Phosphorus

Additional information on environmental fate and behaviour

Administrative data

Endpoint:

additional information on environmental fate and behaviour

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Cross-reference

Reason / purpose for cross-reference:

reference to same study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

1985

Report date:

1085

Materials and methods

Principles of method if other than guideline:

2.0g samples of red phosphorus with butyl rubber (RP/BR) were held in a desiccator at 25°C at different relative humidity’s (87% and 31%). Periodically, samples were removed, weighed, and heated in boiling water, and the aqueous phase was analyzed by titrimetry.

GLP compliance:

no

Type of study / information:

Oxidation in Air

Test material

Test material information

Constituent 1

Reference substance name:

Phosphorus

EC Number:

231-768-7

EC Name:

Phosphorus

Cas Number:

7723-14-0

IUPAC Name:

phosphine

Details on test material:

The powder sample of red phosphorus with butyl rubber was obtained from Aberdeen Proving Grounds. This material is produced as pellets and is
very spongy and hydroscopic. Analysis of eight samples for elemental phosphorus by combustion followed by boiling of the residue in water and
potentiometric titration yielded a phosphorus content of 87.9 % +/- 3.0%. An additional 3.2% phosphorus is present as surface oxides, titratable by
boiling the uncombusted mixture of red phosphorus with butyl rubber in water. Thus, surface oxides coat most mixture of red phosphorus with butyl
rubber pellets. Combustion studies showed the butyl rubber to amount to 5.2% of the formulation.

The pellet samples of mixtures of red phosphorus with butyl rubber pellets (size 0.6 cm x 0.6 cm, corresponding ca. 0.4 cm²) and powder (size 0.09 cm, corresponding to a surface of ca. 0.01cm²) were examine regarding the surface area measurements. As measured by a continuous volumetric method, the surface areas for powder and pellets were 0.2 m² /g and 0.15 m² /g +/- 20%, respectively. A repeat of analysis using a one-point BET method (Brunaller, Emmett, Teller surface area determination) resulted in a value of 0.1 m² /g for both samples, which is slightly lower that the volumetric result but within the uncertainty of the measurement. Scanning electron microscopy (SEM) showed the surfaces of the pellets and powder are similarly rough.

Remark: The report does not contain any additional information of the origin of the powder sample which might also be from the same company Aberdeen Proving Grounds

Results and discussion

Any other information on results incl. tables

The pellets were found to be very hydroscopic, with weight gain rates of 0.23 mg/g*h at 87% relative humidity and 0.20 /g*h at 37% relative humidity.  This is not unusual due to the known desiccating properties of P₂0₅(P₄0₁₀), an expected oxidative tranformation product (hydrolysis yields orthophosphoric acid).

Oxidation of RP/BR as a function of time appears to be independent of relative humidity and follows zero-order kinetics over the first 600 hr.  From these data, a oxidation rate of 0.08%/day and a lifetime of 3.5 years was calculated.  At some point we might expect the oxidation to deviate from linearity and become limited by oxygen diffusion through the surface oxide layers.  However, from the length of the projected lifetime the aoutors would expect that RP/BR surfaces would be renewed by natural precipitation

Applicant's summary and conclusion

Conclusions:

The oxidation of red phosphorus in air is independent from th humidity with a rate of about 0.08%/day and a calculated liftime of 3.5 years.

Executive summary:

The oxidation of red phosphorus in air is independent of the humidity with a rate of about 0.08%/day and a calculated liftime of 3.5 years.