Silicic acid, aluminum magnesium sodium salt

Particle size distribution (Granulometry)

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

particle size distribution (granulometry)

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

comparable to guideline study

Qualifier:

according to guideline

Guideline:

other: ISO 13320-1 (Laser diffraction methods)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Remarks:

Ministerium für Arbeit, Integration und Soziales des Landes Nordrhein-Westfalen

Type of method:

other: air stream

Type of distribution:

other: angular intensity distribution of the light scattered by the particles

Mass median aerodynamic diameter:

11.7 µm

Geometric standard deviation:

0.9

Percentile:

D10

Mean:

3.7 µm

St. dev.:

0.13

Key result

Percentile:

D50

Mean:

11.7 µm

St. dev.:

0.9

Key result

Percentile:

D90

Mean:

157.4 µm

St. dev.:

26.3

The sample volume vs. particle size distribution found under these test conditions is displayed in the following table:

Total sample volume:	100 %
Cumulative mass fraction [%]	5	10	50	70	90
Particle size [µm]	<=2.8*	<=3.7	<=11.7	<=30*	<=157

*estimated from the cumulative distribution plot

D10 =   3.7 +/- 0.13 µm (n = 6)

D50 = 11.7 +/- 0.9 µm (MMAD) (n = 6)**

D90 = 157.4 +/- 26.3 µm (n = 6)

Conclusions:

The mass median aerodynamic diameter (MMAD) of the test item Silic acid Aluminium Magnesium Sodium Salt is calculated as 11.7 µm (D50).
D10: 3,7 pm
D50: 11,7 pm Median diameter = MMAD
D90: 157,4 pm

Reference 2

Endpoint:

particle size distribution (granulometry)

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

comparable to guideline study

Qualifier:

according to guideline

Guideline:

other: DIN 66165 / ISO 3310: Sieve analysis - dry-sieving; sieves according DIN 66165 ISO 3310

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Remarks:

Ministerium für Arbeit, Integration und Soziales des Landes Nordrhein-Westfalen

Type of method:

sieving

Type of distribution:

mass based distribution

Mass median aerodynamic diameter:

92 µm

Key result

Percentile:

D10

Mean:

66 µm

St. dev.:

0

Remarks on result:

other: no St.dev. was given

Key result

Percentile:

D50

Mean:

92 µm

St. dev.:

0

Remarks on result:

other: no St.dev. was given

Key result

Percentile:

D90

Mean:

119 µm

St. dev.:

0

Remarks on result:

other: no St.dev. was given

The study was performed using a guideline-conform dispersion technique and analytical method:

The sieving method supplies the mass distribution of particles of varying size of a powder sample. This method is considered to represent one of the least destructive techniques, because the energy input is relatively gentle. Therefore, sieving delivers the particles with a higher grade of agglomeration, resulting in a shift of the distribution curve to the “right side”, i.e. to particles with a greater mean mass and diameter.

This procedure is supposed to be more representative of common conditions under normal handling and use rather than high-energy dispersion techniques.

However, the resolution at the low end of the distribution curve is poor. Hence, the mass fraction of particles with a diameter of <= 10 or <= 5 µm could not be determined.

Conclusions:

low energy input -> D50 = 92 µm

Reference 3

Endpoint:

particle size distribution (granulometry)

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

comparable to guideline study

Qualifier:

no guideline available

Principles of method if other than guideline:

A set of different measurement techniques was employed to ensure a comprehensive quantification of particle size distribution (PSD) and particle release into air:
- transmission electron microscopy (TEM)
- laser diffraction spectrometry (LDS)
- differential electrical mobility analysis (DEMA)
- time-of-flight analysis (TOF)
- wet sieving analysis (WSA)
- dynamic light scattering (DLS)
- particle tracking analysis (PTA)
In addition, SEM images were employed for a qualitative morphological characterisation.

GLP compliance:

yes (incl. QA statement)

Type of method:

Laser scattering/diffraction

Remarks:

Laser diffraction spectrometry (DLS)

Key result

Percentile:

D50

Mean:

302.9 µm

St. dev.:

0

Remarks on result:

other: standart deviation not reported

System       parameters       d10,3       d16,3       d50,3       d84,3       d90,3     d99.3

[μm]        [μm]        [μm]       [μm]        [μm]        [µm]

GRADIS       -                   169.9      197.2      302.9    412.3      437.0        507.2

RBG 1000 3.5bar              0.76        0.92        2.50        7.72        9.73        18.13

Conclusions:

DEMA results for airborne particles
The characterisation of the aerosolised powder by DEMA reveals that the dry dispersion intensity has a significant effect on the particle size distribution.

SEM-Analysis:
The morphology of the particulate objects can be described as densely packed multiscale aggregates, with primary particles at the nanoscale and intermediate structures in the submicrometre range. The global shape of the agglomerates is clearly non-spherical.

LDS/WSA:
Reveals that the wet dispersion intensity has only a slight impact on the volume-weighted size distributions.
LDS results show that dry and wet dispersion affect the granulometric state differently.

DLS:
The polydispersity is at a moderate level and the shape of the size distribution is monomodal.

Granulometric characterisation of sodium magnesium aluminium silicate powder including primary particle size, aggregate size, agglomerate size and number-weighted size distribution. In general, the aggregates/agglomerates are irregular shaped and loosely packed. Laser diffraction spectrometry (LDS) results show that dry and wet dispersion affect the granulometric state differently. And it is revealed that the dry dispersion intensity has a significant impact on the volume-weighted particle size distribution. In contrast to the dry dispersion, the granulometric state after wet dispersion is hardly affected by the chosen intensity levels. In general, the results based on aerosol analyses imply a good dispersibility of the material.

