236 



ANNUAL REPORT SMITHSONIAN INSTITUTION, 1923 



having a purity of at least 99.5. The pure worked material resem- 

 bles platinum very much in color and appearance. Its melting point 

 may at present be taken as 2,850° C. The specific gravity of the 

 worked metal is 16.6. The pure metal is characterized by toughness 

 and by its great ductility and malleability. 



It has been found possible to reduce a bar of tantalum about three- 

 eighths inch in diameter to wire of only a few mils in diameter 

 without any intermediate heating to the annealing or equiaxing 

 temperature, although the material is subject to strain hardening, re- 

 sembling the .more common metals such as silver or copper in this 

 respect. Tantalum, however, resembles tungsten and molybdenum 

 in that they may all be worked severely at temperatures below their 

 equiaxing temperatures. Copper and silver may be worked at room 

 temperature, but these metals become quite rapidly strain-hardened 

 so that a further reduction makes it necessary to anneal the metal. 

 Tungsten and molybdenum must be worked at elevated temperatures 

 in the early stages, and if they are to be worked at room tempera- 

 ture in the finer sizes any operation corresponding to ordinary an- 

 nealing must be avoided. Tantalum may be worked at room tem- 

 perature to a remarkable extent without annealing. 



The tensile strength of drawn tantalum wire may reach 130,000 

 pounds, which is considerably more than that of hard drawn copper, 

 nickel, or platinum, but less than that of molybdenum or tungsten. 



The linear coefficient of expansion is more than that of molybde- 

 num or tungsten and only slightly less than platinum. For this 

 reason it is possible to seal tantalum into glass. 



Density.. --• 



Atomic value -.- 



Tensile strength, lb. per sq. in. 



Compressibility, kg. per sq. 

 cm 



Young's modulus of elasticity, 



kg. per sq. mm 



Melting point, deg. C 



Boiling point, deg. C 



Specific heat, cal. per gram per 



Linear coefficient of expansion 

 per deg. C 



Thermal cond. in cal. per cc... 



Temp, coefficient of expansion. 



Electric resistance, microhm 



per cc. at 25 deg. annealed— . 



Tungsten 



10.6 

 9.4 



490,000 



0. 28X10-* 



42,000 

 3,350 



0.034 



4.3X10-" 

 0.35 



0.0051 



5.2 



Tantalum 



16.6 

 10.9 



130, 000 



0.50X10-" 



19,000 

 2,770 



0.0365 



7. 9X10-» 



0.130 



0.00335 



14.6 



Molybde- 

 num 



10.2 



8.8 



260,000 

 0.47X10-* 



2,550 

 3,617 



0.072 



5. 15X10-« 

 0.346 

 0.005 



4.8 



Platinum 



f i 54, 000 

 i » 42, 000 



i Hard. 



1,755 

 3,907 



0.0323 



8.84X10-' 

 0.1664 

 0.0039 



9.97 

 2 Annealed. 



Copper 



.80 



» 62, 000 

 •35,000 



0. 76XHH> 



1,083 

 2,310 



0.0936 



0. 7198 

 0. 00393 



1.87 



Nickel 



8.84 



1120,000 

 » 70, 000 



22,000 

 1,452 



0. 1084 



13X10-* 



0.140 



0.0066 



6.4 



