Coordination driers

Zirconium. Zirconium 2-ethyIhexanoate [22464-99-9] is classified as an auxihary drier and is the most widely used replacement for lead. Zirconium improves through dry mainly by the formation of coordination bonds. It has excellent color, a low tendency to yellow, and better durability compared to other auxiliary metals. 

Constipation can be due to primary and secondary causes (Table 18-1). Primary or idiopathic constipation is typified by normal-transit constipation, slow-transit constipation, and dyssynergic defecation. In the normal-transit type, colonic motility is unchanged and patients tend to experience hard stools despite normal movements. In the slow-transit type, motility is decreased leading to infrequent harder, drier stools. In dyssynergic defecation (also known as pelvic floor dysfunction), patients have lost the ability to relax the anal sphincter while coordinating muscle contractions of the pelvic floor. Some causes of secondary constipation are listed in Table 18-1. 

Thus a drier, less sintered support is obtained by calcining in CO rather than air. Unfortunately the chromium will not tolerate such a severe reduction treatment, and unless Cr is added secondarily [as in the above (Section V,B) examples] a dead catalyst results. This is shown in Fig. 5, where it is apparent that reduction at 350°C improves activity, whereas higher temperatures destroy it. This does not indicate overreduction, as some have claimed. Rather, it indicates a rearrangement of the Cr(II) into a less coordinatively unsaturated form—possibly aggregates. 

Lead was used for years as a very effective through-drier, but for ecological and toxicity reasons, is rarely used in recent years. Zirconium driers are by far the most widely accepted replacements for lead. They improve through-drying mainly by the formation of coordination bonds with hydroxyl and carboxylic acid groups of the resin, and also by increasing the catalytic effect of primary driers. 

This group of raw materials is used in relatively small amounts to give coatings certain necessary properties (driers really belong in this category). Since additive compositions are not normally revealed by manufacturers, the following discussion refers to trade names. On occasion, additives are used at the job site if problems arise. In such cases, there should be close coordination with and supervision by the paint manufacturer to avoid even greater problems. 

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