It has been discovered that macro-spherical tungsten disulfide particles may be produced in a two-step process. The substantially spherical particles have an average particle diameter of from about 5 to about 50 micrometers, and more preferably from about 10 to about 25 micrometers. The particles tend to be hollow and possess an onion-like structure whereby the outer layers can be peeled away. Because of this, a fraction of the powdered material is comprised of pieces of the macro-spherical particles which appear much like broken egg shells.

 

In a first step, the macro-spherical particles of tungsten oxide are produced by heating a spray-dried ammonium metatungstate (AMT) powder in air at about 500° C. As shown in FIG. 2, the spray-dried AMT particles have a spherical morphology with a number of the particles appearing to comprise hollow spheres.

 

In a second step, the tungsten oxide particles are converted to tungsten disulfide by heating in a carbon disulfide-containing atmosphere at about 750° C.

 

In another embodiment, a bimodal distribution of macro-spherical and smaller, dispersed micron- to submicron-sized fine particles of tungsten disulfide are prepared by heating spray-dried powders of ammonium metatungstate in air, mixing the resultant tungsten trioxide with a tungsten metal powder, and sulfidizing the mixture in carbon disulfide at about 750° C. The resultant tungsten disulfide powder contains a bimodal distribution of the macro-spherical tungsten disulfide particles and fine tungsten disulfide particles having an average particle diameter of from about 0.5 to about 5 micrometers. Preferably, the fine particles have an average particle diameter of from about 1 to about 3 micrometers.

 

 

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