Question
Why particular alloy of platinum-iridium is chosen to make the rod used to define the unit of mass?
Solution
The platinum-iridium alloy is highly chemically stable. The relatively inert nature of the material minimises surface contamination and enhances the mass stability.
Platinum and its alloys are reasonably easy to machine, enabling a good surface finish to be achieved on the artifact that again reduces the effect of surface contamination. The addition of 10% iridium to the platinum greatly increases its hardness and so reduces wear.
Platinum and its alloys are reasonably easy to machine, enabling a good surface finish to be achieved on the artifact that again reduces the effect of surface contamination. The addition of 10% iridium to the platinum greatly increases its hardness and so reduces wear.
