Ann. occup. Hyg., Vol. 46, No. 4, pp. 409-421, 2002
© 2002 British Occupational Hygiene Society
Published by Oxford University Press
Comparison by X-ray Diffraction and Infrared Spectroscopy of Two Samples of 
Quartz with the NIST SRM 1878a Quartz
INRS, Departement Metrologie de Polluants, Laboratoire d’Analyses Physiques, Avenue de Bourgogne, BP 27, F-54501 Vandoeuvre les Nancy, France
Received 17 May 2001; in final form 24 December 2001
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONREFERENCES |
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The aim of this study was to compare the X-ray diffraction and infrared spectrophotometric patterns of two samples of
quartz (QUIN1 and QUIN2) with that of NIST SRM 1878a quartz certified 100% crystalline. As it is known that the intensity diffracted and the absorbance per mass unit for a given type of quartz depend on its particle size, this factor was taken into account. To do this, different types of quartz were sampled on filters using a Dorr-Oliver cyclone to select particle size. Variation in the flow rate of the cyclone in the range 1.2–2.8 l/min allowed the volume median diameter of the sampled particles to be varied. For the four strongest diffraction lines it was observed that the intensity per mass unit increased with the volume median diameter of the particles. For infrared spectrophotometry for analytical band wavelengths close to 12.5 µm, it was observed that the absorbance per mass unit decreased as particle size increased. The opposite effect was noted for analytical band wavelengths >14.4 µm. Compared with SRM 1878a quartz, certified 100% crystalline, the purity of QUIN1 quartz was 93.1% (confidence interval 92.4–93.8%) when measured by X-ray diffraction and 91.5% (confidence interval 90.1–92.9%) when measured by infrared spectrophotometry. In the case of QUIN2 quartz the purity was globally lower.
Keywords: crystallinity; infrared spectrophotometry; particle size; quartz; X-ray diffraction
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONREFERENCES |
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Quartz is one of the most abundant minerals found in the Earth’s crust (12% of its weight). It is a major component of numerous igneous and sedimentary rocks and is present in an impure state in many siliceous rocks. Cristobalite and tridymite are the other most common forms of what is commonly known as crystalline silica. Potentially, exposure to crystalline silica can occur during mining and quarrying, during stone cutting and construction, in foundries and in numerous other activities, including sanding, sandblasting, polishing and grinding (IARC, 1987). Silicosis is the oldest and most well-known disease attributed to inhaling crystalline silica. More recently, the IARC reassessed the carcinogenic effects of silica. Taking into account all the available data, quartz and cristobalite from occupational sources were classified as carcinogenic in humans (IARC, 1997).
The seriousness of the illnesses associated with inhaling crystalline silica dusts has led to a multiplication of the number of workplace concentration measurements intended to verify compliance with the exposure limit values. The techniques and methods used to analyse air samples include gravimetric and chemical analyses as well as infrared spectrophotometry and X-ray diffraction (Rose et al., 1995). To improve the analytical accuracy of the results, proficiency tests such as PAT (Proficiency Analytical Testing) (Shulman et al., 1992) and WASP (Workplace Analysis Scheme for Proficiency) (Jackson and West, 1992) have been organized on a regular basis. Recently, the variability of the results of analysing silica in the PAT test was evaluated (Eller et al., 1999). Compared to the analysis of other pollutants encountered in industrial hygiene, this variability was found to be somewhat high. It has been suggested that considerable improvements could be possible by standardizing the analytical methods and using a common reference material.
It was this policy that was adopted in France when the first proficiency test relative to the quantitative analysis of quartz was launched in 2000. The same quartz, termed QUIN1, was distributed, after particle size selection, as the standard to all participating laboratories.
Laboratories using a direct method for analysis received filters that they could directly use for calibration. These filters were prepared by air filtration using the same size of separation device as that used for sampling in the workplaces (the Dorr-Oliver cyclone). Such reference material directly deposited by air sampling on filters is not available at the moment from the National Institute for Standards and Technology (NIST), and the NIST 1878a quartz reference material is available in quantities too small to allow its use directly on a large scale in generation chambers. The aim of this article is to show how this sample of silica was compared, using X-ray diffraction and infrared spectroscopy techniques, to a sample of SRM 1878a quartz (National Institute of Standards and Technology, 1999) certified by NIST. The results for a second sample of quartz, QUIN2, which was also compared, are also presented.
