I am a little confused by a catalytic reaction

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SUMMARY

The discussion centers on the use of Sodium Hydroxide (NaOH) to remove aluminum from steel sputtering masks. Participants clarify that NaOH is not a catalyst but rather a chemical agent that dissolves aluminum, leading to the formation of aluminum hydroxide. The reaction slows down as the solution becomes saturated with aluminum hydroxide, which consumes hydroxide ions (OH^-), diminishing the effectiveness of NaOH. The conversation highlights the complexity of the reaction and the importance of understanding the chemical processes involved.

PREREQUISITES
  • Understanding of basic chemistry concepts, particularly acid-base reactions.
  • Familiarity with the chemical properties of Sodium Hydroxide (NaOH).
  • Knowledge of aluminum chemistry and its reactions with hydroxides.
  • Basic understanding of reaction kinetics and saturation effects in solutions.
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  • Research the chemical properties and reactions of Sodium Hydroxide (NaOH) in various contexts.
  • Explore the formation and behavior of aluminum hydroxide (Al(OH)3) in alkaline solutions.
  • Investigate alternative materials for sputtering masks that are less reactive with NaOH.
  • Study the principles of reaction kinetics to understand how saturation affects reaction rates.
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Chemists, materials scientists, and professionals involved in metal processing or surface treatment who seek to optimize the removal of aluminum from steel substrates.

fly_boy_bc
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When Sodium hyroxide is used to remove aluminum from a steel sputtering mask the reaction is energetic at first but after a while the solution gets dirty and the reaction slows down until we need to replace it. As I understand it the caustic soda is a catalyst in this reaction and is not consumed or changed by it. So why does it lose effectiveness? Is it "poisoned" by the steel? Is there another material I could use for the mask that would not poison the Lye? (I am amused by the fact that it has so many names).

Or is the water too saturated with aluminum?

Gary
 
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NaOH is not a catalyst, it is chemically dissolving Al.
 
Well! That would explain THAT then wouldn't it? Hmmmm I guess I figured it was a catalytic reaction just because using it as an electrolyte to separate water is catalytic. Dumb guy thank chemistry ppl for help! ugh!
 
fly_boy_bc said:
Well! That would explain THAT then wouldn't it? Hmmmm I guess I figured it was a catalytic reaction just because using it as an electrolyte to separate water is catalytic. Dumb guy thank chemistry ppl for help! ugh!
The reaction is not so simple as it seems. With little amounts of Al hydroxide dispersed in the solution and little concentrations of OH^-, I'd say that OH^- acts a bit as a catalyst:

2Al\ +\ 6H_2O\ -(basic\ solution)\rightarrow 2Al(OH)_3\ +\ 3H_2\uparrow

But if the concentration of OH^- is enough and there is enough hydroxide dispersed, OH^- reacts with the aluminum hydroxide:

Al(OH)_3\ +\ OH^-\ \rightarrow Al(OH)_4^-

and so the base is consumed.
 

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