Magnesium hydroxide

Particle size distribution (Granulometry)

Link to relevant study record(s)

Reference

Endpoint:

particle size distribution (granulometry)

Type of information:

experimental study

Adequacy of study:

key study

Study period:

30-04-2010 to 17-05-2010

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

other: ISO 13320:2009

Deviations:

no

Qualifier:

according to guideline

Guideline:

other: CIPAC MT 187

Deviations:

no

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 110 (Particle Size Distribution / Fibre Length and Diameter Distributions)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Type of method:

Laser scattering/diffraction

Type of distribution:

other: Counted and volumetric distribiution

Specific details on test material used for the study:

- Name: Magnesium hydroxide
- Batch no. 20BR0026
- CAS No.: 1309-42-8
- Purity: 99.9 %
- Expiry date: 31 January 2012
- Storage Room Temp. in the dark

Mass median aerodynamic diameter:

21.601 µm

Percentile:

D10

Mean:

2.013 µm

St. dev.:

0.14

Key result

Percentile:

D50

Mean:

13.915 µm

St. dev.:

0.63

Remarks on result:

other: Median

Percentile:

D90

Mean:

154.107 µm

St. dev.:

32.43

No.:

#1

Size:

< 2.013 µm

Distribution:

10 %

No.:

#2

Size:

< 13.915 µm

Distribution:

50 %

No.:

#3

Size:

< 154.107 µm

Distribution:

90 %

Optical microscope analysis:

Standard visual observation: Sample observed to be medium size, white powder with clusters.

Observation at 100 x magnification: The particles appeared to be irregularly shaped, round edged particles. The smallest individual particle size was approximately 3 µm and the largest individual particle size was approximately 8 µm. This analysis ignores clusters and agglomerates.

Observation at 400 x magnification: The sample was observed to be made up of agglomerated particles.

Laser diffraction particle size analysis:

The method development phase of the analysis indicated that the most appropriate test and material parameters to obtain the optimum measurement were:

Dispersant:                            Air

Dispersion pressure:              0.5 barg

Refractive index (sample):     1.559 n

Absorption:                            0 AU

Analysis model:                      General purpose (normal)

Using the identified parameters, the particle size was analysed over the range 0.02 µm to 2000 µm. The results of the formal analysis are presented in Table 1, and the standard deviation results are recorded in Table 2. In addition, a graph of volume (%) versus particle diameter (µm), and full particle size distribution, is provided which is an average of the 5 runs.

Table 1. Full Test Results

	Run 1	Run 2	Run 3	Run 4	Run 5	Average*
Volume weighted mean	48.763	53.790	39.690	39.096	38.125	43.893
Median (d.50)	14.982	14.349	13.574	13.415	13.350	13.915
Mode (µm)	15.169	14.261	14.099	14.066	14.034	14.311
MMAD	23.258	22.275	21.072	20.826	20.725	21.601
10 % of material is <	2.266	2.113	1.944	1.921	1.893	2.013
50 % of material is <	14.982	14.349	13.574	13.415	13.350	13.915
90 % of material is <	176.935	211.778	135.845	134.752	126.672	154.107

* Average result is calculated from the entirety of data captured in each run and is not a simple arithmetic mean.

34.19 % by volume of sample was seen to be < 10.0 µm.

Table 2. Standard Deviation Results

Run No.	1	2	3	4	5	STDVP	% STDV
d10	2.266	2.113	1.944	1.921	1.893	0.14	7.00
d50	14.982	14.349	13.574	13.415	13.350	0.63	4.55
d90	176.935	211.778	135.845	134.752	126.672	32.43	20.63
d15.78	5.202	4.825	4.103	4.005	3.827	0.53	12.03
GSD (geometric standard deviation)	2.880	2.974	3.308	3.350	3.488	0.23	7.27
MMAD	23.258	22.275	21.072	20.826	20.725	0.98	4.55

Coefficient of variation is outside the normal acceptable limits (d50 should be less than 3 %; d10 and d90 should be less than 5 %). This is due to agglomerations in the sample that could not be separated. Earlier attempts to separate these agglomerations failed resulting in poor reproducibility and uncertainty as to the accuracy of the results. Whilst the results for the material tested in the "as received" condition are still variable, they do reflect the particle size distribution of the sample in the "as received" condition.

Conclusions:

The MMAD (Mass Median Aerodynamic Diameter) was determined to be 21.601 µm. 34.19 % by volume of sample was seen to be < 10.00 µm.

Executive summary:

In a GLP study and according to OECD 110, CIPAC MT 187 and ISO 13320:2009 the particle size was analysed via laser diffraction. The MMAD (50% percentile) was 21.601 µm.

	Average (µm)
Volume weighted mean	43.893
Median (d.50)	13.915
Mode (µm)	14.311
MMAD (mass median aerodynamic diameter)	21.601
10 % of material is <	2.013
50 % of material is <	13.915
90 % of material is <	154.107

Description of key information

The MMAD (mass median aerodynamic diameter) was determined to be 21.601 µm.

Additional information

The MMAD (mass median aerodynamic diameter) was determined to be 21.601 µm. 34.19 % by volume of sample was seen to be < 10.00 µm.