ASTM D4042 Test Method for Sampling and Testing for Ash and Total Iron in Steel Mill Dispersions of Rolling Oils
7. Iron Content
7.1 Apparatus:
7.1.1 Analytical Balance, 200-g capacity, accurate to 0.1 mg.

7.1.2 Beakers, 400-mL, borosilicate glass, Griffin form.

7.1.3 Buret, 50-mL with 0.1-mL graduations.

7.2 Reagents:
7.2.1 Purity of Reagents - Reagent grade chemicals shall be used in all tests. Unless otherwise indicated, it is intended that all reagents shall conform to the specifications of the Committee on Analytical Reagents of the American Chemical Society, where such specifications are available. Other grades may be used, provided it is first ascertained that the reagent is of sufficiently high purity to permit its use without lessening the accuracy of the determination.

7.2.2 Purity of Water - Unless otherwise indicated, references to water shall be understood to mean reagent water as defined in Specification D 1193, Type II.

7.2.3 Hydrochloric Acid (HCL) (36 %).

NOTE 10 - Warning: Poison - Causes severe burns. Harmful or fatal if swallowed or inhaled.

7.2.4 Iron Standard Solution (1 mL = 0.10 mg Fe) - Make in accordance with Practices E 50, iron, standard solution, or as follows: Transfer 1.000 g of NBS Standard 55e (ingot iron) or equivalent to a 100-mL beaker (Note 11). Dilute 10 mL of HCl with 10 mL of distilled water. Add this solution to the 100-mL beaker. Cover and heat below the boiling temperature to dissolve the iron. Cool the solution and transfer quantitatively to a 1-L volumetric flask. Cool to room temperature and dilute to 1-L volume with distilled water. Mix thoroughly. One millilitre of standard iron solution = 1 mg of iron.

NOTE 11 - Prior to use, all beakers and glassware must be cleaned as follows: Add approximately 1/4 the total volume of HCl to beaker or other glassware. Cover loosely and heat to boiling under a fume hood. Maintain boiling for approximately 10 min. Cool and rinse thoroughly with distilled water.

7.2.5 Mercuric Chloride Solution (saturated) - (Warning - See Note 12) - Add 100 g of mercuric chloride (HgCl2) to 1000 mL of hot distilled water and mix thoroughly. Allow to stand 12 to 24 h to obtain a saturated solution at room temperature.

NOTE 12 - Warning: Poison - May cause skin irritation. Harmful or fatal if swallowed.

7.2.6 Potassium Dichromate (0.020 N) (Warning - See Note 13) - Transfer 1.0 g of potassium dichromate (K2Cr2O7) to a 1-L volumetric flask. Dissolve in distilled water and dilute volume to 1 L. Allow to stand 12 to 24 h prior to standardization and use. Standardize in accordance with Annex A1.

NOTE 13 - Warning: Causes skin irritation.

7.2.7 Sodium Diphenylamine Sulfonate Indicator Solution (2 g/L) - Dissolve 1 g of sodium diphenylamine sulfonate in 500 mL of distilled water.

7.2.8 Stannous Chloride (15 g/L) (Warning - See Note 13 - Dissolve 7.5 g of stannous chloride (SnCl2•2H2O) in 150 mL of HCI (36%). When solution is complete, dilute to 500 mL with distilled water and add 5 g of tin metal. Some undissolved tin metal should be present at all times to maintain the stannous chloride in the reduced state.

7.2.9 Sulfuric-Phosphoric Acid Mixture (150 mL H2SO4 + 150 mL H3PO4 + 700 mL H2O) - Transfer 700 mL of distilled water to a 1-L borosilicate-glass beaker. Slowly add 150 mL of concentrated sulfuric acid (95%) (Warning - See Note 10), stirring the solution during addition of the acid. Cool the solution to room temperature. Carefully add 150 mL of phosphoric acid (86 %) (Warning - See Note 14) and mix thoroughly.

NOTE 14 - Warning: Causes skin irritation. Do not get in eyes, on skin, or on clothing.

7.3 Procedure:
7.3.1 Obtain ashed samples of (1) oil sample and polyethylene bag (6.2.7) and (2) new empty polyethylene-sample bag (6.2.9) in original evaporating dishes or beakers.

NOTE 15 - If total iron analysis only is desired, (no percent ash determination) Steps 6.2.6, 6.2.7, 6.2.8, 6.2.10, and 6.3.1 may be eliminated in the ash content procedure.

7.3.2 Add 10 mL of HCl to the ashed samples (1) and (2). Cover and heat slowly below the boiling point to digest to effect the solution of all iron present.

7.3.3 Cool the samples (1) and (2) to room temperature and transfer each to individual 400-mL beakers. Rinse the original evaporating dish or beaker with HCl and add the rinse to the respective beaker.

7.3.4 Cover the beakers loosely and digest by heating near boiling for 5 min.

7.3.5 Rinse the cover and sides of the beakers with distilled water, heat to near boiling and add stannous chloride solution dropwise until the solution changes from yellow to colorless. Add one drop in excess. Cover and just bring to a boil.

7.3.6 Cool to room temperature. Rinse the cover and sides of the beakers with freshly boiled distilled water. Add 10 mL of HgCl2 solution to each and allow to stand for 3 to 5 min.

7.3.7 To each beaker add 20 mL of sulfuric-phosphoric acid mixture. Dilute each solution to approximately 300 mL with freshly boiled and cooled distilled water. To each solution add 10 to 15 drops of indicator solution and titrate to a violet end point, with potassium dichromate (K2Cr2O7, 0.02 N).

7.3.8 Record the millilitres of potassium dichromate (K2Cr2O7) used for titration of the ashed sample plus bag and new empty bag as K1 and K2 respectively.

7.4 Calculation:
7.4.1 Calculate the iron content of the dispersion sample as follows:
Fe, ppm = ((K1 - K2) x (mg Fe/mL K2Cr2O7) x 1000)/(WS1 - WB1)
where:
K1 = millilitres of K2Cr2O7 used for ashed sample and bag (7.3.8),
K2 = millilitres of K2Cr2O7 used for ashed empty bag (7.3.8),
(mg Fe/mL K2Cr2O7) = Iron equivalent of K2Cr2O7 (Annex A1).
where:
WS1 = grams of sample and bag (6.2.2), and
WB1 = grams of empty bag (5.2.2 or 6.2.10, Note 8).