Boron carbide

Water solubility

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

water solubility

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

November 17,2009 - March 03, 2010

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 105 (Water Solubility)

Deviations:

no

Qualifier:

according to guideline

Guideline:

EU Method A.6 (Water Solubility)

Deviations:

no

GLP compliance:

no

Type of method:

flask method

Water solubility:

< 1 mg/L

Temp.:

20 °C

pH:

7

Details on results:

The preliminary visual experiments showed that the water solubility of the test item is < 9.1 mg/|. According to the guidelines the water solubility should be determined with the column elution method. For the column elution method an inert support material (sea sand) is coated with an excess of the test item by dissolving the test item in a volatile solvent. As the test item is an inorganic material insoluble in volatile solvents, it is not possible to dissolve it in such a solvent. Therefore, the column elution method is not applicable for this test item and the water solubility was determined by the "flask method".

Usually, the quantity of test substance necessary to saturate the desired volume of water is estimated from the preliminary test and about five times that quantity is used for the flask method. Boron carbide itself is insoluble in water and therefore a minimal amount of the substance (1 crystal) is enough to saturate any volume of water. Boron carbide always contains as an impurity soluble diboron trioxide (B2O3), which stems from the production process (boric acid as starting raw material, see section 3.1). To determine the amount of soluble boron oxide in the test item, 2.023 g of boron carbide were used to perform the flask method. The concentration of boron in the water extracts was determined to be 0.19 g/L (RSD 7.5 %) when extracting 2.023 g of boron carbide with 25 ml water. This corresponds to a boron oxide content in the boron carbide sample of 0.756 % by weight.

When calculating the theoretical solubility of boron carbide from these values, a weight of sample of 10 mg/l (amount of sample high enough to generate a saturated solution according to the results of the preliminary test) was used. The resulting theoretical solubility of boron carbide is 0.0234 mg/l. This is not an upper limit value, because the amount of boron in the water extracts of boron carbide is directly linked to the weight of sample taken to produce the water extracts. In contrast, even sample weights < 1 mg would be sufficient to prepare a saturated solution. Therefore, boron carbide can be classified as insoluble.

Conclusions:

Interpretation of results (migrated information): insoluble (< 0.1 mg/L)

Executive summary:

The water solubility of boron carbide was determined according to the OECD test guideline No. 105 and the European Commission Regulation (EC) No.44012008, 4.6.. As the test item is an inorganic substance it is not possible to determine the water solubility of the complete test item. Therefore, the saturation mass concentration of the constituent boron was determined using ICP-OES method. The preliminary visual experiments showed that the water solubility of the test item is < 9.1 mg/l. According to the guidelines the water solubility should be determined with the column elution method. For the column elution method an inert support material (sea sand) is coated with an excess of the test item by dissolving the test item in a volatile solvent. As the test item is an inorganic material insoluble in volatile solvents, it is not possible to dissolve it in such a solvent. Therefore, the water solubility was determined by the "flask method". Boron carbide itself is insoluble in water and therefore a minimal amount of the substance (1 crystal) is enough to saturate any volume of water. Boron carbide always contains as an impurity soluble diboron trioxide (B2O3), which stems from the production process (boric acid as starting raw material, see section 3.1). To determine the amount of soluble boron oxide in the test item, 2.023 g of boron carbide were used to perform the flask method. The concentration of boron in the water extracts was determined to be 0.19 g/L (RSD 7.5 %) when extracting 2.023 g of boron carbide with 25 ml water. This corresponds to a boron oxide content in the boron carbide sample of 0.756 % by weight. When calculating the theoretical solubility of boron carbide from these values, a weight of sample of 10 mg/l (amount of sample high enough to generate a saturated solution according to the results of the preliminary test) was used. The resulting theoretical solubility of boron carbide is 0.0234 mg/l. This is not an upper limit value, because the amount of boron in the water extracts of boron carbide is directly linked to the weight of sample taken to produce the water extracts. In contrast, even sample weights < 1 mg would be sufficient to prepare a saturated solution. Therefore, boron carbide can be classified as insoluble.

Reference 2

Endpoint:

water solubility

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2010

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 105 (Water Solubility)

Deviations:

no

GLP compliance:

no

Type of method:

flask method

Water solubility:

<= 0.072 mg/L

Temp.:

20 °C

pH:

7

Remarks on result:

other: The solubility has been calculated from the measured boron concentration in the extracts.

Details on results:

The solubility of the chosen boron carbide powder at 20 °C was determined to (calculated as B4C from the measured boron concentration in the water extracts):
Single results: 0.075 / 0.070 / 0.072 mg/L
Mean value: 0.072 mg/L
Standard deviation: 0.003 mg/L
RSD: 3.7 %

Conclusions:

Interpretation of results: insoluble (< 0.1 mg/L)
The water solubility of boron carbide can be regarded as being lower than 0.072 mg/L, as the measured value (soluble boron) is a sum of soluted boron oxide and boron carbide particles not separable by sedimentation methods.

Description of key information

The water solubility of boron carbide has been determined by the flask method OECD 105 as 0.072 mg/L at 20 °C. This is set as an upper limit, since the test substance always contains soluble boron oxide (B₂O₃) as an impurity.

Key value for chemical safety assessment

Water solubility:

0.072 mg/L

at the temperature of:

20 °C

Additional information

Boron carbide (B4C) always contains soluble diboron trioxide (B2O3) as an impurity, which stems from the production process (boric acid as starting raw material, see section 3.1). As the solubility of boron carbide calculated from boron concentration in water extracts is < 0.1 mg/L, boron carbide can be considered as insoluble.