Differences in the responses of various quartz samples may be due to variations in crystallinity, as already mentioned by Murata and Norman (1976), but also to differences in their particle size distributions (Gordon and Harris, 1955; Edmonds et al., 1977; Bhaskar et al., 1994). Particular attention was paid during the comparison to ensure that differences in particle size distribution between the reference sample (SRM 1878a) and the secondary samples (QUIN1 and QUIN2) were taken into account.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONREFERENCES |
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To ascertain the
quartz best suited for use as a secondary standard, preliminary tests were carried out on bulk samples of quartz of different origins to determine those with the highest purity (i.e. those for which the intensity diffracted per mass unit was highest for the same particle size distribution). More thorough tests were then performed after air sampling of QUIN1 and QUIN2 quartz samples on filters.
Bulk samples
The quartz samples of different geological and commercial origins used in the preliminary tests were as follows.
SIKRON C300, C400, C500 and C600 quartz supplied by SIFRACO (produced at Compiègne, France), varieties C300–C600 representing different particle size distributions of the same quartz.
SIKRON F500 and F600 quartz also supplied by SIFRACO (produced at Frechen, Germany); SIKRON F600 quartz is termed QUIN2 in the remainder of this article.
J silica supplied in the 1970s by Moulin des Prés (Saint Aubin sur Scie, France). This sample of quartz, termed QUIN1 in what follows, was studied in its original particle size distribution as well as in a finer range (respirable fraction).
The volume median diameter of the different quartz samples was measured by the Coulter counter technique. This instrument measures the volume distribution of the test particles when dispersed in a suitable electrolyte, based on the assumption that the voltage pulse generated when a particle passes through a small orifice is directly proportional to the particle volume. To plot calibration curves, the deposits of these different varieties of quartz were ensured by liquid filtration on pre-weighed Nuclepore filters (diameter 25 mm, pore size 0.4 µm) in the range 1–10 mg. Five unused Nuclepore filters were used as blanks. Figure 1 is an example of the calibration curves obtained.
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Deposition on filters
Samples of SRM 1878a, QUIN1 and QUIN2
quartz were also prepared by air filtration on pre-weighed Gelman PVC filters (diameter 25 mm, pore size 5 µm). The filters were positioned in a three-section Millipore cassette coupled to a Dorr-Oliver cyclone. To vary the size distribution of the particles deposited, the flow rate of the cyclone was varied between 1.2 and 2.8 l/min during the different tests.
The dust chamber used to generate the SRM 1878a quartz was similar to that described in method MDHS 51/2 (HSE, 1988). The generation system employed a fluidized bed charged with bronze beads, as described by Lorbereau et al. (1990). However, in accordance with a specific provision of French legislation, this system was not equipped with a 210Po source to neutralize the electrostatic charges. A larger dust chamber already used for animal experiments (Kauffer et al., 1987) was employed for the QUIN1 and QUIN2 quartz samples. This chamber allows an increase in the number of simultaneous samplings (nine instead of four) and provides better concentration control than the smaller one. It cannot, however, be used when only small amounts of quartz are available, as is the case with certified materials.
To characterize the aerosol a Grimm dust monitor (model 1-108) was used. This instrument determines the size distribution of the sampled particles by quantifying the angular dispersion caused by passage of particles of various sizes through a light beam produced by a laser diode. This dust monitor was connected to one of the sampling apertures in each chamber, which was also equipped with a cyclone. As the nominal flow rate of the dust monitor was 1.2 l/min and as the flow rate of the cyclone could vary from 1.2 to 2.8 l/min, an additional pump was used to compensate for any differences. The volume median diameter of the sampled particles was calculated on the basis of the data supplied by the dust monitor, excluding the data of the first three channels (particle diameters of <0.65 µm), which in certain cases appeared abnormally high. Accordingly, three samplings on filters could be carried out simultaneously in the small unit and eight in the larger unit.
Calibration curves were plotted for a fixed flow rate, and therefore for a particular particle size distribution, from three samplings with SRM 1878a quartz and from four simultaneous samplings with QUIN1 quartz. For the QUIN2 quartz the calibration curves were plotted from eight sampling filters whose loading varied between 0.2 and 1 mg. In this case, the particle size distribution measured corresponded to the mean particle size distribution over the longest sampling duration. Fourteen unused filters were used as blanks. In total, 24 curves at different flow rates were plotted with SRM 1878a quartz, 26 with QUIN1 quartz and 15 with QUIN2 quartz. A total of 296 filters were sampled [(3 x 24) + (4 x 26) + (8 x 15)]. For the sampling carried out at 2 l/min, Fig. 2 shows the calibration curves obtained by X-ray diffraction (101 diffraction line) for the different varieties of quartz. Similar results obtained by infrared spectrophotometry (798 cm–1 absorbance band) are shown in Fig. 3.
