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metal
what is the most abundant metal in the earths crust resistant to corrosion.
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Something told me this would result in a debate!
Of the two elements, it is true that aluminium is more abundant in the earth�s crust than titanium. Titanium is third in line behind iron and aluminium in the most common metals list. Both pure titanium and pure aluminium are protected by a thin layer of metallic oxide that forms virtually instantaneously upon contact with the oxygen in air, and it is this layer which is responsible for their resistance to corrosion.
However, aluminium is far from being the ideal corrosion resistant metal and titanium surpasses it in many qualities.
Aluminium in the form of the pure metal is unable to withstand sustained atmospheric pollution and �acid rain�. The pure metal pits and eventually corrodes when used in exterior architectural structures. Atmospheric pollutants such as dilute sulphuric and hydrochloric acids attack it, although it is virtually inert to nitric acid at all concentrations. Consequently, pure aluminium used in exterior structures has a limited lifespan.
Solutions of alkalies such as sodium hydroxide (caustic soda) and potassium hydroxide rapidly attack aluminium in all but the lowest concentrations (< 0.001%)
Pure aluminium readily corrodes in marine environments, with seawater causing considerable corrosion in very short time. It is not used in the petrochemical industry, again because contact with a large number of organic chemicals will corrode the metal.
You will note that these environmental conditions are far from being out of the ordinary and aluminium corrosion is quite commonplace.
(continued)
Of the two elements, it is true that aluminium is more abundant in the earth�s crust than titanium. Titanium is third in line behind iron and aluminium in the most common metals list. Both pure titanium and pure aluminium are protected by a thin layer of metallic oxide that forms virtually instantaneously upon contact with the oxygen in air, and it is this layer which is responsible for their resistance to corrosion.
However, aluminium is far from being the ideal corrosion resistant metal and titanium surpasses it in many qualities.
Aluminium in the form of the pure metal is unable to withstand sustained atmospheric pollution and �acid rain�. The pure metal pits and eventually corrodes when used in exterior architectural structures. Atmospheric pollutants such as dilute sulphuric and hydrochloric acids attack it, although it is virtually inert to nitric acid at all concentrations. Consequently, pure aluminium used in exterior structures has a limited lifespan.
Solutions of alkalies such as sodium hydroxide (caustic soda) and potassium hydroxide rapidly attack aluminium in all but the lowest concentrations (< 0.001%)
Pure aluminium readily corrodes in marine environments, with seawater causing considerable corrosion in very short time. It is not used in the petrochemical industry, again because contact with a large number of organic chemicals will corrode the metal.
You will note that these environmental conditions are far from being out of the ordinary and aluminium corrosion is quite commonplace.
(continued)
Let�s look at Titanium. Titanium passivates just like aluminium, but marginally more rapidly and with a more tenacious oxide layer. This layer has been identified as rutile, a tetragonal form of titanium dioxide. The oxide layer is instantaneously self-healing in the presence of oxygen. The metal is resistant to non-oxidising acids at dilutions of 2-5% although in solution, the presence of hydroxyl ions promotes the formation of the passivating film.
Titanium is resistant to concentrated nitric acid although it is attacked by hot, concentrated sulphuric acid and hydrofluoric acid. It is also resistant to various concentrated acid mixtures such as aqua regia. Titanium is also unaffected by weak to moderate concentrations of alkalies. It�s used in the marine environments because it�s immune from the effects of seawater and is the first choice of material in the petrochemical industry and chemical industries � it shows remarkable resistance to moist chlorine gas, chlorinated solvents and other organic chemicals.
Titanium displays no corrosion upon sustained exposure to atmospheric pollutants. It can withstand sulphurous atmospheres, unlike aluminium and rarely displays galvanic corrosion again unlike aluminium.
Titanium is used in the construction of the �legs� of sea oil platforms not only for its strength but also for its immunity to corrosion. It is also the metal of choice in de-salination plants the world over because of it�s resistance to sodium chloride. In essence, titanium is totally immune to environmental attack.
