Investigation of the systems KAlF4–M3AlF6 (M=Rb, Cs)

Phase relations in the systems KAlF4–Rb3AlF6 and KAlF4–Cs3AlF6 were investigated by DTA and XRD methods for the purpose of finding a low melting, non-corrosive aluminum flux. In each system, congruent compounds Rb3AlF6·2KAlF4 and 2Cs3AlF6·3KAlF4 were observed, respectively. Eutectics located at 46 mol% Rb3AlF6 and 511°C, 25 mol% Rb3AlF6 and 512°C for the former system, and 48 mol% Cs3AlF6 and 550°C, 25 mol% Cs3AlF6 and 480°C in the latter were confirmed. The phase α-2Cs3AlF6·3KAlF4 was XRD indexed as having an orthorhombic cell a=10.401±0.003, b=10.078±0.006, c=8.792±0.006 Å.