What is Iron
Iron is widely distributed in life, accounting for 4.75% of the earth's crust content, second only to oxygen, silicon, and aluminum, and ranking fourth in the earth's crust. Pure iron is a flexible and malleable silver-white metal that can be used for the iron cores of generators and motors. Iron and its compounds are also used to make magnets, medicines, inks, pigments, abrasives, etc. It is one of the "black metals" referred to in the industry (the other two are chromium and manganese).
| I | O | |||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 1 | 1 H |
II | III | IV | V | VI | VII | 2 He |
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| 2 | 3 Li |
4 Be |
5 B |
6 C |
7 N |
8 O |
9 F |
10 Ne |
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| 3 | 11 Na |
12 Mg |
III | IV | V | VI | VII | VIII | I | II | 13 Al |
14 Si |
15 P |
16 S |
17 Cl |
18 Ar |
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| 4 | 19 K |
20 Ca |
21 Sc |
22 Ti |
23 V |
24 Cr |
25 Mn |
26 Fe |
27 Co |
28 Ni |
29 Cu |
30 Zn |
31 Ga |
32 Gc |
33 As |
34 Se |
35 Br |
36 Kr |
| 5 | 37 Rb |
38 Sr |
39 Y |
40 Zr |
41 Nb |
42 Mo |
43 Tc |
44 Ru |
45 Rh |
46 Pd |
47 Ag |
48 Cd |
49 In |
50 Sn |
51 Sb |
52 Te |
53 I |
54 Xe |
| 6 | 55 Cs |
56 Ba |
57-71 La-Lu |
72 Hf |
73 Ta |
74 W |
75 Re |
76 Os |
77 Ir |
78 Pt |
79 Au |
80 Hg |
81 Tl |
82 Pb |
83 Bi |
84 Po |
85 At |
86 Rn |
| 7 | 87 Fr |
88 Ra |
89-103 Ac-Lr |
104 Rf |
105 Db |
106 Sg |
107 Bh |
108 Hs |
109 Mt |
110 Ds |
111 Rg |
112 Uub |
||||||
| La-Lu | 57 La |
58 Ce |
59 Pr |
60 Nd |
61 Pm |
62 Sm |
63 Eu |
64 Gd |
65 Tb |
66 Dy |
67 Ho |
68 Er |
69 Tm |
70 Yb |
71 Lu |
|||
| Ac-Lr | 89 Ac |
90 Th |
91 Pa |
92 U |
93 Np |
94 Pu |
95 Am |
96 Cm |
97 Bk |
98 Cf |
99 Es |
100 Fm |
101 Md |
102 No |
103 Lr |
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- Item Name: Iron
- Element Symbol: Fe
- Atomic Number: 26
- Atomic Weight: 55.845
- Atomic Radius: 124pm
- Density: 7.86g/cm3
- Melting Point: 1538°C
- Boiling Point: 2750°C
- Electronic Layout: [Ar]3d64s2
The Atomic Structure of Iron
Physical Properties
Pure iron is a metallic crystal with silver-white metallic luster, and its color is usually gray. Pure iron is relatively soft. If iron is alloyed with other elements or there are impurities in pure iron, the melting point will decrease and the hardness will increase.
Chemical Properties
At room temperature, iron is not easy to react with non-metallic elements such as oxygen, sulfur, and chlorine in dry air. If there are impurities, it is easy to rust in humid air. Iron rusts faster in the air in the presence of acid, alkali, or salt solutions. At high temperatures, iron reacts violently. For example, iron will burn in oxygen, and high temperature iron and water vapor will also react. It can react with halogen, sulfur, silicon, carbon and phosphorus when heated.
Iron is easily soluble in dilute inorganic acid and emits hydrogen. When it encounters concentrated sulfuric acid or concentrated nitric acid at room temperature, an oxide protective film will be formed on the surface of iron to passivate it. Therefore, iron products can be used to hold cold concentrated sulfuric acid or cold concentrated nitric acid. When heated, iron can react with concentrated sulfuric acid or concentrated nitric acid.
Introduction to the Crystal Structure of Iron
Iron has the properties of allotropes. Iron at room temperature has a body-centered cubic structure and is called α-iron. When iron is heated to 912°C, the structure of iron changes to a face-centered cubic structure, which is called γ-iron. When heating continues to 1394°C, the iron will change back to a body-centered cubic structure, and the iron at this time is called δ-iron. The figure below shows the three structures of iron:
Three Structures of Iron
The Role of Iron in Superalloys
The Role of Iron in Iron-based Superalloys
In iron-based superalloys, iron is used as the matrix. Other elements can be solid-dissolved into γ-iron austenite for alloying. As mentioned earlier, iron has the property of isomeric transformation. This makes iron itself unable to have a stable austenite structure at all temperatures. Therefore, a certain amount of nickel must be added to almost all iron-based superalloys. Nickel has a face-centered cubic structure at any temperature, so it can stabilize austenite in iron-based alloys.
The Role of Iron in Nickel-based Superalloys
Iron can play a certain solid solution strengthening effect in nickel-based superalloys. This is mainly due to the 3% difference between the lattice constants of iron and nickel, and iron can reduce the stacking fault energy of nickel-based austenite. For example, Inconel 718 contains 18% iron for solid solution strengthening.
718
Si
C
Al
Ti
Co
Nb
Ta
Mo
Fe
Cr
Ni
The Role of Iron in Cobalt-based Superalloys
Iron can also play a solid solution strengthening effect in cobalt-based superalloys, but the effect is relatively small. Cobalt also has allotropic transformations. It is a hexagonal close-packed structure at room temperature, and a face-centered cubic structure at high temperature. Therefore, in cobalt-based alloys, the role of iron is mainly to expand the austenite region.
In addition, iron in the alloy can effectively reduce costs.
Conclusion
Iron has limited corrosion resistance, and it mainly plays a role in solid solution strengthening, stabilizing austenite and reducing costs in superalloys.
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