Properties of Zirconium Alloy

Absorption Cross Section

• "Absorption cross-section" is a physics term that describes the probability of an absorption process. Specifically, it describes whether or not two particles will interact. Zirconium's absorption cross-section for thermal neutrons is 0.18 barn, which is much lower than the absorption cross-section for thermal neutrons for other metals.

Oxidation and Passivation

• Zirconium does readily react with oxygen, but no firm consensus exists about whether or not zirconium and zirconium alloys have the same oxidation rate, even though zirconium is the main component of zirconium alloys. Zirconium alloys are corrosion-resistant, however, because of a process called passivation. When a zirconium alloy begins to oxidize, a non-reactive film forms spontaneously, inhibiting further corrosion.

Thermal Properties

• With regard to thermal properties, zirconium alloys are often far superior to other materials considered for nuclear uses. Zirconium alloys' thermal expansion occurs at 25 degrees Celsius. With a linear coefficient of thermal expansion that is almost one-third that of stainless steel, zirconium alloys have a significant dimensional stability at high temperatures. Plus, the thermal conductivity of zirconium alloy is 30 percent higher than the thermal conductivity of stainless steel.

Heat Capacity and Melting Point

• Heat capacity is the number of units of heat needed to raise a subject's temperature by 1 degree. Zirconium alloys have a heat capacity of 0.285 J/g- C (0.07 BTU/lb- C). Their melting point is 1850 C (3,362 F). A low heat capacity and high melting point are properties that make zirconium alloys good for industrial and nuclear uses.

Anisotropy

• Zirconium alloys have a hexagonal, closely packed crystal structure at room temperature as an alpha phase. As a result, they have different values when measured in different directions, which is called anisotropy. That gives them high yield strength and allows optimization of their properties.