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Apparatus and analytical conditions
X-ray diffraction
The calibration curves were plotted on a Philips PW 1729 powder X-ray diffractometer fitted with an automatic sample changer. The operating parameters of the diffractometer were as follows: 2.2 kW long fine focus Cu X-ray tube run at 40 kV and 44 mA; secondary beam graphite monochromator; 2° divergence slit; 1° diffusion slit; 0.3 mm analytical slit; sample spinner.
The diffractometer was calibrated on the four strongest lines (101, 100, 112 and 211) by measuring the net peak areas for each of the filter standards. The net peak areas were determined by scanning over the peaks, integrating to obtain the gross peak areas and then making a simple linear background correction. The total count time on each line is governed by the width of the base of the peak; for all four diffraction peaks this was 1.4°2
, making a total count time of 700 s. The most intense peak of a sample of polycrystalline silicon which was recorded regularly was used to correct any drift of the instrument over time.
For the deposits on Nuclepore filters the intensity was corrected for matrix absorption by measuring the attenuation of the peaks of an aluminium support on which the Nuclepore filter was placed in accordance with the principle described by Altree-Williams et al. (1977).
Infrared spectrophotometry
The calibration curves were plotted on an infrared spectrophotometer with Fourier transform. The apparatus used was a Nicolet Magna 560 (OMNIC, TQ Analyst Macrobasic software). The beam splitter of the interferometer and the DTGS detector window were made of caesium iodide to allow analysis of the quartz in the far-field infrared. The spectral range explored extended from 6400 to 200 cm–1.
The analytical bands were located at 798, 780, 695, 398 and 374 cm–1. Subtraction of the spectra of blank filters took into account spectral interference due to the filter.
The following spectrophotometer settings were used: number of scans, 32; resolution, 4 cm–1; gain, auto; speed of the mobile mirror of the interferometer, 0.63 cm s–1; aperture, 100%; spectral range, 4000–280 cm–1.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONREFERENCES |
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On bulk
quartz samples (preliminary test)Figure 4 represents the intensity diffracted per mass unit as a function of particle volume median diameter for different varieties of
quartz (QUIN1, QUIN2 and SIKRON series C). The intensity diffracted per mass unit was determined on the most intense diffraction line (101) after depositing the different quartz samples on the Nuclepore filters by liquid filtration. The particle volume median diameter was determined by the Coulter counter technique. The curves linking the intensity diffracted per mass unit to the particle volume median diameter were plotted for the varieties of quartz for which results for different particle size distributions were available. If the intensities diffracted per mass unit of these different varieties of quartz are compared for the particle volume median diameter corresponding to QUIN2 quartz (3.93 µm), we find, on a relative scale where QUIN1 quartz is 100%, 96% for QUIN2 quartz and 91.4% for the quartz of the SIKRON C series. On the basis of these preliminary results, it was decided to carry out more thorough tests on QUIN1 and QUIN2 quartz and to compare their responses with NIST SRM 1878a reference quartz.
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On
quartz deposited on a filter by air samplingFigures 5–8 represent the variations in intensity diffracted per mass unit as a function of the particle volume median diameter of SRM 1878a, QUIN1 and QUIN2
quartz for the diffraction lines 100, 101, 112 and 211. Likewise, Figs 9–13 give the results obtained by infrared spectroscopy for the absorption bands located at 798, 780, 695, 398 and 374 cm–1.
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The correlation coefficients of the data for either the four X-ray diffraction lines or the five absorbance bands are given in Table 1. These data suggest a linear relationship between the measured intensity or the absorbance per mass unit and the volume median diameter of the particles, except for the 780 cm–1 absorbance band, where the measured absorbance does not seem dependent on the volume median diameter of the particles. The dispersion of the data may be due to weighing errors when estimating the mass of dust deposited on the filters and also to errors in evaluating the volume median diameter of the sampled particles. Taken as a whole, the correlation coefficients obtained for QUIN2
quartz are lower than those obtained for 1878a and QUIN1 quartz. This is probably due to the narrower range of variation of the volume median diameter of the QUIN2 quartz.
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To model the relation between the variation in the intensity diffracted or the absorbance per mass unit Y and the particle volume median diameter (d50) a proportional linear relationship was used. For the SRM 1878a
quartz, certified 100% pure and crystalline, the relationship is expressed as: Yro = ar + br (d50 – 3)
where r depends on the X-ray line or absorbance band used. For the other quartz (q = 1 or 2) it is written as:
Yrq = Crq[ar + br (d50 – 3)].
