Sodium sesquicarbonate

Bronze disease necessitates immediate action to halt the process and remove the cause. For a long time, stabilization was sought by removal of the cuprous chloride by immersing the object in a solution of sodium sesquicarbonate. This process was, however, extremely time-consuming, frequentiy unsuccesshil, and often the cause of unpleasant discolorations of the patina. Objects affected by bronze disease are mostiy treated by immersion in, or surface appHcation of, 1 H-henzotriazole [95-14-7] C H N, a corrosion inhibitor for copper. A localized treatment is the excavation of cuprous chloride from the affected area until bare metal is obtained, followed by appHcation of moist, freshly precipitated silver oxide which serves to stabilize the chloride by formation of silver chloride. Subsequent storage in very dry conditions is generally recommended to prevent recurrence. 

The dissociation of hypochlorous acid depends upon pH and, to a much lesser extent, temperature (6). At 25°C, it is - 0% at pH 5, about 50% at pH 7.5, and - 100% at pH 10, see Figure 1. Because of the acidity formed by chlorine gas, addition of soda ash (Na2C02) or sodium sesquicarbonate (Na2C03-NaHC03) is necessary to maintain the proper pH and to replenish alkalinity. 

In 1864 Ernest Solvay, a Belgian chemist, invented his ammonia-soda process. A few years later the soda ash price was reduced one third. The Solvay process had completely replaced the LeBlanc method by 1915. The Solvay method is still very popular worldwide. However, in this country large deposits of natural trona ore were found in the 1940s in Green River, Wyoming. In the last few years there has been a tremendous conversion from synthetic to natural soda ash. The first and last Solvay plant in the U.S. closed in 1986 (a large Allied Chemical plant in Solvay, NY). Trona ore is found about 500 m below the surface. It is called sodium sesquicarbonate... 

Sodium Sesquicarbonate occurs as white crystals or flakes or as a crystalline powder. It is soluble in water, and its solutions are alkaline to litmus. 

FIGURE 9-3 Hydrogen atom positions of water in sodium sesquicarbonate. 

C. J. Brown, H. S. Peiser, and A. Turncr-Jones. Acta Cryst. 2,167-74 (1949). Crystal structure sodium sesquicarbonate. 

In humid air, there is a slow decarboxylation of NaHCOs, where as sodium sesquicarbonate Na2C03 NaHCOs 2H2O is formed. ... 

Carbonate ion. Redetermination of the C—0 bond length in calcite and in K2CO3. 3 H2O gives values close to 1-29 A, though the lower value 1 25 A was found in sodium sesquicarbonate (p. 314) which has been studied by both X-ray and neutron diffraction. 

See soda ash sal soda sodium bicarbonate sodium carbonate monohydrate sodium sesquicarbonate. 

CAS 497-19-8. Na,C0) NaHC0) 2H20. A natural sodium sesquicarbonate and the most important of the natural sodas. 

Because complexation with Ca2+ results in insoluble CaCC>3, which deposits on items being washed, carbonate alone is not an effective builder system. In contrast, tripolyphosphate forms a soluble calcium salt, preventing deposition of insoluble salts. Sodium sesquicarbonate (Na2CC>3 NaHC03 -2 0) and sodium bicarbonate (NaHCCb) have not been used in LADD formulations, except where buffering action is needed. 

If there is a conservation laboratory nearby, immerse the artefact straight away in an electrolyte, which passivates any exposed metal. The pH can be ascertained from the relevant E-pH diagram for the metal concerned and examples for ferrous artefacts would be 0.5 M sodium hydroxide, 0.2 M sodium sesquicarbonate or 0.5 M sodium carbonate. 

Sodium sesquicarbonate, Na3HY2.2HgO, where H2Y=carbonic acid, was mentioned in the introduction. Its structure (75) is partially of Type A j. Salts of the cations cis- and /mws-[Coe gCl2]+ with maleic, glutaric, malonic, thiodiacetic and other acids have been prepared, with variously superacid compositions (76). 

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