 Rhenium improves the properties of tungsten . Tungsten @-@ rhenium alloys are more ductile at low temperature , allowing them to be more easily machined . The high @-@ temperature stability is also improved . The effect increases with the rhenium concentration , and therefore tungsten alloys are produced with up to 27 % of Re , which is the solubility limit . One application for the tungsten @-@ rhenium alloys is X @-@ ray sources . The high melting point of both compounds , together with the high atomic mass , makes them stable against the prolonged electron impact . Rhenium tungsten alloys are also applied as thermocouples to measure temperatures up to 2200 ° C. 
