YS/T 581.15-2021Determination of chemical content and physical properties of aluminium fluoride - Part 15: Free alumina content (English PDF)

4.1 Principle

The fluoride salt in the specimen is dissolved in the hot boric acid-sodium hydroxide solution, whilst the free Al2O3 is not dissolved. After filtration, burn it and weigh the mass of the precipitate. Calculate the free alumina content.

4.2 Reagents

Unless otherwise stated, only reagents confirmed to be of analytical grade and distilled or deionized water or water of relative purity, are used in the analysis.

4.2.1 Boric acid-sodium hydroxide solution: Dissolve 12.5 g of boric acid and 30 g of sodium hydroxide in 500 mL of water. Mix well.

4.2.2 Phenolphthalein ethanol solution: 10 g/L.

4.3 Instruments and equipment

4.3.1 Platinum crucible: The top diameter is about 30 mm, the bottom diameter is about

20 mm, the height is about 35 mm. It is equipped with a lead lid.

4.3.2 High temperature furnace: It can control the temperature at 1000 °C ± 20 °C.

4.4 Specimen

Grind and mix the sample, to make it pass through a 74 µm standard sieve. Bake it in an oven at 110 °C ± 5 °C for 2 h. Cool it to room temperature, in a desiccator.

4.5 Test procedures

4.5.1 Sample

Weigh 1.0 g of specimen (4.4), accurate to 0.0001 g.

4.5.2 Parallel test

Conduct two tests in parallel. Take the average value.

4.5.3 Determination

4.5.3.1 Place the platinum crucible and lid (4.3.1) into the high temperature furnace

(4.3.2). Burn it, at 1000 °C ± 20 °C for 30 minutes. Take out the platinum crucible and lid. Put them into a desiccator. Cool it to room temperature. Weigh the platinum crucible and lid (m0), accurate to 0.0002 g.

4.5.3.2 Place the specimen into a 400 mL beaker. Add 150 mL of water. Use a glass rod to stir it, to evenly distribute the specimen at the bottom of the beaker. Cover with a watch glass. Heat and boil for 15 min ~ 20 min (continuously stir and maintain the original volume). Then add 50 mL of boric acid-sodium hydroxide solution (4.2.1).

Continue to heat and boil for 15 minutes (continuously stir and maintain the original volume). Remove it. Use slow filter paper to filter it. Transfer the precipitate to the filter paper. Use hot water to rinse it, until it is neutral (use phenolphthalein ethanol solution (4.2.2) for inspection).

4.5.3.3 Place the precipitate together with the filter paper into a constant weight

platinum crucible (4.5.3.1). Ash it on the electric furnace. Then move it to a high temperature furnace (4.3.2), which has a temperature of 1000 °C ± 20 °C. Burn for 30 minutes. Take out. Put in a desiccator. Cool to room temperature. Weigh it (m1), accurate to 0.0001 g.

4.6 Processing of test data

The content of free alumina is calculated as the mass fraction of free alumina wAl2O3, which is calculated according to formula (1):

Where:

m1 - The mass of the platinum crucible, lid, sediment, in grams (g);

m0 - The mass of the platinum crucible and lid, in grams (g);

m - The mass of sample, in grams (g).

Calculation results are expressed to two decimal places. Numerical rounding off is performed, in accordance with the provisions of GB/T 8170.

4.7 Precision

4.7.1 Repeatability

For the measured value of two independent test results, which are obtained under repeatability conditions, within the average range given below, the absolute difference between the two test results does not exceed the repeatability limit (r); those exceeding the repeatability limit (r) does not exceed 5%. The repeatability limit (r) is obtained, by linear interpolation or extrapolation method, according to the data in Table 1.

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