Which property of timber makes it resistant to corrosion and rust?
🧪 The Chemistry of Degradation: Corrosion vs. Decay
Corrosion and rust are specific terms for the electrochemical breakdown of metals. Rusting, for example, is the oxidation of iron or its alloys. This process requires a metal, oxygen, and an electrolyte (like water).
Timber, on the other hand, degrades through biological processes like fungal or insect attack, which we call decay or rot. The question asks what property prevents timber from suffering from the *metallic* form of degradation.
📝 Detailed Analysis of the Options
(a) High strength
While timber has good strength for its weight, this property has no bearing on its chemical reactivity or resistance to corrosion. A strong material can still corrode if it is metallic.
(b) High moisture absorption
This is a property of wood, but it is actually a disadvantage. Absorbing moisture makes timber susceptible to biological decay (rot), which is its primary form of degradation. It does not prevent corrosion.
(c) Low density
The low density of timber is an advantage for construction (good strength-to-weight ratio), but it is not the reason it resists corrosion. Many low-density metals are highly susceptible to corrosion.
(d) Non-metallic composition
This is the correct answer. The term "non-metallic composition" means that wood does not contain the metals that are susceptible to oxidation processes which cause rust and corrosion. Timber is an organic material, composed mainly of cellulose, hemicellulose, and lignin. Since it lacks the free electrons and metallic structure required for electrochemical corrosion to occur, it simply cannot rust or corrode in the way that steel or iron does.
📊 Degradation: Timber vs. Steel
| Property | Timber | Steel (Iron Alloy) |
|---|---|---|
| Composition | Organic, Non-metallic | Metallic |
| Primary Degradation | Biological Decay (Rot, Insects) | Electrochemical Corrosion (Rust) |
| Resistance to Rust | Immune (cannot rust) | Susceptible (requires protection) |
💡 Study Tips
- Corrosion = Metals Only: The most important concept is that rust and corrosion are processes that happen to metals. If a material isn't a metal, it can't corrode.
- Wood is Organic: Remember the basic composition of wood. It's a natural, organic polymer. This is fundamentally different from a metallic element or alloy.
- Decay, Not Corrosion: Be precise with terminology. Wood decays or rots. Steel corrodes or rusts. Knowing the correct term for each material's weakness is key.