Pressure-atomized sulfur coatings

Figure 16. Cross section showing poorly developed mosaic texture and low elasticity of intergranular sulfur in pressure-atomized sulfur coating...

When urea is coated with pressure-atomized sulfur at about 180 °F and quickly cooled, a mosaic texture is developed, as in the cross section of the sulfur coating in Figure 15. This mosaic texture is well developed and is characterized by high ratios of the areas of crystalline to carbon disulfide-insoluble sulfur. The mosaic texture in such samples is different... 

Figure 22. Exterior surface with pat- Figure 23. Spherical void in the cross terned cracks in an improperly cooled section of a pressure-atomized sulfur sulfur coating coating...

In many of the cross sections of pressure-atomized coatings, spherical voids are common and occasionally have diameters that are a significant fraction of the total coating thickness. This causes a localized decrease in the effective coating thickness (Figure 23) and may reflect gas entrainment associated with the relatively large size of the pressure-atomized sulfur droplets. 

The products described here were produced in the TVA pilot plants and represent a range of dissolution rates that can be correlated with different coating and cooling temperatures, as well as with coating thicknesses. The coatings were applied by air and pressure atomization of the sulfur. 

Figure 14. Partially coated urea gran- Figure 15. Cross section of well de-ule showing positive contact angle he- veloped mosaic texture in higher tem-tween sulfur droplets and the exterior perature pressure-atomized coating surface of the granule cooled quickly...

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