The chemical properties that matter most here are corrosion resistance, flammability, and hygroscopy. Designers assess each property against the product’s operating environment, safety requirements, expected lifespan, and maintenance needs.
How Each Property Affects Selection
| Chemical property | Meaning and material-selection significance | Example |
|---|---|---|
| Corrosion resistance | The ability to resist deterioration caused by chemical or electrochemical reactions with the environment. High resistance is important when a product encounters water, salts, acids, or atmospheric oxygen. | Stainless steel may be selected for outdoor equipment because its protective oxide layer limits further corrosion. |
| Flammability | The tendency of a material to ignite and sustain combustion. Designers must also consider ignition, flame spread, heat release, smoke, and toxic combustion products. | A flame-retardant polymer may be selected for an electrical enclosure to reduce fire risk. |
| Hygroscopy | The tendency of a material to absorb water vapour from the surrounding air. Moisture uptake may change mass, dimensions, strength, surface quality, or electrical insulation. | Low-hygroscopic materials are preferable for dimensionally precise components used in humid environments. |
These properties matter because chemical interaction can change a material during the product’s life cycle. For example, corrosion can reduce the cross-sectional area and strength of a metal component, while moisture absorption may cause wood to swell or warp.
A designer can sometimes improve performance through coatings, sealants, flame retardants, or protective finishes. However, these treatments introduce additional cost, manufacturing processes, maintenance requirements, and possible environmental impacts.
A common misconception is that hygroscopy means the same as waterproofness. Hygroscopy specifically concerns absorbing moisture from the air; water resistance concerns preventing liquid water from penetrating or damaging the material.
IB Exam Technique
For an A3.1 material-selection question, do not merely name a property. Explain how the service environment interacts with the material, state the resulting performance or safety consequence, and justify why the selected material is appropriate. Avoid confusing corrosion with mechanical wear, because corrosion involves chemical or electrochemical deterioration.