Mn. Gardos, Magneli phases of anion-deficient rutile as lubricious oxides. Part II. Tribological behavior of Cu-doped polycrystalline rutile (TinO2n-1), TRIBOL LETT, 8(2-3), 2000, pp. 79-96
As a follow-up to the work described in part I of this paper series, a prel
iminary study was conducted with polycrystalline rutile TiO2-x to render it
s friction and wear performance independent of the environment. The main go
al was to confine the most tribologically desirable oxygen stoichiometries
of the crystallographic shear-induced Magneli phases (CSMP) of rutile by do
ping with cations similar in size and polarizability to the Ti4+, but with
lower valences. The resultant chemical expulsion of oxygen from the rutile
lattice was intended to generate CSMP free of friction and wear variations
caused by changes in the thermal-atmospheric environment. Copper, iron, cob
alt and nickel ions were tried as dopants introduced as their stable oxides
via a simple ball-milling, hot-pressing and annealing procedure, but only
a (Ti+Cu)O-1.80 model blend resulted in a desired reaction. A portion of th
e copper entered the lattice to form a new titanium-copper CSMP, resembling
the well-known V3Ti6O17 catalyst equivalent to an undoped rutile CSMP with
an O/Ti ratio of 1.89. Although the shear behavior of this new, wear-resis
tant compound was in accordance with predictions, its friction is higher an
d more variable than desired for a wide environmental regime lubricant. The
preparation technique was only sufficient to demonstrate that oxygen vacan
cy-induced creation of low-friction CSMP may be possible by doping; it does
not appear to be useful for formulating practical, rutile-based lubricious
oxides.