Metal is a substance with gloss, good electrical conductivity, thermal conductivity and mechanical properties, and a positive temperature resistivity. Metal is a big family. There are 86 kinds of metals in the world. People usually divide metals into two categories, ferrous metals and non-ferrous metals.
The names of ferrous metals and non-ferrous metals are often misunderstood, thinking that ferrous metals must be black, but they are not. There are only three types of ferrous metals: iron, manganese and chromium. And none of them are black! Pure iron is silver-white; manganese is silver-white; chromium is off-white. Because the surface of iron is often rusty, it is covered with a mixture of black ferroferric oxide and brown ferric oxide, which looks black. No wonder people call it “black metal”. The “ferrous metallurgical industry” often referred to mainly refers to the steel industry. Because the most common alloy steels are manganese steel and chromium steel, people regard manganese and chromium as “ferrous metals”.
Except for iron, manganese, and chromium, all other metals are considered non-ferrous metals.
In non-ferrous metals, there are various classification methods. For example, in terms of specific gravity, aluminum, magnesium, lithium, sodium, potassium, etc. have a specific gravity less than 5 and are called “light metals”, while copper, zinc, nickel, mercury, tin, lead, etc., have a specific gravity greater than 5 and are called “heavy metals.” Gold, silver, platinum, osmium, and iridium are more expensive and are called “precious metals”; radium, uranium, thorium, polonium, etc. are radioactive and are called “radioactive metals”, and there are also materials such as niobium, tantalum, zirconium, lutetium, gold, and radium. Because the content of, hafnium, uranium, etc. in the earth’s crust is small or relatively scattered, people also call them “rare metals.”