Classification and Properties of Non-Ferrous Metals

Posted on Dec 14, 2024 in Chemistry

Classification of Non-Ferrous Metals

Non-ferrous metals are essential and are increasingly used in industry to manufacture many products. They are classified as follows:

  • Heavy: Density greater than 5 kg/dm3. Examples include tin, copper, zinc, and lead.
  • Light: Density between 2 and 5 kg/dm3. Examples include aluminum and titanium.
  • Ultralight: Density less than 2 kg/dm3. Examples include magnesium and beryllium.

Non-ferrous metals are generally soft and have low mechanical strength. Therefore, they are often alloyed with other metals to improve their properties. Ordered from highest to lowest use, they are:

Copper (and its alloys), aluminum, tin, lead, zinc, nickel, chromium, titanium, and magnesium.

Tin

Tin is quite rare in the Earth’s crust. Fortunately, it is usually found concentrated in deposits, although the ore grade is often quite low (0.02%). The most exploited tin ore is cassiterite, in which the metal is in the form of tin oxide (SnO2).

Tin Features

  • Pure tin has a very bright color. At room temperature, it oxidizes and loses its exterior gloss.
  • At room temperature, it is very malleable and soft and can be formed into sheets of a few tenths of a millimeter thick. However, when hot, it is fragile and brittle.
  • Below -18°C, it starts to decompose and turn into a gray powder. This process is known as “tin disease” or “tin pest.”
  • When bent, you can hear a crack called “tin cry.”

Main Tin Alloys

  • Bronze: An alloy of copper and tin.
  • Solder: Alloys of tin and lead in proportions between 25% and 90%.
  • Low-melting-point alloys:
    • Darcet’s alloy: (25% Sn + 25% Pb + 50% Bi), which melts at 97°C.
    • Cerrolow alloy: (8.3% Sn + 22.6% Pb + 44.7% Bi + 5.3% Cd + 19.1% In), which melts at 47°C.

One of the most important applications of tin is the manufacture of tinplate, which consists of a steel sheet coated with two thin layers of pure tin. The tin protects the steel against oxidation.

Copper

Copper ores used today are in the form of native copper, sulfides (chalcopyrite and chalcocite), and oxides (malachite and cuprite).

Copper Characteristics

  • It is very ductile and malleable.
  • It has high electrical and thermal conductivity.

The addition of other non-ferrous metals to copper substantially improves its mechanical properties and oxidation resistance, but slightly decreases its electrical and thermal conductivity.

Common Copper Alloys

  • Bronze (copper and tin):

    1. Regular: Contains only copper and tin (5% to 30%). Used in bells and gears.
    2. Special: Contains copper, tin, and other elements. Used in sculptures and electrical cables.

  • Brass (an alloy of copper and zinc):

    1. Regular: Contains only copper and zinc (30% to 55%). Used in hardware.
    2. Special: Contains copper, zinc, and other elements. Used in taps, nuts, and bolts.

Titanium

Titanium is abundant in nature, as it is a component of almost all volcanic rocks that contain iron. The extraction of titanium is a complex process, which increases the final product’s cost. Currently, the minerals from which titanium is obtained are rutile and ilmenite.

Titanium Characteristics

  • It is a silvery-white metal that is more resistant to oxidation and corrosion than stainless steel.
  • Its mechanical properties are similar or even superior to those of steel, but it has the advantage that it retains them up to 400°C.

Titanium Applications

Because of its low density and high mechanical performance, it is mainly used in the manufacture of structures and machine parts in aeronautics (aircraft, rockets, missiles, and communication satellites).

Magnesium

Magnesium is a lightweight metal. The most widely used magnesium-containing minerals are carnallite (in the form of magnesium chloride, which is derived from seawater), dolomite, and magnesite.

Magnesium Characteristics

  • In liquid or powder form, it is very flammable.
  • It has a white color, like silver.
  • It is more malleable and ductile than aluminum.
  • It is more durable than aluminum and is used in aviation.

