N,N-Diethylhydroxylamine (DEHA) is a chemical marvel, lauded for its dual capabilities as a potent oxygen scavenger and a highly effective polymerization inhibitor. These functionalities are rooted in its molecular structure and its ability to interact with reactive species, particularly free radicals and dissolved oxygen. Understanding the underlying mechanisms provides insight into why DEHA is a preferred choice in demanding industrial applications.

At its core, DEHA functions as a radical scavenger due to the presence of the hydroxylamine group (-N(C2H5)2OH). This group can readily donate a hydrogen atom to neutralize highly reactive free radicals. In polymerization processes, free radicals are the species that propagate the polymer chain. By scavenging these radicals, DEHA effectively terminates the chain growth, thus acting as a 'short-stopper' and preventing unwanted or excessive polymerization. This controlled inhibition is vital for maintaining product quality and process safety, especially with reactive monomers like olefins, styrene, and butadiene.

The mechanism for DEHA's action as an oxygen scavenger is also based on its reducing properties. Dissolved oxygen in water systems, particularly in boilers, acts as an oxidizer and drives the corrosion process. DEHA acts as a reducing agent, reacting with dissolved oxygen and converting it into less harmful substances. The reaction stoichiometry, often cited as 2.8 moles of DEHA reacting with 1 mole of O2, highlights its efficiency. This process effectively removes oxygen from the water, thereby preventing the electrochemical reactions that lead to metal corrosion and pitting. The resulting products of this reaction are generally considered non-corrosive and can even contribute to the passivation of metal surfaces.

A significant aspect of DEHA's efficacy as an oxygen scavenger in boiler systems is its volatility. Unlike non-volatile scavengers, DEHA can vaporize along with the steam. This allows it to travel throughout the entire steam circuit, including condensate return lines, providing protection against corrosion in areas that might not be directly reached by liquid-phase treatments. This steam-borne distribution ensures comprehensive system protection, a critical advantage in complex industrial setups. Moreover, DEHA contributes to metal passivation by forming a protective magnetite layer on ferrous surfaces, which further inhibits corrosion.

The breakdown products of DEHA also contribute to its overall effectiveness. When subjected to the high temperatures and pressures within a boiler, DEHA can degrade into volatile neutralizing amines, such as diethylamine and ethylmethylamine. These amines serve the dual purpose of elevating the pH of the condensate, making it less corrosive, and acting as additional oxygen scavengers or passivating agents. This multi-pronged approach ensures robust protection for the entire boiler system, from feedwater intake to steam condensate return.

In summary, the efficacy of DEHA as both a polymerization inhibitor and an oxygen scavenger is a direct result of its chemical structure and reactivity. Its ability to neutralize free radicals and reduce dissolved oxygen, coupled with its advantageous physical properties like volatility and breakdown into beneficial amines, makes it an indispensable chemical for critical industrial operations. Professionals in water treatment and polymer manufacturing rely on DEHA for its performance, safety, and comprehensive system protection capabilities.