The material that composes most weapons is metal. Both guns and knives and other bladed instruments are almost always composed of metal. So what is a metal and what makes it so useful for the creation of weapons?
Metal
The physical properties of metals include shininess, malleability, ductility, and conductivity. A malleable (mal ee uh bul) material is one that can be hammered or rolled into flat sheets and other shapes. A ductile material is one that can be pulled out, or drawn, into a long wire. For example, copper can be made into thin sheets and wire because it is both malleable and ductile.
Metallic Bonding
mraaachemclass (YouTube)
Metals can therefore be shaped into almost any form needed. But metals are also hard which means once formed into a shape by smelting (liquefying using heat) or beating, the shape is maintained. The properties of malleability and ductility comes from the ability of the atoms in the metal to roll over each other into new positions without breaking the metallic bonds that hold them together. If a small stress is put onto the metal, the layers of atoms will start to roll over each other. If the stress is released again, they will fall back to their original positions:
If you beat the metal harder, the layers remain in their new orientation:
This property of metallic structure comes from their atomic structure:
Metal atoms are arranged around each other into what is called a cubic cell (shown above). The nuclei (represented as spheres) are arranged into fixed orientations while the electrons are free to flow around them. This gives metals their ability to conduct heat and electricity well. There are three main types of packing in the transition metals: Face-Centred Cubic (FCC), Body-Centred Cubic (BCC) and Hexagonal Close Packed (HCP).
Smelting or physically beating a metal causes the metal to become stronger. This is because of the Metallic Microstructure. The atoms in a metallic solid are arranged in close packed crystalline arrangements as shown above. However, during solidification of a molten metal or recovery from a stressor like beating different regions are forced to crystallize at the same time. This gives rise to various "grains". Grains are regions of irregular structure that exist in the overall crystalline structure of the metal.
Grains of Metal
Grains can be large or small depending on the process by which they were formed. Grain size can be controlled by the time in which the metal is allowed to cool. The faster the cooling process the smaller the grains that form and the harder the metal becomes. This hardness comes about because the metal atoms are no longer aligned so that they can easily slide across each other, the areas of irregular patterning prevent it. So the smaller the grains the less malleable (stronger) the metal becomes.
Properties and Grain Structure
moodlemech (YouTube)
Early man discovered the process of "working" metal to form weapons as far back as 7000 BC. The Age of Copper is defined as such because we note that Neanderthals at the time were hammering copper into crude knives and farming instruments. Immediately following the Age of Copper(Cu) is the Bronze Age (2800 BC). Bronze is an alloy of two metals: Copper (Cu) and Tin (Sn). When these two metals are combined they create a stronger metal: Bronze. The discovery that they made a harder metal was probably just a fortuitous accident but ushered in a higher level of industry in early civilizations. Smelting of copper and later bronze started around 3000 BC.
The next metal to come into use was Iron (Fe). The Iron Age (1500 BC) started once the ability to smelt the metal (which has a much higher melting point: 2,800°F (1,538°C)) became available. The use of iron (Fe) is maintained in weaponry until about 1100 BC when the discovery of Steel came about again probably by accident.
If iron (Fe) is reheated in a furnace with charcoal (containing carbon), some of the carbon is transferred to the iron. This process hardens the metal; and the effect is considerably greater if the hot metal is rapidly reduced in temperature, usually achieved by quenching it in water. The new material is steel. It can be worked (or 'wrought') just like softer iron, and it will keep a finer edge, capable of being honed to sharpness. Steel is still the most common metal alloy used in weapons today.
STEEL: From Start to Finish
Alliance for American Manufacturing (YouTube)
Wood
The Chemistry of Wood
Dan Ridley-Ellis (Vimeo)
Another common material used to make weapons is wood. Wood is a mixture of compounds: cellulose, hemicelluloses, lignin, and extractives. Wood comes from plants and trees. The cellulose in wood makes it strong and resistant to breakage, the lignin in wood makes it resistant to compression.
Cellulose Structure
Lignin Structure
The components of wood are generally what we call polymers. Polymers are long chains of interlinked molecules. It is the polymeric structure that gives wood most of its properties.
Wood when used for a weapon is generally shaped into a club or bat and sometimes mixed with metals to make it more lethal. Some of the typical "wooded" weapons are shown below:
The advantage of a wooden weapon is that it is incredibly strong compared to its weight. The average density of wood is between 0.50 and 1 gram/cm3 while metals are 1.5 to 16 gram/cm3. Carrying a wooden weapon is therefore much easier than a metal one.
The Ligature
A ligature is a piece of rope or wire that is used to suffocate the victim. Therefore a ligature is made of either metal or fibers that in a lot of ways resemble wood. Rope is made of cellulose as well and therefore has a similar polymer composition as wood.