Separate and simultaneous determination of zirconium and hafnium in nickel-base alloys with xylenol orange

Abstract

The use of xylenol orange as a spectrophotometric reagent for zirconium and hafnium has been investigated for their determination in the range 0·002 to 0·2 per cent. in complex nickel-base alloys, and the effects of major alloying elements, and likely impurities, have been studied. A simple, direct procedure, based on the formation of the red xylenol orange complexes in 0·8 N hydrochloric acid, has been successfully applied to the determination of either metal in nickel alloys containing chromium, cobalt, iron, molybdenum, titanium and aluminium.

For alloys containing both zirconium and hafnium, a procedure developed for their simultaneous determination is based on the relative effect of acid concentration on the xylenol orange complexes. Preliminary mercury cathode and hydroxide separations are followed by measurement of the total optical densities at three levels of acidity, 0·35, 1·12 and 2·0 N perchloric acid. This “three-point” method has proved satisfactory with synthetic alloy solutions and when applied to complex nickel alloys containing both zirconium and hafnium. Confirmatory evidence of the results was obtained by X-ray fluorescence, emission and mass spectrometry.

The simultaneous procedure provides a simple and sensitive chemical method of differentiating between microgram amounts of zirconium and hafnium, and should be capable of wider application to other alloy systems. The simpler direct method should also prove advantageous when mutual interference does not arise.