A representative sampling of each clinker was obtained through use of a random-stratified sampling scheme and totaled nine samples. Each of these samples was split into replicates designated a and b for a total of 18 specimens. Each replicate was analyzed twice, so for all three clinkers, there were 54 samples and 108 scans. The specimen analysis sequencing was randomized so as to avoid confounding with any effects of machine drift. For example, RM 8486 sample 1, replicates a and b, were analyzed during scans 12, 46, 32, and 65.
The clinkers are provided as millimeter-sized fragments to provide a relatively homogeneous material, yet still be large enough for microscopic analysis. Particle size requirements for XRD necessitate reduction in particle size to below 10 µm. This maximizes the number of particles analyzed, improves powder homogeneity and packing characteristics, and minimizes microabsorption-related problems.
Each vial of clinker (about 10 g) was split into replicates using the cone-and-quarter technique. The splits were ground individually to fineness less than about 250 µm using a mortar and pestle. Final grinding employed a micronizing mill1, 2 to reduce the clinker to a mean particle size of about 2 µm in 10 min, using 200-proof ethanol (about 5 ml) as a grinding lubricant. The median particle size estimate is based upon a single measurement using an X-Ray absorption particle settling system. The ground clinker was vacuum filtered to remove the ethanol, dried at 60 º C, and then placed in a sealed vial over dessicant in a vacuum dessicator.
2 McCrone micronizing mill, McCrone Research, Chicago, Illinois.