In these relationships the values of the volume median diameter are centred around 3 µm.
The coefficient Crq is interpreted as the ratio of the intensities diffracted or the absorbancies per mass unit between QUIN1 or QUIN2 quartz and reference 1878a quartz for each diffraction line or absorbance band r. This model was fitted to the data using linear regression (BUGS software; Spiegelhalter et al., 1996). Table 2 gives, for QUIN1 and QUIN2 quartz and for the different diffraction lines, the estimated values of the Crq coefficients as well as the 95% confidence interval (CI), which takes into account the variability of the experimental points, i.e. the accuracy obtained for the calibration curves. As for QUIN1 the Crq coefficients are not statistically different for the four X-ray diffraction lines, a Cq coefficient common to all the lines was also computed. The values of coefficients ar and br along with their CIs are given in Table 3. Similar results obtained by infrared spectroscopy are given in Tables 4 and 5.
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For the three varieties of
quartz studied, the ranges of variation of the particle volume median diameter (measured by the Grimm counter technique) as a function of the ranges of variation of the cyclone flow rate are indicated in Table 6. The particle volume median diameters measured on the bulk materials by means of the Coulter counter technique are also shown in Table 6.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONREFERENCES |
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Table 6 shows that the volume median diameter of the particles sampled can be easily modified by varying the flow rate of the cyclone. The variations in d50 obtained were
1 µm for QUIN1 and QUIN2 quartz and 2 µm for the reference SRM 1878a quartz. Although the values of d50 measured for QUIN1 and QUIN2 quartz by the Grimm counter technique were lower than those measured with the Coulter counter technique for the bulk materials, this was not the case for the reference SRM 1878a quartz. In this case, the volume median diameters measured after cyclone selection were higher than those measured on the bulk materials (2.5 µm). This divergence becomes even greater if reference is made to the value mentioned in the NIST certificate of analysis (1.59 µm) obtained by laser diffusion. This drift towards the larger particles of the SRM 1878a quartz particle size distribution probably results from agglomeration of particles during generation. The existence of electrostatic forces promoting the agglomeration of particles was confirmed by observing a deposit on the walls of the experimental chamber during generation. The previous NIST reference quartz literature (SRM 1878) mentioned this tendency of formation of particle clusters. However, this is no longer indicated on the certificate accompanying the most recent reference material.
Figures 5–8 clearly show that, whatever the variety of quartz, the intensity diffracted per mass unit increases with the volume median diameter of the particles. This effect has already been described at length in the literature. In this respect, the work of Gordon and Harris (1955) and Edmonds et al. (1977) are worthy of particular mention. The reason generally put forward to explain the increase in the intensity diffracted per mass unit as a function of the particle volume median diameter of the particles is the presence of a layer of amorphous silica on the surface (Brindley and Udagawa, 1959; Altree-Williams et al., 1981). Certain authors have evaluated the thickness of this layer at 0.03 µm (Nagelschmidt et al., 1952). If the hypothesis is made that the thickness of this layer is constant whatever the diameter of the particles, then the smaller the particles the greater will be the relative proportion of amorphous silica compared with the total particle mass. This could therefore indeed explain the increase in the intensity diffracted per mass unit as a function of the volume median diameter of the particles. This explanation unfortunately does not fit in with our own experimental data as this effect should not be observed for the reference quartz (SRM 1878a), which is totally crystalline and therefore does not contain amorphous silica.
Another approach is possible. It draws on the technique used to prepare standard filters. The filters were prepared by sampling air containing quartz as opposed to liquid filtration of a suspension of particles. The air filtration method was preferred as it allowed the volume median diameter of the sampled particles to be varied by varying the flow rate of the cyclone. It is probable, as has already been reported by Foster and Walker (1984), that in this case the particle size distribution, on account of forces of inertia, can vary locally on the surface of the sampling filter. Over-representation of the largest particles can thus be expected in the central part of the filter, the opposite effect being observed at the periphery. Assuming this to be the case, the greater the median diameter of the particles sampled the greater the local density should be in the central part of the filter. As the diameter of the X-ray beam in our experimental configuration was less than the diameter of the particle deposit on the filter, this could have led to observing an increase in the intensity diffracted per mass unit when the median diameter of the particles increased. In other words, for a given X-ray beam diameter, the mass of particles included in the beam increased as the volume median diameter of the sampled particles increased.
