Corrosion product chemical cleaning procedures

For the determination of weight loss, the corrosion products have to be removed. Inhibited acids are normally used for this purpose, but it is important to be sure that such acids remove only the corrosion products and do not attack the base metal. For example, the following acids could be used inhibited hydrochloric acid for iron, sulfuric acid for copper, and chromium trioxide solutions for zinc. The chemical cleaning procedures for the removal of corrosion products are further described in ISO 8407 (3). The removal of corrosion products is also necessary to confirm homogenous corrosion and exclude possible local corrosion attack. 

Chemical Cleaning Procedures for Removal of Corrosion Products ... 

CHEMICAL CLEANING PROCEDURES FOR REMOVAL OF CORROSION PRODUCTS 45... 

Shortening units are constructed of carbon steel. The water phase in margarine is corrosive, and sanitation procedures require that all of the equipment used to manufacture it must be chemically cleaned. Margarine processing units contain chromium-plated commercially pure nickel heat transfer tubes and stainless steel for all product-contacted metal surfaces. 

Moreover, some of the gases have chemical properties (corrosive, highly toxic, self-igniting) that require the use of special equipment on the compressed gas containers (i.e. remotely controlled, pneumatically operated cylinder valves, flow restrictors, metal-to-metal seal between cylinder valve and process lines). Containers for electronic gases are subject to special cleaning procedures to remove particles, organic impurities, deposits and corrosion products from their inner surface. Depending on the chemical properties of the respective product and the speciflc demands in the respective field of application, apart from the usual steel containers also inside polished containers of steel, stainless steel or aluminium are used. 

SACHEM Inc., located in Cleburne, Texas, is a producer of high-purity bulk chemicals for companies that have high-purity requirements in their chemical processing. As stated in Workplace Scene 1.2, one of their products is tetramethylammonium hydroxide (TMAH), which is sold to semiconductor industries. The analysis of TMAH for trace anions such as chloride, nitrate, nitrite, and carbonate is critical for SACHEM s quality control laboratory. If these ions are present on the integrated circuit boards manufactured by one of their semiconductor customers, they may cause corrosion severe enough to affect the functionality and performance of the electronic devices in which the circuit boards are used. In SACHEM s quality control laboratory, ion chromatography procedures have been developed to measure the anion concentrations in TMAH. Because the concentration levels are trace levels, a clean room environment, like that described in Workplace Scene 1.2, is used. A special procedure for carbonate analysis is required so that the absorption of carbon dioxide from the atmosphere can be minimized. 

Friedel-Crafts acylation is one of the most important methods for the synthesis of ketones [1]. To achieve satisfactory reaction rates, catalysts such as aluminium chloride are usually needed in more than stoichiometric amounts because of complexation to starting materials and/or products. Work-up often involves hydrolysis, which leads to loss of the catalyst and causes problems with corrosion and disposal of potentially toxic wastes. Also, reactions are not always clean and may lead to mixtures of products. Recourse to recoverable and regenerable solid catalysts can overcome many problems of these types [2]. Therefore, the development of new heterogeneous catalytic procedures for the acylation of organic compounds has become a priority for the chemical industry. 

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