Explanation

Gibbs theorem, also known as Gibbs rule, is used to determine the relationship between the number of phases and the number of independent components, as well as other independent variables that affect the equilibrium state in a multicomponent multiphase equilibrium system. In general, it can be expressed as: F=C - P+2, where F represents the degree of freedom, indicating the strength factors (such as temperature, pressure and concentration of each phase) that can change freely and independently in the equilibrium system when each phase remains unchanged. C is the number of independent components in the system, which is equal to the number of species in the system minus the number of independent limiting conditions (such as chemical reaction equations, concentration relationships, etc.). The number "2" is a special case that generally only considers two external conditions: temperature and pressure. When there are surface, electromagnetic field, gravity and other effects, the relationship becomes: F=C-P+2+S+G, where S and G represent the corresponding number of external conditions. MAX phase ceramics is a binary layered carbon (nitrogen) compound, the general expression is M (n+1) AX (n), where M represents the transition metal element, A represents the second A or VA group element, and X is the carbon or nitrogen element, whose n value is generally in the range of 1 to 3, but up to 6. This kind of materials combines the characteristics of ceramics and metals, and has good conductivity and thermal conductivity. It has low hardness, high elastic modulus and shear modulus at room temperature, and is easy to machine. In addition, they have high yield strength, good thermal stability and oxidation resistance, so they are widely used in high-temperature structural materials, high-temperature heating materials, electrode brush materials, chemical anti-corrosion materials and other fields. Such materials can be prepared by in phase reaction synthesis or chemical vapor deposition.

Classification