Ablative material

Ablative materials in design and construction, are materials that are generally resistant to high temperatures and used for thermal protection, such as an ablative batt. Ablation itself means the removal or destruction of something, normally the upper layer by chipping, erosion, decomposition or vaporisation, and so might be referred to as a sacrificial layer.

There are in effect three types of ablative materials, which relate to the way the react to heat;

[edit] Subliming ablators

Subliming ablators, act as heat sinks until the surface reaches sublimation or melting point (thus also referred to as - subliming / melting ablators), thus removing the heat from the protected object. In some cases a layer of gas is formed which helps remove heat from the object, in other cases an endothermic reaction occurs increasing the material temperature whilst decreasing the surrounding temperature, sacrificially. In doing this ablative materials may pyrolyse mitigating a heat load, so in effect they decompose or change as a result of the heat being applied. These types of materials are often carbon related composites such as Teflon.

[edit] Charring ablators

Charring ablators, partially burn and blacken, creating a greater surface thermal resistance. For example in a char rating, which measures the depth of char of a timber being burnt, divided by the time period for this to occur, where a lower char rate indicates a slower rate of burn. Charring ablation describes where the surface chemical reaction (decomposition at high temperature) gradually consumes the char layer of the material, so is completely decomposed.

[edit] Intumescent ablators

Intumescent ablators, swell as a result of heat exposure, which leads to an increase in the volume and decrease in density. Intumescence refers to the process of swelling and the most common examples in construction are known as Intumescence strips, used in fire proofing.

[edit] Related articles on Designing Buildings

• Ablative batt.
• Batt.
• BS 476.
• Cavity barrier.
• Compartment floor.
• Compartment wall.
• Fire resistance.
• Fire separation.
• Fire.
• Fire-separating element.
• Fire-stopping.
• Pyrolysis
• Sacrificial timber.

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