Table 1. Some properties of iron triad elements

	Fe	Co	Ni
density, g/сm^3	7.87	8.90	8.91
tm, ^oС
Rа, nm	0.125	0.125	0.124
Ionisation energy Е ® Е^+, kJ∙mol^-1	762.5	760.4	737.1
Е^+ ® Е^2+, kJ∙mol^-1	1561.9		1753.0
Е^2+ ® Е^3+, kJ∙mol^-1
Е^o(Е^2++ 2е = Е), V	-0.44	-0.29	-0.25

Iron is a fairly soft metal, existing in different forms according to temperature (Fig. 1):

a-Fe b-Fe g-Fe d-Fe.

Figure 1. Phase diagram of pure iron

Alpha iron, also known as ferrite, is the most stable form of iron at normal temperatures. It is a fairly soft metal that can dissolve only a small concentration of carbon (no more than 0.021% by mass at 910 °C).

Above 912 °C and up to 1400 °C α-iron undergoes a phase transition from bcc to the fcc configuration of γ-iron, also called austenite (Fig. 2). This one is similarly soft and metallic but can dissolve considerably more carbon (as much as 2.04% by mass at 1146 °C). This form of iron is used in the type of stainless steel used for making cutlery, and hospital and food-service equipment.

Figure 2. The body centered cubic unit cell (bcc or ccc) of a-Fe and face-centered cubic unit cell (fcc) of γ-Fe

Magnetic properties of iron [1]. Below t = 770°С it’s ferromagnetic substance (this temperature of ferro(ferri-)magnetic-paramagnetic transition is called the Curie point), in the range 770-910 ^оС it’s paramagnetic substance (b-Fe). At 910-1401°С it’s a paramagnetic (g-Fe) with a face-centred cubic lattice. At 1401-1539°С (b.p.) it’s d-Fe with body-centred cubic lattice.

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