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TITANIUM


          
This page deals with the uses of titanium and its extraction from the ore, rutile.

          

          
Introduction

          
Uses of titanium

          
Titanium is corrosion resistant, very strong and has a high melting point.  It has a relatively low density (about 60% that of iron).  It is also the tenth most commonly occurring element in the Earth's crust.  That all means that titanium should be a really important metal for all sorts of engineering applications.

          
In fact, it is very expensive and only used for rather specialised purposes.

          
Titanium is used, for example:

          
    
            
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    in the aerospace industry - for example in aircraft engines and air frames;
    
            
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    for replacement hip joints;
    
            
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    for pipes, etc, in the nuclear, oil and chemical industries where corrosion is likely to occur.
    
            
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Why is titanium so expensive?

          
Titanium is very expensive because it is awkward to extract from its ores -  for example, from rutile, TiO2.

          
You can't use carbon reduction

          
Titanium can't be extracted by reducing the ore using carbon as a cheap reducing agent.  The problem is that titanium forms a carbide, TiC, if it is heated with carbon, so you don't get the pure metal that you need.  The presence of the carbide makes the metal very brittle.

          
That means that you have to use an alternative reducing agent.  In the case of titanium, the reducing agent is either sodium or magnesium.  Both of these would, of course, first have to be extracted from their ores by expensive processes.

          
Other problems

          
    
            
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    The titanium is produced by reacting titanium(IV) chloride, TiCl4 - NOT the oxide - with either sodium or magnesium.  That means that you first have to convert the oxide into the chloride.  That in turn means that you have the expense of the chlorine as well as the energy costs of the conversion.
    
            
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    Titanium(IV) chloride reacts violently with water.  Handling it therefore needs care.
    
            
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    Traces of oxygen or nitrogen in the titanium tend to make the metal brittle.  The reduction has to be carried out in an inert argon atmosphere rather than in air.  That also adds to costs.
    
            
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    High temperatures are needed in both stages of the reaction.
    
            
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    Titanium is made by a batch process.  In the production of iron, for example, there is a continuous flow through the Blast Furnace.  Iron ore and coke and limestone are added to the top, and iron and slag removed from the bottom.  This is a very efficient way of making something.
    
              
    With titanium, however, you make it one batch at a time.  Titanium(IV) chloride is heated with sodium or magnesium to produce titanium.  The titanium is then separated from the waste products, and an entirely new reaction is set up in the same reactor.  This is a slow and inefficient way of doing things.
    
            
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Titanium extraction

          
Conversion of titanium(IV) oxide, TiO2, into titanium(IV) chloride, TiCl4

          
The ore rutile (impure titanium(IV) oxide) is heated with chlorine and coke at a temperature of about 900°C.

          

      

      

        
        
          

          

          Note:  There are other reactions occurring as well in which the other product is either carbon dioxide or carbonyl chloride, COCl2.  The equation given is the one UK A level students are likely to need.

          
          

          

          

      

      

        
Other metal chlorides are formed as well because of other metal compounds in the ore.  Very pure liquid titanium(IV) chloride can be separated from the other chlorides by fractional distillation under an argon or nitrogen atmosphere, and is stored in totally dry tanks.

      

      

        
        
          

          

          Note:  Titanium(IV) chloride is a typical covalent chloride.  It is a colourless liquid which fumes in moist air due to reaction with water to give titanium(IV) oxide and fumes of hydrogen chloride.  Everything has to be kept very dry to prevent this happening.

          
          

          

          

      

      

        
Reduction of the titanium(IV) chloride

          
Reduction by sodium

          
This is the method which is used in the UK.

          
The titanium(IV) chloride is added to a reactor in which very pure sodium has been heated to about 550°C - everything being under an inert argon atmosphere.  During the reaction, the temperature increases to about 1000°C.

          

          
After the reaction is complete, and everything has cooled (several days in total - an obvious inefficiency of the batch process), the mixture is crushed and washed with dilute hydrochloric acid to remove the sodium chloride.

      

      

        
        
          

          

          Note:  To save you the bother of asking, I have no idea why hydrochloric acid is used to do this rather than just water!

          
          

          

          

      

      

        
Reduction by magnesium

          
This is the method used in the rest of the world.

          
The method is similar to using sodium, but this time the reaction is:

          

          
The magnesium chloride is removed from the titanium by distillation under very low pressure at a high temperature.

      

      

        
        
          

          

          Note:  If you are a UK A level student, just learn the sodium reduction.

          
          

          

          

      

      

        

          

            

              
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