Rhodium alloys black

Figure 4.28. STM image of a PtRh(lOO) surface. Although the bulk contains equal amounts of each element, the surface consists of 69% of platinum (dark) and 31 % of rhodium (bright), in agreement with the expected surface segregation of platinum on clean Pt-Rh alloys in ultrahigh vacuum. The black spots are due to carbon impurities. It is seen that platinum and rhodium have a tendency to cluster in small groups of the same elements.

Uses.—Rhodium is used, both alone but generally alloyed with platinum, in the construction of scientific apparatus such as crucibles. A rhodium crucible is, for all practical purposes, as resistant as one of iridium, and is both cheaper and lighter.7 It has also found application in the manufacture of thermo-electric couples.8 Rhodium black has been used for producing a black colour in the decoration of poree lain.9... 

When platinum is heated in a luminous coal-gas flame a black layer is formed. If the carbon is now burnt off in air the metal is left in a rough and brittle condition, but without having undergone any loss in weight. The action is considerably enhanced by the presence of alloyed rhodium or iron, whilst iridium has a less marked effect.8... 

Occurrence and History of Rhodium—Preparation—Proportion- Colloidal Rhodium—Rhodium Black—Uses—Atoraio Weight —Alloys. 

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