X-ray Laboratory
The X-ray lab contains three major research instuments. At the heart of the lab is a Phillips 2404 XRF vacuum spectrometer equipped with a 102 position sample changer and a 4 kW Rh X-ray tube. The lab also contains a Phillips 3520 X-ray Diffraction system equipped with a monochrometer and a Cu X-ray tube. A Zeiss scanning electron microscope, model 962, equipped with an Oxford ISIS energy dispersive system is also available. The XRF in particular is available for contract work. Please contact Dr. Stan Mertzman for details concerning cost per sample analysis, turn around time, etc.
The personnel who handle day-to day operation of the XRF-portion of the X-ray lab are Dr. Stan Mertzman, Professor of Earth and Environment; Steve Sylvester, Research Specialist; Karen, Senior lab technician; and Julie, part-time lab technician.
Analytical Procedures employed in the XRF lab.
Brief Overview
Cutting and Crushing
Major Element Technique
Trace Element Technique
LOI and Iron Titration Technique
Precision and Accuracy
Picture Guide Through the Lab
X-ray Lab
X-ray Diffraction Instructions
Brief Overview
1. 3.6000 grams +/- 0.0002 of lithium tetraborate is weighed out into a clean glass bottle (24ml glass bottle from Thomas Scientific) followed by 0.4000 grams +/- 0.0001 of the rock powder and are mixed for 10 minutes in a Spex Mixer Mill. The homogeneous powder is transferred into a 25 cc. 95% Pt-5% Au crucible, 3 drops of a 2% solution of Lil is added to the powder to reduce the viscosity of the mixture as it is heated over a Meeker burner while mounted on a standard ringstand. During the heating the crucible is covered with a 95% Pt-5% Au lid which will also act as the mold into which the molten sample will be poured and cast into a disc shape. The bottom of the Pt lid is flat and highly polished, thus, the side of the disc in contact with the Pt lid is the one exposed to the primary X-ray beam.
2. The heating period is normally 10 minutes in duration with the sample being vigorously stirred while holding the crucible with a pair of Pt-tipped tongs at both the 3 minute and 6 minute marks. After sufficient heating so that the molten sample is thoroughly convecting, the Pt-lid is removed from the crucible with a pair of tongs and heated over a second bunsen burner until it is red-hot. With a second pair of tongs the crucible is removed rapidly from suspension on the ringstand over the first burner and emptied onto the hot Pt-lid. With some practice virtually all of the crucible's contents are transferred to the lid. Immediately upon completing the pouring event the still hot crucible is dropped into a warm beaker containing sufficient 4N HCl to cover the crucible. With the other hand, the crucible which has been held quite level is now carefully sat down on a flat surface; in our lab this is a flat polished piece of granite. The sample will cool in 3 to 5 minutes so that the glass disc can be labeled with a magic marker, labeled on the side of the disc exposed to the air. The disc can be stored indefinitely in a desiccator. The major elements are determined via this technique together with Sr, Zr, Cr and V.
3. Working curves for each element of interest are determined by analyzing geochemical rock standards, data for which has been synthesized in Abbey (1983) and Govindaraju (1994). Between 30 and 50 data points are gathered for each working curve; various elemental interferences are also taken into account, e.g., SrKý on Zr, RbKý on Y, etc. The Rh Compton peak is utilized for a mass absorption correction. Slope and intercept values, together with correction factors for the various wavelength interference, are calculated and then stored on a computer. A Philips 2404 X-ray fluorescence vacuum spectrometer equipped with a 102 position sample changer and a 4 kW Rh x-ray tube is used for automated data acquisition and reduction.
4. The amount of ferrous Fe is titrated using a modified Reichen and Fahey (1962) method and loss on ignition is determined by heating an exact aliquot of the sample at 950oC for one hour. Naturally the x-ray procedure determines the total Fe content as Fe2O3T.
5. Trace element analysis is accomplished by weighing out 7.0000 grams + /- 0.0004 of whole rock powder and adding 1.4000 grams +/- 0.0002 of high purity copolywx powder, mixing for 10 minutes, and pressing the sample into a briquette. Data are reported as parts per million (ppm). The elements measured this way include: Rb, Sr, Y, Zr, Nb, Ni, Ga, Cu, Zn, U, Th, Co, Pb, Sc, Cr and V. La, Ce, and Ba have been calibrated using an L x-ray line and a mass absorption correction.
6. Please Note--Always keep in mind that the original rock/mineral powder must be crushed so that ALL of the sample passes through a clean 80 mesh sieve screen. Do NOT use Tungsten Carbide grinding vessels if at all possible.
References
Abbey, S., 1983, Studies in "Standard Samples" of silicate rocks minerals 1969-1982: Geological Survey of Canada Paper 83-15, pp. 1-114.
Bennett, H. and Oliver, G.1992, XRF Analysis of Ceramic, Minerals and Allied Materials, John Wiley & Sons, LTD (ISBN 0 471 93457 7 (cloth)) 298pp.
Boyd, F.R., and Mertzman, S.A., (1987): Composition of structure of the Kaapvaal lithosphere, southern Africa: In: Magmatic Processes - Physicochemical Principles, B.O. Mysen, Ed., The Geochemical Society, Special Publication #1, pp. 13-24 . (Contains description of XRF methodology)
Govindaraju, K. 1994: 1994 Compilation of Working Values and Sample Description for 383 Geostandards: Geostandards Newsletter, Vol. 18, Special Issue, pp. 1-158.
Hower, J., 1959, Matrix corrections in the X-ray spectrographic trace element analysis of rocks and minerals. Amer. Mineral. 44, pp. 19-32.
Reichen, L.E. and Fahey, J.J., 1962, An improved method for the determination of FeO in rocks and minerals including garnet. U.S. Geol. Surv. Bull. 1144B, pp. 1-5.
on to cutting and crushing >
For further information regarding these techniques please feel free to email Stan Mertzman at stan.mertzman@fandm.edu or call him at 717-291-3818 or mail questions to him at:
Dr. Stan Mertzman
Franklin and Marshall College
Department of Earth and Environment
P.O. Box 3003
Lancaster, PA 17604-3003
Mail packages to:
Warehouse
Franklin and Marshall College
Attention: Stan Mertzman
501 Harrisburg Pike
Lancaster, PA 17603
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