A new technology provides for automated sample handling and movement of coarse-grained powder or other solid materials to enable analysis by a robotic or totally automated computer system. Currently, many analytical instruments require a powder sample to control the shape and/or volume of the specimen, to increase the surface area of the specimen, to increase the statistical representation of a specimen when samples are not homogeneous with regard to the characterized property, and/or to increase the statistical representation of the specimen spatial orientation when the properties being characterized are not equivalent in different viewing directions. Grinding the material down to an ideal grain size is sometimes impossible, and conditioning the sample for analysis is often time-consuming and labor-intensive. In the new approach, the powder is handled as a fluid, using mechanical vibrations in conjunction with a driving force (gravity or gas flow), and requiring few or no moving parts.
This invention is a system and associated method for causing a fine-grained powder in a sample holder to undergo at least one of three motions (vibration, rotation, or translation) at a selected motion frequency in order to expose a statistically relevant population of grains in random orientation to a diffraction or fluorescent source. One or more measurements of diffraction, fluorescence, spectroscopic interaction, transmission, absorption, and/or reflection can be made on the sample using x-rays or light in a selected wavelength region.
In one embodiment, the invention allows the relaxation of sample preparation and handling requirements for powder X-ray diffraction (pXRD). The sample, held between two thin plastic windows, undergoes granular convection similar to a heated liquid, causing the individual grains to move past a collimated X-ray beam in random orientation over time. The result is an X-ray diffraction pattern having the correct diffracted intensities without a requirement for specialized mechanical motions. A major improvement over conventional sample preparation and handling techniques for pXRD is the potential to characterize larger grain-size material, resulting in a significant relaxation of the constraints on sample preparation (grinding). The powder handling system extends the range of useful grain sizes for XRD/X-ray fluorescence (XRF) from a few to several hundred micrometers.