These methods offer a means for controlling the effectiveness of the etchant which is normally used for preparing the surface of aluminum alloys for subsequent adhesive bonding. As the etchant reacts with the aluminum, hexavalent chromium is converted to trivalent chromium; a measure of the two and the difference can be used to determine the amount of dichromate used. The sulfochromate solution can be replenished by restoring the sodium dichromate and the sulfuric acid to the original formulation levels. Reagent grade chemicals shall be used in all tests. Unless otherwise indicated, it is intended that all reagents shall conform to the requirements specified. Unless otherwise indicated, references to water purity shall be understood to mean reagent water conforming to the requirements specified. The procedure and calculations for sulfochromate etch solution analysis are presented in details.

1.1 These methods offer a means for controlling the effectiveness of the etchant which is normally used for preparing the surface of aluminum alloys for subsequent adhesive bonding. As the etchant reacts with the aluminum, hexavalent chromium is converted to trivalent chromium; a measure of the two and the difference can be used to determine the amount of dichromate used.

1.2 The sulfochromate solution can be replenished by restoring the sodium dichromate and the sulfuric acid to the original formulation levels. The lower limit of usefulness will vary depending upon solution storage, adhesives used, critical nature of bond capability, variety of metals processed, etc. and should be determined. Replenishment will be limited to the number of times the chemical ingredients can be restored and maintained to the required levels and should be determined by the user. Sludge collecting in the bottom of a tank should be minimized by periodic removal of sludge. For some applications, the hexavalent chromium should not fall below the trivalent chromium content.

1.3 A typical aqueous sulfochromate acid etch solution formulation is as follows:

Sodium dichromate (Na₂Cr₂O₇)

4.5 oz/gal (33.7 g/litre)

Sulfuric acid (sp gr 1.84)

45 oz/gal (337.1 g/litre)

1.4 Maintenance of the aqueous concentrations is suggested as follows by appropriate additions of sodium dichromate or sulfuric acids.

Sodium dichromate

3.0 to 6.0 oz/gal (22.5 to 44.9 g/litre)

Sulfuric acid

40 to 50 oz/gal (299.6 to 374.5 g/litre)

1.5 Method A is intended for measuring the sulfuric acid content of a sulfochromate solution. Method B is intended for measuring the hexavalent and trivalent Chromium content of a sulfochromate solution. Method C is intended as an alternative method for measuring the hexavalent and trivalent Chromium content of a sulfochromate solution.

1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.

1.7 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.