Clay mineral X-ray diffraction

It is an experimental method in which a beam of X-rays is made to pass through a sample of the material being tested.

The presence and size of a charge balancing cation in the inter-layer of T-O-T clays will also effect the Z dimension.

Because of this, clay minerals are typically identified by preparing samples so that they are oriented to increase basal (00l) reflection .

[3] D positions are calculated using Bragg’s law but because clay mineral analysis is one dimensional, l can substitute n, making the equation l λ = 2d sin Θ.

[1] Well-crystallized and pure samples are ideal for x-ray diffraction, but this is rarely the case for clay.

Some common minerals associated with naturally occurring clays are; quartz, feldspars, zeolites, and carbonates organic matter is sometimes present.

The coefficient of variation (CV) is the percent standard deviation of the average of d(001) calculated from various reflections.

Lightly crushing breaks apart the soft clays while keeping harder nonclays intact for easier removal.

A glass microscope slide is covered with a suspension of sample in water then placed in an oven at 90 °C and left to dry.

This method produces thin films which provide inaccurate diffraction intensities at moderate and high angles.

The powder is then mixed with a few drops of a dispersant solution, usually ethanol but others are available, and spread evenly over the slide.

[3] This technique prevents size segregation by using either quick filtration or rapid stirring to overcome settling velocities.

Fast filtration allows a representative particle size to collect on the filter paper which is then inverted and exposed when mounted on a slide.

A special apparatus designed to hold a porous ceramic plate is placed into a centrifuge container and filled with suspended sample.

An advantage of this method is that exchangeable cations can be removed by passing a chloride solution through the plate once the sample has been dried.

Structure of a two-layer clay, kaolinite (T-O) and pyrophyllite (T-O-T) with red arrow to represent the Z dimension. T-O-T clays are naturally larger in the Z direction because of the extra layer provided by the additional tetrahedral layer.
X-ray diffraction pattern of a Nontronite standard purchased from the clay mineral society. Red boxes represent a wide peaks attributed to nontronite. Blue box represents a sharp peak attributed to quartz present in the standard.