An amendment study aimed to analyse whether the particle size distribution of DURAFILL® 200 decreases by a further increase of wet dispersion intensity or not. Laser diffraction spectrometry (LDS) results show that dry and wet dispersion affect the granulometric state differently: Wet dispersion intensity has only a slight impact on the volume-weighted size distributions.

Executive summary:

In general, the results based on aerosol analyses imply a good dispersibility of the material. The size distribution is greatly affected by the level of dry dispersion intensity due to switching from weak to moderate or intense dry dispersion, while the shift due to switching from moderate to intense dry dispersion is less pronounced.

Weak dry dispersion led only to agglomerates in the micrometre size range, which break under moderate dry dispersion into aggregates > 100 nm. In the case of intense dry dispersion DEMA analyses showed a significant content of fragments in the nanometre size range.

In contrast to the dry dispersion, the granulometric state after wet dispersion is hardly affected by the chosen intensity levels.

For the material DURAFILL® 200 moderate dry dispersion lead to a granulometric state which is slightly finer than the ones after moderate and intense wet dispersion as de-termined by LDS.

In conclusion, dry and wet dispersion of DURAFILL® 200 generates highly polydisperse aerosols and suspensions, respectively.

Description of key information

The mass median aerodynamic diameter (MMAD = D50) of the test item Silic acid Aluminium Magnesium Sodium Salt under standard conditions is: 11.7 µm.

Stintz 2017

Granulometric characterisation of sodium magnesium aluminium silicate powder including primary particle size, aggregate size, agglomerate size and number-weighted size distribution. In general, the aggregates/agglomerates are irregular shaped and loosely packed. Laser diffraction spectrometry (LDS) results show that dry and wet dispersion affect the granulometric state differently. And it is revealed that the dry dispersion intensity has a significant impact on the volume-weighted particle size distribution. In contrast to the dry dispersion, the granulometric state after wet dispersion is hardly affected by the chosen intensity levels. In general, the results based on aerosol analyses imply a good dispersibility of the material.

Moderate dry dispersion led already to finer size distributions than moderate and intense wet dispersion. This implies that high-pressure air jet dispersion is more effective for the particle system than ultrasonication.

Stintz 2017, Amendment

This amendment study aimed to analyse whether the particle size distribution of DURAFILL® 200 decreases by a further increase of wet dispersion intensity or not . Laser diffraction spectrometry (LDS) results show that dry and wet dispersion affect the granulometric state differently: Wet dispersion intensity has only a slight impact on the volume-weighted size distributions.

Stintz 2013, electrostatical method

Electrostatically precipated aerosol particles which have been dispersed with different dispersing intensities:

a) Rotating brush generator (RBG) -> high dispersing intensity

b) Suction tube dosing system (NSD) -> low dispersing intensity

The dispersing intensity influences the number and size of the agglomerates significantly:

MMAD / D50 >= 2.5 µm <= 302.9 µm

 

Bütfering 2012, air stream method

Medium energy input -> MMAD / D50 is about 11.7 µm

(and 157.4 µm: Double peak, latter peak based on agglomerates which resisted shear-forces and not converted into smaller aggregates, energy input is not sufficient to break down all agglomerates into aggregate size. )

Under normal use conditions the particle size is above 10µm which is crucial for the exposure.

 

Bütfering 2012, sieve method

Low energy input / shear forces -> D50 = 92 µm

Additional information

Sodium Aluminium Magnesium Silicate (SMAS) tends to form stable agglomerates of high mass median aerodynamic diameters that are not respirable (MMAD >> 10µm). For SMAS the D50-value has been found at 302.9 µm. The respirable fraction (< 10µm) comprises less than 1 wt.% (Stintz 2013).

 

The particle size distribution of Sodium Aluminium Magnesium Silicate (SMAS) is strongly depending on the dispersion process and the energy used for the dispersion of the substance:

Constituent particle number modal value (peak) size was measured by TEM at about 15 nm, whereas the number based aggregate size after worst dispersion with RBG (Rotating Brush Generator) was measured with SMPS to about 150 nm and volume based with laser diffraction to about 1 µm. The respective median sizes are larger.

 

Even it might be considered Sodium Aluminium Magnesium Silicate (SMAS) falls into the scope as nanomaterial according to EU recommendation:

The European Commission published in 2011 a recommendation on the definition of nanomaterial 2011/696/EU that comprises:

“natural, incidental or manufactured materials containing particles in an unbound state or as an aggregate or as an agglomerate and where, for 50 % or more of the particles in the number size distribution, one or more external dimension is in the size range 1 nm - 100 nm.”

 

It has to be pointed that this substance forms due to the wet manufacturing process (precipitation) stable and large agglomerates (see also Fig 2.5 in Stintz 2013) which are not nanoparticles but nanostructured particles. Only under standard measure conditions and depending on the disperging intensities these agglomerates are broken into smaller aggregates leading to test results like MMAD = 11.7 µm.

 

Important for the assessment of toxicity and ecotoxicity:

Due to a MMAD > 10 µm Silicic acid, aluminium magnesium sodium salt is not respirable. Further, in the aqueous the agglomerates of this substance are dissolved continuously into smaller particles of increasing water solubility. Finally it is dissolved completely and undergoes a transformation into soluble ions such as Magnesium, Silicium, Sodium and Aluminium. Thus no nanoparticles are left! This is shown also by the studies (see Affolter 2013) about water solubility: No light scattering (Tyndall effect) was seen in the aqueous solutions indicating that no colloidal dispersed particles are present.