If the values of the ratio Crq (Table 2) linking the intensities diffracted per mass unit of QUIN1 and QUIN2 quartz with reference SRM 1878a quartz for each diffraction line r are now considered, it can be seen that these ratios are probably not statistically different for the four diffraction lines of QUIN1 quartz (overlap of the corresponding CIs), whereas a significant difference appears between the coefficients measured for lines 101 and 100, on the one hand, and between lines 112 and 211, on the other, with QUIN2 quartz. In the case of QUIN2 quartz this is probably due to preferential orientation of the deposit favouring the 101 or 100 lines to the detriment of the 112 and 211 lines. As indicated in Table 2, the purity of QUIN1 determined by taking the mean of the four diffraction lines is equal to 93.1% crystalline quartz (CI 92.4–93.8%). The two faces of the PVC filters used for sampling had different appearances: one was smooth, whereas the other had a coarser appearance. During sampling it was the coarser face, which minimized the effects of preferential orientation, that was used (Henslee and Guerra, 1977). Using the other face of the filtration medium or using another type of filtration medium during sampling would have the effect of modifying the Crq coefficients given in Table 2, at least in the case of QUIN2 quartz.
Jeyaratman and Nagar (1993) also compared a secondary quartz standard (HSE A9950) to the former NIST reference sample (SRM 1878). The QUIN2 and HSE A9950 quartz came from the same quarry (Quartzwerke, Frechen, Germany) and had the same brand name, SIKRON F600. The purity of the HSE A9950 quartz was 95.5%, whereas that of the QUIN2 quartz during this study was <90%. It is, however, impossible to interpret these differences as the HSE A9950 and QUIN2 quartz samples were quarried at different times (1980 and 1999, respectively). It is therefore uncertain whether the same material was involved, even though the brand names are identical.
Verma and Shaw (2001) also compared two standards, SIKRON F-600 and HSE A9950, apparently coming from the same quarry in Germany, with the NIST-SRM 1878 standard. Their results are markedly lower than those obtained by Jeyaratman and Nagar (1993): 80% compared with 100% if we do not take into account that the NIST-SMR 1878 quartz was certified 95.5% crystalline. A possible explanation given by the authors is that the difference could be because of the use of an alternative technique (infrared spectrophotometry in the Verma and Shaw study as opposed to X-ray diffraction in the Jeyaratman and Nagar study).
The results obtained in our study by the two techniques are in close agreement and do not seem to support the possible explanation given by Verma and Shaw (2001). Obviously, if differences between the two techniques did exist, as has already been mentioned by other authors (Dewell and Ambidge, 1980; Biggins, 1982), this would raise the question of the coherence of the two techniques when performing quartz analysis. This important point probably needs further research for clarification.
Figures 9–13 show that the absorbance per mass unit depends on the volume median diameter of the particles. The extent of the effect depends on the wavelength of the infrared radiation. The smallest effect was obtained for the absorption band located at 780 cm–1. In addition, the sign of the effect was different for the bands located at 798 and 780 cm–1 and for the bands located at 695, 398 and 374 cm–1. The diversity of the experimental conditions makes comparison of these results with those obtained by other authors difficult. In this respect, certain authors worked on KBr pellets, others on filters, the particles in the latter case being deposited either by air filtration or by liquid filtration. In the case of cristobalite particles deposited on a filter by liquid filtration, Shinohara (1996) also observed that the slope of the curve linking absorbance per mass unit with particle diameter depends on the wavelength of the infrared radiation.
Several explanations can be put forward to account for both the intensity and direction of the effects observed, although determining those which are determinant is not easy.
The mode of selecting particles when sampling on a filter with the 10 mm cyclone involves the mass of particles included in the infrared beam being higher the greater the volume median diameter (Foster and Walker, 1984). This effect is more pronounced the smaller the diameter of the beam, which is the case with the spectrophotometer used during this study (beam diameter 6 mm).
Light diffusion phenomena, which depend both on the wavelength of the infrared source and the diameter of the particles. Qualitatively, any increase in the radiation diffused will reduce absorbance.
The variation in the porosity of particles with their size. Salisbury and Eastes (1985) therefore assign the highest particle absorption to a higher porosity of these particles, which allows the photons to penetrate more deeply into the grains and thereby increase absorbance.
