Study on the structure of PbS nanoparticles coated with dialkyldithiophosphate
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Study on the structure of PbS nanoparticles coated with dialkyldithiophosphate Shuang Chen, Weimin Liu,a) and Laigui Yu Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Science, Lanzhou 730000, People’s Republic of China (Received 21 July 1998; accepted 11 January 1999)
PbS nanoparticles modified with di-n-hexadecyldithiophosphate (DDP) were prepared by the chemical surface modification method. The structure of the PbS nanoparticles coated with DDP was investigated by means of infrared spectroscopy (ir), x-ray photoelectron spectroscopy (XPS), x-ray diffraction (XRD), transmission electron microscopy (TEM), and 31 P nuclear magnetic resonance spectroscopy (31 P NMR). The thermal stability of DDP coating on the PbS nanoparticles was compared with that of pyridinium di-n-hexadecyldithiophosphate (PyDDP) using a thermogravimetric analyzer (TGA). It was found that coated PbS nanoparticles had an average diameter of about 5 nm. Surface modification with DDP prevented water adsorption and effectively improved the dispersive capacity and antioxidative stability of PbS nanoparticles. The thermal stability of DDP coating on the surface of nano-PbS particles was higher than that of modifier PyDDP because of the chemical interaction between PyDDP and PbS during the coating process.
I. INTRODUCTION
Nanosized particles have received considerable attention in recent years because of their special physical and chemical properties. A variety of methods for preparing nanoparticles and evaluating their properties have been developed recently.1–5 In the past few years, the focus has been on preparation of nanoparticles using surface modification.6–9 By coating the surface with modification agents of high molecular weight hydrocarbon, the nanoparticles thus prepared would have good disperse capacity in organic solvents and in lubricating oil. Sulfides have been widely used in lubricating grease to improve the antiwear ability. However, they are not suitable for lubricating oils because of their poor dispersive capacity. Similarly, nanosized sulfides are not expected to be good candidates for such purpose because they are liable to oxidize and tend to agglomerate when exposed in air, and have poor dispersive capacity in lubricating oils. Therefore, the application of various nanoparticles as novel potential additives for lubricating oils is impractical unless improvement in their thermal and antioxidant stability and dispersive capacity is realized rationally. Nanoparticles of di-n-hexadecyldithiophosphate (DDP) coated MoS2 and organic acid coated TiO2 were successfully synthesized in our laboratory, and the antiwear ability of the modified nanoparticles as additives in liquid paraffin was investigated as well.9–11 It has been a)
Address all correspondence to this author. J. Mater. Res., Vol. 14, No. 5, May 1999
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found that they exhibited good dispersion capacity and excellent antiwear behav
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