Compositional Analysis of NIST Reference Material Clinker 8486.
Compositional Analysis of NIST Reference Material
Stutzman, P. E.; Leigh, S. D.
Accuracy in Powder Diffraction III. Proceedings.
Poster #2. April 22-25, 2001, Gaithersburg, MD, 2001
AND Cement Microscopy, 22nd International Conference.
Proceedings. April 29-May 4, 2000, Montreal, Canada,
22-38 pp, 2000, 2001.
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clinkers; x ray diffraction; quantitative analysis;
Certification of the phase compositions of the three
NIST Reference Clinkers will be based upon more than one
independent method. The current reference values were
established using an optical microscope examination,
with additional optical microscope data taken from an
ASTM C 1356 round robin The present X-ray powder
diffraction (XRD) study provides the second, independent
estimate of the phase abundance. Reitveld refinement of
the powder diffraction data allowed calculation of a set
of best-fit reference patterns and their scale factors.
Because of significant contrast in the linear absorption
coefficients of ferrite and periclase, relative to the
estimated mean matrix linear absorption coefticient, the
scale factors were adjusted for microabsorption effects.
The XRD data agree with the optical data with the
exception of aluminate. This disagreement may reflect
the difficulty in resolving this fine-sized phase using
the optical microscope. The XRD data did show greater
precision than replicate measurements by microscopy.
Measurements from different sources, laboratories,
instruments, and from different methods can exhibit
significant between-method variability, as well as
distinct within-method variances. The data sets were
treated uusing both unweighted and weighted schemes to
establish the best-consensus values and to provide
meaningful uncertainties. While the mean values of
individual phase abundance do not vary, the 95%
uncertainty level values do. The
Mandel-Paule-Vangel-Rukhin method of combining the data
sets is favored as this method produces a weighted mean
whose weighting scheme does not necessarily skew the
consensus value in the direction of the large number of
XRD values, and that takes between- as well as
within-method variation into account.