Human History and Material Science: From Stone to Polymers

Posted on Jan 7, 2025 in Chemistry

ITEM 7. Humans and Materials

7.1 The First Materials

A. It All Started with a Couple of Stones

It is estimated that the beginning of the use of materials made by man was about 2.5 billion years ago. The Stone Age was followed by the Bronze Age and the Iron Age.

  • Stone Age

    Edged stones were refined, and eventually, axes, arrows, spears, knives, and many other tools appeared that facilitated their daily activities. The Stone Age was born, and so was technology.

    Humans worked in tunnels and caves to find better-quality stones. Two other important advances in materials development were the development of pottery initially and then metallurgy.

    • To indicate the transition between the Stone Age and the Bronze Age, the name Copper Age or Chalcolithic is given.
  • Bronze Age

    Humans discovered how to produce a new material that was difficult to find in pure form in nature and that now they could produce at will. It was metallic copper.

    Their tools were not as sharp as stone, but they had some advantages:

    • They were much less brittle.
    • They could be made larger than stone.
    • They could take many different forms, impossible to achieve with stone.

    After a few thousand years using copper, humans improved their properties by adding another metal, tin. The advantages of bronze were twofold:

    • Bronze melts at a lower temperature.
    • The tenacity of bronze is considerably greater than copper.
  • Iron Age

    Why did it take so long to get from the Bronze Age to the Iron Age?

    The explanation must be sought in the furnaces that were available at that time. The temperatures reached were not enough to melt iron.

    Iron was much harder than bronze. The secret was that it had to be worked very hot.

    What are the benefits of iron over bronze?

    • The first is the abundance of iron ore in the earth’s crust compared to the shortage of copper and tin ores.
    • It is much more tenacious than bronze, so it surpassed it in many applications.

7.2 Metals

Metals are chemical elements in the crust. Most of them undergo oxidation processes, while others remain unchanged. All metals are good conductors of heat and electricity.

A. Properties of Metals

The mechanical properties of metals are:

  • Firmness
  • Elasticity
  • Toughness
  • Malleability
  • Ductility
  • Mechanical strength

B. Classification of Metals

The simplest classification of metals is to separate them into:

  • Ferrous metals are those containing iron. Products made from iron are called iron and steel products.
  • Non-ferrous metals are those that do not contain iron. In turn, these are divided according to their density:
    • Heavy metals: copper
    • Light metals: aluminum or titanium
    • Ultralight metals: magnesium

C. Use of Metals

  • Ferrous Metals:
    • Steel: Used as a building material for all types of structures, machines, and mechanisms.
    • Foundries: It is possible to obtain complex geometric parts.
  • Non-ferrous Metals:
    • Copper: Used mainly for the manufacture of electrical conductors or pieces that have to behave as such.
    • Bronze: Among its various uses, we highlight its use in jewelry items.
    • Brass: An application of hardware, jewelry, etc.
    • Tin: Used for soldering.
    • Zinc: Used in covert buildings to make pipes, etc.
    • Aluminum: Used from the manufacture of doors and windows to high-strength structures.

7.3 Polymers

There are organic compounds of high molecular weight, called macromolecules. In addition, a number of substances such as plastics, rubbers, etc., are large molecules called polymers, which are obtained from simple molecules repeated thousands of times.

The introduction of polymers in our society has undoubtedly been an important step in our standard of living since a large number of everyday objects are made of this type of chemical, and many are irreplaceable in today’s technological world.

B. Classification of Polymers

The most natural classification gives us three types:

  • Natural polymers: They come directly from plants or animals. E.g., wool.
  • Artificial polymers: Changes are the result of chemical processes of certain natural polymers. E.g., nitrocellulose.
  • Synthetic polymers: They are obtained by controlled polymerization processes by man. E.g., melamine.