T.O. 33B-1-12-53Figure 2-18. Diffusion of Emulsifier into Penetrant during the Lipophilic Emulsifier Dwell.2.5.5.3.1.1The physical action of the penetrant/emulsifier mixture draining from a part removes some of the excess penetrant.The remainder of the surface penetrant is removed as the penetrant/emulsifier mixes with water during the spray rinseand drains away. Generally oil and water do not mix, that is, they are immiscible. However, this is not always thecase. If equal amounts of oil and water are placed in a bottle, they will immediately separate into two distinct layers. Ifthe bottle is shaken, the oil will form into globules, which are dispersed throughout the mixture. When the bottle isallowed to rest, the globules will rise to the surface and reform into a separate oil layer. The process of the globulescombining to form this layer is called coalescence. If the amount of oil is small compared to the quantity of water, andthe bottle is violently shaken, the oil will be broken into very small droplets. On standing, most of the droplets willcoalesce at a slower rate than previously described. However, some of the very small droplets will remain suspended inthe water giving it a cloudy or milky appearance. Depending on the droplet size, it may require an extremely long timefor separation to take place. This cloudy water mixture is called a colloidal suspension and the process by which it isformed is termed emulsification. Certain chemicals have the ability to combine with oily materials to form an easilyemulsifiable mixture. This is the case when an emulsifier is applied to a penetrant on a part. The penetrant is oil thatrepels water and resists removal. However, when combined with an emulsifier, the resulting colloidal mixture can beremoved with a water spray.
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