CLAYS AND LAYERED SILICATES


X-ray powder diffraction analysis of clay minerals and layered silicates is carried out along the guidelines of the United States Geological Survey. Detailed procedures for sample preparation, particle size separation, and other specific treatments to identify the types of clay can be found here. In addition to important applications in soil geology, clays also play a significant role as purification agents in pharmaceutical applications.

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    Recording of the basal layer peak shift from 15.5 to 17.5 upon ethylene glycol treatment of smectite (Cu-Kα rad)

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Magnesium aluminum silicate identification as per USP protocol
 (X-ray Diffraction <941> Cu-Kα rad)

XRD clay analysis of geological samples typically begins with sample reduction and the pulverization of rock, since only a few grams of fine material are needed for the actual analysis.  XRD data sets are collected on a wide angle diffractometer in the following order:

  • Survey san(d?) over an extended range from a random powder mount
  • Detailed scans in the the low-angle region from oriented slide mounts after drying in air and (being?) exposed to an ethylene glycol atmosphere
  • Heat treated slide.

Data from a random powder mount usually provides an idea about the general mineral composition with major and minor constituents. Oriented slide mounts provide the means to determine the clay mineralogy of the sample. Slides are prepared from the <2um fraction of the sample, which was obtained by gravity sedimentation. An additional heat treatment can be applied as well to further determine the type of clay mineral. The effects of the above treatments on the various types of clay can be found here.

Certain applications require a quantitative breakdown of the observed mineral phases. This is accomplished with the use of FULLPAT. We have established a working library with the most common rock forming minerals and clays readily available. On the rare occasion when we observe unlisted mineral phases, the library is quickly expanded with the new addition.

In addition to important applications in soil geology, clays also play a significant role as purification agents in pharmaceutical applications. Clays and layered silicates for pharamceutical applications are analyzed according to USP protocol 941.

In addition to the importance of clays in geological and medical applications, they are also natural nano-particles. This is utilized in polymer suspensions with various clay loads. The clays used for these applications are usually modified smectite clays. The analytical tool is small angle X-ray scattering (SAXS).