Respirable silica (alpha quartz) measurements
Crystalline silica is a very common, naturally occurring mineral consisting
of silicon and oxygen. Differences in temperatures and pressures can cause the
atomic structure to change creating polymorphs of silica. These are commonly
known as alpha quartz, beta quartz, cristobalite and tridymite.
Damage to lungs and respiratory systems, known as silicosis, can be traced to
exposure to very small particles of crystalline silica and acidic reactions
within the human body. A recommended exposure limit (REL) of 50 μg/m3
has been established by the National Institute for Occupational Safety and
Health (NIOSH) to protect workers from these dangers.
X-ray diffraction is an excellent analytical technique for detection of crystalline silica, more accurate than many other methods due to its ability to distinguish between the different polymorphic phases. The MiniFlex II benchtop diffractometer can easily meet the NIOSH REL with a simple easy scan and a very simple software module of JADE called EASY QUANT.
Figure 1
This is accomplished by measuring a series of known concentrations of quartz sample. These are short scans over selected regions so the data collection times are short. The collected data is shown in Figure 1. Figure 2 shows the calibration curve from the known samples. In this case, samples from 10 to 40 micrograms were used to create the calibration curve. It is well documented that calibration curves for alpha quartz are non-linear, which is reinforced by the results shown in Figure 2. Easy Quant's calibration program allows for a second order polynomial fit. The non-linerar fit is shown in Figure 3.
Figure 2
Figure 3
After the calibration curve is created an unknown can be scanned using the same data collection parameters. The unknown concentration is determined by matching the intensity to the calibration curve. Figure 4 shows the XRD data for an unknown sample. Matching the intensity to the calibration curve (Figure 5) shows the unknown sample to have a concentration of 19 micrograms per mL .
Figure 4
Figure 5
Tags: composition, MiniFlex II, powder XRD, silica, calibration