Particle Size Analysis by Laser Diffraction Spectrometry: Application to Cementitious Powders.
Particle Size Analysis by Laser Diffraction
Spectrometry: Application to Cementitious Powders.
Hackley, V. A.; Lum, L. S.; Gintautas, V.; Ferraris, C.
NISTIR 7097; 70 p. March 2004.
laer diffraction spectrometry; cementitious powders;
Particle size distribution (PSD) measurements are now
routinely employed to characterize cement powders. A
variety of techniques are available for this purpose.
However, at present, an industry standard does not exist
for PSD analysis, nor do uniform methods exist for
sample preparation. Two recent international round-robin
tests sponsored by ASTM committee CO 1.25.01 revealed
high variability in reported PSDs, even among
participants using similar instruments. The round-robin
studies also identified laser diffraction spectrometry
(LDS) as the most common technique used by the cement
community for routine determination ofPSD. Therefore,
studies were conducted to identify and examine the
factors that significantly influence the determination
of the PSD in cement powder by LDS. Potentially, the
single most significant influence on measurement of the
PSD arises from the requirement that powders be
dispersed prior to analysis by LDS; dispersion
efficiency will depend on factors such as solids
concentration, choice of dispersion medium, and the
application of chemical and/or mechanical
deagglomeration methods. Another potentially significant
source of error originates from the conversion of the
measured optjcal spectrum to a PSD, a process that
requires application of an appropriate optical model.
The Mie model requires input of optical constants (real
and imaginary refractive index) for the solid phase. The
choice of optical constants can greatly influence the
PSD, especially the ultrafme fraction (below about 1 ~m
djameter). The current work was undertaken with the
objective of improving the precision, and therefore the
degree of confidence, associated with the LDS technique
in its application to cement characterization, and to
assess the overall measurement precision of LDS under
controlled conditions. We report all relevant
experimental data gathered in the course of these
studies, and briefly summarize each set of results
pertajning to a specific influence or parameter.