McCrone, Producing the Micronising Mill

The McCrone Micronising mill is widely acknowledged to be one of the most effective means of reducing sample preparation to sub-micron sizes suitable for X-Ray diffraction; X-Ray Fluorescence; Infra-Red Spectroscopy and Atomic Absorption Analysis.

What makes it so effective is the unique grinding action of the cylinders producing both linear contact blows and planar shearing

The result is a short grinding time with virtually no sample loss, as well as exceptionally even particle size distribution. There is virtually no chemical degradation of the particles and a significant reduction in the crystal lattice disturbance. The McCrone Mill is used throughout the world in laboratories where integrity of the sample is of paramount importance. The Mill is indispensable for leading geologists, chemists, mineralogists and materials scientists.

X-Ray Diffraction and Infra Red Spectroscopy:

Wet grinding results in the least damage to the samples' crystal structure which is crucial for XRD and IR. It also makes for easier total sample recovery, eliminates the manual element and vessel cleaning, and reduces sample oxidation and cross contamination. It is superior to dry grinding in that it yields much smaller particles, narrower particle size distributions and gives more uniform phase distributions.

X-Ray Diffraction:

Dry grinding can be used to induce microstrains in the crystal lattice for the determination of ultrastructural damage by XRD line broadening measurements. Sample weight, grinding element type and grinding time are the only variables which need to be specified when describing the amount of induced lattice deformation.

Atomic Absorption Analysis:

In the case of samples which are difficult to dissolve, grinding with the mill is found to facilitate subsequent acid digestion or alkali fusion greatly.

Principle of Operation

A 125 ml polypropylene jar containing 48 grinding pellets in ordered array is gyrated around a horizontal axis.

Grinding may be carried out wet or dry.

It is absolutely necessary to maintain the ordered array of 6 layers of 8 pellets in the jar.

During grinding each pellet moves with respect to its neighbours so that both the ends and the sides of the pellets contribute to the reduction of the sample. The powder is continuously circulated around the grinding pellets and is rapidly ground.

The mill must be secured to a substantial, rigid bench to ensure that neither the bench nor the mill move during operation. All the vibrational energy available should be directed to the grinding jar and holder and not to any other structure.

Ideally vibration of the mill unit itself should be barely detectable.

On wet grinding runs the mill is operated for periods ranging from 2 to 30 minutes, depending on the fineness of the product required and the fineness, volume and grinding resistance of the starting sample. Changes in grinding time affect the particle size distribution of the product.

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