http://www.dri.edu
	Spring 2007

New Applications of XRD Technology for Atmospheric Sciences

Michael Skiba, left, and Johann Engelbrecht fine tune DRI's new XRD.
photo by Sara Marcus

One of the important things that helps keep DRI’s faculty at the forefront of research is instrumentation for analyzing samples. There are many analytical instruments available to DRI faculty, and an important recent addition is an X-ray diffractometer, or XRD for short. Funded by a National Science Foundation grant, a new XRD came on-line at DRI in March 2006 for DRI researchers to use. Running the new XRD laboratory is DRI faculty member Dr. Johann Engelbrecht, and funding has been provided internally by DRI for a post-doctoral fellow, Dr. Michal Skiba, to work on several projects using the XRD for analysis.

What makes this instrument potentially so valuable to many DRI faculty? Part of the answer lies in what an XRD can do and how it analyzes samples. X-ray diffraction can be used to identify crystalline solids based on their inherent atomic structure. An X-ray tube produces X-rays that interact with the atomic structure of a mineral or other material and produce a unique X-ray diffraction pattern, which can be used as a “fingerprint” of the material being analyzed. The diffraction pattern is then compared to known patterns, and the identity of the solid is then determined. The advantage of X-ray diffraction is that the sample is not destroyed and can be further analyzed using other methods. DRI’s XRD facility was customized to analyze a large number of different types of powder samples, from soils and rocks to air pollution samples on filters. The system includes a robot that can automatically select and analyze up to 90 samples, without operator assistance.

Engelbrecht is excited at the many potential projects and new opportunities that can be explored using the XRD. He notes that the XRD is an interdisciplinary facility that “can serve to bring the divisions closer together.” Currently the XRD is being used to analyze samples for faculty from each of the divisions at DRI. In conjunction with a project on the clarity of Lake Tahoe water, Engelbrecht and Skiba are working with Dr. Alan Heyvaert to help determine the mineral content of sediments that are contributing to decreasing the clarity of the lake water. In conjunction with other Division of Atmospheric Sciences faculty, the XRD is being used to measure the mineral content of airborne dust particles contributing to haze in the air. Certain minerals, such as asbestos and sometimes quartz, are known health hazards and, therefore, it is important to know what minerals are present in the air and in what form they exist.

Another project the XRD instrument is being used for is the quantification of minerals in desert dust from the Sahara, Middle East and China. This study is partly in collaboration with faculty in the Division of Earth and Ecosystem Sciences. Funded by the U.S. Department of Defense, dust samples have been collected from 15 sites in the Middle East, including places such as Tikrit and Baghdad, Iraq. These, together with other samples, are being analyzed at DRI for their chemical, mineralogical and optical properties.

Skiba, who hails from Poland, is particularly interested in clay minerals. He feels that the new XRD is essential for the analysis of clay minerals in soils and dust. By analyzing the clay minerals in a sample, Skiba hopes to trace their primary origin. By determining where the clays in a sample originate, numerous factors, such as transport distance and weathering rates, may be determined. In an area such as Lake Tahoe, knowing where minerals are coming from may help prevent dust from reaching the lake, which, in turn, could contribute to improved water clarity.

~ story by Sara Marcus