Physical Properties of Tungsten
Tungsten possesses numerous physical properties that are unique among metals. For example, the melting point of tungsten can reach up to 3410°C—the highest among all metals—and it has the lowest vapor pressure and evaporation rate among all metals. Moreover, the degree of variation of the thermal expansion coefficient of tungsten is least susceptible to changes in the ambient temperature among all refractory metals. Hence, tungsten has been used in extensive and significant applications owing to its prominent properties.
Tungsten Physical Properties
|Atomic Number||74||Evaporation Rate/[kg/(m2.s)]|
|Atomic Radius nm||0.1368||3100K||1.06x10-5|
|Ionic Radius nm||0.068 (W4+ )|
|Melting Point/。 )C||3410+/-20||3273K||2.06x10-4|
|Melting Heat/(kJ/g)||255||Liquid Vapor Pressure/Pa|
|1273K||1.51x102||Solid Vapor Pressure/Pa|
|Boiling Point/。 )C||5900~6000||2503K||8.81x10-6|
|Heat of vaporization(Below boiling point)/(kJ/g)||4.957||3003K||9.44x10-3|
|1100K||1.17x102||Electrical Resistivity/μΩ. cm|
Chemical Properties of Tungsten
Tungsten enjoys high chemical stability; it can resist the corrosion caused by nearly all acid and alkaline liquids at room temperature and several molten metals at high temperatures. Tungsten is, therefore, a favorable choice for smelting molds or containers for molten metals.
Mechanical Properties of Tungsten
The tensile properties of tungsten depend on its preparation method. In particular, tungsten prepared by electron beam smelting exhibits the lowest strength and highest ductility. In contrast, tungsten prepared by vapor deposition exhibits barely higher strength than that prepared by electron beam melting. Moreover, tungsten prepared by powder metallurgy and arc melting presents the highest strength with poor ductility. Powder metallurgy is an industrialized method applied in the production of tungsten materials. Other methods are adopted only for specific needs (such as ultra-high purity tungsten). Hardness measurement is a fast and economical means of roughly measuring the strength of a material. The strength of tungsten is strongly anisotropic.
Regarding the elastic modulus of tungsten, energy is converted to elastic deformation energy when the energy consumed by elastic deformation is stored in the material completely. In addition, the material recovers its original properties with the release of the elastic deformation energy after removing the external force. In that case, the effect of tungsten’s elasticity on the deformation treatment must be considered in the deformation process.
As tungsten is a body-centered cubic crystal, its brittleness has an inherent characteristic. More specifically, the ratio of volumetric elastic modulus k to shear elastic modulus µ is considered to represent intrinsic brittleness in the active slip system. The higher the percentage, the lower the DBTT (Ductile-Brittle Transition Temperature), and vice versa. The k/µ values of tungsten and molybdenum materials range from 1.22 to 2.02, indicating that both materials’ high DBTT can be found.