ASTM-A90/A90M:21 pdf free download – Standard Test Method for Weight [Mass] of Coating on Iron and Steel Articles with Zinc or Zinc-Alloy Coatings.
hydrochloric acid-antimony trichloride method. Hydrochloric acid fumes are present, and hydrogen gas is evolved in the stripping process. Therefore, the test should be performed under conditions of adequate ventilation. A fume hood is recommended for large numbers of samples or where the test is to be carried out frequently over extended periods of time.
5.2 Warning—Mixing of sulfuric acid with water could result in severe injuries if not properly done. Mixing must be done by slowly adding sulfuric acid to water due to the heat generated and possible splashing. Under no circumstances should the water be added to the acid. The mixing should he performed under an acid fume hood.
6. Sampling
6. 1 Zinc-Coated Shees—Samples for weight I mass I of coating determination shall he secured in accordance with Specifications A653/A653M, A792/A792M, A875/A875M, A 1046/Al 046M, A 1057/Al 057M, Al 063/Al 063M, or Al 079 depending on the type of coating.
NOTE 2—For convenience in calculating test results in inch-pound units, the specimen should have an area of 5.08 in.2 of sheet (2.25 ± 0.01 in. square or 2.54 ± 0.01 in. in diameter). The weight [mass] of coating in grams on a specimen of that area is numerically equal to the weight jmass] of coating in ounces per square foot of sheet. For results to be reported in metric units, the specimen should have an area of 3330 mm2 of sheet (57.7 ± 0.1 mm square or 65.1 ± 0.1 mm in diameter).
6.2 Zinc-Coated Wire—Samples shall be secured as designated in the appropriate specification. The specimen of wire may he of any length over 12 in. [305 mm], hut preferably about 24 in. [609 mm], Where a continuous length is not available, shorter lengths totaling over 12 in. 1300 mm], but preferably about 24 in. j600 mmj, shall he used. Since the density of the steel is known 0.283 lb/in.3 [7830 kg/rn31, it is not necessary to use a specific length of specimen.
6.3 Zinc- Coated Articles Other Than Sheet or Wire— Samples for weight [massi of coating determination shall he secured as designated in the appropriate specification. Except as otherwise provided, the specimens should have a minimum area of 3 in.2 12000 mm2l of zinc-coated surface. For very small items, several pieces may have to be stripped to obtain the minimum area.
6.3.1 In the case of threaded articles, such as bolts and screws, the determination shall be made on a portion of the articles that does not include any thread.
7. Procedure
7.1 Strip the zinc coating from the specimens by using one of the following methods: hydrochloric acid (1 + 1), hydrochloric acid-antimony trichloride solution, or sulfuric acid (25 + 75). For zinc alloy coatings containing less than 90 % zinc, the stripping shall be done using hydrochloric acid (1 + I) or sulfuric acid (25 + 75).
7.2 Clean the specimens by washing with solvent naphtha or other suitable solvent, then rinse with alcohol, and dry thoroughly.
7.3 Determine the weight [mass] of the specimens individually to the nearest 0.01 g, except for articles other than sheet or wire with a specimen weight [mass] greater than 125 g.