ANNEX
(Mandatory Information)
A1. ASSESSING THE X-RAY DIFFRACTOMETER
A1.1 Introduction—This Annex provides a procedure for
assessing the diffractometer to assure the validity of the QXRD
procedure over a long period of time (several years or longer).
A QXRD analysis of portland cement and portland-cement
clinker is made particularly difficult by the fact that individual
clinker phases used for standardization are not stable over long
periods of time, because they hydrate easily, and are not easily
synthesized. Thus it is difficult to assess standardizations
directly by reanalysis of one or more standardization specimens.
In addition, it is not desirable to repeat the standardization
unless absolutely necessary. A more reasonable strategy is
to use an external standard to assess the diffractometer and to
decide when it is necessary to re-qualify a particular procedure.
This Annex provides a procedure for assessing the diffractometer
to assure the validity of the QXRD procedure over a long
period of time (several years or longer).
A1.2 Overview:
A1.2.1 As long as certain aspects of the procedure are not
changed, the relationship between peak intensity ratio and
mass ratio is assumed to be universal (that is, valid over an
indefinite period of time, even after changes in the diffractometer
such as realignment and replacement of the X-ray tube,
and transferable from one diffractometer to another).
A1.2.2 The requirements for the QXRD standardization to
be universal are: (1) specimens are free from preferred orientation,
primary extinction, and microabsorption, (2) the irradiated
volume of the specimen is constant and independent of
scattering angle, (3) monochromator polarization effects are
corrected, (4) integrated peak intensity is used, (5) when using
an internal standard, standardization and analyses are carried
out with an internal standard from the same lot because
differences in the particle size distribution between lots of the
same material can cause significant difference in peak intensity,
and (6) standardization and analyses are carried out with the
diffractometer in proper geometric alignment.
A1.2.3 If analyses are carried out using only the instrument
on which the standardization was carried out, then it is
necessary only that preferred orientation, extinction, microabsorption,
irradiated volume, and integrated peak intensity are
reproducible. In that case, the standardization is valid (though
not universal, in that it cannot be transferred from one
diffractometer to another) as long as methods of specimen
preparation, specimen mounting, and data collection are suitable
and are not changed. For example, thus the use of a
variable divergence slit for traditional standardization-based
analyses is acceptable, because it provides reproducible irradiated
volume (see Note A1.1).
NOTE A1.1—Variable divergence slits maintain a fixed irradiated area
on the specimen surface. For lower angle regions, they keep the beam
from spreading beyond the specimen, while at higher angles they provide
a larger irradiated area (and so, volume) than do fixed slit systems.
However, Rietveld analysis requires the constant volume provided by a
fixed divergence slit. Therefore, data collected with a variable slit needs to
be transformed to fixed slit by multiplying by sinQ (7).
A1.3 Terminology:
A1.3.1 extinction—a decrease in intensity during diffraction
due to interference by successive crystal planes.
A1.3.1.1 Discussion—Extinction is affected by the crystallite
size and is negligible for specimens ground to a particle
diameter of 5 or 10 μm.
A1.3.2 irradiated volume—the volume of specimen that
produces XRD signal.