Zr-Al 16 wt. % and Na2CrO4 composite particles used for Na dispenser and its reaction kinetic

Abstract

An alkali metal dispenser is the core device for vacuum evaporation in producing multialkali photocathodes. However, the reaction kinetic of alkali metal chromate being reduced by a Zr-Al alloy, which is the most commonly used alkali metal dispenser, has not been reported. In this work, we made composite particles of Zr-Al 16 wt. % powders with Na2CrO4 by a method of liquid precipitation. Through thermal analysis of its reaction, we found that the difference of a Zr-Al particle size would affect the reaction starting temperature but would not make a significant difference on the apparent activation energy. Through the comparison method by Sharp, we found that the 3D Avrami–Erofeev equation fits for this reaction and established a reaction degree-temperature function, and the reaction kinetic was further verified by a vacuum evaporation experiment. Through an in situ XRD measurement, the chemical change during an Na dispenser’s working process is found to be Na2CrO4 → Na2CrO4, Na2CrO3, and Cr2O3 coexist → NaCrO2. This work may serve as a reference for the design of alkali metal dispensers and help to improve the control precision for an evaporation process.