In nitric acid production, what are the substances that are harmful to platinum mesh?
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What are the substances harmful to platinum mesh during nitric acid production? How to prevent it?
Rust, dust, CO, phosphides, acetylene, water vapor, and the like can all have an adverse effect on the lifespan and activity of platinum meshes.
Sulfides and organic substances are also harmful.
Question for the lazy polymerization experts: What are the specific organic substances? Are all organic substances harmful to it?
Dust (various metal oxides), iron particles in ammonia, lubricating oils in gases, H2S, C2H2, PH3, and water vapor can cause temporary poisoning of the platinum mesh.
Water vapor can cause temporary poisoning of the platinum mesh; whether the other substances cause permanent poisoning is unknown.
(1) Phosphine, PH3, is a highly toxic substance that causes permanent poisoning of platinum. When the concentration of PH3 in the gas is 0.00002%, the ammonia oxidation rate drops to 80%; at a concentration of 0.02%, it drops to 3.9%. Phosphine has a strong corrosive effect on platinum, reacting with it to form compounds such as PtP2, Pt2P, and Pt3P5, thereby rendering the platinum completely inactive. (2) H2S is similar to PH3. (3) Flammable compounds such as acetylene C2H2 can cause temporary poisoning of platinum; the carbon formed during combustion deposits on the surface of the platinum through vapor deposition, thereby reducing its activity. (4) Halogen elements can all react with platinum in an ammonia-oxidizing environment to form yellow-green substances. (5) Metal and non-metal impurities such as Fe, Ca, Mg, Al, Si, As, etc. form low-temperature eutectics with platinum, causing the melting of platinum. (6) The surrounding environment is harsh; sand, coal ash, cement dust, etc., cover the platinum mesh, reducing its activity.