NON-FERROUS METALS: STRUCTURE, TYPES, CHARACTERISTICS - CHEMISTRY - 2025

The non - ferrous metals are those that have no or negligible amounts of iron. These, in different mass proportions, are used to create alloys that exhibit better physical properties than individual metals.

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

Bronze is a non-ferrous alloy; It mainly consists of a golden mixture of copper and tin (statue in the image above). The copper in the alloy oxidizes 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 rust. Depending on the stability of their oxides, they protect alloys to a lesser or greater degree against corrosion and external factors.

Structure

Iron is just one of all the 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 metallic bonds: compact hexagonal (hcp), compact cubic (ccp), and body-centered cubic (bcc).

Compact Hex (hcp)

Of the three structures, this is the least dense and compact, being at the same time the one with the largest volume interstices.

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

Examples

- Vanadium (V).

- Niobium (Nb).

- Chromium (Cr).

- Alkali 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 crystal structures apply only to pure metals.

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

In fact, the exact knowledge and manipulation of these arrangements allow the design and manufacture of alloys with desired physical properties 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 (except for aluminum, nickel and others).

Similarly, rare earth metals are considered non-ferrous (cerium, samarium, scandium, yttrium, thulium, gadolinium, etc.). Lastly, radioactive metals also count as non-ferrous (polonium, plutonium, radium, francium, astate, 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 less mineral abundance.

Examples

In the metallurgical industry there are many options in the manufacture of non-ferrous metals and alloys; the most common are: copper, aluminum, zinc, magnesium, titanium and the 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 strong, malleable and ductile, so many practical designs can be obtained from it: from pipes to jars to coins. It has also been used to reinforce the keel of ships, 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 ₂ O ₃ layer that protects its surface.

Given its properties, it is an ideal metal especially in aeronautics, the automotive and construction industries, 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 in bicycle housings, in bridge parapets and in welded structures.

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

Titanium

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

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

Superalloys

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

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

References

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