Magnesium Alloys

  1. Alloys for forging:
    • Magnam: Mg + Mn
    • Magzine: Mg + Zn
    • Magal: Mg + Al
  2. Alloys for casting:
    • Fumagcin: Mg + Zn
    • Fumagal: Mg + Al

In its purest form, magnesium has few uses, except in making fireworks and as a flux in steel foundries.

Other Important Copper Alloys

  • Cuproaluminum: Copper and aluminum alloy. Used in propellers, turbines, etc.
  • Alpaca: Copper, nickel, and zinc alloy. It has a silver color. Used in cheap jewelry and silverware.
  • Cupronickel: Copper-nickel alloy (40% to 50%). Used in coins and electrical contacts.

Zinc

The main minerals used in zinc extraction are sphalerite and calamine.

Zinc Characteristics

  • It is very resistant to oxidation and corrosion in air and water but not very resistant to attack by acids and salts.
  • It has the highest coefficient of thermal expansion of all metals.
  • At room temperature, it is brittle, but between 100°C and 150°C, it is very malleable.

Commercial Uses of Zinc

  1. In alloy form:
    • Brass (copper and zinc): Because zinc is cheaper than tin, it is replacing bronze in many applications.
    • German silver or nickel silver (Cu + Ni + Zn): Used in ancient cutlery and now in making cheap jewelry.
    • Zamak (Al + Cu + Zn): Used in the production of parts with high precision and high surface quality that do not require machining.
  2. In its purest form:
    • Sheets of different thicknesses: Used for covering roofs, gutters, ledges, downpipes, water tanks, and battery coatings.
  3. Coating:
    • Electrolytic galvanizing: A metal part is coated with a thin layer of zinc (about 15 thousandths of a millimeter) by electrolysis.
    • Hot-dip galvanizing: A part is dipped into a bath of molten zinc. Once cooled, the zinc is bonded to and protects the part.
    • Metallic: Tiny particles of zinc mixed with paint are projected onto the surface to be protected.
    • Sherardizing: A steel part is coated with zinc dust and placed in an oven. The heat causes the zinc to penetrate the steel.
  4. Other forms:
    • Zinc oxide: Used in sunscreens, deodorants, dyes, glues, preservatives, etc.

Lead

The most commonly used lead ore is galena, which consists of lead sulfide.

Lead Characteristics

  • It is very pliable and soft.
  • It is grayish-white and very bright when freshly cut. It is easily oxidized, forming a basic carbonate that protects it.
  • It has good resistance to hydrochloric and sulfuric acids but is attacked by nitric acid and sulfur vapor.

Because of its ability to resist weathering and chemicals well, lead has many applications, both in its pure form and in alloys. The most important are:

  • In its purest form:
    • Lead oxide: Used to make antioxidant paints.
    • Pipes: Currently underutilized.
    • Batteries.
    • Coating for protection against nuclear radiation (X-rays).
  • In alloy form:
    • Solder, made of lead and tin, is used as a filler material.

Aluminum

Aluminum is the most abundant metal in nature. It is found as a component of clay, shale, feldspar, slate, and granite rocks, making up 8% of the Earth’s crust. Unfortunately, it is not found in nature in its purest form but combined with oxygen and other elements. The mineral from which aluminum is obtained is called bauxite, which is composed of alumina and is red.

Aluminum Characteristics

  • It is very light.
  • It is stainless in air because it forms a very thin film of aluminum oxide (Al2O3) that protects it.
  • It is a good conductor of electricity and heat. It is often used in power lines because it also weighs less.
  • It is very malleable (aluminum foil for packaging) and ductile.

Aluminum Applications and Classes

Aluminum is used alloyed with other metals to improve its hardness and resistance. However, it is also sold in pure form.

  1. Aluminum Alloys:

    • Aluminum + copper (Duralumin or aluminum bronze): Used in the base of pans, tires, cars, bicycles, etc.
    • Aluminum + magnesium: Used mainly in aerospace and automotive applications.
    • Aluminum + copper + silicon: Ideal for injection molding parts.
    • Aluminum + nickel + cobalt (Alnico): This alloy produces powerful permanent magnets.

  2. Pure Aluminum (powder): Mixed with paint, it provides good protection from the elements.

The forms usually employed in the marketing of aluminum are wires, sheets, rods, and bars.