ASTM D2674-72(2004)e1

Standard Methods of Analysis of Sulfochromate Etch Solution Used in Surface Preparation of Aluminum

ABSTRACT
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.
SCOPE
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 dichromate3.0 to 6.0 oz/gal (22.5 to 44.9 g/litre)Sulfuric acid40 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.
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 and health practices and determine the applicability of regulatory limitations prior to use.

General Information

• Status: Historical
• Publication Date: 31-Mar-2004
• ICS: 71.060.50 - Salts
• Technical Committee: D14 - Adhesives
• Drafting Committee: D14.80 - Metal Bonding Adhesives

Relations

• Replaces: ASTM D2674-72(1998) - Standard Test Methods for Analysis of Sulfochromate Etch Solution Used in Surface Preparation of Aluminum
• Effective Date: 01-Apr-2004
• Referred By: ASTM D2651-01(2016) - Standard Guide for Preparation of Metal Surfaces for Adhesive Bonding
• Effective Date: 01-Apr-2004
• Referred By: ASTM D6465-99(2016) - Standard Guide for Selecting Aerospace and General Purpose Adhesives and Sealants
• Effective Date: 01-Apr-2004
• Referred By: ASTM E864-20 - Standard Practice for Surface Preparation of Aluminum Alloys to Be Adhesively Bonded in Honeycomb Shelter Panels
• Effective Date: 01-Apr-2004

