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Conceptual Approach to Thermal Analysis and Its Main Applications

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Prospect. Vol. 15, No. 2, Julio-Diciembre de 2017, 117-125 Conceptual approach to thermal analysis and its main applications Aproximación conceptual al análisis térmico y sus principales aplicaciones Alejandra María Zambrano Arévalo1*, Grey Cecilia Castellar Ortega2, William Andrés Vallejo Lozada3, Ismael Enrique Piñeres Ariza4, María Mercedes Cely Bautista5, Jesús Sigifredo Valencia Ríos6 1*M.Sc. Chemical Sciences, Full Professor, Universidad de la Costa. Barranquilla-Colombia. 2M.Sc. Chemical Sciences, Full Professor, Universidad Autónoma del Caribe. Barranquilla-Colombia. 3Ph.D. Chemical Sciences, Full Professor, Universidad del Atlántico. Barranquilla-Colombia. 4M.Sc. Physical Sciences, Occasional Full Professor, Universidad del Atlántico. Barranquilla-Colombia. 5Ph.D. Engineering, Full Professsor, Universidad Autónoma del Caribe. Barranquilla-Colombia. 6Ph. D. Universidad Nacional de Colombia, Vicerrector Universidad Nacional de Colombia (Sede Palmira). Palmira-Colombia. E-mail: [email protected] Recibido 12/04/2017 Cite this article as: A. Zambrano, G.Castellar, W.Vallejo, I.Piñeres, M.M. Aceptado 28/05/2017 Cely, J.Valencia, Aproximación conceptual al análisis térmico y sus principales aplicaciones, “Conceptual approach to thermal analysis and its main applications”. Prospectiva, Vol 15, N° 2, 117-125, 2017. ABSTRACT This work shows to the reader a general description about the techniques of classic thermal analysis as known as Differential Scanning Calorimetry (DSC), Differential Thermal Analysis (DTA) and Thermal Gravimetric Analysis. These techniques are very used in science and material technologies (metals, metals alloys, ceramics, glass, polymer, plastic and composites) with the purpose of characterizing precursors, following and control of process, adjustment of operation conditions, thermal treatment and verifying of quality parameters. Key words: Physical chemistry; Calorimetry; Thermochemistry; Thermal analysis. RESUMEN Este trabajo muestra al lector una descripción general acerca de las técnicas del clásico análisis térmico conocido como calorimetría Diferencial de Barrido (DSC), el Análisis Térmico Diferencial (ATD) y el Análisis Térmico Gravimétrico. Estas técnicas son muy usadas en la ciencia y en la tecnología de materiales (metales, aleaciones metálicas, cerámicos, vidrio, polímeros, plásticos y composite con el propósito de caracterizar a precursores, seguimiento y control de procesos, ajustes de las condiciones de operación, tratamiento térmico y verificación de los parámetros de calidad. Palabras clave: Química física; Calorimetría; Termoquímica; Análisis térmico. Doi: http://dx.doi.org/10.15665/rp.v15i2.1166 117 Conceptual approach to thermal analysis and its main applications 1. INTRODUCTION raw materials, thermal analysis is applied to charac- terize wood and fiber, minerals, fuels (coal, tars and The International Confederation of Thermal Analysis oil), soils (rocks, clays), food and natural products [6, and Calorimetry [1] defines “Thermal Analysis” as a 7] (fats, carbohydrates, proteins). In the area of che- set of techniques where a physical or chemical proper- mical, thermal analysis is used to determine reaction ty is determined and controlled in function of time, enthalpies, heat capacity, energy phase transition, heat temperature or heat flow, depending on the system of combustion, binding energy, purity, thermal stabili- temperature, that high enough (isothermal operation) ty of inorganic compounds, complexes and metal ions it is maintained or amending linearly. in coordination polymers etc [8]. This definition and terminology associated had been In the context of science and materials technology, a also accepted by the International Union of Pure and close relationship between synthesis (preparation and Applied Chemistry (IUPAC) [2] and the American So- processing), the structure (composition), the (physical ciety of Testing and Materials (ASTM E473-14). and chemical behavior) properties and functionality (delivery and performance) is recognized. The ther- Nowadays different procedures exist to examine and mal analysis, in its various form, is a set of very useful quantify the effect of the addition of heat to the physi- and crucial tools in the characterization and proces- cal system properties. Some of the techniques are the sing of natural materials (wood, fibers, leather, bone, Differential Thermal Analysis (DTA), Thermogravi- plaster, clay, zeolites), metals and alloys (ferrous and metric Analysis (TGA) and the Differential Scanning nonferrous), ceramics [9] (oxidic and non-oxidic) and Calorimetry (DSC), these above are considered “clas- glasses [10] (siliceous, metallic and non-siliceous), sical methods” of