Evaluation of the detectability and quantification of respirable crystalline silica by X-ray powder diffraction methods

Abstract

X-ray powder diffraction is one of the most sensitive methods for the analysis of crystalline forms of silica. In addition to detection and quantification, it can determine the specific crystalline species in the sample. The principal limitations of the method depend on the effective volume of the sample in the X-ray beam and the number of crystallites in the proper orientation to diffract. Detection limits are usually reported as 2 μg in thin-film filter mounts and 0.1% in bulk samples that are free of interference from associated minerals. Filter methods are most often used for air quality monitoring and several standardized procedures have been certified. Standard procedures for bulk samples are difficult to certify because of the variability of the matrices and their potential interferences. All of the methods of quantification require calibration with known samples of quartz or cristobalite. Certification of standard samples involves characterization of the particle and crystallite size and size distribution and amorphous content as well as determining the X-ray diffraction response. Although quartz is readily available and cristobalite is easy to synthesize, preparation of quantities of sufficient uniformity and stability is a limiting factor in certifying such samples for reasonable costs. Conventional diffraction equipment can be used for crystalline silica analysis at the present detection limits required by safety standards. Relatively simple modifications of the diffractometer will increase its sensitivity to small amounts of silica and improve the lower limits of quantification.

Occupational Exposure Assessment for Crystalline Silica Dust: Approach in Poland and Worldwide

“…In determining free crystalline silica, the dusts isolated from workplace air usually contain many other substances that may have infl uence on the results of analysis. The dust components in question include feldspars, micas, kaolinite, clay minerals, graphite, large quantities of amorphous silica as well as other silicate and aluminosilicate minerals [93,96,97,99,[101][102][103][104]. The fact that an analyzed sample contains a mixture of different silica forms is another disadvantage, making it diffi cult to determine the quantity of each component.…”

A combined polarizing microscope, XRD, SEM, and specific gravity study of the petrified woods of volcanic origin from the Çamlıdere-Çeltikçi-Güdül fossil forest, in Ankara, Turkey

“…When they were considered as a material, these features are very important for retailers and buyers, because petrified woods, if cut and polished, are used widely as both decorative in- Elzea and Rice (1996), Flörke et al (1991, Heaney and Post (1992), Jones and Segnit (1971), Miehe et al (1984), Miehe and Graetsch (1992), Murashov and Svishchev (1998), and Smith (1992, 1997, 1998.…”

“…In the comparative matching technique used in this study, the X-ray diffraction data of the samples were compared with the ideal X-ray diffraction data compiled from the American Mineralogist Crystal Structure Database (2009) by Downs et al (1993), Elzea and Rice (1996), Flörke et al (1991), Graetsch et al (1994), Heaney and Post (1992), Jones and Segnit (1971), Miehe et al (1984), Miehe and Graetsch (1992), Murashov and Svishchev (1998), Smith (1992, 1997, 1998, Minerals arranged by X-ray powder diffraction by webmineral.com (2009), and ASTM (1963)-PDF cards 38-0360 (for moganite); 38-0448 (for opal); and 46-1045 (for chalcedony). When the peaks in the XRD patterns of this study were not matched with any reference peak, they were left blank.…”

“…When the polarizing microscope images and the X-ray diffraction patterns of the silica-building phases of petrified wood samples as microcrystalline silica species are inves- tigated, the microcrystalline silica-building phases are generally detected in two ways as follows; polarizing microscope images (coarsely) and X-ray diffraction patterns (in detail). Cryptocrystalline silica-building phases can be divided into two main types based on granular crystallite habit, fibrous (granular), and massive (granular) quartz images (Keene, 1983;Flörke et al, 1976;Landmesser, 1988;Lynne and Campbell, 2003;Pretola, 2001;Smith, 1997) (Table 3). Heaney and Post (1992) have reported from polarizing microscope images that pure moganite is optically length-slow quartz, but chalcedony with less than approximately 20% moganite by weight is optically length-fast quartz.…”

Summary of Notifiable Noninfectious Conditions and Disease Outbreaks: Surveillance for Silicosis — Michigan and New Jersey, 2003–2010

“…Details of these methods are presented in Table 7. Although IR is less specific than XRD (IR methods cannot readily distinguish crystalline silica polymorphs), the technique is less expensive and can be optimized for measuring quartz in well-defined sample matrices [Madsen et al 1995;Smith 1997;Hurst et al 1997]. Samples that contain other silicates (such as kaolinite) and amorphous silica can present interferences in the analyses.…”