Wurster

Wurster s salts Stable radical cations formed... 

Wurster process Wurster salts Wurtz-Fittigcoupling Wurtz-Fittig reaction Wurtzite... 

Fig. 8. Schematic diagram of a Wurster coating chamber. Courtesy of the Coating Place.

Air-Suspension Coa.ting. The Wurster process utilizes a cylindrical chamber in which the cores are suspended in a controlled stream of air. Film coatings are appHed by introducing the coating solution into the airstream, where the solvent evaporates quickly. The process is much quicker than film coating however, care must be taken to avoid destmction of the cores by attrition in the air stream. 

Scotts technology (17) uses fluid-bed (Wurster column) technology to apply polymeric coatings to a number of fertilizer substrates including urea, potassium nitrate, potassium sulfate, and monoammonium phosphate (MAP). The coating material is appHed as a water-borne latex onto the fluidized substrate. As the substrate is fluidized with warm air (40—50°C), water is driven off and the latex coalesces into a continuous film around the fertilizer particle. The particular latex compositions used have selected glass-transition and blocking temperatures, which enable quick removal of the water before the soluble fertilizer core dissolves. This obviates the need to use precoats prior to the latex appHcation. 

Draft Tube Designs and Spouted Beds A draft tube is often employed to regnlate particle circnlation patterns. The most common design is the Wurster draft tnbe flnidbea employed extensivelvin the pharmacentical industry, nsnally for coating and layered growtJi applications. The Wurster coater nses a bottom positioned spray, bnt other variations are available (Table 20-47). 

Wurster, R. Water Electrolysis and Solar Hydrogen Demonstration Projects 27... 

Peroxides N,N-Dimethyl-1,4-phenylenediamine (N,N-DPDD), N,N,N, N -tetra-methyl-l,4-phenylene-diamine (TPDD) Peroxides, e. g. alkyl hydroperoxides, oxidize N,N-DPDD to Wurster s red and TPDD to Wurster s blue. [17] [34]... 

Peroxides oxidize N,N-DPDD to Wurster s red, a semiquinone diimine derivative [4]. Similarly Wurster s red is also produced from N,N-DPDD by reaction with halogen-containing substances in the presence of sodium ethylate and UV light and by reaction with the chlorinated triazines produced by reaction with chlorine [7]. 

The substances methoprotryn (hRf 30-35), desmetryn (h/ f 40-45), ametryn (hRf 55-60), prometryn (h/Jf 65-70) and dipropretryn (h/ f 70-75) separated using mobile phase 1 and the components cyanazine (hRf 20-25), simazine (tiRf 30-35), atrazine (hRf 35-40), terbutylazine (h/Jj 45-50) and anilazine (h/ f 60-65) chromatographed with mobile phase 2 all yielded intense grey to brown-colored zones on a light brown background, that appear intense purple-red when viewed from the back of the plate (Wurster s red). 

Peroxides oxidize TPDD to Wurster s blue, a product with a semiquinone diimine structure [1]. Similarly Wurster s blue is also produced from TPDD by reaction with halogen-containing substances produced by the reaction of aromatic amines and triazines with chlorine gas. 

Table 1 Comparison of the reaction of pesticides (amounts applied 0.8 ng, without chromatographic development) with N,N-DPDD (Wurster s Red) and TPDD (Wurster s Blue) reagents [4] - = negative, (+) = weakly positive and + + + = positive reaction.

Substance dass/Substance Wurster s Red Reaction Wurster s Blue Reaction... 

Van Urk-Salkowski Reagent Wurster s Blue Reagent Wurster s Red Reagent... 

Peroxides, e.g. alkyl hydroperoxides, oxidize N.N-DPDD to Wurster s red and TPDD to Worster s blue. 

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