Removing Rust From Tools

  I had a pair of vernier calipers that had some annoying rust spots it and decided to look into ways of removing them Sunday evening. One can clean silver by using a tarnish remover but that is essentially a method of polishing the silver. Wikipedia indicated that electrolysis can be used to remove rust so I decided to try this method. There are a number of YouTube videos that show the process in action.

  When two electrodes are placed in water the voltage difference between them produces chemical changes in the water. Dissolving a salt, such as washing soda, in the water results in some of it being broken up into its positive and negative ions increasing the conductivity of the water. The positive electrode is at a higher electrical potential and is known as the anode while the negative electrode is at a lower potential and is known as the cathode. Negative ions are attracted to the positive anode and are therefore known as anions. Similarly, positive ions are attracted to negative cathode and are known as cations. A water solution has H ⁺ and OH ⁻ ions in equilibrium with the water present so the positive hydrogen ions are attracted to the negative electrode and the negative hydroxide ions are attracted to the positive electrode where they are respectively released as hydrogen and oxygen bubbles.

  The negative electrode is attached to the tool from which the rust is to be removed. The hydrogen ions attracted to this cathode combine with the oxygen in the rust to produce iron which stays on the tool and hydroxide ions which go into solution. Chemically this is a reduction reaction. At the positive electrode oxygen is combined with a sacrificial piece of steel, producing rust in the process, via an oxidation reaction.

  I used supplies from my kitchen to clean the vernier calipers. I placed some water in a casserole dish and the calipers and a used joist bracket as by piece of sacrificial metal. Instead of washing soda I added baking soda to the water which worked fairly well. Technically the resulting hydroxides of iron in the waste water should probably be neutralized before disposal. A variable Radio Shack dc power supply was connected to the electrodes and the current was set to half and amp.

  Two and an half hours later I removed the calipers and rinsed them off. The surface was somewhat lackluster so I used some steel wool to polish them after disassembly. Then I oiled them with cooking spray to prevent rust before reassembly. I felt the cooking spray would be less volatile than WD40 and its nonstick properties would allow the parts to slide easier. The cooking spray has a greasy/waxy feel to it which is probably due to the lecithin in it.

  The method used to refurbish the calipers was probably not the optimal method. It would probably take some testing to arrive at the best way of doing this. One could compare different oils to see which prevents rust from reforming the best. The Wikipedia article indicates that lecithin is an antioxidant. An electrochemical method known as cathodic protection is used to prevent corrosion. Just placing tools on an aluminium, zinc or magnesium foil might also provide some protection against rust formation.