From: William 02/03/2000 22:58:00 Subject: Corrosion post id: 43419 I'm struggling to find simple answers for year 7 science on corrosion. Some of the answers I know but these others I can't find anything simple. What is rust? What is corrosion? Give an example of where rust can be beneficial. What is surface protection? What advantage does galvanised iron have over just iron? From: Di 02/03/2000 23:22:00 Subject: re: Corrosion post id: 43421 What is corrosion? Corrosion is the electrochemical deterioration of a metal. What is rust? Rust is what you get when iron corrodes. (air, water and iron is all you need) Give an example of where rust can be beneficial. Errrr creates jobs? What is surface protection? Protects the surface from water and oxygen, so it can't rust. Like, painting it or sticking another metal over the top. What advantage does galvanised iron have over just iron? Galvanised is where the iron is covered in a zinc layer that will be oxidised more easily than the iron will. Good luck! From: Alan™ 02/03/2000 23:29:00 Subject: re: Corrosion post id: 43422 Probably better to explain the first 2 in reverse order. When a material including plastic reacts with oxygen a process known as oxidation occurs. What happens is that some of the atoms in the material bond with oxygen. Corrosion is a more specific case of oxidation only involving metals. So that the metal atoms bond with oxygen. It can occur with any metal, ie aluminium, iron, copper. Rust is very specific, only iron can rust. Yet this same rust could be called corrosion or oxidation. The same principle occurs. The iron atoms bond with oxygen. Where can rust be beneficial, thats a tough question are sure they don't mean corrosion? There are a few examples. Where the iron is used to protect another metal from being corroded. Probably the best example I can think of is in high temperature iron alloys used for jet engine components (turbine blades etc). What is surface protectionprotection? In this context of questions, it a coating which protects the metal from corrosion. There are 3 forms of metal coating. Firstly some metals (aluminium mainly) can be have an actificial oxide layer grown on it (using a acid both and running a current through it so that the aluminium is an anode. Secondly a metal coating can be applied so that the electro potential is so high that the coating will not corrode and as long as the coating remains fully protecting the base metal it wont corrode. Tin plating on steel cans. The third form, the metal is covered by a sacrificial metal which corrodes in preference to the base metal as in galvanising where a zinc coating covers the base metal. What advantage does galvanised iron have over just iron? Well the galvanised iron has a coating of zinc on it , which will corrode in preference to the iron. But the iron by itself will just corrode. Rust From: Alan™ 02/03/2000 23:53:00 Subject: re: Corrosion post id: 43427 Where can rust be beneficial, thats a tough question are sure they don't mean corrosion If it was corrosion and not rust, you could answer with either anodising or galvanising be areas where a corrosion has or is occurring to protect the base metal. Stuffed up the html before, to tired and excited :-) From: Peter C 02/03/2000 23:56:00 Subject: re: Corrosion post id: 43428 Rust is Iron Oxide (or Fe3O2, hopefully I've got the symbols right). Corrosion is the process by which the physical properties of of a metal is degraded and rust is formed. Iron oxide is physically weaker than unrusted iron and will go brittle. However in some metals surface oxidation of the metal occurs (eg. copper). Copper 'rusts' to form copper oxide which is green however since it forms on the surface it protects the underlying layers from rusting. Hence rust can be beneficial in some metals. When Iron is mixed with Zinc it is known as Galvanisation. The mixed zinc protects the iron by a process known as Anodic Protection. When Iron is covered or coated with zinc it is known Zinc Plating. This differs from Galvanisation Galvanisation is different to Zinc Plating and offers stronger protection to corrosion. From: Alan™ 03/03/2000 0:09:00 Subject: re: Corrosion post id: 43431 Peter C just to save some confusion for William. Only iron and iron based allows "rust" other metals corrode leaving behind "corrosion product or the specific oxide ie copper oxide but this cannot be classed as rust (unless its iron). Galvanising is a form of zinc plating and the most usual way it's done. It's a process where by the iron is dipped into molten zinc. It's nothing to do with mixing the iron and zinc in the form of an alloy. Other forms of zinc plating involve the electro-deposition of zinc onto the iron or rolling zinc onto the iron. From: Alan™ 03/03/2000 0:29:00 Subject: re: Corrosion post id: 43435 Where can rust be beneficial, thats a tough question are sure they don't mean corrosion? There are a few examples. Where the iron is used to protect another metal from being corroded. Probably the best example I can think of is in high temperature iron alloys used for jet engine components (turbine blades etc). Sorry I didn't split my two examples there it reads as one. The second example should read. Another example is in high temperature iron alloys.......jet engine components, where the oxide layer formed is used to protect the base material. I keep reading your contribution Peter and shaking my head. But I don't have time to fix it all up, sorry. Rust can occur in the forms FeO, Fe2O3, Fe3O4. Fe2O3 is the flakey orange / red form while FeO is black and often protect the base iron. From: steve(primus) 03/03/2000 0:35:00 Subject: re: Corrosion post id: 43439 Oxidation of the metal is important in sculpture, particularly with bronze. The sculptor expects the statue to oxidise and works with the colour it is going to be in mind rather than the colour of the raw bronze. (I read this in a biography of Benvenuto Cellini, the Florentine sculptor) From: bob s 03/03/2000 7:02:00 Subject: re: Corrosion post id: 43455 When oxygen reacts with iron ( a reaction enhanced by water) the volume of the oxide is greater than the volume of the original metal so that the oxide does not adhere very well to the surface so that air and water can get in to cause more rusting. With aluminium the oxide formed has almost the same volume of the original metal so it forms a protective coating on the metal. Aluminium is so reactiive with oxygen that if the oxide did not form a protective coating it would burn away spontaneously in air at room temperature. The process of anodising artificially enhances the thickness of the oxide coating. Zinc also has a protective oxide coating so is slow to oxidise. In the presence of water the zinc protects iron because of the anodic protection explained. This works well where the area of exposed iron is small but when a large area of iron is exposed by removal of zinc then the rate of removal of zinc is accelerated. Alloying of iron with nickel and chromium allows an oxide coating to be formed on the metal with a volume near equal to the underlying metal so that it adheres and forms a protection. This you could say is a case where rust is beneficial. From: spud(adonai) 03/03/2000 11:32:00 Subject: re: Corrosion post id: 43499 Rust in the name of my band! rust = FeO2 From: phil 03/03/2000 12:10:00 Subject: re: Corrosion post id: 43519 Rust is benificial in reinforced concrete, If the steel reinforcing is lightly rusted the concrete sticks to it better. From: Mike V 03/03/2000 19:20:00 Subject: re: Corrosion post id: 43698 I'd vote for anodising as the best example of useful oxidisation. 70% of equipment used in the film industry is anodised aluminum. God love it. Also, check out BMX bicycles from the 80's ..... This forum is un-moderated. The views and opinions expressed are those of the individual poster and not the ABC. The ABC reserves the right to remove offensive or inappropriate messages.