thermal analysis [1]. Other techni- electric and magnetic, liquid crystals, polymers [11, ques such as the Mechanical Thermal Analysis (MTA), 12] and plastic (elastomers and adhesives), paints and Dynamic Mechanical Analysis (AMD), Dielectric coatings, inks and dyes, powders and explosives, se- Analysis (DEA), Thermal Microscopy and the Con- miconductors and superconductors, dielectrics, and duction Calorimetry are called “modern techniques” composites (metal matrix, ceramic matrix polymer of thermal analysis. These techniques are counting matrix). with the developing of high technology instrumenta- tion to perform combined methods, focusing on struc- For each and every of this applications the literature tural, thermal, electrical and magnetic properties of makes extensive reference to the thermal analysis as a materials [3]. set of techniques useful in the identification, characte- rization, exploration and technical application of phy- Thermal analysis is an appropriate methodology to sical systems [13, 14]. assess a wide range of properties of substances, many of them associated with a particular technique [4], Currently, thermal analysis methods continue to grow whereby, the identification is made, the physical and in two directions: On the one hand, these techniques chemical stability is checked, changes of phase are de- are moving towards achieving more accurate, faster tected and fundamental kinetic studies are performed. and ever smaller samples measured; this will give va- Furthermore, thermal analysis permits to find transi- luable information on the interfaces, the microstruc- tion points (melting, sublimation, solidification), make ture and morphology of the substances in condensed measurements of enthalpy and build thermal history, phase. Second, the thermal analysis techniques can determine the heat capacity (specific heat), quantify be conjugated with other analytical methodologies, thermal expansion (diagometría), establish mass loss such as diffraction and X-ray scattering, microscopy, (gravimetry), estimate voltages flow (rheology), per- mechanical testing, electrical and magnetic characte- form studies of viscosity, recognize the processing rization, and some spectroscopies, to perform in situ rate, quantify the amount of water (fisiadsorbida, crys- or in experiments operating conditions, structural and tallization, dehydroxylation), track processes of dena- dynamic studies. turation, evaluate the elastic modulus and damping capacity, examine the evolution of gases and volatile 2. THERMAL ANALYSIS compounds, obtain phase diagrams, measure the crys- tallinity, determine purity, investigate polymorphic When a substance (system) is supplied (heating) or is transitions and make studies of hardness, tempering, withdrawn (cooling) thermal energy as heat, various annealing, tempering and recrystallization [5]. changes can occur sequentially or in parallel; these changes include the synthesis reactions, decompo- Given the different fields of application of the techni- sitions and phase transitions, among which nuclea- ques of thermal analysis can be seen in the bibliogra- tion and crystal growth. After identifying the target phical references in the field of natural resources and system, thermal analysis makes use of a heat source, 118 Prospect. Vol. 15, No. 2, Julio-Diciembre de 2017, 117-125 dispenses heat flow, monitors progress of temperature Figure 1. Basic assembly to determine curves of hea- and builds temperature diagrams, differential tempe- ting or cooling. rature and mass loss, depending on the system tempe- Figura 1. Montaje básico para determinar curvas de rature (you can use an inert gas as reference) or heat calentamiento o de enfriamiento. flow. The diagrams obtained are called thermograms. Beyond the classic calorimetry, represented in the existence of different devices (adiabatic calorimeter, isothermal or isoperibólicos) which are used to mea- sure the enthalpy and other properties that are asso- ciated with different thermodynamic processes (state changes, reactions, dissolution, immersion, crystalli- zation), thermal analysis has modalities represented in the differential thermal analysis (DTA) [15], ther- mogravimetric analysis (TGA) [16] and differential scanning calorimetry (DSC) [17] that currently are powerful tools for characterization of substances; additionally, in these configurations, thermal analysis can be performed with the system immersed in an at- mosphere can be inert, oxidizing or reducing. To the extent that heat flows into the system, the tem- Under the consideration that some solids, especially perature of the substance, initially assumed solid, will upon presentation of finely divided or porous solids increase with time by describing a slope whose value exhibit adsorption phenomena of gases and vapors, depends on
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