ALLOY PREPARATION BY LEVITATION MELTING

Levitation melting is an ideal technique for the preparation of small quantities of alloys for reference material or nuclear applications. T he method avoids contamination of the melt and electromagnetic stirrin g ensures good mixing in the molten state. Evaporation losses under in ert atmosphere are usually small allowing close control of alloy compo sition. Very dilute alloys, containing alloying additions at ppm level s, can be prepared using several dilution steps chosen to minimize err ors in concentration. Different levitation methods allow the melting o f low or high density metal in quantities from a few grammes up to 1 k g or more, although metals with high vapour pressure or low surface te nsion can be difficult to handle. Good homogeneity has been demonstrat ed for 20 g aluminium alloy samples chill-cast into water-cooled coppe r moulds. Examples of alloys prepared at CBNM by levitation melting ar e solid standards for atomic absorption spectrometry, U-Pu metal ''spi kes'' for material accountancy measurements by mass spectrometry and a lloy reference materials for reactor neutron dosimetry.