Heat capacity (CP with units such as J mol-1 K-1 or J kg-1 K-1) is defined as the quantity of thermal energy required to raise the temperature of a substance one degree . In practice, heat capacity and the term specific heat are used almost interchangeably. For ionic solids, atoms can be modeled as centers of mass that can vibrate independently in three dimensions . The vibrational energy of the atoms increases as thermal energy is added to the system. The heat capacity of all solids approaches 3NAk with temperature (where NA is Avagadro’s number and к is the Boltzmann constant) or 3R (where R is the ideal gas constant) per mole of atoms, the familiar Dulong-Petit law. At low temperature, the models of Einstein and Debye can be used to estimate heat capacity . In practice, heat capacity in terms of energy and mass is more useful and is compiled as a function of temperature in any number of reference books [2, 3, 60]. Experimentally, heat capacity can be determined using such heat flow techniques as differential scanning calorimetry.
Heat capacity is important because it regulates the amount of energy required to raise the temperature of a thermal load (e. g., ware to be fired plus kiln furniture). Such data can be used to compute furnace efficiency, which is the ratio of fuel usage to the thermal energy requirement of a process. In addition, knowledge of heat capacities of products, kiln furniture, and refractories is essential for good furnace design.
Refractory oxides are an important class of materials that enable processes to exploit extreme environments. A wide variety of unary, binary, and ternary oxides can be considered refractory, based on their melting temperatures. Refractory oxides are generally prepared from powdered precursors using standard ceramic forming techniques such as casting, pressing, or extrusion, and subsequently sintered to achieve final density. In addition to chemical compatibility, the physical properties of refractory oxides such as thermal expansion coefficient, thermal conductivity, modulus of elasticity, and heat capacity must be considered when selecting an oxide for a specific application.