Showing papers on "Ammonium tetrathiomolybdate published in 1997"

XPS studies of MoS2 formation from ammonium tetrathiomolybdate solutions

Abstract: Preparation of MoS 2 by acidification of ammonium tetrathiomolybdate solution has been studied by X-ray photoelectron spectroscopy (XPS). The precipitates formed from the solution are mainly composed of MoS 3 , the Mo 3d chemical shift of which is approximately 4.2eV. Heat treatments of the above product at 450 and 850°C, in a vacuum of 1.33 × 10 −4 Pa, lead largely to formation of MoS 2 , with typical chemical shifts of abouth 1.2eV. The MoS 2 formed consists of nano-sized, crystalline particles of hexagonal (2H-type) structure. The validity of MoS 2 formation by this route is confirmed by comparative study, namely the decomposition of ATT solids under the same respective heat treatment conditions. Apart from these main aspects, origins of minor XPS peaks are also considered.

Synthesis and characterization of molybdenum disulphide formed from ammonium tetrathiomolybdate

Abstract: An investigation has been carried out into the possibility of in situ formation of MoS2 within porous anodic films on aluminium, to improve subsequent tribological behaviour, by re-anodizing in thiomolybdate electrolyte. Acidification of thiomolybdate was employed to simulate the conditions for formation of the sulphide at the anodic film/electrolyte interface, followed by appropriate vacuum heat treatments to study possible temperature effects on the sulphide due to either friction or Joule heating during anodizing. The products of both acidification and heat treatment, characterized by X-ray powder diffraction and scanning electron microscopy, were compared with those formed by direct thermal decomposition of ammonium tetrathiomolybdate crystals. The precipitate formed by acidification was mainly amorphous molybdenum trisulphide (MoS3), which on heat treatment at 450 and 850°C yielded 3R-MoS2. 3R-MoS2 also formed by the thermal decomposition of thiomolybdate crystals. Thermogravimetric and differential thermal analyses showed that the decomposition of MoS3 to MoS2 occurred in the range 220–370°C and revealed the sequence of reaction steps. The findings suggest that mainly amorphous MoS3 is formed as a consequence of changes in the pH of the film/electrolyte interface during re-anodizing but the product is relatively easily transformed to crystalline MoS2 on moderate heating which may occur during wear processes.

Development and tribological assessment of self-lubricating anodic films on aluminium

Abstract: The self-lubricating, porous anodic films formed on aluminium by a re-anodizing treatment in ammonium tetrathiomolybdate electrolyte is examined by transmission electron microscopy and X-ray photoelectron spectroscopy. Precipitation of mainly amorphous MoS 3 , or a mixture of MoS 2 and S, is revealed, which leads to a significantly reduced coefficient of friction.

Poisoning and Inhibition of Dispersed Liquefaction Catalyst Activity by Exposure to Coal

Abstract: The activity of a dispersed MoS2 catalyst prepared in situ from ammonium tetrathiomolybdate was measured in octacosane containing various amounts of Argonne Premium Illinois No. 6 coal using microa...