Nitric acid, highly concentrated

Zirconium resists attack by nitric acid at concentrations up to 70 wt % and up to 250°C. Above concentrations of 70 wt %, zirconium is susceptible to stress-corrosion cracking in welds and points of high sustained tensile stress (29). Otherwise, zirconium is resistant to nitric acid concentrations of 70—98 wt % up to the boiling point. 

Aluminum is resistant to nitric acid at concentrations above 80%. At 50% nitric acid concentration at room temperature, corrosion rates are as high as 0.08 in. (0.20 cm) per year. 

The viscosity of the sol, which is very important in relation with the dropping, will be controlled by the concentration of the powder, urea and nitric acid. Pseudoboehmite concentrations as high as 33 wt.% are possible. Urea addition lowers the viscosity of the sol and there is an optimum viscosity, depending on the amount of acid added. To obtain a good dispersion of the alumina particles in the sol, the sol must be made by using a high shear mixer. The sol of the correct viscosity is pumped through the orifices and the droplets will fall into the oil... 

Low-level aqueous wastes from steps 6 and 8 are processed for further recovery of plutonium and uranium, then concentrated for recovery of water and nitric acid. High-level aqueous wastes from step 4 are concentrated by evaporation, with recovery of condensed nitric acid in step 11. 

STERICOL (1300-71-6) see xylenols. STIBINE (7803-52-3) SbHj Flammable, highly poisonous, and thermally unstable gas (Fire Rating 4). Reacts with moisture, forming explosive hydrogen. Elevated temperatures above 390°F/198°C can cause fire and explosion. Reacts violently or explosively with strong oxidizers, nitric acid (especially concentrated HNOj), halogenated hydrocarbons, ammonia, ozone. Forms heat-sensitive explosive mixtures with ammonia. Only if flow can be stopped on small fires, use dry chemical powder (such as Purple-K-Powder), foam, or COj extinguishers. If flow cannot be stopped, evacuate and let fire bum itself out. 

Chlorinated and aromatic hydrocarbons, organic esters, aromatic hydroxy compounds, and certain ketones have an adverse effect on neoprene, and consequently, only limited serviceability can be expected with them. Highly oxidizing acid and salt solutions also cause surface deterioration and loss of strength. Included in this category are nitric acid and concentrated sulfuric acid. 

Lead metal resists hydrochloric acid, highly concentrated sulfuric acid and hydrofluoric acid, but it dissolves readily in warm, dilute nitric acid. Lead is also corroded by weak organic acids such as acetic acid or tartaric acid in the presence of oxygen [7]. 

Nitration of Alkenes. Alkenes may also be nitrated by nitric acid. This reaction has been exploited in tbe synthesis of a number of steroid derivatives. Fuming nitric acid converts cholesteryl acetate to 6-nitrocbolesteryl acetate in good yield (eq 5). The nitration of the more highly functionalized dienyl acetate (eq 6) provides the corresponding nitro steroid. Treatment of 1,1-dichloro-2-fluoroethylene with nitric acid in concentrated sulfuric acid provides fluoronitroacetyl chloride in 16% yield. 2-Sulfolenes have also been nitrated. ... 

However, even accepting that there are examples of instable MOFs, several MOFs have been reported in the literature whose chemical stability has been demonstrated beyond any doubt. Among these robust MOFs, ones that have been widely used in catalysis are MIL-100 and MIL-101. These two MOFs are so stable that they can stand even nitric acid in concentrations that are sufficiently high to produce nitration of the organic linker. Under these conditions, many zeolites such as zeolite Y would undergo damage to a very large extent. 

As demand for nitric acid increased, efforts were made to improve the process by operation at higher pressures, which would allow the use of smaller equipment with lower capital costs. High pressure could also provide higher acid concentrations with more efficient absorption and an increased rate of reaction in converting nitrogen oxides to nitric acid. High-pressure operation was made possible when chromium and chromium/nickel alloy steels replaced ceramic materials. 

Therefore, in order to prevent as far as possihio in the action of nitric acid on glycerine the formation of mono- and di-nitro-glycerine, care must be taken to remove the freshly formed water as soon as possible, and this can be done by mixing the nitric acid with concentrated sulphuric acid. The re.sulting water is at once bound by the sulphuric acid, and during the whole process the nitric acid keeps tlic necessary high concentration. 

It is found experimentally, however, that if benzene is treated with concen trated nitric acid alone, the yield of nitrobenzene is small. If, however, the nitric acid is first mixed with concentrated sulphuric acid, a high yield of nitrobenzene results. 

Solutions of nitric acid in 100% sulphuric acid have a high electrical conductivity. If nitric acid is converted into a cation in these solutions, then the migration of nitric acid to the cathode should be observed in electrolysis. This has been demonstrated to occur in oleum and, less conclusively, in concentrated acid, observations consistent with the formation of the nitronium ion, or the mono- or di-protonated forms of nitric acid. Conductimetric measurements confirm the quantitative conversion of nitric acid into nitronium ion in sulphuric acid. ... 

Accepting, for the moment without further evidence, that the nitro-nium ion formed by heterolysis of nitric acid is the active reagent in the solutions imder discussion, it remains to consider briefly why nitration in such solutions depends on the concentrations of nitric acid to such high powers (fig. 3.1), and why different solvents behave so differently (table 3.2). 

Here we have the formation of the activated complex from five molecules of nitric acid, previously free, with a high negative entropy change. The concentration of molecular aggregates needed might increase with a fall in temperature in agreement with the characteristics of the reaction already described. It should be noticed that nitration in nitromethane shows the more common type of temperature-dependence (fig. 3.1). 

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