Development of ultrasonic transducers for ranging and imaging in heavy liquid metal

The paper describes the development of high temperature, γ and neutron radiation resistant ultrasonic transducers which must operate continuously in liquid Pb/Bi up to 450°C. Known ultrasonic transducers are not intended for such harsh conditions. The main problems are acoustic coupling of the piezoelement to the protector and wetting of the transducer by a heavy liquid metal. For the first time, the piezo-element was attached to the transducer body by a gold-to-gold diffusion bonding process; acoustic coupling between the transducer and the liquid metal alloy was achieved by coating the front face by a protective diamond-like carbon (DLC) layer. Due to the high radiation, only a limited number of materials may be used in the transducer design. Transducers with bismuth titanate piezoelectric elements showed no noticeable changes of pulse responses and transfer coefficients. The housing of the transducer is made of AISI 316 stainless steel, it is laser welded and high temperature 1 mm diameter, 15 m long, mineral cable is used.