Wood and Metals: Properties, Types, and Applications

Posted on Apr 4, 2025 in Technology

Wood: A Natural Vegetable Material

Composition and Structure

Wood is a raw vegetable material obtained from the trunks and branches of trees. It is primarily composed of cellulose fibres (providing flexibility) and lignin (which makes it rigid and hard).

Technical Characteristics of Wood

  • Density: Wood is generally a light material compared to metals or stone.
  • Hardness: Resistance to scratching or indentation; varies greatly between wood types.
  • Toughness: Ability to absorb shock or impact without breaking.
  • Thermal and Electric Insulation: Wood is a good insulator against heat and electricity.
  • Mechanical Resistance: Wood possesses good resistance to forces like traction (pulling) and compression (pushing), although this varies with grain direction and wood type.
  • Aesthetic Characteristics: Wood is often pleasing to the senses due to its natural smell, varied colors, and textures (softness/smoothness).

How Wood is Obtained

  1. Cutting / Felling: Harvesting the tree.
  2. Removing Branches (Delimbing): Stripping branches from the trunk.
  3. Transporting: Moving logs from the forest.
  4. Removing the Bark (Debarking): Taking off the outer layer.
  5. Sawing: Cutting logs into lumber (boards, planks).
  6. Drying (Seasoning): Reducing the moisture content to prevent warping or decay.
  7. Planing: Smoothing the surfaces of the lumber.

Types of Wood

Hardwoods

  • Come from deciduous trees (trees that lose their leaves seasonally).
  • These trees generally grow slowly.
  • Wood can be found in many different colors.
  • These types of wood are typically very strong, hard, and resistant.
  • Often more difficult to work with than softwoods.

Softwoods

  • Come from evergreen trees, especially conifers (cone-bearing trees).
  • These trees generally grow quickly.
  • This wood is usually light-colored.
  • These types of wood are typically lighter in weight and may be resinous.
  • Generally easier to work with than hardwoods.

Prefabricated Wood (Engineered Wood)

  • Made from wood fibers, chips, or veneers compressed and glued together.
  • Available in a wide variety of sizes and finishes.
  • Often treated to resist parasites.
  • Typically cheaper than solid natural woods.
  • Usually easy to work with.
Plywood

Thin sheets (veneers) of wood glued together and compressed. These wood layers are laid with their grain directions alternating (usually at 90 degrees) for strength. Plywood always has an odd number of layers.

Chipboard (Particleboard)

Made with wood chippings (particles) glued together and compressed under heat and pressure.

Wood Derivatives

Paper

Wood is pulped (mechanically or chemically ground) and mixed with water and chemical products to create cellulose paste. This paste is then processed, compressed, and rolled out by a machine until it becomes a sheet of paper.

Cardboard

It is made by compressing several layers of paper pulp or recycled paper while wet to thicken it and produce a heavier, more rigid texture.

Cork

Cork is obtained from the thick outer bark of the cork oak tree.

Other Vegetable Materials

Other plant-based materials used similarly to wood include:

  • Reeds
  • Wicker (often from willow or rattan)
  • Esparto (a type of grass)

Metals: Properties and Classification

Source and Extraction

Metals are typically extracted from minerals contained within rocks. Examples include:

  • Bauxite: Source of Aluminium
  • Siderite: Source of Iron
  • Malachite: Source of Copper

To obtain metals, we need to mine these minerals. The mined rock consists of:

  • Ore: The part of the mineral rich enough in the desired metal to be economically extracted.
  • Gangue: The unwanted rock and minerals mixed with the ore.

Alloys

Metallic materials are not usually used in their pure state because pure metals often lack desired properties (like sufficient hardness or strength). They are typically alloyed (mixed) with other metals or non-metals to enhance their characteristics.

  • Brass: Copper + Zinc
  • Bronze: Copper + Tin
  • Steel: Iron + Carbon (typically < 2%)

Common Properties of Metals

  • Hard: They resist scratching and piercing.
  • Strong: They resist deformation under force.
  • Tough: They resist breaking upon impact.
  • Malleable and Ductile: They can be hammered or rolled into thin sheets (malleable) or drawn into wires (ductile).
  • Good Conductors: They conduct heat, sound, and electricity efficiently.
  • State: They are solid at room temperature (except for Mercury).
  • Dense: They generally have high density and feel heavy for their size.
  • Lustrous: Metals typically have a characteristic shine when polished.

Classification of Metals

Ferrous Metals

Metals that contain iron as their main component.

  • Iron (Pure): Good magnetic properties but is relatively soft, brittle, and has poor mechanical properties for structural use.
  • Cast Iron: An alloy of Iron + Carbon (typically 2% – 6% Carbon). It is hard and resistant to compression but can be brittle.
  • Steel: An alloy of Iron + Carbon (typically 0.2% – 2% Carbon). It is very hard, tough, and strong. Steel is versatile and fairly inexpensive.
  • Steel Alloys: Steel mixed with other elements (e.g., chromium, nickel) to achieve specific properties (e.g., stainless steel).

Non-ferrous Metals

Metals that do not contain iron as a primary component.

  • Copper: Excellent conductor of heat and electricity, resistant to corrosion, ductile.
  • Aluminium: Very light, good conductor, resistant to corrosion, non-toxic.
  • Tin: Non-toxic, very easy to work with, resistant to corrosion (used in plating, pewter).
  • Zinc: Used for galvanizing steel (corrosion protection), alloys like brass.
  • Lead: Very heavy, soft, dense, toxic.
Other Non-ferrous Metals
  • Nickel: Used in alloys (like stainless steel), plating, coins.
  • Magnesium: Very light. Uses include pyrotechnics and aerospace components.
  • Titanium: Highly resistant to corrosion and rust, strong and light. Uses include medical prostheses and aerospace.