Small concentrations o f many elements may have both, a desired or a detrimental effect. Sometimes both effects are in a very close neighborhood. Only a small variation in concentration or a variation in the composition of the basic alloy will change a desired addition into an impurity.

Small amounts of e.g. iridium, ruthenium, zinc and also silicon can improve the casting properties of an alloy.

However, a not correctly adapted concentration or the use with an inappropriate alloy will cause troubles.

Other impurities are detrimental in any case, e.g. lead and phosphorous.

Author: Dieter Ott