1. Application

This applies to the test method of green sand active clay content determination.

2. Definition

Green sand active clay content is defined as the part of clay that retains binding force in the total bentonite added.

3. Instrument and apparatus

3.1 Methylene blue solution

Methylene blue¹⁾ (C₁₆H₁₈N₃S・Cl・nH₂O, where n=3) of the amount equivalent to 3.74g²⁾is dissolved in 1000ml of pure water.

Note¹⁾: The material should be that of Japan Pharmacopeia or a special class chemical.
Note²⁾: The methylene blue used must be checked at each solution for the water content. Weigh 1g of methylene blue and dry at 93±3 degree C until reaching a constant weight. The amount that should be sampled for the solution is obtained by the following equation.
For reference, the molecular weight of methylene blue having three molecules of water of crystallization is 374.

\[sample \ weight \ of \ methylene \ blue \ (eqival.of \ 3.74g) = { 0.855 \over weight \ after \ drying \ (g) } \times 3.74 \]

3.2 2% solution of sodium pyrophosphate

Sodium pyrophosphate (Na₄P₂O₇・10H₂O)³⁾ of 20g is dissolved in 1000ml of pure water.
Note³⁾: The material should be that of the special class chemical.

3.3 Balance

A balance of the precision of 0.01g is used.

3.4 Conical flask

A conical flask of the capacity of 300ml is used.

3.5 Filter paper

A filter paper of No.5C with the diameter of 110mmφ is convenient for hallo evaluation.

3.6 Supersonic disperser

A disperser of frequency 25 to 30kHz and power of 150 to 200W is used.

4. Sample

Green sand is dried until reaching a constant weight and cooled in a desiccator to be used as a sample.

Note: The amount of green sand for one test is about 10g, and the drying time necessary is about 1 hour.

5. Testing procedure

5.1 Dispersion of active clay in water

Either of the following methods is used.

1. Boiling method Sample of 5g is put in a conical flask of 300ml capacity and 50ml of sodium pyrophosphate is added. The solution is gently boiled⁵⁾ for about 10 minutes, while preventing evaporation of water by using a cooling pipe⁴⁾ or by covering with a glass dish, and cooled.
   Note⁴⁾: An air cooler may be fitted to the flask opening for preventing evaporation.
   Note⁵⁾: Heating should be controlled so as to maintain very weak boiling. A hot plate with a temperature controller is conveniently used.
2. Use of a supersonic disperser Sample of 5g is put in a conical flask of 300ml capacity and 50ml of sodium pyrophosphate is added. The solution is treated with a supersonic disperser for about 10 minutes for dispersion and cooled.

5.2 Operation

After cooling, methylene blue solution is added to the solution by 1ml. At each addition, the solution is stirred for 30 seconds. After stirring, a droplet is sampled with a glass rod and dropped on a filtering paper. The operation is repeated until a light blue hallo is observed around a deep blue spot on the paper. Then the solution is stirred for another two minutes and a spot is made again. If a hallo of a width of 1.5 to 2mm is again observed, the titration is judged to have reached the end. If a hallo is not observed, the operation of methylene blue addition is continued further.

5.3 Calculation of adsorbed methylene blue

The amount of adsorbed methylene blue is calculated by the following equation⁶⁾.

\[methylene \ blue \ adsorption \ (mmol/100g) = { consumption \ of \ 0.01N \ methylene \ blue \ solution \ (ml) } \over 0.5(g) \]

Note⁶⁾: mmol/100g is equivalent to 0.01N methylene blue equivalent. After calculating methylene blue adsorption, green sand active clay is obtained by referring to the calibration curve⁷⁾.
Note⁷⁾: A calibration curve is made using the same lot of the bentonite as that added to the green sand.

6. Expression

The active clay content is expressed in % using the calibration curve.

7. Record

The result is calculated to the second decimal place. Test is repeated two times or more and averaged using values within 5% deviation.