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
´1
Designation:D2674–72(Reapproved2004)
Standard Methods of
Analysis of Sulfochromate Etch Solution Used in Surface
Preparation of Aluminum
This standard is issued under the fixed designation D2674; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
´ NOTE—Keywords were added editorially in April 2004.
1. Scope measuring the hexavalent and trivalent Chromium content of a
sulfochromate solution. Method C is intended as an alternative
1.1 These methods offer a means for controlling the effec-
method for measuring the hexavalent and trivalent Chromium
tivenessoftheetchantwhichisnormallyusedforpreparingthe
content of a sulfochromate solution.
surface of aluminum alloys for subsequent adhesive bonding.
1.6 This standard does not purport to address all of the
As the etchant reacts with the aluminum, hexavalent chromium
safety concerns, if any, associated with its use. It is the
is converted to trivalent chromium; a measure of the two and
responsibility of the user of this standard to establish appro-
the difference can be used to determine the amount of dichro-
priate safety and health practices and determine the applica-
mate used.
bility of regulatory limitations prior to use.
1.2 The sulfochromate solution can be replenished by re-
storing the sodium dichromate and the sulfuric acid to the
2. Referenced Documents
original formulation levels. The lower limit of usefulness will
2.1 ASTM Standards:
vary depending upon solution storage, adhesives used, critical
D1193 Specification for Reagent Water
nature of bond capability, variety of metals processed, etc. and
E50 Practices for Apparatus, Reagents, and Safety Consid-
should be determined. Replenishment will be limited to the
erations for Chemical Analysis of Metals, Ores, and
number of times the chemical ingredients can be restored and
Related Materials
maintained to the required levels and should be determined by
the user. Sludge collecting in the bottom of a tank should be
3. Purity of Reagents and Water
minimized by periodic removal of sludge. For some applica-
3.1 Purity of Reagents—Reagent grade chemicals shall be
tions, the hexavalent chromium should not fall below the
used in all tests. Unless otherwise indicated, it is intended that
trivalent chromium content.
all reagents shall conform to the specifications of the Commit-
1.3 A typical aqueous sulfochromate acid etch solution
tee onAnalytical Reagents of theAmerican Chemical Society,
formulation is as follows:
where such specifications are available. Other grades may be
Sodium dichromate (Na Cr O ) 4.5 oz/gal (33.7 g/litre)
2 2 7
used, provided it is first ascertained that the reagent is of
Sulfuric acid (sp gr 1.84) 45 oz/gal (337.1 g/litre)
sufficiently high purity to permit its use without lessening the
1.4 Maintenance of the aqueous concentrations is suggested
accuracy of the determination.
as follows by appropriate additions of sodium dichromate or
3.2 Purity of Water—Unless otherwise indicated, references
sulfuric acids.
to water shall be understood to mean reagent water conforming
Sodium dichromate 3.0 to 6.0 oz/gal (22.5 to 44.9 g/litre)
to Specification D1193.
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
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
content of a sulfochromate solution. Method B is intended for
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website.
1 3
These methods are under the jurisdiction of ASTM Committee D14 on Reagent Chemicals, American Chemical Society Specifications, American
Adhesives and are the direct responsibility of Subcommittee D14.80 on Metal Chemical Society, Washington, D.C. For suggestions on the testing of reagents not
Bonding Adhesives. listed by the American Chemical Society, see Analar Standards for Laboratory
Current edition approved April 1, 2004. Published April 2004. Originally Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia
approved in 1967. Last previous edition approved in 1998 as D2674 – 72 (1998). and National Formulary, U.S. Pharmacopeial Convention, Inc., (USPC), Rockville,
DOI: 10.1520/D2674-72R04E01. MD.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
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D2674–72 (2004)
METHOD A 8.2.1 Pipet 10 mL into a 400-mL beaker. Add 150 mL of
water plus 5 mL of H SO (sp gr 1.84) and 1 drop of the
2 4
4. Apparatus phenanthroline ferrous complex. Titrate with the KMnO
solution just to disappearance of the indicator color. If the
4.1 pH Meter.
normality does not fall within 0.051 to 0.049, discard the 0.05
N solution.
5. Reagents
8.3 Hydrochloric Acid (1 + 1)—Mix 1 volume of concen-
5.1 Methyl Orange Indicator Solution—Prepare in accor-
trated hydrochloric acid (HCl) with 1 volume of water.
dance with Practices E50.
8.4 Ortho-Phenanthroline Ferrous Complex Indicator
5.2 Sodium Hydroxide, Standard Solution (1.0 N)—
Solution—Prepare in accordance with Practices E50.
Dissolve 40 g of sodium hydroxide (NaOH) in 1 liter of water
8.5 PotassiumPermanganate,StandardSolution(0.05N)—
and standardize.
Dissolve 1.6 g of potassium permanganate (KMnO ) in 1 litre
of water and standardize.
6. Procedure
8.6 Silver Nitrate Solution (1 weight %).
6.1 Pipet a 5-mLsample of sulfochromate etch solution into
8.7 Sulfuric Acid (sp gr 1.84)—Concentrated sulfuric acid
a250-mLbeaker.Add100mLofwater.Titratethesamplewith
(H SO ).
2 4
the NaOH solution to a pH of 3.5, using a pH meter.
6.2 An alternative method may be used whereby, instead of
Determination of Hexavalent Chromium as Sodium
the pH meter, 1 drop of methyl orange indicator solution is
Dichromate
added and, the titration continued until the color of the solution
loses all trace of orange. 9. Procedure
9.1 Pipet1mLofthesampleintoa400-mLbeaker.Add150
7. Calculation
mL of water, followed by 5 mL of H SO (sp gr 1.84). Titrate
2 4
7.1 Calculate the sulfuric acid content of the sulfochromate
with the standard ferrous ammonium sulfate solution (using 1
solution, A in oz/gal, B in g/litre, as follows:
drop of the ferrous complex indicator) (Note 1) until the
indicator turns pink and then add about 5 ml of the standard
A 5 1.3 VN (1)
ferrous ammonium sulfate solution in excess. Record the total
volume of the standard ferrous solution added. Back-titrate
B 5 9.81 VN (2)
with the potassium permanganate solution until the color of the
solution becomes very slightly green.
where:
NOTE 1—Barium diphenylamine sulfonate i
...