15/12/2019 1 State-of-the-art analysis of respirable crystalline silica by direct-on-filter XRD and recent findings from workplace samples Martin Mazereeuw, John Volpato, Akemi Ichikawa TestSafe Australia – SafeWork NSW 3/12/2019 2 Silica analysis: XRD and FTIR XRay Signal Lamp Detector Filter Lamp Detector IR Signal XRD and FTIR used for RCS analysis ➢ Direct-on-filter approach ➢ Different technology ➢ Different performance Diffraction technique Transmission technique 1 2
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Silica analysis: XRD and FTIR · by direct-on-filter XRD and recent findings from workplace samples Martin Mazereeuw, John Volpato, Akemi Ichikawa TestSafe Australia –SafeWork NSW
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15/12/2019
1
State-of-the-art analysis of respirable crystalline silica by direct-on-filter XRD and recent findings from workplace samples
Martin Mazereeuw, John Volpato, Akemi IchikawaTestSafe Australia – SafeWork NSW
3/12/2019 2
Silica analysis: XRD and FTIR
XRay Signal
Lamp Detector
Filter
Lamp Detector
IR Signal
XRD and FTIR used for RCS analysis
➢ Direct-on-filter approach
➢ Different technology
➢ Different performance
Diffraction
technique
Transmission
technique
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XRD Analysis
Method: NH&MRC (1984), HSE(2014)
Response factor: Peak intensity of Q (101) diffraction
Criteria: Q(101)/average*= 90-110%, Dust<2mg
Q (100), (112) when Q(101) interfered
Overload correction implemented when overloadedQ
(10
0)
Q(1
12)
Q(1
01)
Ag(1
11)
Ag(2
00)
Measurement area
(24mm diameter)
*average= {Q(100)+Q(101)+Q(112)}/3
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FT-IR Analysis
Method: HSE(2014)
Blank subtraction implemented
Response factor: Absorption peak height of Si-O vibration
Criteria: PH800/PH780 = 1-1.4, Dust<1mg
PV
C
Measurement area
(8mm diameter)
Q 8
00
Q 7
80
*
PV
C
PV
C
PV
C
PV
C
PH 800 PH 780
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Equipment
XRD
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a-quartz calibration curves
XRD r2=0.998 FT-IR r2=0.996
pure quartz = linear result
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XRD vs FT-IR (α-quartz samples)
r2=0.991n=43(valid results)
Pure α-quartz (No matrix)
Good agreement
r2=0.99
FT-IR values: XRD values
y=x
y=0.8x
y=1.2x
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Real workplace samples
n=253
Sampled 34 different workplaces
in Australia (2014-18)
Industry:
- Road construction/ Tunneling (47%)
- Coal mining (23%)
- Kitchen benchtop (25%)
- Others (5%)
Compositions depend on
individual samples
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XRD vs FT-IR (real workplace samples)
n=253(all measured
results: Included
invalid results)
y=x
y=0.8x
y=1.2x
Outliers
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XRD vs FT-IR (real workplace samples)
n=171(valid results)
y=x
y=0.8x
y=1.2x
32% of FT-IR data failed
(PH criteria, Dust >1mg)
r2=0.97
FT-IR values: ~10% higher
than XRD
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FT-IR Spectra (α-quartz vs Silicates)
Q(7
80
)
Q(8
00
)
Peak overlap on Quartz (800) Blank subtracted
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XRD Spectra (α-quartz vs Silicates)
Q(1
00
)
Q(1
12
)
Ag(1
11)
Q(1
01
)
Ag(2
00)
No major peak overlap on Quartz (101)
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Recovery of α-quartz (with Silicates)
FT-IR showed positive bias
w/ Kaolinite (>60%),
Albite (>90%)
Cristobalite(>10%)
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Cristobalite
α-Quartz Tridymite Cristobalite
T > 800 ºC T > 1100 ºC
Quartz transforms to Cristobalite (Tridymite) by heat process
>~800degC and influenced by alkalinity.
Pure Quartz transforms to Cristobalite at ~1400degC.
Quartz most commonly present (stones, soils).
Cristobalite (Tridymite) presence in nature related to volcanic activity.
Cristobalite (Tridymite) presence in engineered stones.
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Cristobalite
Engineered stone
Cristobalite found regularly
in dust samples
Sometimes at high %
10-15 % of cristobalite found in all jobs offered.
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SDS – engineering stones
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Quartz-Cristobalite
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Estimated LOD
For “Direct-on-filter” using XRD with old instrument
Major limitation: Signal to Noise Ratio (SNR)
XRD can achieve
2 µg LODwhen needed
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Estimated LOD
For “Direct-on-filter” using XRD with new instrument
XRD can achieve
800 ng LODwhen needed
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Blanks
Lowering exposure limit Lowering reporting limit
Analysis usually done
against a blank signal
When lowering detection limits,
quality of blank becomes important
Found: Not all blanks are blank
➢ Contamination control
➢ Blank variability
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Transfer/ Handling the sample
Do not use flat plastic bag Do not tape the sample
Dust came off from the filter
Dust came off when tape removed/
Interference from tape
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Recommended casePlace the sample and clip the edge,
collected surface (to be analysed) should be upside