Water atomization is better suited to high-volume production of metal fluoride than conventional methods.

Atomization of a molten mixture of BaF₂ and CaF₂ has been found to be superior to crushing of bulk solid BaF₂- CaF₂ as a means of producing eutectic BaF₂-CaF₂ powder for use as an ingredient of the powder feedstock of a hightemperature solid lubricant material known as PS304. Developed to reduce friction and wear in turbomachines that incorporate foil air bearings, PS304 is applied to metal substrates by plasma spraying. The constituents of PS304 are:

• An alloy of 80 weight percent Ni and 20 weight percent Cr,
• Cr₂O₃,
• Ag, and
• The BaF₂-CaF₂ eutectic — specifically, 62 weight percent BaF₂ and 38 weight percent CaF₂.

Water Atomization produces particles intermediate in shape to those producedby gas atomization and crushing. Water atomization may be economicallythe most advantageous of the three techniques.

Two well-known atomization processes (gas atomization and water atomization) have been investigated, in comparison with crushing, as means of producing eutectic BaF₂-CaF₂ powders (see figure). The particles produced by gas atomization are the most nearly spherical, but each batch contains only a small proportion of particles in the size range (20 to 100 μm) suitable for plasma spraying and a much larger proportion of undesired finer particles. Water atomization yields particles that are less spherical in character but still more rounded than those produced by crushing, and yields a greater proportion of usable particles.

As one might expect from the intermediate nature of the shapes of water-atomized BaF₂-CaF₂ particle shapes, the flow properties of PS304 powders containing water-atomized BaF₂- CaF₂ are intermediate to those of PS304 powders containing equal proportions of gas-atomized BaF₂-CaF₂ and those containing equal proportions of crushed BaF₂-CaF₂. Inasmuch as water atomization tends to be less expensive and better suited to high-volume production than is gas atomization, water atomization could be preferable for applications in which the shapes of the eutectic BaF₂-CaF₂ particles are not required to closely approximate spheres and the intermediate flow properties are acceptable.

This work was done by Christopher DellaCorte of Glenn Research Center and Malcolm K. Stanford of the University of Dayton.

Inquiries concerning rights for the commercial use of this invention should be addressed to NASA Glenn Research Center, Innovative Partnerships Office, Attn: Steve Fedor, Mail Stop 4–8, 21000 Brookpark Road, Cleveland, Ohio 44135. Refer to LEW-17709-1.

This Brief includes a Technical Support Package (TSP).

Atomized BaF2-CaF2 for Better-Flowing Plasma-Spray Feedstock (reference LEW-17709-1) is currently available for download from the TSP library.

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