Sulfuric-Nitric Acid Pickle

Immerse parts for 5—20 s in the solution shown in (Table 6.14) at room temperature 

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Other Metals. Metals such as the austenitic series. Types 301—347, and the ferritic series. Types 409—446, of stainless steels may be enameled, as well as a number of other alloys (17). The metal preparation usually consists of degreasiag and grit blasting. Copper, gold, and silver are also enameled. These metals are usually prepared for appHcation by degreasiag. Copper is pickled usiag either a nitric acid [7697-37-2] or a sulfuric acid [7664-93-9] solution, followed by a dilute nitric acid dip. Silver may be pickled in hot dilute sulfuric acid followed by a dip in a nitric acid solution (18). 

About 3 billion kilograms of hydrochloric acid are produced each year, mostly as a by-product of the plastics industry. The largest single use of hydrochloric acid is the pickling of steel. The pickling process removes iron(III) oxide (FC2 O3, rust) from the surface of the metal. About a third of all hydrochloric acid is used to produce other chemicals, mostly ionic compounds. Other strong acids have specialized applications in indushy and research laboratories, but none approaches the importance of sulfuric, nitric, and hydrochloric acids. 

In the case of the production of copper wire, additional complications are present because of the chemical reduction of cupric oxide to a cuprous oxide coating, which cannot be removed by sulfuric acid. This coating has normally been treated by a secondary pickle of chromic acid-sulfuric acid, chromic acid-ammonium bifluoride mixtures, or by nitric acid. All of these techniques produce additional pollutants. Each of the three to four drawing steps required to produce fine copper wire from copper rod requires these pickling and rinse steps. 

Sulfur Mortars Hot melt-and-pour sulfur mortars are ancient, doubtless one of the oldest of all chemical resistant materials still used today. They are very resistant to non-oxidizing acids and weak alkalies below 200°F over a pH range of 0-12. Three types of sulfur mortars are typically employed (1) One containing an all-silica filler with minimum plasticizer, used to bond acid brick (2) A mortar with an all-carbon filler and minimum plasticizer, used primarily to lay carbon brick for nitric-hydrofluoric acid pickling tanks (to clean stainless steels) and the underlying floors and (3) A much more flexible all-silica filled product with double the amount of plasticizer of the other two mortars, used to join vitrified clay (terra cotta) pipe conveying waste acids and other effluent chemicals, and to assemble "pole line hardware" for the power industry. 

Figure 15 shows other products that are made with acids. Sulfuric acid is used in the production of fertilizers, steel, paints, and plastics. Acids often are used in batteries because their solutions conduct electricity. For this reason, it sometimes is referred to as battery acid. Hydrochloric acid, which is known commercially as muriatic acid, is used in a process called pickling. Pickling is a process that removes impurities from the surfaces of metals. Hydrochloric acid also can be used to clean mortar from brick walls. Nitric acid is used in the production of fertilizers, dyes, and plastics. 

USE Manuf of nitric acid and as catalyst in the manuf of sulfuric acid. Manuf sodium nitrite, glass, enamels for pottery in matches for improving burning properties of tobacco pickling meats as color fixative in meats. The technical grade is used as fertilizer. 

Processing rather concentrated mixtures of hydrochloric, nitric, or sulfuric acids with their metal salts, resulting, for example, from metal acid pickling, has been the successive niche of the acid retardation process [115]. The latter actually presents a very fortunate experimental finding, the physical sense of which remained obscure tiU our days. For this reason its application was limited to the partial recovery of excess acid from its mixtures with salts by frontal chromatography on strong anion exchanging resins. 

Chemical Methods. Chemical methods include pickling, which can be used to remove scale and metal oxides. Sulfuric acid and hydrochloric acid are usually used to treat steel and zinc, while nitric acid, nitric acid-hydrofluoric acid, or sulfuric acid-hydrofluoric acid are used for aluminum. Although pickling in phosphoric acid is somewhat slower, it has the advantage that a thin conversion layer of the substrate phosphates is produced, which provides temporary corrosion protection... 

The nitric acid distills off at 86°C. Sulfuric acid is also used for the manufacture of soluble phosphate fertilizers, of ammonium sulfate for use as a fertilizer, and of other sulfates, and in the manufacture of many chemicals and drugs. Steel is usually cleaned of iron rust (is pickled ) by immersion in a bath of sulfuric acid before it is coated with zinc, tin, or enamel. Sulfuric acid is used as the electrolyte in ordinary lead sulfate electric storage cells. 

Phosphoric acid-nitric acid - 647, 738 Phosphoric acid pickling solution - 696 Phosphoric acid scrap liquor - 44, 45 Phosphoric acid slurry - 697 Phosphoric acid-sulfuric acid - 697, 725 Phosphoric acid, wet process - 697, 698 Phosphoric anhydride (see Phosphorus pentoxide) Phosphorous acid - 42, 43, 237, 245, 386, 390, 554,661,795... 

Like nitric acid, sulfuric acid is used to manufacture fertilisers, detergents, paints, pigments, dyes and synthetic fibres, ft is also used to make various chemicals and plastics, as well as being used in car batteries, tanning leather and cleaning metal surfaces ( pickling ). 

The acidic pickling can be done by using acidic solutions of different acids like sulfuric acid, phosphoric acid, hydrofluoric acid, nitric acid, or chromic acid. The etching depth can vary from a few micrometers only to about 50 pm. The etching rate depends on which acid is used it is high for sulfuric acid and low for nitric acid. 

Zinc and Zinc Alloys. Zinc metal is highly reactive in acid solutions such as sulfuric, hydrochloric, and nitric dissolving rapidly at acid concentrations normally used to pickle steel and aluminum. Dilute (1—4%) solutions of these acids can be used with caution to remove zinc oxides. 

Zirconium is readily attacked by acidic solutions containing fluorides. As Httle as 3 ppm flouride ion in 50% boiling sulfuric acid corrodes zirconium at 1.25 mm/yr. Solutions of ammonium hydrogen fluoride or potassium hydrogen fluoride have been used for pickling and electropolishing zirconium. Commercial pickling is conducted with nitric—hydrofluoric acid mixtures (see Metal surface treatments). 

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