Importance of Systematic Classification
The systematic classification of materials allows material scientists to better understand the properties and characteristics of materials. Basic classifications include solids, liquids, and gases.
Factors used for classification:
- Chemical composition
- Mode of occurrence in nature
- Refining and manufacturing processes required before economic importance
- Internal structure (atomic and crystalline arrangements)
- Industrial applications
Significant Classification Systems
1. Metals and Non-metals Classification
- Provides better understanding of distinct properties, including chemical reactivity
- Allows effective utilisation based on characteristic properties
- Important for identifying potential hazards through grouping similar materials
2. Chemical Composition
- Helps in understanding different behaviours and characteristics of materials
3. Mechanical Properties
- Classification based on strength, stiffness, toughness, hardness, and ductility
Fundamental Material Types
Elements
- Chemically simple substances made up of atoms of the same kind
Compounds
- Formed when two or more elements chemically combine in fixed proportions by weight
Mixtures
- Formed when two or more pure substances (elements or compounds) are mechanically mixed together in any proportion
Distinction Between Metals and Non-metals
Metals
- Solid at room temperature
- Malleable and ductile
- Good thermal and electrical conductors
- Can form alloys with other metals
Non-metals
- Can exist as solids, liquids, or gases
- Often brittle and dull in solid form
- Usually poor conductors (insulators)
- Cannot form alloys but can chemically combine to make compounds
Key Metal-Related Terms
Alloy
- A substance combining more than one metal or mixing a metal with non-metallic elements
- Example: Brass (combination of copper and zinc)
Clad Metal
- A composite of materials bonded by two or more metals together
- Creates a layered structure where each metal contributes specific properties
- Used to improve corrosion resistance and enhance conductivity
- Example: Coins covered by nickel or copper
Coated Metal
- Designed to protect the surface from rust, corrosion, dirt, and debris
- Example: Galvanized steel, where small scratches self-repair due to the coating
Non-ferrous Metals
- Metals that do not contain significant amounts of iron
- Not magnetic
- Examples: Copper, aluminum, lead, and zinc
Sintered Metals
- Created through the process of “sintering”
- Powdered metals are compacted and heated below their melting point
- Process fuses materials to form a solid mass with desired properties
- Examples: Steel gears and bearings used in automotive applications
Organic vs. Biological Materials
Organic Materials
- Usually derived mainly from carbon
- Examples: Crude oil, natural gas, coal, wood, and rubber
Biological Materials
- Derived from or produced by biological organisms (plants and animals)
- Examples: Bone from animals, wood from plants
Classification of Natural vs. Manufactured Materials
Naturally Occurring Materials:
- Coal
- Native copper
- Timber
- Natural rubber
- Dimension stone
- Limestone
- Diatomaceous earth
Justification: All these materials can be found naturally on Earth and are not manufactured in factories
Manufactured Materials:
- Polythene
- Mild steel
- Bone leather
Justification: These materials are manufactured within factories or have been modified through human-made processes
Inorganic Materials
Inorganic materials are materials that have no trace of carbon (examples include gases such as oxygen, nitrogen, or silicon)
Important Groups of Inorganic Materials:
- Ionic compounds
- Molecular materials
These two groups form the basis of many substances found in nature.
Effects of Tanning on Animal Hide
Tanning transforms animal hide from a perishable material into durable leather by:
- Chemically altering the collagen fibers in the skin
- Making it resistant to decay
- Increasing pliability
- Example application: Furniture production (involves removing hair from and cleaning the hide)
Rock Types and Formation
Igneous Rocks
- Formation: Formed from melted rocks that have cooled and solidified (magma or lava)
- Characteristics:
- Do not include fossil deposits
- Include multiple mineral deposits
- Can be either glassy or coarse in texture
- Usually do not react with acids
- Mineral deposits may appear in patches of various sizes
Sedimentary Rocks
- Formation: Formed from accumulation and lithification of smaller particles (“sediments”) such as sand, silt, and organic materials that settle out of water or air, or from precipitation of minerals from water
- Characteristics:
- May contain fossils of plants and animals
- Made up of distinguishable layers, with color determined by layer contents
- Can be chemical, organic, or inorganic in nature
- Can contain oil, natural gas, coal, phosphates, salt deposits, groundwater, and other natural resources
- Layers reflect conditions present when sediment was deposited
Metamorphic Rocks
- Rocks transformed from their original state (igneous or sedimentary) due to intense heat and pressure deep within Earth’s crust
- Often termed “secondary rocks” because they form from pre-existing rocks that underwent metamorphism
Special Material Types
Pozzolanic Materials
- Solid waste materials that react with calcium hydroxide to create compounds with cementitious properties
- Can be either natural or artificial
Ceramic Materials
Essential features include:
- Hardness: Resistant to scratching and rubbing
- Brittleness: Can easily break when impacted suddenly
- Chemical stability: Resistant to chemical reactions with other materials, useful for storing and transporting corrosive substances
Metals in Nature
Gold and silver often occur in their free states in nature, while iron must be extracted from its ores. This is because:
- Gold and silver are significantly less reactive compared to iron
- They are classified as “noble metals” due to their low chemical reactivity
- They are more resistant to corrosion and oxidation compared to iron
Critical Comparison: Stone/Coal vs. Metals
The statement “Some inorganic materials like stone and coal are stronger than most metals” is incorrect because:
- Stone and coal are far weaker compared to metals
- They lack tensile strength, ductility, and toughness
- Stone is strong under compression but brittle and inflexible
- Coal is impractical for structural applications
Advantages of metals:
- More malleable and tough
- Greater ductility
- Can be welded or forged into many shapes
- Can absorb impacts without breaking
- Many metals (e.g., stainless steel) resist corrosion and environmental damage