Ablation (physics)

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In physics, ablation refers to the removal of material through heating, for example through a laser or through atmospheric friction .

Applications

physics

With laser ablation , the surface of a body to be examined is heated so much by a laser that a plasma is created. The method can be used to process materials, to create thin layers ( pulsed laser deposition ) and to analyze materials.

Space travel

In space travel , the ablation of parts of the heat protection system is used when a spaceship re- enters the atmosphere . The main mechanism of this heat protection consists in the insulating effect of the cooler boundary layer created by pyrolysis compared to the plasma created by adiabatic compression. The amounts of heat consumed by sublimation and endogenous heat of reaction make a comparatively small contribution to heat protection. Ablative heat protection was or is used in the landing capsules of the Apollo and Soyuz spaceships. See also: Ablative heat shield .

Fire protection

Ablative substances are regularly used in preventive structural fire protection. As a rule, it is necessary to delay the transfer of heat. In the case of endothermic substances, as well as intumescent substances, chemically bound water represents the thermal brake, because water is known to have a boiling point of 100 ° C. The heat energy that has to be used to separate the water is withdrawn from the fire. As soon as the water is used up, the temperature of the side facing away from the fire rises. According to DIN 4102-2, the temperature increase on the side of a component facing away from the fire, such as a fire wall , must not be more than 140 K above the starting temperature on average ; it must not exceed 180 K at any measuring point. The period of time that elapses until a critical temperature increase is reached has a major influence on the fire resistance of a component that is clad with an ablative material.

Other ablative fire protection materials also contain foamed silicones which, however, do not contain hydrates, but rather contribute to the fire load and are therefore used in Germany , e.g. B. as sealing material, have not obtained approval from the German Institute for Building Technology . In cases of ablative materials that do not contain cooling hydrates, the ablative fire protection effect consists of the period of time until the material is used up by the action of fire. The latter is uncommon in Germany and is mainly, but not exclusively, used in the nuclear power plant area of North America, where there is no requirement for approval for passive fire protection, as is generally customary in the normal construction sector.

Individual evidence

  1. ↑ Basics of laser-material interaction (accessed on April 2, 2020)

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