(continued)
Titanium is resistant to concentrated nitric acid although it is attacked by hot, concentrated sulphuric acid and hydrofluoric acid. It is also resistant to various concentrated acid mixtures such as aqua regia. Titanium is also unaffected by weak to moderate concentrations of alkalies. It�s used in the marine environments because it�s immune from the effects of seawater and is the first choice of material in the petrochemical industry and chemical industries � it shows remarkable resistance to moist chlorine gas, chlorinated solvents and other organic chemicals.
Titanium displays no corrosion upon sustained exposure to atmospheric pollutants. It can withstand sulphurous atmospheres, unlike aluminium and rarely displays galvanic corrosion again unlike aluminium.
Titanium is used in the construction of the �legs� of sea oil platforms not only for its strength but also for its immunity to corrosion. It is also the metal of choice in de-salination plants the world over because of it�s resistance to sodium chloride. In essence, titanium is totally immune to environmental attack.
(continued)
Human body fluids generally have a pH of from slightly alkaline to well into the acid range. Bioinert titanium is used for prosthetic joints, heart valves, plates and other implants because it is inert to such acidity and does not corrode. Titanium implant have been removed from patients twenty years after their operations and have been found to be as corrosion free as the day they were inserted. Aluminium would corrode in weeks in such a harsh environment.
I think most people will agree that the environments I cited as being unsuitable for aluminium are not that unusual. It should be apparent that when we consider that pure aluminium corrodes in atmospheric conditions and is unsuitable for marine use, it does somewhat restrict its use. Because of this, it�s clear that aluminium is not as corrosion resistant as is often claimed. Therefore, I think it should be precluded when we come to consider the most corrosion resistant metal in the earth�s crust.
Incidentally, I am aware that the questioner asked about the most abundant corrosion resistant metal and not the �best� or most resistant to corrosion metal. The trouble is when we discount pure aluminium because of it�s ability to corrode in conventional environments, we have no choice but to adopt titanium as the true answer as it is virtually totally inert as well as being the next most abundant corrosion resistant metal.
Hamish is correct in that titanium is in the �top ten� most abundant elements in the earth�s crust � other similarly inert elements are far less abundant in the earth�s crust.
I think most people will agree that the environments I cited as being unsuitable for aluminium are not that unusual. It should be apparent that when we consider that pure aluminium corrodes in atmospheric conditions and is unsuitable for marine use, it does somewhat restrict its use. Because of this, it�s clear that aluminium is not as corrosion resistant as is often claimed. Therefore, I think it should be precluded when we come to consider the most corrosion resistant metal in the earth�s crust.
Incidentally, I am aware that the questioner asked about the most abundant corrosion resistant metal and not the �best� or most resistant to corrosion metal. The trouble is when we discount pure aluminium because of it�s ability to corrode in conventional environments, we have no choice but to adopt titanium as the true answer as it is virtually totally inert as well as being the next most abundant corrosion resistant metal.
Hamish is correct in that titanium is in the �top ten� most abundant elements in the earth�s crust � other similarly inert elements are far less abundant in the earth�s crust.
Just realised I'd forgotten about calcium. Let's try again.
The most abundant metals in the earth's crust are generally regarded as:
1. Aluminium
2. Iron
3. Calcium
4. Titanium
Some authorities insist on magnesium being in third-place, including Wikipedia. Some may push titanium further down the list.
Furthermore, it's important to realise that metals are not synonymous with elements (to illustrate, whilst aluminium is the most abundant metal in the earth's crust, it's only the third most abundant element on earth, surpassed by silicon and oxygen)
At the end of the day, it's immaterial where titanium is in the list as it's unquestionably in the "top ten" and no other metal in that list of ten possesses such unsurpassable resistance to corrosion.
The most abundant metals in the earth's crust are generally regarded as:
1. Aluminium
2. Iron
3. Calcium
4. Titanium
Some authorities insist on magnesium being in third-place, including Wikipedia. Some may push titanium further down the list.
Furthermore, it's important to realise that metals are not synonymous with elements (to illustrate, whilst aluminium is the most abundant metal in the earth's crust, it's only the third most abundant element on earth, surpassed by silicon and oxygen)
At the end of the day, it's immaterial where titanium is in the list as it's unquestionably in the "top ten" and no other metal in that list of ten possesses such unsurpassable resistance to corrosion.
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