In other words, the Arrhenius equation is not valid for metal electrochemical corrosion reactions and the rate of the reaction is not doubled for every 10°C (50°F) increase in the storage temperature above room temperature. Consequently, increasing temperature does not reduce the time needed for a corrosion stability test. I’ve observed many situations where: 1. Aerosol containers were perforated at room temperature and were corrosion-free at the higher temperature; 2. Containers were corrosion-free at room temperature and perforated at a higher temperature, and 3. The depth and amount of corrosion was not twice the amount for each 10°C (50°F) increase in the storage temperature above room temperature. It’s tempting to say that the second situation is actually a worst-case-scenario and thus a valid test technique. However, in the second example—corrosion-free at room temperature and perforated at the higher temperature—a commercially viable formula would be rejected because of the higher temperature results. In other words, worst-case testing is not recommended for today’s highly competitive markets, particularly when every successful new formula and formula derivative contributes to competitiveness and market leadership. Am I recommending not conducting tests at higher temperatures? No. Higher temperature testing is needed, particularly when your products are marketed in regions with high summer temperatures. However: • Don’t use the higher temperature to accelerate package material corrosion rates in order to reduce test times; • Use higher temperature storage to determine if there are possible formula thermal instability issues that could cause package material corrosion; • Conduct tests at higher temperatures that reflect the actual high temperatures for the regions in which your products are marketed; • Use higher temperature test lengths that reflect the actual number of hours per year when the temperature is at or above a threshold temperature, such as 32°C (89.6°F). Pair O Docs has a state-of-the art corrosion testing laboratory, and in 2016 we introduced a Corrosion Partnership Program that provides a cost effective mix of all Pair O Docs services under a single purchase order. Contact: rustdr@pairodocspro. com; 608-831-2076; www.pairodocspro.com if you would like to know more or want to have our Elements course taught at your R&D facility. Thanks for your interest and I’ll see you in April. Spray info@condensa.cl • www.condensa.com • +56 225 195 759 • 2879 Marathon Av. - Santiago - Chile - 7810772 March 2017 Spray 37
Spray March 2017
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