Hexaferrum

Figure 1: The epsilon field in the unary iron phase diagram.[1]

Figure 2: Molar volume vs. pressure for ε-Fe at room temperature.

Hexaferrum and epsilon iron (ε-Fe) are synonyms for the hexagonal close-packed (HCP) phase of iron that is stable only at extremely high pressure. Takahashi and Bassett at the University of Rochester mixed 99.8% pure α-iron powder with sodium chloride, and pressed a 0.5-mm diameter pellet between the flat faces of two diamond anvils. The deformation of the NaCl lattice, as measured by x-ray diffraction (XRD), served as a pressure indicator. At a pressure of 130 kbar (13 GPa) and room temperature, the body-centered cubic (BCC) ferrite powder transformed to the HCP phase in Figure 1. When the pressure was lowered, ε-Fe transformed back to ferrite (α-Fe) rapidly. A specific volume change of −0.20 cm/mole ± 0.03 was measured. Hexaferrum, much like austenite, is more dense than ferrite at the phase boundary. A shock wave experiment confirmed the diamond anvil results. Epsilon was chosen for the new phase to correspond with the HCP form of cobalt.

单词	Hexaferrum
释义	Hexaferrum 英语百科 Hexaferrum Hexaferrum and epsilon iron (ε-Fe) are synonyms for the hexagonal close-packed (HCP) phase of iron that is stable only at extremely high pressure. Takahashi and Bassett at the University of Rochester mixed 99.8% pure α-iron powder with sodium chloride, and pressed a 0.5-mm diameter pellet between the flat faces of two diamond anvils. The deformation of the NaCl lattice, as measured by x-ray diffraction (XRD), served as a pressure indicator. At a pressure of 130 kbar (13 GPa) and room temperature, the body-centered cubic (BCC) ferrite powder transformed to the HCP phase in Figure 1. When the pressure was lowered, ε-Fe transformed back to ferrite (α-Fe) rapidly. A specific volume change of −0.20 cm/mole ± 0.03 was measured. Hexaferrum, much like austenite, is more dense than ferrite at the phase boundary. A shock wave experiment confirmed the diamond anvil results. Epsilon was chosen for the new phase to correspond with the HCP form of cobalt.
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