Characterization of the Friction Properties of Ceramic Powders

M.A. SPRAGUE and W.R. BLUMENTHAL  
Material Science and Technology Division
Los Alamos National Laboratory 
Los Alamos, New Mexico 87545, USA


Measurements of the friction behavior of spray-dried alumina ceramic
powders were performed using an annular shear cell.  In this test, the
torque resulting from a pre-compacted ceramic powder bed was measured
as one side of the cell  was slowly rotated against the other, while
confined under a series of high normal stresses (50-1000 psi). 
"Static" coefficient of friction values were then determined from a
linear fit of the plot of the peak shear, which occured sharply at the
beginning of the test, versus the normal load values. The linear
relationship is equivalent to the critical compaction yield locus
(CCYL) obtained from the Jenike shear cell test. "Dynamic" coefficient
of friction values were also determined from a plot of minimum shear
load versus normal load values. Powder-powder friction coefficients
were generated using fixtures with very rough surfaces which forced the
shear failure plane into the powder bed.  Powder-wall friction
coefficients were obtained using smooth fixture surfaces so that the
shear failure plane remained at the powder-fixture (wall) interface. 
Typical values of the "static" and "dynamic" powder-powder coefficients
of friction were 0.8 and 0.7, respectively, and typical powder-wall
coefficients were 0.4. Powder characteristics and humidity conditions
were varied in this study and complemented parallel die compaction
studies.

Presented at the American Ceramic Society Meeting,  May 4, 1997, 
Cincinnati, Ohio.