# Materials
### 1. Basic Classification

The first thing to say: materials are usually split into two big families.

- **Metals** _(kovy)_ – usually strong, hard, good conductors of heat and electricity. Most can be melted and reshaped.
- **Non-metals** _(nekovy)_ – includes plastics, ceramics, glass, wood, rubber and composites. Usually lighter and often used as insulators.

### 2. Metals (Two main groups)

- **Ferrous metals** _(železné kovy)_ – contain **iron (Fe)**. Examples: **steel** (iron + carbon), **cast iron**, **stainless steel** (steel + chromium, doesn't rust).
    - Property: strong but heavy, and most of them **corrode / rust** when exposed to moisture.
- **Non-ferrous metals** _(neželezné kovy)_ – do not contain iron. Examples: **copper, aluminium, brass, bronze, gold, silver, zinc, tin**.
    - Property: usually lighter, don't rust, often better conductors.

- _IT connection:_ **Copper** is used for wires and PCB tracks because of excellent conductivity. **Gold** is used to plate connectors (CPU pins, RAM contacts) because it doesn't oxidise. **Aluminium** is used for heat sinks and laptop chassis because it's light and conducts heat well.

### 3. Non-metals

- **Plastics / Polymers:** Lightweight, cheap, easy to mould, good electrical insulators. Used for cable insulation, computer cases, keyboards.
    - **Thermoplastics** can be melted and reshaped many times (e.g. PVC, PET, ABS — ABS is the typical computer-case plastic).
    - **Thermosets** harden permanently and can't be remelted (e.g. epoxy resin used in PCBs).
- **Ceramics:** Hard, brittle, heat-resistant, electrical insulators. Used in CPU substrates, capacitors, and spark plugs.
- **Glass:** Transparent, brittle. Used in screens, optical fibres for fast internet.
- **Composites:** A combination of two or more materials (e.g. **carbon fibre** = carbon + resin, **fibreglass**). Very strong but light — used in cars, planes, drones.
- **Wood, rubber, leather:** Traditional natural materials, still common in furniture, tyres, etc.

### 4. Semiconductors (The "IT" connection)

This is your strongest area — definitely mention it.

- **Semiconductors:** Materials that conduct electricity better than insulators but worse than metals. Their conductivity can be controlled.
- **Silicon (Si):** The most important semiconductor — the base of every CPU, GPU, RAM chip and microchip. That's why Silicon Valley is called Silicon Valley.
- **Germanium** was used in older transistors; today **gallium arsenide (GaAs)** is used in high-frequency and optical devices like LEDs and solar panels.

### 5. Material Properties (Useful vocabulary)

If you need to extend your speaking time, describe properties:

- **Hardness** _(tvrdost)_ – resistance to scratching. Diamond is the hardest natural material.
- **Strength** _(pevnost)_ – how much force a material can take before breaking.
- **Toughness** _(houževnatost)_ – resistance to cracking under impact.
- **Elasticity** _(pružnost)_ – returns to original shape after stretching.
- **Plasticity** _(tvárnost)_ – can be permanently shaped without breaking.
- **Ductility** _(taživost)_ – can be drawn into a wire (typical for copper, gold).
- **Malleability** _(kujnost)_ – can be hammered into thin sheets.
- **Conductivity** _(vodivost)_ – conducts electricity or heat well.
- **Density** _(hustota)_ – mass per volume; lead is dense, aluminium is light.
- **Corrosion resistance** – doesn't react with oxygen/water (gold, stainless steel).
- **Melting point** – temperature at which a solid turns into liquid.

### 6. Manufacturing / Processing

Quick vocabulary in case the examiner asks how materials are worked.

- **Casting** _(odlévání)_ – pouring molten metal into a mould.
- **Forging** _(kování)_ – shaping by hammering.
- **Welding** _(svařování)_ – joining two metal parts by melting them together.
- **Machining** _(obrábění)_ – cutting, drilling, milling on a machine tool (CNC).
- **3D printing / Additive manufacturing** – building up a part layer by layer from plastic, resin or metal powder.
- **Injection moulding** – melted plastic is injected into a mould; how plastic parts (keyboard keys, phone cases) are mass-produced.

### 7. Recycling and Environment

Good closing topic — easy to fill time and link to other subjects (Environment).

- Metals like aluminium and copper are **100% recyclable** without losing quality. Recycling aluminium uses about **95% less energy** than producing it from ore.
- Plastics are sorted by codes (PET, HDPE, PVC, etc.) but many types are hard to recycle.
- **E-waste** _(elektroodpad)_ is a growing problem — old phones and laptops contain valuable metals (gold, copper, rare earths) but also toxic materials (lead, mercury).

**How to use this at the exam:**

This topic links easily to almost every technical theme. Start with the basic split (metals vs non-metals), then jump to your strong area: _"In my specialisation, the most important material is silicon, because..."_ From there you can talk about copper wires, aluminium heat sinks, ABS plastic cases — and finish with recycling and e-waste to connect it to the environment topic.