What is the reason for oil production at the end of rust treatment with hydrochloric acid?
Thread Content
I use hydrochloric acid to treat rust for experiments. After the treatment, oil appears after some time – what is the reason for this? Can the amount of oil produced be used to determine the quality of the hydrochloric acid? I hope experts can provide a detailed explanation. Thank you :handshake
This post was last edited by Wang Genrong on 2018-10-22 at 08:46. Theoretically, when rust is mixed with hydrochloric acid, only iron chloride is formed; at the same time, elemental iron reacts with hydrochloric acid to produce ferrous chloride, and no oily substance is generated. Reaction phenomena: Rust disappears, the solution turns yellow, and bubbles may form. If there is enough rust and enough time, the color of the solution will gradually darken from yellow-green to dark green to ink-green. Reaction processes: Fe2O3 + 6HCl == 2FeCl3 + 3H2O; Fe + 2HCl == FeCl2 + H2. Possible reasons for the formation of an oily substance: The iron product was coated with oil to prevent rusting before or during the rusting process, or the rust was contaminated by oil.
From personal experience, on templates, samples, tubes, etc., oil and grease were originally attached to them; the presence of these substances was not noticeable once rust formed a layer over them. However, after heating them and wiping them thoroughly with a tissue or cotton cloth, the oil and grease did appear again. This problem is often encountered during chemical cleaning processes. Solution 1) Heat ； 2) Wipe after pre-polishing.