Degassing is the removal of dissolved gases from liquids, solids, or surfaces. This procedure is applied across various scientific and industrial fields to achieve specific material properties or environmental conditions. It focuses on extracting gases present within a substance rather than on its exterior.
The Science Behind Degassing
The ability of a gas to dissolve in a liquid is influenced by temperature and pressure. Liquids hold less dissolved gas at higher temperatures and lower pressures, encouraging gases to escape.
Gases exist in equilibrium between the liquid and the space above it. When conditions change, this equilibrium shifts, prompting gas to move out of the liquid phase. For instance, reducing external pressure causes dissolved gas molecules to expand and form bubbles, which then rise to the surface and release the gas. Conversely, raising temperature provides energy to gas molecules, allowing them to overcome forces holding them in solution and escape.
Where Degassing Matters
Degassing occurs in many everyday situations and is employed in diverse industrial applications. A common example is a carbonated beverage going “flat” when left open, as dissolved carbon dioxide escapes. In manufacturing, new products, especially from plastics or composites, can release residual gases over time in a process known as “outgassing.”
Industrially, degassing prevents defects in materials like plastics, metals, and glass. During semiconductor production, for instance, dissolved gases can create imperfections that compromise device performance. In vacuum systems, such as those used in scientific research or space simulation, removing gases from surfaces and materials is necessary to achieve and maintain a high vacuum. Degassing is also used in water treatment to remove gases like methane and hydrogen sulfide, which can impart unpleasant tastes or odors to drinking water.
Techniques for Degassing
Several methods remove dissolved gases from substances. Heating a liquid reduces gas solubility, causing them to escape. For example, boiling water effectively removes dissolved oxygen and carbon dioxide. Vacuum application is another common technique, where reducing pressure above a liquid forces dissolved gases to come out of solution and bubble away.
Mechanical agitation, such as stirring or shaking, can physically dislodge dissolved gas molecules, helping them form bubbles and escape. Ultrasonication, which uses high-frequency sound waves, creates microscopic bubbles that rapidly expand and collapse, effectively forcing dissolved gases out of the liquid. Inert gas sparging involves bubbling an inert gas, like nitrogen or argon, through a liquid to displace and carry away dissolved gases.
Consequences of Degassing
The outcomes of degassing can be both beneficial and, in some contexts, undesirable. In manufacturing, intentional degassing produces clear resins, glass, and other materials free from bubbles, which can impair their strength or appearance. It also improves the performance and longevity of vacuum systems by reducing gas molecules that could interfere with operations.
However, degassing can have negative effects, such as flavor loss in carbonated beverages as carbon dioxide escapes. In sensitive environments, outgassing from materials can contaminate surrounding equipment or processes. For example, in space applications, materials that outgas can deposit films on optics or delicate instruments. Controlling or monitoring degassing is important to ensure product quality and system integrity.