Soda attack

On the other hand, the specimens with a silica/alumina ratio of 40 60 consisted largely of mullite and formed a sodium aluminate rather than a sodium silicate. First, the soda attacked the excess alumina to form a sodium aluminate. As the reaction with soda proceeded, the mullite decomposed, forming nepheline and more sodium aluminate. 

Current practice is to use magnesia-zircon brick that contain 14 to 19% forsterite in lower checkers when V2O5 attack is anticipated The potential for liquid formation is dependent on many factors, including the concentration of V2O5 and the temperature at which the checker is operating. In addition, soda attack on forsterite can be a consideration under certain conditions, such as in reducing atmospheres. 

Mona.Zlte, The commercial digestion process for m on a site uses caustic soda. The phosphate content of the ore is recovered as marketable trisodium phosphate and the rare earths as RE hydroxide (10). The usual industrial practice is to attack finely ground m on a site using a 50% sodium hydroxide solution at 150°C or a 70% sodium hydroxide solution at 180°C. The resultant mixed rare-earth and thorium hydroxide cake is dissolved in hydrochloric or nitric acid, then processed to remove thorium and other nonrare-earth elements, and processed to recover the individual rare earths (see... 

There are two serious problems associated with continuous tar distillation. Coal tar contains two types of components highly corrosive to ferrous metals. The ammonium salts, mainly ammonium chloride, associated with the entrained Hquor remain in the tar after dehydration, tend to dissociate with the production of hydrochloric acid and cause rapid deterioration of any part of the plant in which these vapors and steam are present above 240°C. Condensers on the dehydration column and fractionation columns are also attacked. This form of corrosion is controlled by the addition of alkaU (10% sodium carbonate solution or 40% caustic soda) to the cmde tar in an amount equivalent to the fixed ammonia content. 

Copper alloys are attacked at high pH. However, attack is usually caused not by elevated pH alone but because of copper complexation by ammonia or substituted ammonium compounds. In fact, copper resists corrosion in caustic solutions. For example, corrosion rates in hot caustic soda may be less than 1 mil/y (0.025 mm/y). 

Copper-alloy corrosion behavior depends on the alloying elements added. Alloying copper with zinc increases corrosion rates in caustic solutions whereas nickel additions decrease corrosion rates. Silicon bronzes containing between 95% and 98% copper have corrosion rates as low as 2 mil/y (0.051 mm/y) at 140°F (60°C) in 30% caustic solutions. Figure 8.2 shows the corrosion rate in a 50% caustic soda evaporator as a function of nickel content. As is obvious, the corrosion rate falls to even lower values as nickel concentration increases. Caustic solutions attack zinc brasses at rates of 2 to 20 mil/y (0.051 to 0.51 mm/y). 

The amine attacks cork and rubber and absorbs carbon dioxide from the air. It is best distilled in a flask having an in-set side arm and collected in a distilling flask protected by a soda-lime tube. 

Chemical Reactivity - Reactivity with Water Reacts violently, forming corrosive and toxic fumes of hydrogen bromide Reactivity with Common Materials Attacks and corrodes wood and most metals in the presence of moisture. Flammable hydrogen gas may collect in enclosed spaces Stability During Transport Stable if protected from moisture Neutralizing Agents for Acids and Caustics Hood with water, rinse with dilute sodium bicarbonate or soda ash solution Polymerization Not pertinent Inhibitor of Polymerization Not pertinent. 

Chemical Reactivity - Reactivity with Wo/er.- Reacts with moisture in air forming a dense white fume. Reaction with liquid water gives off heat and forms hydrochloric acid Reactivity with Common Materials The acid formed by reaction with moisture attacks metals, forming flammable hydrogen gas Stability During Transport Stable Neutralizing Agents for Acids and Caustics Acid formed by the reaction with water can be neutralized by limestone, lime, or soda ash Polymerization Not pertinent Inhibitor of Polymerization Not pertinent. 

High-silicon irons are inferior to unalloyed grey irons in their resistance to attack by alkalis. For example, boiling 20% caustic soda solution or 50% caustic soda at 80°C will attack high-silicon irons at rates of the order of l-27mm/y (grey iron would be attacked at rates not greater than 0-25 mm/y). 

No dimensional change Proprietary brands of alkaline cleaners may be used provided these do not attack metal Soda ash with washing soda and soap are suitable for preparing alkaline cleaning baths No dimensional change unless much impurity is present For small delicate parts 0 1-0-5% silver chromate may be added to reduce attack caused by impurities such as chloride in corrosion product... 

Molybdenum is extremely resistant to attack by molten glass up to 1 000° C if sulphur is present, and up to 1 400°C in its absence. In addition, any reaction products formed by the two materials are colourless. Consequently molybdenum is used in the production of optical and soda lime glasses. Molybdenum is, however, corroded by lead glasses which lose their gloss as a result of the interaction between the two materials. ... 

Silica is susceptible to attack by all three reagents, the rate of corrosion increasing with temperature and concentration. Hence 5% caustic soda solution can be contained in fused silica at room temperature, but attack becomes significant at pH values greater than 9, as shown in Fig. 18.3. 

Attention must be directed to the fact that alkaline solutions, particularly if concentrated, attack glass. They may be preserved, if required, in polythene bottles, which are resistant to alkali. Furthermore, solutions of the strong bases absorb carbon dioxide from the air. If such solutions are exposed to the atmosphere for any appreciable time they become contaminated with carbonate. This may be prevented by the use of a storage vessel such as is shown in Fig. 3.9 the guard tube should be filled with soda-lime. A short exposure of an alkali hydroxide solution to the air will not, however, introduce any serious error. If such solutions are quickly transferred to a burette and the latter fitted with a soda-lime guard tube, the error due to contamination by carbon dioxide may be neglected. 

Borosilicate glass (known by several trade names, including Pyrex) is used for chemical plant as it is stronger than the soda glass used for general purposes it is more resistant to thermal shock and chemical attack. 

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