Californium is a silvery white actinide metal[10] with a melting point of 900 ± 30 °C (1,650 ± 50 °F) and an estimated boiling point of 1,745 K (1,470 °C; 2,680 °F).[11] The pure metal is malleable and is easily cut with a razor blade. Californium metal starts to vaporize above 300 °C (570 °F) when exposed to a vacuum.[12] Below 51 K (−220 °C) californium metal is either ferromagnetic or ferrimagnetic (it acts like a magnet), between 48 and 66 K it is antiferromagnetic (an intermediate state), and above 160 K (−113 °C; −172 °F) it is paramagnetic (external magnetic fields can make it magnetic).[13] It forms alloys with lanthanide metals but little is known about them.[12]
The element has two crystalline forms under 1 standard atmosphere of pressure: A double-hexagonal close-packed form dubbed alpha (α) and a face-centered cubic form designated beta (β).[b] The α form exists below 900 °C (1,650 °F) with a density of 15.10 g/cm3 and the β form exists above 900 °C with a density of 8.74 g/cm3.[15] At 48 GPa of pressure the β form changes into an orthorhombic crystal system due to delocalization of the atom's 5f electrons, which frees them to bond.[16][c]
The bulk modulus of a material is a measure of its resistance to uniform pressure. Californium's bulk modulus is 50 ± 5 GPa, which is similar to trivalent lanthanide metals but smaller than more familiar metals, such as aluminium (70 GPa).[16]
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