ABSTRACT
When matter is heated, it undergoes certain physical and chemical changes. Physical changes include phase changes such as melting, vaporization, crystallization, transitions between crystal structures, changes in microstructure in metal alloys and polymers, changes in protein structure, volume changes (expansion and contraction), adsorption, absorption and desorption of gases, and changes in mechanical behavior. Chemical changes include reactions to form new products, oxidation, corrosion, decomposition, dehydration, chemisorption, and binding between compounds (e.g., proteins and drugs). These physical and chemical changes take place over a wide temperature range. The rates of chemical reactions vary with temperature, and the properties of some materials, such as semicrystalline polymers and metal alloys, depend on the rate at which they are cooled. Materials are used over a wide range of temperatures, from arctic cold to tropical heat, in corrosive environments, variable humidity, and under load (stress). It is necessary to characterize materials and their behavior over a range of temperatures to determine what materials are suitable for specic uses and to determine what temperature range materials or chemicals can withstand without changing. This sort of information is used in many ways: to predict safe operating conditions for products, such as which type of tire material is best for vehicles in extremely cold or extremely hot climates, the average expected lifetime of materials such as paints and polymers exposed to temperature changes, processing conditions for materials, the curing times and temperatures for dental lling material, and optimum storage conditions for food, among other uses.
