AVS 50th International Symposium
    Surface Science Monday Sessions
       Session SS2-MoA

Paper SS2-MoA9
Reaction of Trimethylphosphate with TiC and VC(100) Surfaces

Monday, November 3, 2003, 4:40 pm, Room 327

Session: Tribology, Adhesion, and Friction
Presenter: H.I. Kim, The Aerospace Corporation
Authors: H.I. Kim, The Aerospace Corporation
P. Frantz, The Aerospace Corporation
S.V. Didziulis, The Aerospace Corporation
L.C. Fernandez-Torres, University of Houston
S.S. Perry, University of Houston
Correspondent: Click to Email
Hard coatings, such as titanium carbide (TiC), are emerging technologies for various tribological applications, including spacecraft bearings due to their higher hardness and greater wear resistance compared to metal components. However, their surface chemical properties, especially with respect to high-performance lubricants, are poorly understood. Therefore, the adsorption and chemical reaction of a model lubricant additive, trimethylphosphate [(CH3O)3PO] (TMP), were investigated on the surfaces of TiC and VC(100) as a function of temperature using high-resolution electron energy loss spectroscopy (HREELS), X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD). TMP adsorbs molecularly on both surfaces at cryogenic temperature, and chemical bonding to the surface is evident upon warming to approximately 200 K. At higher temperatures, surface chemical reaction on TiC leads to phosphate-like and carbonaceous products that persist on the surface after heating up to 873 K. The stability of these surface species at such high temperature presents potential implications for modification and lubrication of hard coating surfaces at high temperatures where most organic adsorbates fail to provide tribological benefits. The reaction pathway and the reaction products are determined to be dependent on the initial coverage as well as the substrate chemistry, i.e. TiC vs. VC. These results have interesting implications for potential applications in boundary additives on hard coatings, where desired surface chemical protection may be tuned by the concentration of the organophosphate ester additives in the lubricant and the substrate chemistry.