Non-Ferrous Metals: Structure, Types, Characteristics, Properties and Examples

The Nonferrous metals they are all those who lack or have negligible amounts of iron. These, in different mass proportions, are used for the creation of alloys that exhibit better physical properties than individual metals.

Thus, its crystalline structures and metal interactions are the cornerstone of the applications of non-ferrous alloys. However, these pure metals find fewer uses because they are very sensitive and reactive. For this reason, they serve as a base and additive for alloys.

Bronze is a non-ferrous alloy; It consists mainly of a golden mixture of copper and tin (statue in the image above). The copper of the alloy is oxidized and forms CuO, a compound that blackens its golden surface. In humid environments, CuO hydrates and absorbs carbon dioxide and salts to form blue-green compounds.

For example, the Statue of Liberty is covered by layers of copper carbonates (CuCO ₃ ) known as patina. In general, all metals are oxidized. Depending on the stability of their oxides, they protect to a lesser or greater degree the alloys against corrosion and external factors.

Structure

Iron is just one of all metals in nature, so the structures and alloys of non-ferrous metals are more diverse.

However, under normal conditions most metals have three crystalline structures established by their metal bonds: compact hexagonal (hcp), compact cubic (ccp) and cubic centered in the body (bcc).

Hexagonal compact (hcp)

In this structure, the metallic atoms are packaged in the form of a hexagonal prism, thus taking advantage of all the spaces.

Of all the structures, this is the densest, so it can be expected that the metals are the same. In this, all atoms are surrounded by twelve neighbors.

Examples

- Titanium (Ti).

- Zinc (Zn).

- Magnesium (Mg).

- Cadmium (Cd).

- Cobalt (Co).

- Rutenio (Ru).

- Osmio (Os).

- Alkaline earth metals (with the exception of barium and francium).

Compact cubic (ccp)

This crystalline structure is less dense than the hcp, and in this each atom is surrounded by twelve neighbors.

Here, the interstices (empty spaces) are larger than in the case of hcp, so these metals can contain in these molecules and small atoms (such as molecular hydrogen, H ₂ ).

Examples

- Aluminum (Al).

- Nickel (Ni).

- Silver (Ag).

- Copper (Cu).

- Gold (Au).

- Rhodium (Rh).

- Iridium (Go).

Cubic centered on the body (bcc)

Of the three structures, this is the least dense and compact, being at the same time the one that presents the interstices of greater volumes.

Therefore, it more easily accommodates small molecules and atoms. Likewise, in this cube each atom is surrounded by eight neighbors.

Examples

- Vanadio (V).

- Niobium (Nb).

- Chromium (Cr).

- Alkaline metals.

- Tungsten (W).

In addition, there are other structures, such as the simple cubic and other more complex ones that consist of less dense or distorted arrangements of the first three. However, the above crystalline structures apply only to pure metals.

Under conditions of high impurity, pressure and temperature, these arrangements are distorted and, when they are components of an alloy, they interact with other metals to generate new metal structures.

In fact, the exact knowledge and manipulation of these arrangements allow the design and elaboration of alloys with physical properties desired for a specific purpose.

Types

In very general terms, non-ferrous metals can be classified into three types: heavy (lead), light (copper and aluminum) and ultralight (magnesium). In turn, these are divided into two subclasses: those with medium melting points and those with high melting points.

Other types of non-ferrous metals correspond to noble (or precious) metals. Examples of these are metals with ccp structures (with the exception of aluminum, nickel and others).

Likewise, rare earth metals are considered non-ferrous (cerium, samarium, scandium, yttrium, thulium, gadolinium, etc.). Finally, radioactive metals also count as non-ferrous (polonium, plutonium, radium, francium, astatine, radon, etc.).

Characteristics and properties

Although the characteristics and properties of metals vary in their pure states and in alloys, they present generalities that differentiate them from ferrous metals:

- They are malleable and excellent electrical and thermal conductors.

- They are less affected by heat treatments.

- They have greater resistance against oxidation and corrosion.

- They do not present so much paramagnetism, which allows them to be materials used for electronic applications.

- Its manufacturing processes are easier, including casting, welding, forging and rolling.

- They have more attractive colorations, so they find uses as ornamental elements; In addition, they are less dense.

Some of its disadvantages compared to ferrous metals are: low resistance, high costs, lower demands and lower mineralogical abundance.

Examples

In the metallurgical industry there are many options in the manufacture of metals and non-ferrous alloys; the most common are: copper, aluminum, zinc, magnesium, titanium and nickel-based superalloys.

Copper

Copper has been used for a wide variety of applications due to its advantageous properties, such as its high thermal and electrical conductivities.

It is resistant, malleable and ductile, so that many practical designs can be obtained from pipes to jars and coins. It has also been used in the reinforcement of the keel of boats, and finds much use in the electrical industry.

Although in its pure state it is very soft, its alloys (between these brass and bronze) are more resistant and are protected by layers of Cu ₂ O (reddish oxide).

Aluminum

It is a metal that is considered light due to its low density; It has high thermal and electrical conductivities, and is resistant to corrosion thanks to the Al coating ₂ OR ₃ that protects its surface.

Given its properties, it is an ideal metal especially in aeronautics, in the automotive and construction industry, among others.

Zinc and magnesium

Zinc alloys (such as KAYEM, with 4% aluminum and 3% copper by mass) are used for the manufacture of complex castings. It is intended for construction and engineering works.

In the case of magnesium, its alloys have applications in architecture, as well as bicycle housings, bridge parapets and welded structures.

It also finds use in the aerospace industry, in high-speed machinery and in transport equipment.

Titanium

Titanium forms slightly light alloys. They are super resistant, and are protected from corrosion by a layer of TiO ₂ . Its extraction is expensive and has a bcc crystal structure above 882 ° C.

In addition, it is biocompatible, so it can be used as a material for medical prostheses and implants. Additionally, titanium and its alloys are present in machinery, in navy, in jet components and in chemical reactors.

Superalloys

Superalloys are very resistant solid phases composed of nickel (as base metal) or cobalt.

They are used as vanes in turbines and aircraft engines, in materials for reactors that withstand aggressive chemical reactions and in heat exchanger equipment.

References

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