Fumes, silica

Nanomaterial crystalline phase

Administrative data

Endpoint:

nanomaterial crystalline phase

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2016

Report date:

2016

Materials and methods

Type of method:

x-ray diffraction (XRD)

Details on methods and data evaluation:

quantification of amorphous and crystalline phases in silica fume via spiking with alumina

Test material

Specific details on test material used for the study:

random silica fume samples from all 4 sites in Norway (Bremanger, Bjølvefossen, Thamshavn, Salten)

Applicant's summary and conclusion

Conclusions:

The degree of amorphicity of silica fume lies between 96 and 99 %. Identified crystalline phases are considered impurities: silicon carbide, quartz, sodium chloride, elemental silicon, cristobalite, iron(III)oxide.
The nature of crystalline silica impurities in silica fume has already been addressed in the CSR (see Aqura report). It is important to point out that the amount of respirable crystalline silica (< 5 µm) is < 0.1 %.
Furthermore, although the chemical analysis shows silica content of e.g. < 87 %, the degree of amorphicity is still > 96 %. This means that the impurities are also incorporated in the amorphous silica matrix.

Executive summary:

A portion (~1g) of each sample was weighed in together with corundum standard (NIST SRM 676a), to make concentrations with ~10 wt% corundum, and then mixed with a polyamide ball in a Retsch MM400 mixer mill for 60 seconds at a frequency of 30 s-1.

The mixtures were analyzed using a D8 Advance XRD instrument, working at 40 kV and 40 mA with a Cu X-ray tube. The diffraction patterns were collected in continuous, locked coupled scan mode with a step size of 0.02° in the 2θ range 10° - 80°.

The spiking method entails that we add a known amount of a well-defined phase to our sample, in this case NIST corundum. Knowing its concentration allows the program to calculate the amorphous content in the original (unspiked) sample.

The quantitative results for the original, unspiked samples are presented in the table below:

sample	deg of amorphicity (%)	quartz (%)	SiC (%)	NaCl (%)	Si (%)	Cristobalite (%)	Fe2O3 (%)
Bjølvefossen	96,5	0,6	0,9	1	0,1	0,3	0,5
Bremanger	99,4	0,2	0,3	0,1
Thamshavn	98,7	0,3	0,7		0,1	0,1
Salten	99	0,2	0,4	0,1		0,2