9.4 Thermal analysis applications

Thermal analysis techniques like TGA, DTA, and DSC are powerful tools for studying materials. They measure changes in mass, temperature, and heat flow as samples are heated or cooled, revealing crucial info about composition, thermal stability, and phase transitions.

These methods are widely used to characterize polymers, pharmaceuticals, and inorganic materials. They help determine key properties like melting points, glass transitions, and decomposition temperatures, which are essential for optimizing material performance and processing conditions.

Thermogravimetric Analysis (TGA)

Principles and Instrumentation

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• Measures change in mass of a sample as a function of temperature or time in a controlled atmosphere
• Provides quantitative information about composition and thermal stability by monitoring mass change during heating
• Typical TGA instrument consists of:
  • High-precision balance
  • Sample pan
  • Programmable furnace
  • Purge gas system to control sample environment

Applications and Data Interpretation

• Studies various processes: decomposition, oxidation, reduction, vaporization, sublimation, adsorption/desorption
• Determines moisture content, volatile components, ash content in materials (polymers, pharmaceuticals)
• Evaluates thermal stability and decomposition kinetics (polymers, pharmaceuticals, other materials)
• Characterizes composition and purity of inorganic compounds (metal oxides, ceramics)
• Investigates oxidation and reduction behavior of metals and alloys
• TG curve plots mass change (percentage or absolute units) against temperature or time
• DTG curves (derivative of TG curve) provide information about rate of mass change and identify overlapping thermal events

Differential Thermal Analysis (DTA) and Differential Scanning Calorimetry (DSC)

Principles and Instrumentation

• DTA measures temperature difference between sample and reference material during heating or cooling
• DSC measures heat flow required to maintain sample and reference at the same temperature
• Provide information about thermal transitions and reactions: melting, crystallization, glass transition, phase changes
• Typical DTA or DSC instrument consists of:
  • Sample and reference holder
  • Thermocouples or heat flux sensors
  • Programmable furnace
  • Data acquisition system

Applications and Data Interpretation

• Studies thermal behavior of various materials (polymers, pharmaceuticals, food products, inorganic compounds)
• Determines melting and crystallization temperatures, enthalpies, purities of materials
• Characterizes glass transition temperatures and thermal transitions in polymers
• Evaluates stability and compatibility of drug formulations and excipients
• Investigates phase transitions and reaction kinetics in inorganic materials
• DTA and DSC curves plot temperature difference (DTA) or heat flow (DSC) against temperature or time
• Shape, position, and area of peaks provide quantitative and qualitative information about thermal events in the sample

Thermal Analysis Applications in Material Characterization

Polymers

• Determines glass transition temperature (Tg) for processing and end-use properties
• Analyzes melting and crystallization behavior affecting mechanical properties and morphology
• Assesses thermal stability and decomposition kinetics for long-term performance and safety
• Performs compositional analysis (filler content, residual solvents, moisture)

Pharmaceuticals

• Determines melting point, purity, and polymorphic forms of drug substances and excipients
• Evaluates stability and compatibility of drug-excipient mixtures in formulations
• Studies dehydration, desolvation, and degradation processes of pharmaceutical compounds
• Investigates release kinetics and thermal behavior of controlled-release drug delivery systems (transdermal patches, microspheres)

Inorganic Materials

• Characterizes phase transitions (solid-state reactions, crystallization, melting) in ceramics, glasses, metal oxides
• Studies oxidation and reduction behavior of metals and alloys for corrosion resistance and high-temperature performance
• Determines thermal stability, decomposition, and reactivity of inorganic compounds (catalysts, adsorbents)
• Investigates sintering and densification processes in ceramic and powder metallurgy materials (3D printing, additive manufacturing)

Comprehensive Material Characterization

• Combines thermal analysis data with other analytical techniques (X-ray diffraction, spectroscopy, microscopy)
• Provides a comprehensive understanding of structure-property relationships in polymers, pharmaceuticals, inorganic materials
• Enables optimization of material properties, processing conditions, and end-use performance