TANTALUM BALKE 235 



Metallic tantalum powder can be produced by the reduction of the 

 double fluoride with metallic sodium or potassium. It is impossible 

 by this process to produce a powder characterized by high purity. 

 For best results by this method the reaction should be carried out 

 in a vacuum, the boats or crucibles containing the mixture of 

 double fluoride and metallic sodium or potassium being placed in 

 a tube or furnace which can be evacuated before the mixture is raised 

 to the reaction temperature. 



The product from this reaction can be treated with water and 

 mineral acids in order to free the metal powder as completely as 

 possible from adhering salt and other impurities. This powder is 

 then compressed into bars and subjected to heat treatment and 

 finally fusion in a vacuum furnace, the high temperature of fusion 

 eliminating the impurities which may be present. If this process 

 has been completely successful, the fused metal will be found to be 

 ductile and susceptible to mechanical working. 



The most characteristic chemical property of tantalum is its un- 

 usual resistance to chemical corrosion. It is not attacked by hydro- 

 chloric or nitric acids or by aqua regia, either hot or cold. It is not 

 attacked by dilute sulphuric acid at ordinary or more elevated tem- 

 peratures, but appears to be slowly attacked by boiling concentrated 

 sulphuric acid. Solutions of caustic alkalis do not attack the metal. 

 Hydrofluoric acid seems to be the only chemical agent which will 

 attack it, and in the case of very pure metal and very pure hydro- 

 fluoric acid the action is very slow. A mixture of hydrofluoric and 

 nitric acids will attack the metal with avidity, causing it to go into 

 solution as tantalum fluoride. 



If tantalum is heated in the air, the surface becomes blue at a 

 temperature of about 400° C, and at a somewhat higher temperature 

 nearly black. Above a dull red heat the white oxide is produced and 

 the metal gradually burns. This metal combines with avidity 

 with hydrogen, oxygen, or nitrogen. It will take up seven hundred 

 and forty times its own volume of hydrogen, producing a very coarse- 

 grained brittle product. 



Tantalum containing dissolved gases will be harder than the pure 

 metal, and if their quantity is appreciable the metal may even be 

 brittle, so that all annealing or heating operations with tantalum 

 must be carried out in a vacuum. Tantalum burns readily when 

 heated in chlorine gas, producing the volatile pentachloride. Solu- 

 tions of chlorine, however, are without any action on the metal. 

 Tantalum is not affected by any of the chemicals or antiseptics used 

 in dentistry or surgery, probably without exception. 



PHYSICAL PROPERTIES OF TANTALUM 



It has been possible to produce metallic tantalum of an exceedingly 

 high degree of purity, and to produce it in commercial quantities, 



