Determining the Amorphous Content in Glass and Quartz Mixtures

In diverse industrial applications, the properties of a mixture of compounds is considerably influenced by their amorphous content. Among pharmaceutical preparation procedures, the crystallinity is an essential component of an agent's bio-availability, and therefore it is crucial to determine the amorphous content of such mixtures.

The amorphous content of bulk metallic glasses (BMG) is a guide to the physical characteristics of the compound, and consequently for product quality, much like for cements and slags. X-ray diffraction (XRD) represents a user-friendly technique for the efficient observation of the amorphous content of mixtures.

Instrument

The Thermo Scientific™ ARL™ EQUINOX 100 X-ray diffractometer engages a bespoke Cu (50 W) or Co (15 W) micro-focus tube fitted with mirror optics. These low wattage requirements negate the need for an external water chiller, as well as other peripheral infrastructure, and therefore permit the instrument to be effectively conveyed between laboratories.

Figure 1. ARL EQUINOX 100 X-ray diffractometer

The ARL EQUINOX 100 (c.f. Figure 1) offers very rapid data acquisition rates in comparison to competing diffractometers, due to its distinctive curved position sensitive detector (CPS). This calculates all diffraction peaks simultaneously, and in real time, and is consequently ideally suited for both reflection and transmission calculations.

Experimental

Ball milled (three minutes, 20 Hz) mixtures of glass and quartz (wgt% quartz 10, 30, 50, 70) were calculated in reflection mode utilizing Cu Kα (1.541874 Å) radiation for three minutes, with the sample revolving during the experiment. Determination of the amorphous content utilized standard-less deconvolution techniques executed in MAUD and JADE.

Results

For amorphous contents of less than 40%, the deviation from the weight portion is ±1.5% with both MAUD and JADE, while for lower contents there is an increase of deviation (Figure 2). The moderately different algorithms employed by the programs, coupled with the susceptibility to errors of the FWHM, determined in accordance to ASTM D5187, most likely account for the divergences.

Figure 2. Rietveld fit (JADE) of a 90% glass / 10% quartz sample

Figure 3. Rietveld fit (MAUD) of a 90% glass / 10% quartz sample

Figure 4. Rietveld fit (JADE) of a 70% glass / 30% quartz sample

Conclusion

The ARL EQUINOX 100 is an appropriate tool for the evaluation of the amorphous content in glass and quartz mixtures. This is undertaken by engaging a standard-less deconvolution methodology, which utilizes MAUD or JADE with reasonable accuracy down to ~25% amorphous content. A spiking method is recommended for lower content.

This information has been sourced, reviewed and adapted from materials provided by Thermo Fisher Scientific - Elemental Analyzers.

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