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We will be exhibiting at this year’s American Association of Petroleum Geologists Annual Conference and Exhibition (AAPG ACE 2015) in Denver, CO from May 31-June 3.

Stop by our Booth #2152, speak to our team of experts, and check out video demos of what is happening at Texray. We will be handing out gifts and hosting a contest for some great prizes.

We look forward to seeing you there. If you are interested in attending but have not registered, Contact Us on how you can get a FREE Exhibit Registration. 

XRD is the preferred analytical method of testing free crystalline silica in workplace atmospheres.   At Texray, we offer respirable silica testing using the NIOSH 7500 method, so we thought those of you in industries such as concrete, construction, glass, milling, mining, hydraulic fracking and sandblasting will find it important to know that OSHA has proposed an update to the current rules.  The most notable change is a decrease in OSHA’s Permissible Exposure Limits (PEL) from 100 mg/m3 of air for general industries and 250 mg/m3 of air for construction industries to 50 mg/m3 of air for all industries.  OSHA, along with other independent occupational health institutions, feel the current PELs are outdated and inadequate, and rightfully so, considering limits were last set in 1971 and based on 1960s research.  However, most of these industries may not feel an impact from such as change, as many employers already use preventative measures to reduce dust exposure.

Would this rule change affect the analytical testing procedure?

Photo Courtesy of New Jersey Department of Health

Photo Courtesy of New Jersey Department of Health

No, XRD limits of detection (LOD) for NIOSH 7500 are 0.005 mg/m3 for an 800 L air sample.  This rule change would not affect the testing method, since the LODs for silica in the form of quartz and cristobalite are well below the newly proposed PEL.  However, the rule change may increase the number of industrial sites needing to test their work environments for respirable silica.

According to OSHA, “The proposed rule is expected to prevent thousands of deaths from silicosis, lung cancer, other respiratory diseases, and kidney disease. OSHA estimates that the proposed rule will save nearly 700 lives and prevent 1,600 new cases of silicosis per year once the full effects of the rule are realized.”  The rule change was proposed last September and the hearing was recently concluded at the beginning of April.  Final decision will be coming soon. We will keep you posted.

In my last post, I hinted towards the importance of literature searches before attempting to analyze a new material, and then someone in one of my discussion groups posted a link to the 30 Most Downloaded Advanced X-ray Analysis Articles from the ICDD. I thought some of you might find this helpful, so I am reposting the link.

30 Most Downloaded AXA Publications

The articles are free to download and written by well-known, respected professionals that have been in the business of X-ray analysis for many years. The topics range from sample preparation to applications to instrumentation hardware. Enjoy!

Over the past 15 years, Barnett Shale has become a major resource for natural gas in Texas.  Being located in the North Texas region, it is easy to see the boom of drilling rigs and wells popping up in the suburban and rural areas between Ft. Worth and Denton.  Collaborations between Geologists at universities and major oil companies have put a large amount of research into characterizing shale.  In 2001, Środoń et al. published a journal article in Clays and Clay Minerals that discussed the importance of sample preparation for sediments, such as shale, to be analyzed using X-ray diffraction.

Powder X-ray diffraction is the preferred and best technique to identify and quantify mineral compositions in geological materials such as rocks, sediments, and soils.  Sample preparation and loading are two important factors for accurate quantitative XRD analysis using Rietveld refinement.  Proper sample grinding and using a side-loader or backside loader are common practices to avoid preferred orientation.  At Texray, we have a variety of sample holders for different applications, and we can even custom build holders for those random parts.  However, in this study we wanted to see for ourselves the effect of sample grinding and particle size, and also we wanted to test out our new McCrone Micronizing Mill.  We already knew what the results would be from experience and previous work by Środoń et al., 2001 and Klug and Alexander, 1974, but this was a fun experiment to try with shale.

Shale rock from the North Texas region

Shale Rock from the North Texas region

The rocks (pictured above) were broken up into smaller pieces using a mortar and pestle, and then half was transferred to the McCrone mill for wet grinding and the other half we continued to grind manually using the mortar and pestle.  By the way if you are running out of bench space in the laboratory and are looking for a mill, I highly recommend the McCrone Micronizing Mill because it takes up very the little space and it’s capable of grinding below 10 μm in less than 10 minutes.  After grinding, we loaded the powder samples into a backside loader and analyzed them using a Bruker D5000 X-ray Diffractometer.

Shale XRD Pattern

XRD pattern of Mortar & Pestle Ground Shale (blue) vs McCrone Mill Ground Shale (red)

In the XRD pattern shown above the main differences you will notice between the two grinding methods are peak intensities and a small 2-theta peak shift.  Both of these differences are effects related to particle size distribution and sample loading.  Wet grinding the shale in a McCrone Mill creates smaller uniform particles (~5μm), therefore when loading the sample into holders the powders pack easier and tighter creating a denser layer of material for the X-rays to penetrate, hence higher peak intensities compared to manual grinding.  Sample preparation is one of the most important aspects to quantitative XRD because of preferred orientation and sample displacement.  In order to reduce user error such as, induced preferred orientation, it is essential we learn from previous research and take the proper steps to prepare samples.  The ICDD is a great source for free literature on applications involving XRD and XRF.  We will be posting more discussions on sample preparation and applications in the future.