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Water vapor is the gaseous phase of water, produced through evaporation or boiling of liquid water or sublimation of ice. It's transparent and less dense than most other atmospheric constituents. Unlike steam, water vapor specifically refers to water molecules dispersed in air at ambient temperatures rather than through boiling.

Water vapor plays several important roles in chemical processing:

1. Surface Passivation: Water vapor reacts with metal surfaces (like aluminum) to create protective oxide films, forming a bilayer structure of hydroxide and oxide that prevents further corrosion.

• Adsorption Applications: In thermal conversion systems, water vapor adsorption on porous materials like metal-organic frameworks (MOFs) is used for heating, cooling, and energy storage applications.

• Chemical Vapor Deposition (CVD): Water vapor can significantly influence thin film growth in CVD processes. In nickel and cobalt film deposition, controlled amounts of water vapor can improve metallic film growth and reduce carbon contamination, though excessive amounts lead to oxidation.

• Pyrolysis Modification: In coal carbonization, water vapor affects the physicochemical properties of semicoke, influencing pore structure, surface functional groups, and combustion performance.

• Separation Processes: Specialized gas separating membranes can selectively remove water vapor from mixed gases like natural gas, air, and fermentation gases.

Water vapor is also environmentally significant as the most prevalent greenhouse gas, causing roughly half of the planet's warming by trapping heat radiated from Earth's surface.

Perplexity A.I. Deepsearch assisted description, 31^st Mar 2025.