Potassium tetra-silicic fluoro-micas (K-TSFMs) having variable amounts of K and Li were synthesized and crystallized from melts of the designated compositions; the ideal, K-deficient and Li-bearing yangzhumingite [K1.0Mg2.5Si4O10F2, K0.8Mg2.6Si4O10F2 and K0.7Li0.3Mg2.5Si4O10], as well as tainiolite [K0.9Li0.5Mg2.3Si4O10F2]. Their crystal structures were refined to examine the crystal chemistry of Li in the K-TSFMs. Single crystal XRD data were obtained using automated 4-circle diffractometers with synchrotron radiation in addition to the monochromatized Mo Kα radiation. The lattice parameters, a=5.2471(7), b=9.0883(16), c=10.1483(16) Å, β=99.909(12)°, Z=476.72(13) Å3 (ideal yamgthumingite); a=5.2470(17), b=9.090(4), c=10.172(6) Å, β=99.9092(7)°, Z=477.9(4) Å3 (K-deficient yangzhumingite); a=5.2503(13), b=9.092(3), c=10.148(3) Å, β=99.94(2)°, Z=477.2(2) Å3 (Li-bearing yangzhumingite); a=5.2511(6), b=9.0914(14), c=10.1544(13) Å, β=99.883(10)°, Z=477.58(11) Å3 (tainiolite), showed no remarkable fluctuation among them, and are intermediate between those of trioctahedral and dioctahedral micas. The octahedral volumes of K-TSFMs are comparable to each other, and are larger than di-octahedral micas, but smaller than tri-octahedral micas. It is suggested that Li+ can replace Mg2+ without volume change in the octahedral sites in K-TSFMs by the equivalent octahedral volumes between tainiolite and Li-free yangzhumingite. The refinement on crystal structure of Li-bearing yangzhumingite suggests that Li+ can occupy the octahedral sites together with Mg2+, as well as Li+ in tainiolite.
Tribological properties of a base oil (poly alpha olefine with 20 wt% deuterated n-hexadecane) were evaluated with a ball-on-flat type tribotest. The addition effect of a lecithin-modified clay to the base oil was studied. The presence of deuterium species inside the steel disk after friction tests was investigated by a TOF-SIMS analysis. Deuterium species were observed inside the steel disk with 60 nm depth after friction with the base oil for 60 min. On the other hand, deuterium species were not observed inside the steel disk with 20 nm depth after friction with the oil containing 12 wt% of the lecithin-modified clay. The lecithin-modified clay could be used as a valuable additive for lubricants with hydrogen barrier properties.
A ceramic coating of a submicron order was successfully fabricated on a stainless steel surface by spin coating of an aqueous paste of hectorite clay followed by calcination at 873 K. A structural analysis of the clay-derived ceramic coat revealed that clay fragments were stacked in the coating and exhibited excellent adhesion at the interface between the stainless steel and the ceramic.