Scanning Electron Microscopy


Ocean ferromanganese crusts are composed of interlayered phases of manganese oxide, iron oxide and oxyhydroxide, calcium carbonate/phosphate, silica, and alumino-silicates. These interlayers are so thin and fine-grained that each phase could not be isolated under the beam of a scanning electron microscope for quantitative x-ray microanalysis. A test was conducted to determine if the grain size of the phases was small enough to allow conventional ZAF techniques to be used without serious errors in the results. A "synthetic" ferromanganese crust was prepared by pelletization of a 1:1 mix of two fine-grained (<5 >micrometer) components. The mean of the energy dispersive analyses of the mix, using an area-scan method (25 x 30 μm square), shows good agreement (generally within 5 to 10 percent, relative) to the arithmetic combination of the x-ray analyses of each component. Analyses performed by x-ray fluorescence, inductively-coupled argon plasma spectroscopy, flame atomic absorption spectrometry, ion chromatography, spectrophotometry and sulfur analyzer are provided for the purposes of comparison. The results of the energy dispersive analyses were normalized using ignition-loss values and a calculation of fluorine from the P2O5 content to reflect the presence of light elements (Z<11). The results were reasonably consistent with other methods of bulk analyses, demonstrating that this method can be used where other instrumentation is not available or where sample size is too small for other methods.

Included in

Biology Commons