhanced solubility of paracetamol nanoparticles in water and thermal decomposition of GaN nanowires are demonstrated as examples of size effect in nanosystems.

The historical aspects of ceramic production, as well as the modern approaches to the technical side of ceramic production, especially solgel technology as the path to modern nanotechnologies, are discussed. It is pointed out that the most essential significance of the nanostate for the applied sciences lies in the possibility of merging the inorganic, organic, and biological worlds, thus creating a prodigious number of new materials.

Porosity of textiles is one of the main factors influencing their thermal conductivity and insulation. Porosity in textile fabrics is the combination of fiber porosity, yarn packing density, and voids due to fabric construction. It is shown that assemblies from very fine fibers tend to suppress radiation and convection heat transfers because of huge total surface area, which restricts the free flow of air passing through them. For effective thermal insulation especially at low temperatures, it should be selected sufficiently high thickness of textile layer as well. Porosity is therefore decisive parameter for the evaluation of thermal comfort expressed in special units “clo.” The main aim of this chapter is the prediction of the effect of porosity of fabrics and fibers on the thermal conductivity and insulation. The changes of thermal comfort due to the use of hollow fibers and multilayer corrugated nonwovens are described. The thermal properties of highly porous aerogel structures are discussed. Enhancement of insulation by their inclusion into textiles is investigated as well.

Over the past few decades, biomaterial science has emerged as a new field in which a regeneration or replacement of damaged tissue has become one of the main focuses. Also, great advances in the application of multifunctional nanoparticles for biomedical applications have been made. Implementation of nanomedicine in cellular, preclinical, and clinical studies has led to exciting advances ranging from fundamental to applied research. This chapter will examine the key aspects of application of traditional biomaterials, their physicochemical properties, and behavior in biological system. Moreover, the unique properties of nanomaterials are highlighted in relation to their vast nanostructural characteristics and the field of application. With 164 references.

Methodological scheme of thermal analysis is used for portraying the Earth environmental research and climate changes, showing particularly the history, effect of atmosphere reflection (albedo), and absorption (so-called greenhouse effect included). The net behavior of the Earth as a black body is reviewed. The most influential on climate changes is the alteration of the geometry of the Earth trajectory and the irradiative power of the Sun (as a standard thermoanalytical pair of the sample and radiator). Thermodynamic basis of water vapor impacts is pointed out, the absorption spectra of atmosphere are emphasized, and temperature gradients are indicated. The historical course of the Earth temperature and CO₂ concentration is put in analogy with the method of gas desorption analysis, which supports the view that the variation of CO₂ concentration recorded in the past may not be alone blamed for temperature changes. The influences of atmosphere nanoparticles on weather, climate, and human health are discussed, as well. With 91 references.

Thermodynamics and economics have developed independently through the last centuries. Only in the last three decades, scientists have realized the close relationship between economics and physics. The name of the new field is econophysics: In double-entry accounting, the sum of monetary and productive accounts is zero. In calculus, monetary and productive accounts may be represented by Stokes integrals. In engineering, Stokes integrals lead to the two levels hot and cold of Carnot motors. In production, Stokes integrals lead to the two-level process: buy cheap and sell expensive. In economics, the two-level mechanism of capital and labor is called capitalism. A heat pump can extract heat from a cold river and heat up a warm house. A monetary circuit extracts capital from a poor population and makes a rich population richer! A running motor gets hotter, the efficiency, the difference in temperatures, grows with time. A running economy gets richer, the efficiency, the difference between rich and poor, grows.

The choice of the mathematical structure of physical quantities, which is natural for the description of finite physical reality and related problems, is discussed from the historical and the epistemological points of view. We show that for the establishment of physical quantities is fully sufficient the system of rational numbers which are equivalent to the finite ordered sets of integers, while the currently used system of real numbers is quite redundant for such a purpose. These facts may have far reaching consequences not only for pure epistemology but for the interpretation of many fundamental physical phenomena as well. Finally, the relation between the chosen structure of physical quantities and the so-called Principle of conformity of physics and mathematics is shortly discussed.

In the course of the last thirty years, science enjoys a remarkable quantitative boom. For example, the total number of substances, registered in the Chemical Abstracts Service Registry File (CAS RF) at the end of the year 1985, was about 8 millions while at the end of the year 2015 it reached up to 104 millions. But, still more and more behind this quantitative boom of science are some of its qualitative aspects. So, e.g., the x–y–z coordinates of atoms in molecules are presently known for no more than 1 million of substances. For the majority of substances registered in CAS RF, we do not know much on their properties, how they react with other substances and to what purpose they could serve. Gmelin Institute for Inorganic Chemistry and Beilstein Institute for Organic Chemistry, which systematically gathered and extensively published such information since the nineteenth century, were canceled in 1997 (Gmelin) and 1998 (Beilstein). The number of scientific papers annually published increases, but the value of information they bring falls. The growth of sophisticated ‘push-and-button’ apparatuses allows easier preparation of publications while facilitating ready-to-publish data. Articles can thus be compiled by mere combination of different measurements usually without idea what it all is about and to what end this may serve. Driving force for the production of ever growing number of scientific papers is the need of authors to be distinguished in order to be well considered in seeing financial support. The money and fame are distributed to scientists according to their publication and citation scores. While the number of publications is clearly a quantitative criterion, much hopes have been placed on the citation, which promised to serve well as an adequate measure of the genuine scientific value, i.e., of quality of the scientific work. That, and why these hopes were not accomplished, is discussed in detail in our contribution. Special case of Journal of Thermal Analysis and Calorimetry is discussed in more particulars.