If the values of the ratio Crq (Table 4) linking for each absorbance band the absorbances per mass unit of QUIN1 and QUIN2 quartz to those of reference SRM 1878a quartz are now considered, it can be seen that for the same quartz these ratios are not statistically different for the five absorbance bands, including the band located at 798 cm–1. If it is assumed that the differences between the responses of QUIN1 and QUIN2 quartz and of SRM 1878a quartz are due to the presence of a surface layer of amorphous silica, it could be thought that the band located at 798 cm–1 should be more intense than the others insofar as this band is subject to strong interference by amorphous silica. This was not the case, which could suggest that the differences between QUIN1 and QUIN2 quartz and SRM 1878a quartz may be due to global deterioration inside the quartz grains rather than to separation between an amorphous phase and a crystalline phase.
The results obtained by X-ray diffraction and by infrared spectrophotometry during this study are close. The purity of QUIN1 when measured by X-ray diffraction was equal to 93.1% crystalline quartz (CI 92.4–93.8%, mean of four X-ray diffraction lines). The same value obtained by infrared spectrophotometry was 91.5% (CI 90.1–92.9%, mean of five absorbance bands). In contrast, the dispersion of results was greater between the five absorbance bands (88.4–94.9%) than it was between the four X-ray diffraction lines (91.7–93.6%). The purity of QUIN2 was 84.9% crystalline quartz and this confirms the results obtained by X-ray diffraction, where the purity of QUIN2 quartz was lower than that of QUIN1 quartz.
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CONCLUSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONREFERENCES |
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Certified reference samples are generally available only in small amounts. This is why it appeared necessary to couple a specimen of
quartz (QUIN1) which is used as a secondary standard in France with the SRM 1878a quartz standard certified by NIST. In addition, a second sample of quartz, termed QUIN2 (trade name SIKRON F-600), was also compared. The comparison was carried out on filters following particle size selection using a Dorr-Oliver cyclone and deposition by means of air filtration.
The purity of QUIN1 when measured over the four most intense diffraction lines for which no significant differences had been observed was 93.1% crystalline quartz (CI 92.4–93.8%). In the case of QUIN2 quartz the purity was globally lower. For this variety of quartz, on account of preferential orientation problems, comparison with the certified primary standard depends on the diffraction lines used.
The comparison of these two specimens of quartz by infrared spectrophotometry provided the opportunity to make a number of observations regarding the relationship between absorbance per mass unit of quartz and particle size distribution. In particular, it was shown that this relation varies according to infrared wavelength. For infrared wavelengths close to 12.5 µm it was observed that the absorbance per mass unit decreased as particle size increased. The opposite effect was noted for wavelengths >14.4 µm. Compared with SMR 1878a quartz, the purity of QUIN1 was 91.5% (CI 90.1–92.9%). This value is close to that found by X-ray diffraction. The purity of QUIN2 quartz was lower at 84.9% (CI 83.3–86.4%).
Acknowledgements—The authors would like to thank the Aerosol Metrology Laboratory for determining the particle size distribution of the bulk materials.
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FOOTNOTES |
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* Author to whom correspondence should be addressed.
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONREFERENCES |
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  P. Stacey, E. Kauffer, J.-C. Moulut, C. Dion, M. Beauparlant, P. Fernandez, R. Key-Schwartz, B. Friede, and D. Wake An International Comparison of the Crystallinity of Calibration Materials for the Analysis of Respirable {alpha}-Quartz Using X-Ray Diffraction and a Comparison with Results from the Infrared KBr Disc Method Ann. Hyg., August 1, 2009; 53(6): 639 - 649. [Abstract] [Full Text] [PDF]
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E. KAUFFER, A. MASSON, J. C. MOULUT, T. LECAQUE, and J. C. PROTOIS Comparison of Direct (X-Ray Diffraction and Infrared Spectrophotometry) and Indirect (Infrared Spectrophotometry) Methods for the Analysis of {alpha}-Quartz in Airborne Dusts Ann. Hyg., November 1, 2005; 49(8): 661 - 671. [Abstract] [Full Text] [PDF]
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J. CHISHOLM Comparison of Quartz Standards for X-ray Diffraction Analysis: HSE A9950 (Sikron F600) and NIST SRM 1878 Ann. Hyg., June 1, 2005; 49(4): 351 - 358. [Abstract] [Full Text] [PDF]
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D. K. VERMA and D. S. SHAW Comparison of Crystalline Silica ({alpha}-Quartz) Calibration Standards NIST-SRM 1878 and NIST-SRM 1878a by Fourier Transform Infrared Spectrophotometry Ann. Hyg., June 1, 2005; 49(4): 359 - 361. [Full Text] [PDF]
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