Sodium hydroxide anodization

Sodium hydroxide anodization Recently Kennedy et al. have claimed that anodization in 5 M sodium hydroxide at 20 1°C for 30 min at 10 volts produced more durable bonds than did a 10-volt chromic acid anodization process. ... 

A number of attempts have been made to develop an alkaline peroxide anodize for titanium. However, the process requires careful control in order to provide durable adhesive joints. A recently developed sodium hydroxide anodize treatment appears to provide excellent durability and easy process control. The wedge test was used with exposure times of up... 

FIGURE 14. STEM photomicrographs of (a) a sodium hydroxide anodized surface (100,000 x) and (b) a pickled sodium hydroxide anodized surface (100,000x). (From Reference 19.)... 

Sodium hydroxide is manufactured by electrolysis of concentrated aqueous sodium chloride the other product of the electrolysis, chlorine, is equally important and hence separation of anode and cathode products is necessary. This is achieved either by a diaphragm (for example in the Hooker electrolytic cell) or by using a mercury cathode which takes up the sodium formed at the cathode as an amalgam (the Kellner-Solvay ceW). The amalgam, after removal from the electrolyte cell, is treated with water to give sodium hydroxide and mercury. The mercury cell is more costly to operate but gives a purer product. 

Electrolytic Preparation of Chlorine and Caustic Soda. The preparation of chlorine [7782-50-5] and caustic soda [1310-73-2] is an important use for mercury metal. Since 1989, chlor—alkali production has been responsible for the largest use for mercury in the United States. In this process, mercury is used as a flowing cathode in an electrolytic cell into which a sodium chloride [7647-14-5] solution (brine) is introduced. This brine is then subjected to an electric current, and the aqueous solution of sodium chloride flows between the anode and the mercury, releasing chlorine gas at the anode. The sodium ions form an amalgam with the mercury cathode. Water is added to the amalgam to remove the sodium [7440-23-5] forming hydrogen [1333-74-0] and sodium hydroxide and relatively pure mercury metal, which is recycled into the cell (see Alkali and chlorine products). 

Sodium was made from amalgam ia Germany duriag World War II (68). The only other commercial appHcation appears to be the Tekkosha process (74—76). In this method, preheated amalgam from a chlor—alkali cell is suppHed as anode to a second cell operating at 220—240°C. This cell has an electrolyte of fused sodium hydroxide, sodium iodide, and sodium cyanide and an iron cathode. Operating conditions are given ia Table 6. 

Chlorate. Conversion to metal anodes has also taken place in this process. Sodium hydroxide, which is formed at the cathode, reacts to form the sodium chlorate product (see Alkali and chlorine products). 

The generated chlorine dioxide must be air stripped from the anode compartment in order to achieve high chlorite conversion efficiency. Sodium ions from the anode compartment are transported into the cathode compartment, forming sodium hydroxide [1310-73-2] and hydrogen gas coproducts ... 

Other industrial applications of electrolysis include extraction/purification of metals from ores, electroplating, and the manufacture of certain chemicals such as sodium hydroxide. In the latter, sodium chloride solution when electrolysed is converted to sodium hydroxide to produce chlorine at the anode and hydrogen at the cathode. Both of these gaseous by-products are collected for industrial use chlorine is used in the production of bleach and PVC hydrogen is used as a fuel, to saturate fats, and to make ammonia. 

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