Boiling nitric acid test

The evaluation of heat treatments or the effectiveness of stabilisation by limiting carbon content of these stainless steels can be determined by subjecting specimens to the ASTM standardised acid copper sulphate test or boiling nitric acid test (ASTM A262 1986 see also Sections 9.5 and 1.3). 

This test has been developed and used by Streicher as a screening test to be used in conjunction with the tedious boiling nitric acid test for assessing the susceptibility of stainless steels to intergranular attack as specified in ASTM A262 1986, and will be considered subsequently in the section concerned with intergranular attack of Cr-Ni-Fe alloys. 

Part 1, p 874, Test A262-44T ("Tentative Recommended Practice for Boiling Nitric Acid Test for Corrosion-Resisting Steels ) Part 1, p 878, Test A279-44T (Total Immersion Corrosion Test for Stainless Steels) 18) Kirk Othmer 4 (1949)... 

DeLong, W. B., "Testing Multiple Specimens of Stainless Steels in a Modified Boiling Nitric Acid Test Apparatus," Symposium for Evaluation Tests for Stainless Steels, ASTM STP 93, ASTM International, West Conshohocken, PA, 1949, pp. 211-216. 

A 65% solution of boiling nitric acid test revealed that ILLIUM PD is up to 10 times more resistant to attack than 316 stainless steel Test results... 

Nitric acid test t 65 wt.% HNOj Five 48 h exposures to boiling solution refreshed after period Average mass loss per unit area of five testing periods -1- 0-99 to -1- 1-20 1. Chromium-depleted areas 2. <7-phase 3. Chromium carbide... 

Nitrate of silver gives a white clotty precipitate, soluble in boiling nitric acid and which, when dried and heated in a test tube, evolves fumes of cyanogen, which burn with a violet or bluish colored flame. A watch glass, moistened with this test and inverted over matter containmg hydrocyanic acid, be-oomos opaque and white firom the formation of cyamde of flAver. 

Characters and Tests.—Colourless liquid, with a peculiar odour. Sp. gr. 0 997. With potassium hydrate and a mixture of ferrous and ferric sulphates it yields, after being acidulated with hydrochloric acid, a precipitate of Prussian blue. Silver nitrate furnishes a white curdy precipitate of silver cyanide, which is soluble in ammonia and in boiling nitric acid. Barium chloride should give no precipitate, proving the absence of sulphuric acid and sulphates. 

Characters and Tests.—Colourless odourless, translucent, fibrous masses, tough and difficult to powder soluble in water and in rectified spirit. Its aqueous solution, heated with potassium hydrate, evolves ammoniacal gas, which may be recognised by its odour with silver nitrate it gives a white curdy precipitate (silver chloride), insoluble in boiling nitric acid, soluble in ammonia. 

Characters and Tests.—Small, white, crystalline grains, or transparent cubic crystals, free from moisture purely saline taste soluble in water. Its aqueous solution mixed with hydrochloric acid and platinic chloride yields no precipitate, showing that it is neither an ammonium nor a potassium-salt. It imparts a yellow, colour to fiame, indicating that sodium is present and its aqueous solution gives with silver nitrate a white precipitate (silver chloride) soluble in ammonia, but Soluble in boiling nitric acid, proving the salt to be a chloride. 

Remove the Nitric Acid Test from ASTM A 262 and establish it as a separate ASTM Test At present, the boiling 65 % nitric acid test (Practice C) is specified for materials to be used in nitric acid service. Only this test is sensitive to sigma-phase in molybdenum-bearing austenitic stainless steels. Also, problems such as end-grain corrosion associated with hexavalent chromium derived from corrosion products are unique to this solution. While this test also detects susceptibility to intergranular attack associated with chromium carbide precipitates, there are other tests that perform this function in less time and with greater simplicity. 

As in any strongly conductive medium, aluminium is prone to galvanic corrosion in contact with other metals (see Chapter B.3) such as stainless steel. Tests have shown that in boiling nitric acid, the dissolution rate of aluminium is multiplied by five while that of stainless steel is divided by two. 

Reaction with alcoholic silver nitrate. To carry out the test, treat 2 ml. of a 2 per cent, solution of silver nitrate in alcohol with 1 or 2 drops (or 0 05 g.) of the compound. If no appreciable precipitate appears at the laboratory temperature, heat on a boiling water bath for several minutes. Some organic acids give insoluble silver salts, hence it is advisable to add 1 drop of dilute (5 per cent.) nitric acid at the conclusion of the test most silver salts of organic acids are soluble in nitric acid. 

Adds.—A free acid may be at once identified by its solubility in a holution of sodium carbonate and by being reprecipitated by concentrated hydrochloric acid. If a metal has been dis-coveied in the piehminary examination, a careful examination must be made for an organic acid. As the substance is insoluble ill water the metal will probably not be an alkali metal. Boil the substance with sodium carbonate solution. The sodium salt of the acid passes into solution and the metallic carbonate IS precipitated. Filter boil the filtrate with a slight excess of nitric acid, add excess of ammonia and boil until neutral, tests may then be applied in order to identify one of the common acids and the ni.p. determined but beyond this it is impossible to carry the investigation in a limited time. 

Add dilute ammonia solution until a faint permanent turbidity is obtained and then clear the solution by careful addition of a little dilute nitric acid. To the boiling solution add a slight excess of a solution of pure pyrogallol in air-free water. Continue boiling for a short time, test for completeness of precipitation and filter. Wash the precipitate with 0.05M nitric acid and then with water. Dry at 105 °C and weigh as Bi(C6H303) (Section 11.20). 

Procedure. The test solution should contain between 0.001 and 0.02 mg of cobalt. Evaporate almost to dryness, add 1 mL of concentrated nitric acid, and continue the evaporation just to dryness to oxidise any iron(II) which may be present. Dissolve the residue in 10 mL of water containing 0.5 mL each of 1 1 hydrochloric acid and 1 10 nitric acid. Boil for a few minutes to dissolve any solid material. Add 2.0 mL of a 0.2 per cent aqueous solution of nitroso-R-salt and also 2.0 g of hydrated sodium acetate. The pH of the solution should be close to 5.5 check with bromocresol green indicator or with a pH meter. Boil for 1 minute, add 1.0 mL of concentrated hydrochloric acid, and boil again for... 

---